Comparison of sulphide and nitrate removal from synthetic wastewater by pure and mixed cultures of nitrate-reducing, sulphide-oxidizing bacteria

Abstract In this study, the activities of hydrogen sulphide (H 2 S) oxidation and nitrate (N-NO 3 − ) reduction by three pure and mixed strains of nitrate-reducing, sulphide oxidizing bacteria (NR-SOB) were determined. Batch experiments were performed at 35 °C and pH 7.0–8.0 with initial H 2 S concentrations of 650–900 ppm v and N-NO 3 − concentrations of ∼120 mg/L. The strains MAL 1HM19, TPN 1HM1 and TPN 3HM1 were capable of removing 100% gas-phase H 2 S. The co-cultures showed better performance for H 2 S and N-NO 3 − removal. The mixed NR-SOB strains showed a higher H 2 S oxidation rate (143 ± 18 ppm v /h), while the highest N-NO 3 − removal rate (5.5 ± 0 and 5.1 ± 0.6 N-NO 3 −  mg/L·h) was obtained by a mixture of two NR-SOB strains. The 16S rDNA sequence analysis revealed that all strains belonged to the sub-class Alphaproteobacteria and are closely related to Paracoccus sp. (>99%).