Acetoclastic Methanogens Research Articles

Ball-milled Fe0/FeS2 enhanced interaction of Shewanella oneidensis MR-1 with anaerobic microbial community: Impact on 2,4-dichloronitrobenzene reduction and methane yield

The technology of integrating sulfidated zero-valent iron and functional anaerobic bacteria has been extensively explored to improve the removal efficiency of pollutants and enhance the performance of anaerobic microbial system. In this study, the simultaneous DCNB(2,4-dichloronitrobenzene) reduction and methane production by ball-milled 1:1 Fe0/FeS2 (briefly, 1:1 Fe0/FeS2), Shewanella oneidensis MR-1 and microbial consortium (MC) were firstly investigated. The result showed that the DCNB reduction was increased by 2.6 and 1.7 times in 1:1 Fe0/FeS2 + MR-1 group compared to 1:1 Fe0/FeS2 and MR-1, respectively, while it further increased by almost 2 times in 1:1 Fe0/FeS2 + MC + MR-1 group as compared to that of 1:1 Fe0/FeS2 + MR-1 group. Moreover, the methane production was drastically facilitated via the reciprocal interaction among FeS as the reaction product, MR-1 and MC. Dechlorination was not found, mainly due to the inability of 1:1 Fe0/FeS2 and the inexistence of dechlorinating bacteria in original inoculum. Meanwhile, the microbial community was also changed, with genera like Eubacterium capable of reducing nitroaromatic compound and Methanosarcina as acetoclastic methanogen enriched by 1:1 Fe0/FeS2 and MR-1. Therefore, fast DCNB reduction and methane production using 1:1 Fe0/FeS2 in anaerobic microbial system, gives useful reference for both establishment of pollutant removal and biogas production. In conclusion, Fe0/FeS2, as a kind of sulfidated ZVI, is a good candidate for enhancing both pollutant degradation and CH4 production in anaerobic wastewater treatment.

Enhanced sludge digestion using anaerobic dynamic membrane bioreactor: Effects of hydraulic retention time

Performance of conventional anaerobic digestion is limited due to coupling of solid retention time (SRT) and hydraulic retention time (HRT). In this study, the sludge digestion efficiency was enhanced by decoupling SRT and HRT in a pilot-scale anaerobic dynamic membrane bioreactor, with a particular focus on the effects of HRT. With HRT decreased to 10 d, the total solids concentration reached 43.3 g/L in the membrane tank with the influent sludge concentration 23.4 ± 0.7 g/L, while volatile solids (VS) reduction rate and specific biogas production were 41% and 0.59 L/g VS, respectively, achieving simultaneous thickening and digestion of sludge. Microbial community analysis showed that Cloroflexi and Spirochaetota, which had an increased abundance at low HRT, were beneficial to VS reduction and multiple methanogenesis pathways. Methanosaeta, being a strict acetoclastic methanogen dominant at HRT 30 d, decreased in the abundance from 78.4% to 50.7% with HRT changing from 30 d to 10 d. In contrast, the abundance of hydrogenotrophic and methylotrophic methanogens increased from 17.2% to 39.4% with the decrease of HRT, indicating the influence of HRT on methanogenic pathways. Furthermore, the predicted gene analysis confirmed the transformation from dominant acetoclastic methanogenesis to the coexistence of multiple methanogenesis pathways. Finally, the recovered energy from methane increased from 0.43 kWh/kg VS to 0.56 kWh/kg VS as HRT decreased to 10 d from 30 d, and the net energy consumption at HRT of 10 d was 0.47 kWh/kg VS, only 66% of that at HRT of 30 d.

Determination of methanogenesis by nutrient availability via regulating the relative fitness of methanogens in anaerobic digestion.

