The combination of mesophilic anaerobic digestion and thermophilic aerobic digestion (MAN-TAD) has been recognized as a suitable technology to deal with conventional activated sludge. The MAN-TAD system can make sludge achieve better stability. The retention time of anaerobic digestion (AD-time) had an important role in the sludge stabilization process. With the extension of anaerobic digestion retention time, MAN-TAD system can make sludge achieve better stability. In comparison, volatile/total solids ratio (VS/TS) at AD-time of 38 d presented the lowest values among the three different AD-time with the value of 0.32. Long retention time of anaerobic digestion resulted in high amounts of soluble organic compounds (SCOD), and extracellular polymers (EPS) in the supernatant. Such high amount of organic compounds caused deterioration in sludge dewaterability. Compared with sludges of AD-time 17 d and 24 d, sludge of AD-time 38 d became extremely difficult to dewater due to its high capillary water absorption time (CST) at the end of digestion.
Effects of sludge properties in a combined process of mesophilic anaerobic digestion and thermophilic aerobic digestion
