A feasibility study on the treatment and recycling of a wastewater from metal plating

A program of research was initiated to study the treatment of spent rinse water from metal plating using reverse osmosis (RO) to meet the requirements for reuse as an alkaline rinse water. Four categories of spent rinses were treated in the laboratory using flat sheet membranes from different manufacturers. The experimental results showed that CPA2, ESPA1 and TW30 membranes were not suitable for treating the spent solvent rinse. A mechanism for the solvent to attack the composite RO membranes was proposed. For a combination of alkaline, acid and nickel-plating rinses, rejections of conductivity, nickel, nitrate and total organic carbon (TOC) were above 97, 99.8, 95 and 87%, respectively. The permeate conductivity and concentration in terms of nickel, nitrate and TOC were below 45 μS/cm, 0.01, 2.1 and 3.0 ppm, respectively, which met the requirements for reuse as an alkaline rinse water. An appropriate ultrafiltration (UF) pretreatment could reduce fouling of RO membrane and increase the flux of RO membrane by 30–50%. It was found that there was an optimum operating pressure for the treatment of nickel-plating rinses. The results also showed that the feed pH had a significant effect on the rejection of nickel.