Modeling Process Control Strategies for Simultaneous Nitrification Denitirifcation in an Oxidation Ditch

A study was carried out to assess performance and process control strategies at the Falkenburg Advanced Wastewater Treatment Plant (AWWTP) in Hillsborough County, Florida. The Falkenburg AWWTP uses oxidation ditches where both nitrification and denitrification take place simultaneously in a low dissolved oxygen, extended aeration environment. A BioWin model was developed for the process and calibrated using whole plant influent, effluent and operational data. Kinetic parameters were adjusted in the model to accurately model the simultaneous nitrification-denitrification (SND) process. A sensitivity analysis found the ammonia and nitrite-oxidizing bacteria maximum specific growth rates and heterotrophic-denitrification DO half-saturation coefficient had the greatest influence on effluent nitrogen concentrations. Steady-state simulations were run with the calibrated model to observe relationships between mean cell residence time (MCRT), mixed liquor suspended solids (MLSS) concentrations, influent loading, and effluent nitrogen concentrations. One area identified during this study where process improvements could be made to advance efficiency of operation is the adjustment of waste activated sludge (WAS) wasting based on MCRT.