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1.
The effects of temperature on rates and pathways of CH4 production and on the abundance and structure of the archaeal community were investigated in acidic peat from a mire in northern Scandinavia (68°N). We monitored the production of CH4 and CO2 over time and measured the turnover of Fe(II), ethanol, and organic acids. All experiments were performed with and without specific inhibitors (2-bromoethanesulfonate [BES] for methanogenesis and CH3F for acetoclastic methanogenesis). The optimum temperature for methanogenesis was 25°C (2.3 μmol CH4 · g [dry weight]−1 · day−1), but the activity was relatively high even at 4°C (0.25 μmol CH4 · g [dry weight]−1 · day−1). The theoretical lower limit for methanogenesis was calculated to be at −5°C. The optimum temperature for growth as revealed by real-time PCR was 25°C for both archaea and bacteria. The population structure of archaea was studied by terminal restriction fragment length polymorphism analysis and remained constant over a wide temperature range. Hydrogenotrophic methanogenesis accounted for about 80% of the total methanogenesis. Most 16S rRNA gene sequences that were affiliated with methanogens and all McrA sequences clustered with the exclusively hydrogenotrophic order Methanobacteriales, correlating with the prevalence of hydrogenotrophic methanogenesis. Fe reduction occurred parallel to methanogenesis and was inhibited by BES, suggesting that methanogens were involved in Fe reduction. Based upon the observed balance of substrates and thermodynamic calculations, we concluded that the ethanol pool was oxidized to acetate by the following two processes: syntrophic oxidation with methanogenesis (i) as an H2 sink and (ii) as a reductant for Fe(III). Acetate accumulated, but a considerable fraction was converted to butyrate, making volatile fatty acids important end products of anaerobic metabolism.  相似文献   

2.
Mixed-Culture Fermentor for Simulating Methanogenic Digestors   总被引:7,自引:6,他引:1       下载免费PDF全文
Propionate degradation in an anaerobic digestor degrading animal waste (10-day retention time, 5.75 g liter−1 day−1 volatile solids loading rate, 40°C) was 0.304 mM h−1, measured with [2-14C]propionate; this value indicated that CH4 produced from propionate accounted for 14.8% of the CH4 produced in the digestor (34.5%, including acetate produced from propionate). The mean propionate concentration was 0.67 mM, giving a propionate turnover rate of 0.46 h−1. A continuous-, mixed-culture fermentor was developed to mimic the digestor. When degradation rates of methanogenic precursors (H2, CO2, and acetate) equalled those measured in the digestor, propionate degradation was inhibited. When the H2 turnover rate was lowered by decreasing addition of H2-generating substrates or by allowing a portion of the H2 degradation to occur in an isolated compartment, propionate degradation in the fermentor resumed. The possibility is discussed that in digestors, much of the H2 is produced and degraded within microenvironments associated with particles. Thus, the gross turnover rate of H2 measured in digestors is an average, and specific microenvironments within the digestor may have different rates of turnover.  相似文献   

3.
The emission of methane (1.3 mmol of CH4 m−2 day−1), precursors of methanogenesis, and the methanogenic microorganisms of acidic bog peat (pH 4.4) from a moderately reduced forest site were investigated by in situ measurements, microcosm incubations, and cultivation methods, respectively. Bog peat produced CH4 (0.4 to 1.7 μmol g [dry wt] of soil−1 day−1) under anoxic conditions. At in situ pH, supplemental H2-CO2, ethanol, and 1-propanol all increased CH4 production rates while formate, acetate, propionate, and butyrate inhibited the production of CH4; methanol had no effect. H2-dependent acetogenesis occurred in H2-CO2-supplemented bog peat only after extended incubation periods. Nonsupplemented bog peat initially produced small amounts of H2 that were subsequently consumed. The accumulation of H2 was stimulated by ethanol and 1-propanol or by inhibiting methanogenesis with bromoethanesulfonate, and the consumption of ethanol was inhibited by large amounts of H2; these results collectively indicated that ethanol- or 1-propanol-utilizing bacteria were trophically associated with H2-utilizing methanogens. A total of 109 anaerobes and 107 hydrogenotrophic methanogens per g (dry weight) of bog peat were enumerated by cultivation techniques. A stable methanogenic enrichment was obtained with an acidic, H2-CO2-supplemented, fatty acid-enriched defined medium. CH4 production rates by the enrichment were similar at pH 4.5 and 6.5, and acetate inhibited methanogenesis at pH 4.5 but not at pH 6.5. A total of 27 different archaeal 16S rRNA gene sequences indicative of Methanobacteriaceae, Methanomicrobiales, and Methanosarcinaceae were retrieved from the highest CH4-positive serial dilutions of bog peat and methanogenic enrichments. A total of 10 bacterial 16S rRNA gene sequences were also retrieved from the same dilutions and enrichments and were indicative of bacteria that might be responsible for the production of H2 that could be used by hydrogenotrophic methanogens. These results indicated that in this acidic bog peat, (i) H2 is an important substrate for acid-tolerant methanogens, (ii) interspecies hydrogen transfer is involved in the degradation of organic carbon, (iii) the accumulation of protonated volatile fatty acids inhibits methanogenesis, and (iv) methanogenesis might be due to the activities of methanogens that are phylogenetic members of the Methanobacteriaceae, Methanomicrobiales, and Methanosarcinaceae.  相似文献   

