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

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

The potential of insect frass for sustainable biogas and biomethane production: A review.

Insect-based protein production has gained traction in recent years. This has led to the increasing production of frass, the residual substrate from insect farming. As a relatively new substrate with characteristics that are not widely known, its energetic potential still needs to be investigated. In this context, this literature review aims to evaluate the potential of frass as a feedstock for bioenergy production through anaerobic digestion. From the literature search, 11 studies were selected, and showed a wide range of biogas (44 m3/ton VS to 668 m3/ton VS) and methane (26 m3/ton VS to 502 m3/ton VS) production potentials from insect frass, mostly comparable with traditional biomasses of liquid and solid slurry. Results are influenced by factors such as substrate type, digestion conditions and presence of co-digestion substrates. The need of further investigation on the economic viability has been highlighted, with a focus on the possibility of upgrading biogas to vehicle-grade biomethane.

A cyclic shift-temperature operation method to train microbial communities of mesophilic anaerobic digestion.

Temperature is the critical factor affecting the efficiency and cost of anaerobic digestion (AD). The current work develops a shift-temperature AD (STAD) between 35 °C and 55 °C, intending to optimise microbial community and promote substrate conversion. The experimental results showed that severe inhibition of biogas production occurred when the temperature was firstly increased stepwise from 35 °C to 50 °C, whereas no inhibition was observed at the second warming cycle. When the organic load rate was increased to 6.37 g VS/L/d, the biogas yield of the STAD reached about 400 mL/g VS, nearly double that of the constant-temperature AD (CTAD). STAD promoted the proliferation of Methanosarcina (up to 57.32 %), while severely suppressed hydrogenophilic methanogens. However, when the temperature was shifted to 35 °C, most suppressed species recovered quickly and the excess propionic acid was quickly consumed. Metagenomic analysis showed that STAD also promoted gene enrichment related to pathways metabolism, membrane functions, and methyl-based methanogenesis.

Anode potential regulates gas composition and microbiome in anaerobic electrochemical digestion.

Anaerobic electrochemical digestion (AED) is an effective system for recovering biogas from organic wastes. However, the effects of different anode potentials on anaerobic activated sludge remain unclear. This study confirmed that biofilms exhibited the best electroactivity at -0.2 V (vs. Ag/AgCl) compared to -0.4 V and 0 V. Gas was further regulated, with the highest hydrogen content (47 ± 7 %) observed at -0.2 V. The 0 V system produced the largest amount of methane (70 ± 8 %) and exhibited the greatest presence of hydrogen-utilizing microorganisms. The gas yield at -0.4 V was the lowest, with no hydrogen detected. Excess bioelectrohydrogen at -0.2 V and 0 V caused the co-enrichment of Methanobacterium and Acetoanaerobium, establishing a thermodynamically feasible current-acetate-hydrogen electron cycle to improve electrogenesis. These results provide insights into the regulatory strategies of MEC technology during anaerobic digestion, which play a decisive role in determining the composition of biogas.

Establishment of methanogen bacterial interactions during the preweaning period of dairy cattle.

Ruminant livestock are major contributors to anthropogenic methane emissions in the United States and worldwide. Enteric methane is generated by methanogenic archaea residing in ruminant digestive tracts. Information on when methanogens colonize the gut and when they begin to interact with bacteria during the early phases of the ruminant life cycle is less explored. The objectives of this study were (i) to investigate the composition of the methanogenic archaeal community at birth and through the weaning transition and (ii) to determine if and when the methanogenic archaea begin to interact with bacteria in the lower gut of neonatal dairy calves. Ten female Holstein calves (approximately 45kg birth weight) were enrolled in the study. Fecal samples were collected every two weeks (Wk 2, 4, 6, 8, 10, and 12) between birth and weaning and analyzed for methanogenic archaeal diversity via 16S rRNA amplicon sequencing and quantitative real-time PCR (RT-qPCR). Estimates of alpha diversity (Observed species, and Shannon diversity index) and beta diversity (weighted and unweighted UniFrac distances) showed significant differences (P < 0.05) between archaeal communities across timepoints. Both 16S rRNA amplicon sequencing and RT-qPCR analyses revealed Methanobrevibacter was the most prevalent genus at Wk2, Wk4, and Wk6, whereas Methanosphaera gradually increased with time and was most abundant at Wk10 and Wk12. Correlation analysis revealed that Methanobrevibacter and Methanosphaera were inversely correlated with each other and formed distinct cohorts with specific bacterial lineages similar to those reported in the mature rumen, thus revealing that these associations are established during the preweaning period. Therefore, the preweaning period presents a window of opportunity to interfere with early-life methanogenic colonization with the ultimate goal of reducing enteric methane emissions without perturbing ruminal function later in the life of dairy cattle.

