Experimental and mathematical simulation study on the effect of granule particle size distribution on partial nitrification in aerobic granular reactor

The granules in the aerobic granular sludge reactor usually follow certain particle size distribution. In the previous studies, the average granule diameter was usually assumed in the model simulations. In this study, the impact of granule particle size distribution on the partial nitrification in the aerobic granular reactor was examined both in experiment and mathematical simulation. Both experimental and simulation results showed high NOB (nitrite oxidizing bacteria) presence in the small granules under conditions in which the NOB could be outcompeted in the large granules. The presence of NOB in the small granules reduced the nitrite accumulation. The simulation results indicated that NOB was preferentially presented in granules small than 50 μm. The results could be used to improve the operation of granule reactor for partial nitrification, by removing small granules (less than 50 μm) to outcompete NOB selectively. By including a wide particle size spectrum in the biofilm model, the study provided a quantitative tool for modelling granule sludge reactors.