For the first time, Dalhousie researchers and their industrial partners have proven UV LED light has the power to treat municipal wastewater. The game-changing finding established with collaborators AquiSense and Halifax Water is expected to trigger a sea change in the way cities disinfect the water we flush down our drains, promising a safer and more sustainable future for global wastewater management.
The team’s innovation demonstrates that ultraviolet (UV) mercury vapor bulbs currently used by cities around the world to disinfect wastewater can be replaced with ultraviolet light-emitting diodes (LEDs), similar to those used in our TVs and smartphones. This advance opens a new path for wastewater utilities to significantly reduce power consumption, save on equipment costs and maintenance, and eliminate the use of toxic mercury that is currently required.
“Our research shows that UV LEDs have the potential to use energy much more efficiently, which is better from a greenhouse gas emissions standpoint. We don’t use any harmful chemicals and produce less CO2, while delivering the same volume of water with at least the same quality, if not better,” says Dr. Graham Gagnon, director of Dalhousie’s Centre for Water Resources Studies, who led the research partnership with fellow engineering faculty Drs. Amina Stoddart and Sean MacIsaac. Their findings are published in the most recent edition of the leading journal Water Research X.
Currently, water utilities use UV mercury vapor bulbs to kill or deactivate microorganisms like bacteria, viruses, and protozoa. During the final step of treatment, wastewater is bathed in a blast of UV light before returning to waterways. While effective, mercury bulbs gulp energy, soil easily, and come with hefty costs for maintenance and replacement.
Even more critically, the mercury required by the bulbs is a potent neurotoxin, with the potential to damage the brain, nervous system, and other vital organs. The EU has banned mercury in most products, only allowing an exception for wastewater treatment due to the lack of alternatives. Meanwhile, The UN Environment Programme’s Minamata Convention compels countries to end mercury mining by 2032, slamming the breaks on the chemical needed by the industry to continue.
“In eight years, globally, new mercury mines will not be allowed to open, capping the supply. Right now, wastewater treatment is a $2 to 3 billion industry almost exclusively reliant on mercury. We desperately needed an alternative, and now we have it,” says Oliver Lawal, president and CEO of AquiSense Technologies, the world’s largest supplier of UV LED disinfection systems, which collaborated with Dalhousie and Halifax Water on the research project with support from an NSERC Alliance Advantage grant and the Water Research Foundation.
Together, the team has piloted the world’s first UV LED reactor capable of municipal wastewater treatment. The reactor, engineered by AquiSense, has been integrated at Halifax Water’s Eastern Passage wastewater treatment facility since January 2024, where it has effectively treated the full volume of water passing through that facility.
Unlike mercury vapour bulbs, which emit light and heat in all directions, the UV LEDs in the team’s reactor direct light in one direction and radiate heat in the other. Wastewater flows through a large clear pipe surrounded by thousands of tiny UV lights, killing the viruses and bacteria it contains, without the high temperatures common to traditional mercury vapor bulbs.
Dr. Wendy Krkosek, Halifax Water’s acting director of environment, health and safety, says the lack of heat can relieve utilities of significant costs.
“Mercury bulbs produce a significant amount of heat, which causes wastewater material to accumulate on equipment and causes fouling,” says Dr. Krkosek. “By using the UV LED technology, heat is almost non-existent, therefore reducing buildup, which in turn reduces large operation and maintenance costs related to the conventional UV system.”
The researchers say the substantial advantage will lead to swift global adoption once the new technology is approved by regulators. It can be expected that the EU and other jurisdictions will end exceptions for mercury in the wastewater industry, opting for the latest industry innovation now treating wastewater in Eastern Passage.
“In the next few years, we expect to see this UV LED technology used at full scale, and it could be transformative for Halifax Water and the entire industry. We are proud to be at the forefront of this research with Dr. Gagnon and Dalhousie and to know that our commitment to innovation will create greater operational efficiencies that will ultimately benefit our customers” says Dr. Krkosek.
