Critical role of pH in wastewater treatment and resource recovery from the hazardous chemical polishing wastewater

Abstract

Chemical polishing (CP) wastewater offers enormous potential for phosphorus recovery. This study focused on the Al³⁺ removal and phosphate recovery from the CP wastewater by electrochemical (EC) treatment combined with the chemical precipitation method. EC systems with two configurations were established, and multiple batch cycles were operated. The chemical precipitation simulation and Pearson correlation analysis show that the removal pathways of phosphate and Al³⁺ were divided into three steps based on the increasing pH. Step I was the hydrogen reaction to increase pH from 1.21 to 2.78, and then the electrode reaction increased pH from 2.78 to 3.60, named step II. Step III was increasing pH from 3.60 to 7.00 by the addition of NaOH. Al³⁺ was mainly removed as Al(PO)₄ in step II, and phosphate was mainly recovered as vivianite in Step III. The higher pH could increase the Fe(II)/P molar ratio by reducing phosphate concentration in step II, and the higher Fe(II)/P molar ratio could improve vivianite purity in step III. The EC system can run stably for 15 days with a removal efficiency of 99 % and vivianite purity of 57 %. These findings could be exploited for more industrial wastewater treatment, advancing the practical application of EC technology.