TECHNOLOGY FOCUS - BIOLOGY - Preferred Components: The yeast nutrient source comprises tree sap. The yeast cell biofilm comprises baker's yeast cells. The yeast is Saccharomyces cerevisiae. The anode solution includes quantity of a yeast nutrient source.    TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Method: The method involves constructing anode and cathode using predetermined quantity of carbon felt. The anode comprises several electrodes. The method involves using initial anode solution and replacement quantity of initial anode solution each including quantity of electron mediator. The method involves using initial anode solution and replacement quantity of initial anode solution each including 0.01-60 mM/l of methylene blue. The method involves using initial anode solution and replacement anode solution each including 10 mM/l to 3 M/l of sodium chloride. The method involves using cathode solution including quantity of electron mediator. The method involves using cathode solution including 50 mM/ml of potassium ferricyanide. The method involves adding selected quantity of yeast added in 0.001-500 mg/ml of anode solution. The method involves using yeast nutrient source including sugar. The method involves adding selected quantity of yeast nutrient source in glucose having concentration of 0.1-40 wt.% with respect to anode solution. The method involves forming biofilm by electrically biasing the electrode in a standard three electrode configuration at a potential of from about -0.2 to -0.8 volts with respect to a saturated calomel electrode. Preferred Component: The microbial fuel cell comprises resistor connectable across the anode and the cathode to enable conduction of current through a resistance of 10-5000 ohms. The anode solution includes quantity of electron mediator. The electron mediator comprises methylene blue. The cathode solution includes quantity of electron mediator. The electron mediator comprises potassium ferricyanide. The anode solution has a pH of 2-11. EXAMPLE - No suitable example given.