ABSTRACT
80In this study, in situ and ex situ approaches were evaluated for bioremediation of seleniferous soils. As part of in situ remediation approach, effect of organic amendment and bioaugmentation was determined. The effect of soil amendment with different organic sources (fermentable, non-fermentable and non-hydrolysable electron donors) and bioaugmentation with anaerobic granular sludge was evaluated in soil microcosms for in situ reduction of Se oxyanions. Results showed no significant difference in the Se reduction profiles with or without organic amendment or bioaugmentation. This suggested that the indigenous Se reducing microorganisms and oxidisable organic carbon present in the soil are sufficient for in situ soil bioremediation. Moreover, ex situ recovery of selenium from the seleniferous soil was attempted. Ex situ approach involved evaluation of seleniferous soil leaching and Se-leachate treatment in an upflow anaerobic sludge blanket (UASB) reactor. In this ex situ approach, the seleniferous soil was leached and the resulting leachate was biologically treated in an UASB reactor with varying conditions of organic carbon supplementation. This approach has efficiently (90%) removed Se from the soil leachate and recovered from the anaerobic granular sludge. The treated Se-leachate leaving the UASB reactor contained Se at <5 μg L−1 which is in accordance with the USEPA guideline for the selenium discharge in wastewater. This showed the soil leachate biological treatment suitability for both significant Se recovery and environmentally sustainable effluent discharge.
