1-13. SYSTEM TECHNICAL PRINCIPLES OF OPERATION.
General. The ROWPU removes suspended solids (called turbidity), chemicals, and solids held in solution
(called dissolved solids), found in most fresh water and seawater sources to a level fit for human consumption.
This is done by filtering, reverse osmosis, and treating the water with selected chemicals.
Reverse Osmosis. Reverse osmosis is the process by which purified water is separated from the available fresh,
seawater, or brackish water sources. High pressure is applied to the raw water side of a semipermeable
membrane and desalinated product water diffuses through the membrane to the freshwater side. The 600 GPH
ROWPU is arranged so that prefiltered water is pumped under pressure across the semi-permeable membranes,
called R.O. elements. The R.O. elements separate this water stream into a product water stream and a brine
concentrate stream, both of which continuously flow away from the membranes through the R.O. pressure
tubes. About 10 gallon of product water is produced for every 30 gallon of raw water processed.
Water Processing. Water flowing through the ROWPU is processed as follows:
Petroleum contaminated raw water will damage R.O. elements, multimedia filter and
(1) First Stage of Filtration - Multimedia Filter. The multimedia filter is the first stage of filtration. Large
particles of suspended solids are removed by the various layers of filter material in the tank. Polymer,
added to the raw water by the chemical feed pump, collects suspended solids into groups large enough to
be removed by the multimedia filter in a process called coagulation.
(2) Second Stage of Filtration - Cartridge Filter. The cartridge filter removes finer suspended solids that pass
through the multimedia filter.
(3) Reverse Osmosis (R.O.). The R.O. elements remove dissolved solids from the water and any suspended
solids that may have passed through the multimedia and cartridge filters.
Chemical Injection - Chemical Feed Pump. The chemical feed pump is comprised of four liquid heads
which inject chemicals into the water system. Polymer is injected into the raw water before entry into the
multimedia filter. Polymer aids in the removal of suspended solids by the multimedia filter through a
process called coagulation. Sodium hex is injected into the raw water to reduce scaling and corrosion of
pipes, pumps and filters caused by hard water deposits. Chlorine is added to the product water to reduce
bacteria and make the water safe for consumption. Citric acid is injected downstream of the multimedia
filter to remove scale deposits that build up on the R.O. elements and maintain pH.