Manganese dioxide reduction kinetics by Geobacter sulfurreducens and associated biofilm morphology in a flow-through reactor

Biofilm;flow-through reactor;biological reduction;Geobacter sulfurreducens

Berns, Erin ; Valocchi ; Albert J. ; Werth ; Charles J.

关键词: Biofilm;    flow-through reactor;    biological reduction;    Geobacter sulfurreducens;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/88114/BERNS-THESIS-2015.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

In natural aquatic environments such as streams, lakes, and groundwater, microorganisms play an important role in the cycling of metals. Dissimilatory metal reducing bacteria (DMRBs) are a specific type of bacteria that convert metals to lower redox states through oxidation and reduction reactions. They utilize more metal than is needed for biosynthesis because they can conserve energy through the reduction of metals. This ability of DMRBs permits them to influence nutrient cycling in marine and lacustrine environments and control the bioremediation of sediments and waters contaminated with metals. Because of their widespread occurrence and impact on the environment, many kinetic models have been developed to evaluate fate and transport of metals in the presence of DMRBs. These models use various parameters to describe the reduction kinetics of DMRB and oftentimes rely on using parameters that are determined in batch systems.Batch systems do not adequately account for the variation that may exist in kinetic parameters. They are unable to estimate how environmental conditions present in a flow-through system could impact the reduction efficiency of DMRBs. Some of these changes can be accounted for by incorporating more terms into the models, but others are still unable to be quantified in this manner. By exploring how these parameters change under different flow conditions and which ones are impacted the most, we can determine where more work is needed to identify the actual mechanisms that cause differences in parameters. Additionally, batch systems are less useful for estimating kinetic parameters when DMRBs are reducing a solid substrate. This is because estimates of biomass in a biofilm on a solid surface are more difficult to obtain than measuring the cells in solution when a soluble phase substrate is utilized in a batch system.In this study, a flow through system with a solid phase electron acceptor is used to quantify important kinetic parameters at different flow rates. The biomass is estimated using a unique approach that involves coating sections of the reactor with the solid phase electron acceptor and removing these sections intermittently over the course of the experiment to evaluate both total biomass and biofilm morphology. We chose to explore the biofilm morphology throughout each experiment and at different flow rates in hopes of correlating morphology trends to reduction kinetics. A relationship between morphology and reduction kinetics could help explain differences in the parameters estimated from the experiments. This study evaluated the reduction kinetics of manganese dioxide using Geobacter sulfurreducens, an extensively studied DMRB, with acetate as the electron donor. At low flow rates, a yield of 3.44x1010 ± 2.54x1010 cells/mmol MnO2 was calculated and a maximum specific growth rate of 0.02 1/hr was estimated. The half saturation constant was fit with the model and determined to be 0.04 mmol MnO2 for the low flow rate. When the experiment was conducted at higher flow rates, the half saturation constant was determined to be 0.01 mmol MnO2, which indicates more efficient microorganisms. These findings show that higher flow rates, within the range evaluated in this study, may contribute to lower half saturation constants. The difference in half saturation constants may be related to changes in biofilm morphology, but more work needs to be done to conclusively make this comparison.