Q: Is it your understanding that filter press cake from a zinc or zinc cobalt plating line that uses trivelant chromates would be considered non-hazardous, and, therefore, could be disposed into our local sanitary landfill? Thanks for any feedback. S.H.
A: In order for the filter press cake to be disposed of as non-hazardous into your local sanitary landfill, basically, three questions have to be answered.
First, is it NOT a “listed” RCRA hazardous waste under U.S. EPA regulations 40CFR261.31? The typical listing of F006 is defined as “wastewater treatment sludges from electroplating operations except from the following processes: sulfuric acid anodizing of aluminum; tin plating on carbon steel; zinc plating (segregated basis) on carbon steel; aluminum or zinc-aluminum plating on carbon steel; cleaning/stripping associated with tin, zinc, and aluminum plating on carbon steel, and chemical etching and milling of aluminum.” Reviewing the EPA background documents for the hazardous waste listing of F006, the hazardous constituents evaluated were cadmium, chromium, copper, cyanides, gold, lead, nickel, silver, tin, and zinc. Since zinc plating is specifically exempted and cobalt was not evaluated as a hazardous constituent in the F006 background documents, zinc plating and zinc-cobalt plating do not cause the filter press cake to be a “listed” hazardous waste.
Second, is the filter press cake NOT a “characteristic” RCRA hazardous waste under USEPA regulation 40CFR261 Subpart C or applicable state regulations? Even if a waste is not “listed,” it still must not meet the four characteristics of a hazardous waste: ignitable, corrosive (pH <2 or >12.5), reactive and toxicity characteristic leaching procedure (TCLP). Due to the aqueous nature of the filter press cake and the pH conditions under which it was formed, it is not an ignitable or corrosive waste. Unless it contains significant concentrations of free cyanide and sulfide, it is not reactive. This leaves its ability to leach out arsenic, barium, cadmium, chromium, lead, mercury, selenium and silver through the TCLP. Despite using trivalent chromium, if your TCLP results come back greater than 5 mg/L chromium, the filter press cake must be classified as a hazardous waste. Assuming your filter press cake passes the TCLP test, it is a non-hazardous waste.
HINT: Collect filter press cake samples from at least three press loads, and then knead the samples together, as if you are making bread dough, in order to provide the lab with a representative and fairly homogeneous sample; if you observe colored streaks through your filter press cake, they are veins of concentrated metals that will skew results.
Third, is your filter press cake acceptable to the local sanitary landfill? Even though your filter press cake may be a non-hazardous waste, your sanitary landfill has its own rules for acceptance of waste because it is their property. Many times, analyzing your waste just for the hazardous waste characteristics is sufficient, but it is not uncommon for your sanitary landfill to require additional analysis, such as total metal constituents (total chromium, total zinc, total iron, and total cobalt in mg/kg) or TCLP for zinc and cobalt to see how they leach even though they are not hazardous waste constituents. Recently, one of our clients had to have their filter press cake subjected to a distilled water leaching procedure (same as TCLP but using distilled waste instead of the acidic solution) for zinc and chromium since the landfill had its own acceptance criteria (the filter press cake passed).
To sum up, there is a high likelihood that your filter press cake is non-hazardous. Best of luck.