Inhibition Of Methanogenesis Research Articles

Volatile fatty acids production during mixed culture fermentation – The impact of substrate complexity and pH

Volatile fatty acids (VFAs) are obtained during chemical routes from non-renewable petrochemicals. Intensive exploitation of oil resources have renewed the idea of VFAs production during biological routes, mainly throughout anaerobic mixed culture fermentation (MCF). We carried out MCF trials at initial acidic (5.0), neutral (7.0, with addition of specific methanogenesis inhibitor) and alkaline (11.0) pH conditions for four different substrates i.e. maize silage, cheese whey, microalgae biomass and glucose. The goal of the study was to investigate the impact of the substrate complexity on the produced VFAs’ quality and quantity. The highest VFAs concentration occurred in neutral pH proceeded by initial alkaline pH (0.83gVFAs/gSCOD for microalgae biomass, 0.78gVFAs/gSCOD for maize silage and 0.71gVFAs/gSCOD for cheese whey, respectively). In the fermentation of glucose, the highest VFAs concentration was achieved in neutral pH. We demonstrated that the alkaline pH was favorable for hydrolysis of complex organic matter (acidification yield over 71% for maize silage fermentation), while the neutral pH was beneficial for the acidogenesis and the overall VFAs production. Our findings showed that it was possible to carry out efficient and stable MCF process without using a large amounts of acid or base for pH adjustment and that the distribution of VFAs only merely depended on the substrate type.

Effect of Nitrooxy Compounds with Different Molecular Structures on the Rumen Methanogenesis, Metabolic Profile, and Methanogenic Community

Rumen in vitro fermentation was used to evaluate the capacity of nitrooxy compounds to mitigate rumen methane production. The following three nitrooxy compounds, each with different molecular structures, were evaluated: 2,2-dimethyl-3-(nitrooxy) propanoic (DNP), N-[2-(Nitrooxy)ethyl]-3-pyridinecarboxamide (NPD), and nitroglycerin (NG). All three compounds substantially decreased the total gas production, methane production, and the acetate:propionate ratio, while increasing hydrogen production. The growth of methanogens was specifically inhibited by all three compounds, without affecting the abundance of bacteria, anaerobic fungi, or protozoa. However, inhibition of methanogenesis required a much higher dose of DNP when compared to NPD or NG. Further investigations were conducted on NG to determine its effects on the methanogenic community. NG reduced the relative abundance of Methanomassiliicoccales, while increasing the relative abundance of Methanobrevibacter and Methanosphaera. Overall, the results suggested that all three of these nitrooxy compounds could specifically inhibit rumen methanogenesis, but NPD and NG were much more efficient than DNP at rumen methane mitigation.

Response of Methanogenic Microbial Communities to Desiccation Stress in Flooded and Rain-Fed Paddy Soil from Thailand.

Rice paddies in central Thailand are flooded either by irrigation (irrigated rice) or by rain (rain-fed rice). The paddy soils and their microbial communities thus experience permanent or arbitrary submergence, respectively. Since methane production depends on anaerobic conditions, we hypothesized that structure and function of the methanogenic microbial communities are different in irrigated and rain-fed paddies and react differently upon desiccation stress. We determined rates and relative proportions of hydrogenotrophic and aceticlastic methanogenesis before and after short-term drying of soil samples from replicate fields. The methanogenic pathway was determined by analyzing concentrations and δ13C of organic carbon and of CH4 and CO2 produced in the presence and absence of methyl fluoride, an inhibitor of aceticlastic methanogenesis. We also determined the abundance (qPCR) of genes and transcripts of bacterial 16S rRNA, archaeal 16S rRNA and methanogenic mcrA (coding for a subunit of the methyl coenzyme M reductase) and the composition of these microbial communities by T-RFLP fingerprinting and/or Illumina deep sequencing. The abundances of genes and transcripts were similar in irrigated and rain-fed paddy soil. They also did not change much upon desiccation and rewetting, except the transcripts of mcrA, which increased by more than two orders of magnitude. In parallel, rates of CH4 production also increased, in rain-fed soil more than in irrigated soil. The contribution of hydrogenotrophic methanogenesis increased in rain-fed soil and became similar to that in irrigated soil. However, the relative microbial community composition on higher taxonomic levels was similar between irrigated and rain-fed soil. On the other hand, desiccation and subsequent anaerobic reincubation resulted in systematic changes in the composition of microbial communities for both Archaea and Bacteria. It is noteworthy that differences in the community composition were mostly detected on the level of operational taxonomic units (OTUs; 97% sequence similarity). The treatments resulted in change of the relative abundance of several archaeal OTUs. Some OTUs of Methanobacterium, Methanosaeta, Methanosarcina, Methanocella and Methanomassiliicoccus increased, while some of Methanolinea and Methanosaeta decreased. Bacterial OTUs within Firmicutes, Cyanobacteria, Planctomycetes and Deltaproteobacteria increased, while OTUs within other proteobacterial classes decreased.

