Energy Recovery from Waste Buttermilk in Microbial Fuel Cells Equipped with a Gas Diffusion Anode and Non-Precious Metal Cathodes

The valorization of dairy industry by-products and simultaneous energy recovery remain important challenges in sustainable waste management. In this study, waste buttermilk was evaluated as a substrate for bioelectricity generation in a microbial fuel cell (MFC) equipped with a gas diffusion anode (GDE) and non-precious metal cathodes. Three electrode configurations were investigated: GDE/GDE, GDE/Cu–B, and GDE/Ni–Co. Stable operation was achieved for all MFC systems, confirming that waste buttermilk can support electroactive biofilm development. The GDE/Ni–Co configuration exhibited the highest performance, reaching a maximum power density of 25 mW·m−2, compared to 22 mW·m−2 and 17 mW·m−2 for GDE/Cu–B and GDE/GDE, respectively. Coulombic efficiency ranged from 10.83% to 18.82%, depending on the electrode system. A cyclic performance decrease was observed, likely caused by membrane fouling and electrode surface blockage. The results indicate that waste buttermilk can be utilized for simultaneous waste treatment and energy recovery in MFC systems, although further optimization is required to improve long-term stability.