THE EFFECTS OF EQUALIZATION ON THE PERFORMANCE OF BIOLOGICAL PHOSPHORUS REMOVAL SYSTEMS

摘要

In this paper, experimental data are presented that confirms that phosphorus removalrnefficiency in biological excess phosphorus removal (BEPR) systems temporarilyrndecreases when the amount of volatile fatty acids (VFAs) added in the anaerobicrnphase is suddenly increased. This results from the fact that acetate uptake is a veryrnrapid process, and that the phosphate concentration at the end of the anaerobicrnphase increases very rapidly. Because of the non-linear dependence of thernphosphate uptake rate with PAO PHA content, the increase in PAO PHA contentrnassociated with VFA uptake is not able to cause a proportional increase in the rate ofrnphosphate uptake. This will cause a temporary imbalance between phosphate releasernand uptake, leading to lower phosphate removal. The VFA loading to full-scale BEPRrnsystems is not constant throughout the day, and temporary imbalances such as thernones imposed in the batch tests can occur in full-scale systems. This hypothesis wasrndemonstrated through simulation of the behavior of an A/O?system receiving a timedependentrninfluent. Equalization is proposed as a method to diminish the potential forrnimbalances between phosphate release and uptake by avoiding sudden increases ofrnVFA loading to the plant. Significant improvements in the effluent quality from thernsimulated system were achieved using equalization. The improvements are greaterrnwhen the amount of VFAs present in the influent are higher than when they arernformed by fermentation in the anaerobic zone. The simulations considered in thisrnstudy suggested that it may be possible to decrease the amount of phosphorusrndischarged by a factor as high as four, when compared to a system withoutrnequalization. Mass equalization is preferable to flow equalization in terms of increasedrnphosphate removal efficiency. Equalization can be used, in concert with otherrnstrategies for the preservation of the PHB content of PAOs under periods of lowrnloadings, in order to minimize the magnitude of "Monday P peaks".