Methanogenesis inhibition by phosphorus in anaerobic liquid waste treatment

Abstract The effect of a sudden influent phosphorus concentration increase on a completely mixed reactor of an anaerobic liquid waste treatment process was evaluated. Chemical oxygen demand (COD), volatile fatty acids (VFA), suspended solids, pH and gas production were measured for process monitoring. Optical and scanning electron microscopic observations were also performed. Kinetic parameters were estimated from substrate and microorganisms concentrations, mass balances and experimental data. After phosphorus concentration increase, VFA concentration enhanced by 500% approximately and COD removal, gas production, bacterial growth coefficient (Y) and maximum bacterial growth rate (μmax) decreased 20%, 18%, 54% and 35% respectively. An excessive growth of filamentous microorganisms was also observed. The equilibrium established between acidogenic and methanogenic microorganisms was visibly affected causing a decrease of methanogenic activity. The experimental results showed that phosphorous arises as a methanogenesis inhibitor and a growth factor for filamentous microorganism under anaerobic conditions.

Redirection of Metabolic Hydrogen by Inhibiting Methanogenesis in the Rumen Simulation Technique (RUSITEC).

A decrease in methanogenesis is expected to improve ruminant performance by allocating rumen metabolic hydrogen ([2H]) to more energy-rendering fermentation pathways for the animal. However, decreases in methane (CH4) emissions of up to 30% are not always linked with greater performance. Therefore, the aim of this study was to understand the fate of [2H] when CH4 production in the rumen is inhibited by known methanogenesis inhibitors (nitrate, NIT; 3-nitrooxypropanol, NOP; anthraquinone, AQ) in comparison with a control treatment (CON) with the Rumen Simulation Technique (RUSITEC). Measurements started after 1 week adaptation. Substrate disappearance was not modified by methanogenesis inhibitors. Nitrate mostly seemed to decrease [2H] availability by acting as an electron acceptor competing with methanogenesis. As a consequence, NIT decreased CH4 production (−75%), dissolved dihydrogen (H2) concentration (−30%) and the percentages of reduced volatile fatty acids (butyrate, isobutyrate, valerate, isovalerate, caproate and heptanoate) except propionate, but increased acetate molar percentage, ethanol concentration and the efficiency of microbial nitrogen synthesis (+14%) without affecting gaseous H2. Nitrooxypropanol decreased methanogenesis (−75%) while increasing both gaseous and dissolved H2 concentrations (+81% and +24%, respectively). Moreover, NOP decreased acetate and isovalerate molar percentages and increased butyrate, valerate, caproate and heptanoate molar percentages as well as n-propanol and ammonium concentrations. Methanogenesis inhibition with AQ (−26%) was associated with higher gaseous H2 production (+70%) but lower dissolved H2 concentration (−76%), evidencing a lack of relationship between the two H2 forms. Anthraquinone increased ammonium concentration, caproate and heptanoate molar percentages but decreased acetate and isobutyrate molar percentages, total microbial nitrogen production and efficiency of microbial protein synthesis (−16%). Overall, NOP and AQ increased the amount of reduced volatile fatty acids, but part of [2H] spared from methanogenesis was lost as gaseous H2. Finally, [2H] recovery was similar among CON, NOP and AQ but was largely lower than 100%. Consequently, further studies are required to discover other so far unidentified [2H] sinks for a better understanding of the metabolic pathways involved in [2H] production and utilization.

