Peroxide to Purple Powder: Case Studies Controlling Collection System and Solids Handling Odors with Chemical Addition

The 2004 Water Environment Federation (WEF) Manual of Practice (MOP) 25, Control of Odors and Emissions from Wastewater Treatment Plants list several different additives and chemicals that are used for liquid phase treatment to reduce odors. These include:Air and oxygen injectionChemical oxidants such as chlorine compounds, hydrogen peroxide, potassium permanganate, and ozoneNitrate compoundsIron salts (both ferrous and ferric solutions)pH adjustment using magnesium hydroxide, calcium hydroxide, or sodium hydroxideThere are advantages and disadvantages for each of these options, and the choice of an additive is site specific. This paper will review several actual case studies of liquid phase treatment used to control H2S odors and corrosion. The paper will review design features of each system, chemical dosages, monitoring results, safety and handling requirements, and factors that resulted in the selection of each additive. The following case studies will be presented:Brunswick Sewer District, Maine. Currently uses sodium hypochlorite solution to reduce odor emissions from primary and secondary sludge. The system has been operated since 1992City of New London, Connecticut. Uses potassium permanganate addition to the influent sewers entering the wastewater treatment facility to reduce H2S odors and corrosion at the Headworks. The potassium permanganate solution can also be injected into the primary and secondary sludge upstream of mechanical thickening units to reduce odors in the Processing Room. The system has operated since 1995.Regis College, Weston Massachusetts. Injects liquid sodium hypochlorite into its pump station and three mile length force main to reduce downstream corrosion and odor emissions that escape from manholes and plumbing vents in a residential neighborhood at the force main outlet manhole. The system has operated since 2002.City of Rockland, Maine. Uses ferric chloride and/or hydrogen peroxide addition to control odors created by an industrial waste force main discharging to the wastewater treatment plant. These systems have been operated since 2001.Irvine Ranch Water District (IRWD), California. Currently using nitrate solution to control wetwell corrosion and force main odors at several remote package lift stations. These systems have been operating since 2004. As a result of the positive experience with this product, the District included a new below-grade chemical feed system (including bulk storage tanks) at a 16.5 mgd pump station. This system is scheduled to start up in early 2008.Orange County Sanitation District (OCSD), California. Currently using nitrate solution to control odor emissions from the Magnolia Trunk Sewer during on-going rehabilitation investigations. Video inspection activities began in January, 2007 and physical inspections are planned during the summer of 2007. The nitrate addition was used during periods that manhole covers are open to prevent the escape of odors into the surrounding neighborhood. Extensive H2S monitoring data (both before and after the implementation of the chemical addition) have been compiled to demonstrate the effectiveness of the program. This data will be presented in the paper.The paper will also provide a review of other methods to reduce odors (such as vapor phase treatment, and source control) to provide an explanation of why these other methods were not applied at each of these locations.