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A zero-power ballast control system that could be used to float and submerge a device solely using a gas source was built and tested. This system could be used to convey sensors, data loggers, and communication devices necessary for water quality monitoring and other applications by periodically maneuvering up and down a water column. Operational parameters for the system such as duration of the submerged and buoyant states can be varied according to its design. The gas source can be of any origin, e.g., compressed air, underwater gas vent, gas produced by microbes, etc. The zero-power ballast system was initially tested using a gas pump and further tested using gas produced by Clostridium acetobutylicum. Using microbial gas production as the only source of gas and no electrical power during operation, the system successfully floated and submerged periodically with a period of 30 min for at least 24 h. Together with microbial fuel cells, this system opens up possibilities for underwater monitoring systems that could function indefinitely. [ABSTRACT FROM AUTHOR]

A miniature microbial fuel cell (mini-MFC) is described that demonstrates high output power per device cross-section (2.0 cm²) and volume (1.2 cm³). Shewanella oneidensis DSP10 in growth medium with lactate and buffered ferricyanide solutions were used as the anolyte and catholyte, respectively. Maximum power densities of 24 and 10 mW/m² were measured using the true surface areas of reticulated vitreous carbon (RVC) and graphite felt (GF) electrodes without the addition of exogenous mediators in the anolyte. Current densities at maximum power were measured as 44 and 20 mA/m² for RVC and GF, while short circuit current densities reached 32 mA/m² for ISF anodes and 100 mA/m² for RVC. When the power density for GF was calculated using the cross sectional area of the device or the volume of the anode chamber, we found values (3 W/m², 500 W/m³) similar to the maxima reported in the literature. The addition of electron mediators resulted in current and power increases of 30–100%. These power densities were surprisingly high considering a pure S. oneidensis culture was used. We found that the short diffusion lengths and high surface-area-to-chamber volume ratio utilized in the mini-MFC enhanced power density when compared to output from similar macroscopic MFCs. [ABSTRACT FROM AUTHOR]