S159: MFC biofilm growth rates and power production

MFCs represent a promising technology for simultaneous organic waste treatment and sustainable electricity production. We have previously shown that higher energy density levels and optimum biofilm/electrode surface area–to–volume ratios reside within smaller-scale MFC units, probably because of shorter migration paths for protons. Thus, a validated approach to scaling up is through miniaturization & multiplication. This approach has already allowed for the powering of practical applications and a series of autonomous robots. In order to maximise power output, it is clear that a large population of effective electrode-conducting biofilm cells are required, although this assumes that all biofilm cells have significant metabolic rates. In ideal conditions (external load optimised for maximum power transfer), cells metabolise for the purpose of producing progeny, and unless catabolism is seriously uncoupled from anabolism, the higher the growth rate (μ), the higher the metabolic flux and consequent power output in MFCs. One way to improve the latter is enhancing cell growth rate/metabolic rate by increasing supply rate when there is C/E limitation. We have recently shown that, for pure monospecies, a maximised growth rate (μ_max) leads to highest power. Despite the likely importance of μ and its relationship to MFC performance, it is rarely measured yet can be easily monitored with the right methods and model. It should be noted that each change in supply rate changes μ and consequently the rate of proton production and conductivity of cells, ultimately affecting the internal resistance of the system, making impedance matching a necessity.