Abundant carbon substrates drive extremely high sulfate reduction rates and methane fluxes in Prairie Pothole Wetlands.

Inland waters are increasingly recognized as critical sites of methane emissions to the atmosphere, but the biogeochemical reactions driving such fluxes are less well understood. The Prairie Pothole Region (PPR) of North America is one of the largest wetland complexes in the world, containing millions of small, shallow wetlands. The sediment pore waters of PPR wetlands contain some of the highest concentrations of dissolved organic carbon (DOC) and sulfur species ever recorded in terrestrial aquatic environments. Using a suite of geochemical and microbiological analyses, we measured the impact of sedimentary carbon and sulfur transformations in these wetlands on methane fluxes to the atmosphere. This research represents the first study of coupled geochemistry and microbiology within the PPR and demonstrates how the conversion of abundant labile DOC pools into methane results in some of the highest fluxes of this greenhouse gas to the atmosphere ever reported. Abundant DOC and sulfate additionally supported some of the highest sulfate reduction rates ever measured in terrestrial aquatic environments, which we infer to account for a large fraction of carbon mineralization in this system. Methane accumulations in zones of active sulfate reduction may be due to either the transport of free methane gas from deeper locations or the co-occurrence of methanogenesis and sulfate reduction. If both respiratory processes are concurrent, any competitive inhibition of methanogenesis by sulfate-reducing bacteria may be lessened by the presence of large labile DOC pools that yield noncompetitive substrates such as methanol. Our results reveal some of the underlying mechanisms that make PPR wetlands biogeochemical hotspots, which ultimately leads to their critical, but poorly recognized role in regional greenhouse gas emissions.

Differential effects of monensin and a blend of essential oils on rumen microbiota composition of transition dairy cows

In response to oral application, monensin alters the rumen microbiota, increasing ruminal propionate production and energy availability in the animal. Data from different studies indicate that the susceptibility of rumen bacteria to monensin is mainly cell-wall dependent but tracing its activity to specific microbial groups has been challenging. Several studies have shown a similar effect for essential oils but results are inconsistent. To investigate the influence of monensin and a blend of essential oils (BEO, containing thymol, guaiacol, eugenol, vanillin, salicylaldehyde, and limonene) on the rumen microbiome, rumen liquid samples were collected orally on d 56 postpartum from cows that had either received a monensin controlled-release capsule 3 wk antepartum, a diet containing a BEO from 3 wk antepartum onward, or a control diet (n = 12). The samples were analyzed for pH, volatile fatty acid, ammonia, and lipopolysaccharide concentrations and protozoal counts. A 16S rRNA gene fingerprinting analysis (PCR-single-strand conformation polymorphism) and sequencing revealed that the BEO treatment had no effect on the rumen microbiota, whereas monensin decreased bacterial diversity. Twenty-three bacterial species-level operational taxonomic units were identified for which monensin caused a significant decrease in their relative abundance, all belonging to the phyla Bacteroidetes (uncultured BS11 gut group and BS9 gut group) and Firmicutes (Lachnospiraceae, Ruminococcaceae, and Erysipelotrichaceae). Ten bacterial operational taxonomic units belonging to the phyla Actinobacteria (Coriobacteriaceae), Bacteroidetes (Prevotella), Cyanobacteria (SHA-109), and Firmicutes (Lachnospiraceae and Ruminococcaceae) increased in relative abundance due to the monensin treatment. These results confirm the hypothesis that varying effects depending on cell-wall constitution and thickness might apply for monensin sensitivity rather than a clear-cut difference between gram-negative and gram-positive bacteria. No effect of monensin on the archaea population was observed, confirming the assumption that reported inhibition of methanogenesis is most likely caused through a decrease in substrate availability, rather than by a direct effect on the methanogens. The data support the hypothesis that the observed increase in ruminal molar propionate proportions due to monensin may be caused by a decrease in abundance of non-producers and moderate producers of propionate and an increase in abundance of succinate and propionate producers.

