Reverse Osmosis Filters and RO Membrane Elements

Osmosis moves water from a dilute solution toward a concentrated one. Reverse osmosis applies pressure to the feed water to push it the other way: water molecules pass through a semipermeable membrane while dissolved salts and other contaminants are held back. This water purification process removes nearly every dissolved contaminant. The purified water, called permeate, collects in the center tube, and the rejected salts leave the system in a concentrate stream.

Industrial reverse osmosis systems use spiral wound membrane elements. Flat sheets of polyamide thin film composite membrane are wrapped around a permeate tube with feed spacer mesh between the layers, then loaded end to end into pressure vessels. The feed water flows along the element, and each stage of vessels increases recovery.

Every reverse osmosis system depends on its water supply. Membrane performance changes with water quality, water pressure, temperature and pretreatment. A reverse osmosis water filtration system that is fed clean, dechlorinated water and cleaned on schedule holds its flow rate and salt rejection far longer, which extends filter life.

Protect new elements with the right pre-filter cartridges →

AFF offers Toray durable, low energy brackish water reverse osmosis (BWRO) elements and low fouling membrane elements. These elements are built for strong salt and silica rejection at lower operating pressure, which means high quality filtered water with less energy spent on the high pressure pump.

Each element is a spiral wound polyamide thin film composite membrane, 8 inches in diameter and 40 inches long, built to fit standard 8 inch pressure vessels in industrial and commercial RO systems. A wide pH tolerance allows effective membrane cleaning.

Toray membrane elements can be equipped with bi-directional brine seals. The seal works in either direction, so elements load and unload from either end of the pressure vessel and can be cleaned in both directions.

When you replace RO membranes, replace the whole vessel at once when you can, inspect the interconnectors and O-rings, and flush new elements to drain before sending permeate to service. Store spare elements in a cool, dry place out of direct sunlight.

Most RO membrane problems start upstream. Suspended solids foul the feed spacer, chlorine attacks the polyamide membrane, and hardness forms scale as the water is concentrated. Good pretreatment keeps the feed SDI at 5 or less and free chlorine below 0.1 ppm.

A typical pretreatment filter system uses filter bags or sediment cartridge filters to remove particles, carbon filters or chemical dechlorination to remove chlorine, and an antiscalant or water softener for hard water. AFF supplies the filter housings, bags and cartridges for the pre-filter stage.