Treatment of sulfur and nitrogen by microoxygenated microbial sludge: stoichiometry and model

Abstract

A microoxygenated biological reactor (MOBR) was used to treat high concentrations of sulfur, nitrogen and organic pollutants by integrating the processes of sulfate reduction, sulfide oxidation, nitrification, denitrification and organic matter removal into a single reactor under 0·10–0·15 mg/l of dissolved oxygen (DO). Stoichiometric equations and kinetic models describing biochemical reactions catalysed by MOBR sludge were developed. Microcosm experiments were carried out using MOBR sludge to validate the stoichiometric equations and develop a model of microbiological processes in the MOBR. The theoretical predictions from stoichiometric equations agreed well with the experiments, and the kinetic model fit well the experimental data. In sulfate reduction, 95·7% of sulfate was reduced to sulfide and 76·7% of sulfide was oxidised to S0 in the sulfide oxidation process. In the nitrification process, 76·5% of ammonium was oxidised to nitrate and 98·2% of nitrate was denitrified to nitrogen gas (N2). In methanogenesis, methanogens consumed less organic carbon (C) than sulfate-reducing bacteria and denitrifying bacteria. It was found that the maximum specific growth rate of sulfate-reducing bacteria and methanogens under microoxygenation was lower than that under anaerobic conditions. In addition, there was a higher inhibitory effect of sulfide on methanogens in micro-DO than in the anaerobic system.