Membrane Processing in the Metal Finishing Industry

Two important applications of membrane processing in the metal-finishing field are the use of reverse osmosis for electroplating waste treatment, and ultrafiltration for concentration of oily wastes prior to disposal. Waste waters from electroplating contain contaminants of high toxicity, but also of substantial potential value. Reverse osmosis has been used to close the loop on treatment of individual plating bath rinse waters, returning concentrates to the baths, and reusing purified water for rinsing. A discussion of advantages and limitations is presented for treatment of various plating baths. Reverse osmosis has also been used to concentrate electroplating shop mixed effluents, with up to 95 percent water recovery for reuse. The low-volume concentrate is dried for ultimate solids removal, and waste-water treatment becomes closed loop. Data are presented for this application. Spent oil-containing coolants present the metal-finishing industry with a difficult waste-treatment problem. Conventional disposal of the 1–5 percent emulsions by chemical destruction, incineration or contract hauling is expensive. Ultrafiltration has been employed to concentrate emulsions to over 50 percent oil. These are readily incinerated with no fuel addition required, and work has been done which shows that reuse of the oil either upgraded to a fuel or a lubricant is the best answer for the concentrate. Data are presented for concentration of several wastes.