In drinking water treatment reverse osmosis is a method of treatment that uses an external pump to push water through a membrane with microscopic holes (semi-permeable) to remove larger particles from drinking water. Selection of the proper membrane will ensure that the holes are large enough to allow water molecules to pass through, but will small enough to block most inorganic impurities. For the system to work it is important that the membrane is not clogged (fouled). To prevent fouling it is essential that oxidation then filtration to remove the common contaminants, iron and manganese takes place before the reverse osmosis unit. If the water is hard, then it needs to be softened or an anti-scalant to prevent mineral build-up on the membranes.
 |
| from VA Tech |
Reverse osmosis systems can be used to reduce the levels of total dissolved solids and suspended matter in drinking water. The principal uses of reverse osmosis in are for the reduction of high levels of nitrate, lead, mercury, arsenic, cadmium, sulfate, sodium and total dissolved solids. Removal effectiveness depends on the contaminant and its concentration, the membrane selected, the water pressure and proper installation. Proper selection of the membrane and pressure is essential when selecting a reverse osmosis system. The membrane must be selected based on complete water analysis otherwise the entire system might be useless.
In addition, reverse osmosis systems require regular maintenance and monitoring to continue to function properly over an extended period of time. Reverse osmosis has been shown to remove 83%-92% of nitrates from drinking water in both field and laboratory test. This is probably the most appropriate use of reverse osmosis systems. There are two types of systems: point of use and whole house. The point-of-use systems are typically installed under a kitchen sink with a separate dispenser. Point of use systems typically deliver small amounts (2 to 10 gallons per day) of treated water. Whole- house-systems treats all of the water as it comes into your home. A whole-house reverse osmosis system would require a treatment train to treat the water ahead of the reverse osmosis membrane and holding tank. Also, it would require a booster pump and UV light to ensure that the stored water remained contaminant free.
There is no single “best” treatment for home use, only treatment types appropriate for certain problems. The water treatment the industry has expanded to marketing treatment systems designed treat (or at least sold to treat) contaminants that may pose a health hazards. According to the on-going studies by the U.S. Geological Survey micro-contaminants are appearing is groundwater supplies. Unfortunately, the home water treatment industry is inconsistent in the skill and knowledge of the companies and their employees and many of the systems installed are inappropriate, unnecessary or have side effects that create other problems. The free in-home water testing provided by water treatment companies is very limited in scope. The only things that they can test for in the in-home tests are hardness, pH, iron and sulfur. In addition, the sensitivity and accuracy of the tests can be limited. Analysis for organics and bacterial contaminants must be performed in a certified laboratory and before you buy any treatment system you should do a full analysis yourself.
I am not a fan of reverse osmosis systems in many applications. They are often sold as accessory item to solve the taste and sodium problem created when a whole house water softener is installed or for feared problems without proper testing. Reverse osmosis systems use a lot of water. They recover only 5 to 15 percent of the water entering the system. The remainder is discharged as waste water.
The waste water carries with it the rejected contaminants, and methods to re-cover this water are not practical for household systems. Waste water is typically connected to the house drains and will add to the load on the household septic system. A reverse osmosis system delivering 5 gallons of treated water per day may discharge 40 to 90 gallons of waste water per day to the septic system. This is a significant additional load and could impact the life and functioning of your septic system. In addition, the waste water often carries the salt from the water softener and is damaging to the environment. It is to be noted that a whole house reverse osmosis system installed with a storage tank or two and a booster pump wastes much less water. It is estimated to waste only 1 gallon for every 4 gallons it makes.
Effectiveness of reverse osmosis system depends on initial levels of contamination, membrane size and type and water pressure. The application of pressure reverses the natural flow of the flow of water in osmosis from high concentration so that water passes from a more concentrated solution to a more dilute solution through a semi-permeable membrane. As stated above, reverse osmosis systems incorporate pre and post-filters along with the membrane itself in order for a reverse osmosis system to function properly. It is common to have a whole house filter system utilizing activated carbon installed in series with the reverse osmosis system. In addition, because contaminants are removed by forcing water through a membrane, the membrane requires regular maintenance and cleaning. Reverse osmosis systems are normally used to treat only drinking and cooking water in homes; however, it is the method used for desalinization plants.
