Efficient treatment of metal plating wastewater: Comparing batch nanofiltration (NF) vs. batch reverse osmosis (RO) for component reuse

Metal plating generates wastewater polluted by toxic components, such as copper, nickel, chromium, and organics. Reuse of such components avoids the waste stream and reduces the cost of restocking the metal plating process. However, reuse by conventional desalination is challenging because of the high feed osmotic pressure and high concentration factor (and hence high recovery) required, which typically result in high energy consumption. This drawback can be mitigated by batch membrane desalination. In this study, we evaluate experimentally a high-pressure free-piston batch NF/RO system for metal plating wastewater treatment, capable of processing ∼10 m3/day with a specific energy consumption (SEC) <3 kWh/m3. This represents a 40–60× energy savings compared to current methods of wastewater disposal. Comparing batch NF against batch RO, we find that both can effectively recover key components for direct reuse. Batch NF reduces SEC by 30–40 % compared to batch RO, while achieving comparable chromium recovery. However, boric acid rejection is ∼70 % in batch RO and < 10 % in batch NF, necessitating a second-pass batch RO to allow reuse of the permeate stream. The two-pass approach successfully reduces boric acid levels, making the permeate suitable for reuse in rinsing baths and effectively closing the loop.