Evaluation of sludge quality in Indian sewage treatment plants to develop quality control indices.

Dewatered sludges from twenty-two sewage treatment facilities were characterized to develop the quality control indices in India. This study used fertilizer index (FI) and clean index (CI) as a tool for categorizing sludge utilization into different classes (A, B, C and limited use classes LU-1, LU-2, LU-3) by their fertilizing potential, toxicity level, pathogen presence, and vector attraction reduction criteria. The findings revealed that total P (as P2O5), total N, and K (as K2O) in the sludge samples ranged from 0.9 to 5.7%, 1.2 to 3.8%, and 0.1 to 1.5%, respectively. Moreover, all sludges belong to Class C and lower category due to the presence of toxic metals and pathogens. The helminth eggs were found in the range of 25-1450 Numbers/4gTS in sludge samples. The highest number of helminth eggs of 1450/4 g of TS was found in the fecal sludge. The specific oxygen uptake rate (SOUR) values in the sludge samples varied from 0.3 to 4.9, with a median value of 1.3 and an RSD of 86% is way too high. It indicates that the sludge samples need further treatment to be less attractive as a food source for vectors and rodents. However, sludge samples have fertilizing potential and FI values ranges from 4.1 to 4.9, and CI value ranges from 2.5 to 5.0. It indicates that compost is best in quality and has high-fertilizer potential and low heavy-metal content, which is suitable for high-value crops such as organic farming. Further sludge treatment using typical composting, aerobic or anaerobic digestion, and solar or thermal drying could bring the sludges into the Class A and B categories.

Semi-continuous anaerobic co-digestion of thermal and thermal-alkali processed organic fraction of municipal solid waste: Methane yield, energy analysis, anaerobic microbiome.

The semi-continuous anaerobic co-digestion (AcoD) of thermal and thermal-alkali pretreated organic fraction of municipal solid waste (OFMSW) and sewage sludge (SS) was studied under varying hydraulic retention times (HRT) and organic loading rates (OLR Three semi-continuous digesters were operated under control (non-pre-treated), thermally pretreated (125 °C), and thermal-alkali pretreated (125°C-3g/L NaOH) conditions at variable OLRs at 2.5, 4.0, 5.1, and 7.6 kgVS/m3.d and corresponding HRTs of 30, 20, 15, and 10 days. The 10 and 43% higher methane yield (0.445 m3/kgVS) and 11 and 57% higher VS removal (52%) was achieved for thermal-alkali pretreated digester at 5.1 kgVS/m3.d OLR over thermally pretreated (0.408 m3/kgVS, 45% VS removal) and control digesters (0.310 m3/kgVS, 33% VS removal), respectively. Thermal and thermal-alkali digesters failed on increasing the OLR to 7.6 kgVS/m3.d, whereas the control digester becomes upset at 5.1 kgVS/m3.d OLR. The metagenomic study revealed that Firmicutes, Bacteroidetes, Chloroflexi, Euryarchaeota, Proteobacteria, and Actinobacteria were the predominant bacterial population, whereas Methanosarcina and Methanothrix dominated the archaeal community. Energy balance analysis revealed that thermal alkali pretreatment showed the highest positive energy balance of 114.6 MJ/ton with an energy ratio of 1.25 compared with thermally pretreated (81.5 MJ/ton) and control samples (-46.9 MJ/ton). This work pave the way for scaleup of both thermal and thermal-alkali pre-treatment at 125 °C to realize the techno-economic and energy potential of the process.

Advanced steam-explosion pretreatment mediated anaerobic digestion of municipal sludge: Effects on methane yield, emerging contaminants removal, and microbial community.