Mechanistic exploration of COVlD-19 antiviral drug ritonavir on anaerobic digestion through experimental validation coupled with metagenomics analysis.

Aggregation of antiviral drugs (ATVs) in waste activated sludge (WAS) poses considerable environmental risk, so it is crucial to understand the behavior of these agents during WAS treatment. This study investigated the effects of ritonavir (RIT), an ATV used to treat human immunodeficiency virus infection and coronavirus disease 2019, on anaerobic digestion (AD) of WAS to reveal the mechanisms by which it interferes with anaerobic flora. The dosage influence results showed that methane production in AD of WAS decreased by 46.56 % when RIT concentration was increased to 1000 µg/kg total suspended solids (TSS). The AD staging test revealed that RIT mainly stimulated microbial synthesis of the extracellular polymeric substance (EPS), limiting organic matter solubilization. At 500 µg/kg TSS, RIT decreased CHO and CHON levels in dissolved organic matter by 23.12 % and 56.68 %, respectively, significantly reducing substrate availability to microorganisms. Metagenomic analysis of microbial functional gene sets revealed that RIT had greater inhibitory effects on protein and amino acid metabolism than on carbohydrate metabolism. Under RIT stress, methanogens switched from hydrogenotrophic and acetotrophic methanogenesis to methylotrophic and acetotrophic methanogenesis.

Agarose-Based Model Ecosystem for Cultivating Methanotrophs in a Methane-Oxygen Counter Gradient.

Aerobic methane-oxidizing bacteria, known as methanotrophs, serve important roles in biogeochemical cycling. Methanotrophs occupy a specific environmental niche within methane-oxygen counter gradients found in soils and sediments, which influences their behavior on an individual and community level. However, conventional methods to study the physiology of these greenhouse gas-mitigating microorganisms often use homogeneous planktonic cultures, which do not accurately represent the spatial and chemical gradients found in the environment. This hinders scientists' understanding of how these bacteria behave in situ. Here, a simple, inexpensive model ecosystem called the gradient syringe is described, which uses semi-solid agarose to recreate the steep methane-oxygen counter gradients characteristic of methanotrophs' natural habitats. The gradient syringe allows for the cultivation of methanotrophic strains and the enrichment of mixed methane-oxidizing consortia from environmental samples, revealing phenotypes only visible in this spatially resolved context. This protocol also reports various biochemical assays that have been modified to be compatible with the semi-solid agarose matrix, which may be valuable to researchers culturing microorganisms within other agarose-based systems.

Metabolic versatility of aerobic methane-oxidizing bacteria under anoxia in aquatic ecosystems.

The potential positive feedback between global aquatic deoxygenation and methane (CH4) emission emphasizes the importance of understanding CH4 cycling under O2-limited conditions. Increasing observations for aerobic CH4-oxidizing bacteria (MOB) under anoxia have updated the prevailing paradigm that MOB are O2-dependent; thus, clarification on the metabolic mechanisms of MOB under anoxia is critical and timely. Here, we mapped the global distribution of MOB under anoxic aquatic zones and summarized four underlying metabolic strategies for MOB under anoxia: (a) forming a consortium with oxygenic microorganisms; (b) self-generation/storage of O2 by MOB; (c) forming a consortium with non-oxygenic heterotrophic bacteria that use other electron acceptors; and (d) utilizing alternative electron acceptors other than O2. Finally, we proposed directions for future research. This study calls for improved understanding of MOB under anoxia, and underscores the importance of this overlooked CH4 sink amidst global aquatic deoxygenation.

