Scientists discover a simple way to remove heavy metals from water using plant waste
Scientists have just announced that they have created a membrane made from a by-product of vegetable oil manufacturing, which can filter heavy metals from contaminated water.
They found that proteins derived from the by-products of peanut or sunflower oil production can very effectively attract heavy metal ions.
The study showed that this attraction process, called adsorption, was able to purify contaminated water so that it meets international drinking standards.
Current technologies are energy-intensive, require energy to operate, or are very selective in what they filter. However, their membrane has the potential to be a cheap, low-power, durable, and scalable method.
“Heavy metals represent a large group of water pollutants that can accumulate in the human body, causing cancers and mutagenic diseases,” said Professor Ali Miserez from Nanyang Technological University in Singapore (NTU ). Our work puts heavy metal where it belongs: as a musical genre and not as a pollutant in drinking water.
The production of household vegetable oils generates waste by-products called oilseed cakes. These are the protein-rich leftovers that remain after the oil has been extracted from the raw plant.
The NTU-led research team used the oilseed meals of two common vegetable oils, sunflower and peanut oils. After extracting the proteins from the oilseed cakes, the team turned them into nanometer-sized protein amyloid fibrils, which are rope-like structures made of tightly coiled proteins. These protein fibrils are attracted to heavy metals and act as a molecular sieve, trapping heavy metal ions as they pass.
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Turn waste into water filters
“This is the first time that amyloid fibrils have been obtained from sunflower and peanut proteins”, says the first author of the diaryNTU doctoral student, Mr. Soon Wei Long.
The researchers combined the extracted amyloid fibrils with activated charcoal, a commonly used filtration material, to form a hybrid membrane. They tested their membranes on three common heavy metal pollutants: platinum, chromium and lead.
As the contaminated water passes through the membrane, the heavy metal ions stick to the surface of the amyloid fibrils – a process called adsorption. The high surface to volume ratio of amyloid fibrils makes them effective in adsorbing a large amount of heavy metals.
The team found that their membranes filtered out up to 99.89% of heavy metals. Of the three metals tested, the filter was most effective for lead and platinum, followed by chromium.
“The filter can be used to filter out all kinds of heavy metals, as well as organic pollutants like PFAS (perfluoroalkyl and polyfluoroalkyl substances), which are chemicals that have been used in a wide range of consumer and industrial products,” Miserez said. “Amyloid fibrils contain amino acid bonds that trap and sandwich heavy metal particles together while allowing water to pass through.”
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The researchers say the concentration of heavy metals in the contaminated water will determine the volume of water the membrane can filter. A hybrid membrane made with sunflower amyloid protein will only require 35 pounds of protein (16 kg) to filter drinking water from the equivalent of an Olympic-sized swimming pool contaminated at 400 parts per billion.
“The process is easily scalable due to its simplicity and minimal use of chemical reagents, pointing to sustainable, low-cost water treatment technologies,” Soon said. “This allows us to reprocess waste streams for other applications and fully exploit different industrial food wastes in beneficial technologies.
Trapped metals can also be extracted and recycled. After filtration, the membrane used to trap the metals can simply be burned off, leaving the metals behind.
“While metals like lead or mercury are toxic and can be safely disposed of, other metals, like platinum, have valuable applications in the creation of electronic devices and other sensitive equipment,” said said co-author Professor Raffaele Mezzenga of ETH Zurich, Switzerland.
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Gleening precious metals in the process
Retrieving the precious platinum, which costs $33,000 for 2.2 pounds (1 kg), requires only 70 pounds of protein (32 kg), while retrieving the gold, which is worth nearly $60,000, requires only half the protein.
“Since these proteins are obtained from industrial waste with a value of less than USD 1/kg, the cost advantages are significant.”
Another big advantage, according to the researchers, is that this filtration requires little or no energy, unlike other methods like reverse osmosis which require electricity.
“With our membrane, gravity does most or all of the work,” Mezzenga said. “This low-energy filtration method can be very useful in areas where access to power and electricity may be limited.
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Since the publication of their article three months ago in the magazine Chemical Engineering researchers explored commercial applications of their membrane with BluAct, a European water filtration spin-off from ETH Zurich.
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