Practical Considerations for Growth Optimization of Iron-Oxidizing Bacteria for Use in Acid Mine Drainage Remediation

Practical considerations for the design of an AMD treatment plant located in the SundayCreek watershed were investigated. A mixed culture of bacteria originally from and AMDsite located at Wolf Run, Noble County, OH, was enriched under various conditions inAMD from the Sunday Creek site. Following the work of Almomani (2023), the effects ofinoculum size (1%, 2%, 5%, and 10%), nutrient enrichment conditions (reagent-gradeammonium and phosphate, no nutrient addition, and commercially available fertilizers),and temperature (8 °C, room temperature, and 32 °C) on the iron-oxidation kinetics of thisculture were investigated. Inoculum size had no statistically significant effect on oxidationrates, although the oxidation rate at 5% and 10% inoculum (0.175 and 0.171 h^-1 ,respectively) were observed to be nearly twice the oxidation rate at 1% inoculum (0.107 h^-1 ). There was no significant difference between the oxidation rates of samples containing0.1 M ammonium sulfate and 5 mM potassium phosphate (0.156 h^-1 ) and samplescontaining only inoculum (0.108 h^-1 ), and commercial fertilizer was observed to decreaseiron oxidation rates (0.0547 h^-1 ), although the total time from inoculation to total ironoxidation was similar to that of the samples containing only inoculum. Iron oxidation ratesincreased with temperature, and the oxidation kinetics were fitted using the Arrheniusmodel yielding an activation energy of 70.1 kJ mol^-1 °K^-1 and a pre-exponential factor of2.21 ∙ 10^11 h^-1 .A pilot-scale batch reaction experiment was conducted in field conditions at theSunday Creek site in a 1250 gal clarifier. Oxidation rates were observed to be 0.012 h^-1after the second subculturing, which was lower than any rate observed in the laboratoryexperiments. This was explained by a combination of suboptimal factors, including lowtemperatures and inclusion of commercial fertilizer as a secondary nutrient source.Finally, a process optimization and financial analysis was conducted to considerseveral treatment pathways and compare their efficacy. Biological oxidation withoutsecondary nutrient addition was found to be less expensive than chemical oxidation.However, the electrical costs of agitating a large-scale bioreactor may cause the treatmentplant to run at a considerable deficit. Overall, this thesis provides data-driven advice on thedesign considerations that are required for a large-scale bioreactor for the treatment andresource recovery of AMD.