Characteristics of anoxic phosphors removal in sequence batch reactor |
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Authors: | WANG Ya-yi PAN Mian-li YAN Min PENG Yong-zhen and WANG Shu-ying |
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Institution: | 1. College of Civil Engineering and Architecture, Zhejiang University of Technology, Hangzhou 310014, China;Key Lab of Beijing for Water Quality Science, Beijing University of Technology, Beijing 100022, China 2. Biotech Institute, Hangzhou Huadong Medicine Group Co., Ltd, Hangzhou 310011, China 3. College of Civil Engineering and Architecture, Zhejiang University of Technology, Hangzhou 310014, China 4. Key Lab of Beijing for Water Quality Science, Beijing University of Technology, Beijing 100022, China |
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Abstract: | The characteristics of anaerobic phosphorus release and anoxic phosphorus uptake was investigated in sequencing batch reactors using denitrifying phosphorus removing bacteria (DPB) sludge. The lab-scale experiments were accomplished under conditions of various nitrite concentrations (5.5, 9.5, and 15 mg/L) and mixed liquor suspended solids (MLSS) (1844, 3231, and 6730 mg/L). The results obtained confirmed that nitrite, MLSS, and pH were key factors, which had a significant impact on anaerobic phosphorus release and anoxic phosphorus uptake in the biological phosphorous removal process. The nitrites were able to successfully act as electron acceptors for phosphorous uptake at a limited concentration between 5.5 and 9.5 mg/L. The denitrification and dephosphorous were inhibited when the nitrite concentration reached 15 mg/L. This observation indicated that the nitrite would not inhibit phosphorus uptake before it exceeded a threshold concentration. It was assumed that an increase of MLSS concentration from 1844 mg/L to 6730 mg/L led to the increase of denitrification and anoxic P-uptake rate. On the contrary, the average P uptake/N denitrifying reduced from 2.10 to 1.57 mg PO43--P/mg NO3--N. Therefore, it could be concluded that increasing MLSS of the DEPHANOX system might shorten the reaction time of phosphorus release and anoxic phosphorus uptake. However, excessive MLSS might reduce the specific denitrifying rate. Meanwhile, a rapid pH increase occurred at the beginning of the anoxic conditions as a result of denitrification and anoxic phosphate uptake. Anaerobic P release rate increased with an increase in pH. Moreover, when pH exceeded a relatively high value of 8.0, the dissolved P concentration decreased in the liquid phase, because of chemical precipitation. This observation suggested that pH should be strictly controlled below 8.0 to avoid chemical precipitation if the biological denitrifying phosphorus removal capability is to be studied accurately. |
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Keywords: | biological phosphorus removal nitrite MLSS pH denitrifying phosphorus removing bacteria (DPB) anaerobic-anoxic processes batch reactor sequence phosphorus removal phosphors anoxic conditions avoid capability controlled chemical precipitation liquid phase high value release increased rapid as a result of anoxic phosphate uptake reduce specific |
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