4.
The addition of 20 mM MoO42− (molybdate) to a reduced marine sediment completely inhibited the SO42− reduction activity by about 50 nmol g−1 h−1 (wet sediment). Acetate accumulated at a constant rate of about 25 nmol g−1 h−1 immediately after MoO42− addition and gave a measure of the preceding utilization rate of acetate by the SO42−-reducing bacteria. Similarly, propionate and butyrate (including isobutyrate) accumulated at constant rates of 3 to 7 and 2 to 4 nmol g−1 h−1, respectively. The rate of H2 accumulation was variable, and a range of 0 to 16 nmol g−1 h−1 was recorded. An immediate increase of the methanogenic activity by 2 to 3 nmol g−1 h−1 was apparently due to a release of the competition for H2 by the absence of SO42− reduction. If propionate and butyrate were completely oxidized by the SO42−-reducing bacteria, the stoichiometry of the reactions would indicate that H2, acetate, propionate, and butyrate account for 5 to 10, 40 to 50, 10 to 20, and 10 to 20%, respectively, of the electron donors for the SO42−-reducing bacteria. If the oxidations were incomplete, however, the contributions by propionate and butyrate would only be 5 to 10% each, and the acetate could account for as much as two-thirds of the SO42− reduction. The presence of MoO42− seemed not to affect the fermentative and methanogenic activities; an MoO42− inhibition technique seems promising in the search for the natural substrates of SO42− reduction in sediments.  相似文献   

5.
6.
An investigation of the terminal anaerobic processes occurring in polluted intertidal sediments indicated that terminal carbon flow was mainly mediated by sulfate-reducing organisms in sediments with high sulfate concentrations (>10 mM in the interstitial water) exposed to low loadings of nutrient (equivalent to <102 kg of N · day−1) and biochemical oxygen demand (<0.7 × 103 kg · day−1) in effluents from different pollution sources. However, in sediments exposed to high loadings of nutrient (>102 kg of N · day−1) and biochemical oxygen demand (>0.7 × 103 kg · day−1), methanogenesis was the major process in the mediation of terminal carbon flow, and sulfate concentrations were low (≤2 mM). The respiratory index [14CO2/(14CO2 + 14CH4)] for [2-14C]acetate catabolism, a measure of terminal carbon flow, was ≥0.96 for sediment with high sulfate, but in sediments with sulfate as little as 10 μM in the interstitial water, respiratory index values of ≤0.22 were obtained. In the latter sediment, methane production rates as high as 3 μmol · g−1 (dry weight) · h−1 were obtained, and there was a potential for active sulfate reduction.  相似文献   

