Metal finishing Q&As since 1989

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Effluent settlement rates

I have a problem with settling out sludge after effluent treatment, what size settlement tower would be required for a 10 cubic metre flow rate. Our main product line is zinc plating from both alkaline and acid baths

Martin Sullivan
an electroplating shop - Merthyr Tydfil, Mid Glamorgan, United Kingdom
2003

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A clarifier/settler for electroplating wastes virtually requires lamella plates or the similar 55 degree slant tubes and saw tooth overflow weirs. Are you looking for the settling tank size for a clarifier with such plates or tubes and carefully adjusted saw-tooth weirs, or for a more casually designed tank?

Since you are an electroplating shop rather than a municipal treatment works, I'll assume the 10 cubic meters is per hour rather than per minute. The idea is that the rise rate of the fluid must be slower than the settling rate of the floc, but with lamella plates the floc only has to fall a couple of inches while the fluid rises several feet. A lamella clarifier would probably have a surface area of about 20 square feet; a tube settler tank perhaps 3 times that; a tank without plates or tubes would need to be 5 or 10 times larger than that. The thing to do is treat a sample in a beaker [beakers on eBay or Amazon], watch it settle and clock it, then add a generous factor of safety.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003