Phosphorus Removal Performance in EBPR System under Extra-low Dissolved Oxygen Condition

Abstract

Two sequencing batch reactors (SBRs) were operated with alternating anaerobic/oxic (An/O) for 127 days to study the phosphorus removal efficiency and process performance of the EBPR under different dissolved oxygen gradient. For the reactor (R1) in which DO was not controlled and measured as high as 6 mg·L-1 during the aerobic stage, a stable phosphorus removal performance was achieved in the former 65 days during the operational period. The phosphorus removal efficiency was greater than 95.9% and the total phosphorus in effluent was less than 0.5 mg·L-1. However, the phosphorus removal performance subsequently deteriorated after 65 days and completely broke up until 97 day due to long-term excessive aeration. Throughout the operational period,only 39.4% of effluent TP met the national wastewater discharge standard A. For the test reactor (R2) in which DO was controlled at the levels of 2, 1, 0.5, 0.2, 0.1 mg·L-1 during the aerobic stage, respectively, the phosphorus removal performance showed a slight fluctuation at the beginning of each stage but rapidly increased to a stable state. According to the statistics, 94.6% of effluent TP in reactor R2 could meet the national wastewater discharge standard A throughout the operational period. In only 6 days out of the 127 days, effluent TP failed to meet the national standard and the process performance was far better than that of R1. The specific phosphate uptake rate under DO=2 mg·L-1 was found to be nearly the maximum, but it was greatly influenced by the low DO. In addition, limited filamentous bulking resulted from low organic matter degradation rate under extra-low DO level (0.1 mg·L-1) was observed. Nevertheless, 100% of effluent TP during this stage could meet the national standard. As a result, the phosphorus removal in micro-aerobic EBPR system for saving energy was feasible.