Effects Of Temperature And Carbon Sources On Phosphate Accumulating And Glycogen Accumulating Organisms And Phosphorus Removal Efficiency In Biological Phosphorus Removal Process

Phosphorus (P) is a key nutrient that stimulates the growth of algae and other photosynthetic microorganisms, and must be removed from wastewater to avoid eutrophication in aquatic water systems. In biological phosphorus removal process(BPR), the phosphorus removal can be achieved by polyphosphate accumulating organisms (PAO) which was accumulated through recirculating sludge from anaerobic and aerobic conditions, and is a vital way to control eutrophication. When operated successfully, the process is a relatively inexpensive and environmentally sustainable option for P removal; however, the stability and reliability, as well as the sensitivity to environment conditions and high operation demanding can be a problem. The enrichment of glycogen accumulating organisms (GAO) who competed with PAO for substrate has been hypothesised to be the cause of the degradation in P removal, and the control of GAO growth is significant for the stability of BPR. Among the factors which influence the growth of GAO, temperature is considered to be the key for the stability and catalytic efficiency of microorganism. Meanwhile, substrates take part in the competition of PAO and GAO directly. From the stoichiometry and kinetics aspect, systemic batch test with enriched PAO and GAO was employed to study the effects of temperature and carbon sources on the metabolism of PAO and GAO. Also the numerical simulation of the operation characteristics under the bybrid effects of temperature and carbon sources was studied. Through the study, the metabolic processes and competition relationship under different temperature and carbon sources could be well understood, and it can be a reference for improving the operation stability under low temperature condition.The enrichment of PAO and GAO could be achieved by traditional and stepwise limiting way, and the fluorescence in situ hybridization(FISH) results showed that the PAO(Accumulibacter) and GAO(Competibacter) content was 86% and 78% respectively. Maintaining the batch test temperature of 5, 10, 15, 20, 25 and 30℃,the effects of temperature on the metabolism of PAO and GAO was investigated. The anaerobic batch test suggested temperature has little influences on the stoichiometry of PAO, but a obvious reduction was observed for GAO in 5 and 10℃, which means a alterative metabolic pathway for GAO to cover the energy. With respect to kinetic process, the temperature has a significant effect on the anaerobic reaction rate. The reaction rate reached the maximum at 20℃and 25～30℃for PAO and GAO, respectively. The uptake rate of PAO and GAO was comparable when the temperature was below 20℃, but the anaerobic ATP maintenance coefficient was lower than that of GAO, which resulted in the superior competition to GAO. In the aerobic batch test, the temperature has a little effects on the aerobic stoichiometry of PAO and GAO, only a reduciton of GAO was found at 30℃. The aerobic kinetic rates increased with the temperature,but medium dependence was found for the aerobic kinetic. Although the growth rate of GAO was always lower than PAO, the competition superior of GAO to PAO was determined by the higher uptake rate above 20℃.The carbon source had a significant influence on PAO and GAO under low temperature. The anaerobic uptake test suggested, PAO had no preferable choice to acetate or propionate, and both the uptake rate was similar. The uptake rate of propionate was only of 31% with that of acetate by GAO by contrast. The adaptable capcity of PAO to PHA compositon was weak which resulted in a lower uptake rate of phosphorus with propionate than that with acetate. The main reason was the differences of PHV and PH2MV synthesized in propionate metabolism to PHB in acetate metabolism. A preliminary test was employed to study the effects of carbon source on denitrifying phosphorus removal. It was found that the low temperature BNR system contained a certain content of denitrifying PAO. The phosphorus release and denitrifying phosphorus removal was higher with acetate as substrate, but the uptake of phosphorus with NO3--N as acceptor was depressed for the component of PHA was PHB. On the other hand, the phosphorus release with compounds and propionate was close to that of acetate, but utilization of NO3--N was improved for the proportion of PH2MV increased.Glucose could be taken as the substrate in low temperature biological phosphorus removal process, but the startup strategy and operation characters were complex. The stability could be implemented by extend the aerobic reaction time and sludge retention time, reduce the aerobic reaction time and dissolved oxygen. The glycogen synthesization was observed in the anaerobic process with glucose as substrate, which caused the energy replaced by the hydrolyzation of glycogen. Compared to the acetate, the phosphorus release and the synthesization PHA was lower, and PHV was the main component in PHA.The competition of PAO/GAO under various temperature and carbon source was evaluated with a incorporated model. The simulation results was well accordance with the operation status. The simulated biomass of PAO and GAO showed that the carbon source on PAO was neglectable under low temperature, and the dominance of PAO was determined by temperature only. Under moderate temperature and acetate or the compounds as substrate, the biomass was composed of PAO and GAO simultaneously. However, the PAO was up to 76% when the sole propionate as substrate. Under high temperature and acetate or the compounds as substrate, the biomass of GAO was higher than PAO. As the substrate was propionate, the biomass of PAO and GAO was 45% and 24% respectively with the PAO as dominance.