Sulfide-bearing gases produced by anaerobic digestion of proteinaceous and other organic materials corrode gas-handling equipment and contribute to odor problems requiring expensive sulfide-control measures. Laboratory-scale, two-phase anaerobic digestion (TPAD) research was undertaken
to examine the feasibility of sequestering biological sulfate reduction from methane fermentation to reduce the H2S concentration of gases produced in the separate methane-phase digester (MPD) of the TPAD Process. Parallel two-phase and single-stage digestion studies were conducted
utilizing complete-mix reactors that were charged with 5 wt% TS-content primary sludge. Both systems were operated at 35°C at a system HRT of 15.4 days. The acid-phase digester (APD) of the TPAD Process had an HRT of 3 days. The single-stage digester served as the control to provide
baseline performance data. Both systems were spiked with Na2SO4 to ensure the presence of adequate sulfate for the sulfate-reducing bacteria (SRB). Hydrogen sulfide concentration in the acid-phase digester (APD) gas ranged from 10,000 to 20,000 ppm by volume compared
with 900 ppm for the MPD and 2100 ppm for the single-stage digester. SRB were selectively enriched in the APD. A nitrogen content of 41% in the APD indicated vigorous, sulfidogenic denitrification activity.
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