Sulfide Production Control in UASB Reactor by Addition of Iron Salt

Hydrogen sulfide (H2S) is one of the main odorant gases emitted from anaerobic sludge blanket (UASB) sewage treatment plants (STPs) and other anaerobic environments. The present work is an attempt to quantify H2S formation in seven full-scale UASB reactors across India and suppression of sulfide formation using pilot-scale UASB reactors and adopting a liquid-phase odor and corrosion control method that enhances sulfate (SO42-) concentration in raw sewage up to 100-120mg/L. Results for full-scale UASBs reveal that H2S varies 0-20.3ppm because of high influent sulfates that range 100-150mg/L as the result of ingress of industrial wastewater in domestic sewage. However, results for the pilot-scale UASBs reveal that SO42- in the influent (38-40mg/L) converted to sulfide (15-20mg/L) at ORP and pH to the safe range (ORP=-75mV; pH=6.9-7.3). After sulfate enhancement, sulfide was observed to be 30-40mg/L; COD removal, 80-85%; and ORP ranging from -65 to -103mV. Furthermore, iron salt (FeCl3), which was added at 30mg/L (a 1:1 ratio to sulfide concentration) minimized sulfide in the reactor up to 99%.