Self-assembly of cell-embedding reduced graphene oxide/ polypyrrole hydrogel as efficient anode for high-performance microbial fuel cell

Humic acid-anchored hydrochar for enhancing methane production in anaerobic digestion of cow manure

This study assesses the effectiveness of two hydrochar variants-humic acid-anchored hydrochar and sodium hydroxide-modified hydrochar-in enhancing biogas production from high-solids anaerobic digestion of cow manure. The purpose of humic acid modification is that its abundant oxygen-containing functional groups promote direct interspecies electron transfer and improve microbial efficiency in anaerobic digestion. Humic acid-anchored hydrochar was prepared by anchoring humic acid to hydrochar. To further optimize the electron transfer capacity and structural properties of the hydrochar, the humic acid-anchored hydrochar was subsequently treated with sodium hydroxide to produce sodium hydroxide-modified hydrochar. The alkali modification effectively removes pore impurities and enhances the redox properties of the material, thereby improving the electron exchange between microorganisms. Experiments were conducted in 500 mL anaerobic serum bottles at a total solids content of 10 %. In the control group, high ammonia nitrogen concentrations inhibited methane production, yielding only 49.54 mL/g volatile solids. In contrast, the addition of sodium hydroxide-modified hydrochar increased cumulative methane production by 80.13 %, reaching 112.38 mL/g VS. Additionally, electron transfer system activity and coenzyme F420 levels increased 94.13 % and 96.58 %, respectively. Microbial analysis revealed an enrichment of bacteria involved in direct interspecies electron transfer and an optimized community structure. Correlation analysis demonstrated a significant positive relationship between enhanced interspecies electron transfer capacity and methane production. The incorporation of modified hydrochar enabled the anaerobic digestion system to maintain high methane yields despite elevated ammonia nitrogen levels. These findings offer valuable insights for improving livestock and poultry manure management and advancing environmental protection efforts.

Microbial degradation and pollutant control in aerobic composting and anaerobic digestion of organic wastes: A review

Aerobic composting (AC) and anaerobic digestion (AD) are promising technologies for organic waste treatment, but their efficiency and safety are influenced by complex waste composition and persistent contaminants. This review identifies the advances in understanding microbial community dynamics, enzymatic degradation pathways, and the fate of contaminants during AC and AD processes. The findings indicate that substrate composition shapes dominant microbial populations and their degradative enzymes, with this correlation potentially useful for predicting functional microbial communities. Additionally, AC shows advantages in antibiotic elimination while AD excels in heavy metal immobilization, with both contributing to removing certain antibiotic resistance genes (ARGs). The strategic manipulation of environmental conditions, particularly temperature and oxygen levels, can drive microbial succession to optimize organic matter decomposition while minimizing ARG proliferation. Economic analyses reveal that AC offers lower operational costs and AD generates valuable by-products with potential energy recovery from organic waste. Case studies indicate that integrating both technologies can overcome individual limitations and enhance degradation efficiency compared to conventional single-technology approaches. This work proposes a comprehensive framework for developing coupled AC-AD systems to achieve more efficient and safer organic waste valorization than conventional single-technology approaches. This review has important implications for advancing sustainable waste management practices and mitigating the spread of antibiotic resistance in the environment.

Anaerobic Volatile Fatty Acid Production Performance and Microbial Community Characteristics from Solid Fraction of Alkali-Thermal Treated Waste-Activated Sludge: Focusing on the Effects of Different pH Conditions

The waste-activated sludge (WAS) is rich in organic matter and various nutrients. Alkali-thermal hydrolysis of WAS can be employed to produce a liquid fertilizer with high plant-promoting nutrient content. However, the solid fraction (abbreviated as SF) generated from this process requires further treatment. Although there have been studies on the recovery of plant nutrients from WAS via alkali-thermal hydrolysis, researches on the safe treatment of the SF are limited. This study aims to explore the potential and the microbiological mechanisms on anaerobic volatile fatty acid (VFA) production from the SF under different pH conditions (i.e., 6, 7, 8, 9, and 10). The results showed that the VFA yield was highest at pH 6, reaching 4095.84 mg COD/L (i.e., 0.16 g-COD/g-volatile solids), followed by pH 10, 8, 7, and 9, with acetate being the main component (> 56%). Microbial community analysis revealed that members in phyla Firmicutes and Bacteroidota constituted the main acid-producing microbial community during the anaerobic fermentation of SF. Furthermore, different pH conditions influenced the yield and composition of VFAs by altering the structure and functions of microbial community. This research provides a new direction for the fully resourceful utilization of sludge by producing both liquid fertilizer and VFAs from WAS.

