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New Filtration Technology Enhances Wastewater Purification, Makes It Energy-Efficient

[Estimated read time: 3 minutes]
  • A new type of membrane requires much lower pressure than standard membranes to filter suspended particles from water. 
  • It lasts 3 times longer and saves twice as much energy than conventional transmembrane.

Water purification techniques decrease the concentration of certain matter like bacteria, fungi, viruses, algae, parasite, and suspended particles. There are several physical, biological and chemical processes, and over the last couple of decades, we have been using electromagnetic radiation like UV light to purify water.

The process of water filtration and treatment — for drinking and chemical and industrial applications — accounts for nearly 13% of total electricity consumption in the United States, which releases 290 million metric tons of carbon dioxide into the atmosphere annually. To put this into context, it’s equivalent to the combined weight of all humans in the world.

To purify water, it’s usually passed through a membrane with tiny pores. The size of these pores is small enough to filter out impurities or particles bigger than water molecules. Since these membranes tend to ‘wear and tear’ due to clogging, they require higher voltages to push water molecules, and often clogged membranes need to be replaced, increasing the cost of water treatment.

Now, researchers at Harvard University have developed a new type of membrane that requires much lower pressure than traditional membranes to filter suspended particles from water. They are calling it liquid-gated membranes (LGMs). It is twice efficient (in terms of energy consumption) and lasts three times longer than existing membranes.

LGMs can be used in a wide range of water-processing settings, reducing the electricity consumption and cost of large industrial processes, including gas and oil drilling.

How It Works?

Every liquid-gated membrane is coated with a special liquid that fills and seals the pores in a ‘closed’ phase, serving as a reversible gate. When you apply the pressure (to filter water), the liquid within the membrane’s pores is dragged towards the ends, forming open pores, which could be configured to let certain gases or liquids pass through.

Reference: AIP | doi:10.1063/1.5047480 | Harvard University 

This prevents ‘wear and tear’ of membranes due to the slippery surface of the liquid. And since LGMs is capable of separating target substance(s) from different liquid mixtures, it could be used in industrial liquid processing.

Transmembrane pressure (TMP) for standard and gated membrane | Courtesy of researchers 

To create an LGM, researchers infused tiny disks (25 millimeters) of a conventional filter membrane with a special liquid lubricant, perfluoropolyether, which has been used in the airline industry for over 3 decades.

Testing and Applications

Researchers mixed bentonite clay in water and passed it through LGMs pores by applying appropriate pressure. Then they compared the results with conventional membranes.

The liquid-gates membranes showed signs of wear and tear much later than conventional ones: they effectively filtered water 3 times longer than untreated membranes before needing a process to manually remove substances piled up on the membrane. Also, they had 60% less nanoclay gathered on their membrane during filtration.

Read: A New Way To Remove Contaminants From Storm Water

To initiate filtration, LGMs require 16% less pressure, saving more energy. This could boost the filtration rate of water treatment mechanisms used in various industries, including textiles, petrochemical, biopharmaceutical manufacturing, and food and beverage processing.

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