Influence of sulfide to nitrate ratios on denitrifying sulfide removal and elemental sulfur reclamation from wastewater containing high organic carbon concentration

This study evaluated the effect of sulfide to nitrate (S/N) ratios on elementary sulfur biotransformation in a simultaneous autotrophic and heterotrophic denitrifying sulfide removal(DSR) process, at a carbon to nitrate (C/N) ratio of 3/1. Four groups of batch tests were conducted at S/N ratios of 5/2, 5/5, 5/6 and 5/8, respectively. Results showed a low accumulation of elementary sulfur. Elementary sulfur was first obtained by the oxidizing of sulfide through DSR process and then was reduced back to sulfide with the interaction of surplus acetate. The highest elementary sulfur transformation rates at S/N ratios of 5/2, 5/5, 5/6 and 5/8 were 47.1%, 94.7%, 94.0% and 93.5%, respectively. It can be concluded from analysis of the stoichiometric proportion of the bio-chemical reactions that the proportion of acetate consumed in DSR process to the whole acetate consumption in the first 6 hours were no more than 50%, indicating a low efficiency of DSR process under high concentration of organic carbons, except for the condition under S/N of 5/6, during which period the highest proportion can be as much as 85.6%. Given the elemental sulfur transformation rate and the acetate consumption proportion in DSR process, it can be concluded that adjusting the ratio of sulfide to nitrate at an appropriate level (around 5/6) would be an appropriate strategy for higher elemental transformation.