Bio-Solids Process Enhancements Resulting From the Use of Hydrogen Peroxide for Hydrogen Sulfide Odor Control - The San Antonio Experience

The paper will present results of a trial initiated in February 2004 by the San Antonio Water System (SAWS) to quantify the impacts of hydrogen peroxide injection prior to dissolved air flotation thickening of wastewater sludges.Since February 2000, the San Antonio Water System has successfully used iron salts (FeSO4) for odor and corrosion control in the Dos Rios Water Recycling Center (WRC) collection system. In May of 2003 the Dos Rios WRC began receiving about 300,000 gallons per day of a mixture of primary and waste activated sludges from SAWS'. Leon Creek WRC. When the Dos Rios WRC facility started receivingsludge from Leon Creek, several negative impacts were observed.Operators immediately noticed a significant increase in sulfide odors from the DAF units treating the Leon Creek sludge. Also, a 2–3% decrease in percent solids of combined Leon Creek/Dos Rios belt filter press dewatered sludge was observed. In addition, volatile solids reduction through the anaerobic digestion process decreased dramatically. Finally, an expected increase in methane production due to increased sludge volume was not realized.In order to investigate the efficacy of hydrogen peroxide (H2O2) towards resolving these negative impacts, SAWS initiated a trial involving injection of H2O2 into the Leon Creek sludge line several minutes ahead of the DAF units. Impacts to be quantified were H2S odors, polymer usage, volatile solids destruction, methane production, and dewatering efficiency. Past experience had suggested that hydrogen peroxide may enhance the performance of flotation thickening and sludge dewatering, and may result in a reduction of polymer use. It had also been suggested that hydrogen peroxide (in the presence of iron salts) could potentially increase methane production through partial oxidation of organic compounds (e.g. lignins) in the sludge, which may be recalcitrant to anaerobic digestion. Finally, it was thought that the hydrogen peroxide residuals in the Leon Creek sludge would also react to regenerate the iron salts from the Dos Rios sludges and achieve additional odor control in a blend tank where Leon Creek and Dos Rios sludges are mixed.