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Waterfiltration Photo Manuel Darío Fuentes Hernández , Pixabay
10.11.2024

New filtration material could remove long-lasting chemicals from water

Membranes based on natural silk and cellulose can remove many contaminants, including “forever chemicals” and heavy metals.

Water contamination by the chemicals used in today’s technology is a rapidly growing problem globally. A recent study by the U.S. Centers for Disease Control found that 98 percent of people tested had detectable levels of PFAS, a family of particularly long-lasting compounds also known as “forever chemicals,” in their bloodstream.

A new filtration material developed by researchers at MIT might provide a nature-based solution to this stubborn contamination issue. The material, based on natural silk and cellulose, can remove a wide variety of these persistent chemicals as well as heavy metals. And, its antimicrobial properties can help keep the filters from fouling.

Membranes based on natural silk and cellulose can remove many contaminants, including “forever chemicals” and heavy metals.

Water contamination by the chemicals used in today’s technology is a rapidly growing problem globally. A recent study by the U.S. Centers for Disease Control found that 98 percent of people tested had detectable levels of PFAS, a family of particularly long-lasting compounds also known as “forever chemicals,” in their bloodstream.

A new filtration material developed by researchers at MIT might provide a nature-based solution to this stubborn contamination issue. The material, based on natural silk and cellulose, can remove a wide variety of these persistent chemicals as well as heavy metals. And, its antimicrobial properties can help keep the filters from fouling.

The findings are described in the journal ACS Nano, in a paper by MIT postdoc Yilin Zhang, professor of civil and environmental engineering Benedetto Marelli, and four others from MIT.

PFAS chemicals are present in a wide range of products, including cosmetics, food packaging, water-resistant clothing, firefighting foams, and antistick coating for cookware. A recent study identified 57,000 sites contaminated by these chemicals in the U.S. alone. The U.S. Environmental Protection Agency has estimated that PFAS remediation will cost $1.5 billion per year, in order to meet new regulations that call for limiting the compound to less than 7 parts per trillion in drinking water.

Contamination by PFAS and similar compounds “is actually a very big deal, and current solutions may only partially resolve this problem very efficiently or economically,” Zhang says. “That’s why we came up with this protein and cellulose-based, fully natural solution,” he says.

“We came to the project by chance,” Marelli notes. The initial technology that made the filtration material possible was developed by his group for a completely unrelated purpose — as a way to make a labelling system to counter the spread of counterfeit seeds, which are often of inferior quality. His team devised a way of processing silk proteins into uniform nanoscale crystals, or “nanofibrils,” through an environmentally benign, water-based drop-casting method at room temperature.

Zhang suggested that their new nanofibrillar material might be effective at filtering contaminants, but initial attempts with the silk nanofibrils alone didn’t work. The team decided to try adding another material: cellulose, which is abundantly available and can be obtained from agricultural wood pulp waste. The researchers used a self-assembly method in which the silk fibroin protein is suspended in water and then templated into nanofibrils by inserting “seeds” of cellulose nanocrystals. This causes the previously disordered silk molecules to line up together along the seeds, forming the basis of a hybrid material with distinct new properties.

By integrating cellulose into the silk-based fibrils that could be formed into a thin membrane, and then tuning the electrical charge of the cellulose, the researchers produced a material that was highly effective at removing contaminants in lab tests.

The electrical charge of the cellulose, they found, also gave it strong antimicrobial properties. This is a significant advantage, since one of the primary causes of failure in filtration membranes is fouling by bacteria and fungi. The antimicrobial properties of this material should greatly reduce that fouling issue, the researchers say.

“These materials can really compete with the current standard materials in water filtration when it comes to extracting metal ions and these emerging contaminants, and they can also outperform some of them currently,” Marelli says. In lab tests, the materials were able to extract orders of magnitude more of the contaminants from water than the currently used standard materials, activated carbon or granular activated carbon.

