Simultaneous sulfide and acetate oxidation under denitrifying conditions using an inverse fluidized bed reactor

Background: Simultaneous removal of sulfur, nitrogen and carbon compounds from wastewaters is a commercially important biological process. The objective was to evaluate the influence of the CH₃COO^-/ NO₃^- molar ratio on the sulfide oxidation process using an inverse fluidized bed reactor (IFBR). Results: Three molar ratios of CH₃COO^-/NO₃^- (0.85, 0.72 and 0.62) with a constant S^2-/NO₃^- molar ratio of 0.13 were evaluated. At a CH₃COO^-/NO₃^- molar ratio of 0.85, the nitrate, acetate and sulfide removal efficiencies were approximately 100%. The N₂ yield (g N₂ g^-1 NO₃^- -N consumed) was 0.81. Acetate was mineralized, resulting in a yield of 0.65 g inorganic-C g^-1 CH₃COO^- -C consumed. Sulfide was partially oxidized to S⁰, and 71% of the S^2- consumed was recovered as elemental sulfur by a settler installed in the IFBR. At a CH₃COO^-/ NO₃^- molar ratio of 0.72, the efficiencies of nitrate, acetate and sulfide consumption were of 100%, with N₂ and inorganic-C yields of 0.84 and 0.69, respectively. The sulfide was recovered as sulfate instead of S⁰, with a yield of 0.92 g S0₄ ^2- -S g^-1 S^2- consumed. Conclusions: The CH₃COO^-/NO₃ ^- molar ratio was shown to be an important parameter that can be used to control the fate of sulfide oxidation to either S⁰ or sulfate. In this study, the potential of denitrification for the simultaneous removal of organic matter, sulfide and nitrate from wastewaters was demonstrated, obtaining CO₂, S⁰ and N₂ as the major end products.