Biological oxidation of thiosulfate in mixed heterotrophic/autotrophic cultures

The biological oxidation of thiosulfate was examined using aerobic, continuous-flow reactors containing both heterotrophic and autotrophic microbial populations. Complete oxidation of thiosulfate at influent concentrations up to 600 mg/l as S took place with production of equivalent concentrations of sulfate. Removal of influent chemical oxygen demand and ammonia as well as nitrification were not adversely impacted by the presence of thiosulfate. Observed microbial yields were obtained based on experimental data and theoretical yields were calculated based on bioenergetics. Batch kinetic experiments were performed using mixed liquors from both a thiosulfate-deprived and a thiosulfate-amended continuous-flow reactor. The ability of the thiosulfate-deprived reactor to oxidize thiosulfate declined with increasing reactor operation time. Thiosulfate oxidation followed Monod kinetics. The following biokinetic parameter values for the biological oxidation of thiosulfate were determined: maximum specific substrate utilization rate (k) 19.8 mg thiosulfate-S/mg VSS-d and half-velocity coefficient (Ks) 14 mg thiosulfate-S/l.