Microbial community structure in a thermophilic aerobic digester used as a sludge pretreatment process for the mesophilic anaerobic digestion and the enhancement of methane production

► A combined process was developed for sludge reduction and methane production. ► Biological TAD pretreatment highly increased soluble organic matters. ► Bacteria species using DGGE were examined in a combined process. ► Methanogen species using a real-time PCR were examined in the MAD. ► Methane enhancement by TAD pretreatment was observed in a combined process.