Aqueous phase disinfection with power ultrasound: process kinetics and effect of solid catalysts

The effectiveness of power ultrasound as a viable alternative for destroying pathogenic organisms in homogeneous and heterogeneous mixtures of aqueous solutions was investigated. The method involved monitoring of total coliform bacteria during sonication of E. coli suspensions in the absence and presence of equivalent mass concentrations of ceramic, metallic zinc, and activated carbon. It was found that disinfection by ultrasound is accelerated with solids in the order activated carbon > ceramic > metallic zinc. Process kinetics for each test system were assessed by nonlinear regression analysis of bacterial density vs time data, and the predicted model was found to resemble a well-known expression describing chlorination kinetics. The model denoted that in the presence of activated carbon the process rate was pseudo first order, and the required contact time to accomplish 50% kill was 2.8, 2.4, and 4 times shorter than it was in the zinc-catalyzed, ceramic-catalyzed, and noncatalyzed systems, respectively. It was further found that catalytic effects faded away with increased sonication time and/or reduced number of bacteria, denoting (i) decreased probability of bacterial contact with the solid-liquid interface; (ii) erosion of solid surfaces by vibrational effects; and (iii) reduced cavity formation due to degassing effects of ultrasound.