While the new work serves as a proof of principle, Marelli says, the team plans to continue working on improving the material, especially in terms of durability and availability of source materials. While the silk proteins used can be available as a byproduct of the silk textile industry, if this material were to be scaled up to address the global needs for water filtration, the supply might be insufficient. Also, alternative protein materials may turn out to perform the same function at lower cost.

Initially, the material would likely be used as a point-of-use filter, something that could be attached to a kitchen faucet, Zhang says. Eventually, it could be scaled up to provide filtration for municipal water supplies, but only after testing demonstrates that this would not pose any risk of introducing any contamination into the water supply. But one big advantage of the material, he says, is that both the silk and the cellulose constituents are considered food-grade substances, so any contamination is unlikely.

“Most of the normal materials available today are focusing on one class of contaminants or solving single problems,” Zhang says. “I think we are among the first to address all of these simultaneously.”

“What I love about this approach is that it is using only naturally grown materials like silk and cellulose to fight pollution,” says Hannes Schniepp, professor of applied science at the College of William and Mary, who was not associated with this work. “In competing approaches, synthetic materials are used — which usually require only more chemistry to fight some of the adverse outcomes that chemistry has produced. [This work] breaks this cycle! ... If this can be mass-produced in an economically viable way, this could really have a major impact.”

The research team included MIT postdocs Hui Sun and Meng Li, graduate student Maxwell Kalinowski, and recent graduate Yunteng Cao PhD ’22, now a postdoc at Yale University. The work was supported by the U.S. Office of Naval Research, the U.S. National Science Foundation, and the Singapore-MIT Alliance for Research and Technology.

Co-friendly textiles without PFAS Image: Empa
22.04.2024

Co-friendly textiles without PFAS

Rain jackets, swimming trunks or upholstery fabrics: Textiles with water-repellent properties require chemical impregnation. Although fluorine-containing PFAS chemicals are effective, they are also harmful to human health and accumulate in the environment. Empa researchers are now developing a process with alternative substances that can be used to produce environmentally friendly water-repellent textile fibers. Initial analyses show: The "good" fibers repel water more effectively and dry faster than those of conventional products.

Rain jackets, swimming trunks or upholstery fabrics: Textiles with water-repellent properties require chemical impregnation. Although fluorine-containing PFAS chemicals are effective, they are also harmful to human health and accumulate in the environment. Empa researchers are now developing a process with alternative substances that can be used to produce environmentally friendly water-repellent textile fibers. Initial analyses show: The "good" fibers repel water more effectively and dry faster than those of conventional products.

If swimming trunks are to retain their shape after swimming and to dry quickly, they must combine two properties: They must be elastic and must not soak up water. Such a water-repellent effect can be achieved by treating the textiles with chemicals that give the elastic garment so-called hydrophobic properties. In the 1970s, new synthetic fluorine compounds began to be used for this purpose – compounds that seemed to offer countless application possibilities, but later turned out to be highly problematic. This is because these fluorocarbon compounds, PFAS for short, accumulate in the environment and are harmful to our health (see box). Empa researchers are therefore working with Swiss textile companies to develop alternative environmentally friendly processes that can be used to give fibers a water-repellent finish. Dirk Hegemann from Empa's Advanced Fibers laboratory in St. Gallen explains the Innosuisse-funded project: "We use so-called highly cross-linked siloxanes, which create silicone-like layers and – unlike fluorine-containing PFAS – are harmless."

Empa's plasma coating facilities range from handy table-top models to room-filling devices. For the coating of textile fibers, the siloxanes are atomized and activated in a reactive gas. They thereby retain their functional properties and enclose the textile fibers in a water-repellent coating that is only 30 nanometers thin. Fibers coated this way can then be processed into water-repellent textiles of all kinds, for example garments or technical textiles such as upholstery fabrics.