7.
Rapid Methane Oxidation in a Landfill Cover Soil   总被引:28,自引:5,他引:28       下载免费PDF全文
Methane oxidation rates observed in a topsoil covering a retired landfill are the highest reported (45 g m−2 day−1) for any environment. This microbial community had the capacity to rapidly oxidize CH4 at concentrations ranging from <1 ppm (microliters per liter) (first-order rate constant [k] = −0.54 h−1) to >104 ppm (k = −2.37 h−1). The physiological characteristics of a methanotroph isolated from the soil (characteristics determined in aqueous medium) and the natural population, however, were similar to those of other natural populations and cultures: the Q10 and optimum temperature were 1.9 and 31°C, respectively, the apparent half-saturation constant was 2.5 to 9.3 μM, and 19 to 69% of oxidized CH4 was assimilated into biomass. The CH4 oxidation rate of this soil under waterlogged (41% [wt/vol] H2O) conditions, 6.1 mg liter−1 day−1, was near rates reported for lake sediment and much lower than the rate of 116 mg liter−1 day−1 in the same soil under moist (11% H2O) conditions. Since there are no large physiological differences between this microbial community and other CH4 oxidizers, we attribute the high CH4 oxidation rate in moist soil to enhanced CH4 transport to the microorganisms; gas-phase molecular diffusion is 104-fold faster than aqueous diffusion. These high CH4 oxidation rates in moist soil have implications that are important in global climate change. Soil CH4 oxidation could become a negative feedback to atmospheric CH4 increases (and warming) in areas that are presently waterlogged but are projected to undergo a reduction in summer soil moisture.  相似文献   

8.
Methanogenesis was studied using stirred, bench-top fermentors of 3-1 working volume fed on a semi-continuous basis with waste obtained from cattle fed a high grain, finishing diet. Digestion was carried out at 40 and 60°C. CH4 production was 11.8, 18.3, 61.9 and 84.5% higher in the thermophilic than the mesophilic digestor at the 3, 6, 9 and 12 g volatile solids (VS) l–1 reactor volume loading rates, respectively. When compared on an energetic basis CH4 production was 7.4, 18.3, 72.9 and 107.3 kJ day higher in the thermophilic than the mesophilic digestor. CH4 production decreased more rapidly with each increase in VS loading rate and decrease in retention time (RT) in the mesophilic than the thermophilic digestor. When expressed as l g–1 VS fed or as kJ kJ–1 fed, the amount of CH4 was 49% less at the highest compared to the lowest loading rate in the mesophilic digestor. In the thermophilic digestor the decrease was only 16%. Propionate accumulated in the mesophilic digestor at the two highest loading rates, reaching concentrations of about 50 mM, but were only about 13 mM in the thermophilic digestor. Isobutyrate, isovalerate plus 2-methylbutyrate, and valerate also accumulated at the higher loading rates.  相似文献   

9.
The effects of 2-bromoethanesulfonate, an inhibitor of methanogenesis, on metabolism in sludge from a thermophilic (58°C) anaerobic digestor were studied. It was found from short-term experiments that 1 μmol of 2-bromoethanesulfonate per ml completely inhibited methanogenesis from 14CH3COO, whereas 50 μmol/ml was required for complete inhibition of 14CO2 reduction. When 1 μmol of 2-bromoethanesulfonate per ml was added to actively metabolizing sludge which was then incubated for 24 h. it caused a 60% reduction in methanogenesis and a corresponding increase in acetate accumulation; at 50 μmol/ml it caused complete inhibition of methanogenesis and accumulation of acetate. H2, and ethanol.  相似文献   

10.
A study of anaerobic sediments below cyanobacterial mats of a low-salinity meltwater pond called Orange Pond on the McMurdo Ice Shelf at temperatures simulating those in the summer season (<5°C) revealed that both sulfate reduction and methane production were important terminal anaerobic processes. Addition of [2-14C]acetate to sediment samples resulted in the passage of label mainly to CO2. Acetate addition (0 to 27 mM) had little effect on methanogenesis (a 1.1-fold increase), and while the rate of acetate dissimilation was greater than the rate of methane production (6.4 nmol cm−3 h−1 compared to 2.5 to 6 nmol cm−3 h−1), the portion of methane production attributed to acetate cleavage was <2%. Substantial increases in the methane production rate were observed with H2 (2.4-fold), and H2 uptake was totally accounted for by methane production under physiological conditions. Formate also stimulated methane production (twofold), presumably through H2 release mediated through hydrogen lyase. Addition of sulfate up to 50-fold the natural levels in the sediment (interstitial concentration, ~0.3 mM) did not substantially inhibit methanogenesis, but the process was inhibited by 50-fold chloride (36 mM). No net rate of methane oxidation was observed when sediments were incubated anaerobically, and denitrification rates were substantially lower than rates for sulfate reduction and methanogenesis. The results indicate that carbon flow from acetate is coupled mainly to sulfate reduction and that methane is largely generated from H2 and CO2 where chloride, but not sulfate, has a modulating role. Rates of methanogenesis at in situ temperatures were four- to fivefold less than maximal rates found at 20°C.  相似文献   

