Methane-producing Activity Research Articles

Dynamics of Gastrointestinal Activity and Ruminal Absorption of the Methane-Inhibitor, Nitroethane, in Cattle.

Nitroethane is a potent methane-inhibitor for ruminants but little is known regarding simultaneous effects of repeated administration on pre- and post-gastric methane-producing activity and potential absorption and systemic accumulation of nitroethane in ruminants. Intraruminal administration of 120 mg nitroethane/kg body weight per day to Holstein cows (n = 2) over a 4-day period transiently reduced (P < 0.05) methane-producing activity of rumen fluid as much as 3.6-fold while concomitantly increasing (P < 0.05) methane-producing activity of feces by as much as 8.8-fold when compared to pre-treatment measurements. These observations suggest a bacteriostatic effect of nitroethane on ruminal methanogen populations resulting in increased passage of viable methanogens to the lower bovine gut. Ruminal VFA concentrations were also transiently affected by nitroethane administration (P < 0.05) reflecting adaptive changes in the rumen microbial populations. Mean (± SD) nitroethane concentrations in plasma of feedlot steers (n = 6/treatment) administered 80 or 160 mg nitroethane/kg body weight per day over a 7-day period were 0.12 ± 0.1 and 0.41 ± 0.1 μmol/mL 8 h after the initial administration indicating rapid absorption of nitroethane, with concentrations peaking 1 day after initiation of the 80 or 160 mg nitroethane/kg body weight per day treatments (0.38 ± 0.1 and 1.14 ± 0.1 μmol/mL, respectively). Plasma nitroethane concentrations declined thereafter to 0.25 ± 0.1 and 0.78 ± 0.3 and to 0.18 ± 0.1 and 0.44 ± 0.3 μmol/mL on days 2 and 7 for the 80 or 160 mg nitroethane/kg body weight per day treatment groups, respectively, indicating decreased absorption due to increased ruminal nitroethane degradation or to more rapid excretion of the compound.

Assessing the effect of green tuff as a novel natural inorganic carrier on methane-producing activity of an anaerobic sludge microbiome

The upflow anaerobic sludge blanket (UASB) process is an anaerobic biological system that is widely used for the treatment of a variety of wastewater owing to its benefits such as low energy requirements and energy recovery as methane gas; however, unstable reactor performance is often observed. To solve this problem, several inert inorganic carriers and polymer materials have been studied for stabilization of the sludge microbial community and promotion of methane production. In this study, we demonstrate the effects of green tuff (GT) as a novel natural inorganic carrier on methane-producing activity (MPA) in combination with syntroph/methanogen-utilizable substrates and on the microbial community assembly of methanogenic batch cultures fed with granular sludge collected from UASB reactors treating milk- (MMW) or soy sauce- (SSW) manufacturing wastewater. The MPAs of MMW cultures with GT were 4.56- (propionate), 2.01- (n-butyrate), 1.37- (n-valerate), and 1.22- (benzoate) fold higher than those without GT. Likewise, SSW cultures with GT showed 1.34- (acetate) and 1.42- (propionate) fold higher MPA than those without GT. These results indicate that GT has potential to enhance MPAs during methanogenic degradation of these substrates. According to 16S rRNA transcripts-based community profiling, populations of syntrophic bacteria (Syntrophobacter and Smithella) and hydrogenotrophic methanogens (Methanobacterium and Methanolinea) in the cultures with GT were higher than in those without GT. Therefore, GT can be a potential solution for the activation of syntrophic partnerships and improvement/stabilization of reactor performance.

Associations between residual feed intake and apparent nutrient digestibility, in vitro methane-producing activity, and volatile fatty acid concentrations in growing beef cattle1.

