Performance evaluation of aquacultural processing waste-derived biochar as a cathode catalyst in constructed wetland microbial fuel cell

The swift development in aquaculture has resulted in the production of nutrient-rich effluents and organics that require a sustainable treatment solution. In this research, aquacultural processing wastes (fish scales and shrimp shells) were co-pyrolyzed to convert into a cathodic biochar-based electrocatalyst (AQ-900) for a vertical up-flow constructed wetland microbial fuel cell (CWMFC). Physicochemical analyses of AQ-900 confirmed a hierarchically porous carbon matrix with a high content of Ca and P-containing calcium phosphate phases and heteroatom functional groups to enhance electron transfer and catalytic capability. The electrochemical assessments established that oxygen reduction reaction kinetics in the cathode were amended. The catalyst-coated cathodes demonstrated a four times higher exchangeable current density (io, 2.88 mA cm−2) and much lower charge transfer resistance (Rct, 8.92 Ω) than the original carbon felt (0.70 mA cm−2 and 36.65 Ω, respectively). After an operation of a total of 160 days in synthetic wastewater followed by real fish market wastewater, the CWMFC registered a maximum power density of 16.10 ± 2.27 mW m−2. The system achieved a chemical oxygen demand (COD) removal of 85.63 ± 1.33%, and NH4+-N removal of ~ 90%. Additionally, the amplified coulombic efficiency (6.41 ± 0.21%) and normalized energy recovery (184.01 ± 0.02 Wh kgCOD−1 removed) over the control (almost two times) highlighted its dual role as a conductive modifier and catalytic promoter. These contributions strengthen the field-scale application of CWMFC and support the principles of a circular bioeconomy, aligning with the Sustainable Development Goals that address clean water, affordable energy, and responsible consumption.