Electrifying waste: Lebanese olive cake as novel bioenergy substrate in microbial fuel cells

Abstract

The use of agro-industrial waste as a bioenergy source offers a viable approach for sustainable energy generation. The present study investigates the viability of Lebanese olive cake as an innovative carbon source for bioelectricity production in double-chamber microbial fuel cells (MFCs) using Streptomyces fimicarius A1, a lignocellulose-degrading actinobacterium isolated from dumpsite soil. Essential operational parameters, such as substrate concentration, inoculum amount, electrode shape, and concentrations of mediators and electron acceptors, were methodically tuned. The physicochemical characterization of olive cake, including its polyphenol, fiber, and metal content, underscored its abundant composition favorable for microbial metabolism. The research further investigated the impact of external resistance, internal resistance, biofilm development, MFC architecture (series vs. parallel), and fed-batch operation on system efficacy. The system was optimized using 10 g/L olive cake as the substrate, a 10% inoculum level, and cuboid-shaped electrodes. The cathodic chamber was supplied with potassium ferricyanide (0.05 M) as the electron acceptor, and methylene blue (300 µM) served as the redox mediator. Under fed-batch operation and various electrical configurations, the system demonstrated enhanced performance. The series-connected MFCs achieved a maximum voltage of 1509 mV, electric current of 0.19 mA, and power output of 286.71 mW, whereas the parallel configuration produced 757 mV, 0.38 mA, and 287.66 mW. These results provide significant insights into the integration of agro-waste management with renewable energy technologies in Lebanon and worldwide, underscore the efficiency of olive cake as a sustainable substrate and highlight the role of optimized biological, electrochemical, and operational parameters in improving MFC performance.