Enhanced removal of phosphate by electrogenerated iron combined with mechanically activated calcite

Abstract

Fe electrocoagulation is efficient for the removal of phosphate with low energy consumption, whereas suffers from the high concentrations of the total dissolved Fe (TDFe) in the effluent. In this study, mechanically activated calcite was used to combine with the electrogenerated Fe to improve the removal efficiency of phosphate and reduce the concentrations of TDFe. The removal efficiency of phosphate (initial concentration 1.0 mg/L) in 30 min was significantly increased (88 %) by mechanically activated calcite combined with electrogenerated Fe method, compared with mechanically activated calcite method (43 %) and electrogenerated Fe method (53 %) separately. The concentration of TDFe in the effluent reduced from 4.9 mg/L with electrogenerated Fe method to 0.2 ∼ 0.5 mg/L with mechanically activated calcite combined with the electrogenerated Fe method. The mechanically activated calcite combined with electrogenerated Fe method was confirmed by the efficient removal of phosphate in the biological treatment effluent from a municipal wastewater treatment plant reached a removal efficiency of approximately 100 % (reduced from 1.33 mg/L to 0.006 mg/L) and in the rainfall runoff from a fertilizer enterprise reached a removal efficiency of 98 % (reduced from 3.86 mg/L to 0.075 mg/L). The removal mechanism was proposed. The Fe-P polymer was formed in the dissolved phase. The mechanical activation improved the solubility of calcite and provided dissolved Ca2+, as well as increased the surface area of calcite and provided more adsorption sites. Therefore, the mechanical activation promoted the adsorption of the Fe-P polymer onto the surface of the mechanically activated calcite. This study provided an efficient method for the removal of phosphate in wastewater and simultaneously reducing the concentrations of TDFe in the effluent.