The Effects of Operational Conditions on Ebpr Performance

Excessive nitrogen and phosphorus can cause eutrophication in water bodies and needs to be reduced in most wastewaters before discharge to receiving waters. The excess biological phosphorus removal (EBPR) process has been shown to be an economical and environmentally compatible method of reducing phosphorus from wastewaters. Despite the complexity of EBPR mechanisms, appropriately designed and operated treatment plants can easily achieve phosphorus (P) removal as long as EBPR-available organic substrates such as short chain volatile fatty acids (VFAs) and an anaerobic-aerobic reactor configuration are provided. Some factors and operating conditions, however, adversely affect the performance of EBPR plants. For this paper, the effects of aerobic recycle and SRT on system performance were investigated using modified UCT configuration systems operated at 20 (System 1) and 5C (System 2), respectively. The results showed that electron acceptor loadings of 999 and 552 mgO2/d to the respective anoxic reactors reduced P removal performance by 12 and 29 mg/L in Systems 1 and 2, respectively. The reason for the difference in the magnitude of the reduced performances was that the denitrifying bacteria of System 1 used internally stored PHA for denitrification, while the denitrifying bacteria of System 2 used externally available acetate. The study also implied that the best P removal can be achieved with a total SRT value of at least 16 days at 5C. The washout biomass solids retention time (SRT) of the EBPR functions was determined to be 3.5 and 1.8 days at 5 and 10 C, respectively. These values are significantly lower than the value predicted by Mamais and Jenkins (1992). The reason for this difference is the presence of highly enriched poly-P organisms (55% and 39% P as VSS at 5 and 10 C, respectively) in this study. The high