First Extended Anaerobic Phase Enhanced Nitrogen and Phosphorus Removal by Aerobic Granular Sludge Under Intermittent Gradient Aeration

Abstract

In this study, a SBR reactor was selected to explore the effect of nitrogen and phosphorus removal by aerobic granular sludge under different initial anaerobic time using intermittent gradient aeration (decreasing dissolved oxygen concentration in each aeration section) and actual domestic wastewater with low C/N ratio as the influent matrix. The results showed that the initial anaerobic stage of intermittent gradient aeration increased from 50 min to 90 min, which increased the carbon source reserves in granular sludge. This improved delayed anaerobic condition led to the improvement of nitrogen and phosphorus removal efficiency of granular sludge. When delayed to 70 and 90 min, the removal efficiency of COD, TN, and TP reached 84.74%, 70.05%, and 89.7% and 86.65%, 78.81%, and 85.5%, respectively. However, after the first anaerobic phase time was increased to 110 min, the sludge loss was more severe owing to the disintegration of some cells, leading to a decrease in internal carbon source reserves by about 13.6%. Owing to this, the pollutant removal efficiency decreased. In the process of prolonging the first anaerobic phase time from 50 min to 90 min, the content of PS in LB-EPS changed minimally; when it was delayed to 110 min, the content of PS increased to about 7.18 mg·g-1, and the PN content increased to about 5.56 mg·g-1. The contents of PN and PS in TB-EPS were stable, which indicated that the effect of internal carbon storage on LB-EPS was greater than that of TB-EPS, and the decrease in sludge settling performance was closely related to the increase in PS content in LB-EPS. The proportion of DPAOs in granular sludge increased as the first anaerobic phase time increased, and the proportion of DPAOs reached 51.5% when the first anaerobic phase time was 70 min.