Data-driven model development for the prediction of photocatalytic CO2 conversion
Meenatchi Sundaram K., Franco Aguado A.J., Uddin M.R., Juneja A., Rajendran K.
Article, Fuel, 2026, DOI Link
View abstract ⏷
The rising level of global carbon dioxide (37.5GtCO2e annually) remains a major contributor to climate change, highlighting the urgent need for effective carbon capture and utilization (CCU) strategies. Photocatalysis and electrocatalysis offer promising CO2 reduction routes but are limited by complex reaction mechanisms and low selectivity. In this study, a machine learning (ML) model was developed to predict product yields based on catalyst properties and reaction conditions using literature-derived experimental data. Six ML algorithms including Decision Tree (DT), Random Forest (RF), K-Nearest Neighbors (kNN), Multi-Layer Perceptron Regressor (MLPR), Support Vector Regressor (SVR), and Gradient Boosting Regressor (GBR) were evaluated. Among these, GBR achieved the highest accuracy of 98 %, with predictions generated in under <1 s. Feature importance analysis was used to identify wavelength and light intensity as the most influential parameters. This data-driven approach offers a powerful tool for catalytic systems and accelerates the development of sustainable CO2 utilization technologies.
Reprint of “Optimizing aeration efficiency and forecasting dissolved oxygen in brackish water aquaculture: Insights from paddle wheel aerator”
Ramesh P., Jasmin A., Tanveer M., U R.R., Ganeshan P., Rajendran K., Roy S.M., Kumar D., Chinnathambi A., Brindhadevi K.
Article, Journal of the Taiwan Institute of Chemical Engineers, 2025, DOI Link
View abstract ⏷
Background: Aquaculture relies significantly on effective aeration systems to ensure optimal conditions for aquatic organisms. This 96-day study investigates the dynamic relationship between Oxygen Transfer Rates (OTR) and seasonal variations, with a specific focus on the impact of seasonal dynamics and the placement of paddle wheel aerators. The study recognizes the pivotal role of Total Dissolved Solids (TDS) and Total Suspended Solids (TSS) as key water quality parameters influencing aeration efficiency. Methodology: A series of water circulation experiments were conducted at regular intervals to assess mixing rates, revealing a nuanced trajectory ranging from 27.05 to 14.22 m³/kWh. The study scrutinized the influence of TDS and TSS on these rates. Additionally, water velocity variations, ranging from 0.45 to 1.67 m/s, were examined, highlighting density-dependent changes, particularly evident post four weeks of operation. Oxygen stratification analysis provided insights into deviations in Dissolved Oxygen (DO) concentrations, with particular attention to climatic aberrations. Rigorous statistical analyses, including chi-squared, Pearson correlation, Gaussian distribution checks, and student's t-tests, validated the methodological robustness and data reliability. Significant findings: Employing a Seasonal Auto Regressive Integrated Moving Average (SARIMA) model, the study achieved a remarkable 97 % accuracy in forecasting DO levels for the subsequent 96 days. Real-time validation, complemented by a Chi-square goodness of fit test, reaffirmed the model's reliability, establishing congruence between observed and forecasted values. This research underscores the critical roles of strategic aerator placement and seasonal considerations in optimizing pond aeration efficiency, providing substantive insights for the sustainable management of aquaculture ecosystems.
Life cycle assessment of insulated fish transport systems in India
Article, Journal of Industrial Ecology, 2025, DOI Link
View abstract ⏷
The fish transport sector plays a crucial role in both domestic and export markets in India, with insulated vehicles accounting for approximately 60% of fish transit immediately after landing. These insulated vehicles, although essential for maintaining fish quality and minimizing spoilage, contribute significantly to environmental concerns, including increased greenhouse gas emissions, energy consumption, and material use, particularly given their reliance on fossil fuels. This study assessed the environmental impact of using insulated vehicles to transport 1 tonne of fish over a distance of 200 km. Using SimaPro (V9.3) for a life cycle assessment, a landing-to-consumer approach was adopted, incorporating questionnaire-based and secondary data collection. The results revealed significant impacts on human health, with vehicle operations posing high risks (1.13E-05 disability-adjusted life years) due to diesel engine emissions. The long-term global warming potential from vehicle operations was higher than that from depreciated vehicle construction, with emissions measured at 4.44 kg CO2 equivalent per tonne per trip over 100 years. The findings indicated that emissions from insulated vehicles during fish supply contributed approximately 0.4% of global emissions, underscoring the need for environmentally sustainable transportation practices in the fish transport system. Adopting electric vehicles, hybrids, biofuels, and emission controls can enhance sustainability in fish transport. Policies like the National Green Hydrogen Mission, carbon-neutral practices, and green exports support this transition in the fish transport system.
Anaerobic digestion in global bio-energy production for sustainable bioeconomy: Potential and research challenges
Duan Y., Wang Z., Ganeshan P., Sar T., Xu S., Rajendran K., Sindhu R., Binod P., Pandey A., Zhang Z., Taherzadeh M.J., Awasthi M.K.
Review, Renewable and Sustainable Energy Reviews, 2025, DOI Link
View abstract ⏷
Wastes are unceasingly generated in the world, and most of them can be recycled, reused, or recovered to promote a circular economy. Among waste treatment approaches, the anaerobic digestion (AD) process has been considered as an ideal process due to its ecological benefits (reduction of unpleasant odor, pathogens accumulation, or greenhouse gas emission), social and economic advantages, and energy saving. In addition to biogas production, this process can be used to produce various bioproducts, such as biopolymers, bioplastics, biomass, biofertilizers, and biolipids. Interestingly, the AD process residue or digestate is a nutrient-rich by-product that can be used as a biofertilizer for agronomical purposes to balance N-P cycle in the soils. Despite of numerous benefits of AD, less than 1 % of waste is treated by this process. This process has the potential to be integrated with other waste treatment approaches to increase waste treatment efficiency. Therefore, it is essential to focus on each advantage and clarify ambiguity in order to satisfy more countries for employing AD for waste treatment. In this review, various benefits of AD are evaluated; and its potential impacts on particularly agriculture are examined in detail. Additionally, potential biomass and wastes that can be used for anaerobic digestion worldwide are deliberated. Besides, a critical perspective has been developed on the economic, environmental, and social evaluation of the benefits of AD and, as a final point, focused on an integrated circular cascading approach.
Green ammonia as hydrogen carrier: current status, barriers, and strategies to achieve sustainable development goals
Vigneswaran V.S., Gowd S.C., Ravichandran V., Karthikeyan M., Ganeshan P., Kandasamy S., Lee J., Barathi S., Rajendran K.
Review, Science of the Total Environment, 2025, DOI Link
View abstract ⏷
Hydrogen, a carbon-free fuel, has the potential to aid global nations in achieving eight of the 17 Sustainable Development Goals (SDG). The shortcomings associated with H2 transportation and storage can be mitigated by using NH3 as hydrogen carrier because of its better safety, physical, and environmental properties. However, to achieve the global climate target, green ammonia production must be incremented by four times (688 MT) from the current level. Hence, understanding of advanced green NH3 production and storage technologies, along with the factors that influence them becomes necessary. It also aids in identifying the factors hindering green H2 and NH3 production, which can be resolved by promoting research. At the same time, drafting policies that encourage green H2 and NH3 production can abet in overcoming the bottleneck faced by the industry. Presently, green ammonia production can be made feasible only when the renewable electricity cost is less than $20/MWh and carbon price of $150/t of CO2 emissions is levied. Approximately 80 % of the energy consumed during NH3 is spent on H2 generation; therefore, it is necessary to enact policies that promote green H2 production globally. Producing green H2 can aid in mitigating ∼90 % of the greenhouse gases emitted during NH3 manufacturing thereby facilitating to reduce the carbon footprint of H2 carrier and decarbonize NH3 industry.
Factors affecting student diversity in higher education institutions: a data-driven case study from India
Article, Discover Education, 2025, DOI Link
View abstract ⏷
Student diversity plays a crucial role in fostering inclusive education, which enhances innovation, creativity, and problem-solving. In India, while the student mobility is increasing, disparities across regions and institutions continue to influence students’ decision in choosing an institution. Understanding student’s decision making will enhance equal opportunity for quality education. This study aims to identify the factors affecting interstate student diversity in Indian higher education. Secondary data from a national ranking body were analysed using statistical techniques and supervised machine learning algorithms using tool OriginPro 2024 and MATLAB’s R2024a respectively. Statistical analyses, including Pearson correlation, Spearman correlation, and Kruskal–Wallis tests, were employed to analyse relationships among factors, while machine learning models such as Gaussian Process Regression, Ensemble methods, Support Vector Machines, and Kernel-based approaches were used to assess feature importance. The findings show that the factors of student diversity vary across institution types. In Central Government Funded Institutions (CGFIs), location (23%) and course offerings (9%), while in State Government Funded Institutions (SGFIs), international student proportion (17%), were significant factors. For Self-Financed Institutions (SFIs), institutional rank (13%) and placement opportunities (10%) were key factors. These insights can guide policies and strategies to enhance student diversity and promote inclusive education in alignment with National Education Policy (NEP) 2020 and quality education Sustainable Development Goals (SDG) 4.
The water footprint in bioenergy and other primary energy sources
Barathi A., Srihari S., Neupane B., Rajendran K., Jacob S., Kundu D.
Book chapter, Water Footprints: Achieving Sustainable Development Goals, 2025, DOI Link
View abstract ⏷
Energy and water are two basic resources that are intricately connected, and hence, they become a vital component to the functioning of regional, national, and international economies. Water is a finite resource, and many regions around the world are already experiencing water scarcity. About a quarter of the world’s population are living in water-scarce countries. If the same trend continues, by 2040 the world would not be able to meet the demands of ensuring safe drinking water for all people and generating energy for the growing population at the same time. Hence, an innovative is to be devised and implemented in the energy sector so that the water and energy demands can be met to ensure water and energy availability to the global citizens. This chapter focuses on the innovative approach of water footprint throughout the various energy production sectors critically focusing on the renewable energy sector. Moreover, to overcome the excess water consumption, few strategies to overcome the excessive water usage and comparative analysis on water consumption between bioenergy and other renewable energy sectors are also discussed.
Machine Learning Assisted Image Analysis for Microalgae Prediction
Article, ACS ES and T Engineering, 2025, DOI Link
View abstract ⏷
Microalgae-based wastewater treatment has resulted in a paradigm shift toward nutrient removal and simultaneous resource recovery. However, traditionally used microalgal biomass quantification methods are time-consuming and costly, limiting their large-scale use. The aim of this study is to develop a simple and cost-effective image-based method for microalgae quantification, replacing cumbersome traditional techniques. In this study, preprocessed microalgae images and associated optical density data were utilized as inputs. Three feature extraction methods were compared alongside eight machine learning (ML) models, including linear regression (LR), random forest (RF), AdaBoost, gradient boosting (GB), and various neural networks. Among these algorithms, LR with principal component analysis achieved an R2 value of 0.97 with the lowest error of 0.039. Combining image analysis and ML removes the need for expensive equipment in microalgae quantification. Sensitivity analysis was performed by varying the train-test splitting ratio. Training time was included in the evaluation, and accounting for energy consumption in the study leads to the achievement of high model performance and energy-efficient ML model utilization.
Sustainability performance of microalgae as a negative emission technology for wastewater treatment
Gowd S.C., Barathi S., Lee J., Rajendran K.
Article, Journal of Water Process Engineering, 2025, DOI Link
View abstract ⏷
Microalgae cultivation is gaining interest as a sustainable alternative to the conventional wastewater (WW) treatment and nutrient recovery. Current study presents a comprehensive life cycle assessment (LCA) of microalgae cultivation in distinct wastewaters. Two different microalgae species in three different wastewaters were compared for sustainability performance in six scenarios. LCA was conducted using SimaPro (v9.3.0.3) and ReCiPe 2016 Midpoint method. The findings of the study reveal that global warming potential ranged between −678 and − 1357 g CO2eq./m3. Chlorella sp. cultivated in dairy WW shown higher environmental performance across the scenarios with GWP of −1357 g CO2eq./m3. The average global warming potential (GWP) of single-pot microalgae-based wastewater treatment got reduced by 240 %. The key inference of this study is that cultivation of the microalgae as single-pot treatment system not only helps in environmental sustainability but also holds significant promise for combating climate change as negative emission technology (NET).
Time series forecasting of microalgae cultivation for a sustainable wastewater treatment
Meenatchi Sundaram K., Kumar D., Lee J., Barathi S., Rajendran K.
Article, Process Safety and Environmental Protection, 2025, DOI Link
View abstract ⏷
The use of micro-algae for wastewater treatment is a promising technique that contributes to CO2 capture and nutrient recovery. However, the lack of effective forecasting models limits the scalability of this technique. This study aims to develop a time-series-based forecasting model to predict the growth curve of microalgal biomass under environmental conditions similar to those found in wastewater. Data collected on microalgal growth was used to train six time-series models: Long Short-Term Memory (LSTM), Extreme Gradient Boosting (XGBoost), Auto-Regressive Integrated Moving Average (ARIMA), Random vector functional link (RVFL), Physics-informed neural networks (PINN) and Prophet. The model performance metrics were compared, and the best model was identified. The results demonstrated that the RVFL was the most accurate model, with minimal prediction errors ( < 0.01). Residual analysis confirmed a normal distribution of errors without outliers, supporting the model's reliability. These findings suggest that the proposed RVFL model can effectively forecast microalgal growth, potentially reducing the need for costly and labour-intensive laboratory trials and advancing microalgae-based wastewater treatment.
Microalgae as a single-pot system for nutrient removal and wastewater treatment: comparison of effluents and species performance
Article, Clean Technologies and Environmental Policy, 2024, DOI Link
View abstract ⏷
Microalgae paves the way towards a negative emission technology; however, single-pot systems combining nutrient removal and wastewater treatment are scarce in the literature. In this study, three different types of wastewater (university, municipality, and dairy industries) were studied using microalgae towards treatment and nutrient removal using Scenedesmus sp. and Chlorella sp. The experiments were carried out in 20 L reactors, for 9 days, where in achieving a maximum of algal growth rate of 770 and 725 mg/L for Scenedesmus sp. and Chlorella sp., respectively. Of the three wastewaters, dairy wastewater had the highest influent COD (3488 mg/L), which was reduced by 92% after 9 days. The pigment content was highest after 6 days (0.22 ± 0.03%), and there was no significant improvement after 9 days, suggesting a trade-off between nutrient removal, photosynthetic performance, and COD reduction. Microalgae act as a sustainable solution and negative emission technology to solve the crisis of wastewater treatment, nutrient removal and production of high-value products. Graphical abstract: (Figure presented.)
Emerging technologies for pretreatment of lignocellulosic biomass
Liu H., Ganeshan P., Rajendran K., Kumar V., Sindhu R., Pandey A., Awasthi M.K.
Book chapter, Biofuels Production from Lignocellulosic Materials, 2024, DOI Link
View abstract ⏷
Lignocellulosic biomass is the richest regenerative resource in nature. Especially in the context of continuous consumption of fossil energy and environmental pollution, it is urgent to use lignocellulosic biomass to prepare clean energy such as biofuels. But lignocellulose has a strong natural barrier against degradation, which needs to be pre-treated by physical, chemical and microbial means and then converted into biofuels and other high value-added products at lower cost and higher efficiency. This chapter mainly describes the pretreatment techniques of lignocellulose in recent years, including traditional physical methods, chemical methods and biological methods. And the mechanism of each pretreatment method is briefly introduced, and its advantages and disadvantages are analysed and summarized. At the same time, the economic feasibility and influencing factors of these technologies are discussed and analysed. Finally, the development and application of lignocellulosic pretreatment technology are prospected and suggested, aiming at providing some reference for the more efficient development and utilization of cellulose.
Role of Green Hydrogen in Decarbonizing Heavy Industries in India
Book chapter, ACS Symposium Series, 2024, DOI Link
View abstract ⏷
Heavy industries play a crucial role in the economic growth of India through their contribution towards meeting demand, including exports and GDP. Every functional unit of the production process related to hard-to-abate industries has to depend upon power sources for manufacturing the final product. The major power source for heavy industries namely power plants, iron and steel, cement, paper, and fertilizer are coal. During the process of energy conversion from coal through combustion, they produce a large amount of greenhouse gases. As production capacity is increased to meet the growing demand, it is essential to mitigate carbon emissions. There are many routes adopted by various sectors to decarbonize the production process. These include the use of alternative fuels, using the best available techniques, carbon capture utilization, and storage. Most of these techniques have shown positive impacts after implementation. In this study, the production process of each sector is analyzed to find the hotspots, the mitigation strategies followed by each industry, and mainly the use of green hydrogen as a power source. It elaborates on the routes of production of green hydrogen, the major challenges in the implementation part, the policy making of green hydrogen in India, its relationship to heavy industries, and how green hydrogen plays a role in net-zero emission goals.
Environmental impacts and effects on greenhouse gas emissions in shrimp feed production system for aquaculture – A case study in India
Ramesh P., Jasmin S A., Tanveer M., Ganeshan P., Rajendran K., Kamilya D., Brindhadevi K.
