In order to extend the lives of reverse osmosis elements, pretreatment is essential. Proper pretreatment selection will maximize efficiency and membrane life by minimizing fouling, scaling and membrane degradation while optimizing operating and maintenance costs.

For most POU RO systems, a softener is all that is needed along with regular replacement of the cartridge and carbon filters on the RO system. For POE or small commercial and industrial systems, one should carefully match the pretreatment with the water quality to minimize fouling on the membrane surface.

The four major types of fouling are listed below.

• Colloidal fouling occurs when particulate or colloidal matter — such as iron flocs or silt — becomes entrapped in the membrane.
• Biological fouling, also known as biofouling, refers to the growth of a biofilm.
• Organic fouling is adsorption of specific organic compounds such as humic substances and oil onto the membrane surface.
• Scaling refers to the precipitation and deposition within the system of sparingly soluble salts, including calcium carbonate, barium sulfate, calcium sulfate, strontium sulfate and calcium fluoride.

In order to determine the proper pretreatment, a complete and accurate analysis of the feedwater should be made. Without a water quality analysis, it would be impossible to conclude what type of pretreatment is needed for long-term, successful operation.

Applied Membranes Inc.

KDF Fluid Treatment Inc.