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Biofiltration is an increasingly popular technology for treating of foul air at biosolids composting facilities employing static pile or invessel processes. The Rancho Las Virgenes Composting Facility (Rancho), located in western Los Angeles County, provides biosolids treatment, including anaerobic digestion, dewatering, and in-vessel composting, for customers served by the Rancho Las Virgenes Municipal Water District (District), the facility operator, and Triunfo Sanitation District. Rancho employs an in-vessel system to treat dewatered, anaerobically digested solids and produces a soil amendment for local distribution and marketing. Over several years, the District has worked closely with Black & Veatch Corporation to investigate the operation of the Biofilter and to develop enhancements that optimize performance.In 2000, Black & Veatch conducted a study to evaluate the performance of the Biofilter and recommend improvements to enhance its short-term and long-term operability. A $1 million construction project was recommended to provide a major renovation and expansion of the Biofilter. The recommended design included complete rehabilitation of four existing zones of Biofilter, two new-slab-on grade concrete zones equipped with air distribution channels and drainage system, and other improvements. The schedule requires that the two new concrete zones be in service by the end of October 2001 and other improvements to be completed by the end of December 2001.After award and negotiation of the contract, an equipment vendor approached Black & Veatch, the District, and the Contractor about modifying the design of the concrete zones to use BacTee aeration floor system. Benefits to the District include savings in capital costs and construction time, enhanced air and moisture distribution, longer media life, and potential energy saving. The District negotiated a construction change order to incorporate the aeration floor system. This paper presents the results of the study, including the Biofilter's operating history, long-term design recommendations, and a cost analysis of biofiltration options. Discussion of how the design recommendations were refined and incorporated in the final detailed design of the Biofilter and how the change order for the aeration floor system was incorporated to provide a state-of-the art biofilter is also included.

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