Evaluating the Feasibility of Two Reduced Sulfur Compounds as Energy Sources and Electron Donors for Partial Autotrophic Denitrification: Thiocyanate and Sulfite
Guihua Xu, Chang Cui, Yanping Zhang, Zixuan Xin, Chaoyue Li
Abstract
Autotrophic denitrification using sulfur compounds is considered an alternative to heterotrophic denitrification for the treatment of organic carbon-deficient wastewaters. However, the stoichiometric characteristics of denitrification using different sulfur species, particularly thiocyanate (SCN−) and sulfite (SO32−), remain poorly understood. Here, partial autotrophic denitrification driven by thiocyanate or sulfite was studied in two batch reactors. The stoichiometry of thiocyanate-oxidizing denitrification was assessed based on valence and ultimate product analysis. No nitrate removal was observed in the sulfite-fed system, indicating that sulfite could not serve as an effective electron donor for autotrophic denitrification under the tested conditions. In contrast, simultaneous removal of SCN− and NO3− was achieved in the thiocyanate-fed system, with removal efficiencies of 100% and 92.5 ± 3.6%, respectively. After 36 h, total nitrogen removal reached 63.3%, with nitrite identified as the dominant intermediate product (26.7%). NO2− and NH4+ accumulated during the process could be further removed through anaerobic ammonium oxidation. Thiocyanate sulfur was primarily oxidized to sulfate via elemental sulfur as a transient intermediate. These findings provide a theoretical basis for applying thiocyanate-driven partial autotrophic denitrification to nitrogen removal from industrial wastewaters, particularly those generated via coal gasification and cyanide-utilizing gold mining processes.