Biological Nitrification in an Up Flow Fixed Bed Reactor (UFBR)

Abstract

This paper describes a kinetic model for ammonification and nitrification in an upflow fixed bed reactor (UFBR) with direct injection of air into the support material. Modeling has been based on the computation of active biomass concentration along the reactor. The tests, which extended over a period of one year and have been applied to municipal sewage after conventional treatment using activated sludge, have shown that the filtration rate is the most important factor as regards both the overall quantity of biomass found in the system and the distribution of this biomass within the reactor. The optimum quantity of biomass is obtained with a filtration rate of around 5 m3.m2.hr. Under these conditions, it is then possible to reach active biomass concentrations 8 to 9 times higher than the ones found in conventional processes based on the use of nitrifying activated sludge. It is also clearly evidenced that ammonification will, in most cases, be incomplete and this will limit the efficiency of the overall reaction Total N → NO3−. Other parameters also greatly influence the process : among these parameters, the influence of the ratio air process rate/influent rate has been the subject of special examination.