Continuous removal and recovery of tellurium in an upflow anaerobic granular sludge bed reactor

Continuous removal of tellurite (TeO32−) from synthetic wastewater and subsequent recovery in the form of elemental tellurium was studied in an upflow anaerobic granular sludge bed (UASB) reactor operated at 30 °C. The UASB reactor was inoculated with anaerobic granular sludge and fed with lactate as carbon source and electron donor at an organic loading rate of 0.6 g COD L−1 d−1. After establishing efficient and stable COD removal, the reactor was fed with 10 mg TeO32−. L−1 for 42 d before increasing the influent concentration to 20 mg TeO32−. L−1. Tellurite removal (98 and 92%, respectively, from 10 and 20 mg Te. L−1) was primarily mediated through bioreduction and most of the removed Te was retained in the bioreactor. Characterization using XRD, Raman spectroscopy, SEM-EDX and TEM confirmed association of tellurium with the granular sludge, typically in the form of elemental Te(0) deposits. Furthermore, application of an extracellular polymeric substances (EPS) extraction method to the tellurite reducing sludge recovered up to 78% of the tellurium retained in the granular sludge. This study demonstrates for the first time the application of a UASB reactor for continuous tellurite removal from tellurite-containing wastewater coupled to elemental Te(0) recovery.