Abstract:
Sonication and thermalization can be applied successfully to disrupt the complex waste activated sludge
(WAS) floc structure and to release extra and intra cellular polymeric substances into soluble phase along
with solubilization of particulate organic matters, before sludge digestion. In this study, sonication has
been combined with thermalization to improve its disintegration efficiency. It was aimed that rise in
temperature occurring during the sonication of sludge was used to be as an advantage for the following
thermalization in the combined pre-treatment. Thus, the effects of sonication, thermalization and sonothermalization
on physical and chemical properties of sludge were investigated separately under different
pre-treatment conditions. The disintegration efficiencies of these methods were in the following
descending order: sono-thermalization > sonication > thermalization. The optimum operating conditions
for sono-thermalization were determined as the combination of 1-min sonication at 1.0 W/mL and thermalization
at 80 C for 1 h. The influences of sludge pre-treatment on biodegradability of WAS were experienced
with biochemical methane potential assay in batch anaerobic reactors. Relative to the control
reactor, total methane production in the sono-thermalized reactor increased by 13.6% and it was more
than the sum of relative increases achieved in the sonicated and thermalized reactors. Besides, the volatile
solids and total chemical oxygen demand reductions in the sono-thermalized reactor were enhanced
as well. However, it was determined that sludge pre-treatment techniques applied in this study was not
feasible due to their high energy requirements.