Article, Environmental Research, 2024, DOI Link
View abstract ⏷
Attributional life cycle assessment study examines the environmental impact of raw materials, machinery, and unit operations. In the present work, an attributional life cycle assessment (LCA) was employed to assess the environmental and greenhouse gas impacts of a shrimp feed production system. A commercial shrimp feed mill in Tamil Nadu, India, provided inventory data for one-ton shrimp feed (functional unit) for a Cradle-to-Gate evaluation using environmental impact methodologies, specifically Impact 2002+ in SimaPro® (V9.3.0.3) software. The results showed that human health (0.003357 DALY), ecosystem quality (2720.518 PDF × m2 × yr), climate change (2031.696 kg CO2 eq), and resources (71019.42 MJ primary) were the most significantly impacted. The human health category was found to be the most prominent after normalization and weighting (0.47 pt), and strategies were suggested accordingly. The GWP20 and GWP100 measures for long-term climate change were calculated to be 8.7 and 7.33 kg CO2 eq, respectively. Cast iron used in machinery production (GWP 20–15.40%, GWP100–134.5%) and electricity use (GWP 20–6.13%, GWP 100–6.9%) accounted for sizable portions of the burden. Feed production is estimated to contribute 0.2% of global CO2 emissions within the proposed global context. These findings are significant regarding economically and environmentally sustainable shrimp feed production worldwide.
Optimizing aeration efficiency and forecasting dissolved oxygen in brackish water aquaculture: Insights from paddle wheel aerator
Ramesh P., Jasmin A., Tanveer M., U R.R., Ganeshan P., Rajendran K., Roy S.M., Kumar D., Chinnathambi A., Brindhadevi K.
Article, Journal of the Taiwan Institute of Chemical Engineers, 2024, DOI Link
View abstract ⏷
Background: Aquaculture relies significantly on effective aeration systems to ensure optimal conditions for aquatic organisms. This 96-day study investigates the dynamic relationship between Oxygen Transfer Rates (OTR) and seasonal variations, with a specific focus on the impact of seasonal dynamics and the placement of paddle wheel aerators. The study recognizes the pivotal role of Total Dissolved Solids (TDS) and Total Suspended Solids (TSS) as key water quality parameters influencing aeration efficiency. Methodology: A series of water circulation experiments were conducted at regular intervals to assess mixing rates, revealing a nuanced trajectory ranging from 27.05 to 14.22 m³/kWh. The study scrutinized the influence of TDS and TSS on these rates. Additionally, water velocity variations, ranging from 0.45 to 1.67 m/s, were examined, highlighting density-dependent changes, particularly evident post four weeks of operation. Oxygen stratification analysis provided insights into deviations in Dissolved Oxygen (DO) concentrations, with particular attention to climatic aberrations. Rigorous statistical analyses, including chi-squared, Pearson correlation, Gaussian distribution checks, and student's t-tests, validated the methodological robustness and data reliability. Significant findings: Employing a Seasonal Auto Regressive Integrated Moving Average (SARIMA) model, the study achieved a remarkable 97 % accuracy in forecasting DO levels for the subsequent 96 days. Real-time validation, complemented by a Chi-square goodness of fit test, reaffirmed the model's reliability, establishing congruence between observed and forecasted values. This research underscores the critical roles of strategic aerator placement and seasonal considerations in optimizing pond aeration efficiency, providing substantive insights for the sustainable management of aquaculture ecosystems.
Machine learning for high solid anaerobic digestion: Performance prediction and optimization
Article, Bioresource Technology, 2024, DOI Link
View abstract ⏷
Biogas production through anaerobic digestion (AD) is one of the complex non-linear biological processes, wherein understanding its dynamics plays a crucial role towards process control and optimization. In this work, a machine learning based biogas predictive model was developed for high solid systems using algorithms, including SVM, ET, DT, GPR, and KNN and two different datasets (Dataset-1:10, Dataset-2:5 inputs). Support Vector Machine had the highest accuracy (R2) of all the algorithms at 91 % (Dataset-1) and 87 % (Dataset-2), respectively. The statistical analysis showed that there was no significant difference (p = 0.377) across the datasets, wherein with less inputs, accurate results could be predicted. In case of biogas yield, the critical factors which affect the model predictions include loading rate and retention time. The developed high solid machine learning model shows the possibility of integrating Artificial Intelligence to optimize and control AD process, thus contributing to a generic model for enhancing the overall performance of the biogas plant.
Economic viability of two-stage biohydrogen and biomethane production from cassava stillage residue focusing on solids content and pretreatment
Article, International Journal of Hydrogen Energy, 2024, DOI Link
View abstract ⏷
Biohythane (a mixture of hydrogen and methane) may play a significant role in a future decarbonised energy system. The production of biohythane can be achieved by sequential dark hydrogen fermentation and anaerobic digestion. However, the technology readiness level of biohythane can be limited by many process constraints negatively affecting its commercial feasibility. Here, a pilot experiment on fermentative hythane production from cassava stillage residue (CSR) incorporating dilute acid pretreatment and enzymolysis was undertaken. The production of hydrogen and methane was 72.0 ± 10.7 and 295.4 ± 28.5 mL/g volatile solid, respectively. Different scenarios for techno-economic analysis were developed in terms of the dried/wet form of CSR and total solids content during fermentation. Results suggested that hythane from CSR was not economically feasible with a high production cost (1.39–2.33 €/m3). There was a trade-off relationship between the increase in methane yield through pretreatment and the associated cost.
Biochemical engineering for elemental sulfur from flue gases through multi-enzymatic based approaches – A review
Awasthi M.K., Amobonye A., Bhagwat P., Ashokkumar V., Gowd S.C., Dregulo A.M., Rajendran K., Flora G., Kumar V., Pillai S., Zhang Z., Sindhu R., Taherzadeh M.J.
Review, Science of the Total Environment, 2024, DOI Link
View abstract ⏷
Flue gases are the gases which are produced from industries related to chemical manufacturing, petrol refineries, power plants and ore processing plants. Along with other pollutants, sulfur present in the flue gas is detrimental to the environment. Therefore, environmentalists are concerned about its removal and recovery of resources from flue gases due to its activation ability in the atmosphere to transform into toxic substances. This review is aimed at a critical assessment of the techniques developed for resource recovery from flue gases. The manuscript discusses various bioreactors used in resource recovery such as hollow fibre membrane reactor, rotating biological contractor, sequential batch reactor, fluidized bed reactor, entrapped cell bioreactor and hybrid reactors. In conclusion, this manuscript provides a comprehensive analysis of the potential of thermotolerant and thermophilic microbes in sulfur removal. Additionally, it evaluates the efficacy of a multi-enzyme engineered bioreactor in this process. Furthermore, the study introduces a groundbreaking sustainable model for elemental sulfur recovery, offering promising prospects for environmentally-friendly and economically viable sulfur removal techniques in various industrial applications.
Data-driven model development for prediction and optimization of biomass yield of microalgae-based wastewater treatment
Meenatchisundaram K., Gowd S.C., Lee J., Barathi S., Rajendran K.
Article, Sustainable Energy Technologies and Assessments, 2024, DOI Link
View abstract ⏷
Microalgae-based nutrient recovery has the potential to efficiently recover nutrients while simultaneously treating wastewater. However, the absence of an optimization model for this technology hinders its full potential. This study has developed a model to optimize the biomass yield in micro algae-based wastewater treatment. Seven machine learning models, including Decision Trees (DT), Random Forest (RF), K-Nearest Neighbours (KNN), Gradient Boosting Regressor (GBR), Multi-Layer Perceptron Regression (MLPR), Support Vector Regression (SVR), and Artificial Neural Networks (ANN), were compared. Among other algorithms, ANN performed superiorly, achieving an R2 value of 0.98 with the lowest error. The optimal biomass yield of 948 mg/L was obtained when the COD, phosphate, nitrate, nitrite, pH, and retention times were maintained at 350 mg/L, 50 mg/L, 60 mg/L, 140 mg/L, 7.1, 9 days respectively. When compared to experimental yield, the prediction shows 31.7 % higher biomass yield. The pH and retention time were the critical factors for prediction of algal biomass. 20 % of variation in the train test split ratio caused 21 % increase in the error value and 75:25 ratio was found to be optimal for better performance of the model. This study serves as a valuable reference point for integration of artificial intelligence (AI) with algae-based wastewater treatment.
Exploration of upgrading of biomass and its paradigmatic synthesis: Future scope for biogas exertion
Awasthi M.K., Rajendran K., Vigneswaran V.S., Kumar V., Dregulo A.M., Singh V., Kumar D., Sindhu R., Zhang Z.
Article, Sustainable Chemistry and Pharmacy, 2024, DOI Link
View abstract ⏷
Natural gas is extracted from the subsoil which is not a renewable source, however, the dominance of this product in the international market is significantly higher in future. It reflects the global view of renewable sources (biogas) and hinders the sustainable development of bioenergy. It describes the major issues and trends in the development of biogas industry, paying special attention to current biomass upgrading technologies, methane activation for fuel production and model compounds investigation. The conducted research gives reason to believe that the valorization of organic waste generated worldwide during the production of biomethane that can potentially satisfy. No more than one fifth of global demands for natural gas due to technical difficulties and economic constraints associated with the purification of biogas. The existing production potential of biogas production is focused on obtaining biomethane and high growth rates of demand for biohydrogen. A pressing need arises the possibilities for further development of biogas industry lie in optimizing the biomethanation processes, which allows to reduce the costs of biogas modernization system and decreasing the negative effect on climate changes by replacing petrochemical derived fuels with biofuels in various sectors of economy.
Pathways for decarbonizing the sponge iron industries: Effect of energy balance and impact assessment
Article, Journal of Cleaner Production, 2024, DOI Link
View abstract ⏷
The major share of energy consumption during steel manufacturing is spent on iron making. The unavailability of the required quantity of recyclable steel in India has made the industries depend on sponge iron (SI) for steel manufacturing. However, 78.5% of the SI manufactured in India uses coal as an energy source. Thus, increasing the carbon footprint of steel manufactured in India by 18% compared to the global level. Hence, in this study, the potential of palm kernel shell charcoal (PKSC) to decarbonize the rotary kiln-based SI production process was analysed by framing three scenarios and comparing them with the business-as-usual (BAU). Meanwhile, the life cycle assessment of the SI production through different scenarios was done to identify the sustainability of the process. A cradle-to-gate approach was adopted, and it was found that during BAU, the net greenhouse gas (GHG) emissions were 2525 CO2eq./t SI. However, usage of PKSC (scenario 3) in the SI production process aided in achieving negative net GHG emissions of −41 kg CO2eq./t SI. Meanwhile, the net GHG emission was 1092 kg CO2eq./t SI and 1197 kg CO2eq./t when the coal used in the feed and injection end was replaced with PKSC in scenario 1 and scenario 2, respectively. Thus, the usage of the PKSC instead of coal can abet in decarbonizing the sponge iron industry thereby aiding in reducing the GHG emitted during the production of 1 t of steel in India to 2.4 t by 2030–31.
Advances on characteristics and valorization of food waste towards the sustainable production of bio-methane and purification
Review, Fuel, 2024, DOI Link
View abstract ⏷
Food waste is primarily generated in marketplaces, agricultural fields, hotels, food manufacturers units, and halls. Food waste have a major impact on food security, quality and safety, economic development, and cause environment pollution. The improper disposal of food waste without proper treatments leads to generation of new diseases, unpleasant odour, air, water, and soil pollution. Nevertheless, food waste is a good substrate which can be disintegrated by digestion process because it exhibits more water contents and biodegradability. The conversion of food waste into biomethane is an appreciable solution in food waste management steps. This manuscript reviews the physico-chemical properties of food waste, various pretreatment methods of food waste to enhance the efficiency of anaerobic digestion (AD) process used to produce biomethane and discussed the impact of operational factors on biomethane production. Subsequently, the need for a biomethane upgradation using physical, chemical, and biological purification approaches was reviewed. In order to improve the efficiency of the anaerobic digestion (AD) process to a large-scale industrial level, the challenges and possible future developments needed to enhance biomethane generation from food waste were also reviewed significantly.
Beyond tradition: charting a greener future for cassava starch industry using multi-criteria decision-making
Ravichandran V., Kumar D., Mani S., Rajendran K.
Article, Biofuel Research Journal, 2024, DOI Link
View abstract ⏷
Cassava, a staple food crop, is widely used for starch production, but its inconsistent supply, price volatility, and substantial waste generation pose challenges to the cassava industrial market's growth. This study aims to identify a sustainable biorefinery pathway by optimizing conventional cassava starch plants (business-as-usual, BAU) for economic and environmental benefits. Four scenarios were evaluated: animal feed from peel waste (Scenario 1), fungal protein from thippi waste (Scenario 2), fish feed from digested wastewater (Scenario 3), and conversion of all waste streams into animal feed, fish feed, and fungal protein (Scenario 4). Scenario 4 emerged as the best pathway using the multi-criteria decision-making (MCDM) approach, with a performance score of 0.282. Despite the highest energy consumption (18.91 MWh), Scenario 4 was favored for producing four value-added products alongside starch, yielding the highest profit at USD 8.85 million. In contrast, profits for BAU, Scenario 1, Scenario 2, and Scenario 3 were 1.91, 2.30, 5.01, and USD 8.79 million, respectively. Waste valorization in Scenarios 1, 2, 3, and 4 resulted in CO2 avoidance of 36.5., 42.6., 21.7, and 57.45 t CO2eq., respectively. However, producing value-added products increased energy consumption by 13, 73, 7, and 74% compared to BAU (4.58 MWh). The global warming potential analysis showed negative values for scenarios 2 and 4, at -436 and -434 kg CO2eq./t root, respectively. This study highlights the potential of a biorefinery approach for sustainable cassava starch production, providing insights for future research and policy development.
Techno-economic analysis on biofuels and bioproducts produced from woody biomass
Book chapter, Sustainable Biorefining of Woody Biomass to Biofuels and Biochemicals, 2023, DOI Link
View abstract ⏷
Bioenergy resources, when harvested sustainably, have the potential not only to satisfy the growing energy demand but can also aid in achieving a negative carbon footprint. The Intergovernmental Panel on Climate Change (IPCC) has also identified bioenergy resources as an effective tool to achieve zero emissions by 2050 because biomass can be valorized into various products, namely, producer gas, syngas, bioethanol, biomethanol, biochar, bio-oil, etc. by adopting different conversion pathways, thus, aiding in the reduction in consumption of fossil fuel, thereby decreasing the anthropogenic greenhouse gas (GHGs) emission into the atmosphere. However, it is necessary to analyze the economic viability of these biorefinery systems for the faster penetration of these products into the global market and to identify the bottleneck haunting its faster dissemination. In this regard, this chapter analyses the technical and economic factors which affect the biorefinery of woody biomass by employing thermo-chemical and bio-chemical conversion processes.
The influence of policies in commercializing biofuels and bioproducts from woody biomass
Book chapter, Sustainable Biorefining of Woody Biomass to Biofuels and Biochemicals, 2023, DOI Link
View abstract ⏷
The global nations are under pressure to develop a renewable and environmentally friendly fuel/technology from sustainable feedstock, such as woody biomass, to reduce greenhouse gas emissions and meet the energy demand. But several factors must be addressed to achieve the daunting task, which includes technological advancement, financial viability, environmental sustainability, and finally government backing in the form of sensible regulations and increased public awareness. To reduce the world's reliance on fossil fuels and ensure a sustainable future, biofuel policies are crucial. The production of biofuel from woody biomass makes the system not only to reduce the cost of the feedstock but also to decrement the dependency on first-generation feedstocks, which dominates the present biofuel market. Hence, this chapter deals with the need for governing bodies to draft an effective policy for the successful adoption of woody biomass-based biorefinery technologies to mitigate global emissions and to fulfill the growing energy demand thereby enabling a sustainable economy.
Scope for commercialization and market analysis of bio-based alcohols, fuels, and chemicals
Book chapter, Higher Alcohols Production Platforms: From Strain Development to Process Design, 2023, DOI Link
View abstract ⏷
The energy sector accounts for three-quarters of the greenhouse gas emission happening around the world. So, it is necessary to move toward a sustainable fuel with minimal carbon emissions to mitigate the rise in global temperature. Bioenergy is considered an effective resource to satisfy the rising global energy demand with minimal carbon emissions. The presence of proven and well-mature technology to convert biomass into various forms of fuels and chemical products provides an upper hand to bioresources over other energy sources. However, the rise in the cost of feedstocks, transportation cost of low-density bioresources, and lack of reliable biomass supply chain network has made them least preferred when compared to solar and wind energy technologies. Hence, it is important to access the scope for commercialization of biomass-based products, which will aid in framing policies to create a sustainable market for them.
How does techno-economic analysis and lifecycle assessment help in commercializing the biohydrogen supply chain?
Ganeshan P., Vigneswaran V.S., Gowd S.C., Kondusamy D., Sanjay kumar C., Krishnamoorthy N., Kumar D., Juneja A., Paramasivan B., Raju N.N., Rajendran K., Pugazhendhi A.
Article, Fuel, 2023, DOI Link
View abstract ⏷
Hydrogen is considered as the fuel of the future not only because of its high energy density but also due to its zero-carbon emission potential during combustion. However, to achieve sustainable growth, the hydrogen generation process must be techno-economically feasible and have minimum carbon footprint. The techno-economic analysis (TEA) of various hydrogen generation process aids in identifying the effective bio-hydrogen generation process at minimal cost thereby aiding in faster dissemination of the system by attracting investors. Among the various techniques available for bio-hydrogen production, gasification was found to be most economical ($1.2/kg H2) followed by anaerobic digestion process ($1.25/kg H2). Meanwhile, after carrying out the life cycle analysis (LCA) of the different bio-hydrogen generation process, it was found that generation of bio-hydrogen by gasification of eucalyptus wood produced least carbon foot of −1.6 kg CO2eq./kg H2. Thus, the TEA and LCA of different biohydrogen production process also helps to identify the bottlenecks haunting the penetration of hydrogen in energy market which can be overcome by framing effective policies by the governing agencies.
