Concurrent tellurite reduction, biogenesis of elemental tellurium nanostructures and biological nutrient removal in aerobic granular sludge sequencing batch reactor

Abstract

This study investigated the metabolic potential of aerobic granular sludge (AGS) to simultaneously remove tellurium oxyanion (tellurite, TeO32-), COD, ammonium-nitrogen and phosphorus in a sequencing batch reactor (SBR). AGS readily converted soluble and toxic tellurite to biogenic elemental tellurium (Bio-Te0) by following first-order reaction. Bio-Te0 was dark black in colour and largely entrapped in the granules. Although endogenous substrates acted as source of electrons for tellurite reduction, it was sustained by supplying exogenous electron donor. A lab-sale SBR was seeded with AGS and operated at varied initial tellurite concentrations for 185 days to investigate tellurite reduction and biological nutrient removal (BNR). Stable removal efficiencies of > 98% Te was achieved from simulated wastewater containing 0.01–1 mM tellurite. Soluble tellurite was converted to Bio-Te0 and retained in the AGS. SEM-EDS, XRD and Raman spectroscopy confirmed formation of Bio-Te0 and its association with the granules. Enrichment of Bacteroidia, Petrimonas sp. and several other tellurite-reducing bacteria was confirmed by 16S rRNA gene sequencing. Enrichment of ammonium oxidizing bacteria, elimination of nitrite oxidizing bacteria and profiles of reactive-nitrogen compounds suggested occurrence of nitriation-denitriation pathway. Although ammonium removal was inhibited by tellurite, recovery occurred much quickly in the presence of up to 0.1 mM tellurite. Higher P removal under tellurite-reducing condition was linked to hydroxyapatite precipitation as confirmed by EDS and P-fractionation. Efficient BNR under toxic pollutant conditions and excellent metal(loid) immobilization capabilities implicate prospective use of AGS technology in metal-laden waste management and metal(loid) biorecovery applications.