Resilience and response of anaerobic digestion systems to short-term hydraulic loading shocks: Focusing on total and active microbial community dynamics

Anaerobic digestion is known to be sensitive to operational changes, such as hydraulic loading shock, yet the impact on the microbiome, particularly the active RNA-based community, has not been fully understood. This study aimed to investigate the performance of anaerobic reactors and their microbial communities under short-term hydraulic loading shocks. Using synthetic wastewater, the reactor was subjected to 24-h shocks at three-fold and seven-fold the baseline loading rate, followed by DNA and RNA analyses to assess the system's resiliency and microbial responses. The research focused on shifts in major microbial groups and their functions, paying close attention to the active RNA community during loading shock events to better reflect the system's immediate condition. Findings indicated that although the microbial community structure, particularly among the archaea, was altered, the reactor quickly regained its balance. Differences were observed between DNA and RNA profiles and between regular and shock loadings; however, the alpha diversity and functions of the overall community were sustained. This study offers important insights for the design and operation of wastewater treatment plants, with the goal of achieving stable and efficient anaerobic digestion systems.

Biochar@MIL-88A(Fe) accelerates direct interspecies electron transfer and hydrogen transfer in waste activated sludge anaerobic digestion: Exploring electron transfer and biomolecular mechanisms

Adding additives exogenously is an effective strategy to enhance methanogenic activity and improve AD stability. Corn straw-based biochar@MIL-88A(Fe) (BM) was synthesized herewith and used as an exogenous additive to boost methane (CH4) production. After adding BM at 250 mg/g WAS VS, the accumulative CH4 production and maximum CH4 yield increased by 1.2 and 1.9 times, respectively, with CH₄ comprising 88% of the biogas. BM accelerated electron transfer through its unsaturated sites and surface functional groups, while also enhancing metabolic functions for facilitating enzymatic activities and converting organic substrates. The abundance of syntrophic bacteria and methanogen were higher after BM addition. BM-mediated DIET and IHT pathways effectively oxidized propionate and butyrate, promoting methane generation. Higher expression of key genes involved in methane production correlated with shifts in microbial structure and increased CH4 yield after BM dosage. The invention of BM may provide more solutions for addressing low energy recovery during AD.

Harnessing the Energy Potential and Value-Added Products from the Treatment of Sugarcane Vinasse: Maximizing Methane Production Through Co-Digestion with Sugarcane Molasses and Enhanced Organic Loading

This study assessed the impact of organic loading rate (OLR) on methane (CH4) production in the anaerobic co-digestion (AcoD) of sugarcane vinasse and molasses (SVM) (1:1 ratio) within a thermophilic fluidized bed reactor (AFBR). The OLR ranged from 5 to 27.5 kg COD.m-3.d-1, with a fixed hydraulic retention time (HRT) of 24 h. Organic matter removal varied from 56 to 84%, peaking at an OLR of 5 kg COD.m-3.d-1. Maximum CH4 yield (MY) (272.6 mL CH4.g-1CODrem) occurred at an OLR of 7.5 kg COD.m-3.d-1, while the highest CH4 production rate (MPR) (4.0 L CH4.L-1.d-1) and energy potential (E.P.) (250.5 kJ.d-1) were observed at an OLR of 20 kg COD.m-3.d-1. The AFBR exhibited stability across all OLR. At 22.5 kg COD.m-3.d-1, a decrease in MY indicated methanogenesis imbalance and inhibitory organic compound accumulation. OLR influenced microbial populations, with Firmicutes and Thermotogota constituting 43.9% at 7.5 kg COD.m-3.d-1, and Firmicutes dominating (52.7%) at 27.5 kg COD.m-3.d-1. Methanosarcina (38.9%) and hydrogenotrophic Methanothermobacter (37.6%) were the prevalent archaea at 7.5 kg COD.m-3.d-1 and 27.5 kg COD.m-3.d-1, respectively. Therefore, this study demonstrates that the organic loading rate significantly influences the efficiency of methane production and the stability of microbial communities during the anaerobic co-digestion of sugarcane vinasse and molasses, indicating that optimized conditions can maximize energy yield and maintain methanogenic balance.

