共查询到20条相似文献,搜索用时 906 毫秒
1.
The effects of crude glycerol on the performance of single-stage anaerobic reactors treating different types of organic waste were examined. A reactor treating the organic fraction of municipal solid waste produced 1400 mL CH 4/d before the addition of glycerol and 2094 mL CH 4/d after the addition of glycerol. An enhanced methane production rate was also observed when a 1:4 mixture of olive mill wastewater and slaughterhouse wastewater was supplemented with crude glycerol. Specifically, by adding 1% v/v crude glycerol to the feed, the methane production rate increased from 479 mL/d to 1210 mL/d. The extra glycerol-COD added to the feed did not have a negative effect on the reactor performance in either case. Supplementation of the feed with crude glycerol also had a significant positive effect on anaerobic fermentation reactors. Hydrogen yield was 26 mmole H 2/g VS added and 15 mmole H 2/g VS added in a reactor treating the organic fraction of municipal solid waste and a 1:4 mixture of olive mill and slaughterhouse wastewater. The addition of crude glycerol to the feed enhanced hydrogen yield at 2.9 mmole H 2/g glycerol added and 0.7 mmole H 2/g glycerol added. 相似文献
2.
Methane, a non-expensive natural substrate, is used by Methylocystis spp. as a sole source of carbon and energy. Here, we assessed whether Methylocystis sp. strain SC2 is able to also utilize hydrogen as an energy source. The addition of 2% H 2 to the culture headspace had the most significant positive effect on the growth yield under CH 4 (6%) and O 2 (3%) limited conditions. The SC2 biomass yield doubled from 6.41 (±0.52) to 13.82 (±0.69) mg cell dry weight per mmol CH 4, while CH 4 consumption was significantly reduced. Regardless of H 2 addition, CH 4 utilization was increasingly redirected from respiration to fermentation-based pathways with decreasing O 2/CH 4 mixing ratios. Theoretical thermodynamic calculations confirmed that hydrogen utilization under oxygen-limited conditions doubles the maximum biomass yield compared to fully aerobic conditions without H 2 addition. Hydrogen utilization was linked to significant changes in the SC2 proteome. In addition to hydrogenase accessory proteins, the production of Group 1d and Group 2b hydrogenases was significantly increased in both short- and long-term incubations. Both long-term incubation with H 2 (37 d) and treatments with chemical inhibitors revealed that SC2 growth under hydrogen-utilizing conditions does not require the activity of complex I. Apparently, strain SC2 has the metabolic capacity to channel hydrogen-derived electrons into the quinone pool, which provides a link between hydrogen oxidation and energy production. In summary, H 2 may be a promising alternative energy source in biotechnologically oriented methanotroph projects that aim to maximize biomass yield from CH 4, such as the production of high-quality feed protein. 相似文献
3.
This study concerned the anaerobic treatment of five different industrial wastewaters with a diverse and complex chemical composition. The kinetics of biotransformation of this wastewater at different chemical oxygen demand (COD) were studied in a batch reactor. Wastewater from an amino acid producing industry (Fermex) and from a tank that received several types of wastewaters (collector) contained 0.83 g l−1 and 0.085 g l−1 sulfate, respectively. During the study period of 20 days, methane formation was observed in all types of wastewaters. Studies on COD biodegradation showed the reaction velocity was higher for Fermex wastewater and lower for collector wastewater, with values of 0.0022 h−1 and 0.0011 h−1, respectively. A lower methanogenic activity of 0.163 g CH4 day−1 g−1 volatile suspended solids (VSS) and 0.20 g CH4 day−1 g−1 VSS, respectively, was observed for paper producing and brewery wastewater. Adapted granular sludge showed the best biodegradation of COD during the 20-day period. The sulfate-reducing activity in pharmaceutical and collector wastewater was studied. A positive effect of sulfate-reducing activity on methanogenic activity was noted for both types of wastewaters, both of which contained sulfate ions. All reactions of methane generation for the tested industrial wastewaters were first-order. The results of this study suggest that the tested wastewaters are amenable to anaerobic treatment. 相似文献
4.
The improvement of H 2 production capabilities of hydrogen (H 2)-producing microorganisms is a challenging issue. Microorganisms have evolved for fast growth and substrate utilization rather than H 2 production. To develop good H 2-producing biocatalysts, many studies have focused on the redirection and/or reconstruction of cellular metabolisms. These studies included the elimination of enzymes and carbon pathways interfering or competing with H 2 production, the incorporation of non-native metabolic pathways leading to H 2 production, the utilization of various carbon substrates, the rectification of H 2-producting enzymes (nitrogenase and hydrogenase) and photophosphorylation systems, and in silico pathway flux analysis, among others. Owing to these studies, significant improvements in the yield and rate of H 2 production, and in the stability of H 2 production activity, were reached. This review presents and discusses the recent developments in biohydrogen production, with a focus on metabolic pathway engineering. 相似文献
5.
