Hydrogen sulfide mitigation using electrochemically generated ferrous iron

Sulfide production in sewer systems causes several problems, including odor issues, health risks to sewer workers, and corrosion of sewer infrastructure. Various control strategies exist, often involving the addition of chemicals, but many of these methods are impractical for smaller pumping stations, particularly when multiple pumping stations are connected to the same force main. An alternative approach is by use of electrochemistry. A pilotscale unit was constructed and operated to generate ferrous iron electrochemically for the precipitation of sulfide ions in wastewater. The system was designed to operate independently of the raw wastewater flow and composition. The current density was set between 0.5 and 3 mA/cm² in a four-cell unit, with an 8 mm spacing between the cells. Iron ion production increased linearly with the current density. The unit effectively reduced sulfide content in raw wastewater. The hydrogen sulfide concentration in the headspace was reduced by 85% by electrochemical release of ferrous iron. By reversing polarity, a high and constant average current density was maintained over the three-days operation period. Contrary to the traditional approach of adding iron dissolved in acidic media, the pH remained stable at near neutral conditions throughout the process. Thus, the system is an attractive option for small end-of-pipe treatment systems (up to 10 m³/day) with high hydrogen sulfide concentrations.