Experimental study of waste activated sludge treatment using a rotational hydrodynamic cavitation generator and ultrasonication.

In the present work, the performance of a waste-activated sludge (WAS) treatment using a novel rotational hydrodynamic cavitation generator (RHCG) was investigated. To verify the performance, a comparison with an ultrasonic device was conducted in four experimental cases at the same specific energy input using three assessment factors. The RHCG consisted of a rotor and three covers with inserted dimples. Ultrasonication was performed using a general ultrasonic bath. The experimental parameters were established to calculate the specific energy input of the sludge passing through the RHCG for a total of 5, 10, 15, and 20 times. Disintegration performance using particle size distribution and SVI, solubilization rate using soluble COD, and oxidation performance using total COD and VSS reduction rate were analyzed as assessment factors. For oxidation and particle disintegration, the RHCG showed overwhelming performance and was superior to the ultrasonic device at low energy input. The tCOD and VSS of the sludge treated five times in the RHCG were reduced by 52.9 and 66.0%, respectively, and the median particle size of the sludge treated 10 times in the RHGG was reduced by 92.7%. Otherwise, at comparable specific energy inputs, sludge treated by the ultrasonic device were reduced by 0, 26.4, and 67.6%, respectively. However, due to the contradictory interactions of particle disintegration and oxidation, the two treatment methods showed similar performance in terms of solubilization rate and reached up to 42.3 and 41.4% in the RHCG and ultrasonic device, respectively. In the present work, the RHCG is proposed as a new novel WAS treatment technique.