[Effect of ethanol on sulfate reduction and methanogenesis]

Base on the different niche characteristics of sulfate-reducing bacteria (SRB), acidogenic bacteria (AB) and methane-producing bacteria (MPB), this experiment used two-stage anaerobic treatment and circular gas stripping. Sucrose and ethanol were used as organic substrate (COD = 6 000 mg x L(-1). The effect of ethanol concentration on sulfate reduction, COD removal and methanogenesis, the effect of sulfide stripping and the best recycle ratio were investigated respectively at different COD/SO4(2-) ratios. The results indicate that the addition of ethanol promotes SO4(2-) reduction, reduces inhibition of competition resulted from COD/SO4(2-) decreasing, and makes SRB, AB and MPB in good synergetic metabolism. The efficiency of the system was improved obviously after ethanol/SO4(2-) ratio enhanced from 0 to 2. When the ratios of COD/SO4(2-) were 12, 6 and 4, SO4(2-) reduction efficiencies increased from 7.7%, 8.1%, 14.1% to 84.7%, 87.6%, 82.5%, COD removal efficiencies increased from 83.3%, 76.5%, 69.6% to 92.8%, 93.5%, 89.7%, and CH4/COD increased from 225.7, 204.6, 178.6 mL x g(-1) to 278.5, 253.7, 236.1 mL x g(-1), respectively. Dilution at a recycle ratio of 10 and stripping 30%-55% sulfide controlled sulfide concentrations less than 27.8, 38.4, 52.4 mg x L(-1), which inhibited effectively the toxicity of H2S. But higher recycle ratio (r = 20) made substrate gradient too little and SO4(2-) reduction efficiency reduced, while lower recycle ratio (r = 5) made sludge bed shrunken and COD removal efficiency reduced.