Remediation processes of hexavalent chromium from groundwater: a short review

Abstract

Understanding the sources and controlling processes of various groundwater contaminants and their removal methods is extremely important, as groundwater contamination is intricately linked to human health. Chromium (Cr) is a common groundwater contaminant with both natural and anthropogenic origins. Dissolved Cr exists in hexavalent and trivalent forms – while the former is carcinogenic and more soluble – the latter is a micronutrient at low levels and is less soluble. Therefore, most chromium removal methods rely on reducing the hexavalent chromium to its trivalent state to decrease the Cr-toxicity. In recent years, several experimental methods have been attempted for hexavalent chromium removal from aqueous media/groundwater. This paper reviews the recent findings on Cr removal by important, effective, and widely used methods such as adsorption by nanoscale zero-valent Fe-based and conventional materials, electrocoagulation (EC), and bioremediation. The reaction pathways, mechanisms, and effectiveness of each method are also highlighted. The role of parameters such as solution pH and temperature, initial Cr(VI) concentration, contact time with the reducing agent, adsorbent dose, and the presence of competing ions on Cr removal was evaluated. Many of the methods exhibit high (>90%) Cr removal efficiency; the main challenge would be to apply these methods for large-scale water treatment. HIGHLIGHTS Adsorption, electrocoagulation, and biological methods for Cr removal are reviewed in this study.; Stabilizer-based nanoscale zero-valent iron has proven to be an emerging technique for chromium mitigation.; pH of the aqueous medium seems to be the most influential parameter in determining Cr removal.; Future research should focus more on scaling-up the existing methods.;

Keywords

• chromium removal
• groundwater contamination
• nanoparticles
• reduction method
• zero-valent iron