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• PHMG caused CH 4 reduction and ARGs propagation during sludge digestion. • PHMG shaped the syntrophic interactions between bacteria and archaea. • PHMG down-regulated genes associated with methane biosynthesis. • Anaerobes exhibited partial adaptation to low level of PHMG interference. • PHMG enhanced metabolic functions related with ARGs propagation. Waste activated sludge (WAS) presents both resource recovery potential and pollution risks, making its efficient treatment challenging. Anaerobic digestion is broadly recognized as a green and sustainable approach to WAS treatment, whose efficiency is easily impacted by the exogeneous pollutants in WAS. However, the impact of polyhexamethylene guanidine (PHMG), as a widely-used non-antibiotic disinfectant, on WAS digestion under semi-continuous flow conditions remains unclear. In this study, CH 4 production decreased from 16.1 mL/g volatile suspended solids (VSS) in the control to 13.2 mL/g VSS and 0.3 mL/g VSS under low and high PHMG exposure, respectively, while PHMG increased the number of antibiotic resistance gene (ARG) copies per bacterium by 4.6–12.7 %. Molecular docking analysis revealed that PHMG could spontaneously bind to and disintegrate WAS (binding energy:2.35 and -9.62 kcal/mol), increasing the likelihood of microbial exposure to PHMG. This led to an increase in bacterial abundance and a reduction in archaeal populations, resulting in bacterial dominance in ecological niches. The network topology index in PHMG-treated reactors was consistently lower than in the control, with a higher proportion of negatively correlated links, indicating a more antagonistic relationship between bacteria and archaea. Consequently, PHMG significantly interfered with key genes involved in CH 4 biosynthesis (e.g., mch and mtd). Interestingly, methanogenic activity and archaeal chemotaxis (e.g., rfk and cheA) partially recovered under low PHMG exposure due to archaeal adaptation through quorum sensing and two-component systems. However, this adaptation process also contributed to the propagation of ARGs through horizontal gene transfer, facilitated by the enhancement of mobile genetic elements and ARGs hosts. These findings confirm the ecological risks of PHMG and highlight the need for effective WAS disposal strategies. [Display omitted] [ABSTRACT FROM AUTHOR]

• Seasonal LGD-derived CH 4 is controlled by hydro-biogeochemical process. • Great change in seasonal LGD rate is controlled by intense water level fluctuation. • Seasonal CH 4 cycling in groundwater changes significantly in different seasons. • Seasonal LGD-derived CH 4 contributes to significant differences of lake CH 4 emissions. Methane (CH 4) inputs to lakes through lacustrine groundwater discharge (LGD-derived CH 4) represent a potentially important but often overlooked source of lake methane emissions. Although great efforts have been made to quantify LGD-derived CH 4 fluxes and their spatial variablity, the underlying mechanisms controlling seasonal LGD-derived CH 4 fluxes and their influence on lake CH 4 emissions remain poorly understood, particularly in humid inland areas. To address this gap, we applied the 222Rn mass balance model, as well as hydrological, isotopic and microbial methods to assess seasonal LGD-derived CH 4 fluxes and their influence on the seasonal variability of lake methane emissions in a typical oxbow lake, central Yangtze River. The results revealed wide seasonal differences in LGD-derived CH 4 fluxes, which were controlled by hydrological and biogeochemical processes. During the dry season, although more intense methane oxidation and weaker methanogenesis occurred in groundwater, the much higher LGD rate (51.71 mm/d) produced a higher LGD-derived CH 4 flux (16.41 mmol/m2/d). During the wet season, methanogenesis was more active and methane oxidation was weaker, but a lower LGD rate (12.16 mm/d) led to a lower LGD-derived CH 4 flux (5.33 mmol/m2/d). Furthermore, higher LGD-derived CH 4 flux in the dry season resulted in higher CH 4 emissions from the lake and diminished the extent of methane oxidation in the lake. In comparison to other regions, the differences in LGD-derived CH 4 fluxes and their seasonal variations were found to be controlled by climatic conditions and lake types in different global regions. Higher LGD-derived CH 4 fluxes and more pronounced seasonal variations could be associated with higher temperature, larger water depth and more intense water level fluctuations. This study provides a novel perspective and broader implications for the comprehension and evaluation of seasonal methane emissions and understanding the carbon cycle in global lake ecosystems in humid areas with intense water level fluctuations. [Display omitted] [ABSTRACT FROM AUTHOR]

• High DO (1–3 mg/L) and long woodchip age (5-year) negatively impacted NO 3 - removal. • Accumulation of N 2 O (>180 mg N 2 O N m-3) in woodchip was observed only at high DO. • CH 4 production rate was >3 times higher in fresh woodchip than aged woodchip. • Significant CH 4 production was observed after the completion of NO 3 - removal. • Longer HRT (> 2–5 days) may promote CH 4 emission and reduce N 2 O production. The accurate evaluation of denitrification rate and greenhouse gas (GHG) emission in field-scale woodchip bioreactors for onsite wastewater treatment are problematic due to inevitably varied environmental conditions and underestimated GHG production with limited analysis of dissolved gas in field samples. To address these problems, batch incubation experiments were conducted with controlled conditions to precisely evaluate the denitrification kinetics and N 2 O and CH 4 emission of both gaseous and dissolved phases in fresh (6 months) and aged (5 years) woodchip bioreactors treating onsite wastewater at high (1–3 mg L-1) and no (0 mg L-1) dissolved oxygen (DO) levels. NO 3 - removal rate decreased from 37.5–119.0 g NO 3 --N m-3d-1 at no DO to 8.8–16.6 g NO 3 --N m-3d-1 at high DO (1–3 mg L -1) due to the growth suppression of NO 2 - reducing microorganisms (37–55 % lower nirS + nirK abundance). However, the presence of high DO increased N 2 O emission level from 5.6–6.9 mg N 2 O N m-3 at no DO to 179.5–273.6 mg N 2 O N m-3) due to the enhanced growth of NO reducing microorganisms (1–7 times higher norB levels) and the decreased abundance of N 2 O reducing microorganisms (53–75 % lower nosZ abundance). On the other hand, increased DO level negatively correlated with CH 4 production (1.0–3.9 g CH 4 -C m-3d-1) in fresh woodchips, while showed insignificant impact on CH 4 production (0.1–1.4 g CH 4 -C m-3d-1) in aged woodchips. Woodchip age increase (5 years) negatively impacted the NO 3 - removal rate (75–85 % lower than fresh woodchips) and CH 4 production rate (>3 times lower than fresh woodchips), probably due to the reduced biomass density of NO 2 - reducing microorganisms (52–58 % lower nirS + nirK abundance) and methanogens (95–98 % lower mcrA levels). The incubation results suggested that long hydraulic retention time (>2–5 days) and anaerobic/anoxic condition are preferred for the optimal NO 3 - removal and low N 2 O emission potential of woodchip bioreactors treating onsite wastewater. [Display omitted] [ABSTRACT FROM AUTHOR]

• BMPs aggravate N 2 O and CH 4 emissions from sediments more severely than NBMPs. • BMPs facilitate denitrification, while NBMPs inhibit nitrogen metabolism. • Nitrifier denitrification dominates over NH 2 OH oxidation after BMPs exposure. • Microplastics promote hydrogen-dependent methanogenic pathway. Freshwater ecosystems, such as urban lake sediments, have been identified as important sources of greenhouse gases (GHGs) to the atmosphere, as well as persistent sinks for ubiquitous microplastics due to the high population density and frequent anthropogenic activity. The potential impacts of microplastics on GHG production, however, remain underexplored. In this study, four types of common biodegradable microplastics (BMPs) versus four conventional non-biodegradable microplastics (NBMPs) were artificially exposed to urban lake sediments to investigate the responses of nitrous oxide (N 2 O) and methane (CH 4) production, and make a comparison regarding how the biodegradability of microplastics affected GHG emissions. Importantly, results suggested that BMPs aggravated N 2 O and CH 4 production in urban lake sediments more severely than conventional NBMPs. The production rates of N 2 O and CH 4 increased by 48.78–71.88 % and 30.87–69.12 %, respectively, in BMPs groups, while those increased by only 0–25.69 % and 6.46–10.46 % with NBMPs exposure. Moreover, BMPs insignificantly affected nitrification but facilitated denitrification, while NBMPs inhibited both processes. BMPs not only created more oxygen-limited microenvironment, greatly promoting N 2 O production via nitrifier denitrification pathway, but also provided dissolved organic carbon favoring heterotrophic denitrification, which was primarily supported by the enriched denitrifiers and functional genes. In contrast, NBMPs slightly upregulated nitrifier denitrification pathway to generate N 2 O, and showed a toxic inhibition on both nitrifiers and denitrifiers. In addition, both BMPs and NBMPs promoted hydrogen-dependent methanogenic pathway but suppressed acetate-dependent pathway. The greater enhancement of CH 4 production with BMPs exposure was attributed to the additional organic carbon substrates derived from BMPs and the stimulated microbial methane metabolism activities. [Display omitted] [ABSTRACT FROM AUTHOR]

• Large variability of CH 4 oxidation rates in a tropical river network. • Temperature response of CH 4 oxidation exceeded that of CH 4 = production. • A model for CH 4 oxidation is developed for tropical fluvial systems. • Stark contrast in the response of CH 4 oxidation to oxygen between rivers and lakes. • CH 4 emission may increase with temperature and organic pollution in Asian rivers. Aerobic methane oxidation (MOX) significantly reduces methane (CH 4) emissions from inland water bodies and is, therefore, an important determinant of global CH 4 budget. Yet, the magnitude and controls of MOX rates in rivers – a quantitatively significant natural source of atmospheric CH 4 – are poorly constrained. Here, we conducted a series of incubation experiments to understand the magnitude and environmental controls of MOX rates in tropical fluvial systems. We observed a large variability in MOX rate (0.03 - 3.45 μmol l-1d-1) shaped by a suit of environmental variables. Accordingly, we developed an empirical model for MOX that incorporate key environmental drivers, including temperature, CH 4 , total phosphorus, and dissolved oxygen (O 2) concentrations, based on the results of our incubation experiments. We show that temperature dependency of MOX (activation energy: 0.66 ± 0.18 eV) is lower than that of sediment methanogenesis (0.71 ± 0.21 eV) in the studied tropical fluvial network. Furthermore, we observed a non-linear relationship between O 2 concentration and MOX, with the highest MOX rate occuring ∼135 μmol O 2 l-1, above or below this "optimal O 2 " concentration, MOX rate shows a gradual decline. Together, our results suggest that the relatively lower temperature response of MOX compared to methanogenesis along with the projected decrease of O 2 concentration due to organic pollution may cause elevated CH 4 emission from tropical southeast Asian rivers. Since estimation of CH 4 oxidation is often neglected in routine CH 4 monitoring programs, the model developed here may help to integrate MOX rate into process-based models for fluvial CH 4 budget. [Display omitted] [ABSTRACT FROM AUTHOR]

