Reverse Osmosis Systems

What Is Reverse Osmosis?

Reverse osmosis, also known as hyper filtration, is the finest water filtration known. This process will allow the removal of particles as small as ions from a solution. Reverse osmosis is used to purify and remove salts and other impurities in order to improve the color, taste or properties of the fluid. It can be used to purify fluids such as ethanol and glycol, which will pass through the reverse osmosis membrane, while rejecting other ions and contaminants from passing. The most common use for reverse osmosis is in purifying water. It is used to produce water that meets the most demanding specifications that are currently in place.

Reverse osmosis uses a membrane that is semi-permeable, allowing the fluid that is being purified to pass through it, while rejecting the contaminants that remain. Most reverse osmosis technology uses a process known as cross flow to allow the membrane to continually clean itself. As some of the fluid passes through the membrane the rest continues downstream, sweeping the rejected species away from the membrane. The process of reverse osmosis requires a driving force to push the fluid through the membrane, and the most common force is pressure from a pump. The higher the pressure, the larger the driving force. As the concentration of the fluid being rejected increases, the driving force required to continue concentrating the fluid increases.

Reverse osmosis is capable of rejecting bacteria, salts, sugars, proteins, particles, dyes, and other constituents that have a molecular weight of greater than 150-250 daltons. The separation of ions with reverse osmosis is aided by charged particles. This means that dissolved ions that carry a charge, such as salts, are more likely to be rejected by the membrane than those that are not charged, such as organics. The larger the charge and the larger the particle, the more likely it will be rejected.

While the principle of reverse osmosis is simple, the RO process cannot go on indefinitely unless steps are taken to ensure that the membrane does not become clogged by the precipitated impurities forced against by the pressurized stream of feed water. To significantly reduce the rate of membrane fouling, RO systems employ cross-flow filtration, which allows water to pass through the membrane while the separate flow of concentrate sweeps rejected impurities away from the membrane surface.

First, the water is softened using a water softener system.  The softener uses a resin bed that imparts a weak ion exchange to remove calcium and magnesium from the water.  By removing the ‘hard’ minerals from the water it is now considered ‘soft’.  Chlorine will destroy the reverse osmosis membrane if left in the water and must be removed.  The water softener will not remove chlorine.  An activated charcoal carbon filter is used to accomplish this.  The carbon filter removes the chlorine from the water. The water should then be filtered to remove any stray particles before it moves on to the RO membrane.   It should be noted that once the chlorine has been removed if the water is to be used for human consumption it must be treated by passing through an UV tube or some other means to kill any bacteria. 

Next, the water enters a reverse osmosis unit. In the RO system, pressure is applied to the water via a multi-stage centrifugal pump and H2O is forced through the very fine membrane, leaving all impurities behind.

The purified water is then stored in a tank for use.  A single membrane can only supply a certain amount of water efficiently.  More pressure could produce more water but would also decrease the life of the membrane. To create enough RO water for a given application were a larger volume is needed multiple membranes are used.

Car washes are not the only industry that uses reverse osmosis.  Some form of water filtration is used by almost every major food chain, movie theater and beverage company around the world. Through years of experience, food service water filtration has proven to decrease machinery breakdowns and increases product quality and taste.

Water Filtration for Post Mix (soda fountains)
A chlorine level or 1 PPM in your water supply is not uncommon, but it may give your soda a watered down taste. This is why customers may complain that "the soda tastes watery".  To compensate more syrup can be added. This extra syrup costs more and adding more syrup may not help, instead you end up with soda that is "too sweet". To remedy this problem the chlorine must be removed from the water. This will enable you to achieve the correct ratio of syrup to water as established by the syrup manufacturer. Because the quality of your water will be consistent, the taste of your soda will be consistent.

Water Filtration for Ice
If you have problems with your ice machine, sediment and hardness minerals in the water can block the water flow to your ice machine causing reduced ice production. Mineral deposits (scale) from the water actually form a thermal barrier that coats the ice machine’s evaporator plate. This means your ice machine needs to work a lot harder to make ice and use much more electricity. Eventually you may have to pay to have your ice machine de-scaled. Chlorine in the water can form a mild form or Hydrochloric Acid. This acid slowly eats away at the ice bin. Replacement of the ice bin can be costly.

Even if you lease your icemaker there are major benefits to filtering the incoming water. Filtered ice is harder and melts slower. Filtered ice tastes fresher. The taste of expensive "mineral water" will improve by using filtered ice. Installing a water filter on a leased or rented machine will decrease machine breakdowns. Even though you may not pay for the repair, you do pay for the downtime.

Water Filtration for Coffee, Espresso and Cappuccino
By brewing coffee with chlorinated water, you extract excess oils and acids from the coffee grinds. This will limit your pot life to about thirty minutes before it needs to be poured out.  If you throw away only one pot of coffee every day because of bitter coffee, based on a $5.00 per pot resale price, it will cost you about $1,800.00 per year in lost revenue. Not taking into account "this coffee is bitter" customer reaction if accidentally served.  Particles and rust in the incoming water clog up the fine capillary tubes inside cappuccino makers resulting in expensive repairs. Mineral deposits (scale) from the water actually form a thermal barrier that coats the machine’s heating element. This means your coffee and cappuccino machines need to work a lot harder and use much more electricity. Scale inhibition also reduces clogging. Coffee bars and food vendors around the world agree that coffee water must be filtered.

Water Filtration for Table Water
Everything you put in front of your customers is a reflection on your restaurant. The spotless silverware, the kind of bread you serve to the tablecloth and napkins, customers pay attention. One of the best ways to impress a customer is to serve water that tastes good. Many restaurants have begun to advertise filtered water in menus and advertisement. Think about it, clean and safe water makes a statement about the establishment. It conveys to the customer a message of quality.

Water Filtration for Steamers
Scale also effects steamers. The scale build-up on the heating coils will increase your cooking time because it reduces the efficiency of the coils.  Boiler replacement costs $500 to $3000.

Purified water will make almost all prepared foods and beverages taste better. With conditioned water, you'll save on energy, plumbing repairs and general maintenance. You can extend the life of linens, fixtures, and appliances. And you can save on chemicals, detergents and coffee and other beverages made from concentrate. Your customers will also enjoy softer towels, cleaner glassware and better tasting coffee.

For more information:
*.pdf documents from Osmonics • Pure Water Handbook 
• Filtration Spectrum • Filtration & Separation Spectrum • EPA Water Chart