Reverse osmosis (RO) is a water purification technology that uses a semipermeable membrane to remove ions, molecules, and larger particles from drinking water. In reverse osmosis, an applied pressure is used to overcome osmotic pressure, a colligative property, that is driven by chemical potential differences of the solvent, a thermodynamic parameter. Reverse osmosis can remove many types of dissolved and suspended species from water, including bacteria, and is used in both industrial processes and the production of potable water. The result is that the solute is retained on the pressurized side of the membrane and the pure solvent is allowed to pass to the other side. To be "selective", this membrane should not allow large molecules or ions through the pores (holes), but should allow smaller components of the solution (such as solvent molecules) to pass freely.
BASIC COMPONENTS OF A REVERSE OSMOSIS SYSTEM: -
1. Cold Water Line Valve:
Valve that fits onto the cold water supply line. The valve has a tube that attaches to the inlet side of the RO pre filter. This is the water source for the RO system.
2. Pre-Filter(s):
Water from the cold water supply line enters the Reverse Osmosis Pre Filter first. There may be more than one pre-filter used in a Reverse Osmosis system, the most common being sediment and carbon filters. These pre-filters are used to PROTECT the RO membranes by removing sand silt, dirt, and other sediment that could clog the system. Additionally, carbon filters may be used to remove chlorine, which can damage the RO membranes.
3. Reverse Osmosis Membrane:
The Reverse Osmosis Membrane is the heart of the system. The semipermeable RO membrane is designed to remove a wide variety of both aesthetic and health-related contaminants. After passing through the membrane, the water goes into a pressurized storage tank where treated water is stored.
4. Storage Tank:
The standard RO storage tank holds from 2 - 4 gallons of water. A bladder inside the tank keeps water pressurized in the tank when it is full. The typical under counter Reverse Osmosis tank is 12 inches in diameter and 15 inches tall.
5. Post filter(s):
After the water leaves the RO storage tank, but before going to the RO faucet, the treated water goes through a final “post filter”. The post filter is usually a carbon filter. Any remaining tastes or odors are removed from the product water by post filtration “polishing” filter.
6. Automatic Shut Off Valve (SOV):
To conserve water, the RO system has an automatic shut off valve. When the storage tank is full, the automatic shut off valve closes to stop any more water from entering the membrane and blocks flow to the drain. Once water is drawn from the RO faucet, the pressure in the tank drops; the shut off valve then opens to send the drinking water through the membrane while the contaminated wastewater is diverted down the drain.
7. Check Valve:
A check valve is located in the outlet end of the RO membrane housing. The check valve prevents the backward flow of treated water from the RO storage tank. A backward flow could rupture the RO membrane.
8. Flow Restrictor:
Water flowing through the RO membrane is regulated by a flow restrictor. There are many different styles of flow controls, but their common purpose is to maintain the flow rate required to obtain the highest quality drinking water (based on the gallon capacity of the membrane). The flow restrictor also helps maintain pressure on the inlet side of the membrane. Without the additional pressure from the flow control, very little drinking water would be produced because all the incoming water would take the path of least resistance and simply flow down the drain line. The flow control is most often located in the RO drain line tubing.
9. Faucet:
The RO unit uses its own faucet, which is usually installed on the kitchen sink. Some areas have plumbing regulations requiring an air gap faucet, but non-air gap models are more common
10. Drain line:
This line runs from the outlet end of the Reverse Osmosis membrane housing to the drain. The drain line is used to dispose of the wastewater containing the impurities and contaminants that have been filtered out by the reverse osmosis membrane.
Are filtered out and flushed away, leaving clean, delicious drinking water. Reverse osmosis is capable of removing up to 99 percent of 65 different contaminants including lead, fluoride, chlorine, dissolved salts, and more.
Definitions of Abbreviations:
CTA - Cellulose tri-acetate - membrane is chlorine tolerant
TFC - Thin film composite - not chlorine tolerant but has a higher production capacity
PSI - Pounds per square inch
TDS - Total dissolved solids
mg/L - Milligram’s per liter
GPG - Grains per gallon
NTU - Nephelometric turbidity units
THERE ARE GENERALLY FIVE STAGES IN THE REVERSE OSMOSIS PROCESS:
1) Sediment Filter:
This pre-filter stage is designed to strain out sediment, silt, and dirt and is especially important as the sediment filter protects dirt from getting to the delicate RO membranes that can be damaged by sediment.
2) Carbon Filter:
The carbon filter is designed to remove chlorine and other contaminants that affect the performance and life of the RO membrane as well as improve the taste and odor of your water.
3) Reverse Osmosis Membrane:
The semipermeable RO membrane in your RO system is designed to allow water through, but filter out almost all additional contaminants.
4) Polishing Filter:
In a four-stage RO System, a final post filter (carbon filter) will “polish” off the water to remove any remaining taste and odor in the water. This final filter ensures you’ll have outstanding drinking water.
5) Storage of water tank: -
Polishing filter are completed the process . After passing through the membrane, the water goes into a pressurized storage tank where treated water is stored.
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