Water pollution is one of the major global issues in many parts of the world. Heavy metals represent a large group of water pollutants that can accumulate in the human body, causing cancer and mutagenic diseases. Current technologies used to treat polluted wastewater of heavy metals are energy-intensive due to high pressure and power requirements or are highly selective in what they filter, making drinking water less affordable in developing countries.
Now, researchers from Nanyang Technological University, Singapore (NTU Singapore), in collaboration with ETH Zurich, Switzerland (ETHZ), have created a membrane made from a waste by-product of vegetable oil manufacturing, which can filter out heavy metals from contaminated water. The NTU-led research team used the oilseed meals from two common vegetable oils, sunflower, and peanut oil.
The team started by extracting the proteins from oilseed metal and then turned them into nano-sized rope-like structures known as protein amyloid fibrils. These protein amyloid fibrils are drawn to heavy metals and act as molecular sieves, trapping heavy metal ions as they pass by. Researchers then combined the extracted amyloid fibrils with activated carbon to form a hybrid membrane.
These membranes were used to filter water contaminated with common heavy metal pollutants: Platinum, chromium, and lead. As contaminated water flows through the membrane, heavy metal ions stick onto the surface of the amyloid fibrils. The high surface-to-volume ratio of amyloid fibrils makes them efficient in adsorbing a large amount of heavy metals.
The team found that their membranes filtered up to 99.89% of heavy metals. The filter was most effective for lead and Platinum, followed by chromium. The researchers say a hybrid amyloid-based membrane made with sunflower protein amyloids will require only 16kg of protein to filter the equivalent volume of an Olympic-sized swimming pool contaminated with 400 parts per billion (ppb) of lead into drinking water.
The trapped metals (such as Platinum) can also be extracted and further recycled. After filtration, the membrane used to trap the metals can simply be burnt, leaving behind the metals.
The new protein-based membrane has the potential to be a cheap, low-power, sustainable, and scalable method to decontaminate heavy metals from water. In addition, it provides a sustainable use for oilseed waste which would otherwise be discarded or used as food for animal feedstock. Researchers say this filtration requires little or no energy, unlike traditional technologies such as reverse osmosis, which is not only more expensive but also requires a source of electricity.
“Our protein-based membranes are created through a green and sustainable process and require little to no power to run, making them viable for use throughout the world and especially in less developed countries. Our work puts heavy metal where it belongs – as a music genre and not a pollutant in drinking water,” said Prof Miserez, who led the study.