July 2001
Volume 43 Number 7
 

Reverse Osmosis: Carbon Block or RO? It’s a Matter of Taste
by Andy Palframan, CWS-V   Pages: 

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Bottled water is trendy.

Bottled water is the fastest growing segment of the beverage market. In 1999, U.S. bottled water sales rose 13.9 percent to top $5.2 billion, according to the Beverage Marketing Corporation. Sales are expected to grow at a compounded rate of 15 percent over the next five years. In contrast, carbonated beverage sales are flat.

Obviously, a lot of people prefer the taste of high-quality water. Many upscale consumers choose bottled water over tap water for reasons of taste, perceived safety, convenience and fashion. But bottled water isn’t the only option available to consumers who want high quality water.

Choices and decisions

As water treatment professionals, it’s your job to educate the public about the in-home options that provide high quality water for a fraction of the cost of bottled water (see "Making the case for RO -- Choose your weapon" after author biography below).

Carbon block filtration and reverse osmosis (RO) are two point-of-use (POU) drinking water filtration systems that can significantly improve drinking water quality in the home or office. There are distinct differences, however. When deciding whether to install a carbon block filter or RO system, the homeowner’s specific water concerns should drive your recommendation.

Block vs. membrane

Carbon block filtration involves forcing water through a tightly compressed activated carbon block. The carbon block’s micron rating is a key determinant as to the level of contaminants filtered out. The carbon also has adsorptive qualities, which further removes or reduces contaminants from water. Carbon block filters vary in their micron rating. The more efficient carbon block filters are capable of reducing contaminants of less than 1-micron (um) in size. Particles smaller than the filter’s micron rating will pass through the filter and into the drinking water.

In contrast, RO systems filter out extremely small particles, down to 0.009 um in size. RO systems force water molecules through a semi-permeable membrane, separating suspended matter and an extremely high percentage of dissolved substances from the water. RO systems also use carbon filters before and after water passes through the membrane. The carbon prefilter removes free chlorine, which can deteriorate thin film composite (TFC) membranes over time. Postfilters are generally used to remove tastes and odors that may be picked up from the storage tank bladder. Some postfilters are certified to take out volatile organic chemicals (VOCs) and trihalomethanes (THMs).

An RO system requires additional plumbing and its dispensing capacity is limited by its storage tank, which typically holds two gallons. Because a carbon block filter doesn’t require a storage tank, maintenance issues are usually the only limit to its daily production capacity.

Containing contaminants

Both POU systems can significantly reduce an impressive list of contaminants. It’s important to ensure that an individual unit has been tested and certified for a particular contaminant, as all units may not remove or reduce all of the contaminants listed below:
* Chlorine
* Turbidity
* Lead
* Cryptosporidium parvum oocysts and Giardia lamblia cysts
* THMs
* VOCs

Some carbon filters may reduce these contaminants. There's a multitude of carbon choices that will affect what contaminants are filtered out. The differences are primarily in the carbon's origin (i.e. bone char wood, anthracite, coal, coconut or other shell), preparation for water treatment (acid- or water-washed), and form (powdered activated carbon, granular activated carbon and carbon block). Depending upon the manufacturer, the carbon can be impregnated with compounds that offer additional water treatment qualities such as bacteriostatic or catalytic (i.e., silver, etc.). Incorporating impregnated carbon with other materials such as plastic compounds can offer even tighter pore structures for finer removal of contaminants. Carbon block, either molded or extruded, is generally considered the best form of effective water treatment.

Because it provides filtration down to a molecular or ionic level, RO systems reduce contaminants in addition to those mentioned above. Again, check to make sure that the particular unit being installed has been tested and certified for the identified contaminants. To name a few, an RO system may reduce:
* Chromium,
* Mercury,
* Nitrates,
* Selenium,
* Radium 226/228,
* Copper,
* Cadmium, and
* Total Dissolved Solids (TDS).

This is only a short list of what RO may be able to remove. The list of contaminants for which RO systems may be tested for reduction can be quite long (see http://www.nsf.org/consumer/consumer_dwt.html#standards for details).

Pre-treatment to remove hardness, iron, hydrogen sulfide (H2S) and manganese is recommended for in-home RO systems. Without pretreatment, these contaminants can clog prefilters and foul the membrane. In addition, some RO membranes may be adversely affected by chlorine -- another reason for pretreatment. Thus, RO systems often incorporate sediment and/or GAC filters before and after (as a polishing step) the membrane.

A solids issue

The major selling point for RO systems is their ability to reduce TDS, which can dramatically improve the taste of water. Keep in mind, though, that many people may believe that their water tastes and looks good, particularly if they have municipally supplied water. When you’re designing a home water treatment system, the water problem being addressed should drive your choice of technology.

Most homeowners will notice a profound improvement in water taste after installing an RO unit. The unit also significantly reduces sodium in water, which may be an attractive feature to people on low-sodium diets.

