Methanogenic Populations Research Articles

Impact of feeding essential oils on feed fermentation and rumen microbial profile in crossbred cattle calves

The essential oils (EOs), viz. ajwain (Trachyspermum copticum, AjO), lemongrass (Cymbopogon citratus, LO), clove (Syzygium aromaticum) oleoresin (CO) and a blend (BEO) of the 3 were screened using in vitro gas production test for their potential to mitigate methane production. Inclusion of all the 3 EOs and BEO at the rate of 1.0 μl/ml of incubation medium resulted in a depression in total gas and methane production with a maximum reduction of 91.6 and 97.2% by BEO. Feed digestibility was significantly reduced by all the 3 EOs and BEO as compared to control but was similar among the 4 treatments. The level of total volatile fatty acids, acetic and propionic acids in fermented medium was significantly decreased by inclusion of EOs and BEO. Based on the results of these results, BEO was selected for the feeding trial. Ten crossbred cattle calves (average body weight, 68±5 kg) were divided into 2 groups of 5 animals each and subjected to 2 treatments i.e. diet without (control) and with BEO @ 0.1 mL/kg BW (treated). The diet comprised concentrate mixture (21.9%, CP and 71.1% TDN) and wheat straw in 50:50 ratio. There was no impact of BEO feeding on rumen metabolites and enzyme profile. As assessed by real time PCR, the population of protozoa and Ruminococcus albus reduced, whereas, bacteria, fungi, Fibrobacter succinogenes and Ruminococcus flavefaciens remained unaffected by BEO feeding. Methanogen population density tended to reduce by BEO feeding. The results clearly indicated that BEO exhibited antimethanogenic activity in in vitro system. By feeding BEO, the decreased population density of protozoa and methanogens in the rumen, the 2 major microbial groups involved in methanogenesis, also supported antimethnogenic property of BEO.

Production of biogas: relationship between methanogenic and sulfate-reducing microorganisms

AbstractThe production of high-quality methane depends on many factors, including temperature, pH, substrate, composition and relationship of the microorganisms. The qualitative and quantitative composition of methanogenic and sulfate-reducing microorganisms and their relationship in the experimental bioreactors has never been studied. The aim of this research was to characterize, for the first time, the diversity of the methanogenic microorganisms and sulfate-reducing bacteria, and study their relationship and biogas production in experimental bioreactors. Amplification of 16S rRNA gene fragments was carried out. Purified amplicons were paired-end sequenced on an Illumina Mi-Seq platform. The dominant morphotypes of these microorganisms in the bioreactor were homologous (99%) by the sequences of 16S rRNA gene to theMethanosarcina,Thermogymnomonas,Methanoculleusgenera andArchaeondeposited in GenBank. Three dominant genera of sulfate-reducing bacteria,Desulfomicrobium,DesulfobulbusandDesulfovibrio, were detected in the bioreactor. The phylogenetic trees showing their genetic relationship were constructed. The diversity and number of the genera, production of methane, hydrogen sulfide and hydrogen in the bioreactor was investigated. This research is important for understanding the relationship between methanogenic microbial populations and other bacterial physiological groups, their substrate competition and, in turn, can be helpful for controlling methanogenesis in bioreactors.

Microbial and Isotopic Evidence for Methane Cycling in Hydrocarbon-Containing Groundwater from the Pennsylvania Region.

The Pennsylvania region hosts numerous oil and gas reservoirs and the presence of hydrocarbons in groundwater has been locally observed. However, these methane-containing freshwater ecosystems remain poorly explored despite their potential importance in the carbon cycle. Methane isotope analysis and analysis of low molecular weight hydrocarbon gases from 18 water wells indicated that active methane cycling may be occurring in methane-containing groundwater from the Pennsylvania region. Consistent with this observation, multigenic qPCR and gene sequencing (16S rRNA genes, mcrA, and pmoA genes) indicated abundant populations of methanogens, ANME-2d (average of 1.54 × 104 mcrA gene per milliliter of water) and bacteria associated with methane oxidation (NC10, aerobic methanotrophs, methylotrophs; average of 2.52 × 103 pmoA gene per milliliter of water). Methane cycling therefore likely represents an important process in these hydrocarbon-containing aquifers. The microbial taxa and functional genes identified and geochemical data suggested that (i) methane present is at least in part due to methanogens identified in situ; (ii) Potential for aerobic and anaerobic methane oxidation is important in groundwater with the presence of lineages associated with both anaerobic an aerobic methanotrophy; (iii) the dominant methane oxidation process (aerobic or anaerobic) can vary according to prevailing conditions (oxic or anoxic) in the aquifers; (iv) the methane cycle is closely associated with the nitrogen cycle in groundwater methane seeps with methane and/or methanol oxidation coupled to denitrification or nitrate and nitrite reduction.

