Wastewater Discharge Non-Compliance

Ask an Expert From: Products Finishing, , from Hixson Inc.

Posted on: 11/1/2005

Question: We operate a metal fabrication shop with our own five-stage iron phosphate washer.

Question:

We operate a metal fabrication shop with our own five-stage iron phosphate washer. After the washer, the metal parts are dried, spray painted or powder coated and then cured. The washer is our only process wastewater discharge so we are regulated under EPA’s metal finishing pretreatment regulations by the city. The only wastewater pretreatment we have is pH adjustment and a sampling flume. This system has been in operation for more than 15 years, and we have never had a compliance problem with metals, although once in a while, our wastewater will approach the daily maximum for zinc (2.61 mg/liter). Even then, the zinc concentrations for the other sampling days are low enough that we are comfortably below our monthly average limit of 1.48 mg/liter. One of our major customers has approached us with a product and the steel is already coated with zinc, apparently electrogalvanized. In order to properly paint it, we still need to run it through our washer. My concern is if we accept this project our wastewater zinc will increase to the point of causing non-compliance, and then we will have to install a full wastewater pretreatment system for zinc removal. Needless to say, this wastewater pretreatment system would be a major capital and operating cost increase to our operation. Would appreciate your thoughts. K.P.

Answer:

Since I am not familiar with your specific operation, I could not say for sure whether or not this new product would cause non-compliance with your wastewater discharge permit or not. There are a number of factors, including your washer’s chemistry (highly caustic and highly acidic solutions have a tendency to dissolve zinc) and operating temperature (higher temperatures mean more aggressive chemistry), this product’s percent of washer throughput, and distribution of washer throughput (long single runs vs. many short runs).

If you are able, I would recommend that you agree with your customer to several test runs. During these test runs, sample all stages of your washer AND process wastewater before, at the middle, and at the end of the run; a minimum of three test runs should be made. From these results, you will be able to determine the impact of these parts on your overflow rinses and process solutions that are periodically dumped.

Based upon our experience, we think you will find that this material’s impact upon your flowing rinses will be minimal and not likely cause non-compliance. However, if there is sufficient production of this product, it is possible that your process solutions, particularly cleaners and iron phosphate, could accumulate enough zinc that would cause non-compliance on days they are dumped. If this is the case, you have basically four options:

  1. Install holding tank(s) so that these process solutions could be bled into rinse waters over a long period of time,
  2. Install a batch pretreatment system for these process solutions for the removal of zinc,
  3. Store these waste solutions and haul off-site for treatment and disposal,
  4. Store these waste solutions, evaporate excess water, and haul off-site for treatment and disposal.

Obviously, option 1 is the least costly, although its feasibility is based upon expected metal concentrations, volume of process solution dumps, and frequency of these dumps. While option 2 has the highest capital costs, options 3 and 4 have the highest operating costs.

If you choose option 2, 3, or 4, you will need to sample and analyze the waste in order to determine if it is a RCRA hazardous or non-hazardous waste so that the proper treatment and disposal methods are engaged.

Based upon our experience, we would expect the sludge from option 2 to be a RCRA non-hazardous waste, while the liquid waste of options 3 and 4 could be RCRA hazardous due to either corrosivity (pH < 2.0, pH > 12.5) or Toxicity Characteristic Leaching Procedure (TCLP) for metals, particularly lead. If you found the pH to be either below 2 or above 12.5, you could manually adjust it in the storage tank without needing a hazardous waste treatment permit (although CA may be different) due to “elementary neutralization” exemption.

While zinc is not a RCRA metal, the eight (8) RCRA metals are arsenic, barium, cadmium, chromium, lead, mercury, selenium, and silver. The RCRA metal that sometimes gives us trouble is the ubiquitous lead. Yes, you can run the TCLP procedure on a liquid. In summary, a portion of the sample is filtered and the filtrate collected and held. The collected solids are then run through the TCLP procedure using an acidic extraction solution; the TCLP fluid is filtered, the filtrates combined, and then analyzed. So basically, in a liquid sample such as washer waste process solutions, if you analyze the waste stream for total concentration of the eight (8) RCRA metals and find at least one above their respective TCLP threshold (ex, TCLP threshold for lead is 5.0 mg/liter), then it is very good odds that the process solution would fail TCLP for that metal. The storage and disposal of RCRA hazardous waste is significantly more expensive and time consuming as compared to non-hazardous waste. In fact, if we found this to be the case, option 2 would likely be the least costly option.

 


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