EMISSIONS OF HAZARDOUS AIR-POLLUTANTS FROM AERATION TANKS

Regulated under the 1990 Clean Air Act Amendments (CAAA), Publicly Own ed Treatment Works (POT Ws) need to inventory and control their hazard ous 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 ha ve been investigated by systematic monitoring and mathematical modelin g. Using a verified off-gas sampling system and CC-MS analytical metho d, a large wastewater treatment plant has been tested to understand th e air emission from its aeration basins. Variations of VOC emission al ong the length of the aeration units have been tested and modeled. Mos t 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 cae where the aeration tanks ar e operated with varied airflow rates along the tank length. Using this simple model, air emission scan be accurately estimated and the stimu lation results are useful to support an emission control analysis. Thi s stud also reveals that simple multiplication of measured off-gas con centration and total airflow over-estimates the overall emissions.