New membranes resist biofouling using sunlight

Membranes in large-scale water-treatment processes are often fouled by accumulation of bacteria or their biofilms. Now, a team of researchers from Washington University St. Louis (WUSTL; St. Louis, Mo.; www.wustl.edu) have combined graphene oxide and bacterial nanocellulose to design a highly efficient ultrafiltration membrane that resists biofouling. “Photothermal nanomaterials like graphene oxide absorb light effectively, and the absorbed light is quickly converted into heat. Thus, the membrane gets hot, killing microorganisms on its surface and minimizing biofilm formation. This new membrane design uses the natural energy of sunlight to resist biofouling on membranes,” explains Young-Shin Jun, professor of Energy, Environmental & Chemical Engineering at WUSTL. Previously reported nanomaterial-enabled membranes often suffer from short operational lifetimes and poor physical and chemical stability that can result in nanomaterials leaching into water, adds Srikanth Singamaneni, professor of Mechanical Engineering and Materials Science at WUSTL. To secure the photothermal materials within the membrane’s structure, the team from WUSTL started with a bacterial culture medium where cellulose nanofibers grow into a matrix. Next, as graphene oxide nanosheets are incorporated into the medium, the bacteria build a nanocellulose matrix with embedded graphene oxide. “You end up with a composite membrane consisting of interlocked graphene oxide and nanocellulose, so particulate matter from the membrane itself does not leach out into the water,” adds Singamaneni.

According to Jun, combining the bacteria-killing properties of photothermal materials with the mechanical and chemical integrity of a nanocellulose network results in a membrane with a longer life and higher liquid flux than commercially available membranes operating at the same pressure. The team believes that the new membranes will be readily scalable, since the technology depends on culturing bacterial nanocellulose, a process that is already conducted at large scales.