Integrated application of nanoscale zero-valent iron for sulfide and methane control in sewers and improved wastewater treatment

Abstract

Sewer systems are critical water infrastructures for sewage collection and transportation services but are frequently challenged by odour nuisance, corrosion and greenhouse gas emissions, primarily driven by sulfide and methane production. This study investigated the effectiveness of multifunctional nanoscale zero-valent iron (nZVI) in controlling sulfide and methane, along with its downstream impacts on wastewater treatment. Two continuous flow laboratory-scale reactor systems were used: sewer reactors and sequencing batch reactors (SBRs). Intermittent doses of 50 mg Fe/L of nZVI were introduced daily for a 6-h cycle in the experimental sewer reactors. Results indicated reduced sulfide (by 8.5±0.5 mg S/L during dosing; 4.2±0.6 mg S/L off-dosing) and methane (by 16.6±1.9 mg COD/L during dosing; 12.6±1.3 mg COD/L off-dosing) concentrations compared to the control. This reduction involved sulfide removal (0.12±0.01 g S/g Fe or 0.20±0.02 mol S/mol Fe) and the inhibition of microbial sulfate-reducing and methanogenic activities. Sulfate-reducing bacteria (SRB) and methanogenic archaea (MA) activities exhibited dynamic inhibition with long-term nZVI addition (SRB: 58 % after the first dose, 21 % after 3 months; MA: 27 % to 39 %). Additionally, the sewer-dosed nZVI improved downstream phosphorus removal (0.42±0.04 mg P/mg Fe or 0.76±0.07 mol P/mol Fe) and enhanced sludge settleability and dewaterability. These findings highlight the potential of intermittent nZVI dosing for effective sulfide and methane control in sewers while delivering downstream benefits for integrated urban wastewater management.