[Concentration of Nitrate in Main Anoxic Stage and PHA, TP Metabolism for Nitrogen and Phosphorus Removal in Single Sludge System with Continuous Flow]

Abstract

Based on test results and mass balance, PHA, TP metabolic regularity was revealed under different nitrate nitrogen concentrations in main anoxic stage [c(NO₃)] for nitrogen and phosphorus removal in single sludge system with continuous flow, then the effectiveness of using c(NO₃) as control parameter was proved from the perspective of the reaction mechanism. During experiment period, the influent COD, total nitrogen (TN), and total phosphorus (TP) concentrations were stabilized at (285.78±18.19), (58.13±3.79), and(7.14±0.51) mg·L^-1, respectively. The experiment was carried out under the condition that the c(NO₃) values were 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5 and 4.0 mg·L^-1 based on the feedback control structure using PLC automatic control system to control the nitrifying liquid flow with the water quality. The sludge load of COD was (0.253±0.071)kg·(kg·d)^-1, the sludge load of TP in anaerobic stage was (0.006±0.001) kg·(kg·d)^-1, the sludge load of TN in aerobic stage was (0.049±0.006) kg·(kg·d)^-1, the hydraulic retention time (HRT) in bioreactor was 9h, the sludge recycle flow was 0.5, and the mixed liquor recycle was 1.0. The results showed that effect of c(NO₃) value on PHA synthesis and storage rate in the ANS was conspicuous, and the percentage of PHA storage occupied 74% of COD removal when c(NO₃) value was 2.5 mg·L^-1.The impact of c(NO₃) value on PHA degraded in the main anoxic stage was great, and the percentage of PHA degradation in the main anoxic stage occupied 55% of total PHA degradation when c(NO₃) value was 2.5 mg·L^-1. The phosphorus released in anaerobic stage changed along with increasing c(NO₃), and the amount of phosphorus released obtained the maximum value 6.16 g·d^-1 when c(NO₃) value was 2.5 mg·L^-1. In addition, under c(NO₃) value of 2.5 mg·L^-1, the amount of total phosphorus uptake and anoxic phosphorus uptake obtained the maximum values of 8.04 g·d^-1 and 3.67 g·d^-1, respectively. Then it was confirmed thatc(NO₃) could serve as a run controlling parameter with the best value of 2.5 mg·L^-1 from the perspective of PHA and TP metabolic mechanism.

Keywords: PHA; continuous flow; mass balance; nitrate nitrogen in main anoxic stage; phosphorus.