Reusing drain water from DI Plant

I am from Biomedical engineering Industry and we are OEM of Clinical chemistry analysers.

We use De-ionised (DI) water for washing and dilution of specific reagents and samples.

We generate lots of drain water from these DI water plants and this water goes as waste into municipal drains.

My question here is, Can we use/utilise this drain water for any other general purposes, for example, car wash, floor wash, utensils wash in office canteen, gardening, water harvesting etc.

As water is becoming scarce resource, I feel we should utilise it.

This is an excellent idea provided that you take a few precautions.

DI regenerations consist of both concentrated and dilute flows. Initially, if there is a backwash, this is a dilute flow, followed by displacement of the water in the vessels by the regenerant chemicals, which is also a dilute flow. This is followed by concentrated chemicals and regenerated ions, which in general should not be re-used.

Following the chemical, there is usually a slow and then a fast rinse, part of which is concentrated waste and part of which is dilute. After this there is often a recycle of water until the water quality reaches specifications.

Any of the dilute portions can be re-used, provided that you adjust the pH back to a reasonable range. A pH of 6.5-8.5 is preferable. To separate the regeneration flow into dilute portions to re-use, and concentrated portions that are sent to waste, you can use conductivity controls and automatic diverter valves on the drain pipes. A suggestion is to recycle any flow that has a conductivity less than 1000 uS, or less than 2.5 times the conductivity of your feed water (whichever is greater). This can be as much as 30-40% of the total flow.

Very clear cut and informative, Lyle. Thanks!

Regards,

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