| As the issue of eutrophication grows more severely and the regulatory requirements of wastewater discharge become increasingly stricter, economical and efficient removal of nitrogen and phosphorus has been a focus of wastewater treatment research. Though biological nitrogen and phosphorus removal process has been applied widely as one of economical and sustainable processes, it has some inherent problems that need to be solved. For example, the contradictions of substrates competition and SRT between the nitrogen and phosphorus removal, have inhibited the enhancement of removal efficiency. Some novel theories of nitrogen and phosphorus removal, such as denitrifying phosphorus removal and simultaneous nitrification and denitrification supply new ideas in solving theses contradictions.Based on the theory of denitrifying phosphorus removal, A/O/A simultaneous nitrogen and phosphorus removal process was adopted as research subject. Dynamic changes in the removal efficiencies and morphologies of activated sludge of two A/O/A processes which treated with synthetic wastewater and domestic wastewater respectively were investigated systematically, and the differences of granular sludge characteristics in the two systems were analyzed comprehensively. Short and long -term influences of environmental factors on the removal efficiency of the A/O/A process were analyzed compar comparatively. Microbial community succession in the systems during the start-up period and the effect of environmental factors on the microbial population structure were investigated. Isolated denitrifying phosphorus removing bacteria were identified, and their phosphorus removal efficiency were further studied.During the start-up period, flocculent sludge transformed into granular sludge gradually with the enhancement of removal efficiency, and lots of protozoa appeared in the A/O/A nitrogen and phosphorus removal processes. Granular sludge in the two systems treating different wastewater were quite distinct under the same operational condition in the stable phase. Granular sludge cultivated with real domestic wastewater was smaller in particle size, slower in sedimentation, larger in pore size, smaller in specific surface area, lighter in specific weight, higher in water content, higher in activity, more in extracellular polymeric content, lower in intracellular polymeric content, less in phosphorus release, and better in dintrification, compared with that cultivated with synthetic wastewater.Environmental factors had vital influence on the performance of A/O/A nitrogen and phosphorus removal process in short-term. Sodium acetate and sodium propionate were optimal carbon source, and sodium succinate was slightly worse than them. Ethanol and glucose were unsuitable carbon source, and isovalerate was the worst carbon source. As pH value of influent changed from 6.0 to 8.0, no significant effect on the COD removal efficiency of the system were found. Influent pH at 7.0, perfect performance was achived. Value of C/N in the range of 0.5 to 8.3 had little effect on the COD removal efficiency. Total nitrogen removal efficiency increased with the increase of influent C/N. phosphorus removal efficiency of the system was perfect while C/N was in the range of 0.5 to 6.1, but it deteriorated when C/N was larger than 6.1. Value of C/N in the range of 0.5 to 8.3 had little effect on the COD removal efficiency. Total nitrogen removal efficiency increased with the increase of influent C/N. phosphorus removal efficiency of the system was perfect while C/N was in the range of 0.5 to 6.1, but it deteriorated when C/N was larger than 6.1. Effect of calcium, magnesium and potassium cations absence on the COD and nitrogen removal efficiency of the system was invisible. Calcium, magnesium and potassium cations were all involved in phosphorus release and uptake reactions, and the molar ratio of them to phosphorus were 6.1×10-2,3.8×10-1,2.8×10-1, respectively. Absence of calcium, magnesium and potassium cations in the influent led to surplus phosphorus release, and the order of the amounts of phosphorus release was obtained as follow: potassium absence >calcium absence >magnesium absence >normal system. In the range of 10oC to 30oC, changes in temperature had slightly effect on the COD removal efficiency, and the rate of phosphorus release and uptake both rose with the increase of temperature. Nitrification of the system got worse at temperature 10oC. Below 30mg/L, both nitrate and nitrite could be used as electron acceptor instead of oxygen for phosphorus uptake, and the order of phosphorus uptake rate was observed as follow: oxygen > nitrate > nitrite.The effects of environmental factors on the A/O/A nitrogen and phosphorus removal procss in long-term and short-term were not entirely consistent. When sodium acetate and sodium propionate were used as influent carbon source in long-term, the system could keep favorable performance. But sodium succinate as carbon source led decrease in nitrogen removal efficiency, and the phosphorus removal deteriorated with the reduction of nitrogen removal efficiency. Favorable removal performance was achieved as pH in the range of 7.5 to 8.5. The performance got worse gradually, when the system was operated at pH 6.5 in long-term. As C/N in the range of 2.63.3, the performance of the system was excellent. However, with the increase of influent C/N, the phosphorus concentration in the effluent increased and removal efficiency of the system decreased gradually. In the start-up phase, Dynamic changes were observed in microbial species structure the A/O/A nitrogen and phosphorus removal process. In the synthetic wastewater system, partial dominant bacteria such as Candidatus Accumulibacter phosphatis always existed, partial dominant bacteria such as Rhodospirillales was eliminated and replaced by new strains, e.g Rhodocyclaceae and Candidatus Accumulibacter phosphates. Microbial commuities succession also occured in the domestic wastewater. Bacteria M1 and M3 (β- proteobacteria ) were always dominant, bacteria M14 (β- proteobacteria ) appeared with the operation of the system. Environmental factors had extraordinary influences on the microbial community structure. Dominant bacteria such as Denitrifying bacterium and Uncultured Chloroflexi bacterium with strong tolerance were resident bacteria, and some dominant bacteria such as Ammonia oxidizing bacterium were gradually washed out from the system with the transformation of the operational condition.Through primary and secondary screening tests, four efficient phosphorus removing strains named as JL4, FH6, FQ3 and FQ4 were chosen from twenty-five strains isolated from the system with stable performance. Strain JL4 was identified as Pseudomonas sp., and strains FH6, FQ3 and FQ4 were identified as Bacillus sp. By the methods of physiological-biochemical tests, fatty acid identification and phylogenetic analysis of 16S rDNA clone. Environmental factors such as pH value, carbon source and temperature had distinguished effects on the growth and phosphorus removal efficiency of strains. The growth of strains had almost ceased and phosphorus removal performance deteriorated under the condition of pH 5, and the optimal pH was neutral. The optimum temperature was 30oC for strains JL4, FH6 and FQ3, but 25oC for strain FQ4. Cultivated with different carbon source, the sequence of the growth rate and phosphorus removal efficiency of the strains was concluded as follow: Sodium acetate > sodium propionate > sodium succinate >glucose.
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