A microbial fuel cell, set in marine sediments, was

							     Microbial fuel cell design sufficient to power a
       hydrophone over a several month period
         Drs. Ken Richter and Bart Chadwick
          SPAWAR Systems Center Pacific
       53475 Strothe Rd. San Diego, CA 92152
                   Dr. Lenny Tender
              Naval Research Laboratory
    4555 Overlook Ave. SW Washington DC, 20375

A microbial fuel cell, set in marine sediments, was
designed to power a 20 mW multi-frequency hydrophone.
The hydrophone is operating as a detector of acoustically-
tagged green sea turtles in San Diego Bay, CA. Initial
field studies showed that organic content in the sediment
was critical in determining fuel cell energy density, while
water oxygen concentrations, varying with the
semidiurnal tide, added a small ripple on power output
(see figure). Power density is approximately 8 mW m-2
graphite anode. Tidally-driven temperature fluctuations in
the sediment and water column were unimportant in
power output. Steady-state power output was attained in
approximately 4 weeks, accompanied by an explosive
growth of bacterial populations near the anode in the
sediment.




          The design and operating characteristics of the
fuel cell and hydrophone will be presented as well
environmental measurements that led to the design.