Emissions Control Options For POTWs

ublicly owned treatment works (POTWs) are beginning the process of identifying air emissions from their wastewater treatment and collection facilities. Many of these facilities will be required by local and state regulatory agencies to reduce emissions to meet air quality or health risks standards. Emissions include odors and toxic, reactive, volatile and criteria pollutants. A wide range of residential, commercial and industrial sources contribute pollutants to POTWs. In most cases, pollutant concentrations are low and vary greatly with time. They are subject to a variety of competing mechanisms, such as volatilization, sorption to solids and biodegradation, and may be emitted from many different processes. Because of low off-gas pollutant concentrations, many “traditional” control technologies used by other industries are largely ineffective or unproven. Developing accurate estimates for how much a given pollutant is being emitted and from what wastewater treatment or combustion process has always been the key to determining proper controls and program emphasis. Federal, state and local air quality laws and regulations are expected to increase the aeed fcr accwate emission facttxs, comprehensive air emissions inventories and viable, cost-effective control strategies for both criteria pollutants and air toxics. POTWs have both stack and large fugitive air emissions sources. Stack emission sources are combustion exhaust vents andor covered and ducted wastewater treatment processes such as headwork scrubbers, activated sludge reactors and sludge handling building blower vents. Fugitive emission sources include large uncovered wastewater or solids areas such as settling basins, clarifiers, weirs, compost piles and channels. Air emissions for publicly owned treatment works are characterized by high off-gas flow rates that have high moisture content and trace air emissions concentrations, are corrosive, and can contain aerosols. Wastewater discharges to POTWs are highly variable both in hydrocarbon concentrations and flow. Hydrocarbon concentrations are a result of industrial and commercial discharges, household product disposal and formulation byproducts of chemical addition (for example, formation of chloroform by chlorination of wastewater and water supplies).l