SUMMARY
The reuse of treated wastewaters could contribute to reducing water stress. In this research, ultrasound application on bacterial inactivation in municipal wastewater (MWW) was evaluated. Total and fecal coliforms were used as standard fecal indicators; volatile suspended solids (VSS) were analyzed too. Samples were taken from the effluent of secondary clarifiers. In addition, inactivation tests were carried out on pure cultures of E. coli (EC) and B. subtilis (BS). Sonication was performed at 20 kHz, 35% amplitude and 600 W/L for 15, 30 and 45 min. After 15 min of sonication, bacterial density was reduced by 1.85 Log10 MPN/100 mL for EC and 3.16 Log10 CFU/mL for BS. After 30 min, no CFU/mL of BS were observed in MWW and, after 45 min, the reduction of total and fecal coliforms was practically 6.45 Log10 MPN/100mL. Inactivation mechanism was made by cavitation, which causes irreversible damage to the cell wall. Although high bacterial densities were employed, percentages of inactivation >99% were reached at 45 min. This research contributes to the implementation of ultrasound as a disinfection technique with high potential due to its high efficiency without producing byproducts. In fact, the water meets the guidelines for reuse in direct human contact services.