Nitrate decreases methane production also by increasing methane oxidation through stimulating NC10 population in ruminal culture

Studies proved that addition of nitrate in rumen could lead to reduction of methane emission. The mechanism of this function was involved in the competition effect of nitrate on hydrogen consumption and the inhibitory effect of generated nitrite on methanogen proliferation. The present study investigated an alternative mechanism that denitrifying anaerobic methane oxidizing (DAMO) bacteria, DAMO archaea and anammox bacteria may co-exist in rumen, therefore, more methane can be oxidized when addition of nitrate. Ruminal batch culture model was used to test the effects of addition of 5 mM NaNO3, 4 mM NH4Cl, or both into the culture substrate on methane production, fermentation patterns, and population of methanogens, NC10 and anaerobic methanotrophic-2d (ANME-2d). Our results showed that NC10 in the ruminal culture was detected by polymerase chain reaction (PCR) when using NC10 special primer sets, and addition of nitrate reduced methane production and the relative proportions of methanogen, whereas increased the relative proportion of NC10. A combined addition of ammonia salt and nitrate did not show further inhibitory effect on methane production but accelerated nitrate removal. We did not detect DAMO archaea in ruminal culture by real-time PCR when using ANME-2d special primer sets. The present study may encourage researchers to pay more attention to methane oxidation performed by anaerobic methanotroph when studying the strategies of inhibiting ruminal methane emission.

The influence of plant polyphenols from oil palm (Elaeis guineensis Jacq.) leaf extract on fermentation characteristics, biohydrogenation of C18 PUFA, and microbial populations in rumen of goats: in vitro study

ABSTRACTOil palm leaf is rich source of secondary metabolites. An in vitro study was conducted to identify the effects of oil palm leaf extract (OPLE) on rumen characteristics of goats by adding 0% (CON), 2.5% (T1), 5% (T2), and 10% (T3)/250 mg DM in 30 mL of buffered rumen fluid for 24 h. Methane gas production (mL/g DM) decreased (P < .05) with increasing levels of OPLE. Acetic to propionic acid ratio was lower (P < .05) in T3 (2.46) compared to the CON (3.12). Real-time PCR analyses indicated that the populations of total methanogens and Methanobacteriaceae in OPLE treatment groups decreased (P < .05) compared to CON, without any significant changes in the population of cellulolytic bacteria. Supplementation of the diet with OPLE significantly (P < .05) decreased the concentration of C18:0 while increased (P < .05) the concentration of C18:1 t-11 and c-9, t-11 CLA after 24 h of incubation.

Effect of initial bulk density on high-solids anaerobic digestion of MSW: General mechanism

Initial bulk density (IBD) is an important variable in anaerobic digestion since it defines and optimizes the treatment capacity of a system. This study reveals the mechanism on how IBD might affect anaerobic digestion of waste. Four different IBD values: D1 (500–700kgm−3), D2 (900–1000kgm−3), D3 (1100–1200kgm−3) and D4 (1200–1400kgm−3) were set and tested over a period of 90days in simulated landfill reactors. The main variables affected by the IBD are the methane generation, saturation degree, extraction of organic matter, and the total population of methanogens. The study identified that IBD >1000kgm−3 may have significant effect on methane generation, either prolonging the lag time or completely inhibiting the process. This study provides a new understanding of the anaerobic digestion process in saturated high-solids systems.

