Project at a Glance

Title: Emissions of volatile and potentially toxic organic compounds from sewage treatment plants and collection systems

Principal Investigator / Author(s): Chang, Daniel P Y

Contractor: Department of Civil Engineering, UC Davis

Contract Number: A5-127-32

Research Program Area: Emissions Monitoring & Control

Topic Areas: Stationary Sources, Toxic Air Contaminants


Publicly owned treatment works (POTWs) are a source of potentially toxic organic compound (PTOC) emissions for which limited data are available. This study was commissioned by the California Air Resources Board (CARB) in order to assess the potential for PTOC emissions from municipal wastewater treatment plants (MWTPs) and collection systems throughout California. The fates of 16 PTOCs were reviewed in terms of volatilization, biodegradation, and adsorption to solids and biomass as the primary removal mechanisms from wastewater. For the compounds that were studied, it was concluded that volatilization is the dominant removal mechanism in MWTPs. However, the paucity of existing data regarding the occurrence and distribution of PTOCs in collection systems made it impossible to estimate emissions from those sources. A methodology was developed to predict PTOC emissions from 589 MWTPs in California. A limited but growing database was used along with extrapolation methods to estimate speciated PTOC emissions from MWTPs on statewide, county-by-county, and plant-by-plant bases. The results indicated that approximately 800 tons per year (tpy) of total PTOCs were emitted from MWTPs throughout California. Toluene and methylene chloride dominated the total PTOC emissions. Each was estimated to have been emitted in excess of 200 tpy. A small number of the 589 MWTPs were identified as having accounted for a large fraction of the total PTOC emissions. Furthermore, a comparison of PTOC emissions from two large MWTPs in the South Coast Air Basin (SCAB) suggested that emissions of some PTOCs from those sources were comparable to, and possibly greater than, emissions from the largest known point sources in the SCAB. Finally, specific MWTPs and treatment processes were recommended for future source sampling, and areas that will require future research in order to reduce the uncertainties in emissions estimates were identified.

For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753

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