Wastewater treatments plants (WWTP) discharge antibiotic resistant bacteria with the treated wastewater. In this project we quantified the extent to which different WWTP in Switzerland eliminate and discharge resistant bacteria and how this affects the receiving waters.
Oxidative wastewater treatment is an important strategy for the removal of micropollutants from wastewater, and is one of the main technologies that will be used for this purpose in Switzerland. In this project we studied how this treatment affects resistant bacteria. Laboratory studies were performed to obtain detailed information on how ozonation damages resistant cells and resistance genes to provide Information about dose dependence and kinetics of the process. Investigations at the first full scale ozonation plant in Switzerland, ARA Neugut, provided data from a real world implementation of this treatment process.
The project showed that ozonation of wastewater ultimately provides a less complete disinfections and a less effective deactivation of DNA (and thus resistance genes) in wastewater ozonation then simple laboratory experiments may suggest. The interactions with the complex chemistry in the wastewater matrix, microbiological populations that are less sensitive than laboratory strains such as E. coli, and the formation of larger biomass structures (flocs) all interfere. Under process conditions that are optimized for micropollutant reduction most bacterial cells are killed, but a residual population survives, and the genetic material (theoretically capable of being taken up and incorporated into the genome of other bacteria) survives. The full scale plant in Neugut revealed another potential problem – the biological post-treatment of ozonated water, which is necessary to reduce toxic oxidation products, allows resistant bacteria to grow, reducing the overall effectiveness of the process for reducing the load of resistant bacteria with the wastewater stream into rivers and lakes. Further research will be necessary to identify potential improvements to maximize the potential of wastewater ozonation as a barrier to the dissemination of antibiotic resistance into the environment.
- Czekalski et al. (2016) Antibiotikaresistenzen im Wasserkreislauf. Ein Überblick über die Situation in der Schweiz, Aqua & Gas, 96(9), 72-80. https://www.dora.lib4ri.ch/eawag/islandora/object/eawag:10653
- Czekalski et al. (2016) Inactivation of antibiotic resistant bacteria and resistance genes by ozone: from laboratory experiments to full-scale wastewater treatment, Environmental Science and Technology, 50(21), 11862-11871. https://www.dora.lib4ri.ch/eawag/islandora/object/eawag:14002
- Lee et al. (2016) Inactivation efficiency of Escherichia coli and autochthonous bacteria during ozonation of municipal wastewater effluents quantified with flow cytometry and adenosine tri-phosphate analyses, Water Research, 101, 617-627. https://www.dora.lib4ri.ch/eawag/islandora/object/eawag:10617
- Böhler et al. (2017) Biologische Nachbehandlung von kommunalem Abwasser nach Ozonung – ReTREAT. Schlussbericht, Dübendorf: Eawag. https://www.dora.lib4ri.ch/eawag/islandora/object/eawag:16638