Bioenergy recovery and carbon emissions benefits of short-term bio-thermophilic pretreatment on low organic sewage sludge anaerobic digestion: A pilot-scale study.

Sewage sludge in cities of Yangzi River Belt, China, generally exhibits a lower organic content and higher silt contentdue to leakage of drainage system, which caused low bioenergy recovery and carbon emission benefits in conventional anaerobic digestion (CAD). Therefore, this paper is on a pilot scale, a bio-thermophilic pretreatment anaerobic digestion (BTPAD) for low organic sludge (volatile solids (VS) of 4%) was operated with a long-term continuous flow of 200 days. The VS degradation rate and CH4 yield of BTPAD increased by 19.93% and 53.33%, respectively, compared to those of CAD. The analysis of organic compositions in sludge revealed that BTPAD mainly improved the hydrolysis of proteins in sludge. Further analysis of microbial community proportions by high-throughput sequencing revealed that the short-term bio-thermophilic pretreatment was enriched in Clostridiales, Coprothermobacter and Gelria, was capable of hydrolyzing acidified proteins, and provided more volatile fatty acid (VFA) for the subsequent reaction. Biome combined with fluorescence quantitative polymerase chain reaction (PCR) analysis showed that the number of bacteria with high methanogenic capacity in BTPAD was much higher than that in CAD during the medium temperature digestion stage, indicating that short-term bio-thermophilic pretreatment could provide better methanogenic conditions for BTPAD. Furthermore, the greenhouse gas emission footprint analysis showed that short-term bio-thermophilic pretreatment could reduce the carbon emission of sludge anaerobic digestion system by 19.18%.

Effect of lysozyme combined with hydrothermal pretreatment on excess sludge and anaerobic digestion.

Anaerobic digestion (AD) is widely employed for sludge stabilization and waste reduction. However, the slow hydrolysis process hinders methane production and leads to prolonged sludge issues. In this study, an efficient and eco-friendly lysozyme pre-treatment method was utilized to address these challenges. By optimizing lysozyme dosage, hydrolysis and cell lysis were maximized. Furthermore, lysozyme combined with hydrothermal pretreatment enhanced overall efficiency. Results indicate that: (1) When lysozyme dosage reached 90 mg/g TS after 240 min of pretreatment, SCOD, soluble polysaccharides, and protein content reached their maxima at 855.00, 44.09, and 204.86 mg/L, respectively. This represented an increase of 85.87%, 365.58%, and 259.21% compared to the untreated sludge. Three-dimensional fluorescence spectroscopy revealed the highest fluorescence intensity in the IV region (soluble microbial product), promoting microbial metabolic activity. (2) Lysozyme combined with hydrothermal pretreatment significantly increased SCOD, soluble proteins, and polysaccharide release from sludge, reducing SCOD release time. Orthogonal experiments identified Group 3 as the most effective for SCOD and soluble polysaccharide release, while Group 9 released the most soluble proteins. The significance order of factors influencing SCOD, soluble proteins, and polysaccharide release is hydrothermal temperature > hydrothermal time > enzymatic digestion time.(3) The lysozyme-assisted hydrothermal pretreatment group exhibited the fastest release and the highest SCOD concentration of 8,135.00 mg/L during anaerobic digestion. Maximum SCOD consumption and cumulative gas production increased by 95.89% and 130.58%, respectively, compared to the control group, allowing gas production to conclude 3 days earlier.

Uncovering the toxic effects and adaptive mechanisms of aminated polystyrene nanoplastics on microbes in sludge anaerobic digestion system: Insight from extracellular to intracellular.

The impacts of polystyrene nanoplastics (PS NPs) with amino functional groups on sludge anaerobic digestion process and the underlying microbial feedbacks remains unclear. Herein, PS NPs coated with and without amino functional groups were employed to explore their impacts on the sludge digestion performance. Experimental results showed that aminated PS NPs (PS-NH2) deteriorated the methane yield and hydrolysis rate. The Derjaguin-Landau-Verwey-Overbeek theory analysis suggested that the PS-NH2 decreased the interaction energy barrier, making it easier to contact with sludge and disrupting the structure of extracellular polymeric substances. Metagenomic analysis showed that the abundance of functional microbes (e.g., Longilinea, Leptolinea, and Methanosarcina) decreased, accompanied with lower network complexity and fewer keystone taxa. Molecular docking revealed that PS-NH2 occupy the antioxidant enzyme active binding sites through hydrogen bonding and hydrophobic interactions, impairing degradation of reactive oxygen species. The severe intracellular oxidative stress up-regulated genes associated with quorum sensing (e.g., luxI and luxR) and protein biosynthesis (e.g., algA, trpG and trpE), and further inducing compact tryptophan-like proteins as a defense against NPs. These findings provide new understanding of the toxic effects from PS-NH2 in biological systems and offer valuable insights into the regulation strategies aimed at alleviating NPs inhibition.