The objectives of this study were to examine the relationship between residual feed intake (RFI) and DM and nutrient digestibility, in vitro methane production, and volatile fatty acid (VFA) concentrations in growing beef cattle. Residual feed intake was measured in growing Santa Gertrudis steers (Study 1; n = 57; initial BW = 291.1 ± 33.8 kg) and Brangus heifers (Study 2; n = 468; initial BW = 271.4 ± 26.1 kg) fed a high-roughage-based diet (ME = 2.1 Mcal/kg DM) for 70 d in a Calan-gate feeding barn. Animals were ranked by RFI based on performance and feed intake measured from day 0 to 70 (Study 1) or day 56 (Study 2) of the trial, and 20 animals with the lowest and highest RFI were identified for subsequent collections of fecal and feed refusal samples for DM and nutrient digestibility analysis. In Study 2, rumen fluid and feces were collected for in vitro methane-producing activity (MPA) and VFA analysis in trials 2, 3, and 4. Residual feed intake classification did not affect BW or BW gain (P > 0.05), but low-RFI steers and heifers both consumed 19% less (P < 0.01) DMI compared with high-RFI animals. Steers with low RFI tended (P < 0.1) to have higher DM digestibility (DMD) compared with high-RFI steers (70.3 vs. 66.5 ± 1.6% DM). Heifers with low RFI had 4% higher DMD (76.3 vs. 73.3 ± 1.0% DM) and 4 to 5% higher (P < 0.01) CP, NDF, and ADF digestibility compared with heifers with high RFI. Low-RFI heifers emitted 14% less (P < 0.01) methane (% GE intake; GEI) calculated according to Blaxter and Clapperton (1965) as modified by Wilkerson et al. (1995), and tended (P = 0.09) to have a higher rumen acetate:propionate ratio than heifers with high RFI (GEI = 5.58 vs. 6.51 ± 0.08%; A:P ratio = 5.02 vs. 4.82 ± 0.14%). Stepwise regression analysis revealed that apparent nutrient digestibilities (DMD and NDF digestibility) for Study 1 and Study 2 accounted for an additional 8 and 6%, respectively, of the variation in intake unaccounted for by ADG and mid-test BW0.75. When DMD, NDF digestibility, and total ruminal VFA were added to the base model for Study 2, trials 2, 3, and 4, the R2 increased from 0.33 to 0.47, explaining an additional 15% of the variation in DMI unrelated to growth and body size. On the basis of the results of these studies, differences in observed phenotypic RFI in growing beef animals may be a result of inter-animal variation in apparent nutrient digestibility and ruminal VFA concentrations.

Paenibacillus 79R4, a potential rumen probiotic to enhance nitrite detoxification and methane mitigation in nitrate-treated ruminants

The effects of supplemental nitrate administered alone or with a denitrifying ruminal bacterium, designated Paenibacillus 79R4 (79R4) intentionally selected for enhanced nitrate- and nitrite-metabolizing ability, on select rumen fermentation characteristics was examined in vivo. Rumen and blood samples were collected from cannulated Holstein steers one day prior to and one day after initiation of treatments applied as three consecutive intra-ruminal administrations of nitrate, to achieve the equivalent of 83 mg sodium nitrate/kg body weight day, given alone or with the nitrite-selected 79R4 (provided to achieve 106 cells/mL rumen fluid). Results revealed a day effect on methane-producing activity, with rates of methane production by ruminal microbes being more rapid when collected one day before than one day after initiation of treatments. Nitrate-metabolizing activity of the rumen microbes was unaffected by day, treatment or their interaction. A day by treatment interaction was observed on nitrite-metabolizing activity, with rates of nitrite metabolism by rumen microbes being most rapid in populations collected one day after initiation of treatment from steers treated with nitrate plus 79R4. A day by treatment interaction was also observed on plasma methemoglobin concentrations, with concentrations being lower from steers one day after initiation of treatments than from collected one day prior to treatment initiation and concentrations being lowest in steers treated with nitrate plus 79R4. A major effect of treatment was observed on accumulations of most prominent and branched chain volatile fatty acids produced and amounts of hexose fermented in the rumen of animals administered nitrate, with concentrations being decreased in steers administered nitrate alone when compared to steers treated with nitrate plus the 79R4. These results demonstrate that the nitrite-selected Paenibacillus 79R4 may help prevent nitrite toxicity in nitrate-treated ruminants while maintaining benefits of reduced methane emissions and preventing inhibition of fermentation efficiency by the microbial ecosystem.

