Isolation and characterization of bacteria capable of reducing tellurium oxyanions to insoluble elemental tellurium for tellurium recovery from wastewater

The recovery of tellurium as an important rare metal from wastes and wastewater must be promoted to satisfy its increasing demand for use in many industries. For development of a biological process for recovering tellurium from wastewater, three bacterial strains capable of reducing soluble tellurite into insoluble elemental tellurium were isolated from the drainage wastewater of a metal refinery plant. The bacterial strains, Stenotrophomonas maltophilia TI-1, Ochrobactrum anthropi TI-2 and O. anthropi TI-3, resisted up to 30 mM tellurite, and removed 86-89 % of 1 mM tellurite from water phase within 21 h in a reductive reaction. They showed a considerably higher tellurite removal rate than the previously reported tellurite-reducing bacteria. Tellurite-reducing activity was observed at 20-40 C, pH 6.2-8.5 and 0.05-5 % NaCl (0.1 mM/h at maximum). The tellurite-reducing activities of strains TI-2 and TI-3 were not considerably different from each other, however strain TI-1 showed higher tellurite-reducing activity at low temperatures, low pH and high NaCl concentrations than the other strains. Because deposits of elemental tellurium were formed on and free from the bacterial cells, it is possible to recover tellurium from the water phase by centrifugation, ultrafiltration, or coagulation following tellurite reduction. All bacterial strains isolated in this study are inferred to be great candidates to establish bacterial tellurium recovery processes from industrial wastewater containing high concentrations of tellurite.