Efficacy of methanogenic biomass acclimation in mesophilic anaerobic digestion of ultrasound pretreated sludge.

Methanogenic biomass plays a key role with regard to methane production during anaerobic bioconversion of organic substrates. In this study, the effect of two different acclimated inocula on digestion performances was investigated by means of anaerobic batch tests on untreated and sonicated waste-activated sludge. Organics solubilization and removal kinetics, the abundance and physiological conditions of archaeal cells on ultimate methane yield were evaluated. The simultaneous presence of Methanosarcina and Methanosaeta in the archaeal biomass, the higher initial archaeal cells relative abundance and their occurrence in the aggregated forms were the main factors positively affecting the conversion into methane. The presence of the acclimated inoculum at the start-up influenced positively the methane improvement due to sonication, and the methane-specific production increased from 0.335 ± 0.03 to 0.420 ± 0.05 Nm3/kg VSfed. Moreover, the better physiological state of methanogens permitted to appreciate the effect of hydrolysis improvement by ultrasound pretreatment.