Cleaning up with clay

14 December 2020

Researchers investigate a less costly route for protecting waterways from pharmaceutical contaminants.

Scientists from University of Science and Technology Houari Boumediene Algeria, and NOVA School of Science and Technology, Portugal, have taken bentonite clay and modified it to create what could one day be a cheaper route for removing synthetic oestrogens and other pharmaceutical contaminants from water.

The impact of synthetic oestrogens, present in surface water, on the growth and reproduction of fish is well documented. However, the processes for removing such contaminants are expensive.

The researchers have taken bentonite clay and modified it with either sodium, sodium and iron or sodium and L-tryptophan. These synthetic clays were characterised to assess structural changes, compared with the natural material.  The team then compared the ability of these modified clays to adsorb 17α-ethynylestradiol (17EE), a common constituent of birth control pills excreted in urine and found in surface waters at ng/L levels.  They have so far found that the maximum adsorption from an initial concentration of 10mg/L of 17EE was 4.2mg/g using bentonite modified with sodium and L-tryptophan.

The researchers said bentonite was selected for the study due to its cation exchange capacity, hydration, swelling and the presence of active adsorption sites and hydrophilicity that allow easy binding of biomolecules and adsorption of a great diversity of substances.
Bentonite costs €0.17/kg, while activated carbon, commonly used in existing purification processes costs, around €7/kg.

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