The one-stage autothermal thermophilic aerobic digestion for sewage sludge treatment: Effects of temperature on stabilization process and sludge properties

One-stage autothermal thermophilic aerobic digestion (ATAD) has potential application in wastewater treatment plants due to its simplicity and small area occupation. Aimed to investigate the effects of digestion temperature on stabilization process and sludge properties, batch experiments were carried out at 35, 45, 55, and 65 °C in simulated one-stage ATAD digesters with effective volume of 5 L. Thermophilic digestion systems at 45 and 55 °C attained more rapid volatile solids (VS) removal than a mesophilic digester at 35 °C, however raising digestion temperature to 65 °C adversely affected sludge stabilization. At the end of the experiment (i.e. 552 h), VS removals in the 35, 45, 55 and 65 °C digesters were 33.6%, 42.9%, 45.0% and 24.5%, respectively. Digestion temperature has significant effect on VS reduction. As volatile fatty acids (VFA) accumulated rapidly from 72 to 264 h, acetic and propionic acids became the main VFA constituents in the thermophilic digester with digestion temperature of 55 °C, however only acetic acid was a major constituent of VFA in the 35 °C digester. After digestion for 552 h, characteristic absorption bands of carboxyl group, aliphatic chains, carboxylate group and amine group were significantly weakened in the 35 and 55 °C digesters. VS concentration is well fitted by an exponential decay function over a range of 35–55 °C.

► Thermophilic digestion at 45 and 55 °C had better VS removal than mesophilic digestion at 35 °C. ► High digestion temperature at 65 °C resulted in the deteriorated digestion condition. ► Characteristic groups such as carboxyl group became weaker after sludge digestion. ► Kinetics equation of VS concentration is given as VS = VS0 exp(−5.0 × 10−4 × 1.024(T−20) · t).