Evaluation of Nitrifying Bacteria Specific Growth Rate Sensitivity to Carbon Dioxide for Full-Scale Activated Sludge and Municipal Wastewater

Biological ammonia removal in wastewater treatment plants is a slow process. It has been theorized that the dissolved CO2 concentration and pH are important parameters in optimizing the specific growth rate of nitrifying bacteria. Five wastewater treatment plants (WWTP) representing the three major plant configurations, extended aeration (EA), Modified Ludzack-Ettinger (MLE), and Bardenpho, were evaluated based upon their operating conditions and activated sludge properties. The specific growth rates of the nitrifying bacteria were calculated for field and optimal conditions for pH and dissolved CO2 concentrations and suggest potential for improvement. Evaluation of nitrification in activated sludge at defined dissolved CO2 concentrations and constant pH 7 verified these findings. Fluorescence in situ hybridizations (FISH) were used to determine the abundance of nitrifying bacteria populations in the activated sludge from each WWTP and lab-scale reactors. Changes in the community structure of the nitrifying bacteria suggest sensitivity to dissolved CO2.