Selenomonas ruminantium is a nonsporeforming anaerobe that ferments carbohydrates primarily to lactate, propionate, acetate and CO 2. H 2 production by this species has not been previously reported. We found, however, that some strains produce trace amounts of H 2 which can be detected by sensitive gas chromatographic procedures. H 2 production is increased markedly, in some cases almost 100-fold, when the selenomonads are co-cultured with methane-producing bacteria. Growth of the methane-producing bacteria depends on H 2 production by the selenomonads and the subsequent use of H 2 for the reduction of CO 2 to CH 4. Although no free H 2 accumulates in the mixed cultures, the amount of H 2 formed by the selenomonads can be calculated from the amount of methane produced. These studies indicate that the conventional methods for measuring H 2 production by pure cultures do not provide an adequate estimate of an organism's potential for forming H 2 in an anaerobic ecosystem where H 2 is rapidly used, e.g., for formation of CH 4. 相似文献
6.
The metabolic pathways involved in hydrogen (H 2) production, utilization and the activity of methanogens are the important factors that should be considered in controlling methane (CH 4) emissions by ruminants. H 2 as one of the major substrate for CH 4 production is therefore should be controlled. One of the strategies on reducing CH 4 is through the use of hydrogenotrophic microorganisms such as fumarate reducing bacteria. This study determined the effect of fumarate reducing bacteria, Mitsuokella jalaludinii, supplementation on in vitro rumen fermentation, CH4 production, diversity and quantity. M. jalaludinii significantly reduced CH 4 at 48 and 72 h of incubation and significantly increased succinate at 24 h. Although not significantly different, propionate was found to be highest in treatment containing M. jalaludinii at 12 and 48 h of incubation. These results suggest that supplementation of fumarate reducing bacteria to ruminal fermentation reduces CH 4 production and quantity, increases succinate and changes the rumen microbial diversity. 相似文献
7.
Many feeding trials have been conducted to quantify enteric methane (CH 4) production in ruminants. Although a relationship between diet composition, rumen fermentation and CH 4 production is generally accepted, the efforts to quantify this relationship within the same experiment remain scarce. In the present study, a data set was compiled from the results of three intensive respiration chamber trials with lactating rumen and intestinal fistulated Holstein cows, including measurements of rumen and intestinal digestion, rumen fermentation parameters and CH 4 production. Two approaches were used to calculate CH 4 from observations: (1) a rumen organic matter (OM) balance was derived from OM intake and duodenal organic matter flow (DOM) distinguishing various nutrients and (2) a rumen carbon balance was derived from carbon intake and duodenal carbon flow (DCARB). Duodenal flow was corrected for endogenous matter, and contribution of fermentation in the large intestine was accounted for. Hydrogen (H 2) arising from fermentation was calculated using the fermentation pattern measured in rumen fluid. CH 4 was calculated from H 2 production corrected for H 2 use with biohydrogenation of fatty acids. The DOM model overestimated CH 4/kg dry matter intake (DMI) by 6.1% ( R2=0.36) and the DCARB model underestimated CH 4/kg DMI by 0.4% ( R2=0.43). A stepwise regression of the difference between measured and calculated daily CH 4 production was conducted to examine explanations for the deviance. Dietary carbohydrate composition and rumen carbohydrate digestion were the main sources of inaccuracies for both models. Furthermore, differences were related to rumen ammonia concentration with the DOM model and to rumen pH and dietary fat with the DCARB model. Adding these parameters to the models and performing a multiple regression against observed daily CH 4 production resulted in R2 of 0.66 and 0.72 for DOM and DCARB models, respectively. The diurnal pattern of CH 4 production followed that of rumen volatile fatty acid (VFA) concentration and the CH 4 to CO 2 production ratio, but was inverse to rumen pH and the rumen hydrogen balance calculated from 4×(acetate+butyrate)/2×(propionate+valerate). In conclusion, the amount of feed fermented was the most important factor determining variations in CH 4 production between animals, diets and during the day. Interactions between feed components, VFA absorption rates and variation between animals seemed to be factors that were complicating the accurate prediction of CH 4. Using a ruminal carbon balance appeared to predict CH 4 production just as well as calculations based on rumen digestion of individual nutrients. 相似文献
8.
