Bioaugmentation of UASB reactors with immobilized <Emphasis Type="Italic">Sulfurospirillum barnesii</Emphasis> for simultaneous selenate and nitrate removal |
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Authors: | Markus Lenz Anne Marie Enright Vincent O’Flaherty Adriaan C van Aelst Piet N L Lens |
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Institution: | Markus Lenz, Anne Marie Enright, Vincent O’Flaherty, Adriaan C. van Aelst and Piet N. L. Lens |
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Abstract: | Whole-cell immobilization of selenate-respiring Sulfurospirillum barnesii in polyacrylamide gels was investigated to allow the treatment of selenate contaminated (790 μg Se × L−1) synthetic wastewater with a high molar excess of nitrate (1,500 times) and sulfate (200 times). Gel-immobilized S. barnesii cells were used to inoculate a mesophilic (30°C) bioreactor fed with lactate as electron donor at an organic loading rate
of 5 g chemical oxygen demand (COD) × L−1 day−1. Selenate was reduced efficiently (>97%) in the nitrate and sulfate fed bioreactor, and a minimal effluent concentration
of 39 μg Se × L−1 was obtained. Scanning electron microscopy with energy dispersive X-ray (SEM–EDX) analysis revealed spherical bioprecipitates
of ≤2 μm diameter mostly on the gel surface, consisting of selenium with a minor contribution of sulfur. To validate the bioaugmentation
success under microbial competition, gel cubes with immobilized S. barnesii cells were added to an Upflow Anaerobic Sludge Bed (UASB) reactor, resulting in earlier selenate (24 hydraulic retention
times (HRTs)) and sulfate (44 HRTs) removal and higher nitrate/nitrite removal efficiencies compared to a non-bioaugmented
control reactor. S. barnesii was efficiently immobilized inside the UASB bioreactors as the selenate-reducing activity was maintained during long-term
operation (58 days), and molecular analysis showed that S. barnesii was present in both the sludge bed and the effluent. This demonstrates that gel immobilization of specialized bacterial strains
can supersede wash-out and out-competition of newly introduced strains in continuous bioaugmented systems. Eventually, proliferation
of a selenium-respiring specialist occurred in the non-bioaugmented control reactor, resulting in simultaneous nitrate and
selenate removal during a later phase of operation.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. |
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Keywords: | Denitrification Whole-cell immobilization Dissimilatory selenium reduction Bioprecipitation Drainage water treatment |
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