Investigation of the potential of a Membrane BioReactor followed by solar Fenton oxidation to remove antibiotic-related microcontaminants

There is limited research regarding alternative technologies of controlling the presence of antibiotic residues and antibiotic tolerance/resistance in urban wastewater treatment plants (UWTPs). This study deals with the efficiency of a Membrane BioReactor (MBR) integrated with solar Fenton oxidation for the removal of selected antibiotic-related microcontaminants, at a pilot scale. More specifically, the aspects examined in this study included: (i) the removal of three antibiotics, namely sulfamethoxazole (SMX), erythromycin (ERY) and clarithromycin (CLA), (ii) the prevalence of total and antibiotic-tolerant bacteria, (iii) the total DNA and antibiotic resistance genes (ARG) removal efficiency of the integrated process, as well as the abundance of taxon-specific markers. The quantitative examination of the presence of antibiotic residues in the MBR-treated effluent revealed a concentration of SMX of 5.5 ng L⁻¹, of CLA of 7.2 ng L⁻¹, while ERY concentration was below the limit of detection (LOD). Due to the low antibiotic concentrations in the MBR effluent, spiking of the examined antibiotics (100 μg L⁻¹) was done to examine their photo-persistence after solar Fenton oxidation. SMX and ERY concentrations were below the LOD after t_30Wn = 119.2 min, while CLA was reduced by 84%. Total and antibiotic-tolerant cultivable bacteria Escherichia coli and Klebsiella spp. were completely inactivated. On the other hand, there was repair of Pseudomonas aeruginosa observed, with 2 CFU 100 mL⁻¹ growing on the selective media 24 h after solar Fenton oxidation. The total DNA concentration was reduced by 97%, while in the remaining total DNA determined after treatment, the Enterococcus spp. specific gene marker (3.9 log₁₀ CE 100 ng⁻¹ DNA), and the ARG sul1 and ermB (1.56 and 1.53 log₁₀ CE 100 ng⁻¹ DNA, respectively) were still present, indicating the further challenge of their removal.