Sensitivity analysis of uranium reduction and its reoxidation by Fe(III)- (hydr)oxides biogeochemical reaction dynamics

Sensitivity analysis is a useful tool in modeling environmental systems to identify how variations in model parameters would impact model outputs. In modeling environmental processes in biological systems, the rates and processes of biodegradation reactions are described using biokinetic parameters. Reducing the parameter uncertainty in modeling efforts would be important for reliable and accurate model results. Understanding the impact of variations in the biokinetic parameters would be highly critical to help to reduce the uncertainity in model predictions. This study presents a sensitivity analysis of the biokinetic parameters affecting the biogeochemical reaction network for uranium biotransformation dynamics. The main reactions included in the network are sulfate bioreduction, Fe(III) bioreduction, U(VI) reduction to U(IV), Fe(III) reduction by sulfide, U(IV) reoxidation to U(VI) and sulfur precipitation-dissolution reactions. The sensitivity analysis results revealed that changes in the biokinetic parameters to the sulfate bioreduction reaction had the most significant impact to the model outputs. Among the parameters, maximum substrate utilization rate and yield coefficient had the most significant impact, whereas half-saturation constants had slightly less impact on model results. U(VI) concentration predictions were the most sensitive towards variations in biokinetics parameters among the species monitored within the biogeochemical reaction network. Fe(III) bioreduction, Fe(III) reduction by sulfide and sulfur precipitation/dissolution reactions were not shown to be sensitive to any changes in the biokinetic parameters.