Abstract
The purpose of this study is to investigate the effect of free nitrous acid (FNA) and free ammonia (FA) on the anoxic phosphorus uptake rate (PUR) of polyphosphate-accumulating organisms (PAOs) via the utilization of nitrite. With this goal, upon developing a PAO-enriched culture in a sequential batch reactor, a series of batch experiments were conducted to examine the effects of nitrite and ammonium on the anoxic phosphorus uptake rate at different pH levels. According to the results, both free nitrous acid and free ammonia were found to inhibit anoxic PUR to a degree similar to their respective effects on aerobic PUR reported in previous studies, suggesting that phosphorus removal via the anoxic pathway may be just as susceptible as that via the aerobic pathway. The effect of FNA on anoxic PUR is optimally described by a non-competitive inhibition model with a KiFNA value of 1.6 μg N L−1, while the Levenspiel model with an SFA* value of 37 mg N L−1 provided the best fit for the FA effect on PAOs anoxic activities. The results of this study provide new insights regarding the viability of EBPR under high nitrogen loading conditions.
Highlights
Enhanced biological phosphorus removal (EBPR) is rightfully considered a simple and effective method for the removal of phosphorus from wastewater
This could be expected, as free ammonia (FA) is a known inhibitor of several microbial groups such as ammonium oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB)
The application of this method relies on the suppression of NOB by high FA and free nitrous acid (FNA) concentrations that are governed by the nitrogen loading rate, along with dissolved oxygen (DO) concentration and the aerobic solid retention time (SRT)
Summary
Enhanced biological phosphorus removal (EBPR) is rightfully considered a simple and effective method for the removal of phosphorus from wastewater. EBPR relies on the selective growth of polyphosphate-accumulating organisms (PAOs) achieved with the inclusion of an anaerobic phase prior to the aerobic and/or anoxic phases in activated sludge systems. PAOs uptake volatile fatty acids (VFAs) and store them intracellularly as polyhydroxyalkanoates (PHAs) by hydrolyzing their intracellular polyphosphate chains. Once in the presence of an electron donor, PAOs oxidize the stored PHAs, taking up orthophosphates in the process for the reformation of their polyphosphate chains [1]. The produced nitrate may be reduced to nitrogen gas using common heterotrophs under anoxic conditions, effectively removing it from the medium. It is possible to partially or completely bypass the nitratation process by inhibiting NOB, allowing ammonium to be removed by nitritation/denitritation
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