Nano-engineered microbial electrodes for olive mill wastewater valorization

A biohybrid microbial anode integrating intact cells of the anoxygenic photosynthetic bacterium Rhodobacter capsulatus (R. caps) with a nanocomposite of histidine-functionalized reduced graphene oxide sheets decorated with gold nanoparticles is reported to tackle inefficient extracellular electron transfer. The nanoengineered biohybrid electrode achieved enhanced current generation while utilizing olive mill wastewater (OMW) as a model waste-derived substrate. The system was benchmarked against a previously developed bioelectrode based on R.caps immobilized in a polydopamine matrix, with the nanoengineered microbial anode demonstrating a 2fold increase in current density (achieving 12.0 +/- 0.6 & micro;A cm- 2) and a 6-fold enhancement in total charge generation under solar light irradiation. The developed biohybrid anode operating in a complete single chamber microbial fuel cell with a 1:1 (v/v) mixture of Lovley and Phillips electrolyte and OMW allowed achieving a power density of 2.1 +/- 0.3 & micro;W cm- 2. The result is attributed to the biohybrid architecture, which reduces charge transfer resistance and enhances faster electron transport kinetics at the bio-nano interface. Overall, this work demonstrates a promising strategy for engineered photoelectrochemical systems aimed at waste valorization and renewable energy conversion.