Economic perspectives and policy insights on carbon capture, storage, and utilization for sustainable development
Review, Science of the Total Environment, 2023, DOI Link
View abstract ⏷
Carbon capture storage and utilization (CCSU) has the potential to become a key tool to mitigate climate change, thus, aiding in achieving the objectives of the 2015 Paris Agreement. Even though the relevant remediation technology has achieved technical maturity to a certain extent, implementation of CCSU on a larger scale is currently limited because of non-technical parameters that include cost, legalization, lack of storage reservoir, and market mechanism to penalize CO2 emitter. Among these, cost emerges as the primary barrier to the dissemination of CCSU. Hence, necessary policy frameworks and incentives must be provided by governing agencies to enable faster dissemination of carbon capture and utilization (CCU) and carbon capture and storage (CCS) globally. Meanwhile, strict implementation of a carbon tax across nations and market demand for products generated using captured CO2 can aid in the fast adoption of CCU and CCS. This review assessed the economic feasibility and sustainability of CCS and CCU technologies to identify the barriers to commercializing these technologies.
Advanced approaches for resource recovery from wastewater and activated sludge: A review
Awasthi M.K., Ganeshan P., Gohil N., Kumar V., Singh V., Rajendran K., Harirchi S., Solanki M.K., Sindhu R., Binod P., Zhang Z., Taherzadeh M.J.
Review, Bioresource Technology, 2023, DOI Link
View abstract ⏷
Due to resource scarcity, current industrial systems are switching from waste treatment, such as wastewater treatment and biomass, to resource recovery (RR). Biofuels, manure, pesticides, organic acids, and other bioproducts with a great market value can be produced from wastewater and activated sludge (AS). This will not only help in the transition from a linear economy to a circular economy, but also contribute to sustainable development. However, the cost of recovering resources from wastewater and AS to produce value-added products is quite high as compared to conventional treatment methods. In addition, most antioxidant technologies remain at the laboratory scale that have not yet reached the level at industrial scale. In order to promote the innovation of resource recovery technology, the various methods of treating wastewater and AS to produce biofuels, nutrients and energy are reviewed, including biochemistry, thermochemistry and chemical stabilization. The limitations of wastewater and AS treatment methods are prospected from biochemical characteristics, economic and environmental factors. The biofuels derived from third generation feedstocks, such as wastewater are more sustainable. Microalgal biomass are being used to produce biodiesel, bioethanol, biohydrogen, biogas, biooils, bioplastics, biofertilizers, biochar and biopesticides. New technologies and policies can promote a circular economy based on biological materials.
Bioenergy with carbon capture, storage and utilization: Potential technologies to mitigate climate change
Ganeshan P., V S V., Gowd S.C., Mishra R., Singh E., Kumar A., Kumar S., Pugazhendhi A., Rajendran K.
Article, Biomass and Bioenergy, 2023, DOI Link
View abstract ⏷
Bioenergy with carbon capture and storage (BECCS) is gaining attention as an energy source and the most effective path to achieve negative CO2 emissions by photosynthesis and capturing CO2. However, BECCS has certain challenges and limitation which needs to be addressed to make the technology feasible. Concerns about food security, land, water use, and the possibility of large-scale implementation are critical in commercialization. As an emerging field, BECCS will need dynamic research and development over the next few decades, as well as strong policy backing, to clinch that it can be implemented on time for fulfilling the Paris agreement targets. The goal of this critical review is to find the impending obstacles that BECCS is facing, as well as the approaches to overcome them, while also emphasizing the advances in the field over the last decade. Detailed technology assessment is provided for a better understanding.
Utilization of woody biomass for biogas production
Sakthi Vignesh N., Vimali E., Rajkeerthana S., Kaleeshwari R., Kiruthika M., Ashokkumar B., Varalakshmi P., Yesodharan V., Vigneswaran V.S., Rajendran K.
Book chapter, Sustainable Biorefining of Woody Biomass to Biofuels and Biochemicals, 2023, DOI Link
View abstract ⏷
Woody biomass, the most abundant and high energy density bioenergy resource, is used inefficiently to satisfy the domestic heating and cooking demands of the people. Despite being a carbon-neutral source when harvested sustainably, the inefficient use of biomass to satisfy the cooking demand of marginalized people led to poor indoor air quality and causing respiratory health problems. Hence, it is necessary to identify a technology that enables the conversion of woody biomass into fuel that does not affect indoor air quality. In this regard, the conversion of woody biomass into biogas by anaerobic digestion emerges as the viable option. However, the recalcitrance nature of woody biomass necessitates a pretreatment before being fed to an anaerobic digestor, increasing the capital and operating cost of the biogas system. But usage of this technology to convert woody biomass to gaseous fuel can aid in sustainable development. The waste digested from the anaerobic digestor can be used as manure for agricultural crops in rural areas. Meanwhile, fly ash generated during the combustion of the woody biomass is also inhibited thereby resulting in an improvement in air quality. In this regard, this chapter presents the recent developments and factors affecting biogas production from woody biomass.
Biochemical conversion of woody biomass to liquid biofuels
Hossain M.S., Therasme O., Rajendran K., Volk T.A., Kumar V., Kumar D.
Book chapter, Sustainable Biorefining of Woody Biomass to Biofuels and Biochemicals, 2023, DOI Link
View abstract ⏷
Woody lignocellulosic biomass is identified as a promising feedstock for liquid biofuel production since it is available throughout the year at a low cost in addition to carbon negative emission capability and no scrutiny as a food source. However, using woody biomass incurs expensive and energy-intensive pretreatment and processing steps in fuel production. This chapter covers woody biomass processing through biochemical routes for liquid transportation fuels (bioethanol and biobutanol) and aviation fuel production. It includes sources of various hardwood and softwood species alongside their compositions. Available pretreatment and hydrolysis techniques and different biochemical conversion approaches are discussed. Lastly, this chapter critically analyzes different studies to identify their processing approaches and operating conditions used for liquid biofuel yield enhancement. It is seen that biochemical conversion fermentation is primarily used for bioethanol and biobutanol production, whereas various thermochemical conversion processes are dominated in bio-jet fuel production from woody biomass. This critical discussion can be helpful for future liquid biofuel production planning, scale-up, and energy policy preparation.
Pretreatment technologies for lignocellulosic biomass refineries
Juneja A., Kumar D., Rajendran K., Mittal A.
Book chapter, Advances in Lignocellulosic Biofuel Production Systems, 2023, DOI Link
View abstract ⏷
Pretreatment is a critical step in processing lignocellulosic biomass into biofuel and bioproducts and is considered the energy and cost center of the biomass conversion process. Although a large number of pretreatment technologies have been developed, not all the techniques are viable on a commercial scale at this stage. Moreover, the technology choice and process conditions depend highly on the type of biomass and the overall biorefinery scheme. This chapter provides an overview of different pretreatment methods, including their mechanism, important process parameters, current status, and challenges. The opportunities associated with new technologies and approaches are presented. Emphasis is placed on low-severity thermal pretreatment technologies. The chapter also provides a brief discussion of the challenges to achieving the economic viability of the technologies on a commercial scale.
Sustainable Biorefining of Woody Biomass to Biofuels and Biochemicals
Kumar D., Kumar S., Rajendran K., Ray R.C.
Book, Sustainable Biorefining of Woody Biomass to Biofuels and Biochemicals, 2023, DOI Link
View abstract ⏷
Sustainable Biorefining of Woody Biomass to Biofuels and Biochemicals explores various technologies and pathways for the valorization of woody biomass to produce sustainable biofuels and bioproducts. Focusing on commercialization, the book discusses woody biomass availability, including harvesting, transportation and storage, biomass structure, advanced biorefinery technologies, and the economic and environmental sustainability of woody biomass-based biorefineries. Various technologies are described and assessed from a commercial perspective and practical solutions to the latest challenges are provided. The last section of the book is dedicated to the commercialization aspects of biorefineries, providing details about the techno-economic viability and environmental impact of various biorefinery approaches.This book provides readers with a unique and comprehensive reference that will help students and researchers alike identify and overcome the challenges involved in woody-biomass biorefining for biofuels and biochemicals. It will also be of interest to researchers and professionals involved more broadly in bioenergy and renewable energy, and interdisciplinary teams working across biotechnology, chemistry and chemical engineering, environmental science, and plant sciences.
Perspective on the strategies and challenges in hydrogen production from food and food processing wastes
Shanmugam S., Mathimani T., Rajendran K., Sekar M., Rene E.R., Chi N.T.L., Ngo H.H., Pugazhendhi A.
Article, Fuel, 2023, DOI Link
View abstract ⏷
A phenomenal increase in food and food processing wastes is a leading global concern, as over one-third of all food and its derivatives produced globally are discarded. At this juncture, an intriguing solution is to utilize food waste to produce biohydrogen, which may be used as a fuel. The emphasis on the hydrogen economy is an effort to reduce our emissions and decarbonize our energy systems. The conversion of food and food-processing wastes to (bio)hydrogen is possible via biochemical and electrochemical methods. This review examines the primary methodologies for producing hydrogen from food and food-processing industry waste streams, and discusses the associated challenges. The combination of dark and light fermentation, metabolic engineering, and bioaugmentation are considered as approaches for enhancing biohydrogen production. Once the process robustness, quality, and performance of biological and electro-chemical routes for biohydrogen production are optimized and pilot-scale studies are demonstrated, food and food-processing wastes may be plausible candidates for the transition to a sustainable circular hydrogen economy.
Production of biochar from tropical fruit tree residues and ecofriendly applications – A review
Ding Z., Ge Y., Gowd S.C., Singh E., Kumar V., Chaurasia D., Kumar V., Rajendran K., Bhargava P.C., Wu P., Lin F., Harirchi S., Ashok kumar V., Sirohi R., Sindhu R., Binod P., Taherzadeh M.J., Awasthi M.K.
Retracted, Bioresource Technology, 2023, DOI Link
View abstract ⏷
Environmental contamination is considered a major issue with the growing urbanization and industrialization. In this context, the scientific society is engaged in searching for a sustainable, safe, and eco-friendly solution. Sustainable materials such as biochar play an important role in environmental contamination. It has some specific properties such as micropores which increase the surface area to bind the pollutants. This review endeavors to analyze the potential of fruit wastes especially tropical fruit tree residues as potential candidates for producing highly efficient biochar materials. The review discusses various aspects of biochar production viz. pyrolysis, torrefaction, hydrothermal carbonization, and gasification. In addition, it discusses biochar use as an adsorbent, wastewater treatment, catalyst, energy storage, carbon sequestration and animal feed. The review put forward a critical discussion about key aspects of applying biochar to the environment.
A comprehensive review on thermochemical, and biochemical conversion methods of lignocellulosic biomass into valuable end product
Awasthi M.K., Sar T., Gowd S.C., Rajendran K., Kumar V., Sarsaiya S., Li Y., Sindhu R., Binod P., Zhang Z., Pandey A., Taherzadeh M.J.
Article, Fuel, 2023, DOI Link
View abstract ⏷
Lignocellulosic wastes have emerged as a potential feedstock in the last decades. There are multiple reasons for its abundance, easy availability, economic, and abundant sources. It can be used to produce several value-added products. Among them, fuel is considered one of the important requirements. Production of fuel from lignocellulosic biomass is a tricky business. The major reason for its failure is the low product yield. Therefore, high yield and low-cost are the two key parameters which need significant optimization. To achieve the target several newer technologies such as pyrolysis, hydrothermal liquefaction and gasification have emerged. These techniques are much more efficient than that of conventional acid or alkali. At the same time quality of the product is also improved. The focus of this review is to analyze the efficiency of chemical conversion of lignocellulosic residues into valuable fuels keeping in mind the cost-reduction strategies.
Editorial Preface of the Special Issue on “The 5th International Conference on Alternative Fuels, Energy & Environment: Futures and Challenges (ICAFEE 2021)”
Atabani A.E., Pugazhendhi A., Almomani F., Rajendran K.
Editorial, Fuel, 2023, DOI Link
Life cycle assessment of comparing different nutrient recovery systems from municipal wastewater: A path towards self-reliance and sustainability
Article, Journal of Cleaner Production, 2023, DOI Link
View abstract ⏷
Nutrient recovery systems can help to mitigate the negative effects of N and P in WW (wastewater), which when not recovered causes eutrophication in aquatic ecosystems. Using SimaPro (V9.3), the lifecycle assessment (LCA) of four nutrient recovery systems and sewage treatment plant (STP) were compared in this study. The findings showed that a fuel cell with a single-pot WW treatment system can function as a negative emission system with a global warming potential (GWP) of −234 gCO2 Eq./m3 of WW. Nutrient recovery reduces carbon footprint by 56–98% when compared to traditional fertilizers like diammonium phosphate (DAP) and urea. One of the main conclusions of this research was that single-pot systems perform better for the environment than add-on systems, which suggests that microalgae could perform better for the environment in a single-pot system. Recovering nutrients from WW not only improves self-reliance in the economy by decrementing the fertilizer import but also saves the environment.
Poly(3-hydroxybuyrate) production from industrial hemp waste pretreated with a chemical-free hydrothermal process
Paul A., Jia L., Majumder E.L.-W., Yoo C.G., Rajendran K., Villarreal E., Kumar D.
Article, Bioresource Technology, 2023, DOI Link
View abstract ⏷
In this study, a mild two-stage hydrothermal pretreatment was employed to optimally valorize industrial hemp (Cannabis sativa sp.) fibrous waste into sugars for Poly(3-hydroxybuyrate) (PHB) production using recombinant Escherichia coli LSBJ. Biomass was pretreated using hot water at 160, 180, and 200 °C for 5 and 10 min (15% solids), followed by disk refining. The sugar yields during enzymatic hydrolysis were found to improve with increasing temperature and the yields for hot water-disk refining pretreatment (HWDM) were higher compared to only hot water pretreatment at all conditions. The maximum glucose (56 g/L) and cellulose conversion (92%) were achieved for HWDM at 200 °C for 10 min. The hydrolysate obtained was fermented at a sugar concentration of 20 g/L. The PHB inclusion and concentration of 48% and 1.8 g/L, respectively, were similar to those from pure sugars. A pH-controlled fermentation resulted in a near bi-fold increase in PHB yield (3.46 g/L).
Sustainable Conversion of Biowaste to Energy to Tackle the Emerging Pollutants: A Review
Li Y., Meenatchisundaram K., Rajendran K., Gohil N., Kumar V., Singh V., Solanki M.K., Harirchi S., Zhang Z., Sindhu R., Taherzadeh M.J., Awasthi M.K.
Review, Current Pollution Reports, 2023, DOI Link
View abstract ⏷
Biowaste is a major source of organic material that can be converted into energy through various processes such as anaerobic digestion, composting, and pyrolysis. However, emerging pollutants, such as pharmaceuticals, pesticides, herbicides, and personal and household products, are a growing concern in wastewater treatment that can be effectively removed by biowaste-to-energy processes. While these contaminants pose significant challenges, the development and implementation of effective monitoring programs and risk assessment tools help to mitigate their impact on human health and the environment. Likewise, monitoring programs, challenges, legislations, and risk assessment tools are essential for understanding and managing the risks associated with emerging pollutants. Biowaste recycling is an important aspect of a biocircular economy perspective as it involves the conversion of organic waste into valuable resources that can be reused sustainably. The review discusses the modern approaches that offer several advantages, including reducing the waste disposal and generating renewable energy while addressing emerging wastewater treatment pollutants. To achieve the goal of a circular economy, modern biotechnological approaches including anaerobic digestion, composting, bioleaching, bioremediation, and microbial fuel cells offer a sustainable and effective way to convert waste into valuable products. These bioproducts alongside energy generation using waste-to-energy technologies can provide economic benefits through revenue generation, reduced waste disposal costs, and improved resource efficiency. To achieve a biocircular economy for biowaste valorization, several stakeholders, including waste collectors, waste management companies, policymakers, and consumers need to be involved. The sustainable conversion of biowaste to energy is an essential and instrumental technology in environmental sustainability. Graphical Abstract: [Figure not available: see fulltext.].
Comparative study of pyrolysis and hydrothermal liquefaction of microalgal species: Analysis of product yields with reaction temperature
Xia C., Pathy A., Paramasivan B., Ganeshan P., Dhamodharan K., Juneja A., Kumar D., Brindhadevi K., Kim S.-H., Rajendran K.
Article, Fuel, 2022, DOI Link
View abstract ⏷
Renewable and sustainable biofuel production from algal biomass has been explored vigorously due to the owing potential of overcoming the limitations of first and second-generation biofuel feedstocks. Thermochemical conversion technologies are considered promising routes for bioenergy production from algal biomass and have been extensively investigated over the last few years. This paper aims to review the various pyrolysis (slow, fast, and microwave -assisted) processes and hydrothermal liquefaction (HTL) techniques. The fast pyrolysis is involving a higher heating rate and shorter residence time compared to slow pyrolysis. Microwave-assisted pyrolysis (MAP) is considered a highly efficient process due to uniform heating. Due to a high moisture feedstock, the HTL process is considered the most energy-efficient processing option for algal biomass. In all these processes, the process temperature is considered the most critical parameter affecting product yield. This paper provides a detailed analysis and discussion on the effect of temperature and heating rates on the product (biochar, bio-oil, and syngas) yields for various microalgal species. The process details, different approaches, and process conditions investigated, challenges and recent advancements achieved in both technologies have been discussed in detail that provides useful insights to design a sustainable process and understand the process feasibility.
Dynamic simulation and optimization of anaerobic digestion processes using MATLAB
Article, Bioresource Technology, 2022, DOI Link
View abstract ⏷
Time series-based modeling provides a fundamental understanding of process fluctuations in an anaerobic digestion process. However, such models are scarce in literature. In this work, a dynamic model was developed based on modified Hill's model using MATLAB, which can predict biomethane production with time series. This model can predict the biomethane production for both batch and continuous process, across substrates and at diverse conditions such as total solids, loading rate, and days of operation. The deviation between literature and the developed model was less than ± 7.6%, which shows the accuracy and robustness of this model. Moreover, statistical analysis showed there was no significant difference between literature and simulation, verifying the null hypothesis. Finding a steady and optimized loading rate was necessary to an industrial perspective, which usually requires extensive experimental data. With the developed model, a stable and optimal methane yield generating loading rate could be identified at minimal input.
