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.

FILMTEC™ food processing elements are specially designed and manufactured for food and dairy applications. The spiral element design is one of the most compact and inexpensive designs available for filtration modules. Through innovative design, high-quality membrane and superior filtration capabilities, Nomenclature 8.0" diameter, 40" long spiral-wound RO module with 30-mil-thick feed spacer RO-8040/30-FF { { Product Membrane Type Typical Applications Available in USDA/3A Configuration? RO Reverse osmosis Product concentration/dewatering Yes ROHR High rejection reverse osmosis Condensate polishing No ROPHT High temperature/pH reverse osmosis Product concentration/dewatering Yes NF45 Nanofiltration Product desalting/enrichment Yes NF70 High-rejection nanofiltration Product concentration Pending UF20 20,000 MWCO Ultrafiltration Whey protein concentration Yes UFPHT20 High temperature/pH 20,000 MWCO Milk standardization/WPC Yes FS50 50,000 MWCO Ultrafiltration Brine clarification Pending Full-fit design Nominal feed spacer thickness (in 1/1000 of an inch) Nominal element length (in inches) Nominal outer diameter (in inches, implied decimal) Membrane type (RO,ROHR, ROPHT, NF45, NF70, UF20, UFPHT20 or FS50) FILMTEC membranes are the best in the market. In a spiral element the feed solution flows across the membrane surface. Liquid permeates through the membrane while selected components in the feed are retained. Turbulent mixing of the feed flow is created with a plastic netting material, referred to as the "feed spacer." Depending on the thickness and design of the feed spacer, spiral elements can be used for filtering liquids with different viscosities and suspended solids content. The permeate flow is carried through a synthetic fabric called "permeate spacer" and is collected in the permeate tube.

Dow FILMTEC™ Membranes Continue to Provide Consistent, Reliable Performance in Industrial Water Production from Brackish Sources Dow FILMTEC™ Brackish Water Elements Offer Alternate Strategies to Lower Your Cost to Produce Water Whether you seek the latest innovative solution or the most cost effective one, our brackish water product line offers the right balance of quality, performance, reliability, and cost. With new products, technologies, and strategies for lowering the cost of water, FilmTec can maximize your system output to unprecedented performance. This is one reason FILMTEC™ elements are more durable and clean more effectively over the widest pH range (1-12) than other reverse osmosis (RO) elements. Our low energy elements enable operational cost savings through lower energy usage and higher system productivity than other elements. Automated precision fabrication with a minimum 28 mil feedspacer reduces the effect of overall fouling, maximizes element efficiency, and lowers your operating costs. Higher surface area elements permit RO system designs that meet productivity targets with fewer elements. These new designs result in lower installed system cost by reducing the number of components and installation expense.

FILMTEC™ Nanofiltration Elements Offer Solutions for Solute-Specific Separations Including Softening, Pesticide and Organic Removal In every application, with every customer, FilmTec seeks to offer the optimum balance of quality performance, reliability, and cost. And with the unique capability of Filmtec’s nanofiltration (NF) membranes we enable you to customize the water composition you require as well. FILMTEC™ nanofiltration membranes have a pore size in the order of nanometers (10 angstroms). Nanofiltration membranes typically operate at less than 100 psi (7 bars). FilmTec offers a portfolio of nanofiltration membranes that can remove organics with molecular weights greater than 200 (e.g. Total Organic Carbon (TOC) and disinfection by-products) while allowing varying amounts of salt and hardness passage. NF200 Medium to high salt passage, medium calcium passage (50-65%), high atrazine rejection (95%), NF270 High salt passage, medium calcium passage (40-60%), high TOC removal. NF90 High salt removal (90%), high iron removal, pesticide, herbicide removal, and TOC removal.

Seawater typically contains approximately 36,000 ppm of total dissolved solids (TDS). The World Health Organization has established a maximum TDS level of less than 500 ppm for potable water. Quite obviously, any water treatment technology capable of making seawater drinkable must be able to reduce the total dissolved solids by 99% or more. Reverse osmosis is especially well suited to this application. As a matter of fact, desalination of seawater and treatment of brackish water were among the first practical applications of reverse osmosis. RO technology is particularly cost-effective, requiring lower capital costs than alternate treatment methods such as evaporation and distillation. In addition, reverse osmosis is far less energy intense which lowers operating cost. Newer membranes are effective at lower pressure than older types, and also exhibit higher product water to feedwater (i.e., recovery) ratios. This all contributes to lower cost-per-gallon of water produced. In general, a water treatment system involving RO will feed raw water through a series of filters to remove solid impurities as well as to treat turbidity and other problems. Water pressure is increased by pumps to force the feedwater through the reverse osmosis membranes. The resulting purified water is then treated with standard drinking water chlorination, and is fed directly into the potable water storage and distribution system.

Dow FILMTEC™ home drinking water RO elements are constructed using advanced automated manufacturing technology. Unlike the hand-rolled elements sold by some manufacturers, Dow FILMTEC elements are built to optimum physical tolerances, minimizing element-to-element differences. In addition, critical fastening points are sonic-welded for maximum strength and durability. For ease of installation, we also offer dry low-pressure RO elements. Finally, extensive testing ensures that every FILMTEC™ element we ship meets our high standards for fabrication quality.