Solar photocatalytic treatment of pulp mill effluent for water recycling and conservation

wastewater treatment results
Pulp mill wastewater before and after the solar photocatalysis treatment.

Pulp and paper production represents one of Canada’s most valuable industries in the natural resource sector. The pulp and paper industry has made significant progress in reducing water usage intensity over the past decades, but its water footprint is still much higher than other natural resource sectors. Further effort is needed to improve water use efficiency, especially in light of anticipated pressures on freshwater resources from climate change. Unfortunately, the wastewater discharge from pulp mills is strongly coloured. This prevents the reuse of water from this process, as it could stain pulp and negatively impact its value. The current biological water treatment processes in place at mills are inefficient in eliminating colour, and in some cases even increase it.

A ChemE collaboration between Postdoctoral Fellow Tim Leshuk, Professors Grant Allen and Frank Gu uses solar photocatalysis to eliminate colour from pulp mill effluents rendering the wastewater optically clear and fit for re-use in the pulping process. This innovative strategy could significantly reduce the water footprint of the pulp and paper sector.

“Solar photocatalysis is an environmental nanotechnology that uses sunlight together with reusable catalyst materials to degrade persistent water contaminants,” explained Leshuk. “While many pulp mills already use outdoor, sunlight exposed lagoons for wastewater treatment, solar photocatalysis has not been well studied for this industry. We have developed buoyant catalyst beads that passively float on the water surface and absorbs sunlight to degrade contaminants to the water below. Only a relatively low-intensity treatment may be needed afterwards to transform wastewater to usable process water,” elaborated Leshuk.

The solar photocatalytic treatment of pulp mill effluent for water recycling and conservation project promotes industrial water conservation and helps reduce the environmental impact on aquatic ecosystems, which ultimately benefits everyone. This truly collaborative project was made possible through the support of U of T’s Pulp & Paper Centre, Mitacs and H2nanO Inc. Leshuk presented their findings at the 2021 Canadian Chemical Engineering Conference and is currently preparing a paper to further spread the news of their ground-breaking innovation.