Fact Sheet: Rinsewater Reduction for a Metal Finishing Shop

Virginia Waste Minimization Program
Vol. 1 Issue 4

A Waste Reduction Success Story from the Virginia Waste Minimization Program on rinsewater reduction for a metal finishing shop.

Rinsewater Reduction For a Metal Finishing Shop

Abstract

A metal finishing job shop reduced rinsewater volume and ensured compliance with discharge regulations by installing a staged rinse system. segregating waste streams, and modifying processing solutions.

Background

Deburring, Inc. in Shoreview, Minnesota, is a job shop involved in tumbling, passivating, and electropolishing, all of which are processes that clean and smooth surfaces of metal parts. Shopw aste consists of water and solids from these three operations. The rinsewater contains high levels of copper, nickel, lead, zinc, and chromium. Pretreatment of this effluent is necessary before discharge to the sewer system in order to meet local discharge limitations as well as EPA electroplating pretreatment standards.

Implementation

The company implemented the following pretreatment options:

• Waste stream segregation Waste streams from the tumbling, passivating, and electropolishing processes were previously sewered together. In the new system, the tumbling waste stream, which contains a large amount of metal-bearing sludge, is segregated from the passivating and electropolishing stream before pretreatment.

• Staged rinse system Work pieces from the electropolishing and passivating operations are passed through a staged rinse system. Water from the initial spray rinse is returned to the electropolish tank to recover some of the metal and electropolish solution dragout. Total water usage is decreased in the new staged rinse system, which controls water flow.

• Modified tumbling compound Deburring, Inc. is researching the option of reducing its solid waste by lowering the amount of wood flour in its tumbling compound. The tumbling process removes metal burrs by tumbling the part with a medium such as stones or ceramic, and a tumbling compound such as soap and finely ground sawdust (wood flour). Using less wood flour ensures a decrease in the amount of solids generated in the tumbling process. Improving housekeeping should also lower the volume of solid produced.

• Modified passivating solution The passivating process is used to remove contamination from the surfaces of parts by immersing them in a solution of 20% nitric acid and proprietary agents. Omitting chromium from the passivating solution removes this heavy metal from the rinse water.

Results

Implementation of the recommended changes eliminates the need to buy a $50,000 precipitation system to generate sludge for disposal. The modifications for the new rinse system cost approximately $500. Deburring, Inc.'s process improvements should ensure compliance with regulations and facilitate lower water use.

(This article was reprinted with permission from the Minnesota Technical Assistance Program.)

This Waste Reduction Success Story is provided as a service of the Virginia Waste Minimization Program, a technical assistance program of the Virginia Department of Waste Management.

For more information on opportunities to reduce waste contact:

Virginia Waste Minimization Program
11th Floor Monroe Building. 101 North 14th Street
Richmond, Virginia 23219
804-371-8716 or 1-800-552-2075
TDD 804-371-8737