Evaluation of energy recovery, pollutant removal, and microbial dynamics in aged refuse bioreactor for landfill leachate treatment

The study evaluates the effectiveness of aged refuse bioreactors (ARBs) in treating young landfill leachate and recovering energy through biogas production. Over 90 days, duplicate reactors (ARB1 and ARB2) were operated through three 30-day recirculation cycles under anaerobic conditions, utilizing aged refuse from a closed landfill in Bangalore, India. The study was extended by an additional 900 days without further leachate addition to assess long-term gas generation potential. Cumulative gas production amounted to 1384 L in ARB1 and 1182 L in ARB2, with maximum methane production per gram of chemical oxygen demand (COD) recorded at 0.474 L and 0.387 L, respectively. Variability in biogas production was correlated with differences in volumetric moisture content, which also influenced pollutant removal and led to significant improvements in the leachate pollution index, decreasing from 24.4 to 12.84 in ARB1 and to 16.46 in ARB2. COD levels were decreased by 70-90%, and TDS by 46-63%. Heavy metal concentrations, including copper, chromium, cadmium, lead, zinc, and nickel, were reduced by 95-99% to acceptable levels, though increases in ammonia and total phosphorus were noted. Key mechanisms in the ARB included anaerobic degradation, adsorption, oxidation-reduction reactions, and precipitation. In the fourth cycle, without leachate recirculation, gas production reached 320 L in ARB1 and 358.8 L in ARB2, indicating effective conversion of carbon retained from aged refuse and leachate treatment into biogas. Microbial analysis identified dominant communities of Methanosarcina and Methanomicrobia. Overall, this study demonstrates that ARBs are effective in treating young landfill leachate and recovering energy, offering insights into sustainable waste management.

Methanosarcina thermophila bioaugmentation with biochar growth support for valorisation of food waste via thermophilic anaerobic digestion

Methanosarcina thermophila bioaugmentation on biochar as the growth support particle has previously been shown to enhance biomethane production of anaerobic digestion of food waste. In this paper, the duration of the beneficial effects is examined by a semi-continuous thermophilic regime starting from pooled digestate from a previous batch digestion. An additional experiment is performed to decouple the solids retention time, mitigating the washout effect and resulting in improved methane yield for 17 days. The second experiment is extended incorporating various permutations of biochar amendment, and the findings suggest that liquid soluble supplements are essential for prolonging the advantages. Experimental and microbiological analyses indicate that the biochar's enhancement is likely due to microbial factors like direct interspecies electron transfer (DIET) or syntrophic interactions, rather than physicochemical mechanisms.

The potential role of iron-carbon micro-electrolysis materials in curtailing lag-phase stimulates kitchen waste anaerobic digestion at different solid contents: Performance, synergistic effect and microbial response

High-solid anaerobic digestion (HSAD) of kitchen waste was generally faced to the common problems such as systemic acidification, prolonged lag-phase time and low methane production. Iron-carbon micro-electrolysis (ICME) materials exhibited advantages that porous structure, large specific surface area and excellent conductivity. It was beneficial for organic compounds to hydrolysis. Moreover, ICME materials could establish direct interspecies electron transfer (DIET) pathway between bacteria and methanogens. ICME materials were commonly used to enhance the AD of wastewater, but they were rarely applied to HSAD of kitchen waste. In this study, ICME materials were utilized to enhance HSAD of kitchen waste at different solid content conditions. The results showed that the highest cumulative biogas yield (705.23 mL/g VS) was obtained in the experimental group (TS = 10%), which was 94.15% higher than that of the control group. At the same time, the addiction of ICME could shorten lag-phase time. Electrochemical characteristics and XPS analysis showed that ICME materials promoted the release of Fe2+ in the AD system and acceleration of direct interspecies electron transfer between microorganisms. Microbial community analysis showed that ICME materials enriched electroactive bacteria (Proteiniphilum), Methanosarcina, Methanobrevibacter and Methanofollis. Functional gene prediction revealed that ICME materials increased the relative abundance of carbohydrate transport and metabolism and coenzyme transport and metabolism. It provided a potential measure to treat kitchen waste.

