Hydrogenotrophic Methanogenic Pathway Research Articles

Microbial community development on different cathode metals in a bioelectrolysis enhanced methane production system

Methane production enhanced by electrode respiring microorganisms is a recently developing technology for bioelectrolysis assisted anaerobic digestion. The direct interspecies electron transfer between electrodes and microbe has been recognized as the core mechanism for methanogenesis in this coupled system. However, the detailed mechanisms of methane electrosynthesis on cathodes need in-depth investigation. This work is to evaluate the effects of hydrogen evolution capacity of cathode on methane production and biocathode community that developed on commonly used cathode materials (copper, nickel and stainless steel). Integrated reactors with nickel cathode exhibited a maximum methane yield of 59.2 mL CH4/gVSS with a higher current density of 9 A/m2 compared to copper electrode and stainless-steel electrode. About 40% increase of methane production rate is achieved in the coupled reactors with nickel electrode compared to traditional anaerobic digestion technique. Analysis of microbial community structure reveals that the bioelectrolysis cathode persuades the whole system towards the hydrogenotrophic methanogenic pathway. A methanogenic system derived from Methanobacterium is formed on metal electrodes, which simultaneously utilizes both electrons and hydrogen to produce methane. However, higher hydrogen evolution reaction capacity leads to higher electrochemical contribution for methane synthesis, which results in an improved conversion efficiency.

Mesophilic and thermophilic anaerobic digestion of soybean curd residue for methane production: Characterizing bacterial and methanogen communities and their correlations with organic loading rate and operating temperature

To find the optimal operation parameters and provide an explanation of methanogenic pathway for methane production in mesophilic (35 °C) and thermophilic (55 °C) anaerobic digestion (MAD, TAD) of soybean curd residue (SCR), MAD and MAD were contrastively investigated for 95 days. The maximum available OLR was identified as 3.3 gVS/L for both MAD and TAD. Compared to MAD, TAD exhibited a 20% higher average methane yield (0.591 L/gVS) and a 7.5% higher volatile solids removal efficiency (74.1 ± 10.4%). Bacterial phyla Bacteroidetes, Firmicutes and Proteobacteria dominated in MAD digesters while genus Defluviitoga was selectively enriched in TAD digesters due to higher temperature and organic loading pressure. Principal coordinates analysis of methanogen community showed that both temperature and OLR were crucial environmental variables shifting the taxonomic patterns of the methanogens. The enriched methanogen genus Methanothermobacter (93%) with a hydrogenotrophic methanogenic pathway had a close correlation with the TAD performance.

Mitigation of ammonia inhibition through bioaugmentation with different microorganisms during anaerobic digestion: Selection of strains and reactor performance evaluation

The effect of bioaugmentation with different microorganisms on anaerobic digestion to mitigate the ammonia inhibition problem was investigated. Seven pure strains of microorganisms (including obligate aceticlastic methanogen, facultative aceticlastic methanogen, hydrogenotrophic methanogen, syntrophic acetate oxidizing bacteria (SAOB) were selected and thirteen bioaugmentation approaches were tested. Bioaugmentation with hydrogenotrophic methanogen Methanobrevibacter smithii (MBS) and SAOB Syntrophaceticu schinkii together was the optimal choice, methane production (MP) was 71.1% higher than that in Blank, the activity of hydrogenotrophic methanogenesis was greatly heightened according to specific methanogenic activity analysis. Bioaugmentation with facultative aceticlastic methanogen Methanosarcina barkeri (MSB) alone without SAOB addition was also proven efficient (MP was 59.7% higher than that in Blank), both aceticlastic and hydrogenotrophic methanogenesis were enhanced. Further evaluation with carbon isotope fractionations analysis indicated that balancing the activities of the aceticlastic and hydrogenotrophic methanogenic pathways is of great importance. 16s rRNA gene sequencing results showed that Methanobacterium spp. and Methanosaeta spp. were the dominant archaea in all 14 reactors. Nevertheless, bioaugmentation with Methanosaeta spp. did not result in a positive effect on MP. On the other hand, Methanobrevibacter spp. and Methanosarcina spp. were non-dominant archaea (even after bioaugmentation with MBS or MSB, the relative abundances were still poor (<2%)), but displayed pivotal roles in determining the overall microbial consortium and, in turn, improved the overall performance.

Novel insight into high solid anaerobic digestion of swine manure after thermal treatment: Kinetics and microbial community properties

Compared to traditional anaerobic digestion (AD), high solid anaerobic digestion (HSAD) had the advantages of small digester, low heating energy and less digestate. However, the methane production was poor. In our previous study, thermal treatment (70 ± 1 °C, 3 days) without any dilution could satisfactorily enhance the methane production rate of HSAD by up to 39.5%. However, effects of solid content on HSAD after thermal treatment were not yet studied. In this study, HSAD was conducted at 11.7–17.6% solid content, and the control experiment was conducted at low solid content (4.4% solid content). Results showed that HSAD's methane production rate was the highest at 11.7% solid content (158 mL CH4/g VS), and could reach up to 89.2% of that at 4.4% solid content. The utilization of organics was revealed by kinetics analysis that the readily biodegradable organics could be utilized at increasing solid content with decreasing hydrolysis rate. Furthermore, it was notable that methylotrophic methanogens predominated in HSAD with the abundance of 82.6%. This was quite unique from the general belief that AD system was usually dominated by acetoclastic or hydrogenotrophic methanogenic pathways. In this study, the microbial community structure of HSAD after thermal treatment was firstly studied, its unique specific methanogenic pathways was firstly revealed.