11.
Methanogenic activity was investigated in a petroleum hydrocarbon-contaminated aquifer by using a series of four push-pull tests with acetate, formate, H2 plus CO2, or methanol to target different groups of methanogenic Archaea. Furthermore, the community composition of methanogens in water and aquifer material was explored by molecular analyses, i.e., fluorescence in situ hybridization (FISH), denaturing gradient gel electrophoresis (DGGE) of 16S rRNA genes amplified with the Archaea-specific primer set ARCH915 and UNI-b-rev, and sequencing of DNA from dominant DGGE bands. Molecular analyses were subsequently compared with push-pull test data. Methane was produced in all tests except for a separate test where 2-bromoethanesulfonate, a specific inhibitor of methanogens, was added. Substrate consumption rates were 0.11 mM day−1 for methanol, 0.38 mM day−1 for acetate, 0.90 mM day−1 for H2, and 1.85 mM day−1 for formate. Substrate consumption and CH4 production during all tests suggested that at least three different physiologic types of methanogens were present: H2 plus CO2 or formate, acetate, and methanol utilizers. The presence of 15 to 20 bands in DGGE profiles indicated a diverse archaeal population. High H2 and formate consumption rates agreed with a high diversity of methanogenic Archaea consuming these substrates (16S rRNA gene sequences related to several members of the Methanomicrobiaceae) and the detection of Methanomicrobiaceae by using FISH (1.4% of total DAPI [4′,6-diamidino-2-phenylindole]-stained microorganisms in one water sample; probe MG1200). Considerable acetate consumption agreed with the presence of sequences related to the obligate acetate degrader Methanosaeata concilii and the detection of this species by FISH (5 to 22% of total microorganisms; probe Rotcl1). The results suggest that both aceticlastic and CO2-type substrate-consuming methanogens are likely involved in the terminal step of hydrocarbon degradation, while methanogenesis from methanol plays a minor role. DGGE profiles further indicate similar archaeal community compositions in water and aquifer material. The combination of hydrogeological and molecular methods employed in this study provide improved information on the community and the potential activity of methanogens in a petroleum hydrocarbon-contaminated aquifer.  相似文献   

12.
Methane production in meromictic Ace Lake,Antarctica   总被引:3,自引:0,他引:3  
Methane occurred in the monimolimnion, at depths greater than 11 m, of an antarctic meromictic lake, Ace Lake (depth 24.7 m). Although the water of the lake was of approximate marine salinity, bottom waters were depleted in sulfate (less than 1 mmol 1–1). The temperature of the bottom waters of the lake were constantly between 1 °C and 2 °C. Rates of methanogenesis from 14C-labelled precursors (bicarbonate, formate and acetate) were determined in time course experiments with the detection of 14CH4 produced by a gas chromatography-gas proportional counting system. Rates of 14CH4 production were difficult to determine as the reactions were always near our limit of detection.Reliable determinations of rates of methanogenesis at some depths using some precursors were obtained, the fastest rate being 2.5 µmol kg–1 day–1 at depth 20 m. Assuming constant rates of methanogenesis with time, this would equate to a turnover of methane in the lake every two years.The slow rate of methanogenesis suggests that the methanogens in Ace Lake may be working at well below their optimum temperature although definitive statements regarding the presence of psychrophilic methanogens in this antarctic lake must await isolation attempts or longer field studies using alternative methodologies.  相似文献   

13.
Freshwater macroalgae represent a largely overlooked group of phototrophic organisms that could play an important role within an industrial ecology context in both utilising waste nutrients and water and supplying biomass for animal feeds and renewable chemicals and fuels. This study used water from the intensive aquaculture of freshwater fish (Barramundi) to examine how the biomass production rate and protein content of the freshwater macroalga Oedogonium responds to increasing the flux of nutrients and carbon, by either increasing water exchange rates or through the addition of supplementary nitrogen and CO2. Biomass production rates were highest at low flow rates (0.1–1 vol.day−1) using raw pond water. The addition of CO2 to cultures increased biomass production rates by between 2 and 25% with this effect strongest at low water exchange rates. Paradoxically, the addition of nitrogen to cultures decreased productivity, especially at low water exchange rates. The optimal culture of Oedogonium occurred at flow rates of between 0.5–1 vol.day−1, where uptake rates peaked at 1.09 g.m−2.day−1 for nitrogen and 0.13 g.m−2.day−1 for phosphorous. At these flow rates Oedogonium biomass had uptake efficiencies of 75.2% for nitrogen and 22.1% for phosphorous. In this study a nitrogen flux of 1.45 g.m−2.day−1 and a phosphorous flux of 0.6 g.m−2.day−1 was the minimum required to maintain the growth of Oedogonium at 16–17 g DW.m−2.day−1 and a crude protein content of 25%. A simple model of minimum inputs shows that for every gram of dry weight biomass production (g DW.m−2.day−1), Oedogonium requires 0.09 g.m−2.day−1 of nitrogen and 0.04 g.m−2.day−1 of phosphorous to maintain growth without nutrient limitation whilst simultaneously maintaining a high-nutrient uptake rate and efficiency. As such the integrated culture of freshwater macroalgae with aquaculture for the purposes of nutrient recovery is a feasible solution for the bioremediation of wastewater and the supply of a protein resource.  相似文献   

