Formation and characterization of conductive magnetite-embedded granules in upflow anaerobic sludge blanket reactor treating dairy wastewater.

Promoting direct interspecies electron transfer (DIET) with conductive additives has proved effective in improving anaerobic digestion performance and stability. However, its application is limited by the need to replenish the washout loss of conductive materials. This study reports the formation of conductive magnetite-embedded granular sludge and its long-term influence on the performance of upflow anaerobic sludge blanket reactors treating dairy wastewater. The magnetite-supplemented reactor maintained better performance than the no-magnetite control, with greater sludge settling and electron transport activity, throughout the 192-d experiment at increasing organic loading rates (1.2-8.5 g chemical oxygen demand/L·d). The abundance of electroactive microbes also remained higher in the magnetite-supplemented reactor. The results suggest that DIET-based electric syntrophy was promoted in the magnetite-embedded granules. This study is the first to demonstrate the self-embedment of submicron conductive material into granular sludge and its benefits. These findings offer a new approach to enhancing anaerobic granular sludge systems.