DOM evolution and microbial function during anaerobic digestion under supplementing Fenton sludge: A comparative study

Certain Fe(III) compounds are utilized to stimulate dissimilatory iron reduction (DIR), thereby accelerating the transformation of dissolved organic matter (DOM) during anaerobic digestion. The effects of four specific Fe(III) compounds—Fenton sludge (FS), ferrihydrite, Fe 2 O 3 , and Fe(OH) 3 —on DOM evolution and microbial function dynamics during anaerobic digestion were investigated in this study. Batch experiments revealed that the FS exhibited superior performance in DIR efficiency and DOM transformation compared to other Fe(III) compounds, which is attributed to its relatively low crystallinity that enhances bioavailability and the higher predicted relative abundance of pil A gene, which is consistent with enhanced extracellular electron transfer. Combined size exclusion chromatography and fluorescence excitation emission matrix analysis demonstrated that the FS effectively degraded and transformed medium molecular weight humic-like substances. Furthermore, pathway analysis confirmed that the FS augmented acidification efficiencies, triggered by elevated activity of the propionate CoA-transferase pathway. Five genera, including Paludibacter , Macellibacteroides , Bact-08 , TM7a , and Clostridium sensu stricto 12 , were identified as keystone genera via network analysis. These genera maintained the bacterial community’s functional stability through their potential involvement in the DIR process and regulation of organic matter metabolism. Overall, these findings highlight FS as a promising Fe(III) source that drives efficient DIR-coupled DOM transformation, suggesting its potential for the resource recovery of Fenton sludge.