Geochemical modeling of chromium release in natural waters and treatment by RO/NF membrane processes

In this work, a geochemical approach was used as a strong scientific tool for the pre-selection of suitable remediation systems to treat Cr-contaminated groundwaters. The geochemical characterization allowed the selection of Nano filtration (NF) and Reverse Osmosis (RO) as suitable remediation processes, whereas a new geochemical modeling studied the evolution of water chemistry during the water-rock interaction. The new reaction path modeling re-evaluated the role of Fe as the main oxidant in the system, reproducing the analytic concentrations of relevant solutes, including Cr(VI). The spring with the highest Cr(VI) content was treated to lower its concentration below the threshold values. A laboratory-scale set-up conducted both NF and RO experiments on different commercial membranes, varying the operating pressures. The results showed high Cr(VI) rejections (around 95%) for all tested membranes, leading to Cr(VI) concentrations below the threshold limits. The high flux obtained, already at lower operating pressures, combined with high selectivity towards Cr(VI), makes NF a favorable remediation option.