Bioreduction of tellurite to elemental tellurium by Pseudomonas mendocina MCM B-180 and its practical application J.M. Rajwade, K.M. Paknikar * Division of Microbial Sciences, Agharkar Research Institute, G.G. Agarkar Road, Pune 411 004, India Abstract A microbiological process using Pseudomonas mendocina MCM B-180 was developed for the removal of tellurite from solutions. During the process tellurite was transformed into metallic tellurium. The process, when carried out in a 2-l continuously stirred tank reactor in the presence of sucrose and diammonium hydrogen phosphate as nutrients, removed 10 mg/l tellurium in 12 h with an efficiency exceeding 99.8%. The process could sustain wide variations in pH (5.5 – 8.5), temperatures (25–45 jC) and initial tellurium concentration (10 – 100 mg/l). An integrated biosorption – bioreduction process for the treatment of waste photovoltaic modules demonstrates the utility of microbial tellurite reduction. D 2003 Published by Elsevier B.V. Keywords: Tellurite; Bioreduction; Pseudomonas mendocina; Photovoltaic cells 1. Introduction Tellurium and its compounds have been used primarily as an additive to steel to increase its ductil- ity, as a brightner in electroplating baths, as an additive to catalysts for the cracking of petroleum and as a coloring material in the manufacture of colored glasses. The metalloid tellurium is known to be toxic to microorganisms. The toxicity of tellurite may be related to its ability to act as a strong oxidant. Strains of Corynebacterium diphtheriae, Strepto- coccus faecalis, Staphylococcus aureus, Alcaligenes faecalis and Alcaligenes denitrificans and some members of the family Enterobacteriaceae were, however, reported to be resistant to tellurite (Walter and Taylor, 1992). The biochemical basis for resis- tance has been studied by many workers. In one of the recent studies carried out on Thermus sp. (Chiong et al., 1988), three different protein fractions with tellurite reducing activities were purified and characterized. It was proposed that reduction was a mechanism of tolerance to this salt. van Iterson and Leene (1964a,b) reported that tellurite could be used to locate the intracellular oxidoreductases as these enzymes are capable of reducing tellurite. Tucker et al. (1962) reported that even susceptible bacteria growing on subinhibitory concentrations of tellurite produce jet-black colonies as a result of the reduc- tion of tellurite and the formation of intracellular granules of metallic tellurium. Bioreduction of tellurite has, however, not been studied with respect to the recovery of tellurium from industrial wastes. The present paper deals with the studies carried out in our laboratory for the develop- ment of a microbiological tellurite reduction process. 0304-386X/$ - see front matter D 2003 Published by Elsevier B.V. doi:10.1016/S0304-386X(03)00162-2 * Corresponding author. Tel.: +91-20-5654357; fax: +91-20- 5651542. E-mail address: paknikar@vsnl.com (K.M. Paknikar). www.elsevier.com/locate/hydromet Hydrometallurgy 71 (2003) 243 – 248