Zinc Alloy Plating Affecting Wastewater Treatment Sludge Revisted

Is the filter press sludge hazardous even if it doesn’t exceed TCLP requirements? Are any of these processes considered hazardous because we process aluminum? How about the polishing filters after the clarifier?


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Q. In your answer to R.Y. in January 2006’s EH&S Clinic, you stated that if aluminum parts are processed through a zinc phosphate line, the waste water filter press cake becomes listed as a RCRA hazardous waste F019.

As a job shop, we periodically process aluminum parts through our five-stage and three-stage washers as well as through an iron phosphate immersion line and an aluminum conversion (potassium permanganate) line. All rinse waters from these lines are sent thru a clarifier for treatment.

  1. Is the filter press sludge hazardous even if it doesn’t exceed TCLP require- ments?
  2. Are any of these processes considered hazardous because we process alumi- num?
  3. How about the polishing filters after the clarifier? G.G.


A. It is understandable to be “confused” that a metal that exhibits relatively low toxicity and is not regulated by USEPA as one of the eight hazardous waste metals (arsenic, barium, cadmium, chromium, lead, mercury, selenium, and silver) could render a waste “hazardous.” But according to USEPA documents, the “phosphating” of aluminum does cause the F019 designation. In addition, you say that you also have an “aluminum conversion” line using potassium permanganate. The F019 designation is—“treatment sludges from the conversion coating of aluminum.” Here is why.

First, USEPA cites its background listing document for F019, which describes conversion coating as “processes (that) apply a coating to the previously deposited or basis metal for increased corrosion protection, lubricity, preparation of the surface for additional coatings or formulation of special surface appearances. This manufacturing operation includes chromating, phosphating, metal coloring, and immersion plating.”

Second, the industry had tried to convince USEPA that chemical conversion coating of aluminum does not occur during phosphating since the process does not impart a crystalline coating as described in the background document. USEPA responded that its intention is a broader definition that includes both crystalline and amorphous coatings. USEPA then refered to ASTM Standard B374-80 which defines conversion coating as “a process produced by chemical or electrical treatment of the metallic surface that gives a superficial layer containing a compound of metal.”

Also, unfortunately, USEPA does not seem to consider other language in its F019 background document that states “phosphate conversion coatings are formed by the immersion of iron, steel, or zinc-plated steel in a dilute solution of phosphoric acid plus other reagents” or recognize that your process does not contain the chromate and/or cyanide for which F019 was originally listed.
Currently, the only USEPA exemption from F019 listing is wastewater treatment sludges from the zirconium phosphating of aluminum cans.

Furthermore, even if you process aluminum parts only periodically, all of your filter press cake is RCRA hazardous due to USEPA’s mixture rule; that is, unless specifically exempted, if a listed hazardous waste, such as F019, is mixed with a non-hazardous solid waste, such as the wastewater treatment sludge produced during phosphating of steel parts, the mixture becomes the listed hazardous waste even if it does not exhibit any characteristics of a hazardous waste (ignitability, corrosivity, reactivity, and TCLP).

So to answer your questions:
• Since your filter press cake is a listed hazardous waste under F019 desig- nation, it does not matter that your waste passes the Toxicity Characteristic Leach- ing Procedure (TCLP),
• Yes, the processing of aluminum does cause the waste to be hazardous, and
• Since your polishing filters catch “wastewater treatment sludge” that leaves the clarifier, yes, these cartridges are also F019 hazardous waste due to USEPA’s “mixture” rule.
One possibility to remove the F019 designation is to turn off the phosphate stage of your washers when processing aluminum and to bypass your iron phosphate immersion and aluminum conversion lines’ wastewater around your clarifier and polishing filters, assuming that compliance can still be maintained. If this is feasible, we would recommend that you get your state EPA to agree with concept before proceeding.

I am sure that you are disappointed in my response, and it is my opinion that the F019 listing is not based upon sound science. These processes have changed, chemical wise, dramatically since the background documents were published by USEPA back around 1980. In fact, it has been our experience that “wastewater treatment sludges” from the processing of aluminum is very “clean” as compared to phosphating of steels. In fact, the TCLP metals are typically found below or near levels of detection.

The good news is that USEPA is considering amending the F019 designation. Between 1997 and 2004, USEPA had granted 12 delisting petitions for individual plants across the United States to exclude F019 from regulation. In a letter written in 2000, the Alliance of Automobile Manufacturers and the Aluminum Association asked the agency to standardize its regulations and amend the F019 rule, removing the barriers to using aluminum in manufacturing automobiles. USEPA is “scheduled” to publish a Notice of Proposed Rulemaking (NPRM) in July, 2006, although it looks like it may be geared only for automobile manufacturing plants. When USEPA finally does publish this NPRM, it behooves you and the metal finishing industry to respond to make sure this unreasonable and wasteful regulatory burden is removed from all facilities that perform conversion coating of aluminum, especially if there is no hexavalent chromium or cyanide compounds used in the process.

If you desire to explore this issue further, you can go to www.epa.gov/rcraonline.

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