Sterols and Anionic Surfactants in Urban Aerosol: Emissions from Wastewater Treatment Plants in Relation to Background Concentrations

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Abstract
Aerosol particles that are emitted from aeration tanks of wastewater treatment plants (WWTPs) can be enriched with environmentally relevant wastewater constituents. In this study, aerosol particles were sampled simultaneously at the pre-aeration tank of a municipal WWTP and at two urban locations approximately 1 km away from the WWTP to evaluate the significance of these aerosol emissions. Moreover, aerosol particles were sampled at a small wastewater irrigation facility and at a rural site. In aerosol particles and wastewater, six sterols (cholesterol, coprostanol, campesterol, β-sitosterol, stigmasterol, stigmastanol) and anionic surfactants (expressed in terms of methylene blue active substances, MBAS) were quantified. The results showed significantly higher concentrations of sterols and MBAS at the WWTP than at the urban locations. At the WWTP, average concentrations of cholesterol (848 ± 321 pg m-3), coprostanol (1132 ± 565 pg m-3), and MBAS (132 ± 43 ng m-3) in aerosol were approximately twice as high. This can be attributed to emissions from the treatment tank. Coprostanol, a unique tracer for wastewater, was detected only occasionally at the urban locations. The results of this study show that the aeration of wastewater is a continuously operating local source for organic compounds in aerosol. The wastewater irrigation facility was a minor source of aerosol-bound sterols (coprostanol, 287 ± 218 pg m-3) and anionic surfactants (64 ± 32 ng m-3). Except for coprostanol, all compounds were also present in samples of rural aerosol.

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