Response of microbial community to nutrient availability in anaerobic digestion (AD) remains elusive. Prokaryotic communities in AD batch cultures with 0, 1, 3, 5, 7, 11, 15, 20, and 25 g/L peptone were monitored using massive parallel sequencing and quantitative PCR over a 34-day experimental period. Methane production displayed a hump-shaped response to the nutrient gradient (peaking at 15 g/L peptone). Moreover, total and acetoclastic methanogens showed hump-shaped responses (both peaking at 11 g/L peptone). However, prokaryotic population increased with nutrient concentration (linear regression, R2 = 0.86) while diversity decreased (R2 = 0.94), and ordination analysis showed a gradual succession of community structure along the first axis. Network analysis revealed that extent of interspecific interactions (e.g., edge number and clustering coefficient) exhibited a hump-shaped response. The combined results indicate that abundant species became more dominated with increasing nutrient, which can result in a gain or loss of interspecific interaction within the community. Network module analysis showed that one module dominated the network at each nutrient level (comprising 41%-65% of the nodes), indicating that AD community formed a core microbial guild. The most abundant phylotypes, Macellibacteroides and Butyricicoccaceae, were consistently negative with acetoclastic methanogens in the dominant modules. Their predominance at ≥15 g/L peptone can explain the hump-shaped responses of methanogenesis and methanogens. Collectively, methanogenesis and microbial network exhibited hump-shaped responses, although microbial community exhibited monotonic responses. Therefore, nutrient availability can determine the methanogenesis through regulating the relative fitness of methanogens within the community.

Distinguishing responses of acetoclastic and hydrogenotrophic methanogens to ammonia stress in mesophilic mixed cultures

A shift from the acetoclastic to the hydrogenotrophic pathway in methanogenesis under ammonia inhibition is a common observation in anaerobic digestion. However, there are still considerable knowledge gaps concerning the differential ammonia tolerance of acetoclastic and hydrogenotrophic methanogens (AMs and HMs), their responses to different ammonia species (NH4+, NH3), and their recoverability after ammonia inhibition. With the successful enrichment of mesophilic AMs and HMs cultures, this study aimed at addressing the above knowledge gaps through batch inhibition/recovery tests and kinetic modeling under varying total ammonia (TAN, 0.2-10 g N/L) and pH (7.0-8.5) conditions. The results showed that the tolerance level of HMs to free ammonia (FAN, IC50=1345 mg N/L) and NH4+ (IC50=6050 mg N/L) was nearly 11 times and 3 times those of AMs (NH3, IC50=123 mg N/L; NH4+, IC50=2133 mg N/L), respectively. Consistent with general belief, the AMs were more impacted by FAN. However, the HMs were more adversely affected by NH4+ when the pH was ≤8.0. A low TAN (1.0-4.0 g N/L) could cause irreversible inhibition of the AMs due to significant cell death, whereas the activity of HMs could be fully or even over recovered from severe ammonia stress (FAN≤ 0.9 g N/L or TAN≤10 g N/L; pH ≤8.0). The different tolerance responses of AMs and HMs might be associated with the cell morphology, multiple energy-converting systems, and Gibbs free energy from substrate-level phosphorylation.

Acetoclastic methanogenesis pathway stability despite the high microbial taxonomic variability in the transition from acidogenesis to methanogenesis during food waste anaerobic digestion

