Phosphate Removal By Coagulation Method Based On Addition Of Seawater In The Coastal City Sewage Treatment Plants, Applied Research

Eutrophication is a serious environmental problem which plaguing humankind very much,one of the most important causations of eutrophication is the discharging of wastewater which contain high level of phosphorus into the surface water;With the increasingly stringent enviroumental requiementa,the national standard of TP amount discharged into receiving water body has been controlled in a more and more strict level,currently,a large numberof sewage treatment plants can not reach the TP standards,and the need of chemical phosphorus removal precess is necessary to assist the current drainage technology.Therefore,the research and practical application of the cost effective chemical phosphorus removal technology in a sewage treatment plant di becoming urgent.The study of LCH Sewage Treatment Plant of Qingdao(Qingdao ShouChuang RuiHai Water Supplies Co.,LTD.) found thatthe supematant liquor from the sludge thickening tank,Digester and centrifuge contains a large amount of phosphate (PO₄^3--P),and the plant disposed this wastewater by means of circumfluence, which made the final effluent with high concentration of phosphate.Under such circumstances,the finding and application of a cost-effective chemical technology to deal with the phosphorus-rich supernatant and to reach the TP discharge standards are on the schedule.The prophase experiment showed that the traditional aluminum,iron salt,lime, and other chemical phosphorus removal technologies did not apply to the acurent phosphorus removal process in the sewage treatment plants in Qingdao.Under certain conditions the Ca²⁺,Mg²⁺ and other natural minerals in seawater can react rapidly with PO₄^3--P in the wastewater,coagulating a steady phosphate precipitation,so as to achieve the purpose of phosphate removal,which is the technique "Phosphate Removal by coagulation Method based on Addition of Seawater"This article starts from the study of phosphorus-rich supernatant in LCH Sewage Treatment Plant,and further with the optimization Phosphate Removal by coagulation Method based on Addition of Seawater of and as focus on the application and promotion of this technology in the coastal city sewage treatment plant.The objects of the study are to realize TP＜5mg / 1 after treatment,unit cost of water＜0.45 yuan / m3, and sewage treatment plant effluent TP＜1mg / 1.During the phosphorus-rich supematant laboratory experiment NaOH are need to regulat PH value,and the process conditions were optimized through orthogonal experiments as follows:the water temperature was 20℃,the volume proportion of wastewater to seawater was 5:1,the pH was 10.5,and the reaction time was 20 min.if we Treat the wastewater under the best craft conditions,the removal rates of PO₄^3--P and NH₄⁺-N in the wastewater were 95%and 34%respectively.The on-site using of optimum conditions in the sewage treatment plant indicated that this method is effective both staticly and dynamicly.The removal rate ofauxiliary Pharmacy in the waste water was stabilized at around 95%,and the sediments during the experiment can be recycled.When we calculating the cost,we find out that the use of NaOH to regulate PH value for 1m³ phosphorus-rich supernatant will cost us 0.46 yuan,It is necessary to find a cheaper auxiliary Pharmacy to replace NaOH,so as to reduce the operating costs.As dyeing wastewater PH value can reach about 13,we can use wastewater to regulate the PH value,with lower costs.Experiments show that the dyeing wastewater has the same effect in removing the PO₄^3--P with the NaOH and even with less reaction time,but the yield increase sediment and COD had increase.The pilot plant will be testing the water,as well as access to analog mixed-related information and found that the use of dyeing wastewater PH value adjustment under the conditions of water coagulation of biological treatment system has not been significantly affected.The using of seawater as the precipitating agent to deal with the phosphorus-rich supernatant is not only good in effect but also cheep in cost.When the dyeing wastewater is used to regulate the PH value,the operating cost will be saved a lot.This method is the first innovation domestically,and particularly apply to the coastal areas sewage treatment plant.