Plant and microorganisms support media for electricity generation in biological fuel cells with living hydrophytes

• Graphite and tezontle can be used in biofuel cells with plants to produce electricity.
• The graphite packed system worked under mixed control: ohmic and kinetic.
• The mixed control may be avoided by the growth of a healthy microbial population.
• Tezontle packed reactor operated under kinetic control with an activation resistance.

Plant support media may impact power output in a biological fuel cell with living plants, due to the physical and biochemical processes that take place in it. A material for support medium should provide the suitable conditions for the robust microbial growth and its metabolic activity, degrading organic matter and other substances; and, transferring electrons to the anode. To consider the implementation of this type of bio-electrochemical systems in constructed wetlands, this study analyzes the electrochemical behavior of biological fuel cells with the vegetal species Phragmites australis, by using two different support media: graphite granules and a volcanic slag, commonly known as tezontle (stone as light as hair, from the Aztec or Nahuatl language). Derived from the results, both, graphite and tezontle have the potential to be used as support medium for plants and microorganisms supporting a maximum power of 26.78 mW/m2 in graphite reactors. These reactors worked under mixed control: with ohmic and kinetic resistances of the same order of magnitude. Tezontle reactors operated under kinetic control with a high activation resistance supplying 9.73 mW/m2. These performances could be improved with stronger bacterial populations in the reactor, to ensure the rapid depletion of substrate.

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