Recycling of domestic sludge cake as the inoculum of anaerobic digestion for kitchen waste and its benefits to carbon negativity.

Organic waste recovery has been a concerning issue in line with resource conservation. In the present study, the kitchen waste of vegetables, fish, and beef was digested anaerobically using domestic sludge as the inoculum, the methane and carbon dioxide were monitored, and the environmental benefits of the anaerobic digestion (AD) process were evaluated. AD using sludge cake as the inoculum was shown to treat kitchen waste effectively. Raw beef was found to produce more gas than raw fish or vegetables. Investigations also indicated that celluloses within vegetables were not as readily biodegradable as the proteins in beef and fish. Moreover, cooking altered the protein structures in beef and fish, thus increasing methane production. Meanwhile, oil inhibited methane generation as carbon dioxide generation remained, implying that the hydrolysis and acedogenesis still proceeded in the digestion process containing oil. Anaerolineaceae and Synergistaceae are the two most abundant microbial species observed in an anaerobic digestion system. However, the carbon conversions to liquid (i.e., leachate), solid (i.e., digestate), and gaseous (i.e., methane and carbon dioxide) occurred in the AD process, showing a diverse transforming process from waste to reusable valuables. Moreover, the kitchen waste treatment by domestic sludge cake was shown to have positive effects on reducing carbon dioxide emissions compared to the conventional treatment of kitchen waste and domestic sludge. More environmental benefits could be expected if the resulting products (i.e., methane gas, leachate, digestate) were applied as an energy source, liquid fertilizers, and soil conditioners.

An energy-efficient upconcentration of the bio-based carboxylic acids using multiple-effect evaporators.

This study proposes an integrated process chain to upconcentrate short-chain carboxylic acids (SCCA) like acetic, propionic, and butyric acid, produced from anaerobic fermentation of the organic fraction of municipal solid waste. The starting point is the residual biogas, which is produced from the anaerobic digestion of the solid fraction obtained after the acid fermentation. Using this biogas energy, integrated multiple-effect evaporator scenarios with varying SCCA initial concentrations from 10 to 40 g/L in the liquid fraction were simulated in Aspen Plus®. Using four-effects and starting from 20 g/L, SCCA can be upconcentrated to 526 g/L with only minor acids loss. This process requires 9.8 kWh energy/kg SCCA produced, which was provided by the biogas generated from the solid residue post-digestion. Also, the accuracy of the simulation results across different pressure ranges has been confirmed through the validation of the input model used in Aspen Plus®. The carbon footprint of this process was 1.24 kg CO2-eq./kg SCCA produced, which was 50% lower than the existing processes producing fossil-based SCCA. A techno-economic assessment have also been performed for different evaporator configurations.

Effect of aeration pretreatment on anaerobic digestion of swine manure.

To investigate the effects of aeration pretreatment on the anaerobic digestion (AD) of swine manure, five pretreatment groups were established with dissolved oxygen (DO) in each group set to 0.0, 0.4, 0.8, 1.4, and 2.0 mg/L, respectively. The results demonstrated that compared to the non-aeration group, methane production increased to varying degrees with different aeration pretreatments (AP), with a maximum increase of 27.98% (DO = 2.0 mg/L). AP reduced the hydrogen sulfide (H2S) content of biogas. The H2S concentration in the DO = 2.0 mg/L was only 0.209%, and this represented an increased H2S removal rate of 49.27% compared to that of the DO = 0.0 mg/L (0.412%). Simultaneously, AP increases the hydrolysis rate. When the DO concentration reached 2.0 mg/L, the hydrolysis rate reached its maximum. An increase in the hydrolysis rate further enhanced the removal rate of organic matter. The organic matter removal rate was highest (36.96%) at DO = 2.0 mg/L. AP effectively prolonged the methane generation time and shortened the lag time of methane generation. AP creates a brief micro aerobic environment, accelerates substrate hydrolysis, and promotes the production and consumption of total volatile fatty acids, particularly acetic acid. Additionally, AP promoted the symbiotic relationship between Caldicoprobacter (20.93%-34.96%) and Metanosaeta (14.73%-18.45%).

