Mathematical Modeling of an Electrode-Integrated Fixed-Bed Bioreactor for Treatment of Sulfate

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Mathematical Modeling of an Electrode-Integrated Fixed-Bed Bioreactor for Treatment of Sulfate

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2021-04

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High levels of sulfate can alter sulfur cycling in natural systems, particularly freshwater, and in engineering environments. This may cause substantial environmental and health problems including a potential contribution to methylation of mercury, sulfide toxicity and eutrophication. Bioelectrochemical systems have promising potential to clean up a variety of contaminants including high levels of sulfate. This study has developed a mathematical model to determine key design, operational, and biological characteristics for an effective electrode-integrated fixed-bed bioreactor for sulfatetreatment. The bioreactor stimulates and sustains biological sulfate reduction and simultaneously facilitates the subsequent removal of the reduced sulfide by applying iron electrolysis under low electrical potential. The model was constructed using six coupled reaction-advection-dispersion equations for biomass, dissolved hydrogen gas, sulfate, dissolved hydrogen sulfide, total dissolved iron, and iron sulfide. The model’s sensitivity to pumping rate, applied current, and kinetic parameters was evaluated. Increased residence time and increased applied current were strongly correlated with improved performance while kinetic parameters from differing literature sources had no significant effect. A simulated system with multiple cathode and anode pairs demonstrated that increased hydrogen production could offset a lower residence time of 3.5 days and fully remove 1000 mg/L sulfate from the influent. The effect of electrode spacing and surface area on the current was experimentally examined. The ohmic resistance due to electrode spacing was shown to be significantly smaller than the resistance due to processes at the electrodes which are surface area limited. The mathematical model was evaluated with the experimental results from a bioelectrochemical reactor with three cathode and anode pairs to treat a ~890 mg/L sulfate impacted influent. The sulfate concentration simulated using the model was in good agreement with ~100-200 mg/L sulfate reduction over the first 60 days but did not predict the significant sulfate decrease after a change in applied potential from days 60-90. Finally, the bioelectrochemical model was applied to design a treatment solution for sulfate elevated outflow from the St. James Pit in Northern Minnesota. A biofiltration system with integrated electrodes was designed to treat 293 gpm of 290 mg/L sulfate influent to below 10 mg/L.

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University of Minnesota M.S. thesis.April 2021. Major: Civil Engineering. Advisor: Chan Lan Chun. 1 computer file (PDF); ix, 63 pages.

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Deen, Tobin. (2021). Mathematical Modeling of an Electrode-Integrated Fixed-Bed Bioreactor for Treatment of Sulfate. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/220570.

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