Biological removal of selenate in saline wastewater by activated sludge under alternating anoxic/oxic conditions
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RESEARCH ARTICLE
Biological removal of selenate in saline wastewater by activated sludge under alternating anoxic/oxic conditions Yuanyuan Zhang1, Masashi Kuroda1, Shunsuke Arai2, Fumitaka Kato2, Daisuke Inoue1, Michihiko Ike (✉)1 1 Division of Sustainable Energy and Environmental Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan 2 Nippon Steel & Sumitomo Metal Corporation, 20-1 Shintomi, Futtsu, Chiba 293-8511, Japan
HIGHLIGHTS
GRAPHIC ABSTRACT
• Removal of selenate in saline wastewater by activated sludge was examined. • Sequencing batch reactor was operated under alternating anoxic/oxic conditions. • Above 97% removal of soluble selenium (Se) was achieved continuously. • Major Se removal mechanism varied depending on the length of aeration period. • Various Se-reducing bacteria likely contributed to coordinately to Se removal.
ARTICLE INFO Article history:
Received 30 January 2019 Revised 23 April 2019 Accepted 12 June 2019 Available online 30 July 2019 Keywords: Activated sludge Selenate reduction Saline wastewater Sequencing batch reactor Alternating anoxic/oxic conditions Selenium biovolatilization
ABSTRACT Selenium (Se)-containing industrial wastewater is often coupled with notable salinity. However, limited studies have examined biological treatment of Se-containing wastewater under high salinity conditions. In this study, a sequencing batch reactor (SBR) inoculated with activated sludge was applied to treat selenate in synthetic saline wastewater (3% w/v NaCl) supplemented with lactate as the carbon source. Start-up of the SBR was performed with addition of 1–5 mM of selenate under oxygenlimiting conditions, which succeeded in removing more than 99% of the soluble Se. Then, the treatment of 1 mM Se with cycle duration of 3 days was carried out under alternating anoxic/oxic conditions by adding aeration period after oxygen-limiting period. Although the SBR maintained soluble Se removal of above 97%, considerable amount of solid Se remained in the effluent as suspended solids and total Se removal fluctuated between about 40 and 80%. Surprisingly, the mass balance calculation found a considerable decrease of Se accumulated in the SBR when the aeration period was prolonged to 7 h, indicating very efficient Se biovolatilization. Furthermore, microbial community analysis suggested that various Se-reducing bacteria coordinately contributed to the removal of Se in the SBR and main contributors varied depending on the operational conditions. This study will offer implications for practical biological treatment of selenium in saline wastewater. © Higher Education Press and Springer-Verlag GmbH Germany, part of Springer Nature 2019
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Introduction
Selenium (Se) is an essential minor element with pivotal functions in human beings and animals. It plays a significant role in cellular metabolism at relatively low
✉ Corresponding author E-mail: [email protected]
levels. However, when ingested at levels up to 400 mg/d, it has been identified to be highl
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