Anaerobic digestion (AD) is a microbial-mediated biogeochemical process that includes hydrolysis, acidogenesis, acetogenesis and methanogenesis. AD instability usually occurs in the transition from the acidogenesis phase (AP) to the methanogenesis phase (MP) due to over acidification. However, the underlying microbial mechanism of this transition has not been well characterized. In the present study, the transition of bacterial and methanogenic community composition, methanogenesis functional gene expression and metabolic pathways from AP to MP during food waste (FW) AD were investigated in a bioreactor using metagenomics and reverse transcription PCR technology. AP and MP were identified by changes in methane production, gas accumulation, pH and volatile fatty acids (VFAs). Concomitant with the changes in these physiochemical parameters, the bacterial and methanogenic community composition showed succession patterns. The bacterial composition transformed from acidogenic bacteria (Propionispira and Bacteroides) to hydrolytic bacteria (Smithella, Syntrophus and Syntrophorhabdus), and the methanogen composition transformed from the domination of acetoclastic methanogens (Methanosaeta) to the codomination of hydrogenotrophic methanogens (Methanoculleus, Methanolinea and Methanobacterium) and acetoclastic methanogens (Methanosaeta). The expression level of the methanogenesis functional gene mcrA significantly (p < 0.05) increased in response to the increasing methane production. In contrast, acetoclastic methanogenesis as the main methanogenesis metabolic pathway remained stable. These results showed that FWAD key physiochemical parameters drive the variation in microbial community composition and functional genes expression but not the methanogenesis metabolic pathway. The finding suggests that FWAD process may be better predicted by methanogenic functional characteristics than by microbial community composition.

Anaerobic digestion of organic fraction of municipal solid waste using a novel two-stage solid-liquid system

Organic fraction of municipal solid waste (OFMSW) has high volatile solid and moisture content, which is mainly treated via anaerobic digestion (AD). Since the composition of OFMSW is complicated and inconstant, it is difficult to maintain the AD process stable and effective. In this study, a novel two-stage AD system, including a tank-type acidogenic phase and a fixed-bed methanogenic phase, was implemented for OFMSW treatment to demonstrate the feasibility of the two-stage configuration. Results showed that 84% of potential CH4 yield was achieved and the methane content reached 77.83% on average in methanogenic phase. The acetoclastic methanogens, Methanosaeta and Methanosarcina, which can participate in direct interspecies electron transfer, were the dominant genera in solid digestate and the biofilm. The hydrogenotrophic methanogens, Methanospirillum and Methanoculleus, accounted for high proportions in liquid digestate. Our study provides a novel approach to treat OFMSW with less water consumption, high stability and efficiency.

Biodegradation of early thermogenic gas and generation of secondary microbial gas in the Tieliekedong region of the northern Tarim Basin, NW China

Some important progress has been made in coalbed gas (CBG) exploration in the Kuqa-Bay coalfield in the northern Tarim Basin, where a demonstration base of CBG development and utilization has been established in the Tieliekedong (TD) region. Currently, there has been no detailed study of the formation mechanism of the CBG in the TD region, which has restricted the next phase of the CBG exploration. In this study, gas and water samples in the TD region were collected and analyzed to determine the genesis of the CBG, the formation pathways of the microbial gas, the source of the coalbed water, the composition of the microbial community, and the accumulation process of the CBG. The results indicate that the CBG in the TD region is a mixture of biodegraded thermogenic gas and secondary microbial gas. The geochemical characteristics of the water samples indicate that the coalbed water actively receives recharge from surface water, and it exhibits the characteristics of a weak-runoff water environment (i.e., a relatively closed system). Based on the stable isotope compositions of the gas-water samples, CO2 reduction is the main metabolic pathway for generating the microbial gas. That is, in the relatively closed system, initial CO2 from the different sources was converted to CH4 by hydrogenotrophic methanogens (e.g., Methanobacterium), and the residual CO2 became progressively enriched in 13C (i.e., high positive δ13C-CO2 and δ13C-dissolved inorganic carbon values). However, the microbial community composition indicates that acetogenic bacteria (e.g., Acetobacterium, and Lentimicrobium) and acetoclastic methanogens (i.e., Methanosaeta) are widely developed in the coalbed water, so acetoclastic methanogenesis should also take place. According to the priority of the biodegradation, the microbial oxidation of thermogenic C2+ components (e.g., ethane and propane) mainly occurred in the early stage and lasted for a short period of time, primarily producing CH4 enriched in 12C. After these components were consumed, the bacteria began to degrade the organic matter in the coal, and the methanogens continued to generate secondary microbial gas, finally forming a 13C-enriched pool of carbon species. Based on these results, the CBG accumulation in the TD region was determined. The results of this case study provide an obvious supplement to the geological theory of CBG accumulation, and have a guiding significance for CBG exploration in the TD region.

