The differences in disinfection

Dec. 9, 2014

A closer look into the capabilities and limitations of common treatment solutions.

Across the U.S., disinfection technologies such as chlorination are commonly used in municipal water treatment plants to help safeguard against bacteria, viruses, germs and pathogens. However, factors such as environmental issues and an aging infrastructure can introduce bacteria into treated supplies in water’s journey to your customers’ homes. Consumers, especially privately-owned well owners/operators, should always test and, if needed, disinfect their water supplies to ensure safety and equipment performance. 

For the purpose of this article, we will focus on three of the most common disinfection technologies: Chlorine, ozone and ultraviolet (UV). Each option comes with its own capabilities and limitations with regards to disinfecting water.

Understanding the differences within these disinfection technologies can help dealers properly educate consumers and provide the best treatment options available, ensuring optimal water quality and safety.

The crucial role of water testing

Water sources, regardless of previous treatment, can become contaminated with harmful pathogens. There are several components that can place a water source at a higher risk for contamination, including environmental factors such as agricultural runoff and flooding, aging/damaged infrastructure, private wells versus public water supplies, etc.; for this reason, consumers should regularly test their water.

“It’s good practice to have private potable water supplies microbiologically tested three to four times per year unless local risk factors dictate a higher frequency,” explains VIQUA Product Manager Phil Jones, CWS VI, CChem, MRSC. “Public water supplies are tested more frequently as mandated locally.”

With fluctuations in the potential for microbiological contamination depending on consumers’ specific situations, a higher frequency in annual testing may be needed. However, as a general rule of thumb, Pieter de Vries, product development manager for UV Dynamics Inc., suggests testing water seasonally, while taking into account the local climate changes.

“If you lived in the northern climate where you have a lot of rainfall and snow runoff and stuff in the springtime, [these] would be the best times to do the sampling, if you [decided to test] twice a year,” suggests de Vries.

Once the water source has been properly tested, dealers can educate customers on the type of disinfection technology needed as well as how often to treat the water and how to properly maintain the equipment.

Chlorine disinfection

Chlorine is a powerful oxidizer and is very effective at treating pathogens such as bacteria and viruses. However, chlorine can result in various issues if levels become higher than what is currently regulated (EPA requires a MCL of 4 mg/l) and produce disinfection byproducts (DBPs). Applying additional treatment, such as activated carbon, may be needed to lower or reduce the levels of chlorine in the water supply. Some water treatment professionals suggest using chloramine solutions in lieu of chlorine.

Shock chlorination is a popular treatment for disinfecting a well. The treatment commonly utilizes a sodium hypochlorite, a strong chlorine bleach, solution within the water well and throughout the distribution piping. An unscented household chlorine bleach can be used to sanitize wells. The chlorine bleach is a sodium hypochlorite (NaOCl) solution consisting of around three to six percent of available chlorine.

For shock treatment, safety precautions are essential, such as using gloves and goggles and arranging for an alternative drinking water supply during the treatment process; and certain information on the well will be needed before treatment, including the volume of water in the well, the depth of the well, sizing of the casing and the static water level. 

Ozone disinfection

Ozone is also an oxidizing agent and is largely effective at eliminating germs in water. Ozone is most commonly generated by exposing a stream of air to either UV light or to a high voltage electrical discharge. It is produced onsite by corona discharged in dried air or oxygen; and because ozone is very unstable, it cannot be stored or packaged and proper expertise in handing the oxidizer is crucial.

“Ozone requires a bit of know-how in properly applying it,” says Tim Chew, market manager for CleanWater Tech LLC, Laundry and Pool & Spa. “So it requires a dealer that has experience in dissolving the gas into solution, usually by means of using a Venturi to create suction and pull the gas into the stream. From there, mass transfer takes place, where the gas dissolves into the water.”

Jones warns of bromide ion when considering ozone disinfection. “Ozone should never be used if there are traces of bromide ion in the water, otherwise potentially harmful bromate can be formed.”

According to the “Wastewater Technology Fact Sheet: Ozone Disinfection” provided by EPA, ozone’s effectiveness in disinfecting water will depend on the concentration of ozone, susceptibility of the targeted pathogens and contact time.

For best results, Chew recommends using certified ozone equipment, offering UL, CE and NSF as common certifications. However, he adds a few common mishaps to watch out for when using ozone disinfection. “Common mistakes are using too small of a generator for a job. CT value, or concentration of dissolved ozone measured in ppm multiplied by time, provides a value that is used to meet specific organisms at different logs.”

Chew continues, “In real-world context, a simple 1 ppm is a good rule of thumb to meet basic bacteria. So 1 ppm for one minute of time will do the job.”

UV disinfection

UV light is produced when an electric arc is struck in mercury, in traditional lamps. “UV is more of a mechanical process; we are actually destroying the DNA and RNA in the organism so they can no longer multiply,” explains de Vries. For this reason, UV disinfection is considered to be an effective treatment for water contaminated with bacteria and parasites. However, Jones suggests using a larger, more powerful UV system when treating viruses.

UV disinfection technologies are growing in popularity in the water treatment industry, including residential and light commercial settings. Many end users select a UV system because of its ability to disinfect water without removing any beneficial minerals in the water and without adding any chemicals.

The effectiveness of UV disinfection will depend on the clarity of the water, the intensity of the UV light, contact time and the wavelengths being generated. UV will commonly be used in conjunction with filtration units.

“What you are seeing now are a lot of systems that combine cartridge filtration with the UV system and various formats,” says de Vries. “You have multiple filters along with the UV system on a single bracket.”

Like with any disinfection treatment, certifications can help end users trust the effectiveness and productivity of their systems. “Certain jurisdictions insist that disinfection equipment meets performance criteria set forth by bodies such as WQA, NSF and/or U.S. EPA,” notes Jones.


Supplying consumers with ample education of the various disinfection technologies over simply providing the products and services needed, will warrant happy customers, increasing the chances for further sales.

Also, for dealers, having adequate knowledge of disinfection, in accordance with following the latest trends in technologies and supplying certified products and services, helps ensure the most effective treatment solutions are being provided to consumers.

“Ongoing development efforts focused on product improvement, in addition to emerging pathogen research, is a major contributor to increased effectiveness,” concludes Jones. “In the future, expect more novel breakthroughs throughout the field of water disinfection.”

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