Ro-Man 200 GPD Installation Manual - Net Pressure Correction
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Example Question: If a thin-film membrane permeate rate at 77 degrees Fahrenheit = 100 gallons/day. What is the permeate
rate at 59 degrees Fahrenheit?
Answer: Temperature correction factor (from table above) = 1.47permeate flow at 59 degrees Fahrenheit = 100÷1.47 = 68.03
gallons (us)/day.
Net Pressure Correction
Performance of the reverse osmosis membrane element is affected by two key factor; temperature of the feed water and the
net driving pressure across the element. These two factors must be taken into account before comparing or evaluating the
performance of a membrane element or a reverse osmosis system.
The higher the net pressure on a membrane element, the higher the permeate rate. The osmotic pressure to water can be
calculated roughly by the following rule of thumb:
OSMOTIC PRESSURE (PSI) = TOTAL DISSOLVED SOLIDS (TDS) ÷ 100
To estimate the effect of net pressure, follow these steps:
Calculate the Net Pressure at which the membrane is rate (Pr)
Pr = (Rate Pressure) - (Osmotic Pressure of Test Solution)
Nominal Rejection Characteristics of Thin Film Composite
Reverse Osmosis Membrane
Calcium
93-99%
Sodium
92-98%
Magnesium
93-98%
Potassium
92-96%
Manganese
96-98%
Iron
96-98%
Aluminium
96-98%
Copper
96-99%
Nickel
96-99%
Cadmium
93-97%
Silver
93-96%
Zinc
96-98%
Mercury
94-97%
Hardness Ca&Mg
93-97%
Radioactivity
93-97%
Chloride
92-98%
Ion
92-98%
Bromide
90-95%
Phosphate
95-98%
Cyanide
90-97%
Sulphate
96-99%
Thiosulfate
96-98%
Silicate
92-95%
Silica
90-98%
Nitrate
90-95%
Boron
50-70%
Borate
30-50%
Fluoride
92-95%
Polyphosphate
96-98%
Orthophosphate
96-98%
Chromate
85-95%
Bacteria
99+%
Lead
95-98%
Arsenic
50-90%
Note: The above percent rejection is for reference only. Actual rejection will depend heavily on the exact chemistry,
temperature, pressure and TDS content of the feed water.