Evaluation of cation inhibition and adaptation based on microbial activity and community structure in anaerobic wastewater treatment under elevated saline concentration

Continuous flow and batch experiments were carried out under mesophilic conditions (35°C) to determine the effects of gradual increases in cation concentrations on specific methane producing activity (MPA) and microbial community structure in an upflow anaerobic sludge blanket (UASB) reactor fed with molasses wastewater for 300days. The cation inhibition assay based on MPA as a function of potassium concentration was performed using the retained sludge. The 50% inhibitory concentration for potassium was 600mM for H2/CO2 substrate, 300mM for acetate, and 280mM for propionate, and inhibition levels were clearly proportional to potassium concentration. The tolerance of retained sludge to potassium inhibition was not clearly changed from low to high saline conditions (day 59, 111, and 201). The 16S rRNA gene sequencing analysis revealed that Methanobacterium and Methanosaeta were the dominant archaea, and the archaeal community was not obviously changed at the genus level during operation.

Electrochemical control of redox potential affects methanogenesis of the hydrogenotrophic methanogen Methanothermobacter thermautotrophicus

To investigate the precise effect of the redox potential on the methanogenesis of the hydrogenotrophic methanogen Methanothermobacter thermautotrophicus by using an electrochemical redox controlling system without adding oxidizing or reducing agents. A bioelectrochemical system was applied to control the redox conditions in culture and to measure the methane-producing activity of M.thermautotrophicus at a constant potential from +0·2 to -0·8V (vs Ag/AgCl). Methane production and growth of M.thermautotrophicus were 1·6 and 3·5 times increased at -0·8V, compared with control experiments without electrolysis, respectively, while methanogenesis was suppressed between +0·2 and -0·2V. A clear relationship between an electrochemically regulated redox potential and methanogenesis was revealed.

Inhibition effects of heavy metals (copper, nickel, zinc, lead) on anaerobic sludge

The inhibition effects of heavy metals (Cu, Ni, Zn, Pb) on to anaerobic sludge were investigated using glucose (3000 mg/l COD) as carbon source and electron donor with a batch experiments (serum bottle assays). The seed sludge was obtained from a UASB (upflow anaerobic sludge blanket) reactor treating yeast wastewater of the Pakmaya Yeast Factory in izmit, Turkey. The heavy metal concentrations tested were copper (1–1000 mgCu/l), nickel (1–3000 mgNi/l), zinc (1–1000 mgZn/l, and lead (1–10,000 mgPb/l). According to relative inhibition effects of heavy metals on methane producing activity of anaerobic sludge and COD removal in serum bottles experiments during incubation time (12 d) were Cu(most toxic) > Ni ˜ Zn > Pb(least toxic). In general, cumulative methane production (ml) decreased with increasing heavy metal concentrations above 10 mg/l. Inhibition effects of heavy metal values (1–10 mg/l) were low on COD removal. Heavy metals measurements in influent and effluent of serum bottles were also compared. E...

Effects of dietary tannin source on performance, feed efficiency, ruminal fermentation, and carcass and non-carcass traits in steers fed a high-grain diet

The objective of this study, which was part of an integrated project to investigate the antimicrobial effects of dietary tannins on native food borne pathogens in beef cattle, was to examine the effects of source of tannin (condensed, CT, vs. hydrolysable, HT) on performance, feed efficiency, ruminal fermentation parameters, and carcass and non-carcass traits in finishing beef steers. Thirty-six crossbred steers averaging 414 ± 40 kg BW were stratified by initial BW and randomly assigned to one of three treatments: control (CN), CT, or HT tannins. Commercially available tannin extracts were added to a high-grain diet (ME = 11.9 MJ/kg DM) at 14.9 g/kg DM. Mimosa and chestnut extracts provided condensed tannin and hydrolysable tannin, respectively. Steers were individually fed using Calan gate feeders a high-grain diet. Rumen fluid was collected on days 0, 21, and 42 via stomach tube and analyzed for VFA and in vitro methane producing activity. Cattle were harvested at the end of the study and carcass data collected 24-h postharvest. There was no effect ( P>0.05) of tannin supplementation on animal performance, ruminal fermentation parameters, in vitro methane producing activity, or carcass and non-carcass traits, except for HCW, EBW, and rumen mass and empty GIT (g/kg EBW). Condensed tannin steers had 3.7% lower ( P<0.05) HCW compared to CN with HT steers having intermediate HCW. Hydrolysable tannin treated steers had 2.8% lower ( P<0.05) EBW compared to CN while CT steers had intermediate EBW; CT treated steers also had 15.2% higher ( P<0.05) rumen mass (g/kg EBW) compared to HT with CN steers being intermediate. This resulted in a 10.2% increase ( P<0.05) in total empty GIT (g/kg EBW) for HT steers compared to CT steers with CN steers bring intermediate. There was a treatment × day interaction for butyrate concentration. For steers fed CT, there was a linear increase in butyrate while the HT steers remained relatively stable and the control steers had numerically lower butyrate. Despite the significant interaction, treatment means on day 42 were not significantly different. Results indicate that neither source of dietary tannin affected performance and feed efficiency. There were no detrimental effects of tannins on other offal measured indicating that tannins supplementation may be a viable option in finishing beef cattle if bactericidal efficacy is established. More research is needed to further our understanding of how tannin supplementation may fit into real-life feedlot situations.

