Reverse Osmosis: What is it?

  • RO is a form of filtration using osmosis in reverse
  • Water passes from a more concentrated solution to a less concentrated solution
  • To accomplish this a force or pressure MUST be applied
  • RO requires 1 psi of pressure for every 100 ppm of TDS
  • RO is used to remove dissolved solids from water but it can also improve taste, odor & color of water
  • RO membranes have the capability to remove particles as small as ions i.e. magnesium ions or sodium ions
  • RO membrane will reject most compounds based largely on size
  • Dissolved ions, such as salts, carry an electric charge and will also be rejected by membrane

Reverse Osmosis: How does it work?

  • Feed water flows into RO unit with the force of line pressure
  • Water is forced through membrane by cross flow filtration
  • Cross flow filtration is most commonly used in RO as it allows membrane to continually clean itself
  • Membrane then either rejects or repels contaminants
  • Two exit streams generated: waste & product stream
  • Waste stream consists of: A concentrate (reject) stream which carries contaminants (compounds too large to pass through membrane)
  • Permeate stream consists of: Product water which has been forced through the membrane & is virtually free of TDS

Parameters that affect RO:

Water Temperature: RO system ratings are based on 770F/ 250C water temperature

i.e. : RO system rated at 20 GPD (gallons per day) at 340F/10C will only produce 6 GPD

Feed Water Pressure: A lack in water pressure (less than 40 PSI) will reduce product water; this can be helped with the aid of a booster pump

Contaminants in Feed Water: Large particles, iron concentration or high levels of hardness in feed water can cause clogging of the membrane. Clogging of the membrane can decrease its life

Microorganisms: RO membranes can filter out bacteria, depending on the bacteria size, however this may cause fouling of the membrane as bacteria can begin to grow through pores of membrane causing BACTERIA CREEP – RO systems should not be installed on non-potable water