Wastewater treatment of iron and zinc phosphate conversion coating processes
Q. I am from University of North Carolina at Charlotte, and working for a small metal finishing company with a waste water flow of 62000 gallons/month. This company has an Iron Phosphate system and tumbling, deburring, and Punch Press unit. A few months back they start noticing an elevated level of Zinc in their waste water. We have a speculation that this might be from the Mill Oil they are clearing during these processes but did not now the exact relationship. The Facility also has had higher BOD level during the same weekly testing period. Could someone explain any correlation between oil & grease, Zinc and BOD. Thanks you very Much.
UNC - Charlotte - Charlotte, North Carolina
A. Hi, Kshitiz. I think what you might best do is to track down the various effluent pipes that are feeding the waste water treatment system, and see what pipe the zinc is coming in from. Then you have to continue to work backward until you find it. Guessing where the zinc is coming from is just speculation. It could be the oil, the reagent chemicals, or a stripping operation--but it could be other things. Sorry. Good luck!
Ted Mooney, P.E.
Pine Beach, New Jersey
A. When a waste effluent characteristic changes it is usually because of a change in the waste presented to the system. Deburring and cleaning chemical suppliers are famous for providing heavy loads of sequestering agents (chelators) in their formulations because they work so well. Check upstream, and you will probably find EDTA or some such chelator is present. Then work on your supplier to eliminate it.
- Shiner, Texas, USA
Q. We use phosphoric acid to remove flash rust of steel parts prior to the barrel zinc phosphate process. We have some difficulty removing the total phosphorous from our discharge into a POTW. Can someone help us on this issue?
- Red Lion, Pennsylvania, USA
A. Adding Calcium (such as from hydrated lime [linked by editor to product info at Amazon] or Calcium Chloride Solution) to your wastewater stream will precipitate most of the Phosphates, thus removing them from your filtered or clarified effluent - but adding Calcium Phosphate to your solid waste stream. The amount required will depend not only upon the pounds per day of phosphate currently going to the Sanitary District, but also on the amounts of other cations which are insoluble with Calcium. The most common of these is sulfate, you might want to consider switching a Sulfuric pickle to Hydrochloric to avoid generating excess sludge.Craig Haseltine
- St Charles, Illinois, USA
A. Depending on what your doing, how much water you are using, and the parts you are working with, you might find that a closed loop system will give you better control over effluent - essentially by not discharging with exception of batch treatment of regenerants, which gives you complete control over the discharge BEFORE it happens by testing. Also, you could perhaps look at acid recovery for the phosphoric bath, and return the rinses back to the bath for make-up. This eliminates the build up of contaminants and also allows you to close that loop as well. You essentially do not have to dump the bath, which would eliminate a source of phosphorus in your effluent streams.
wastewater treatment specialist
A. You can try the ferric chloride to precipitate itJack, Cui
Q. Can anyone help me find out about the safety issues with Iron Phosphatizing and any wastewater issues. Are there any articles out there that discusses these issues. I need as much info as I can get.Rosy DeSimone
Employee - Kansas City, Missouri, USA
A. Iron phosphating is a Federal categorical process, with defined pretreatment discharge limits. The most likely contaminant in spent rinse water is zinc, if you are applying this coating on galvanized steel. An adjustment of the pH to 9 - 9.5, followed by the addition of flocculant, and settling, should leave the residual Zn in the decant below this limit. (monthly average = 1.48 mg/l; daily max = 2.61 mg/l)
Your local POTW may have restrictions on the discharge of iron and/or phosphorus. Get with them and see what their policy is.
Both the settled sludge from this operation, and the tank bottoms, are categorical hazardous wastes. They need to be dewatered, and hauled to a haz waste landfill.
Consultant - The Bronx, New York
Phosphatizing is a listed process in Section 433 of EPA regulations for the Metal Finishing Category. However, if you are doing iron phosphatizing and not zinc phosphatizing, you may not have any worries, since iron discharges are not regulated in these regulations. However, as the previous responder noted, zinc and nickel (a common ingredient in zinc phosphate coating solutions) are regulated.
Most iron phosphate operations that I know of have no waste treatment other than possibly neutralization. These operations often haul any concentrated dumps off-site for treatment and disposal.
Even if there are no Federal Regulations that apply to your situation, you would still need to meet the requirements of your local sewer use code. Many local codes allow up to 50 mg/L or more of iron, and allow a fairly high concentrate of phosphates before any surcharge would be levied. So, if you are just doing iron phosphate coating, I suggest that you contact your local sewer authority for advice.
consultant - Cleveland, Ohio
December 27, 2017
A. I would ask a consulting firm to look into this, and should quickly determine the point of the introduction of Zinc. There are strict EPA regulations when discharging Zinc into the effluent. Our plant has a complete waste water system to floc and add product to the water prior to discharge to the city wastewater plant. Most are not equipped or prepared for Zinc.
Our local water company has a pull meter at the manhole just prior to leaving our property. In addition, all of our tests, titrations, etc., are kept on file. The City then sends these samples to an independent lab for analysis.
I prefer the wastewater treatment, to allow our system to Zinc Phosphate for pre-treatment of various coatings to AL and metals for superior finishes.
Trison Coatings inc. - Lewisburg, Tennessee, USA
July 20, 2018
Q. I have a comment on phosphate: Where can I get more information on phosphate and where can I get the permit to allow increase of phosphate? But my question is whether phosphate tank will push our ppm past our allotted approval rating?Israel Rodriguez
- Houston, Texas
A. Hi Israel. If you are discharging to a sewer/POTW rather than direct to a river, the POTW is usually authorized and required by the EPA to administer the permit program for industrial discharges. But what limits you have may depend upon what industry sector you are in.
If you are unsure of your status, but are responsible for it, you probably should hire an environmental consultant because there can be lot to it. Best of luck.
Ted Mooney, P.E. RET
Pine Beach, New Jersey
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