DYNAMIC MODELING OF THE PH INFLUENCE IN N ITRIFICATION OF HIGHLY CONCENTRATED WASTE-WATER

Wastewater with high ammonia concentrations is produced by many indust ries, e.g. in the production of fertilizer and explosives and in the a gricultural and food industry. A direct discharge into rivers and lake s has to be avoided: Oxidation of ammonia requires 4.56 g DO/g NH4+-N and results in a decrease of dissolved oxygen concentration. Moreover, nitrate stimulates the proliferation of algae, with regard to the eut rophication of natural waters. For municipal wastewater with an ammoni a concentration less than 50 mg/L NH4+-N nitrification is a standard p rocess. However, the removal of higher loaded industrial effluents sti ll poses many questions. Recently, lab-scale and pilot-scale investiga tions show remarkable advances in the increase in nitrification effici ency and in the stabilization of the process. But because of changing flowrates and concentrations, the aid of advanced control algorithms i s necessary. Some of the most important variables of biochemical react ors can be determined only with difficulty, at times only with off-lin e measurements. Model-aided measurement approaches try to determine th ese variables indirectly from easily measured variables. An experiment ally-prove reactor model is required. Therefore, a dynamic model of ni trification in ideally mixed reactors is proposed based on mass balanc es for the components ammonia, nitrite, nitrate, dissolved oxygen DO, carbon dioxide, pH, nitrosomonas, and nitrobacter. The biological reac tion rates consider oxygen limitation and substrate inhibition. The pr ocess model presented is tested by lab scale experiments using an aera ted stirred tank reactor and a fluidized bed reactor. Conformity betwe en the predictions of the model and the observed data was positive. It has been shown that the nitrite oxidation by nitrobacter is the most sensible step in nitrification.