Methanogenic population dynamics regulated by bacterial community responses to protein-rich organic wastes in a high solid anaerobic digester

The large amount of protein-rich organic waste generated annually is an extremely valuable substrate of anaerobic digestion. Although free ammonia (FAN, NH3) and ammonium (NH4+) are so far the most widely acknowledged inhibitors affecting operational stability, the detailed inhibition mechanisms in the processing of protein-rich material remain unclear. The present study aimed to determine the single or synergistic effects initiated by the anaerobic degradation of highly loaded protein, in hopes of understanding how a microbial ecosystem responds to altered environmental conditions such as changes in NH3, NH4+, acetate, volatile fatty acids (VFA), pH, and alkalinity. A high solid anaerobic digester with protein-rich organic wastes was operated semi-continuously which endured a complete stable-inhibited-recovered cycle during the whole operation of 125days. The kinetics of methanogenesis from acetic acid (HAc) in the system was analyzed and modelled to clarify the physiologic properties of methanogens under inhibition conditions. The community dynamics of archaea and bacteria during the operation were monitored by 16S rRNA pyrosequencing following the QIIME pipeline, and nonmetric multidimensional scaling (NMDS) analysis was conducted to ordinate the ecological community with kinetics fitting parameters. As a result, the inhibition and recovery in methane production are intrinsically attributed to the changes in total ammonium nitrogen (TAN), alkalinity, and VFA (acetate), because these factors dictate the changes in a bacterial community, triggering the shift in the methanogenic pathway from acetoclastic to hydrogenotrophic methanogenesis. The more sensitive responses from the bacterial community than the methanogenic community also indicated that specific bacterial species, such as T78 (before day 38), RFN20 (days 40–56), Tepidimicrobium (days 60–66), and unclassified Clostridia (after day 70), might be better biomarkers of digester performance.

In-situ biogas upgrading with pulse H2 additions: The relevance of methanogen adaption and inorganic carbon level

Surplus electricity from fluctuating renewable power sources may be converted to CH4 via biomethanisation in anaerobic digesters. The reactor performance and response of methanogen population of mixed-culture reactors was assessed during pulsed H2 injections. Initial H2 uptake rates increased immediately and linearly during consecutive pulse H2 injections for all tested injection rates (0.3 to 1.7LH2/Lsludge/d), while novel high throughput mcrA sequencing revealed an increased abundance of specific hydrogenotrophic methanogens. These findings illustrate the adaptability of the methanogen population to H2 injections and positively affects the implementation of biomethanisation. Acetate accumulated by a 10-fold following injections exceeding a 4:1 H2:CO2 ratio and may act as temporary storage prior to biomethanisation. Daily methane production decreased for headspace CO2 concentrations below 12% and may indicate a high sensitivity of hydrogenotrophic methanogens to CO2 limitation. This may ultimately decide the biogas upgrading potential which can be achieved by biomethanisation.

Effects of dietary supplementation of active dried yeast on fecal methanogenic archaea diversity in dairy cows

This study aimed to investigate the effects of dietary supplementation of different dosages of active dried yeast (ADY) on the fecal methanogenic archaea community of dairy cattle. Twelve multiparous, healthy, mid-lactating Holstein dairy cows (body weight: 584 ± 23.2 kg, milk produced: 26.3 ± 1.22 kg/d) were randomly assigned to one of three treatments (control, ADY2, and ADY4) according to body weight with four replicates per treatment. Cows in the control group were fed conventional rations without ADY supplementation, while cows in the ADY2 and ADY4 group were fed rations supplemented with ADY at 2 or 4 g/d/head. Real-time PCR analysis showed the populations of total methanogens in the feces were significantly decreased (P < 0.05) in the ADY4 group compared with control. High-throughput sequencing technology was applied to examine the differences in methanogenic archaea diversity in the feces of the three treatment groups. A total of 155,609 sequences were recovered (a mean of 12,967 sequences per sample) from the twelve fecal samples, which consisted of a number of operational taxonomic units (OTUs) ranging from 1451 to 1,733, were assigned to two phyla, four classes, five orders, five families and six genera. Bioinformatic analyses illustrated that the natural fecal archaeal community of the control group was predominated by Methanobrevibacter (86.9% of the total sequence reads) and Methanocorpusculum (10.4%), while the relative abundance of the remaining four genera were below 1% with Methanosphaera comprising 0.8%, Thermoplasma composing 0.4%, and the relative abundance of Candidatus Nitrososphaera and Halalkalicoccus being close to zero. At the genus level, the relative abundances of Methanocorpusculum and Thermoplasma were increased (P < 0.05) with increasing dosage of ADY. Conversely, the predominant methanogen genus Methanobrevibacter was decreased with ADY dosage (P < 0.05). Dietary supplementation of ADY had no significant effect (P > 0.05) on the abundances of genera unclassified, Candidatus Nitrososphaera, and Halalkalicoccus. In conclusion, supplementation of ADY to the rations of dairy cattle could alter the population sizes and composition of fecal methanogenic archaea in the feces of dairy cattle. The decrease in Methanobrevibacter happened with a commensurate increase in the genera Methanocorpusculum and Thermoplasma.