Of course, taste is a personal judgment and some people may be particularly sensitive to the presence of any dissolved solids. There are several filtering options available (as well as distillation), but RO is arguably the best choice for improving water taste and appearance.

Considering that bottled water may cost up to a dollar or more per gallon depending upon the level of treatment and/or if it has a designer or imported label, an RO system is a bargain. The cost of the system, installation and maintenance equals pennies per gallon for a typical family. RO water is just as delicious, and can be of higher quality, than some bottled water.

Technology matters

When it comes to choosing an activated carbon block filter, it’s the density that matters. Generally speaking, it’s a mechanical process -- the denser the block, the tighter the pore structure and the finer the filtering.

There’s more to consider when purchasing an RO unit. Look for membrane capacity, system configuration (primarily whether the system shuts down when the holding tank is full), and the type of membrane used. TFC membranes reject more solids but cannot tolerate chlorine. Again, if chlorine is present, then carbon pretreatment is required. Cellulose membranes are resistant to chlorine -- so pre-treatment isn’t required although it may extend membrane life -- and are often recommended for municipal water systems.

Make sure your customers know what they’re buying. Does the RO unit include quick-connect fittings? Is a faucet included? If so, does the faucet come in a variety of colors and styles to suit your customer’s décor?

Look for ANSI/NSF or Water Quality Association Gold Seal certifications on the RO unit and check the manufacturer's performance data sheet. Companies willing to submit their products to NSF, WQA or another third-party laboratory for testing and certification are demonstrating their confidence in their products’ capabilities.

Installation & maintenance

Carbon block filter units are less expensive to buy and install, and will vary in price based on system configuration and installation requirements. The carbon block should be replaced every year or at 500 gallons processed, depending on the units rated capacity. A separate drinking water faucet is required.

RO systems are more expensive, and will vary in price based upon the model and installation. The installation is more costly because RO systems require an additional connection for wastewater plus an air gap, as well as a separate drinking water faucet. The plumbing isn’t complex, however. Pre-and post-filters should be changed every six to 12 months, depending on the source water’s quality and volume of water processed. The membrane itself can last for several years, but will eventually degrade or foul.

While a plugged-up carbon filter won’t allow water to pass through the unit and out of the tap, a compromised RO system will. To ensure the satisfaction of your customers, preemptive service should include examining the membrane when filters are changed and tested for TDS reduction. Some systems include instrumentation for monitoring the unit's effectiveness.

RO systems may require more frequent service calls than a carbon block system; however, a carbon block filter is more expensive than replacement RO membranes. Plus, RO membranes will almost always outlast the life of a carbon block filter. So, in terms of maintenance costs, the two approaches can be comparable.

Conclusion

Studies circulated by the Centers for Disease Control and Prevention (CDC) suggest that approximately one million Americans are sickened by drinking water annually. Both carbon block filtration and RO systems can improve the safety of drinking water. RO filters out significantly more impurities than carbon block, but both have their merits. It’s in your best interest to steer your customers to the product that best suits their needs and preferences.

About the author

Andy Palframan is the total quality manager at Aquion Partners, L.P., and is responsible for managing the Technical Services/Quality Control Departments of RainSoft Water Treatment Systems, a Division of Aquion Partners. Both are based in Elk Grove Village, Ill. RainSoft is an industry leader in the manufacture and marketing of residential and commercial water treatment systems. Its products are sold and serviced by more than 500 extensively trained independent dealers in 25 countries. Palframan has achieved the Water Quality Association's Certified Water Specialist, Level 5, designation. He can be contacted at (800) 437-9400, (847) 758-5965 (fax) or email: apalframan@aquion.com

 

Making the case for RO -- Choose your weapon

As a water treatment professional, you already know the benefits of reverse osmosis. But how do you express the value of an RO system to a cost-conscious customer? Here are some marketing techniques to help close the sale:

* Conduct a water taste test. Have two bottles of chilled water available -- one bottle contains local tap water, the other contains water from an RO system. Let customers discover for themselves the taste, appearance (i.e., color and clarity) and odor benefits of RO water.

* Ask customers if they ever buy bottled water -- at home, at the gym or on the road. If they do, then they may already be paying for RO water -- the purification process used by most drinking water bottlers. At anywhere up to $1 to $1.50 or more per individual-use bottle, the savings realized by refilling the bottle at home with RO water (about two cents per refill) can add up fast.

* Explain the difference between the three types of residential water: potable water -- provided by the municipality for watering grass and other uses; softened water -- for laundry, cleaning and household use; and RO or bottled-grade -- for cooking and drinking. The health and taste benefits of RO drinking water can give a homeowner extra peace of mind.

* Point out that RO systems remove sodium. This can be a very attractive benefit for people on sodium-restricted diets.


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