Heterogeneous photocatalysis using UVA-LEDs for the removal of antibiotics and antibiotic resistant bacteria from urban wastewater treatment plant effluents

Secondary urban wastewater samples were spiked with azithromycin (AZT), trimethoprim (TMP), ofloxacin (OFL) and
sulfamethoxazole (SMX) at 100 μg L−1 to investigate the efficiency of a TiO2-photocatalytic treatment using UVA-LEDs.
Different operating parameters were studied, such as the irradiation conditions, catalyst load and the use of methanol as
carrier solvent and radical scavenger. The most efficient conditions to treat spiked urban wastewater (4 LEDs symmetrically
distributed and 1.00 g L−1 of catalyst) were also assessed on the removal of the antibiotics at real concentrations,
as well as on the inactivation and regrowth of bacteria after 3-day storage (total and resistant heterotrophs,
Escherichia coli and enterococci). Clindamycin (CLI) was targeted when SMX was not detected. One-hour treatment was
enough to reduce the analysed antibiotics to values below the detection limits and to decrease the bacterial load by 2
log-units. Bacterial regrowth was observed for total heterotrophs, after the storage of photocatalytic treated wastewater,
to values close to pre-treatment. However, the antibiotic resistance percentage of such stored wastewater was always
similar or lower than that of secondary urban wastewater. Thus, the potential of this process as part of the tertiary
treatment is demonstrated, but conditions must be adjusted to minimize microbial regrowth.