Chemical precipitation and membrane distillation process for the treatment of acidic anodic oxidation wastewaters

Abstract

The acidic anodic oxidation plating facility has high-strength wastewater which contains pollutants such as sulfate, chemical oxygen demand (COD), conductivity, aluminum, and iron. This study investigated the treatability of acidic wastewater provided by an anodized plating facility using chemical precipitation and membrane distillation (MD) techniques. Sodium hydroxide (NaOH), calcium carbonate (CaCO3), and calcium hydroxide (Ca(OH)2) were used for pre-treatment. NaOH was determined to be the most suitable chemical for pollutants removal. After pre-treatment, the MD process was used as a post-treatment. Different pore size hydrophobic membranes were used in the MD process. The removal efficiency of the MD process for COD and total organic carbon (TOC) is 83.3% and 88.6% and above, respectively. Furthermore, the achieved removal efficiency for sulfate, conductivity, iron and aluminum was around 100%. The results show that the treatment of acidic anodic oxidation plating wastewater by the MD process is promising. However, to decrease the high concentration of sulfate and minimize membrane fouling, the pH of the wastewater should be adjusted with a pre-treatment. Post-MD treatment results provided effluent quality respecting the discharge standards of the Turkish Water Pollution Control Regulation.