The Effects of Secondary-Phosphorus Release on Biological-Phosphorus Removal in a Pre-anoxic Process

Abstract

In this study, a sequencing batch reactor (SBR) with fill, anaerobic, oxic1, anoxic, oxic2, settle, decant and sludge pre-anoxic process, was used to investigate the performance efficiency of biological nutrient removal which occurs secondary- phosphorus release during different pre-anoxic hydraulic time (PAHRT). The results of the study showed that the processes of secondary-phosphorus release and secondary-phosphorus removal were significantly affected by PAHRT, whereas the removal of chemical oxygen demand (COD), ammonia nitrogen (NH4 -N) + and total nitrogen (TN) removal were only slightly affected. The research also showed that when PAHRT for 120 min., and MLVSS was 5330 mg/1, the secondary-phosphorus-release concentration was lower than 0.15 mg/L, and the removal efficiency of the total phosphorus (TP) was higher than 80.98%. Moreover, it was found that there is a negative correlation between secondaryphosphorus release and TP removal efficiency and between secondary-phosphorus release and the quantity of released anaerobic phosphorus. The study also showed that phosphate-accumulating organisms (PAOs) can be used to break down poly-p without PHA synthesis during the process of secondary- phosphorus release, resulting in a reduction of PHA content in PAOs. As a result, the rate of anaerobic-phosphorus release and oxic-phosphorous uptake decreases , leading to a duction in phosphate- removal efficiency. It is thus necessary to reduce or, avoid a secondary- phosphorus- release event in a pre-anoxic system. In summation, this project’s findings show that a decrease of secondary-phosphorus release in a pre-anoxic process is an effective way of enhancing biological- phosphorus removal.