High ammonium loading and nitrification modelling in a fixed-bed bioreactor

Abstract

The aim of this study was to investigate ammonia load removable by a fixed-bed bioreactor. In this study, high ammonia loads, up to 4.5kgN/m3d were applied on a fixed bed reactor colonised by two pures nitrifying bacteria: Nitrosomonas europaea ATCC® 19718 and Nitrobacter winogradskyi ATCC® 25391. The loads were similar to the highest values reported in literature especially with a two bacteria population. The complete ammonia removal efficiency in our installation has reached 2.5 kgN/m3.d for a full nitrification. An N-tank in series model was used to represent the fixed bed reactor and to predict the nitrification in the installation. The developed model was accurate and representative of the nitrification assumed by Nitrosomonas europaea ATCC® 19718 and Nitrobacter winogradskyi ATCC® 25391. This model was also used to predict the biomass and oxygen concentrations during the experiment under various operational conditions. The biofilm fixed on the solid support (polysterene beads 2mm diameter) was mainly present in the bottom of the reactor where the ammonia load was applied. It is demonstrated that in this region of the column the oxygen concentrations reached the lowest values.