Recovery of Elemental Tellurium Nanoparticles by the Reduction of Tellurium Oxyanions in a Methanogenic Microbial Consortium

This research focuses on the microbial recovery of elemental tellurium (Te⁰) from aqueous streams containing soluble tellurium oxyanions, tellurate (Te^VI), and tellurite (Te^IV). An anaerobic mixed microbial culture occurring in methanogenic granular sludge was able to biocatalyze the reduction of both Te oxyanions to produce Te⁰ nanoparticles (NPs) in sulfur-free medium. Te^IV reduction was seven times faster than that of Te^VI, such that Te^IV did not accumulate to a great extent during Te^VI reduction. Endogenous substrates in the granular sludge provided the electron equivalents required to reduce Te oxyanions; however, the reduction rates were modestly increased with an exogenous electron donor such as H₂. The effect of four redox mediators (anthraquinone-2,6-disulfonate, hydroxocobalamin, riboflavin, and lawsone) was also tested. Riboflavin increased the rate of Te^IV reduction eleven-fold and also enhanced the fraction Te recovered as extracellular Te⁰ NPs from 21% to 64%. Lawsone increased the rate of Te^VI reduction five-fold, and the fraction of Te recovered as extracellular material increased from 49% to 83%. The redox mediators and electron donors also impacted the morphologies and localization of Te⁰ NPs, suggesting that NP production can be tailored for a particular application.