A Review of Methods for the Removal of Endocrine-Disrupting Compounds with a Focus on Oestrogens and Pharmaceuticals Found in Wastewater

Abstract

Steroid hormones are micropollutants that contaminate water worldwide and have significant impacts on human health and the environment, even at very low concentrations. The aim of this article is to provide an overview of technologies for the removal of endocrine-disrupting compounds with a focus on oestrogens (estrone E1, 17β-oestradiol E2, estriol E3), the synthetic oestrogen (17α-ethinylestradiol EE2 and bisphenol A BPA), and pharmaceuticals found in wastewater. Hormonal and pharmaceutical contaminants are mostly persistent organic compounds that cannot be easily removed using conventional wastewater treatment processes. For this reason, researchers have tried to develop more efficient tertiary wastewater treatment technologies to reduce micropollutant concentrations in wastewater. This review covers the following processes: Advanced oxidation, nanofiltration, ultrasound, electro-Fenton processes, electrolysis, adsorption, ozonation, photolysis, photocatalysis, ultrafiltration, and electrocoagulation. Attention was paid to the effectiveness of the processes in terms of eliminating hormones and pharmaceuticals from wastewater, as well as on economic and environmental aspects. The combination of different processes can be a promising treatment scheme for retaining and degrading hormonal and pharmaceutical compounds from wastewater. With hybrid technologies, the advantages of the methods are combined to maximise the removal of pollutants. However, optimal methods of wastewater treatment depend on the quality and quantity of the wastewater, as well as the residual hormonal and pharmaceutical compounds and their hazardous effects.

1. Introduction

Water pollution is one of the key environmental challenges of the modern world. Despite various measures and efforts to protect water quality, uncontrolled water pollution caused by human activities has become a serious public and environmental problem [1,2]. Anthropogenic chemicals pollute natural waters and significantly affect the aquatic ecosystem due to their high toxicity and persistence [3]. Directive 2013/39/EU introduced a so-called “watch list” of substances that may pose a risk to the aquatic environment and human health. This list includes hormones such as E2 and EE2 and anti-inflammatory drugs such as diclofenac. The aim is to monitor their presence in surface waters and assess potential risks to human health and ecosystems [4].

Endocrine disruptors (EDCs) are of particular concern because they interfere with endocrine regulation, potentially causing cancer and other health problems in humans and animals. EDCs cover a broad group of compounds, including pesticides, natural and synthetic oestrogens, and pharmaceutical compounds. Of these, oestrogens such as E1, E2 and EE2, E3, and BPA are characterised by powerful endocrine-disrupting effects that pose potential risks to human health [3,5,6]. Oestrogens are potent hormones that play a key role in the human and animal reproductive system. E2 and EE2 are partially absorbed by organisms, and most are excreted intact or partially degraded in urine and faeces. Therefore, synthetic hormone therapies and natural secretions from humans and animals increase oestrogen hormone (E2 and EE2) concentrations in water bodies in levels ranging from ng/L to μg/L [7,8,9,10]. However, even at trace concentrations, these compounds can disrupt the endocrine function of aquatic organisms, leading to the feminisation of male fish, altered sex ratios, and reproductive impairment. Furthermore, the half-life of EE2 in drinking water is 108 days [11,12]. Oestrogens and other organic contaminants are partially removed by biological processes and during adsorption on solids [6]. The most commonly used adsorbent for the removal of steroid hormones is activated carbon [13]. Consequently, hormones have been detected in water bodies, in part due to the inefficiency of municipal wastewater treatment plants [14,15]. During the past 20 years, numerous studies have been performed to increase the efficiency of oestrogen removal from treated wastewater, with reported removal amounts ranging from 0 to 100% [16,17,18,19,20,21]. Various methods have been proposed to remove oestrogens from water, including membrane filtration, adsorption, biological treatment, and advanced oxidation processes that include photocatalysis and ozonation. Nanofiltration and reverse osmosis, in particular, can effectively remove oestrogens but are expensive processes [7]. Although there are new and highly efficient nanomaterials and technologies that could significantly reduce the emission of EDCs, including hormones and pharmaceuticals, in most cases, the cost and complex synthesis methods hinder their use in wastewater treatment plants.

Conventional wastewater treatment plants are typically designed primarily to remove organic matter and nutrients and are therefore not adequately equipped to effectively remove E1, E2, EE2, E3, and BPA. Consequently, the Directive of the European Parliament and of the Council on the Treatment of Urban Waste Water [22] has been amended. The directive requires all urban wastewater treatment plants to have a p.e. of at least 150,000 to introduce fourth-stage treatment. The fourth stage will be responsible for the elimination of micropollutants. This provision will become mandatory starting in 2045 [22].

The aim of this article is to review the current chemical, biological, and hybrid methods used to eliminate EDCs, in particular hormones and pharmaceuticals, from wastewater from different sources. Advantages and disadvantages, including costs and the degree of reduction in micropollutants of the processes, are listed. The review of the literature shows that advanced oxidation processes can degrade persistent hormones and pharmaceuticals. However, oxidation can also introduce toxic byproducts if the processes are not properly monitored and implemented. Using a combination of different processes can be an ideal purification solution to retain and degrade both hormonal and pharmaceutical compounds. With hybrid methods, the advantages of multiple methods are combined to maximise the removal of contaminants.

2. Methods of Eliminating Hormones and Pharmaceuticals

Conventional wastewater treatment plants are generally not designed to remove pharmaceuticals and hormones. Wastewater treatment plants (WWTPs) are designed mainly to remove organic carbon compounds, phosphorus or nitrogenous substances [23]. As a result, basic processes such as straining, sedimentation, flocculation, and biological treatment are not sufficient to remove micropollutants [24]. Mechanical wastewater treatment processes are ineffective due to their hydrophilic nature [23]. Most pharmaceuticals have low logKow [mol·dm⁻³] values, indicating their high solubility in water, and the probability of adsorbing on settling particles is very low.

