Spectral optimisation enhances simultaneous wastewater treatment, power generation, and carbon sequestration in algal microbial fuel cells treating biogas slurry

Algal microbial fuel cells (AMFCs) offer a promising platform for simultaneous wastewater treatment, renewable energy generation, and carbon capture. This study investigates the critical role of light colour (natural, red, yellow, green, blue; 4,500 Lux) in optimising AMFC performance using Chlorella-based biocathodes and biogas slurry as anodic substrate. Results demonstrate that blue light maximised contaminant removal, achieving 95.70% Chemical Oxygen Demand (COD) and 96.28% Ammonia nitrogen (NH₄⁺-N) elimination, while red light enabled peak power density (570.86 mW·m⁻²). Electrochemical and kinetic analyses demonstrated that the blue/red spectra optimised AMFC performance by enhancing Chlorella photosynthesis. This increased the cathodic dissolved oxygen concentration, driving a reduction in internal resistance and a remarkable 55.1% (blue) and 48.5% (red) improvement in coulombic efficiency (CE) over natural light. The higher efficiency was directly linked to the enrichment of electroactive Proteobacteria (e.g. +11.89% under blue light). Concurrently, the degradation of organics was accelerated and was well-described by first-order kinetics (R² > 0.98). Furthermore, blue/red light intensified carbon sequestration, increasing CO₂ fixation rates to 17.99% (blue) and 19.55% (red) and elevating chlorophyll content by 30.8% (blue). Microbial community analysis confirmed light-specific shifts, with red light promoting microbial richness and blue light optimising community stability. This work establishes spectral control as a strategic tool to amplify AMFC efficacy in wastewater valorisation, energy recovery, and carbon neutrality. Future studies should explore hybrid light regimes and scalable configurations to advance practical implementation.