Biomachining is the use of microorganisms to remove material from metal workpieces. It is a sustainable and environmentally friendly alternative to conventional chemical or physical machining processes. However, there are no industrial applications so far.

Estíbaliz Díaz-Tena, University of the Basque Country, Bilbao, Spain, and colleagues have developed two different strategies to promote the industrial implementation of the method. Firstly, they analyzed various methods to improve the preservation of biomachining microorganisms (freeze-drying, freezing, and drying). They found that freezing at –80 °C, using betaine as a cryoprotective agent, has the highest bacteria survival rate with a cell recovery of 40 %.

Secondly, the team developed a procedure for treating the liquid residue generated in the biomachining process. Here, Fe²⁺ and Cu²⁺ are removed in two consecutive steps by the precipitation of Fe(OH)₃ and Cu(OH)₂. The team was able to remove 99.9 % of iron and copper. This result has two advantages: not only is the remaining liquid residue more environmentally friendly, but the dissolved metals are recovered as high purity precipitates.

• Biomachining: Preservation of Acidithiobacillus ferrooxidans and treatment of the liquid residue,
  Estíbaliz Díaz-Tena, Naiara Rojo, L. Gurtubay, Adrián Rodríguez-Ezquerro, Luis Norberto López de Lacalle, Iñigo Oyanguren, Francisca Barbero, Ana Elías,
  Eng. Life Sci. 2016.
  DOI: 10.1002/elsc.201600124