Eventually the day comes when your RO system will require cleaning. Cleaning is
recommended when your RO shows evidence of fouling, just prior to a long term
shutdown, or as a matter of scheduled routine maintenance. Fouling characteristics
that signal you need to clean are a 10-15% decrease in normalized permeate flow, a
10-15% decrease in normalized permeate quality, or a 10-15% increase in
normalized pressure drop as measured between the feed and concentrate headers.
RO cleaning frequency due to fouling will vary by site. A rough rule of thumb as to an
acceptable cleaning frequency is once every 3 to 12 months. If you have to clean
more than once a month, you should be able to justify further capital expenditures for
improved RO pretreatment or a re-design of the RO operation. If cleaning frequency is
every one to three months, you may want to focus on improving the operation of your
existing equipment but further capital expenditure may be harder to justify.
One RO design feature that is commonly over-looked in reducing RO cleaning
frequency is the use of RO permeate water for flushing foulants from the system.
Soaking the RO elements during standby with permeate can help dissolve scale and
loosen precipitates, reducing the frequency of chemical cleaning.
What you clean for can vary site by site depending on the foulant. Complicating the
situation frequently is that one more than one fulant can be present. Typical foulants
are:
• Calcium carbonate scale
• Sulfate scale of calcium, barium or strontium
• Metal oxides of iron, manganese, aluminum, etc.
• Silica scale
• Colloidal deposits (inorganic or mixed inorganic/organic)
• Organic material of natural origin or man-made origin
• Biological (bioslime, mold, or fungi)
There are a number of factors involved in the selection of a suitable cleaning chemical
(or chemicals) and proper cleaning protocol. The first time you have to perform a
cleaning, it is recommended to contact the manufacturer of the equipment, the RO