The Effect Of Temperature On The Performance And Microbial Community Structure Of Enhanced Biological Phosphorus Removal (EBPR) System

Phosphorus is a key element for the growth of algae and other photosynthetic microorganisms. However, excessive phosphorus will lead to eutrophication of water.There are many methods to remove phosphorus from the wastewater, among which the enhanced biological phosphorus removal(EBPR) is the most economical and effective method, and it is widely used in the practical engineering. Biological phosphorus removal is achieved via poly-phosphate accumulating organisms(PAOs) to accumulate phosphorus beyond their normal metabolism needs. However, due to the constraints of environmental and operational conditions, biological phosphorus removal process often faced the problem of poor operation stability and even failed to operate. The main reason for this result is the emergence and enrichment of the bacteria(GAOs) which has no ability of phosphorus removal. Among many factors affecting the proliferation of GAOs, the temperature is the key factor to determine the stability of microorganism and its catalytic performance, so it had been widely concerned and there were a lot of inconsistent views. In this study, an SBR reactor was used to study the competition between PAOs and GAOs under different temperatures in order to provide theoretical evidence for the stability of the urban sewage treatment plant.In this study, the effects of temperature on the competitive relationship of PAOs and GAOs were studied by using the A/O process in the SBR reactor with snythetic wastewater. Through measuring the performance(phosphorus removal efficiency, the phosphorus release and uptake rate of phosphorus and substrate utilization rate) of SBR reactor under the different temperature, and used the fluorescence in situ hybridization(FISH) to analyse the relative amount and distribution of the main functional microbes(PAOs and GAOs) in activated sludge.The study mainly investigated the temperature range from 20℃ to 30℃, which was the temperature range of laboratory room temperature. The results obtained would be useful in devising an operational strategy for the EBPR process in the tropics.Results are as follows:When the temperature was at 20℃, the effluent of the SBR was lower than 0.1mg/L, the phosphorus removal efficiency was more than 99%, the anaerobic phosphorus release rate, aerobic phosphorus uptake rate were 57.5、43.9mgP/g VSS/h,and acetate uptake rate was 112.8mg HAc/gVSS. Phosphorus release/acetate uptake ratio reached0.50 P-mol/C-mol. PAOs dominated in the activated sludge, the proportion of PAOs in total bacteria was more than 90%, but the proportion of GAOs was only 3%. But as the temperature rose, the phosphorus removal efficiency, phosphorus release and uptake rate and the proportion of PAOs declined, but the proportion of glycogen accumulating organisms(GAOs) increased, which implied that GAOs had the competitive advantage over PAOs under high temperatures, resulting in the decline of the phosphorus removal efficiency.When the water temperature increased to 30℃, the phosphorus removal efficiency decreased to less than 5%. Phosphorus release and uptake rates were 28.3 mgP/gVSS/h and 18.9 mg P/g VSS/h. Acetate uptake rate was 186.7mgHAc/g VSS. Phosphorus release/acetate uptake ratio reached 0.17 P-mol/C-mol. GAOs dominated more than80% of the total bacteria. The proportion of PAOs in the whole microorganisms was less than 8%.However, when the system was at 30℃ for a long time, the phosphorus removal ability gradually recovered, the amounts of PAOs gradually increased, after a short recovery, the numbers of PAOs detected were more than 87%, while the GAOs gradually decreased to 4%. Phosphorus removal efficiency was more than 99% same with 20 ℃, but its phosphorus release and uptake rates was 2 to 3 times of 20 ℃, were147.1, 83.7mgP / g VSS / h respectively, acetic acid absorption rate 276.1mgHAc / g VSS / h.The phenomenon of the good performance under the high temperature is not due tothe high pH, because a short term test via artificial adding acid into the aerobic phase to maintain the pH values less than or equal to 7.6 was carried out for more than two SRTs,During this period, the system was able to normal operation and the phosphorus removal efficiency was still more than 99%. The change of phosphorus release rates, phosphorus uptake rates and acetate uptake rates changed little, PAOs and GAOs accounted for the proportion of total activated sludge remained almost unchanged.Therefore, the experiment result showed that the pH is not the important factor in this study.