Benefits of conductive additive for direct interspecies electron transfer in anaerobic digestion

Abstract Conductive additive such as biochar have been extensively employed to enhance anaerobic digestion (AD) performance for over a decade. Among the proposed mechanisms, conductive additive-facilitated direct interspecies electron transfer (DIET) is frequently cited as a key contributor to these performance improvements. Because this process is believed to bypass traditional diffusible intermediates (e.g., H 2 or formate), it can enable more efficient energy transfer between syntrophic partners and accelerate substrate degradation, potentially leading to higher methane yields and improved overall stability of the anaerobic digestion process. However, benefits regarding conductive additive-facilitated DIET often rely on indirect indicators rather than direct experimental evidence. Here, we advocate for a critical reassessment on the benefits of conductive additive for DIET in AD. Specifically, we emphasize the importance of establishing standardized experimental protocols and obtaining direct evidence to confirm the occurrence and significance of DIET in conductive additive-amended AD system. Furthermore, it is essential to distinguish DIET from other enhancement mechanisms such as pH buffering and toxin adsorption that may independently contribute to improved AD performance, with the goal of advancing its practical implementation.