| This paper considered that it was not only because of the process technology but also the method that resulted in the conflict of SRT, the competition of substrate, inhibiting of the products in the traditional biological system for nitrogen (N) and phosphorus (P) removal, on the base of reviewing the theory and technology on N and P removal. It was more important to find a new method to remove the N and P efficiently. According to the special way of the PAOs (phosphorus accumulating organisms) transformation, at first time, the author brought forward creatively that effective P removal could also be realized by discharging the P-rich sewage produced during anaerobic reactor than by discharging the p-rich sludge produced during aerobic stage, and the new method could avoid the conflict in SRT between N and P removal.This paper made a systematic research on the new method and the corresponding process ERP-SBR which based on the new method. Detailed work included that: research on removal ability of N and P by compared and theoretic experiment in ERP-SBR system; Experimental research on main factors such as operation behaviors, COD loading, SRT, DO (dissolved oxygen), temperature; activity of the sludge and the ability of the releasing phosphorus of the anaerobic sludge; Experiments research and theoretical analysis on the disposal of the P-rich wastewater and P recycle.The conclusions were as follows:(1)From the experiment research on the ability of sludge P-releasing in anaerobic reactor and P-absorbing of the aerobic sludge, the author found that the activity of PAOs in process which SRT was more than 50 days could be activated by discharging the p-rich sewage and the alternation condition between anaeration and aeration. When operating with long SRT in ERP-SBR system, experimental results showed that when SRT=50~80d, COD 238~639 mg/L ,NH3-N 25.1~51.4 mg/L, TN 29.7~58.3 and TP 5.48~11.45mg/L in influent, COD≤43mg/L,NH3-N≤1.38 mg/L,TN≤6.02mg/L,TP≤0.27 mg/L in effluent. The efficiency of COD, NH3-N, TN, TP were 95.3%, 98.9%, 90.7%, 98.4% respectively, and ERP-SBR system was more effective and steadier in N and P removal than the single P or N removal systems.(2)According to mechanism of P-releasing of PAOs in anaerobic condition and P-absorbing in aerobic condition, the author firstly brought forward the quantificational relationship between SRT, the ability of P removal and substrate: BOD/TP = 0.863 SRT + 17.2. By the classification of excessive P-absorbing ability of PAOs, the author considered that P could be removed prior to P-absorbing in ERP-SBR, and PAOs only having the excess P-absorbing ability of "the first type" which was higher than the need for substrate could be removed effectively and excess P-absorbing ability of "the second type" more than potential P-releasing ability had a good resistance to impact of P-load.(3)Stage research to sludge activity in anaerobic condition and aerobic condition, the author firstly found that the specific mass and the VSS/MLSS of the sludge in anaerobic condition were larger than that in aerobic condition. Moreover, longer SRT was, larger the VSS/MLSS was. Dehydrogenation enzyme activity and have different change rules that the dehydrogenation enzyme activity increased in aerobic condition and decreased in anoxic condition; SOUR increased in anaerobic condition and decreased in aerobic condition. In author's opinion, SOUR could only reflect the potential ability of the sludge to absorb oxygen. For the long SRT in system, lower sludge activity had good substrate reverse and staged characters, which thus made the ERP-SBR system has good ability to resist the impact of the load. (4)The author also found that the nitrogen loss could be about 70% in the total of removed nitrogen in aerobic stage for ERP-SBR, and it became the main way of N-removal. According to the analysis on each stage of N- removal, the author found there was a linearity relationship between SRT and the N-removal in aerobic condition, that was: . The experiment also showed th...
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