April 2009

Water Filtration 4-1-1

With a growing number of filtration systems coming to market today, your ability to tailor water filtration by concept and store is greater than ever before. Here's how to sort out your options.

To see a variety of water filtration devices/systems, click here for the Water Filtration Gallery.

By Mike Sherer

We all know water has become a scarce and expensive commodity. Drought, growing demand and years of neglectful treatment of both resources and wastewater have resulted in poorer quality in many areas of the country, too. More than ever, water filtration systems have become essential to every aspect of your operation that uses water—that is, virtually your entire operation.

Water not only affects the taste of everything from soups and sauces to hot and cold beverages, it also affects the performance and life of equipment ranging from ice machines to combi ovens. Potable water provided by your local utility must meet EPA standards for safety, but even high-quality, good-tasting water may contain minerals, chemicals or contaminants that can alter taste or damage equipment.

Key categories of contaminants include sediment, the dirt that water can pick up on its way to your door; chemicals both good (e.g., chlorine to kill bacteria) and bad (e.g., volatile organic compounds); minerals or total dissolved solids; and, of course, any microorganisms that made it past your water utility's defenses (e.g., bacteria, viruses or cysts like Cryptosporidium). Different filters and/or treatment systems can handle each of these to varying degrees. The trick is finding the combination that works best for your water and your applications.

Starting With The Basics
Your first line of defense against contaminants is a mechanical water filter. Mechanical filters remove sediment from water in much the same way filters in your ventilation hood remove grease particles. Sediment includes all the "rocks and twigs," the dirt and debris, that water collects on its journey from surface or ground water sources to your tap.

Filter makers produce two basic types of mechanical filters: depth and surface. Depth filters capture particles throughout the filtration medium. Typically, depth filters are constructed from one of several types of plastic like polypropylene that is shaped into different forms. Common designs are spun fiber, string-wound and pleated.

Depth filters effectively remove larger particles in the range of 5 to 20 to microns and do so relatively inexpensively. Some are designed to remove particles as small as 1 micron. In many cases, a good depth filter may be all you'll need in a water filtration system. Where water is particularly "dirty," though, you may need to use a couple of depth filters in a series or one as a pre-filter before using a surface filter.

A surface filter, as the name implies, collects dirt and sediment on the surface of the filtration medium. A surface filter—usually a membrane of some type through which water is forced—captures much smaller particles, down to 0.1 microns in the case of microfilters, and as small as 0.01 microns in ultrafiltration systems.

Ultrafiltration systems are a lot more common in foodservice than they were four years ago when we last covered this category. Since they can remove such small particles, they're an effective barrier against virtually all cysts, bacteria and viruses. They also can be flushed to clean the filter.

A self-cleaning cycle can be programmed on most of these systems to accommodate your specific water conditions. That increases both the effectiveness and the life of the filter. Newer systems have more sophisticated electronic controllers that not only make operation more trouble-free, but also provide a wide range of valuable usage data.

While the upfront cost of an ultrafiltration system is substantially higher than what you'd pay for depth filters, savings in replacement filter cartridges and sometimes eliminating additional filters helps these systems pay for themselves over time. And several manufacturers now make ultrafiltration systems, so you have more choices.

The Next Level
Carbon filters are your second line of defense in most operations, as they remove most of the chemicals and volatile organic compounds that affect taste and odor.

Suppliers manufacture four common types of carbon filters. From least to most expensive these include granulated activated carbon, carbon-coated fiber, extruded carbon block and molded carbon block.

Carbon removes impurities through adsorption—the impurities cling to the surface of the carbon—so the more surface area a carbon filter has, the better. That might suggest granulated carbon would be most effective, but water can sometimes find channels through the granules that allow it to pass untouched.

Carbon also tends to be porous, which allows water to pass through, while it provides more nooks and crannies (surface area) for impurities to adhere to. One manufacturer claims its "hollow carbon" design has more pores, providing greater flow rate and better adsorption.

Because carbon filters act as mechanical filters in addition to their abilities to remove VOCs and other impurities, they can quickly clog up with sediment if you don't have a good pre-filter or other mechanical filter in front of them. But in some applications, they can serve quite adequately as mechanical and chemical filter, eliminating the need for additional filters.

A big reason to use a carbon filter is its ability to remove chlorine and chloramine from water. Chlorine is added to municipal water supplies to kill microorganisms. In some cases, chlorine produces carcinogenic trihalomethanes when it comes into contact with certain organic compounds in water. To prevent that, some water utilities also add ammonia to water, creating chloramine.

Both chlorine and chloramine add what can be an unpleasant taste and odor to water (and beverages made with that water). They're also corrosive and potentially damaging to equipment such as ice machines, combi ovens and steamers. A number of ice machine manufacturers now use plastic parts and suggest that chlorine inhibits mold in the cabinet, but others still recommend carbon filters.

Taking On Scale
Water also typically contains minerals such as calcium and magnesium as well as other inorganic or organic solids held in suspension called total dissolved solids, or TDS. Water also can contain alkaline substances such as bicarbonate. Water's alkalinity determines how easily the minerals and TDS in water will form scale. When heated, for example, bicarbonate in water binds with calcium, forming calcium carbonate that precipitates or clumps together as scale on surfaces like heating elements or the walls of boilers, steamers or combi ovens.

Most utilities can give you a report of your water's hardness or mineral content, measured in parts per million (ppm) or milligrams per liter (mg/L); total dissolved solids (TDS), also expressed in ppm or mg/L; and alkalinity, shown as a measure of pH. (A pH of 7.0 is neutral; up to 14.0 is acidic; down to 0 is alkaline.)

