Evaluation of Thiosulfate-Based Autotrophic and Mixotrophic Denitrification Performances under Different Operational Conditions

Abstract

The aim of this study was to investigate the factors affecting the autotrophic and mixotrophic denitrification performances in sequencing batch reactor (SBR). Findings obtained from this study will shed light on the full-scale applicability of the autotrophic and mixotrophic denitrification processes in carbon deficient wastewaters. In this study, the effect of cycle time, varying concentrations of electron donor source and the addition of external organic carbon source was evaluated by sulfate, nitrate, nitrite, ORP and inorganic carbon parameters. Firstly, SBR was operated with thiosulfate (S2O3 2-) based autotrophic denitrification process at different cycle times (8h-4h-2h). Further, autotrophic denitrification process was optimized the under varying S2O3 2-/ NO3ratios (1.5-1.25-1.0) at the optimum cycle time of 2h. The maximum nitrate removal efficiency of 84% was accomplished at operational conditions containing 2h cycle time and 1.5 S2O3 2-/NO3ratio. In the rest of the study,the impact of increasing C/N ratio by methanol supplementation (0.35-0.7-1.05)was evaluated on mixotrophic denitrification performance. It was observed that nitrate was completely consumed at the C/N ratio of 1.05 and nitrate removal rate improved with increasing methanol supplementation as organic carbon source.