INDOOR COMPOSTING FACILITY ODOR CONTROL: PERCEPTION, PROCESS, AND PERFORMANCE

Odor management can make or break a compost facility. When the Inland Empire Utilities Agency (IEUA) and County Sanitation Districts of Los Angeles County (CSDLAC) proposed to develop a 300,000 wet tons of biosolids and amendment per year compost facility to create a Class A product, odor control was one of the key success factors identified.Designing a successful odor control system requires answers to the following issues:Location – who are the neighbors and what are the current and future background odors?Compost Process – where and why are odors generated in the process?Odorous Compounds – which are the dominating compounds to be treated?Odor Control System – which process meets the need of the facility: organic or inorganic biofiltration, scrubbers, biotowers, or a combination?Building Ventilation – what are the required rates to capture the foul air?Worker Safety and Health – how will indoor air quality be addressed?Degree of Flexibility and Redundancy – how do we balance flexibility and cost?Siting of the Inland Empire Regional Composting Facility (IERCF) was fortuitous in an existing warehouse adjacent to IEUA's Regional Wastewater Plant No.4 in the unincorporated area of San Bernardino County, California. The other neighbors of the IERCF include a retail store warehouse, a prison, and a power plant. A background air dispersion model was considered to document nearby odor sources, sensitive receptors, and the level of odor control required to minimize off-site odors.The first step in odor control is understanding the process and how to minimize odor generation. The sources of odors at composting facilities are typically the delivery and handling biosolids and amendments, active composting, screening, curing, and the odor control system itself.Factors that impact the odor potential of the composting process include: aeration, moisture, porosity, pH, temperature, and time. Other factors that effect odors include biosolids odor quality, amount and storage time of green wastes, oxygen concentration, biological activity, and type/amount of polymer used during dewatering. The two most odorous compounds from an aerated static pile are ammonia and reduced sulfur compounds. Most of the odors during composting are significantly reduced during the first 14 days.In order to treat these odors, the IERCF is considering a two-stage odor control system: an inline misting system followed by a biofilter. The proposed misting system will cool and humidify the air stream prior to the biofilter. Based on the availability of compost and the low cost and maintenance requirements, the proposed biofilter has an above-grade profile with media comprised of woodchip/compost blend. Biofilters are considered best available control technology for odors and volatile organic compounds by the air quality regulatory agency.Design of the building ventilation impacts the size of the biofilter, fans and ductwork; the potential for fog formation and fugitive emissions; and worker health and safety. For the IERCF, the proposed biofilter size is approximately 3 acres, based on the loading factor, ventilation rate, and degree of redundancy assumed. Performance data from similar biosolids compost facilities and operator experience at those facilities are the inputs as this regional facility is designed.