Natural materials remove pollutants from water

PFAS is a family of problematic pollutants also known as “forever chemicals” because of their chemical stability and environmental persistence. These substances can be found in a large range of products, including Teflon pan coating, fire-fighting foam, flame retardants, and water repellent additives. They reach the groundwater in various ways, including agricultural irrigation using treated wastewater and fire-fighting substances seeping into the soil. As a result of their chemical stability, they remain intact in the ground for a long time, leading to extensive contamination of drinking sources, which in turn significantly increases human exposure.

International studies have demonstrated the many health risks posed by exposure to PFAS, including cancer, heart and liver disease, fertility problems, birth defects, and damage to the immune system. Consequently, Israel has begun monitoring these substances. In fact, last summer the extraction of potable water in the Krayiot region was stopped following the discovery of a high PFAS concentration, writes Technion – Israel Institute of Technology – in a press release.

Today, removing these substances from drinking water is accomplished through relatively simple and inexpensive adsorption techniques. However, these methods are not sufficiently efficient, and, most importantly, they only transfer the pollutants from the water to the adsorbent material – which requires additional purification steps to get rid of the toxic adsorbed substances. Furthermore, these methods are not selective: they can also remove substances that are essential for people’s health.

Combining two pre-existing methods

There are two new and promising solutions: using oxidation processes and using targeted polymers that efficiently adsorb the polluting substances. Yet, until now these technologies have not exhibited satisfactory results.

The new research examined the possibility of combining these two methods – separating the pollutants with special polymers, and then using advanced oxidation processes to eliminate them. The findings indicate that proper planning leads to high efficiency under a wide range of acidity (pH) and salinity. The method depicted in the article shows the removal of seven types of PFAS – even when all of them are found in the same unit of fluid – at a level of efficiency that approaches 90%, and it does so within a few minutes.

Cleaning water with natural materials

The system described in the article is based on natural materials that are both safe and inexpensive. The researchers used ubiquitous soil minerals – iron oxides and clays, together with cyclodextrin polymers. The clay-iron-polymer composites act as accelerators that confine the PFAS on the surface and then accelerate the oxidation process that destroys the pollutants into non-toxic substances (fluoride ions, water, and carbon dioxide). This combination efficiently removes the PFAS and does not release unwanted substances in water used for drinking.

In their article, the researchers show that this system makes it unnecessary to carry out complementary processes such as heating, UV radiation, and using sound waves, which make the task more complicated and more expensive.

The research was conducted in the Soil Chemistry Laboratory in the Faculty of Civil and Environmental Engineering. The researchers wish to thank the Lady Davis Foundation for Samapti Kundu’s post-doctoral research grant.

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