A team of researchers from Khalifa University has developed a sustainable and green membrane using graphene oxide and carbon nanotubes to safely and effectively remove excess nutrients from wastewater.
Dr. Shadi W. Hasan, Associate Professor and Director of the Khalifa University Center for Membranes and Advanced Water Technology (CMAT), Prof. Fawzi Banat, Chair of the Khalifa University Chemical Engineering Department, Dr. Hanaa Hegab, Postdoctoral Fellow, Dr. Vijay Wadi, Research Scientist, Hiyam Khalil and Lobna Nassar, both graduate students, developed a membrane with the potential for practical use in real wastewater-treatment applications.
They published their results in npj Clean Water.
High levels of nutrients sounds like a benefit to an ecosystem, but when an environment sees excessive nutrient inputs, otherwise known as eutrophication, algal blooms and hypoxic waters can kill fish and seagrass, setting off a chain reaction in the ecosystem. Large amounts of carbon dioxide from the decomposing plant matter acidify the water, slowing the growth of fish and shellfish. Eutrophication is a threat as well — a reduced catch for commercial and recreational fisheries means smaller harvests and more expensive seafood.
“The high accumulation of nutrients, including nitrogen and phosphorus, discharged into surface water, rivers, and reservoirs can accelerate eutrophication and cause great damage to the aquatic ecosystem,” Dr. Hasan said. “We need to control the levels of nutrients and develop innovative technologies to treat water and remove excess nutrients.”
Several treatment technologies already exist. Nitrogen can be chemically removed through methods that include chlorination or nitrification, and there are also biological approaches available. However, each has its limitations. Chemical methods can introduce undesirable byproducts, while biological treatments take much longer and are inefficient in the use of nitrogen. Additionally, no available method offers complete water purification.
Novel membrane technology, however, may be the solution. The KU research team has developed a composite polylactic acid (PLA) and nanomaterial membrane to remove nutrients from wastewater.
The membrane works via adsorption. The research team used a functionalized positively charged multi-walled carbon nanotube/graphene oxide hybrid nanomaterial to simultaneously remove nitrogen (as ammonia) and phosphorus from wastewater while enhancing water permeability. The nutrients are filtered out by collecting in the pores of the nanotubes at the surface of the membrane.
Water permeability in such a membrane is a concern. As more nutrients adsorb and collect, the amount of water passing through decreases. The research team’s membrane, however, offers high water flux even when filtering the nutrients. The carbon nanotubes increase membrane tensile strength significantly, while the graphene oxide enhances thermal stability, tensile strength, and provides antibacterial properties. This supports water flux and provides hydrophilicity to the end product.
While the effects of graphene oxide and carbon nanotubes in water purification are well-documented in the literature, studies are limited when it comes to combining the two as a nanohybrid.
“After a comprehensive review of the literature, our research group is the first to report the fabrication of such composite PLA membranes for the removal of nutrients from synthetic and real wastewater,” Dr. Hasan said.
Wastewater with high levels of nutrients such as nitrogen and phosphorus is inevitable, so a sustainable and green approach to filtration is critical.
“Our results confirm this membrane’s potential for practical use in real wastewater-treatment applications and can open the door to efficient and sustainable methods for nutrient removal,” Dr. Hasan said. The next step is to scale-up the membranes for commercialization.
19 January 2023