Q. We are planning to install an anodizing system at our facility. The system’s designer and builder are proposing to use extensive counterflow rinsing, recirculation of rinsewater through ion exchange columns and evaporation of rinsewaters to establish a closed loop system. While the ion exchange columns will be transported off-site for regeneration by a third party, there is a possibility that the evaporator will have a periodic discharge to the plant sewer. There has been some debate whether or not this very small amount of wastewater would need a permit. Since the process is sulfuric acid based with no chromate or nickel acetate seals, the concentration of metals, except for aluminum, is expected to be low. We currently have no other wet processes in the facility. J.R.
A. Unfortunately, the metal finishing categorical pretreatment standards (40CFR433) do not have a low-flow threshold below which the wastewater would not be regulated. Furthermore, the evaporation system would be considered a form of wastewater pretreatment and its discharge regulated for the metals of cadmium, chromium, copper, lead, nickel, silver and zinc. Even though your process does not use chromates and nickel acetate sealers, aluminum alloys can contain regulated metals, such as copper and with the evaporation of the wastewater, these metal concentrations could rise to levels of concern. If you want to avoid regulation of your proposed anodizing operation under the metal finishing categorical pretreatment standard, you will need to have no discharge. If your system’s designer and builder can do so, we would recommend that the system be redesigned so as to have no discharge due to the high regulatory cost and aggravation for what is likely a very small amount of discharge.
You did not describe how you will dispose of the waste cleaner and waste anodizing solutions; due to their corrosivity (high pH for the cleaners and low pH for anodizing solution), these will likely need to be disposed off-site as a RCRA hazardous waste. Also, you will need to analyze the spent ion exchange resin to determine whether or not it fails the Toxicity Characteristic Leaching Procedure (aka TCLP) for the eight RCRA metals of arsenic, barium, cadmium, chromium, lead, mercury, selenium and silver. If it fails this test, the spent resin will need to be stored, transported and treated as a hazardous waste.
If you still decide to pursue sewer discharge, you need to contact your local sewer district and obtain their local limits. You may find that their local limits for metals are more stringent than the metal finishing standards as well as regulate other metals, including aluminum. If you still decide to pursue sewer discharge, USEPA requires that you submit a Baseline Monitoring Report (40CFR403.12) at least 90 days before start of discharge, and your local sewer district or state EPA will require a discharge permit application submission.