Combination of nitrate and sodium nitroprusside dosing for sulfide control with low carbon source loss in sewer biofilm reactors.

Nitrate has been widely used in sewer systems for sulfide control. However, significant chemical consumption and the loss of carbon source were observed in previous studies. To find a feasible and cost-effective control strategy of the sulfide control, the effect of nitrate combined with sodium nitroprusside (SNP) dosage strategy was tested in lab-scale sewer biofilm reactors. Results showed that nitrate and SNP were strongly synergistic, with 30 mg N/L nitrate and 20 mg/L SNP being sufficient for sulfide control in this study. While large amount of nitrate alone (100 mg N/L) is required to achieve the same sulfide control effectiveness. Meanwhile, the nitrate combined with SNP could reduce the organic carbon source loss by 80%. Additionally, the high-throughput sequencing results showed that the relative abundance of autotrophic, nitrate reducing-sulfide oxidizing bacteria genera (a-NR-SOB) such as Arcobacter and Sulfurimonas was increased by around 18%, while the heterotrophic, nitrate-reducing bacteria (hNRB) such as Thauera was substantially reduced. It demonstrated that the sulfide control was mainly due to the a-NR-SOB activity under the nitrate and SNP dosing strategy. The microbial functional prediction further revealed that nitrate and SNP promoted the dissimilatory nitrate reduction process which utilizes sulfide as an effective electron donor. Moreover, economic assessment indicated that using the combination of nitrate and SNP for sulfide control in sewers would lower the chemical costs by approximately 35% compared with only nitrate addition.