Oxidation of sulfides following anaerobic municipal wastewater treatment for non-potable reuse applications†

Anaerobic secondary biological wastewater treatment could increase energy efficiency by avoiding energy-intensive aeration while producing methane that could be harvested for energy production. However, sulfides produced by biological sulfate reduction can inhibit efforts to reuse wastewater by interfering with chlorine or UV disinfection. At laboratory- and pilot-scale, this study compared oxidation of sulfides in a pilot-scale anaerobic secondary effluent by hydrogen peroxide (H₂O₂) or chlorine (NaOCl) and disinfection by UV or NaOCl with respect to meeting water quality guidelines for non-potable reuse applications. Chlorine oxidized sulfides within 6 minutes but required high chlorine doses (∼200 mg-Cl₂ L⁻¹) and formed particulate elemental sulfur at pH ≥ 6.2, necessitating filtration. H₂O₂ oxidized sulfides within 24 min, forming elemental sulfur near pH 7 and thiosulfate at pH >8. UV disinfection at ∼200 mJ cm⁻² average UV fluence achieved <2.2 MPN/100 mL total coliform and 5-log inactivation of bacteriophage MS2, while NaOCl disinfection only controlled total coliform. Initial cost estimates indicated that the lowest cost options (∼$0.40 per m³) to meet water quality goals for non-potable reuse involved sulfide oxidation either at pH 7 followed by filtration or at pH ∼8.3 without filtration, and then UV disinfection at 200 mJ cm⁻² average UV fluence and addition of NaOCl to achieve a 5 mg-Cl₂ L⁻¹ total chlorine residual for distribution.