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Abstract: The influence of solids retention time (SRT) on continuous H2 production in a submerged membrane bioreactor (MBR) was investigated using mixed mesophilic microflora. The bioreactor was continuously operated at the four SRTs of 2, 4, 12.5 and 90 d on a glucose medium under the hydraulic retention time (HRT) of 9h and the mesophilic condition of 35°C±0.5. Stable biogas production with H2 content of 50.8%–60% was achieved at SRTs ranging from 2 to 12.5 d. No methane gas was observed in monitoring the experimental conditions. The H2 production increased from 17.62 to 26.1l-H2/d when the SRT increased from 2 to 12.5 d, but decreased to 9.1l-H2/d at the 90 d SRT. The best H2 yield, 1.19mol-H2/mol-glucose, was observed at the SRT of 2 d and the highest H2 production rate, 5.8l-H2/l/d, was obtained at the SRT of 12.5 d. Stable H2 production was achieved by maintaining the SRT in the range of 2 - 12.5 d, regardless of the fermentative pathway related to higher lactate production. The decrease in H2 yield was observed at long SRTs due to the low volatile suspended solids/total suspended solids (VSS/TSS) as well as the high extracellular polymeric substances (EPS) concentrations. These results suggest that the SRT is the key factor enabling sustainable H2 fermentation in MBR, and that an SLR value of around 1.6kg-DOC/kg-VSS/d might be the specific condition for achieving optimum H2 production. [Copyright &y& Elsevier]

Abstract: The effect of FeSO4 on continuous H2 production in a membrane bioreactor (MBR) was investigated using anaerobic mixed microflora under mesophilic condition. The H2 production of 41.6l/day was obtained at 10.9mgFeSO4/l, which was 1.59 times higher than that at 2.7mgFeSO4/l. Between 2.7 and 13.7mgFeSO4/l, the H2 production rate increased in parallel with the H2 yield under high-cell-density condition. For the same amounts of FeSO4, increases in butyric acid together with decreases in lactic acid promoted a reduction of the number of protons and the resultant release of H2. The hydrogenase activity of 1.08mg methylene blue (M.B) reduced/min at 10.9mgFeSO4/l was about sixfold higher than at 2.7mgFeSO4/l. These results suggest that the addition of iron and sulfur to an MBR is an important key factor in the enhancement of H2 production. [Copyright &y& Elsevier]