Advanced steam explosion pretreatment, i.e., the Thermal hydrolysis process (THP) is applied mainly to improve the sludge solubilization and subsequent methane yield in the downstream anaerobic digestion (AD) process. However, the potential of THP in pretreating the high solids retention time (SRT) sludges, mitigating the risk of emerging organic micropollutants and effects on anaerobic microbiome in digester remains unclear. In this study, sludge from a sequencing batch reactor (SBR) system operating at a SRT of 40 days was subjected to THP using a 5 L pilot plant at the temperature ranges of 120-180 °C for 30-120 min. The effect of THP on organics solubilization, methane yield, organic micropollutant removal, and microbial community dynamics was studied. The highest methane yield of 507 mL CH4/g VSadded and volatile solids (VS) removal of 54% were observed at 160°C- 30min THP condition, i.e., 4.1 and 2.6 times higher than the control (123 mL CH4/gVSadded, 20.7%), respectively. The experimental values of hydrolysis coefficient and methane yield have been predicted using Modified Gompertz, First order, and Logistics models. The observed values fitted well with all three models showing an R2 value between 0.96 and 1.0. THP pretreated sludges showed >80% removal of Trimethoprim, Enrofloxacin, Ciprofloxacin, and Bezafibrate. However, Carbamazepine, 17α-ethinylestradiol, and Progesterone showed recalcitrant behavior, resulting in less than 50% removal. Microbial diversity analysis showed the dominance of Proteobacteria, Firmicutes, Chloroflexi, and Bacteroidetes, collectively accounting for >70-80% of bacterial reads. They are mainly responsible for the fermentation of complex biomolecules like polysaccharides, proteins, and lipids. The THP-mediated anaerobic digestion of sludge shows better performance than the control digestion, improved methane yield, higher VS and micropollutants removal, and a diverse microbiome in the digester.

Prevalence of pharmaceuticals and personal care products, microplastics and co-infecting microbes in the post-COVID-19 era and its implications on antimicrobial resistance and potential endocrine disruptive effects.

The COVID-19 (coronavirus disease 2019) pandemic's steady condition coupled with predominance of emerging contaminants in the environment and its synergistic implications in recent times has stoked interest in combating medical emergencies in this dynamic environment. In this context, high concentrations of pharmaceutical and personal care products (PPCPs), microplastics (MPs), antimicrobial resistance (AMR), and soaring coinfecting microbes, tied with potential endocrine disruptive (ED) are critical environmental concerns that requires a detailed documentation and analysis. During the pandemic, the identification, enumeration, and assessment of potential hazards of PPCPs and MPs and (used as anti-COVID-19 agents/applications) in aquatic habitats have been attempted globally. Albeit receding threats in the magnitude of COVID-19 infections, both these pollutants have still posed serious consequences to aquatic ecosystems and the very health and hygiene of the population in the vicinity. The surge in the contaminants post-COVID also renders them to be potent vectors to harbor and amplify AMR. Pertinently, the present work attempts to critically review such instances to understand the underlying mechanism, interactions swaying the current health of our environment during this post-COVID-19 era. During this juncture, although prevention of diseases, patient care, and self-hygiene have taken precedence, nevertheless antimicrobial stewardship (AMS) efforts have been overlooked. Unnecessary usage of PPCPs and plastics during the pandemic has resulted in increased emerging contaminants (i.e., active pharmaceutical ingredients and MPs) in various environmental matrices. It was also noticed that among COVID-19 patients, while the bacterial co-infection prevalence was 0.2-51%, the fungi, viral, protozoan and helminth were 0.3-49, 1-22, 2-15, 0.4-15% respectively, rendering them resistant to residual PPCPs. There are inevitable chances of ED effects from PPCPs and MPs applied previously, that could pose far-reaching health concerns. Furthermore, clinical and other experimental evidence for many newer compounds is very scarce and demands further research. Pro-active measures targeting effective waste management, evolved environmental policies aiding strict regulatory measures, and scientific research would be crucial in minimizing the impact and creating better preparedness towards such events among the masses fostering sustainability.

Microplastics in landfill leachate: Occurrence, health concerns, and removal strategies.