Degradação dos homólogos do alquilbenzeno linear sulfonato em lodo anaeróbio disperso

RESUMO: Avaliou-se a degradação anaeróbia do alquilbenzeno linear sulfonato (LAS) e seus homólogos em experimento em escala de laboratório. Foi usado lodo disperso para minimizar o efeito da adsorção. Em primeiro lugar, determinaram-se a maior concentração de LAS (substrato) e a menor concentração de etanol (cossubstrato) que manteriam os micro-organismos ativos, resultando em 25 e 200 mg.L-1, nessa ordem. Posteriormente, o experimento (90 dias) foi realizado em um reator somente com etanol (controle) e outro (reator teste, triplicata) com ambos os substratos nas concentrações anteriores. Os micro-organismos apresentaram crescimento exponencial em 48 h para os 2 reatores; não ocorreu toxicidade pelo LAS no reator teste durante esse período inicial, quando o etanol foi todo consumido. Após então, houve decréscimo de micro-organismos, indicando possível toxicidade por LAS ou intermediários. Observou-se também a diminuição ou ausência da produção de ácidos graxos voláteis e de metano. Portanto, com lodo disperso, a maior parcela da remoção foi por conta da biodegradação, porém, com formação de intermediários que não o acetato nem o metano, apontando a inibição à acidogênese e à metanogênese. Ao final, a remoção do LAS foi de 35% por biodegradação e apenas 0,35% por adsorção ao lodo. A ordem preferencial de biodegradação para os homólogos foi de C13 para C12, C11 e C10, com percentual de degradação em relação à massa inicial de 49, 31, 24 e 17%, respectivamente. A mesma ordem deu-se para a adsorção, da maior para a menor cadeia alquílica, sendo a remoção por adsorção de 0,85; 0,32; 0,13 e 0,01%, respectivamente.

In vitro Evaluation of Calcium Nitrate and a Blend of Plants Containing Secondary Metabolites for their Impact on Methanogenesis and Feed Fermentation

Two blends of plant parts containing plant secondary metabolites; BPa-blend of fruit pulp of Terminalia chebula (harad), fruit pulp of Terminalia bellerica (bahera), seed cake of Madhuca longifolia (mahua), seed cake of Azadirachta indica (neem) mixed in equal proportion and BPb-a blend of fruit of Phyllanthus emblica (amla), seed of Foeniculum vulgare (fennel) and seed of Trachyspermum ammi (ajwain) mixed in equal proportions were tested at 0, 10 and 20% of the substrate along with 0, 5 and 10% of calcium nitrate (CN) for their effects on in vitro methane production and feed fermentation. Inclusion of BPa (20%) + CN (10%) and BPb (20%) + CN (10%) did not affect gas production and feed digestibility but there was a significant (P<0.05) reduction (65 and 83.4 per cent) in methane production. Total volatile fatty acids were not affected by any of the treatments, whereas, acetate was increased and propionate and butyrate were significantly reduced resulting in increased acetate to propionate ratio by increasing the level of nitrate. Ammonia production was significantly increased by inclusion of CN irrespective of BPa doses but not affected when CN was used along with PBb. The results indicated that inclusion of CN was detrimental but when combined with either BPa or BPb, the values for in vitro feed digestibility were at par with control. However, BPb seems to be better than BPa, as inclusion BPb with CN maintained feed digestibility better than BPa and BPb also maintained ammonia nitrogen levels unchanged. The mixture of CN and BPb can be used as a feed additive for inhibition of methanogenesis in buffaloes without affecting feed fermentation.

