Role of magnetite in methanogenic degradation of different substances

For better understanding the role of magnetite in methanation of different substrates, two up-flow anaerobic sludge bed reactors (RM with magnetite; RS with silica) were built using acetate (stage I), propionate + butyrate (stage II), and sucrose (stage III) as the substrates, respectively. RM reactor showed better COD removal efficiency and adaptability to different substrate impacts. More extracellular polymeric substances (EPS) were produced for anaerobic sludge granulation, and the sludge in RM had better intensity, hydrophobicity and electroactivity compared with those in RS. Interestingly, magnetite had different promoting effects on methanogenic degradation of different substrates, and magnetite facilitated different syntrophic partners, like Desulfovibrio, Smithella, unidentified Clostridiates and Methanosaeta in different stages. The strengthening factor of biogas production from sucrose was the highest (1.23 ± 0.03), and analysis of key enzyme activities indicated that the potential magnetite-induced direct interspecies electron transfer (DIET) improved the process between the glycolysis, oxidation of pyruvate and CO₂-dependent methanogenesis.