Reverse osmosis systems are never not appropriate for treating water supplies that are contaminated by coliform bacteria (neither nuisance nor fecal) because they do not remove bacteria. Reverse osmosis units on the market range in cost from $1,000 to over $10,000 for a whole house unit with an anti-scalant. The units vary in quality and effectiveness. Homes on well water need to purchase low pressure units which are slightly more expensive than the systems designed for municipal water. The size and membrane type are one of the factors that will determine cost. Replacement membranes cost $100 to $200 and filter cartridges around $50. Reverse osmosis is a proven technology that has been used successfully on a commercial basis most famously for removing salt from seawater.
In addition, reverse osmosis systems require regular maintenance and monitoring to continue to function properly over an extended period of time. Reverse osmosis has been shown to remove 83%-92% of nitrates from drinking water in both field and laboratory test. This is probably the most appropriate use of reverse osmosis systems. There are two types of systems: point of use and whole house. The point-of-use systems are typically installed under a kitchen sink with a separate dispenser. Point of use systems typically deliver small amounts (2 to 10 gallons per day) of treated water. Whole- house-systems treats all of the water as it comes into your home. A whole-house reverse osmosis system would require a treatment train to treat the water ahead of the reverse osmosis membrane and holding tank. Also, it would require a booster pump and UV light to ensure that the stored water remained contaminant free.
There is no single “best” treatment for home use, only treatment types appropriate for certain problems. The water treatment the industry has expanded to marketing treatment systems designed treat (or at least sold to treat) contaminants that may pose a health hazards. According to the on-going studies by the U.S. Geological Survey micro-contaminants are appearing is groundwater supplies. Unfortunately, the home water treatment industry is inconsistent in the skill and knowledge of the companies and their employees and many of the systems installed are inappropriate, unnecessary or have side effects that create other problems. The free in-home water testing provided by water treatment companies is very limited in scope. The only things that they can test for in the in-home tests are hardness, pH, iron and sulfur. In addition, the sensitivity and accuracy of the tests can be limited. Analysis for organics and bacterial contaminants must be performed in a certified laboratory and before you buy any treatment system you should do a full analysis yourself.
I am not a fan of reverse osmosis systems in many applications. They are often sold as accessory item to solve the taste and sodium problem created when a whole house water softener is installed or for feared problems without proper testing. Reverse osmosis systems use a lot of water. They recover only 5 to 15 percent of the water entering the system. The remainder is discharged as waste water.
The waste water carries with it the rejected contaminants, and methods to re-cover this water are not practical for household systems. Waste water is typically connected to the house drains and will add to the load on the household septic system. A reverse osmosis system delivering 5 gallons of treated water per day may discharge 40 to 90 gallons of waste water per day to the septic system. This is a significant additional load and could impact the life and functioning of your septic system. In addition, the waste water often carries the salt from the water softener and is damaging to the environment. It is to be noted that a whole house reverse osmosis system installed with a storage tank or two and a booster pump wastes much less water. It is estimated to waste only 1 gallon for every 4 gallons it makes.
Effectiveness of reverse osmosis system depends on initial levels of contamination, membrane size and type and water pressure. The application of pressure reverses the natural flow of the flow of water in osmosis from high concentration so that water passes from a more concentrated solution to a more dilute solution through a semi-permeable membrane. As stated above, reverse osmosis systems incorporate pre and post-filters along with the membrane itself in order for a reverse osmosis system to function properly. It is common to have a whole house filter system utilizing activated carbon installed in series with the reverse osmosis system. In addition, because contaminants are removed by forcing water through a membrane, the membrane requires regular maintenance and cleaning. Reverse osmosis systems are normally used to treat only drinking and cooking water in homes; however, it is the method used for desalinization plants.
Reverse osmosis systems are never not appropriate for treating water supplies that are contaminated by coliform bacteria (neither nuisance nor fecal) because they do not remove bacteria. Reverse osmosis units on the market range in cost from $1,000 to over $10,000 for a whole house unit with an anti-scalant. The units vary in quality and effectiveness. Homes on well water need to purchase low pressure units which are slightly more expensive than the systems designed for municipal water. The size and membrane type are one of the factors that will determine cost. Replacement membranes cost $100 to $200 and filter cartridges around $50. Reverse osmosis is a proven technology that has been used successfully on a commercial basis most famously for removing salt from seawater.
Thanks for sharing this post. :-)
ReplyDelete