Nitrification in rotating disc systems—I: Criteria for transition from oxygen to ammonia rate limitation

Abstract

Identification of the rate limiting substrate and half-order rate constants are presented on the basis of biofilm kinetics for triple substrate conditions (organic matter, ammonia and oxygen) in a rotating biological disc system. These findings have been verified by pilot-scale experiments. The transition from ammonia rate limitation to oxygen rate limitation occurs at a bulk ammonia-nitrogen concentration to bulk oxygen concentration ratio of approx. 0.4. Accordingly, oxygen is the rate limiting substrate. For most practical purposes the experiments showed that the oxygen limited half-order reaction constant in the presence of simultaneous organic matter degradation is reduced compared to nitrification alone by a factor which is a function of the growth of the heterotrophs and the nitrifiers in the biofilm.