Reverse Osmosis Filters

Reverse osmosis filters are the newest but most effective type of water filters available today providing highest level of protection. They are the most sophisticated and, therefore, considered to be one of the most expensive type of filter.

A reverse osmosis filter combined with a pre-filter and a post-filter is capable of removing most of the harmful and unhealthy elements and other contaminants from water. It can efficiently remove Lead (Pb), Copper (Cu), Arsenic (As), Cadmium (Cd), Chlorine (Cl), Giardia, Pesticides, Salt, Tri-Halo-Methanes, Sulphates, Cysts, Nitrates, etc.

Osmosis: Osmosis is the process of diffusion of fluid through a semi-permeable membrane from a solution which has a low solute concentration to a solution, which has a higher solute concentration, until the concentration of fluid on both sides of the membrane be equal.

Reverse Osmosis: But actually what happens in the reverse osmosis filters is just the opposite of the process defined above. The process of osmosis is stopped and reversed by applying pressure to the water with the higher concentration and forcing it against the membrane. The reverse osmosis has been used in this manner for years to remove salt from seawater to make it drinkable.

Working of RO Filters

The Reverse Osmosis filters remove the dissolved inorganic solids (such as salts) from water. The water is pushed through a semi permeable membrane (which is about as thick as cellophane). It allows only the water to pass through, not the impurities or contaminates. These impurities and contaminates are flushed down the drain.


Basic Components and Functions of a RO Filter System
Basic Components and The Functions of a RO Filter System These basic components are common to all reverse osmosis systems :

• Cold Water Line Valve: It is the valve, which fits onto the cold water supply line. It has a tube that is attached to the inlet side of the RO pre filter. It acts as the water source for the RO system.
  
  
• Pre-Filter(s): At first the water, from the cold water supply line, enters the RO pre-filter. The number of pre filters may vary depending on the requirements. There may be more than one pre-filter used in a reverse osmosis system. Sediment filters are the most commonly used pre-filters. They are used for removing sand silt, dirt and other sediments. Carbon filters may be used to remove chlorine from the water. However, carbon pre-filters are not used if the RO system contains a CTA (cellulose tri-acetate) membrane.
  
  
• Reverse Osmosis Membrane: It is the most important part of a RO system. It is considered the heart of the system. The most popular one is a spiral wound, which is mainly of two types. One is CTA (Cellulose Tri-Acetate), which is chlorine tolerant, and other is TFC/TFM (Thin Film Composite /Material), which is not chlorine tolerant.
  
  
  
  
  
• Post Filter(s): The post filter is usually carbon (Granular or Carbon Black Form). After passing through pre filters and membrane, and before going to the RO faucet, the product water goes through the post filter(s). Its main function is to remove the remaining tastes and odors (if any) from the product water.
  
  
• Automatic Shut Off Valve (SOV): The main function of the shut-off-valve is to stop the flow of water, as soon as the storage tank is full, from entering into the membrane thus stopping the water production. As water is drawn from the drinking tap, the pressure in the storage tank drops and the shut off valves opens, thus allowing water to flow to the membrane.
  
  
• Check Valve: A check valve is attached to the outlet end of the RO membrane housing. It prevents the backward flow of product water, from the RO storage tank to the membrane unit. It could lead to the rupture of RO membrane.
  
  
• Flow Restrictor: It maintains the flow rate required to obtain the highest quality drinking water. The flow restrictor also helps maintain the pressure on the inlet side of the membrane. Without its use, very little drinking water would be produced because all the incoming tap water would take the path of least resistance and simply flow down the drain line.
  
  
• Storage Tank: The storage tank holds up the purified water. The standard size is up to 2.5 gallons. A bladder is fit inside the tank, which keeps water pressurized in the tank when it is full.
  
  
• Faucet: The RO unit has its own faucet. It is normally installed on the kitchen sink.
  
  
• Drain Line: This line originates from the outlet end of the reverse osmosis membrane to the drain. It is used to throw out the impurities and contaminants found in the incoming water source.

Advantages of Reverse Osmosis Over Conventional Processes
Reverse osmosis has proved itself as the most efficient means of removing impurities, like chemical contaminants, salts, and heavy metals, such as lead, from drinking water. It is a better option of water filtration compared to other conventional water treatment processes. For waters with total dissolved solids of around 200, some less or more, reverse osmosis is preferred over the ion exchange for removal of silica and organics. It is less expensive. If compared with the distillation, reverse osmosis uses only a part of the total energy required and does not have high temperature problems or scaling and corrosion.

Effect of RO in Combination with Others
Reverse osmosis is the most effective way of removing impurities and contaminants from drinking water. It works even better, and purify water more effectively, in combination with other methods. Most of the filtration systems, whether the residential or municipal, combine the RO system with a pre-filtering method in order to remove larger particles suspended in the water that would gum up the filter and reduce its effectiveness. After removing the bigger insoluble particles, dissolved particles are removed by the RO filter, which is very effective in removing most minerals, metals and many organic impurities from the water. Further, the filtered water may be forced through a final 'polishing filter', often activated carbon, which will remove the remaining bacterial contaminants, and most objectionable odors and tastes from the water.