Influence of Diet Composition on Cattle Rumen Methanogenesis: A Comparative Metagenomic Analysis in Indian and Exotic Cattle.

Comparative metagenomics approach has been used in this study to discriminate colonization of methanogenic population in different breeds of cattle. We compared two Indian cattle breeds (Gir and Kankrej) and two exotic cattle (Holstein and Jersey) breeds. Using a defined dietary plan for selected Indian varieties, the diet dependent shifts in microbial community and abundance of the enzymes associated with methanogenesis were studied. This data has been compared with the available rumen metagenome data from Holstein and Jersey dairy cattle. The abundance of genes for methanogenesis in Holstein and Jersey cattle came from Methanobacteriales order whereas, majority of the enzymes for methanogenesis in Gir and Kankrej cattle came from Methanomicrobiales order. The study suggested that by using slow/less digestible feed, the propionate levels could be controlled in rumen; and in turn, this would also help in further reducing the hydrogenotrophic production of methane. The study proposes that with the designed diet plan the overall methanogenic microbial pool or the individual methanogens could be targeted for development of methane mitigation strategies.

Effect of a Blend of Essential Oils on Buffalo Rumen Microbial and Enzyme Profiles and In Vitro Feed Fermentation

Three rumen-fistulated adult Murrah buffaloes (BW 426±45 kg) were arranged in a 3×3 LSD. The treatments involved supplementation of a blend (BEO-CL) of clove bud oleoresin and lemongrass oil (in 1:1 ratio) at the rate of 0, 0.75 and 1.5% of BW. After 20d of feeding, the rumen liquor and rumen contents were sampled before (0h) and 4h after feeding and analyzed for various parameters. There was neither any effect of feed additive nor sampling time on the concentration of VFAs, NH3-N, lactic acid and activities of select enzymes (carboxymethylcellulase, avicelase, xylanase, amylase, β-glucosidase, α-glucosidase and acetyl esterase). The population of rumen bacteria, fungi, ciliate protozoa, Fibrobacter succinogenes, Ruminococcus flavefaciens, Ruminococcus albus and methanogens were not affected by BEO-CL supplementation. In vitro gas production test to evaluate various feedstuffs namely hays (berseem, oat and maize); dry roughages (wheat straw, paddy straw and sugarcane bagasse) complete feeds with 20:80, 35:65 and 50:50 concentrate: roughage ratio) as substrates was conducted using rumen liquor of these buffaloes as inocula. There was an increase in gas production with rumen liquor of BEO-CL supplemented buffaloes irrespective of substrate. Methane production was decreased with 0.75% BEO-CL supplemented inoculum but not with paddy straw and sugarcane bagasse. The in vitro true digestibility (IVTD) of feed was increased with BEO-CL inoculum only with complete diet having 20:80 concentrate:roughage ratio as substrate. It is concluded that BEO-CL at the level of 0.75% of BW did not affect rumen characteristics and major microbial populations but inhibited in vitro methane production; hence, it can be further explored for its use as a feed additive to mitigate methane emission in buffaloes.

Unexpected competitiveness of Methanosaeta populations at elevated acetate concentrations in methanogenic treatment of animal wastewater.

