Higher Methane Production Rate Research Articles

Using a non-precious metal catalyst for long-term enhancement of methane production in a zero-gap microbial electrosynthesis cell

Microbial electrosynthesis (MES) cells exploit the ability of microbes to convert CO2 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 H2 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.

Production of Methane and Hydrogen from Mild-Strength Industrial Wastewater

Over the past two decades, fossil fuel reserves have sharply shrunk, which has resulted in a global fall in energy sources. Alternative carbon-neutral renewable energy sources have caught the interest of experts due to the erratic nature of energy prices and their severe ecological effects. The treatment plant’s mild-strength effluent from an equalization tank at an industrial factory was used in this study to generate hydrogen and methane. This mild-strength effluent had a chemical oxygen demand (COD) content of 2.8 ± 1.0 g COD/L. A double stage anaerobic digestion system’s hydrogen-generating digester was run at a hydraulic retention time of 8 h while the methane-generating digester was run at a hydraulic retention time of 24 h. The highest methane production rate (MPR), methane yield (MY), methane content and COD elimination were, in order, 71 ± 30 mL/L-d, 57 ± 10 mL/g COD, 90 ± 1% and 77%, respectively. In this experiment, energy efficiency was assessed using the following criteria: Maximum heating was at a value of 2.1 × 108 kcal/y. Utilizing energy-equivalent coal, natural gas, or fuel reduced annual carbon emissions by 8.7 × 104 kg CO2/y, 5.1 × 104 kg CO2/y and 7.1 × 104 kg CO2/y, respectively.

Innovative organic waste pretreatment approach for efficient anaerobic bioconversion: Effect of recirculation ratio at pre-processing in vortex layer apparatus on biogas production

Agricultural waste, called biomass, is of great interest as a renewable energy source. The purpose of this work was to determine the optimal recirculation rate (RR) values of the solid digestate when applying a new approach to the intensification of anaerobic conversion, providing a high quality biogas yield. This approach includes solid digestate recirculation and pre-processing a mixture of raw waste and solid digestate in a vortex layer apparatus. For this, the operation of an experimental biogas plant without recirculation and with recirculation was considered, starting from very low RR values, from 0.034 to 1, to ensure a high methane production rate (MPR) and methane yield (MY). From the point of view of MPR and MY, the recirculation ratios of 0.034 and 0.071 look the most attractive, however, with a recirculation ratio of 0.5, the content of hydrogen sulfide de-creased to 14 ppm with a simultaneous increase in MPR by 12 % compared to the control.

Revealing Co-N4 @Co-NP Bridge-Enabled Fast Charge Transfer and Active Intracellular Methanogenesis in Bio-Electrochemical CO2 -Conversion with Methanosarcina Barkeri.

To significantly advance the bio-electrochemical CO2 -conversion rate and unfold the correlation between the abiotic electrode and the attached microorganisms, an atomic-nanoparticle bridge of Co-N4 @Co-NP crafted in metal-organic frameworks-derived nanosheets is integrated with a model methanogen of Methanosarcina barkeri (M. barkeri). The direct bonding of N in Co-N4 and Fe in member protein of Cytochrome b (Cytb) activates a fast direct electron transfer path while the Co nanoparticles further strengthen this bonding via decreasing the energy gap between the p-band center of N and the d-band center of Fe. This multiorbital tuning operation of Co nanoparticles also enhances the coenzyme F420-mediated electron transfer by enabling the electron flow direct to the hydrogenation sites. Particularly, the increased surface electric field of the Co-N4 @Co-NP bridge-based nanosheet electrode facilitates the interfacial Na+ accumulation to expedite ATPase transport for powering intracellular CO2 conversion. Remarkably, the self-assembled M.barkeri-Co-N4 @Co-NP biohybrid achieves a high methane production rate of 3860mmol m-2 day-1 , which greatly outperforms other reported biohybrid systems. This work demonstrates a comprehensive scrutinization of biotic-abiotic energy transfer, which may serve as a guiding principle for efficient bio-electrochemical system design.

