Abstract
Sediment microbial fuel cells (SMFCs) generate electricity through the oxidation of reduced compounds, such as sulfide or organic carbon compounds, buried in anoxic sediments. 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. 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. Here we address these issues through a laboratory microcosm experiment. Two SMFCs placed in high organic matter sediments were operated for 96 days and compared to open circuit and sediment only controls. The impact on sediment geochemistry was evaluated with microsensor profiling for oxygen, sulfide, and pH. 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. Depth integrated sulfide inventories in the SMFCs were only 20% that of the controls. 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. The data presented here indicate that SMFCs have potential for the remediation of sulfidic sediments around aquaculture operations.
Highlights
Sediment microbial fuel cells (SMFCs) generate electricity through the oxidation of reduced compounds, such as sulfide or organic carbon compounds, buried in anoxic sediments
This allows sediment microbes to access more favorable electron acceptors than would otherwise be available. This suggests sediment microbial fuel cells (SMFCs) could be used for the remediation of sediments impacted by point-source organic matter loading, such as the accumulation of aquaculture waste beneath fish-pens. We examined this question with a SMFC microcosm laboratory experiment that addressed two specific questions: (1) do SMFCs lower sediment oxygen demand (SOD) by accelerating organic matter decomposition? and (2) can SMFCs lower porewater sulfide concentrations to levels sufficient for the remediation of sediments beneath aquaculture farms?
Though consumption did decrease throughout the experiment, there was no difference between the SMFCs and controls
Summary
Sediment microbial fuel cells (SMFCs) generate electricity through the oxidation of reduced compounds, such as sulfide or organic carbon compounds, buried in anoxic sediments. 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 We address these issues through a laboratory microcosm experiment. 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 This allows microbes to take advantage of more favourable redox pairings than they would otherwise have access to in their immediate vicinity. One application that has shown promise is sediment microbial fuel cells (SMFCs)[16] These are MFCs that take advantage of the naturally occurring redox gradients in organic rich sediments. 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
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