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Urban Wastewater Treatment Plants (UWTPs) treating mixed urban sewage and industrial wastewater are among the major hotspots for the spread of Antibiotic Resistance Genes (ARGs) into the environment. This study addresses the impact of the wastewater origin on ARG dynamics in a full-scale UWTP (15,000 Population Equivalent, PE) by operating the plant with and without industrial wastewater. Composite samples (4 L) from different treatment points were characterized for their chemical composition, bacterial abundance and for the abundance of four resistance genes against tetracycline, sulfonamides, erythromycin, and quinolones (tetA, sul2, ermB, and qnrS), and of the class 1 integrons (intI1). Although the chemical composition of the outflow significantly differed when the plant operated with or without industrial wastewater, the system efficiency in the removal of bacterial cells, ARGs, and intI1 was constant. The final disinfection by peracetic acid (PAA) did not affect the removal of ARGs, independently of the wastewater origin and the chemical characteristics of the inflows. Our results demonstrated that a well-functioning small size UWTP could treat a significant amount of industrial wastewater mixed in the urban sewage without affecting the overall ARGs and class 1 integrons released into the environment.

The efficiency of a new Advanced Oxidation Process (AOP), namely the photo Fenton like process UV- C/H 2 O 2 /IDS-Cu, in removing determinants of antibiotic resistance and pathogenic bacteria was compared to a consolidated AOP (namely UV-C/H 2 O 2 ) in a secondary treated municipal WasteWater (WW). A re- ductionist experimental laboratory-based approach was applied on real WW and the parameters were collected by an alternative integrated approach using (i) flow cytometry to enumerate bacteria and test for the fitness of the bacterial communities and (ii) molecular analyses to define the community com- position (16S rRNA amplicon sequencing) and the abundances of Antibiotic Resistance Genes (ARGs) and of the class 1 integron ( int I1 gene) (by quantitative PCR). The same approach was applied also to post- treatment regrowth tests (24 h) to define the potential persistence of the tested parameters. These exper- iments were performed in both, human pathogens favorable conditions (HPC, in rich medium and 37 °C) and in environmental mimicking conditions (EMC, original WW and 20 °C). UV-C/H 2 O 2 /IDS-Cu process re- sulted to be more effective than the UV-C/H 2 O 2 in inactivating bacterial cells in the EMC post-treatment regrowth experiments. Both AOPs were efficiently abating potential human pathogenic bacteria and ARGs in the HPC regrowth experiments, although this trend could not be detected in the measurements taken immediately after the disinfection. In comparison with the UV-C/H 2 O 2 , the UV-C/H 2 O 2 /IDS-Cu process did not apparently offer significant improvements in the abatement of the tested parameters in the WW effluent but, by evaluating the results of the regrowth experiments it was possible to extrapolate more complex trends, suggesting contrasting efficiencies visible only after a few hours. This study offers a de- tailed view on the abatement efficiency of microbiological/genetic parameters for the UV-C/H 2 O 2 /IDS-Cu process, calling for technical adjustments for this very promising technology. At the same time, our re- sults clearly demonstrated the inadequacy of currently applied methodologies in the evaluation of specific parameters (e.g. determinants of antibiotic resistance and pathogenic bacteria) in WW.

A multi-barrier approach including advanced oxidation by Fenton (FO), air stripping (AS) and biological activated sludge (B-AS) processes was investigated as possible treatment of mature landfill leachate (MLL) in an urban wastewater treatment plant (UWTP). Three different conditions were compared to the control line (B-AS treatment of simulated urban wastewater (SWW)): MLL pre-treated with FO process and diluted to 17% with SWW; MLL pre-treated with AS and diluted to 17% with SWW; MLL pre-treated with FO, AS and diluted to 17% with SWW. Preliminary tests aimed to investigate the best operating conditions of FO for MLL (pH = 3, t = 120 min, H2O2/Fe2+ = 1, H2O2= Fe2+ = 3500 mg/L) were carried out with regard to COD removal (82%) and biodegradability (BOD5/COD = 0.32). FO and AS were very efficient to remove COD (82%) and NH3 (92%) respectively, before pre-treated MLL was mixed to SWW. The multi-barrier treatment (FO + AS + B-AS) was very efficient to remove COD (85%) and NH3 (79%). Furthermore, the absence of one of the two pre-treatments, FO or AS, adversely affected the biological process, by reducing COD (47%) and NH3 (14%) removal efficiency, respectively. The management cost analysis showed that the investigated multi barrier system is economically feasible only at low dilution ratio between FO-AS pre-treated MLL and real urban wastewater (

We carry out a mesocosms experiment to assess the impact of high-quality treated wastewater intended for agricultural reuse (HQWR) on freshwater bacteria seldom exposed to anthropogenic pollution. Effects were assessed by comparing the abundance and composition of bacterial communities as well as their resistance profile under control (source water from an unpolluted lake) and treatment conditions (source water mixed 1:1 with HQWR, with and without 5 μg L−1 of cefotaxime). We investigated the effect of the different conditions on the abundance of genes encoding resistance to β-lactams and carbapenems (blaTEM, blaCTX-M, blaOXA, and blaKPC), fluoroquinolones (qnrS), tetracyclines (tetA), sulfonamides (sul2), macrolides (ermB), arsenic and cadmium (arsB and czcA, respectively), and on the gene encoding the Class 1 integron integrase (intI1). Bacterial communities exposed to HQWR showed a significant higher abundance of tetA, arsB, czcA, and intI1 genes, whereas those exposed to Cefotaxime-amended HQWR did not. Genes conferring resistance to carbapenems, β-lactams, fluoroquinolones, and macrolides were below detection limit in all treatments. Besides, the higher availability of nutrients under treatment conditions favored bacterial growth in comparison to those exposed to control conditions. Particularly, Acinetobacter spp. and Pseudomonas spp. were significantly enriched after 22 days of treatment exposure. The presence of cefotaxime (a third generation cephalosporine) in the feeding medium caused an enrichment of bacterial communities in sequences affiliated to Acinetobacter thus suggesting that these resistant forms may possess resistance genes other than those studied here (blaCTX-M, blaOXA, and blaKPC). Although derived from a mesocosm experiment in continuous cultures, our results call attention to the need of refined regulations regarding the use of reclaimed water in agriculture since even high-quality treated wastewater may lead to undesired effects on receiving bacterial communities in terms of composition and dissemination of antibiotic resistance genes.