Acetoclastic methanogenesis is a key metabolic process in anaerobic digestion, a technology with broad applications in biogas production and waste treatment. Acetoclastic methanogenesis is known to be performed by two archaeal genera, Methanosaeta and Methanosarcina. The conventional model posits that Methanosaeta populations are more competitive at low acetate levels (<1mM) than Methanosarcina and vice versa at higher acetate concentrations. While this model is supported by an extensive body of studies, reports of inconsistency have grown that Methanosaeta were observed to outnumber Methanosarcina at elevated acetate levels. In this study, monitoring of anaerobic digesters treating animal wastewater unexpectedly identified Methanosaeta as the dominant acetoclastic methanogen population at both low and high acetate levels during organic overloading. The surprising competitiveness of Methanosaeta at elevated acetate was further supported by the enrichment of Methanosaeta with high concentrations of acetate (20mM). The dominance of Methanosaeta in the methanogen community could be reproduced in anaerobic digesters with the direct addition of acetate to above 20mM, again supporting the competitiveness of Methanosaeta over Methanosarcina at elevated acetate levels. This study for the first time systematically demonstrated that the dominance of Methanosaeta populations in anaerobic digestion could be linked to the competitiveness of Methanosaeta at elevated acetate concentrations. Given the importance of acetoclastic methanogenesis in biological methane production, findings from this study could have major implications for developing strategies for more effective control of methanogenic treatment processes.

Fluid chemistry in the Solitaire and Dodo hydrothermal fields of the Central Indian Ridge

AbstractFluid chemistry and microbial community patterns in chimney habitats were investigated in two hydrothermal fields located at the Central Indian Ridge. Endmember hydrothermal fluid of the Solitaire field, located ~3 km away from the spreading center, was characterized by moderately high temperature (307°C), Cl depletion (489 mm), mildly acidic pH (≥4.40), and low metal concentrations (Fe ≤ 105 μm and Mn = 78 μm). Chloride depletion indicates that the subseafloor source fluid had undergone phase separation at temperatures higher than ~390°C while the metal depletion was likely attributable to fluid alteration occurring at a venting temperature of around 307°C. These different temperature conditions suggested from fluid chemistry might be associated with an off‐spreading center location of the field that allows subseafloor fluid cooling prior to seafloor discharge. The microbial community in the chimney habitat seemed comparable to previously known patterns in typical basalt‐hosted hydrothermal systems. Endmember hydrothermal fluid of the Dodo field, standing on center of the spreading axis, was characterized by high H2 concentration of 2.7 mm. The H2 enrichment was likely attributable to fresh basalt–fluid interaction, as suggested by the nondeformed sheet lava flow expansion around the vents. Thermodynamic calculation of the reducing pyrite–pyrrhotite–magnetite (PPM) redox buffer indeed reproduced the H2 enrichment. The quantitative cultivation test revealed that the microbial community associated with the hydrothermal fluid hosted abundant populations of (hyper)thermophilic hydrogenotrophic chemolithoautotrophs such as methanogens. The function of subseafloor hydrogenotrophic methanogenic populations dwelling around the H2‐enriched hydrothermal fluid flows was also inferred from the 13C‐ and D‐depleted signature of CH4 in the collected fluids. It was observed that the hydrothermal activity of the Dodo field had ceased until 2013.

Methane production improvement and associated methanogenic assemblages in bioelectrochemically assisted anaerobic digestion

Microbial electrolysis cell (MEC) was incorporated into anaerobic digestion (AD) to evaluate the methane recovery from digestion of glucose and sludge and the pertinent methanogenic population. At the poise voltages of 0.3 and 0.6V, the MEC-assisted AD systems increased the yields of methane from glucose degradation by 9.4±0.4% and 9.4±0.5%, respectively. The energy recovery efficiencies from the electricity use in the MEC-assisted systems were 41.6% and 33.7%, respectively. For waste sludge, methane yields increased by 8.1±0.5% and 8.5±0.6% at 0.3 and 0.6V, respectively. qPCR studies of population dynamics, reveal that the composition of acetoclastic methanogens was not impacted by the MEC-assisted systems, but the population of hydrogenotrophic methanogens such as Methanomicrobiales and Methanobacteriales increased by up to 17.2 times. Our results suggest that applying a low voltage (0.3V) to AD systems is beneficial to hydrogenotrophic methanogens, resulting in an increase in methane production.