Changes in process performance and microbial characteristics of retained sludge during low-temperature operation of an EGSB reactor

A lab-scale expanded granular sludge bed (EGSB) reactor was seeded with granular sludge and operated to investigate the influence of temperature decrease on both process performance and the microbial community structure of the granular sludge. Synthetic wastewater containing sucrose and volatile fatty acids was used as feed. The EGSB reactor was brought online at a starting temperature of 15°C and was reduced stepwise to a final temperature of 5°C. The reactor exhibited sufficient COD removal efficiency between 10°C and 15°C. However at 5°C serious deterioration of process performance was observed. The methane-producing activity of the retained sludge increased when it was compared to the activity of the seed sludge (day 0) during 10°C to 15°C operation. When hydrogen fed, sludge showed much higher methanogenic activity as compared with seed sludge activity at test temperatures of 15°C and 20°C on day 196 of reactor operation. At this time, proliferation of the genus Methanospirillum in the retained sludge was observed and a decrease in Methanobacterium species was also measured. Throughout the experiment, the genus Methanosaeta was detected in abundance and the community structure of the Domain Bacteria was stably maintained. The sugar-degrading acid-forming bacteria, Lactococcus and Anaerovibrio were detected in the retained sludge throughout the experiment as well and the propionate-degrading acetogen Syntrophobacter fumaroxidans was also detected, although its population size decreased at 5°C.

Inhibitory effect of heavy metals on methane-producing anaerobic granular sludge

Heavy metals could potentially have a negative impact on methane-producing anaerobic granular sludge. The objective of this study was to investigate the inhibitory effect of zinc(II), chromium(VI), nickel(II), and cadmium(II) on the methane-producing activity of granular sludge sampled from the upflow anaerobic sludge blanket reactor that treats the wastewaters of a yeast factory, for a range of concentrations between 0 and 128 mg L −1. The modified Gompertz, Logistic, and Richards equations were applied to describe the inactivation of anaerobic culture by heavy metals. According to these models, the values of methane production potential (mL) for a heavy metal concentration of 128 mg L −1 were in the following order: Ni (44.82 ± 0.67) > Cd (28.73 ± 0.11) > Cr (15.52 ± 1.63) > Zn (0.65 ± 0.00). The IC 50 values, the metal concentrations that cause a 50% reduction in the cumulative methane production over a fixed period of exposure time (24 h), for the individual heavy metals were found to be in the following order: Zn (most toxic; 7.5 mg L −1) > Cr (27 mg L −1) > Ni (35 mg L −1) ≈ Cd (least toxic; 36 mg L −1).

Anaerobic Biochemical Treatment of Wastewater Containing Highly Concentrated Organic Cyanogen

The first and second stage of chilled wastewater in acrylic fibersitrile process and wastewater in acrylic fibers process are biodegraded under anaerobic conditions. Toxicity of acrylonitrile, acetonitrile, polymers, and cyanide in the wastewaters to the production of methane has been studied. Results suggest that the first and second stage chilled wastewaters from acrylonitrile process and wastewater from acrylic fibers process cannot be biodegraded well. CODBD of the first and second stage chilled wastewaters from acrylonitrile process is 36.3 and 45.8. CODBD of the wastewater from acrylic fibers process is 53.0. Acetonitrile, acrylonitrile, polymers, and cyanide are toxic to anaerobic bacteria in the highly concentrated organic cyanogens containing wastewater, inhibiting the methane-producing activity. Half inhibition concentration (50% IC) to anaerobic methane-producing activity is 1,300, 320, 85, and 50 mg/L for polymers, acetonitrile, acrylonitrile, and cyanide, respectively. Acrylonitrile is a metabolizing and physiological toxin, acetonitrile and polymers a metabolizing toxin, and cyanide a physiological and sterilizing toxin.

