Effect of torrefaction on the physiochemical and fuel properties of major Indian waste biomasses
Review, Sustainable Energy Technologies and Assessments, 2025, DOI Link
View abstract ⏷
The increasing importance of biomass-based energy production as a critical component of sustainable energy resources and effective waste management necessitates a comprehensive understanding of the fundamental properties of biomass feedstocks. This review critically evaluates the physicochemical and fuel characteristics of seven widely available biomass sources in India (sugarcane bagasse, sugarcane tops, rice husk, rice straw, maize stalks, maize cobs, and empty palm oil fruit bunches), with a particular focus on the impact of torrefaction. Despite the well-documented benefits of torrefaction in improving biomass properties, limited studies have compared the specific effects of this thermal pretreatment process across diverse biomass sources. This review addresses this gap by critically analyzing the impact of torrefaction on key biomass properties, including hemicellulose, cellulose, lignin, elemental composition (carbon, hydrogen, nitrogen, and sulphur), moisture content, volatile matter, and high heating value, providing a comparative analysis to determine the optimal biomass for energy applications. Moreover, the review critically analyzes the impact of torrefaction on key biomass properties, including hemicellulose, cellulose, lignin, elemental composition (carbon, hydrogen, nitrogen, and sulphur), moisture content, volatile matter, and high heating value. Furthermore, the review synthesizes recent findings to identify optimum torrefaction conditions that enhances the properties of each corresponding biomass. By providing a comprehensive analysis of the complex relationships between biomass characteristics and their practical applications, this review contributes to the advancement of sustainable energy production by optimising biomass-based energy systems and promoting waste-to-energy strategies.
Polyculture microalgae for the removal of organics, nutrients, and emerging contaminants from greywater
Mishel V., Mohit A., Neelancherry R.
Article, Journal of Applied Phycology, 2025, DOI Link
View abstract ⏷
This study explores the potential of polyculture microalgae for removing emerging contaminants – paracetamol (PCT) and caffeine (CAF) – along with organics and nutrients from greywater, while assessing their impact on microalgal growth and overall treatment efficiency. Several reactors containing varying concentrations of PCT and CAF (3 – 10 mg L−1) were monitored for total organic carbon (TOC), nitrate, phosphate removal, and microalgal growth. Polyculture microalgae achieved maximum PCT and CAF removal efficiencies of 94.3% and 43.3%, respectively, with the highest increase in microalgal dry weight (0.41 g L−1) in the run with high PCT and low CAF concentration. The polyculture microalgae achieved higher PCT removal efficiency (94.3%) compared to previous studies using monocultures, demonstrating the potential of polycultures for greywater treatment. The highest TOC (73.6%), nitrate (65.6%), and phosphate (41.4%) removal were observed in the run with the absence of contaminants. The addition of PCT and CAF led to a decrease in the removal efficiencies of TOC by 0.6 – 21.9%, nitrate by 8.7 – 63.0%, and phosphate by 18.5 – 33.1%, suggesting that these contaminants impacted the regular nutrient consumption of the microalgae. However, organic consumption increased as PCT and CAF were also used as carbon sources. Despite reduced nutrient consumption, microalgal growth increased by 24.2%.
Production of engineered algal biochar through microwave pyrolysis for nutrient recovery from aqueous solution
Mishra B., Remya N., Mohit A.
Article, Environmental Quality Management, 2024, DOI Link
View abstract ⏷
Biochar adsorbs contaminants from wastewater. However, biochar's modification, its application in nutrient removal from wastewater, and its mechanism of nutrient removal need to be explored. In this study, nitrate and phosphate were recovered from secondary treated domestic wastewater using microalgal biochar (Spirulina sp.). The biochar was obtained by microwave pyrolysis of algae at 400 W power for 10 min. The biochar was modified using Mg(OH)2 under different conditions. Three pre-and post-treated biochars with varied Mg(OH)2 percentages (2%, 4%, and 6% by weight) were produced. All the modifications in biochar improved its specific surface area. Highest specific surface area of the modified biochar reached 33 m2/g compared to 12 m2/g of the unmodified biochar. SEM analysis showed improvement in the porosity of the modified biochars. Modification also introduced ‒OH, ‒C=C‒ and ‒C‒O‒C‒ functional groups on the biochar surface. All these modifications improved the nutrient adsorption capability of the biochar. Adsorption studies indicated that 4% post-treated biochar (Po4) was the best. The adsorption data fit the pseudo second order kinetic model with R2 being 0.99 and 0.96 for phosphate and nitrate respectively. Among different isotherm models, the Freundlich isotherm model showed the best fit for phosphate and nitrate, with their respective R2 being 0.96 and 0.97, indicating multi-layer physical-chemical adsorption, including the intra-particle diffusion. The equilibrium time for adsorption for nitrate and phosphate was 7 and 6 h, respectively. The optimum pH was 5 and 6 for nitrate and phosphate, respectively, and the optimum dosage was 2 g/L. The maximum adsorption capacity for nitrate and phosphate was 7.9 and 8.9 mg/g, respectively. Po4 showed potential as a fertilizer as it had 5.84 and 3.02 g of extractable phosphate and nitrate per kg of biochar.
