## 2 Methods of Eliminating Hormones and Pharmaceuticals
### Physical Methods
#### 2.1.4 Reverse Osmosis  
Reverse osmosis (RO) is one of the most effective membrane processes used to remove micropollutants from wastewater, including pharmaceuticals and hormones. Its main advantage is minimal chemical consumption and the ability to treat both municipal and industrial wastewater. Hormonal compounds such as E2, E1, and ethinylestradiol are removed almost completely (up to 99%) [80,81]. The effectiveness of the process depends on operating parameters such as pressure, pH, inlet temperature, and contaminant concentration [82]. Reverse osmosis typically operates at higher pressures, which can improve the rate of contaminant removal [83]. Under conditions of a high contaminant concentration, the process demonstrates higher efficiency in removing hormonal compounds due to its ability to operate at higher pressures and the design of the membrane [84]. The accumulation of contaminants on the membrane surface can reduce removal efficiency and increase operating costs due to the need for frequent cleaning and maintenance [85,86]. Reverse osmosis is exceptionally effective in removing most micropollutants, achieving 99% or more efficiency for other compounds such as amoxicillin, caffeine, carbamazepine, and oestrogens (such as E2 and EE2) [80, 81, 82, 83].  
In terms of energy costs, reverse osmosis is a process that requires high operating pressure, which results in significant energy consumption. According to the literature, energy consumption for reverse osmosis can range from 3 to 8 \(\mathrm{kWh/m^{3}}\)[28]. This process is more expensive in terms of energy compared to other conventional processes such as coagulation-floculation or biological filtration [79]. In terms of operation, reverse osmosis operates at high pressures, typically between 5 \(\times\) 10\({}^{5}\) and 7 \(\times\) 10\({}^{6}\) Pa, which leads to higher energy consumption. At high pressures, this can cause greater membrane wear, which requires close monitoring of operating conditions [28]. Membranes require regular maintenance, including periodic cleaning to remove contaminants and biofouling. The cost of replacing them is also high, ranging from USD 100 to 500 per m\({}^{2}\)[28]. It should be noted that despite the high initial cost of membranes, their effectiveness in removing new contaminants justifies the investment; moreover, they may prove to be more cost-effective in terms of efficiency and durability [87,88]. When assessing costs, the life cycle of the membranes should be taken into account [89,90], including not only purchase and replacement costs, but also energy consumption and maintenance expenses [84,86,91].  
RO processes most often use thin-film composite (TFC) membranes consisting of three layers: A polyester support layer, a microporous polysulfone layer, and a thin, selective active layer of polyamide, which is responsible for separation properties. TFC membranes are characterised by high chemical and mechanical resistance and selectivity towards organic compounds. Their structure enables the effective separation of micropollutants with a molecular weight above 200 Da, such as diclofenac, ibuprofen, and carbamazepine. Retention efficiency also depends on the hydrophilicity and surface charge of the membranes--more hydrophilic membranes with a negative charge are more effective at removing pharmaceuticals. High-pressure RO membranes are also used in combination with other technologies, such as activated sludge, which improves their efficiency and reduces the risk of fouling [80, 81,82,87,89,90,91].  
The discussed level of efficiency of the reverse osmosis process is illustrated in Figure 4, which shows the percentage removal of selected hormones and pharmaceuticals from wastewater. As can be seen, RO enables the almost complete removal of estradiol, EE2, and pharmaceuticals such as amoxicillin and carbamazepine. The high values (above 95%) confirm the benefit of implementing this process in advanced municipal wastewater treatment.