Atmospheric transfer of emerging contaminants from wastewater aeration: real-time and offline characterization using a laboratory bubbling-bursting setup

Wastewater treatment plants (WWTPs) are increasingly recognized as significant, yet potentially underestimated, sources of emerging contaminants (ECs) released into the atmosphere.^1-3 The activated sludge process is one of the most widely used technologies in WWTPs, where continuous aeration generates rising and bursting bubbles. This dynamic can lead to substantial particulate emissions through similar mechanisms to sea-spray aerosol formation. Recent field studies have reported the presence of pharmaceuticals and persistent organic pollutants in the air surrounding WWTPs at pg/m³ to ng/m³ levels.^4-6 Theseemissions are attributed to both aerosolization and volatilization processes. This work aimed to experimentally characterize water-to-air transfer processes under controlled laboratory conditions using a bubbling-bursting setup.

The setup consisted of a glass reactor containing synthetic wastewater spiked with eleven ECs. Synthetic air was injected through a sintered filter to simulate aeration, with flow rates ranging from 0.5 to 4 L/min. A dual analytical strategy was employed: offline sampling using glass filters and polyurethane foams for targeted High-Performance Liquid Chromatography – High-Resolution Mass Spectrometry (HPLC-HRMS) analysis, and online monitoring for real-time aerosol characterization. Specifically, a Scanning Mobility Particle Sizer (SMPS) monitored aerosol size distributions, while a Bromine Chemical Ionization Mass Spectrometer (Br-CIMS) equipped with a thermal desorber provided high-frequency chemical analysis of the particulate phase. This setup enabled the evaluation of the effects of contaminant concentration, temperature, dissolved organic matter (DOM), surfactants, and aeration flow rate on emission dynamics.

The study demonstrated the emissions of both semi-volatile and low-volatility compounds. Clear and reproducible releases were observed for venlafaxine, the macrolide antibiotics erythromycin and clarithromycin, carbamazepine, and irbesartan. Macrolides showed the highest airborne concentrations , reaching 28–53 ng/m³ at a water concentration of 1 µg/L in water. Even compounds with extremely low vapour pressures were emitted, confirming that aeration-driven aerosolization can transfer substances unlikely to volatilize. Emission intensities increased with aqueous concentration and aeration flow rate and were significantly influenced by temperature, DOM, and surfactant content. No homogeneous emission pattern was observed across all compounds, highlighting the influence of their intrinsic physicochemical properties. Aerosols were predominantly in the ultrafine range, with a mean diameter of approximately 44 nm, while DOM and surfactants significantly enhanced both particle size and aerosol mass. For the first time, erythromycin, clarithromycin, and irbesartan were successfully detected in real-time using online Br-CIMS

These results demonstrated that aeration-driven aerosolization in WWTPs enabled the atmospheric emission of  low-volatility ECs, as confirmed by both offline and real-time particulate-phase measurements. Ongoing  work extends this approach to real wastewater matrices, with combined online monitoring of particulate and gas phases using non-target screening strategies.

Acknowledgement - The authors thank the ANR – FRANCE (French National Research Agency) for its financial support of the WECARE project n°ANR-23-CE01-0007.

(1) Wang et al., 2024 - The Innovation  https://doi.org/10.1016/j.xinn.2024.100612.

(2) Barroso et al,. 2019 - Environmental Science and Technology.https://doi.org/10.1080/10643389.2018.1540761.

(3) Ferrey et al,. 2018 - Science of The Total Environment https://doi.org/10.1016/j.scitotenv.2017.06.201.

(4) Lin et al,. 2020 - Water Research. https://doi.org/10.1016/j.watres.2020.115495.

(5) Shoeib et al,. 2016 - Environmental Pollution  https://doi.org/10.1016/j.envpol.2016.07.043.

(6) Sanli et al,. 2025 - Chemosphere  https://doi.org/10.1016/j.chemosphere.2024.144038.