Mitigating hydrogen sulfide emissions from wastewater sludge using ferric chloride-foam spraying: an effective alternative to FC mixing.

Hydrogen sulfide (H2S) emissions from wastewater sludge generate intense odors and cause corrosion in wastewater treatment facilities. While mixing ferric chloride (FC) with sludge is commonly employed to reduce H2S formation and emissions, its effectiveness diminishes at high concentrations. This study explores the application of FC-foam on sludge as an alternative method to mitigate H2S emissions and compares its efficacy with traditional FC-mixing techniques. In batch tests, FC-foam application achieved an 86.44 % reduction in cumulative H2S emissions, compared to a 49.22 % reduction with FC mixing. Similarly, in semi-continuous tests, FC mixing decreased cumulative H2S concentrations by 71.38 % (from 5125 ppm to 1465 ppm), while FC-foam attained a 91.40 % reduction (from 5125 ppm to 440 ppm). FC-foam mitigates H2S emissions through two primary mechanisms: forming a stable barrier for approximately 28 h and leaching FC to react with sulfide ions. Additionally, the study evaluated the biodegradability and corrosion-inhibition properties of the AOS surfactant in FC-foam. Biodegradability tests indicated that the surfactant was nearly fully degraded within 10 days, and corrosion tests demonstrated a 61.19 %-67.04 % reduction in corrosion on carbon steel compared to FC mixing. These findings suggest that surface application of FC-foam can effectively maintain H2S concentrations around 6-8 ppm, offering a viable alternative that addresses the corrosion and reaction time limitations associated with conventional FC-mixing methods.