Evaluation of the effect of glycerol supplementation on the anaerobic digestion of real municipal solid waste in batch mode

The effect of low glycerol supplementation (<1% v/v) in the thermophilic anaerobic digestion (AD) of real municipal solid waste (RMSW) on methane production (MP) is not known. This study explores the effect of five different glycerol supplementations (0%, 0.1%, 0.25%, 0.5% and 1%) on effluent characteristics, anaerobic consortia and MP. Specifically, by adding 0.25% v/v crude glycerol to the feed, the methane production rate increased by 48% (from 7.40±1.17 l CH4/l to 11.01±1.66 l CH4/l), in line with the increase in total volatile solids (TVS) removal (from 65±7% to 81±7) and methanogenic activity (from 110∗10−12±17∗10−12 l CH4/cell to 156∗10−12±24∗10−12 l CH4/cell). Extra glycerol added to the feed (0.5% or 1%) was shown to be non-feasible for thermophilic AD of RMSW, as inhibition of methanogenesis was observed. Fluorescent in situ hybridization (FISH) studies showed that the percentages of Eubacteria, Archaea, H2-utilising methanogens (HUM) and acetate-utilising methanogens (AUM) were stable within the 94.0–97.0%, 6.0–3.0%, 1.8–3.6% and 0.6–2.8% ranges, respectively.

Effects of the operational conditions on the production of 1,3-propanediol derived from glycerol in anaerobic granular sludge reactors.

The aim of this study has been to produce 1,3-propanediol (1,3-PDO) from glycerol (gly) fermentation by means of a microbial mixed culture (granular sludge), as well as to establish the operational conditions of two up-flow anaerobic sludge blanket (UASB) reactors in order to achieve a maximum 1,3-PDO yield. The UASB reactors with initial pH values set at 6.8 and 5.5 were operated at 30 °C during 165 days. Thirteen variables were previously screened by a Plackett-Burman (PB) design; results showed that yeast extract, MgSO4 and methanogenesis inhibition (by heat shock) showed a positive effect, whereas high glycerol concentration, tryptone and CaCl2 showed a negative impact on the 1,3-PDO produced by glycerol degradation. Following four experimental periods, the highest average yield of 0.43 mol 1,3-PDO mol-1 gly was achieved when sodium bicarbonate was added to the reactors. Propionate and acetate were also produced and a high microorganism diversity was detected; however, the restrictive operational conditions of the reactors led to the death of the methanogenic archaea. Nevertheless, the continuous production of 1,3-PDO from glycerol within UASB reactors inoculated with granular sludge can be considered highly feasible.

Structure and function of methanogenic microbial communities in soils from flooded rice and upland soybean fields from Sanjiang plain, NE China

About 50 years ago, most of the natural wetlands in northeast China, the Sanjiang plain, were converted to either flooded rice fields or to upland soybean fields. After the conversion, natural wetland soils were either managed as artificial wetland or as drained upland resulting in soil microbial community changes. The purpose of our study was to understand how methanogenic microbial communities and their functions had changed in the two different soils upon conversion, and whether these communities now exhibit different resistance/resilience to drying and rewetting. Therefore, we determined function, abundance and composition of the methanogenic archaeal and bacterial communities in two soils reclaimed from a Carex wetland 25 years ago. We incubated the soils under anoxic conditions and measured the rates and pathways of CH4 production by analyzing concentration and δ13C of CH4 and acetate in the presence and absence of methyl fluoride, an inhibitor of aceticlastic methanogenesis. We also analyzed the abundance of bacterial and archaeal 16S rRNA genes, and of mcrA (coding for a subunit of the methyl coenzyme M reductase) using qPCR. The composition of the archaeal and bacterial 16S rRNA genes was determined by using MiSeq illumina sequencing. Our results showed clear differences in structure and function of methanogenic archaeal communities in rice field soil versus upland soil. Furthermore, in both soils composition of bacteria and archaea changed after artificial drying and became less diverse. The archaeal and bacterial signature species in the two soils were also different. However, functional changes were similar, with rates of CH4 production and contribution of aceticlastic methanogenesis decreasing upon drying and rewetting in both soils.