Landfills are commonly used to manage solid waste, but they can contribute to microplastic (MPs) pollution. As plastic waste degrades in landfills, MPs are released into the surrounding environment, contaminating soil, groundwater, and surface water. This poses a threat to human health and the environment, as MPs can adsorb toxic substances. This paper provides a comprehensive review of the degradation process of macroplastics into microplastics, the types of MPs found in landfill leachate (LL), and the potential toxicity of microplastic pollution. The study also evaluates various physical-chemical and biological treatment methods for removing MPs from wastewater. The concentration of MPs in young landfills is higher than in old landfills, and specific polymers such as polypropylene, polystyrene, nylon, and polycarbonate contribute significantly to microplastic contamination. Primary treatments such as chemical precipitation and electrocoagulation can remove up to 60-99% of total MPs from wastewater, while tertiary treatments such as sand filtration, ultrafiltration, and reverse osmosis can remove up to 90-99%. Advanced techniques, such as a combination of membrane bioreactor, ultrafiltration, and nanofiltration (MBR + UF + NF), can achieve even higher removal rates. Overall, this paper highlights the importance of continuous monitoring of microplastic pollution and the need for effective microplastic removal from LL to protect human and environmental health. However, more research is needed to determine the actual cost and feasibility of these treatment processes at a larger scale.

Microplastics as emergent contaminants in landfill leachate: Source, potential impact and remediation technologies.

A significant amount of plastic waste is generated each year on a global scale, in which the maximum quantity of plastic waste is typically dumped in landfills in various parts of the world. Moreover, dumping plastic waste in landfills cannot address the issue of proper disposal; it simply delays the process. Exploiting waste resources entails environmental hazards because plastic wastes buried in landfills gradually break down into Microplastics (MPs) due to physical, chemical, and biological effects. The possibility of landfill leachate as a source of MPs in the environment has not received much attention. Without systematic treatment, MPs in leachate increase the risk to human health and environmental health since they contain dangerous and toxic pollutants and antibiotic resistance genes transmitted by leachate vectors. Due to their severe environmental risks, MPs are now widely recognized as emerging pollutants. Therefore, the composition of MPs in landfill leachate and the interaction of MPs with other hazardous contaminants are summarised in this review. The available potential mitigation or treatment methods of MPs in landfill leachate as of now, along with the drawbacks and challenges of the present leachate treatment for eliminating MPs, are described in this review. Since it is unclear how MPs will be removed from the current leachate facilities, it is crucial to develop innovative treatment facilities as quickly as possible. Finally, the areas that require more research to provide complete solutions to the persistent problem of plastic debris are discussed.

Global distribution of pesticides in freshwater resources and their remediation approaches.

The role of pesticides in enhancing global agricultural production is magnificent. However, their unmanaged use threatens water resources and individual health. A significant pesticide concentration leaches to groundwater or reaches surface waters through runoff. Water contaminated with pesticides may cause acute or chronic toxicity to impacted populations and exert adverse environmental effects. It necessitates the monitoring and removing pesticides from water resources as prime global concerns. This work reviewed the global occurrences of pesticides in potable water and discussed the conventional and advanced technologies for the removal of pesticides. The concentration of pesticides highly varies in freshwater resources across the globe. The highest concentration of α-HCH (6.538 µg/L, at Yucatan, Mexico), lindane (6.08 µg/L at Chilka lake, Odisha, India), 2,4, DDT (0.90 µg/L, at Akkar, Lebanon), chlorpyrifos (9.1 µg/L, at Kota, Rajasthan, India), malathion (5.3 µg/L, at Kota, Rajasthan, India), atrazine (28.0 µg/L, at Venado Tuerto City, Argentina), endosulfan (0.78 µg/L, at Yavtmal, Maharashtra, India), parathion (4.17 µg/L, at Akkar, Lebanon), endrin (3.48 µg/L, at KwaZuln-Natl Province, South Africa) and imidacloprid (1.53 µg/L, at Son-La province, Vietnam) are reported. Pesticides can be significantly removed through physical, chemical, and biological treatment. Mycoremediation technology has the potential for up to 90% pesticide removal from water resources. Complete removal of the pesticides through a single biological treatment approach such as mycoremediation, phytoremediation, bioremediation, and microbial fuel cells is still a challenging task, however, the integration of two or more biological treatment approaches can attain complete removal of pesticides from water resources. Physical methods along with oxidation methods can be employed for complete removal of pesticides from drinking water.

