Changes and stage disparity of aerobic sludge granulation with increasing organic load rate under low organotrophic conditions

The experiment focused the impact of increasing organic load rate (OLR) (0.6 kg COD·m−3·d−1 →1.2 kg COD·m−3·d−1) on the development of aerobic granular sludge (AGS) under low organotrophic conditions. During the sludge granulation process, the sludge characteristics and pollutant removal performance as the OLR increased under low organotrophic conditions in the reactor were better than that at constant OLR. At the end of the experiment, the mixed liquid suspended solid concentration and average particle size increased to 5.6 g/L and 1288.6 μm, and the removal efficiency of pollutants reached more than 80% with increasing OLR. However, the strengthening effect of the increasing OLR under low organotrophic conditions varied at the different stages during sludge granulation, indicating its stage disparity. In addition, the increase in OLR under low organotrophic conditions changed the extracellular polymeric substances distribution and chemical structure characteristics, with protein changes being more sensitive. With increasing OLR at granule formation stage, the microbial community structure varied obviously. Furthermore, the function bacterial Zoogloea, Plasticicumulans, and unclassified_Rhodocyclaceae were enriched, which might be the underlying cause of the stage disparity.