Membranes, filter cartridges and filtration media are the consumables of water treatment. They are bought repeatedly, and small differences in specification can have a large effect on plant performance and running cost.
Because many products look alike on paper, the key to buying well is comparing like with like: the same test conditions, the same rating method and the same dimensions and connections.
What falls under this category
- RO and NF membrane elements
- Spiral-wound elements, most commonly 4040 (4 × 40 inch) and 8040 (8 × 40 inch), in brackish, low-energy, fouling-resistant and seawater variants.
- Ultrafiltration modules
- Hollow-fibre or tubular modules, commonly PVDF or PES, operated inside-out or outside-in.
- Cartridge and bag filters
- Melt-blown, string-wound and pleated cartridges, and bag filters for higher solids loads.
- Filter media
- Sand, anthracite, garnet, activated carbon and catalytic media for iron and manganese removal.
- Filter housings
- Cartridge and bag housings in plastic, FRP or stainless steel.
Specifications to compare
- RO element performance
- Nominal permeate flow and stabilised salt rejection are always quoted at the manufacturer's standard test conditions (feed concentration, pressure, temperature, recovery). Only compare elements tested under the same conditions.
- Active area and element type
- Membrane area per element and whether the element is designed for low energy, high rejection or fouling resistance. The right type depends on your feed and priorities.
- Chlorine tolerance
- Polyamide membranes typically tolerate almost no free chlorine (datasheets commonly state below 0.1 mg/L). Check the limit and the maximum feed pressure.
- Dimensional compatibility
- 8040 elements are broadly interchangeable across major manufacturers, but check interconnector, adapter and brine-seal compatibility with your pressure vessels.
- Cartridge micron rating
- A nominal rating means the filter captures a stated share of particles at that size; an absolute rating means it captures essentially all of them. A nominal 5 µm and an absolute 5 µm cartridge are not equivalent.
- Cartridge format
- Length (10, 20, 30 or 40 inch), diameter (standard or jumbo), end cap (double open end or single open end with a specified O-ring) and recommended flow per 10-inch length.
- Activated carbon grade
- Base material (coconut shell, coal or wood), particle size, iodine number as an indicator of adsorption capacity, and whether the product is suitable for potable water.
- Housing rating
- Material, design pressure, number of cartridges and closure type. Stainless housings for seawater or high-chloride water need suitable alloys.
Information to send suppliers with your enquiry
- The model of your existing element or cartridge, or the plant design report if you are replacing a full set.
- Water source and flow.
- Quantity and delivery schedule.
- Documents you need: certificate of analysis, element test data sheets, potable-water approvals.
Common sourcing mistakes
- Treating nominal and absolute-rated cartridges as interchangeable.
- Buying membranes without asking for the manufacturing date and how they have been stored. Elements should be kept preserved, out of direct sunlight and never frozen.
- Mixing new and old elements within the same pressure vessel, which uses the new elements unevenly.
- Not verifying authenticity. Ask for serial numbers and check them with the manufacturer where it offers verification.