Obviously, scale buildup on equipment from ice machines to steamers negatively impacts performance and reduces life. It's also difficult to remove, and deliming agents can be noxious and dangerous to use. There are two ways to reduce the amount of scale your water can produce. You can inhibit scale formation, or reduce or remove the substances that cause it.

If you have very hard water, one common way to reduce scale formation is to install a water softener. Water softeners are ion exchangers. Most are designed to exchange a sodium ion for a calcium ion in the water. That reduces the amount of calcium that can combine with bicarbonate to form scale, but it makes water salty, affecting taste. Softened water also makes lousy coffee and carbonated beverages.

Scale inhibitors act in a way that keeps calcium carbonate in suspension so it doesn't have a chance to clump or collect on surfaces. Polyphosphates are the most common type of scale inhibitor. Relatively inexpensive, they come in a variety of forms for different applications.

Most polyphosphates start breaking down at temperatures above 150° F, however, so they're not the best solution for steamers. They also interact with tea, making it cloudy, and shouldn't be used in tea brewers. Some filtration companies make scale inhibitor media designed for higher temperatures, up to 200° F, for example.

A relatively new type of scale inhibitor reverses the polarity of calcium and magnesium particles, causing them to form crystals instead of clumping together. When the crystals grow to a certain size, they break away from the inhibitor media and remain in suspension. Unaffected by temperature, the inhibitor is ideal for high-heat applications like espresso machines or steamers and boilers that have a flush cycle.

Removing substances that cause scale is a more expensive proposition, but some operators have chosen this route to ensure a consistent water "recipe" from store to store. Reverse osmosis systems remove more than 96% of TDS from water along with virtually everything else, essentially purifying it and giving it a neutral pH.

The benefit of water filtered through R/O is that it resolves almost all the issues we've talked about so far—taste and odor, scale, microorganisms and so forth. R/O systems, though, have their own drawbacks. The first is that water stripped of substances becomes aggressive and caustic to metals. R/O also doesn't remove chlorine, so you may still need carbon filters for some applications. And if your water has a lot of sediment, you'll need a pre-filter to keep the system from clogging up frequently.

R/O systems also waste a high percentage of the water they filter, so they're expensive to operate as well as purchase. But suppliers are working on this point. For example, a new system recently introduced promises much greater efficiency and far less wasted water.

Putting It All Together
Figuring out what type of filtration you need and how to specify a system has gotten easier. First and foremost, make sure any water filters or system components you spec meet NSF standards. NSF-certified filters will perform as claimed by manufacturers. Key standards to be aware of are NSF 42, which applies to water aesthetics (taste, odor, appearance); NSF 53, which filters must meet to make health claims (reduction of metals like lead, cysts and VOCs); and NSF 58, which sets standards for R/O systems (including cyst and VOC reduction).

Manufacturers are making the process easier, too. In many cases, they'll analyze your water, find out where you use water in your operation, and recommend the best filtration products for your needs. One manufacturer offers this service free of charge. Others may have similar programs.

Most filtration systems can be installed at point-of-entry, changing the characteristics of water used throughout your facility, or point-of-use, affecting water only where it's being used. How you approach systems in your stores will depend on local water quality, applications in your stores requiring filtration or treatment, and how important water consistency is in each of those applications.

So, for example, a coffee shop concept built on the taste of its coffee and espresso drinks may be more likely to insist on specific water characteristics than a full-service chain. In that case, a point-of-entry system may be most effective. The full-service concept, however, may want to ensure its soft drinks are consistent. In that case, a point-of-use system may work better.

Most manufacturers offer both "all-in-one" filters that combine mechanical filtration with some type of carbon filter in an easy-to-replace cartridge and modular systems. All-in-one filters may suit some operations just fine, but they could cost you more in the long run in replacement cartridges than installing a modular system or putting specific filters where they're most needed. Where water is particularly high in sediment, for example, an all-in-one filter may have to be replaced long before its ability to remove chlorine and VOCs has dissipated. Better solutions might be installing pre-filters in front of a carbon filter, or using mechanical filters at POE and carbon filters only where taste, odor or chlorine are issues.

Another area you'll want to bone up on is flow rates. If filters are NSF certified, claims about their capabilities are governed by the NSF standards. The ratings also pertain only to taste and odor reduction (under NSF 42) or health claims (under NSF 53). Manufacturers can claim high flow rates through a filter, but they're meaningless if the filter doesn't remove impurities. And just because a filter has a high flow rating doesn't necessarily mean you'll get that kind of output in your stores. Flow rates obviously decline as filters become increasingly full, and NSF tests filters at 60 psi, which you may not have in all stores.

Capacity is a good way to evaluate how filters will perform in your stores. A carbon filter may have a high capacity for chlorine and VOCs (which it's primarily intended for), but clog up quickly with sediment, shortening its life. Likewise, a mechanical pre-filter with low capacity will quickly affect flow rates of any other mechanical or carbon filters down the line.

Most manufacturers and dealers will help guide you through the process of putting together systems that work best for your stores, but it helps to know what questions to ask. One key point to remember is that unlike some of your production and cooking equipment, "one size" usually doesn't fit all when it comes to water filtration. Water quality varies so widely across the country (and around the world) that you'll likely end up tweaking or customizing filtration systems from one area to the next. Fortunately, filtration companies are constantly making that easier to do.

To see a variety of water filtration devices/systems, click here for the Water Filtration Gallery.