FIELD VERIFICATION OF PERFORMANCE AND “TOTAL ODOR REMOVAL” OPTIMIZATION OF ODOR CONTROL SYSTEMS

The Louisville and Jefferson County Metropolitan Sewer District (MSD) provides wastewater collection and treatment for Jefferson County, Kentucky. MSD's facilities are distributed throughout Jefferson County, with 5 regional treatment plants located in suburban areas of the County, and the 105 mgd Morris Forman Wastewater Treatment Plant (MFWTP) located just a few miles southwest of the downtown business district. Controlling odors from this wide-spread network of facilities is a major challenge for MSD. Over the past decade, MSD has evaluated odor emissions from a variety of sources, and selected odor control technologies that match the requirements of each different installation. As a result, MSD is currently operating a wide variety of odor control devices and systems, including:Activated carbon adsorbersWet scrubbersThermal oxidizersBiofilters (natural and synthetic media)Diffusion of odorous gases in activated sludge basinsLiquid-phase chemical addition (chlorine, iron salts, and nitrate compounds)Oxygen ionization systems (OIS)Each system has appropriate applications, depending on the odor source (industrial discharge, collection system-generated, or treatment process-generated); odor type (hydrogen sulfide, other reduced sulfur compounds, volatile organics, etc.); odor location (collection system, unstaffed facility, or staffed treatment plant); frequency of odor emissions (intermittent, seasonal, or continuous); and other factors.MSD's experiences with these odor control systems demonstrate the need to consider the total odor emission profile, rather than focusing on a single odor-causing constituent, such as hydrogen sulfide (H2S). Failure to consider the full range of odorous compounds can result in a system that treats one odor source, but unmasks others. This can result in an odor control system that removes the constituent that it was designed to remove, but does not significantly reduce overall odor emissions or odor complaints. MSD has completed extensive community odor surveys, dispersion modeling of air emissions, and installed continuous H2S monitors to quantify and confirm the extent of odor emissions in the neighborhoods.This paper will describe MSD's experiences with control of unconventional odors, and will describe the methods used to overcome the “bumps in the road” that have been encountered as conventional odor control systems are put in service to control unconventional odors. Examples of the lessons learned include the following:Wet scrubber systems – MSD installed 2 packed bed liquid scrubbers on the discharge from the Bioroughing Towers at the MFWTP. Given the high loading of the Bioroughing Towers, development of hydrogen sulfide odors was a concern, so the scrubbers were designed to provide for high levels of H2S removal in this air stream. When installed, the scrubbers were able to demonstrate excellent performance removing H2S (greater than 98% H2S removal). The exhaust gases from the scrubbers were still highly odorous, however, due to other reduced sulfur compounds and volatile organic compounds stripped out of the wastewater. MSD's solution is to modify the chemical feed strategy by selecting ORP and pH setpoints to optimize total odor removal, rather than just H2S removal.Biofilters – MSD has successfully implemented biofilter odor control systems at a number of pump stations throughout the system. Biofilters were installed on 4 large solids holding tanks at the MFWTP, with less success. These biofilters provided excellent removal of H2S, but developed a strong odor not related to H2S. In this case it was extraordinarily high loadings of reduced sulfur compounds other than H2S were overloading the biofilters. Attempts to improve performance of these filters was unsuccessful, and they were subsequently abandoned, and the vent gases from the solids storage tanks routed to a thermal oxidizer system for destruction. Oxygen ionization systems - The oxygen ionization system (OIS) has been in use in Europe for many years in a wide variety of odor control applications. Marketed in North America under the trade names Bentex and Bioclimatic, OIS technology has not been widely used in the wastewater industry to date. MSD has purchased 2 OIS units. At the time of this abstract preparation, one is installed and undergoing performance testing in a dissolved air flotation thickener room at the MFWTP. A second OIS system is currently out for bid, to be installed in a major pump station (100 mgd) that has a history of odor problems. This system will be installed and performance tested in the spring of 2002.Summary – MSD's odor control program is multi-faceted, including both well proven and cutting-edge innovative techniques. MSD's field verification experiences illustrate the importance of considering the overall profile of odor-causing agents to develop an odor control system to effectively reduce odor complaints.