Through electrolysis we can neutralize soil contaminants

The Federal Institute of Technology in Zurich has developed an electrochemical method for breaking down contaminants, recovering harmless salt and other useful products for the chemical industry. This frees the soil from the presence of stable toxins

by Matteo Cavallito

A technical solution based on electrolysis could tackle soil pollution by transforming contaminants into useful, harmless products. The method has been proposed by researchers at ETH Zurich, the Swiss Federal Institute of Technology in Zurich, who have focused on the treatment of persistent organic pollutants, the substances contained in products that are no longer in use—such as certain insecticides that were once widely available—which can accumulate in soil, water, and animal fat tissue, thus entering the human food chain.

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Raw materials are recovered from contaminants

For some time now, various scientists have been developing techniques to remediate contaminated sites by intercepting and neutralizing these highly stable substances. However, the solution proposed by Swiss researchers goes further: instead of simply breaking down pollutants, the method developed by ETH Zurich aims to convert them into valuable raw materials for the chemical industry.

According to a statement, the system allows the carbon skeleton of these substances to be recycled and reused, while at the same time sequestering their halogen atoms in the form of harmless inorganic salt. This method, researchers explain, differs from all others previously used, which, in contrast, are ultimately energy inefficient, expensive and harmful to the environment.

Electrolysis is the solution

“The key advance of this new technology is the use of alternating current to sequester the problematic halogen atoms as innocuous salts such as NaCl (table salt), while still generating valuable hydrocarbons,” explained Bill Morandi, professor of synthetic organic chemistry at ETH. Use of electrolysis is therefore crucial, as it not only separates the salts but also allows useful substances such as benzene, diphenylethane, and cyclododecatriene to be extracted.

These are intermediate by-products that are highly requested in the chemical industry, for example for the production of plastics, paints, coatings, and pharmaceutical applications.

The reactor used in the process, the scientists explain, consists of an undivided electrolytic cell in which dimethyl sulfoxide (DMSO) is used as a solvent. This, in turn, is a by-product of the pulp processing involved in paper production. The process, which has already been successfully tested on past contaminants such as lindane and DDT, the researchers explain, can be applied to both pure substances and mixtures from polluted soils that do not require further separation processes.

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A solution to contamination

This method appears promising for solving contamination problems that remain unresolved. In this sense, attention would focus not only on pollutants that are no longer on the market but also, inevitably, on other substances that, although not explicitly mentioned by ETH researchers, remain the focus of interest in remediation operations.

Among these, fluorine-based compounds contained in pesticides such as PFASs (perfluoroalkyl and polyfluoroalkyl substances) stand out. These are defined, not surprisingly, as ‘forever chemicals’, an expression that highlights their proverbial and dangerous stability.

According to a study, the half-life of certain fluorinated compounds – i.e., the time it takes for their presence in the environment to be halved after spraying – can reach two and a half years. This is less than the time required for some older pesticides such as DDT, but still 15 times higher than the 60-day limit set by the US Environmental Protection Agency (EPA) for defining a pollutant as ‘persistent’.