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 (E_g = 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.

Direct current electrodeposited Sn–Ni/TiO₂ nanostructured coatings were produced by embedding two different doped types of TiO₂ particles within the alloy matrix, a commercially available doped carbon-based and doped N,S-TiO₂ particles. The structural characteristics of the composite coatings have been correlated with the effect of loading, type of particles in the electrolytic bath, and the applied current density. Regardless of the type of doped particles TiO₂, increasing values of applied current density resulted in a reduction of the co-deposition percentage of TiO₂ particles and an increase of Tin content into the alloy matrix. The application of low current density values accompanied by a high load of particles in the bath led to the highest codeposition percentage (~3.25 wt.%) achieved in the case of embedding N,S-TiO₂ particles. X-ray diffraction data demonstrated that in composite coatings the incorporation of the different types of TiO₂ particles in the alloy metal matrix modified significantly the nano-crystalline structure in comparison with the pure coatings. The best photocatalytic behavior under visible irradiation was revealed for the composite coatings with the highest co-deposition percentage of doped N,S-TiO₂ particles, that also exhibited enhanced wear resistance and slightly reduced microhardness compared to pure ones.