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Water Conditioning & Purification Magazine, Water Quality Associaton WQA, USGS,
Please Note: replacement water filters and reverse osmosis membranes advertised herein are not manufactured by the companies that manufacture the underlying water treatment equipment unless so noted. Our use of registered trademarks, such as EverPure ®, Culligan ®, or RainSoft ® etc., is for identifying compatible replacement water filters and reverse osmosis membranes only, and does not suggest any association, sponsorship or endorsement of products by manufacturers of the underlying equipment.

Well Water Treatement - some points to consider

Ultra Violet UV Water Purification - what's that?

Ultraviolet (UV) light is Electro Magnetic Radiation that has a wavelength that is shorter than visible light but longer than x-rays. The UV light region runs from the extreme UV region (1-31 nm) to the near UV region (200-400 nm).

The effectiveness of Ultra Violet light to deactivate the pathogenic DNA, is affected by several factors: UV dose. This is a function of UV light intensity and exposure time. and Absorbing Compounds in the water these act as shields for the microbes found in water. They absorb some of the UVC light, meaning that the microbes don't get the full applied dose.

Ultra Violet is an invisible band of radiation at the upper end of the visible light spectrum. As mentioned before, ultraviolet starts at the end of visible light and ends at the beginning of X-rays. Wavelengths are from 10 to 400 nm. The primary source of ultraviolet light is the sun. And, although ultraviolet (UV) light is widely known as a disinfectant, it is also used to erase EPROM chips. After several minutes of exposure to UV light, the EPROM can be programmed again.

The range of Ultra Violet wave lengths is often sub-divided into

• UVA (400-315 nm), also known as Long Wave or blacklight
• UVB (315-280 nm), also known as Medium Wave
• UVC (< 280 nm), also known as Short Wave or "germicidal".

UV Disinfection technology was mainly used for applications in wastewater treatment, however recently it's being used in drinking water and Well Water treatment. It used to be thought that UV disinfection was more effective for bacteria and viruses, which have more exposed genetic material, than for larger pathogens which have outer coatings or that form cyst states (e.g., Giardia) that shield their DNA from the UV light. However, it was recently discovered that ultraviolet radiation can be somewhat effective for treating the microorganism Cryptosporidium. The findings resulted in two US patents and the use of UV radiation as a viable method to treat drinking water. Giardia in turn has been shown to be very susceptible to UV-C when the tests were based on infectivity rather than excystation. It turns out that protists are able to survive high UV-C doses but are sterilized at low doses.

What types of equipment create a Reverse Osmosis Water Filter System?

A typical reverse osmosis treatment system for your home is shown here. The Reverse Osmosis system is usually located beneath the kitchen sink since it is used to treat the water for drinking and cooking purposes. A three stage RO system consists of the Pre-Filter, Reverse Osmosis Membrane, a storage tank (pressurized) for the water treated, a post filter and a separate tap for the treated water supply.

Figure 1. A Typical Home RO System Includes: (1) particle sediment filter, (2) RO reverse osmosis membrane, (3) pressurized treated-water storage tank, (4) carbon absorption post-filter, and (5) separate tap for the treated-water.

The water supply entering the Reverse Osmosis RO unit shall be bacteriologically safe. RO units will remove virtually all microorganisms but are NOT recommended for this because of the possibility of contamination through pinhole leaks or deterioration due to bacterial growth. Water softeners are commonly used in Minnesota and the Dakotas in advance of the RO system.

1. Prefilter: The particle prefilter is sometimes referred to as a sediment water filter. It removes small suspended particles to extend the life of the membrane. Some membrane units are damaged by chlorine and others by bacterial growth. Where chlorine is present, a carbon prefilter may also be recommended.

2. RO Membrane: Several kinds of reverse osmosis membranes are available. The most common materials are cellulose acetate or polyamide resins. Mixtures or variations of these materials are also used. Each product has certain advantages and limitations and these need to be considered carefully.

Some of the factors that should be investigated are:

• The contaminant(s) involved and their initial concentration(s).
• The water supply rate, or whether the system will deliver enough water to meet normal daily drinking and cooking requirements.
• The rejection rate, or the percentage of contaminants to be removed by the membrane.
• The water pressure required to meet the supply and rejection rates. That is, can this unit be operated on the normal operating pressure of a home water system or will a booster pump be required?
• How can the system's performance be monitored? That is, how can leaks or other problems be detected or how is the time for servicing or replacement determined? Some systems have built-in monitors, but many do not. Conductivity meters, pressure gauges and other devices can be used to detect problems where monitors are not included. Where coliform bacteria or other special contaminants are a known or suspected problem, periodic testing is recommended.

