Peracetic acid activated by ferrous ion mitigates sulfide and methane production in rising main sewers

Iron-based peracetic acid (PAA) advanced oxidation process (AOP) is widely used in water purification because of its high efficiency and low toxicity. In this study, for the first time, ferrous iron (Fe²⁺) and PAA were dosed jointly into the rising main sewer reactor, to verify the feasibility of sulfide and methane control as well as investigate the comprehensive mechanism of Fe²⁺/PAA on sewer biofilm. Results demonstrated the superior biocidal effect of Fe²⁺/PAA dosing than that of PAA alone. Intermittent Fe²⁺/PAA dosing showed that the average inhibitory rate of sulfide production rate (SPR) and methane production rate (MPR) was 52.0% and 29.9%, respectively, at a Fe²⁺/PAA molar ratio of 1:1 and PAA concentration of 3 mmol/L (i.e., the mass-based concentrations of Fe²⁺ and PAA were 6.79 mg-Fe/L and 228 mg/L, respectively). Beside, sewer biofilm was found to be resistant to PAA during repeated dosing events. However, resistance could be alleviated by introducing sulfide in situ in the Fe²⁺/PAA process, and SPR and MPR were further reduced to 27.39% and 67.32% of the control, respectively. LIVE/DEAD Staining showed that Fe²⁺/PAA exhibited a strong destructive effect on microbial cells, with the proportion of viable cells being 26.34%. Electron paramagnetic resonance (EPR) and free radical quenching results indicated that the inhibitory order was R-O• > •OH > Fe(IV), which led to the disruption of cellular integrity (i.e., 17.24% increase in LDH) and intracellular enzyme system (i.e., cellular metabolic disorders). Microbial analysis revealed that long-term Fe²⁺/PAA dosing decreased the sulfate-reducing bacteria (SRB) abundance, and the dominant genus of methanogenic archaea (MA) shifted from Methanofastidiosum, Methanobacterium to Methanosaeta. The cost of Fe²⁺/PAA dosing on methane and sulfide control in rising main sewers was $1.81/kg-S, economically and environmental-friendly attractive for practical applications.