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Pretreat feed water well.

RO systems shall excel.

Pretreat feed water well

RO membrane is susceptible to contamination.

Like a successful performance, it comes with diligent preparation. RO membrane is vulnerable to fouling – caused by scale, silt, bacteria, organic compounds or by a combination of these. Learn more →

Various pretreatment options are available. Subject to the content of the feed water, they are either used singularly or in combination. Any pretreatment process selected shall reduce a few most critical contaminants to the desired levels for RO membrane to achieve optimal recovery, and with a reasonable life cycle of 3-5 years in operations.


Turbidity. SDI. And others.

Don’t leave them untreated.

Fouling by excessive micro-organism, organic matter and silt (content of colloidal particulates), and scaling by cumulative deposit of soluble salts, such as calcium sulphate, barium sulphate, calcium carbonate, silica etc, are the most common problems of many RO applications. In the assessment and selection of pretreatment options for RO systems, some critical feed water’s parameters and their limits may be useful guides, though other undesired content shall not be neglected too. While chlorine is often used to eliminate/ minimise harmful bacteria and viruses upstream, and prevent biofouling, residual chlorine is not acceptable to thin-film RO membrane. The oxidation effect of chlorine will cause rapid degradation of membrane. Learn more >

(1) Total cumulative chlorine tolerance is up to 1000 ppm-hours (ppm x hours of exposure to chlorine).


Sand filter (SF).

Using the basic to
remove the basics.

Sand filtration process is one of the simplest and most affordable conventional options. It is used mainly to remove large contaminant particulates down to 25 – 50 microns in size. For the purpose of pretreatment prior to RO application, finer filtration process post-sand filter may be needed to meet the RO feed water’s quality criteria.

Sand filter

Multimedia filter (MMF).

Multi layers remove more.

This filter process consists of 3 or more layers of media of different grades and sizes. The different density in each layer of medium allows the larger particulates to be retained and removed near the top of the media, and the smaller particulates being retained deeper into the media downward. This makes the filter run time much longer between backwash and more efficient particulate removal. A well operated multimedia system can remove particulates down to 15 – 20 microns in sizes.

Multimedia filter

Granular activated
carbon (GAC) filter.

Removing what SF & MMF don’t.

This is commonly used to remove organic constituents and residual disinfectant (especially chlorine) in the water. The process helps remove any undesired odour and tastes as well, apart from protecting RO membrane form getting oxidised by residual disinfectants. GAC comes in a wide range of specifications – careful selection to suit each application is essential. To produce ingredient water for F&B applications, sanitisation options of the GAC by hot water or steam shall be made available.

Granular activated

Ultrafiltration (UF).

Unconventional & most reliable.

The filtration process pretreatment of feed water to RO systems is the most unconventional. UF is effective in removing contaminant particulate down to 0.01 – 0.1 micron, and is the most reliable option in producing consistent feed water’s qualities for RO applications. For large plant, UF option helps save substantial footprint (than MMF method) for the same purpose. However, as most UF processes require chlorination to prevent fouling, GAC filter must be in place to remove this disinfectant for RO applications. Learn more about UF >


Cartridge filter.

RO membrane’s last defence.

These filters are often used as the last step in pretreatment to protect RO membrane from damage by any “escaped” suspended particles from the upstream process. They are sometimes called “membrane protectors”. 5-micron filter cartridges are most commonly used. Cartridges are usually constructed from 100% Polypropylene material. They can be housed in PP casings or SS316 (recommended for F&B applications) vessels.

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