Study of the Autotrophic Denitrification Process with Different Electron Acceptors on Sulfide Control in an Anoxic CSTR

Sulfide autotrophic denitrification (SADN) is a biological process performed by sulfur-oxidizing nitrogen-reducing (SO-NR) cultures in an anoxic environment. This process can effectively remove both sulfide (S-S2−), nitrate (N-NO3−) and nitrite (N-NO2−), which is an alternative technology in mainstream biological sulfide and nitrogen removal. The study aim is to determine the optimal operating condition of a SADN-Continuous Stirred Tank Reactor (CSTR) that can effectively eliminate S-S2− while also generating elemental sulfur (S-S0) and nitrogen gas (N2) as bioproducts. To investigate the performance and biological sulfur and nitrogen conversion processes, a laboratory-scale SADN-CSTR was employed to treat high S-S2− wastewater and vary nitrate and nitrite per sulfide molar ratios ([N-NO3−] + [N-NO2−]/[S-S2−] ratios) ranging from 0.6 + 0.0 to 0.0 + 0.6. The results illustrated that when fed wastewater at [N-NO3−] + [N-NO2−]/[S-S2−] ratios at 0.6 + 0.0 to bioreactor achieved the S-S2− removal rate (SRR) around 7.74 ± 0.10 mol-S/L·d and sulfide removal efficiency (SRE) was 99.8%. However, when feeding the bioreactor with wastewater at the ratio of 0.3 + 0.3 and 0.0 + 0.6, the SRR declined to 7.32 ± 0.11 and 6.79 ± 0.17 mol-S/L·d·(SRE were 93.42 ± 2.98% and 86.93 ± 2.52%). The S-S0 production rate was found maximum, as 6.47 ± 0.12 mol-S/L·d at the ratio of 0.4 + 0.2. When the bioreactor was run at the ratios of 0.3 + 0.3 and 0.0 + 0.6, more remained S-S2− increased, and detected more N-NO2− in the effluent. The results of this work can be used as a practical reference for the development for S-S2− control by use N-NO3− and N-NO2− as electron acceptors in SAND process.