Concentrating hexavalent chromium electroplating wastewater for recovery and reuse by forward osmosis using underground brine as draw solution

Abstract

The purpose of this work was to investigate forward osmosis (FO) for the concentration of hexavalent chromium (Cr (VI)) in electroplating wastewater from processing Acrylonitrile Butadiene Styrene/Polycarbonate plastics to enable the reuse of recovered Cr(VI) in the plating baths. The feed solution (FS) was chromium galvanic wastewater, while the draw solution (DS) was underground brine with osmotic pressures of 28 and 226.8 bar, respectively. Baseline and FO filtrations were performed using commercially available Aquaporin Inside membrane hollow fibre FO (AIM™ HFFO) modules. Each filtration procedure consisted of a sequence of performed baselines, filtrations and cleanings. During the first filtration (F1), the water flux decreased on average from an initial value of 28.7 LMH at 46.7 % water recovery to 18.5 LMH and from 20.1 LMH at 28.4 % water recovery to 16.8 LMH for the second filtration (F2). The corresponding FS volume reduction factors were 1.9 and 1.4 with a concomitant FS concentration factor of Cr (VI) of 1.6 and 1.3 for F1 and F2, respectively. After 1.5 h of filtration, the Cr (VI) rejection by the membrane was 99.74 % and 95.83 % for FO1 and FO2, respectively. As the AIM™ HFFO membrane is negatively charged electrostatic repulsion between the membrane surface and the negative ions (HCrO4− and Cr2O72) will contribute to the rejection of Cr (VI). A loss of integrity of the AIM™ HFFO was observed after the cleaning step which was ascribed to chemical degradation of the membrane due to the oxidizing character of Cr (VI) in the draw solution. Thus, the results show that FO can be used in this type of application, but the membrane material must be adapted to withstand harsh environments.