Polluted Water as a Source of Fertilizer

It may well be possible to remove nitrate from polluted groundwater and at the same time produce ammonia in a sustainable way, according to PhD candidate Phebe van Langevelde and Professor Marc Koper of the Leiden Institute of Chemistry in Joule on January 26, 2021. Together with a German colleague, they conducted a literature study into the possibilities.

Two birds, one stone

Nitrate is a pollutant that originates from traffic, industry, and agriculture. It is a nitrogen compound: NO3-. Environmental technologists are looking for a method to convert this into nitrogen gas, N2, but that turns out to be difficult. Ammonia, the nitrogen compound NH3, is an important raw material in chemistry, for instance to produce fertilizer. It is made from nitrogen gas, but that process takes place at high pressure and temperature and therefore requires use of fossil fuels.

A solution for both problems would be to combine these processes and convert nitrate directly into ammonia, according to Phebe van Langevelde. With her colleagues, she evaluated the options. “That total picture is new,” she says.

Bacteria versus elektrochemistry

The current method to convert nitrate to nitrogen gas uses bacteria. Electrochemistry could be a cheaper and more robust alternative. The starting material is dissolved in a liquid in which two electrodes are placed, coated with a catalyst. When voltage is applied to the electrodes, chemical reactions take place at their surface, depending on the catalyst applied. “So far, it has not been possible to convert nitrate into pure nitrogen gas in this way. Too many other products are formed,” Van Langevelde tells. “It turns out to be much easier to convert nitrate into ammonia, for which suitable catalysts have been designed in the last few years, based on new materials.”

Sustainable and safe

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