Phosphorus Removal With Lime-sodium Fluoride Composite Flocculant

Phosphorus is one of the main factors leading to eutrophication. With the development of economy and the increase in population of city, the total amount of phosphorus in wastewater increases, and the original phosphorus removal technology has not meet the waste water discharge requirements.The methods for wastewater phosphorus removal include chemical and biological methods, crystallization, adsorption and so on. The most widely used and successful method is chemical and biological. In this paper chemical method was used for phosphorus removal. The main results are as follows:(1) The water-soluble phosphate is dominant in the wastewater, accounting for 93.7%. Organic phosphorus is relatively less.(2) The addition of sodium fluoride can cause floc structure compact, increase settling speed and decrease sedimentation volume. The phosphorus removal of lime and sodium fluoride composite flocculant is superior to Ca(OH)2, Al2(SO4)3, FeCl3 and MgCl2.(3) The optimum reaction conditions for phosphorus removal in this paper are as follows:lime 300 mg/L, sodium fluoride 30 mg/L, Ca/P>1.67, additive A+PAC (9:1) 0.1% or additive A+ neutral PAM (1:9) 0.8%. The precipitates in the system probably include fluorapatite, apatite and calcium phosphate and so on.