The granular capacitive moving bed reactor for the scale up of bioanodes

BACKGROUND: Scaling up bioelectrochemical systems for the treatment of wastewater faces challenges. Material costs, low conductivity of wastewater and clogging are issues that need a novel approach. The granular capacitive moving bed reactor can potentially solve these challenges. In this reactor, capacitive activated carbon granules are used as bioanode material. The charge storage capabilities of these capacitive granules allow for the physical separation of the charging and the discharging process and therefore a separation of the wastewater treatment and energy recovery process. RESULTS: This study investigates the performance of the granular capacitive moving bed reactor. In this reactor, activated granules were transported from the bottom to the top of the reactor using a gas lift and settled on top of the granular bed, which moved downwards through the internal discharge cell. This moving granular bed was applied to increase the contact time with the discharge anode to increase the current density. The capacitive moving bed reactor (total volume 7.7 L) produced a maximum current of 23 A m⁻² normalized to membrane area (257 A m⁻³_granules). Without granules, the current was only 1.4 A m⁻²_membrane. The activity of the biofilm on the granules increased over time, from 436 up to 1259 A m⁻³_granules. A second experiment produced similar areal current density and increase in activity over time. CONCLUSION: Whereas the produced current density is promising for further scaling up of bioanodes, the main challenges are to improve the discharge of the charged granules and growth of biofilm on the granules under shear stress.