The occurrence of antibiotics in urban wastewater treatment plants (UWTPs) may result in the development of antibiotic resistance and subsequently in the release of multidrug resistant bacteria (MDR) and genes into the effluent. Conventional disinfection processes are only partially effective in controlling ARB spread, so advanced oxidation processes (AOPs) have been investigated as alternative option in this work. In particular, the aim of this work was to comparatively assess the efficiency of solar disinfection and solar driven AOPs (namely H 2 O 2 /sunlight, TiO 2 /sunlight, H 2 O 2 /TiO 2 /sunlight, natural photo-Fenton) for the inactivation of a multidrug (namely ampicillin, ciprofloxacin and tetracycline) resistant E. coli strain isolated from the effluent of the biological process of an UWTP. Different concentrations of H 2 O 2 (0.588–1.470–2.205 mM), TiO 2 (50–100 mg L −1 ), H 2 O 2 /TiO 2 (0.147 mM/50 mg L −1 , 0.588 mM/100 mg L −1 ) and Fe 2+ /H 2 O 2 (0.090/0.294, 0.179/0.588, 0.358/1.176 mM) were evaluated at pilot-scale (in compound parabolic collector reactor) in real biologically treated wastewater. All investigated processes resulted in a complete inactivation (5-log decrease) of bacteria until detection limit, but the best disinfection efficiency in terms of treatment time (20 min to reach the detection limit) and required energy (0.98 kJ L −1 ) was observed for photo-Fenton at pH 4 (Fe 2+ /H 2 O 2 :0.090/0.294 mM). Antimicrobial susceptibility was tested by Kirby-Bauer disk diffusion method. Ampicillin and ciprofloxacin (to which the selected strain is resistant), cefuroxime and nitrofurantoin were chosen as tested antibiotics. None of the investigated processes affected antibiotic resistance of survived colonies.

Solar disinfection and solar-driven advanced oxidation processes (AOPs) (namely H2O2/sunlight, TiO2/sunlight, H2O2/TiO2/sunlight, solar photo-Fenton) were evaluated in the inactivation of indigenous antibiotic-resistant bacteria (ARB) in real urban wastewater. A multidrug resistant (MDR) Escherichia coli strain isolated from the effluent of the biological process of an urban wastewater treatment plant was the target ARB. The higher inactivation rates (residual density under detection limit, 2 CFU mL−1) were achieved with H2O2/TiO2/sunlight (cumulative energy per unit of volume (QUV) in the range 3–5 kJ L−1, depending on H2O2/TiO2 ratio) and H2O2/sunlight (QUV of 8 kJ L−1) processes. All investigated processes did not affect antibiotic resistance of survived colonies. Moreover, H2O2/sunlight was compared with conventional chlorination process to evaluate bacterial regrowth potential and particularly the proportion of indigenous MDR E. coli with respect to total indigenous E. coli population. Chlorination (1.0 mg Cl2 L−1) was more effective than H2O2/sunlight (50 mg H2O2 L−1) to achieve total inactivation of MDR E. coli (15 min Vs 90 min) but less effective in controlling their regrowth (24 h Vs 48 h). Interestingly, the percentage of MDR E. coli in H2O2/sunlight treated samples decreased as incubation time increased; the opposite was observed for chlorinated samples.

The effect of TiO₂ photocatalysis on the inactivation of an antibiotic resistant Escherichia coli strain selected from an urban wastewater treatment plant (UWWTP) effluent was investigated. Different light sources including a 250 W wide spectrum lamp, a 125 W UV-A lamp and solar radiation, as well as, photocatalysts loadings (TiO₂ Degussa P25) in the range from 0.05 to 2.00 g TiO₂ L(-1) were evaluated. The higher efficiency (total bacterial inactivation after 10 min of irradiation) was observed in the absence of TiO₂ when the wastewater was irradiated using the 250 W lamp. In the presence of TiO₂ a decreasing inactivation trend was observed (99.76% and 72.22% inactivation after 10 min irradiation at 0.10 and 2.00 g TiO₂ L(-1) respectively). Under solar simulated conditions the highest inactivation efficiency (93.17%) after 10 min of irradiation was achieved at the lower photocatalyst loading (0.05 g TiO₂ L(-1)). The concept of "reactor optical thickness" was introduced to explain the rates of disinfection observed. The optimum photocatalyst loading estimated by radiation absorption-scattering modeling was found to be 0.1 g TiO₂ L(-1) for all lamps. The difference between experimental tests and modeling may be due to TiO₂ particles aggregation. Comparative kinetic tests between solar and solar simulated photocatalytic (SSP) processes using 0.05 g TiO₂ L(-1) in suspension showed a quite similar inactivation behavior up to 30 min of irradiation, but only the SSP process resulted in a total inactivation of bacteria after 60 min of exposure. Antibiotic resistant test (Kirby-Bauer) on survived colonies showed that the SSP and SP processes affected in different ways the resistance of E. coli strain to the target antibiotics.