Oct 19, 2026
Filter Cartridge Selection: Micron Ratings, Materials, and Sizing for RO Pretreatment
How to select filter cartridges for RO pretreatment: micron rating, cartridge material (PP, PES, PTFE, carbon), housing type, and changeout economics.
The Cartridge Guard Filter's Job
The cartridge filter ahead of an RO membrane is a safety barrier, not a treatment stage. Its job is to catch particles that escaped upstream pretreatment - resin fines, carbon dust, pipe scale - before they foul the membrane's feed spacer. Getting it wrong either lets particles through or creates excessive pressure drop and changeout cost.
Micron Rating: 5 Micron Is the Standard
Five micron nominally rated cartridges are the industry default ahead of RO. One micron absolute cartridges are used where upstream quality is uncertain or membrane warranty requires it, but they load faster and cost more per changeout.
Do not use a finer cartridge to compensate for poor pretreatment. A 1-micron filter on high-turbidity feed blinds in days and becomes an expensive bandage. Fix the upstream clarifier or UF instead.
Cartridge Materials
Melt-Blown Polypropylene
The workhorse: low cost, high dirt-holding capacity, and adequate chemical compatibility. Best for general RO pretreatment where particles are the main load.
String-Wound
Higher pressure tolerance and predictable depth filtration. Common in high-flow industrial skids and where melt-blown cartridges collapse under differential pressure.
Pleated (PP, PES, PTFE, Nylon)
Pleated cartridges offer high surface area, low pressure drop, and absolute ratings. PES and PTFE suit aggressive chemicals and high-temperature service; PTFE is the choice for strong solvents and oxidants.
Activated Carbon
Carbon block and granular carbon cartridges remove chlorine, taste, and odor. They are mandatory ahead of EDI and thin-film composite RO where chlorinated feed would destroy the membrane. Change them before breakthrough, not after.
Resin and Ceramic
Resin cartridges provide small-scale softening or deionization in polishing loops. Ceramic cartridges tolerate high temperature and aggressive chemistry in specialized industrial service.
Housing and Sizing
Size the housing for a starting pressure drop below 0.2 bar and a changeout differential of 0.8-1.0 bar. Flow per 10-inch cartridge varies by rating: plan roughly 0.5-1.5 m3/h per cartridge for standard 5-micron elements, and check the manufacturer's flow-pressure curve.
Use code 3 (222 O-ring) or code 7 (226 bayonet) connections for sanitary and high-purity service. Clamp and swing-bolt housings suit general industrial duty and speed up changeouts.
Changeout Economics
Track differential pressure and changeout frequency. A cartridge that lasts three weeks is telling you pretreatment is failing; a cartridge that never reaches its differential limit suggests it is oversized and can be reduced.
Request a Cartridge Proposal
Tell us flow rate, feed quality, chemical exposure, and temperature. We will specify cartridge type, micron rating, housing size, and annual changeout cost.