| Eutrophication in aquatic water systems caused by excessive P emissions was the environmental problem that was uppermost concerned by national government and the public. Around the world, a growing awareness of the need to control P emissions, which is reflected in increasingly stringent regulations, has made P removal more widely employed in wastewater treatment. Enhanced biological phosphorus removal (EBPR) promotes the removal of P from wastewater without the need for chemical precipitants. But that process is unstable. When the EBPR process failed, the dominant microorganisms are changed from Phosphate Accumulating Organisms (PAOs) to Glycogen Accumulating Organisms (GAOs). PAOs and GAOs are competitive organisms in EBPR system and once GAOs dominated in EBPR system, the phosphorus removal efficiency will be worse.Sequencing Biological Reactors (SBRs) were operated with activated sludge enriched of PAOs long-term cultivated with synthentic wastewater using alternating acetate/propionate as a carbon source. On this basis, the effects of differents substrate (the ratios of C/N/P) and water temperature on PAOs and GAOs metabolism were investigated. With the comprehensive, in-depth research of water quality analysis, the changes of intracellular polymers (PHA) and their constituents and the changes of microbial community structure, control strategies in favor of PAOs growth and metabolism were proposed. At the same time, control strategies that were not in favor of GAOs growth and metabolism were also proposed. It aims to provide regulating possibility for PAOs' competition over GAOs, and to create greater stability of biological phosphorus removal.SBRs were operated with activated sludge enriched with PAOs long-term cultivated. After 20d, the entire response system is already in stable state. PAOs took up volatile fatty acids (VFAs) with the release of phosphate under anaerobic conditions, while absorbed orthophosphate and storage as poly-P in the subsequent aerobic phase. The phosphorus removal rate was as high as 90%in this system, and P/C ratio (mol P/ mol C) was in an exponential functional relation with anaerobic time. With molecular biological method, there are abundant species of organism existing in the SBR process, and the microbial community structure was stable. Although the function of individual micro-organisms in phosphorus removal process has not be exactly confirmed except Pseudomonas, PAOs were successful enriched in the system.In order to investigate the influent COD/P ratio effects on the EBPR system, five lab-scale anaerobic-aerobic SBRs were operated with activated sludge enriched with PAOs cultivated respectively with an average COD/P rations of 30:1,25:1,20:1,15:1 and 10:1.With the comprehensive, in-depth research of water quality analysis, the changes of intracellular polymers (PHA) and their constituents and the changes of microbial community structure, it was found that GAOs are the main micro-organisms to cause of the EBPR failure in high C/P ratio. However, the EBPR was also deterioration in performance in low C/P ratio (10:1) because PAOs or GAOs were not able to proliferate under high phosphate concentration. According to the curve equation for PHA/C ratio with C/P ratio changing in the anaerobic phase, the C/P ratio of 14:1 is the best theory environment for PAOs growth, and the C/P ratio of 30:1 is the best theory environment for GAOs growth. Experiences showed that stoichiometric coefficient YSS-P was in an functional relation with COD/P rations.Based on the best C/P ratio for PAOs growth, five lab-scale anaerobic-aerobic SBRs were operated with activated sludge enriched with PAOs cultivated respectively with an average C/N/P rations of 200: 1:13.200:5:13,200:10:13,200:15:13和200:20:13.It was found that increasing the influent ammonia concentration was conducive to the growth of PAOs. The EBPR was deterioration in performance because PAOs or GAOs were not able to proliferate under low ammonia concentration. Moreover, GAOs are the main micro-organisms to cause of the EBPR failure when the ammonia concentration was from 5 to 10 mg/L. However, DNA sequencing results showed that Acinetobacter sp was well growth in that condition. When the ammonia concentration was as high as 15 mg/L, PAOs had became dominant bacteria in the system, however, that's not to say the higher the better, when the ammonia concentration increased to 20 mg/L, the aerobic phosphate uptake would also be suppressed. According to the curve equation for PHA/C ratio with C/N/P ratio changing in the anaerobic phase, the C/N/P ratio of 200: 17.49:13 is the best theory environment for PAOs growth.Lab-scale anaerobic-aerobic SBRs supplied with synthentic wastewater were operated to study the effect of temperature on the activity of PAOs and GAOs in the EBPR system. The phosphorus removal efficiency decreased with increasing temperature from 20 to 35℃. The experimental evidence obtained suggests that GAOs tend to become stronger competitors with PAOs at higher temperatures. However, when the temperature was 35℃, the short-term warming was in favor for GAOs proliferating, PAOs were completely inhibited or even eliminated. After a period of adapting, GAOs proliferation had also been inhibited. Meanwhile, DNA sequencing results showed that Acinetobacter sp was well growth in high temperature. When the growth and metabolism of PAOs or GAOs were inhibited, Acinetobacter sp was gradually becoming dominant bacteria. According to the curve equation for PHA/C ratio with temperature changing in the anaerobic phase, the temperature of 32.67℃is the best theory environment for GAOs growth. Experiences showed that stoichiometric coefficient YSS-P was in an functional relation with COD/P rations.Therefore, the temperature of 20℃is the best theory environment for PAOs growth when the temperature from 20 to 35℃. The damaged ceiling temperature of EBPR system was 30℃. After running over the damaged ceiling temperature, the system will be failed as soon as possible and could not be recovered.KEYWORDS:enhanced biological phosphorus removal (EBPR); phosphate accumulating organisms (PAOs); glycogen accumulating organisms (GAOs); C/N/P rations; temperature...
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