Evaluating and modeling biological sulfur production in the treatment of sulfide-laden streams containing ammonium

BACKGROUND: Biological treatment of effluents containing H₂S and ammonium are of great interest as both can trigger serious environmental problems when disposed of. The aim of this study was to optimize the production of biosulfur from the partial oxidation of sulfide in sulfide- and ammonium-containing streams. Biological performance was evaluated under various aerating conditions and key kinetic parameters were adjusted based on an existing mathematical model adapted to this system. RESULTS: An optimal conversion of sulfide to S⁰ of 86% (w/w) was found at an oxidation–reduction potential (ORP) of −380 ± 10 mV and at an O₂/S²⁻ molar ratio of 0.44. Partial nitrification was observed at ORP higher than −200 mV and in excess of oxygen supply. Sulfide-oxidizing bacteria (SOB) outcompeted ammonium-oxidizing bacteria (AOB) in the competition for dissolved oxygen. In a modeling effort, the maximum specific growth rate for SOB, the sulfur shrinking kinetic constant, the maximum specific growth rate for AOB and the AOB oxygen half-saturation constant were adjusted to 10.1 day⁻¹, 0.3 mg^2/3 VSS mg^−2/3 S, 1.75 day⁻¹ and 1.5 mg L⁻¹, respectively, during model calibration. CONCLUSIONS: Optimal S⁰ production was found under limiting O₂ conditions in which AOB were not able to outcompete SOB. The mathematical model described satisfactorily the experimental profiles for ammonium, nitrite, sulfide and sulfate as a function of the aeration flow rate.