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In continuously stirred tank reactor experiments, with manure as substrate at thermophilic temperatures, the use of volatile fatty acids (VFA) as process indicators was investigated. Changes in VFA level were shown to be a good parameter for indicating process instability. The VFA were evaluated according to their relative changes caused by changes in hydraulic loading, organic loading or temperature. Butyrate and isobutyrate together were found to be particularly good indicators. Butyrate and isobutyrate concentrations increased significantly 1 or 2 days after the imposed perturbation, which makes these acids suitable for process monitoring and important for process control of the anaerobic biological system. In addition it was shown in a batch experiment that VFA at concentrations up to 50 mM did not reduce the overall methane production rate. This showed that VFA accumulation in anaerobic reactors was the result of process imbalance, not the cause of inhibition, thus justifying the use of VFA as process indicators. 相似文献
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In recent years, increasing attention has been paid to the use of renewable biomass for energy production. Anaerobic biotechnological
approaches for production of liquid energy carriers (ethanol and a mixture of acetone, butanol and ethanol) from biomass can
be employed to decrease environmental pollution and reduce dependency on fossil fuels. There are two major biological processes
that can convert biomass to liquid energy carriers via anaerobic biological breakdown of organic matter: ethanol fermentation
and mixed acetone, butanol, ethanol (ABE) fermentation. The specific product formation is determined by substrates and microbial
communities available as well as the operating conditions applied. In this review, we evaluate the recent biotechnological
approaches employed in ethanol and ABE fermentation. Practical applicability of different technologies is discussed taking
into account the microbiology and biochemistry of the processes. 相似文献
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The two-stage process for extreme thermophilic hydrogen and thermophilic methane production from wheat straw hydrolysate was investigated in up-flow anaerobic sludge bed (UASB) reactors. Specific hydrogen and methane yields of 89 ml-H2/g-VS (190 ml-H2/g-sugars) and 307 ml-CH4/g-VS, respectively were achieved simultaneously with the overall VS removal efficiency of 81% by operating with total hydraulic retention time (HRT) of 4 days . The energy conversion efficiency was dramatically increased from only 7.5% in the hydrogen stage to 87.5% of the potential energy from hydrolysate, corresponding to total energy of 13.4 kJ/g-VS. Dominant hydrogen-producing bacteria in the H2-UASB reactor were Thermoanaerobacter wiegelii, Caldanaerobacter subteraneus, and Caloramator fervidus. Meanwhile, the CH4-UASB reactor was dominated with methanogens of Methanosarcina mazei and Methanothermobacter defluvii. The results from this study suggest the two stage anaerobic process can be effectively used for energy recovery and for stabilization of hydrolysate at anaerobic conditions. 相似文献
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Acetate Oxidation Is the Dominant Methanogenic Pathway from Acetate in the Absence of Methanosaetaceae 总被引:1,自引:0,他引:1
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Dimitar Karakashev Damien J. Batstone Eric Trably Irini Angelidaki 《Applied microbiology》2006,72(7):5138-5141
The oxidation of acetate to hydrogen, and the subsequent conversion of hydrogen and carbon dioxide to methane, has been regarded largely as a niche mechanism occurring at high temperatures or under inhibitory conditions. In this study, 13 anaerobic reactors and sediment from a temperate anaerobic lake were surveyed for their dominant methanogenic population by using fluorescent in situ hybridization and for the degree of acetate oxidation relative to aceticlastic conversion by using radiolabeled [2-14C]acetate in batch incubations. When Methanosaetaceae were not present, acetate oxidation was the dominant methanogenic pathway. Aceticlastic conversion was observed only in the presence of Methanosaetaceae. 相似文献
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Integrated biogas upgrading and hydrogen utilization in an anaerobic reactor containing enriched hydrogenotrophic methanogenic culture 总被引:1,自引:0,他引:1
Biogas produced by anaerobic digestion, is mainly used in a gas motor for heat and electricity production. However, after removal of CO2, 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 CO2 to CH4 by addition of H2. Enrichment at thermophilic temperature (55°C) resulted in CO2 and H2 bioconversion rate of 320 mL CH4/(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 CH4 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 CH4 content to around 90%. Further study showed that by decreasing the gas–liquid mass transfer by increasing the stirring speed of the mixture the CH4 content was increased to around 95%. Finally, the CH4 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