Individual Phenolic Acids in Distillery Stillage Inhibit Its Biomethanization

Polyphenols that are abundant in various organic wastes can inhibit anaerobic degradation of these wastes. This study investigated the effect of the concentration of individual phenolic acids (p-OH benzoic, vanillic, ferulic, sinapic, syringic, and p-coumaric acids) and their mixture on the methane potential of distillery stillage. An increase in phenolic acid concentration adversely affected biogas production and composition, as well as the methane-production rate. The inhibition constants for methane production were 0.5–1.0 g/L of individual phenolic acids and 1.5 g/L of the mixture of these acids. At lower concentrations, the phenolic acids were utilized as a carbon source, but the process was impeded when their concentrations exceeded the threshold value, due to their negative effect on microbial growth. When distillery stillage was spiked with vanillic acid, two-phase methane production was observed. Spiking distillery stillage with vanillic, p-coumaric, syringic, or ferulic acids affected anaerobic digestion the most; 2 g/L of these acids completely inhibited methane production. With 4.0 g/L of all individual phenolic acids, no methane production was observed. As the concentration of these phenolic acids increased from 0.5 to 4.0 g/L, the abundance of methanogenic Archaea, in which acetoclastic methanogens predominated, decreased by about 30 times.

Complex network analysis of slaughterhouse waste anaerobic digestion: From failure to success of long-term operation

The study explored slaughterhouse waste (SHW) as prime feedstock associated with and without supplement of an external slowly degradable lignocellulosic carbon source to overcome the synergistic co-inhibitions of ammonia and fatty acids. Long-term solid-state digestion (SSD) and liquid-state digestion (LSD) were investigated using a mixture of pork liver and fat. At 2.0 g volatile solids (VS) L−1 d−1 of organic loading rate (OLR), the two reactors of SSD experienced operational instability due to ammonia inhibition and volatile fatty acid (VFA) accumulation while LSD successfully produced 0.725 CH4 L CH4 g−1VS during 197 d of working days under unfavorable condition with high total ammonia nitrogen (>4.7 g/L) and VFAs concentration (>1.9 g/L). The network analysis between complex microflora and operational parameters provided an insight for sustainable biogas production using SHW. Among all, hydrogenotrophic methanogens have shown better resistance than acetoclastic methanogens.

METHANATION TECHNOLOGIES FOR PRODUCING SYNTHETIC RENEWABLE METHANE

Methanation, or the generation of synthetic methane through the combination of carbon dioxide and hydrogen, has been attracting more and more attention of researchers and energy scientists in recent years due to the fact that the development of an effective and economically feasible technology for the implementation of this process will allow solving a number of energy and environmental problems. First, it is the accumulation of excess renewable electricity from solar and wind power plants by using it in the creation of another energy-intensive product, namely synthetic natural gas, which removes the problem of coordinating unstable sources of electricity with energy networks. Secondly, methanation becomes another technology for enriching biogas and turning it into biomethane, which will allow it to be used through existing gas networks and contribute to solving the problem of natural gas shortage.&#x0D; The development and improvement of methanation technologies are engaged in many organizations of the world - Germany, Denmark, France, the USA, Japan and others. Research is conducted in two main directions: catalytic methanation and biological methanation. In the first direction, methanation is carried out through the Sabatier reaction using catalysts. The problems of such methanation are: the development of catalysts with high activity, selectivity and resistance to the heat of reaction, the provision of optimal reaction modes, in particular temperature and pressure, through the use of various methods of reactor cooling, control of the reaction mechanism, the use of three-phase reactors, changing their structure, and so on. Biological methanation is carried out using of biological methanogens - so-called archaea, which act as a kind of catalyst. The methanation is carried out either directly in the biomass anaerobic digestion reactor (in-situ methanation) or in a separate reactor into which biogas and hydrogen are fed separately (ex-situ methanation). One of the main problems of in-situ methanation is the simultaneous provision of optimal conditions for both acetoclastic and hydrogenotrophic methanogens. This problem is solved by ex-situ methanation, in which the optimal conditions for anaerobic digestion and methanation processes are provided separately. It is clear that optimal conditions are also provided for biomethanation of pure CO2 and H2, when the «broth» for archaea is created separately. A comparison of catalytic and biological methanation technologies shows that catalytic methanation provides higher energy efficiency and requires much smaller reactor sizes than biological methanation for the same methane yield. However, the latter has a higher resistance to harmful impurities than the catalytic one.

