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Water reuse from iron phosphating process

I want to propose to the managerial staff the reuse of the wastewater generated from our five-step iron phosphating process. I'm planning to start with a reverse osmosis to remove dissolved solids, because weren't treating it at all, it goes from rinse tanks to the sewer. Its pH is from 7 to 8, and TDS close to 500.
Do you have any experience with this?, do you know any other recommended alternatives?. Is there any reference or book I can be guided with?

Rigo Carrizo
chemist process - Nogales, Sonora, Mexico
August 19, 2011

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August 22, 2011

I have recycled rinsewaters from a variety of phosphate lines, sometimes with DI and sometimes with RO equipment. Normally, with only 500 mg/L of TDS, I would use DI equipment to recycle over 90% of the rinse water. However, the DI system regenerations require treatment, and if you have no waste water treatment equipment, then you can probably use an RO to recycle 65-80% of the rinsewater.

This difference in the percentage of water recycled becomes important if your cost for water and sewerage is high, and the rinses run 24 hours per day.

The main thing that you need to be concerned with are that everything remains soluble in the RO concentrate, particularly the iron. This may require pH adjustment. Fortunately, iron fouled membranes are easily cleaned with dilute acid.

A second concern is the quality of the make-up water. It should be softened or RO or DI water.

A final concern is whether or not the RO concentrate will meet your discharge limits, since it will be several times higher in TDS, iron and possibly other metals than your present discharge.

Good luck!

Lyle Kirman
consultant - Cleveland Heights, Ohio

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If your main goal is to save water, you should certainly evaluate common water conservation practices such as counterflow rinse tanks, conductivity controls on the fresh incoming water to each rinse, spray rinsing, etc. In many cases, it is more feasible, more economical, and less troublesome to just tighten up the process and treat the wastewater compared to recycling. If your main goal is to avoid waste treatment, then recycling doesn't necessarily help you as Lyle has explained.

Jon Barrows, MSF, EHSSC
GOAD Company

Independence, Missouri

August 25, 2011