Suppressing dissolved hydrogen sulfide in a sewer network using chemical methods

Corrosion process and odor emission concerns caused by H2S are a constant focus for many sewage system municipalities, usually from the first day of system operation. This study investigates the effect of several chemicals on prohibition of H2S generation in sewage, where reagents were applied either individually or in combinations. Various concentrations of calcium peroxide, calcium hypochlorite, magnesium hydroxide, ferric chloride, and their combination with certain ratios were examined. Oxidation reduction potential (ORP) and pH were measured as the indicators for mitigation of H2S. Although both methods (adding chemicals individually or in combination) raised the ORP and pH to the safe range (that is ORP≥50 mV and 8.5≤pH≤9), experiments revealed that designed combination of chemicals resulted in more promising outcomes. The most cost effective combination was an admixture of 2 mg FeCl3/L and 2.5 mg Mg(OH)2/L with 30 min effective reaction time which could reduce the hydrogen sulfide greater than 95%. This combination is a blend for only 25% of the optimum dosage of these chemicals compared to when they were used individually. As a result, the aforementioned combination saved 12% on chemical costs compared to use of calcium peroxide as the most effective individual chemical.   Key words: Hydrogen sulfide, chemical, corrosion, sewage.