The advantage over conventional wet-chemical processes: Even with complex structured textiles, the seamless distribution of the hydrophobic substances is guaranteed right into all turns of the intertwined fibers. This is crucial, because even a tiny wettable spot would be enough for water to penetrate into the depths of a pair of swimming trunks, preventing the garment from drying quickly. "We have even succeeded in permanently impregnating more demanding, elastic fibers with the new process, which was previously not possible," says Hegemann.

Great interest from industry
In initial laboratory analyses, textiles made from the new fibers with an environmentally friendly coating are already performing slightly better than conventional PFAS-coated fabrics. They absorb less water and dry faster. However, the miraculous properties of the fluorine-free coating only really come into their own after the textiles have been washed several times: While the performance of conventional PFAS coatings in stretchy textiles declines considerably after repeated wash cycles, the fluorine-free fibers retain their water-repellent properties.

Hegemann and his team are now working on scaling up the fluorine-free laboratory process into efficient and economically viable industrial processes. "The industry is very interested in finding sustainable alternatives to PFAS," says Hegemann. The Swiss textile companies Lothos KLG, beag Bäumlin & Ernst AG and AG Cilander are already on board when it comes to developing environmentally friendly fluorine-free textiles. "This is a successful collaboration that combines materials, fiber technology and plasma coating and leads to an innovative, sustainable and effective solution," says Dominik Pregger from Lothos. And Bernd Schäfer, CEO of beag, adds: "The technology is environmentally friendly and also has interesting economic potential."

More information:
Empa PFAS Plasma Fibers
Source:

Dr. Andrea Six, EMPA

Firefighter Photo: 12019 at Pixabay
11.12.2023

Study tests firefighter turnout gear with, without PFAS


Transitioning away from per- and polyfluoroalkyl substances (PFAS), which offer water- and oil-repelling properties on the outer shells of firefighter turnout gear, could bring potential performance tradeoffs, according to a new study from North Carolina State University.

The study showed that turnout gear without PFAS outer shell coatings were not oil-repellent, posing a potential flammability hazard to firefighters if exposed to oil and flame, said Bryan Ormond, assistant professor of textile engineering, chemistry and science at NC State and corresponding author of a paper describing the research.

“All oil repellents can also repel water, but all water repellents don’t necessarily repel oil,” Ormond said. “Diesel fuel is really difficult to repel, as is hydraulic fluid; in our testing, PFAS-treated materials repel both. In our tests, turnout gear without PFAS repelled water but not oil or hydraulic fluid.


Transitioning away from per- and polyfluoroalkyl substances (PFAS), which offer water- and oil-repelling properties on the outer shells of firefighter turnout gear, could bring potential performance tradeoffs, according to a new study from North Carolina State University.

The study showed that turnout gear without PFAS outer shell coatings were not oil-repellent, posing a potential flammability hazard to firefighters if exposed to oil and flame, said Bryan Ormond, assistant professor of textile engineering, chemistry and science at NC State and corresponding author of a paper describing the research.

“All oil repellents can also repel water, but all water repellents don’t necessarily repel oil,” Ormond said. “Diesel fuel is really difficult to repel, as is hydraulic fluid; in our testing, PFAS-treated materials repel both. In our tests, turnout gear without PFAS repelled water but not oil or hydraulic fluid.

“Further, oils seem to spread out even more on the PFAS-free gear, potentially increasing the hazard.”

PFAS chemicals – known as forever chemicals because of their environmental persistence – are used in food packaging, cookware and cosmetics, among other uses, but have recently been implicated in higher risks of cancer, higher cholesterol levels and compromised immune systems in humans. In response, firefighters have sought alternative chemical compounds – like the hydrocarbon wax coating used in the study – on turnout gear to repel water and oils.

Besides testing the oil- and water-repelling properties of PFAS-treated and PFAS-free outer garments, the NC State researchers also compared how the outer shells aged in job-related exposures like weathering, high heat and repeated laundering, and whether the garments remained durable and withstood tears and rips.

