Emissions of hazardous air pollutants from aeration tanks

Regulated under the 1990 Clean Air Act Amendments (CAAA), Publicly Owned Treatment Works (POT Ws) need to inventory and control their hazardous air pollutant (HAP) emissions, primarily from the aeration tanks. The spatial characteristics of hazardous air pollutant (HAP) emissions, primarily from the aeration tanks. The spatial characteristics of hazardous air pollutants in the form of volatile organic compounds (VOCs) from the aeration units of POTWs have been investigated by systematic monitoring and mathematical modeling. Using a verified off-gas sampling system and CC-MS analytical method, a large wastewater treatment plant has been tested to understand the air emissions from its aeration basins. Variations of VOC emissions along the length of the aeration units have been tested and modeled. Most VOCs have decreasing concentration profiles. A simple PFR model has been developed to obtain the spatial information of the VOC fate. This model can be easily used to validate model parameters and accurately simulate the process especially in the case where the aeration tanks are operated with varied airflow rates along the tank length. Using this simple model, air emissions can be accurately estimated and the simulation results are useful to support an emissions control analysis. This study also reveals thatmore » simple multiplication of measured off-gas concentration and total airflow over-estimates the overall emissions.« less