To speed up reaching UN Sustainable Development Goal 6 for safe sanitation by 2030, integrating high-solid anaerobic digestion (HSAD) into decentralized systems could recycle fecal slag (FS) and food waste (FW), aiding a circular economy and toilet revolution. In this study, a percolate recirculation system and conductive material were used to improve mass transfer, stability, and enhance methane production in HSAD of FS and FW. This setup consists of a percolate tank and a digester tank, where nano-zero valent iron (nZVI) was dosed in the percolate tank (P nZVI in P ) and the digester tank (P nZVI in D ) and compared with a control with no additive (P Control ). The highest cumulative methane yield of 519.43 mL/gVS was achieved in P nZVI in D , which was 4.52 and 3.59 times higher than that of P Control (144.59 mL/gVS) and P nZVI in P (114.96 mL/gVS). This finding demonstrates that the dosing strategy of P nZVI in D facilitated effective interaction among organic matter, microbial communities, and nZVI, resulting in organics removal efficiencies of 67.42 % (total solid) and 77.22 % (volatile solid). Moreover, microbial community analysis supported the efficacy of the P nZVI in D strategy, revealing the enrichment of Clostridium sensu stricto 1 (46.91 %), which potentially engaged in interspecies electron transport (Interspecies hydrogen transfer (IHT) and direct interspecies electron transfer (DIET)) with Methanobacterium (81.19 %) and Methanosarcina (17.11 %). These interactions contribute to enhanced methane yield and stability maintenance in the HSAD system with percolate recirculation. The findings of this study demonstrate that the implementation of HSAD of FS and FW, coupled with percolate recirculation and the addition of nZVI, holds promise for enabling sustainable sanitation practices in developing regions. Moreover, this approach not only facilitates resource recovery but also eliminates the requirement for water., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Cyanobacteria-derived organic carbon has been reported to intensify greenhouse gas emissions from lacustrine sediments. However, the specific processes of CH 4 and CO 2 production and release from sediments into the atmosphere remain unclear, especially in eutrophic lakes. To investigate the influence of severe cyanobacteria accumulation on the production and migration of sedimentary CH 4 and CO 2 , this study examined the different trophic level lakes along the middle and lower reaches of the Yangtze River. The results demonstrated that eutrophication amplified CH 4 and CO 2 emissions, notably in Lake Taihu, where fluxes peaked at 929.9 and 7222.5 μmol/m 2 ·h, mirroring dissolved gas levels in overlying waters. Increased sedimentary organic carbon raised dissolved CH 4 and CO 2 concentrations in pore-water, with isotopic tracking showing cyanobacteria-derived carbon specifically elevated CH 4 and CO 2 in surface sediment pore-water more than in deeper layers. Cyanobacteria-derived carbon deposition on surface sediment boosted organic carbon and moisture levels, fostering an anaerobic microenvironment conducive to enhanced biogenic CH 4 and CO 2 production in surface sediments. In the microcosm systems with the most severe cyanobacteria accumulation, average CH 4 and CO 2 concentrations in surface sediments reached 6.9 and 2.3 mol/L, respectively, surpassing the 4.7 and 1.4 mol/L observed in bottom sediments, indicating upward migration of CH 4 and CO 2 hotspots from deeper to surface layers. These findings enhance our understanding of the mechanisms underlying lake sediment carbon emissions induced by eutrophication and provide a more accurate assessment of lake carbon emissions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

Concerns regarding membrane fouling and suboptimal bioenergy recovery have constrained the implementation of anaerobic membrane bioreactor (AnMBR) for treating low-strength municipal wastewater. This study presents a novel anaerobic cathodic dynamic membrane bioreactor (AnCDMBR) designed to address these challenges. A self-formed cathodic dynamic membrane (CDM) on inexpensive carbon cloth was developed to function as both a membrane and biocathode to achieve dual-function effects of mitigating membrane fouling and accelerating organics conversion. Compared with common dynamic membrane (1.52 kPa/d) and commercial membranes (7.52 kPa/d), the developed CDM presented a significantly reduced fouling rate (1.02 kPa/d), exhibiting the potential as a substitute for high-cost conductive membranes. Furthermore, efficient and stable biomethanation occurred in AnCDMBR with a superior methane yield rate of 0.26 L-CH 4 /g-COD (CH 4 content > 95 %), which was 1.42 times higher than the control, linked to the higher activities of microbial metabolism and methanogenic-related key enzymes. Further analysis revealed that electrostimulation-induced niche differentiation of microbiota regulated interspecies interactions between electroactive microorganisms and complex anaerobic digestion microbiomes, facilitating organic matter conversion to methane and leading to superior bioenergy recovery. This study offered a new strategy for effectively mitigating fouling and recovering bioenergy from low-strength wastewater, potentially expanding the application of AnMBRs., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

• Microplastics (MPs) significantly promoted CH 4 emissions from estuarine wetlands. • Biodegradable MPs had higher promoting effect on CH 4 emission than conventional MPs. • Conventional MPs stimulated CH 4 emission by inhibiting CH 4 consumption. • Biodegradable MPs accelerated CH 4 production and concurrently reducing CH 4 oxidation. Increasing microplastic (MP) pollution poses significant threats to estuarine and coastal ecosystems. However, the effects of MPs on the emission of methane (CH 4), a potent greenhouse gas, within these ecosystems and the underlying regulatory mechanisms have not been elucidated. Here, a combination of 13C stable isotope-based method and molecular techniques was applied to investigate how conventional petroleum-based MPs [polyethylene (PE) and polyvinyl chloride (PVC)] and biodegradable MPs [polylactic acid (PLA) and polyadipate/butylene terephthalate (PBAT)] regulate CH 4 production and consumption and thus affect CH 4 emission dynamics in estuarine and coastal wetlands. Results indicated that both conventional and biodegradable MPs enhanced the emission of CH 4 (P < 0.05), with the promoting effect being more significant for biodegradable MPs. However, the mechanisms by which conventional and biodegradable MPs promote CH 4 emissions were different. Specifically, conventional MPs stimulated the emission of CH 4 by inhibiting the processes of CH 4 consumption, but had no significant effect on CH 4 production rate. Nevertheless, biodegradable MPs promoted CH 4 emissions via accelerating the activities the methanogens while inhibiting the oxidation of CH 4 , thus resulting in a higher degree of promoting effect on CH 4 emissions than conventional MPs. Consistently, quantitative PCR further revealed a significant increase in the abundance of methyl-coenzyme M reductase gene (mcrA) of methanogens under the exposure of biodegradable MPs (P < 0.05), but not conventional MPs. Furthermore, the relative abundance of most genes involved in CH 4 oxidation exhibited varying degrees of reduction after exposure to all types of MPs, based on metagenomics data. This study reveals the effects of MPs on CH 4 emissions in estuarine and coastal ecosystems and their underlying mechanisms, highlighting that the emerging biodegradable MPs exhibited a greater impact than conventional MPs on promoting CH 4 emissions in these globally important ecosystems, thereby accelerating global climate change. [Display omitted] [ABSTRACT FROM AUTHOR]

• A novel bioreactor using hollow fiber membrane to enhance the methane delivery was developed. • Around 100 % of methane and ammonium utilization efficiencies were achieved. • The highest SCP yield was determined to be 1.36 g SCP/g CH 4 and 5.05 g SCP/g N. • A high relative abundance of essential amino acids above 42 % was achieved. Single cell protein (SCP, or microbial protein) is one of the emerging alternative protein sources to address the global challenge of food insecurity. Recently, the SCP produced from methane has attracted substantial attention since methane is a renewable resource attainable from anaerobic digestion. However, the supply of methane, an insoluble gas in water, is one of the major challenges in producing methane-based SCP. This work developed a novel bioreactor configuration, in which hollow fiber membrane was used for efficient methane supply while microorganisms were growing in the suspended form favourable for the biomass harvest. Over a 312-day operation, the impacts of three critical parameters on the SCP production were investigated, including the ratio of methane loading to ammonium loading, the ratio of methane loading to oxygen loading, and the sludge retention time (SRT). Under the condition of 4 g CH 4 /g NH 4 +, 4 g O 2 /g CH 4 , and SRT of 4 days, the highest SCP production yield was observed and determined to be 1.36 g SCP/g CH 4 and 5.05 g SCP/g N, respectively. The protein content was up to 67 %, which is higher than the majority of reported values to date. Moreover, the methane and ammonium utilization efficiencies were both close to 100 %, suggesting the highly efficient utilization of substrates in this new bioreactor configuration. A high relative abundance of essential amino acids (EAA) above 42 % was achieved, representing the highest EAA content reported. These findings provide valuable insights into SCP production using methane as a feedstock. [Display omitted] [ABSTRACT FROM AUTHOR]

• Non-precious metal nimo catalyst was used in a 128-day test producing methane. • Using the catalyst enabled a low internal resistance and high current density. • High CH 4 production rate of 4.7–5.4 L/L-d was achieved at –1 V vs Ag/agcl. • No significant differences in the biocathode communities with different catalysts. • Methanobacterium was the main genus enriched on the biocathode. Microbial electrosynthesis (MES) cells exploit the ability of microbes to convert CO 2 into valuable chemical products such as methane and acetate, but high rates of chemical production may need to be mediated by hydrogen and thus require a catalyst for the hydrogen evolution reaction (HER). To avoid the usage of precious metal catalysts and examine the impact of the catalyst on the rate of methane generation by microbes on the electrode, we used a carbon felt cathode coated with NiMo/C and compared performance to a bare carbon felt or a Pt/C-deposited cathode. A zero-gap configuration containing a cation exchange membrane was developed to produce a low internal resistance, limit pH changes, and enhance direct transport of H 2 to microorganisms on the biocathode. At a fixed cathode potential of –1 V vs Ag/AgCl, the NiMo/C biocathode enabled a current density of 23 ± 4 A/m2 and a high methane production rate of 4.7 ± 1.0 L/L-d. This performance was comparable to that using a precious metal catalyst (Pt/C, 23 ± 6 A/m2, 5.4 ± 2.8 L/L-d), and 3–5 times higher than plain carbon cathodes (8 ± 3 A/m2, 1.0 ± 0.4 L/L-d). The NiMo/C biocathode was operated for over 120 days without observable decay or severe cathode catalyst leaching, reaching an average columbic efficiency of 53 ± 9 % based on methane production under steady state conditions. Analysis of microbial community on the biocathode revealed the dominance of the hydrogenotrophic genus Methanobacterium (∼40 %), with no significant difference found for biocathodes with different materials. These results demonstrated that HER catalysts improved rates of methane generation through facilitating hydrogen gas evolution to an attached biofilm, and that the long-term enhancement of methane production in MES was feasible using a non-precious metal catalyst and a zero-gap cell design. [Display omitted] [ABSTRACT FROM AUTHOR]