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Studies of the degradation of the two isomeric forms of butyrate in different anaerobic environments showed isomerization betweenn- andi-butyrate. Degradation rates were similar for the different examined systems and degradation rates forn-butyrate degradation were generally higher than fori-butyrate. Degradation rates forn-butyrate ranged from 0.52 to 1.39 day–1, while the rates fori-butyrate were from 0.46 to 1.15 day–1. Production of isomers was not observed when the volatile fatty acid degradation was inhibited by addition of bromoethane sulfonic acid, indicating that isomerization was coupled to the methanogenic degradation of the acid. The degree of isomerization observed duringn-butyrate degradation was similar to the degree duringi-butyrate degradation. Experiments indicated that the isomerization degree was higher for the thermophilic than for the mesophilic inocula. 相似文献
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Electricity production from acetate, glucose and xylose with humic acid as mediator was investigated in two chambers microbial fuel cells (MFCs). Acetate produced the highest voltage (570 mV with 1000 Omega) and maximum power density (P(maxd)=123 mW/m(2)) due to a simpler metabolism than with glucose and xylose. Glucose and xylose resulted in P(maxd) of 28 mW/m(2) and 32 mW/m(2) at lower voltage of 380 mV and 414 mV, respectively. P(maxd) increased by 84% and 30%, for glucose and xylose respectively, when humic acid (2g/l) was present in the medium. No significant effect was found with acetate since the internal resistance possessed a limiting effect. The increase of P(maxd) due to humic acid presence was attributed to its ability to act as mediator. Even though pH decreased to 5 with glucose and xylose, due to production of acetate and propionate, the voltage remained on the same level of 250-350 mV. 相似文献
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J. Palatsi M. Laureni M.V. Andrés X. Flotats H.B. Nielsen I. Angelidaki 《Bioresource technology》2009,100(20):4588-4596
Long chain fatty acids (LCFA) concentrations over 1.0 g L−1 were inhibiting manure thermophilic digestion, in batch and semi-continuous experiments, resulting in a temporary cease of the biogas production. The aim of the work was to test and evaluate several recovery actions, such as reactor feeding patterns, dilution and addition of adsorbents, in order to determine the most appropriate strategy for fast recovery of the reactor activity in manure based plants inhibited by LCFA. Dilution with active inoculum for increasing the biomass/LCFA ratio, or addition of adsorbents for adsorbing the LCFA and reducing the bioavailable LCFA concentration, were found to be the best recovery strategies, improving the recovery time from 10 to 2 days, in semi-continuously fed systems. Moreover, acclimatization was introduced by repeated inhibition and process recovery. The subsequent exposure of the anaerobic biomass to an inhibitory concentration of LCFA improved the recovery ability of the system, indicated as increasing degradation rates from 0.04 to 0.16 g COD_CH4/g VS day. The incubation time between subsequent pulses, or discontinuous LCFA pulses, seems to be a decisive process parameter to tackle LCFA inhibition in manure anaerobic co-digestion. 相似文献
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Prasad Kaparaju María Serrano Anne Belinda Thomsen Prawit Kongjan Irini Angelidaki 《Bioresource technology》2009,100(9):2562-2568
The production of bioethanol, biohydrogen and biogas from wheat straw was investigated within a biorefinery framework. Initially, wheat straw was hydrothermally liberated to a cellulose rich fiber fraction and a hemicellulose rich liquid fraction (hydrolysate). Enzymatic hydrolysis and subsequent fermentation of cellulose yielded 0.41 g-ethanol/g-glucose, while dark fermentation of hydrolysate produced 178.0 ml-H2/g-sugars. The effluents from both bioethanol and biohydrogen processes were further used to produce methane with the yields of 0.324 and 0.381 m3/kg volatile solids (VS)added, respectively. Additionally, evaluation of six different wheat straw-to-biofuel production scenaria showed that either use of wheat straw for biogas production or multi-fuel production were the energetically most efficient processes compared to production of mono-fuel such as bioethanol when fermenting C6 sugars alone. Thus, multiple biofuels production from wheat straw can increase the efficiency for material and energy and can presumably be more economical process for biomass utilization. 相似文献