spacer
spacer

Measuring R. O. Effectiveness

REVERSE OSMOSIS TOPIC LINKS:
Impurities Removed by R.O.
Measuring R.O. Effectiveness
Disadvantages of Reverse Osmosis
Equipment used in RO system
RO Purchase, Operational, Etc. Costs
Pre-Purchase Considerations

Also See: R.O. Defined
(How Reverse Osmosis Works)

And: Testing Your Water Supply

How is effectiveness measured?

The effectiveness of RO units is characterized by the rejection rate or rejection percentage. The rejection rate is the percent of a contaminant that does not move through, or is rejected by, the membrane. Some typical rejection rates for common contaminants are shown in Table 1. These rejection rates are for single contaminants under design conditions

Table 1. Typical Rejection Rates for

Common Contaminant

———————————————————————————————-
Rejection Rate Range*
Contaminant Laboratory

Tests

 Field Tests
Nitrates 83 – 92 % ** – 92%
Total Dissolved 95 – 99 % 60% – 99%
Solids
Sulfates 90 – 98 % 60% – 98%
Sodium 87 – 93 % 60% – 93%
——————————————————————————————–
*These values are for properly maintained units. Poorly maintained units will not be as effective at removing contaminants and, in the worst case, may not be removing any contaminants.

Where water contains more than one contaminant, the rejection rate for each contaminant may be reduced or one of the contaminants may be reduced in preference to the other contaminant. For example, cases have been reported where water supplies containing either high TDS levels or high sulfates in combination with nitrates show no decrease in nitrates after treatment. (Nitrates as used in this publication refers to nitrate-nitrogen or NO3-N.)

Rejection rates need to be high enough to reduce the contaminant level in the untreated water to a safe level. To determine the needed rejection rate, it is necessary to consider the initial concentration. For example, if a water supply contains nitrates at a concentration of 20 milligrams per liter (mg/l), an RO unit rejecting at a rate of 85 percent, which means 15 percent remaining, would reduce the level to 3 mg/l (20 times 0.15 = 3).

Water with very high levels of nitrates (such as 100 mg/l) would remain near or above health standard levels even after treatment. Nitrate levels this high are not expected in this region and indicate unusual problems that require special investigation and handling. The National Sanitation Foundation (NSF) recommends that special designs be used for RO units where the NO3-N level exceeds 40 mg/l.

Posted Under: NEWS & INORMATION
This post was written by whitey on March 22, 2009 Comments (0)

spacer