A modified ASM1 for nitritation/denitritation for the treatment of sludge reject water in a sequencing batch reactor

A modified ASM1 model was developed to simulate nitritation/denitritation in a sequencing batch reactor (SBR) treating sludge reject water. The model was validated using real data from a pilot SBR. The effect of a number of operating parameters on the nitritation/denitritation efficiency was tested including, among others, the volumetric nitrogen loading rate (vNLR), the solids retention time (SRT) and the number of cycles. Both the vNLR and the number of cycles critically affected the processes. Specifically, very high nitritation (>90%) was accomplished for vNLR <0.5 KgN/md for an SRT of 10 d and 0.75 KgN/md for SRTs between 15-20d. When vNLR>0.9 KgN/md for an SRT of 10 d and vNLR>1.4KgN/md for SRTs between 15-20 d nitritation was practically inhibited. The increase in the number of cycles of the SBR from 1 to 4 significantly improved the denitritation process. However, at 5 cycles and SRT=10 days the nitritation process was inhibited due to the decrease of the duration of the process time.