Iron-carbon micro-electrolysis material enhanced high-solid anaerobic digestion: Performance and microbial mechanism

Iron-carbon micro-electrolysis (ICME) materials are widely used as composite conductive materials for wastewater treatment to promote the degradation of volatile solids (VS), but there is virtually no research on their effect on high-solid anaerobic digestion (HSAD). This study aimed to investigate the effect of 10–50 g/L ICME dosages on HSAD and to reveal the microbial enhancement mechanism. The batch experiments (working volume of 400 mL) were conducted in a constant temperature water bath shaker. The results showed that the ICME materials promoted methane production by HSAD. The highest methane production rate was 297.79 mL/ g VS at a dosage of 50 g/L, which was 28% higher than that of the control. Scanning electron microscopy results showed that the ICME materials increased the attachment area of microorganisms. Further analyses of microbial community indicated that ICME materials facilitate symbiotic metabolism of syntrophic acetate-oxidizing bacteria (Synergistaceae) and hydrogenotrophic methanogens (Methanospirillum). This potentially promotes the conversion of the acetoacetic methanogenesis pathway to the syntrophic acetate oxidation and hydrogenotrophic methanogenesis pathways. This study revealed ICME material enhancement in HSAD as well as new insights into the microbial mechanisms.

A comprehensive analysis of key factors influencing methane production from CO2 using microbial methanogenesis cells

With increasing attention on carbon capture and utilization (CCU) technologies for the conversion of CO2 into chemical products, microbial methanogenesis cells (MMCs) have been extensively studied over the past few decades for biomethane production. Using rapidly accumulating data for MMCs with varying configurations and operating conditions, a comprehensive analysis was conducted here to investigate the critical factors that influence methane production rates (MPR) in these systems. A comparison of MPR and set potentials or current densities showed weak linear relationships (R2 < 0.6, p < 0.05), indicating the significant contributions of other important factors impacting methane production. A non-quantitative analysis of these additional parameters indicated the potential importance of using metal catalysts for anode materials where oxygen evolution reaction occurs, while most previous MMC research focused more on cathode materials where the biocatalytic reaction occurs. The use of undefined mixed anaerobic cultures as inocula was found to be sufficient for producing high MPRs, as the electrochemical environment at the cathode provides a strong selective pressure to converge on desirable methanogenic cultures. Other operational parameters, such as catholyte pH control and CO2 supply methods, were also important factors impacting MPR in MMCs, indicating the cumulative impact of these various factors will require careful consideration in future research.

Insight into the metabolic pathway of EAD based on metabolic flux, microbial community, and enzyme activity

Electrochemical anaerobic digestion (EAD) is essential for methane production. In this study, a cell net analyzer (CNA) was used to analyze the EAD metabolic flux and pathway and explore the dynamic changes in microbial community composition and critical enzyme activities by next-generation sequencing (NGS) and enzyme-linked immunosorbent assay (ELISA) to explore the reason for the high methane production rate of EAD. The results showed that EAD was more inclined toward hydrogen reduction of CO2 than conventional anaerobic digestion. Metabolic flux analysis (MFA) confirmed that the Embden–Meyerhof–Parnas (EMP) pathway was the main glycolysis pathway. According to metabolic flux analysis, hydrogen production from the electrodes accounted for 45.04%. Fermentimonas enhances the source of hydrogen, thereby facilitating the pathway of methane production by hydrogen reduction of CO2. Methanobacterium is the only dominant hydrotropic methanogen. Nicotinamide adenine dinucleotide (NAD) upregulates the hydrogen production pathway, whereas methylofuran (MFR) and tetrahydromethanopterin (MH4) are specific enzymes in the hydrogen-reducing CO2 pathway. Therefore, the results of this study help further reveal the electrochemical and biological principles related to EAD and provide theoretical support for the methanogenesis metabolism mechanism of EAD.

Anaerobic digestion of liquid dairy manure pretreated by the microwave-enhanced advanced oxidation process

ABSTRACT The microwave-enhanced advanced oxidation process (MW-AOP) was utilized for the treatment of liquid dairy manure, prior to anaerobic digestion (AD). A significant amount of soluble chemical oxygen demand (SCOD) was formed in the treated solution, but there was no or little increase in volatile fatty acid (VFA). In this study, up-flow anaerobic sludge blanket (UASB) reactors were used in both the conventional AD system and as the methane phase reactor in a two-phase anaerobic digestion (TPAD) system. Both AD systems were capable of operating at very short hydraulic retention times (HRTs) to as low as about 3 days, and very high methane production rates were achieved. However, much higher methane production was obtained in the TPAD system. The phase separation of the acidogenesis and the methanogenesis in the TPAD system not only increased methane production but also maintained reactor stability throughout the experimental period. Thus, the combination of MW-AOP treatment and TPAD appears to be an effective means of energy recovery from dairy manure.

