French and Swiss scientists have used computer simulations to shed light on how organic waste can be used to remove toxic metals from drinking water.
Pollutant levels in freshwater environments have steadily increased in recent years. The leakage of pesticides, chemicals, pharmaceuticals as well as household waste into groundwater is a matter of concern, especially in developing countries where clean water has become an invaluable resource. In these regions, water reservoirs are often contaminated with heavy metals such as lead, cadmium or mercury. Their impact on human health is often seriously detrimental: lead, for example, can accumulate in bones, teeth and brain tissue and cause chronic intoxication which can lead to deterioration of the nervous system.
Yet, according to the 2017 World Water Development report, only 20% of global wastewater is properly treated before being discharged into natural water bodies.
With populations about to explode, water purification technologies are more important than ever. In the past, prohibitive costs have made these innovations, ranging from membrane filtration and activated carbon absorption to electrocoagulation, less feasible for governments looking to implement clean water solutions.
Wanda Andreoni, professor emeritus of physics at the Federal Polytechnic School of Lausanne (EPFL), Switzerland, plans to change this state of affairs.
Over the past two decades, the physicist has been experimenting with an inexpensive, low-tech alternative to conventional water purification technologies. By using bio-waste such as fruit peels, coffee grounds or used tea bags, he hopes to remove metal toxins from fresh water.
âThere is overwhelming evidence that natural waste can effectively capture heavy metals from water. Nonetheless, related research efforts have been modest, âhe said.
A 2018 study conducted in India proved that spent coffee grounds could remove lead from contaminated water with a 90% success rate while a 2020 study in Turkey showed that brewed tea waste could be used to remove four different types of heavy metals from a water sample. .
Professor Andreoni and his colleagues performed molecular simulations, using PRACE supercomputing resources, to shed light on how organic waste manages to capture toxins from contaminated water. The team chose to study the molecular structure of hemicellulose, which is made up of several different sugar chains. The results indicated that the free energy barriers for hemicellulose to adsorb lead ions from water are negligible. This means that the polysaccharide can easily absorb lead ions from water and is an effective agent for removing heavy metals from water.
The simulations also identified the chemical groups responsible for the efficient binding of heavy metals in hemicellulose, which are the carboxylate groups of sugars (R-COO-) and, to a lesser extent, their hydroxy groups (R-OH).
According to Professor Andreoni, future research on the subject must involve a mixture of laboratory experiments and computer simulations, the aim being to develop new bio-inspired materials and processes that help ensure a clean water supply in developing countries.
âOur belief that this can be an effective strategy lies in the fact that such collaborative efforts have been successfully applied in an equally difficult area: drug discovery. “