Phosphate Removal From Phosphate-rich Wastewater By Chemical Precipitation Process Based On The Addition Of Seawater

Eutrophication is a serious environmental problem which plaguing humankind very much, one of the important causations of eutrophication is the discharging of wastewater which contain high level of phosphorus into the surface water, meanwhile phosphorus is a valuable non-renewable resource, so with the development of science and society, the removal of phosphorus from wastewater and the realization of phosphorus in wastewater as a resource attract more and more attention from the people.There was high concentration of phosphate in the supernatant liquor of Licunhe wastewater treatment plant, and the plant disposed this wastewater by means of circumfluence, which made the final effluent with high concentration of phosphate. In this study, based on the comprehensive survey of methods and experimental researches, the author put forward a new method to disposal the phosphate-rich wastewater in Licunhe wastewater treatment plant.According the principle of chemical precipitation, the addition of seawater containing Ca²⁺and Mg²⁺ may lead to phosphate removal from wastewater because of the reaction between PO₄^3- and metal ions. In the course of the lab-scaled experiments, the author first used artificial wastewater to study the feasibility of the reaction, and then 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. Treating the wastewater under the best craft conditions, the removal rate of PO₄^3--P and NH4+-N in the wastewater were 95% and 34% respectively. The results of the pilot scale experiments showed that this method could disposal the phosphate in wastewater efficiently and it also had a virtue of low cost.