Simplified Modeling of High-Solids Anaerobic Digestion of Dairy Manure in a Pilot-Scale Stirred Tank Anaerobic Digester

Highlights HSAD is a cost-effective approach for managing high-solids manure. Batch digestion of HSAD at a low inoculum ratio is unsuitable. Mixing once a day was enough to maintain a stable digestion process. The stoichiometric method with an appropriate biodegradability factor provided perfect prediction. Simplified biokinetics can predict methane productivity at steady-state conditions. Abstract. Anaerobic digestion (AD) is considered one of the most effective methods of managing dairy manure. To effectively and economically treat the huge volumes of manure produced by commercial dairy farms, high-solids anaerobic digestion (HSAD) is to be encouraged. In this manuscript, batch and semi-continuous anaerobic digestion experiments of dairy manure with a high volatile solid (VS) content were conducted in a pilot-scale stirred digester with an effective volume of 1.63 m3, operated under mesophilic temperature conditions. Three intermittent mixing treatments (50, 100, and 150 rpm) were mixed once a day during feeding with a constant mixing duration of 5 minutes, including a non-mixed experiment, operating at a 30-day hydraulic retention time. The objectives were to determine an optimum mixing intensity to enhance HSAD efficiency and economy and to apply simplified models to model the digestion process. The simplified kinetic models were modified to accurately predict methane growth, yield, and production rates. The modified Gompertz growth model predicted the methane growth at the batch experiment perfectly. The first-order kinetic model predictions of the biodegradability factor, the specific methane yield, and the specific methane production rate were consistent with the batch experimental results. The stoichiometric method and the Karim model were modified to accurately model the effect of mixing intensity on the methane yield and the specific methane production rate. Three linear equations were successfully developed to predict the methane production rate. Optimized mixing intensity and organic loading rate are critical for high methane production rates. This study contributes to the ongoing research to improve the efficiency of HSAD. Keywords: Dairy manure, High-solids anaerobic digestion, Methane productivity, Mixing intensity.

Methane Production of Sargassum spp. Biomass from the Mexican Caribbean: Solid-Liquid Separation and Component Distribution.

In the last decade, Sargassum spp. seaweed species have caused massive flooding on the Caribbean Sea coasts. These seaweed species have a high content of recalcitrant compounds, such as insoluble fibers and polyphenols, which generate low methane yields in anaerobic digestion (AD). This study investigated the effect of solid-liquid separation of Sargassum biomass on biodegradability and methane yield. A biochemical methane potential (BMP) test was conducted with both fractions and raw biomass (RB). A mass balance was developed to assess the distribution of the components. The obtained liquid fraction (LF) showed high biodegradability and a high methane production rate, and it generated a methane yield of 159.7 ± 7.1 N L kg VS-1, a value that corresponds to approximately twice that achieved with RB and the solid fraction (SF). The component distribution analysis showed that about 90% of total solids (TS), volatile solids (VS), ash, carbon, and cellulose were retained in the SF. In conclusion, the LF had high biodegradability and methane yield. This suggests the potential for LFs of Sargassum biomass to be treated in large-scale high-load reactors; however, studies applied to SFs are needed because they retain a large amount of organic matter with low biodegradability.

Two problems in one shot: Vinasse and glycerol co-digestion in a thermophilic high-rate reactor to improve process stability even at high sulfate concentrations

