Most of the sludge pre-treatment methods to improve the anaerobic digestibility are not adopted in the fields because of low economical efficiency. The venturi cavitation system (VCS) using hydrodynamic cavitation is simple in design and operates with a low operating cost compared to most of the current sludge pretreatment methods. Research was conducted to investigate the optimum design and operating conditions of the VCS for pretreatment of waste activated sludge. The experimental results indicate that the optimum number of venturis in series is three (three-venturi units). The suction mode operation of the pump used yielded 1.6 times higher solubilization efficiency per unit of energy consumption than the discharge mode. Variations in the size of the venturi throat diameter with the three-venturi unit did not affect solubilization efficiency. Also, a parallel installation with two three-venturi units yielded 30% higher solubilization efficiency per unit of energy consumption than did a single three-venturi unit. With the parallel venturi unit, the solubilization efficiency was 5.6 mg △SCOD/g TS/kWh, which is higher than previously reported values.

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