Life cycle assessment and technoeconomic analysis of biofuels produced from polyculture microalgae cultivated in greywater
Mohit A., Mishel V.K., Remya N.
Article, Journal of Environmental Management, 2024, DOI Link
View abstract ⏷
This study evaluated the environmental and economic impacts of substituting synthetic media with greywater for cultivating microalgae in the biofuel production process. Life cycle assessment (LCA) and technoeconomic assessment (TEA) were employed to compare the impacts of two scenarios – one containing bold's basal (BB) media and another containing greywater as growth mediums for microalgae cultivation. Scenarios 1 and 2 mitigated 1.74 and 2.14 kg CO2 per kg of biofuel production, respectively. Substituting BB media with greywater resulted in a 16.3% reduction in energy requirements, leading to a 79.3% increase in net energy recovered. LCA findings demonstrate a reduction in all seven environmental categories. TEA reveals that, despite a 21.7% higher capital investment, scenario 2 proves more economically viable due to a 39.8% lower operating cost and additional revenue from wastewater treatment and carbon credits. The minimum selling price of biofuel dropped from Rs 73.5/kg to Rs 36.5/kg, highlighting the economic and environmental advantages of substituting BB media with greywater in microalgal biofuel production.
Exploring effects of carbon, nitrogen, and phosphorus on greywater treatment by polyculture microalgae using response surface methodology and machine learning
Article, Journal of Environmental Management, 2024, DOI Link
View abstract ⏷
The microalgae-based wastewater treatment is a promising technique that contribute to achieving sustainable development goals (SDGs), such as SDG-6, “Clean Water and Sanitation”. However, it is strongly influenced by the initial composition of wastewater. In this study, the impact of initial organics and nutrient concentration on the removal of total organic carbon (TOC), total carbon (TC), ammonium (NH4 +), total nitrogen (TN), and phosphate (PO4 3−) from greywater using native polyculture microalgae was explored. Response surface methodology was employed along with two machine learning approaches, AdaBoost and XGBoost, to evaluate the interactions among three main factors: TOC, NH4 +, and PO4 3−, and their effects on treatment efficiency. The C/N ratios for achieving maximum TOC and TC removal efficiency of 99.2% and 97.7% were determined to be 10.3, and 65.4–73.6, respectively. Notably, the N/P ratio did not significantly affect their removal. The highest NH4 + removal efficiency, reaching 96.2%, was attained at C/N ratios of 4.3, 24.0, 38.2, and 212.9, coupled with N/P ratios of 0.3, 2.6, and 23.4. Highest TN removal efficiency of 77.2% was achieved at C/N and N/P ratios of 12.2 and 2.0, respectively. Highest PO4 3− removal of 78.8% was obtained at N/P ratio 12.8. However, C/N ratio did not affect the removal efficiency. Maintaining these specified C/N and N/P ratios in the influent greywater would ensure that the treated greywater meets the required standards for various reuse applications, including flushing, groundwater recharge, and surface water discharge. The integration of RSM with AdaBoost and XGBoost provided accurate predictions of removal efficiencies. For all the models, XGBoost had the highest R2, and lowest MAE and MSE values. The cross validation of RSM models with AdaBoost and XGBoost further reinforced the reliability of these models in predicting treatment outcomes.
