ESTIMATING WASTEWATER TREATMENT EMISSIONS USING EPA's WATER9 MODELING SOFTWARE

As part of a biological wastewater pretreatment investigation, CH2M HILL was retained to provide volatile organic compound (VOC) predictions for federal and state air permitting. These predictions were performed using the U.S. Environmental Protection Agency's (EPA's) WATER9 model. WATER9 is a Microsoft® Windows-based program consisting of analytical expressions for estimating air emissions from individual wastewater units. WATER9 is able to evaluate a wastewater treatment facility's unit processes that may contain multiple streams, collection systems, and complex treatment configurations. The emission predictions are based on a combination of biological kinetics calculations and vapor equilibrium calculation that consider the properties of the compound and its concentration in the stream.The Dow Chemical Company conveys wastewater from their production facility to a secondary wastewater treatment facility owned and operated by an independent corporation. The industrial wastewater is pretreated before its transfer to the treatment facility. CH2M HILL was retained to estimate the existing air emissions from the treatment facility and develop pretreatment options for the wastewater. The need was to predict VOC, hazardous air pollutant (HAP), and state air toxic emission rates from the existing treatment facility and different biological pretreatment options.Conventional activated sludge, sequential batch reactors (SBRs), and surface aerators were evaluated. The conventional activated sludge option requires the construction of two aeration tanks and two clarifiers. Blowers would provide air for microbial processes and tank mixing through coarse bubble diffusers. The SBRs option requires the conversion of two existing tanks. Blowers would provide air for microbial processes and tank mixing through coarse bubble diffusers. The surface aerators option requires the conversion of a basin and construction of two clarifiers. Floating surface aerators would provide air for microbial processes and mixing.The WATER9 model was used to predict emissions from these biological pretreatment options. Since the WATER9 model is applicable to a continuous process, CH2M HILL had to develop an approach to model the SBRs. This report contains the key findings from using the WATER9 model on these systems and the method used to predict emissions from the batch reactors.