The use of infrared thermography as an indicator of methane production in hair sheep.

Infrared thermography may be an alternative technology for measuring the amount of CH4 produced and has the advantages of low cost, speed and efficiency in obtaining results. The study's objective was to determine if the infrared thermography is adequate for predicting the emission of CH4 in hair sheep and the best time after feeding to carry out the measurement. Twelve Santa Inês lambs (females, non-pregnant, with twelve months old and mean body weight of 39.3 ± 2.1 kg) remained for two days in respirometric chambers, in a semi-closed system, to determine the CH4 production. The animals were divided into two treatments, according to the diet provided. During this period, seven thermographic photographs were taken, at times - 1 h, -0.5 h, 0 h, 0.5 h, 1 h, 2 h, 3 h, 5 h, and 7 h, according to the feeding time, defined as 0 h. CH4 production was measured over 24 h. Thermographic images measured the maximum, minimum, average and point temperatures at the left and right flanks. The temperature difference between the left and right flanks (left minus right) was calculated each time. Pearson correlation coefficients, multiple regression and principal component analysis were carried out in SAS®. The best prediction of emission intensity of CH4 (kg of CH4 per dry matter intake) was obtained at 3 h after feeding: CH4/DMI = 13.9016-0,38673 * DifP2 + 3.39089 * DifMed2 (R² = 0.48), using the difference between left and right flanks for point and average temperature measures. Therefore, infrared thermography can be used as an indicator of CH4 production in hair sheep three hours after feeding.

Methane fluxes in tidal marshes of the conterminous United States.

Methane (CH4) is a potent greenhouse gas (GHG) with atmospheric concentrations that have nearly tripled since pre-industrial times. Wetlands account for a large share of global CH4 emissions, yet the magnitude and factors controlling CH4 fluxes in tidal wetlands remain uncertain. We synthesized CH4 flux data from 100 chamber and 9 eddy covariance (EC) sites across tidal marshes in the conterminous United States to assess controlling factors and improve predictions of CH4 emissions. This effort included creating an open-source database of chamber-based GHG fluxes (https://doi.org/10.25573/serc.14227085). Annual fluxes across chamber and EC sites averaged 26 ± 53 g CH4 m-2 year-1, with a median of 3.9 g CH4 m-2 year-1, and only 25% of sites exceeding 18 g CH4 m-2 year-1. The highest fluxes were observed at fresh-oligohaline sites with daily maximum temperature normals (MATmax) above 25.6°C. These were followed by frequently inundated low and mid-fresh-oligohaline marshes with MATmax ≤25.6°C, and mesohaline sites with MATmax >19°C. Quantile regressions of paired chamber CH4 flux and porewater biogeochemistry revealed that the 90th percentile of fluxes fell below 5 ± 3 nmol m-2 s-1 at sulfate concentrations >4.7 ± 0.6 mM, porewater salinity >21 ± 2 psu, or surface water salinity >15 ± 3 psu. Across sites, salinity was the dominant predictor of annual CH4 fluxes, while within sites, temperature, gross primary productivity (GPP), and tidal height controlled variability at diel and seasonal scales. At the diel scale, GPP preceded temperature in importance for predicting CH4 flux changes, while the opposite was observed at the seasonal scale. Water levels influenced the timing and pathway of diel CH4 fluxes, with pulsed releases of stored CH4 at low to rising tide. This study provides data and methods to improve tidal marsh CH4 emission estimates, support blue carbon assessments, and refine national and global GHG inventories.

Sustainable production of C50 carotenoid bacterioruberin from methane using soil-enriched microbial consortia.

