Recycling of Wastewater for Surface Finishing by Desalination with Reverse Osmosis Membrane and Deionization with Ion Exchange Resin

To recycle waste rinse water from metal surface finishing, the discharge is desalinated with a reverse osmosis(RO) membrane after filtration and its pH is adjusted to an acidic state. The fouling index(FI) had a reading of 4 in the acid(pH5) liquid after micro filtration by a 1μm cartridge filter element. The flow speed for the concentrated fluid was maintained at more than 0.1m/s to prevent precipitation of a suspended solid or adherence of an insoluble material to the membrane. This pretreatment allowed effective and stable desalination process for the waste rinse water using the RO membrane.The desalinated water was passed through a cation exchange resin column and an anion exchange resin column in a series. Water deionized by the ion exchange method after its desalinization using a RO membrane can be reused in the final rinsing process. The electric conductivity of permeated water from the RO membrane did not exceed 4.5mS/m and effluent from the anion exchange column was nearly 1mS/m.Based on these results, this process is a practical recycling system for discharge from surface finishing.