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

## TL;DR

Using low-frequency ultrasound before ozonation improves microbial removal in wastewater and saves energy and costs.

## Contribution

Demonstrates that low-frequency ultrasound pretreatment enhances ozonation's antimicrobial efficacy and reduces treatment costs.

## Key findings

- LF-US pretreatment increased antimicrobial efficiency of ozonation for all tested microorganisms.
- The most significant improvement was 5.16 Log CFU/mL for Pseudomonas fluorescens.
- Combined treatment saved 67% of energy and reduced costs by up to 15.1 €/m³ of treated water.

## Abstract

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.

Ozonation significantly reduces the microbial viability in wastewater.Pretreatments with low‐frequency ultrasound improve the effect of ozonation.Weibull‐tail inactivation modeling supports the identification of energy‐ and cost‐efficient treatment conditions.

Ozonation significantly reduces the microbial viability in wastewater.

Pretreatments with low‐frequency ultrasound improve the effect of ozonation.

Weibull‐tail inactivation modeling supports the identification of energy‐ and cost‐efficient treatment conditions.

In urban wastewater contaminated with
Salmonella enterica
,
Escherichia coli
,
Enterococcus faecium
, and
Pseudomonas fluorescens
, a low‐frequency ultrasound pretreatment enhanced the antimicrobial effectiveness of ozonation. Additionally, pretreatment led to energy and cost savings compared to ozonation alone, highlighting the potential of this sequential method for efficient and economical wastewater sanitation.