Dual-Function Biophotovoltaic Cell with Titanium Dioxide-Modified Anode for Efficient Wastewater Treatment and Power Generation

Abstract This study evaluated the potential of mixed microalgae-bacteria cultures as electroactive microorganisms to enhance electricity production while simultaneously treating wastewater in emerging biophotovoltaic (BPV) systems. Graphite felt decorated with TiO₂ nanotubes (TiO₂-NTs) was used as the anode, supporting the growth of a biofilm composed of mixed microalgae-bacterial cultures. Batch BPV reactors treated real domestic-industrial wastewater and were compared with BPV systems using bare graphite felt anodes, both with and without microalgae-bacteria cultures. All BPVs operated under a 12-h light/dark cycle, with continuous current monitoring and water quality assessments performed at the beginning and end of the experiments. The TiO₂-NT BPV exhibited the highest power output, reaching 2.37 mW/m 2 . BPVs with bare graphite felt anodes achieved power densities of 1.48 mW/m 2 and 0.41 mW/m 2 with and without microalgae, respectively. Systems inoculated with microalgae-bacteria cultures also showed lower ohmic losses, reaching open circuit voltages between 0.125 and 0.130 V, whereas systems without microalgae reached only 0.050 V and exhibited faster potential drops. In terms of wastewater treatment, TiO₂-NT BPVs achieved the highest removal efficiencies for chemical oxygen demand (COD) and nitrogen, exceeding 90% COD removal and over 80% removal of total ammoniacal nitrogen and nitrate. This study demonstrates that integrating mixed microalgae-bacteria cultures with TiO₂ nanostructured anodes in multifunctional BPV systems significantly enhances both wastewater treatment performance and power generation.