Development of oriented multi-enzyme strengthens waste activated sludge disintegration and anaerobic digestion: Performance, components transformation and microbial communities

Low methane production and long retention time are the main dilemmas in current anaerobic digestion (AD) of waste activated sludge (WAS). This work used WAS as only substrate to prepare oriented multi-enzyme (ME) that directly used for WAS pretreatment. Under the optimal parameters, the highest activities of protease and amylase in ME could respectively reach 16.5 U/g and 580 U/g, and the corresponding methane production attained 197 mLCH4/g VS, which was increased by 70.4% compared to blank group. It was found that ME pretreatment could strengthen WAS disintegration and organic matters dissolution, lead to the soluble chemical oxygen demand (SCOD) was increased from the initial 486 mg/L to 2583 mg/L, and the corresponding volatile suspended solid (VSS) and extracellular polymeric substances (EPS) were reduced by 27% and 73.8%, respectively. The results of three-dimensional excitation-emission matrix (3D-EEM) and Fourier transform infrared spectroscopy (FTIR) indicated that protein disintegration may be the critical step during the process of WAS hydrolysis with ME, of which the release of tyrosine-like proteins achieved the better biodegradability of WAS, while the results of X-ray photoelectron spectroscopy (XPS) showed that the formation of protein derivatives was the main harmful factor that could extend the lag phase of AD process. Microbial communities analysis further suggested that ME pretreatment facilitated the enrichment of acetogenic bacteria and acetotrophic methanogens, which caused the transition of the methanogenesis pathway from hydrogenotrophic to acetotrophic. This study is expected to furnish valuable insight for ME pretreatment on enhancing WAS disintegration and methane production.

A comprehensive review on the production and enhancement techniques of gaseous biofuels and their applications in IC engines with special reference to the associated performance and emission characteristics

The increasing global demand for energy, coupled with environmental concerns associated with fossil fuels, has led to the exploration of alternative fuel sources. Gaseous biofuels, derived from organic matter, have gained attention due to their renewable nature and clean combustion characteristics. The paper extensively explores production pathways for gaseous biofuels, including biogas, syngas, and hydrogen, providing insightful discussions on various sources and processes. The energy content, physical, and chemical properties of gaseous biofuels have been analysed, highlighting their potential as viable alternatives to conventional fuels. Distinctive properties of biogas, producer gas, and hydrogen that impact combustion characteristics and engine efficiency in IC engines are underscored. Furthermore, the review systematically reviews enhancement techniques for gaseous biofuels, encompassing strategies to augment quality, purity, and combustion efficiency. Various methods, ranging from substrate pretreatment for biogas to membrane separation for hydrogen, illustrate effective means of enhancing fuel performance. Rigorous examination of performance parameters such as brake thermal efficiency, specific fuel consumption and emissions characteristics such as NOx, CO, CO2, HC of gaseous biofuels in dual-fuel mode emphasizes efficiency and environmental impact, offering valuable insights into their feasibility as engine fuels. The findings of this review will serve as a valuable resource for researchers, engineers, and policymakers involved in alternative fuels and sustainable transportation, while also highlighting the need for further research and development to fully unlock the potential of gaseous biofuels in IC engines.

Enzyme modified biodegradable plastic preparation and performance in anaerobic co-digestion with food waste

A modified biodegradable plastic (PLA/PBAT) was developed by through covalent bonding with proteinase K, porcine pancreatic lipase, or amylase, and was then investigated in anaerobic co-digestion mixed with food waste. Fluorescence microscope validated that enzymes could remain stable in modified the plastic, even after co-digestion. The results of thermophilic anaerobic co-digestion showed that, degradation of the plastic modified with Proteinase K increased from 5.21 ± 0.63 % to 29.70 ± 1.86 % within 30 days compare to blank. Additionally, it was observed that the cumulative methane production increased from 240.9 ± 0.5 to 265.4 ± 1.8 mL/gVS, and the methane production cycle was shortened from 24 to 20 days. Interestingly, the kinetic model suggested that the modified the plastic promoted the overall hydrolysis progression of anaerobic co-digestion, possibly as a result of the enhanced activities of Bacteroidota and Thermotogota. In conclusion, under anaerobic co-digestion, the modified the plastic not only achieved effective degradation but also facilitated the co-digestion process.

The future in the litter bin - bioconversion of food waste as driver of a circular bioeconomy

Bioconversion of organic waste requires the development and application of rather simple, yet robust technologies capable of transferring biomass into energy and sustainable materials for the future. Food waste plays a significant role in this process as its valorisation reduces waste and at the same time avoids additional exploitation of primary resources. Nonetheless, to literally become "litterate". extensive research into such robust large-scale methods is required. Here, we highlight some promising avenues and materials which fulfill these "waste to value" requirements, from various types of food waste as sustainable sources for biogas, bioethanol and biodiesel to fertilizers and antioxidants from grape pomace, from old-fashioned fermentation to the magic of anaerobic digestion.

