The development of an artificial gill to supply oxygen to a submerged microbial fuel cell

Abstract

The development of an effective system for extracting dissolved oxygen from water would enable humans to work underwater for extended periods. This would have applications to science, industry, exploration, military, and recreation. Human sustenance would require a very sophisticated and high capacity gill system, one that has not been developed to date. The overall aim of this research was to develop an artificial gill that would operate with a realistic and useful load. The load chosen for this research was a microbial fuel cell operating underwater. Countercurrent gill plates were constructed to evaluate several different candidates for use as the oxygen transfer membrane. The oxygen gain of each membrane was measured by comparing dissolved oxygen readings before and after the gill. Celgard 2500 (Celgard, Inc. Charlotte NC), a microporous polypropylene membrane, was chosen as the most suitable candidate; it sustained an oxygen gain greater than 2 mmol/sec. This was a much higher gain than necessary to sustain the fuel cell, which is on the order of 10 nmol/sec. The original fuel cell (NCBE, University of Reading, UK) was then redesigned. The new system was more modular, allowing for a multitude of different experimental configurations. Two of the configurations included an integrated gill, with no moving parts and therefore no power consumption. The cathode of the fuel cell was modified to respond more quickly to changes in oxygen supply. Experiments were conducted measuring the power output of the modified fuel cell and the oxygen uptake of the gill. The MFC ran for multiple days for each test cycle, and data was recorded on a Tattletale Model 8 microcontroller (Onset, Pocasset, MA). It was demonstrated that providing the cathode of the cell with oxygen enabled the cell to sustain much higher voltages than without a continuous oxygen supply. Typical experiments yielded a few microwatts of power between 100 and 200 mV