Accurately Modeling the Effect of Dissolved Oxygen on Nitrification

The prime objective of the work described in this paper was to determine the correct half saturation dissolved oxygen coefficients, KDO,AOB and KDO,NOB for the ammonia oxidizing and nitrite oxidizing bacteria, respectively for accurately simulating the Greeley WPCF, using the Biowin 3™ software. These parameters are often considered to be constants, whose values are generally accepted to be the default values embedded in the Biowin 3™ software. However, they are in fact not constants, and unless care is taken in the assignment of the proper values, errors in predicted air quantities or the required DO concentrations to achieve the necessary effluent ammonia concentrations will result. Determining the specific KDO value for a given application is important because it impacts the rate of nitrification achieved for a given oxygen concentration, the SRT, the consequent size of the aeration reactors, and the energy required to maintain required DO levels. Our other experiences subsequent to the work described in this paper showed that simulation results achieved by using the half saturation coefficients determined in this paper provide a much better goodness of fit than the current Biowin 3™ default values. For future plant simulations, the same type of stress tests carried out for this work are recommended as part of the wastewater characterization and calibration exercises. However, if this is not possible, adjusting the default values in Biowin 3™ to the values presented in this paper is recommended. The work presented in this paper can only be accomplished using a properly calibrated dynamic model. A steady state modeling approach would not produce the required results and would not be suitable to confirm nitrifier growth rates with plant scale measurements. Source: WEFTEC 2009 Proceedings