Anaerobic co-digestion (AcoD) of sugarcane vinasse and glycerol can be profitable because of the destination of two biofuel wastes produced in large quantities in Brazil (ethanol and biodiesel, respectively) and the complementary properties of these substrates. Thus, the objective of this study was to assess the effect of increasing the organic loading rate (OLR) from 2 to 20 kg COD m−3 d−1 on the AcoD of vinasse and glycerol (50 %:50 % on a COD basis) in a thermophilic (55 °C) anaerobic fluidized bed reactor (AFBR). The highest methane production rate was observed at 20 kg COD m−3 d−1 (8.83 L CH4 d−1 L−1), while the methane yield remained stable at around 265 NmL CH4 g−1 CODrem in all conditions, even when influent vinasse reached 1811 mg SO42− L−1 (10 kg COD m−3 d−1). Sulfate was not detected in the effluent. Bacterial genera related to sulfate removal, such as Desulfovibrio and Desulfomicrobium, were observed by means of shotgun metagenomic sequencing at 10 kg COD m−3 d−1, as well as the acetoclastic archaea Methanosaeta and prevalence of genes encoding enzymes related to acetoclastic methanogenesis. It was concluded that process efficiency and methane production occurred even in higher sulfate concentrations due to glycerol addition.

Biochar-assisted anaerobic membrane bioreactor towards high-efficient energy recovery from swine wastewater: Performances and the potential mechanisms

A high-efficient energy recovery system of biochar-assisted anaerobic membrane bioreactor (BC-AnMBR) was established for swine wastewater treatment. Comparing with a conventional AnMBR, biochar addition accelerated volatile fatty acids (VFA) degradation during start-up stage, thereby shortened start-up duration by 44.0 %. Under a high organic loading rate (OLR) of 21.1 gCOD/L/d, BC-AnMBR promoted COD removal efficiency from 90.1 % to 95.2 %, and maintained a high methane production rate of 4.8L CH4/L/d. The relative abundance of Methanosaeta declined from 53.9 % in conventional AnMBR to 21.0 % in BC-AnMBR, whereas that of Methanobrevibacter dramatically increased from 10.3 % to 70.9 %, respectively. Metabolic pathway analysis revealed that biochar not only strengthened hydrogenotrophic methanogenesis pathway, but also upregulated the genes encoding electron transfer carriers and riboflavin metabolism, suggesting the role of biochar facilitating direct interspecies electron transfer for syntrophic methanogenesis. The excellent energy yield performances under high OLR confirmed BC-AnMBR as an advanced system for high-strength swine wastewater treatment.

Enhanced Electron Uptake and Methane Production by Corrosive Methanogens during Electromethanogenesis.

Electromethanogenesis is an interesting next-generation technology to produce methane from CO2 and electricity by using methanogens. Iron-corroding methanogens might be of special interest for that application due to their natural ability for electron uptake. Methanococcus maripaludis Mic1c10 and KA1 were tested in bioelectrochemical systems. Strain Mic1c10 showed a 120% higher current density and an 84% higher methane production rate (16.2 mmol m-2 d-2) than the non-corrosive strain Methanococcus maripaludis S2, which was identified earlier as the best methane producer under the same experimental conditions. Interestingly, strain KA1 also showed a 265% higher current density than strain S2. Deposits at the cathodes were detected and analyzed, which were not described earlier. A comparative genome analysis between the corrosive methanogen and the S2 strain enables new insights into proteins that are involved in enhanced electron transfer.

Multi-cycle anaerobic digestion of hydrothermal liquefaction aqueous phase: Role of carbon and iron based conductive materials in inhibitory compounds degradation, microbial structure shaping, and interspecies electron transfer regulation

Anaerobic digestion is commonly performed to treat hydrothermal liquefaction aqueous phase (HTL-AP), but the conversion is limited by the inhibitory compounds. This study was conducted to investigate the effects of adding granular activated carbon, biochar, and magnetite on the digestion of HTL-AP. Moreover, the enriched aggregates and conductive materials were recovered after experiment, and then reused to study the effects of multi-cycle digestion on organics degradation, microbial activity, and methane production. Results showed that the conductive materials significantly contributed to the digestion performance and maintained high activity after recycling. The degradation of organic matters, especially the removal of toxic compounds, the enrichment of functional microbes, as well as the production of methane can be further enhanced with the reuse of conductive materials. Specifically, a 77% higher methane production rate was observed in magnetite assisted digester after recycling. More than 80% of the nitrogen organics were degraded with biochar, and all potential inhibitors were completely removed with GAC addition. The diversity and abundance of microbes were improved, and the dominant structure was established in the first batch, then the enrichment was further stabilized after the recycling. Meanwhile, the sludge conductivity was increased by 28.1 and 8.5 times in GAC and magnetite digesters in the first batch and was further enhanced by 8.0% and 16.4% after the recycling, indicating the improved expression of conductive pili and cytochromes of the microbes. These results point to the establishment of direct interspecies electron transfer. This study showed promising prospects for the utilization and recycling of conductive materials in the anaerobic digestion of HTL-AP and its long-term applications.

