Wastewater from Aluminum Processing

Question: We currently have a five-stage phosphate washer followed by an electrocoat system that is used to process steel parts.


We currently have a five-stage phosphate washer followed by an electrocoat system that is used to process steel parts. Wastewaters from this operation, up to 25 gal/min, are pretreated before discharge to sanitary sewer; sludge is hauled out to a sanitary landfill.

A customer has approached us about electrocoating aluminum parts. We know that there may be needed changes to our washer’s chemistry. Are there any environmental issues that would arise if we do decide to process aluminum parts? F.B.


For your wastewater, processing aluminum parts will not change how the wastewater is regulated; it will still be covered by the Metal Finishing Pretreatment Standards under 40CFR433.

However, this change will have a significant impact upon the regulatory status of your wastewater pretreatment system’s filter press cake (sludge). By processing ANY aluminum through your washer, all of your filter press cake will become a listed RCRA hazardous waste. Since phosphating is considered a chemical conversion process by U.S.EPA, wastewaters from this process will produce a listed RCRA hazardous waste under 40CFR261.31, “F019: wastewater treatment sludges from the chemical conversion coating of aluminum.” Because of U.S.EPA’s “mixture” rule, whenever a listed hazardous waste is mixed with other solid wastes, the entire mixture becomes a listed hazardous waste; therefore, all of the filter press cake generated would be a listed hazardous waste, even on days when only steel is processed.

As a RCRA hazardous waste, the disposal cost of your filter press cake could increase ten times. Furthermore, if you are not already a hazardous waste large quantity generator (greater than 2,200 lb per calendar month), the amount of filter press cake generated could easily move you into this new status (1 cu yd of filter press cake weighs about 2,100 lb). The regulatory requirements for a hazardous waste large quantity generator are quite extensive, including notification, storage, written procedures, contingency plan, initial and annual training, waste minimization plan, annual reports, inspections and DOT issues.

Before making this change in production, I urge you to thoroughly research its implications. If you do not have the research capacity within your company, outside professional assistance would be valuable.

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