In a deep aquifer associated with an accretionary prism, significant methane (CH 4) is produced by a subterranean microbial community. Here, we developed bioreactors for producing CH 4 and hydrogen (H 2) using anaerobic groundwater collected from the deep aquifer. To generate CH 4, the anaerobic groundwater amended with organic substrates was incubated in the bioreactor. At first, H 2 was detected and accumulated in the gas phase of the bioreactor. After the H 2 decreased, rapid CH 4 production was observed. Phylogenetic analysis targeting 16S rRNA genes revealed that the H 2-producing fermentative bacterium and hydrogenotrophic methanogen were predominant in the reactor. The results suggested that syntrophic biodegradation of organic substrates by the H 2-producing fermentative bacterium and the hydrogenotrophic methanogen contributed to the CH 4 production. For H 2 production, the anaerobic groundwater, amended with organic substrates and an inhibitor of methanogens (2-bromoethanesulfonate), was incubated in a bioreactor. After incubation for 24 h, H 2 was detected from the gas phase of the bioreactor and accumulated. Bacterial 16S rRNA gene analysis suggested the dominance of the H 2-producing fermentative bacterium in the reactor. Our study demonstrated a simple and rapid CH 4 and H 2 production utilizing anaerobic groundwater containing an active subterranean microbial community. 相似文献
9.
Flooded rice fields, which are an important source of the atmospheric methane, have become a model system for the study of interactions between various microbial processes. We used a combination of stable carbon isotope measurements and application of specific inhibitors in order to investigate the importance of various methanogenic pathways and of CH 4 oxidation for controlling CH 4 emission. The fraction of CH 4 produced from acetate and H 2/CO 2 was calculated from the isotopic signatures of acetate, carbon dioxide (CO 2) and methane (CH 4) measured in porewater, gas bubbles, in the aerenchyma of the plants and/or in incubation experiments. The calculated ratio between both pathways reflected well the ratio determined by application of methyl fluoride (CH 3F) as specific inhibitor of acetate‐dependent methanogenesis. Only at the end of the season, the theoretical ratio of acetate: H 2 = 2 : 1 was reached, whereas at the beginning H 2/CO 2‐dependent methanogenesis dominated. The isotope discrimination was different between rooted surface soil and unrooted deep soil. Root‐associated CH 4 production was mainly driven by H 2/CO 2. Porewater CH 4 was found to be a poor proxy for produced CH 4. The fraction of CH 4 oxidised was calculated from the isotopic signature of CH 4 produced in vitro compared to CH 4 emitted in situ, corrected for the fractionation during the passage from the aerenchyma to the atmosphere. Isotope mass balances and in situ inhibition experiments with difluoromethane (CH 2F 2) as specific inhibitor of methanotrophic bacteria agreed that CH 4 oxidation was quantitatively important at the beginning of the season, but decreased later. The seasonal pattern was consistent with the change of potential CH 4 oxidation rates measured in vitro. At the end of the season, isotope techniques detected an increase of oxidation activity that was too small to be measured with the flux‐based inhibitor technique. If porewater CH 4 was used as a proxy of produced CH 4, neither magnitude nor seasonal pattern of in situ CH 4 oxidation could be reproduced. An oxidation signal was also found in the isotopic signature of CH 4 from gas bubbles that were released by natural ebullition. In contrast, bubbles stirred up from the bulk soil had preserved the isotopic signature of the originally produced CH 4. 相似文献
10.
Biogas produced by anaerobic digestion, is mainly used in a gas motor for heat and electricity production. However, after removal of CO 2, biogas can be upgraded to natural gas quality, giving more utilization possibilities, such as utilization as autogas, or distant utilization by using the existing natural gas grid. The current study presents a new biological method for biogas upgrading in a separate biogas reactor, containing enriched hydrogenotrophic methanogens and fed with biogas and hydrogen. Both mesophilic‐ and thermophilic anaerobic cultures were enriched to convert CO 2 to CH 4 by addition of H 2. Enrichment at thermophilic temperature (55°C) resulted in CO 2 and H 2 bioconversion rate of 320 mL CH 4/(gVSS h), which was more than 60% higher than that under mesophilic temperature (37°C). Different dominant species were found at mesophilic‐ and thermophilic‐enriched cultures, as revealed by PCR–DGGE. Nonetheless, they all belonged to the order Methanobacteriales, which can mediate hydrogenotrophic methanogenesis. Biogas upgrading was then tested in a thermophilic anaerobic reactor under various operation conditions. By continuous addition of hydrogen in the biogas reactor, high degree of biogas upgrading was achieved. The produced biogas had a CH 4 content, around 95% at steady‐state, at gas (mixture of biogas and hydrogen) injection rate of 6 L/(L day). The increase of gas injection rate to 12 L/(L day) resulted in the decrease of CH 4 content to around 90%. Further study showed that by decreasing the gas–liquid mass transfer by increasing the stirring speed of the mixture the CH 4 content was increased to around 95%. Finally, the CH 4 content around 90% was achieved in this study with the gas injection rate as high as 24 L/(L day). Biotechnol. Bioeng. 2012; 109: 2729–2736. © 2012 Wiley Periodicals, Inc. 相似文献
11.
