It is generally recognized that institutions such as schools in rural communities in developing countries lack access to electricity produced in cost-effective and “climate friendly” ways. Microbial fuel cells (MFC) can directly produce 100 W of electricity per m3 reactor from sugar and other biobased compounds in wastewater. A MFC is similar to a fuel cell with anode and cathode electrodes but the difference is that it uses bacteria to produce electrons from biobased compounds. This project aims at making a MFC with biobased electrode materials such as biochar and coal since these resources are available in many developing countries and easy to produce. Efficient utilization of the biobased compounds will be obtained by connecting several reactors in series to a multistep MFC since the community of bacteria will be adapted in each step and create a more robust process. The multistep MFC will finally be produced at a size of 1 m3 for electricity supply to lighting in a school in Ghana and for water purification resulting in recirculation of the nutrient content for application in the agriculture.
Project Completion Report:
WP 1 Reactor design: Three cathode types using dissolved oxygen (DOCs), ferricyanide (FeCs) and air (AiCs) were assessed to improve the reactor design. Electricity generation was evaluated by quantifying current generation response to external resistance. At the lowest resistance of 27 Ohm, FeC-MFC generated highest electrical current of 1630 mA/m2 followed by AiC-MFC with 802 mA/m2 and DOC-MFC with 184 mA/m2. The AiC-MFC was however most sustainable since it is catalysis based in contrast to ferricyanide with the FeC.
WP 2 Bacterial inoculation: The MFC process requires anode electrode biofilm with a microbial community rich in electrogenic bacteria. Usually this microbial community is established from inoculation with naturally occurring anaerobic inocula. The microbial community was optimized by testing three inocula including domestic wastewater, lake sediment (LS) and biogas sludge. The electrogenic bacterium Geobacter sulfurreducens was 4 identified in all inocula and its abundance was positively correlated to the MFC performance. The LS inoculated MFCs showed highest abundance of G. sulfurreducens (18%), maximum current density of 90 mA/m2 and coulombic efficiency (29%). The data obtained improved the understanding of the positive link between electrogenic bacterial abundance and electricity generation.
WP 3 Substrate: This study assessed electricity generation and anode electrode microbial community composition in response to initial substrate. The MFCs initially fed with acetate showed shorter initiation time (1 day) and higher cell voltage (634 mV) than those initially fed with xylose. The acetate-initiated MFCs exhibited longer adaptation time (21 h) when the substrate was switched to bioethanol effluent (BE) in the acetate-initiated MFCs. The microbial community in acetate-initiated MFCs was less diverse and contained most electrogenic bacteria (14%) including Geobacter sulfurreducens. After switching the substrate to BE, the microbial community became more diverse. Acetate-initiated MFCs showed best performance in utilizing BE and BE could not be used in the initiation phase.
WP 4 Cheap electrode materials: This study introduces a simple and efficient electrode material in the form of palm kernel shell activated carbon (AC). This can be produced in rural communities to improve the viability of MFCs. The maximum voltage and power density obtained (under 1000 Ohm load) using an H-shaped MFC with AC as both anode and cathode electrode material was 0.66 V and 1.74 W/m3, respectively. The power generated by AC was as high as 86% of the value obtained with the extensively used carbon paper which proves that there is a potential.