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Could UV LEDs be the future of wastewater treatment?

Posted by Engineering Communications on April 23, 2024 in News
Dr. Amina Stoddart, Dr. Graham Gagnon and their team of researchers at Halifax Water’s Eastern Passage wastewater plant
Dr. Amina Stoddart, Dr. Graham Gagnon and their team of researchers at Halifax Water’s Eastern Passage wastewater plant

Dalhousie Engineering Professor Dr. Amina Stoddart specializes in wastewater treatment. When the COVID-19 pandemic emerged, like many others, she actively sought out ways to utilize her expertise to aid in the crisis.

Monitoring local wastewater levels, Stoddart played a key role in the development of a rapid and highly efficient test for detecting SARS-CoV-2, the virus responsible for COVID-19. Additionally, when high-quality masks were in short supply, she worked on a technique to disinfect N95s using UV LED lights.

That project has led to exciting new research focused on using UV LEDs for municipal wastewater treatment. If the lights could disinfect masks, what about water?

Mechanical wastewater treatment involves several steps. The last stage in the process involves using UV lights to eliminate micro-organisms by disrupting their DNA. However, standard UV lights come with drawbacks. They contain mercury, posing an issue if they break. Stoddart says if the bulbs heat up, "some of the contaminants still in the wastewater can bake onto the bulb” and diminish its efficacy. "They are huge lights that are on all the time, so they require a ton of energy," she adds.

Enter the UV LEDs. “The light on your phone is an LED. If you think about that from an engineering perspective — wow! You’ve got so many more design capabilities.” In contrast with long, fragile, energy-intensive mercury based lights, LEDs can be clustered together, and don’t generate heat in the same way as conventional lights.

Stoddart is currently running a study using the lights in a reactor at Halifax Water’s Eastern Passage wastewater plant, which can treat about 450 litres of water a minute, or 648,000 litres a day. (The full plant treats 25 million litres daily.)

“Halifax Water have attached this reactor for us, which is kind of a side stream. It pulls water into our reactor right before it hits their UV lights,” where it is exposed to the LEDs, Stoddart says. So far, data shows the UV LEDs are “better or the same as conventional treatment.”

Graduate student Bailey Reid is leading the analysis of treatment results. She says Stoddart encouraged her to pursue graduate studies, and she’s glad she was persuaded. “I’m really liking what I do. There are so many opportunities. I’m working with a reactor that’s the first in the world... I don’t know anyone doing this scale of stuff. It’s incredible.”

Another of Stoddart’s students, Esther Osei-Ampong, is conducting research into the use of UV LEDs at Halifax Water’s Dartmouth Wastewater Treatment Facility.

Osei-Ampong already has a master’s in wastewater resource and environmental engineering, from the Kwame Nkrumah University of Science and Technology, in Ghana. She chose to continue her studies at Dalhousie, because the school “has the facilities and resources to help me achieve my aims… I want to be one of the best researchers and go back and help my country. At Dal, there is always hands-on practice,” she says. “They make everything practical.”

Her research involves working on a smaller scale than Reid, playing with different light intensities and chemical oxidants to remove organic matter from wastewater through advanced oxidation.

“We are doing this in the lab on a bench scale to see how it will work, and then we can maybe try it on a larger scale,” she says.

Preliminary results show that, used with the UV LEDs, hydrogen peroxide works well at lower doses, while chlorine is most effective at higher doses, she notes, adding: “It’s not conclusive yet, but it looks very promising.”

Wastewater treatment is serious business, and new treatments have to be backed by solid evidence before going into use. Stoddart says the research is promising, but there is still a lot of work ahead to see if approaches involving UV LEDs can be ramped up to a larger scale. “You must control effluents into the harbour, it’s very serious. Things have to work. It can’t just be trial and error kind of stuff.”