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- Impact of disinfection processes on bacterial community in urban wastewater: Should we rethink microbial assessment methods?Publication . Cesare, Andrea Di; Corno, Gianluca; Manaia, Célia M.; Rizzo, LuigiThe development of new methods and technologies for microbial characterization as well as their increasing availability at more affordable costs, has made evident the limitations of the conventional and routinely applied (typically cultivation based) methods to exhaustively and fully characterize the actual effect of disinfection process in urban wastewater treatment plants (UWWTPs). Such problem is even more relevant and of concern if microbial challenges, such as the occurrence of pathogens as well as the spread of antibiotic resistance, are taken into account. Such threats move scientists to investigate new and more effective disinfection processes from one side and new methods, techniques and approaches to characterize disinfection process efficiency from the other side. In this opinion paper, the limitations of routine detection methods are discussed according to the relevant and updated scientific literature to explain how research oriented methods and technologies (namely, quantitative real-time PCR, flow cytometry, metagenetics and metagenomics) can allow a better evaluation of disinfection processes. After a short introduction to the main disinfection processes, the application of different microbial characterization methods is discussed according to distinct challenges, such as pathogens inactivation or antibiotic resistance dissemination, when wastewater safety is of concern (for example in reuse scenarios). The routine and research oriented techniques can be successfully used in complementary way to evaluate disinfection process efficiency. Recommendations for UWWTPs managers for internal control of disinfection process are proposed.
- Immobilised cerium-doped Zinc oxide as a photocatalyst for the degradation of antibiotics and the inactivation of antibiotic-resistant bacteriaPublication . Zammit, Ian; Vaiano, Vincenzo; Ribeiro, Ana R.; Silva, Adrián M. T.; Manaia, Célia M.; Rizzo, LuigiThe threat of antibiotic resistance to the wellbeing of societies is well established. Urban wastewater treatment plants (UWTPs) are recognised sources for antibiotic resistance dissemination in the environment. Herein a novel cerium-doped zinc oxide (Ce-ZnO) photocatalyst is compared to ZnO and the benchmark TiO2-P25 in the immobilised form on a metallic support, to evaluate a photocatalytic process as a possible tertiary treatment in UWTPs. The catalysts were compared for the removal of two antibiotics, trimethoprim (TMP) and sulfamethoxazole (SMX), and for the inactivation of Escherichia coli (E. coli) strain DH5-Alpha in isotonic sodium chloride solution and of autochthonous bacteria in real secondary wastewater. In real wastewater, E. coli and other coliforms were monitored, as well as the respective fractions resistant to ofloxacin and azithromycin. In parallel, Pseudomonas aeruginosa and the respective sub-population resistant to ofloxacin or ciprofloxacin were also monitored. Photocatalysis with both ZnO and Ce-ZnO was faster than using TiO2-P25 at degrading the antibiotics, with Ce-ZnO the fastest against SMX but slower than undoped ZnO in the removal of TMP. Ce-ZnO catalyst reuse in the immobilised form produced somewhat slower kinetics maintained >50% of the initial activity, even after five cycles of use. Approximately 3 log10 inactivation of E. coli in isotonic sodium chloride water was recorded with reproducible results. In the removal of autochthonous bacteria in real wastewater, Ce-ZnO performed better (more than 2 log values higher) than TiO2-P25. In all cases, E. coli and other coliforms, including their resistant subpopulations, were inactivated at a higher rate than P. aeruginosa. With short reaction times no evidence for enrichment of resistance was observed, yet with extended reaction times low levels of bacterial loads were not further inactivated. Overall, Ce-ZnO is an easy and cheap photocatalyst to produce and immobilise and the one that showed higher activity than the industry standard TiO2-P25 against the tested antibiotics and bacteria, including antibiotic-resistant bacteria.