Win32 Virus Removal

Due to many recent publicized outbreaks of contamination in public drinking water systems, consumers are becoming more aware of the need to be more vigilant about the quality of water they are consuming. Unfortunately, even with stringent national and local regulations and due diligence by water utilities, microbiological contamination in water supplies is a reality.

More often than not, the many variables between the water plant and delivery of the water to the user increase the potential for microorganisms to enter into and grow in the water.

One major potential contamination factor is the surface of the distribution piping. Microorganisms can attach to such surfaces and develop into a biofilm, which is a collection of bacteria or other microorganisms surrounded by the slime-like substance they secrete.

Biofilm can form as soon as clean water enters a pipe, and it has been found to be 150 to 3,000 times more resistant to disinfection chemicals than free-floating bacteria. Microorganisms can multiply in biofilms and release or slouch off cells that contaminate the water stream.

Specific pathogens, including Legionella pneumophila and Salmonella bacteria, the hepatitis A virus, the Cryptosporidium protozoan and the Aspergillus fungi, are waterborne and can enter drinking water systems, creating potential health risks. Though drinking water is generally safe, it is always prudent to consider and, when feasible, eliminate any potential risk for microbial contamination as close as possible to the point where the water is consumed or used.

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When choosing a system to effectively and sustainably prevent microbial contamination, there are several factors to consider, including the technologys ability to remove microorganisms, its functionality on normal line pressure, its energy requirements, and the amount of wastewater produced.

For point-of-use/point-of-entry (POU/POE) water treatment, among the most popular technologies are ultraviolet (UV) treatment, activated carbon, reverse osmosis (RO) systems, membrane ultrafiltration (UF), and membrane microfiltration (MF).

While each method provides a step in the right direction for ensuring safer drinking water, a closer look at the pros and cons of each technology is key to finding the most effective and sustainable choice.

Non-membrane technologies
Ultraviolet. Using a UV light source, UV irradiation attacks and deactivates the DNA of microorganisms. UVs results depend greatly on specific circumstances. Fouling of the lamps glass surface by microorganisms or other contaminants in the water can prevent UV rays from reaching microorganisms. The configuration of the system and the flow rate also influence interaction time between UV light and the microorganisms. UV light is also less effective in killing protozoa, due to their thick outer coating.

Because UV doesnt remove the microorganisms from the water stream, they can be used as a food source by other organisms. UV also requires a prefilter to remove sediment and an electrical power supply.

Activated carbon. Due to its prevalent use in water treatment, it is important to mention activated carbon. Although often referred to as a filter, activated carbon is not a filter but an adsorption media. It is a highly porous material that effectively removes chemical substances such as chlorine and medicine residues from water, which are not removed by UF, MF or UV.

Microorganisms such as bacteria, viruses and cysts can simply pass through activated carbon. Activated carbon is also the perfect breeding ground for biofilm build-up. The addition of antimicrobials such as silver can prevent this build-up, but the contact time is normally too short to kill all incoming bacteria. As a result, activated carbon on its own is not a sufficient media for microbiological remediation.

Membrane technologies
Membrane technology can be used to create a physical barrier to microorganisms, while allowing water to pass through. An illustration of the pore size and retention capacities of RO, UF and MF membranes is shown in the illustration (see sidebar, The Filtration Spectrum).

Reverse osmosis. RO membranes have a dense structure and are capable of removing even many of the smallest molecules, including microorganisms. Because the dense structure of the RO membrane limits the rate of water production, a storage tank is needed to provide a sufficient quantity of water for daily use; such a tank is a potential location for biofilm buildup.

In theory, microorganisms should be retained (kept out of the permeate, or product water) with RO, but in practice RO membrane systems may in some cases not meet retention standards, perhaps due to low membrane integrity or imperfect gluing and sealing in the spiral-wound configuration. When looking at the sustainability of RO systems, the fact that they require energy to operate and that they generate wastewater during permeate water production must be taken into consideration.

Ultrafiltration. UF membranes contain billions of pores that retain bacteria, viruses and cysts in addition to other microorganisms. These membranes are especially suited for removing harmful microorganisms, sediment and turbidity from water, while maintaining an acceptable water flow and allowing essential minerals to pass through into product water.

Some UF membranes in POU/POE equipment have been independently tested to show a more than log 4 (99.99 percent) removal for viruses and a more than log 6 (99.9999 percent) removal for bacteria. UF membranes work on normal line pressure, use no energy, do not generate any wastewater in the filtering process, retain vital minerals, and do not alter the taste of the water.

Microfiltration. In some applications, where higher flow rates are required and virus removal is not needed, microfiltration is the better option. In these applications the membrane surface/flow rate ratio requires the use of MF membranes, to ensure a sufficient flow rate for, say, a proper shower or a heavily-used water cooler.

MF membranes used in certain water filters and medical fiilters have been independently tested to a show a more than log 6 removal for bacteria and otherwise have the same advantages as UF membranes.

Flow changes
A potential drawback of membranes is a decrease in the flow of water over time due to buildup of retained (filtered) materials. In some commercially available membrane water filtration systems, initial water flow is high even near the end of the membrane service life, so the flow rate provides a sufficient quantity of water for daily use. Furthermore, the decreased flow can be seen as a fail-safe mechanism to prompt timely replacement of the membrane cartridge.

Backwashing is not needed in POU applications of UF. In POE applications of UF, due to the potentially large volume of water filtered, backwashing is sometimes needed. Usually backwashing once a day for one minute is sufficient, which corresponds to 5 to 15 gallons of water. However, for low water demand or high-quality water applications, a controllable system significantly decreases backwashing frequency.

Overall, UF is an excellent way to eliminate uncertainty and ensure consistent delivery of high-quality water, with no additional energy requirement or wasted water.