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Wastewater zinc problem in small 1000 Gal system

August 4, 2010

Summary of waste system:
1. UF membrane for oil separation
2. Adjust pH to 3.0, add precipitant PC-9000 (60-120 stroke/min), Calcium Chloride (32% at 35 stroke/min)
3. Adjust pH to 8.6, Chemetall Enprox 5165 (sodium sulfide at 45 strokes/min)
4. Add Floc, Chemetall Enprox 8110 (150 ml-200 ml/40-43 Gal at 40-55 stroke/min)
5. Floc Mix
6. 1000 Gal Clarifier then filter press

Problems:
Black oxide section of the plant requires Zn daily max of 2.61 and monthly average of 1.48. Our current avg is 2.8 and we are in trouble. NEED ZINC FINAL TREATMENT METHOD TO ENSURE ZINC REMOVAL AND COST NO MORE THAN 2000/MO. Anyone please help.

Nicholas Graff
new industrial employee - Greeneville, Tennessee, US

Hi, Nicholas.
The first step in such a project is jar testing: that is, you try your idea on a beaker of wastewater in the lab before you commit to installing changes to your treatment system.

I think your pH of 8.6 is too low for good Zinc precipitation. I would suggest that you try raising the pH to about 10.0. An advantage of this approach is that if it works, all you need to do for "final treatment" then is to lower the pH back to a level acceptable for discharge (no need for secondary clarification and filtration). Hopefully you can reach acceptable zinc levels without the need for a sulfide post treatment system.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
August 4, 2010

I agree with Ted..the pH is a little low at 8.6. Optimum pH I have found for precipitation of zinc is 9.45 - above this pH level zinc is 're-introduced' back in to solution in zincate form leading to further problems. Hope this helps!

Nigel Gill, BSc CSci CChem MRSC MIMF
- Glasgow, Scotland
September 7, 2010

September 8, 2010

So far, it is unanimous. 8.6 is too low a pH, between 9.2 and 9.5 works better based on my experience.

Lyle Kirman

Lyle Kirman
consultant - Cleveland Heights, Ohio

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