Bound extracellular polymeric substances (EPS) are complex, high-molecular-weight polymer mixtures that play a critical role in pore clogging, foulants adhesion, and fouling layer formation during membrane filtration, owing to their adhesive properties and gelation tendencies. In this study, a novel electrochemical anaerobic membrane bioreactor (EC-AnMBR) was constructed to investigate the effect of sludge bound-EPS solubilization on methane bioconversion and membrane fouling mitigation. During the 150-days' operation, the EC-AnMBR demonstrated remarkable performance, characterized by an exceptionally low fouling rate (transmembrane pressure (TMP) < 4.0 kPa) and high-quality effluent (COD removal > 98.2 %, protein removal > 97.7 %, and polysaccharide removal > 98.5 %). The highest methane productivity was up to 38.0 ± 3.1 mL/L reactor /d at the applied voltage of 0.8 V with bound-EPS solubilization, 107.6 % higher than that of the control stage (18.3 ± 2.4 mL/L reactor /d). Morphological and multiplex fluorescence labeling analyses revealed higher fluorescence intensities of proteins, polysaccharides, total cells and lipids on the surface of the fouling layer. In contrast, the interior exhibited increased compression density and reduced activity, likely attributable to compression effect. Under the synergistic influence of the electric field and bound-EPS solubilization, biomass characteristics exhibited a reduced propensity for membrane fouling. Furthermore, the bio-electrochemical regulation enhanced the electroactivity of microbial aggregates and enriched functional microorganisms, thereby promoting biofilm growth and direct interspecies electron transfer. Additionally, the potential hydrogenotrophic and methylotrophic methanogenesis pathways were enhanced at the cathode and anode surfaces, thereby increasing CH₄ productivity. The random forest-based machine learning model analyzed the nonlinear contributions of EPS characteristics on methane productivity and TMP values, achieving R² values of 0.879 and 0.848, respectively. Shapley additive explanations (SHAP) analysis indicated that S-EPS PS and S-EPS PN were the most critical factors affecting CH₄ productivity and membrane fouling, respectively. Partial dependence plot analysis further verified the marginal and interaction effects of different EPS layers on these outcomes. By combining continuous operation with interpretable machine learning algorithms, this study unveils the intricate impacts of EPS characteristics on methane productivity and membrane fouling behaviors, and provides new insights into sludge bound-EPS solubilization in EC-AnMBR., Competing Interests: Declaration of competing interest All of the authors declare that they have no conflict of interest.., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Substantial nutrient inputs from reservoir impoundment typically increase sedimentation rate and primary production. This can greatly enhance methane (CH 4 ) production, making reservoirs potentially significant sources of atmospheric CH 4 . Consequently, elucidating CH 4 emissions from reservoirs is crucial for assessing their role in the global methane budget. Reservoir operations can also influence hydrodynamic and biogeochemical processes, potentially leading to pronounced spatiotemporal heterogeneity, especially in reservoirs with complex tributaries, such as the Three Gorges Reservoir (TGR). Although several studies have investigated the spatial and temporal variations in CH 4 emissions in the TGR and its tributaries, considerable uncertainties remain regarding the impact of reservoir operations on CH 4 dynamics. These uncertainties primarily arise from the limited spatial and temporal resolutions of previous measurements and the complex underlying mechanisms of CH 4 dynamics in reservoirs. In this study, we employed a fast-response automated gas equilibrator to measure the spatial distribution and seasonal variations of dissolved CH 4 concentrations in XXB, a representative area significantly impacted by TGR operations and known for severe algal blooms. Additionally, we measured CH 4 production rates in sediments and diffusive CH 4 flux in the surface water. Our multiple campaigns suggest substantial spatial and temporal variability in CH 4 concentrations across XXB. Specifically, dissolved CH 4 concentrations were generally higher upstream than downstream and exhibited a vertical stratification, with greater concentrations in bottom water compared to surface water. The peak dissolved CH 4 concentration was observed in May during the drained period. Our results suggest that the interplay between aquatic organic matter, which promotes CH 4 production, and the dilution process caused by intrusion flows from the mainstream primarily drives this spatiotemporal variability. Importantly, our study indicates the feasibility of using strategic reservoir operations to regulate these factors and mitigate CH 4 emissions. This eco-environmental approach could also be a pivotal management strategy to reduce greenhouse gas emissions from other reservoirs., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The continuous increase in sulfate (SO 4 2- ) concentrations discharged by anthropogenic activities lacks insights into their dynamics and potential impact on CH 4 budgets in freshwater lakes. Here we conducted a field investigation in the lakes along the highly developed Yangtze River basin, China, additionally, we analyzed long-term data (1950-2020) from Lake Taihu, a typical eutrophic lake worldwide. We observed a gradual increase in SO 4 2- concentrations up to 100 mg/L, which showed a positive correlation with the trophic state of the lakes. The annual variations indicated that eutrophication intensified the fluctuation of SO 4 2- concentrations. A random forest model was applied to assess the impact of SO 4 2- concentrations on CH 4 emissions, revealing a significant negative effect. Synchronously, a series of microcosms with added SO 4 2- were established to simulate cyanobacteria decomposition processes and explore the coupling mechanism between sulfate reduction and CH 4 concentrations. This was attributed to the competition for cyanobacteria-supplied substrates between sulfate reduction bacteria (SRB) and methane production archaea (MPA). Our study highlights the importance of considering the unexpectedly increasing SO 4 concentrations and initial SO 4 2- levels (R 2 = 0.83), indicating that higher initial SO 4 2- concentrations led to lower final CH 4 concentrations. This was attributed to the competition for cyanobacteria-supplied substrates between sulfate reduction bacteria (SRB) and methane production archaea (MPA). Our study highlights the importance of considering the unexpectedly increasing SO 4 2- concentrations in eutrophic lakes when estimating global CH 4 emission budgets., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Considering the high organic matter contents and pollutants in sewage sludge (SS) and food waste (FW), seeking green and effective technology for energy recovery and pollutant control is a big challenge. In this study, we proposed a integrated technology combing SS mass separation by hydrothermal pretreatment, methane production from co-digestion of hydrothermally treated sewage sludge (HSS) centrate and FW, and biochar production from co-pyrolysis of HSS cake and digestate with heavy metal immobilization for synergistic utilization of SS and FW. The results showed that the co-digestion of HSS centrate with FW reduced the NH 4 -N concentration and promoted volatile fatty acids conversion, leading to a more robust anaerobic system for better methane generation. Among the co-pyrolysis of HSS cake and digestate, digestate addition improved biochar quality with heavy metals immobilization and toxicity reduction. Following the lab-scale investigation, the pilot-scale verification was successfully performed (except the co-digestion process). The mass and energy balance revealed that the produced methane could supply the whole energy consumption of the integrated system with 26.2 t biochar generation for treating 300 t SS and 120 t FW. This study presents a new strategy and technology validation for synergistic treatment of SS and FW with resource recovery and pollutants control.+ -N concentration and promoted volatile fatty acids conversion, leading to a more robust anaerobic system for better methane generation. Among the co-pyrolysis of HSS cake and digestate, digestate addition improved biochar quality with heavy metals immobilization and toxicity reduction. Following the lab-scale investigation, the pilot-scale verification was successfully performed (except the co-digestion process). The mass and energy balance revealed that the produced methane could supply the whole energy consumption of the integrated system with 26.2 t biochar generation for treating 300 t SS and 120 t FW. This study presents a new strategy and technology validation for synergistic treatment of SS and FW with resource recovery and pollutants control., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

The emission of methane (CH 4 ) from streams and rivers contributes significantly to its global inventory. The production of CH 4 is traditionally considered as a strictly anaerobic process. Recent investigations observed a "CH 4 paradox" in oxic waters, suggesting the occurrence of oxic methane production (OMP). Human activities promoted dissolved organic carbon (DOC) in streams and rivers, providing significant substrates for CH 4 production. However, the underlying DOC molecular markers of CH 4 production in river systems are not well known. The identification of these markers will help to reveal the mechanism of methanogenesis. Here, Fourier transform ion cyclotron mass spectrometry and other high-quality DOC characterization, ecosystem metabolism, and in-situ net CH 4 production rate were employed to investigate molecular markers attributing to riverine dissolved CH 4 production across different land uses. We show that endogenous CH 4 production supports CH 4 oversaturation and positively correlates with DOC concentrations and gross primary production. Furthermore, sulfur (S)-containing molecules, particularly S-aliphatics and S-peptides, and fatty acid-like compounds (e.g., acetate homologs) are characterized as markers of water-column aerobic and anaerobic CH 4 production. Watershed characterization, including riverine discharge, allochthonous DOC input, turnover, as well as autochthonous DOC, affects the CH 4 production. Our study helps to understand riverine aerobic or anaerobic CH 4 production relating to DOC molecular characteristics across different land uses., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

• Methane and electron acceptors intersected in the groundwater table fluctuation (GTF) zone. • Anaerobic oxidation of methane (AOM) activity was notably high in the GTF zone. • Ca. Methanoperedens was highly abundant (85.4 % of Archaea) and active in the GTF zone. • Ca. Methanoperedens GTF50 oxidizes methane via the "reverse methanogenesis" pathway. Rice paddies are globally important sources of methane emissions and also active regions for methane consumption. However, the impact of fluctuating groundwater levels on methane cycling has received limited attention. In this study, we delved into the activity and microbial mechanisms underlying anaerobic oxidation of methane (AOM) in paddy fields. A comprehensive approach was employed, including 13C stable isotope assays, inhibition experiments, real-time quantitative reverse transcription PCR, metagenomic sequencing, and binning technology. Geochemical profiles revealed the abundant coexistence of both methane and electron acceptors in the groundwater table fluctuation (GTF) zone, at a depth of 40–60 cm. Notably, the GTF zone exhibited the highest rate of AOM, potentially linked to the reduction of iron oxides and nitrate. Within this zone, Candidatus Methanoperedens (belonging to the ANME-2d group) dominated the Archaea population, accounting for a remarkable 85.4 %. Furthermore, our results from inhibition experiments, RT-qPCR, and metagenome-assembled genome (MAG) analysis highlighted the active role of Ca. Methanoperedens GTF50 in the GTF zone. This microorganism could independently mediate AOM process through the intriguing "reverse methanogenesis" pathway. Considering the similarity in geochemical conditions across different paddy fields, it is likely that Ca. Methanoperedens-mediated AOM is prevalent in the GTF zones. [Display omitted] [ABSTRACT FROM AUTHOR]

