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 CH
3COO
?/NO
3? molar ratio on the sulfide oxidation process using an inverse fluidized bed reactor (IFBR). RESULTS: Three molar ratios of CH
3COO
?/NO
3? (0.85, 0.72 and 0.62) with a constant S
2?/NO
3? molar ratio of 0.13 were evaluated. At a CH
3COO
?/NO
3? molar ratio of 0.85, the nitrate, acetate and sulfide removal efficiencies were approximately 100%. The N
2 yield (g N
2 g
?1 NO
3?‐N consumed) was 0.81. Acetate was mineralized, resulting in a yield of 0.65 g inorganic‐C g
?1 CH
3COO
?‐C consumed. Sulfide was partially oxidized to S
0, and 71% of the S
2? consumed was recovered as elemental sulfur by a settler installed in the IFBR. At a CH
3COO
?/NO
3? molar ratio of 0.72, the efficiencies of nitrate, acetate and sulfide consumption were of 100%, with N
2 and inorganic‐C yields of 0.84 and 0.69, respectively. The sulfide was recovered as sulfate instead of S
0, with a yield of 0.92 g SO
42?‐S g
?1 S
2? consumed. CONCLUSIONS: The CH
3COO
?/NO
3? molar ratio was shown to be an important parameter that can be used to control the fate of sulfide oxidation to either S
0 or sulfate. In this study, the potential of denitrification for the simultaneous removal of organic matter, sulfide and nitrate from wastewaters was demonstrated, obtaining CO
2, S
0 and N
2 as the major end products. Copyright © 2008 Society of Chemical Industry
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