Rumen microbial community and nitrogen metabolism in goats fed blend of palm oil and canola oil

This study assessed the influence of dietary blend of 20% palm oil and 80% canola oil on the population of rumen microbiota and nitrogen economy in goats. Twenty-four Boer bucks (4–5 months old; initial BW, 20.54 ± 0.474 kg) were randomly allotted to diets containing on a dry matter basis, 0, 4 or 8% oil blend, fed daily for 100 days and slaughtered. The rumen microbiota was examined by quantitative real-time polymerase chain reaction (PCR) using the 16S rRNA gene. The population of total protozoa and methanogens was lower (p < .05) while the population of Fibrobacter succinogenes was greater (p < .05) in goats fed oil blend compared with the control goats. The population of total bacteria was greater (p < .05) in goats fed 8% oil blend compared with those fed other diets. The population of Ruminococcus albus and Ruminococcus flavefaciens was greater (p < .05) in goats fed 4% oil blend compared with those fed other diets. Diet had no effect (p> 0.05) on microbial N yield, microbial protein synthesis, efficiency of microbial protein synthesis and the intake, retention and excretion of N. Dietary supplementation of blend of palm oil and canola oil altered rumen microbial profile but did not affect nitrogen metabolism in goats.

Assessment of active methanogenic archaea in a methanol-fed upflow anaerobic sludge blanket reactor.

Methanogenic archaea enrichment of a granular sludge was undertaken in an upflow anaerobic sludge blanket (UASB) reactor fed with methanol in order to enrich methylotrophic and hydrogenotrophic methanogenic populations. A microbial community assessment, in terms of microbial composition and activity-throughout the different stages of the feeding process with methanol and acetate-was performed using specific methanogenic activity (SMA) assays, quantitative real-time polymerase chain reaction (qPCR), and high-throughput sequencing of 16S ribosomal RNA (rRNA) genes from DNA and complementary DNA (cDNA). Distinct methanogenic enrichment was revealed by qPCR of mcrA gene in the methanol-fed community, being two orders of magnitude higher with respect to the initial inoculum, achieving a final mcrA/16S rRNA ratio of 0.25. High-throughput sequencing analysis revealed that the resulting methanogenic population was mainly composed by methylotrophic archaea (Methanomethylovorans and Methanolobus genus), being also highly active according to the RNA-based assessment. SMA confirmed that the methylotrophic pathway, with a direct conversion of methanol to CH4, was the main step of methanol degradation in the UASB. The biomass from the UASB, enriched in methanogenic archaea, may bear great potential as additional inoculum for bioreactors to carry out biogas production and other related processes.

Medicinal herbs as a potential strategy to decrease methane production by rumen microbiota: a systematic evaluation with a focus on Perilla frutescens seed extract.

Mitigation of the methane (CH4) emission from ruminants is needed to decrease the environmental impact of ruminant animal production. Different plant materials and chemicals have been tested, but few are both effective and practical. Medicinal herbs contain biological compounds and antimicrobials that may be effective in lowering the CH4 production. However, few studies have systematically evaluated medicinal herbs for their effect on CH4 production or on the rumen microbiota. In this study, extracts from 100 medicinal herbs were assessed for their ability to decrease CH4 production by rumen microbiota in vitro. The extracts of 12 herbs effectively lowered the CH4 production, with the extract of Perilla frutescens seeds being the most effective. The major components of P. frutescens seed extract were identified, and the effects of the extract on the fermentation characteristics and populations of rumen methanogens, fungi, protozoa, and select bacteria were also assessed. The decreased CH4 production induced by the P. frutescens seed extract was accompanied by an increased abundance of Ruminobacter, Selenomonas, Succinivibrio, Shuttleworthis, Pseudobutyrivbrio, Anaerovibrio, and Roseomonas and a decreased abundance of Methanobrevibacter millerae. The abundance of Pedobacter, Anaeroplasma, Paludibacter, Ruminococcus, and unclassified Lachnospiraceae was positively correlated with the CH4 production, with no effects on volatile fatty acids. This study suggests that medicinal herbs may be used to mitigate the CH4 emission from ruminants.