Zoonotic bacterial populations, gut fermentation characteristics and methane production in feedlot steers during oral nitroethane treatment and after the feeding of an experimental chlorate product

Nitroethane inhibits the growth of certain zoonotic pathogens such as Campylobacter and Salmonella spp., foodborne pathogens estimated to cause millions of human infections each year, and enhances the Salmonella- and Escherichia coli-killing effect of an experimental chlorate product being developed as a feed additive to kill these bacteria immediately pre-harvest. Limited studies have shown that nitroethane inhibits ruminal methane production, which represents a loss of 2–12% of the host's gross energy intake and contributes to global warming and destruction of the ozone layer. The present study was conducted to assess the effects of 14-day oral nitroethane administration, 0 (0X), 80 (1X) or 160 (2X) mg nitroethane/kg body weight per day on ruminal and fecal E. coli and Campylobacter, ruminal and fecal methane-producing and nitroethane-reducing activity, whole animal methane emissions, and ruminal and fecal fermentation balance in Holstein steers ( n = 6 per treatment) averaging 403±26 (SD) kg BW. An experimental chlorate product was fed the day following the last nitroethane administration to determine effects on E. coli and Campylobacter. The experimental chlorate product decreased ( P < 0.001 ) fecal, but not ruminal ( P > 0.05 ) E. coli concentrations by 1000- and 10-fold by 24 and 48 h, respectively, after chlorate feeding when compared to pre-treatment concentrations (>5.7 log 10 colony forming units/g). No effects ( P > 0.05 ) of nitroethane or the experimental chlorate product were observed on fecal Campylobacter concentrations; Campylobacter were not recovered from ruminal contents. Nitroethane treatment decreased ( P < 0.01 ) ruminal (8.46, 7.91 and 4.74±0.78 μmol/g/h) and fecal (3.90, 1.36 and 1.38±0.50 μmol/g/h) methane-producing activity for treatments 0X, 1X and 2X, respectively. Administration of nitroethane increased ( P < 0.001 ) nitroethane-reducing activity in ruminal, but not fecal samples. Day of study affected ruminal ( P < 0.0001 ) but not fecal ( P > 0.05 ) methane-producing and nitroethane-reducing activities ( P < 0.01 ); treatment by day interactions were not observed ( P > 0.05 ). Ruminal accumulations of acetate decreased ( P < 0.05 ) in 2X-treated steers when compared with 0X- and 1X-treated steers, but no effect ( P > 0.05 ) of nitroethane was observed on propionate, butyrate or the acetate to propionate ratio. Whole animal methane emissions, expressed as L/day or as a proportion of gross energy intake (%GEI), were unaffected by nitroethane treatment ( P > 0.05 ), and were not correlated ( P > 0.05 ) with ruminal methane-producing activity. These results demonstrate that oral nitroethane administration reduces ruminal methane-producing activity but suggest that a microbial adaptation, likely due to an in situ enrichment of ruminal nitroethane-reducing bacteria, may cause depletion of nitroethane, at least at the 1X administration dose, to concentrations too low to be effective. Further research is warranted to determine if the optimization of dosage of nitroethane or related nitrocompouds can maintain the enteropathogen control and anti-methanogen effect in fed steers.

