[Concentration of Nitrate in Main Anoxic Stage and PHA, TP Metabolism for Nitrogen and Phosphorus Removal in Single...

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.