By Phil Jones
Point of entry (POE) is the term commonly used to define any water treatment system or combination of systems, designed to alleviate water quality issues at the point where water enters a building, prior to distribution to the water heater, kitchen and washrooms. This in contrast to POU systems designed to be installed under the counter or even directly on to a drinking water faucet, with limited treatment capabilities. The most applicable system is usually determined by assessment of a comprehensive water test, understanding consumer expectations and offering a range of appropriate options.
Equipment used in POE systems can range in sophistication from a simple hardware store purchased sediment filter to a suite of products performing complimentary tasks, designed to provide aesthetically pleasing, palatable and safe drinking water. In major population centres of the developed world, the most familiar piece of POE equipment is usually a water softener, which works by employing the principle of ion exchange (exchange of calcium and magnesium dissolved ions with sodium or potassium ions). The removal of dissolved calcium and magnesium, the all too familiar hardness resulting in clogged shower heads, excessive detergent use and damaged water heaters, is not an economically viable proposition for municipalities and as such becomes the home-owners problem to deal with. For those people living off the grid, however, whose water source is typically a drilled well or perhaps a lake, there are a number of other issues, not so familiar to the city dweller, requiring application of various POE options. Some of the significant issues (in addition to hardness), affecting these water supplies are:
- Turbidity – cloudy, visually unappealing water
- Iron and iron bacteria – bad taste, staining, and possible gelatinous growth
- Sulphur – rotten egg odour associated with sulphur reducing bacteria
- Microbial contamination – including fecal coliforms, E.coli and parasitic cysts
Turbidity
Although the appearance of milky water at the tap is largely an aesthetic concern, especially if the turbidity is inorganic in nature (such as clay or sand), it should be remembered that the presence of particulates might compromise any disinfection system employed to eradicate microbial contamination. Turbidity is also a surrogate parameter for indicating the potential presence of bacteria and protozoan cysts. For this reason, turbidity in municipally supplied water, caused by flooding or mechanical breakdown, invariably results in Boil Water Advisories. In addition, where organic matter contributes to the turbidity, this can encourage bacterial growth by providing microbial nutrients. This can cause rapid loss of residual disinfectant and lead to the deterioration of water quality. General purpose filter cartridges designed to deal with turbidity are typically rated at five microns and provide acceptable filtration quality without excessive pressure drop, based on turbidity levels. Filtration recommendations are one micron or better for water drawn from a surface source susceptible to contamination by parasites such as Giardia which gives rise to Giardiasis (beaver fever).
Iron and iron bacteria
The presence of iron bacteria is often the most unpleasant side effect of using water containing traces of dissolved iron. The resulting bloom that grows in such places as toilet tanks can be identified by its orange colour and stringy or gelatinous appearance. Even without the presence of the bacteria, dissolved iron levels of only 0.3 mg/L give rise to significant staining on bathroom fixtures as water evaporates and the iron becomes oxidised to rust. Iron can be removed with POE equipment, either by employing a pre-oxidation and filtration step (typically air entrainment and back-washable filter system) or by way of ion exchange softening. Water conditioners are now available that employ specifically designed media and do not suffer from the limitations of traditional resin based systems which have the tendency to become fouled by iron that is not completely removed during regeneration. The new breed of combined iron and hardness removal systems also internally generate chlorine from the salt used in regeneration, effectively eliminating iron bacteria. Attempting to do this with a resin based softener may compromise the resin in a very short time.
Sulphur
Most of us have experienced the unpleasant smell of water contaminated with hydrogen sulphide, especially when using hot water! The presence of anaerobic bacteria is the causative factor when this gas is detected in water supplies. POE equipment designed for this problem typically uses the same principle as the iron oxidation method mentioned above. By oxidising the hydrogen sulphide gas to elemental sulphur using air (typically), the resulting solid can be trapped in the filter bed and backwashed to the drain.
Microbial contamination
While all of the preceding descriptions deal with what are largely aesthetic issues (unpleasant yes, but not normally a risk to health), contamination of water by pathogenic microorganisms is naturally of very serious concern. Municipalities provide safe drinking water by using flocculation and filtration followed by, increasingly, a combination (or multi-barrier) approach using chlorine treatment and sometimes other treatment steps such as membrane filtration, ozone or ultraviolet disinfection. Good pre-filtration of water is vital for the subsequent disinfection stage(s) to be effective. For those who do not have access to municipal water, treatment with chlorine chemicals can be challenging in terms of handling, correct dosage calculation and palatability of the treated water. UV disinfection is very widely employed in the non-municipal, residential sector, offering an easy-to-use, cost-effective solution with no after taste issues. In certain regions, three consecutive zero coliform tests are required when selling a home where the water is supplied from a private well. Of particular interest where water is supplied from a surface water source (e.g. lake), eradication of parasites such as Cryptosporidium and Giardia is easily achieved by the combined application of filtration and UV technology.
Conclusion
POE treatment applications certainly cover a wide range of aesthetic concerns, but more importantly are often the only means of providing safe drinking water to those households that rely on a private water source. Multi-barrier strategies are generally considered to be the best approach to resolving water quality issues, while UV disinfection equipment, installed as the final stage of the treatment process, is an affordable, reliable and safe technique for ensuring that water is free from pathogenic microorganisms.
About the author
Phil Jones, a Chartered Chemist affiliated through the Royal Society of Chemistry (UK), has been active in the water treatment field for more than 20 years. He presently heads the Inside Sales and Technical Support functions at VIQUA – a Trojan Technologies Company. Jones can be contacted via email, [email protected]
About the company
VIQUA, part of the Trojan Technologies Company, is a leading water treatment technology company driven by a passion for solving drinking water-related environmental problems. In over 100 countries, VIQUA’s UV systems are disinfecting water in homes and light commercial applications including: apartment complexes, manufacturing facilities, campgrounds, resorts, hotels and hospitals. Every minute, VIQUA systems treat over 4.9 million gallons (18.9 million litres) of water.