Sediment MFCs

Microbial Fuel Cells. By Bruce E. Logan Copyright 2008 John Wiley Sons, Inc. 

The same type of SMFC was tested by Ryckelynck et al. (2005) in Yaquina Bay, OR, with the device located at water depth of 5 m (low tide). The electrodes were the same as used by Tender et al. (2002), except here the available surface area was defined based on all exposed surfaces (0.542 m ). The reactor produced continuous power at 11 mW/m. If the projected surface area is instead used, this is equivalent to 33 W/m, which is a range similar to that reported by Tender et al. (2002) for this device at the Newport location. Iron and sulfur were enriched on the anode 400 and 20 times, respectively, after operation at this site. Community analysis of the bacteria showed a predominance of 8-Proteobacteria, primary sulfate reducing bacteria consisting of Desulfobulbus spp. and Desulfocapsa spp. It was concluded that sulfides (primarily FeS and FeS2) were the primary chemical sources used by bacteria for power generation. 

Reimers et al. (2006) conducted field tests with a new type of SMFC consisting of a single graphite rod anode (8.4 cm diameter, 91.4 cm long) imbedded in the sediment at a deep-ocean cold seep, along with 1 -m long cathodes made of carbon-fiber/titanium wire 

sulfides can serve as a source of power in both the absence and presence of carbon sources. 

Bergel et al. (2005) discovered that the formation of seawater improved the performance of stainless steel cathodes used in seawater applications of hydrogen fuel cells. The amount of improvement depended on the electrode sizes and pH. The fuel cell produced 41 mWW in the presence of the biofilm, but only 1.4 mW/m when the biofilm was removed, an increase of 30x (power normalized to cathode projected surface area). Increasing the pH of the anode compartment from 8.2 to 12.5 increased power to 270 mWW, which was almost lOOx larger than that with the cathode biofilm removed (2.8 mWW). The highest power output was 325 mW/m, which was obtained by decreasing the cathode surface area from 9 to 1.8 cm.  

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MxC is the term used for research that can be applied to either an MFC or an MFC. In a microbial desalination cell (MDC), a third, middle, compartment is installed that can be filled with salt water to be desalinated by the electric field [7]. S-MFC and P-MFC denote a sediment MFC and a plant MFC [8], respectively. 

Two psychrotolerant strains isolated from the anode of a sediment MFC were shown to produce electricity and could grow at temperatures as low as 4°C to 30°C with an... 

FC304 and Fe304+ Ni were added to graphite paste, and Mn + Ni were added to a graphite-ceramic mixture to make anodes used in sediment fuel cells using the same procedure employed by Park and Zeikus (2002). These anodes produced 1.7- to 2.2-foId greater current than plain graphite electrodes under similar conditions Lowy et al. 2006). The Mn -based electrode, which performed best in these laboratory tests, was also field-tested in sediment MFCs and produced 105 mW/m, versus 20 mW/m obtained in previous tests. 

Plain carbon cathodes. The efficiency of a catalyst is often assessed by comparing current or power densities to those with plain carbon electrodes of the same surface area. Oxygen reduction still proceeds in the absence of the catalyst, but the rate is reduced. In general, current and power are reduced by a factor of 10 or more with plain carbon materials. However, if the cathode surface area is substantially increased, it is possible to achieve much higher power densities. Reimers et al. (2006) tested a sediment MFC that had 1-m long carbon brush cathodes. They reached power densities of 34 mW/m by positioning the MFC over a deep ocean cold seep in Monterey Canyon in California. Power decreased over time due to sulfide build up on the anode with no indication of... 

Fig. 10.1 Concept of using a sediment MFC as a remote power source on the seafloor either for powering a data coliection device or serving a refueiing station. (Graphic by R. Brennan.)...

Fig. 10.2 Sediment MFCs tested by Tender et al. (2002), referred to as benthic underwater generators (BUGs), at a field site near Tuckerton, NJ. [Reprinted from Logan and Regan (2006b) with permission of the American Chemical Society.]...

Fig. 10.3 Components of a sediment MFC tested at a cold seep consisting of (A) a single grahite rod anode, and (B) electronic housing and brush cathodes shown by arrow 1. The second arrow shows a second unit in the background. [From Reimers et al. (2006), reprinted with permission from Wiley-Blackwell.)...

Fig. 11.1 (A) Sediment MFC designed by Abbie Groff, and (B) newspaper clipping noting her winning the Lancaster County science fair. (Reprinted with permission from Lancaster Newspapers, Inc. March 16, 2005 issue of Inteiligencer Journal.)...

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