Low-Cost Greywater Treatment Using Polyculture Microalgae—Microalgal Growth, Organics, and Nutrient Removal Subject to pH and Temperature Variations During the Treatment
Article, Applied Biochemistry and Biotechnology, 2024, DOI Link
View abstract ⏷
Organics and nutrient removal studies are rarely done using polyculture microalgae, and that too in outdoor conditions, as they are often not deemed effective for wastewater treatment purposes. This study examined the organics and nutrient removal efficiency of polyculture microalgae cultivated in greywater. The reactor was operated in outdoor conditions. Hence, it was subjected to natural pH and temperature variations. A growth rate of 0.05 g L−1 day−1 was observed for temperatures up to 37 °C, beyond which the growth rate declined by 0.07 g L−1 day−1. During the treatment, the pH of the system was observed to be between 7.4 and 8.4. However, the growth rate would again pick up (0.05 g L−1 day−1) when the pH and temperature moved towards the optimum range, indicating that the polycultures adapt very quickly to their environment. The maximum biomass concentration reached 0.82 gL−1. The highest removal efficiency of organic carbon, ammonia, and phosphate was 80.7, 61.9, and 58.4%, respectively. Nitrate and nitrite concentrations remained ≤ 1.3 mgL−1 and ≤ 2 mgL−1, respectively, indicating the absence of nitrification/denitrification and ammonia volatilization. The mass balance of microalgae indicated that the primary removal mechanism of nitrogen and phosphorus removal was assimilation by the microalgae. The study proved polyculture microalgae to be as effective as some monoculture species in wastewater treatment, which require costlier controlled growth conditions. The high organics and nutrient removal by polycultures in outdoor conditions could pave the way to reducing wastewater treatment costs.
Multifaceted application of modified biochar for water and wastewater treatment
Mohit A., Remya N., Priyadarshini U.
Review, Environmental Quality Management, 2024, DOI Link
View abstract ⏷
Biochar, a carbon-rich material produced through the pyrolysis of biomass, has been shown to have the potential to remove contaminants from water and wastewater. However, due to the weak adsorption capacity and narrow adsorption range of pure biochar, it is modified, either chemically or physically, in order to optimize its applications in water and wastewater treatment. This study summarizes the recent advancements in the application of modified biochar for water and wastewater treatment. Modification of biochar increases its surface area and porous structure, which makes it an effective adsorbent to immobilize a range of contaminants, such as heavy metals, dyes, and organic contaminants. It can also be used as a catalyst in the biodegradation of organic pollutants as it can provide a substrate for microbial growth and metabolism, enhancing pollutant degradation. This study also summarizes various biochar modifications such as gas, acid, alkali, metal, organic compounds, and oxidizing agents. Among the metal-modified biochar, Iron-modified biochar has shown the highest tetracycline (TC) removal efficiency (90.7%) and nitrate adsorption capacity (32.33 mg g−1). N-doped biochars were found to be the most effective biochars for removing heavy metals such as Cd2+ or Cu2+ and aromatic compounds as they can increase the adsorption of raw biochar by up to 70%. Increasing the number of functional groups on the surface of the biochar by using organic compounds like acrylonitrile and chitosan showed a two to three-fold increase in the adsorption capacity of pollutants such as Cd2+ and Hg2+. According to this review, modified biochar technology is a cost-effective and environmentally friendly wastewater treatment method.
Pyrolysis characteristics and kinetics study of native polyculture microalgae using thermogravimetric analysis
Article, Biomass Conversion and Biorefinery, 2024, DOI Link
View abstract ⏷
Native polyculture microalgae have significant potential as feedstocks for biofuels, but a thorough understanding of their pyrolysis kinetic parameters is required to convert them to biofuels efficiently. This study used thermogravimetric analysis (TGA) to examine the pyrolysis properties and kinetics of native polyculture microalgae. The biomass was pyrolysed from room temperature to 800 °C at four heating rates: 10, 20, 30, and 40 °C min−1. The thermal decomposition was analysed using two model-free methods: Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO). It was found that thermal decomposition occurred in three stages: the dehydration stage, the active pyrolysis stage, and the passive pyrolysis stage. The maximum decomposition occurred between 186.7 to 531.7 °C, indicating the simultaneous decomposition of carbohydrates and proteins. The higher heating rates increased the total volatile matter and moved the peak pyrolysis temperature to a higher value due to limited heat transfer. The average activation energy determined by the KAS method (144.11 kJ mol−1) and the FWO method (147.43 kJ mol−1) were in agreement with each other, indicating that the obtained results are reliable. Also, a high R2 of 0.96 – 0.99 indicates that the points fit well. These findings provide useful information for designing pyrolytic systems using polyculture microalgal feedstock and suggest that polyculture microalgae could be a cost-effective alternative for biofuel production.