Feasibility study of a pilot-scale sewage treatment system combining an up-flow anaerobic sludge blanket (UASB) and an aerated fixed bed (AFB) reactor at ambient temperature

A feasibility test of a 17 m 3-pilot-scale sewage treatment system was carried out by continuous feeding of raw municipal sewage under ambient temperature conditions. The system consisted of a UASB and an aerated fixed bed reactor. Some of the effluent from the fixed bed reactor was returned to the UASB influent in order to provide a sulfate source. The total BOD of 148–162 mg l −1 in the influent was reduced to a more desirable 11–25 mg l −1 in the final effluent. The levels of methane-producing activity from acetate and H 2/CO 2 gas at 10 °C were only 2% and 0% of those at 35 °C, respectively. On the other hand, the sulfate-reducing activity levels of the UASB sludge were relatively high at 10 °C, for example, 18% for acetate and 9% for H 2/CO 2 gas, compared to the activity levels at 35 °C. Therefore, BOD oxidization by sulfate reduction in the UASB was greater than that by methane production under low temperature conditions. This sulfate-reducing activity tended to be proportional to the copy number of adenosine-5′-phosphosulfate (APS) reductase genes in DNA extracted from the sludge.

Effect of oral nitroethane and 2-nitropropanol administration on methane-producing activity and volatile fatty acid production in the ovine rumen

Strategies are sought to reduce economic and environmental costs associated with ruminant methane emissions. The effect of oral nitroethane or 2-nitropropanol administration on ruminal methane-producing activity and volatile fatty acid production was evaluated in mature ewes. Daily administration of 24 and 72 mg nitroethane/kg body weight reduced ( P < 0.05) methane-producing activity by as much as 45% and 69% respectively, when compared to control animals given no nitroethane. A daily dose of 120 mg 2-nitropropanol/kg body weight was needed to reduce ( P < 0.05) methane-producing activity by 37% from that of untreated control animals. Reductions in methane-producing activity may have been diminished by the last day (day 5) of treatment, presumably due to ruminal adaptation. Oral administration of nitroethane or 2-nitropropanol had little or no effect on accumulations or molar proportions of volatile fatty acids in ruminal contents collected from the sheep. These results demonstrate that nitroethane was superior to 2-nitropropanol as a methane inhibitor and that both nitrocompounds reduced ruminal methanogenesis in vivo without redirecting the flow of reductant generated during fermentation to propionate and butyrate.

Performance and characteristics of an anaerobic baffled reactor

The performance and the characteristics of a laboratory scale anaerobic baffled reactor (ABR) were investigated using synthetic wastewater. The experimental results showed that among different volatile fatty acids (VFAs), acetate was the main intermediate of acidogenic degradation of glucose. The VFA concentration decreased longitudinally down the reactor. The analysis of the biogas composition revealed that methane concentration increased steadily from compartment 1 to 5, while hydrogen content decreased in the first compartments. There was no detectable hydrogen in the last two compartments. The methane-producing activity of anaerobic sludge in different compartments depended on the substrate, which suggests that the proper anaerobic consortium in each separate compartment was developed according to the substrate(s) availability and the specific environmental conditions. The ABR has the potential to provide a higher efficiency at higher loading rates and be applicable for extreme environmental conditions and inhibitory compounds.

Nitrogen management in bioreactor landfills

One scenario for long-term nitrogen management in landfills is ex situ nitrification followed by denitrification in the landfill. The objective of this research was to measure the denitrification potential of actively decomposing and well decomposed refuse. A series of 10-l reactors that were actively producing methane were fed 400 mg NO 3-N /l every 48 h for periods of 19–59 days. Up to 29 nitrate additions were either completely or largely depleted within 48 h of addition and the denitrification reactions did not adversely affect the leachate pH. Nitrate did inhibit methane production, but the reactors recovered their methane-producing activity with the termination of nitrate addition. In well decomposed refuse, the nitrate consumption rate was reduced but was easily stimulated by the addition of either acetate or an overlayer of fresh refuse. Addition of acetate at five times the amount required to reduce nitrate did not lead to the production of NH 4 + by dissimilatory nitrate reduction. The most probable number of denitrifying bacteria decreased by about five orders of magnitude during refuse decomposition in a reactor that did not receive nitrate. However, rapid denitrification commenced immediately with nitrate addition. This study shows that the use of a landfill as a bioreactor for the conversion of nitrate to a harmless byproduct, nitrogen gas, is technically viable.