The effects of Tetrakis-hydroxymethyl phosphonium sulfate (THPS), nitrite and sodium chloride on methanogenesis and corrosion rates by methanogen populations of corroded pipelines

The effects of some biocides on methanogens associated with pipeline corrosions were investigated. The crude oil transporting pipeline showed higher methane production (60%) and corrosion rates (42%) than the water transporting pipeline. Higher concentrations of biocide (0.7% Tetrakis-hydroxymethyl phosphonium sulfate) and 40mM nitrite were required for both pipelines to sufficiently inhibit methanogenesis and corrosion rates. A sudden increase in corrosion rate happened only in samples that produced higher than 1.5mmole of methane. Pyrosequencing surveys shows dominance of acetotrophic, hydrogenotrophic and methylotrophic methanogens in the samples. The methane productions and corrosion rates were strongly correlated under all the conditions.

Study of microbial community plasticity for anaerobic digestion of vegetable waste in Anaerobic Baffled Reactor

Anaerobic baffled reactor (ABR) provides a selective environment for the microbial community and their respective metabolic activities, which supports the physiochemical conditions required for an optimal performance of reactor. Hydrolysis and methanogenesis are rate limiting steps of anaerobic digestion which are very sensitive to changes in pH. Effluent recirculation provides buffering environment as well as prevents loss of some methanogenic population. In the present study, we used four chambered (C-1, 2, 3, and 4) anaerobic baffled reactor treating vegetable waste under three operating conditions (OCs); no effluent recirculation (OC I), 25% effluent recirculation (OC II), 100% effluent recirculation (OC III) and studied changes in microbial diversity along with selected parameters. OC I showed dominance of Bacteroidetes and Firmicutes in C-1 while remaining chambers were dominated by Proteobacteria, Bacteroidetes, Thermotogae, Spirochaetes and Chloroflexi. This demonstrated that the hydrolytic and fermentative taxa colonized chamber C-1 while syntrophic acetogenic population dominated the remaining chambers. However, a drastic change was observed during OC III, advocated by an increase in diverse population from Firmicutes and Actinobacteria in all chambers. Our results suggest plasticity in microbial population, which could ensure a better reactor performance under different OCs in ABR for methanogenesis.

Anaerobic Toxicity Assay of Polychlorinated Biphenyl: Focus on Fermentative-Methanogenic Community

This study aims to evaluate extensively the inhibition of six PCB (polychlorinated biphenyls) congeners in batch reactors under fermentative-methanogenic condition. The reactors with anaerobic sludge were fed with mineral medium, co-substrates (ethanol and sodium formate), and five PCB concentrations. The maximum methane production (MMP) in the reactor without PCB (RC), with 0.5 (R0.5), 1.5 (R1.5), 3.0 (R3.0), 4.5 (R4.5), and 6.0 mg/L (R6.0) of PCB, was 654.83, 193.08, 111.65, 104.60, 96.67, and 79.50 μmolCH4/gTVS, respectively. The methane inhibition for the reactors R0.5, R1.5, R3.0, R4.5, and R6.0 were 70, 83, 84, 85, and 88 %, respectively. The concentration that causes 50 % of inhibition (IC50) for PCB was 0.03 mg/L. The inhibition results present two different profiles according to the concentration range. The concentration range of 0.5 to 3.0 mg/L of PCB inhibited the acetoclastic microorganisms and the concentration of 4.5 to 6.0 mg/L inhibited both methanogenic and acidogenic population. The acidogenic populations were less sensitive to the PCB than the methanogenic. Lower methane production and organic matter removal were verified in all reactors with PCB compared to RC, without PCB. The microbial community highlighted lower diversity index for reactors with higher PCB concentration. In the reactors with PCB, the populations of bacteria domain were more susceptible to composition changes than the archaea domain. The inhibitory effect of PCB is concentration-dependent and affected differently the populations of organisms in the reactor. Moreover, the range of 4.5 to 6.0 mg/L of PCB severely inhibited the anaerobic community.