Bacterioruberin is widely used in medicine, food, and cosmetics owing to its prominent characteristics of antioxidants and bioactivities. Bioconversion of methane into bacterioruberin is a promising way to address biomanufacturing substrate costs and greenhouse gas emissions but has not been achieved yet. Herein, this study aimed to upcycle methane to bacterioruberin by microbial consortia. The microbial consortia consist of Methylomonas and Methylophilus capable of synthesizing carotenoids from methane was firstly enriched from paddy soil. Through this microbial community, methane was successfully converted into C50 bacterioruberin for the first time. The bioconversion process was then optimized by the response surface methodology. Finally, the methane-derived bacterioruberin reached a record yield of 280.88 ± 2.94 µg/g dry cell weight. This study presents a cost-effective and eco-friendly approach for producing long-chain carotenoids from methane, offering a significant advancement in the direct conversion of greenhouse gases into value-added products.

The use of microencapsulated banana flower powder pellet on in vitro ruminal fermentation, digestibility, microbial diversity, and methane production.

Ruminant animals constitute major contributors to greenhouse gas (GHG) emissions and play an important part in sustainable agricultural systems. A bioactive compound (BC) with antibacterial properties was utilized to inhibit rumen methanogens and decrease ruminant methane emissions. The bio efficacy of ruminant nutrition was frequently employed using a new technology through microencapsulation technique to produce stable products. The microencapsulated banana flower powder pellet (mBAFLOP) powder was used as a BC in the diets. Consequently, this study aimed to evaluate the effects of mBAFLOP supplementation on in vitro gas production kinetics, rumen fermentation, microbial population, and methane production. A completely randomized design (CRD) was used to randomly assign respective treatments at 0, 1, 2, and 3% of the total dry matter (DM) substrate. Ruminal pH, in vitro dry matter degradability and volatile fatty acid profile both at 12, and 24 h were not negatively affected by supplementation with mBAFLOP. The supplemented mBAFLOP (3% of total DM substrate) resulting in ruminal ammonia-nitrogen concentrations was linearly increased (P < 0.01) different among treatments, while methane production was reduced when compared with other treatment (quadratic effect, P < 0.05). Moreover, Ruminococcus flavefaciens was increased when the proportion of mBAFLOP supplement was increased. Furthermore, there was a linear effect (P < 0.05) of decreasing Methanobacteriales in the rumen with increased levels of mBAFLOP supplementation. Based on this study, the use of mBAFLOP at 3% could enhance NH3N concentration and cellulolytic bacteria especially Ruminococcus flavefaciens was increased. Furthermore, supplementation with mBAFLOP decreased methane production. Therefore, a possible dietary plant-based bioactive compound, mBAFLOP supplementation cloud enhances rumen fermentation and mitigates methane production.

Could exhaled methane be used as a possible indicator for hemodynamic changes in trauma induced hemorrhagic shock? Scientific basis supported by a case study.

INTRODUCTION: Identification of severe blood loss and hemorrhagic shock in polytrauma patients poses a key challenge for trauma teams across the world, as there are just a few objective parameters, on which clinicians can rely. We investigated the relationship between exhaled air methane (CH4) concentration and blood loss in a polytrauma patient. Decreased blood flow in the superior mesenteric artery (SMA) is one of the first compensatory responses to blood loss. Gases produced by the anaerobic flora of the intestinal segment supplied by the SMA are the primary source of exhaled CH4, which diffuses through the intestinal microvessels into the circulation and is finally eliminated through the lungs. We hypothesized that diminution of exhaled CH4 indicates blood loss and tested our theory in a severely injured patient. METHODS: Exhaled CH4 concentrations of a severely injured patient were measured using a photoacoustic spectroscope (PAS) attached to the exhalation side of the breathing circuit. The primary objective was to investigate the relationship between exhaled CH4 and conventional indicators of hemorrhage including hemoglobin (Hb) levels, base deficit (BD) values and vital parameters (heart rate and systolic blood pressure) in the early phase of in-hospital care (first 4 h). RESULTS: A severely injured patient was admitted with unstable hemodynamic parameters and incomplete left lower limb amputation, (Injury Severity Score: 38, 74/36 mmHg, 76 bpm). At the time of arrival, considerably lower CH4 levels were detected (22,800 PAU) in the exhaled air. During the first 4 h fluid and massive blood resuscitation, the exhaled CH4 levels were continuously rising in parallel with Htc and Hb values. Corresponding to these changes, BD values displayed a decreasing tendency. DISCUSSION: Our study was conducted to characterize the changes in exhaled air CH4 concentration in response to hemorrhagic shock and to provide data on a viable clinical use of an experimental technique. According to our results, the real-time detection of exhaled air CH4 concentration is an applicable and promising technique for the early detection of bleeding and hemorrhagic shock in severely injured patients. Further research on large sample size and refinement of the PAS technique is required.

