Control of Odor Emissions from Aeration Basins: The Palm Beach Experience

Statement of the Problem Palm Beach County Water Utilities Department (PBCWUD) wished to control odor emissions from the Southern Region Water Reclamation Facility (SRWRF) in response to citizen concerns. The primary goal of this project was to enhance community relations. The objectives were to determine the source(s) of odor emissions that could affect the plant's neighbors and develop cost-effective control methods for these sources.The SRWRF is a 35 million gallons per day (MGD) facility (based on three month average daily flow) treating an average of 24.3 MGD of wastewater from a large part of Palm Beach County. The treatment processes include screening and grit removal, step-feed aeration and final clarification. The effluent is then filtered, disinfected with chlorine and discharged to the reuse water system. Effluent not discharged to the reuse water system is either used to sustain two wetlands adjacent to the plant site or is injected into deep wells. Sludge is thickened, anaerobically digested and dewatered using belt filter presses. The dewatered cake solids are used on farmland or placed in a landfill.Odor control was already in place for the headworks and the solids handling facilities at the plant. Treatment of the foul was provided by one two stage packed bed caustic scrubber systems at each location. Sampling was conducted on potential odor sources at the plant. The odor samples were also tested for specific odor-causing compounds. Modeling of the odor source information indicated that the aeration basins were the most significant sources of off-site odors, followed by the headworks scrubber. The aeration basins are operated in the step feed mode. Each of the four basins is divided into four channels. The return activated sludge (RAS) is introduced at the head of the first pass of each basin. Raw wastewater is currently fed at the head of each of the four passes in each basin.Three general methods for controlling the odor were explored. These methods were:Reducing the hydrogen sulfide loads by adding chemicals to the collection system to reduce dissolved sulfideAdjusting the operation of the plant to reduce odorsCapturing and treating malodorous airThe addition of chemicals to the collection system successfully reduced the dissolved sulfide entering the plant, but no corresponding reduction in odor emissions was observed. Adjustments in the operation of the plant were made and the impact on the odor emission rates was measured. Operational changes evaluated include relocating the return sludge feed point from the first pass of an aeration basin to the headworks channel and changing the operation of the aeration basins from step feed to plug flow. Rerouting of the RAS proved to be inconclusive for reducing odor emissions from the aeration basins. Converting the aeration basins from step feed to plug flow did reduce the overall odor emissions from the basins.The remaining odor emissions from the aeration basins will be controlled by capturing and treating the foul air. A phased plan that involves covering portions of the aeration basins and treating the foul air has been developed in the event that the operational adjustments are unsuccessful in controlling odor emissions.This paper will present the base odor emission data and the impact of chemical addition in the collection system on the aeration basin odor emission rate as well as the results of the proposed operational changes on the odor emission rate. The results of a life cycle cost analysis of the possible solutions will also be presented.