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Proper process for evaporating wastewater

Hi, I am at a new company (Chem-film, Sulfuric Anodize, Passivation) and they use an evaporator to dispose of their wastewater. Can anyone tell me the correct way to evaporate? Their current system has a holding tank that pumps up into a forced air evaporator. The process is so slow, and barrels of wastewater is building up. I thought that wastewater should be pumped into holding tank, PH should be raised to precipitate solids as well as adding a coagulant before being precipitated...I have been looking for instructions for the process, but have come up empty handed. Any help would be greatly appreciated.

Thanks!

Natalie Henry
Plating shop employee - Tucson, Arizona
November 27, 2009

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You may not need to adjust the pH and to precipitate metals before evaporation, as long as they do not precipitate as they are concentrated. Often, a 90-95% volume reduction is possible without precipitation and removal of the metals.

The only way to increase the evaporation rate is to put more heat into the water, and to make sure that you are getting all of the air flow that your evaporator is designed for.

Regardless of the airflow, it still takes about 980 BTU's of heat to evaporate one pound of water. With some losses this works out to nearly 10,000 BTU's or about 2.9 KW-Hr per gallon of water evaporated. It is likely that you need to increase the amount of heat you are adding to the water.

Lyle Kirman
consultant - Cleveland Heights, Ohio
December 7, 2009

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First of two simultaneous responses --

Natalie

Search "metal hydroxide precipitation" and you should get quite a number of leads. Depending on your local discharge requirements, you may be able to perform simple neutralization on your waste water that does not have nickel, chrome, or other regulated metals- you would need to isolate the metal-bearing waste streams. You then reduce the volume of ww that needs evaporation.

Willie Alexander
- Colorado Springs, Colorado
December 7, 2009

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Second of two simultaneous responses --

It appears both water and energy is being wasted in evaporating water! You may perhaps consider using solar energy ( I suppose Arizona has it in abundance )and save energy and produce distilled water too.

H.R. Prabhakara - Consultant
Bangalore Plasmatek - Bangalore Karnataka India
December 8, 2009