Sustainable biorefinery approaches towards circular economy for conversion of biowaste to value added materials and future perspectives
Duan Y., Tarafdar A., Kumar V., Ganeshan P., Rajendran K., Shekhar Giri B., Gomez-Garcia R., Li H., Zhang Z., Sindhu R., Binod P., Pandey A., Taherzadeh M.J., Sarsaiya S., Jain A., Kumar Awasthi M.
Article, Fuel, 2022, DOI Link
View abstract ⏷
With the huge energy demand inevitably exacerbates the non-renewable resources depletion and ecological-social challenges, renewable energy has become a crucial participant in sustainable strategy. Biorefinery emerged as a sustainable approach and recognized promising transformation platforms for products, to achieve circular bioeconomy which focuses on the biomass efficient and sustainable valorization, promotes resource regeneration and restorative. The emerged biowaste biorefinery has proved as sustainable approach for integrated bioproducts and further applied this technology in industrial, commercial, agricultural and energy sectors. Based on carbon neutral sustainable development, this review comprehensive explained the biowaste as renewable resource generation and resource utilization technologies from the perspective of energy, nutrient and material recovery in the concept of biorefinery. Integrate biorefinery concepts into biowaste management is promise for conversion biowaste into value-added materials and contribute as driving force to cope with resource scarcity, climate changes and huge material demand in circular bioeconomy. In practice, the optimal of biorefinery technologies depends on environmentally friendly, economic and technical feasibility, social and policy acceptance. Additionally, policy interventions are necessary to promote biowaste biorefinery implements for circular bioeconomy and contribute to low-carbon cleaner environment.
Impact of light on microalgal photosynthetic microbial fuel cells and removal of pollutants by nanoadsorbent biopolymers: Updates, challenges and innovations
Khan M.J., Singh N., Mishra S., Ahirwar A., Bast F., Varjani S., Schoefs B., Marchand J., Rajendran K., Banu J.R., Saratale G.D., Saratale R.G., Vinayak V.
Article, Chemosphere, 2022, DOI Link
View abstract ⏷
Photosynthetic microbial fuel cells (PMFCs) with microalgae have huge potential for treating wastewater while simultaneously converting light energy into electrical energy. The efficiency of such cells directly depends on algal growth, which depends on light intensity. Higher light intensity results in increased potential as well as enhancement in generation of biomass rich in biopolymers. Such biopolymers are produced either by microbes at anode and algae at cathode or vice versa. The biopolymers recovered from these biological sources can be added in wastewater alone or in combination with nanomaterials to act as nanoadsorbents. These nanoadsorbents further increase the efficiency of PMFC by removing the pollutants like metals and dyes. In this review firstly the effect of different light intensities on the growth of microalgae, importance of diatoms in a PMFC and their impact on PMFCs efficiencies have been narrated. Secondly recovery of biopolymers from different biological sources and their role in removal of metals, dyes along with their impact on circular bioeconomy have been discussed. Thereafter bottlenecks and future perspectives in this field of research have been narrated.
Wastewater in India: An untapped and under-tapped resource for nutrient recovery towards attaining a sustainable circular economy
Gowd S.C., Ramakrishna S., Rajendran K.
Article, Chemosphere, 2022, DOI Link
View abstract ⏷
Wastewater (WW) contains nitrogen (N) and phosphorus (P), where N oxidizes to nitrate followed by denitrification to release N2 and P is accumulated in sludge. Higher concentrations of N and P leads to eutrophication and algal blooming, thereby threatening the aquatic life systems. Such nutrients could be potentially recovered avoiding the fertilizer requirements. Distinct nutrient recovery systems have been demonstrated including chemical precipitation, ion-exchange, adsorption, bio-electrochemical systems, and biological assimilation at various scales of volumes. This study focusses on the nutrient recovery possibility from wastewater in India. The resource estimation analysis indicates that at 80% recovery, 1 million liters per day (MLD) of sewage can generate 17.3-kg of struvite using chemical precipitation. When compared with traditional fertilizers, nutrient recovery from sewage has the potential to avoid 0.38-Mt/a in imports. Replacing conventional fertilizer with struvite recovered from WW avoids 663.2 kg CO2eq/ha in emissions (53%). Prevailing WW treatment looks at maintaining the discharging standards while recovering nutrients is an advanced option for a self-reliant and sustainable circular economy. However, more detailed assessments are necessary from techno-economic and environmental perspective in realizing these technologies at an industrial scale.
Latest trends and developments in microalgae as potential source for biofuels: The case of diatoms
Mourya M., Khan M.J., Ahirwar A., Schoefs B., Marchand J., Rai A., Varjani S., Rajendran K., Banu J.R., Vinayak V.
Article, Fuel, 2022, DOI Link
View abstract ⏷
Microalgae are microscopic plants which are found in water, snow as well as land. They are one of the major resources of biofuel. However, the phenomenon of biolipid accumulation and its downstream processing into biofuel for commercialization and industrialization has yet to be standardized at economical scale. Among microalgae, diatoms are third generation microalgae which produces abundant oil and thus serves as one of the biggest sources of fossil fuel energy. They account for more than 25% of global biomass production. Diatoms would suffice world's energy crisis if they are milked/harvested for oil without being sacrificed. Simultaneously in order to get benefitted for crude oil the biochemical modeling of oleaginous microalgae would help in increasing its lipid accumulation to be able to be used in diatom solar panels for Diafuel™ (biofuel from diatoms) production. Such types of living algal solar panels grow in the presence of nitrogen, phosphorus, potassium, silicates, trace metals, few other micro nutrients and even in wastewater. Additionally, molecular tools like Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) offers targeted genome modification in diatoms for increasing oil production deploying specific genes. The review adds the scope to unravel such techniques in diatoms to harvest lipid for Diafuel™ production from a wide range of diatom strains. Several such genetically modified or naturally selected diatom strains rich in oil serve as an important ingredient for diatom solar panels. The main target of this review is to widen the scope of metabolic pathways for enhancing lipid and biofuel in diatoms under nutrient stress media and adapting genetic engineering tools to identify genes responsible for them. It also targets to study the quality of biofuel and life cycle assessment of lipids from diatoms.
Nutrient recovery from wastewater in India: A perspective from mass and energy balance for a sustainable circular economy
Gowd S.C., Kumar D., Lin R., Rajendran K.
Article, Bioresource Technology Reports, 2022, DOI Link
View abstract ⏷
Limited phosphorus availability and increased eutrophication (due to discharge of nitrogen) have pushed everyone to rethink, on how to recover these nutrients. Wastewater (WW) is a potential source to recover N, and P, whereas, in India, it is scarcely explored. In this work, four different nutrient recovery methods were compared from a mass- and energy-balance perspective to understand the overall process flow. From 1000-m3 WW, chemical precipitation yielded 33.8 kg struvite, while micro-algae resulted in 299.1 kg (dry powder). Energy consumption was lowest for the fuel cells at 216.2 kWh/1000 m3, while microalgae used the highest energy at 943.3 kWh/1000 m3. Nonetheless, the cost-saving analysis showed that microalgae (78.6$/1000 m3) as a nutrient recovery choice, had higher savings than any other methods compared. For a country like India, where the two-thirds of urban wastewater is untreated, wastewater-biorefinery options such as nutrient recovery hold the key to a sustainable circular economy.
Towards green whiskey production: Anaerobic digestion of distillery by-products and the effects of pretreatment
Kang X., Lin R., Wu B., Li L., Deng C., Rajendran K., Sun Y., O'Shea R., Murphy J.D.
Article, Journal of Cleaner Production, 2022, DOI Link
View abstract ⏷
Using renewable biogas from the anaerobic digestion of distillery by-products as a low-carbon heat source can decarbonize the distillery process and support the distillery industry to transition to a more sustainable production process. This study investigated the anaerobic digestion performance of different types of whiskey by-products and the effects of acid pretreatment on the digestion of solid by-products. Results of biomethane potential assays showed that the methane yield from the unprocessed by-products was 330 mL/g volatile solids (VS) from draff, 495 mL/g VS from thin stillage, and 503 mL/g VS from thick stillage. For the processed by-products the specific methane yield was 370 mL/g VS from cake maize, 382 mL/g VS from wet distillers’ grains with solubles (WDGS), and 545 mL/g VS from syrup. Acid pretreatment (1% H2SO4 at 135 °C for 15 min) did not significantly improve the methane yield from solid by-products (such as draff and WDGS) but reduced the digestion time by 54.5% for cake maize. The microbial community analysis revealed that methane production from the untreated and acid-pretreated solid by-products (draff and WDGS) was mainly through the hydrogenotrophic methanogenesis pathway. The gross thermal energy in the form of methane produced from 100 tonnes of mixed unprocessed by-products (draff, thin stillage, and thick stillage) was calculated as 24.4 MWthh equivalent to 60.6% of the thermal energy consumed in whiskey production, which effected the same percentage of CO2 emissions reduction.
Myco-biorefinery approaches for food waste valorization: Present status and future prospects
Awasthi M.K., Harirchi S., Sar T., VS V., Rajendran K., Gomez-Garcia R., Hellwig C., Binod P., Sindhu R., Madhavan A., Kumar A.N.A., Kumar V., Kumar D., Zhang Z., Taherzadeh M.J.
Review, Bioresource Technology, 2022, DOI Link
View abstract ⏷
Increases in population and urbanization leads to generation of a large amount of food waste (FW) and its effective waste management is a major concern. But putrescible nature and high moisture content is a major limiting factor for cost effective FW valorization. Bioconversion of FW for the production of value added products is an eco-friendly and economically viable strategy for addressing these issues. Targeting on production of multiple products will solve these issues to greater extent. This article provides an overview of bioconversion of FW to different value added products.
Recovery of value-added products from biowaste: A review
Zhou Y., Kumar V., Harirchi S., Vigneswaran V.S., Rajendran K., Sharma P., Wah Tong Y., Binod P., Sindhu R., Sarsaiya S., Balakrishnan D., Mofijur M., Zhang Z., Taherzadeh M.J., Kumar Awasthi M.
Retracted, Bioresource Technology, 2022, DOI Link
View abstract ⏷
This review provides an update on the state-of-the art technologies for the valorization of solid waste and its mechanism to generate various bio-products. The organic content of these wastes can be easily utilized by the microbes and produce value-added compounds. Microbial fermentation techniques can be utilized for developing waste biorefinery processes. The utilization of lignocellulosic and plastics wastes for the generation of carbon sources for microbial utilization after pre-processing steps will make the process a multi-product biorefinery. The C1 and C2 gases generated from different industries could also be utilized by various microbes, and this will help to control global warming. The review seeks to expand expertise about the potential application through several perspectives, factors influencing remediation, issues, and prospects.
The marginal abatement cost of co-producing biomethane, food and biofertiliser in a circular economy system
Bose A., O'Shea R., Lin R., Long A., Rajendran K., Wall D., De S., Murphy J.D.
Article, Renewable and Sustainable Energy Reviews, 2022, DOI Link
View abstract ⏷
Biomethane from anaerobic digestion of agricultural feedstock is a versatile energy vector for decarbonising agriculture, heavy transport and heat. To lower costs and increase the emission-savings potential, photosynthetic biogas upgrading, cogenerating microalgae with biomethane is investigated here. In a first-of-its-kind work, this paper reports the enviro-economic performance and the marginal (CO2) abatement cost (MAC) of a polygeneration plant co-producing energy (biomethane), food (Spirulina powder) and bio-fertiliser (digestate) from agricultural feedstock using photosynthetic biogas upgrading at small, medium, and industrial scales. A negative MAC at industrial scale (3 MW biomethane), highlighted the environmental and economic benefit (net present value > 11.5 million€ and internal rate of return >40%) of the process as a low-carbon technology over conventional biomethane production processes at a biomethane sale price of 3 c€/kWh (comparable to natural gas). The operational expenditure, including the cost of the Spirulina cultivation medium and the plant capacity factor had the highest influence on its profitability. Replacing beef as a complete food with Spirulina powder maximised the emission savings rather than replacing beef protein with Spirulina protein. Economic allocation as opposed to energy allocation ensured that the levelised cost and specific greenhouse gas emissions of biomethane (<5 c€/kWh; < 3.5 gCO2-eq/MJ), Spirulina powder (<68 €/kg; < 4 kgCO2-eq/kg) and digestate (<5.60 €/tonne; < 0.41 kgCO2-eq/kg-nitrogen) are better than market-available alternatives across all scales. Trading emission savings from biomethane in the European Union emission trading system should allow the financial viability of smaller-scale processes by 2030.
Evaluation of a biomethane, food and biofertiliser polygeneration system in a circular economy system
Bose A., O'Shea R., Lin R., Long A., Rajendran K., Wall D., De S., Murphy J.D.
Article, Renewable and Sustainable Energy Reviews, 2022, DOI Link
View abstract ⏷
Biomethane is a viable alternative to natural gas and diesel for decarbonising hard-to-abate sectors such as agriculture, industry and heavy transport. Unlike conventional biogas upgrading, photosynthetic biogas upgrading cogenerates biomethane, biofertiliser and microalgal bioproducts with the potential to improve resource utilisation and process performance in a circular economy. In this paper, a photosynthetic biogas upgrading-based polygeneration process is proposed and analysed to co-produce biofuel (biomethane), bio-fertiliser (digestate) and food (Spirulina powder, protein supplement) using agricultural feedstock. Based on a multi-criteria performance assessment, the economic and environmental benefits of the process are demonstrated. Thermodynamic performance of the process revealed that reducing the energy for greenhouse heating to cultivate microalgae would enable a higher energy output than input. Using economic allocation, a carbon footprint of biomethane less than 10 gCO2-eq/MJ (lower than 32.9 gCO2-eq/MJ for sustainable biomethane use in transport in the EU Renewable Energy Directive (Recast) (RED-II)); Spirulina protein of 0.8 kgCO2-eq/100 g protein (compared to 50 kgCO2-eq/100 g protein for beef); and digestate of 0.4 kgCO2-eq/kgN (comparing positively to 1.5–3 kgCO2-eq/kgN for synthetic nitrogenous fertiliser) was achieved. Unlike the current RED-II mandated methodology, the analysis established that the energy, CO2 emissions, land and water footprints of each co-product are best represented using an economic allocation principle. Based on the extended nutrition profile, Spirulina as a complete food outperforms most meat and plant-based protein alternatives in terms of CO2 emissions, land, and water footprints.
Recovery of value-added materials from wastewater
Veluchamy C., Loganath R., Sharma D., Gowd S.C., Rajendran K., Varma V.S.
Book chapter, Current Developments in Biotechnology and Bioengineering: Strategic Perspectives in Solid Waste and Wastewater Management, 2021, DOI Link
View abstract ⏷
Recovery of value-added materials from wastewater creates an opportunity for recycling resources to the circular bioeconomy and reduces the burden of the burgeoning demand and depletion of the natural resources. Much progress is focused and found successful in resource recovery options from wastewater in the laboratory scale over the last decade. This chapter aims to highlight and identify the emerging technologies that facilitate the recovery of value-added materials from wastewater systems focusing on subjective opinions and several key challenges. Value-added products such as biofuels, biopolymers, biopesticides, bioflocculants, biosurfactants, proteins and enzymes, and nutrient recovery from wastewater by various biotechnological advanced methodologies and other mechanical/chemical methods have been the primary focus and objective. Foreseeing the future generation of wastewater treatment plants with these resource recovery units along with the traditional treatment plant design would pave a way for the sustainable and circular bioeconomy concept. This helps to identify the potential application of treatment methodologies for the value-added products with further technological advancements. It is also important to understand and identify these knowledge gaps in converting the final end product to a profitable market, with a more sustainable and energy efficient way.
Production of advanced fuels through integration of biological, thermo-chemical and power to gas technologies in a circular cascading bio-based system
Wu B., Lin R., O'Shea R., Deng C., Rajendran K., Murphy J.D.
Review, Renewable and Sustainable Energy Reviews, 2021, DOI Link
View abstract ⏷
In the transition to a climate neutral future, the transportation sector needs to be sustainably decarbonized. Producing advanced fuels (such as biomethane) and bio-based valorised products (such as pyrochar) may offer a solution to significantly reduce greenhouse gas (GHG) emissions associated with energy and agricultural circular economy systems. Biological and thermochemical bioenergy technologies, together with power to gas (P2G) systems can generate green renewable gas, which is essential to reduce the GHG footprint of industry. However, each technology faces challenges with respect to sustainability and conversion efficiency. Here this study identifies an optimal pathway, leading to a sustainable bioenergy system where the carbon released in the fuel is offset by the GHG savings of the circular bio-based system. It provides a state-of-the-art review of individual technologies and proposes a bespoke circular cascading bio-based system with anaerobic digestion as the key platform, integrating electro-fuels via P2G systems and value-added pyrochar via pyrolysis of solid digestate. The mass and energy analysis suggests that a reduction of 11% in digestate mass flow with the production of pyrochar, bio-oil and syngas and an increase of 70% in biomethane production with the utilization of curtailed or constrained electricity can be achieved in the proposed bio-based system, enabling a 70% increase in net energy output as compared with a conventional biomethane system. However, the carbon footprint of the electricity from which the hydrogen is sourced is shown to be a critical parameter in assessing the GHG balance of the bespoke system.
The role of techno-economic implications and governmental policies in accelerating the promotion of biomethane technologies
Kondusamy D., Kaushal M., Ahlawat S., Rajendran K.