• A model comprising C/N/S-related bioprocesses was developed and evaluated. • Impact of H 2 S on MBfR/granular bioreactor performing anammox/n-DAMO was assessed. • H 2 S content in inflow gas (v/v: 0∼5%) did not significantly affect MBfR. • Influent H 2 S of granular bioreactor lowered TN removal or increased energy demand. The coupling between anammox and nitrate/nitrite-dependent anaerobic methane oxidation (n-DAMO) has been considered a sustainable technology for nitrogen removal from sidestream wastewater and can be implemented in both membrane biofilm reactor (MBfR) and granular bioreactor. However, the potential influence of the accompanying hydrogen sulfide (H 2 S) in the anaerobic digestion (AD)-related methane-containing mixture on anammox/n-DAMO remains unknown. To fill this gap, this work first constructed a model incorporating the C/N/S-related bioprocesses and evaluated/calibrated/validated the model using experimental data. The model was then used to explore the impact of H 2 S on the MBfR and granular bioreactor designed to perform anammox/n-DAMO at practical levels (i.e., 0∼5% (v/v) and 0∼40 g/S m3, respectively). The simulation results indicated that H 2 S in inflow gas did not significantly affect the total nitrogen (TN) removal of the MBfR under all operational conditions studied in this work, thus lifting the concern about applying AD-produced biogas to power up anammox/n-DAMO in the MBfR. However, the presence of H 2 S in the influent would either compromise the treatment performance of the granular bioreactor at a relatively high influent NH 4 +-N/NO 2 −-N ratio (e.g., >1.0) or lead to increased energy demand associated with TN removal at a relatively low influent NH 4 +-N/NO 2 −-N ratio (e.g., <0.7). Such a negative effect of the influent H 2 S could not be attenuated by regulating the hydraulic residence time and should therefore be avoided when applying the granular bioreactor to perform anammox/n-DAMO in practice. [Display omitted] [ABSTRACT FROM AUTHOR]

• Nitrite-dependent anaerobic methane oxidation (nitrite-DAMO) microbes are enriched in sewers. • Nitrite-DAMO process is stimulated due to in-sewer nitrate-dosing for sulfide control. • Candidatus Methylomirabilis are likely to be the key microbe in inducing nitrite-DAMO process. • The finding of nitrite-DAMO process opens a new path to sewer methane mitigation. Nitrate or nitrite-dependent anaerobic methane oxidation (n-DAMO) is a microbial process that links carbon and nitrogen cycles as a methane sink in many natural environments. This study demonstrates, for the first time, that the nitrite-dependent anaerobic methane oxidation (nitrite-DAMO) process can be stimulated in sewer systems under continuous nitrate dosing for sulfide control. In a laboratory sewer system, continuous nitrate dosing not only achieved complete sulfide removal, but also significantly decreased dissolved methane concentration by ∼50 %. Independent batch tests confirmed the coupling of methane oxidation with nitrate and nitrite reduction, revealing similar methane oxidation rates of 3.68 ± 0.5 mg CH 4 L−1 h−1 (with nitrate as electron acceptor) and 3.57 ± 0.4 mg CH 4 L−1 h−1 (with nitrite as electron acceptor). Comprehensive microbial analysis unveiled the presence of a subgroup of the NC10 phylum, namely Candidatus Methylomirabilis (n-DAMO bacteria that couples nitrite reduction with methane oxidation), growing in sewer biofilms and surface sediments with relative abundances of 1.9 % and 1.6 %, respectively. In contrast, n-DAMO archaea that couple methane oxidation solely to nitrate reduction were not detected. Together these results indicated the successful enrichment of n-DAMO bacteria in sewerage systems, contributing to approx. 64 % of nitrite reduction and around 50 % of dissolved methane removal through the nitrite-DAMO process, as estimated by mass balance analysis. The occurrence of the nitrite-DAMO process in sewer systems opens a new path to sewer methane emissions. [Display omitted] [ABSTRACT FROM AUTHOR]

• 125 mg/L fulvic acid improved the methane yield by 51.72 % in anaerobic digestion. • Fulvic acid acted as an electron mediator among microorganisms in anaerobic digestion. • Interspecific electron transfer mediated by fulvic acid reinforced carbon recovery. • Fulvic acid enhanced microbial metabolic activity through oxidative phosphorylation. Fulvic acid, prevalent in humus derived from the anaerobic digestion of kitchen wastewater, is crucial in organic matter transformation. However, its effects and underlying mechanisms remain unclear. In this study, the fate of anaerobic digestion of artificial and kitchen wastewater with different fulvic acid contents was investigated. The results showed that 125 mg/L fulvic acid resulted in a 64.02 and 51.72 % increase in methane production in synthetic and kitchen wastewater, respectively. Fulvic acid acted as an electron mediator and increased substrate oxidation by boosting NAD and ATP levels, thereby increasing microbial metabolic rates and ensuring an adequate substrate for methane generation. Isotope analysis suggested that fulvic acid boosts the conversion of volatile fatty acids to methane via the interspecies electron transfer pathway. Gene expression analysis revealed that cytochrome c, FAD, and other electron transport coenzymes were upregulated by fulvic acid, thereby enhancing substrate utilisation and biogas quality. Fulvic acid presented a dual stimulatory and inhibitory effect on anaerobic digestion, with concentrations over 125 mg/L diminishing its positive impact. This dual effect may stem from the properties and concentrations of fulvic acid. This study revealed the effect mechanism of fulvic acid and provided insights into the humus performance in anaerobic digestion [Display omitted] [ABSTRACT FROM AUTHOR]

• Fe(III) induced ammonium formation via DNRA during nitrate dependent AOM. • N 2 O was produced during simultaneous Fe(III) and nitrate dependent AOM. • The Nrf bypass and reverse HURM-Cyt P460 pathways contributed to N 2 O production. • ' Ca. M. nitroreducens' producing N 2 O may offset its greenhouse gas reduction potential. ' Candidatus Methanoperedens nitroreducens' is an archaeal methanotroph with global importance that links carbon and nitrogen cycles and great potential for sustainable operation of wastewater treatment. It has been reported to mediate the anaerobic oxidation of methane through a reverse methanogenesis pathway while reducing nitrate to nitrite. Here, we demonstrate that ' Ca. M. nitroreducens' reduces ferric iron forming ammonium (23.1 %) and nitrous oxide (N 2 O, 46.5 %) from nitrate. These results are supported with the upregulation of genes coding for proteins responsible for dissimilatory nitrate reduction to ammonium (nrfA), N 2 O formation (norV, cyt P460), and multiple multiheme c-type cytochromes for ferric iron reduction. Concomitantly, an increase in the N 2 O-reducing SJA-28 lineage and a decrease in the nitrite-reducing ' Candidatus Methylomirabilis oxyfera' are consistent with the changes in ' Ca. M. nitroreducens' end products. These findings demonstrate the highly flexible physiology of ' Ca. M. nitroreducens' in anaerobic ecosystems with diverse electron acceptor conditions, and further reveals its roles in linking methane oxidation to global biogeochemical cycles. ' Ca. M. nitroreducens' could significantly affect the bioavailability of nitrogen sources as well as the emission of greenhouse gas in natural ecosystems and wastewater treatment plants. [Display omitted] [ABSTRACT FROM AUTHOR]

• Dissolved methane from anaerobic effluents was eliminated in an anoxic reactor. • Eliminated dissolved methane was used for nitrate/nitrite reduction with magnetite. • AOM coupled to nitrate/nitrite reduction occurred and magnetite facilitated it. • AOM coupled to nitrate/nitrite reduction was proceeded by syntrophic consortia. • Syntrophic consortia exchanged electrons more effectively with magnetite. Discovery of nitrate/nitrite-dependent anaerobic methane oxidation (DAMO) challenges the conventional biological treatment processes, since it provides a possibility of simultaneously mitigating dissolved methane emissions from anaerobic effluents and reducing additional carbon sources for denitrification. Due to the slow growth of specialized DAMO microbes, this possibility has been just practiced with biofilms in membrane biofilm reactors or granular sludge in membrane bioreactors. In this study, simultaneous elimination of dissolved methane from anaerobic effluents and nitrate/nitrite reduction was achieved in a conventional anoxic reactor with magnetite. Calculations of electron flow balance showed that, with magnetite the eliminated dissolved methane was almost entirely used for nitrate/nitrite reduction, while without magnetite approximately 52 % of eliminated dissolved methane was converted to unknown organics. Metagenomic sequencing showed that, when dissolved methane served as an electron donor, the abundance of genes for reverse methanogenesis and denitrification dramatically increased, indicating that anaerobic oxidation of methane (AOM) coupled to nitrate/nitrite reduction occurred. Magnetite increased the abundance of genes encoding the key enzymes involved in whole reverse methanogenesis and Nir and Nor involved in denitrification, compared to that without magnetite. Analysis of microbial communities showed that, AOM coupled to nitrate/nitrite reduction was proceeded by syntrophic consortia comprised of methane oxidizers, Methanolinea and Methanobacterium , and nitrate/nitrite reducers, Armatimonadetes_gp5 and Thauera. With magnetite syntrophic consortia exchanged electrons more effectively than that without magnetite, further supporting the microbial growth. [Display omitted] [ABSTRACT FROM AUTHOR]

• Biogas yield increased by 32.1 % in EC-AnMBR compared to traditional AnMBR. • Long-term operation of EC-AnMBR stimulated enrichment of keystone electro-microbes. • Composite anode membrane (CAM) upgraded the functional genes in metabolic pathways. • CAM stimulated transfer of electrons and degradation of organic pollutants. • EC-AnMBR uniquely shaped the spatio-temporal distribution of microbial communities. Electrochemical anaerobic membrane bioreactor (EC-AnMBR) by integrating a composite anodic membrane (CAM), represents an effective method for promoting methanogenic performance and mitigating membrane fouling. However, the development and formation of electroactive biofilm on CAM, and the spatio-temporal distribution of key functional microorganisms, especially the degradation mechanism of organic pollutants in metabolic pathways were not well documented. In this work, two AnMBR systems (EC-AnMBR and traditional AnMBR) were constructed and operated to identify the role of CAM in metabolic pathway on biogas upgrading and mitigation of membrane fouling. The methane yield of EC-AnMBR at HRT of 20 days was 217.1 ± 25.6 mL-CH 4 /g COD, about 32.1 % higher compared to the traditional AnMBR. The 16S rRNA analysis revealed that the EC-AnMBR significantly promoted the growth of hydrolysis bacteria (Lactobacillus and SJA-15) and methanogenic archaea (Methanosaeta and Methanobacterium). Metagenomic analysis revealed that the EC-AnMBR promotes the upregulation of functional genes involved in carbohydrate metabolism (gap and kor) and methane metabolism (mtr, mcr, and hdr), improving the degradation of soluble microbial products (SMPs)/extracellular polymeric substances (EPS) on the CAM and enhancing the methanogens activity on the cathode. Moreover, CAM biofilm exhibits heterogeneity in the degradation of organic pollutants along its vertical depth. The bacteria with high hydrolyzing ability accumulated in the upper part, driving the feedstock degradation for higher starch, sucrose and galactose metabolism. A three-dimensional mesh-like cake structure with larger pores was formed as a biofilter in the middle and lower part of CAM, where the electroactive Geobacter sulfurreducens had high capabilities to directly store and transfer electrons for the degradation of organic pollutants. This outcome will further contribute to the comprehension of the metabolic mechanisms of CAM module on membrane fouling control and organic solid waste treatment and disposal. [Display omitted] [ABSTRACT FROM AUTHOR]

