Removal of antibiotics, antibiotic-resistant bacteria and their associated genes by graphene-based TiO 2 composite photocatalysts under solar radiation in urban wastewaters

Abstract The present work investigated: (i) the removal of the antibiotics sulfamethoxazole (SMX), erythromycin (ERY) and clarithromycin (CLA); (ii) the inactivation of the total and antibiotic-resistant E. coli along with their regrowth potential after treatment; (iii) the removal of the total genomic DNA content; and (iv) the removal of selected antibiotic resistance genes (ARGs), namely sul 1, amp C, erm B, mec A, as well as species-specific sequences, namely ecf X for Pseudomonas aeruginosa and enterococci-specific 23S rRNA, by graphene-based TiO 2 composite photocatalysts under solar radiation, in real urban wastewaters. TiO 2 -reduced graphene oxide (TiO 2 -rGO) composite photocatalysts were synthesized by two ex-situ synthesis methods, namely hydrothermal (HD) treatment and photocatalytic (PH) treatment, starting from graphene oxide and Aeroxide P25 TiO 2 , and were characterized with various techniques, such as XRD, FT-IR, Raman, XPS, SEM and surface area (BET) analyses. The potential of the synthesized TiO 2 -rGO composites for the removal of the abovementioned antibiotic-related microcontaminants was compared to the efficiency shown by pristine Aeroxide P25 TiO 2 under simulated solar radiation, in real urban wastewater effluents treated by a membrane bioreactor. The results showed that TiO 2 -rGO-PH was more efficient in the photocatalytic degradation of ERY (84 ± 2%) and CLA (86 ± 5%), while degradation of SMX (87 ± 4%) was found to be slightly higher with Aeroxide P25 TiO 2 . It was also demonstrated that more than 180 min of treatment were satisfactory for the complete inactivation and complete absence of post-treatment regrowth of E. coli bacteria ( 2 -rGO-HD. Moreover, the synthesized graphene-based photocatalysts successfully removed amp C and significantly reduced ecf X abundance of Pseudomonas aeruginosa , but sul 1, erm B and 23S rRNA for enterococci sequences were found to be persistent throughout treatment with all catalyst types. Finally, the total DNA concentration remained stable throughout the photocatalytic treatment (4.2–4.8 ng μL −1 ), indicating the high total genomic DNA stability in treated wastewater and its resistance to photocatalytic treatment.