Adaptation of a microbial consortium to pelagic Sargassum modifies its taxonomic and functional profile that improves biomethane potential.

In recent years, pelagic Sargassum has invaded the Caribbean coasts, and anaerobic digestion has been proposed as a sustainable management option. However, the complex composition of these macroalgae acts as a barrier to microbial degradation, thereby limiting methane production. Microbial adaptation is a promising strategy to improve substrate utilization and stress tolerance. This study aimed to investigate the adaptation of a microbial consortium to enhance methane production from the pelagic Sargassum. Microbial adaptation was performed in a fed-batch mode for 100 days by progressive feeding of Sargassum. The evolution of the microbial community was analyzed by high-throughput sequencing of 16S rRNA amplicons. Additionally, 16S rRNA data were used to predict functional profiles using the iVikodak platform. The results showed that, after adaptation, the consortium was dominated by the bacterial phyla Bacteroidota, Firmicutes, and Atribacterota, as well as methanogens of the families Methanotrichaceae and Methanoregulaceae. The abundance of predicted genes related to different metabolic functions was affected during the adaptation stage when Sargassum concentration was increased. At the end of the adaptation stage, the abundance of the predicted genes increased again. The adapted microbial consortium demonstrated a 60% increase in both biomethane potential and biodegradability index. This work offers valuable insights into the development of treatment technologies and the effective management of pelagic Sargassum in coastal regions, emphasizing the importance of microbial adaptation in this context.

Unveiling the deterministic dynamics of microbial meta-metabolism: a multi-omics investigation of anaerobic biodegradation.

BACKGROUND: Microbial anaerobic metabolism is a key driver of biogeochemical cycles, influencing ecosystem function and health of both natural and engineered environments. However, the temporal dynamics of the intricate interactions between microorganisms and the organic metabolites are still poorly understood. Leveraging metagenomic and metabolomic approaches, we unveiled the principles governing microbial metabolism during a 96-day anaerobic bioreactor experiment. RESULTS: During the turnover and assembly of metabolites, homogeneous selection was predominant, peaking at 84.05% on day 12. Consistent dynamic coordination between microbes and metabolites was observed regarding their composition and assembly processes. Our findings suggested that microbes drove deterministic metabolite turnover, leading to consistent molecular conversions across parallel reactors. Moreover, due to the more favorable thermodynamics of N-containing organic biotransformations, microbes preferentially carried out sequential degradations from N-containing to S-containing compounds. Similarly, the metabolic strategy of C18 lipid-like molecules could switch from synthesis to degradation due to nutrient exhaustion and thermodynamical disadvantage. This indicated that community biotransformation thermodynamics emerged as a key regulator of both catabolic and synthetic metabolisms, shaping metabolic strategy shifts at the community level. Furthermore, the co-occurrence network of microbes-metabolites was structured around microbial metabolic functions centered on methanogenesis, with CH4 as a network hub, connecting with 62.15% of total nodes as 1st and 2nd neighbors. Microbes aggregate molecules with different molecular traits and are modularized depending on their metabolic abilities. They established increasingly positive relationships with high-molecular-weight molecules, facilitating resource acquisition and energy utilization. This metabolic complementarity and substance exchange further underscored the cooperative nature of microbial interactions. CONCLUSIONS: All results revealed three key rules governing microbial anaerobic degradation. These rules indicate that microbes adapt to environmental conditions according to their community-level metabolic trade-offs and synergistic metabolic functions, further driving the deterministic dynamics of molecular composition. This research offers valuable insights for enhancing the prediction and regulation of microbial activities and carbon flow in anaerobic environments. Video Abstract.

