What could buses and sewage treatment plants have in common?

The co-location of hydrogen production by electrolysis at a wastewater facility produces hydrogen for fuel cells to run buses and oxygen to feed beneficial bacteria in the treatment tanks.

The co-location of hydrogen production by electrolysis at a wastewater facility produces hydrogen for fuel cells to run buses and oxygen to feed beneficial bacteria in the treatment tanks.

The Queensland University of Technology (QUT) research team of Rickey Donald, Dr Fanny Boulaire and Associate Professor Jonathan G Love developed a simulation model. The goal was to determine the environmental benefits of integrated hydrogen production and wastewater treatment. The team published its findings in the Journal of Environmental Management. The paper was titled “Contribution to net zero emissions of integrating hydrogen production in wastewater treatment plants.”

PhD researcher Rickey Donald is from the QUT Center for Clean Energy Technology and Practices and QUT School of Chemistry and Physics. He said hydrogen production by electrolysis at a wastewater treatment plant (WWTP) made sense. This is because the WWTP could provide the water needed for electrolysis. The oxygen it produced, usually considered a waste stream, could be used for wastewater treatment.

“A WWTP needs vast quantities of oxygen to feed the beneficial bacteria in the large tanks,” Donald said. Currently, this oxygen is provided by pumping huge volumes of air through submerged fine bubble diffusers, like an aquarium air stone but on a massive scale, using a lot of electricity. When a solar PV system provides the electricity required by electrolysis, it produces green hydrogen because it does not use electricity from a fossil-fueled main grid, avoiding carbon dioxide emissions. This green hydrogen can be used in a fuel cell to power a bus to replace diesel engines and avoid carbon dioxide equivalent emissions.”

Supporting hydrogen production

Donald said electricity from a solar PV system peaked at midday. However, it was also subject to cloudy conditions. This makes oxygen production variable over the day.

“The oxygen requirement of a WWTP also varies, according to wastewater flow rate and concentration,” Donald said. “Unlike the output from a solar PV system, it peaks in the morning and again in the evening. To meet the challenge of surplus oxygen around midday and a lack of oxygen at night (no solar PV), the extra oxygen could be compressed and stored to match demand. By using compressed oxygen to replace the air blowers, the system reduces the need for fossil-fueled energy when solar energy is unavailable. Using oxygen in this way acts as an energy storage mechanism for a WWTP, like a large battery. This leads to higher utilization of renewable electricity.”

Donald said the researchers’ modelling compared the traditional systems for wastewater treatment and diesel buses’ energy use and emissions. They considered whether it is better to export renewable electricity to the grid or use it to produce hydrogen and oxygen by electrolysis.

Modelling shows opportunities for hydrogen production

“The modelling showed that by around 2031, about 2,000 tons of carbon emissions would be prevented each year,” said Donald. “The proposed new integrated system will have better emissions outcomes than simply building solar PV to offset WWTP grid electricity usage and diesel use in buses. As the electricity grid becomes more decarbonized in the future, the benefits accelerate when using renewable electricity for hydrogen production and oxygen for wastewater treatment.”

Co-researcher Professor Jonathan Love said Donald’s decades of experience in WWTP have been used to create new impact for the WWTP industry as it seeks to transition to net zero emissions.

“Donald’s research exemplifies how experienced industry practitioners can add impact to their industry from PhD research at QUT,” Love said.

“He can leverage the outcomes of this and his previous research to be instrumental in building a new industry—integrated hydrogen WWTPs that have net zero emissions.

“This new industry could be part of Australia’s green hydrogen production at scale for use in domestic green hydrogen off-take markets such as local heavy vehicles, chemical industries and renewable energy needs of remote communities.”

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