COULOMBIC EFFICIENCY IN A PMFC, EFFECT OF EXUDATES TYPE AND CONCENTRATION, AND OXYGEN

摘要

Estimating the coulombic efficiency for a plant microbial fuel cell (MFC) is more complicated than for a normal microbial fuel cell (PMFC) 1. While a MFC is manually fed with a measurable amount of soluble COD, a PMFC is supplied with an unknown amount of soluble and solid COD via rhizodeposition of a plant. The exact carbon and electron flow from the plant into the rhizosphere and finally the anode is difficult to determine without disturbing the root system. The final current density of a PMFC is determined by the total carbon/electron flow of the plant into the rhizosphere and is diminished by the competitive processes that convert the flow to other products than current. The exudation differs per plant species, the plant age and stage of development; and by environmental factors as culture conditions, nutrient deficiency, pH, water availability, temperature etc., and varies in chemical structure (Grayston et al., 1997). Rhizodeposition comprises five different exudates varying from soluble CODas low-molecular weight carboxylates to solid COD as mucilage. The percentage of the electron flux from the root that is eventually converted to electrons by electrical active bacteria is referred to as the coulombic efficiency.