Everyone wants pure drinking water, but traditional point-of-use (POU) purification systems sometimes drive consumers toward bottled water. Pitcher-based filtration systems remove few contaminants. Conventional RO systems treat water at low flow rates and generally require a storage tank. Another factor is taste. For example, RO filtration systems remove nearly all of the minerals that contribute to taste. To truly compete with bottled water, consumer water purification systems should deliver significant volume of water that tastes as good as bottled water, should be easy and cost-effective to use, and not be wasteful.
From a niche market in the early 1980s, bottled water has grown into a $23 billion worldwide business because it satisfies several important consumer needs:
- There is a perception (actually, a fact in many parts of the world) that bottled water is safer because it contains fewer contaminants than available drinking water.
- People appreciate the choice provided by the wide variety of bottled waters available. Bottled waters can be cate gorized as spring, mineral or treated. Their composition and tastes range widely, and many people have a favorite.
- Bottled water is portable, and our fast-paced lifestyles need this flexibility.
However, bottled water comes with a price. It often costs more per gallon than gasoline, ranging from $0.50 to more than $20 per gallon. A hidden cost of bottled water is the energy consumed in the packaging, transporting, recycling and eventual disposal of the bottles.
New Technology Offers Choices
A new POU drinking water treatment system now provides the consumer with the security of treated water without the lack of taste. Refilling bottles at home with this new system would save the consumer substantial money, time and energy. This POU system wastes 10% less water than most RO systems and provides water at 0.5 gpm without a storage tank, saving space.
LINX Technology
The new system is based on LINX technology from Pionetics. The first LINX technology patent, Electro-chemically Assisted Ion Exchange, was granted in 1998 and describes fundamentally new devices for removing ions from solution. LINX devices comprise cells, which include replaceable cartridges built with a special type of ion exchange membrane, called a water-splitting membrane. Pionetics’ first implementation of this technology, the LINX 120 drinking water system, comprises two cells, sediment and carbon prefilters, a flow sensor and the Dial-a-Taste module, to provide a continuous supply of water in a home or small business.
LINX devices operate on a two-step process. The first step is a deionization, or ion removal process. Figure 1 shows a schematic of a LINX cell in deionization. Feed water enters the inlet at the top, flows between the water-splitting membranes and exits at the outlet. As seen in Figure 1, water-splitting membranes comprise two layers: cation exchange material (e.g. strong acid, P-SO3H) secured to an anion exchange material (e.g. quaternary ammonium, P-NR3OH).
The deionization step for removing sodium chloride from solution is shown in Figure 2. This is the classic ion exchange process in which the cation and anion exchange materials are in the acid and base forms, respectively, at the outset. In the LINX process, however, a voltage is applied during the deionization step to accelerate ion removal (ions move faster in the electric field), allowing an increase in flow rates. When the LINX system’s capacity for ions is exhausted, a second step regeneration is required (Figure 3). This step is initiated by reversing the voltage polarity, and preferably the flow direction as well. At the boundary between the cation and anion exchange layers, water splits into its component ions acid (H+) and hydroxide (OH-), which migrate through the ion exchange layers toward the electrode having opposite polarity. Hydrogen ion (H+) replaces sodium in the cation exchange layer, and hydroxide ion (OH-) replaces chloride in the anion exchange layer. Sodium chloride “waste” is concentrated in the solution exiting the LINX device, and the water-splitting membranes are returned to the condition necessary for another deionization cycle.
Drinking Water Benefits
Selectable taste. The Dial-a-Taste control gives the consumer a choice in water taste, effectively offering the same taste variety found in bottled water. The Dial-a-Taste dial increases or decreases the electrical power used during the deionization step. RO and distillation strive for maximum total dissolved solids (TDS) reduction, but the key to taste is not the degree of TDS reduction, but the final TDS concentration. The Dial-a-Taste feature allows the consumer to select a preferred taste with a turn of the dial. Human preferences in water flavor range from 20 to 300 ppm, depending on individual taste. Additionally, the best TDS level for drinking water is not what one would choose for making coffee, orange juice, or preparing dinner. For example, it is generally accepted that the best tasting coffee is obtained with 150 ppm TDS. Reduced wastewater. For each gallon of water consumed, the LINX 120 wastes less than 1 gal of additional water. The volume of water for regeneration is a constant 0.4 gal. For water having 750 ppm TDS, the system deionizes 0.8 gal per cycle, providing a 65% recovery. Water recovery is even greater when feed water is of lower TDS. Figure 4 compares water waste in LINX and RO technologies for two common household scenarios. RO systems for POU waste from 5 to 20 gal for each gallon produced, depending upon use pattern. This wasted water adds about $40 to the typical annual water bill.
High flow rates eliminate storage tanks. Because the LINX 120 produces water at a flow rate of 0.5 gpm, it does not require a storage tank, freeing valuable space under the sink.
Broader contaminant removal improves water purity. The primary benefit of ion exchange materials is their selectivity for ions such as metals, nitrate, perchlorate or arsenic. Pionetics’ membrane material works well for the removal of nitrate and perchlorate ions. Because the LINX membranes are regenerated in the acid and base forms, the technology is also very effective for removal of species for which RO is ineffective, including Arsenic III.
Bacteriastatic environment reduces health worries. LINX cells are bacteriastatic, meaning bacteria does not grow in them due to the hostile environment inside the cells during normal operation.
Operation at low pressure improves deionization performance. Many homes and businesses suffer from low water pressure. In contrast to the RO process, which depends upon pressure for operation, ion exchange processes are more effective for TDS reduction and selective ion removal at low pressures because lower flow rates actually increase the contact time with ion exchange material.
Conclusion
LINX technology offers consumers the water qualities they seek in their favorite bottled water: choice in taste using Dial-a-Taste and security from selective contaminant removal with a bacteriastatic treatment system. The system allows consumers to substantially reduce their drinking water costs, minimize lost space under the sink, and benefit from a system that operates reliably at low pressures. wqp