• Nearly complete dissolved methane removal was achieved by integrating PN/anammox/n-DAMO in MABR. • High-level (> 90 %) N removal from mainstream was achieved simultaneously. • N-DAMO microorganisms were the major contributors to dissolved methane removal. • The presence of n-DAMO microorganisms could relax the requirement of NOB suppression. • The system was robust against dynamic influent compositions. Anaerobic technologies with downstream autotrophic nitrogen removal have been proposed to enhance bioenergy recovery and transform a wastewater treatment plant from an energy consumer to an energy exporter. However, approximately 20–50 % of the produced methane is dissolved in the anaerobically treated effluent and is easily stripped into the atmosphere in the downstream aerobic process, contributing to the release of greenhouse gas emissions. This study aims to develop a solution to beneficially utilize dissolved methane to support high-level nitrogen removal from anaerobically treated mainstream wastewater. A novel technology, integrating Partial Nitritation, Anammox and Methane-dependent nitrite/nitrate reduction (i.e. PNAM) was demonstrated in a membrane-aerated biofilm reactor (MABR). With the feeding of ∼50 mg NH 4 +-N/L and ∼20 mg/L dissolved methane at a hydraulic retention time of 15 h, around 90 % of nitrogen and ∼100 % of dissolved methane can be removed together in the MABR. Microbial community characterization revealed that ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB), anammox bacteria, nitrite/nitrate-dependent anaerobic methane oxidation microorganisms (n-DAMO bacteria and archaea) and aerobic methanotrophs co-existed in the established biofilm. Batch tests confirmed the active microbial pathways and showed that AOB, anammox bacteria and n-DAMO microbes were jointly responsible for the nitrogen removal, and dissolved methane was mainly removed by the n-DAMO process, with aerobic methane oxidation making a minor contribution. In addition, the established system was robust against dynamic changes in influent composition. The study provides a promising technology for the simultaneous removal of dissolved methane and nitrogen from domestic wastewater, which can support the transformation of wastewater treatment from an energy- and carbon-intensive process, to one that is energy- and carbon-neutral. [Display omitted] [ABSTRACT FROM AUTHOR]

Hydrothermal liquefaction (HTL) is a promising thermo-chemical technology for municipal sludge treatment due to its potential for biocrude oil recovery and minimizing biosolids management costs. However, the process generates a high volume of an aqueous byproduct that needs to be treated due to its high chemical oxygen demand (COD) and various organic and inorganic compounds. Although the aqueous phase is known to contain recalcitrant and potentially inhibitory substances that may affect its biological treatment, their molecular weight distribution (MwD) and its impact on anaerobic biodegradability are poorly understood. Ultrafiltration (UF) was conducted to fractionate HTL aqueous into different molecular weight (Mw) fractions using 300, 100, 10, and 1 kDa membranes. Mesophilic biochemical methane potential (BMP) assays were conducted to assess the anaerobic biodegradability of each fraction, and the first-order model was used to calculate the degradation kinetics of potential inhibitory compounds. The highest percentage of organics (65 %) was found in the Mw<1 kDa range, whereas the 10>Mw>1 kDa had the lowest percentage (8 %). There was no significant difference in the cumulative specific methane produced from various Mw fractions (p>0.05). The Mw<1 kDa fraction had the highest first-order specific methane production rate (0.53 day -1 ), whereas the unfiltered HTL had the lowest (0.38 day -1 ). Although UF fractionation increased the rate of anaerobic degradation of HTL aqueous for the Mw<1 kDa fraction, the observed methane potential was only 55 % of the theoretical value. This implies that 45 % of COD remains undegraded even after permeation through the lowest Mw cut-off membrane. Therefore, further characterization of HTL aqueous is needed for compounds with molecular weights below 1 kDa to fully understand the nature of inhibitory organics and their impact on anaerobic digestion. Furthermore, pretreatments utilizing techniques such as adsorption and advanced oxidation may be necessary to enhance the specific methane yields from various HTL aqueous fractions, thereby bringing them closer to the theoretical yield., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Cigdem Eskicioglu reports financial support was provided by Natural Sciences and Engineering Research Council of Canada. Cigdem Eskicioglu reports financial support was provided by Metro Vancouver. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Methanogenesis of waste biomass (WB) is a promising method for global sustainable development, reduction of pollution and carbon emission levels, and recovering bioenergy. Unlike in the methanogenesis of organic wastewater, in which microbial cells come into direct contact with the dissolved substrate, the 'solid-liquid-solid' modes in WB and between WB and microbial cells, which involve numerous solid-liquid interfaces, greatly hinder the methanogenesis efficiency of WB. Amongst all WB, waste activated sludge is the most complex, poorly biodegradable and representative. Herein, we highlight the role of water evaporation-driven solid-liquid interfacial restructuring of sludge in determining its methanogenesis efficiency. Non-free water evaporation increased surface roughness and adhesion, and compressed pore structure with numerous capillaries in sludge, resulting in a new solid-liquid interface of sludge with great capillary force and highly ordered interfacial water molecules, which provides an extremely favourable condition for high mass transfer and proton-coupled electron transfer (PCET) in sludge. This restructuring was confirmed to induce the enhancement of solid-liquid interfacial noncovalent interactions and electron transfer efficiency in the subsequent methanogenesis process (P < 0.05), promoting the effective contact between the sludge substrate and microbial cells, thereby enriching the methanogenic consortia (i.e., Clostridia and Methanosarcina were increased by 290.0 % and 239.7 %, respectively) and improving the activities of key enzymes. Stable isotope tracing and metagenomic analysis further reveal that this restructuring promoted the participation of water molecules in the methane formation by PCET-driven release of protons from water, and enhanced main methanogenesis metabolic pathways, especially the metabolic pathway of CO 2 -reduction methanogenesis (+65.2 %), thereby resulting in a great advance in methane generation (+147 %, P < 0.001). The findings can provide a reference for regulating directional anaerobic biotransformation of water-rich multiphase complex substrates by interfacial restructuring inducement., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper, (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Constructed wetlands (CWs) are frequently used for effective biological treatment of nitrogen-rich wastewater with external carbon source addition; however, these approaches often neglect the interaction between plant litter and biochar in biochar-amended CW environments. To address this, we conducted a comprehensive study to assess the impacts of single or combined addition of common reed litter and reed biochar (pyrolyzed at 300 and 500 °C) on nitrogen removal, greenhouse gas emission, dissolved organic matter (DOM) dynamics, and microbial activity. The results showed that combined addition of reed litter and biochar to CWs significantly improved nitrate and total nitrogen removal compared with biochar addition alone. Compared to those without reed litter addition, CWs with reed litter addition had more low-molecular-weight and less aromatic DOM and more protein-like fluorescent DOM, which favored the enrichment of bacteria associated with denitrification. The improved nitrogen removal could be attributed to increases in denitrifying microbes and the relative abundance of functional denitrification genes with litter addition. Moreover, the combined addition of reed litter and 300 °C-heated biochar significantly decreased nitrous oxide (30.7 %) and methane (43.9 %) compared to reed litter addition alone, while the combined addition of reed litter and 500 °C-heated biochar did not. This study demonstrated that the presences of reed litter and biochar in CWs could achieve both high microbial nitrogen removal and relatively low greenhouse gas emissions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

• First survey of GHG emissions from Brussels ponds. • Small ponds are more subject to edge effects and have higher pCO 2. • Macrophytes enhance methane production in ponds. • City center ponds have higher N 2 O emissions due to atmospheric deposition. • Brussels ponds emissions were equivalent to the carbon sink estimated for the urban green spaces. Freshwaters have been recognized as important sources of greenhouse gases (GHG) to the atmosphere. However, urban ponds have received little attention even though their number is increasing due to expanding urbanisation globally. Ponds are frequently associated to urban green spaces that provide several ecosystemic services such as cooling local climate, regulating the water cycle, and acting as small carbon sinks This study aims to identify and understand the processes producing GHGs (CO 2 , CH 4 , and N 2 O) in the urban ponds of the temperate European city of Brussels in Belgium. 22 relatively small ponds (0.1–4.6 ha) surrounded by contrasted landscape (strictly urban, bordered by cropland or by forest), were sampled during four seasons in 2021–2022. The mean ± standard deviation was 3,667 ± 2,904 ppm for the partial pressure of CO 2 (pCO 2), 2,833 ± 4,178 nmol L−1 for CH 4 , and 273 ± 662% for N 2 O saturation level (%N 2 O). Relationships of GHGs with oxygen and water temperature suggest that biological processes controlled pCO 2 , CH 4 concentration and%N 2 O. However, pCO 2 was also controlled by external inputs as indicated by the higher values of pCO 2 in the smaller ponds, more subject to external inputs than larger ones. The opposite was observed for CH 4 concentration that was higher in larger ponds, closer to the forest in the city periphery, and with higher macrophyte cover. N 2 O concentrations, as well as dissolved inorganic nitrogen, were higher closer to the city center, where atmospheric nitrogen deposition was potentially higher. The total GHG emissions from the Brussels ponds were estimated to 1kT CO 2 -eq per year and were equivalent to the carbon sink of urban green spaces. [Display omitted] [ABSTRACT FROM AUTHOR]