14.
Summary The continuous and simultaneous monitoring of dissolved CH4 and H2 in samples from a laboratory scale thermophilic anaerobic digester contents by use of a silicone rubber-covered probe has enabled control of methanogenesis: regulation of the hydrogen signal in a closed feedback loop was by controlled addition of the carbon source. Dissolved hydrogen became apparent in this system at a lower loading rate than was obtained for a mesophilic anaerobic digestion system (Whitmoreet al., 1986). Controlling the supply of glucose (25 mM) at a dilution rate of 0.02 h–1 and at progressively lower preset hydrogen levels allowed methanogenesis to be significantly prolonged before inhibition of the process occurred.  相似文献   

15.
Propionate consumption was studied in syntrophic batch and chemostat cocultures of Syntrophobacter fumaroxidans and Methanospirillum hungatei. The Gibbs free energy available for the H2-consuming methanogens was <−20 kJ mol of CH4−1 and thus allowed the synthesis of 1/3 mol of ATP per reaction. The Gibbs free energy available for the propionate oxidizer, on the other hand, was usually >−10 kJ mol of propionate−1. Nevertheless, the syntrophic coculture grew in the chemostat at steady-state rates of 0.04 to 0.07 day−1 and produced maximum biomass yields of 2.6 g mol of propionate−1 and 7.6 g mol of CH4−1 for S. fumaroxidans and M. hungatei, respectively. The energy efficiency for syntrophic growth of S. fumaroxidans, i.e., the biomass produced per unit of available Gibbs free energy was comparable to a theoretical growth yield of 5 to 12 g mol of ATP−1. However, a lower growth efficiency was observed when sulfate served as an additional electron acceptor, suggesting inefficient energy conservation in the presence of sulfate. The maintenance Gibbs free energy determined from the maintenance coefficient of syntrophically grown S. fumaroxidans was surprisingly low (0.14 kJ h−1 mol of biomass C−1) compared to the theoretical value. On the other hand, the Gibbs free-energy dissipation per mole of biomass C produced was much higher than expected. We conclude that the small Gibbs free energy available in many methanogenic environments is sufficient for syntrophic propionate oxidizers to survive on a Gibbs free energy that is much lower than that theoretically predicted.  相似文献   

16.
Studies on product inhibition of a thermophilic butyrate-degrading bacterium in syntrophic association with Methanobacterium thermoautotrophicum showed that a gas phase containing more than 2 × 10−2 atm (2.03 kPa) of hydrogen prevented growth and butyrate consumption, while a lower hydrogen partial pressure of 1 × 10−3 to 2 × 10−2 atm (0.1 to 2.03 kPa) gradually inhibited the butyrate consumption of the coculture. No inhibition of butyrate consumption was found on the addition of 0.75 × 10−3 atm (76 Pa) of hydrogen to the gas phase. A slight inhibition of butyrate consumption by the coculture occurred at an acetate concentration of 16.4 mM. Inhibition gradually increased with increasing acetate concentration up to 81.4 mM, when complete inhibition of butyrate consumption occurred. When the culture contained an acetate-utilizing methanogen in addition to M. thermoautotrophicum, the inhibition of the triculture by acetate was gradually reversed as the acetate concentration was lowered by the aceticlastic methanogen. The results show that optimal growth conditions for the thermophilic butyrate-degrading bacterium depend on both hydrogen and acetate removal.  相似文献   

