RO water Vs. DI water in industrial applications

A. Lina,

I've used DI and RO in my plant. DI water quality was better (lower dissolved solids) than the RO. If you don't need that quality of water (say less than 20 ppm) I would go with RO. Consistency is better (you really need to keep an eye on the output, when the resin is exhausted pH can really go crazy), it is safer (no chemicals for regeneration), the only waste products are the salt brine reject water, and labor is practically nil with proper pretreatment.

That said, if you need really good water I would still go with RO and put a DI after it to polish the water. Good water going into a DI will greatly extend regeneration cycles.

Good Luck

A. The best choice between RO and DI depends on several factors. The most important of these are

-your raw water analysis
-what quality of water you need to produce
-your costs for water and sewer, acid and caustic

In general, for water with less than 500 mg/L of dissolved solids, the operating costs for a DI system are lower than the operating costs for an RO system. The quality of water produced by a DI system is usually better than the quality from an RO system.

But, a DI system requires acid and caustic for regenerations and a neutralization system for the wastewater. If you don't have a neutralization system and don't have other strong, corrosive chemicals in your plant, and don't want them, then this may favor an RO system.

Some special considerations in Mexico are the high cost for water, relatively high TDS, and most particularly a high silica concentration. High silica concentration limits the recovery that an RO system can deliver.

Since each location is unique, it is best to compare the capital and the operating costs for each technology before making a decision.

A. I would add to Mr Kirman's advice. The low TDS you get from R/O treated water will be slightly different from the IX systems.
Silica, Hardness and TSS all limit R/O's performance.
If it is ground water, and has nitrates, you will get very low removal with R/O.
My experience in Mexico has been that the ground water is very hard and has very high alkalinity. The DI systems can be designed to be far more efficient than R/Os in terms of operating costs. The alkalinity is removed by conversion to CO2 and degassed, saving much of the chemical costs Mr. Kirman refers to. Like he says, without a water analysis, all this advice is general rule-of-thumb. If you send Mr. Kirman your analysis, I am sure the right solution will be offered to you.

A. You must also consider that true DI water is very reactive, and as such can be damaging to your plumbing unless some minerals are added back. Make sure the engineer/installation company you use acknowledges this risk and helps you weigh the costs and benefits appropriately. You might contact Tech Support at a major distributor such as Thermo-Fisher to learn more about appropriate selection. They even offer a free water test of your current water.