Effect of sodium formate and lactic acid bacteria treated rye silage on methane yield and energy balance in Hanwoo steers.

This study was performed to evaluate the effects of rye silage treated with sodium formate (Na-Fa) and lactic acid bacteria (LAB) inoculants on the ruminal fermentation characteristics, methane yield and energy balance in Hanwoo steers. Forage rye was harvested in May 2019 and ensiled without additives (control) or with either a LAB inoculant or Na-Fa. The LAB (Lactobacillus plantarum) were inoculated at 1.5 × 1010 CFU/g fresh matter, and the inoculant was sprayed onto the forage rye during wrapping at a rate of 4 L/ton of fresh rye forage. Sixteen percent of the Na-Fa solution was sprayed at a rate of approximately 6.6 L/ton. Hanwoo steers (body weight 275 ± 8.4 kg (n = 3, group 1); average body weight 360 ± 32.1 kg (n = 3, group 2)) were allocated into two pens equipped with individual feeding gates and used in duplicated 3 × 3 Latin square design. The experimental diet was fed twice daily (09:00 and 18:00) during the experimental period. Each period comprised 10 days for adaptation to the pen and 9 days for measurements in a direct respiratory chamber. The body weights of the steers were measured at the beginning and at the end of the experiment. Feces and urine were collected for 5 days after 1 day of adaptation to the chamber, methane production was measured for 2 days, and ruminal fluid was collected on the final day. In the LAB group, the ratio of acetic acid in the rumen fluid was significantly lower (p = 0.044) and the ratio of propionic acid in the rumen fluid was significantly higher (p = 0.017). Methane production per DDMI of the Na-FA treatment group was lower than that of the other groups (p = 0.052), and methane production per DNDFI of the LAB treatment group was higher than that of the other groups (p = 0.056). The use of an acid-based additive in silage production has a positive effect on net energy and has the potential to reduce enteric methane emissions in ruminants.

Intermittent aeration mitigating carbon emission from landfills with gas-water joint regulation.

Landfill is a significant source of atmospheric CH4 and CO2 emissions. In this study, four landfill reactor systems were constructed to investigate the effects of different ventilation methods, including continuous aeration (20 h d-1) and intermittent aeration (continuous aeration for 4 h d-1 and 2 h of aeration every 12 h, twice a day), on properties of landfilled waste and emissions of CH4 and CO2, in comparison to a traditional landfill. Compared with continuous aeration, intermittent aeration could reduce the potential global warming effect of the CH4 and CO2 emissions, especially multiple intermittent aeration. The CH4 and CO2 emissions could be predicted by the multiple linear regression model based on the contents of carbon, sulfur and/or pH during landfill stabilization. Both intermittent and continuous aeration could enhance the methane oxidation activity of landfilled waste. The aerobic methane oxidation activity of landfilled waste reached the maximums of 50.77-73.78 µg g-1 h-1 after aeration for 5 or 15 d, which was higher than the anaerobic methane oxidation activity (0.45-1.27 µg g-1 h-1). CO2 was the predominant form of organic carbon loss in the bioreactor landfills. Candidatus Methylomirabilis, Methylobacter, Methylomonas and Crenothrix were the main methane-oxidating microorganisms (MOM) in the landfills. Total, NO2--N, pH and Fe3+ were the main environmental variables influencing the MOM community, among which NO2--N and pH had the significant impact on the MOM community. Partial least squares path modelling indicated that aeration modes mainly influenced the emissions of CH4 and CO2 by affecting the degradation of landfilled waste, environmental variables and microbial activities. The results would be helpful for designing aeration systems to reduce the emissions of CH4 and CO2, and the cost during landfill stabilization.

Perfluorooctanoic acid effect and microbial mechanism to methane production in anaerobic digestion.

