A pilot study on a membrane process for the treatment and recycling of spent final rinse water from electroless plating

Abstract

A hybrid process that includes microfiltration, UV irradiation, carbon adsorption, nanofiltration and ion exchange for treating and recycling spent final rinse water from an electroless plating operation has been developed. The process comprises four steps: (1) wastewater stream segregation, in which spent final rinses are segregated from other more heavily contaminated rinses and are combined to form a raw feed water stream for treatment; (2) pretreatment, in which the raw feed water stream is treated to remove particulates, microorganisms and free chlorine, and to reduce TOC; (3) heavy metal removal, in which the pretreated water is separated into a concentrate stream (containing salts) and a permeate stream (clean water) using a nanofiltration membrane; (4) polishing step, in which the permeate is further deionised using a mixed bed. The polished permeate stream is then recycled back to the plating operation rinsing system. The results of a pilot study showed that high quality product water (heavy metals free and <5 μS/cm in conductivity) is being consistently produced using a NF membrane system with an overall water recovery of 90%. The product water treated using this hybrid process is being recycled for use in the plant operation with no detrimental effects. The design data for a full scale NF plant with a treatment capacity of 25 m3/h has been obtained and the estimated payback period is between 13 and 18 months. The process is more applicable for reclaiming wastewater containing mainly heavy metals but low in monovalent ions.