Yields based on carbon are usually reported in prebiotic experiments, while energy yields (moles cal –1) are more useful in estimating the yields of products that would have been obtained from the primitive atmosphere of the earth. Energy yields for the synthesis of HCN and H 2CO from a spark discharge were determined for various mixtures of CH 4, CO, CO 2, H 2, H 2O, N 2 and NH 3. The maximum yields of HCN and H 2CO from CH 4, CO, and CO 2 as carbon sources are about 4×10 –8 moles cal –1. 相似文献
12.
Methane and hydrogen emission rates and the 13C of CH 4 were observed for various termites in Australia, Thailand and Japan. Combined with the already reported emission rates of CH 4 in the literature, the phylogenetic trend was examined. Emission rates of the observed termites were categorized into five groups: group I with high CH 4 and low H 2 emission rates with a CH 4/H 2 ratio of typically 10/1; group II with high CH 4 and high H 2 emissions with a CH 4/H 2 ratio of 4/1–1/2; group III with low emission rates of CH 4 and H 2; group IV with high H 2 and insignificant CH 4 emissions; and group V with insignificant emissions for both CH 4 and H 2. In lower termites, there are both colonies infected and uninfected with methanogens even in the same species, and no specific trend in CH 4 and H 2 emissions was observed within a genus. Whether protozoa in the hindgut of termites are infected with methanogens or not and the differences in species compositions of protozoa are possibly responsible for the inter-colonial variations. The proportions of infected colonies were possibly small for the family Kalotermitidae (dry wood feeders), and relatively large for families of wet or damp wood feeders. The hydrogen emission rate possibly depends on the locality of methanogens: namely, whether they are intracellular symbionts of protozoa or whether they are attached to the hindgut wall. Emission rates of higher termites were classified into groups according to genera and the diet. Most species of soil or wood/soil interface feeders classified into group I, while the soil feeders Dicuspiditermes in Thailand and Amitermes in Australia were classified into groups with high H 2 emission rates. Typical wood-feeding termites and fungus-growing termites were classified into group III. The results indicate that higher termites tend to increase the CH 4 emission rate during dietary evolution from wood- to soil-feeding, and two types of the system with different efficiencies of interspecies transfer of H 2 have been formed. The 13C of CH 4 was discernible with a difference in the decomposition process in the termite–symbiont system among lower termites, fungus-growing termites and other higher termites. 相似文献
13.
Hydrogenotrophic methanogens can use gaseous substrates, such as H 2 and CO 2, in CH 4 production. H 2 gas is used to reduce CO 2. We have successfully operated a hollow-fiber membrane biofilm reactor (Hf-MBfR) for stable and continuous CH 4 production from CO 2 and H 2. CO 2 and H 2 were diffused into the culture medium through the membrane without bubble formation in the Hf-MBfR, which was operated at pH 4.5–5.5 over 70 days. Focusing on the presence of hydrogenotrophic methanogens, we analyzed the structure of the microbial community in the reactor. Denaturing gradient gel electrophoresis (DGGE) was conducted with bacterial and archaeal 16S rDNA primers. Real-time qPCR was used to track changes in the community composition of methanogens over the course of operation. Finally, the microbial community and its diversity at the time of maximum CH 4 production were analyzed by pyrosequencing methods. Genus Methanobacterium, related to hydrogenotrophic methanogens, dominated the microbial community, but acetate consumption by bacteria, such as unclassified Clostridium sp., restricted the development of acetoclastic methanogens in the acidic CH 4 production process. The results show that acidic operation of a CH 4 production reactor without any pH adjustment inhibited acetogenic growth and enriched the hydrogenotrophic methanogens, decreasing the growth of acetoclastic methanogens. 相似文献
14.
