UNSW scientists have discovered a way to purify methane from biogas produced in wastewater plants, which could be used as a source of renewable energy that could one day fuel buses.

Graphene filters, made up of a mesh of carbon atoms, have been used in water purification processes. But they can also be used to filter out certain gases, Dr Rakesh Joshi says.

Dr Joshi, lead researcher and senior lecturer in the School of Materials Science and Engineering at UNSW, says that the graphene filter can be tweaked to meet different needs.

“If you have a mixture of gases, we can tune the graphene-oxide membranes to selectively filter out gases through the membranes,” he told Government News.

Dr Heri Bustamante, Principal Scientist in Treatment at Sydney Water, said that biogas produced in the wastewater treatment process at Sydney water is currently being used to generate energy.

“The use of graphene will enable increased capture of methane to expand potential uses beyond the requirements of Sydney Water,” he said in a statement.

“Production of methane to fuel buses could be a potential future use, for example. This would contribute to the potential of creating a circular economy at Sydney Water.”

Dr Joshi has been working with his team on the graphene membrane for the past four years. Although there is more work to be done, he says the gas discovery is promising.

“It’s challenging, we’re still progressing on that area but we can say this shows that we’ve done it – we can selectively separate the gases,” he said.

Dr Joshi says graphene is fundamentally one of the strongest materials.

“It’s stronger than a steel, so it can be used for hard materials, and it’s a very flexible material and strong,” he said.

“It can be used in electronic applications, it has very good electronic properties, so it has a lot of potential for many areas of advanced materials being used.”

A water filter like no other

The discovery came about last year when Dr Joshi and his team were working on a water purification project with Sydney Water, where they developed a laboratory-scale graphene filter to improve the quality of drinking water.

The graphene filter works like a regular water filter, however, it has the smallest pores of any filter system, Dr Joshi said.

“The performance of a filter depends on the pores, and graphene oxide-based membrane so far has the smallest pores… so even the smallest impurities can be filtered,” he said.

While working on the water purification project, Dr Joshi and his team looked for other uses of the graphene filter.

“We had been doing some research on using graphene for water purification, and we thought of using it for other applications,” Dr Joshi said.

The economic modelling for cost effectiveness of the graphene filter has yet to be completed by Dr Joshi and his team, however, they are in the process of making it more cost effective.

“The whole graphene community from the last ten years wants to make it cost effective, that’s the common goal. We want to have a good performance and with the cost also,” he said.

Right now, the team is working on scaling up the graphene filter so it can be used commercially and be able to filter for a larger scale.

“The next step is to make the performance better and to make it useful for the people,” Dr Joshi said.