The amount of hormones and pharmaceuticals eliminated using the wastewater treatment process in Korea was 28% [25]. According to a study in a wastewater treatment plant in Korea, the removal of pharmaceutically active compounds (PhAC) by nanofiltration was shown to be 97%, and that for naproxen and diclofenac was about 60% [26,27]. The disadvantage of this system is the incomplete removal of salts and monovalent ions. Reverse osmosis removed 99% of PhAC. However, this process has a number of disadvantages that are not conducive to its use, including high pressure, and the membranes have a short life span and sensitivity. In terms of energy consumption, studies show that the reverse osmosis process requires between 3 and 8 kWh/m [28].

The efficiency of micropollutant decomposition during ozonation and photolysis depends on both the operating conditions of the process, the type of compound (BPA, E2, or EE2), and the water matrix (deionised water solution, model drain, and actual drain). In this respect, in the case involving the need to eliminate micropollutants that are not very susceptible to decomposition (e.g., bisphenol A) from water, the use of complex systems (UV/O₃) is more favourable. Their efficiency can reach up to ca. 94%. Before ozonation, a filtration process should be performed for better results and multistage contact columns can be used, allowing for the precise contact time of wastewater with ozone to be determined [29].

Table 1. Comparison of processes used to eliminate hormones and pharmaceuticals from wastewater; authors’ own elaboration based on [30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49].

Method	Hormone Removal Efficiency [%]	Pharmaceutical Removal Efficiency [%]	Advantages	Disadvantages	Costs	By-Product Formation Summary
Adsorption (e.g., activated carbon)	80–90%	50–85%	Effective for broad spectrum of pharmaceuticals. Proven and accessible technology. Simple equipment.	Need for sorbent regeneration or replacement. No degradation of pollutants.	Capital: low–medium (filters); operational: 0.045–0.15 PLN/m3	No chemical reactions; no by-products formed
AOP (UV/H2O2, Fenton, photo-Fenton)	90–95%	70–95%	Very high mineralisation efficiency. Relatively instant PPCP removal. High removal for hormones and pharmaceuticals.	High cost of reagents (H2O2 and Fe2⁺). Intermediates possible (retention). Formation of residual compounds. Complex operation.	Capital: PLN 0.5–2.5 million; operational: 0.20–0.25 PLN/m3	Complex organic intermediates may be generated; removal often requires additional processes
Ozonation (O3)	90–95%	60–90%	High oxidation efficiency of organic pollutants. No residues (in ideal conditions).	Potential formation of toxic by-products (bromates, aldehydes, ketones, etc.). High operational cost. Requires pH adjustment. Short half-life of ozone.	Capital: PLN 1–5 million; operational: 0.12–0.25 PLN/m3	Aldehydes, ketones, brominated compounds depending on bromide concentration and pH
UV Photolysis	50–80%	30–60%	Effective for some pharmaceuticals. Simple operation.	Low efficiency for many PPCPs. Low efficiency in water turbidity.	Capital: medium (UV lamps); operational: 0.15–0.3 PLN/m3	Photoproducts such as hydroxylated derivatives or quinones
Photocatalysis (e.g., TiO2, ZnO)	40–85%	50–90%	Mineralisation of pollutants. UV and visible light activation. More efficient than photolysis alone.	Low efficiency at high loads. High catalyst consumption.	Capital: moderate (TiO2); operational: 0.15–0.3 PLN/m3	Intermediates such as aldehydes and acids; catalyst recovery required
Photocatalysis + AC (e.g., TiO2/AC)	60–90%	70–95%	Faster degradation. Simultaneous adsorption and photodegradation.	Higher material wear. Larger reactor volume required.	Capital: PLN 2–4.1 million; operational: 0.2–0.45 PLN/m3	Reaction by-products from both catalyst and adsorbent degradation
Ultrafiltration (UF)	70–90%	40–80%	Removes suspended solids, bacteria. Simple membrane separation.	Membranes susceptible to fouling. Requires chemical cleaning.	Capital: medium; operational: 0.10–0.25 PLN/m3	Limited—mostly physical retention; no chemical degradation
Nanofiltration (NF)	60–90%	60–90%	Removes more PPCPs than UF. Lower pressure requirement than RO.	Concentrate disposal required. Expensive membranes.	Capital: high; operational: 0.20–0.30 PLN/m3	Some retention of PPCPs; no transformation products
Reverse Osmosis (RO)	95–99%	95–99%	Retains almost all PPCPs. Removes almost all pollutants.	High energy demand. Practically none, but highly concentrated waste requires treatment.	Capital: very high; operational: 0.25–0.5 PLN/m3 UV/N2; energy: 0.2–0.5 PLN/m3	Practically none, but highly concentrated waste requires treatment
Infiltration	10–50%	10–80%	Natural and cheap. Simple technology. Ecological process.	Low PPCP removal. Dependency on soil type and permeability.	Capital: low; operational: near zero	Physicochemical retention; no degradation
Mechanical filtration (sand)	10–40%	5–20%	Low cost. Simple process. Preliminary barrier.	Ineffective for PPCPs. Only suspended solids are removed.	Capital: very low; operational: 0.01–0.1 PLN/m3	No transformation; only particles retained
Ultrasound	10–60%	20–80%	Can change organic micropollutants via reaction with H2O2 and radical formation.	Low efficiency in real wastewater. May generate by-products.	Capital: medium; operational: 0.2–0.35 PLN/m3	Radical formation and cavitation may lead to by-products
Electro-Fenton	80–95%	90–95%	Effective for persistent compounds. Generates hydroxyl radicals.	Expensive anodes and power consumption. Sludge disposal required.	Capital: high; operational: 0.3–1.5 PLN/m3	Intermediates depending on electrode type; sludge disposal required
Electrolysis	60–90%	70–90%	High degradation of selected PPCPs. Effective for persistent organics. Automated process.	Chlorinated by-product formation. Limited scalability.	Capital: high; operational: 0.3–1.0 PLN/m3	Possible chlorinated organics; intercontrol needed
Electrocoagulation	40–75%	60–90%	Simple to operate. Limited chemical input. Simultaneous sludge removal.	Requires maintenance. Sludge and metallic coagulants. Limited oxidation.	Capital: medium; operational: 0.1–0.25 PLN/m3	Sludge and metallic coagulants; limited oxidation

provides a summary of the processes in terms of the elimination of hormones and pharmaceuticals from wastewater, along with their disadvantages, advantages, and by-products.