Membrane-inlet mass spectrometry was used to investigate the effects of increasing the concentration of the rumen metabolites, formate and glucose, upon CH 4 and H 2 production during fermentation by unfractionated rumen liquor. Additions of formate up to 3.6 m M stimulated CH 4 and then excess H 2 production. Each addition caused a large accumulation of H 2 (>40 µ M), which returned to in situ concentrations after periods of more than 1 h. Glucose additions up to 2.0 m M gave linear increases in CH 4 and H 2 production. The conversion of substrate carbon into CH 4 was found to decrease from 34% to 9% for formate, as concentrations were increased (1.6–3.6 m M); approximately 13.5% of the glucose carbon was converted to CH 4. 相似文献
15.
Cellulose in wastewater was converted into H 2 by a mixed culture in batch experiments at 55°C with various wastewaters pH (5.5–8.5) and cellulose concentrations (10–40 g l –1). At the optimal pH of 6.5, the maximum H 2 yield was 102 ml g –1 cellulose and the maximum production rate was 287 ml d –1 for each gram of volatile suspended solids (VSS). Analysis of 16S rDNA sequences showed that the cellulose-degrading mixed culture was composed of microbes closely affiliated to genus Thermoanaerobacterium. 相似文献
16.
Emission rates of CH 4 were measured in microcosms of submerged soil which were planted with rice. Drainage of the rice microcosms for 48 h resulted in drastically decreased CH 4 emission rates which only slowly recovered to the rates of the undrained controls. Drainage also resulted in drastically increased sulphate concentrations which only slowly decreased to nearly zero background values after the microcosms were submerged again. The mechanisms responsible for the decrease of CH 4 production by aeration were investigated in slurries of a loamy and a sandy Italian rice soil. Incubation of the soil slurries under anoxic conditions resulted first in the reduction of nitrate, sulphate and ferric iron before CH 4 production started. Incubation of the soil slurries for 48 h under air resulted in immediate and complete inhibition of CH 4 production. Although the soil slurries were then again incubated under anoxic conditions (N 2 atmosphere), the inhibition of CH 4 production persisted for more than 30 days. The redox potential of the soil increased after the aeration but returned within 15 days to the low values typical for CH 4 production. However, the concentrations of sulphate and of ferric iron increased dramatically after the aeration and stayed at elevated levels for the period during which CH 4 production was inhibited. These observations show that even brief exposure of the soil to O 2 allowed the production of sulphate and ferric iron from their reduced precursors. Elevated sulphate and ferric iron concentrations allowed sulphate-reducing and ferric iron-reducing bacteria to outcompete methanogenic bacteria on H 2 as common substrate. Indeed, concentrations of H 2 were decreased as long as sulphate and ferric iron were high so that the Gibbs free energy of CH 4 production from H 2/CO 2 was also increased (less exergonic). On the other hand, concentrations of acetate, the more important precursor for CH 4, were not much affected by the short aeration of the soil slurries, and the Gibbs free energy of CH 4 production from acetate was highly exergonic suggesting that acetotrophic methanogens were not outcompeted but were otherwise inhibited. Aeration also resulted in increased rates of CO 2 production and in a short-term increase of N 2O production. However, these increases were < 10% of the decreased production of CH 4 and did not represent a trade-off in terms of CO 2 equivalents. Hence, short-term drainage and aeration of submerged paddy fields may be a useful mitigation option for decreasing the emission of greenhouse gases. 相似文献
17.
