Effects of oxygen transport limitation on nitrification in the activated sludge process

Apseudohomogeneous model of the nitrifying activated sludge process was developed to investigate the effects ofmass-transport resistance and heterotrophic/nitrifier competition on the apparent relationship between dissolved oxygen (DO) concentration and nitrification . The kinetics of both heterotrophic carbon oxidation and autotrophic ammonia oxidation within activated sludge flocs were described by an interactive-type, multiple-substrate-limiting model. The values for the model's parameters were estimated from a series of experiments that were conducted in laboratory-scale nitrifying activated sludge reactors . Using the estimated parameter values, the model was used to simulate the effect oforganic shock loads and steady-state nitrification efficiency over a typical range of mean cell retention times (MCRTs), DO concentrations, and levels of mass-transport resistance . Varying oxygen transport effects, MCRTs, and heterotrophic/autotrophic competition for DO can combine to give apparent nitrification-limiting DO concentrations that range from 0.5 mg/L to as high as4.0 mg/L. Res. J. Water Pollut. Control Fed., 63, 208 (1991) .