3/18/2024 0 Comments Aqua mail text reflow![]() ![]() The sediments beneath aquaculture operations may be one such environment 21, 22. SMFCs may be useful when there are localized point sources of organic matter loading. However, it is unclear how such an SMFC could be scaled up to combat eutrophication over an entire bay (Tokyo Bay for example has a surface area of 1,500 km 2). 13 deployed a set of five SMFCs in the organic rich sediment (12% w/w organic carbon) of Tokyo Bay, and found a reduction in porewater sulfide concentrations, identifying SMFC’s potential as a remediation technology for organic matter contaminated sediments. SMFCs have been tested as a means to provide energy to low power oceanographic sensors in remote settings 11, 12, 16, 18 and for bioremediation 14, 19, 20. By placing an electrode (anode) in the reduced layer of sediment and connecting it to a cathode in the overlying oxygenated water, an SMFC can drive current using oxygen in the water column as an electron accepter,essentially bypassing the transport limitation that gives rise to the redox gradient. These alternatives are preferentially used according to available free energy along a vertically structured redox gradient 17 (i.e., nitrate reduction, Fe and Mn reduction, sulfate reduction, methanogenesis). In sediments, diffusive transport limits oxygen supply, causing a buildup of reducing equivalents and a switch to alternative electron acceptors. These are MFCs that take advantage of the naturally occurring redox gradients in organic rich sediments. One application that has shown promise is sediment microbial fuel cells (SMFCs) 16. However, despite promising research and proof-of-concept protypes, they have yet to be adapted for widespread use in society, primarily due to low power generation, challenges in scaling up laboratory prototype systems, and the inability to demonstrate improvements upon current technologies 10, 15. Since discovery of this phenomena over 100 years ago 8 there has been interest in harnessing it for practical applications 9.ĭevices that exploit this are termed microbial fuel cells (MFCs) and proposed uses include energy capture from wastewater treatment 9, environmental sensors 10, power sources for low energy devices in remote locations 11, 12 and bioremediation 13, 14. ![]() This allows microbes to take advantage of more favourable redox pairings than they would otherwise have access to in their immediate vicinity. To do this, electrons generated by an oxidation reaction at an anode are transferred to a circuit either extracellularly 4, 5 or with the aid of mediators 3, 6, 7, and used by another microbial population at the cathode for reduction. In some cases when microbes are provided with an electrically conductive connection across a redox gradient, they will use energy from only a single half reaction and transfer electrons to the electric circuit, capturing energy for their growth and metabolism, and producing modest amounts of electrical power as a consequence 3. While most organisms carry out both oxidation and reduction entirely within their own cells, a small subset of microbes are able to decouple these reactions, using redox shuttles and mediators, direct connections, or appendages called nanowires to access reactants outside the organism 1, 2. Living organisms harvest energy for their growth and metabolism by catalyzing redox reactions. The data presented here indicate that SMFCs have potential for the remediation of sulfidic sediments around aquaculture operations. However, the SMFCs also lowered pH in the sediments and the consequences of this acidification on sediment geochemistry should be considered if developing SMFCs for remediation. Depth integrated sulfide inventories in the SMFCs were only 20% that of the controls. The SMFCs had no discernable effect on oxygen profiles, however porewater sulfide was significantly lower in the sediment microcosms with functioning SMFCs than those without. The impact on sediment geochemistry was evaluated with microsensor profiling for oxygen, sulfide, and pH. Two SMFCs placed in high organic matter sediments were operated for 96 days and compared to open circuit and sediment only controls. Here we address these issues through a laboratory microcosm experiment. However, for SMFCs to be a viable technology they must remove sulfide at a scale relevant to the environmental contamination and their impact on the sediment geochemistry as a whole must be evaluated. The ability to remove sulfide suggests their use in the remediation of sediments impacted by point source organic matter loading, such as occurs beneath open pen aquaculture farms. Sediment microbial fuel cells (SMFCs) generate electricity through the oxidation of reduced compounds, such as sulfide or organic carbon compounds, buried in anoxic sediments.
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