IFAS Process for Nitrogen Removal with an HRT of 4 Hours

This paper presents the experimental results obtained in an Integrated Fixed Film – Activated Sludge (IFAS) Bardenpho pilot plant (320 litres) operated at a Hydraulic Retention Time (HRT) of 4 hours and the comparison with HRT of 9 hours. The aerobic fraction was about 57% and divided into two main reactors (N1 and N2) which were filled with AnoxKaldnes K3 carriers (500 m2/m3). In addition, the plant was capable of providing methanol dosaging to the second anoxic reactor for the purposes of denitrification.Batch tests of the nitrate production rate (NPR) and the endogenous carbonaceous oxygen uptake rate (OUR) were carried out in order to quantify the activity and the concentrations of nitrifying (XA) and heterotrophic (XH) bacteria in each location (the suspension and biofilms of the N1 and N2 aerobic reactors). The calculated concentrations of XH and XA were analysed on the basis of equations developed in a conceptual approach in which the bacteria concentrations are expressed as a function of the substrate removal rates, the solids retention times (SRT) and the lysis.The operation at an HRT of 9 hours and high temperature revealed that the concentration of nitrifiers in suspension was high, but in the case of the N2 reactor was low in the biofilm. This occurred because the aerobic SRT turned out to be higher than the inverse of the nitrifier growth rate. However, at an HRT of 4 hours and T = 16°C, nitrifier concentrations in all the locations (in the suspension and biofilms of the N1 and N2 reactors) were high, resulting in very high nitrification rates (393 gN/m3aer·d) for the whole process. Concerning denitrification, reasonable effluent nitrate concentrations were achieved so as to meet the requirement of total nitrogen below 10 mgN/L.