Solving next generation challenges in the water and resource area
Professor Vicki Chen explains why the growing need to treat more difficult effluents, utilise low value heat, reduce discharge volumes, and recover valuable resources has driven a renewed interest in membrane distillation and pervaporation desalination.
Water treatment technology and research is entering a new phase as advanced processes such membrane distillation and pervaporation desalination are being developed to both purify the water from recalcitrant waste streams and recover the valuable materials they contain.
Right on the cutting edge of these advanced processes, explains Professor Vicki Chen, are the team at the UNESCO Centre for Membrane Science and Technology (UCMST).
“Knowing how to manage these highly concentrated contaminant streams has suddenly become very important because the cost of disposing of them is rapidly escalating,” she says. “In some cases, disposing of the waste is more expensive than the operating costs of the water purification plant itself.”
Chen’s primary research focus is using advanced membrane technology, in both materials and process development, particularly for environmental applications. This includes water treatment, reuse, carbon dioxide removal and greenhouse gas separation. She says that it is not just economics influencing the change, environmental considerations are top of mind too.
“Traditional methods of disposing of the brines produced inland as a by-product of the energy sector in large evaporation ponds, for example, is no longer seen as an appropriate response,” Chen continues. “Companies are increasingly looking closely at how they can better manage concentrated reject streams, and this has generated great interest in our research,” she says.
Companies are increasingly increasingly looking closely at how they can better manage concentrated reject streams, and this has generated great interest in our research.
Professor Vicki Chen, UNESCO Centre for Membrane Science and Technology and Head of School, UNSW Chemical Engineering
Cost is one driver, protecting the environment is another and thirdly, says Chen, there are materials in many of these waste streams and brines which could be recycled and resold. “These waste streams contain valuable minerals such as lithium and other rare earth materials which are becoming an issue in terms of shortages,” she says. “If we can work out effective and efficient ways to recover them to make industrial products, there is a huge opportunity there.”
Although the technique has been around for some time, Chen and her team have been refocusing on membrane distillation as a solution because of the interest in using low-value heat to drive the separation.
“Rather than using pressure, we heat the solution to a modest temperature then use a hydrophobic material, so the water vapour can go through, but the salts and other contaminants are rejected,” Chen says.
“This technique allows us to treat very high salt concentrations which are difficult to achieve through conventional filtration such as reverse osmosis.”
According to Chen, pervaporation desalination is another technique that has been around for a while but is enjoying a resurgence because of the success they are achieving in using low-value heat and could potentially tolerate even more difficult feed streams.
“In this case the membrane is dense, so the water absorbs into the selective layer and then we usually use a vacuum to vaporise and recover that pure water on the other side. The contaminants are rejected by the thin selective layer,” she says.
As one of the leading research groups exploring this approach, which has exploded in interest in the last four years, one of the things that distinguishes UCMST is that they work on everything, from making new materials all the way to modelling and designing new modules and field testing with industrial partners.
“It’s a great field to be in and we are exploring plenty of ideas for practical application,” says Chen who explains that in one collaboration with colleagues in UNSW Mechanical and Manufacturing Engineering they are looking at coupling membrane distillation with a concentrated solar thermal power plant for use in remote areas.
“One of the by-products from this solar power plant is low-value heat, so we’re thinking, ‘Could we use that waste heat to do water purification, and therefore get power and water treatment in one go?” Chen says. “This is just one of many thematic areas we are exploring.”
Written by: Penny Jones