Sedifilt - Syntech Fibres (Pvt)

New developments in filter cartridges for reverse osmosis pre-filtration

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Courtesy of Sedifilt - Syntech Fibres (Pvt)

Reverse osmosis (RO) pretreatment systems are designed to reduce suspended solids to a level that will provide the most suitable conditions for the performance of the membrane system. Depending upon the quality of the feed water, pretreatment may include settlement, clarification, multi-media filtration, and chemical treatment. However, sediment pre-filtration is always required to ensure that suspended materials in the source water do not permanently clog or foul the membrane. Reduction of suspended matter in RO feed water is a standard requirement to ensure cost-effective and efficient water treatment and enhanced RO system life.

In the early days, only cotton string wound onto a steel core was available for filtration. Today there is a wide choice in filter cartridges and filter media. The advantages and dis-advantages of various types of filter cartridges need to be considered to make the right choice for RO prefiltration.

Conventional String-wound Filter Cartridges
Polypropylene string wound cartridges, due to their inertness and wide range of chemical resistance, are among the most commonly used filters for reducing sediments and other suspended impurities in liquids and water. Traditionally these cartridges are made from 'friction-spun' yarns.

Despite their great popularity, these string wound cartridges have many major drawbacks. Fibers on the surface of yarn tend to come loose with flow of liquid and pressure surges in the system.

In the standard textile yarn manufacturing process a spin-finish has to be necessarily applied on the surface of the fibers. Spin-finish contains a number of chemicals like lubricants, surfactants, antioxidants, antistatic agents, emulsifiers, and bactericides, etc. Unless the media is pre-washed (though some residue will remain), these chemicals start to leach out and can be often observed as foaming in the filtrate. The leaching out of these chemicals can be detrimental for the filtrate as well as downstream treatments.

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