• Lake CO 2 and CH 4 concentrations varied with seasons and mixing regimes on a regional scale. • System productivity directly affected the carbon concentrations in the dry season and stratified sites. • Direct impacts of lake morphology and geoclimatic factors were found except for the dry season. • The effects of season and mixing regime should be considered in estimating lake carbon emissions. Due to the large spatiotemporal variability in the processes controlling carbon emissions from lakes, estimates of global lake carbon emission remain uncertain. Identifying the most reliable predictors of CO 2 and CH 4 concentrations across different hydrological features can enhance the accuracy of carbon emission estimates locally and globally. Here, we used data from 71 lakes in Southwest China varying in surface area (0.01‒702.4 km2), mean depth (< 1‒89.6 m), and climate to analyze differences in CO 2 and CH 4 concentrations and their driving mechanisms between the dry and rainy seasons and between different mixing regimes. The results showed that the average concentrations of CO 2 and CH 4 in the rainy season were 23.9 ± 18.8 μmol L−1 and 2.5 ± 4.9 μmol L−1, respectively, which were significantly higher than in the dry season (10.5 ± 10.3 μmol L−1 and 1.8 ± 4.2 μmol L−1, respectively). The average concentrations of CO 2 and CH 4 at the vertically mixed sites were 24.1 ± 21.8 μmol L−1 and 2.6 ± 5.4 μmol L−1, being higher than those at the stratified sites (14.8 ± 13.4 μmol L−1 and 1.7 ± 3.5 μmol L−1, respectively). Moreover, the environmental factors were divided into four categories, i.e., system productivity (represented by the contents of total nitrogen, total phosphorus, chlorophyll a and dissolved organic matter), physicochemical factors (water temperature, Secchi disk depth, dissolved oxygen and pH value), lake morphology (lake area, water depth and drainage ratio), and geoclimatic factors (altitude, wind speed, precipitation and land-use intensity). In addition to the regression and variance partitioning analyses between the concentrations of CO 2 and CH 4 and environmental factors, the cascading effects of environmental factors on CO 2 and CH 4 concentrations were further elucidated under four distinct hydrological scenarios, indicating the different driving mechanisms between the scenarios. Lake morphology and geoclimatic factors were the main direct drivers of the carbon concentrations during the rainy season, while they indirectly affected the carbon concentrations via influencing physicochemical factors and further system productivity during the dry season; although lake morphology and geoclimatic factors directly contributed to the carbon concentrations at the vertically mixed and stratified sites, the direct effect of system productivity was only observed at the stratified sites. Our results emphasize that, when estimating carbon emissions from lakes at broad spatial scales, it is essential to consider the influence of precipitation-related seasons and lake mixing regimes. [Display omitted] [ABSTRACT FROM AUTHOR]

• Multiple methane cycling processes in shallow groundwater are evidenced by multiple methods. • CO 2 reduction, acetate fermentation and methane oxidation all occurred in groundwater. • CO 2 reduction dominated acetate-fermentation in two methanogenic pathways in groundwater. • Various factors may lead to contrasting groundwater methane cycling in different settings. Groundwater rich in dissolved methane is often overlooked in the global or regional carbon cycle. Considering the knowledge gap in understanding the biogeochemical behavior of methane in shallow aquifers, particularly those in humid alluvial-lacustrine plains with high organic carbon content, we investigated methane sources and cycling pathways in groundwater systems at the central Yangtze River basins. Composition of multiple stable isotopes (2H/18O in water, 13C in dissolved inorganic carbon, 13C/2H in methane, and 13C in carbon dioxide) was combined with the characteristics of microbes and dissolved organic matter (DOM) in the study. The results revealed significant concentrations of biogenic methane reaching up to 13.05 mg/L in anaerobic groundwater environments with abundant organic matter. Different pathways for methane cycling (methanogenic CO 2 -reduction and acetate-fermentation, and methane oxidation) were identified. CO 2 -reduction dominated acetate-fermentation in the two methanogenic pathways primarily associated with humic DOM, while methane oxidation was more closely associated with microbially derived DOM. The abundance of obligate CO 2 -reduction microorganisms (Methanobacterium and Methanoregula) was higher in samples with substantial CO 2 -reduction, as indicated by isotopic composition. The obligate acetate-fermentation microorganism (Methanosaeta) was more abundant in samples exhibiting evident acetate-fermentation. Additionally, a high abundance of Candidatus Methanoperedens was identified in samples with apparent methane oxidation. Comparing our findings with those in other areas, we found that various factors, such as groundwater temperature, DOM abundance and types, and hydrogeological conditions, may lead to differences in groundwater methane cycling. This study offered a new perspective and understanding of methane cycling in worldwide shallow alluvial-lacustrine aquifer systems without geothermal disturbance. [ABSTRACT FROM AUTHOR]

• Higher microbiome dynamic in hydrolysis fermenter than in main fermenter. • This open hydrolysis fermenter does not improve the degradation of complex carbohydrates. • Degradation of complex carbohydrates takes place in the main fermenter. The yield and productivity of biogas plants depend on the degradation performance of their microbiomes. The spatial separation of the anaerobic digestion (AD) process into a separate hydrolysis and a main fermenter should improve cultivation conditions of the microorganisms involved in the degradation of complex substrates like lignocellulosic biomass (LCB) and, thus, the performance of anaerobic digesters. However, relatively little is known about such two-stage processes. Here, we investigated the process performance of a two-stage agricultural AD over one year, focusing on chemical and technical process parameters and metagenome-centric metaproteomics. Technical and chemical parameters indicated stable operation of the main fermenter but varying conditions for the open hydrolysis fermenter. Matching this, the microbiome in the hydrolysis fermenter has a higher dynamic than in the main fermenter. Metaproteomics-based microbiome analysis revealed a partial separation between early and common steps in carbohydrate degradation and primary fermentation in the hydrolysis fermenter but complex carbohydrate degradation, secondary fermentation, and methanogenesis in the main fermenter. Detailed metagenomics and metaproteomics characterization of the single metagenome-assembled genomes showed that the species focus on specific substrate niches and do not utilize their full genetic potential to degrade, for example, LCB. Overall, it seems that a separation of AD in a hydrolysis and a main fermenter does not improve the cleavage of complex substrates but significantly improves the overall process performance. In contrast, the remaining methanogenic activity in the hydrolysis fermenter may cause methane losses. [Display omitted] [ABSTRACT FROM AUTHOR]

• CO 2 dominated 90 % of warming effect, leaving 2.8 % from CH 4 and 7.2 % from N 2 O. • Addition to the river input, sediment is the external source of GHGs in PRE. • Estuarine GHGs dynamics were studied by developed endmember mixing model. • Internal processes in estuary reduce estuarine greenhouse gas emissions. Estuary acts as a hotspot of greenhouse gases (GHGs, including CO 2 , CH 4 and N 2 O) to the atmosphere. However, the GHGs budgets, including input/output fluxes through interfaces and biogeochemical source/sink processes in water columns, of the estuarine systems are still not well constrained due to the lacking of comprehensive observational data. Here, we presented the spatial distributions of GHGs of surface/bottom water and sediment porewater along the Pearl River Estuary (PRE) and adjacent region during summertime. The incorporation of the monitoring for the sediment-water interface (SWI) with these of the water-air interface (WAI) allows us to close the budget revealing additional information of internal consumption/production processes of the three GHGs. The oversaturated CO 2 (481–7573 μatm), CH 4 (289–16,990 %) and N 2 O (108–649 %) in surface water suggested PRE is a significant GHGs source to the atmosphere, in which CO 2 is the major contributor accounting for 90 % of total global warming potential (GWP), leaving 2.8 % from CH 4 , and 7.2 % from N 2 O. Addition to the river input, the SWI releases GHGs to the overlying water with fluxes of 3.5 × 107, 10.8 × 104 and 0.7 × 104 mol d−1 for CO 2 , CH 4 and N 2 O, respectively. Although all three GHGs exhibited emission to the atmosphere, our mass balance calculation showed that 16.9× 107 mol d−1 of CO 2 and 1.0 × 104 mol d−1 of N 2 O were consumed, respectively, inside the estuary water body, while extra-production (13.8 × 104 mol d−1) of CH 4 was demanded in the water body to support its output flux. This is the first experiment quantitatively assessing the importance of internal carbon and nitrogen biogeochemical processes in the PRE. Our finding is of guiding significance to constrain the GHGs budget and draw up realistic pathways for modeling works of GHGs prediction. [Display omitted] [ABSTRACT FROM AUTHOR]

Shallow lake ecosystems are highly sensitive to temperature fluctuation because of their high water surface-to-volume ratios. Shallow lakes have been increasingly identified as a hotspot of CO 2 and CH 4 emissions, but their response to temperature variation remains unclear. Here, we report from a 5-month outdoor mesocosm experiment where we investigated the impacts of a projected 3.5 °C future warming and monthly temperature changes on lake CO 2 and CH 4 , as well as the key drivers affecting the lake carbon cycling. Our results show that CO 2 and CH 4 concentrations had a significantly positive correlation with monthly temperatures. CH 4 concentration was primarily regulated by monthly temperature, while nutrients effects on CO 2 concentration overrode climate warming and temporal temperature changes. These findings imply the varied roles that temperature and nutrient levels can play on CO 2 and CH 4 dynamics in shallow lake systems. The relationship between temperature and CO 2 concentration was nonlinear, showing a threshold of approximately 9 °C, at which CO 2 concentration could be strongly modified by nutrient level in the lake systems. Understanding this complex relationship between temperature with CO 2 and CH 4 concentrations in shallow lakes is crucial for effective lake management and efficient control of greenhouse gases (GHGs) emissions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Utilizing H 2 -assisted ex-situ biogas upgrading and acetate recovery holds great promise for achieving high value utilization of biogas. However, it faces a significant challenge due to acetate's high solubility and limited economic value. To address this challenge, we propose an innovative strategy for simultaneous upgrading of biogas and the production of medium-chain fatty acids (MCFAs). A series of batch tests evaluated the strategy's efficiency under varying initial gas ratios (v/v) of H 2 , CH 4 , CO 2 , along with varying ethanol concentrations. The results identified the optimal conditions as initial gas ratios of 3H 2 :3CH 4 :2CO 2 and an ethanol concentration of 241.2 mmol L -1 , leading to maximum CH 4 purity (97.2 %), MCFAs yield (54.2 ± 2.1 mmol L -1 ), and MCFAs carbon-flow distribution (62.3 %). Additionally, an analysis of the microbial community's response to varying conditions highlighted the crucial roles played by microorganisms such as Clostridium, Proteiniphilum, Sporanaerobacter, and Bacteroides in synergistically assimilating H 2 and CO 2 for MCFAs production. Furthermore, a 160-day continuous operation using a dual-membrane aerated biofilm reactor (dMBfR) was conducted. Remarkable achievements were made at a hydraulic retention time of 2 days, including an upgraded CH 4 content of 96.4 ± 0.3 %, ethanol utilization ratio (URethanol) of 95.7 %, MCFAs production rate of 28.8 ± 0.3 mmol L -1 d -1 , and MCFAs carbon-flow distribution of 70 ± 0.8 %. This enhancement is proved to be an efficient in biogas upgrading and MCFAs production. These results lay the foundation for maximizing the value of biogas, reducing CO 2 emissions, and providing valuable insights into resource recovery., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Ltd.)