Combined sodium citrate and ultrasonic pretreatment of waste activated sludge for cost effective production of biogas.

This study aimed to pretreat the waste activated sludge (WAS) by ultrasonication in an energy efficient way by combining sodium citrate with ultrasonic pretreatment at 0.03 g/g suspended solids (SS) of dosage. The ultrasonic pretreatment was done at various (20-200 W) power levels, sludge concentration (7 to 30 g/L), sodium citrate dosages (0.01 to 0.2 g/g SS). An elevated COD solubilization of 26.07 ± 0.6 % was achieved by combined pretreatment at a treatment time of 10 min, ultrasonic power level of 160 W when compared to individual ultrasonic pretreatment (18.6 ± 0.5 %). A higher biomethane yield of 0.26 ± 0.009 L/g COD was achieved in sodium citrate combined ultrasonic pretreatment (SCUP) than ultrasonic pretreatment (UP) 0.145 ± 0.006 L/g COD. Almost 50% of the energy can be saved through SCUP when compared to UP. Future study evaluating SCUP in continuous mode anaerobic digestion is vital.

Resolution of conflict of reduced sludge production with EBPR by coupling OSA to A2/O process in a pilot scale SBR.

The pinnacle of all the efforts of nutrient removal is practically put-down the moment biological cells are lysed, hydrolyzed or digested causing subsequent reappearance of assimilated nitrogen and phosphorus in any biological process. While sludge reduction requires high SRT, the enhanced phosphorus assimilative uptake demands low SRT. A novel reactor configuration for enhanced sludge and phosphorus removal was put to test by incorporating a side stream anaerobic reactor to an Anaerobic-Anoxic-Aerobic (A2O) SBR with a pre-anoxic chamber and an influent receiving inlet anaerobic reactor. The reactor was operated at the average and lowest range of prevailing carbon/phosphorus (C/P) ratio of 50 and 15 in the sewage. The phosphorus enrichment was 0.0469-0.135 mgTP/mgVSS resulting in 1.76-5.05-fold increase from cellular content by virtue of maintaining sludge recycle from SBR aeration tank to side stream anaerobic reactor from 3.78 to 9.78 (average 4.4-8.2) gVSS/gVSS present in the reactor. However, the sludge was also reduced from 3% to 51% on an average basis during the same recirculation regime. This novel configuration consists of an inlet anaerobic reactor, one pre-anoxic chamber and one intermittent oxic anoxic reaction SBR and a side stream anaerobic reactor. The first anaerobic reactor at inlet followed by pre-anoxic chamber was provided for increased ortho-p released and nitrification respectively and a side stream anaerobic reactor for sludge reduction through sludge fasting mechanism. The EBPR and lesser sludge growth were two conflicting parameters reconciled to the extent that if sludge recycled up to 6.41 gVSS/gVSS the sludge growth would be reduced by 25% and phosphorus enrichment could be attained up to 3.46 times the stoichiometric value. Any further recirculation would reduce the sludge further but at the expense of enhanced phosphorus uptake as released phosphorus from side stream anaerobic reactor also recycled back to main SBR causing looping and at more than 6.41gVSSrecycled/gVSS it nullified the enhanced effect.

Hydrothermal and thermal-alkali pretreatments of wheat straw: Co-digestion, substrate solubilization, biogas yield and kinetic study.

