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Thermophilic Conditions (thermophilic + condition)
Selected AbstractsEffect of temperature change on the composition of the bacterial and archaeal community potentially involved in the turnover of acetate and propionate in methanogenic rice field soilFEMS MICROBIOLOGY ECOLOGY, Issue 2 2010Matthias Noll Abstract The microbial community structure was investigated together with the path of methane production in Italian rice field soil incubated at moderate (35 °C) and high (45 °C) temperature using terminal restriction fragment length polymorphism and stable isotope fractionation. The structure of both the archaeal and bacterial communities differed at 35 °C compared with 45 °C, and acetoclastic and hydrogenotrophic methanogenesis dominated, respectively. Changing the incubation of the 45 °C soil to different temperatures (25, 30, 35, 40, 45, 50 °C) resulted in a dynamic change of both microbial community structure and stable isotope fractionation. In all treatments, acetate first accumulated and then decreased. Propionate was also transiently produced and consumed. It is noteworthy that acetate was also consumed at thermophilic conditions, although archaeal community composition and stable isotope fractionation indicated that acetoclastic methanogenesis did not operate. Instead, acetate must have been consumed by syntrophic acetate oxidizers. The transient accumulation and subsequent consumption of acetate at thermophilic conditions was specifically paralleled by terminal restriction fragments characteristic for clostridial cluster I, whereas those of clostridial clusters I and III, Acidaminococcaceae and Heliobacteraceae, paralleled the thermophilic turnover of both acetate and propionate. [source] Wastewater treatment for production of H2S-free biogasJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 8 2008Sk Z Ahammad Abstract BACKGROUND: In anaerobic wastewater treatment processes, the presence of sulfate-reducing bacteria (SRB) produces H2S. Many techniques are being used to remove H2S from biogas to obtain H2S-free biogas but none of those are cost effective or efficient enough to remove the H2S completely. The objective of the present study was to introduce some changes/modifications to the process parameters of the wastewater treatment operation to eliminate SRB from the system. RESULTS: The growth of SRB was found to be completely suppressed under thermophilic conditions (55 °C) but not at 37 °C. H2S-free biogas containing 56.5% methane was obtained at 55 °C after 180 days of treatment. The effect of higher concentrations of volatile fatty acids (VFAs) on the growth of SRB and methanogens at 37 °C and 55 °C were also studied. At higher VFA concentrations, SRB outgrew the methanogens at 37 °C but at 55 °C the situation was found to be reversed. For continuous operation at 55 °C and low dilution rate (0.0075 h,1), SRB was suppressed and biogas having 29% methane but free of H2S was obtained. CONCLUSION: Operating the reactor at high temperature (550C) and low hydraulic retention time (HRT) can result in the production of H2S-free biogas, with a high concentration of methane. Copyright © 2008 Society of Chemical Industry [source] Municipal sludge degradation kinetic in thermophilic CSTRAICHE JOURNAL, Issue 12 2006Ángeles de la Rubia Abstract The performance of a pilot-scale continuous-flow stirred-tank reactor (CSTR) treating municipal sludge under thermophilic conditions has been studied. Two pilot-scale reactors (CSTR1 (175 L) and CSTR2 (850 L)) were operated at different hydraulic residence times (,: 40 to 15 days). The anaerobic sludge processes are generally affected by variations in the concentration of substrate (determined as influent volatile solids, VS) and volumetric flow, both of which lead to a modification in biomass concentration and VS removal efficiency. This unsteady-state situation is mathematically explained in terms of an autocatalytic kinetic model. The general kinetic equation in this model has been applied to experimental data obtained in CSTR1. The fit of the experimental data to the model was used to estimate kinetic parameters and the yield coefficients (,max, ,, YP/S). The estimated parameters were ,max: 0.175d,1, ,: 0.358, YP/S: 0.309 m3CH4/kgVS). These parameters were subsequently used to model the substrate utilization rate and the methane generation rate in CSTR2. The model with the estimated parameters was found to provide excellent results, and is satisfactory in describing the concentration of VS and the methane generation rate in an actual digestion plant. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source] Pilot-scale anaerobic thermophilic digester treating municipal sludgeAICHE JOURNAL, Issue 1 2006M. A. de la Rubia Abstract The work reported concerns anaerobic thermophilic municipal sludge digestion (55°C) in a completely mixed anaerobic digester on a pilot-plant scale (850 L). The experimental protocol was defined to examine the effect of increasing the organic loading rate (OLR) on the efficiency of this digester and to report on its steady-state performance. The reactor had previously been converted from mesophilic to thermophilic conditions following the protocol previously proposed by the authors: this was achieved by a modified method that combined systems investigated in Chicago and in Vancouver. The reactor was subsequently subjected to a program of steady-state operation over a range of sludge retention times (SRTs) of 27, 20, and 15 days. The digester was fed with raw sludge [containing approximately 34.8 g/L volatile solids (VS)] three times per day. Under thermophilic conditions and with a 27-day SRT, the reactor was operated with an OLR of 1.48 kg VS m,3 day,1. The solids removal efficiency of the reactor was 42.9%, whereas the volumetric methane production rate in the digester reached 0.35 m3 m,3 day,1. Over an operating period of 150 days, an OLR of 2.63 kg VS m,3 day,1 was achieved with 41.8% VS removal efficiency in the pilot sludge digester (SRT: 15 days). During this period the volumetric methane production rate in the digester reached 0.20 m3 m,3 day,1 and 0.20 m3/kg VSr (VS reduction). The greatest efficiency in terms of substrate removal was 54.3% for an OLR of 1.71 kg VS m,3 day,1 and SRT of 20 days. Under these conditions, the generation of biogas and methane was at levels of 0.86 and 0.58 m3 m,3 day,1, respectively, with a methane yield of 0.70 m3/kg VSr. © 2005 American Institute of Chemical Engineers AIChE J, 2006 [source] Anaerobic digestion as final step of a cellulosic ethanol biorefinery: Biogas production from fermentation effluent in a UASB reactor,pilot-scale resultsBIOTECHNOLOGY & BIOENGINEERING, Issue 1 2010H. Uellendahl Abstract In order to lower the costs for second generation bioethanol from lignocellulosic biomass anaerobic digestion of the effluent from ethanol fermentation was implemented using an upflow anaerobic sludge blanket (UASB) reactor system in a pilot-scale biorefinery plant. Both thermophilic (53°C) and mesophilic (38°C) operation of the UASB reactor was investigated. At an OLR of 3.5,kg-VS/(m3,day) a methane yield of 340,L/kg-VS was achieved for thermophilic operation (53°C) while 270,L/kg-VS was obtained under mesophilic conditions (38°C). For loading rates higher than 5,kg-VS/(m3,day) the methane yields were, however, higher under mesophilic conditions compared to thermophilic conditions. The conversion of dissolved organic matter (VSdiss) was between 68% and 91%. The effluent from the ethanol fermentation showed no signs of toxicity to the anaerobic microorganisms. However, a high content of suspended matter reduced the degradation efficiency. The retention time of the anaerobic system could be reduced from 70 to 7,h by additional removal of suspended matter by clarification. Implementation of the biogas production from the fermentation effluent accounted for about 30% higher carbon utilization in the biorefinery compared to a system with only bioethanol production. Biotechnol. Bioeng. 2010;107: 59,64. © 2010 Wiley Periodicals, Inc. [source] | |||||||||||||