Abstract
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.
Highlights
Antibiotics are frequently found at concentrations ranging from a few ng L−1 to μg L−1 in many aquatic compartments, namely wastewater influents and effluents, surface waters, groundwater and even in drinking water [1,2,3]
The degradation efficiencies by UVA of the antibiotics spiked in urban wastewater (UWW), in the absence of MeOH and using 4 light emitting diodes (LEDs), revealed the following resilience order: TMP ≈ SMX > AZT > OFL (Fig. 1)
Real matrices can play an important role on their indirect photodegradation, exceptions being found in some cases as fluoroquinolones, which are reported to be more susceptible to UV photolysis in pure water than in UWW [38,40]
Summary
Antibiotics are frequently found at concentrations ranging from a few ng L−1 to μg L−1 in many aquatic compartments, namely wastewater influents and effluents, surface waters, groundwater and even in drinking water [1,2,3]. The presence of antibiotics, antibiotic resistant bacteria and antibiotic resistant genes (A&ARB& ARGs) in the environment, in particular throughout the urban water cycle and food chain, is considered a severe public health issue. In this regard, new approaches to reduce A&ARB&ARGs in water and to avoid the negative impacts on the downstream environment are necessary, in particular when the objective is to achieve good quality standards for possible reuse of urban wastewater (UWW) [10,11,12]
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