LGMs hold potential for industrial wastewater treatment

Dec. 10, 2018
Research from Harvard University shows liquid gated-membranes (LGMs) filter with twice the efficiency, three-times longer time to foul

I’m all about efficiency, and although I may not completely understand the efficiency goals of an industrial facility, I can appreciate any innovation attempting to fine-tune a process to improve desired results and decrease expense and energy. One recent example of this comes via research from the Wyss Institute for Biologically Inspired Engineering at Harvard University, in collaboration with researchers at Notheastern University and the University of Waterloo.

The research, which was published in APL Materials in November, showed that Wyss’ liquid-gated membranes (LGMs) can filter nanoclay particles from water with two-times the efficiency, almost three times longer time to foul, and reduced pressure needed for filtration compared with a traditional membrane, according to an article from The Harvard Gazette by Lindsay Brownell titled “Liquid-gate membrane filtration system improves wastewater purification, saves money.”

“This is the first study to demonstrate that LGMs can achieve sustained filtration in settings similar to those found in heavy industry, and it provides insight into how LGMs resist different types of fouling, which could lead to their use in a variety of water-processing settings,” said first author Jack Alvarenga, a research scientist at the Wyss Institute, in the article.

In the study, the LGMs were found to filter water three times longer than traditional membranes before requiring a backwash. Going further, 60% less nanoclay accumulated in the LGMs during filtration, giving LGMs a longer lifespan than their standard counterparts. Additionally, the LGMs showed potential for energy savings as they required 16% less pressure to initiate filtration, the article reports.

According to the article, LGMs function similar to the liquid-filled pores in nature that control the movement of liquids and gases.

Brownwell explains how they work: “Each LGM is coated with a liquid that acts as a reversible gate, filling and sealing its pores in the ‘closed’ state. When pressure is applied to the membrane, the liquid inside the pores is pulled to the sides, creating open, liquid-lined pores that can be tuned to allow the passage of specific liquids or gases, and that resist fouling due to the liquid layer’s slippery surface. The use of fluid-lined pores also enables the separation of a target compound from a mixture of different substances, which is common in industrial liquid processing.”

This animation compares the transmembrane pressure (TMP) between a standard membrane filter and a liquid-gated membrane filter (depicted by pressure gauge in bottom right corner), and demonstrates how both systems respond to fouling. The liquid gated membrane technology also enables multiphase separation and is compatible with standard filtration materials. Source: Wyss Institute at Harvard University

For the study, the team tested LGMs on a suspension of bentonite clay in water, mimicking the wastewater produced in the oil and gas industry. 25mm discs of standard filter membrane were infused with perfluoropolyether to convert them into LGMs, and were then placed under pressure to draw in water while leaving nanoclay particles behind.  

“LGMs have the potential for use in industries as diverse as food and beverage processing, biopharmaceutical manufacturing, textiles, paper, pulp, chemical and petrochemical, and could offer improvements in energy use and efficiency across a wide swath of industrial applications,” said corresponding author Joanna Aizenberg, a founding core faculty member of the Wyss Institute and the Amy Smith Berylson Professor of Material Sciences at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), in the article.

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