Different contribution of exoelectrogens in methanogenesis via direct interspecies electron transfer (DIET) by the different substrate in continuous anaerobic bioreactor

Direct interspecies electron transfer (DIET) is a syntrophic mechanism for electron transfer between exo- and endoelectrogens. Previous studies have demonstrated that methanogenesis performance was significantly improved via the DIET mechanism through conductive materials (CMs) under batch conditions with a single substrate, while that under continuous condition is still under investigation. To investigate how the DIET via CM on methanogenesis performance was changed in response to the different substrates (acetate versus glucose)-fed in continuous anaerobic bioreactors, continuous bioreactors were operated by cross-feeding with acetate and glucose. Acetate-fed conditions showed 0.40 day shorten lagtime, 1.88- and 1.22-folds higher methane production rate, and ultimate methane production than glucose-fed conditions, respectively. Burkholderiaceae- and Anaerolineaceae-related exo-electrogenic populations were enriched with low abundance of Geobacter species in batch reactors. Furthermore, influent substrates affected the distribution of the enriched populations. Taken together, the results suggested that different syntrophic associations contributed methane production by DIET in continuous bioreactors.

Characterization of the gassy sediment layer in shallow water using an acoustical method: Lake Kinneret as a case study

AbstractRemote characterization and parameterization of gassy sediments have significant environmental importance for quantifying the global methane budget and assessing its impact on climate change. Acoustic techniques that have been developed hold advantages over direct sediment sampling (e.g., using pressurized and frozen cores), as they permit comparatively quick and cost‐effective assessments over the large bottom areas. This paper proposes a non‐invasive acoustic method that allows simultaneous assessments of the free gas content () and the thickness () of a gassy layer in the aquatic surface sediments. The method is based on amplitude measurements and frequency analysis of the bottom reflection coefficient in the wide frequency band (300–3500 Hz). The spatial variability of and in freshwater Lake Kinneret (Israel) is studied, where the upper sedimentary layer is characterized by a high organic matter content, high methane production rates, and a large . The assessed values of and varied from 0.1% to 0.6%, and from 20 to 40 cm, respectively, depending on the location of measurements. These results are in reasonable agreement with gas void fractions measured directly in frozen sediment cores, where the depth‐averaged varied from to . The suggested methodology should have considerable practical implementation for remote spatiotemporal monitoring of shallow gassy sediments in aquatic ecosystems.

Influence pathway of iron ions with different valences for methane fermentation of vegetable waste

Anaerobic digestion (AD) is a promising approach for vegetable waste (VW) recycling and energy recovery but methanogenesis is always inhibited by acid accumulation. The addition of a mixture of iron and other elements has proved effective on reducing acid inhibition during AD of VW, but the effect of use of iron alone has rarely been assessed. In the present study, we compared the effects of Fe0 and Fe2+ on methane fermentation from VW at an organic loading rate of 1.5 gVS/L/d. The results indicated that Fe0 maintained a pH &amp;gt; 7.7, oxidation reduction potential &amp;lt;−520, and methane production rate (MPR) at 250–300 mL/gVS/d. Partial least squares path modeling and correlation analysis revealed Fe0 maintained pH for high MPR mainly through enhancing the conversion of propionic and butyric acids to acetic acid, causing the total acid decreasing to 1500 mg/L. In contrast, Fe2+ caused an accumulation of all volatile fatty acids up to 4000 mg/L and aggravated acid inhibition, resulting in a significant reduction in MPR to 148 mL/gVS/d. In all treatments, the influence of ammonia nitrogen was not significant. This study provided a direction for the determination of engineering monitoring indicators and regulation measures in AD of VW.

