Study On Preparation And Application Of Phosphorus Removing Flocculant For Treating Phosphating Wastewater

Eutrophication of waterbody is one of difficult problems of environmental protection.Compared with nitrogen,phosphorus is the key factor of eutrophication of waterbody.So we should try our best to reduce the phosphorus wastewater discharged into the water body.Phosphating is widely used in the metal machining and surface painting industry,and has become an important and indispensable part of surface treatment in painting industry.A great deal of reagents contained phosphorate were applied during the phosphating process,consequently phosphate concentration of phosphating wastewater exceeded wastewater discharge standard,so we must remove phosphate from phosphorus-containing wastewater in order to reduce the contamination of water body.In wastewater treatment technology,chemical and biological methods are successfully applied.At first,in this paper comparison between the chemical and biological methods of phosphorus removal,the characteristics of phosphate wastewater is high levels of phosphorus and chemical oxygen demand less,It is difficult to achieve the emission requirements by biological method,it is appropriate to use chemical method treatment.However,the main problem of chemical method is that the amount of flocculants dosage,high-cost and arising from the mud volume,so we need to study a novel,efficient flocculant to solve this problem,and improve the effectiveness of phosphorus removal.An object of study is phosphatizing wastewater during the processing of phosphating,and applied CaO and NaF compositing to dephosphorize,Ca²⁺,F^- and phosphate can react and form the insoluble phosphate precipitation,and join them in the assistant flocculant A,for improving the ratio of phosphorus removal.This composite flocculant can play inorganic,organic flocculants synergies to achieve the purpose of dephosphorization.Determine the best composite flocculant dosage,and analysis of the pH value, reaction time,and the precipitation time,stirring speed and other factors on the effect of phosphorus removal through experiments.The results of experiment showed that the concentration of phosphorus is able to reduced to below 0.5 mg·L^-1 from 135 mg·L^-1 in raw water,when the dosage of lime and NaF is 4.0 g·L^-1 and 20,and mg·L^-1 respectively,reacting 15min,pH value is 8-9,and the rate of phosphorus removal is up to 99.6%,this result came up to the national standard of discharged wastewater. The cost of deal with ton wastewater is 0.79 yuan.The rate of phosphorus removal with the composite flocculant is enhanced 7.6% compared with only lime,the dosage of lime is reduced 30%,resulting in the volume of precipitation is reduced 20%.With the traditional aluminum and iron,phosphorus removal rate increased by 14.2%and 15.18%respectively,and the effect of phosphorus removal by lime - sodium fluoride compound is obviously better than that of using lime-PAC and lime-PFS,phosphorus removal rate increased by 9.6%and 12.3%.Since the introduction of fluoride to dephosphorize,it is inevitab that some is in exit water,the concentration of fluoride ion was measured,the results showed that fluoride in exit water content is 3.4 mg·L^-1 this content is in full compliance with the effluent standards of limited value(less than 10 mg·L^-1).It was proved that this composite flocculant would not cause secondary pollution to the environment.So this composite flocculant has obvious economic and environmental benefits.