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

[Display omitted] •New strains of nitrate-reducing, sulphide-oxidizing bacteria (NR-SOB) were isolated.•Mixture of NR-SOB strains showed the highest N-NO3− removal rate (5.5 mg N-NO3−/L h)•The NR-SOB strains were closely related to Paracoccus spp. (99% similarity)•The pure and mixed strains of NR-SOB removed 100% gas-phase H2S. In this study, the activities of hydrogen sulphide (H2S) oxidation and nitrate (N-NO3−) 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 H2S concentrations of 650–900 ppmv and N-NO3− concentrations of ∼120 mg/L. The strains MAL 1HM19, TPN 1HM1 and TPN 3HM1 were capable of removing 100% gas-phase H2S. The co-cultures showed better performance for H2S and N-NO3− removal. The mixed NR-SOB strains showed a higher H2S oxidation rate (143 ± 18 ppmv/h), while the highest N-NO3− removal rate (5.5 ± 0 and 5.1 ± 0.6 N-NO3− 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%).