High-rate microbial electrosynthesis using a zero-gap flow cell and vapor-fed anode design

Microbial electrosynthesis (MES) cells use renewable energy to convert carbon dioxide into valuable chemical products such as methane and acetate, but chemical production rates are low and pH changes can adversely impact biocathodes. To overcome these limitations, an MES reactor was designed with a zero-gap electrode configuration with a cation exchange membrane (CEM) to achieve a low internal resistance, and a vapor-fed electrode to minimize pH changes. Liquid catholyte was pumped through a carbon felt cathode inoculated with anaerobic digester sludge, with humidified N2 gas flowing over the abiotic anode (Ti or C with a Pt catalyst) to drive water splitting. The ohmic resistance was 2.4 ± 0.5 mΩ m2, substantially lower than previous bioelectrochemical systems (20–25 mΩ m2), and the catholyte pH remained near-neutral (6.6–7.2). The MES produced a high methane production rate of 2.9 ± 1.2 L/L-d (748 mmol/m2-d, 17.4 A/m2; Ti/Pt anode) at a relatively low applied voltage of 3.1 V. In addition, acetate was produced at a rate of 940 ± 250 mmol/m2-d with 180 ± 30 mmol/m2-d for propionate. The biocathode microbial community was dominated by the methanogens of the genus Methanobrevibacter, and the acetogen of the genus Clostridium sensu stricto 1. These results demonstrate the utility of this zero-gap cell and vapor-fed anode design for increasing rates of methane and chemical production in MES.

Acoustic Mapping of Gas Stored in Sediments of Shallow Aquatic Systems Linked to Methane Production and Ebullition Patterns

Bubble-mediated transport is the predominant pathway of methane emissions from inland waters, which are a globally significant sources of the potent greenhouse gas to the atmosphere. High uncertainties exist in emission estimates due to high spatial and temporal variability. Acoustic methods have been applied for the spatial mapping of ebullition rates by quantification of rising gas bubbles in the water column. However, the high temporal variability of ebullition fluxes can influence estimates of mean emission rates if they are based on reduced surveys. On the other hand, echo sounding has been successfully applied to detect free gas stored in the sediment, which provide insights into the spatial variability of methane production and release. In this study, a subtropical, midsize, mesotrophic drinking water reservoir in Brazil was investigated to address the spatial and temporal variability of free gas stored in the sediment matrix. High spatial resolution maps of gas content in the sediment were estimated from echo-sounding surveys. The gas content was analyzed in relation to water depth, sediment deposition, and organic matter content (OMC) available from previous studies, to investigate its spatial variability. The analysis was further supported by measurements of potential methane production rates, porewater methane concentration, and ebullition flux. The largest gas content (above average) was found at locations with high sediment deposition, and its magnitude depended on the water depth. At shallow water depth (&amp;lt;10 m), high methane production rates support gas-rich sediment, and ebullition is observed to occur rather continuously. At larger water depth (&amp;gt;12 m), the gas stored in the sediment is released episodically during short events. An artificial neural network model was successfully trained to predict the gas content in the sediment as a function of water depth, OMC, and sediment thickness (R2 = 0.89). Largest discrepancies were observed in the regions with steep slopes and for low areal gas content (&amp;lt;4 L m−2). Although further improvements are proposed, we demonstrate the potential of echo-sounding for gas detection in the sediment, which combined with sediment and water body characteristics provides insights into the processes that regulate methane emissions from inland waters.

Research on the electrochemistry synergied cellulase enzymes strengthens the anaerobic fermentation of cow dung.

Lignocellulose degradation (LCD) was the key factor limiting the development of anaerobic fermentation (AF) by the cow dung (CD). In the research, the effects of cellulase pretreatment (CP) and microvoltage (MV) alone and combination on the gas production and LCD during the AF were investigated. The results showed that both CP and MV had an significant effect on the AF, though the synergistic reaction was more pronounced. The total biogas yield (TBY) could reach 11521mL, and the highest methane production rate was 73% in the synergistic reactions, which was increased by 18.7% and 10.0% compared to CP and MV alone respectively. Meanwhile, the degradation rates of cellulose and lignin could be increased by 33.44% and 22.23%, respectively. The results of SEM, FT-IR and excitation emission matrix demonstrated that CP and MV played an important role in improving the fermentation efficiency. The microbial biomass change results indicated that the synergistic effect of CP and 0.8V MV on the LCD was achieved by promoting the growth of lignocellulose-degrading bacteria. Moreover, the electricity could not only accelerate the movement of microorganisms and enzymes, but also promoted and enhanced the activity of enzymes, which provided an important reference for further development of the AF technology and the biogas industry.