Book chapter, Emerging Technologies and Biological Systems for Biogas Upgrading, 2021, DOI Link
View abstract ⏷
Biomethane production and upgrading technologies have gained significance in Europe, since the introduction of the EU landfill directive in 1999. This directive banned the landfilling of organic wastes in the EU region; failing to comply with the directive incurred a penalty of €75/t. Most renewable energy technologies face hurdles in competing with conventional technologies. From an industrial perspective for commercialization, the technology needs to be economically viable. If it is not economically viable, the industry needs start-up support through policies and incentives. Biomethane is no different from other renewable energy systems where initial policy support is needed to kick-start the industry in any country. This chapter deals with the role of techno-economic studies and effective policies in providing a decision-support system for successful implementation of biomethane technologies.
Mechanism and challenges behind algae as a wastewater treatment choice for bioenergy production and beyond
Yadav G., Shanmugam S., Sivaramakrishnan R., Kumar D., Mathimani T., Brindhadevi K., Pugazhendhi A., Rajendran K.
Article, Fuel, 2021, DOI Link
View abstract ⏷
Conventional wastewater (WW) treatment uses activated sludge process, which is accepted worldwide. However, the sustainability of such a process is questioned in terms of emissions, energy savings, and economic benefits. Microalgae based WW treatment has been proposed as a viable alternative to conventional WW treatment. In microalgae treatment, WW including organics and nutrients gets converted to algae, while reclaimed water is discharged back to the environment. Microalgae could be used as a precursor for biochemicals, biofuels or other bio-based products. There are different technologies within microalgae-based WW treatment including adsorption, accumulation, and immobilization of algae. This review attempts to understand the mechanisms of these technologies on how nutrients and organics are removed from WW. Though it is a viable alternative, there are several challenges and limitation that exist in this technology which needs to be addressed to have a commercial perspective. Algae based WW treatment is analysed for its limitation and has been reported here. Beyond WW treatment, this method should also be looked as an emission reduction strategy through CO2 fixation.
A case study on integrated systems analysis for biomethane use
Book chapter, Biomass, Biofuels, Biochemicals: Green-Economy: Systems Analysis for Sustainability, 2021, DOI Link
View abstract ⏷
There is a lack of maturity with biomethane in catching up the fossil energy sources. The commercialization of biomethane needs an in-depth understanding of many factors via integrated systems analysis. Such analysis exponentiates our ability in overcoming the limitations of commercialization and helps us to leap forward in directions to replace conventional energy sources. This fundamental study focuses on integrative systems analysis, including factors such as technology, economics, environment, policy, social, and market in-depth to evaluate the challenges and remedial measures needed to improvise biomethane situations. This case study talks about the Irish biomethane industry, and the incentives needed to sustain it commercially. An in-depth analysis of the choice of feedstock and upgrading techniques, including carbon capture highlights the ease and difficulties of the workability of biomethane in Ireland. The scenarios included wastes from urban, rural, and coastal regions. Urban wastes needed high capital expenditure for upgrading. Water scrubbing, power to gas, and microalgae are the upgrading techniques considered in which water scrubbing has the maximum yield efficiency. Incentives needed for biomethane commercialization are in ranges between 0.13/m3 and 1.03/m3. Finally, an elaborate perspective outlines how integrative systems analysis helps to tackle the biomethane industry in Ireland and elsewhere.
Recent developments and strategies in genome engineering and integrated fermentation approaches for biobutanol production from microalgae
Shanmugam S., Hari A., Kumar D., Rajendran K., Mathimani T., Atabani A.E., Brindhadevi K., Pugazhendhi A.
Article, Fuel, 2021, DOI Link
View abstract ⏷
The major hurdles causing difficulties in mechanized transportation are the depletion of fossil fuels and the high cost of alternative plant-based substrates for producing biofuels. To solve these issues, biofuels were emerged as effective alternatives to reduce pollution caused by the emission of greenhouse gases. Among biofuels, biobutanol is gaining attention as a feasible, renewable, cost-effective, alternative fuel. But the usages of conventional agricultural crops as feedstock are sensitive and controversial due to the growing concern over the availability of food worldwide. Microalgae are an excellent resource to overcome these challenges, which grows on both the sea and freshwater. Microalgae reducing their land usage with agriculture, and there is no food and fuel conflict exist. In addition, microalgae utilize inorganic carbon from the atmosphere for growth; hence they can reduce the emission levels as well as produce clean energy. Therefore, microalgae as third-generation feedstock came into practice due to their fast growth rate and higher carbohydrate content. The main focus of the present review is to discuss in detail about the major challenges faced as a feedstock, genetic engineering strategies adopted and future perspectives to improve the production of biobutanol from microalgae.
A state of the art review on the cultivation of algae for energy and other valuable products: Application, challenges, and opportunities
Kumar B.R., Mathimani T., Sudhakar M.P., Rajendran K., Nizami A.-S., Brindhadevi K., Pugazhendhi A.
Review, Renewable and Sustainable Energy Reviews, 2021, DOI Link
View abstract ⏷
Algae have long been investigated as a plausible reserve of several biofuel and bioactive compounds attributed to their fast-growing characteristics, shorter doubling time, and capability of accumulating lipids. Compounds extracted from algae are being studied in various sectors namely, pharmaceutical, cosmetics, cancer biology, nanoscience, food industry, etc. In view of the rich potentials of algae, this present review is aimed to highlight the significance of different cultivation aspects of microalgae like open pond and photobioreactor and advantages and disadvantages thereof. This state-of-the-art review provides the limitations of energy (biodiesel, bioethanol, biohydrogen, biomethane) products obtained from the algae in a perspective of shifting lab-scale into a field scale. In addition to the cultivation systems and biofuels, several non-energy products or value-added products obtained from algae were critically compared and presented. Data from plethora literatures discussing the advanced methods for the extraction of omega-3, omega-6 fatty acids, vitamins and nanoparticles from algae have been discussed extensively. Further, bioactive compounds extracted from several algal strains were listed. Considering the health benefits, anti-angiogenic, and anti–cancer properties of algal bioactive compounds were described along with other industrial applications. Overall, this comprehensive review will help in understanding status of algal biofuel, cultivation systems, metabolites and their application for the betterment of the human society.
Renewable biohydrogen production from lignocellulosic biomass using fermentation and integration of systems with other energy generation technologies
Bhatia S.K., Jagtap S.S., Bedekar A.A., Bhatia R.K., Rajendran K., Pugazhendhi A., Rao C.V., Atabani A.E., Kumar G., Yang Y.-H.
Review, Science of the Total Environment, 2021, DOI Link
View abstract ⏷
Biohydrogen is a clean and renewable source of energy. It can be produced by using technologies such as thermochemical, electrolysis, photoelectrochemical and biological, etc. Among these technologies, the biological method (dark fermentation) is considered more sustainable and ecofriendly. Dark fermentation involves anaerobic microbes which degrade carbohydrate rich substrate and produce hydrogen. Lignocellulosic biomass is an abundantly available raw material and can be utilized as an economic and renewable substrate for biohydrogen production. Although there are many hurdles, continuous advancements in lignocellulosic biomass pretreatment technology, microbial fermentation (mixed substrate and co-culture fermentation), the involvement of molecular biology techniques, and understanding of various factors (pH, T, addition of nanomaterials) effect on biohydrogen productivity and yield render this technology efficient and capable to meet future energy demands. Further integration of biohydrogen production technology with other products such as bio-alcohol, volatile fatty acids (VFAs), and methane have the potential to improve the efficiency and economics of the overall process. In this article, various methods used for lignocellulosic biomass pretreatment, technologies in trends to produce and improve biohydrogen production, a coproduction of other energy resources, and techno-economic analysis of biohydrogen production from lignocellulosic biomass are reviewed.
Process simulation and techno-economic assessment of vinasse-to-biogas in Cuba: Deterministic and uncertainty analysis
Alfonso-Cardero A., Pages-Diaz J., Contino F., Rajendran K., Lorenzo-LLanes J.
Article, Chemical Engineering Research and Design, 2021, DOI Link
View abstract ⏷
This paper presents a process simulation model in Aspen Plus® and a techno-economic assessment for the anaerobic digestion of Cuban sugarcane vinasses considering three scenarios for biogas application: electricity production (S_1), biomethane as vehicle fuel (S_2), and biomethane for gas grid injection (S_3). From the simulation model, non-significant differences (p_value ≥ 0.1779) between experimental and simulation results were found. S_1 showed the best economic performance among the assessed biogas applications. From the sensitivity analysis, the mean electricity price leading to a net present value of zero for S_1 was 90 USD/MWh, while for S_2 and S_3 the mean incentive required was 0.33 USD/m3biomethane and 0.67 USD/m3biomethane, respectively. The uncertainty analysis showed a chance for investment failure in S_1 less than 10%, whereas for S_2 and S_3 it ranged between 31–37%. The minimum scale required (milling and distillery capacities, ethanol yield) for getting profits from biomethane projects was targeted at 10,800 tcane/day, 108 m3ethanol/d at 10 Lethanol/tcane, respectively. To this end, Cuban plants should significantly increase their average capacities; otherwise, a centralized biomethane production by limiting the number of biomethane plants to one or two per province could be implemented.
Techno-economics and life-cycle assessment of biological and thermochemical treatment of bio-waste
Awasthi M.K., Sarsaiya S., Wainaina S., Rajendran K., Awasthi S.K., Liu T., Duan Y., Jain A., Sindhu R., Binod P., Pandey A., Zhang Z., Taherzadeh M.J.
Review, Renewable and Sustainable Energy Reviews, 2021, DOI Link
View abstract ⏷
The energy sector contributed to three-fourth of overall global emissions in the past decade. Biological wastes can be converted to useful energy and other byproducts via biological or thermo-chemical routes. However, issues such as techno-economic feasibility and lack of understanding on the overall lifecycle of a product have hindered commercialization. It is needed to recognize these inter-disciplinary factors. This review attempts to critically evaluate the role of technology, economics and lifecycle assessment of bio-waste in two processing types. This includes: 1. biological and, 2. thermo-chemical route. The key findings of this work are: 1. Policy support is essential for commercialization of a waste treatment technology; 2. adequate emphasis is necessary on the social dimensions in creating awareness; and 3. from a product development perspective, research should focus on industrial needs. The choice of the treatment and their commercialization depends on the regional demand of a product, policy support, and technology maturity. Utilization of bio-wastes to produce value-added products will enhance circular economy, which in turn improves sustainability.
Insights into diatom microalgal farming for treatment of wastewater and pretreatment of algal cells by ultrasonication for value creation
Khan M.J., Harish, Ahirwar A., Schoefs B., Pugazhendhi A., Varjani S., Rajendran K., Bhatia S.K., Saratale G.D., Saratale R.G., Vinayak V.
Article, Environmental Research, 2021, DOI Link
View abstract ⏷
Wastewater management and its treatment have revolutionized the industry sector into many innovative techniques. However, the cost of recycling via chemical treatment has major issues especially in economically poor sectors. On the offset, one of the most viable and economical techniques to clean wastewater is by growing microalgae in it. Since wastewater is rich in nitrates, phosphates and other trace elements, the environment is suitable for the growth of microalgae. On the other side, the cost of harvesting microalgae for its secondary metabolites is burgeoning. While simultaneously growing of microalgae in photobioreactors requires regular feeding of the nutrients and maintenance which increases the cost of operation and hence cost of its end products. The growth of microalgae in waste waters makes the process not only economical but they also manufacture more amounts of value added products. However, harvesting of these values added products is still a cumbersome task. On the offset, it has been observed that pretreating the microalgal biomass with ultrasonication allows easy oozing of the secondary metabolites like oil, proteins, carbohydrates and methane at much lower cost than that required for their extraction. Among microalgae diatoms are more robust and have immense crude oil and are rich in various value added products. However, due to their thick silica walls they do not ooze the metabolites until the mechanical force on their walls reaches certain threshold energy. In this review recycling of wastewater using microalgae and its pretreatment via ultrasonication with special reference to diatoms is critically discussed. Perspectives on circular bioeconomy and knowledge gaps for employing microalgae to recycle wastewater have been comprehensively narrated.
An overview on bioethanol production from lignocellulosic feedstocks
Toor M., Kumar S.S., Malyan S.K., Bishnoi N.R., Mathimani T., Rajendran K., Pugazhendhi A.
Article, Chemosphere, 2020, DOI Link
View abstract ⏷
Lignocellulosic ethanol has been proposed as a green alternative to fossil fuels for many decades. However, commercialization of lignocellulosic ethanol faces major hurdles including pretreatment, efficient sugar release and fermentation. Several processes were developed to overcome these challenges e.g. simultaneous saccharification and fermentation (SSF). This review highlights the various ethanol production processes with their advantages and shortcomings. Recent technologies such as singlepot biorefineries, combined bioprocessing, and bioenergy systems with carbon capture are promising. However, these technologies have a lower technology readiness level (TRL), implying that additional efforts are necessary before being evaluated for commercial availability. Solving energy needs is not only a technological solution and interlinkage of various factors needs to be assessed beyond technology development.
Advancing anaerobic digestion through two-stage processes: Current developments and future trends
Rajendran K., Mahapatra D., Venkatraman A.V., Muthuswamy S., Pugazhendhi A.
Review, Renewable and Sustainable Energy Reviews, 2020, DOI Link
View abstract ⏷
Two-stage biogas production is reported to overcome the drawbacks of productivity in anaerobic digestion (AD). Recent publications indicate an increase in methane yield between 10 and 30% via two-stage AD. However, the industrial acceptance is minimal due to their reliability and operational issues. This paper critically reviews the two-stage AD for biogas production. Some of the research gaps identified in two-stage AD include lack of techno-economic analysis to show the industry about the feasibility of this process. There is a clear trade-off between the increase in the methane yield vs. the cost it takes to build the second digester. Practically, building a second digester is not economically feasible due to economies of scale. Other technical challenges include the recirculation leads to ammonia accumulation in the system, and disturbance in syntrophic relationships of microbes between the two-stages. Techno-economic analysis suggests that two stage AD could be about 3% expensive than a single stage AD. Further detailed analysis is required to show clear evidence about the economics and feasibility of two stage AD. The parasitic energy demand of the two-stage system will be higher than a single stage AD due to the reason that two reactors are involved for mixing or maintaining temperature. Most of the two-stage AD, operates at a different temperature and hence the energy demand will be different for different reactors. Some of the problem in the literature includes assessing the stage wise OLR, HRT data, and TS/VS balance before and after the process. To address these issues, further work is necessary to standardize the way two-stage experiments are carried out including the parameters that are necessary to be measured for reproducibility.
Competing Reactions Limit Production of Sugars in Hydrothermal Hydrolysis of Grass Silage: An Assessment of the Effect of Temperature on Sugar Production and Parasitic Energy Demand
Lin R., Deng C., Rajendran K., Bose A., Kang X., Murphy J.D.
Article, Frontiers in Energy Research, 2020, DOI Link
View abstract ⏷
Grass represents a major renewable feedstock in temperate climate zones, but its efficient utilization is challenging in biorefineries and advanced biofuels due to its structural recalcitrance. Here hydrothermal hydrolysis (100–180°C, for up to 40 min duration) was investigated to improve sugar yields from grass silage. The optimal conditions (140°C for 20 min duration) showed the highest sugar yield of 0.29 g/g volatile solid (VS) of grass silage. Further increasing the temperature to 180°C favored degradation of sugars (such as glucose, xylose) to by-products (such as furfural, hydroxymethylfurfural). A first-order reaction model confirmed a two-step reaction with the first step hydrolysis and the second step degradation. An energy balance calculation indicated that pre-treatment at 140°C required an energy input of 16.5 kJ/g VS, which could be significantly reduced to 5.1 kJ/g VS through efficient heat recovery. This research assists in understanding of the hydrolysis mechanism and provides a practical solution to produce grass-based sugars for further advanced biofuel and biorefinery applications.
Techno-economic analysis of bioethanol plant by-product valorization: Exploring market opportunities with protein-rich fungal biomass production
Bulkan G., Ferreira J.A., Rajendran K., Taherzadeh M.J.
Article, Fermentation, 2020, DOI Link
View abstract ⏷
The feasibility of dry-grind bioethanol plants is extremely dependent on selling prices of ethanol and by-products, known as Dried distillers grains with solubles (DDGS), and sold as animal feed. Increasing the amount and quality of the by-products can widen potential feed and food markets and improve the process economy and robustness to price fluctuations of ethanol and grain. In this study, the techno-economic analysis of a bioethanol plant was investigated. Integration of edible filamentous fungi into the process leading to the conversion of sidestreams into ethanol and protein-rich fungal biomass for food and feed applications was considered, and its impact was investigated. Sensitivity analysis considered variations on process capacity, on the price of grain and ethanol, and on the price of fungal biomass considering its use for various animal feed (e.g., pig and fish) and human food markets. Selling the fungal biomass in the human food market resulted in 5.56 times higher NPV (net present value) than the base case bioethanol plant after 20 years. Integration of a low-performing strain towards ethanol, followed by the usage of the fungal biomass in the food sector, was found to be the most resistant scenario to the low ethanol selling price and increasing grain price. This study showed that the competitiveness of ethanol plants in the fuel market could be reinforced while meeting the increasing demand for protein sources.
Economics and cost analysis of waste biorefineries
Dhamodharan K., Ahlawat S., Kaushal M., Rajendran K.
Book chapter, Refining Biomass Residues for Sustainable Energy and Bioproducts: Technology, Advances, Life Cycle Assessment, and Economics, 2019, DOI Link
View abstract ⏷
Biorefineries and bio-based products are vital in reducing global emissions and decarbonizing our energy systems. A common hurdle in the commercialization of biorefineries is its economic viability. The economic hurdle starts from procuring biomass and its logistics, technology maturity, and policy support. The rate of commercialization of biorefineries is slow primarily due to the lack of policy support. Biorefineries have to compete with well-established petrochemical products. Policy support can drive innovation, help a technology to mature, create competitiveness to a market which intern could reduce the cost, thus making the economic viability of biorefineries a reality.
