Letter 21077

How to remove lead from wastewater [Minnesota] 

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I have a waste stream created by aqueous parts washers that have a high level of lead from cleaning brass parts. (100 to 150 mg/L) Besides mechanical evaporation is there another method, maybe chemical that I can use to remove the lead from the wastewater?

John Zacharias
- Waseca, Minnesota, USA

John,

I'm going to give you some data on what Assay labs use before the chemicals are neutralized.

This consists briefly of a prelimary TALL tank so that solids will settle out along with a dead simple prefilter design.

1. Use an open top Polyethylene moulded tank.
2. Tank to be definitely tallish
3. About l foot from the top or less, have an 'overflow' outlet ... leading, say, into the neutralization tank.
4. Liquid inlet pipe to be located say l foot BELOW the overflow and facing down.
5. At the bottom of the tank, provide a largish drain outlet so that solids can be collected although they could be scooped up if the tank size is small due to low flow rates
6. Re # 3 ... have a LARGE pipe extending inside the tank by, say, l foot. Where it passes through the wall, reduce down to a normal size (eg for small, Assay lab flows, the outlet pipe is, say, l" or l-l/2" dia BUT the inside pipe is 6" or 8" diameter.
7. Filter design a la K.I.S.S. principle. a) Get a LOOSE fitting cap. Then cut out a large hole in the end of it. Then get some ordinary Jay cloth (l or 2 layers should do) and sleeve it over the inlet. Then push on the cap and, if necessary, use a s.s. screw to just hold it in place.

It may be necessary to machine the cap I.D. a hair. Then you may want to use some other type of filter cloth. But the idea is that the solids will fall to the bottom and any detritus will collect on the cloth WHICH is very easily accessible for cleaning or replacing. If this concept is of any use to you, I'd sure appreciate knowing.

Freeman Newton - White Rock, B.C. Canada

Freeman,

I think John wants to remove dissolved lead.

First, you should already have an EPA (Hazardous Waste Generator's) ID #.

Second, what quantity is involved? It might not be worthwhile to go through the rigmarole of obtaining a Hazardous Waste treatment permit, setting up a treatment tank and its secondary containment, doing effluent analyses to satisfy regulators, and still eventually dealing with disposal. You might instead drum it up and have it hauled periodically to an EPA-licensed treatment facility.

Third, if using a commercial cleaner, talk to the vendor about treatment options. Some solutions contain chelating agents or emulsifiers which may limit your treatment options. Also, the vendor may have a recycling program.

Fourth, you have Cu and Zn in addition to Pb, so the treatment should handle all 3 metals. Depending upon volume and cleaning solution characteristics, I can think of 3 methods:
a) Ion exchange. Find a treatment facility that will contract a heavy metal-specific cation resin bed exchange program for you.
b) Evaporation. Boil off the water in a stainless steel kettle. [a low pressure evaporation unit is only justifiable for high volumes, and you may need an air permit] Depending upon your regulators (and if you have a low solids, non-phosphate cleaner), you may be able to go for years before disposal of residual solids.
c) Conventional precipitation (as hydroxides)*. Do a batch process. Add a coagulant containing 10 g/L of Fe(+3), raise the pH to 10.0 with either caustic soda solution or lime, then add a polymer flocculant and let settle for a few hours (longer is better). Decant or siphon off the clear water (you will need to have it analyzed for the heavy metals). If you are dealing with large quantities, the next step is filter pressing. If small quantities, you might try to minimize the slurry by evaporation. Eventually, you will have to dispose of the dried sediment or filter cake in either lined 55 gal open top steel drums (with lids) or 1 cubic yard polypropylene supersacks.

*A number of wastewater treatment companies sell precipitating agents. Contact some of the environmental and chemical companies via links below. Some will send small samples of their product for trial; others will ask for a sample of your solution.

Ken Vlach - Goleta, California

Ken,

That was a very detailed method of disposal and collection. I sure couldn't have collated that data! Let's hope it will help John Z.

I fully realize, Ken, that the lead etc must be dissolved. In assay labs they use totally vicious acids (some, like Perchloric, have the U.S. plating industry in a major panic mode !) and they sure can dissolve EVERYTHING.

Hence my idea, which I'm sure others have thought of or have used, is an inexpensive & simple way of removing/capturing the vast bulk of solids ... but in the case of the Assay labs, sometimes the solids are valuable, very valuable ! I did err in saying that the outlet pipe should be l2" below the liquid level, maybe 3 or 2" would be far better in terms of access to the filter/strainer.

Freeman Newton - White Rock, B.C. Canada

Thank you Mr. Vlach and Mr. Newton for your assistance. I appreciate your help. Yes it is dissolved lead I am tring to remove. We do have a treatment system for our plating wastewater using aluminum sulfate, sodium hydrosulfite, and sodium sulfide. I wasnt too sure how effective this would be since we use some heavy duty detergents hence my request for information on other treatment methods. So you recommend a coagulant containing ferrous sulfate, Mr. Vlach? I think I will try your method in our lab and see what we end up with.

Thanks again for your advice.

John Zacharias
- Waseca, Minnesota

Dear John,

Sometimes the best cure for a back end problem is to take a good look at the front end. Do you really need to use a leaded brass? Could one of the unleaded brasses be used in your process, you might want to check with your metal supplier. I've chased my tail many times on back end fixes only to find that if I changed something on the front end, I wouldn't have the problem.

Best regards,

Jim Sivertsen
- Alden, N.Y., U.S.A.

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