Synergistic sodium alginate- and biochar-immobilized cells for enhancing fermentative hydrogen production from food waste.

An immobilized hydrogen-producing consortium investigated biohydrogen production from food waste using a combination of sodium alginate and cassava rhizome biochar. We investigated the effect of varying the biochar concentration from 0 to 3% and the size of immobilized cells from 1 to 7 mm. Immobilized cells were prepared using 50% (v/v) enriched hydrogen-producing consortium, 2% (w/v) sodium alginate, and 0 to 3% (w/v) cassava rhizome biochar. The optimal conditions for achieving the highest hydrogen production in the batch fermentation reactor were identified as a biochar concentration of 2% (w/v) and an immobilized cell size of 2 mm. The highest hydrogen yield, maximum hydrogen production rate, and lag time recorded were 0.69 mmol H2/g-COD, 0.02 mmol H2/g-COD.h, and 41.51 h, respectively. This research highlights the potential of cassava biochar technology for efficient biohydrogen production from food waste, contributing to renewable energy generation and sustainable waste management.

The effect of Fenton sludge on anaerobic digestion of papermaking wastewater in an upflow anaerobic sludge blanket reactor.

An upflow anaerobic sludge blanket (UASB) reactor was used to investigate the effect of adding Fenton sludge (FS) on the anaerobic digestion of actual papermaking wastewater. The results showed that a one-time addition of 10 g/L FS could sustainably promote the performance of UASB for more than 40 days. The organic matter removal efficiency increased by 15.56%, and the biogas production increased by 24.52%. The proportion of methane in biogas increased by 12.87%. Adding FS increased the capacitance values of sludge extracellular polymeric substances and the electron transfer system activity in reactor increased by 1.76 times. The dehydrogenase activity and coenzyme F420 of the sludge increased by 1.54 and 2.11 times, respectively. Adding FS enriched the iron-reducing bacteria (Thermodesulfobacteriota) and hydrolytic acid-producing bacteria (Chloroflexota and Synergistota), thereby promoting the hydrolysis and acidification process. Adding FS was beneficial to the enrichment of methanogen, especially Methanosaeta, significantly increasing the methane production.

Insights into links between redox cycling of dissolved organic matter ranked by molecular weight and methanogen-bacteria symbiosis-driven methane production.

Molecular weight (MW) of dissolved organic matter (DOM) governs its redox capacity, playing pivotal roles in methanogen-bacteria symbiosis-driven CH4 production. However, the effect of redox capacity of DOM ranked by MW on these symbiotic associations during anaerobic digestion have never been investigated. The electron-donating (EDC) and -accepting capacity (EAC) of DOM with different MW were quantified, elucidating their impacts on bacteria-methanogen symbiosis-driven CH4 production. By contrast, DOM with 7000 > MW > 14,000 Da constituted the primary contribution to EAC, with an average contribution of 44.63 %. DOM with MW > 14,000 Da emerged as the predominant contributor to EDC, with an average contribution of 49.10 %. Random forest showed that EAC/EDC of DOM ranked by MW was the important factors for methanogenesis by driving shifts in microbial symbiotic relationships. 46 genera (relative abundance of 69.55 %) of microorganisms exhibited robust associations with EAC/EDC. EDC of DOM with 3500 < MW < 7000 Da exerted positive effect on CH4 by modulating the corporation of Caldicoprobacter, norank_o__TSCOR001-H18, norank_o__MBA03 and Methanobrevibacter. EDC of DOM (7000 < MW < 14,000 Da) promotes CH4 production by regulating cooperation of Corynebacterium, Pseudomonas and Methanosarcina, Methanothermus. EDC of DOM (MW > 14,000 Da) enhances CH4 production by modulating cooperation of Ureibacillus, Treponema and methanomassiliicoccus, methanogenium. EAC of DOMs were negatively correlated with CH4. This study broadens our knowledge on the intricate process of methanogenesis and holds significant importance in developing a microbial symbiosis regulation strategy based on electron transfer system.

Mechanisms of horizontal gene transfer and viral contribution to the fate of intracellular and extracellular antibiotic resistance genes in anaerobic digestion supplemented with conductive materials under ammonia stress.

