As 2.9 million barrels of oil are extracted from the ground each day in the UAE, seven to ten times more barrels of oily wastewater are generated as an unwanted byproduct.
Treating this oily wastewater so it can be safely discarded is a significant financial and energy expense for oil and gas companies. However, an innovative membrane developed at Masdar Institute may soon help make separating waste oil from water significantly cheaper, easier and more sustainable.
A research team being led by Masdar Institute’s Dr. TieJun Zhang, Assistant Professor of Mechanical and Materials Engineering, has designed a novel membrane made of copper mesh coated with nanostructured titanium oxide to treat produced oily wastewater from the petroleum industry. The membrane can recover water by separating oil more effectively than traditional polymer-based membranes. These membranes have remarkable separation efficiencies (over 99%) with extremely low levels of remaining oil residue. And as the membrane can be cleaned with sunlight rather than harsh chemicals, it is significantly more environmentally-friendly and sustainable than other types of membranes.
The high separation efficiency and sunlight-sensitive cleaning properties of the membrane are mainly due to its nanostructure and material composition.
“The mesh is composed of nanostructured titanium dioxide grown on bare copper and nanostructured covered copper oxide. This makes it superhydrophillic – meaning it attracts water – and underwater oleophobic – meaning when wet, it repels oil. As the water flows through the mesh, it creates a barrier layer that forbids the oil to permeate,” said Dr. Aikifa Raza, a post-doctoral researcher at Masdar Institute and lead author of a paper that was published today on the team’s research in the journal Scientific Reports, a journal of the Nature Publishing Group.
The novelty of the work is the enhanced light absorption properties of these meshes, which enable them to degrade contaminants responsible for fouling – which is the build-up of contaminants and bio-materials on the surface of a membrane that drastically reduces its efficiency – when exposed to sunlight.
When fouling occurs, the membrane can be cleaned quickly and efficiently with sunlight, a feature achieved by the membrane’s titanium dioxide coating. Experimental testing revealed that after approximately two hours of sunlight exposure, the fouled membrane was completely cleaned. This sustainable and efficient cleaning method will reduce the energy, environmental and financial costs that are exacted by conventional cleaning processes, which rely on expensive and environmentally-unfriendly chemicals that can take up to several hours to clean.
Additionally, the membrane has been designed to operate with a cross-filtration technique, which allows only water to flow downwards, leveraging the pull of gravity rather than relying on energy-intensive pressures or pumps often required by conventional water treatment solutions. This technique reduces both the energy requirement and financial cost of the membrane.
The resulting membrane not only effectively and efficiently recovers water from produced oily wastewater, it can also be used to help collect extra oil or clean up oil spills by separating the oil from the body of water it has polluted.
And while the published research paper highlights the membrane’s application for oily wastewater treatment, the membrane’s design can be altered to treat other types of wastewater, such as wastewater that is high in dirt and sand concentration.
“We just need to play around with the membrane’s nanostructures and wettability, which we grow on the surface of the copper mesh substrate,” Dr. Raza explained.
By changing the nanostructures’ properties, certain features of the membrane can be altered, like which type of liquid will pass through it and which type of liquid or substance will remain behind. This allows the membrane to treat a diverse range of wastewater streams.
New potential applications will capitalize on the membrane’s unique properties. Its inorganic materials make it significantly more stable than conventional polymer-based membranes. This stability enables it to withstand much higher temperatures (up to 250° Celsius) and increases its resilience to fouling.
With a goal to reuse maximum amounts of wastewater produced in all sectors, this sustainable membrane and its commercial applications could give a critical boost to the UAE’s ambitious wastewater reclamation efforts and environmental preservation activities.
News and Features Writer
10 May 2016