As our global population grows, so our water supplies are experiencing greater pressure to meet people’s needs – from drinking to irrigation to sanitation – and bringing us face to face with a looming water crisis. According to WHO, around 33% of people in the world – or one in three- do not have access to safe drinking water, while a similar proportion cannot access proper sanitation. As we steadily climb closer to the projected 9.7bn population figure by 2050, these numbers will mirror the rising trend and water consumption will boom.
In addition to population-induced scarcity, climate change is accelerating water accessibility, with an August 2021 report by the Intergovernmental Panel on Climate Change stating that extreme drought – which typically occurs once every decade – is now 1.7 times more likely to happen due to man-made temperature increases. Finally, we have a problem with wastewater. According to a 2017 UN report, more than 80% of the world’s wastewater is dumped untreated into the surrounding environment. High treatment costs and public reluctance to drink recycled water means wastewater is not seen as the asset it could be as we seek to meet skyrocketing water demands.
In sum, we have a growing need to find solutions to our dwindling water supply, and it is not one that will wait for answers.
Finding ways to filter
While the problem may be a pressing one, innovators around the world are working hard to make recycled water not only available but also accepted as a solution to our thirsty nations. One such team is that from Tufts University School of Engineering in Massachusetts, which has developed a novel membrane filter to purify water supplies. While designed for drinking water, the method has scale-up potential for deployment in a host of other industries.
The team began developing their novel filter membrane as a response to fluoride toxicity in water supplies. While the mineral is sometimes intentionally added to water to protect teeth, at too high a level it can cause severe bone deformities and is unsafe for human consumption. Using their new targeted method, the team was able to separate fluoride from chloride and other ions, in a process that has potential to not only improve drinking water but also be upscaled to improve environmental remediation, industrial and chemical production, and mining, among other processes.
“The main drive for this project was to develop a membrane filter that can separate salts from each other, even if they are really similar in charge and size,” says Ayse Asatekin, associate professor of chemical and biological engineering at the school. “This is necessary for removing toxic ions from drinking water, removing contaminants from wastewater, or recovering valuable compounds from waste or drainage from recycling or landfill areas.”
“We have filters that can essentially hold back most ions and pass salt – the same ones used in seawater desalination for example,” Asatekin adds. “But it is really hard to separate one salt from another – particularly, allow sodium chloride, table salt, to pass through but hold back undesired components, so you don’t waste energy removing non-problematic ions and then spend money putting them back.”
In particular, the team focused on areas with high levels of fluoride in groundwater resources, developing a filter that could decrease concentrations of the mineral without removing all the salt.
“We used specially designed polymers that self-assemble to form 1-1.5 nm pores, filled with special functional groups called zwitterions,” Asatekin says. “Zwitterions are very hydrophilic, so they suck water into these pores and allow them to pass through. This also keeps them very clean – they love water so much that they don’t allow organic compounds, oil, and similar foulants to stick to the surface. As a result, they can operate stably even with really challenging water streams that quickly foul and clog other membranes. Finally, they have interesting interactions with different ions. They interact differently with fluoride versus chloride. We found that if you make these pores so small that only one ion can fit in it at a time, these differences in interaction can enable us to separate these ions from each other.”
What’s next for the project?
Models of these zwitterionic membranes are currently being commercialised by ZwitterCo, a start up founded by a team mostly consisting of Tufts students, and which Asatekin is the Senior Scientific Advisor for. The team will also be exploring the membrane’s application in industrial settings.
“They have scaled up manufacturing to roll out systems and build rigs that can be located at industrial locations whose wastewater is extremely challenging to treat,” Asatekin says. “They are an amazing team. We still work with them, and conversations with their team helps us identify applications where there is a technological gap to direct our research efforts when we can. We are hoping that, if as successful as we think it will be, they can be the partner to commercialise this work (or others targeted at different separations).”
While the team’s primary focus is on fluoride/chloride separation, Asatekin says they hope to expand the tech’s reach to also work on arsenic and selenium, and even in the recycling of rare earth metals such as lithium. Indeed, in a University announcement on the subject, Asatekin commented that the filter system can be deployed at low cost and with environmentally sustainable outcomes, making it a viable option for ‘improving agricultural water supplies, cleaning up chemical waste and improving chemical production’.
The process could theoretically even improve lithium and uranium yields, used in battery production and nuclear power respectively.
Application of this tech on an industrial scale is still very much at a theoretical stage, however the team’s membrane technology demonstrates the multitude of benefits effective water treatment can have. Given that we are currently only able to use 1% of our world’s water, developing methods to make more of our world’s water resources accessible is a growing necessity to support all elements of society – from industrial to community levels.