Polyculture microalgae and Zno/GAC-nanocomposite system for greywater treatment
Bhanu M., Mohit A., Remya N.
Article, Biomass and Bioenergy, 2024, DOI Link
View abstract ⏷
The study addressed the need for sustainable greywater treatment, aiming to mitigate water scarcity and pollution. The potential of using microalgae cultivated in greywater with zinc oxide nanoparticles (ZnO/GAC-nanocomposite) was investigated for these purposes. A batch photobioreactor was employed for 15 d. The nanocomposite system significantly improved nutrient removal, with optimal removal efficiency of 80 % for TOC, 94.2 % for PO43−, and 99.6 % for NH4+. The presence of nanocomposites improved microalgae growth, achieving a density of 1.8 g/L compared to 0.83 g/L without nanocomposites. The microalgal biomass obtained had a high volatile matter content of 74.4 %, low ash content of 5.1 %, and fixed carbon of 20.4 %. The biomass includes 46.74 % carbon, 5.72 % hydrogen, and 38.75 % oxygen, with a high heating value of 18.32 MJ/kg. The reusability of ZnO/GAC-nanocomposite was also assessed, which maintained effective nutrient removal after four cycles, with NH4+, PO43−, and TOC removal rates of 86.1 %, 83.2 %, and 69.8 %, respectively. Comparison of treated greywater with a pH of 8.5, turbidity <4 NTU, COD, NH4+, PO43− of 34, 0.032, and 0.48 mg/L, respectively, with various reuse standards, indicated its potential reuse for toilet flushing.
Optimization of biochar production from greywater grown polyculture microalgae using microwave pyrolysis
Article, Bioresource Technology, 2023, DOI Link
View abstract ⏷
Biochar was produced from polyculture microalgae cultivated in greywater using microwave pyrolysis. The highest biochar yield and fixed carbon content of 49.9% and 68.7% were obtained at microwave power (P) of 800 W and reaction time (T) of 8.6 min. The developed quadratic models, 166.96 – 0.23P – 3.87 T – 3.49 x10-3PT + 1.73 x10-4P2 + 0.13 T2 and – 73.79 + 0.29P + 1.86 T – 1.80 x10-4P2 could predict biochar yield and fixed carbon content respectively with errors of 6.2 and 7.9%. The volatile matter (VM), fixed carbon (FC), and high heating value (HHV) of the biomass were 69.2%. 23.4% and 17.6 MJ/Kg, respectively. VM, FC, and HHV for biochar obtained at optimum conditions were 20.2%, 68.7%, and 28.3 MJ/Kg, respectively. The process had a net positive energy balance of 11.32 MJ/Kg and energy efficiency of 1.76. This study paves the way for biochar production from greywater-grown microalgae, contributing to waste valorization and energy sustainability.
Application of Biochar for Removal of Emerging Contaminants
Book chapter, Energy, Environment, and Sustainability, 2022, DOI Link
View abstract ⏷
Biochar is a carbon-rich product obtained under reducing thermal conditions by the decomposition of biomass. The feedstock characteristics and production methods are the key factors in biochar production. In addition, the modification by different methods improved the morphological and physicochemical properties of biochar and offered diversified use in wastewater treatment. Biochar is extensively used in the removal of emerging contaminants (ECs) like personal care products (PCPs) and pharmaceutically active compounds (PhACs), which are not removed well during conventional wastewater treatment. The status quo of functionalization and characterization of the biochar and recent advancements in the use of as-derived or modified biochar in ECs removal from wastewater will be discussed in this chapter.
Removal of the pharmaceutical compounds from wastewater by biochar
Book chapter, BioChar: Applications for Bioremediation of Contaminated Systems, 2022, DOI Link
View abstract ⏷
Water pollution from pharmaceutical compounds is a critical global challenge. The pharmaceutical compounds and their subsequent metabolites are termed emerging contaminants. The detection of these compounds in surface water and groundwater as well as conventional wastewater treatment plant effluent necessitates a sustainable solution to remove these pollutants to protect water resources. Multiple biological, chemical, and physical methods have been employed to clean the wastewater from the pharmaceuticals. However, they are either low efficiency or expensive. Recently, adsorption has gained prominence in removing pharmaceutical contaminants due to its high efficiency and low capital requirement. Several investigations are conducted to produce low-cost but highly efficient adsorbents for pharmaceutical removal. Biochar, a solid carbonized by-product obtained from biomass pyrolysis, is considered a cheap replacement to commercially available materials to clean the wastewaters. Biochar with or without modification is used for the removal of pharmaceutical contaminants and their metabolites. The biochar modifications such as alkali/ acid modification, magnetic biochar, metal impregnated biochar, microwave-activated biochar, the improvement in biochar properties with these modifications, and enhanced adsorptive removal of pharmaceutical compounds by modified biochar will be discussed in this chapter.