17.
The denitrification rates in a marine sediment, estimated by using 15N-nitrate, Vmax, Km, and sediment nitrate concentrations, were 12.5 and 2.0 nmol of N2-N cm−3 day−1 at 0 to 1 and 1 to 3 cm, respectively, at 12°C. The total rate was 165 nmol of N2-N m−2 day−1.  相似文献   

18.
Microbial Methanogenesis and Acetate Metabolism in a Meromictic Lake   总被引:10,自引:8,他引:2       下载免费PDF全文
Methanogenesis and the anaerobic metabolism of acetate were examined in the sediment and water column of Knaack Lake, a small biogenic meromictic lake located in central Wisconsin. The lake was sharply stratified during the summer and was anaerobic below a depth of 3 m. Large concentrations (4,000 μmol/liter) of dissolved methane were detected in the bottom waters. A methane concentration maximum occurred at 4 m above the sediment. The production of 14CH4 from 14C-labeled HCOOH, HCO3, and CH3OH and [2-14C]acetate demonstrated microbial methanogenesis in the water column of the lake. The maximum rate of methanogenesis calculated from reduction of H14CO3 by endogenous electron donors in the surface sediment (depth, 22 m) was 7.6 nmol/h per 10 ml and in the water column (depth, 21 m) was 0.6 nmol/h per 10 ml. The methyl group of acetate was simultaneously metabolized to CH4 and CO2 in the anaerobic portions of the lake. Acetate oxidation was greatest in surface waters and decreased with water depth. Acetate was metabolized primarily to methane in the sediments and water immediately above the sediment. Sulfide inhibition studies and temperature activity profiles demonstrated that acetate metabolism was performed by several microbial populations. Sulfide additions (less than 5 μg/ml) to water from 21.5 m stimulated methanogenesis from acetate, but inhibited CO2 production. Sulfate addition (1 mM) had no significant effect on acetate metabolism in water from 21.5 m, whereas nitrate additions (10 to 14,000 μg/liter) completely inhibited methanogenesis and stimulated CO2 formation.  相似文献   

19.
Methane Metabolism in a Temperate Swamp   总被引:4,自引:1,他引:3       下载免费PDF全文
Comparisons between in situ CH4 concentration and potential factors controlling its net production were made in a temperate swamp. Seasonal measurements of water table level and depth profiles of pH, dissolved CH4, CO2, O2, SO42-, NO3-, formate, acetate, propionate, and butyrate were made at two adjacent sites 1.5 to 2 m apart. Dissolved CH4 was inversely correlated to O2 and, in general, to NO3- and SO42-, potential inhibitors of methanogenesis. At low water table levels (August 1992), maximal CH4 (2 to 4 μM) occurred below 30 cm, whereas at high water table levels (October 1992) or under flooded conditions (May 1993), CH4 maxima (4 to 55 μM) occurred in the top 10 to 20 cm. Higher CH4 concentrations were likely supported by inputs of fresh organic matter from decaying leaf litter, as suggested by high acetate and propionate concentrations (25 to 100 μM) in one of the sites in fall and spring. Measurements of potential CH4 production (and consumption) showed that the highest rates generally occurred in the top 10 cm of soil. Soil slurry incubations confirmed the importance of organic matter to CH4 production but also showed that competition for substrates by nonmethanogenic microorganisms could greatly attenuate its effect.  相似文献   

20.
High-Rate Anaerobic Treatment of Wastewater at Low Temperatures   总被引:2,自引:0,他引:2       下载免费PDF全文
Anaerobic treatment of a volatile fatty acid (VFA) mixture was investigated under psychrophilic (3 to 8°C) conditions in two laboratory-scale expanded granular sludge bed reactor stages in series. The reactor system was seeded with mesophilic methanogenic granular sludge and fed with a mixture of VFAs. Good removal of fatty acids was achieved in the two-stage system. Relative high levels of propionate were present in the effluent of the first stage, but propionate was efficiently removed in the second stage, where a low hydrogen partial pressure and a low acetate concentration were advantageous for propionate oxidation. The specific VFA-degrading activities of the sludge in each of the modules doubled during system operation for 150 days, indicating a good enrichment of methanogens and proton-reducing acetogenic bacteria at such low temperatures. The specific degradation rates of butyrate, propionate, and the VFA mixture amounted to 0.139, 0.110, and 0.214 g of chemical oxygen demand g of volatile suspended solids−1 day−1, respectively. The biomass which was obtained after 1.5 years still had a temperature optimum of between 30 and 40°C.  相似文献   

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