It is well known and firmly established that the rate of chemical and biochemical reactions slow down as temperature decreases. Nevertheless, several studies have reported that the efficiency of enhanced biological phosphorus removal (EBPR) improves as temperature decreases. However, several recent studies have reported that EBPR reaction rates decrease with temperature decrease in accordance with the Arrhenius relationship. This study was designed to more thoroughly investigate this controversy using two UCT plants fed with a synthetic wastewater consisting primarily of acetate as the COD form, and a small amount of supplemental yeast extract. Experiments were performed over temperatures ranging from 5 to 20 degrees C. The results showed that, even though the kinetic rates decrease as temperature decreases, EBPR systems perform better at colder temperatures. The reason for better system performance is apparently related to reduced competition for substrate in the non-oxic zones, which results in an increased population of PAOs and, thus, greater EBPR efficiency. The proliferation of PAOs apparently occurs because they are psychrophilic whereas their competitors are not. The experiments showed that the EBPR sludges accumulated high concentrations of both PHA and glycogen at 20 degrees C, but accumulated more PHA and much less glycogen at 5 degrees C. Although the results could be interpreted as the result of changes in the PAO-GAO competition, Mann-Whitney non-parametric comparisons of transmission electron microscopy examinations revealed no indication of the presence of GAOs population under any temperature conditions. Regardless, mass balances of the glycogen data showed that the involvement of glycogen is less at cold temperature, even though EBPR was greater. Unlike current EBPR models (e.g. Mino model), the results suggest that glycogen metabolism is not a precursor for EBPR biochemistry. The results also indicate that temperature not only may cause selective pressure on the dominant organisms, but also may force them to use a different metabolic pathway as temperature decreases.

A UCT type pilot plant fed with synthetic wastewater was operated with influent COD/TP ratios of 18, 12 and 8 to investigate the role of intracellular storage products on EBPR mechanisms. Acetate was the sole carbon source and other nutrients were provided in excess during plant operation at an SRT value of 10 days and at 20 0 C temperature. COD utilization, P-release and -uptake, PHA and glycogen storage and utilization of the system were monitored. The steady state data showed that PHA storage, glycogen production and system performance were influenced by the COD/TP ratio. System P removal performance decreased as COD/TP ratio decreased and some deterioration in overall performance occurred at the lowest COD/TP ratio. Very good stoichiometry was obtained between both organic storage and its utilization, and P release and P uptake. Glycogen production and P-uptake were observed in the absence of extracellular organics and in the presence of NO 3 -N. The consumption and production of glycogen in anaerobic and aerobic reactors favored the Mino model over the Comeau/Wentzel model for EBPR. At the lowest COD loading, glycogen was not generated and energy obtained through PHA utilization apparently was used for maintenance energy needs.

Reduced EBPR performance in full and bench-scale EBPR studies was linked to the proliferation of GAOs but often time with the lack of any evidence. In this study, a detailed enzymatic study was coupled with batch tests and electron microscopy results for a realistic explanation. The results eliminated the possibility of population shift from PAO to GAO or other non-PAO due to the short batch test period provided which would not allow a population shift and further justified with the electron microscopy results. The results indicate that glycogen serves not only as source of reducing power for PHA production but also serves as an alternative energy source when the poly-P pool of the PAOs is depleted. Slow generation of ATP via glycolytic pathway at 5 degrees C cannot satisfy energy requirements of EBPR cells to complete several cell functions including acetate uptake and PHA storage. However, the glycolytic pathway is efficiently operable at warm temperatures (> 20 degrees C). The reduced performance of enhanced EBPR facilities operated at warm temperature may not be a result of GAO proliferation; instead it may be related the efficient use of the glycolytic pathway by PAOs which results in more glycogen storage and less P uptake, thereby reducing the EBPR performance.

Improved design strategies at BNR plants should include cost reductions so that the consumers and water authorities will be more willing to build EBPR plants instead of conventional activated sludge plants. Through efficient design, actual savings in construction and operation costs can be realized. For this reason, anaerobic stabilization of COD needs to be seriously considered during design for direct energy savings at the plants. The existence of anaerobic stabilization has been demonstrated through experimental work. Evaluation of operational data from existing plants has also indicated the definite presence of anaerobic stabilization at plants that include anaerobic zones for EBPR as part of their operation. By exploring the biochemical reactions taking place in EBPR process, particularly the involvement of the storage mechanisms for PHA, poly-P and glycogen storage, the potential mechanisms of the anaerobic stabilization of COD in EBPR systems was explored. The resultant balances pointed out the importance of glycogen metabolism in terms of conserving carbon and providing a sink for the reducing equivalents produced under aerobic conditions. This mechanism is different from those observed in anoxic-aerobic and conventional aerobic activated sludge systems, and appears to be at least partially responsible for the observed anaerobic stabilization of COD.

It is well known and firmly established that the rate of chemical and biochemical reactions slow down as temperature decreases. Nevertheless, several studies have reported that the efficiency of enhanced biological phosphorus removal (EBPR) improves as temperature decreases. However, several recent studies have reported that EBPR reaction rates decrease with temperature decrease in accordance with the Arrhenius relationship. This study was designed to more thoroughly investigate this controversy using two UCT plants fed with a synthetic wastewater consisting primarily of acetate as the COD form, and a small amount of supplemental yeast extract. Experiments were performed over temperatures ranging from 5 to 20 o C. The results showed that, even though the kinetic rates decrease as temperature decreases, EBPR systems perform better at colder temperatures. The reason for better system performance is apparently related to reduced competition for substrate in the non-oxic zones, which results in an increased population of PAOs and, thus, greater EBPR efficiency. The proliferation of PAOs apparently occurs because they are psychrophilic whereas their competitors are not. The experiments showed that the acclimated EBPR sludges accumulated high concentrations of both PHA and glycogen at 20 o C, but accumulated more PHA and much less glycogen at 5 o C. Although the results could be interpreted as the consequence of changes in the PAO-GAO competition, comparisons of transmission electron microscopy examinations revealed no indication of the presence of GAO population under any temperature condition. Regardless, mass balances of the glycogen data showed that the involvement of glycogen is less at cold temperature, even though PHA production and EBPR performance was greater. Unlike current EBPR models (e.g., the Mino model, 1987), the results suggest that involvement of glycogen metabolism in EBPR biochemistry is a requirement as suggested by Mino model (Mino et al. 1987) but its involvement depends on the environmental conditions. EBPR stoichiometry was presumed to be insensitive to temperature changes (Brdjanovic et al. 1997). However, this study showed that the stoichiometry of EBPR was sensitive to temperature The results also indicate that temperature not only causes selective pressure on the dominant organisms, but also may force them to use different metabolic pathways as temperature decreases.