Influential aspects in waste management practices
Rajendran K., Lin R., Wall D.M., Murphy J.D.
Book chapter, Sustainable Resource Recovery and Zero Waste Approaches, 2019, DOI Link
View abstract ⏷
Sustainable waste management practices have become challenging due to our consumption behavior and changing socioeconomic conditions. Waste management is a multidimensional problem that requires technology, economics, and sociocultural and political activities to go hand in hand. This chapter attempts to summarize the key influential aspects in waste management practices, including the interaction of the abovementioned factors. Furthermore, the chapter provides some brief data on global waste generation followed by an update on advanced waste management technologies available today. The interaction between the different factors is highlighted. Finally, case studies comparing waste management activities in three different countries is presented.
Review on cultivation and thermochemical conversion of microalgae to fuels and chemicals: Process evaluation and knowledge gaps
Mathimani T., Baldinelli A., Rajendran K., Prabakar D., Matheswaran M., Pieter van Leeuwen R., Pugazhendhi A.
Review, Journal of Cleaner Production, 2019, DOI Link
View abstract ⏷
Over the last decades, microalgae have gained a commendable role in the rising field of biofuel production as they do not compete with food supply, reduce greenhouse gases emission, and mitigate CO2. Specifically, thermochemical processing of microalgae yields products, which can be used both for energy and other industrial purposes, depending on the algal strain, processing method and operative conditions. Algae are converted into various high-value products, including nutraceuticals, colourants, food supplements, char, bio-crude, electricity, heat, transportation fuel, and bio-oil. Therefore, microalgae are believed to be a strategic resource for the upcoming years and their utilization is meaningful for many industrial sectors. In this framework, this review addresses the various thermochemical processing of microalgae to various biofuels and their industrial significance. The obstacles in various thermochemical conversion methods have been critically flagged, in order to enable researchers to choose the optimal method for fuel production. Furthermore, light is shed on cultivation systems to generate rapidly microalgal biomass for thermochemical processing. Eventually, all recent literature advancements concerning microalgae cultivation and thermochemical processing are critically surveyed, and summarized.
What is the level of incentivisation required for biomethane upgrading technologies with carbon capture and reuse?
Rajendran K., Browne J.D., Murphy J.D.
Article, Renewable Energy, 2019, DOI Link
View abstract ⏷
This paper documents a techno-economic assessment of biomethane feedstocks from urban, rural, and coastal settings. Additionally, the effect of three upgrading technologies was investigated, ranging from commercialised systems (water scrubbing) to more advanced systems: power to gas systems employing hydrogen to capture CO2; and microalgae cultivation utilising CO2 in biogas. In total, nine scenarios were investigated based on a combination of the three feedstock groups and the three upgrading technologies. The levelized cost of energy and the incentive required to allow financial sustainability were assessed. The assessment showed that water scrubbing was the cheapest upgrading method. The optimum scenario was the combination of urban based feedstock (food waste) with water scrubbing upgrading costing 87€/MWh, equivalent to 87c/L diesel equivalent. The incentive required was 0.13 €/m3 (or per L of diesel equivalent), however if power to gas was used to upgrade, an incentive of 0.40 €/m3 was required. This was expected as food waste attracts a gate fee. Rural-based plants (using slurries and grasses) are expected to provide the majority of the resource however, for this to become a reality incentive in the range 0.86–1.03 €/m3 are required.
Artificial neural network–genetic algorithm-based optimization of biodiesel production from Simarouba glauca
Sivamani S., Selvakumar S., Rajendran K., Muthusamy S.
Article, Biofuels, 2019, DOI Link
View abstract ⏷
A transesterification reaction was carried out employing an oil of paradise kernel (Simarouba glauca), a non-edible source for producing Simarouba glauca methyl ester (SGME) or biodiesel. In this study, the effects of three variables – reaction temperature, oil-to-alcohol ratio and reaction time – were studied and optimized using response surface methodology (RSM) and an artificial neural network (ANN) on the free fatty acid (FFA) level. Formation of methyl esters due to a reduction in FFA was observed in gas chromatography–mass spectroscopy (GC–MS) analysis. It was inferred that optimum conditions such as an oil-to-alcohol ratio of 1:6.22, temperature of 67.25 and duration of 20 h produce a better yield of biodiesel with FFA of 0.765 ± 0.92%. The fuel properties of paradise oil meet the requirements for biodiesel, by Indian standards. The results indicate that the model is in substantial agreement with current research, and simarouba oil can be considered a potential oil source for biodiesel production.
The combined role of policy and incentives in promoting cost efficient decarbonisation of energy: A case study for biomethane
Rajendran K., O'Gallachoir B., Murphy J.D.
Article, Journal of Cleaner Production, 2019, DOI Link
View abstract ⏷
The levelized cost of energy of biomethane from food waste was assessed at 87 €/MWh, (87 c/L diesel equiv ). Allowing for gate fees the incentive required for financial viability was 0.13 €/m 3 (13 €/MWh). For context, various successful renewable energy policies were analysed across the EU including photovoltaics and biogas in Germany and electric vehicles in Norway. The schemes were compared with an incentive applied (or required) per tCO 2 avoided. For Ireland, this study predicts that biomethane needs a financial subsidy of less than 180 €/tCO 2 avoided, while most successful EU systems offer incentivisation levels less than 260 €/tCO 2 avoided. In terms of incentives per tCO 2 avoided Electric Vehicles (EV) stand out. When including all incentives such as grants and avoided parking costs, EVs can receive a sixteen-fold higher incentive as compared to biomethane based on tCO 2 emissions avoided. The rationale for this high incentive and supporting policy is based on the requirement to initiate a new infrastructure that would not otherwise happen without intervention of a government incentivising decarbonised transport and clean air. Biomethane as a transport fuel requires a very significant change in infrastructure, including the provision of compressed natural gas service stations and natural gas vehicles. Initially (as for other successful renewable energy systems) larger incentives would be required to allow initiation of the industry, but these subsidies can be reduced over time. Biomethane as a transport fuel offers similar rewards as for electric vehicles, decarbonised transport and clean air along with energy security, renewable energy, indigenous jobs and supporting greening of agriculture.
Techno-economic and life cycle assessments of anaerobic digestion – A review
Article, Biocatalysis and Agricultural Biotechnology, 2019, DOI Link
View abstract ⏷
Techno-economic analysis and life cycle assessments are crucial for any processes to be sustainable using the tri-fold metrics including technical feasibility, economic viability, and environmental sustainability. Anaerobic digestion is portrayed as one of the mature technologies for handling solid waste management and bioenergy generation. Nonetheless, a clear assessment of the tri-fold sustainability metrics is not available yet and this review attempts to address this knowledge gap. Important problems in techno-economic analysis and life cycle assessments such as assumptions used, extrapolation of research data, robustness and reproducibility of results, the openness of materials were discussed. Anaerobic digestion helps in treating organic wastes that could be used for different purposes including electricity, vehicle fuel, natural gas substituent, heating, and cooking fuel. However, sustainability in terms of technology, economics and environment remains the question for it to be industrialized.
A critical review of organic manure biorefinery models toward sustainable circular bioeconomy: Technological challenges, advancements, innovations, and future perspectives
Awasthi M.K., Sarsaiya S., Wainaina S., Rajendran K., Kumar S., Quan W., Duan Y., Awasthi S.K., Chen H., Pandey A., Zhang Z., Jain A., Taherzadeh M.J.
Article, Renewable and Sustainable Energy Reviews, 2019, DOI Link
View abstract ⏷
Total livestock emissions account for up to 14.5% of man-made greenhouse gas emissions. Counteractive measures, such as circular economy concepts and negative emission technologies are necessary to limit global warming below 1.5 °C. Possible treatment options for organic manure include anaerobic digestion, combustion, gasification, hydrothermal liquefaction and composting. The choice of treatment varies depending on the economics, the requirement of a specific product, and sociocultural factors. Commercialization of these treatments needs a blend of appropriate technology, feasible economics, policy support and agreeable socio-cultural conditions. Key findings of this study include the following: 1. Increasing scientific awareness about manure management and treatment; 2. Building a sustainable cooperative model to commercialize technologies; 3. Creating a market for manure recycling products; 4. The role of policy in supporting technologies and consumers; and 5. The codigestion of substrates for better efficacy. Current trends show minimal actions in place as opposed to the high-rate of acceleration that is necessary.
Are electrofuels a sustainable transport fuel? Analysis of the effect of controls on carbon, curtailment, and cost of hydrogen
McDonagh S., Deane P., Rajendran K., Murphy J.D.
Article, Applied Energy, 2019, DOI Link
View abstract ⏷
Variable renewable electricity (VRE) decarbonises the electricity grid, but its intermittency leads to variations in price, carbon intensity, and curtailment over time. This has led to interest in utilising difficult to manage electricity to produce electrofuels (such as hydrogen via water electrolysis) for transport. The vast majority of the environmental impact of electrofuels is contained in the electricity they consume however, only consuming otherwise curtailed electricity (produced when supply exceeds demand) leads to prohibitively expensive hydrogen due to low run hours. Using a model which bids for wholesale electricity, two operational strategies (controls) aimed at increasing sustainability without requiring policy changes were tested in electricity system models of 40–60% renewable electricity penetration. (1) Bid price control set a maximum price the plant will pay for electricity. (2) Wind forecast control dictated that the plant may only run when a minimum forecast VRE production is met. It was shown that sourcing electricity at times of low cost or high forecast wind power can lead to more decarbonised hydrogen production (up to 56% more) at a lower cost (up to 57% less). When economically optimised (minimising levelised costs) the bid price control reduced the carbon intensity of the electrofuel produced by 5–25%, and the wind forecast control by 14–38%, compared to the grid average. Both controls demonstrated a high proclivity to utilising otherwise curtailed electricity and can be said to aid grid balancing. The bid price control also greatly reduced the average cost of electricity to the plant. The positive impacts increased with renewables penetration, and significant synergies between economic and environmentally conscious operation of the plants were noted. The operational strategies tested in this paper allow for transport fuels to be produced from grid electricity, without exacerbating the mismatch of supply and demand. Future decentralised quasi-storage using these operating strategies may economically produce transport fuel, and aid grid balancing.
How to optimise photosynthetic biogas upgrading: a perspective on system design and microalgae selection
Bose A., Lin R., Rajendran K., O'Shea R., Xia A., Murphy J.D.
Review, Biotechnology Advances, 2019, DOI Link
View abstract ⏷
Photosynthetic biogas upgrading using microalgae provides a promising alternative to commercial upgrading processes as it allows for carbon capture and re-use, improving the sustainability of the process in a circular economy system. A two-step absorption column-photobioreactor system employing alkaline carbonate solution and flat plate photobioreactors is proposed. Together with process optimisation, the choice of microalgae species is vital to ensure continuous performance with optimal efficiency. In this paper, in addition to critically assessing the system design and operation conditions for optimisation, five criteria are selected for choosing optimal microalgae species for biogas upgrading. These include: ability for mixotrophic growth; high pH tolerance; external carbonic anhydrase activity; high CO2 tolerance; and ease of harvesting. Based on such criteria, five common microalgae species were identified as potential candidates. Of these, Spirulina platensis is deemed the most favourable species. An industrial perspective of the technology further reveals the significant challenges for successful commercial application of microalgal upgrading of biogas, including: a significant land footprint; need for decreasing microalgae solution recirculation rate; and selecting preferable microalgae utilisation pathway.
Emission of volatile organic compounds from composting: A review on assessment, treatment and perspectives
Dhamodharan K., Varma V.S., Veluchamy C., Pugazhendhi A., Rajendran K.
Review, Science of the Total Environment, 2019, DOI Link
View abstract ⏷
Composting is a sustainable technology in treating organic pollutants and controlling odorous gas emissions from different organic solid waste, by reducing its size and volume. When the process parameters are handled efficiently, composting process is greatly effective than other waste treatment options in terms of operational costs, income generation out of compost, reduced air and water pollution. The successful composting operation does not count only the final product, but also the odorous gas emissions being released off to the atmosphere. Biofiltration is a relatively successful air treatment technology for polluted gases containing biodegradable compounds. By optimizing and focusing the operational parameters of biofiltration technology, 90% of treatment efficiency could be achieved with more economical advantage compared to other air treatment technologies. However, the complexity and the uncertainty measures in operating the system and understanding the process biodegradation mechanism is very crucial for the successful performance. Therefore, this review focusses and provides an assessment and treatment of different odorous gas emissions emitted during the composting processes. The recent advancements and treatment options for various volatile organic compounds (VOCs) and other odorous gas emissions during composting is updated. The advancements in bio-trickling filters, bioscrubber technology and membrane bioreactors treating VOCs has been focused. The use of different models in evaluating the process optimization and gas mitigation is also explained. Finally, the environmental impact of VOC compounds released into atmosphere from composting plants has been discussed.
Economics of Solid Waste Management
Rajendran K., Sudharsan Varma V., Mahapatra D.M., Kondusamy D.
Book chapter, Energy, Environment, and Sustainability, 2018, DOI Link
View abstract ⏷
The concept of gazing trash or waste as a worthwhile resource is augmenting exponentially. Despite its worthiness, there are distinct factors which affect the profitability of a plant which processes waste to worthwhile products such as fuels, fertilizers, energy, or chemicals. There is the adequate literature of different processing methods of wastes; however, the majority of the studies do not consider economic perspective. This chapter focusses on the economics of handling wastes including collection and transportation and processing it into value-added products such as compost, electricity, or fuel. Different countries have different legislation for waste handling, and this chapter addresses the waste handling costs in different countries. Furthermore, the profitability of different processing methods was discussed. The critical factors affecting the profitability of waste treatment and handling were identified, and workable solutions or directions were provided to the scientific community to address the problems with an industrial outlook including profitability.
Insect-based biorefinery for bioenergy and bio-based products
Rajendran K., Surendra K.C., Tomberlin J.K., Khanal S.K.
Book chapter, Waste Biorefinery: Potential and Perspectives, 2018, DOI Link
View abstract ⏷
Developing novel approaches for harnessing the resources from nature is not new. And, while using insects to produce bioenergy might seem to be an emerging approach, such concept has been proposed several decades ago. The growing global population coupled with rising affluence has resulted in an increased demand for resources with concomitant production of organic wastes. Insect-based model provides an opportunity to produce bioenergy and bio-based products with concomitant organic waste remediation. This paper critically reviews insect models, especially black soldier flies (BSF), to produce bioenergy and bio-based products. An insect such as BSF larvae can digest about 50% (dry wt.) of organic wastes producing protein- and oil-rich larval biomass. Several studies have focused on small-scale insect larvae production. There are, however, several challenges with respect to mass production due to issues including, but are not limited to, sustainable egg production, waste nutritional variability, heat generation, air distribution, harvesting larvae/prepupae, and process scale-up, among others.
Wastewater Algae to Value-Added Products
Mahapatra D.M., Varma V.S., Muthusamy S., Rajendran K.
Book chapter, Energy, Environment, and Sustainability, 2018, DOI Link
View abstract ⏷
Globally, treatment and management of wastewater are a serious challenge. Voluminous wastewaters are generated on a day-to-day basis that is being either partly treated or untreated finds its ways into surface and groundwater thus enriching the systems with nutrients, pollutants and pathogens. In purview of the increasing water scarcity, rapid water deterioration, higher primary productivity in surface waters due to nutrient enrichment, towering wastewater production and complications related to its treatment, the understanding of water footprint, underlying mechanisms of wastewater treatment and transformation of terrestrial nutrients into value-added products and various downstream processes for their recovery needs to be understood. In this context, the algal treatment systems not only provides a simple and economical solution to wastewater treatment but also aids in the production of many valued bio-based products like lipids as feedstock for biofuels, single-cell proteins, Omega 3 fatty acids, carotenoids as astaxanthin and β-Carotene. The present chapter throws light on various mechanisms and strategies of wastewater transformations into value-added products while evaluating the techno-economics and feasibility of such systems for assessing its potential to be a bio-based industry. Various strategies for algal species selection targeting specific wastewater pollutants grown either as natural population or as engineered consortia with numerous wastewater treatment approaches until the production of valorized biomass is being discussed. Lastly, key techno-economics, environmental challenges and the scope of wastewater transformations into bio-based products are enumerated.
Phytoremediation of Textile Dye Effluents
Muthusamy S., Govindaraj D., Rajendran K.
Book chapter, Energy, Environment, and Sustainability, 2018, DOI Link
View abstract ⏷
Water is the vital source to live and the textile dye effluent is one of the major contaminants present in the wastewater which is highly toxic to all form of lives. Though some effective various methods such as physical, chemical, and biological methods are available to remove the textile dye effluents, phytoremediation is the most economical, eco-friendly, easy to do to degrade the contaminates completely/partially present in effluent. The different plants are found with naturally inhabited metabolic pathways to utilize different dyes and some of the genetically engineered plants are also produced in order to effectively degrade the dyes and to sustain different environmental conditions. Symbiotic relationships between the plant and microbes are also used to help the plants to overcome different kinds of stress. The enzymes like oxidoreductases which are extracted from the plants have shown potent activity against dyes. The significant decrease in color, turbidity, conductivity, total suspended solids (TSS), total dissolved solids (TDS), chemical oxygen demand (COD), and biological oxygen demand (BOD) are taken as indicators of effectiveness of phytoremediation. Several researchers have done extensive studies in phytoremediation area in order to understand the exact mechanism to during treatment of effluents. This chapter mainly focusses on various phytoremediatic methods and its mechanism used in textile effluents treatments.
Techno-economic analysis of biogas upgrading via amine scrubber, carbon capture and ex-situ methanation
Vo T.T.Q., Wall D.M., Ring D., Rajendran K., Murphy J.D.