The addition of conductive materials (CMs) is an effective strategy for mitigating ammonia inhibition during anaerobic digestion (AD). However, the introduction of CMs can result in increased antibiotic resistance genes (ARGs) pollution, potentially facilitated by enhanced horizontal gene transfer (HGT). The complex dynamics of intracellular and extracellular ARGs (iARGs/eARGs) and the mechanisms underlying their transfer, mediated by CMs, in ammonia-stressed AD systems remain unclear. In this study, we investigated the effects of three commonly used CMs-nano magnetite (Mag), nano zero-valent iron (nZVI), and granular activated carbon (GAC)-on the fate of iARGs and eARGs during the AD of waste activated sludge under ammonia stress. The results revealed an unexpected enrichment of iARGs by 1.5 %-10.9 % and a reduction of eARGs by 14.1 %-25.2 % in CM-supplemented AD. This discrepancy in the dynamics of iARGs and eARGs may be attributed to changes in microbial hosts and the horizontal transfer of ARGs. Notably, CMs activated prophages within antibiotic-resistant bacteria (ARB) and their symbiotic partners involved in vitamin B12 provision, leading to the lysis of ARB and the subsequent release of eARGs for transformation. Additionally, the abundance of potentially mobile ARGs, which co-occurred with mobile genetic elements, increased by 56.6 %-134.5 % with CM addition, highlighting an enhanced potential for the HGT of ARGs. Specifically, Mag appeared to promote both transformation and conjugation processes, while nZVI only promoted conjugation. Moreover, none of the three CMs had any discernible impact on transduction. GAC proved superior to both nano Mag and nZVI in controlling the enrichment of iARGs, reducing eARGs, and limiting HGTs simultaneously. Overall, these findings provide novel insights into the role of viruses and the mechanisms of ARG spread in CM-assisted AD, offering valuable information for developing strategies to mitigate ARG pollution in practical applications.

Dynamic responses of the inter-microbial synergism and thermodynamic conditions attribute to the inhibition-and-relief effects of chitosan towards anaerobic digestion.

Wide commercial applications of chitosan in food preservation and green packaging fields inevitably lead to the universal existence in food, as well as the food waste (FW) processing system. However, whether and how the chitosan, a class of biomacromolecule substances, lead to dysfunction of anaerobic digestion (AD) process of FW remains less understood. Herein, chitosan exhibited an inhibition-and-relief effect with the AD process proceeding, and 80 mg/g-FW of chitosan decreased the net methane yield of FW by 24.7 %. The dynamic effect was ascribed to the varied fates of chitosan and the coupling biotic/abiotic influencing on multi-steps. Chitosan enhanced substrate flocs agglomeration, restraining the release of organics to liquid phase and reducing the binding affinity to enzymes. Among the various microorganisms involved in different steps, chitosan severely inhibited aceticlastic and hydrogenotrophic methanogen at the levels of microbial abundance, activity and function. Genome-centric metagenomics analyses revealed that transient chitosan decreased the coenzyme-based synergism of various microbial taxa involved in acetic acid generation/consumption metabolisms, including syntrophic propionate-oxidizing bacteria, syntrophic butyrate-oxidizing bacteria and methanogen. With the elimination of chitosan, these inhibitions were relieved, and the accumulated acetic acid and the more favorable thermodynamic conditions finally attributed to the recovery of AD performance.

Interpretation of possible biogas production capacity by investigating the effects of anaerobic digester tank geometry and angular velocity on flow characteristics.

Mixing performance in reactors producing biogas through anaerobic digestion is one of the parameters that directly affect biogas yield. The most commonly used mixing model for bioreactors in biogas-production processes is mechanical mixing. In the present study, we focus on the geometry of the tank, where the mechanical mixing actually takes place. In this context, by using the six-blade standard Rushton impeller in two different types of tank, flow patterns involving velocity, dead zone volume, turbulent kinetic energy, and turbulent eddy dissipation rate in the angular velocity range of 25-100 rpm were observed, and the possible effects of the results on biogas production were interpreted. A new impeller design was proposed that maximizes the interface between the fluid inside the reactor tank and the impeller, which has the potential to reduce the dead zone volume to significantly lower levels. Our results showed that the lowest dead zone volume was achieved for a 60° slope reactor tank compared to the conventional 90° slope reactor tank at an angular velocity of 100 rpm. The dead zone volume decreased to 0.000094 m3 at 100 rpm in the 60° slope reactor tank with a total volume of 0.0305 m3, which by comparison was 0.000374 m3 in the 90° slope reactor tank. The magnitudes of both maximum turbulent kinetic energy and maximum turbulent eddy dissipation were higher in the 60° slope reactor tank at all angular velocities examined, which would be expected to enhance mixing performance. It is hoped that the reader will benefit from the results of this study; however, further studies should be conducted on the use of actual biowaste as the working fluid instead of water.