2.1. Physical Methods

2.1.1. Adsorption

The adsorption process can be cumbersome to manage because of the generation of sludge. In addition, it can hinder separation and cause the release of adsorbed organic micropollutants in the nanofiltration (NF) process. The disadvantages of this process are the formation of by-products and the rapid saturation of activated carbon with contaminants. Adsorption as a process for the elimination of hormones and pharmaceuticals depends on the pH of the solution, the type of absorbent, and the composition of the water in terms of the amount and type of compound, as well as other substances contained in the water. The adsorption efficiency of hormones and pharmaceuticals from wastewater is strongly dependent on the pH of the solution, with numerous studies showing that lower pH values favour more efficient removal of these micropollutants [50,51,52,53]. This is mainly due to the effect of pH on the adsorbent surface charge and the chemical form of the adsorbed compounds. Under acidic conditions, the surface of an adsorbent such as activated carbon often has a positive charge, which favours the adsorption of anionic or undissociated pharmaceutical and hormone molecules, which are more hydrophobic under these conditions and bind more readily to the adsorbent surface [51,53]. In addition, competition from other ions present in the solution, such as OH- or HCO₃-, which can occupy active adsorption sites in alkaline environments, is reduced at low pH [54]. Granular activated carbon (GAC) has been shown to eliminate 98% of E2, 95.4% of progesterone (PRG), and 97.05% of EE2 from wastewater [55,56,57]. On the contrary, magnetic graphene oxide removed 95.20% of EI, 79.40% of E2, 93.20% of EE2, 88.40% of E3, and 98.20% of17α-E2. Hybridised graphene oxide sheets removed EE2 and E2 with efficiencies of 98% and 97%, respectively [16]. In addition, multi-walled carbon nanotubes and single-walled carbon nanotubes removed EE2 with efficiencies of 97% and 98%, respectively [58]. Double sodium hydroxide coated with sodium dodecyl sulphate removed up to 94% of E2, and tea leaf waste eliminated PRG at levels exceeding 68% [59]. Alternative materials such as spent coffee grounds, almond shells, biocarbons, potato-dextrose agar, and chitin have been tested to remove some oestrogens and progesterone and have shown high removal efficiencies (

Table 2. Degree of reduction in hormones with selected absorbents; authors’ own elaboration based on [17,55,60,61].

Absorbent	Effectiveness of Removal		Contact Time	Amount of Adsorbent	Amount of Adsorbate
	E2	EE2
Coffee grounds	100%		15 min	0.1 g	10 mg/L
Almond shells	100%		40 min	0.5 g	100 mg/L
Biocarbon	100%		60 min	0.5 g	50 mg/L
Potato-dextrose agar	100%		̶	̶	̶
Double sodium hydroxide with layer of sodium dodecyl sulphate	94%		20vmin	2 g/L	0.302–0.379 mg/L
Chitin	>82%		220 min	1.45 g/L	5.7 mg/L
Sp2 hybridised graphene oxide sheets	97.19%	98.46%	30 min	̶	̶
Black tea leaf waste		95.75%	60 min	0.5 g	100 mg/L
Granular activated carbon	97.05%	95.40%	120 min	10 mg/L	200 ng/L
Multi-walled carbon nanotubes		97%	24 h	0.5 mg/L	2.5 mg/L
Single-walled carbon nanotubes		98%	<5 h		̶

) [17,55,60,61].

The use of metal–organic frameworks (MOFs) for the adsorptive removal of hormones and pharmaceuticals from wastewater has progressed significantly in recent years. Due to their high porosity, large specific surface area, and potential for functionalisation, MOFs have emerged as promising materials in the treatment of waters contaminated with pharmaceutical and hormonal compounds.

Table 3. Effect of MOF material type on elimination of hormones and pharmaceuticals from wastewater; authors’ own elaboration based on [62,63,64,65,66].

MOF Material	Target Compounds	Adsorption Mechanisms	Removal Efficiency [%]	Ref.
MIL-101-NH2	E2, EE2, E1, mifepristone, other EDCs	Hydrogen bonding, π–π interactions, van der Waals forces	85–95%	[62]
MIL-101(Cr) + urea/melamine	Metronidazole, tinidazole, ornidazole	Hydrogen bonding, electrostatic interactions, enhanced porosity	91–97%	[63]
Ce-DUT-52	Oestradiol, E1, hexestrol	Electrostatic interactions, positive zeta potential	82–90%	[64]
Zr/Fe-MOFs/GO	Tetracycline, orange II dye	π–π interactions, electrostatic attraction, high surface area	96–99%	[65]
UiO-66 and derivatives	Ibuprofen, naproxen, diclofenac	Hydrophobic interactions, metal–ligand coordination, hydrogen bonding	80–93%	[66]
ZIF-8	Sulfamethoxazole, carbamazepine	Molecular sieving effect, hydrophobic pore interactions	75–88%	[66]

shows MOF material types, removal efficiencies, and mechanisms. Many MOFs exhibit high chemical and thermal stability, allowing them to be used repeatedly without significant loss of effectiveness. For example, MIL-101-NH₂ retains its effectiveness after several adsorption–desorption cycles, making it an economically attractive solution [62,63,64,65,66].

