EXPERIENCE WITH BIOLOGICAL ODOR CONTROL AT THE PADRE DAM MUNICIPAL WATER DISTRICT SANTEE, CALIFORNIA

The Padre Dam Municipal Water District operates a 2 million gallon per day (mgd) water recycling facility at the north end of the Santee Lakes Recreation Preserve in Santee, California. The climate in the region is Mediterranean with very few nights below 0°C temperatures. Odor control is provided at the treatment plant and at the influent pump station three miles away.The first odor control system was installed about 10 years ago at the influent pump station. A packed tower chemical scrubber using caustic and hypochlorite provided effective odor removal. However this system required considerable attention to maintain, and required a costly water softener system to pre-treat makeup water. Odor control at the water recycling facility was achieved by collecting off gases from the primary clarifier and using them as the air supply to the aeration process where the biological process consumed the H2S.In 2002 a biofilter was installed at the WRF to treat odors from the primary clarifiers. This unit was a ZABOCS Model 8000, which utilized an inorganic mineral media to treat 1500 cfm of odorous air with inlet H2S concentrations averaging 50 ppm, and peak concentrations over 200 ppm. The ZABOCS biofilter has performed well for 3 years, with minimal maintenance required. Based on the experience with the ZABOCS 8000, PDMWD agreed to pilot a ZABOCS-BTF biotrickling scrubber with the intention of investigating a technology for possible replacement of the chemical scrubber at the influent pump station.The results from the pilot test at the influent pump station showed that there was better than 99% H2S removal at H2S concentrations averaging 10 ppm, and with peak concentrations to 50 ppm.The new ZABOCS BTF biotrickling filter is now installed and operating at the influent pump station. It is designed for a maximum air flow capacity of 2,500 cfm. Normal operation is expected to be 1800 cfm. Initial performance data show better than 99% H2S removal at an average inlet concentration of 10 ppm.