高級脂肪酸の嫌気的分解過程における硫酸塩還元細菌とメタン生成細菌の基質競合

Competitive interaction between sulfate-reducing bacteria (SRB) and methane producing bacteria (MPB) for hydrogen and for acetate in anaerobic degradation of long chain fatty acids (LFAs) was investigated using two different sludge consortia: the one (referred to as R1) grown in a sulfate-free medium and the other (R2) in a sulfate-rich medium. Both sludges were cultivated in parallel for six months in a fill-and-draw mode on palmitate (C 16, saturated LFA).R1 sludge finally reached a very low sulfate-reducing activity (SRA, 0.019 gCOD·gVSS-1·d-1) and a very high methaneproducing activity (MPA, 10.1 gCOD·gVSS-1·d-1) for hydrogen-fed vial test: the ratio of SRA/MPA (both on the basis of COD equivalent) was only 0.0019. On the contrary, R2 sludge was characterized by a high hydrogen-fed SRA (1.15 gCOD·gVSS-1·d-1) and by a low hydrogen-fed MPA (0.0093 gCOD·gVSS-1·d-1): the SRA/MPA ratio was 123. The results of hydrogen-trophic MPN enumeration showed a similar tendency: the SRB/MPB ratios were 1/103.6 and 102.0 for R1 and R2 sludge, respectively. Therefore, degradation of palmitate into acetate was performed by a symbiosis between proton-reducing acetogenic bacteria (PRB) and MPB in R1 sludge, whereas by a syntrophic association between PRB and SRB in R2 sludge.

Characterization of thermophilic consortia from two souring oil reservoirs

The microbial consortia from produced water at two different oil fields in Alaska (Kuparuk) and the North Sea (Ninian) were investigated for sulfate-reducing and methanogenic activity over a range of temperatures and for a variety of substrates. The consortia were sampled on site, and samples were either incubated on site at 60(deg)C with various substrates or frozen for later incubation and analyses. Temperature influenced the rates of sulfate reduction, hydrogen sulfide production, and substrate oxidation, as well as the cell morphology. The highest rates of sulfate reduction and substrate oxidation were found between 50 and 60(deg)C. Formate and n-butyrate were the most favorable electron donors at any tested temperature. Acetate was utilized at 35(deg)C but not at 50 or 70(deg)C and was produced at 60(deg)C. This indicates that the high levels of acetate found in produced water from souring oil formations are due mainly to an incomplete oxidation of volatile fatty acids to acetate. The cell size distribution of the microbial consortium indicated a nonuniform microbial composition in the original sample from the Kuparuk field. At different temperatures, different microbial morphologies and physiologies were observed. Methane-producing activity at thermophilic temperatures (60(deg)C) was found only for the Kuparuk consortium when hydrogen and carbon dioxide were present. No methane production from acetate was observed. Suppression of methanogenic activity in the presence of sulfate indicated a competition with sulfate-reducing bacteria for hydrogen.

ＵＡＳＢ型リアクターによるパン酵母培養廃水の処理特性

The long-term stable anaerobic treatment system at high organic loading rates for molasses wastewater has been investigated. Especially, the effectiveness of pretreatment, in which the molasses wastewater was evaporated under reduced pressure, has been evaluated. Furthermore, the competition between methane producing bacteria and sulfate reducing bacteria has been investigated.A UASB reactor with an effective volume of 10m3 was used.SO42- and K+ concentrations in the molasses, which at high level have inhibitory effects on an anaerobic treatment, could he reduced to 80% or more by the pretreatment. Owing to the pretreatment, the treatment perfommance was excellent with 60-70% removal of CODcr and 90% or more removal of BOD at the CODcr loading rate as high as 25-30 kg·m-3·d-1,The vial activity test results show that the methane producing activity is highly affected by the operating CODcr loading rates of the reactor. The methane producing activity, operating at CODcr loading rates of 10kg·m-3·d-1, has been compared with that of 28kg·m-3·d-1 rates, and a 2.4 times activity increase has been observed.Of the total removed CODcr, 94% had been used in the methane producing reaction and 4% in the sulfide producing reaction. Of the total electron flow, 92% was utilized by methane producing bacteria and 8% by sulfate reducing bacteria. It has been revealed that i) the methane producing reaction was actively undertaken, ii) the sulfide level in the reactor had hardly any inhibitory effects on the methne producing reaction, and iii) there was hardly any competition between methane producing bacteria and sulfate reducing bacteria.