Why pre-filtration and good cartridge filtration is important?
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Membrane Element Protection Matters
* Source: VEOLIA TB1148EN.docx May-22
1. Removal of suspended solids to protect against membrane fouling: Prefiltration (cartridge or depth filtration) is perhaps the most important part of satisfactory performance of RO unit after the RO membranes themselves. The ability of depth and cartridge filters to remove suspended particulates, colloids, and larger color causing organics (NOM) from the feed stream greatly impacts the performance and longevity of any RO equipment, specifically the high performance units. The average size of the openings between the filter media in a depth filter is represented by void fraction, a dimensionless number. Additionally, in cartridge filters, the size of the opening is expressed in microns. For example, a 20-micron rating filter has larger openings than a 5 micron filter. Consequently, the 20-micron filter element will let particles smaller than 20 microns pass through the filter compared to the 5-micron rating cartridge filter. Veolia also makes a 1-micron rated cartridge filter that, in a series configuration with a 5 micron CF, can offer the best in feed water quality to an RO system. This dual cartridge filter arrangement is being used in a number of seawater RO desalination systems.
2. Achieving low SDI to protect against membrane fouling: SDI, Color, and turbidity are the key factors that determine the correct use of any spiral wound RO/NF membrane elements. A good multimedia depth filter followed by robust cartridge filters are designed to decrease “SDI, Color, and turbidity,” increasing the life span of RO/NF elements as well as allowing continuous high performance of spiral wound RO/NF membrane elements.
3. Bacteria removal to prevent biofouling of the membranes: Bacteria range in size from 0.2 to 2 microns in width or diameter and from 1 to 10 microns in length for the non-spherical specie, so a 1 micron filter will remove most bacteria and cysts in waters where biofouling is a concern.
4. Lower operating expense of the system: Proper pretreatment prevents fouling of the membranes and results in lower operating costs. The savings include reduction of chemicals for cleaning, lower power consumption, and extended membrane life.
5. Reduced capital expense: Proper pretreatment allows for consistently low SDI, which results in the designers’ ability to increase design flux of the membranes and thereby reducing the number of membranes required to treat the same volume of water. This results in decreased capital costs and a smaller overall footprint.
2. Achieving low SDI to protect against membrane fouling: SDI, Color, and turbidity are the key factors that determine the correct use of any spiral wound RO/NF membrane elements. A good multimedia depth filter followed by robust cartridge filters are designed to decrease “SDI, Color, and turbidity,” increasing the life span of RO/NF elements as well as allowing continuous high performance of spiral wound RO/NF membrane elements.
3. Bacteria removal to prevent biofouling of the membranes: Bacteria range in size from 0.2 to 2 microns in width or diameter and from 1 to 10 microns in length for the non-spherical specie, so a 1 micron filter will remove most bacteria and cysts in waters where biofouling is a concern.
4. Lower operating expense of the system: Proper pretreatment prevents fouling of the membranes and results in lower operating costs. The savings include reduction of chemicals for cleaning, lower power consumption, and extended membrane life.
5. Reduced capital expense: Proper pretreatment allows for consistently low SDI, which results in the designers’ ability to increase design flux of the membranes and thereby reducing the number of membranes required to treat the same volume of water. This results in decreased capital costs and a smaller overall footprint.
* Source: VEOLIA TB1148EN.docx May-22
05 Jun 2025
