Evaluating Low‐Frequency Ultrasound as a Pretreatment to Improve Ozonation Antimicrobial Efficacy in Urban Wastewater Treatment

Technologies based on oxidation processes, particularly ozonation, have shown great potential for microbiological wastewater (WW) treatment. Applying low-frequency ultrasound (LF-US) can cause sublethal damage to microbial cells by generating nanobubbles, potentially enhancing their sensitivity to ozonation. Thus, primary urban WWs spiked with Salmonella enterica, Escherichia coli, Enterococcus faecium, and Pseudomonas fluorescens were subjected to laboratory-scale ozonation with or without LF-US pretreatment. LF-US pretreatment increased the antimicrobial efficiency of ozonation for all targets, with the most significant increase of 5.16 ± 0.17 Log CFU/mL for P. fluorescens (LF-US 600 s followed by ozone 120 s) and 0.57 ± 0.08 Log CFU/mL for Ent. faecium (LF-US 300 s followed by ozone 30 s). By comparing individual processes with the combined treatment and using inactivation curves from laboratory experiments, it was estimated that ozone treatment following short LF-US pretreatments saved 67 ± 9% of energy and reduced costs by up to 15.1 ± 1.3 €/m³ of treated water. This highlights the potential of this sequential method for effective and cost-efficient WW sanitation.