Change of the pathway of methane production with progressing anoxic incubation of paddy soil

Rates and pathways of methane production in rice fields were found to change with season. However, field conditions are complex and thus, it is still unclear which of the many environmental factors cause these changes. One possible factor is the availability of degradable organic carbon. Therefore, we investigated the change in rate and pathway of CH4 production under controlled laboratory conditions by progressing incubation of Italian paddy soil under anaerobic conditions. We studied the functional (pathway, rate) and structural (abundance, taxonomic composition) responses of methanogenic archaeal communities without and with addition of rice straw. Initially, rice straw significantly enhanced CH4 production rates and acetate accumulation. Later on, the values strongly decreased with the progress of degradation. A high contribution of acetoclastic methanogenesis (62–75%) was initially observed, while hydrogentrophic methanogenesis became dominant in the late degradation phase, both in soil without and with amendment of rice straw. The percentage contribution of the hydrogenotrophic pathway scaled with the percentage of the organic carbon mineralized to CH4 plus CO2 during the incubation time, irrespectively whether or not the soil was amended with rice straw. It was low (<33%), when >60% of the carbon was still available, but increased to >50% when available carbon had decreased to <30%. The methanogenic archaeal communities also exhibited changes over the subsequent degradation phases, but especially when the soil was amended with rice straw. Thus, rice straw amendment initially favored acetoclastic Methanosarcina and hydrogentrophic Methanocella, which subsequently decreased, while acetoclastic Methanothrix (‘Methanosaeta’) was favored and increased in the late degradation phases. The results demonstrate strong functional and structural responses of methanogenic archaeal communities to progressing degradation of rice straw and/or soil organic matter, but indicate that the hydrogenotrophic methanogenic pathway was in particular controlled by the availability of degradable organic carbon.

Methylotrophic methanogenesis in Sphagnum-dominated peatland soils

Although it is generally assumed that CH4 production in peatlands is dominated by the acetoclastic and hydrogenotrophic methanogenic pathways, we found evidence that methylated substrates (including methanol, methylamines, and dimethylsulfide) support methanogenesis in these organic-rich environments. The role of methylotrophic methanogenesis was investigated in three northern Minnesota peatlands by amending surface soils with 13C-labeled substrates. Labeled methanol was converted to enriched δ 13C-CH4 at all three sites. Additionally, dimethylsulfide and monomethylamine were processed through methanogenic pathways, although this was not evident at every site. The addition of 13C labeled methanol and monomethylamine also resulted in the enrichment of δ 13C-CO2, further suggesting that either methanogens or non-methanogenic microbes were processing methylated substrates. Results demonstrate the potential for methylotrophic methanogenesis in northern peatlands and suggest that further studies are warranted to quantify the amount of CH4 produced by this process in comparison to traditional pathways of methanogenesis.

Towards artificial methanogenesis: biosynthesis of the [Fe]-hydrogenase cofactor and characterization of the semi-synthetic hydrogenase.

The greenhouse gas and energy carrier methane is produced on Earth mainly by methanogenic archaea. In the hydrogenotrophic methanogenic pathway the reduction of one CO2 to one methane molecule requires four molecules of H2 containing eight electrons. Four of the electrons from two H2 are supplied for reduction of an electron carrier F420, which is catalyzed by F420-reducing [NiFe]-hydrogenase under nickel-sufficient conditions. The same reaction is catalysed under nickel-limiting conditions by [Fe]-hydrogenase coupled with a reaction catalyzed by F420-dependent methylene tetrahydromethanopterin dehydrogenase. [Fe]-hydrogenase contains an iron-guanylylpyridinol (FeGP) cofactor for H2 activation at the active site. FeII of FeGP is coordinated to a pyridinol-nitrogen, an acyl-carbon, two CO and a cysteine-thiolate. We report here on comparative genomic analyses of biosynthetic genes of the FeGP cofactor, which are primarily located in a hmd-co-occurring (hcg) gene cluster. One of the gene products is HcgB which transfers the guanosine monophosphate (GMP) moiety from guanosine triphosphate (GTP) to a pyridinol precursor. Crystal structure analysis of HcgB from Methanococcus maripaludis and its complex with 6-carboxymethyl-3,5-dimethyl-4-hydroxy-2-pyridinol confirmed the physiological guanylyltransferase reaction. Furthermore, we tested the properties of semi-synthetic [Fe]-hydrogenases using the [Fe]-hydrogenase apoenzyme from several methanogenic archaea and a mimic of the FeGP cofactor. On the basis of the enzymatic reactions involved in the methanogenic pathway, we came up with an idea how the methanogenic pathway could be simplified to develop an artificial methanogenesis system.

