ABSTRACT
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; Fig. 1). Physicochemical analyses of AQ-900 confirmed a hierarchically porous carbon matrix with a high content of calcium and phosphorus-containing hydroxyapatite 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 36.64 Ω, respectively). After an operation 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 kg-COD-1 removed) highlighted its superior electrocatalytic nature (Table 1). These contributions strengthen CWMFC technology and supports the principles of a circular bioeconomy, aligning with the Sustainable Development Goals that address clean water, affordable energy, and responsible consumption.