The ozone and UV revolution

The world is yet again undergoing a revolution in water treatment, this time led by ultraviolet (UV) light and ozone technologies. By Chetan Mistry

Chetan Mistry, strategy and marketing manager, Xylem Africa

The chemical treatment of water is very effective but it also has drawbacks. Other than the environmental concerns, it’s not always practical to use chemicals such as chlorine on a smaller scale or for specific applications. Treatment facilities are also keen to reduce the amount of chemicals they have to stockpile and manage. Ozone and UV have become popular, as either alternatives or complementary additions to chlorine systems.

UV and ozone are very potent nonchemical ways to destroy many types of water contaminants, including bacteria, parasites and viruses (even SARS-CoV-2), as well as the removal of some metals. Both UV and ozone are naturally occurring cleansing agents. UV’s power was discovered 140 years ago when scientists worked out that sunlight kills some types of pathogens.

The UV light triggers chemical reactions inside microorganisms that essentially destroy their genetic structures and make it much harder for them to reproduce. Ozone is far more aggressive, attacking the cell walls and coatings of viruses, cysts, pathogens and bacteria, killing all on contact. Ozone also reacts with colour, taste and odour compounds, leaving a clear, tasteless sparkling water behind.

UV and ozone often complement chlorine treatment systems to create safe drinking water from heavily polluted water sources, allowing for the safe reuse of wastewaters back to potable standards.

Many wastewater facilities want to reduce their chlorine use for safety or environmental reasons. They retrofit selfcontained UV and ozone systems to their lines, which drastically reduces chemical usage and manual oversight hours.

Both technologies also stand on their own. They are commonly used to clean fruits and vegetables of bacteria and fungi – the South African citrus industry is a world leader in using ozone to clean its produce. Hospitals routinely sterilise rooms with ozone – it’s faster and doesn’t leave a chemical residue. Recently, scientists from Japan’s Fujita Health University proved that low-level ozone gas could neutralise coronavirus particles without causing harm to humans.

Ozone systems are also becoming popular for treating swimming pool water and washing vehicles without using corrosive chemicals. Temporary or remote locations, such as construction sites and mines, use ozone and UV to recycle water. A better world with UV and ozone?

Chlorine remains the most popular choice for treating water. It’s cheap, abundant and ruthlessly effective. Ozone and UV don’t necessarily compete with chlorine. Instead, they help reduce chlorine use, lessening risks and environmental impact, and offer alternatives where chlorine is impractical or dangerous.

Ozone and UV systems today are compact and self-contained. The best products require little to no maintenance. They are either highly portable or simple to add to existing infrastructure. All a company typically needs is access to reliable electricity; then they can run an ozone generator and UV contacting systems.

The technologies do have drawbacks, ozone does not last long, breaking back down to oxygen after just a short period. UV is safe but has limited intensity and all contaminants need to be exposed to the UV light for a short period for it to be effective. Nonetheless, UV is still very effective when used for lowerdemand cleansing or with other hygiene methods. Ozone is a heavyweight – one of the best disinfectant agents known to humanity.