High Purity Water Filters Treatment Units
Purity Has Different Meanings to Different Users of Water
The consumer of drinking water wishes to have all harmful dissolved items removed and be assured that there are no microorganisms. Usually water with a total dissolved solids (TDS) level of 10 mg/l or less will suffice.
A food or beverage producer would like essentially the same but with the TDS level in the range of 1 or 2. Electroplaters and electronics manufacturers have higher demands and wish to see the dissolved solids reduced so far below the TDS expression that resistance in ohms per centimeter is used. Values from 1,000,000 to 18,000,000 are quite common.
Once a level of purity is determined, a full water analysis must be reviewed and processes selected. Typically some filtration followed by reverse osmosis is used to get to the 10 PPM level. Often the 1 PPM level is achieved by filtration also followed by R.O., but the R.O. unit is constructed as a 2 pass system where the product water from the fist membranes is run through a second membrane or set of membranes.
The 1,000,000 ohm and higher water quality requirement is usually met with deionization either as a single process or preceded by reverse osmosis to conserve chemicals associated with deionization.
Deionizers remove virtually all ions from water using an acid such as hydrochloric acid or sulfuric acid plus sodium hydroxide which is called caustic soda. They are built in two basic forms – 2 columns with separate cation and anion tanks to achieve 1,000,000 to 5,000,000 ohm resistance and single tank with the two resins mixed to achieve 5,000,000 ohms and up.