Wastewater ozonation is increasingly applied to reduce micropollutants in effluents of wastewater treatment plants. To assess its ecological effects, we conducted flow channel experiments comparing conventionally-treated wastewater, ozonated wastewater, and river water from a location upstream of the WWTP outlet. Both wastewater types were diluted with river water to obtain environmentally relevant pollutant concentrations under low flow conditions. Concentrations of 49 micropollutants (pharmaceuticals, industrial chemicals, agricultural substances) were monitored to quantify pollutant loads and ozonation efficiency. Larvae of two river macroinvertebrate species, Leuctra geniculata (Stephens, 1836) and Hydropsyche incognita Pitsch, 1993, were exposed to the three water types in experimental flow channels for 14 days in May and July 2019. Three response variables were measured: mortality, locomotor activity, and biochemical markers. Micropollutant concentrations were highest in conventionally-treated wastewater, while the additional ozonation reduced concentrations by ∼50%. River water showed the lowest concentrations, except for several industrial and agricultural substances. H. incognita exhibited higher mortality in ozonated wastewater (between 12.5% and 37.5% higher as compared to conventionally-treated wastewater and river water, respectively), whereas responses of L. geniculata were indifferent. Both species displayed significantly higher locomotor activity in ozonated wastewater, indicating sublethal behavioral effects. Both species also showed higher Acetylcholin-Esterase activity in ozonated wastewater, yet only partially significant, while Catalase and Glutathione-S-Transferase activity showed insignificant responses. Although our results in general confirm the additional purification efficiency of ozonation, they also indicate that ozonated wastewater may act as a stressor to aquatic insects, potentially due to transformation products or undetected compounds influencing biological responses. These results suggest that ozonation alone does not guarantee improved wastewater quality. • Ozonation led to ≥ 50% higher purification rates for many of the 49 substances studied. • This applied to 80% of the pharmaceuticals, 62% of the agricultural, but 0% of the industrial substances. • Ozonated wastewater affected survival, locomotion, and AChE activity. • Conventionally-treated wastewater and river water affected the organisms similarly.
Rothe et al. (Fri,) studied this question.