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.

Effects of hydrothermal pretreatment on sulfadiazine degradation during two-stage anaerobic digestion of pig manure.

Antibiotics in animal manure pose significant risks to the environment and health. While anaerobic digestion (AD) is commonly used for pig manure treatment, its efficiency in antibiotic removal has been considerably limited. This study investigated the impact of hydrothermal pretreatment (HTP) on sulfadiazine (SDZ) removal in a two-stage AD system. Results indicated that the HTP process reduced SDZ concentration by 40.61%. Furthermore, the SDZ removal efficiency of the AD system coupling HTP increased from 50.90% to 65.04% compared to the untreated system. Biogas yield was also improved by 26.17% while maintaining system stability. Changes induced by HTP in the microbial communities revealed that Firmicutes, Bacteroidetes, Caldatribacteriota, and Proteobacteria emerged as the primary bacterial phyla. Following HTP, the relative abundance of Prevotella, which exhibited a strong negative correlation with SDZ concentration, increased significantly by 25-fold in the acidogenic stage. Proteiniphilum, Syntrophomonas and Sedimentibacter showed notable increases in the methanogenic stage after HTP. The N-heterocyclic metabolism carried out by Prevotella might have been the predominant SDZ degradation pathway in the acidogenic stage, while the benzene ring metabolism and hydroxylation by the Proteiniphilum emerged as the primary degradation pathways in the methanogenic stages. Furthermore, biodegradation intermediates were proven to be less toxic than SDZ itself, indicating that the HTP-enhanced two-stage AD process could be a viable way to lower the environmental risks associated with SDZ. The findings from this study provide valuable insights for removing SDZ from the environment via two-stage AD.

Effects of exogenous signaling molecules on anaerobic sludge digestion: Quorum sensing and antibiotic resistance genes.

Regulating quorum sensing (QS) signaling molecules could improve wastewater treatment but might increase antibiotic resistance. This study investigated the effects of exogenous C6-HSL on anaerobic sludge under oxytetracycline stress, with a focus on antibiotic resistance genes (ARGs) and the QS response. The results revealed that exogenous oxytetracycline increased the copy number of ARGs by more than 68.8 %. It also facilitated a 3.04-fold increase in the concentration of signaling molecules and increased the abundance of QS genes. Further addition of the C6-HSL accelerated oxytetracycline degradation, and reduced its residual concentration by 70.9 %, alleviating oxytetracycline stress on microbial communities, and correspondingly reducing stress release from AHL by 75.4 %. Importantly, this did not exacerbate antibiotic resistance, with no significant difference (p > 0.05) in the ARG abundance. These findings may provide valuable insights into the relationship between QS process and antibiotic resistance.

Monitoring of volatile fatty acids during anaerobic digestion of olive pomace by means of a hand held near infrared spectrometer.

The accumulation of volatile fatty acids (VFAs) over anaerobic digestion (AD) leads to malfunctioning of industrial reactors, hence decreasing biogas production. Real-time monitoring of VFAs is a challenge due to the complexity and high cost of current methods for their quantification. For this reason, this research evaluated the application of near infrared (NIR) spectroscopy to quantify volatile fatty acids as a tool for AD reactors monitoring. To do that, 129 samples from various AD reactors fed with olive oil pomace were taken and their NIR spectra were acquired with a hand-held spectrometer. After performing grid search, three spectral variable selection methods, namely competitive adaptive reweighted sampling, uninformative variable elimination (UVE) and successive projections algorithm, were assayed before developing PLRS models to correlate the NIR light transmittance through the samples at the wavelengths selected by those methods with their VFAs concentrations. UVE led to the best performance for all the VFAs assayed. Thus, R2 of validation of UVE-PLSR models for acetic, propionic, butyric, valeric and total VFAs were 0.895, 0.622, 0.866, 0.898 and 0.871, respectively. The predictive model for total VFAs achieved the highest accuracy (RMSEV = 539.5 mg/L), explained by the correlation between the light absorption at the wavelengths selected by UVE and the chemical characteristics of VFAs. All in all, the prediction errors achieved suggest that a portable near infrared spectrometer can be used for monitoring VFAs in AD processes.

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.

Anaerobic Degradation of Aromatic and Aliphatic Biodegradable Plastics: Potential Mechanisms and Pathways.