Sludge granulation in ASBR: Reactor performance, sludge physiochemical properties evolution and the unique clustered structure of the granular sludge

Anaerobic granular sludge was successfully cultivated in the anaerobic sequencing batch reactor (ASBR) after 45 days of operation. The results showed that the mature granular sludge exhibited better physicochemical characteristics: granule percentage of 62.6 ± 8.8 %, 0.8–1.2 mm in diameter, with smooth edges and regular shapes, and sludge volume index of 20.0 mL/g SS. 16S rRNA-targeted fluorescence in situ hybridisation (FISH) and scanning electron microscope (SEM) examination revealed that the granular sludge had a unique clustered microbial community structure, which would to be an optimal microbial arrangement for syntrophic colonies. The large substrate concentration gradient that derived from the feast-famine alternation regime of the substrate in a running cycle of ASBR was the major cause of the clustered microbial distribution structure. Lots of syntrophic consortia formed by acetogens and methanogens randomly distributed throughout the interior of the granules, furthermore, the cavities existing amongst the syntrophic consortia were convenient for substrate transfer and biogas liberation, thus enhancing the digestion performance of ASBR and preventing granule disintegration caused by gas scour. With sludge granulation, the methane yield of ASBR increased from the initial 0.23 L/g COD to 0.28 L/g COD, meanwhile, the maximum specific methanogenic activities (SMAs) of acetoclastic and hydrogenotrophic methanogens respectively increased from 0.51 gCOD/(gVSS·d) to 0.73 gCOD/(gVSS·d) and from 0.35 gCOD/(gVSS·d) to 0.62 gCOD/(gVSS·d). The exploration of granular sludge formation, sludge characteristic evolution and treatment performance in ASBR reactor has theoretical value for its engineering promotion.

Selectively facilitating the electron acceptance of methanogens by riboflavin

Direct interspecies electron transfer systems of acetoclastic and hydrogenotrophic methanogens with Geobacter metallireducens have been successfully established. However, the effects of riboflavin (RF) on these cocultures are not yet known. This study established two syntrophic cocultures with RF, acetoclastic Methanosarcina mazei and hydrogenotrophic Methanobacterium sp. YSL with G. metallireducens, and compared their transcriptome profiles. The results showed that a shorter start-up time lag of Methanobacterium sp. YSL was accompanied by unique transcriptome profiles when RF was added. Furthermore, the differential expression of key genes involved in the pathways was analyzed by comparative transcriptomics. Different proposed methanogenic pathways in the coculture systems were activated by M. mazei and Methanobacterium sp. YSL with RF. The earlier start-up of Methanobacterium sp. YSL cocultures was closely related to the overexpression of the gene encoding methyl-coenzyme M reductase (Mcr II) initiated by RF. The results revealed the distinct transcriptome profiles of acetoclastic and hydrogenotrophic methanogens accepting electrons from Geobacter mediated by RF, indicating the selective facilitation of the electron acceptance of methanogens and shedding new light on the fast start-up of anaerobic digesters for wastewater treatment.