The study showed that PFAS-treated and PFAS-free outer shells performed similarly after exposure to UV rays and various levels of heat and moisture, as well as passes through heating equipment – similar to a pizza oven – and through washing machines.

“Laundering the gear is actually very damaging to turnout gear because of the washing machine’s agitation and cleaning agents used,” Ormond said.

“We also performed chemical analyses to see what’s happening during the weathering process,” said Nur Mazumder, an NC State doctoral student in fiber and polymer science and lead author of the paper. “Are we losing the PFAS chemistries, the PFAS-free chemistries or both when we age the garments? It turns out that we lost significant amounts of both of these finishes after the aging tests.”

Both types of garments performed similarly when tested for strength against tearing the outer shell fabric. The researchers say the PFAS and PFAS-free coatings didn’t seem to affect this attribute.

Ormond said that future work will explore how much oil repellency is needed by firefighters out in the field.
“Even with PFAS treatment, you see a difference between a splash of fluid and soaked-in fluid,” Ormond said. “For all of its benefits, PFAS-treated gear, when soaked, is dangerous to firefighters. So we need to really ask ‘What do firefighters need?’ If you’re not experiencing this need for oil repellency, there’s no worry about switching to non-PFAS gear. But firefighters need to know the non-PFAS gear will absorb oil, regardless of what those oils are.”

Andrew Hall, another NC State doctoral student in fiber and polymer science and co-author on the paper, is also testing dermal absorption, or taking the aged outer shell materials and placing them on a skin surrogate for a day or two. Are outer shell chemicals absorbed in the skin surrogate after these admittedly extreme exposure durations?

“Firefighting as a job is classified as a carcinogen but it shouldn’t have to be,” Ormond said. “How do we make better gear for them? How do we come up with better finishes and strategies for them?

“These aren’t just fabrics,” Ormond said. “They are highly engineered pieces of material that aren’t easily replaced.”

The paper appears in the Journal of Industrial Textiles. Funding for the research came from the Federal Emergency Management Agency’s Assistance to Firefighters Grants Program.

Source:

North Carolina State University, Mick Kulikowski

The plasma atmosphere is clearly visible in the reactor through the characteristic glow and flashes of light. © Fraunhofer IGB The plasma atmosphere is clearly visible in the reactor through the characteristic glow and flashes of light.
16.05.2023

Wastewater treatment: Plasma against toxic PFAS chemicals

Harmful PFAS chemicals can now be detected in many soils and bodies of water. Removing them using conventional filter techniques is costly and almost infeasible. Researchers at the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB are now successfully implementing a plasma-based technology in the AtWaPlas joint research project. Contaminated water is fed into a combined glass and stainless steel cylinder where it is then treated with ionized gas, i.e. plasma. This reduces the PFAS molecular chains, allowing the toxic substance to be removed at a low cost.

Harmful PFAS chemicals can now be detected in many soils and bodies of water. Removing them using conventional filter techniques is costly and almost infeasible. Researchers at the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB are now successfully implementing a plasma-based technology in the AtWaPlas joint research project. Contaminated water is fed into a combined glass and stainless steel cylinder where it is then treated with ionized gas, i.e. plasma. This reduces the PFAS molecular chains, allowing the toxic substance to be removed at a low cost.

Per- and polyfluoroalkyl substances (PFAS) have many special properties. As they are thermally and chemically stable as well as resistant to water, grease and dirt, they can be found in a large number of everyday products: Pizza boxes and baking paper are coated with them, for example, and shampoos and creams also contain PFAS. In industry they serve as extinguishing and wetting agents, and in agriculture they are used in plant protection products. However, traces of PFAS are now also being detected where they should not be found: in soil, rivers and groundwater, in food and in drinking water. This is how the harmful substances end up in the human body. Due to their chemical stability, eliminating these so-called “forever chemicals” has been almost impossible up to now without considerable effort and expense.

