Controlling Organic Dust and Bioaerosols at a Biosolids Composting Facility

The City of Longmont, Colorado owns and operates an 8.5 dry tons per day aerated static pile Biosolids composting facility. The composting facility consists of a totally enclosed missing building and a separate, totally enclosed composting/curing screening building.Since the Longmont composting facility began operating in 1991, moisture control throughout the process was very difficult. As a result of the low humidity and extremely dry conditions, the amount of organic dust generated by normal operations has become a concern for worker health and safety.In 1994, the National Institute for Occupational Safety and Health (NIOSH) issued a warning of the dangers of organic dust and the need for prevention. The health effects from organic dust exposure include inflammation, allergy, and infection.In an effort to reduce dust and airborne contaminants at the composting facility, the City of Longmont commissioned a study to assess dust aerospore concentrations at the facility and to determine both operational and facility modifications. Air monitoring was conducted at the facility for total dust, respirable dust, endotoxin, and Aspergillus fumigatus. Samples for dust were taken in the facility and directly on personnel during activities.The highest concentration of total dust was measured during pile teardown and screening The concentrations measured were below the Occupational Safety and Health Administration (OSHA) standard of 15 mg/m3 for airborne particulate matter. Respirable dust concentrations were also below the OSHA exposure standard. Operator measurements showed that exposure was greatest in the mixing area. Endotoxing levels in the facility ranged fromResults of the studyWorker health implicationsMitigation measures implementedApplication to other biosolids composting and management facilities