Anaerobic sequential batch reactor for CO-DIGESTION of slaughterhouse residues: Wastewater and activated sludge

This work aims to determine the potential to produce biomethane by means of an Anaerobic Sequential Batch Reactor used to process two types of slaughterhouse wastes: raw slaughterhouse wastewaters and a sludge obtained after a specific treatment. In this study different hydraulic retention times (15, 10, 8, 6, 4 days) were applied and the reactor's performance was evaluated. The behavior of the main parameters associated to biodegradation processes, such as total biomethane production or anaerobic population dynamics were studied. The highest methane production and biodegrading factors removals were achieved when using 10-8 days of hydraulic retention times, obtaining around 0.31 ± 0.03 LCH4/gCODt and 0.51 ± 0.06LCH4/gTVS with removal percentages between 16 and 22% for COD and between 47 and 34% for TVS thanks to the higher microbial population. Therefore, the proposed AnSBR system has the potential to generate 5.23·105 kW h/year when operating under optimal HRT conditions (HRT 8–10 d). At these conditions, long chain fatty acid hydrolysis limitation are not a problem for a stable AD process performance due to a proper balance of different microbial groups: Eubacteria:Archaea ratio of 2.0; low but stable hydrolytic acidogenic bacteria proportion (13%), high proportion of Acetogens (44%) and preferred acetoclastic methanogen (32%) than hydrogenotropic methanogens (3%). So, the conditioning of the substrate such as pre-treatment of the sludge and the mixture in a proper proportion to the slaughterhouse wastewater achieve optimal organic load and microbial population, that improve the biomethane production in ACoD of Slaughterhouse residues in AnSBR systems during stable operation (HRT 15-8d). Even, a positive linear correlation between organic loading rate and Archaea activity was observed. However, at HRT 6d and 4d hydraulic retention times, the reactors started to suffer destabilization.

Anaerobic digester microbiome dynamics in response to moderate and failure-inducing shock loads of fats, oils and greases

Accidental organic overloading (shock loading) is common during the anaerobic co-digestion of fats, oils and greases (FOG) and may lead to decreased performance or reactor failure due to the effects on the microbiome. Here, adapted and non-adapted lab-scale anaerobic digesters were exposed to FOG shocks of varying organic strengths. The microbiome was sequenced during the recovery periods employed between each shock event. Non-failure-inducing shocks resulted in enrichment of fermentative bacteria, and acetoclastic and methylotrophic methanogens. However, sub-dominant bacterial populations were largely responsible for increased biogas production observed after adaptation. Following failure events, early recovery communities were dominated by Pseudomonas and Methanosaeta while late recovery communities shifted toward sub-dominant bacterial taxa and Methanosarcina. Generally, the recovered microbiome structure diverged from that of both the initial and optimized microbiomes. Thus, while non-failure-inducing FOG shocks can be beneficial, the adaptations gained are lost after a failure event and adaptation must begin again.

A novel green composite conductive material enhancing anaerobic digestion of waste activated sludge via improving electron transfer and metabolic activity

Anaerobic digestion (AD) of waste activated sludge (WAS) is usually limited by the low generation efficiency of methane. The addition of composite conductive materials (CMs) is a promising strategy to enhance AD performance. In this study, a new green magnetic-straw-based biochar (MSBC) was synthesised by a simple ball-milling/carbonisation method, and its effects on AD performance of sludge were investigated. Experimental results showed that the as-synthesised MSBC had an intrinsic graphene-oxide-like structure, with Fe species serving as electroactive sites; these characteristics translate into a high electron transfer (ET) capability. After adding MSBC, the volatile fatty acid production and methane yield were significantly increased by 14.13% and 45.36%, respectively. Analysis of the changes in the ET system activities, hydrogenase activities, Cyt-C concentrations and the electron transfer capacity of the sludge sample with and without the MSBC revealed that the MSBC enhanced intracellular ET and changed the extracellular ET pathway from indirect interspecies hydrogen transfer to direct interspecies electron transfer (DIET), which would be responsible for increasing methane production and proportion in the biogas. However, further analyses of key enzyme activities and the microbial community indicated that the MSBC reinforces the methanogenesis pathway by creating a favourable environment (i.e., by enhancing hydrolysis-acidification and DIET-based CO2 reduction) for acetoclastic methanogens. These findings, however, are expected to provide an important reference for developing CMs application in AD.