The AtWaPlas joint research project aims to change that. The acronym stands for Atmospheric Water Plasma Treatment. The innovative project is currently being run at the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB in Stuttgart in cooperation with the industrial partner HYDR.O. Geologen und Ingenieure GbR from Aachen. The aim is to treat and recover PFAS-contaminated water using plasma treatment.

The research team led by Dr. Georg Umlauf, an expert in functional surfaces and materials, utilizes plasma’s ability to attack the molecular chains of substances. The electrically conductive gas consisting of electrons and ions is generated when high voltage is applied. “Our experiments with plasma have been successful in shortening the PFAS molecule chains in water. This is a significant step towards efficiently removing these stubborn pollutants,” Umlauf is happy to report.

Water cycle in a stainless steel cylinder
Fraunhofer researchers are using a cylindrical construction for this plasma process. Inside is a stainless steel tube, which serves as the ground electrode of the electrical circuit. The outer copper mesh then acts as a high-voltage electrode and is protected on the inside by a glass dielectric. A very small gap is left between the two, which is filled with an air mixture. This air mixture is converted into plasma when a voltage of several kilovolts is applied. It is visible to the human eye by its characteristic glow and discharge as flashes of light.

During the purification process, the PFAS-contaminated water is introduced at the bottom of the stainless steel tank and pumped upwards. It then travels down through the gap between the electrodes, passing through the electrically active plasma atmosphere. The plasma breaks up and shortens the PFAS molecule chains as it discharges. The water is repeatedly pumped through both the steel reactor and the plasma discharge zone in a closed circuit, reducing the PFAS molecule chains further each time until they are completely mineralized. “Ideally, the harmful PFAS substances are eliminated to the point that they can no longer be detected in mass spectrometric measurements. This also complies with the strict German Drinking Water Ordinance (TrinkwV) regulations regarding PFAS concentrations,” says Umlauf.

The technology developed at the Fraunhofer Institute has a key advantage over conventional methods such as active carbon filtering: “Active carbon filters can bind the harmful substances, but they are unable to eliminate them. This means that the filters must be replaced and disposed of regularly. The AtWaPlas technology, on the other hand, is capable of completely eliminating the harmful substances without any residue and is very efficient and low-maintenance,” explains Fraunhofer expert Umlauf.

Real water samples instead of synthetic laboratory samples
In order to ensure true feasibility, the Fraunhofer researchers are testing the plasma purification under more challenging conditions. Conventional test methods involve using perfectly clean water and PFAS solutions that have been synthetically mixed in the laboratory. However, the research team in Stuttgart is using “real” water samples that come from PFAS-contaminated areas. The samples are collected by the project partner HYDR.O. Geologen und Ingenieure GbR from Aachen. The company specializes in cleaning up contaminated sites and also carries out hydrodynamic simulations.

The real water samples that Umlauf and his team work with therefore contain PFAS as well as other particles, suspended solids and organic turbidity. “This is how we verify the purification efficiency of AtWaPlas, not only using synthetic laboratory samples, but also under real conditions with changing water qualities. The process parameters can be adapted and further developed at the same time,” explains Umlauf.

This plasma method can also be used to break down other harmful substances, including pharmaceutical residues in wastewater, pesticides and herbicides, but also industrial chemicals such as cyanides. AtWaPlas can also be used to treat drinking water in mobile applications in an environmentally friendly and cost-effective way.

The AtWaPlas joint research project launched in JuIy 2021. After a successful series of pilot-scale tests with a 5 liter reactor, the Fraunhofer team is now working with the joint research partner to further optimize the process. Georg Umlauf states: “Our current objective is to completely eliminate toxic PFAS by extending process times and increasing the number of circulations in the tank. We also want to make the AtWaPlas technology available for practical application on a larger scale.” The future could see corresponding plants set up as standalone purification stages in sewage treatment plants or used in portable containers on contaminated open-air sites.

Source:

Fraunhofer-Institut für Grenzflächen- und Bioverfahrenstechnik IGB