Bioelectrochemical systems (BES) use microorganisms as catalysts for electrode reactions. Driven by electricity, microorganisms can remove nitrate at low energy input and without chemical addition. This makes BES attractive for treatment of groundwater towards potable quality. A key challenge is to create scalable BES technology to deal with the large volumes of water, here we explore fluidized bed BESs using capacitive particles colonized by electroactive biofilms. In a first phase I will develop a novel 2-chamber fluidized BES. The nitrate removal and electron transfer will be studied using different electrochemical techniques. I will distinguish the charge storage capacity of the activated carbon (AC) particles and the electroactive biofilms (EABs). Second, I will enhance the charge storage capacity by adding an external capacitive material. Graphene oxide (GO) will be converted to conductive and insoluble reduced graphene oxide (rGO) biologically and/or electrochemically then deposit on and in the biofilms, effectively creating a modified bioparticle. The structure of the AC-rGO-EABs granules will be investigated by microscopy in combination with electrochemical analysis. I will determine the ratio of rGO/AC for optimal denitrification efficiency and assess the microbial composition and stratification along the fluidized BES. In a final phase, I will validate the fluidized BES with real nitrate contaminated groundwater from Flanders.