METHOD FOR RECOVERING WASHING WATER DISCHARGED FROM COATING PRETREATMENT LINE

摘要

PROBLEM TO BE SOLVED: To provide a treatment and recovery method capable of again reutilizing washing water discharged from a phosphate chemical conversion treatment process as a chemical conversion treatment liquid and washing water at a low cost with high efficiency. SOLUTION: The washing water discharged from the phosphate chemical conversion treatment process is supplied to a membrane separator together using two or more kinds of reverse osmosis membranes and/or nano-filter membrane mutually different in salt rejection ratio to be separated into a non- permeated concentrated liquid containing a component for chemical conversion treatment (capable of being returned to the chemical conversion process to be reutilized) and permeated water (capable of being reutilized as washing water).