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Wastewater treatment from photovoltaic wafer production industry


Q. My project is to treat wastewater from photovoltaic wafers production industry. Wastewater contains HF, mixed acid etchant, SS, turbidity, SiO2, high oxide particle content. (pH of wastewater is between 2 and 4)
This wastewater is to be treated with Lime ( Ca(OH)2 ), PAC (polyaluminum chloride) coagulant plus polymer flocculant PAA (cationic polyacrylamide).

I intend to mix wastewater, lime milk and PAC in one-single rapidly stirred tank, then add PAA in a second slowly-stirred tank, following by lamella sedimentation.

I'd like to ask:
1) what is the optimum pH or pH range in the first mixing tank?
2) is addition of H2SO4 necessary in the beginning (before mixing e.g., in the equalization tank)?
3) does anyone knows the efficiency of this method in removing fluoride, silica?
4) if metals and P (PO4) are present in wastewater...would these be removed during the sedimentation process?

Thank you in advance..!

Stavros Lefkopoulos
- Thessaloniki, Greece


A. Don't add any more acid, it's quite unnecessary.

I'd suggest adding a combination of Calcium Chloride and lime such that the final pH is about 9, and there's an excess orf dissolved Ca in the liquid of about 500 mg/l. That ought to take the fluoride to less than 10 mg/l.

dave wichern
Dave Wichern
Consultant - The Bronx, New York


November 2, 2017 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I have a water which has high turbidity and fluoride. What can we use to remove it?

Elijah Mwangi
- kenya

November 2017

A. Hi Elijah. We appended your question to a thread which may be helpful, but you probably need to take the time to provide good details of your situation to get proper responses.


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Ted Mooney, P.E. RET
Pine Beach, New Jersey
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