Oxidation of glucose by syntrophic association between Geobacter and hydrogenotrophic methanogens in microbial fuel cell.

To investigate a syntrophic interaction between Geobacter sulfurreducens and hydrogenotrophic methanogens in sludge-inoculated microbial fuel cell (MFC) systems running on glucose with an improved electron recovery at the anode. The presence of archaea in MFC reduces Coulombic efficiency (CE) due to their electron scavenging capability but, here, we demonstrate that a syntrophic interaction can occur between G. sulfurreducens and hydrogenotrophic methanogens via interspecies H2 transfer with improvement in CE and power density. The addition of the methanogenesis inhibitor, 2-bromoethanesulfonate (BES), resulted in the reduction in power density from 5.29 to 2W/m3, and then gradually increased to the peak value of 5.5W/m3 when BES addition was stopped. Reduction of H2 partial pressure by archaea is an efficient approach in improving power output in a glucose-fed MFC system using Geobacter sp. as an inoculum.

1613 Inhibition of methanogenesis by nitrate, with or without defaunation, in continuous culture

With regard to the focus of methane (CH4) mitigation in ruminant production systems, nitrate (NO3) serves as an alternative sink for aqueous hydrogen [H2(aq)] accumulating in the rumen, producing ammonium via NO3 reduction pathways and thereby decreasing CH4 production. Defaunation has also been correlated in meta-analyses with decreased methanogenesis. We hypothesized defaunation might increase the CH4 mitigation effect of NO3 by removal of a symbiotic source of substrate to methanogens. In the present study, we applied a 2 × 2 factorial treatment arrangement in a 4 × 4 Latin square design to continuous culture fermenters (n = 4). Treatments were control (–NO3) vs. nitrate (+NO3; 1.5% of diet DM), factorialized with control (faunated [FAUN]) vs. defaunated (DEF). Fermenters were fed once daily (40 g DM; 50:50 forage:concentrate diet); four periods lasted 11 d with 3 d of sample collection. Buffer dilution and solids passage rate were maintained at 7.0 and 5.0%/h, respectively. There were no main effects of DEF or interaction of faunation status with addition of NO3 (P > 0.05). The main effect of +NO3 increased (P < 0.05) H2(aq) compared with –NO3 by 11.0 μM. The main effect of +NO3 also decreased (P < 0.05) daily CH4 production compared with –NO3 by 8.17 mmol CH4/d. Because there were no treatment effects on NDF digestibility (P > 0.10), the main effect of +NO3 also decreased (P < 0.05) CH4 production compared with –NO3 by 1.43 mmol CH4/g NDF digested. There were no effects of treatment (P > 0.10) on other nutrient digestibilities, N flow, or microbial N flow per gram of nutrient digested. These data support the existing literature that NO3 incorporation in the diet can decrease the methanogenesis by dairy cattle. More importantly, methanogens are not necessarily inhibited by defaunation in a highly reduced environment. However, practical considerations such as nitrite toxicity and on-farm dietary adaptation to NO3 should be considered before implementing this practice in U.S. dairy production systems.

