Enhancing anaerobic digestion of fat, oil, and grease (FOG) using electrically conductive and calcium-rich waste materials: A comparative performance analysis

High-strength organic wastes such as fat, oil, and grease (FOG) are promising co-substrates for anaerobic digestion (AD) due to their high energy content. However, the accumulation of long-chain fatty acids (LCFAs) often leads to microbial inhibition and process instability. This study evaluated the effectiveness of oyster shell biochar (OSB) as a dual-function additive that integrates calcium supplementation and electrical conductivity to improve AD performance. OSB demonstrated enhanced methane production performance, attributed to its ability to accelerate early-stage microbial activity and maintain system stability. Microbial analysis showed the selective enrichment of Methanothrix and Smithella, supporting the potential involvement of direct interspecies electron transfer (DIET). These findings suggest that OSB can simultaneously promote chemical buffering and microbial stimulation. As a low-cost, waste-derived material, OSB offers a practical and sustainable strategy to improve the efficiency of lipid-rich waste digestion and contributes to the advancement of functional biochar applications in AD systems.