2.1.2. Ultrafiltration

Ultrafiltration (UF) is a pressurised membrane process that uses membranes with pores in the range of 0.01–0.1 µm. This technology effectively removes suspended solids, colloidal particles, bacteria, and some organic macromolecules. Yang J. et al. [67] investigated two types of UF-GE and UF-CNT membranes and estimated the retention rate of micropollutants removed from the deionised water solution for the mentioned membranes. For BPA, E2, and EE2, higher removal rates were obtained for the nanotube-modified ultrafiltration membrane than for the commercial membrane. The retention rate of BPA is 5% for the UF-GE membrane and 48% for UF-CNT. For E2 and EE2, the difference in retention between the membranes mentioned above is about 5%. The micropollutant removal efficiency of these membranes depends on their different physicochemical properties. The UF-CNT membrane shows good adsorption properties and has higher porosity with carbon nanotubes. In [67], the effect of carbon nanotubes on membrane hydraulic performance was documented while maintaining a high retention rate of micropollutants. It was also shown that, regardless of the type of membrane used, EE2 was removed at a higher rate compared to the other two micropollutants [67,68].

EE2 has a higher affinity for membrane-forming polymers compared to E2 or BPA due to the higher value of its characteristic partition coefficient between the n-octanol phase and water (logK_ow mol·dm⁻³). The higher the logK_ow value, the more hydrophobic the substance is and the greater its tendency to adsorb to the membrane surface. It was demonstrated in [69] that the mechanism of separation of hydrophobic compounds on the membrane is a two-step process, i.e., in the first step, the chemical substance is adsorbed on the surface of the membrane, and in the second step, it passes through the membrane by diffusion. The value of the logKow parameter for EE2 is 4.15 mol·dm⁻³, that for E2 is 4.01 mol·dm⁻³, and that for BPA is 3.32 mol·dm⁻³, respectively. Furthermore, the molar mass of EE2 is higher than that of E2 and BPA, which also explains the higher retention of EE2 in the membrane compared to other micropollutants. The retention rates for EE2, E2, and BPA when filtering model effluent showed a similar trend as when filtering the deionised water solution [67,68,70].

EE2 was removed the most, while BPA was removed to the lowest extent (

Table 4. Degree of micropollutant reduction depending on type of membrane; authors’ own elaboration based on [68,70].

Type of Wastewater	Membrane Type	E2	EE2	BPA
Model drain	UF-CNT	81%	92%	68%
	UF-GE	78%	83%	19%
Actual outflow	UF-CNT	84%	94%	70%
	UF-GE	74%	84%	20%

). During the filtration of the model effluent, the compounds in Table 3 were removed to a greater degree compared to the filtration of deionised water. In ultrafiltration with UF-CNT and UF-GE membranes, the removal efficiency of micropollutants increases with increasing organic and inorganic contents in the feed. During the filtration of the actual effluent, this also occurs with UF-CNT and UF-GE ultrafiltration membranes. It should be noted that the actual effluent has the highest organic and inorganic contents compared to the other aqueous solutions tested. It should also be taken into account that the presence of additional contaminants can alter the transport–separation properties of the membrane. The presence of additional organic and inorganic substances in the feed promotes the formation of a so-called filter cake on the membrane surface with a porosity smaller than the membrane pores, which constitutes an additional separation layer. It is worth emphasising, however, that the described membrane fouling is a negative phenomenon. Thus, the higher retention rates of the investigated compounds resulting from it are a kind of paradox [68,69]. Figure 1 shows a graph comparing the removal efficiency of E2, EE2, E1, and BPA from wastewater using two types of ultrafiltration membranes: UF-GE (aluminium-epoxy) and UF-CNT (with carbon nanotubes). As can be seen, UF-CNT membranes provide higher contaminant elimination efficiency at any pore size [67,68,71,72,73].

2.1.3. Nanofiltration

Nanofiltration (NF) uses membranes with a pore size of approximately 0.001 µm, which allows for the effective removal of organic compounds with a molecular weight of more than 200–300 Da, including many pharmaceuticals and hormones such as diclofenac, ibuprofen, and ethinylestradiol [68]. NF is dependent on the type of membrane, and a number of comparative studies can be found on this topic in the literature, e.g., studies on the relationship between the retention factor of bisphenol A and the type of nanofiltration membrane for a deionised water solution. The values for bisphenol A retention rates ranged from about 62% (for DK membrane) to approximately 94% (for the NF-90 and HL membranes) [68]. Differences in bisphenol A removal efficiency for the tested membranes were observed due to their different physicochemical properties. When the effect of membrane type and properties on the removal efficiency of the micropollutant under investigation is analysed, both its molar mass limit and hydrophobic properties should be taken into account. This is particularly important when comparing nanofiltration membranes from different manufacturers because despite having a similar membrane-forming polymer, membranes have different surface properties. This is due, among other things, to the addition of various admixtures to the polymer, which are not revealed by the membrane manufacturer. A parameter that represents the hydrophobic properties of a membrane is the wetting angle [74]. According to data from the literature, as the wetting angle increases, the hydrophobicity of the membrane surface increases. In the case of the NF-90 membrane, the authors of [68,74] found a high retention of bisphenol A. The HL membrane showed similar separation properties towards bisphenol A. The NF-90 and HL membranes have similar transport properties, as evidenced by the permeate flux value [68,74].

When assessing the effectiveness of a membrane filtration process for the elimination of micropollutants, it is also imperative to perform tests with solutions containing other organic and inorganic substances that are designed to initiate fouling and/or scaling of the membrane. Fouling and scaling phenomena accompany membrane filtration, contributing to a reduction in membrane performance. The authors of [75,76,77] carried out tests for a model effluent containing model organic and inorganic substances in addition to bisphenol A. During the filtration process, the flux of the permeate volume of the NF-90 membrane, characterised by a high wetting angle, decreased. The compact structure of nanofiltration membranes (including pore size) makes them highly susceptible to adverse phenomena that accompany membrane filtration that contribute to a decrease in membrane hydraulic performance [68,75,76,77].

