| REVERSE OSMOSIS | | | | sulfide (H2S)? A GAC will reduce H2S levels where as |
| The most popular water purification process on the | | | | a pleated or string sediment filter will not. |
| market today, is Reverse Osmosis. This water | | | | CARBON BLOCK filters are usually placed as the third |
| purification process was pioneered in the early 1950s | | | | pre-filter in a RO filter system. Carbon block filters |
| in response to the increasing incidence of kidney | | | | have the potential to filter down as small as one-half |
| disease. RO was designed to replace the filtration | | | | micron. This is very small. As well, carbon blocks are |
| function of the kidney, and is still used in the dialysis | | | | reasonably effective at removing most chemicals and |
| units of hospitals for this purpose today. | | | | pesticides from the water. The effect of placing the |
| Reverse Osmosis utilizes the properties of a | | | | pre-filters in this arrangement contributes to both the |
| membrane to prevent the passage of particles | | | | increased life expectancy of the RO membrane, as |
| through the membrane. Any particle larger than a | | | | well as reduced pre- filter maintenance. The least |
| water molecule is prevented from passing through | | | | expensive of the filters, the 20 micron, takes out the |
| the membrane, while the H2O is permitted to flow | | | | bulky larger substances. The next filter in expense, |
| through to the "pure water" side. Because of the | | | | the GAC, takes out the chlorine and more particles |
| incredibly small pores which the water passes | | | | which the 20 micron could not capture, and the most |
| through, pre- filtration is necessary to prevent the | | | | expensive of the pre-filters, the Carbon Block, is left |
| plugging up of the membrane pores. Pre-filtration can | | | | to just absorb the chemicals. |
| combine 1, 2 or even 3 pre-filters. These pre-filters | | | | THE MEMBRANE is the heart of the Reverse |
| are combined to remove larger particles, chlorine, and | | | | Osmosis System. As the water is forced through the |
| even some chemicals and pesticides, before the | | | | membrane by water pressure, the impurities are held |
| water is subjected to the membrane purification | | | | back and flushed out of the system through the |
| technology. The number and type of pre-filtration | | | | brine water drain line. The membrane is capable of |
| depends on the water quality and impurities which | | | | removing upwards of 95% of all impurities, if |
| are determined to be present in the water. Common | | | | sufficient feed water pressure is available. Higher |
| pre-filtration includes, sediment filtration, chlorine | | | | feed water pressure increases the efficiency of the |
| removal, and chemical absorbent. The purpose of the | | | | membrane. Absolute minimum feed water pressure is |
| pre-filtration is to protect and give longer life to the | | | | 40 psi. If the pressure is not high enough an electric |
| expensive membrane portion of the system. | | | | pressure booster pump must be added before the |
| SEDIMENT is first removed by a 20 micron filter. This | | | | system. |
| filter may be constructed of tight wound cotton | | | | After the purified water has passed through the RO |
| string spun around a spool, or it may be a pleated | | | | membrane, it is stored in a small storage tank, waiting |
| paper filter. By the way, this dot, "." is approximately | | | | to be delivered through a dedicated tap, to the |
| 50 microns in size. Therefore a 20 micron filter would | | | | consumer. The tank only holds about 6-8 liters of |
| remove any substance which is half the size of a dot | | | | water at a time. This small tank is designed to fit |
| such as this one ". " Sediment, might include particles | | | | under the kitchen sink for convenience. Larger tanks |
| released from the inside of the pipes which deliver | | | | can be ordered and easily installed for consumers |
| the water to your home, iron which has come out of | | | | who desire more water available at a moments |
| solution and is now visible in your water as color, or | | | | notice. It generally takes about 2 hours to fill an |
| just debris from the water source where your water | | | | empty 8 liter tank. Most RO systems deliver from |
| is drawn from. | | | | 35-75 gallons (160-340 liters) every 24 hours, |
| GRANULAR ACTIVATED CARBON (GAC) is most | | | | depending on the membrane capacity which came |
| often used as the second filter, if the water source | | | | with the RO system, and depending on the water |
| is chlorinated, as most municipal water is. Chlorine will | | | | pressure. (more pressure = more purified water) |
| destroy the Composite RO membrane quickly, so the | | | | Finally, on some systems the water may pass |
| chlorine must be removed before the water reaches | | | | through a final carbon filter which is installed in the |
| the RO membrane. GAC filters are simple filters which | | | | delivery line between the tank and the faucet, just |
| are filled with small grains of carbon which are highly | | | | as a final polish for good tasting water. |
| absorbent and effectively remove chlorine. When the | | | | CRITICISM is often voiced about RO units because |
| water source does not contain chlorine, the GAC is | | | | for every liter of purified water, 2-3 liters of brine |
| usually replaced with a sediment filter of perhaps 10 | | | | water are discharged to the drain, to clean the |
| microns of effective filtration, although some GAC | | | | impurities out of the water. This is true. However, |
| filters can act as both a taste and odor filter, as well | | | | this water is not gone! It is simply sent back out to |
| as a 10 micron sediment filter. It should be noted | | | | where it came from, the water table. Nothing has |
| though, that because a GAC filter does not give | | | | been added to the water. The impurities it picked up |
| "absolute" filtration results for sediment, the water | | | | as it passed through the ground, is returned to the |
| treatment technologist who is applying the application | | | | ground. |
| for water treatment should be aware of what | | | | CONCLUSION: Reverse Osmosis is the number one |
| objective is to be attained. Is the objective tighter | | | | choice of consumers around the world who wish to |
| filtration after the 20 micron by placement of a 10 | | | | provide pure, safe, good tasting drinking water for |
| micron filter, or is ithe objective taste and odor | | | | themselves and their families. |
| removal, such as the rotten egg smell of hydrogen | | | | |