Agro-waste having lignocellulosic biomass is considered most effective (heating value 16 MJ/kg) for energy production through anaerobic digestion (AD). However, recalcitrant lignocellulosic fraction in agro-waste obstructs its biotransformation and is a rate-limiting step of the process. This study investigated the effects of hydrothermal and thermal-alkaline pretreatment on anaerobic co-digestion of wheat straw (WS). The hydrothermal pretreatment of WS revealed that 60 min was the best pretreatment time to achieve the highest substrate solubilization. It was employed for thermal-alkali pretreatment at variable temperatures and NaOH doses. Thermal-alkali pretreatment at 125°C-7% NaOH shows the highest (34%) biogas yield of 662 mL/gVS, followed by 646 mL/gVS biogas yield at 150°C-1% NaOH assay (31% higher) over control. Although the 125°C-7% NaOH assay achieved the highest biogas yield, the 150°C-1% NaOH assay was found more feasible considering the cost of a 6% higher chemical used in the earlier assay. The thermal-alkali pretreatment was observed to reduce the formation of recalcitrant compounds (HMF, Furfural) and increase the buffering capacity of the slurry over hydrothermal pretreatment. Principal component analysis (PCA) of the various pretreatment and AD operational parameters was carried out to study their in-depth correlation. Moreover, a kinetic study of the experimental data was performed to observe the biodegradation trend and compare it with the Modified Gompertz (MG) and First Order (FO) models.

Principles and potential of thermal hydrolysis of sewage sludge to enhance anaerobic digestion.

Sewage sludge is rich source of carbon, nutrients, and trace elements and can be subjected to proper treatment before disposal to fulfill government legislation and protect receiving environments. Anaerobic digestion (AD) is a well-adopted technology for stabilizing sewage sludge and recovering energy-rich biogas and nutrient-rich digestate. However, a slow hydrolysis rate limits the biodegradability of sludge. In the present study we have attempted to explain the potential of thermal hydrolysis to enhance anaerobic digestion of sewage sludge. Thermal pretreatment improves biodegradability and recycling of the sludge as an excellent energy and nutrients recovery source at reasonable capital (CAPEX) and operational (OPEX) costs. Other pretreatments like conventional (below/above 100 °C), temperature-phased anaerobic digestion (TPAD), microwave and chemically mediated thermal pretreatment have also been accounted. This review provides a holistic overview of sludge's characterization and value-added properties, various techniques used for sludge pretreatment for resource recovery, emphasizing conventional and advanced thermal pretreatment, challenges in scale-up of these technologies, and successful commercialization of thermal pretreatment techniques.

Technological advancements in valorization of second generation (2G) feedstocks for bio-based succinic acid production.

Succinic acid (SA) is used as a commodity chemical and as a precursor in chemical industry to produce other derivatives such as 1,4-butaneidol, tetrahydrofuran, fumaric acid, and bio-polyesters. The production of bio-based SA from renewable feedstocks has always been in the limelight owing to the advantages of renewability, abundance and reducing climate change by CO2 capture. Considering this, the current review focuses on various 2G feedstocks such as lignocellulosic biomass, crude glycerol, and food waste for cost-effective SA production. It also highlights the importance of producing SA via separate enzymatic hydrolysis and fermentation, simultaneous saccharification and fermentation, and consolidated bioprocessing. Furthermore, recent advances in genetic engineering, and downstream SA processing are thoroughly discussed. It also elaborates on the techno-economic analysis and life cycle assessment (LCA) studies carried out to understand the economics and environmental effects of bio-based SA synthesis.

Critical insights into anaerobic co-digestion of wheat straw with food waste and cattle manure: Synergistic effects on biogas yield and kinetic modeling.