Enhancing anaerobic digestion of sulphate wastewater by adding nano-zero valent iron

ABSTRACT In this paper, the effects of nano-zero valent iron (nZVI) on anaerobic digestion of sulphate wastewater with different /COD ratios, including the COD removal rate, methane yield, intermediate products and the change of microbial community structure, were investigated. The results showed that nZVI could effectively enhance the treatment efficiency and methane yield. Compared with the control group without nZVI, the methane yield increased from 348.6833 to 1007.05 mL CH4/gCODremoval with 4 g nZVI loading at /COD = 0.1. nZVI could make electron flow from sulphate reduction to methane production, which increased methane yield even at high sulphate concentration. The microbial community analysis showed that adding nZVI could increase the abundance of acetoclastic methanogens, which accelerated hydrolysis acidification.

Effect of magnetite addition on transcriptional profiles of syntrophic Bacteria and Archaea during anaerobic digestion of propionate in wastewater sludge.

Anaerobic digestion (AD) is an important technology for the effective conversion of waste and wastewater to methane. Here, syntrophic bacteria transfer molecular hydrogen (H2 ), formate, or directly supply electrons (direct interspecies electron transfer, DIET) to the methanogens. Evidence is accumulating that the methanation of short-chain fatty acids can be enhanced by the addition of conductive material to the anaerobic digester, which has often been attributed to the stimulation of DIET. Since little is known about the transcriptional response of a complex AD microbial community to the addition of conductive material, we added magnetite to propionate-fed laboratory-scale reactors that were inoculated with wastewater sludge. Compared to the control reactors, the magnetite-amended reactors showed improved methanation of propionate. A genome-centric metatranscriptomics approach identified the active SCFA-oxidizing bacteria that affiliated with Firmicutes, Desulfobacterota and Cloacimonadota. The transcriptional profiles revealed that the syntrophic bacteria transferred acetate, H2 and formate to acetoclastic and hydrogenotrophic methanogens, whereas transcription of potential determinants for DIET such as conductive pili and outer-membrane cytochromes did not significantly change with magnetite addition. Overall, changes in the transcriptional profiles of syntrophic Bacteria and Archaea in propionate-fed lab-scale reactors amended with magnetite refute a major role of DIET in the studied system.

Environmental conditions and mechanisms restricting microbial methanogenesis in the Miquan region of the southern Junggar Basin, NW China

AbstractEarly microbial gas has been sealed in reservoirs in the Miquan region of NW China, with little or no supply of current microbial gas. To date, the environmental conditions and mechanisms restricting microbial methanogenesis are still unclear in the Miquan region. Thus, in this study, a series of gas and water samples from coalbed methane (CBM) exploitation wells and in situ coal samples were collected and analyzed to determine the potential for current microbial gas generation, the methanogenic pathways, the source of nutrients, the influence of the environmental conditions on in situ microbial communities and their methanogenesis, and the mechanisms restricting microbial methanogenesis. The gas-production simulation experiments revealed that the existing microbes in the coalbed water were less efficient at converting coal into methane under the approximate in situ conditions, which further verified that there was little or no supply of current microbial gas. The stable isotope compositions of the gas samples suggested that carbon dioxide (CO2) reduction was the dominant metabolic pathway for generating CBM, whereas the methanogenic communities contained a mixture of acetoclastic and methylotrophic methanogens in local areas. The nutrients available for the microbes mainly included the total dissolved nitrogen (TDN) and total dissolved carbon (TDOC), and the in situ dissolution of the coals was a significant source of the TDN, whereas the TDOC was mainly supplied by surface water. The microbes in the different tectonic settings were significantly controlled by different combinations of environmental factors, and there was no single environmental factor that completely dominated the spatial variability of the microbial communities. The gradual stagnation of the water environment led to an increase in salinity and a decrease in nutrients, which were likely the main factors restricting microbial methanogenesis under in situ conditions. Combined with the results of the rate-limiting stages of the anaerobic fermentation, the mechanisms restricting microbial methanogenesis can be finally determined in the Miquan region. These discoveries presented in this case study provide a significant supplement to the geological theory of CBM accumulation, and have a guiding significance for CBM development in the Miquan region.