The State-of-the-Art Production of Biofuel from Microalgae with Simultaneous Wastewater Treatment: Influence of Process Variables on Biofuel Yield and Production Cost
Review, Bioenergy Research, 2022, DOI Link
View abstract ⏷
Microalgal biofuel production is a useful process to produce sustainable and carbon-neutral biofuels. The choice of microalgal species and the processes adopted in various production stages determine biofuel production. In this review, recent technological advancements made in various stages of microalgal biofuel production are discussed. This review also discussed the recent progress made in harvesting microalgal biomass and lipid extraction. In addition, the viability of using wastewater as a nutrient source for microalgae and its nutrient removal capabilities has been discussed in detail. This is the first study that enlists and compares the minimum achievable cost of biofuel produced in different studies. Also, process optimization strategies adopted to minimize the cost are discussed. The reported biofuel production cost varied from 0.14 $/L to 24.33 $/L based on the variation in the microalgae strains, production method, and optimization strategies.
Integrated wastewater treatment and biofuel production using microalgae
Book chapter, Microbial Technologies for Wastewater Recycling and Management: Recent Trends, Challenges, and Perspectives, 2022, DOI Link
Application of Native Mix Algal Strain for Gray Water Treatment and Biofuel Production: Preliminary Study
Article, Journal of Hazardous, Toxic, and Radioactive Waste, 2021, DOI Link
View abstract ⏷
The application of native mixed algal strains for wastewater treatment will be investigated in this study. Native mixed algal strains will be collected from Khorda district, Odisha, India, and acclimatized to the secondary treated gray water in a stepwise manner. The algal species in the mixed strain were identified as Oscillatoria sp., Nannochloropsis limnetica, Dictyosphaerium ehrenbergianum, and Chlorella vulgaris. The mixed algal strains will be grown in different systems with combinations of natural light (N) or artificial light (A) and open system (O) or closed system (C). The mixed algal strains grew well in natural light compared with artificial light. The maximum algal biomass concentration of 0.99 and 0.79 g/L, respectively, were observed in the natural light open (NO) and natural light closed (NC) systems. In contrast, the algal strains grown in the closed system indicated improved gray water treatment compared with that of the open system. The organics [(measured as chemical oxygen demand (COD)], NO3-, and PO43- removal from gray water were 85.25%, 88.50%, and 73.12%, respectively, in the NC system. In addition, proximate analysis revealed that the biomass obtained from the NC system was slightly superior with the volatile matter, ash content, and fixed carbon of 28.5%, 69.9%, 29%, and 1.6%, respectively. In addition, the heating value of algal biomass obtained from the NC system (3.86 MJ/kg) was slightly higher than that of the NO system (3.52 MJ/kg).
Delineation of groundwater potential zones for hard rock region in Karnataka using AHP and GIS
Aggarwal M., Saravanan S., Jennifer J.J., Abijith D.
Book chapter, Advances in Science, Technology and Innovation, 2019, DOI Link
View abstract ⏷
The satellite based technology adopting the efficacy of Geographical Information System (GIS) plays a dynamic role in groundwater exploration, assessment and management. The current study investigated the demarcation of groundwater potential zones by integrating RS, GIS and Multi-Criteria Analysis for the hard rock terrain of Gundihalla watershed which lies in Bellary district of Karnataka, India. The thematic layers incorporated in this research includes the Geomorphology, Soil, Drainage Density, Lineament Density, Rainfall, and Slope. Saaty’s Analytical Hierarchy Process was used to determine the weights and ranks of all the thematic layers and the significant classes within each layer. All the thematic layers were then integrated to create the groundwater potential zonation map for the study area. The resulting map was categorized into five different groundwater potential zones, viz., ‘very good,’ ‘good,’ ‘moderate,’ ‘poor’ and ‘very poor.’ The area coverage of these zones in the study region are: 263 km2 (18.76%), 332.3 km2 (23.7%), 327 km2 (23.3%), 238 km2 (17%) and 229 km2 (16.3%) respectively.
