Chemical phosphorus removal optimization from coating wastewater using iron–calcium salt

Abstract

Phosphorus is a commonly used compound in coatings; thus, wastewater from coating plants usually contains large amounts of phosphate. Given its unidirectionality in the ecological cycle, phosphorus must be removed from coating wastewater and recycled. Herein, phosphorus was removed and recovered from industrial coating wastewater through chemical precipitation. The effects and mechanisms of this removal and recovery using the iron salt, calcium salt, and iron– calcium salt methods were analyzed. When the proportion of iron in iron–calcium salt exceeded 0.51, the average phosphorus removal rate was more than 62.44% of the average removal rate when the iron salt or calcium salt was used alone. A synergistic phenomenon was demonstrated with the iron–calcium salt method; the phosphorus removal rate reached 96.13% when the molar ratio of iron–calcium salt to phosphorus was 1.50. The precipitation floccules produced using the iron–calcium salt integrated the advantages of the iron and calcium salt methods; they had a large particle size and were easily crystallized. This study demonstrates a valuable method for the removal and recovery of phosphorus from industrial coating wastewater.