Wednesday, November 3, 2010

reverse osmosis water treatment

Reverse osmosis water treatment is a process in which water is forced through a semipermeable membrane that has very small holes or "pores". Clean water passes through and impurities that are too large to pass through the membrane are left behind and dragged.

How Reverse Osmosis Work?

Reverse osmosis water treatment is similar to the membrane filtration treatment. However, there are fundamental differences between reverse osmosis and filtration. The predominant elimination mechanism in the membrane filtration is straining or size exclusion, so the process can theoretically achieve perfect exclusion of particles, regardless of the operating parameters as influent pressure and concentration.

RO (reverse osmosis), however, involves a diffusion mechanism so that the separation efficiency is dependent on the influent solute concentration, pressure and flow rate of water. It works by using pressure to force a solution through a membrane, keeping the solute on one side and allow the pure solvent to pass to the other side. This is the reverse of the normal osmosis process, which is the natural movement of solvent from an area of low solute concentration through a membrane to an area of high solute concentration when no external pressure is applied.

Water chemistry is so complex and no single water treatment device can be used to remove any substances in water. Different drinking water treatment devices have their own advantages and disadvantages. Every household in particular to determine if there is a need for additional water treatment. If this is the case, identify the unit or combination of units best suited to your water needs.

Stages of reverse osmosis:

1. During initial phase of filtration, tap water or well water (pump pressure booster) is passed through a filter (a pre-filter) that removes sediment, silt, sand and clay particles that could clog the I / O membrane.

2. The water is forced through an activated carbon filter that traps minerals and contaminants such as chromium, mercury, copper, chloramines and pesticides. It also removes chlorine, which is important, as chlorine will shorten the life of the membrane.

3. Water pressure is transferred to the R / O module, allowing only clean water to pass through small pores in the membrane. The impurities cannot pass through the membrane are left behind and flushed down the drain.

4. Treated water is sent to a storage tank.

5. Treated water passes through an activated carbon filter before use to further improve water taste and smell.

Water containing hydrogen sulfide, manganese, iron, or must be pre-treated to extend the life of the membrane. A dealer can recommend the necessary pre-treatment.

Note: The reverse osmosis units produce no noise other than the sound of flushing down the drain (usually a sink or drain in the floor).

How Much Does Reverse Osmosis Units Cost?

Reverse osmosis unit prices range from $ 400 for a portable or under sink unit to $ 2,500 for a larger, stationary unit (basement), which installed a booster pump and a pressure system. Replacement Pre-filters range in price from about $ 100 - $ 200 each.

What are the benefits of Reverse Osmosis?

Reverse osmosis can remove dissolved solids, salts, minerals that cause hardness, organic chemicals and other impurities. It can improve water's taste for people who do not like the taste of minerals dissolved solids.

The treated water will not produce scale in kettles and coffee makers. Because eliminating sodium and potassium, people in a prescription of sodium or potassium restricted diet may benefit. R / O units can also remove contaminants such as chromium, mercury and nitrates. Before buying an R / O unit, verify the certification and literature for the special model to see exactly what can and cannot eliminate.

Is Reverse Osmosis - Treated water safe to drink?

Reverse osmosis removes minerals such as calcium and magnesium in drinking water. Water is a minor source of such minerals as compared with food. If you consume a reasonably balanced diet is not necessary to take a supplement of minerals in drinking water treated with a reverse osmosis system. Low levels of minerals in drinking water may be a concern for people living in countries with hot climates.

Factors affecting the quality of treated water and Quantity

Small units of reverse osmosis coexistence that operate in the domestic water pressure will produce one to five gallons per day. Many units of reverse osmosis water treatment are a manufacturer rated 80 psi supply pressure. Typical private water system pressure is closer to 30 to 40 psi, so that water production is often rated capacity about half the manufacturer.

Total dissolved solids in water.

Greater pressure is needed for reverse osmosis to remove higher levels of total dissolved solids. Many units of domestic reverse osmosis water treatment are 25 to 50 psi of pressure. These are only suitable for a maximum of 1,500 to 2,000 ppm total dissolved solids. If you use reverse osmosis to treat water that is higher in total dissolved solids than this, a booster pump will be needed.


Water pressure affects both the quality and quantity of treated water produced. Basically, the higher the pressure, the more treated water produced and the better the quality.


The optimal water temperature for most reverse osmosis membranes is 25 ° C. As the temperature drops to 5 ° C, the capacity of the reverse osmosis unit is reduced to less than half. Long, small diameter lines of the water supply will allow the water to warm up to room temperature (20 ° C) before reaching the membrane. This will increase the production of treated water.

Do I need to maintain the unit?

Reverse osmosis units should be maintained according to manufacturer's recommendations. Typically, the pre-filter sediment and pre-activated carbon filters must be changed at least annually. However, these pre-filters may need changing as often as once every six months if the water entering the unit contains sand, large amounts of chlorine or other substances that affect the efficiency of the filter. Although the membranes in a unit in good condition can last several years, the membrane may need replacing more frequently than the manufacturers suggested timeline.

Additional information is available through health inspectors, specialists in agricultural water or on the web.