Liquid-gated membrane mounted in filtration module prior to testing.Scientists at the Wyss Institute at Harvard University, with collaborators from Northeastern University and the University of Waterloo, have demonstrated a new liquid-gated membrane (LGM) filtration system that controls the movement of liquids, gases and particles through biological filters to improve industrial wastewater purification and reduce energy use. The new system improves the performance of membrane filters for the treatment and reclamation of process water from increasingly common horizontal drilling and hydraulic fracturing to reduce their environmental impact.
With wastewater usually being processed by passing it through a membrane that filters out larger particles, the membranes can get clogged up by the materials they are filtering out, requiring more electricity to push the water through, while the membrane also needs replaced. However, this feasibility study, reported in APL Materials [Alvarenga et al. APL Mater. (2018) DOI: 10.1063/1.5047480], showed how LGMs could filter nanoclay particles out of water with twofold higher efficiency, and close to threefold longer time-to-foul, as well as reducing the pressure required for filtration.
The LGMs are coated with a liquid that acts as a reversible gate, filling and sealing its pores in the closed state. As pressure is applied, the liquid inside the pores is pulled to the side, producing open, liquid-lined pores that can be tuned to allow the passage of specific liquids or gases. There is less fouling because of the slippery surface of the liquid layer, and the pores separate target compounds from different substances, common in industrial liquid processing.
“These results demonstrate the potential of the liquid gating mechanism, which can lead to breakthroughs in membrane technology applications in particle filtration, microfiltration and ultrafiltration”Jack Alvarenga and Joanna Aizenberg
The team tested the LGMs on a suspension of bentonite clay in water, infusing discs of a standard filter membrane with a liquid lubricant to convert them into LGMs, before positioning the membranes under pressure to draw water through the pores but leaving the nanoclay particles where they are. Using a scalable process, this enhanced the performance of conventional membrane filters by reducing the transmembrane pressure for filtration of particles by approximately 15% and reducing irreversible fouling by more than 60%.
With less persistent fouling the membranes last longer, and there is less unnecessary use of treated water and cleaning chemicals. The increased effectiveness of backwashing for pressure recovery and sustained filtration in LGMs was also demonstrated for the first time. As the team told Materials Today, “These results demonstrate the potential of the liquid gating mechanism, which can lead to breakthroughs in membrane technology applications in particle filtration, microfiltration and ultrafiltration”.
The LGMs are candidates for filtration applications such as water treatment, food and beverage processing, biomanufacturing and other high-impact industrial processes, and the team now hopes to carry out pilot studies to garner insight into the longer-term operation of the LGMs and filtering more complex mixtures of substances with a view to their commercial viability.