https://phys.org/news/2018-05-low-cost-membrane-heavy-oils.html

"This technology offers an effective and eco-friendly way to reduce the negative impacts of oily water and wastewater, which are being produced by domestic, municipal and industrial processes every day," says Chun Haow (Bryan) Kung, a chemical engineering master's student at UBC who led the study. "Other oil-water separation methods, such as those that rely on skimming, combustion and solvents, are either too expensive, too cumbersome, or inefficient."

While there are other membrane treatments that can switch from oil removal to water removal, they often rely on toxic, unstable chemical coatings that take time to activate. They also tend to produce relatively impure oil and water that need to be processed further, noted Kung.