Synergistic improvement of methane production and phosphorus recovery from anaerobic digestion of waste activated sludge by Fe2O3-assisted electroactive microorganisms.

Conductive materials and electroactive microorganisms (EAM) are key factors on enhancing methane production in anaerobic digestion of waste actived sludge via the direct interspecies electron transfer (DIET). However, their combined impact on simultaneous methane production and phosphorus recovery remains unclear. The Fe2O3 and EAM were added together to synergistically improve anaerobic processes, resulting in a 1.53-fold increase in methane production and a remarkable 12.03-fold enhancement in phosphorus removal. The co-additon of Fe2O3 and EAM promoted Fe(III/II) redox cycling, increased enzyme activity, and enhanced electron transport system (ETS) functionality while enriching DIET-associated bacteria (e.g., Brooklawnia, Anaerolineae) and methanogens (Methanosarcina). Metagenomic analysis revealed the upregulated genes related to phosphorus and iron metabolism, ETS, and DIET-coupled electron bifurcation. Notably, Fe2O3 may act as an alternative to cytochromes and pili in mediating DIET in electron transfer processes.