## 3 Remediation Techniques with the Use of Nanoparticles  
Remediation facilities and therein applied techniques have revealed various effects toward specific PPCPs. It is important to note that the problem is a global one to which we, in European Union countries, are not immune. Studies concerning PPCPs carried out in Greece [31] showed that during purification processes in a municipal wastewater treatment plant, the removal efficiency varied for individual compounds. These included purification processes such as screening and grit-removal followed by chemical (FeClSO4), mechanical (sedimentation), and biological (nitrification, and denitrification) treatment. Only ten out of thirty-two pharmaceuticals were removed with relatively high ca. 80% efficiency including analytes such as paracata  
Figure 1: Pharmaceuticals and personal care products in the environment; PPCPs—pharmaceuticals and personal care products. mol, salicylic acid, and limomycin. Moreover, some substances were removed much less effectively, moderately, or only slightly. This was particularly observed in active pharmaceutical ingredients (API) such as carbamazepine, metoprolol, venlafaxine, ciprofloxacin, and simvastatin. The concentrations of fourteen pharmaceuticals, six hormones, two antibiotics, three PCPs, and one flame retardant were studied in two conventional wastewater treatment plants in South Korea by [PERSON] et al. (2018), wherein several PPCPs were detected in raw water at low concentrations. Many other studies have raised the issue of numerous PPCPs in different water sources including reservoirs, treated wastewater, surface and groundwater as well as tap water intended for human consumption in places such as Canada, Finland, France, Germany, Italy, and the USA (2018; 2019; 2020). The situation is in fact much worse in the case of dispersed on-site sewage treatment facilities, as shown in findings presented by [PERSON] and [PERSON] (2019). Communal and on-site wastewater treatment plants (WWTPs) were originally designed for the removal of organic matter and suspended solids, and in some cases--nutrients (total nitrogen and total phosphorus) to meet minimum discharge standards (e.g. biochemical oxygen demand--BOD). Remediation facilities are generally not designed for the removal of pharmaceuticals. Therefore, following various reports, pharmaceutical pollutants have been removed with varying degrees of effectiveness (2018; 2019; 2020; 2021; 2022; 2023; 2024; 2025; 2026; 2027; 2028; 2029; 2029;  
several types of reactions can be distinguished including photochemical processes with UV photolysis, the combined effect of UV/H2O2, UV/O3, UV/H2O2/O3, photocatalytic degradation in aqueous semiconductor suspensions, Fenton photoreactions as well as ultrasound processes, radiation processes with ionizing radiation, alone or in combination with O3, H2O2 [48; 49; 50; 51]. Semiconductor nanoparticles can be applied in AOPs as catalysts. They are activated by the light of different wavelengths from ultraviolet by visible light to near-infrared, depending on the energy band gap [52]. The process of photocatalytic oxidation can be influenced by various factors including the type of solvent, temperature, pH of the solution, type of photocatalyst, amount of dissolved oxygen, time, and light intensity. Photocatalytic nanomaterials can be categorized in terms of dimensionality from zero-dimensional nanoparticles with quantum dots via one-dimensional such as nanorods, nanoribbons, nanotubes to two- and three-dimensional such as graphene. Doping metal oxide (MO) nanoparticles (NP) or preparing their heterojunctions can also increase their photocatalytic activities in visible light [53]. Among the photosensizers, MO NPs constitute an intensively studied group of substances for potential applications in the photo-remediation of pharmaceutical and environmental wastewaters.