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Optimization of nitrate and selenate reduction in an ethanol-fed fluidized bed reactor via redox potential feedback control
Journal article   Open access   Peer reviewed

Optimization of nitrate and selenate reduction in an ethanol-fed fluidized bed reactor via redox potential feedback control

S. Yan, K.Y. Cheng, M.P. Ginige, G. Zheng, L. Zhou and A.H. Kaksonen
Journal of Hazardous Materials, Vol.402, Art.123770
2020
DOI: https://doi.org/10.1016/j.jhazmat.2020.123770
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Abstract

Electron donors are a major cost-factor in biological removing oxyanions, such as nitrate and selenate from wastewater. In this study, an online ethanol dosing strategy based on feedback control of oxidation-reduction potential (ORP) was designed to optimize the performance of a lab-scale fluidized bed reactor (FBR) in treating selenate and nitrate (5 mM each) containing wastewater. The FBR performance was evaluated at various ORP setpoints ranging between −520 mV and −240 mV (vs. Ag/AgCl). Results suggested that both nitrate and selenate were completely removed at ORPs between −520 mV and −360 mV, with methylseleninic acid, selenocyanate, selenosulfate and ammonia being produced at low ORP between −520 mV and −480 mV, likely due to overdosing of ethanol. At ORPs between −300 mV and −240 mV, limited ethanol dosing resulted in an apparent decline in selenate removal whereas nitrate removal remained stable. Resuming the ORP to −520 mV successfully restored complete selenate reduction. An optimal ORP of −400 mV was identified for the FBR, whereby near complete selenate and nitrate were removed with a minimal ethanol consumption. Overall, controlling ORP via feedback-dosing of the electron donor was an effective strategy to optimize FBR performance for reducing selenate and nitrate in wastewater.

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