Basal Research On The Competition And Control Of Pao And Gao In EBPR System

In nowadays, people, including the enrironmental experts, the enriomental protection postulants and the government, pay more and more attention on the eutrophication questions because of the degeneration of the waterbody. The standard of the wastewater discharge was controlled more strictly to achieve not only COD removal but also simultaneous COD, nitrogen and phosphorus removal. So the nitrogen and phosphorus removal technology aimed for eutrophication control has been the study focus in the wastewater treatment area. Enhanced biological phosphorus removal system is accepted in many country for its effective and low cost, while it often faced to deteriotated or collapse because of the existence or enrichment of glycogen accumulating organisms(GAO) in the system. GAO can competed with the phosphorus removal sponsor: phosphorus accumulating organisms(PAO) for the limited carbon souce and other substance. In order to accelerate the investigation development of phosphorus removal, especially on the competition principle and control method between PAO and GAO, this research use lab SBR fed with raw water or synthetic wastewater to study the enhanced biological phosphorus removal system(EBPR). We hope this kind of work can benefit for the people who dedicated in the biological phosphoros removal.Because of the absent of PAO or GAO's pure culture in the world, this research aimed to obtain large quantity of PAO,GAO orα-GAO by enrichment works. This kind of enrichment cultures is very important for people to know the physiological and biochemical characterists and the metabolic pathway of these three groups. Other than some suitable conditions just like pH, tempreture and load, P/C and carben source were two important selective factors for this enrichment works. As results, PAO reached 80%of the total bacteria,the efficiency of P removal of the system was over than 98%. GAO could reach 90%of the total bacteria, and also,α-GAO was a absolutely predominant group in its reactor.Although people haven't isolated PAO successfully till now, but this research tried to isolate and purify the phosphorus accumulating bacterial because of the importance of the pure culture for the understanding of the EBPR system.87 strains were isolated from the activated sludge with phosphorus removal ability. After pre-screening by blue-white blaze test, re-screening by phosphorus release/uptake test, 1 strain, P4, with high phosphorus release ability in anaerobic phase and high phosphorus uptake ability in aerobic phase was achieved, and also, it could convert PHA, glycogen and poly-P in the anaerobic-aerobic condititions. Through observing the morphological feature of YP4, analyzing the physiology and biochemistry index, combining the 16SrRNA technique, YP4 was identified as acinetovacter sp.DG880.Among many factors that can affect the competition between PAO and GAO, this research focused on pH, tempreture, carbon source, C/P and nitrite.The short term effect operated by batch test showed that the amount of phosphorus released was related to the anaerobic pH, PAO prefered higher pH for phosphorus release, the higher pH was, the more phosphorus was released into the water. But on the other hand, the varision of pH did nothing on COD removal but it could affect the PHA synthetic significantly. The system fed with raw water showed steady state when anaerobic pH ranged from 6.5 to 8.0. A slight change of pH from 6.5 to 6.0 or from 8.0 to 8.5 led to a complete loss of phosphate-removing capability. Compared to PAO, GAO fed with raw water had a wider anaerobic pH survival range. When the anaerobic pH changed from 6.0 to 8.5, there was no significant effect of pH on GAO. The activated sludge fed by raw water had ability to be suit for the undesired pH conditions. Aerobic pH affect test showed that 6.0 was not fit for PAO to uptake phosphorus, while other pH conditions(6.5-8.0) had nothing to do with phosphorus uptake.The enhanced biological phosphorus removal system, using activated sludge fed by raw water couldn't be operated in low(<15℃)temperature for a long period, for it might destroy the other bacteria's metablic leading to destroy the balance of PAO and the other bacteria.In the orthogonal tests, all the three factors, including the kind of carbon source, quantity of added carbon source and quantity of added phosphate, could affect the phosphorus removal rate. The kind of carbon source was the crucial factor to affect the phosphorus removal rate, and the phosphorus removal rate increased with the addition quantity of carbon source (from 100mg/L to 300mg/L) and the decrease of the phosphate source (from 21mg/L to 5mg/L). The experiment showed that glucose could be utilized by phosphorus accumulating organisms as the most available carbon source compared with both sodium acetate and sodium propionate in actual WWTP operation. A different result from the traditional concept obtained in this study is that the system could release and uptake more phosphorus when it was fed by propionate than when it was fed by acetate, since the system we used is enriched and cultured by raw water, so it showed different performance from the one cultured by synthetic wastewater.Batch experiment showed that phosphorus removal rate varied remarkably with the C/P ratio at the value of 30 or less, while the COD removal rate did not. And also, C/P ratio also effected the COD reduction/ P release greatly.The accumulated nitrite in the aerobic phase would affect the phosphorus removal ability of the system. When the concentration of nitrite was over 10mg/L and increased with a rapid speed, the phosphorus removal rate decreased from 60% to 20% darmatically. So 10mg/L was the endurable highest nitrite concentration for the EBPR system. Besides, nitrite could affect phosphorus uptake more than phosphorus release.After inoculated with floc activated sludge, the culturing of PAO enriched granular sludge could be achieved by using propionate as substrate, alternating the concentration of COD load, shortening settling time, providing hydrodynamic shear stress and high DO concentration. GAO was washed out of the system and PAO became the dominant population when acetate was used as substrate. The PAO enriched granular sludge had perfect COD removal rate of 94% and phosphorus removal rate of 100%. The mature PAO enriched granules had compact structure, with mean diameter of 2mm and white flagellum on the surface. And also, the mature granules had high OUR, density, integrality rate and low aquiferous rate, leading to the reactor could contain high biomass concentration with good settling properties.