In this study, four batch assays were performed to ensure the synergic effects of co-digestion and find out the best inoculums to substrate ratio (ISR), carbon to nitrogen ratio (C:N), and total solid (TS) percentage in sequence. The co-digestion of three feedstocks had a 20% higher biogas yield (416 mL/gVS added) than mono-digestion with 21% volatile solids (VS) degradation. The ISR of 2 leads to the highest biogas yield (431 mL/gVS added) and VS removal (30.3%) over other ISRs (0.5, 1.0, 2.5) studied. The lower ISR (<2) tended to have lower pH due to insufficient anaerobes inside the digester. The C:N 35 (with ISR 2) yielded 17.4% higher biogas (443.5 mL/gVS added) than mono-digestion and was the highest among the C:N ratios studied with 36.6% VS removal. The VFA, alkalinity, and pH in C:N 35 assay were more stable than in other C:N assays. In the fourth batch assay, varying TS% (5, 7.5, 10, 12.5) were used with optimized ISR (2) and C:N (35). Higher TS% (10 and 12.5) had some lag phase but later achieved higher biogas production. The 12.5% TS assay achieved 80% higher biogas yield (679 mL/gVS added) over mono-digestion, i.e., highest among the TS% studied, with 48% VS removal. In conclusion, co-digestion of mixed feedstocks with ISR 2, C:N 35, and TS 12.5% could degrade almost half of the substrate available for biodegradation. Further biodegradation may require pretreatment of the recalcitrant WS. Modified Gompertz, first-order, transference, and logistic models were used for kinetic study and curve fitting of experimental data. For the optimized batch assays, the estimated specific rate constants were 0.08, 0.12, 0.083, and 0.084. The data fits well in all the models, with the coefficient of discrimination (R2) ranging from 0.882 to 0.999.

Biohydrogen production from waste activated sludge through thermochemical mechanical pretreatment.

Generation of excess sludge in large quantities from wastewater treatment plant face huge problem in terms of handling and management, whereas it possess higher organic and inorganic constituents and thus it can be used as a feedstock for the generation of biofuel with proper disintegration techniques.In this regard, an effort has been made in this study to combine thermo-chemo-disperser pretreatment for the disintegration of paper mill waste activated sludge for the production of biohydrogen in an energy efficient way. These combinations of thermo-chemo-disperser (TCD) tend to be effective in disintegration and possess 24.3% COD solubilization and higher suspended solid reduction of 18.8% at the specific energy usage of 2081.82 kJ/kg TS. The pretreatment with TCD technique shows the biohydrogen production of 120.2 mLH2/gCOD as compared to thermochemically pretreated alone (73.6 mLH2/gCOD) sample. Thus, the combined process was considered to be potentially effective in sludge disintegration.

Energy feasibility and life cycle assessment of sludge pretreatment methods for advanced anaerobic digestion.

Energy sustainability is one of the critical parameters to be studied for the successful application of pretreatment processes. This study critically analyzes the energy efficiency of different energy-demanding sludge pretreatment techniques. Conventional thermal pretreatment of sludge (∼5% total solids, TS) produced 244 mL CH4/gTS, which could result in a positive energy balance of 2.6 kJ/kg TS. However, microwave pretreatment could generate only 178 mL CH4/gTS with a negative energy balance of -15.62 kJ/kg TS. In CAMBI process, the heat requirements can be compensated using exhaust gases and hot water from combined heat and power, and electricity requirements are managed by the use of cogeneration. The study concluded that <100 â„ƒ pretreatment effectively enhances the efficiency of anaerobic digestion and shows positive energy balance over microwave and ultrasonication. Moreover, microwave pretreatment has the highest global warming potential than thermal and ultrasonic pretreatments.

Novel insight on ferric ions addition to mitigate recalcitrant formation during thermal-alkali hydrolysis to enhance biomethanation.