The NF-90 membrane showed the highest degree of elimination (Figure 2). Differences in micropollutant retention were observed due to their different physicochemical properties. The nanofiltration membrane has a similar hydraulic capacity to that of deionised water. The average flux of permeate volume for deionised water is approximately 40 × 10⁻⁶ m³ m⁻² s⁻¹, while for the actual outflow, this value decreased to 4 × 10⁻⁶ m³ m⁻² s⁻¹. The NF-90 membrane is not resistant to fouling caused by contaminants present in the actual outflow. It should be noted that the separation of micropollutants is affected by several membrane phenomena, including the reduction in the zeta potential and the presence of a filter cake on the membrane surface. Membrane fouling increases the intensity of the micropollutant adsorption phenomenon and limits the process of diffusion of compounds through the membrane [68,69,78]. Figure 3 shows the relationship between the pore size of HL and NF-90 membranes and the removal efficiency of E2, EE2, E1, and BPA from wastewater by nanofiltration. As can be seen, the NF-90 membrane shows a higher pollutant elimination efficiency with comparable pore sizes.

The nanofiltration process is effective for low concentrations of contaminants (ng/L to μg/L). The elimination of hormone compounds in this process is maintained at 80%. NF, as in reverse osmosis, requires high pressure, resulting in an energy consumption of 1 to 3 kWh·m⁻³ [28]. Another disadvantage of this process is the high cost of membrane purchase and replacement, which ranges from 50 to 200 US dollars per m² [28]. In addition, membranes require regular maintenance, resulting in additional costs for the cleaning, replacement, and disposal of generated waste. Other significant costs include pretreatment, pumping, and handling of the reject stream. On the other hand, NF operates at lower pressures, typically between 5 × 10⁵ and 3 × 10⁶ [Pa], resulting in lower energy consumption (<3 kWh·m⁻¹) compared to reverse osmosis. The choice of the appropriate membrane material is crucial to maximise separation efficiency [28,79].

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 kWh/m³ [28]. This process is more expensive in terms of energy compared to other conventional processes such as coagulation–flocculation or biological filtration [79]. In terms of operation, reverse osmosis operates at high pressures, typically between 5 × 10⁵ and 7 × 10⁶ 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 m² [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 [80,81,82,87,88,89,90,91].

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.

2.1.5. Filtration and Infiltration Process

The purpose of hasty filtration is to separate from flowing water the suspended solids formed mainly after the coagulation process, but all oestrogens are practically not involved in floc formation and are therefore not retained in the filter bed, which explains the low efficiency range of 7% to 35%. Slow filtration and infiltration allow oestrogen removal at levels of 7% for E1, 35% for E2, 15% for E3, and 26% for EE2 [92,93].

2.1.6. Ultrasound

The ultrasonic process is a promising approach to eliminating organic micropollutants, including steroid hormones and pharmaceuticals, from wastewater. The mechanism of action is based on the phenomenon of acoustic cavitation in which high-frequency ultrasonic waves (20–60 kHz) generate microbubbles of gas in a liquid. These bubbles undergo cyclic growth and violent implosion, causing a local increase in temperature (up to approx. 5000 K) and pressure (up to 500 atm), which results in the homolytic breakdown of molecules and the formation of reactive oxygen species (ROS), including hydroxyl radicals [94,95].

Compounds such as 17α-ethynylestradiol (EE2), estrone (E1), and oestradiol (E2) are highly susceptible to radical oxidation reactions due to the presence of reactive phenolic groups. This was confirmed in Roudbari’s studies [96] in which the addition of butyl alcohol, an inhibitor of hydroxyl radicals, reduced the efficiency of oestrogen removal from the range of 56.3–79.2% to 30.8%, clearly indicating the dominant mechanism of radical oxidation. Figure 5 illustrates the effectiveness of the sonodegradation of selected hormones and pharmaceuticals. The highest removal levels were recorded for EE2 (92%), E2 (88%), and E1 (85%), confirming their high reactivity to ROS. In the case of the following pharmaceuticals, removal was lower: paracetamol (82%), ibuprofen (75%), diclofenac (68%), and carbamazepine (55%). The lower removal efficiency of carbamazepine is attributed to its stable molecular structure and low chemical reactivity.

The efficiency of the process depends on many operating parameters, including the frequency and power of the ultrasound, exposure time, pH, and salinity and alkalinity of the environment [97,98,99,100]. The greatest influence is attributed to the frequency and power of ultrasound (approx. 23%), while exposure time was the least important parameter (6.5%) [99]. An increase in frequency and power intensity leads to intensified cavitation, which increases ROS generation and degradation efficiency [100]. For example, an efficiency of 94% was achieved with 120 min of exposure, a frequency of 60 kHz, a power of 110 W, and a pH of 7–10. The effect of pH on the course of the reaction is complex and depends on the type of compound. According to research [101], the degradation of oestrogens was more effective in an alkaline environment (pH 10), where 95% removal was achieved after 10 min. In contrast, Roudbari [96] pointed to higher efficiency in an acidic or neutral environment, and other studies [95] suggest that lowering the pH from 7.8 to 3 may limit the breakdown of EE2, indicating the need for individual optimisation of parameters. Environmental parameters such as salinity and alkalinity also affect the efficiency of the process. The presence of sodium chloride (0.17 M NaCl) and sodium bicarbonate (120 mM NaHCO₃) increases removal efficiency, mainly by improving conductivity and cavitation conditions [100]. Salinity had a stronger effect than alkalinity, and their combined effect led to a synergistic effect.

The advantages of the process include low energy consumption, no formation of toxic by-products, and the possibility of selective degradation of specific compounds [101]. Under laboratory conditions, both immersible systems (ultrasonic probes) and ultrasonic baths are used to control key parameters. Typical conditions are a frequency range of 20–60 kHz, a power range of 60–110 W, an exposure time of 10–120 min, a temperature range of 20–25 °C, and a pH range of 3–10 [94,95,96,97,98,99,100].

