Comparative effects of GAC addition on methane productivity and microbial community in mesophilic and thermophilic anaerobic digestion of food waste

The relative effects of granular activated carbon (GAC) addition (25 g/L) in anaerobic digestion of food waste at mesophilic (37 degrees C) and thermophilic (55 degrees C) temperatures were investigated using biochemical methane potential (BMP) test. The addition of GAC significantly reduced lag phases for methane production in comparison with the unamended control at both temperatures. Microbial community analyses revealed that GAC addition increased the diversity and richness of both bacterial and archaeal communities. Besides, several known or potential electroactive fermentative bacteria (e.g., Calorameter, Sporcumerobacter, Coprothermobacter, etc.) were found in GAC-amended bioreactors at both temperatures, suggesting the possibility of DIET-based syntrophy in these reactors. At mesophilic temperature, GAC amendment increased methane productivity (L CH4/kg-VS) by almost two-fold in comparison with the control; however, methane production at the thermophilic temperature was unaffected by GAC addition. These results indicate that enhanced process kinetics at thermophilic temperature might diminish the visible impact on methane productivity due to the addition of GAC.