Anaerobic methane generation from algae is hindered by the slow and poor algae biodegradability. A novel free ammonia (NH 3 i.e. FA) pretreatment technology was proposed in this work to enhance anaerobic methane generation from algae cultivated using a real secondary effluent. The algae solubilisation was 0.05–0.06 g SCOD/g TCOD (SCOD: soluble chemical oxygen demand; TCOD: total chemical oxygen demand) following FA pretreatment of 240–530 mg NH 3 –N/L for 24 h, whereas the solubilisation was only 0.01 g SCOD/g TCOD for the untreated algae. This indicates that FA pretreatment at 240–530 mg NH 3 –N/L could substantially enhance algae solubilisation. Biochemical methane potential tests revealed that FA pretreatment on algae at 240–530 mg NH 3 –N/L is able to significantly enhance anaerobic methane generation. The hydrolysis rate (k) and biochemical methane potential (P 0) of algae increased from 0.21 d−1 and 132 L CH 4 /kg TCOD to 0.33–0.50 d−1 and 140–154 L CH 4 /kg TCOD, respectively, after the algae was pretreated by FA at 240–530 mg NH 3 –N/L. Further analysis indicated that FA pretreatment improved k of both quickly and slowly biodegradable substrates, and also increased P 0 of the slowly biodegradable substrate although it negatively affected P 0 of the quickly biodegradable substrate. This FA technology is a closed-loop technology. Image 1 • FA pretreatment at 240–530 mg N/L is able to increase methane generation from algae. • FA pretreatment enhances methane potential (P 0) and hydrolysis rate (k) of algae. • Ammonium pretreatment does not affect methane generation from algae. • pH 9.5 pretreatment slightly increases k and P 0 of algae. • FA pretreatment is a closed-loop technology. [ABSTRACT FROM AUTHOR]

Nitrite-dependent anaerobic methane oxidation (N-DAMO) is a newly discovered bioprocess which uses methane as electron donor to reduce nitrite into dinitrogen. It is a promising clean bioprocess for denitrification in wastewater treatment. However, the low reaction rate and slow growth rate of N-DAMO bacteria within NC10 phylum limit the application of the process. In this study, we chose vitamin, heme, nucleobase and betaine to investigate their short- and long-term effects on N-DAMO bacteria. The concentrations of the growth factors of medium were improved according to the short-term experiments. The results were subsequently verified via long-term inoculations and were applied in a magnetically stirred gas lift reactor (MSGLR). The results indicated that nucleobase and betaine (5.0 and 200 μg L−1, respectively) significantly stimulated the N-DAMO activity, whereas vitamin and heme had no significant effects in the tested concentration ranges. During the long-term incubation, N-DAMO bacteria continuously increased and finally achieved a relative abundance of 14.4% on day 300. Notably, larger aggregates of N-DAMO bacteria were observed at the end of the long-term incubation. And the nitrogen removal rate of the MSGLR increased to 70 mg N L−1 day−1, with the total nitrogen removal efficiency over 99.0%. However, the addition of betaine introduced methyl into the reactors and this made methylotrophs account a considerable part of the bacterial community, which limited the enrichment degree of N-DAMO bacteria. This work will contribute to the engineering application and enrichment of N-DAMO bacteria. Image 1 • Nucleobase and betaine significantly stimulated the N-DAMO activity. • N-DAMO bacteria formed larger aggregates by using improved medium. • The nitrogen removal rate reached 70 mg N L−1 day−1 by using improved medium. • The total nitrogen removal efficiency reached 99.0% by using improved medium. • Combined nitritation/N-DAMO is a promising nitrogen removal technology. [ABSTRACT FROM AUTHOR]

Sulfite has been widely employed as a key agent in many industrial processes, leading to a large amount of sulfite-laden wastes generated. Given its antimicrobial function and destructive ability on cell walls, detailed mechanisms for impacts of sulfite on waste activated sludge (WAS) and outcomes of methane production after the sulfite-pretreatment have not been clear so far. In this study, the feasibility of methane production from sulfite pretreated WAS was verified and investigated. Biochemical methane potential tests demonstrated that methane production from WAS after the pretreatment at 800 mg S/L of sulfite (a typical level in sulfite-laden wastes) increased by up to 25%. Kinetic analysis of the test results indicated that sulfite pretreatment increased the sludge hydrolysis rate (k hyd) by 1.71 times while the ultimate biochemical methane potential (B u) by 1.20 times. Further study investigated the effects of sulfite on WAS from the macro-scale (i.e. sludge physicochemical properties) to the micro-scale (i.e. bacterial viability, microbial community). Sulfite concentrations of up to 800 mg S/L substantially enhanced WAS disintegration and solubilization, reducing the particle size by up to 39%, boosting substrate release by 87% and improving cell lysis by 43% through the direct destruction of gram-positive microorganisms (e.g., norank_p_Saccharibacteria) in WAS. Adverse impact on anaerobic digestion by introduction of sulfite was not observed in this study, though a long-term evaluation is needed in the future work. Based on the findings of the present study, sulfite-laden by-products or wastes from industrial processes may be co-treated with WAS when overall cost-effectiveness is concerned. Image 1 • Sulfite enhanced methane production from both inoculum (by 97%) and WAS (by 25%). • Sulfite improved the hydrolysis rate and the ultimate biochemical methane potential of both inoculum and WAS. • Sulfite induced the disintegration and solubilization of WAS within 24 h. • Sulfite caused the cell lysis through the direct destruction of microbes in WAS. [ABSTRACT FROM AUTHOR]

Anaerobic digestion of organic matter is the major route of biomethane production. However, in the presence of sulfate, sulfate-reducing bacteria (SRB) typically outcompete methanogens, which may reduce or even preclude methane production from sulfate-containing wastewaters. Although sulfate-reduction and methanogenesis can occur simultaneously, our limited understanding of the microbiology of anaerobic digesters treating sulfate-containing wastewaters constrains improvements in the production of methane from these systems. This study tested the effects of carbon sources and chemical oxygen demand-to-sulfate ratio (C O D / S O 4 2 − ) on the diversity and interactions of SRB and methanogens in an anaerobic digester treating a high-sulfate waste stream. Overall, the data showed that sulfate removal and methane generation occurred in varying efficiencies and the carbon source had limited effect on the methane yield. Importantly, the results demonstrated that methanogenic and SRB diversities were only affected by the carbon source and not by the C O D / S O 4 2 − ratio. Graphical abstract Image 1 Highlights • Microbial diversity in anaerobic digesters with high-sulfate wastewater was studied. • The C O D / S O 4 2 − ratio did not affect the diversity of methanogens and sulfate-reducers. • The microbial diversity and metabolism were mainly affected by the carbon source. • The presence of sulfate affected methanogenesis in butyrate- and TMA-incubations. [ABSTRACT FROM AUTHOR]

Abstract In addition to undesirable odorous gases, substantial amounts of greenhouse gases (GHG), particularly methane (CH 4), are generated during the storage of livestock manure. To reduce the CH 4 emissions, first, pig slurry (PS) was stored for 40 d at 30 °C after adjusting the pH at 5.0–7.0 using H 2 SO 4 solution. In the control (non-acidified PS), 3.7 kg CO 2 eq./ton PS of CH 4 emissions was detected, which was reduced to 1.8, 0.9, 0.4, 0.2, and 0.1 kg CO 2 eq./ton PS at pH 7.0, 6.5, 6.0, 5.5, and 5.0, respectively. Methanosarcina was found to be the dominant genus (67% of the total archaeal sequence) in the control, whose dominance was reduced as storage pH decreased. The results of ribonucleic acid analysis and specific methanogenic activity test further confirmed the inhibition of indigenous methanogens by acidification. Later, the biochemical CH 4 potential of stored PS was tested. Compared to the control (10.6 L CH 4 /L PS), the acidified PS showed higher CH 4 yields of 12.7–14.6 L CH 4 /L PS, presumably by keeping degradable organic matters in PS under acidic condition. Among different acidification pHs tested, the maximum amount of GHG reduction was achieved at pH 6.0 by reducing CH 4 emission to +0.4 kg CO 2 eq./ton PS during storage while increasing biogas production potential equivalent to 48.3 kWh/ton PS (−22.5 kg CO 2 eq./ton PS), resulting in a further reduction of (−)9.6 kg CO 2 eq./ton PS compared to the control. Graphical abstract Image 1 Highlights • Reduction of GHGs emissions from pig slurry by acidification (pH 5.0–7.0). • CH 4 emissions drop from 3.7 kg CO 2 eq./ton PS to 0.1–1.8 kg CO 2 eq./ton PS. • Methanosarcina was found to be the dominant archaea during storage of PS. • 20–38% of higher BMP value from the acidified PS compared to the control. • Storage at pH 6.0 achieve further reduction of 9.6 kg CO 2 eq./ton PS than control. [ABSTRACT FROM AUTHOR]

Abstract Septic systems inherently rely on microbial communities in the septic tank and leach field to attenuate pollution from household sewage. Operating conditions of septic leach field systems, especially the degree of water saturation, are likely to impact microbial biogeochemical cycling, including carbon (C), nitrogen (N), and phosphorus (P), as well as greenhouse gas (GHG) emissions to the atmosphere. To study the impact of flooding on microbial methane (CH 4) and nutrient cycling, two leach field soil columns were constructed. One system was operated as designed and the other was operated in both flooded and well-maintained conditions. CH 4 emissions were significantly higher in flooded soils (with means between 0.047 and 0.33 g CH 4 m−2 d−1) as compared to well-drained soils (means between −0.0025 and 0.004 g CH 4 m−2 d−1). Subsurface CH 4 profiles were also elevated under flooded conditions and peaked near the wastewater inlet. Gene abundances of mcrA , a biomarker for methanogens, were also greatest near the wastewater inlet. In contrast, gene abundances of pmoA , a biomarker for methanotrophs, were greatest in surface soils at the interface of CH 4 produced subsurface and atmospheric oxygen. 16S rRNA, mcrA , and pmoA amplicon library sequencing revealed microbial community structure in the soil columns differed from that of the original soils and was driven largely by CH 4 fluxes and soil VWC. Additionally, active microbial populations differed from those present at the gene level. Flooding did not appear to affect N or P removals in the soil columns (between 75 and 99% removal). COD removal was variable throughout the experiment, and was negatively impacted by flooding. Our study shows septic system leach field soils are dynamic environments where CH 4 and nutrients are actively cycled by microbial populations. Our results suggest proper siting, installation, and routine maintenance of leach field systems is key to reducing the overall impact of these systems on water and air quality. Graphical abstract Image 1 Highlights • Two leach field soil columns were operated to measure water and air quality impact. • CH 4 fluxes and subsurface concentrations increased under flooded conditions. • Methanogens and methanotrophs had distinct depth profiles. • Both flooded and well-maintained columns had comparable nutrient removals. • Leach field column microbial communities differed from original soils. [ABSTRACT FROM AUTHOR]