Thermal-chemical pre-treatment has proven to facilitate the solubilization of organics and improvement in biogas generation from the organic fraction of municipal solid waste (OFMSW). However, the production of recalcitrant is inevitable when OFMSW is pretreated at high temperatures and alkali dosage. This study develops a strategy to use Fe3+ to reduce the formation of recalcitrant compounds, i.e., 5-HydroxyMethyl Furfural (5-HMF), furfurals, and humic acids (HA) during thermal-alkali pre-treatment. It was postulated that the formation of the recalcitrant compound during pre-treatment can be reduced by Fe3+ dosing to oxidize intermediates of Maillard reactions. A decrease in 5-HMF (45-49%) and furfurals (54-66%) was observed during Fe3+ (optimum dose: 10 mg/L) mediated thermal-alkali pre-treatment owing to the Lewis acid behavior of FeCl3. The Fe3+ mediated assays show a substantial improvement in VS removal (28%) and biogas yield, i.e., 31% (292 mL/gVSadded) in 150 °C + 3 g/L NaOH, 34% (316 mL/gVSadded) in 175 °C + 3 g/L NaOH, and 36% (205 mL/gVSadded) in 200 °C + 3 g/L NaOH assays, over their respective controls (no Fe3+ dosing). The reducing property of Fe3+ rendered a low ORP (-345 mV) in the system than control, which is beneficial to the anaerobic microbiome. Electrical conductivity (EC) also shows a three-fold increase in Fe3+ mediated assays over control, promoting direct interspecies electron transfer (DIET) amongst microbes involved in the electrical syntrophy. The score plot and loading plots from principal component analysis (PCA) showed that the results obtained by supplementing 10 mg/L Fe3+ at 150, 175, and 200 °C were significantly different. The correlation of the operational parameters was also mutually correlated. This work provides a techno-economically and environmentally feasible option to mitigate the formation of recalcitrant compounds and enhance biogas production in downstream AD by improving the degradability of pretreated substrate.

Progress in microalgal mediated bioremediation systems for the removal of antibiotics and pharmaceuticals from wastewater.

Worldwide demand for antibiotics and pharmaceutical products is continuously increasing for the control of disease and improvement of human health. Poor management and partial metabolism of these compounds result in the pollution of aquatic systems, leading to hazardous effects on flora, fauna, and ecosystems. In the past decade, the importance of microalgae in micropollutant removal has been widely reported. Microalgal systems are advantageous as their cultivation does not require additional nutrients: they can recover resources from wastewater and degrade antibiotics and pharmaceutical pollutants simultaneously. Bioadsorption, degradation, and accumulation are the main mechanisms involved in pollutant removal by microalgae. Integration of microalgae-mediated pollutant removal with other technologies, such as biodiesel, biochemical, and bioelectricity production, can make this technology more economical and efficient. This article summarizes the current scenario of antibiotic and pharmaceutical removal from wastewater using microalgae-mediated technologies.

Breakthrough in hydrolysis of waste biomass by physico-chemical pretreatment processes for efficient anaerobic digestion.

Anaerobic digestion (AD) is the most comprehended process to stabilise the waste biomass efficiently and to obtain bioenergy. The AD starts with the hydrolysis process, where the major liability is the action of inhibitors during the hydrolysis process. The biomass pretreatment preceding anaerobic digestion is obligatory to improve feedstock biodegradability for enhanced biogas generation. It can be prevailed by the application of various pretreatment processes. This review explains the major inhibiting compounds and their formation during hydrolysis that affect the efficiency of anaerobic digestion and the benefits of the physico-chemical pretreatment (PCP) method for enhancing hydrolysis in the digestion of waste biomass. The synergistic effect of PCP on macromolecular release, liquefaction and biodegradability were presented. The feasibility of the pretreatment process was evaluated in terms of energy and cost assessment for pilot scale implementation. The outcome of this review reveals that the physico-chemical process is one of the best pretreatment methods to enhance anaerobic digestion by optimising various parameters and increasing the solubilization by about 90%. The thermochemical pretreatment at lower temperature (<100) increases the net energy yield. The solubilization of waste biomass in terms of macromolecular release and liquefaction cannot describe the pretreatment potential. The effectiveness of pretreatment was evaluated by the substrate pre-treatment followed by anaerobic digestibility of pretreated substrate.