Enhancing sustainable crop cultivation: The impact of renewable soil amendments and digestate fertilizer on crop growth and nutrient composition

Utilizing digestate as a fertilizer enhances soil nutrient content, improves fertility, and minimizes nutrient runoff, mitigating water pollution risks. This alternative approach replaces commercial fertilizers, thereby reducing their environmental impact and lowering greenhouse gas emissions associated with fertilizer production and landfilling. Herein, this study aimed to evaluate the impact of various soil amendments, including carbon fractions from waste materials (biochar, compost, and cocopeat), and food waste anaerobic digestate application methods on tomato plant growth (Solanum lycopersicum) and soil fertility. The results suggested that incorporating soil amendments (biochar, compost, and cocopeat) into the potting mix alongside digestate application significantly enhances crop yields, with increases ranging from 12.8 to 17.3% compared to treatments without digestate. Moreover, the combination of soil-biochar amendment and digestate application suggested notable improvements in nitrogen levels by 20.3% and phosphorus levels by 14%, surpassing the performance of the those without digestate. Microbial analysis revealed that the soil-biochar amendment significantly enhanced biological nitrification processes, leading to higher nitrogen levels compared to soil-compost and soil-cocopeat amendments, suggesting potential nitrogen availability enhancement within the rhizosphere's ecological system. Chlorophyll content analysis suggested a significant 6.91% increase with biochar and digestate inclusion in the soil, compared to the treatments without digestate. These findings underscore the substantial potential of crop cultivation using soil-biochar amendments in conjunction with organic fertilization through food waste anaerobic digestate, establishing a waste-to-food recycling system.

Life cycle assessment and cost-benefit analysis of small-scale anaerobic digestion system treating food waste onsite under different operational conditions

This study employed life cycle assessment and cost-benefit analysis to evaluate the environmental and economic profile of a real decentralized small-scale anaerobic digestion (AD) system treating food waste (FW). Different operational conditions, including temperature, biochar addition, biogas engine efficiency, and FW loading, were compared via scenario analysis. Biochar addition could potentially obtain carbon reduction and save fossil fuel. Moreover, at high FW loading and biogas engine efficiency, biochar addition achieved 1-3190% better performance than the system without biochar in all the nine impact categories. The system under mesophilic conditions performed worse than ambient conditions due to high energy demand. All the current scenarios resulted in a monetary loss at US$ 480 k-681 k, while profit was possible if the capital cost and operator salary decreased significantly. Overall, operating the small-scale AD system under ambient temperature with biochar addition was preferred due to its potential environmental benefits and economic profits.

Metataxonomic characterization of the microbial community involved in the production of biogas with microcrystalline cellulose in pilot and laboratory scale

Biogas, produced in anaerobic digestion, is a sustainable alternative for generating energy from agro-industrial and municipal waste. Information from the microbiota active in the process expands the possibilities for technological innovation. In this study, taxonomic annotations, and functional prediction of the microbial community of the inoculum of two processes were carried out: an industrial unit (pilot-scale urban solid waste plant-IU) and a laboratory-scale reactor fed with swine and cattle waste (LS). The biochemical potential of biogas was obtained using tested inoculum with microcrystalline cellulose, obtaining 682 LN/kgVS (LSC-laboratory scale inoculum and microcrystalline cellulose), and 583 LN/kgVS (IUC-industrial unit inoculum and microcrystalline cellulose), which is equivalent to a recovery of 91.5% of total biogas to LSC. The phyla Synergistota and Firmicutes were more abundant in LS/LSC. In the IU/IUC (treatment of restaurant waste and customs seizures), there was a greater microbiological variety and a predominance of the Bacteroidota, Cloacimonadota, Firmicutes and Caldatribacteriota. The genus Methanosaeta predominated in the process, and it was possible to infer the genes (K01895, K00193 and K00625) related to acetoclastic pathway, as well as endoglucanases that are involved in the metabolism of cellulose (LSC). Terpenoids, polyketides, cofactors, and vitamin metabolism were higher in reactors that received different substrates (IU; IUC). The taxonomic and functional differences revealed the importance of determining the microbiota in the analysis of the potential of an inoculum, combined with the use of microcrystalline cellulose, which can provide optimization information in the production of clean energy.