In order to assess the sulfate-induced inhibition of anaerobic digestion of antibiotic manufacturing bio-waste. The effect of COD/SO 4 2- ratio on biogas production potential and substrate utilization characteristics during the acidogenic phase of anaerobic digestion of penicillin bacterial residues were investigated through batch experiments. The results obtained indicated that biogas production was gradually enhanced after 10 days of anaerobic digestion. However, the maximum cumulative methane production probably exceeded about 208 mL•g -1 (on TS basis) since COD/SO 4 2- ≥3. Because adaptive acclimation, more than 71% COD removal, which may have been converted to methane, was achieved. Consequently, at COD/SO 4 2- ≤1.5, methane production was suppressed by 49% and 100% when the organics and SO 4 2- removal rates were less than 17% and 5%, respectively. This indicated that methanogens and sulfate-reducing bacteria were inhibited at high sulfate loading rates. In addition, the COD balance analysis revealed that less than 9.1% of the COD was converted to methane. However, 5.0%-9.0% of the COD was used for sulfate reduction. This means that methanogens are more susceptible than sulfate-reducing bacteria to sulfide-induced inhibition. The S balance showed that the reduced sulfate was mainly present as sulfide in the digester. A small fraction of it was present as hydrogen sulfide in the biogas. The analysis of substrate utilization characteristics during the acidogenic phase revealed that methanation of soluble protein was initiated after methanation of soluble carbohydrate.
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