Plant Waste can Filter Heavy Metals from Water, Study Shows

Recently, researchers revealed that they had developed a membrane that can filter heavy metals from contaminated water and was made from plant waste, particularly that produced from the production of vegetable oil.

They discovered that proteins made from by-products of the production of sunflower or peanut oil can effectively attract heavy metal ions.

The finding suggests that contaminated water could be purified to meet international drinking standards through the process of attraction known as adsorption.

Potentials of a Plant Waste-Based Membrane

The team pointed out that modern technologies use a lot of energy, need electricity to run, or filter information very carefully. However, their membrane has the potential to be a low-cost, scalable, sustainable, and low-power technique.

Professor Ali Miserez from Nanyang Technological University in Singapore explains that a sizable group of water pollutants known as heavy metals can build up in the body of a person and result in cancer and other mutagenic diseases.

Waste byproducts known as oilseed meals are produced during the production of household vegetable oils. These are the protein-rich byproducts that are left over after the raw plant's oil has been extracted.

The oilseed meals from two popular vegetable oils were used by the NTU-led research team. These oils are sunflower and peanut oils. The team separated the proteins from oilseed meals and converted them into protein amyloid fibrils, the rope-like structures made of tightly wound proteins, that are nanoscale in size. These protein fibrils serve as a molecular sieve, trapping heavy metal ions as they pass by because they are drawn to heavy metals.

From Plant Waste to Filter Membranes

Soon Wei Long, a Ph.D. student from NTU, says that this is the first time proteins from peanut and sunflower seeds have been used to produce amyloid fibrils. Soon is the first author of the paper.

To create a hybrid membrane, the researchers mixed activated carbon with the extracted amyloid fibrils. A typical filtration material is activated carbon. Chromium, platinum, and lead were used as the three common heavy metal pollutants on which they tested their membranes.

The heavy metal ions in the contaminated water adhere to the surface of the amyloid fibrils as contaminated water passes through the membrane, a process also known as adsorption. Amyloid fibrils are effective at adsorbing a significant amount of heavy metals due to their high surface-to-volume ratio.

The group discovered that their membranes could remove up to 99.89% of heavy metals. Among the three metals tested, the filter was most effective for lead, then platinum, followed by chromium.

Miserez explained that any kind of heavy metals, as well as organic pollutants like PFAS or perfluoroalkyl and polyfluoroalkyl substances, can be filtered using the filter. Chemicals known as PFAS have been found in a variety of industrial and consumer goods. The amino acid bonds in the amyloid fibrils trap and sandwich heavy metal particles while allowing water to pass through.

According to the researchers, the amount of water the membrane can filter out depends on the number of heavy metals present in the contaminated water. To filter drinking water, a hybrid membrane made of sunflower protein amyloids will only need 16 kilograms of protein if an Olympic-sized swimming pool is contaminated with 400 parts per billion.

Soon outlined how the method is easily scaleable due to its simplicity and low reliance on chemical reagents, emphasizing the need for cost-effective and environmentally friendly water treatment methods. This enables the team to fully utilize various industrial food wastes into advantageous technologies and to reprocess waste streams for additional applications.

Additionally, the trapped metals can be freed and recycled again. After filtration, the metals can simply be removed by burning the membrane that was used to trap them.

Professor Raffaele Mezzenga, a co-author of the study from ETH Zurich, Switzerland, pointed out that Other metals, such as platinum, have valuable applications in the creation of electronics and other sensitive equipment, whereas metals like lead or mercury are poisonous and can be safely disposed of.

Read also: Rising Cases of Water Contamination - Should We Preserve Water for Future Generations? 

Filtering Priceless Metals

Only 32 kg of protein is needed to recover precious platinum, while only half that amount of protein is needed to recover gold. Platinum is valued at $33,000 per kilo, while 1 kg of gold costs almost $60,000.

Mezzenga noted that there are significant financial advantages given that these proteins are produced from industrial waste with a value of less than US$1/kg, Good News Network reports.

The fact that this filtration uses little to no energy, as opposed to other techniques like reverse osmosis that do, is another significant benefit, according to the researchers.

Mezzenga continued by saying that gravity performs most or all of the work in their membrane. In areas with possibly limited access to electricity and power, this low-power filtration technique can be very helpful.

The researchers have been working with BluAct, an ETH Zurich spin-off company that specializes in European water filtration, to investigate the commercial applications of their membrane since publishing their paper in the journal Chemical Engineering three months ago.

Related article: Should You Be Using a Ceramic-Based Water Filter Pitcher?