Wastewater from the distilling industry could be used to produce green H₂—a type of sustainable fuel—using materials developed by scientists at Heriot-Watt University. Distilleries in Scotland alone produce an estimated 1 MM liters a year of wastewater from the whisky distilling process. Globally, the distilling industry is thought to produce around 1 B liters a year of wastewater.

Scientists at Heriot-Watt have developed a way to use this wastewater to produce green H₂, a process which currently consumes 20.5 B liters of fresh water a year.

Dr Sudhagar Pitchaimuthu, a materials scientist in Heriot-Watt’s School of Engineering and Physical Sciences said, “It takes 9 kg of water to produce every 1 kg of green H₂. Meanwhile, every 1 liter of malt whisky production creates about 10 liters of residue. To help protect the planet, we need to reduce our use of fresh water and other natural resources. So, our research focused on how to use this distillery wastewater for green H₂ production with a simple process that removes waste materials present in the water.”

Dr Pitchaimuthu and his team have developed a nanoscale material—a particle that is one in 10,000th the diameter of a human hair—to allow distillery wastewater to replace fresh water in the green H₂ production process. The nanoparticle, called a nickel selenide, treats the wastewater and, in the team’s research, produced similar or slightly higher quantities of green H₂ from the wastewater, compared to the results from fresh water.

The research is published in the Royal Society of Chemistry journal, Sustainable Energy & Fuels, in a paper entitled From brew to clean fuel: harnessing distillery wastewater for electrolysis H₂ generation using nano scale nickel selenide water oxidation catalysts. The paper is authored by Dr Pitchaimuthu’s PhD student, Michael Walsh, who played a key role in conducting the research.

“About one billion liters of wastewater a year is produced from the distilling industry, so the potential of this process is huge,” Dr Pitchaimuthu said. “Using industry wastewater means we can reduce the extensive freshwater footprint associated with green H₂ production. Our research also shows how we can use the world’s resources more sustainably to produce clean energy.”

H₂ is a gas that, unlike fossil fuels, does not emit carbon when it is burned. Green H₂ is generated using renewable energy. The electricity generated from renewable sources—such as wind or solar—is used to power electrolysis. This is the process which produces H₂ by splitting water into H₂ and oxygen.

Electrolyzers – the devices used to perform electrolysis – only work with fresh water and typically fail because of the substances in wastewater, Dr Pitchaimuthu explained. But Heriot-Watt’s nanoparticle overcomes this challenge, he added.

The next steps for the research team include developing their own electrolyzer prototype and scaling up production of their nickel selenide nanoparticles. They will also be analyzing the distillery wastewater to discover whether other materials of value could be salvaged from it, alongside H₂ and oxygen.

The research was funded by Heriot-Watt’s School of Engineering and Physical Sciences and completed in collaboration with the University of Bath’s Department of Chemical Engineering and The Scotch Whisky Research Institute, which supports applied research across the Scotch Whisky production process.

Dr Pitchaimuthu is an Associate Professor at Heriot-Watt’s Institute of Mechanical, Process & Energy Engineering and Associate Director at the University’s Research Centre for Carbon Solutions, which is focused on developing low-carbon systems and solutions. He has a PhD in Physics from Bharathiar University in India and, before joining Heriot-Watt in 2021, worked on materials science research projects in South Korea, Japan, Spain, Northern Ireland and Wales.

Dr Pitchaimuthu’s main research areas are photoelectrochemistry, photocatalysis, electrocatalysis, nanomaterials, solar energy and photo/electrochemical CO₂ recycling. He is a Fellow of the Royal Society of Chemistry, which advances excellence in the chemical sciences.

H₂ and green H₂ are key research areas at a new Global Research Institute for net zero being developed at Heriot-Watt University. Called iNetZ+, the institute will bring together researchers from across the University and collaborate with industry, government and communities to address global sustainability challenges.