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Effect of biogas recirculation and hydrogen removal on the process of thermophilic anaerobic digestion |
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Abstract Two anaerobic sequenced batch reactors (ASBR) fed with glucose and sodium acetate were applied to investigate the effect of biogas recirculation, i.e. recycling the biogas with and without hydrogen removal, on their performance. Acetate metabolic rate, effluent properties and microbial morphologies were studied. Meanwhile, molecular weight (MW) distribution and fluorescence feature of soluble microbial products (SMP) were analyzed by size exclusion chromatography and fluorescence excitation-emission matrix spectroscopy. Gas regulation improved the mixing condition, which accelerated the anaerobic reaction rates such as methanogenesis. The residual volatile fatty acids (VFAs) declined from 238.2mg/L (without hydrogen removal) and 129.6mg/L (with hydrogen removal) to 8.5mg/L and 8.2mg/L, respectively. Biogas recirculation eventually decreased the SMP content, which fell to 36.8% and 59.2% of the initial values respectively after 45days. Hydrogen removal promoted acetogenesis and acetate oxidation, and obviously changed the concentrations of methanogenic precursors and the microbial morphologies. It also promoted the conversion of high MW-SMP to low MW-SMP. Gas recirculation improved the quality of the effluent, while hydrogen removal accelerated the metabolism of acetate, thus is expected to facilitate the release of methanogensis from acidification and enhance the anaerobic conversion of organics.
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Received: 22 June 2010
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