| December24,2002, the Ministry of Environmental Protection and General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China issued the "Discharge standard of pollutants for municipal wastewater treatment plant (GB18918-2002)". The new standards require that the TP of effluent less than1.0mg/L to achieve class A standard for sewage treatment plant built before December31,2005Shanxi Zhengyang WWTP, want to upgrade their SBR process to ensure the effluent achieve this standard and further more to reuse the treated water for miscellaneous consumption in the city and as industrial water for nearby power plant.The phosphorus is intent to be removed by chemical method to ensure the treatment effects. Due to the limited space, it is impossible to add reaction tank and secondary sedimentation tank exclusively for the post precipitation of phosphorus.Therefore the only possible way is synchronous precipitation method by which the PAC or PFS is added to the reactor at the end of the stirring stage of the "aeration4h+stirring1h+precipitation1h+discharge of supernatant and sludge1h+idle1h" SBR operating procedure.Before the implementation of the project, the onsite pilot test of phosphorus removal was carried out. The full scale test which adds PAC in one of the WWPT SBR reactor was then in process according to verify the results of onsite pilot test. By this way, the tests provided effective and reliable preferences for the operation of WWPT.After the testing of chemical phosphorus removal method, the biological phosphorus removal method was also introduced for the purpose of utmost minimization of operation cost meanwhile ensuring the achievement of TP standard of the effluent. It was expected to reduce the phosphorus in the wastewater by the biological phosphorus removal method prior to the chemical phosphorus removal method just by adjusting the schedule of the SBR operation. By this, the dosage of the flocculant was hoped to be reduced.The onsite test indicated when the dosage of PAC and PFS were120mg/L and140mg/L respectively, the TP of the effluent should be less than1.0mg/L, meanwhile the removal rate of CODCr were from77.41%to80.77%,69.79%to78.49%respectively and both of which were lower than the93.25%to95.72%of the control group which were not added with the flocculants. The removal rate of NH3-N were from96.45%to97.43%,96.39%to97.05%respectively while the removal rate of control group without the adding of the flocculants was from94.13%to97.46%. The removal rate of NH3-N of the three groups did not have obvious differences so the flocculants did not influence the removal effect of NH3-N. The color and floccules size of activated sludge added with flocculants were not obviously different in appearance from the control group. But the MLVSS were from46.16%to51.95%and from47.23%to50.69%, which were lower than that from54.04%to60.95%of the control group.In the pilot scale biological phosphorus removal test, the SBR ran in "stirring+aeration" AO process. The results showed that "stirring1.5h+aeration3h" was the best schedule. After0.6h of stirring, the released TP reached the maximum and there was no big change during0.6h～1.5h. The system ran into the aeration stage after1.5h of stirring and the absorption efficient was very high during the first0.5h of aeration. Although there was still TP absorption during the0.5h～3.0h of aeration, the efficient fell very low. The TP of the effluent reached the minimum after3h of aeration,In the "stirring0.5h+aeration3h+stirring2h+aeration1.0h+precipitation0.5h+discharge of supernatant and sludge1h+idle0.5h" procedure, the125mg/L glucose was added after0.5h of second stirring stage. The average TP of the effluent in this "AOAO+carbon" process was0.5mg/L～0.9mg/L and TN was10mg/L～12mg/L. Both of them achieved the class A standard. The added glucose supplemented the content of the low molecular organic carbon and ensured the biological system start up quickly at low temperature. |
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