Engineered bacteria synthesise palladium biosorbent

Genetically modified Escherichia coli can synthesise a protein that could work as a palladium biosorbent to recover the precious metal from polluted water, new research shows.

Catalytic converters are hugely important for controlling car exhaust fumes but small amounts of the palladium, and other platinum group elements, that form their main active component are leaking into and contaminating the environment. ‘Global palladium resources are scarce,’ warns sustainability expert Magdalena Titirici, of Queen Mary University of London, UK, who was not involved in the study. ‘Therefore recovering noble metals such as palladium from the urban environment using low cost and environmentally friendly adsorbents is of major importance.’

Currently, palladium is extracted from the environment through methods that include acid precipitation, adsorption, ion exchange and electrolysis. However, these processes can be energy intensive and involve corrosive solutions that require proper chemical waste disposal. They are also neither selective nor efficient for low concentrations of palladium.

Now, Ian Yunus and Shen-Long Tsai from the National Taiwan University of Science and Technology have made a reusable adsorbent that is selective and efficient in recovering palladium without generating large volumes of hazardous waste. ‘We first adapt E. coli to produce a biomolecule, which is the key component of this adsorbent and has two major functions; one to capture palladium; the other to help rapidly remove the metal from the environment. Once the E. coli produces enough biomolecules, the cells are broken down via sonication. Cellulose is then added to the crude cell lysate and the biomolecule self-assembles onto the cellulose to form the adsorbent,’ they explain.

‘Holistic approaches to the life cycle of elements – for example, extraction, use and recovery – must be developed to meet the challenges of elemental sustainability,’ comments green chemist Andrew Hunt from the University of York, UK. ‘Biosorption is a potential technology for the benign recovery of elements from aqueous waste streams. Once demonstrated at scale, these materials may aid in closing loops with regards to the sustainability of elements.’