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More than one in ten people in the world do not have access to basic drinking water and, by 2025, half of the world's population will live in areas affected by the water stress. That's why access to clean water is one of the big challenges of the National Academy of Engineering. . Engineers at the University of Washington in St. Louis have developed a new membrane technology that purifies water while preventing biofouling, or the buildup of harmful bacteria and other microorganisms that reduce water flow .
And they used bacteria to build such filter membranes.
Srikanth Singamaneni, professor of mechanical engineering and materials science, and Young-Shin Jun, professor of energetic, environmental and chemical engineering, and their teams have combined their expertise to develop an ultrafiltration membrane using l & # 39; graphene oxide and bacterial nanocellulose that they found to be very effective, durable and environmentally friendly. If their technique were to be scaled up, this could benefit many developing countries where drinking water is scarce.
The results of their work were published on the cover in the January 2 issue of Environmental Science & Technology.
Biofouling accounts for nearly half of the fouling of the membranes and it is extremely difficult to eradicate it completely. Singamaneni and Jun have been tackling this challenge together for almost five years. Previously, they had developed other membranes using gold nanostars, but wanted to design one using cheaper materials.
Their new membrane begins with feeding Gluconacetobacter hansenii Bacteria are a sweet substance that forms cellulose nanofibers in water. The team then incorporated graphene oxide (GO) flakes into the bacterial nanocellulose during its growth, essentially retaining the membrane in the membrane to make it stable and durable.
After incorporation of GO, the membrane is treated with a basic solution to kill Gluconacetobacter. During this process, the oxygen groups of GO are eliminated, which reduces it. When the team projected sunlight onto the membrane, the reduced flakes of GO immediately generated heat that is dissipated into the surrounding water and the nanocellulose bacteria.
Ironically, the membrane created from bacteria can also kill bacteria.
"If you want to purify water containing microorganisms, reduced graphene oxide in the membrane can absorb sunlight, heat the membrane and kill bacteria," Singamaneni said.
Singamaneni and Jun and their team exposed the membrane to E. coli bacteria, then lit the surface of the membrane. After being irradiated with light for only 3 minutes, the E. coli the bacteria are dead. The team determined that the membrane was heating rapidly above the 70 degrees Celsius needed to damage cell walls. E. coli bacteria.
While the bacteria were killed, the researchers had a virgin membrane containing high quality nanocellulose fibers, capable of filtering water twice as fast as commercially available ultrafiltration membranes. under high operating pressure.
When they did the same experiment on a bacterial nanocellulose membrane without the reduced GO, the E. coli the bacteria remained alive.
While Singamaneni and Jun recognize that implementing this process in conventional reverse osmosis systems is challenging, they offer a spiral wound module system, similar to a towel roll. It could be equipped with LEDs or a type of nanogenerator that exploits the mechanical energy flow of the fluid to produce light and heat, which would reduce the overall cost.
Paper: Jiang Q, Ghim D, Cao S, Tadepalli S, Liu KK, Kwon H, Luan J, Y Min, Jun YS, Singamaneni S. "Photothermally Active Reduced Graphene Oxide Compounds / Bacterial Nanocellulose as Membranes". biofouling-resistant ultrafiltration. & Technology. Posted online September 14, 2018; print January 2, 2019. DOI: 10.1021 / acs.est.8b02772
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