Wastewater treatment protects human as well as environmental health. And it conserves water. Abu Dhabi researchers offer promising approaches using innovative membranes:

Filtering out nutrients

High levels of nutrients sounds like a benefit to an ecosystem, but when an environment sees too many, otherwise known as eutrophication, algal blooms and waters with too little oxygen can kill fish and seagrass, setting off a chain reaction in the ecosystem.

Large amounts of carbon dioxide from the decomposing matter acidify the water, slowing the growth of fish and shellfish. Eutrophication is an economic threat as well — smaller harvests mean more expensive seafood.

“We need to control the levels of nutrients and develop innovative technologies to treat water and remove excess nutrients,” says Shadi Hasan, director of the Khalifa University Center for Membranes and Advanced Water Technology (CMAT), whose team published its research in npj Clean Water.

The KU team developed a composite polylactic acid (PLA) and nanomaterial membrane to remove nutrients from wastewater.

The membrane works via adsorption, the process by which a solid holds molecules, in this case liquid, as a thin film. The team used a functionalized positively charged multi-walled carbon nanotube/graphene oxide hybrid nanomaterial to remove nitrogen (as ammonia) and phosphorus from wastewater while enhancing water permeability. The nutrients are collected in the pores of the nanotubes at the surface of the membrane.

Removing oil from water

Wastewater can be difficult to treat, especially when trying to remove fine oil droplets.

“The large volume of industrial oily wastewater is difficult to treat due to its emulsified fine oil droplet content,” says Linda Zou, a Khalifa University professor. “Conventional membranes experience low separation efficiency and oil fouling issues, which we wanted to overcome.”

Zou and other researchers incorporated molybdenum disulfide (MOS2) nanospheres into a cellulose acetate matrix. MOS2 nanospheres repel water but attract oil — that is, they are oleophilic — whereas the cellulose acetate polymer has high water affinity and is hydrophilic. The membrane is designed to be amphiphilic, meaning it can target and capture oil droplets in a large volume of water. This is important for separation because the membrane has components that attract the oil droplets but can also facilitate the passage of water.

The membrane’s amphiphilic nature also eliminates fouling caused by oil droplets.

The team found the membrane had a high separation efficiency in tests, with greater than 90 percent removal of oil from the diluted oil-in-water mixture. The membrane also had good stability and durability, meaning it could be used repeatedly without losing performance, which makes it a promising material for industrial application.