JPH05306480

PURPOSE:To drastically decrease the volume of the waste rinsing liquid cont. the high-concn. COD generated from the online rinsing equipment in a production line for surface treated steel sheets, etc. CONSTITUTION:Three rinsing booths 10, 12, 14 for spraying the rinsing liquid to the steel sheets S treated with chemical treating liquids are disposed along a transportation line and circulation tanks A to D more by one than the number of the booths for circulating the rinsing liquid to these booths are installed so that the rinsing liquid can be circulated to the respective booths by means of switching valves from any of all the circulation tanks A to D at the time of subjecting the steel sheets to the rinsing online while continuously transporting the steel sheets. The tank D is used for replenishing the fresh rinsing liquid and the rinsing liquid is circulated to the first to the third booths 10 to 14 respectively from the tanks A to C. The tank D is changed over to the third booth 14 and the tanks B, Care changed over to the booths on the respectively one upstream side when the concn. of the COD in the third booth 14 on the extreme downstream side attains a control value. The rinsing liquid of the tank A is then thrown away and this tank A is used for the next replenishment.