Wastewater contaminants can boost hydrogen production: research

Researchers at RMIT University have developed an experimental process to turn wastewater’s high contaminant load into an advantage for making green hydrogen that could reduce reliance on fresh water. With more than 80% of global wastewater discharged into the environment untreated, the research provides an opportunity to turn this environmental liability into boosted productivity, according to the researchers.

The team’s approach harnesses some of the contaminants in wastewater to speed up hydrogen production and overcome high contaminant loads that normally make wastewater unusable.

The team’s latest work — which also involved The University of Melbourne, Australian Synchrotron and University of New South Wales — builds on previous breakthroughs, including an innovation that rapidly removes microplastics from water using magnets and a technique boosting hydrogen production using sea water.

Lead researcher Associate Professor Nasir Mahmood, from RMIT’s School of Science, said the team found a way to capture platinum, chromium, nickel and other metals in the water and then put these elements to work to enhance green hydrogen production.

“The advantage of our innovation over others to produce green hydrogen is that it harnesses wastewater’s inherent materials rather than requiring purified water or additional steps,” he said.

Their experimental invention comes in the form of electrodes, which are key components for splitting water into hydrogen and oxygen. The electrode is made with an absorbent carbon surface that attracts metals from wastewater to form catalysts that are stable and efficient at conducting electricity, helping to speed up the water splitting.

The materials used to produce the special carbon surface are made from agricultural waste — another cost-effective aspect of the innovation that contributes to a growing circular economy.

“The catalyst speeds up a chemical reaction without being consumed in the process,” Mahmood said. “The metals interact with other elements in the wastewater to boost the electrochemical reactions needed for splitting water into oxygen and hydrogen.”

As part of the experiments, the team used the wastewater samples in a container with two electrodes — an anode (positive) and a cathode (negative) — and powered the water-splitting process with renewable energy. When electricity flows through the water, it causes a chemical reaction.

At the cathode, water molecules gain electrons and form hydrogen gas. At the anode, water molecules lose electrons and form oxygen. The result is a separation of water into its basic components, hydrogen and oxygen, which could then both be collected and used.

“The produced oxygen can be reintegrated into wastewater treatment plants to enhance their efficiency by reducing organic content,” Mahmood said.

The device enabled continuous water splitting for 18 days during experiments in the lab, with minimal decline in performance over that time. As part of the experiments, the team used wastewater that had undergone some treatment including the removal of solid waste, organic matter and nutrients.

RMIT is developing a platform of catalytic systems capable of using previously difficult water resources such as wastewater and sea water and this latest proof-of-concept invention is a further example of the systems under development.

Co-lead researcher Professor Nicky Eshtiaghi, from RMIT’s School of Engineering, said the latest RMIT innovation could potentially reduce the high cost of wastewater treatment while turning it into something valuable — a source of green hydrogen.

“Our innovation addresses both pollution reduction and water scarcity, benefiting the energy and water sectors,” she said. “By using wastewater, the process helps reduce pollution and makes use of materials considered to be waste.

“We are keen to work with companies globally that are addressing energy and waste as cost and sustainability challenges, as well as water authorities. Collaborations could focus on developing commercial systems to use this technology on a large scale.”

Co-researcher Dr Muhammad Haris, from the School of Engineering, said further research was needed to refine the catalyst process, making it even more efficient and suitable for commercial use.

“The method needs to be tested with different types of wastewater to ensure it works universally,” he said.

‘Harnessing wastewater as a catalyst modifier for sustainable hydrogen production’ is published in ACS Electrochemistry.

Image caption: Professor Nicky Eshtiaghi, Dr Muhammad Haris and Associate Professor Nasir Mahmood in their RMIT lab. Image credit: Shu Shu Zheng, RMIT University.