A microfluidic study of acetate conversion kinetics in a microbial electrolysis cell: The role of age, concentration and flow on biofilm permeability
Nastaran Khodaparastasgarabad, Manon Couture, Jesse Greener
Abstract
This work addresses the need for kinetic studies to clarify potentially exploitable mechanisms involved in generating current from flow-based bioelectrochemical systems (BES). Unlike most kinetic studies, which focus on electron transport, we focus on chemical mass transport by controlling the relevant experimental parameters. This is accomplished using a microfluidic 3-electrode setup that recorded output current (I) from a mature Geobacter sulfurreducens electroactive biofilm (EAB) while accurate control is applied over acetate concentration ([Ac]) and flow rate (Q). Additionally, the flow mode (tangential and perpendicular) is controlled to apply expansive or compressive sheer forces against the EAB. A detailed analysis of the effects of the control variables on the current based on data collected for nearly 1 year, the longest timeframe for a microfluidic BES experiment to date. All experimental parameters affect output, but age is the dominant factor. After nearly 1 year, current densities were as high as 29.5 A m-1, which is higher than in any reported 3-electrode experiment on G. sulfurreducens EAB. We conclude that flow-based deacidification of the EAB led to increases to outputs during early growth stages, whereas at later times the increases were related to improved acetate permeability. Additionally, after 5 months each flow mode provokes complementary kinetic properties based on measurements of apparent enzyme/substrate affinity (KM(app)) and maximum current (Imax) values. Therefore, in addition to providing fundamental insights into BES functionality, these findings also open the door to practical applications and a road map to optimization of device design and operational conditions.