3. Storage Tank: Most RO units supply treated water at very low rates so a storage tank of 2 to 5 gallons is used to provide a suitable supply. These units are pressurized to produce an adequate flow when the tap is open. Under sink storage requires minimum pressure to deliver water. Other locations may require increased delivery pressure which may reduce membrane performance.

4. Post-Filter: The main reason for postfiltration is to remove any undesirable taste and any residual organics from the treated water. Usually a carbon filter is used for this purpose. Where a carbon filter is used as a part of the prefiltration step, postfiltration is normally eliminated.

5. Delivery Tap: A separate delivery tap for the treated water is used so that both treated and untreated water are available.

6. Other: No special controls are required on most systems since they operate by the use of pressure-sensitive switches, check valves, or flexible bladders. Shut-off valves are important to conserve water during low use periods. Monitoring gauges or servicing lights are becoming increasingly common and assist greatly in knowing whether the system is or isn't working.

What does an RO System cost?

When deciding on a water treatment system be sure to investigate all options and all costs. To compare purchase to lease or rent options consider the following:

1. Initial Costs of the System: Be sure that all parts are included, especially when comparisons are being made. RO units range in cost from $300 to $3000 and vary in quality and effectiveness. Replacement membranes cost $100 to $200 and filter cartridges around $50.
2. Installation Costs: These costs are generally the responsibility of the purchaser, but who pays installation fees when renting or leasing? Is there enough space to accommodate the system being considered or will some modifications of space be needed?
3. Operating and Maintenance Costs: Electricity to pump the water is the only significant operating cost. Filter cleaning and/or replacement (both pre and post-filters) and RO membrane replacement need to be estimated. Whether routine maintenance can be done by the owner or requires special service is important information when purchasing a system. When renting or leasing, how and when servicing is to be done and who pays for the supplies and service needs to be clearly stated. For example, is the service done on a schedule or an "as needed" basis?

Installation of Reverse Osmosis Water Filter R/O Systems

Typically the total system will take up between one third and one half of the space beneath a sink. The largest component of a reverse osmosis system is the pressure tank that holds treated water and supplies a separate faucet. In general, this tank is about half the size and about the same shape as propane tanks used for outdoor barbeque grills. It is important that the tank be placed in an upright position to prevent leakage. It must be kept in a heated area to prevent freezing in the winter.

The reverse osmosis unit itself is generally one to two feet long and is meant to be hung from a vertical surface beneath the sink. It, like the pressure tank, must be protected from freezing, which will destroy the reverse osmosis membrane. During installation keep in mind that it will be necessary to access the unit for maintenance from time to time. Its location on the wall or the side of the cabinet should allow enough room to change filter cartridges.

Reverse osmosis units are for use on the cold water system only. Reverse osmosis units are not recommended for installation in households served by wells that produce hot water (> 77° F) from geothermal sources. Hot water will destroy the membrane, which is designed for cold-water use only. Most home units produce small volumes (a gallon of clean water every two to four hours) so treated water is available in limited quantities. This means that under the sink reverse osmosis units will not be a good choice for any activity that requires large amounts of water, such as washing clothes, showering, or bathing.

Common Chemicals Removed by Reverse Osmosis Systems

Reverse osmosis was originally designed to produce potable water from seawater and brackish sources. It can be applied in most cases to remove dissolved inorganic materials (minerals). It is also a good technology to remove some pesticides. A reverse osmosis unit readily removes asbestos, because asbestos fibers are too large to pass through the membrane. The National Sanitation Foundation (NSF) maintains a web site that identifies specific brands of reverse osmosis systems and tests system efficiency in removing chemicals.

Summary

Reverse osmosis is a proven technology that has been used successfully on a commercial basis. One of the better known uses of RO is the removal of salt from seawater. Household RO units typically deliver small amounts (2 to 10 gallons per day) of treated water and waste 3 to 20 times the amount of water treated. Reverse osmosis units remove many inorganic contaminants from household drinking water supplies. The removal effectiveness depends on the contaminant and its concentration, the membrane selected, the water pressure and proper installation. RO units require regular maintenance and monitoring to perform satisfactorily over an extended period of time. Before purchasing an RO unit or any other water treatment equipment, purchasers should test their water to be certain that treatment is needed and that the equipment being selected is appropriate to the problem requiring treatment. All costs need to be considered when comparing competitive systems and when making purchase or rental decisions.

Mirrored Source: http://www.ext.nodak.edu / http://www.extension.umn.edu / http://ag.arizona.edu ~ Arthur Fisher, Jennifer Reisig, Mark Walker, Pamela Powell, Fred Bergsrud, Russell Derickson and Bruce Seelig