System Design and Operation
Benthic Microbial Fuel Cells
Led by Jordon Beckler, Ph.D.
Affiliated Home Campus: Harbor Branch
Affiliated Department: Harbor Branch Oceanographic Institute
REU Scholar: Bella Guyll
REU Scholar Home Institution: Iowa State University
PROJECT
One of the driving factors of hypoxic lake and ocean environments is the influx of excess nutrients into water ways. Phosphorus is one of the primary drivers of algae blooms within these regions causing dead zones. The eutrophication of waterways results in lower dissolved oxygen concentrations which has numerous implications for the aquatic environment including the loss of aerobic species, altering of the ecological links, and increased invasive organisms. Nutrients such as phosphorus are stored within the sediment before leaching into the water column, complicating remediation through standard water treatments. The quality of the sediments plays an integral role with that of the water column. Furthermore, the phosphorus within the sediment is constantly recycled back into the water column via diffusive and resuspension fluxes, resulting in the overall accumulation of phosphorous in the system with a low degree of permanent burial.
Sediment microbial fuel cells (SMFCs) have shown promise in the remediation of nutrient-dense sediments. SMFCs are a subset of microbial fuel cells (MFCs) that generate small power densities. This is accomplished through the establishment of a redox gradient between the oxic water column and the anoxic environment of the sediment. Previous research indicates that SMFCs have the capability of altering the speciaton, and in turn triggering the immobilization of phosphorus within the sediment. One of these mechanisms is via the binding of reduced iron Fe(II) with phosphate PO4-3. SMFCs provide the framework for the reduction of Fe(III) allowing for an abundance of Fe(II). Factors that influence the power density of SMFCs include anode depth and circuitry. As anode depth within the sediment increases, power density tends to decrease as the amount of microbial activity dwindles. Furthermore, the greater the load attached to the circuit, the larger the power density. For applied use in the field, whether to generate power, immobilize phosphate, or both, it is critical to determine the optimal site-specific fuel cell parameters prior to installation. However, there exists a paucity of information regarding the role of these variables in eliciting the secondary effects of SMFCs, e.g. the ability to sequester phosphorus within the sediment. The goal of this experiment was to determine the role that load circuitry play on the immobilization and speciation of phosphorus in the sediments of Lake Okeechobee.
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