As I chat with dealers around the country, I have sadly come to realize that many don’t understand the dynamics of what they’re selling. All water treatment technologies involve a physical change to the water that they are processing. The nature of the change truly defines the technology.
Subtractive Treatment
The most commonly understood and frequently used type of water treatment technology is subtractive; something is removed from water for health or aesthetic reasons. Contaminants are physically removed from the water using a physical separation, or adsorptive process.
Within the subtractive realm, filters generally comprise depth, barrier, or membrane types.
Depth filters use physical media in granular form of varying sizes and densities to physically filter contaminants.
Barrier filters use an organic, synthetic, or metallic screen that provides a barrier to passage of contaminants, based on their physical size.
Membrane Separators typically use a semi-permeable membrane wrapped around a central core allowing selective passage of water and contaminants, depending on the size, molecular weight, and even electrical charge of the contaminant/s. Ultrafiltration, Nanofiltration and Reverse Osmosis purifiers are types of membrane separators.
Reverse Osmosis separation is an extremely effective form of water purification. Contaminants are removed from a typical residential Reverse Osmosis purifier through the combined technologies of physical filtration, absorption, adsorption, and membrane separation. Multiple technologies are used to ensure maximum removal of contaminants from the water. Prefilters in a typical Reverse Osmosis purifier are designed to protect the reverse osmosis membrane from oxidants, and physically large contaminants that would prematurely foul the membrane pores. While protected by the prefilters/s, the semi-permeable reverse osmosis membrane works to rejects as many contaminants as possible from the water. The membrane operates under pressure from the municipal supply or with the assistance of a pressure-boosting pump. As a cross-flow filter, the membrane allows passage of purified water through its pores, while a waste stream flow to drain. Back-pressure form the drain restrictor creates sufficient pressure against the membrane to allow for rapid processing while continuously cleaning the membrane. This purification process is quite slow in residential systems, with a typical purifier being able to purify approximately 0.05 Gallons per Minute. Purified water is typically stored in a pneumatically-charged tank that allows for repressurization and accumulation in a sanitary environment.
Manufacturers of residential Reverse Osmosis purifiers make substantial claims to remove contaminants, these claims are required by most states to be verified by an independent certifying/testing body such as the National Sanitation Foundation (NSF) who have established standards of performance.
NSF/ANSI Standard 58 establishes the minimum requirements for the certification of point-of-use (POU) reverse osmosis systems designed to reduce contaminants that may be present in public or private drinking water.
The scope of NSF/ANSI 58 includes material safety, structural integrity, total dissolved solids (TDS) reduction and other optional contaminant reduction claims. The most common optional claims addressed by NSF/ANSI 58 include cyst reduction, hexavalent and trivalent chromium reduction, arsenic reduction, nitrate/nitrite reduction, and cadmium and lead reduction.
Consumers seeking Reverse Osmosis purifiers are looking for water that is as functionally close to pure as possible. This water is often described as “Empty water” to describe its high level of purity. See table 1 for typical performance.
Table 1 -Typical performance of a Reverse Osmosis Purifier
|
pH |
Total Dissolved Solids |
Calcium |
Magnesium |
ORP |
Total Alkalinity |
|
| Untreated Water |
7.5 |
180 ppm |
150 ppm |
30 ppm |
+100 |
180 ppm |
|
|
|
|
|
|
|
|
| Treated Water |
6.9 |
10 ppm |
2 ppm |
0.1 ppm |
+80 |
5 ppm |
Exchange Technology
Exchange technology removes one contaminant from the water while replacing it with an alternate. Both natural, and synthetic materials can act as an ion exchanger, and depending on the functional matrix of the ion exchange media, various positively, and negatively charged contaminants can be removed from water. A water softener is an example of ion-exchange technology.
Additive Technology
Additive technologies change the nature of water through addition of chemicals to the water.
Various things are typically added to water, such as pH neutralizers, ions, phosphate sequesterants, colorants, and flavorings. While the types and quantities of additives will vary from application to application, the effect is to add something to the water that will change its character.
Water “Ionizers” are a type of additive water treatment technology, whereby they add ions to water through the process of electrolysis to create both acidic and alkaline streams of water. They do not filter or purify the water to any appreciable degree.
The residential water “ionizer” will accept municipal water and then pass it through an “ionizing chamber”, which comprises a number of metallic electrodes (usually titanium or platinum). When energized, the electrodes will initiate an electrolysis reaction where the water yields hydrogen (H+) and hydroxyl (OH-) to the remaining water. The unstable Hydroxyl radicals then quickly become hydroxides in the water. Sodium chloride is sometimes added to the feed-water to potentiate the reaction and develop Hypochlorous acid and caustic soda as byproducts. The electrodes are separated within the chamber by semi-permeable membranes the isolate the streams of acidic and alkaline water as they are “created”. Electronic controls allow the user to vary the electric energy input to the chamber, thereby changing the relative strength of the electrolysis reaction. These devices typically process water at a rate of 1 Gallon per Minute and require no additional water storage or repressurization apparatus. See table 2 for typical performance.
The acidic stream is generally used for cleaning, and even disinfection of surfaces. In most residential systems though, this acidic stream is discharged as “waste”.
The alkaline stream is generally used for drinking, skincare, and cleaning. Many claims are made about the health-benefits of drinking this type of water, particularly the elevated pH and negative ORP antioxidant characteristic.
Table 2 – Typical performance of a Water “Ionizer”
|
pH |
Total Dissolved Solids |
Calcium |
Magnesium |
ORP |
Total Alkalinity |
|
| Untreated Water |
7.5 |
180 ppm |
150 ppm |
30 ppm |
+180 |
180 ppm |
|
|
|
|
|
|
|
|
| Treated Water
(Acid) |
3 |
420 ppm |
150 ppm |
30 ppm |
+400 |
180 ppm |
|
|
|
|
|
|
|
|
| Treated Water
(Alkaline) |
10 |
380 ppm |
150 pm |
30 ppm |
-400 |
180 ppm |
Glossary:
pH
pH is a measurement of the acidity or alkalinity of a solution. It provides a value on a scale from 0 to 14 where 7 is neutral, less than 7 is acidic, and greater than 7 is alkaline (or basic).
In water, the pH value is related directly to the ratio of positively charged hydrogen ions [H+] and negatively charged hydroxide ions [OH–].
When water has an equal concentration of H+ ions and OH- ions, it is said to be neutral (pH=7)
When water has a greater concentration of H+ ions, it is said to be acidic (pH<7)
When a solution has a greater concentration of OH-, it is said to be alkaline (pH>7)
ORP
Oxidation-reduction potential, or ORP, is an indication of the degree to which a substance is capable of oxidizing or reducing another substance. ORP is measured in millivolts (mv) using an ORP meter.
A positive ORP reading indicates that a substance is an oxidizing agent. The higher the reading, the more oxidizing it is. As such, a substance with an ORP reading of +400 mv is 4 times more oxidizing than a substance with an ORP reading of +100 mv.
A negative ORP reading indicates that a substance is a reducing agent. The lower the reading, the more anti-oxidizing it is. As such, a substance with an ORP reading of -400 mv is 4 times more anti-oxidizing than a substance with an ORP reading of -100 mv.