The Anodising Industry Wastewater: Considerations of Its Treatment for Environmental Protection

The anodising industry releases toxic effluents which have been treated using various technologies over the years. In this paper, we review separation, oxidative degradation and biological degradation wastewater treatment technologies for the anodising industry effluent. We also examined the suitability of these processes based on the effluent nature and composition. The objective was to synthesise the literature to ensure a proper understanding of the research progress and to highlight grey areas that require more investigative insight. It was observed in the review that the wastewater has a very low pH and is rich in heavy metals like aluminium, magnesium and phosphates and other anions. Techniques like nanofiltration, reverse osmosis and adsorption were shown to be able to effectively handle the variety of pollutant species in the wastewater (achieving pollutant removal percentage of > 90%). Oxidative and biological degradation were unsuitable for treating anodising industry wastewater albeit with a serious dearth in published literature. The major limitations of oxidative degradation processes are the non-biodegradability of heavy metals and the •OH radical scavenging of anions like phosphates, sulphates and nitrates. For biological degradation, the very low pH and high concentration of heavy metals make it unsuitable for the survival of most microorganisms. It is recommended that the improvisation of operating conditions of existing technologies and the consideration of alternative tertiary strategies of wastewater treatment to achieve zero liquid discharge and actualisation of the relevant sustainable development goals should be considered.