DESIGN AND CONTROL OF A LARGE ODOR TREATMENT COMPLEX USING FOAM BIOTRICKLING FILTERS FOLLOWED BY CHEMICAL SCRUBBERS AT THE ORANGE COUNTY SANITATION DISTRICT

The Orange County Sanitation District (OCSD) owns and operates two wastewater treatment plants that treat approximately 240 million gallons per day (mgd). Each plant has extensive foul air collection and treatment facilities that treat over one million cubic feet per minutes (cfm). Odors must be controlled to levels that meet the emission requirements of the local South Coast Air Quality Management District (SCAQMD). In addition, because of the plants' proximity to residential areas, OCSD has voluntarily adopted a “good neighbor” policy that calls for no detectable odor at the plants' boundaries.OCSD's current discharge limit to meet SCAQMD regulations is 1 ppm of hydrogen sulfide (H2S). OCSD is currently designing a new headworks facility to replace the existing headworks facility at its Plant No. 2. The new headworks facility will require odor treatment of foul air. To minimize odors at the plant's boundary, the headworks' odor control facility is being designed to reduce hydrogen sulfide concentrations to 0.15 ppm. The selected odor treatment technology for the project is two-stage treatment: foam biotrickling filters followed by single-stage chemical scrubbers. A majority of the odors will be removed biologically through the biotrickling filter; remaining odors will be removed by the chemical scrubber. Hence, chemical usage and operating cost will be reduced substantially.OCSD has been conducting research for a number of years to optimize a biological process to effectively control odorous emissions at an economical cost. Biological treatment would reduce OCSD's use of chemicals for odor control, providing savings in operating costs and increasing safety for plant staff and the community.The research has led to the development of a foam biotrickling filter system that can be operated at very low gas retention times (2 to 4 seconds compared to 14 to 20 seconds for typical biotrickling filters). OCSD has converted five full-scale chemical scrubbers to foam biotrickling filters by replacing the plastic packing with open-pore polyurethane foam blocks, and replacing the large recirculation pump with a smaller pump. The test results indicated that the performance capabilities of the biotrickling filter are promising for reduction of hydrogen sulfide, reduced sulfur compounds (RSC), odors, and volatile organic compounds. Long-term operation of the biotrickling filter demonstrated its capability to reduce hydrogen sulfide concentrations ranging from 35 ppmv to 50 ppmv by up to 98 percent.The new headworks' odor control facility will be one of the largest biotrickling filter systems in operation in the United States, treating 188,300 cfm of foul air.This paper discusses the design concepts to be used for two-stage treatment systems, including control capabilities to allow for flexibility and redundancy of biological systems.