Reverse Osmosis (RO) is a technology used by the drinking water treatment industry to improve water quality by utilizing a semipermeable membrane to remove ions, molecules, and particles from drinking water. RO works by applying water pressure to overcome naturally occurring osmotic pressure to separate ions through a semipermeable membrane. In the normal osmosis process, the solvent (water) naturally moves from an area of low solute concentration through a semipermeable membrane to an area of high solute concentration. The process generates osmotic pressure due to the solvent (water) moving into the more concentrated solution. RO can reduce several types of dissolved and suspended species from water, and is used to further purify water or desalinate to create potable water.
Although RO is an excellent technology for reducing contaminants found in drinking water, it operates at a very poor water efficiency. The water efficiency of many ROs used in homes today is around 10-20 percent, essentially wasting (sending to drain) nine gallons of water for every gallon of purified water produced. The international popularity of using RO to improve drinking water has exploded throughout Asia and remains popular in North America. However, with the increased demand for quality drinking water and water scarcity issues plaguing countries around the globe, the RO industry is taking active steps to improve the water efficiency of their products.
The water treatment industry approached ASSE International to develop an efficiency standard for residential RO equipment. In the late 1980s, the popularity of residential RO water treatment expanded in the U.S. The industry worked with NSF International and the Water Quality Association to create the NSF/ANSI 58 and WQA S-300 standards. These standards focus on requirements for material safety, structural integrity, and reduction of common water contaminants. In contrast, ASSE Standard #1086, Residential Reverse Osmosis System – Water Efficiency, is being created to require RO water efficiency to exceed 40 percent. The 1086 standard focuses on three key aspects of RO technology that affect water efficiency: membrane life, automatic shut-off valve efficiency and variance, and flow restrictor tolerance.
The membrane life test is an accelerated 20-day test that has been designed to simulate one-year use of an RO membrane. Improving the water efficiency of an RO system increases the propensity of the membrane to become fouled. Fouled membranes no longer produce significant amounts of purified water, requiring them to be replaced.
The one-year simulation test has been created to help ensure the product life of the membrane is a minimum of one year. Without this test, products could be modified to achieve 40 percent efficiency, but may only last a few weeks.
The automatic shut-off valve efficiency and variance test has been created to verify the reliability of the system’s automatic shut-off valve. Automatic shut-off valves are used by the system to automatically turn your RO system on and off according to the storage tank level. An RO automatic shut-off valve is a diaphragm valve that works in conjunction with a pressurized storage tank. When the storage tank is full, the valve turns the system off, and when the tank empties, it turns the system back on to refill the tank with purified water. The valve operates via pressure from the storage tank vs. feed line pressure. The valve diaphragm is engaged when the pressure from the tank exceeds approximately 65 percent of the incoming line pressure. This stops the flow of water through the RO system until the tank level is lowered enough for the pressure to fall below this level. If the RO system’s automatic shut-off valve fails to turn off or operates inconsistently, the water efficiency of the system will be significantly affected. Products tested to ASSE 1086 will require properly designed and functioning automatic shut-off valves.
The flow restrictor tolerance test has been created to require minimum accuracy of capillary flow restriction devices so that membrane rejection rates can be accurately set to optimize the RO efficiency without stressing the membrane to fouling and early failure. RO systems operate by creating a purified permeate steam (product water) and a concentrated reject stream (waste water). A flow restrictor is used to control the amount of reject water produced by forcing water purified through the semipermeable membrane. Controlling the flow rate of product water vs. reject water (system recovery) is essential to optimizing the efficiency of the RO system.
As the demand for better water quality continues to grow and water scarcity issues expand throughout the world because of droughts and increased population, new standards and regulations will help drive innovation. The ASSE 1086 standard is another example of how ASSE International and The IAPMO Group continue to be global leaders in promoting water conservation. For more information about ASSE 1086 or other ASSE standards, contact ASSE Staff Engineering Supervisor Conrad Jahrling at conrad.jahrling@asse-plumbing.org.
