This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/policies/article-withdrawal). This article has been retracted at the request of Elsevier's Research Integrity & Publishing Ethics team and an independent ethics advisor. A journal-wide investigation identified violations of the journal's policies on authorship and conflict of interest related to the submission and review of this paper. Review of this submission was handled by the then Editor-in-Chief (Ashok Pandey) despite an extensive record of collaboration, including co-publication, with four of the paper co-authors (Binod Parameswaran, Raveendran Sindhu, Mukesh Kumar Awasthi, Mohammad J. Taherzadeh). In addition, authorship changes were made during the revision of this paper; the authors Deepanraj Balakrishnan and M. Mofijur were added to the revised paper without validation or authorisation. There was a significant increase of citations of papers authored by the Editor-in-Chief between the original submission and the revised version. In summary, 3 papers by Pandey were cited in the original version of the paper. This increased to 10 papers in the revised version. Acceptance of the article was partly based upon the positive advice of a reviewer who was closely linked to one of the authors (Awasthi). This compromised the editorial process and breached the journal's policies. This investigation was carried out by Elsevier's Research Integrity & Publishing Ethics team, independent of the journal editorial board. The findings and recommendations have been confirmed by an independent ethics advisor. The authors disagree with the retraction and dispute the grounds for it. © 2025 Elsevier Ltd

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. © 2024 Taiwan Institute of Chemical Engineers

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. © 2024 American Chemical Society.

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. © 2025 Elsevier B.V.

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. © 2025 The Institution of Chemical Engineers

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). © 2025 Elsevier Ltd

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. © 2024 Elsevier Ltd

The prevailing global crisis revolves around waste management and the depletion of nonrenewable energy, posing significant challenges for humanity. Fossil fuel refineries, the primary energy and material producers, face scrutiny due to their reliance on nonrenewable sources. The agro- and food industries, which generate vast amounts of biodegradable by-products often labeled as waste, contribute to this environmental dilemma. The diminishing viability of oil extraction stems from escalating fossil fuel prices, their erratic availability, and environmental apprehensions, underscoring the urgency of exploring alternative sustainable solutions to mitigate climate change and reduce fossil fuel dependence. A pivotal area of recent interest is the valorization of food waste (FW) through modern biorefineries and innovative systems capable of converting various biomass sources into biofuels and value-added products. However, implementing a sustainable strategy for biorefineries presents formidable challenges in terms of technical efficiency and economic feasibility. Organic materials such as food waste, grass, and manure can be transformed into high-value volatile fatty acids, carboxylic acids, bioenergy, and bioplastics, offering a promising avenue for waste reduction. Circular bioeconomy has emerged as a viable approach to address global waste and energy challenges. By integrating waste into bioprocesses for the production of valuable goods and metabolites, a sustainable circular bioeconomy can replace petroleum as feedstock, fostering a low-carbon and cleaner environment. This study provides a comprehensive review of organic waste valorization from the agro- and food industries, emphasizing the biorefinery approach to convert waste into bioenergy and value-added products, with a specific focus on bioethanol production and integrated biorefinery applications.

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.

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. © 2024 Elsevier Ltd

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. © 2025 Elsevier Ltd. All rights reserved.

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. © 2024 Taiwan Institute of Chemical Engineers

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.) © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2024.

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. © 2024 Elsevier Ltd

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. © 2024 American Chemical Society.

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 × m 2  × yr), climate change (2031.696 kg CO 2 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 CO 2 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 CO 2 emissions within the proposed global context. These findings are significant regarding economically and environmentally sustainable shrimp feed production worldwide.

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. © 2023 Hydrogen Energy Publications LLC

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. © 2024 Elsevier Ltd

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. © 2024 Elsevier Ltd

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. © 2024 Alpha Creation Enterprise CC BY 4.0.

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.

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. © 2024 Elsevier B.V.

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. © 2023 Elsevier Inc. All rights reserved.

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. © 2023 Elsevier Inc. All rights reserved.

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. © 2024 Elsevier Inc. All rights reserved.

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. © 2023 Elsevier B.V.

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. © 2023 Elsevier Ltd

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. © 2023 Elsevier Ltd

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.

This article has been retracted: please see Elsevier Policy on Article Withdrawal ( https://www.elsevier.com/locate/withdrawalpolicy ). This article has been retracted at the request of Elsevier's Research Integrity & Publishing Ethics team and an independent ethics advisor. A journal-wide investigation identified violations of the journal's policies on conflict of interest related to the submission and review of this paper. Review of this submission was handled by the then Editor-in-Chief (Ashok Pandey) despite an extensive record of collaboration, including co-publication, with five of the paper co-authors (Binod Parameswaran, Raveendran Sindhu, Mukesh Kumar Awasthi, Ranjna Sirohi, Mohammad J. Taherzadeh). Acceptance of the article was solely based upon the positive advice of reviewers who were working on other papers with three of the paper co-authors at the time of review (Awasthi, Sindhu, and Sirohi). This compromised the editorial process and breached the journal's policies. This investigation was carried out by Elsevier's Research Integrity & Publishing Ethics team, independent of the journal editorial board. The findings and recommendations have been confirmed by an independent ethics advisor. The authors disagree with the retraction and dispute the grounds for it.

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. © 2023 Elsevier Ltd

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. © 2023 Elsevier Ltd

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. © 2023 Elsevier Inc. All rights reserved.

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. © 2023 Elsevier Inc. All rights reserved.

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. © 2023 Elsevier Inc. All rights reserved.

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. © 2023 Elsevier Ltd

[No abstract available]

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). © 2023 Elsevier Ltd

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.]. © 2023, The Author(s), under exclusive licence to Springer Nature Switzerland AG.

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. © 2023 Elsevier Inc. All rights reserved.

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/m 3 and 1.03/m 3. Finally, an elaborate perspective outlines how integrative systems analysis helps to tackle the biomethane industry in Ireland and elsewhere.

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-m 3 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 m 3, while microalgae used the highest energy at 943.3 kWh/1000 m 3. Nonetheless, the cost-saving analysis showed that microalgae (78.6$/1000 m 3 ) 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.

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. © 2022 Elsevier Ltd

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% H 2 SO 4 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 MW th h equivalent to 60.6% of the thermal energy consumed in whiskey production, which effected the same percentage of CO 2 emissions reduction.

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.

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.

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.

Wastewater (WW) contains nitrogen (N) and phosphorus (P), where N oxidizes to nitrate followed by denitrification to release N 2 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 CO 2eq /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.

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. © 2022 Elsevier Ltd

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. © 2022 Elsevier Ltd

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. © 2022

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. © 2022

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.

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.

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.

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.

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/m 3 biomethane and 0.67 USD/m 3 biomethane, 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 t cane /day, 108 m 3 ethanol /d at 10 L ethanol /t cane, 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.

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.

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.

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.

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 CO 2 fixation.

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.

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. © 2019 Elsevier Ltd

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.

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.

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.

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.

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.

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.

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 CO 2 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.

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.

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 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.

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.