SECTION 2-3
EQUIPMENT DESCRIPTION
FLOWMAX RO MANUAL REV: B 05/1999
USFilter
United States Filter Corporation
2.2 THEORY OF REVERSE OSMOSIS
Water
Water exists in nature as a pure substance, but typically not in pure form. Many substances will
readily combine with water. When water comes into contact with these substances they either
become dissolved solids, such as minerals, gases and organic compounds or they become
suspended solids such as clay, silt and micro-organisms.
Dissolved Solids
Mixtures containing dissolved solids are commonly called solutions. Solutions form when a
solute material, such as salt (sodium chloride), becomes dissolved in a solvent, such as water.
When a particle of salt contacts water, the salt disintegrates and spreads evenly throughout the
water until the salt as a solid no longer exists. The salt molecules are still present, but they now
exist in a liquid phase as part of the solution and are now referred to as dissolved ions. These
ions carry either a positive or negative electrical charge, and will hereby be referred to as
cations, if they carry a positive charge, and anions if they carry a negative charge.
Suspended Solids
Suspended solids, materials that do not dissolve in a solvent, exist as unevenly distributed
particles in a mixture. Suspended solids larger than 5 microns are filtered out by the cartridge
filters prior to the reverse osmosis membrane elements.
Ionic Content and Water Quality
The presence of ionic material (dissolved solids) in a solution, increases the solution's
conductivity, or the ability to conduct electricity. Consequently, the use of a conductivity
measurement device may be used as a means to approximate the amount of dissolved solids in a
solution. The higher the conductivity potential of the solution, the higher the dissolved solids
content. Unfortunately, the presence of dissolved and suspended solids may be detrimental to
many water based operations, such as the production of steam for power generation, the rinsing
of electronics components after manufacturing, and the preparation of food and pharmaceutical
materials, just to mention a few. Consequently, these dissolved and suspended solids must be
removed from the water prior to use in these and many other applications. One effective method
of removing the majority of these contaminants is referred to as Reverse Osmosis.
Osmosis
Osmosis is a natural phenomenon that occurs when two solutions with different concentrations
of dissolved solutions are separated by a SEMI-PERMEABLE MEMBRANE. In natural
osmosis, the solvent or water in this application travels through the membrane from the solution
with the lower concentration of ionic materials to the solution with the higher ionic
concentration. This process continues until the ionic concentration of both solutions is equal or
until the resultant passage of the water through the membrane reaches the
osmotic pressure
of
the solution if the solutions are trapped in a container.
Reverse Osmosis
Reverse Osmosis is the reversal of this natural phenomenon, by the application of external
pressure on the solution that contains the higher concentration of dissolved ions, thus forcing