Perfluorooctanoic acid (PFOA) as emerging pollutants was largely produced and stable in nature environment. Its fate and effect to the wasted sludge digestion process and corresponding microbial mechanism was rarely reported. This study investigated the different dose of PFOA to the wasted sludge digestion process, where the methane yield and microbial mechanism was illustrated. The PFOA added before digestion were 0-10000 µg/L, no significant variation in daily and accumulated methane production between each group. The 9th day methane yield was significantly higher than other days (p < 0.05). The soluble protein was significantly decreased after 76 days digestion (p < 0.001). The total PFOA in sludge (R2 = 0.8817) and liquid (R2 = 0.9083) phase after digestion was exponentially correlated with PFOA dosed. The PFOA in liquid phase was occupied 54.10 ± 18.38% of the total PFOA in all reactors. The dewatering rate was keep decreasing with the increase of PFOA added (R2 = 0.7748, p < 0.001). The mcrA abundance was significantly correlated with the pH value and organic matter concentration in the reactors. Chloroflexi was the predominant phyla, Aminicenantales, Bellilinea and Candidatus_Cloacimonas were predominant genera in all reactors. Candidatus_Methanofastidiosum and Methanolinea were predominant archaea in all reactors. The function prediction by FAPROTAX and Tax4fun implied that various PFOA dosage resulted in significant function variation. The fermentation and anaerobic chemoheterotrophy function were improved with the PFOA dose. Co-occurrence network implied the potent cooperation among the organic matter degradation and methanogenic microbe in the digestion system. PFOA has little impact to the methane generation while affect the microbe function significantly, its remaining in the digested sludge should be concerned to reduce its potential environmental risks.

Impact of operating conditions on N2O accumulation in Nitrate-DAMO system: Kinetics and microbiological analysis.

Nitrate-dependent anaerobic methane oxidation (Nitrate-DAMO) is a novel and sustainable process that removes both nitrogen and methane. Previously, the metabolic pathway of Nitrate-DAMO has been intensively studied with some results. However, the production and consumption of nitrous oxide (N2O) in the Nitrate-DAMO system were widely disregarded. In this study, a Nitrate-DAMO system was used to investigate the effect of operational parameters (C/N ratio, pH, and temperature) on N2O accumulation, and the optimal operating conditions were determined (C/N = 3, pH = 6.5, and temperature = 20 °C). In this study, an enzyme kinetic model was used to fit the nitrate nitrogen degradation and the nitrous oxide production and elimination under different operating conditions. The thermodynamic model of N2O production and elimination in the system also has been constructed. Multiple linear regression analysis found that pH was the most important factor influencing N2O accumulation. The Metagenomics sequencing results showed that alkaline pH promoted the abundance of Nor genes and denitrifying bacteria, which were significantly and positively correlated with N2O emissions. And alkaline pH also promoted the production of Mdo genes related to the N2O-driven AOM reaction, indicating that part of the N2O was consumed by denitrifying bacteria and the other part was consumed by the N2O-driven AOM reaction. These findings reveal the mechanism of N2O production and consumption in DAMO systems and provide a theoretical basis for reducing N2O production and greenhouse gas emissions in actual operation.

Ferrihydrite Addition Activated Geobacteraceae, the Most Abundant Iron-reducing Diazotrophs, and Suppressed Methanogenesis by Heterogeneous Methanogens in Xylan-amended Paddy Soil Microcosms.

Paddy fields are a major emission source of the greenhouse gas methane. In the present study, the addition of ferrihydrite to xylan-amended paddy soil microcosms suppressed methane emissions. PCR-based and metatranscriptomic ana-lyses revealed that the addition of ferrihydrite suppressed methanogenesis by heterogeneous methanogens and simultaneously activated Geobacteraceae, the most abundant iron-reducing diazotrophs. Geobacteraceae may preferentially metabolize xylan and/or xylan-derived carbon compounds that are utilized by methanogens. Geomonas terrae R111 utilized xylan as a growth substrate under liquid culture conditions. This may constitute a novel mechanism for the mitigation of methane emissions previously observed in ferric iron oxide-applied paddy field soils.