## 2 Methods of Eliminating Hormones and Pharmaceuticals
### Chemical Methods  
#### 2.2.1 Advanced Oxidation/O\({}_{3}\)/H\({}_{2}\)O\({}_{2}\)  
The advanced oxidation process (AOP) has gained a lot of popularity for water treatment over the past decade [102; 103; 104; 105]. AOPs are a group of water and wastewater treatment technologies that have the common feature of generating hydroxyl radicals (-OH). The most commonly used methods include ozonation, photocatalysis (e.g., using TiO\({}_{2}\) and UV light), anodic oxidation, and Fenton and photo-Fenton processes. -OH attack a wide range of organic contaminants, leading to their degradation or complete mineralisation, making it difficult to remove AOPs effective against micropollutants using conventional methods [106]. The O-H bond energy (459 kJ/mol) is higher than the C-H bond energy (411 kJ/mol), which means that the O-H bond is more difficult to break. Nevertheless, in the presence of strong oxidants such as hydroxyl radicals, it is possible to initiate reactions in which even strong chemical bonds are broken [107]. Other radicals such as SO\({}_{4}\)- that have a higher oxidation potential (2.5-3.1 V) than OH (1.9-2.8 V) can also be used as the main driving radical for the degradation of organic pollutants [108; 109; 110; 111]. AOPs are considered effective methods for removing hazardous contaminants by mineralising them to inorganic aliphatic acid, carbon dioxide, and water [112]. The efficiency of eliminating hormone compounds from wastewater using AOP methods is as high as 97% [18; 20]. Advanced oxidation processes (AOPs) based on ozone selectively oxidise organic compounds containing double bonds and high electron density groups, making them particularly effective against many pharmaceuticals and hormones [113]. The ozonation process can proceed in two ways: directly, through a reaction of the molecular ozone (O\({}_{3}\)) with the relevant pollutants, and indirectly, by generating hydroxyl radicals (-OH) through the decomposition of ozone in water. -OH are powerful and non-selective oxidisers capable of degrading a wide range of organic compounds, including those difficult to treat with conventional purification methods. Despite the high efficiency of the process (often exceeding 90% for selected pharmaceuticals--PhAC), ozonation also has some limitations, such as the incomplete mineralisation of intermediates, the need for precise control of reaction conditions, and the relatively high costs associated with ozone generation and dosing. Ozone-based AOPs selectively oxidise organic matter, which has double bonds and a higher electron density [113]. Ozonation can occur directly, through the oxidation of the molecular ozone (O\({}_{3}\)), or indirectly, through the decomposition of ozone into hydroxyl radicals (OH). Hydroxyl radicals, which are highly reactive, can then oxidise organic compounds. Although this process shows high elimination (>90%) of PhAC, there are some limitations, such as incomplete mineralisation and expensive ozone consumption. The amount of ibuprofen eliminated is 93% within 4 h of ozonation, but with the use of an iron-based catalyst, the reaction rate and removal efficiency are increased, and ultimately, the consumption of ozone is reduced [107]. Reactions of ozone with organic compounds usually lead to the formation of aldehydes and carboxylic acids, which do not react further with ozone. As a result, the complete mineralisation of organic matter does not occur. The presence of bromide ions can lead to the formation of brominated by-products such as bromates and brominated organic compounds, which are carcinogenic and genotoxic. Furthermore, oxidative reactions with ozone are relatively slow and selective; therefore, various modifications of the ozonation process have been performed to overcome limitations. During ozonation, hydroxyl radicals are produced by activation methods or by reacting with organic matter present in the water. Activation methods include H\({}_{2}\)O\({}_{2}\) integration, UV irradiation, alkaline pH, and ozone catalysts [113; 114].