A degradation model for high kitchen waste content municipal solid waste

Municipal solid waste (MSW) in developing countries has a high content of kitchen waste (KW), and therefore contains large quantities of water and non-hollocellulose degradable organics. The degradation of high KW content MSW cannot be well simulated by the existing degradation models, which are mostly established for low KW content MSW in developed countries. This paper presents a two-stage anaerobic degradation model for high KW content MSW with degradations of hollocellulose, sugars, proteins and lipids considered. The ranges of the proportions of chemical compounds in MSW components are summarized with the recommended values given. Waste components are grouped into rapidly or slowly degradable categories in terms of the degradation rates under optimal water conditions for degradation. In the proposed model, the unionized VFA inhibitions of hydrolysis/acidogenesis and methanogenesis are considered as well as the pH inhibition of methanogenesis. Both modest and serious VFA inhibitions can be modeled by the proposed model. Default values for the parameters in the proposed method can be used for predictions of degradations of both low and high KW content MSW. The proposed model was verified by simulating two laboratory experiments, in which low and high KW content MSW were used, respectively. The simulated results are in good agreement with the measured data of the experiments. The results show that under low VFA concentrations, the pH inhibition of methanogenesis is the main inhibition to be considered, while the inhibitions of both hydrolysis/acidogenesis and methanogenesis caused by unionized VFA are significant under high VFA concentrations. The model is also used to compare the degradation behaviors of low and high KW content MSW under a favorable environmental condition, and it shows that the gas potential of high KW content MSW releases more quickly.

Long-term operation of anaerobic immobilized biomass reactor treating organic wastewater containing sulfate

This work evaluates the long-term performance (888 days) of a horizontal-flow anaerobic immobilized biomass (HAIB) reactor fed with synthetic wastewater containing organic matter and sulfate. The HAIB reactor achieved stable performance, exhibiting high sulfate and organic matter removal efficiencies subjected to organic matter concentration (expressed as chemical oxygen demand – COD) of 1500mg/L and sulfate of 500mg/L. Sulfate removal efficiency close to 100% was obtained for COD/sulfate ratios equal to or higher than 2.6, decreasing to ∼80% for COD/sulfate ratio of 1.4. Sulfidogenesis was clearly dependent on the availability of electron donor; but not methanogenesis. The smaller COD removal efficiencies (∼93%) were observed at the higher sulfate (1980mg/L) and organic matter (COD of 7000mg/L) concentrations, with COD/sulfate ratio of 3.5. Under these conditions, the presence of volatile fatty acids in the effluent indicates the occurrence of methanogenesis inhibition probably due to sulfide. The fixed-film HAIB reactor did not present bed clogging throughout the entire long-term operation period, thereby leading the way to new perspectives to use the efficient treatment of sulfate-rich wastewater.

Microbial toxicity of ionic species leached from the II-VI semiconductor materials, cadmium telluride (CdTe) and cadmium selenide (CdSe)

This work investigated the microbial toxicity of soluble species that can potentially be leached from the II-VI semiconductor materials, cadmium telluride and cadmium selenide. The soluble ions tested included: cadmium, selenite, selenate, tellurite, and tellurate. Their toxicity towards the acetoclastic and hydrogen-consuming trophic groups in a methanogenic consortium as well as towards a bioluminescent marine bacterium, Aliivibrio fischeri (Microtox® test), was assessed. The acetoclastic methanogenic activity was the most affected as evidenced by the low 50% inhibiting concentrations (IC50) values obtained of 8.6 mg L−1 for both cadmium and tellurite, 10.2 mg L−1 for tellurate, and 24.1 mg L−1 for selenite. Both tellurium oxyanions caused a strong inhibition of acetoclastic methanogenesis at low concentrations, each additional increment in concentration provided progressively less inhibition increase. In the case of the hydrogenotrophic methanogenesis, cadmium followed by selenite caused the greatest inhibition with IC50 values of 2.9 and 18.0 mg L−1, respectively. Tellurite caused a moderate effect as evidenced by a 36.8% inhibition of the methanogenic activity at the highest concentration tested, and a very mild effect of tellurate was observed. Microtox® analyses showed a noteworthy inhibition of cadmium, selenite, and tellurite with 50% loss in bioluminescence after 30 min of exposure of 5.5, 171.1, and 458.6 mg L−1, respectively. These results suggest that the leaching of cadmium, tellurium and selenium ions from semiconductor materials can potentially cause microbial toxicity.

