Decontamination of water in heavy metals using proteins from plant waste

Chemical Engineering Journal (2022). DOI: 10.1016/j.cej.2022.136513″ width=”800″ height=”530″/>

Schematic of process flow from plant seeds to amyloid filtration membrane. a) Production of sunflower and groundnut meal by screw pressing of the seeds. b) Aqueous protein extraction from flours (brown spheres: proteins, green spheres: small molecules, blue spheres: water). c) Protein concentration with ultrafiltration. d) Precipitation of proteins in cold water. e) Formation of amyloid fibrils from vegetable proteins. f) amyloid fibrils. g) Manufacture of an amyloid-carbon hybrid membrane by filtration. h) Filtration of heavy metals by amyloid-carbon hybrid plant membranes. Credit: chemical engineering journal (2022). DOI: 10.1016/j.cej.2022.136513

Scientists 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 oil manufacturing plant that can filter heavy metals from contaminated water.

The research team, led by Professor Ali Miserez from the School of Materials Science and Engineering and the School of Biological Sciences and NTU Visiting Professor Raffaele Mezzenga from the Department of Health Sciences and Technology of ETHZ, discovered that proteins derived from the by-products of peanut or sunflower oil production can very effectively attract heavy metal ions.

In tests, they showed that this attraction process, called adsorption, was able to purify contaminated water to a degree that meets international drinking standards.

The researchers’ membrane has the potential to be a cheap, low-energy, durable and scalable method for decontaminating heavy metals from water.

Professor Miserez said: “Water pollution remains a major global problem in many parts of the world. Heavy metals represent a large group of water pollutants that can accumulate in the human body, causing cancers and mutagenic diseases. Current technologies to eliminate them are energetic. -intensive, requiring energy to operate, or are very selective in what they filter.”

“Our protein-based membranes are created through a green and sustainable process, and require little to no energy to operate, making them viable for use around the world and especially in less developed countries. Our work puts heavy metal where it needs to be, as a musical genre and not a pollutant in drinking water,” said Professor Miserez.

The results of the team’s research have been published in the chemical engineering journal in April. Their research goal to ensure water security is aligned with the NTU 2025 strategic plan and the university’s goal to mitigate humanity’s impact on the environment.

Transform vegetable oilseed meals into water filters

The production of commercial 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 oilseed meals from 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.

One kilogram of oilseed meal produces about 160 g of protein.

The first author of the paper, NTU Ph.DM Student Soon Wei Long, said, “Protein-rich sunflower and peanut flours are low-cost raw materials, from which proteins can be extracted, isolated and self-assembled into functional amyloid fibrils for heavy metal removal. This is the first time amyloid fibrils have been obtained from sunflower and peanut proteins.”

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,” said Professor Miserez. “Amyloid fibrils contain amino acid bonds that trap and sandwich heavy metal particles together while allowing water to pass through.”

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 based on sunflower protein amyloid will require only 16 kg of protein to filter the equivalent volume of an Olympic swimming pool contaminated with 400 parts per billion (ppb) of lead in drinking water.

“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 Professor Miserez.

“Recovering the precious platinum, which costs US$33,000/kg, requires only 32 kg of protein, while recovering gold, which is worth almost US$60,000/kg, requires only 16 kg of protein. proteins. Considering that these proteins are obtained from industrial waste which is worth less than 1 USD/kg, the cost advantages are significant. »

Sustainable filtration with low consumption

The paper’s co-author, Professor Raffaele Mezzenga, had already discovered in 2016 that whey proteins derived from cow’s milk had similar metal-attracting properties.

The researchers realized that proteins from plant oilseed meals could also have similar properties. Their experiments showed that these proteins were not only just as effective, but also cheaper and more sustainable because they used up waste that would otherwise be discarded or used as animal feed.

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,” Prof 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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More information:
Wei Long Soon et al, Herbal Amyloids from Food Waste for the Removal of Heavy Metals from Contaminated Water, chemical engineering journal (2022). DOI: 10.1016/j.cej.2022.136513

Provided by Nanyang Technological University

Quote: Decontaminating heavy metal water using protein from plant waste (2022, June 23) retrieved June 23, 2022 from

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