TECHNOLOGY FOCUS - BIOLOGY - Preferred Components: The microorganisms: are chemolithoautotrophic, mixotrophic and/or chemolithoautotrophic; are freely suspended in the aqueous solution and/or immobilized on a solid support; and includes Leptospirillum (preferably Leptospirillum ferriphilum, Leptospirillum ferrooxidans, Leptospirillum ferrodiazotrophum or Leptospirillum thermoferrooxidans), Ferroplasma (preferably Ferroplasma acidiphilum, Ferroplasma cupricumulans or Ferroplasma acidarmanus), Sulfobacillus (preferably Sulfobacillus thermotolerans, Sulfobacillus thermosulfidooxidans, Sulfobacillus montserratensis, Sulfobacillus sibiricus and unclassified strains of Sulfobacillus), Acidithiobacillus (preferably Acidithiobacillus ferrooxidans), Alicyclobacillus, Acidimicrobium (preferably Ferrimicrobium acidiphilum) or Ferrimicrobium.    TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Method: The method further comprises: heterotrophic, mixotrophic, or chemolithoautotrophic and heterotrophic microorganisms in the aqueous solution for consuming organic by-products produced by the microorganisms; and controlling a ratio of electrical production to biomass production by varying at least one microbial cultivation parameters including an electrical potential of the cathode electrode, a ratio of ferrous ions to ferric ions concentrations, or concentrations of dissolved nutrients. In the method, the biomass production and carbon dioxide consumption responsively occurs due to the fixation of carbon dioxide by the microorganism in the presence of the dissolved nutrients and the ferrous ions. The method comprises: temporarily providing an elevated electrical power with respect to a sustainable electrical power, by reducing the ferric ions to ferrous ions in the fuel cell so that the concentration of ferric ions in the bioreactor depletes over time; allowing the ferric ion concentration in the bioreactor to return to a nominal level by providing a reduced or nominal electrical power for a duration of time; and temporarily providing a reduced electrical power with respect to the sustainable electrical power.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The aqueous solution: includes dissolved nutrients for facilitating growth of the microorganisms, where the nutrients comprises ammonium, potassium ion, calcium ion, magnesium ion, sulfate ion, chloride, phosphate, nitrate, copper, manganese, molybdenum, nickel and/or zinc; and has a pH of 0-1.2. The cathode comprises at least one carbon and stainless steel, and cathode catalyst including gold, platinum, palladium and/or lead. The anode comprises at least one carbon-based material, a carbon-based material with a catalyst, or a catalyst, where the: catalyst is tungsten carbide, iron phosphide and/or cobalt phosphide; and carbon-based material is carbon black, activated carbon powder, activated carbon powder fibers, non-activated carbon powder and/or non-activated carbon powder fibers.    TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The system further comprises: a secondary non-aerated bioreactor disposed so that the microorganisms complete their consumption of oxygen before entering the cathode compartment; and at least one centrifuge or filter for removing excess microorganism growth. The bioreactor is a vessel in flow communication with the cathode compartment and encloses the microorganisms, where the ferrous ions are oxidized by the microorganisms to ferric ions in an aerobic oxidation reaction, and at the cathode, 4 moles of ferric ions and 4 electrons reacts to give 4 moles of ferrous ions.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The fuel having a hydrogen constituent is hydrogen gas, methanol and/or ethanol.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The membrane permeable to protons is: an ion exchange membrane including cation exchange membrane, anion exchange membrane and/or permselective ion exchange membrane; a substantially inert hydrophilic material having pores extending through them, where the pores are less than 100 mu m in diameter; or a hydrogel membrane made of a hydrogel, which is polyvinyl alcohol, polyhydroxyethylmethacrylate and/or polyethylene oxide, which may or may not contain a cross linking agent. The hydrogel membrane is bonded on one surface to a surface of the anode electrode and bonded on an opposing surface to a surface of the cathode electrode or to both. The membrane permeable to protons has: a layered structure, which comprises a first hydrogel membrane bonded to a membrane made of substantially inert material having pores extending through it and having less than 1000 mu m in diameter; a layered structure, where each layer is bonded to adjacent layer, and the structure comprises (in order) the first hydrogel membrane and the membrane made of the inert material, where the first hydrogel membrane is bonded to the anode electrode or the cathode electrode; or a layered structure, where each layer is bonded to adjacent layer, and the structure comprises (in order) the first hydrogel membrane, the membrane made of the inert material and a second hydrogel membrane, where the first and second hydrogel membranes are bonded to the anode electrode and cathode electrode, respectively; or a layered structure, which comprises the first inert material, the hydrogel membrane and second inert material bonded on a surface to an opposing surface of the hydrogel membrane to form a sandwich structure of the two inert materials separated by the hydrogel membrane bonded between them.