The greenhouse gases ( GHGs) derived from agriculture include carbon dioxide, nitrous oxide, and methane ( CH4). Of these GHGs, CH 4, in particular, constitutes a major component of the GHG emitted by the agricultural sector. Along with environmental concerns, CH 4 emission also leads to losses in gross energy intake with economic implications. While ruminants are considered the main source of CH 4 from agriculture, nonruminant animals also contribute substantially, and the CH 4 emission intensity of nonruminants remains comparable to that of ruminants. Means of mitigating CH 4 emissions from enteric fermentation have therefore been sought. Methane is produced by methanogens—archaeal microorganisms that inhabit the digestive tracts of animals and participate in fermentation processes. As the diversity of methanogen communities is thought to be responsible for the differences in CH 4 production among nonruminant animals, it is necessary to investigate the archaeal composition of specific animal species. Methanogens play an important role in energy metabolism and adipose tissue deposition in animals. Higher abundances of methanogens, along with their higher diversity, have been reported to contribute to lean phenotype in pigs. In particular, a greater abundance of Methanosphaera spp. and early dominance of Methanobrevibacter smithii have been reported to correlate with lower body fat formation in pigs. Besides the contribution of methanogens to the metabolic phenotype of their hosts, CH 4 release reduces the productivity that could be achieved through other hydrogen ( H2) disposal pathways. Enhanced participation of acetogenesis in H 2 disposal, leading to acetate formation, could be a more favorable direction for animal production and the environment. Better knowledge and understanding of the archaeal communities of the gastrointestinal tract ( GIT), including their metabolism and interactions with other microorganisms, would thus allow the development of new strategies for inhibiting methanogens and shifting toward acetogenesis. There are a variety of approaches to inhibiting methanogens and mitigating methanogenesis in ruminants, which can find an application for nonruminants, such as nutritional changes through supplementation with biologically active compounds and management changes. We summarize the available reports and provide a comprehensive review of methanogens living in the GIT of various nonruminants, such as swine, horses, donkeys, rabbits, and poultry. This review will help in a better understanding of the populations and diversity of methanogens and the implications of their presence in nonruminant animals. 相似文献
18.
ABSTRACTRecent advances in the field of microbial physiology demonstrate that carbon monoxide is a readily used substrate by a wide variety of anaerobic micro-organisms, and may be employed in novel biotechnological processes for production of bulk and fine chemicals or in biological treatment of waste streams. Synthesis gas produced from fossil fuels or biomass is rich in hydrogen and carbon monoxide. Conversion of carbon monoxide to hydrogen allows use of synthesis gas in existing hydrogen utilizing processes and is interesting in view of a transition from hydrogen production from fossil fuels to sustainable (CO 2-neutral) biomass. The conversion of CO with H 2O to CO 2 and H 2 is catalyzed by a rapidly increasing group of micro-organisms. Hydrogen is a preferred electron donor in biotechnological desulfurization of wastewaters and flue gases. Additionally, CO is a good alternative electron donor considering the recent isolation of a CO oxidizing, sulfate reducing bacterium. Here we review CO utilization by various anaerobic micro-organisms and their possible role in biotechnological processes, with a focus on hydrogen production and bio-desulfurization. 相似文献
19.
When grown in the absence of added sulfate, cocultures of Desulfovibrio desulfuricans or Desulfovibrio vulgaris with Methanobrevibacter smithii ( Methanobacterium ruminantium), which uses H 2 and CO 2 for methanogenesis, degraded lactate, with the production of acetate and CH 4. When D. desulfuricans or D. vulgaris was grown in the absence of added sulfate in coculture with Methanosarcina barkeri (type strain), which uses both H 2-CO 2 and acetate for methanogenesis, lactate was stoichiometrically degraded to CH 4 and presumably to CO 2. During the first 12 days of incubation of the D. desulfuricans-M. barkeri coculture, lactate was completely degraded, with almost stoichiometric production of acetate and CH 4. Later, acetate was degraded to CH 4 and presumably to CO 2. In experiments in which 20 mM acetate and 0 to 20 mM lactate were added to D. desulfuricans-M. barkeri cocultures, no detectable degradation of acetate occurred until the lactate was catabolized. The ultimate rate of acetate utilization for methanogenesis was greater for those cocultures receiving the highest levels of lactate. A small amount of H 2 was detected in cocultures which contained D. desulfuricans and M. barkeri until after all lactate was degraded. The addition of H 2, but not of lactate, to the growth medium inhibited acetate degradation by pure cultures of M. barkeri. Pure cultures of M. barkeri produced CH 4 from acetate at a rate equivalent to that observed for cocultures containing M. barkeri. Inocula of M. barkeri grown with H 2-CO 2 as the methanogenic substrate produced CH 4 from acetate at a rate equivalent to that observed for acetate-grown inocula when grown in a rumen fluid-vitamin-based medium but not when grown in a yeast extract-based medium. The results suggest that H 2 produced by the Desulfovibrio species during growth with lactate inhibited acetate degradation by M. barkeri. 相似文献
20.
Fermentation kinetics for the growth and conversion of H 2 and CO 2 to CH 4 by M. formicicum were modeled by using Monod equations. The maximum specific growth rate and H 2 uptake rate max and q max, were found to be 0.053 h –1 and 0.13 mol/hg cell, respectively. The partial pressure of H 2 was found not to have a significant effect on either growth or H 2 utilization. The yield of CH 4 from H 2 was calculated as 0.27 mol/mol, which is within 7% of the theoretical value of 0.25. 相似文献
|