Abstract In typical anaerobic digestion (AD) systems, the microbial functional assertion is hampered by synchronised versatile metabolism required for heterogeneous substrates degradation. Thus, the intricate methanogenic process from organic compounds remains an enigma after decades of empirical operation. In this study, simplified AD microbial communities were obtained with substrate specifications and continuous reactor operation. Genome-centric metagenomic approach was followed to holistically investigate the metabolic pathways of the AD and the microbial synergistic networks. In total, 63 metagenome assembled genomes (MAGs) were assembled from 8 metagenomes acquired in specific methanogenic niches. The metabolic pathways were reconstructed from the annotated genes and their dynamicity under experimental conditions. The results show that the methanogenic niches nourish unique metabolism beyond current knowledge acquired from cultivation-based methods. A novel glucose mineralization model without acetate formation was proposed and asserted in a pair of syntrophs: Clostridiaceae sp. and Methanoculleus thermophilus. Moreover, the catabolic pathway was elucidated in uncharacterized syntrophic acetate oxidizers, Synergistaceae spp. A remarkable evolutionary insight is the discovery that electron transport and energy conservation mechanisms impose selective pressure on syntrophic partners. Overall, the functional roles of the individual microbes tightly rely on the catabolic pathways and cannot always be physiologically defined in accordance with conventional four-step AD concept. The substrate-specific systems provided a traceable microbial community to dissecting the AD process. The genome-centric metagenomics successfully constructed genomes of microbes that have not been previously isolated and illustrated metabolic pathways that beyond the current knowledge of AD process. This study provides new perspectives to unravel the AD microbial ecology and suggests more attention should be paid on uncharacterized metabolism specifically harboured by AD microbial communities. Highlights • Genome-centric metagenomics was used to unveil the anaerobic digestion process. • Traceable microbial communities were obtained with substrate specifications. • The metabolisms were dissected by stepwise simplified substrates. • A novel glucose mineralization model without acetate formation was proposed. • Electron transfer mechanisms are key factors of selecting syntrophic partners. [ABSTRACT FROM AUTHOR]

• Cation exchange resin (CER) enhanced the sequential recovery of H 2 and CH 4 from sludge. • Ion exchange reactions provided a driving force for hydrogen generation. • CER enriched the hydrogen-producing bacteria and key genes encoding enzymes. • CER played an induced role in methanogenesis in the methane-production stage. • CER-induced reduces energy barriers of mass transfer and enrich functional anaerobes. The recovery of renewable bioenergy from anaerobic digestion (AD) of sludge is a promising method to alleviate the energy problem. Although methane can be effectively recovered through sludge pretreatment by cation exchange resin (CER), the simultaneous enhancement of hydrogen and methane generation from AD using CER has not been extensively investigated. Herein, the effect of CER on the sequential recovery of hydrogen and methane and the corresponding mechanisms were investigated. When CER is introduced, the maximum increases for the hydrogen and methane production are 104.7 % and 35.3 %, respectively, confirming the sequential enhancement effects of CER on the hydrogen and methane production. Analyses of the variations in the main biochemical components with and without the effect of CER demonstrate that CER promotes sludge organic solubilisation, hydrolysis, and acidification in both hydrogen- and methane-production stages. Moreover, investigations of variations in the solid–liquid interfacial thermodynamics and removal rates of main multivalent metals of sludge reveal that the ion exchange reactions between the CER and sludge in the hydrogen-production stage provide the direct driving force of effective contact between bacteria and organic particulates. Additionally, the residual effect of the CER during methane production reduces the energy barrier for mass transfer and provides a driving force for this transfer. Further analyses of the microbial community structure and metagenomics indicate that CER directly drives the enrichment of hydrogen-producing bacteria (+ 15.1 %) and key genes encoding enzymes in the hydrogen-production stage. Moreover, CER indirectly induces the enrichment of methane-producing anaerobes (e.g. Methanosaeta : + 16.7 %, Methanosarcina : + 316.5 %); enhances the bioconversion of different substrates into methyl-coenzyme M; and promotes the metabolism pathway of acetoclastic process and CO 2 reduction in the methane-production stage. This study can provide valuable insights for simultaneously enhancing the production of hydrogen and methane from AD through sequential recovery. [Display omitted] [ABSTRACT FROM AUTHOR]

Fe based chemically enhanced primary sedimentation (CEPS) is an effective method of capturing the colloidal particles and inorganic phosphorous (P) from wastewater but also produces Fe-CEPS sludge. Anaerobic digestion is recommended to treat the sludge for energy and phosphorus recovery. However, the aggregated sludge flocs caused by the coagulation limited sludge hydrolysis and P release during anaerobic digestion process. In this study, cation exchange resin (CER) was employed during anaerobic digestion of Fe-CEPS sludge with aims of prompting P release and carbon recovery. CER addition effectively dispersed the sludge flocs. However, the greater dispersion of sludge flocs could not translate to higher sludge hydrolysis. The maximum hydrolysis and acidification achieved at lower CER dosage of 0.5 g CER/g TS. It was observed that the extents of sludge hydrolysis and acidification had a strongly negative correlation with the organic binding iron (OBI) concentration. The presence of CER during anaerobic digestion favored Fe(III) reduction to Fe(II), and then further induced iron phase transformation, leading to the OBI formation from the released organic matters. Meanwhile, higher CER dosage resulted in higher P release efficiency and the maximum efficiency at 4 g CER/g TS was four times than that of the control. The reduction of BD-P, NaOH-P and HCl-P in solid phase contributed most P release into the supernatant. A new two-stage treatment process was further developed to immigrate the OBI formation and improve the carbon recovery efficiency. Through this process, approximately 45% of P was released, and 63% of carbon was recovered as methane from Fe-CEPS sludge via CER pretreatment., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Thermal hydrolysis (TH) is widely employed in combination with anaerobic digestion (AD) to efficiently treat primary sludge and waste-activated sludge in municipal wastewater treatment plants. In this study, four different scenarios-conventional AD (S1), TH-AD (S2), AD-TH-AD (S3), and characteristics-based AD-TH-AD (S4, primary AD only for primary sludge)-were evaluated to determine the optimal deployment of TH and AD for treating primary sludge and waste-activated sludge to maximize net energy output. The maximum net energy output of 4899 MJ/t-TS fed (per ton total solids of sludge fed) was achieved in S4 when assuming the recovered heat was only used for AD heating and surplus heat was wasted, and the net energy output of S4 was 70.8 % higher than that of S1 and 48.6 % higher than that of S2. This remarkable improvement was attributed to a reduction of > 15.2 % in refractory compounds, resulting in a 17 % increase in methane yield. Importantly, this study provides the first comparison of refractory compounds between inter-thermal hydrolysis (inter-TH) and pre-thermal hydrolysis (pre-TH) using a simulated A 2 O process. Overall, this study provides innovative insights and strategies for enhancing the TH and AD process performance based on the specific characteristics of sewage sludge derived from wastewater treatment plants., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Jianbin Guo reports financial support was provided by Beijing Drainage Group Co. Ltd, Beijing 100,022, China., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Abstract For over a century, anaerobic digestion has been a key technology in stabilizing organic waste streams, while at the same time enabling the recovery of energy. The anticipated transition to a bio-based economy will only increase the quantity and diversity of organic waste streams to be treated, and, at the same time, increase the demand for additional and effective resource recovery schemes for nutrients and organic matter. The performance of anaerobic digestion can be supported and enhanced by (bio)electrochemical systems in a wide variety of hybrid technologies. Here, the possible benefits of combining anaerobic digestion with (bio)electrochemical systems were reviewed in terms of (1) process monitoring, control, and stabilization, (2) nutrient recovery, (3) effluent polishing, and (4) biogas upgrading. The interaction between microorganisms and electrodes with respect to niche creation is discussed, and the potential impact of this interaction on process performance is evaluated. The strength of combining anaerobic digestion with (bio)electrochemical technologies resides in the complementary character of both technologies, and this perspective was used to distinguish transient trends from schemes with potential for full-scale application. This is supported by an operational costs assessment, showing that the economic potential of combining anaerobic digestion with a (bio)electrochemical system is highly case-specific, and strongly depends on engineering challenges with respect to full-scale applications. Graphical abstract Image Highlights • Anaerobic digestion and (bio)electrochemical systems are complementary technologies. • Various hybrid technologies can improve the anaerobic digestion process. • Schemes with full-scale potential are distinguished from transient trends. • An operational cost assessment is essential for full-scale application. [ABSTRACT FROM AUTHOR]

Abstract Anaerobic oxidation of methane (AOM) is a microbial process that consumes dissolved methane (CH 4) in anoxic sediments and soils and mitigates CH 4 release to the atmosphere. The degree to which AOM limits global biospheric CH 4 emissions is not fully understood. In marine sediments, where the process was first described, AOM is responsible for oxidizing >90% of the CH 4 produced. More recently, AOM has been observed in soils, peatlands, and freshwater ecosystems. In lakes, where sediment anoxia, organic carbon turnover, and CH 4 production are common, AOM is not well studied but could represent a significant CH 4 sink and constraint on emissions. Here, we present evidence for the occurrence of AOM in the sediment of thirteen lakes that span a global climatic and trophic gradient. We further quantified and modeled AOM patterns and studied potential microbial controls of AOM using laboratory incubations of sediment and stable isotope measurements in three of the thirteen lakes. We demonstrate that AOM is widespread in freshwater lake sediments and accounts for 29%–34% (95% confidence interval) of the mean total CH 4 produced in surface and near-surface lake sediments. Graphical abstract Image 1 Highlights • Anaerobic oxidation of methane (AOM) was observed in 13 of 14 study lake sediments. • AOM profile was further established in the sediments of three lakes. • AOM ranged from 12 to 87% of the methane produced in the lake sediments. • We conclude that AOM is ubiquitous and reduces largely methane emissions from lakes. [ABSTRACT FROM AUTHOR]

Adding conductive materials can promote methanogenesis via facilitating electron exchange between syntrophic bacteria and methanogenic archaea. However, little is known about how temperature would interact with such an addition and thus affect the compositions and characteristics of endogenous redox mediators (ERMs). In particular, it is of strong interest to understand how the temperature variation would affect the improvement on methanogenesis induced by ERMs with conductive materials. Herein, we have investigated the response of sludge methanogenesis to temperature variation (from 15 to 35 °C) and spectroscopically detected the ERMs induced by conductive red mud. It was demonstrated that the increasing temperature enhanced the stimulating effect of conductive red mud on methane accumulation, and the methane production potential showed a linear relationship with redox parameters such as areal capacitance ( C a ), free charges ( R 2 ) and electron exchange capacity (EEC). 2DCOS spectra further indicated that ν (C-O) and δ (O-H) in humic acids, β -turn type III amide I ν s(C=O) in Cytochrome c , and δ (C-H) in amines and lipids became the main redox groups in ERMs at 35 °C with the addition of red mud. The model revealed that the contribution of ERMs to the CO 2 reduction to CH 4 increased from 35.2 ± 1.4% to 58.6 ± 1.5% when the temperature increased from 15 to 35 °C. Our finding that conductive materials stimulated the formation and electroactivity of ERMs with the increasing temperature during anaerobic digestion can have important implications for the improvement of engineered methanogenic processes. [ABSTRACT FROM AUTHOR]