Urine utilisation by microbial fuel cells, energy fuel for the future

Abstract

Alternative energy sources have been the focus of global interest, as perhaps one viable solution to the growing problem of fossil fuel depletion. Promising technologies such as photovoltaics, wind-turbines and wave-generators, dominate the field of natural energy harnessing for electricity and indeed provide practical solutions in areas where solar radiation, wind force and wave power are abundant. One other type of alternative energy source that has been receiving increased attention, is biomass and its conversion to electricity via Microbial Fuel Cells (MFCs).1 This offers the unique advantage of converting ‘‘too-wet-to-burn’’ low-grade organic matter directly into electricity at high efficiencies and for long periods of time. A wide range of substrates have been reported as suitable fuels for MFCs,2 but one potential fuel, which has so far been neglected—and is therefore underexploited—is urine. Urine is an abundant waste product with an estimated annual global production of B6.4 trillion litres (based on a world population of 6.97 billion and average daily urine production of 2.5 litres/adult human). This short communication for the first time describes the direct conversion of urine into electricity through MFCs. The specific aims of this study were: (i) to investigate whether untreated urine can produce electricity through MFCs; (ii) to compare the responses of a re-circulation MFC system to the addition of large urine volumes into a reservoir or injection of small urine volumes directly into theMFC inlet; (iii) to evaluate the sensitivity of the established MFC anodic community to the addition of neat urine; (iv) to calculate the energy yield from urine when utilised in MFCs.