Article, Applied Energy, 2018, DOI Link
View abstract ⏷
Biogas upgraded to biomethane can provide a renewable gaseous transport fuel and is one of the proposed solutions in meeting the renewable energy supply in transport targets set under the EU Renewable Energy Directive. The upgrading process for biogas involves the removal of CO2. Amine scrubbing is one traditional method of upgrading that is applied due to its low methane slippage and its capability to provide a high purity renewable methane product. However, new technologies such as power to gas (P2G) can also upgrade biogas through biological methanation by combining the CO2 in biogas with H2 to produce renewable methane. The H2 for P2G can be produced through electrolysis of renewable electricity. Through simulation software – SuperPro Designer, the economics of different pathways for upgrading biogas from a grass silage and slurry fed digester are analysed and compared in this paper. Three scenarios were investigated: biogas upgrading through amine scrubbing (scenario 1); biogas upgrading through amine scrubbing with CO2 directed to ex-situ biological methanation (scenario 2) and biogas upgrading through ex-situ biological methanation only (scenario 3). The results show that at a net present value of zero, the minimum selling price (MSP) per m3 of renewable methane for scenario 1, 2 and 3 is €0.76; €1.50 and €1.43, respectively (with an electricity price to produce H2 of €0.10/kWh and a grass silage production cost of €27/t). The electricity price has a significant effect on the cost of renewable methane in both scenarios 2 and 3. The MSP reduces to €1.09 and €1.00 per m3 of renewable methane, respectively for scenarios 2 and 3, if the electricity price is reduced to €0.05/kWh. Since the renewable methane MSP from scenario 2 is higher than scenario 3, it is suggested that direct biogas injection to the methanation reactor is financially more attractive than capturing CO2 from biogas and feeding it to the methanation step. The MSP of renewable methane from both scenarios 2 and 3 are significantly higher than that of scenario 1. However, when considering climate change mitigation, balancing of the electricity network and storage of surplus electricity, utilising P2G can offset some of these costs. The cost of H2 is a significant factor in determining the cost of renewable methane.
Organic Waste and Pollutants Reduction Through Composting
Varma V.S., Muthusamy S., Rajendran K.
Book chapter, Energy, Environment, and Sustainability, 2018, DOI Link
View abstract ⏷
Management of organic solid waste through composting is the sustainable option to prevent leachate and greenhouse gas emissions after disposal/landfilling. Composting reduces a maximum of 65% of the initial volume and also recovers nutrient-rich end product. During composting, the biodegradable organic carbon, micropollutants, and nuisance gases from the organic fractions are biologically transformed into a stabilized product. Millions of indigenous microbial populations act to degrade the waste by releasing off high temperature and gases. The process is largely influenced by the aeration rate, moisture content, C/N ratio, temperature, particle size and volume of the waste material composted. The active thermophilic phase of the composting determines the rate of waste degradation and organic matter transformation during the process. During composting, the waste material undergoes three different temperature phases: (a) initial moderate temperature (less than 40 °C) for a couple of days, (b) the thermophilic temperature (over 40 °C) for few days to several weeks, and finally, (c) the cooling and maturation phase. During the process, the organic carbon and nitrogen are metabolized to moisture, CO2, and other nitrogen gases, significantly reducing the availability of exchangeable carbon and heavy metals in the compost. Furthermore, it also increases the bioavailability of essential plant nutrients total nitrogen (N), ammonium (NH4), phosphate (P2O5), and potash (K2O), and other micronutrients. The release of heavy metals and potential gases during composting is unavoidable, but it can be controlled by adding appropriate bulking agents such as sawdust, dry leaves, wood chips, and optimizing the above-mentioned process parameters. This chapter focusses especially on organic wastes and pollutants reduction through composting. Also, the major influencing factors and process parameters for effective composting of organic waste and treatment of pollutants gases emitted during the process are discussed.
Updates on the pretreatment of lignocellulosic feedstocks for bioenergy production–a review
Rajendran K., Drielak E., Sudarshan Varma V., Muthusamy S., Kumar G.
Review, Biomass Conversion and Biorefinery, 2018, DOI Link
View abstract ⏷
Lignocellulosic biomass is the most abundant renewable energy bioresources available today. Due to its recalcitrant structure, lignocellulosic feedstocks cannot be directly converted into fermentable sugars. Thus, an additional step known as the pretreatment is needed for efficient enzyme hydrolysis for the release of sugars. Various pretreatment technologies have been developed and examined for different biomass feedstocks. One of the major concerns of pretreatments is the degradation of sugars and formation of inhibitors during pretreatment. The inhibitor formation affects in the following steps after pretreatments such as enzymatic hydrolysis and fermentation for the release of different bioenergy products. The sugar degradation and formation of inhibitors depend on the types and conditions of pretreatment and types of biomass. This review covers the structure of lignocellulose, followed by the factors affecting pretreatment and challenges of pretreatment. This review further discusses diverse types of pretreatment technologies and different applications of pretreatment for producing biogas, biohydrogen, ethanol, and butanol.
Biogas from extremophiles
Book chapter, Extremophilic Microbial Processing of Lignocellulosic Feedstocks to Biofuels, Value-Added Products, and Usable Power, 2018, DOI Link
Biofuel policy in India: A review of policy barriers in sustainable marketing of biofuel
Saravanan A.P., Mathimani T., Deviram G., Rajendran K., Pugazhendhi A.
Review, Journal of Cleaner Production, 2018, DOI Link
View abstract ⏷
Global warming issue due to the combustion of fossil fuel pushes the world to produce renewable and environmental friendly fuel from sustainable feedstock. There are several measures on different levels to reduce the global warming including clean energies from wind, solar, and biomass. There are different aspects in bringing these technologies into a reality including development of technology, economic feasibilities, environmental sustainability and finally, support from the government in the form of effective policies and public awareness. Adequate R&D efforts could overcome all the factors but only an effective policy could drive those efforts to reality. Therefore, in this connection this review initially addresses the present state of energy demand, progression of biofuel sources and the bottlenecks in microalgal biofuel production and commercialization. The biofuel policies are essential to change the world's dependence on fossil fuels for a better tomorrow. Hence, this review addresses the salient features of National Biofuel Policy of India that helps in regulating the biofuels production and their marketing. As a part of Policy implementation, government of India introduced several schemes and programs in last two-decades, which includes mandate blending of ethanol with gasoline, diesel with biodiesel, for the future clean energy vision, and incentivizing bio-based products/fuels. In addition, participation of both federal and state governments for clean energy initiatives, capital investments and tax credits were described in detail. Many policies lack easy outreach among public and industries, which needs marketing by the government that secures a clean energy future in India. Though India is in the process of evolution, it might be quite difficult to enact a dedicative legislation to deal with the challenges of biofuel marketing. Therefore, recent initiatives and scope were summarized in this review for future endeavours.
Can power to methane systems be sustainable and can they improve the carbon intensity of renewable methane when used to upgrade biogas produced from grass and slurry?
Article, Applied Energy, 2018, DOI Link
View abstract ⏷
The recast of the renewable energy directive (RED recast) considers power to gas (P2G) an advanced transport biofuel if a 70% greenhouse gas savings as opposed to the fossil fuel displaced is achieved. Power to methane systems can store electricity as gas and the system can be optimised in sourcing CO2 from biogas to upgrade biogas to biomethane. The crucial question in this work is whether P2G systems can be sustainable and if they can improve the sustainability of biomethane systems using traditional upgrading systems. This work evaluates a comparative lifecycle assessment of grass and slurry (50:50 wet weight equivalent to 80:20 volatile solid weight) biomethane using P2G and/or amine scrubbing as an upgrading method. The sustainability of P2G upgrading systems is heavily dependent on the carbon intensity of the source of electricity. Using a 41% decarbonised electricity mix the sustainability was reduced using P2G and would not be deemed sustainable under criterion set by the RED recast. Maintaining a maximum of 2% fugitive CH4 emissions, using 74% slurry (wet weight) in a grass slurry feedstock, allowing for 0.6 t carbon sequestration per hectare per annum in grasslands and using an electricity mix with 85% renewable electricity the whole system including P2G upgrading could satisfy the GHG savings of 70%. However, the traditional system employing amine scrubbing had higher levels of sustainability.
Advanced biohydrogen production using pretreated industrial waste: Outlook and prospects
Prabakar D., Manimudi V.T., Suvetha K S., Sampath S., Mahapatra D.M., Rajendran K., Pugazhendhi A.
Review, Renewable and Sustainable Energy Reviews, 2018, DOI Link
View abstract ⏷
In order to address existing environmental concerns as a result of non-renewable energy sources and to meet future energy demands, biohydrogen offers a suitable alternative energy reserve. Discrete as well as integrative methods of biohydrogen production have been analyzed over time, optimized for achieving high yields. In addition, key process parameters such as temperature, pH, hydraulic retention time, substrate concentration etc., which influence the rate of production have been clarified. Several studies have exploited industrial waste as feed sources for the production of biohydrogen; however, lower yields from these add an additional requirement for suitable pretreatment methods. The present communication examines various pretreatment methods used to increase the accessibility of industrial wastewater/waste for biohydrogen production. Furthermore, a brief overview addresses challenges and constraints in creating a biohydrogen economy. The impacts of pretreating wastes on biohydrogen generation and the latest trends are also supplied. This study helps in the critical understanding of agro-industrial wastes for biohydrogen production, thereby encouraging future outcomes for a sustainable biohydrogen economy.
Optimization of Surfactant Addition in Cellulosic Ethanol Process Using Integrated Techno-economic and Life Cycle Assessment for Bioprocess Design
Kadhum H.J., Rajendran K., Murthy G.S.
Article, ACS Sustainable Chemistry and Engineering, 2018, DOI Link
View abstract ⏷
Surfactants have been demonstrated to be effective in increasing the cellulase enzyme efficacy and overall enzymatic hydrolysis efficiency. However, the impact of the surfactant addition on the economic viability and environmental impacts of the bioethanol process has not been well-investigated. The objective of this study was to determine the economic and the environmental impacts of using five surfactant types - polyethylene glycol (PEG) 3000, PEG4000, PEG6000, PEG8000, and Tween80 - at various concentrations (8%, 5%, 2%, 1%, 0.75%, 0.5%, 0.25%, and 0% (w/w)) during enzymatic hydrolysis and fermentation of pretreated Banagrass. We used an integrated techno-economic and life cycle assesment to guide the selection of optimal surfactant concentration in the bioethanol process. A surfactant concentration of >2% negatively affects the profitability of ethanol, even when there is a statistically significant increase in glucose and ethanol titers. Based on the overall performance indicators for final ethanol, economic viability and environmental impacts, the addition of PEG6000 at 2% (w/w) were determined to be the optimal option. Glucose and ethanol concentrations of 119.2 ± 5.4 g/L and 55.0 ± 5.8 g/L, respectively, with an 81.5% cellulose conversion rate, were observed for 2% (w/w) PEG6000. Techno-economic and life cycle analysis indicated that 2% w/w PEG6000 addition resulted in ROI of 3.29% and had reduced the global warming potential by 6 g CO2/MJ ethanol produced.
Biosorptive removal of Zn(II) ions by Pongamia oil cake (Pongamia pinnata) in batch and fixed-bed column studies using response surface methodology and artificial neural network
Shanmugaprakash M., Venkatachalam S., Rajendran K., Pugazhendhi A.
Article, Journal of Environmental Management, 2018, DOI Link
View abstract ⏷
Design of experiment and artificial neural networks (ANN) have been effectively employed to predict the rate of uptake of Zn(II) ions onto defatted pongamia oil cake. Four independent variables such as, pH (2.0–7.0), initial concentration of Zn(II) ions (50–500 mg/L), temperature (30ºC-50 °C), and dosage of biosorbent (1.0–5.0 g/L) were used for the batch mode while the three independent variables viz. flowrate, initial concentration of Zn(II) ions and bed height were employed for the continuous mode. Second-order polynomial equations were then derived to predict the Zn(II) ion uptake rate. The optimum conditions for batch studies was found to be pH: 4.45, metal ion concentration: 462.48 mg/L, dosage: 2.88 g/L, temperature: 303 K and on the other hand the column studies flow rate: 5.59 mL/min, metal ion concentration: 499.3 mg/L and bed height: 14.82 cm. Under these optimal condition, the adsorption capacity was 80.66 mg/g and 66.29 mg/g for batch and column studies, respectively. The same data was fed to train a feed-forward multilayered perceptron, using MATLAB to develop the ANN based model. The predictive capabilities of the two methodologies were compared, by means of the absolute average deviation (AAD) (4.57%), model predictive error (MPE) (4.15%), root mean square error (RMSE) (3.19), standard error of prediction (SEP) (4.23) and correlation coefficient (R) (0.99) for ANN and for RSM AAD (16.27%), MPE (21,25%), RMSE (13.15%), SEP and R (0.96) by validation data. The findings suggested that compared to the prediction ability of RSM model, the properly trained ANN model has better prediction ability. In batch studies, equilibrium data was used to determine the isotherm constants and first and second order rate constants. In column, bed depth service time (BDST) and Thomas model was used to fit the obtained column data.
Effect of solids loading on ethanol production: Experimental, economic and environmental analysis
Kadhum H.J., Rajendran K., Murthy G.S.
Article, Bioresource Technology, 2017, DOI Link
View abstract ⏷
This study explores the effect of high-solids loading for a fed batch enzymatic hydrolysis and fermentation. The solids loading considered was 19%, 30% and 45% using wheat straw and corn stover as a feedstock. Based on the experimental results, techno-economic analysis and life cycle assessments were performed. The experimental results showed that 205 ± 25.8 g/L glucose could be obtained from corn stover at 45% solids loading after 96 h which when fermented yielded 115.9 ± 6.37 g/L ethanol after 60 h of fermentation. Techno-economic analysis showed that corn stover at 45% loading yielded the highest ROI at 8% with a payback period less than 12 years. Similarly, the global warming potential was lowest for corn stover at 45% loading at −37.8 gCO2 eq./MJ ethanol produced.
How does technology pathway choice influence economic viability and environmental impacts of lignocellulosic biorefineries?
Article, Biotechnology for Biofuels, 2017, DOI Link
View abstract ⏷
Background: The need for liquid fuels in the transportation sector is increasing, and it is essential to develop industrially sustainable processes that simultaneously address the tri-fold sustainability metrics of technological feasibility, economic viability, and environmental impacts. Biorefineries based on lignocellulosic feedstocks could yield high-value products such as ethyl acetate, dodecane, ethylene, and hexane. This work focuses on assessing biochemical and biomass to electricity platforms for conversion of Banagrass and Energycane into valuable fuels and chemicals using the tri-fold sustainability metrics. Results: The production cost of various products produced from Banagrass was $1.19/kg ethanol, $1.00/kg ethyl acetate, $3.01/kg dodecane (jet fuel equivalent), $2.34/kg ethylene and $0.32/kW-h electricity. The production cost of different products using Energycane as a feedstock was $1.31/kg ethanol, $1.11/kg ethyl acetate, $3.35/kg dodecane, and $2.62/kg ethylene. The sensitivity analysis revealed that the price of the main product, feedstock cost and cost of ethanol affected the profitability the overall process. Banagrass yielded 11% higher ethanol compared to Energycane, which could be attributed to the differences in the composition of these lignocellulosic biomass sources. Acidification potential was highest when ethylene was produced at the rate of 2.56 × 10-2 and 1.71 × 10-2 kg SO2 eq. for Banagrass and Energycane, respectively. Ethanol production from Banagrass and Energycane resulted in a global warming potential of - 12.3 and - 40.0 g CO2 eq./kg ethanol. Conclusions: Utilizing hexoses and pentoses from Banagrass to produce ethyl acetate was the most economical scenario with a payback period of 11.2 years and an ROI of 8.93%, respectively. Electricity production was the most unprofitable scenario with an ROI of - 29.6% using Banagrass/Energycane as a feedstock that could be attributed to high feedstock moisture content. Producing ethylene or dodecane from either of the feedstocks was not economical. The moisture content and composition of biomasses affected overall economics of the various pathways studied. Producing ethanol and ethyl acetate from Energycane had a global warming potential of - 3.01 kg CO2 eq./kg ethyl acetate.
Effect of moisture content on lignocellulosic power generation: Energy, economic and environmental impacts
Article, Processes, 2017, DOI Link
View abstract ⏷
The moisture content of biomass affects its processing for applications such as electricity or steam. In this study, the effects of variation in moisture content of banagrass and energycane was evaluated using techno-economic analysis and life-cycle assessments. A 25% loss of moisture was assumed as a variation that was achieved by field drying the biomass. Techno-economic analysis revealed that high moisture in the biomass was not economically feasible. Comparing banagrass with energycane, the latter was more economically feasible; thanks to the low moisture and ash content in energycane. About 32 GWh/year of electricity was produced by field drying 60,000 dry MT/year energycane. The investment for different scenarios ranged between $17 million and $22 million. Field-dried energycane was the only economically viable option that recovered the investment after 11 years of operation. This scenario was also more environmentally friendly, releasing 16-gCO2 equivalent/MJ of electricity produced.
Techno-economic analysis of integrating first and second-generation ethanol production using filamentous fungi: An industrial case study
Rajendran K., Rajoli S., Taherzadeh M.J.