Biodegradable plastics (BDPs) have been widely used as substitutes for traditional plastics, and their environmental fate is a subject of intense research interest. Compared with the aerobic degradation of BDPs, their biodegradability under anaerobic conditions in environmental engineering systems remains poorly understood. This study aimed to investigate the degradability of BDPs composed of poly(butylene adipate-co-terephthalate) (PBAT), poly(lactide acid) (PLA), and their blends, and explore the mechanism underlying their microbial degradation under conditions of anaerobic digestion (AD). The BDPs readily depolymerized under thermophilic conditions but were hydrolyzed at a slow rate under conditions of mesophilic AD. After 45 days of thermophilic AD, a decrease in the molecular weight and significant increase in the production of methane and carbon dioxide production were observed. Network and metagenomics analyses identified AD as reservoirs of plastic-degrading bacteria that produce multiple plastic-degrading enzymes. PETase was identified as the most abundant plastic-degrading enzyme. A potential pathway for the anaerobic biodegradation of BDPs was proposed herein. The polymers of high molecular weight were subjected to abiotic hydrolysis to form oligomers and monomers, enabling subsequent microbial hydrolysis and acetogenesis. Ultimately, complete degradation was achieved predominantly via the pathway involved in the conversion of acetic acid to methane. These findings provide novel insight into the mechanism underlying the anaerobic degradation of BDPs and the microbial resources crucial for the efficient degradation of BDPs.

Sustainable bioenergy potential of peat-moss derived hydrothermal aqueous phase: Insights into methane production and organic transformation.

Achieving Sustainable Development Goal 7 (SDG-7) by exploring bioenergy production from peat-moss derived hydrothermal aqueous phase (HAPs) through anaerobic digestion (AD). This study investigated six combinations of hydrothermal conversion temperature (HCT) and residence time (HCRT). Methane yields varied significantly, with the highest (256 mL/g COD) achieved at 200 °C:4h, while the lowest (97 mL/g COD) was at 320 °C:4h due to formation of toxic and refractory organics. Microtox analysis showed acute toxicity > 98 % for all HAPs. Notably, higher HCT and HCRT led to more complex and diverse organic patterns, promoting the formation of humus-like substances, ester, alkane alcohols, and aromatics. GC-MS analysis revealed a 23 % increase in aldehyde and ketone compounds at 320 °C:4h. Continuous experiments confirmed 29 % COD removal efficiency at 320 °C:4h and identified 13 refractory organics, highlighting challenges in biodegradability. These findings provided valuable insights for optimizing AD processes, enhancing bioenergy production, and advancing sustainable energy solutions in alignment with SDG-7.

Ethanol-mediated Anaerobic Digestion: Functional Bacteria, Metabolic Pathways.

Ethanol-mediated Anaerobic digestion (Ethanol-AD) is a biological process that converts organic waste into biogas, predominantly composed of methane (CH4), hydrogen (H2), and carbon dioxide (CO2), through the breakdown of complex organic materials while ethanol is an intermediate metabolite. Ethanol improves the digestion of complex organic waste by serving as an electron precursor for interspecies electron transfer, leading to enhanced biogas production. It further serves as a substrate for acetogens or syntrophic bacteria, while mean its oxidation leads to acetate formation, which methanogens can then consume to generate methane. Methanogenesis, the final and crucial step in the anaerobic digestion in which methanogens produce methane through various metabolic routes, most notably via the hydrogenotrophic and syntrophic pathways. In hydrogenotrophic methanogenesis, methanogens consume hydrogen as an electron precursor and carbon dioxide as an electron acceptor, leading to methane generation. Alternatively, syntrophic methanogenesis, which is increasingly recognized for its efficiency, is dominated by DIET between syntrophic partners, bypassing the need for hydrogen as a mediator. This mode of electron transfer enhances the metabolic cooperation between microbes, facilitating a more efficient methanogenesis process. As research continues to explore the mechanisms underlying DIET and the role of (semi) conductive materials, there is potential for optimizing AD systems for renewable energy production by advancing the methanogenesis process, and enhancing biogas quality. The novelty of this review lies in its dual exploration of direct and indirect interspecies electron transfer (DIET and IIET) within ethanol-mediated anaerobic digestion. While DIET in ethanol-driven systems has been previously discussed, this review is the first to comprehensively examine the interplay between both direct and indirect electron transfer mechanisms, offering new insights into optimizing microbial interactions and improving methane production efficiency.