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Author: Laura Cooper2021-11-05T11:04:00 00:00

Field studies conducted in Peru have shown that membranes made of milk protein can remove enough arsenic from tap water to reach the recommended safe range for drinking. Not only that, the technology is inexpensive and requires the least energy.

Arsenic pollution is a serious problem in Peru; in some areas, arsenic levels found in groundwater have caused arsenic concentrations in drinking water to exceed 100 times the safe level set by the World Health Organization. The presence of arsenic in the hair and nails of people living in these areas indicates that they have been exposed to this toxin for decades, increasing the risk of various cancers and other diseases.

In 2016, Raffaele Mezzenga and Sreenath Bolisetty from the Swiss Federal Institute of Technology Zurich developed a filtration system using activated carbon and milk protein fiber. They use heat and low pH to convert whey (the main protein in milk and a byproduct of the cheese manufacturing industry) into nanofibers. The amino acids on the surface of whey nanofibers can be used to bind metal or metalloid ions, including arsenic. Therefore, membranes or particulate media using nanofibers as active adsorbents can be used as filters to clean contaminated water.

Source: © Sreenath Bolisetty/ETH Zürich

The team tested milk protein-based systems in home (top) and community filtration units

Now, scientists at ETH Zurich have tested their water filtration systems in various real-life scenarios: household units with pure membrane systems or a combination of membranes and particles, and community-based pure particle units. The study involved three regions in Peru with different levels of arsenic pollution. In some areas, the high turbidity of water means that the membrane must be replaced when it becomes clogged, even if the adsorption site is not saturated. Therefore, users in these areas need to use sand filters for water pretreatment.

'This research is very important because it proves on the spot that this technology can effectively provide safe drinking water for people living in areas severely affected by arsenic pollution. We have performed a number of tasks to screen the overall situation of groundwater pollution by arsenic in Peru, thereby identifying some key areas for field research," Mezanga said.

Analysis of the treated water showed that 99.9% of the arsenic had been removed. "The results of this field study [show] that a filter device using milk protein nanofibers effectively removes arsenic below the WHO recommended standard [10ppb] and is expected to be more widely used," Helena Gomes, an environmental engineer at the university Commented. In Nottingham, England. 'We must also remember that the researchers only analyzed the arsenic concentration. There are many other important parameters of water quality-other metals, persistent organic pollutants and microorganisms.

Regenerating the system with an aqueous sodium hydroxide solution and then flushing with distilled water shows that the membranes used in the most severely affected areas can be reused. "Saturated filters or granular media must be treated according to the regulations of each country," Mezzenga explained. 'In the case of a suitable incinerator, incineration is the recommended way. In Peru, where arsenic comes from groundwater, the safe way to dispose of saturated membranes is through regulated landfills.

Current water treatment methods use reverse osmosis, exchange resin or ultrafiltration, but these technical systems are not suitable for middle-income countries such as Peru. Mezzenga is optimistic about making the filter easier to use, so that safe drinking water is available to the world, and stated that “the cost must be competitive with any available water purification technology, while providing safe drinking water with more sustainable The solution.” I can say that no energy is needed here, because the technology can simply be used for gravity-induced filtration of water instead of the energy-intensive requirements of reverse osmosis.

This article is open access

S Bolisetty, A Rahimi and R Mezzenga, environment. Science: Water Res. Technology, 2021, DOI: 10.1039/d1ew00456e

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