Article, Energies, 2016, DOI Link
View abstract ⏷
The 2nd generation plants producing ethanol from lignocelluloses demand risky and high investment costs. This paper presents the energy- and economical evaluations for integrating lignocellulose in current 1st generation dry mill ethanol processes, using filamentous fungi. Dry mills use grains and have mills, liquefactions, saccharifications, fermentation, and distillation to produce ethanol, while their stillage passes centrifugation, and evaporation to recycle the water and dry the cake and evaporated syrup into animal feed. In this work, a bioreactor was considered to cultivate fungi on the stillage either before or after the centrifugation step together with pretreated lignocellulosic wheat bran. The results showed that the integrated 1st and 2nd generation ethanol process requires a capital investment of 77 million USD, which could yield NPV of 162 million USD after 20 years. Compared to the fungal cultivation on thin stillage modified 1st generation process, the integrated process resulted in 53 million USD higher NPV. The energy analysis showed that the thin stillage modified 1st generation process could reduce the overall energy consumption by 2.5% and increase the ethanol production by 4%. Such modifications in the 1st generation processes and integration concepts could be interesting for the ethanol industries, as integrating lignocelluloses to their existing setup requires less capital investment.
Anaerobic biorefinery: Current status, challenges, and opportunities
Sawatdeenarunat C., Nguyen D., Surendra K.C., Shrestha S., Rajendran K., Oechsner H., Xie L., Khanal S.K.
Review, Bioresource Technology, 2016, DOI Link
View abstract ⏷
Anaerobic digestion (AD) has been in use for many decades. To date, it has been primarily aimed at treating organic wastes, mainly manures and wastewater sludge, and industrial wastewaters. However, with the current advancements, a more open mind is required to look beyond these somewhat restricted original applications of AD. Biorefineries are such concepts, where multiple products including chemicals, fuels, polymers etc. are produced from organic feedstocks. The anaerobic biorefinery concept is now gaining increased attention, utilizing AD as the final disposal step. This review aims at evaluating the potential significance of anaerobic biorefineries, including types of feedstocks, uses for the produced energy, as well as sustainable applications of the generated residual digestate. A comprehensive analysis of various types of anaerobic biorefineries has been developed, including both large-scale and household level applications. Finally, future directives are highlighted showing how anaerobic biorefinery concept could impact the bioeconomy in the near future.
Investigations of red mud as a catalyst in Mahua oil biodiesel production and its engine performance
Senthil M., Visagavel K., Saravanan C.G., Rajendran K.
Article, Fuel Processing Technology, 2016, DOI Link
View abstract ⏷
Biodiesel productions from Mahua oil using two different catalysts, including KOH and activated red mud by catalytic cracking (waste from aluminum industry) were compared in distinctive blends of diesel fuel. Red mud was subjected to characterization studies to find the mechanism of red mud during catalytic cracking using Energy Dispersive Spectroscopy (EDS) and Scanning Electron Microscope (SEM). The cracking process was carried at 300 °C for 2 h and different blends of biodiesel (B25, B50, B75, and B100) were examined for physical properties. Furthermore, the different blends were subjected to a four-stroke diesel engine to study its engine performance. The results showed that the changes in elemental composition during EDS analysis could be an important reason for red mud to have a better calorific value (10,601 kcal/kg) compared to KOH as a catalyst. The NOx emission from KOH biodiesel was 7.5% higher compared to red mud biodiesel when it was blended 100% at 1500 RPM at a maximum brake power (5.2 kW). From the findings of this study, it was evident that using red mud as a catalyst not just increases most of the properties of the fuel, but also reduces the stress on the environment in the form of less emission and fuel consumption. Since red mud was a hazardous waste from aluminum industry, utilizing it for biodiesel productions could also be an economically viable option.
Experimental and economical evaluation of bioconversion of forest residues to biogas using organosolv pretreatment
Kabir M.M., Rajendran K., Taherzadeh M.J., Sarvari Horvath I.
Article, Bioresource Technology, 2015, DOI Link
View abstract ⏷
The methane potential of forest residues was compared after applying organic solvent, i.e., acetic acid, ethanol, and methanol pretreatments using batch anaerobic digestion (AD). The pretreatments were performed at 190°C with 50% (V/V) organic solvent for 60min. The accumulated methane yields after 40days of AD from pretreated forest residues were between 0.23 and 0.34m3 CH4/kg VS, which shows a significant improvement compared to 0.05m3 CH4/kg VS, from untreated forest residues. These improvements count up to 50% increase in the methane yields from the pretreated substrates based on expected theoretical yield from carbohydrates. Among the organic solvents, pretreatments with acetic acid and ethanol led to highest methane yields, i.e., over 0.30m3 CH4/kg VS. However, techno-economical evaluation showed, pretreatment with methanol was more viable financially. The capital investments of the plant operating 20,000tons of forest residues varied between 56 and 60 million USD, which could be recovered in less than 8years of operation.
Impacts of retrofitting analysis on first generation ethanol production: Process design and techno-economics
Rajendran K., Rajoli S., Teichert O., Taherzadeh M.J.
Article, Bioprocess and Biosystems Engineering, 2015, DOI Link
View abstract ⏷
More than half of the bioethanol plants in operation today use corn or grains as raw materials. The downstream processing of mash after fermentation to produce ethanol and distiller grains is an energy-demanding process, which needs retrofitting for optimization. In addition, the fluctuation in the ethanol and grain prices affects the overall profitability of the plant. For this purpose, a process simulation was performed in Aspen Plus<sup>®</sup> based on an existing industrial plant located in Sweden. The simulations were compared using different scenarios including different concentrations of ethanol, using the stillage for biogas production to produce steam instead of distiller grains as a by-product, and altering the purity of the ethanol produced. Using stillage for biogas production, as well as utilizing the steam, reduced the overall energy consumption by 40 % compared to the plant in operation. The fluctuations in grain prices had a high impact on the net present value (NPV), where grain prices greater than 349 USD/ton reached a zero NPV. After 20 years, the plant in operation producing 41,600 tons ethanol/year can generate a profit of 78 million USD. Compared to the base case, the less purified ethanol resulted in a lower NPV of 30 million USD.
Pretreatment of Lignocellulosic Materials
Book chapter, Bioprocessing of Renewable Resources to Commodity Bioproducts, 2014, DOI Link
View abstract ⏷
Lignocelluloses are structural materials in plants expected to withstand physical, chemical, and biological degradation. Nonetheless, biomass, with their content of approximately 70% sugar polymers is attractive materials for production of bioproducts. The purpose of lignocelluloses in nature and their application as sugar sources is hence contrasting to each other. The structure of lignocelluloses and their recalcitrance are matters lifted early in this chapter in order to facilitate the understanding of the factors in need of attention, involving their pretreatment. This discussion is followed by brief descriptions of physical pretreatments, that is, milling, irradiation, steaming, etc., physicochemical methods, that is, explosions with steam, ammonia, CO2, and SO2, chemical pretreatments by alkali, acids, gases, oxidizing agents, and organosolvs, and biological pretreatments by fungi and their enzymes. The different methods for pretreatment of lignocelluloses are compared in terms of their efficiency and from an economic point of view.
A novel process simulation model (PSM) for anaerobic digestion using Aspen Plus
Rajendran K., Kankanala H.R., Lundin M., Taherzadeh M.J.
Article, Bioresource Technology, 2014, DOI Link
View abstract ⏷
A novel process simulation model (PSM) was developed for biogas production in anaerobic digesters using Aspen Plus®. The PSM is a library model of anaerobic digestion, which predicts the biogas production from any substrate at any given process condition. A total of 46 reactions were used in the model, which include inhibitions, rate-kinetics, pH, ammonia, volume, loading rate, and retention time. The hydrolysis reactions were based on the extent of the reaction, while the acidogenic, acetogenic, and methanogenic reactions were based on the kinetics. The PSM was validated against a variety of lab and industrial data on anaerobic digestion. The P-value after statistical analysis was found to be 0.701, which showed that there was no significant difference between discrete validations and processing conditions. The sensitivity analysis for a ±10% change in composition of substrate and extent of reaction results in 5.285% higher value than the experimental value. The model is available at http://hdl.handle.net/2320/12358 (Rajendran et al., 2013b). © 2014 Elsevier Ltd.
Uncertainty over techno-economic potentials of biogas from municipal solid waste (MSW): A case study on an industrial process
Rajendran K., Kankanala H.R., Martinsson R., Taherzadeh M.J.
Article, Applied Energy, 2014, DOI Link
View abstract ⏷
In this study, biogas production from the organic fraction of the MSW (OMSW) was simulated in six different scenarios, using Aspen Plus® based on industrial data. The economic evaluations were made using the Aspen process economic analyzer, considering the plant size and the upgrading methods. The base case had an annual processing capacity of 55,000m3 OMSW. The capital costs and the net present value (NPV) after 20years of operation were 34.6 and 27.2million USD, respectively. The base case was compared to the modified scenarios, which had different upgrading methods, processing capacities, addition of biogas from wastewater sludge treatment, and variation of the substrate (OMSW) between ±200USD/ton. The sensitivity analyses were carried out considering the cost of the OMSW imposed on citizens for collection and transportation of wastes and the different sizes of the plant. The result suggests that producing biogas and selling it, as a vehicle fuel from OMSW is a profitable venture in most scenarios. However, there are some uncertainties, including the collection and transportation costs, landfilling fee, and process operation at lower capacities, which affect its profitability. © 2014 Elsevier Ltd.
A comparative study between single- and two-stage anaerobic digestion processes: Effects of organic loading rate and hydraulic retention time
Aslanzadeh S., Rajendran K., Taherzadeh M.J.
Article, International Biodeterioration and Biodegradation, 2014, DOI Link
View abstract ⏷
The effect of an organic loading rate (OLR) and a hydraulic retention time (HRT) was evaluated by comparing the single-stage and two-stage anaerobic digestion processes. Wastes from the food processing industry (FPW) and the organic fraction of the municipal solid waste (OFMSW) were used as substrates. The OLR was increased at each step from 2gVS/l/d to 14gVS/l/d, and the HRT was decreased from 10days to 3days. The highest theoretical methane yield achieved in the single-stage process was about 84% for the FPW during an OLR of 3gVS/l/d at a HRT of 7 days and 67% for the OFMSW at an OLR of 2gVS/l/d and a HRT of 10days. The single-stage process could not handle a further increase in the OLR and a decrease in the HRT; thus, the process was stopped. A more stable operation was observed at higher OLRs and lower HRTs in the two-stage system. The OLR could be increased to 8gVS/l/d for the FPW and to 12gVS/l/d for the OFMSW, operating at a HRT of 3 days. The results show a conclusion of 26% and 65% less reactor volume for the two-stage process compared to the single-stage process for the FPW and the OFMSW, respectively.
The effect of effluent recirculation in a semi-continuous two-stage anaerobic digestion system
Aslanzadeh S., Rajendran K., Jeihanipour A., Taherzadeh M.J.
Article, Energies, 2013, DOI Link
View abstract ⏷
The effect of recirculation in increasing organic loading rate (OLR) and decreasing hydraulic retention time (HRT) in a semi-continuous two-stage anaerobic digestion system using stirred tank reactor (CSTR) and an upflow anaerobic sludge bed (UASB) was evaluated. Two-parallel processes were in operation for 100 days, one with recirculation (closed system) and the other without recirculation (open system). For this purpose, two structurally different carbohydrate-based substrates were used; starch and cotton. The digestion of starch and cotton in the closed system resulted in production of 91% and 80% of the theoretical methane yield during the first 60 days. In contrast, in the open system the methane yield was decreased to 82% and 56% of the theoretical value, for starch and cotton, respectively. The OLR could successfully be increased to 4 gVS/L/day for cotton and 10 gVS/L/day for starch. It is concluded that the recirculation supports the microorganisms for effective hydrolysis of polyhydrocarbons in CSTR and to preserve the nutrients in the system at higher OLRs, thereby improving the overall performance and stability of the process. © 2013 by the authors.
High-rate biogas production from waste textiles using a two-stage process
Jeihanipour A., Aslanzadeh S., Rajendran K., Balasubramanian G., Taherzadeh M.J.
Article, Renewable Energy, 2013, DOI Link
View abstract ⏷
The efficacy of a two-stage Continuously Stirred Tank Reactor (CSTR), modified as Stirred Batch Reactor (SBR), and Upflow Anaerobic Sludge Blanket Bed (UASB) process in producing biogas from waste textiles was investigated under batch and semi-continuous conditions. Single-stage and two-stage digestions were compared in batch reactors, where 20 g/L cellulose loading, as either viscose/polyester or cotton/polyester textiles, was used. The results disclosed that the total gas production from viscose/polyester in a two-stage process was comparable to the production in a single-stage SBR, and in less than two weeks, more than 80% of the theoretical yield of methane was acquired. However, for cotton/polyester, the two-stage batch process was significantly superior to the single-stage; the maximum rate of methane production was increased to 80%, and the lag phase decreased from 15 days to 4 days. In the two-stage semi-continuous process, where the substrate consisted of jeans textiles, the effect of N-methylmorpholine-N-oxide (NMMO) pretreatment was studied. In this experiment, digestion of untreated and NMMO-treated jeans textiles resulted in 200 and 400 ml (respectively) methane/g volatile solids/day (ml/g VS/day), with an organic loading rate (OLR) of 2 g VS/L reactor volume/day (g VS/L/day); under these conditions, the NMMO pretreatment doubled the biogas yield, a significant improvement. The OLR could successfully be increased to 2.7 g VS/L/day, but at a loading rate of 4 g VS/L/day, the rate of methane production declined. By arranging a serial interconnection of the two reactors and their liquids in the two-stage process, a closed system was obtained that converted waste textiles into biogas. © 2012 Elsevier Ltd.
Experimental and economical evaluation of a novel biogas digester
Rajendran K., Aslanzadeh S., Johansson F., Taherzadeh M.J.
Article, Energy Conversion and Management, 2013, DOI Link
View abstract ⏷
Many developing countries face an energy demand to satisfy the daily needs of the people. Household biogas digesters are among the interesting solutions to meet the energy demands for cooking and lighting, and at the same time taking care of the kitchen wastes. In this study, a novel textile-based biogas digester was developed. The digester was evaluated for biogas production from a synthetic nutrient and an organic fraction of municipal solid waste (OFMSW) as substrates for more than a year. The obtained biogas productivity in both experiments was 570 L/kgVS/day, which indicates that the digester is as efficient in handling of OFMSW as the synthetic nutrients. Based on the obtained biogas production data, the techno-economic evaluation and sensitivity analysis for the process were performed, replacing LPG and kerosene consumption with biogas in households. A 2-m3 digester can supply the fuel needed for cooking for a family of 4-6 people. The sum of investment and 15-years operational costs of this digester was 656 USD, which can be compared with 1455 USD for subsidized-LPG and 975 USD for kerosene, respectively. The results from the sensitivity analysis show that it was a positive investment, unless the price of kerosene goes down to less than 0.18 USD/L. © 2013 Elsevier Ltd. All rights reserved.
Household biogas digesters-A review
Rajendran K., Aslanzadeh S., Taherzadeh M.J.
Review, Energies, 2012, DOI Link
View abstract ⏷
This review is a summary of different aspects of the design and operation of small-scale, household, biogas digesters. It covers different digester designs and materials used for construction, important operating parameters such as pH, temperature, substrate, and loading rate, applications of the biogas, the government policies concerning the use of household digesters, and the social and environmental effects of the digesters. Biogas is a value-added product of anaerobic digestion of organic compounds. Biogas production depends on different factors including: pH, temperature, substrate, loading rate, hydraulic retention time (HRT), C/N ratio, and mixing. Household digesters are cheap, easy to handle, and reduce the amount of organic household waste. The size of these digesters varies between 1 and 150 m3. The common designs include fixed dome, floating drum, and plug flow type. Biogas and fertilizer obtained at the end of anaerobic digestion could be used for cooking, lighting, and electricity. © 2012 by the authors.
Hydrogen generation from algae: A review
Vijayaraghavan K., Karthik R., Kamala Nalini S.P.
Review, Journal of Plant Sciences, 2010, DOI Link
View abstract ⏷
The study focuses on the research involved in generating hydrogen using algae as a renewable energy resource. Due to the decline in fossil fuel resource, the energy derived from biomass seems to be the only major source of world's renewable energy. The hydrogen derived from algae is promising due to its sustainability, no green house gases emission during the combustion of hydrogen and security of its supply even at remote places. The novel approach of generating hydrogen at commercial scale from algae has been a curiosity among many researchers till today. This review study updates the research involved in hydrogen generation from algae based on light intensity and its photoperiod, nitrogen and sulfur content, fermentative metabolism and symbiosis. The following algal species had been widely investigated for hydrogen production namely: Chlamydomonas, Anabaena, Chorella, Oscillatoria, Scenedesmus and their mutant. The generation of hydrogen from algae is still at research level. Hence, this review would be an eye opener for researchers who are interested in generating hydrogen from algae. © 2010 Academic Journals Inc.
Hydrogen production by Chlamydomonas reinhardtii under light driven sulfur deprived condition
Vijayaraghavan K., Karthik R., Kamala Nalini S.P.
Article, International Journal of Hydrogen Energy, 2009, DOI Link
View abstract ⏷
This article explores the possibility of demonstrating sustainable photohydrogen production using Chlamydomonas reinhardtii when grown in sulfur deprived photoautotrophic condition. The hydrogen evolving capability of the algal species was monitored based on alternating light and dark period. Investigation was carried out during the day time in order to exploit the solar energy for meeting the demand of the light period. The results showed that when the reactor was operated at varying photoperiod namely 2, 3 and 4 h of alternating light and dark period, the gas generation was found to be 32 ± 4, 63 ± 7 and 52 ± 5 mL/h, while the corresponding hydrogen content was 47, 86 and 87% respectively. Functional components of hydrogen generation reaction centers were also analyzed, which showed that the PS(I) reaction centers were involved in hydrogen production pathway, as the light absorption by PS(I) was prerequisite for hydrogen generation under sulfur deprived photoautotrophic condition. The findings showed a higher gas yield and hydrogen content under dark period, whereas under light period the gas content was below detectable level for hydrogen due to the reversible hydrogenase reaction. © 2009 Professor T. Nejat Veziroglu.
