The hydrolysis and acidogenesis of solid organic wastes in a rotational drum fermentation system (RDFS) were improved by direct ultrasonic irradiation (DUSI) and a modified ultrasonic treatment (MUST) composed of dilution, ultrasonic irradiation, and filtration. The effect of DUSI on VA desorption from particle surfaces was estimated. DUSI delivered few distinctions from the broth characteristics, but elevated pH and VS degradation rate (53% higher than the control) in the subsequent acidogenesis. The results demonstrated that DUSI could dislodge VA from particle surfaces and disrupt large-size particles by hydromechanical shear force. To improve VA desorption and removal, a MUST process was constructed. The influences of MUST on the characteristics of the fermentation broth and the Subsequent acidogenic performance were investigated. MUST raise the broth pH level from 5.1 to 5.5 and remarkably decreased VA concentration from 11.0 to 3.5 g/L. At the end of the subsequent acidogenesis, VA increasing ratios, VS degradation ratios, and surface based hydrolysis constants of the fermentors with the control broth (CF) and the treated broth (MUSTF) were 166.7% and 732.0%, 17.0% and 26.7%, and 16.9% and 26.8 x 10(-6) kg m(-2) d(-1). respectively. With the assistance of MUST, a considerably improved acidogenic performance of solid organic wastes was accomplished in terms of VA production, VS degradation, and particle hydrolysis. (c) 2008 Elsevier Ltd. All rights reserved.