Carbon based conductive materials mediated recalcitrant toxicity mitigation during anaerobic digestion of thermo-chemically pre-treated organic fraction of municipal solid waste.

High-temperature thermal pretreatment alone or in conjugation with chemical pretreatment (highly acidic or alkaline) produced recalcitrant compounds, which inhibits the anaerobic digestion (AD) process performance. This study aims to develop a strategy to use carbon-based conductive materials to mitigate the recalcitrant toxicity and enhance the methane generation in the downstream AD. The formation of recalcitrant compounds, mainly the furan derivatives, i.e., furfural and 5-HydroxyMethyl furfurals (5-HMF) during thermo-chemical pretreatment of OFMSW at 150 °C, 175 °C, 200 °C with 3 g/L-NaOH dose, and the alleviation of their inhibitory effects by adding 25 g/L of each of granular activated carbon (GAC) and granular biochar (GBC) during mesophilic AD were studied. The addition of conductive materials resulted in the highest biogas yield of 462 mL/gVSadded (GAC) and 449 mL/gVSadded (GBC) for 175°C-3g/L-NaOH pretreatment, which was >45% higher over control. The highest improvement of >65% in biogas yield was observed for 200°C-3g/L-NaOH pretreatment despite the lower biogas yield. The conductive materials amended digester shows a significant decrease in the 5-HMF and furfurals concertation. The highest reduction in 5-HMF (44%) and furfural (51%) concentrations were observed for 200°C-3g/L-NaOH pretreatment, and 25 g/L GBC amended tests. The score plots from the principal component analysis (PCA) of the characterization of the digestate showed that the data were significant, whereas the loading plots depicted the correlation of different experimental parameters studied (like fate of recalcitrant, biogas yield and other parameters post AD of OFMSW when aided with conductive materials). Application of regression models in all the batch assays depicted that a lag phase of 2-4 days was observed in Modified Gompertz Model (MGM), 4-5 days in Logistic Model (LM) and a rapid hydrolysis was proven with the value of hydrolysis coefficient being between 0.003 and 0.029 from the first-order (FO) model.

Recalcitrant compounds formation, their toxicity, and mitigation: Key issues in biomass pretreatment and anaerobic digestion.

Increasing energy demands and environmental issues have stressed the importance of sustainable methods of energy production. Anaerobic digestion (AD) of the biodegradable waste, i.e., agricultural residues, organic fraction of municipal solid waste (OFMSW), sewage sludge, etc., results in the production of biogas, which is a sustainable and cost feasible technique that reduces the dependence on fossil fuels and also overcomes the problems associated with biomass waste management. To solubilize the organic matter and enhance the susceptibility of hardly biodegradable fraction (i.e., lignocellulosic) for hydrolysis and increase methane production, several pretreatments, including physical, chemical, biological, and hybrid methods have been studied. However, these pretreatment methods under specific operating conditions result in the formation of recalcitrant compounds, such as sugars (xylose, Xylo-oligomers), organic acids (acetic, formic, levulinic acids), and lignin derivatives (poly and mono-phenolic compounds), causing significant inhibitory effects on anaerobic digestion. During the scaling up of these techniques from laboratory to industrial level, the focus on managing inhibitory compounds formed during pretreatment is envisaged to increase because of the need to use recalcitrant feedstocks in anaerobic digestion to increase biogas productivity. Therefore, it is crucial to understand the production mechanism of inhibitory compounds during pretreatment and work out the possible detoxification methods to improve anaerobic digestion. This paper critically reviews the earlier works based on the formation of recalcitrant compounds during feedstocks pretreatment under variable conditions, and their detrimental effects on process performance. The technologies to mitigate recalcitrant toxicity are also comprehensively discussed.