Estimating VOC Emissions from Primary Clarifiers

Computer software programs can be used to estimate volatile organic compound (VOC) emissions from wastewater treatment plants. Choice of software influences the prediction. In one study, emission rates estimated with BASTE, TOXCHEM, and WATER7 were compared with measured emission rates. WATER7 nearly always predicted higher emission rates than the other 2 models, particularly in primary clarifiers. The differences between TOXCHEM and TOXCHEM plus and WATER7 and WATER8 in calculating liquid- and gas-phase mass transfer coefficients are described. The effects of wind speed on predictions are outlined. Each model over-predicted VOC emissions. Collection of liquid and air samples was the best method to obtain accurate VOC emission estimates from wastewater treatment plants.