Problem Analysis And Measures Research On Biological Phosphorus Removal Process Of Dongguan City Wastewater Treatment Plant

Economy is growing rapidly in my country, Urbanization level is constantly improving, Urban water environment has been seriously polluted. To combat the growing nitrogen phosphorus pollution and water nutrient over-enrichment, the new "comprehensive wastewater sewage discharge standards" (GB8978-1996) which has been carried out since Jan.l 1998 demand strict nitrogen phosphorus standards in secondary wastewater treatment plants. According to the new standards, the effluent water from secondary wastewater treatment plants, NH3-N<15 mg·L^-1, TP<0.5 mg·L^-1. Currently, Most of the secondary wastewater treatment plants that have been bilut could't meet the new standard. Some wastewater treatment plants are facing serious transformation tasks, many wastewater plants will face a major transformation without reducing the capacity, add system Nutrient phosphorus removal function as an important goal. Some new wastewater treatment plants also can't reach to required phosphorus removal effect because the project design did not take into account changes of inlet water quality. Therefore, it is necessary to research the phosphorus removal effect in lower BOD load. Probe the major factors affecting phosphorus removal and provide some information for the design and operation of wastewater treatment plants.At present, there are two wastewater treatment processes with the treating capacity of 2×l0⁵m³/d.The first phase process adopts A/O biological phosphorus removal process. The second phase process adopts reversed A/A/O process which is the reformed A/O biological phosphorus removal process. Since two wastewater treatment processes were built, the majority of indicates date of the effluent water meet the B standards of the discharge standards of pollutants for municipal wastewater treatment plant (GB 18918-2002) and the first class standards of Guangdong province(DB4426-2001).But two process can't remove TP better. The TP indicate of effluent water can't reach to standards.This paper analyzed the main reasons for the phosphorus removal though the monitoring of the operating condition of the two treatment processes. All our work is aimed at finding the best operating parameter for technics and increasing the phosphorus removal rate. The following conclusions can be drawn according the experiments:1. Low BOD and high DO level of the inlet, great amount nitrate and DO in the returned sludge are the adverse factors to the phosphorus removal.2. Anaerobic tank's HRT(hydraulic retention time) should be 1.5h. Oxic tank's HRT should be between 4.5 and 5.5h. Sedimentation tank's HRT should be 2h.3. It is hard to attain the discharge standard depending on the single biological dephosphorization. Chemical dephosphorization should be added in order to reach to the primary standard of Guangdong province (DB4426-2001).4. When the sludge reflux ratio is 38%, MLSS is about 600mg/L and MLVSS is about 200mg/L, A/A/O process has a pretty good impact in term of BOD and COD removal.5. According to the practical situation of Dongguan city wastewater treatment plant, some suggestions have been put forward to improve the phosphorus removal effect.