Miniature microbial fuel cells and stacks for urine utilisation

MFCs are becoming a stronger contender in the area of alternative energy sources and show great promise in utilising a wide variety of organic sources. This paper describes the utilisation of neat undiluted urine as the main feedstock for different types of individual MFCs and stacks of small-scale MFCs, for direct electricity production, with conversion efficiencies of >50%. The smallest MFC (1.4 mL total volume) produced equal amounts of power to that produced by larger MFCs (6.25 mL), resulting in increased power densities. Power densities of 4.93 mW/m2 (absolute power of 1.5 mW) were recorded when 48 small-scale MFCs were connected as a stack and fed with urine. This study demonstrates the feasibility of using urine as an untreated fuel and that improved power outputs can be achieved through MFC miniaturisation and multiplication into stacks.

► Urine was shown to be an ideal fuel for electricity production using MFCs.
► The elemental composition (C,N,P,K) can be beneficially locked in new biomass.
► Small scale MFCs fed with urine produced higher power than larger units.
► Stacks of MFCs produced higher energy densities than individual MFCs.
► Collective maturing of MFCs within stacks avoids cell polarity reversal.