Effects of cell lysis in gas yield and sludge stabilization by combined process of thermophilic aerobic and anaerobic digestion

A novel process of combining thermophilic (55 degrees C) aerobic digestion as pretreatment with mesophilic (<35 degrees C) anaerobic digestion process (TAD-MAD) was designed to stabilize sludge and produce CH4 biogas. TAD-MAD processes can yield energy-rich biogas, save aeration energy, short retention time, which is prior to single TAD or MAD process. TAD pretreatment play an important role in decomposing cell of sludges and enhancing the hydrolysis process. Other two pretreatment of Alkali and Ultrasonic following MAD process were investigated in this paper to compare with effect of TAD-MAD process on sludge stabilization and biogas production. The results showed that VSS removal rates for three processes of TAD-MAD, Alkali-MAD and Ultrasonication-MAD could achieve 40% at 10d or 11d, which can meet the requirements of the GB18918-2002 guidelines. soluble chemical oxygen demand (SCOD) and volatile fatty acid (VFA) in the supernatant could increase to the highest values at initial 4d for three different processes, and subsequently decline during the latter part of digestion. For TAD-MAD process, SCOD and VFA could rapidly reach to the highest values 16000 mg/L and 7222 mg/L at initial 2d respectively, which achieved more significant effect on cell lysis. All three pretreatments improved biogas production, but TAD-MAD process could produce the most amounts of CH4 (481mL CH4 g-1 VSS) and cumulative biogas production of 12496mL at end of digestion. pH between 7.04 and 7.92 in three systems could maintain in neutral and subalkaline values. Alkalinities of sludge in three systems could meet need for methanogenic population inside the anaerobic digester. In conclusion, TAD-MAD has similar VSS removal rate with other two processes, but could produce more CH4 and biogas yield than other two processes. (C) 2016 Published by Elsevier B.V