Chemically Modified TiO2 Photocatalysts as an Alternative Disinfection Approach for Municipal Wastewater Treatment Plant Effluents

Abstract

Among key issues in municipal wastewater treatment plants (MWTP) is the existence of pathogenic bacteria in the discarded effluents. Conventional disinfectants (ozone, UV irradiation, chlorine) have been insufficient in providing safe water due to the development of undesirable and noxious by-products. TiO2 comprises an attractive alternative to conventional methods because of its versatility and recently explored biocidal efficiency. As a result, within the framework of this study, chemically modified, visible active nanocrystalline TiO2 powders (N-TiO2, N,S-TiO2, and Ag@N-TiO2) were prepared via a low-cost, feasible sol-gel method for the treatment of real municipal wastewater effluents. Wastewater samples were acquired from the outlet of the treatment of Antiparos (Cyclades, Greece) MWTP during the summer period in which a great number of seasonal habitants and tourists usually visit the island, resulting in at least a doubling of the population. All synthesized powders were thoroughly characterized using various morphological and spectroscopic techniques, such as FE-SEM, XRD, micro-Raman, FTIR, DLS, UV-DRS, and XPS. Photocatalytic evaluation experiments were initially conducted towards Rhodamine B degradation under visible light irradiation. Among all studied powders, Ag@N-TiO2 indicated the highest efficiency, reaching total degradation (100%) of RhB within 240 min due to its smaller crystallite size (1.80 nm), enhanced surface area (81 m2g−1), and reduced energy band gap (Eg = 2.79 eV). The effect of the produced powders on the disinfection as assessed in terms of fecal indicator microorganisms (E. coli and total coliforms) inactivation was also examined in a semi-pilot scale-up photocatalytic reactor. Ag@N-TiO2 nanopowder was also found substantially more active for both groups of bacteria, leading to complete inactivation in less than 35 min, probably due to the higher production of H2O2/—OH, as emerged from the photocatalytic mechanism study. In addition, Ag@N-TiO2 nanoparticles demonstrated excellent photocatalytic and disinfection stability even after five subsequent recycling trials (8.34% activity loss and complete inactivation, respectively). The results of the present study demonstrate the feasibility for Ag@N-TiO2 to be utilized as a viable, eco-friendly approach for the photocatalytic pathogenic bacteria inactivation as an alternative disinfection approach for municipal wastewater treatment plant effluents with intense seasonal fluctuations in volume.

Optimization of ZnO Nanoparticles’ Synthesis via Precipitation Method Applying Taguchi Robust Design

“…The utilized photoreactor possessed a system of four parallel lamps at a distance of 10 cm above each powder's surface [73]. Blacklight lamps of 368 nm, 830 lumens, and an incident light flux equal to 0.184 µmol quanta/s made by Sylvania (Sylvania, Wilmington, NC, USA) were used as the source of UV light, and all the experiments were carried out under ambient temperature conditions.…”

“…The absorbance of the ZnO samples prepared in this manner was measured at 554 nm using a Thermo Fisher Scientific Evolution 200 Spectrometer (Thermo Fisher Scientific, Waltham, MA, USA). The C/C 0 ratio, where C represents the concentration of RhB after a specific period of photocatalysis and C 0 is the initial RhB concentration, was determined indirectly by comparing the measured A (absorption at each time) with the initial A (A initial ) [73].…”

Uv/Tio2 Photocatalysis as Post-Treatment for Anaerobic Membrane Bioreactor Effluent for Reuse

“…Adsorption isotherm tests were conducted with TiO 2 dosing concentrations of 0.1, 0.2, 0.5, 1, 2 and 5 g/L. The TiO 2 concentrations, test duration and sampling intervals were all chosen based on previous trials reported for wastewater (Lofrano, G., Libralato, G., Casaburi, A., Siciliano, A., Iannece, P., Guida, M., Pucci, L., Dentice, E.F., Carotenuto, M., n.d.. n.d 624, 461-469. doi:10.1016/j.scitotenv.2017Rivero et al, 2006;Tsoukleris et al, 2023). A 15 ml sample was taken from the beaker with a syringe at regular intervals over the duration of the tests to monitor the adsorbate concentration.…”