High-pressure batch reverse osmosis (RO) for zero liquid discharge (ZLD) in a Cr(III) electroplating process

A batch RO system was designed and built for high-pressure (120 bar) operation. The system was developed for a ZLD application involving treatment of metal plating wastewater from a Cr(III) electroplating process at a major industrial plant. Hybrid semi-batch/batch operation enabled a compact design to be achieved. To maximize water recovery without exceeding a set peak pressure, a method for controlling the switch point between semibatch and batch phases was developed. The system was tested with feed representative of rinse water from the electroplating process. A range of feed concentrations (at 10-20x dilution of the plating bath), feed flows (0.21-0.46 m(3)/h), water fluxes (6-14 LMH) and water recoveries (87-95.7 %) were investigated. The system successfully recovered Cr(III) and restored its concentration to that of the electrolyte bath, thus meeting the requirements for reuse in the electroplating process. Rejection of most species was >99.8 %, sufficient for reuse of the permeate as rinse. However, rejection of boric acid was only 69-80 % such that a second RO pass may be needed to remove boric acid. Specific Energy Consumption was <2.25 kWh per m3 of treated rinse water, representing a 50 -fold saving compared to the current method of treatment and disposal at the industrial plant.