Researchers say they have found a way to filter water using 1,000 times less energy than conventional processes. The trick is to get rid of membranes.
The researchers published their findings in Nature Communications this month. They compared their method to conventional microfiltration, ultrafiltration, and reverse osmosis processes. Each of these processes relies on porous membranes. The downside of membranes, the study said, is that they are linked to high pumping costs and a need for periodic replacement due to fouling.
The researchers show a membraneless method for separating suspended particles. It relies on exposing the colloidal suspension to CO2.
“Dissolution of CO2 into the suspension creates solute gradients that drive phoretic motion of particles. Due to the large diffusion potential generated by the dissociation of carbonic acid, colloidal particles move either away from or towards the gas-liquid interface depending on their surface charge,” the study says.
The researchers managed to create “a scalable, continuous flow, membraneless particle filtration process,” they said. The process “exhibits low energy consumption, three orders of magnitude lower than conventional microfiltration/ultrafiltration processes, and is essentially free from fouling.”
The researchers say the new method could be used to replace or improve existing filtration processes.
“We suggest that the proposed technique could be used either to replace microfiltration and ultrafiltration or benefit such conventional filtration processes by mitigating membrane fouling,” the study said.
Orest Shardt of the University of Limerick in Ireland was one of the researchers on the project.
"We are at the early stages of developing this concept. Eventually, this new method could be used to clean water for human consumption or to treat effluent from industrial facilities," Shardt said in a statement released by the university.
The intersection between water treatment costs and energy costs, discussed under the umbrella term “water-energy nexus,” is a top concern for water utilities. In a blog post published this week, Kate Zerrenner of the Environmental Defense Fund described the nexus like this:
Known as the energy-water nexus, the link refers to the water embedded in energy and the energy embedded in water. Consider the amount of water it takes to produce and distribute electricity. As well, consider the amount of electricity used to treat, pump, and distribute water. And, while many clean energy resources are virtually water-free, traditional sources — such as coal, nuclear, and natural gas — require a significant amount of water to generate power.
Image credit: "electricty," filter forge © 2013, used under an Attribution 2.0 Generic license: https://creativecommons.org/licenses/by/2.0/