A team of German researchers has found that the biomass of some exotic photosynthetic cyanobacteria can efficiently absorb rare earth elements from wastewater.
In a paper published in the journal Frontiers in Bioengineering and Biotechnology, the scientists say that ideal wastewaters for this purpose are those derived from mining, metallurgy, or the recycling of e-waste. The absorbed REEs can afterwards be washed from the biomass and collected for reuse.
“Here we optimized the conditions of REE uptake by the cyanobacterial biomass and characterized the most important chemical mechanisms for binding them. These cyanobacteria could be used in future eco-friendly processes for simultaneous REE recovery and treatment of industrial wastewater,” Thomas Brück, a professor at the Technical University of Munich and the study’s last author, said in a media statement.
Brück explained that biosorption is a metabolically passive process for the fast, reversible binding of ions from aqueous solutions to biomass.
He and colleagues measured the potential for biosorption of the REEs lanthanum, cerium, neodymium, and terbium by 12 strains of cyanobacteria in laboratory culture. Most of these strains had never been assessed for their biotechnological potential before. They were sampled from highly specialized habitats such as arid soils in Namibian deserts, the surface of lichens around the world, natron lakes in Chad, crevices in rocks in South Africa, or polluted brooks in Switzerland.
The authors found that an uncharacterized new species of Nostoc had the highest capacity for biosorption of ions of these four REEs from aqueous solutions, with efficiencies between 84.2 and 91.5 mg per g biomass, while Scytonema hyalinum had the lowest efficiency at 15.5 to 21.2 mg per g. Also efficient were Synechococcus elongates, Desmonostoc muscorum, Calothrix brevissima, and an uncharacterized new species of Komarekiella.
Biosorption was found to depend strongly on acidity: it was highest at a pH of between five and six and decreased steadily in more acid solutions. The process was most efficient when there was no “competition” for the biosorption surface on the cyanobacteria biomass from positive ions of other, non-REE metals such as zinc, lead, nickel, or aluminum.