Exploration and verification of the effect of S/N ratios on elemental sulfur generation in a simultaneous sulfide and nitrate removal process

Abstract

The effect of various S/N ratios (5 : 1, 5 : 1.5, and 5 : 2) on substrate removal and the nature of products was investigated during simultaneous sulfide and nitrate removal; analysis of the microbial community structure and its dominant species was also accomplished. For the influent sulfide concentration range of 120–360 mg L⁻¹, a significant difference in sulfate conversion percentage was evident among the tested S/N ratios. The reactor showed better sulfide removal performance (>96.28%) and a higher elemental sulfur level in the effluent (21.29–62.69%) upon fixing the S/N ratio at 5 : 1 in comparison with the other two ratios. When the influent sulfide concentration was increased to 480–720 mg L⁻¹, there were significant differences in the sulfide removal performance (sulfide removal percentage and elemental sulfur in the effluent) and nitrate removal performance (nitrate removal percentage, nitrite conversion percentage and nitrogen gas conversion percentage) for the tested S/N ratios. For the S/N ratio of 5 : 2, the reactor showed better sulfide removal performance (>72.36%) and a higher elemental sulfur level was observed in the effluent (60.05–63.45%) compared with the other two ratios; however, there was a nitrite accumulation of 32.28–47.59 mg L⁻¹ in the effluent. MiSeq high-throughput sequencing technology showed that Sulfurovum was the dominant bacterial genus in all the reactors, and little differences were noted in the microbial abundance and diversity (Chao, Ace, Shannon and Simpson indices) for the tested substrate ratios (p > 0.05).