Point-of-Entry (POE) devices are whole-house treatment systems mainly designed to reduce contaminants in water intended for showering, washing dishes and clothes,
brushing teeth, and flushing toilets.
Ion exchange operations and the choice of resins to use is highly dependent on the water analysis, what has to be removed and to what level
it has to be reduced. The primary driving force is selectivity. Selectivity is determined by the ionic strength of the charge on the specific ion and the resin type plus this is highly
influenced by the other ions in solution that might compete for the reactive sites. No resin is so highly selective that it is exclusive for a specific contaminant. Since most ion exchange
processes are reversible, the ion exchangers can be regenerated (put back into their original form) and used over and over. Softener salt is a compound of Sodium (+) and Chloride (-). In solution,
the Sodium and Chloride ions are then available as the regenerative for ion exchange resins. Sodium ions are used for Cation resin regeneration and Chloride ions are used for Anion resin
Based on the charge of the ions of the dominant contaminant to be removed, depends on the type of resin
Cation resin is used for removing Positive (+) charged particles such as Hardness, Ferrous Iron, Manganese, Copper, and some other elements.
Anion Exchange for Specific Contaminant Removal
Anion resin is used for removing Negative (-) charged particles from the water.
It is available in different forms for more specific purposes. One type of Anion resin is used for the removal of
Tannins, which is an organic material caused by rotting plant material. Another weak base Anion resin is used for the removal
of Nitrates. Strong base Anion resin is used for the removal of Uranium, Sulfates, Alkalinity, and Arsenic 5.
Cation Exchange Water Softening
Ion exchange water softeners are among the most common and best ways of softening water. The typical ion exchange system consists of a pressure tank filled
with sulfonated, polystyrene beads that are capable of removing hardness ions from water and replacing them with softer ions, such as sodium ions.
These units are connected to a brine tank that’s filled with salt, which periodically regenerates the resin beads. The unit’s tiny beads attract and hold
onto calcium and magnesium ions as water passes through them. When the beads become so saturated they can’t hold any more, the unit rinses them with salt, which scrubs off the mineral deposits and
gets them ready to absorb hardness ions again.
If you own this type of water softener, you can set it to regenerate at preset times (Timer Unit). More sophisticated units can base their regeneration on your actual water use (Metered Unit). Systems that
measure water use and regenerate accordingly, called demand initiated regeneration (DIR), may be more efficient because they only regenerate as needed. Systems that automatically regenerate on set time intervals, called time clocks, simplify the process. However, these units sometimes regenerate more often than necessary, wasting
salt, or they leave users with hard water when water demand is higher than normal.
Although water softeners get rid of some heavy
metals along with hardness, water filtration systems are the best way to remove organic and inorganic materials (such as microbiological contaminants) and
particulates (such as sand, rust and silt). Water filters remove these impurities with a fine physical barrier, chemicals, or some other method to help clean water and make it suitable for drinking
or other uses.
While specialty media and membranes
are available, activated carbon is a widely used filtration substance. Activated carbon targets various volatile organic compounds, such as benzene, trichloroethylene,
and various pesticides and petroleum related compounds. Sediment and tank filtration systems removes contaminants as water enters the home. Large inline filtration systems are installed where water
enters the home plumbing system.
Electrochemical Water Treatment Systems
treatment systems utilize electricity to induce the removal of dissolved contaminants in the water. Positively charged contaminants such as calcium, magnesium, sodium, lead and uranium, are called
cations. Negatively charged contaminants such as chlorides, nitrates, nitrites, sulfates and fluorides, are called anions. The introduction of a negatively charged electrode, or cathode, into the
water will cause positively charged cations to move towards it. Electrochemical water treatment systems take advantage of this property by combining the electrode with ion exchange membranes.
Basically anything that is ionized when dissolved in water will be reduced. A typical target for the product water would be <5 grains per gallon of hardness and <150 ppm of total
dissolved solids, but they are not practical if your aim is to produce soft water with <1 grain of hardness.
Air Stripping Units
Air stripping units are designed to reduce gaseous substances from water such as Radon, Methanes, VOC's, and others, or to Oxidize certain elements such as Arsenic 3 into Arsenic 5
for removal by additional equipment. The system consists of an enclosed tank, which the incoming water is sprayed into the tank, releasing or oxidizing the targeted sustance from the water. A
ventilation fan carries the removed gases through a PVC vent pipe to the exterior of the building. A repressurization pump then delivers the water to additional treatment systems as
Ultra Violet Radiation Systems
Are designed for non-chemical treatment of Bacteria in water. These systems consist of a Control
Module, Exposure or Reaction Chamber, Quartz Glass Sleeve, and a High Intensity Ultra Violet Bulb. The ideal UV Radiation wave length to deactivate Bacteria is 254mJ (milliJoule a unit of energy
measurement). The UV Radiation scrambles the Bacteria's DNA so that it cannot multiply, thus rendering it "sterile". Depending on water quality pre-treatment may be necessary to prevent fouling or a
coating film on the protective Quartz Sleeve, or to eliminate particulate matter from "eclipsing" Bacteria as it moves thru the Exposure Chamber. The maximum Flow of water required and the UV System
must be sized accordingly for proper operation and total deactivation of Bacteria. Most UV bulbs need annual replacement as they do not provide the proper UV emittance thereafter, and the Quartz
Sleeve should be cleaned with a soft cloth at that time. The Quartz Sleeve should be replaced every second year as they will develope "solarization", a darkening of the tube which will reduce the
effective UV radiation.