Analytical techniques such as HPLC-MS/MS, UV-Vis spectrophotometry, and TOC analysis are used to evaluate effectiveness [95,96,97]. The presence of free radical scavengers (e.g., butanol and isopropanol) allows for the degradation mechanism to be identified [96]. Studies on the impact of wastewater composition take into account the presence of inorganic anions, including chlorides and bicarbonates, which modify the cavitation and chemical conditions of the process [100].

The use of ultrasound in the removal of hormones and pharmaceuticals from wastewater is a modern and promising solution in the context of growing requirements for the removal of micropollutants. High efficiency in the degradation of oestrogens and selected pharmaceuticals, combined with limited energy consumption and no secondary pollution, makes sonodegradation technology an attractive alternative or complement to conventional processes. An important advantage is the ability to adjust the operating parameters (frequency, power, and pH) to the specific nature of the pollutants, which increases the efficiency and selectivity of the process. Although not all compounds are degraded with equal efficiency and the impact of wastewater composition can be complex, this method has significant application potential, especially in municipal and hospital wastewater treatment plants, where high concentrations of pharmaceuticals and hormones are present.

2.2. Chemical Methods

2.2.1. Advanced Oxidation/O₃/H₂O₂

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 TiO₂ 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 SO₄⁻ 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 (O₃) 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 (O₃), 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 H₂O₂ integration, UV irradiation, alkaline pH, and ozone catalysts [113,114]. Figure 6 shows the main physicochemical mechanisms and processes, such as UV, O₃, H₂O₂, Fe²⁺, and TiO₂, and their interactions, leading to the formation of hydroxyl radicals.

In the O₃/H₂O₂ process, ozone (O₃) in the presence of hydrogen peroxide (H₂O₂) undergoes accelerated autodecomposition, leading to the formation of hydroxyl radicals (-OH), which exhibit a much higher oxidising potential than ozone itself and act non-selectively against a wide range of organic pollutants. The initiating reaction follows the equation H₂O₂ + O₃ → -OH + O₂ + HO₂-, and the resulting radicals attack the double bonds and aromatic structures present in the molecules of endocrine compounds and drugs, leading to their breakdown and partial or complete mineralisation [50,51,54].

Numerous studies have shown that the elimination efficiency of hormones and pharmaceuticals using the O₃/H₂O₂ process can exceed 90%, especially for biodegradation-resistant compounds such as EE2 and diclofenac [31,34]. Compared to classical ozonation, this method provides faster reaction times and higher degradation efficiencies, even with lower ozone consumption, due to the involvement of highly reactive -OH. Another unquestionable advantage of this process is that it can be integrated with other water treatment technologies, including biological treatment and membrane filtration, thus achieving synergistic treatment effects [118].

Despite its high efficiency, the O₃/H₂O₂ process has significant limitations. Its main drawbacks include high operating costs due to the need for on-site ozone production (usually using electricity) and the use of hydrogen peroxide as a chemical reagent. Depending on the scale of the plant and the operating parameters, operating costs can reach 0.20–0.50 EUR/m³ of treated wastewater, which is significantly higher than typical biological treatment costs [71]. In addition, the efficiency of the process is highly dependent on the physicochemical parameters of the wastewater, including the pH value, the presence of competing oxidants, and the contact time. There is also a risk of the formation of intermediates with unknown toxic profiles, which may require further purification in the final stage. Another challenge is the need for precise dosing of reactants—both excess ozone and H₂O₂ can lead to oxidant losses and even the formation of secondary products with oxidising properties [54].

In conclusion, the O₃/H₂O₂ process is an effective but costly technological solution for the advanced elimination of micropollutants from wastewater. Thanks to the generation of hydroxyl radicals, it is possible to remove a wide spectrum of persistent and toxic organic compounds, but its implementation on a larger scale requires detailed economic and environmental analysis and control over process parameters [54].

2.2.2. Ozonation Process

Studies on the evaluation of ozonation efficiency for bisphenol A and deionised water as a matrix have been reported in the literature. The authors of [68] chose bisphenol A because of its lowest susceptibility to chemical oxidation processes.

Figure 7 shows that the efficiency of BPA removal significantly depends on the ozone dose used. At a dose of 1 mg/dm³, an efficiency of about 40% was obtained, which may indicate an initial oxidation step of BPA; however, this is not sufficient for its full degradation. Increasing the dose to 5 mg/dm³ results in a significant increase in efficiency to 70%, suggesting a more advanced mineralisation of the compound and an intensification of the reaction with hydroxyl radicals formed by ozone degradation. Surprisingly, a further increase in the ozone dose to 10 mg/dm³ results in a decrease in efficacy to 60%. This may be due to several possible reasons, for example, an excessive ozone dose may lead to the oxidation of readily reactive organic compounds present in the wastewater, resulting in competition for ozone and reducing its availability to react with BPA. There is also the possibility of the formation of more stable and more difficult-to-remove intermediates as a result of the incomplete decomposition of BPA [48,50,68].

In light of the data obtained, it can be concluded that the optimum ozone dose for effective BPA degradation is approximately 5 mg/dm³. This value provides the highest efficiency while minimising the side effects associated with excessive ozone dosing [68].

The efficiency of the ozonation process is higher under neutral and alkaline conditions than under acidic conditions (Figure 8). This is due to the different reaction mechanism between the compound to be removed and ozone depending on the pH of the solution. In an alkaline environment, radicals are often rapidly removed by hydroxyl anions or other substances, limiting their participation in the reaction [68].

The efficiency of the BPA ozonation process is strongly dependent on the pH value, which affects both the stability of ozone and the oxidation reaction mechanism. Under strongly acidic conditions (pH = 1), ozone has high stability, which limits its rapid decomposition and allows for oxidative activity to be maintained for a longer period in the reaction medium. However, BPA degradation reactions mainly occur by direct oxidation by molecular ozone without the involvement of hydroxyl radicals (-OH), which translates into low BPA removal efficiencies—estimated at 20–30% [119]. An additional limitation of using an acidic environment is the need for aggressive acidifying agents (e.g., HCl), which generates additional costs and technological risks, and requires a final adjustment of the effluent pH [50].