Tylosin in anaerobic reactors: degradation kinetics, effects on methane production and on the microbial community.

Tylosin eliminated in animal waste, during therapeutic treatment, can be efficiently removed in anaerobic systems. The present study investigated the influence of tylosin concentration and assessed its degradation kinetics and the microorganisms involved in each stage of its anaerobic digestion (hydrolysis/acidogenesis; acetogenesis; methanogenesis). The results showed a stimulating effect on methane production with increasing tylosin concentration in the poultry litter up to 80mg kg-1 tylosin (232.9 NL CH4kg SV-1). As for tylosin degradation, greater removal of antibiotics was observed in the methanogenic phase (88%), followed by acetogenic (84%) and hydrolytic/acidogenic (76%) phases. The higher rate of tylosin degradation obtained in the methanogenic step, is mainly related to the co-metabolic effect exerted by the presence of acetate and its degradation by acetoclastic methanogens. Indeed, metagenomic analyses suggested a syntrophic action between archaea of ​​the genus Methanobacterium, and bacteria such as Clostridium and Flexilinea, which seemed decisive for tylosin degradation.

The Role of Extracellular Polymeric Substances in the Toxicity Response of Anaerobic Granule Sludge to Different Metal Oxide Nanoparticles.

Wastewater treatment plants (WWTP) are regarded as the last barriers for the release of incompletely separated and recycled nanoparticles (NPs) into the environment. Despite the importance and ubiquity of microbial extracellular polymeric substances (EPSs) in the complex wastewater matrix, the interaction between NPs and EPSs of anaerobic microflora involved in wastewater treatment and the resultant impact on the biomass metabolomics are unclear. Thus, the impacts of different metal oxide (TiO2, ZnO, and CuO) NPs on functional bacteria in anaerobic granular sludge (AGS) and the possible toxicity mechanisms were investigated. In particular, the binding quality, enhanced resistance mechanism, and chemical fractional contribution of EPSs from AGS against the nanotoxicity of different NPs was assessed. The results showed that CuO NPs caused the most severe inhibition towards acetoclastic and hydrogenotrophic methanogens, followed by ZnO NPs, whereas TiO2 NPs caused no inhibition to methanogenesis. Excessive EPS production, especially the protein-like substances, was an effective strategy for reducing certain NPs’ toxicity by immobilizing NPs away from AGS cells, whereas the metabolism restriction on inner microorganisms of AGS induced by CuO NPs can deteriorate the protective role of EPS, indicating that the roles of EPS may not be amenable to generalizations. Further investigations with lactate dehydrogenase (LDH) and reactive oxygen species (ROS) assays indicated that there are greatly essential differences between the toxicity mechanisms of metal NPs to AGS, which varied depending on the NPs’ type and dosage. In addition, dynamic changes in the responses of EPS content to different NPs can result in a significant shift in methanogenic and acidogenic microbial communities. Thus, the production and composition of EPSs will be a key factor in determining the fate and potential effect of NPs in the complex biological matrix. In conclusion, this study broadens the understanding of the inhibition mechanisms of metal oxide NPs on the AGS process, and the influence of EPSs on the fate, behavior, and toxicity of NPs.