Enhanced waste activated sludge digestion using a submerged anaerobic dynamic membrane bioreactor: performance, sludge characteristics and microbial community.

Anaerobic digestion (AD) plays an important role in waste activated sludge (WAS) treatment; however, conventional AD (CAD) process needs substantial improvements, especially for the treatment of WAS with low solids content and poor anaerobic biodegradability. Herein, we propose a submerged anaerobic dynamic membrane bioreactor (AnDMBR) for simultaneous WAS thickening and digestion without any pretreatment. During the long-term operation, the AnDMBR exhibited an enhanced sludge reduction and improved methane production over CAD process. Moreover, the biogas generated in the AnDMBR contained higher methane content than CAD process. Stable carbon isotopic signatures elucidated the occurrence of combined methanogenic pathways in the AnDMBR process, in which hydrogenotrophic methanogenic pathway made a larger contribution to the total methane production. It was also found that organic matter degradation was enhanced in the AnDMBR, thus providing more favorable substrates for microorganisms. Pyrosequencing revealed that Proteobacteria and Bacteroidetes were abundant in bacterial communities and Methanosarcina and Methanosaeta in archaeal communities, which played an important role in the AnDMBR system. This study shed light on the enhanced digestion of WAS using AnDMBR technology.

Substrate limitation of sediment methane flux, methane oxidation and use of stable isotopes for assessing methanogenesis pathways in a small arctic lake

Among predicted impacts of climate change in the Arctic are greater thaw depth and shifts in vegetation patterns and hydrology that are likely to increase organic carbon and nutrient loading to lakes. We measured substrate limitation of sediment methane (CH4) flux, examined pathways of methanogenesis, and potential CH4 oxidation using stable isotope labeled acetate in intact sediment cores from arctic lake GTH 112 (68°40′20″N, 149°14′57″W). We hypothesized that the acetoclastic pathway would dominate methanogenesis, reflecting dissolved organic carbon supply from the surrounding landscape, and that sediment CH4 flux would be stimulated by addition of acetate. Experiments demonstrated acetate limitation of sediment CH4 flux with short-term CH4 flux response to availability of acetate, high rates of CH4 oxidation, and strong dominance of the acetoclastic over the hydrogenotrophic methanogenic pathway. The experiments also indicated that isotopic fractionation effects during isotope enrichment experiments are large during methanogenesis and can alter the methanogenic pathways being investigated. Under oxic conditions, CH4 oxidation at the sediment–water interface or in the water column is likely to account for much of diffusive CH4 flux, but under anoxic hypolimnetic conditions and increased substrate availability, conditions that are likely to occur with climate change, sediment CH4 flux will likely increase, with oxidation utilizing a smaller portion of sediment CH4 production.

The microbial diversity, methane production, operational routine of an anaerobic reactor treating maize processing wastewater

Industrial wastewaters have turned out to be a significant problem during the last decades. The best alternative for maize processing wastewaters due to high organic content and slow biodegradability characteristics is anaerobic treatment, which is successfully used in the treatment of medium-high strength industrial wastewaters. This study investigates a full-scale anaerobic expanded granular sludge bed reactor treating a maize industry wastewater in terms of reactor operation, methanogenic activity of reactor sludge, changes in composition and numbers of microbial populations during a 5-month period. Three samples were taken in 2-months intervals when the reactor was re-operated after a shut-down of 2 months. Combination of denaturing gradient gel electrophoresis (DGGE), quantitative real time polymerase chain reactions (Q-PCR) and specific methanogenic activity tests were used to investigate composition, diversity and quantity of microbial community with activity of acetoclastic methanogens. During monitoring period, COD removal efficiencies and organic loading rates varied in ranges of 79–95% and 0.65–3.85 kg COD/m3.d, respectively. Potential methane production rates of the reactor sludges decreased 27% with time that is from 394 to 287 mL CH4/gVSS.d. Archaea, bacteria, and methanogens in the sludge samples were quantified by Q-PCR and the results showed that while amount of archaea was decreasing, quantity of methanogens increased during the monitoring time. The DGGE results of the anaerobic sludge revealed that the microbial diversity dramatically changed, particularly in the last sample. Among these, the differences in archaeal community were more remarkable. Although an average COD removal efficiency of 86%±8.2 which was quite a reasonably stable performance was maintained during the monitoring period, remarkable differences were observed on both acetoclastic methanogenic activity and the methanogenic community. The increase in the numbers of total methanogens despite the decrease of acetoclastic methanogenic activity might be an indicator of dominating hydrogenotrophic methanogenic pathway. Further, construction of clone library was necessary to identify the species and their changes within the all three samples.