On the other hand, under strongly alkaline conditions (pH = 12), there is an intensive autodecomposition of ozone and the generation of hydroxyl radicals, which have high oxidising potential and are the main factor responsible for BPA degradation. As a result, BPA removal efficiencies in this pH range can reach up to 75–85% [50]. Nevertheless, excessive degradation can lead to ozone losses and requires very precise dosing. Furthermore, as in the case of acidic pH, the use of additional reactants (e.g., NaOH) and the neutralisation of the effluent prior to further management are necessary. The formation of secondary oxidation products with unknown toxicological properties cannot be excluded either [31].

In conclusion, although an alkaline environment is conducive to the effective elimination of BPA, from a technical point of view, the two extreme pH ranges (acidic and alkaline) carry important technological and economic constraints that must be taken into account when designing and optimising the ozonation process [31,50].

Table 5. Degree of reduction in BPA depending on ozone dose, pH, and reaction time; authors’ own elaboration based on [68,70].

Type of Wastewater	Process Parameters	Degree of Reduction
	Ozone dose—1 mg·dm−3 Response time—1 min pH—7	0.4%
deionised water	Ozone dose—5 mg·dm−3 Response time—1 min pH—7	0.7%
	Ozone dose—10 mg·dm−3 Response time—1 min pH—7	>90%
	Exposure time—20 min	75%
	Ozone dose—1 mg·dm−3 Response time—1 min pH—7	8%
model drain	Ozone dose—5 mg·dm−3 Response time—1 min pH—7	5%
	Ozone dose—10 mg·dm−3 Response time—1 min pH—7	30%
	Ozone dose—1 mg·dm−3 Response time—1 min pH—7	15%
actual drain	Ozone dose—5 mg·dm−3 Response time—1 min pH–7	43%
	Ozone dose—10 mg·dm−3 Response time—1 min pH—7	>90%

illustrates the removal efficiency of Biphenol A as a function of the ozone dose, reaction time, and pH. The use of a higher dose of ozone at the same pH and reaction time was more effective in reducing bisphenol A in wastewater and deionised water [68,70,75,120].

According to the literature [19,120], while the estrogenicity of EE2 was reduced by ozonation, by-products were produced that had a negative effect on testosterone secretion even after ozonation. If hormonal compounds are effectively eliminated, other undesirable effects may be enhanced by the ozonation process. Although the hydroxyl radical is a stronger oxidant than ozone, its effect on EE2 in water treatment is not as strong as that of ozone. Due to the nonselective nature of the ⋅OH radical, it can be rapidly consumed by many other contaminants that may be present in the water matrix, such as alcohols and other organic compounds, while ozone is more selective because it attracts electron-rich groupings. Oxidation by O₃ is the predominant degradation process of EE2. It oxidises the phenolic functional group, which is responsible for the estrogenic activity of EE2. It is impossible to completely remove estrogenic activity because EE2 reappeared at low levels (0.1–0.2%) after ozonation [19,120,121].

2.2.3. Photolysis

Brudzik-Niemiec E. [68] observed in her study that in the photolysis process, the concentration of bisphenol A decreases with an increasing irradiation time for water, with the greatest reduction in the concentration of this compound occurring at the initial irradiation time. The greatest removal of bisphenol A occurs at an irradiation time of 30 min for the actual tide (

Table 6. Degree of micropollutant reduction depending on exposure time; authors’ own elaboration based on [68,70].

Type of Wastewater	Name of Association	Process Parameter—Exposure Time	Degree of Reduction
deionised water	BPA	0–10 min	60%
model drains	BPA	0–10 min	85%
		20 min	64%
actual drain	BPA	20 min	95%
		30 min	98%
	E2	5 min	94%
	EE2	20 min	93%

). This is due to the fact that chemicals that show effects similar to photosensitisers may be present in effluent after biological treatment. These compounds have the ability to absorb the energy of electromagnetic radiation and transfer it to other substances involved in photochemical reactions [68].

Table 6 shows the degree of removal of E2, EE2, and BPA as a function of exposure times of 5 min and 20 min in the real drain. The first two hormones achieved a very high degree of reduction in the initial exposure time, while bisphenol A needed about 20 min of exposure to achieve a similar result. The different structural and physicochemical properties of the compounds mentioned above directly affect their stability and reactivity in aqueous solutions [70].

The ozonation process combined with photolysis allows for a higher degree of BPA removal to be achieved than that observed when a single photolysis process is carried out for deionised water and actual effluent. In most of the studies presented in the literature on the application of advanced oxidation processes, a higher efficiency of the combined UV/O₃ process was demonstrated compared to single processes, that is, ozonisation or photolysis [96,122,123]. The efficiency of the process is determined by a number of factors, such as, e.g., the reaction, solution composition, or physicochemical properties of the reactant itself [68]. The decomposition rate of both E2 and EE2 in deionised water solution did not increase when ozone was added to the reactor. In contrast, in the case of BPA after the addition of ozonisation, the degree of decomposition of the compound was greater than 75% (an increase of about 20%). Increasing the irradiation time of the solution does not change the concentration of the solution. Brudzik-Niemiec E [68] found that a synergistic effect for E2 and EE2 is not always observed when using different oxidation processes. In a single photolysis process, the efficiency of oestrogen degradation was high. For E2 and EE2 for the actual effluent, different processes did not have a synergistic effect. Ozone reduced the concentration of bisphenol A to approximately 98% (an increase of approximately 40%). The higher degradation of bisphenol A for the actual effluent compared to deionised water occurred due to the fact that chemicals showing similar effects to photosensitisers were present in the effluent after biological treatment [68].

