Phase 1 condition 1
Spring – summer 2019 (duration: 110 days)
- Mixed liquor ozonation (process tank) – 4 mgO3/L
- Tertiary ozonation (after secondary clarifier) – 7.00 mgO3/L
Average Removal end of condition 1
- 3 samplings in june 2019
- 36 compounds analysed
- 21/36 removal efficiency calculable
- Rest never above detection level or not fulfilling the removal rate calculation demands
63% by biology
78% after first point ozonation
93% after multiple point ozonation
Removal efficiency after ozonation condition 1 (june ‘19). In the reference line some micropollutants are removed better than others and this corresponds with the findings from the autum ’18 and gives an average removal of 63%. In the experimental line with 2 times ozone injection a whole other picture is seen. After just one point of ozonation an average removal of 78% was observed and after injecting ozone a second time (tertiary) it reached 93% removal in average!
The main goal is to reach concentrations below PNEC, since PNEC is the concentration of a chemical which marks the limit at which below no adverse effects of exposure in an ecosystem are measured.
At Brædstrup WWTP in the fall of 2018 6/31 compound were above PNEC in the effluent of both process lines.
After the first condition of ozone the concentration were measured both in the reference line and in the experimental line with ozonation, and it’s clear to see the improvement. In the reference line 5/36 compounds were above PNEC in the outlet. However, after multiple point ozonation none of these 5 micropollutants were even detectable in the water phase anymore. In fact, 32/36 came below limit of detection (LOQ) – meaning only 4 compounds could even be quantified (those 4 was still below their respective PNECs).
Antibiotic Resistant Bacteria and E-Coli
Selection of 5 antibiotic targets was based on their coverage of different antibiotic classes: sulfamethoxazole for sulfonamides, trimethoprim belonging to the family of diaminopyrimidines and used either alone or in combination with sulfonamides, ciprofloxacin and ofloxacin for fluoroquinolones and the beta-lactam family including the resistance to the third generation cephalosporine thru the Extended Spectra Beta Lactamase (ESBL) resistance.
The multiple point ozonation achieved an additional log-removal from 0.4 to 1.2.
A similar trend was observed for E. coli and ESBL-producing E. coli for which the whole removal efficiency was up to 1.5 log higher than for the reference line.
Antibiotic Resistant Genes
In this study, different genes conferring resistance to β-Lactam Antibiotics (blaKPC), quinolones (qnrS), sulfonamides (sul1), as well as a class 1 Integrase (intI1) were quantified and normalized against the total bacteria population using 16S rRNA gene quantification.
As observed in the ARB-based study, sulfonamide resistance gene (sul2) and integrase coding gene (intl1) was the most prevalent ARG.
Highest removal effect on the antibiotic resistant genes – qnrs and Intl1 – compared to reference line have been observed.
Toxicological tests were performed as part of the analytical program, to determine whether negative effects were seen in both the reference and experimental line. Normally a sand filter is located as a final step after ozonation. Since there is no such after treatment of the effluent from our experimental line, we decided to test it. This also serves as a reverse measurement of potentially more severe metabolites made during ozone reaction with mother molecules.
We can conclude that the experimental line effluent did not show a potentially more negative effect than the reference line. Contrary, slightly less ecotoxic effects were seen. Therefore, molecules were not broken down to potentially more adverse metabolites by ozonation.