Making Sense of Commercial Reverse Osmosis Membranes.

There have been many technological improvements in RO membrane technology in the last decade. Selecting the correct RO membrane can be confusing at times. Here are some pointers to help you select the correct membrane.

1) Flow rates are always based on 77 degree F inlet temperature. If your water is colder production will be diminished. Therefore if your system has a pump and plumbing to make 2000 gallons per day at 77 degrees and your water temperature is 66 degrees you can run a membrane designed to make 2,500 gpd at 77 degrees (see chart below)
2) There are tape wrapped and fiberglass wrapped membranes. If you are running over 225 psi or using housings that hold more than three membranes fiberglass wrapped membranes are recommended.
3) For many applications 100 psi will product high enough water quality. The old days of having to run 220 psi to get good production are gone. Your system may be able to make more water at lower pressure by running a different membrane. You will need to check pump curves or plumbing specs for your system to assure this will work.

Here is a rundown on some of the popular Dow Filmtec membranes

Filmtec TW30-4040 - This is a tap water membrane. It will produce 2,400 gpd with 99.5% salt rejection @ 225 psi with a 2,000 ppm NaCl feed. This membrane is tape wrapped and has a 34 mil feed spacer thickness.

Filmtec LE-4040 – Replaces the part number BW30LE-4040. This is a low pressure brackish water membrane. It will produce 2,500 gpd with 99% salt rejection @ 150 psi with a 2,000 ppm NaCl feed This membrane is fiberglass wrapped and has a 34 mil feed spacer thickness.

LP-4040 - This is a low pressure tap water membrane. It will produce 2,900 gpd with 99.2% salt rejection @ 145 psi with a 500 ppm NaCl feed. This element replaces the older “cold water” elements with a newer membrane leaf technology. This membrane is tape wrapped and has a 34 mil feed spacer thickness.

XLE-4040 - This is a low pressure tap water membrane. It will produce 2,600 gpd with 99.0% salt rejection @ 100 psi with a 500 ppm NaCl feed. This element replaces the older TW30LE with a newer membrane leaf technology. This membrane is tape wrapped and has a 28 mil feed spacer thickness.

BW30-4040 - This is a brackish water membrane. It will produce 2,400 gpd with 99.5% salt rejection @ 225 psi with a 2,000 ppm NaCl feed. This membrane is fiberglass wrapped and has a 34 mil feed spacer thickness.