ODORS AND VOLATILE ORGANIC COMPOUND EMISSIONS FROM COMPOSTING FACILITIES

Odors are typically the greatest deterrent to siting and maintaining composting facilities. Composting is the biological decomposition of organic matter under controlled, aerobic, thermophilic conditions, which produces a humus-like, stable product. During the decomposition of organic matter, numerous organic compounds are broken down by indigenous microorganisms, often resulting in putrescible by-products. Poor site management, odor control design, and facility siting have led to odor impacts on communities located near composting facilities. This has resulted in the closure of numerous facilities, litigation with emphasis on public health impacts, and difficulty in siting new facilities.The major sources of odors at composting facilities are the delivery and handling of raw feedstocks, active composting, curing, and storage of finished product. The type of feedstock handled determines the type of odors generated. For example, raw sewage sludge is more odorous than digested sludge or treated biosolids. Grass is typically a significant source of odor at yard waste facilities. Fish wastes and certain vegetable wastes are more odorous than food processing wastes. Facility design also affects the types of odors that are generated as well as how odors are released. Aerated static piles (ASPs) provide a large surface off of which odors are constantly released. Windrows are a source of both passively released odors as well as large plumes of odors when turning is conducted. Good management of a facility can help prevent odors through the use of adequate insulation layers on piles, timely mixing of fresh feedstocks, and proper aeration of piles.The odors associated with composting can be attributed to both inorganic compounds, such as hydrogen sulfide and ammonia, and organic compounds. Some of the volatile organic compounds (VOCs) that are most often found at biosolids composting facilities include alphapinene, dimethyl sulfide, and toluene. Most of the odorous compounds are generated during the first 14 days of composting. One study of a biosolids composting facility found that one-weekold windrows were the most significant sources of odors at the facility (Iacoboni, et al., 1980). Another study at an ASP facility found that, regardless of the aeration mode (positive or negative), odor concentrations from the pile surfaces were highest on Day 7 (E&A Environmental Consultants, Inc., 1999). Curing piles may also be a significant source of odors, although curing piles are more stable than composting piles, and the odors generated are different. Similarly, storage of finished compost may generate some odor, but the odors from stabilized biosolids have different characteristics than raw sludge.It is unclear whether, in addition to creating a nuisance, odors constitute an actual health hazard. Some researchers have suggested that odor induces stress and other non-toxicological disorders (Shusterman, 1991). This concept has been applied more frequently to indoor air quality issues. Studies at composting facilities have found that the compounds measured are present in concentrations below the Threshold Limit Values (TLVs) set by the Environmental Protection Agency (EPA), the Occupational Safety and Health Administration, and other worker and public health agencies (Van Durme, 1992). Since many of the compounds released by composting have extremely low odor thresholds (they are detectable at very low concentrations), maintenance of low odor concentrations should prevent health impacts as well.Correct facility design and operation can prevent odor impacts. This can include the installation of odor control systems such as biofilters, improved aeration systems, and management of composting activities in accordance with favorable meteorological conditions. The use of odor modeling can provide guidelines for effective odor management.