Active H2 Harvesting Prevents Methanogenesis in Microbial Electrolysis Cells

Undesired H2 sinks, including methanogenesis, are a serious issue faced by microbial electrolysis cells (MECs) for high-rate H2 production. Different from current top-down approaches to methanogenesis inhibition that showed limited success, this study found active harvesting can eliminate the source (H2) from all H2 consumption mechanisms via rapid H2 extraction using a gas-permeable hydrophobic membrane and vacuum. Active harvesting completely prevented CH4 production and led to H2 yields (2.62–3.39 mol of H2/mol of acetate) much higher than that of the control using traditional spontaneous release (0.79 mol of H2/mol of acetate). In addition, existing CH4 production in the control MEC was stopped once the switch to active H2 harvesting was made. Active harvesting also increased current density by 36%, which increased operation efficiency and facilitated organic removal. Energy quantification shows the process was energy-positive, as the H2 energy produced via active harvesting was 220 ± 10% of external ...

Organic loading rate: A promising microbial management tool in anaerobic digestion

This study investigated the effect of changes in organic loading rate (OLR) and feedstock on the volatile fatty acids (VFAs) production and their potential use as a bioengineering management tool to improve stability of anaerobic digesters. Digesters were exposed to one or two changes in OLR using the same or different co-substrates (Fat Oil and Grease waste (FOG) and/or glycerol). Although all the OLR fluctuations produced a decrease in biogas and methane production, the digesters exposed twice to glycerol showed faster recovery towards stable conditions after the second OLR change. This was correlated with the composition of the VFAs produced and their mode of production, from parallel to sequential, resulting in a more efficient recovery from inhibition of methanogenesis. The change in acids processing after the first OLR increase induced a shift in the microbial community responsible of the process optimisation when the digesters were exposed to a subsequent OLR increase with the same feedstock. When the digesters were exposed to an OLR change with a different feedstock (FOG), the recovery took 7d longer than with the same one (glycerol). However, the microbial community showed functional resilience and was able to perform similarly to pre-exposure conditions. Thus, changes in operational conditions can be used to influence microbial community structure for anaerobic digestion (AD) optimisation. Finally, shorter recovery times and increased resilience of digesters were linked to higher numbers of Clostridia incertae sedis XV, suggesting that this group may be a good candidate for AD bioaugmentation to speed up recovery after process instability or OLR increase.

Enzyme- and gene-based approaches for developing methanogen-specific compounds to control ruminant methane emissions: a review

Methane emissions from ruminants are of worldwide concern due to their potential to adversely affect climate patterns. Methane emissions can be mitigated in several ways, including dietary manipulation, the use of alternative hydrogen sinks, and by the direct inhibition of methanogens. In the present review, we summarise and emphasise studies where defined chemically synthesised compounds have been used to mitigate ruminant methane emissions by direct targeting of methanogens and discuss the future potential of such inhibitors. We also discuss experiments, where methanogen-specific enzymes and pure cultures of methanobacterial species have been used to aid development of inhibitors. Application of certain compounds can result in dramatic reductions of methane emissions from ruminant livestock, demonstrating ‘proof of principle’ of chemical inhibitors of methanogenesis. More recently, genome sequencing of rumen methanogens has enabled an in-depth analysis of the enzymatic pathways required for methane formation. Chemogenomic methods, similar to those used in the fight against cancer and infectious diseases, can now be used to specifically target a pathway or enzyme in rumen methanogens. However, few rumen methanogen enzymes have been structurally or biochemically characterised. Any compound, whether natural or man-made, that is used as a mitigation strategy will need to be non-toxic to the host animal (and humans), cost-effective, environmentally friendly, and not accumulate in host tissues or milk products. Chemically synthesised inhibitors offer potentially significant advantages, including high levels of sustained inhibition, the ability to be easily and rapidly produced for global markets, and have the potential to be incorporated into slow-release vehicles for grazing animals.