Photodegradation is the process of decomposition of pollutants under the influence of electromagnetic radiation (mainly UV) without the involvement of a catalyst. UV radiation falls directly on the micropollutant molecules (e.g., 17β-estradiol and ibuprofen) and the molecules absorb energy and enter an excited state. A breaking of chemical bonds (direct photolysis), reactions with molecular oxygen leading to oxidation, and the formation of partially degraded by-products occur. The efficiency of photodegradation depends on the chemical structure of the compound (whether it absorbs UV), the intensity and wavelength of the light, and the presence of dissolved oxygen or photosensitisers. Some pharmaceuticals and hormones absorb UV light poorly, making the efficiency of the process sometimes low without assistance [124,125].

2.2.4. Photocatalysis Without and with Activated Carbon

For photocatalysis with carbon, the reduction in micropollutant concentrations depends on the exposure time.

Table 7. Degree of degradation of E2, EE2, BPA for actual and model wastewater; authors’ own elaboration based on [68,70].

Type of Wastewater	Name of Association	Process Parameter—Exposure Time	Degree of Reduction
model drains	BPA	10 min	40%
	E2	10 min	90%
	EE2	10 min	80%
		60 min	93%
actual outflow	BPA	10 min	30%
		60 min	<50%
	E2	10 min	80%
		60 min	>90%
	EE2	10 min	60%
		60 min	>70%

shows the removal rate of hormones in deionised water and the actual effluent for E2, EE2, and BPA as a function of the irradiation times of 10 min and 60 min. The greatest reduction in concentration with photocatalysis was observed for E2. Differences in the decomposition efficiency of micropollutants may be related to their physicochemical properties. However, the higher decomposition rate of the tested micropollutants for the model effluent is due to the presence of chemicals in the effluent that enable so-called sensitised photocatalysis to take place. After 60 min of the process, the complete decomposition of E2 occurred, and the EE2 removal rate exceeded 95% [61]. In photocatalysis, the rate of decomposition of the reactions of the micropollutants mentioned above is greater for the model effluent. The values range from about 0.1 min⁻¹ for BPA to more than 0.08 min⁻¹ for E2. In the case of the deionised water solution, the reaction rate constants for hormone oxidation (E2 and EE2) are approximately six times higher compared to the value of this parameter determined for BPA [21,68,70].

According to the literature [21,68,70], photocatalysis with activated carbon was carried out for BPA. It was shown that the performance of the photocatalysis process conducted in the presence of 1 mg/dm³ of activated carbon was comparable to photocatalysis conducted with TiO₂ alone. The process of single adsorption of bisphenol A on the activated carbon surface in the presence of 1 mg/dm3 of activated carbon had a low efficiency. After the process was carried out for 60 min, the concentration of bisphenol A only decreased by about 16%. In contrast, when the researchers used a dose of activated carbon that was five times higher (5 mg/dm³), about 50% of the compound was removed after 20 min of exposure, and after 60 min, about 64% was removed. A total of 10 min of exposure allowed 70% BPA decomposition for the actual drain and 40% for the model drain. Furthermore, for the model drain, a degradation rate of 65% was achieved after 60 min of exposure, while after this time for the actual drain, approximately 90% of bisphenol A was removed.

Photocatalytic wastewater treatment processes, especially using semiconductors such as TiO₂ activated by UV or visible light, represent one of the most promising methods for the elimination of hormones and pharmaceuticals. The mechanism of action is based on the generation of reactive oxygen species, mainly hydroxyl radicals, which efficiently oxidise organic pollutants. As indicated in the work of [31] photocatalysis can lead to the efficient degradation of substances such as E2, EE2, diclofenac, and carbamazepine, even reaching more than 90% efficiency under laboratory conditions with the right choice of pH, catalyst dose, and radiation exposure time [31]. However, the effectiveness of this method may be limited by the presence of other substances in the actual wastewater that compete for active sites on the photocatalyst surface and by the possibility of forming toxic intermediates. Additionally, research conducted by a group of researchers [126], although focusing on plasma properties, can be used to understand the energetics and kinetics of pollutant decomposition in advanced hybrid systems based on plasma-assisted photocatalysis [126].

Photodegradation in the context of the elimination of hormones and pharmaceuticals from wastewater represents an important process based on the ability of light (mainly UV radiation) to initiate chemical reactions, leading to the degradation of complex organic pollutants. Under natural conditions (solar photolysis) or assisted by an artificial UV source, photodegradation can contribute to the removal of substances such as EE2, diclofenac, ibuprofen, or carbamazepine. The mechanism is based on the absorption of light energy by contaminant molecules or photosensitisers (e.g., nitrates and humic substances) present in the water, which leads to their excitation and further photochemical reactions, resulting in fragmentation, oxidation, or total degradation (mineralisation). The effectiveness of the process depends, among other things, on the wavelength, light intensity, the presence of enhancers (e.g., H₂O₂), and the properties of the pollutants themselves—the higher their UV absorption capacity, the more effective the degradation process [42]. Advantages of photodegradation include the lack of need for additional chemicals (in the case of natural photolysis), the possibility of using solar energy, and relatively low operating costs. Disadvantages include low efficacy for some radiation-resistant pharmaceuticals, the need for long exposure times, and the potential formation of toxic intermediates [42].

2.2.5. Electro-Fenton Process

The requirement for an acidic environment is one of the main constraints on the use of the Fenton process (EF) in wastewater treatment. The wastewater must first be acidified to the optimum Fenton reaction value and then neutralised before entering the receiving water. Due to the use of chemical reagents, this process can have an environmental impact and is complex and costly. Furthermore, a process carried out at a pH higher than the optimum precipitates iron in the form of iron hydroxides, thus removing iron dissolved in solution and stopping the process [127,128]. Other factors affecting the degradation of hormones in this process are the concentration of the catalyst, the type of electrolyte, the concentration of H₂O₂, the temperature, and the concentration of dissolved oxygen [127]. Nevertheless, this method is one of the most efficient advanced techniques for the elimination of hormones. The main disadvantages of Fenton processes are the formation of toxic by-products from the oxidation of dissolved organic matter in the wastewater, the dependence on pH, and the production of iron precipitate [129,130]. In addition, the high energy consumption of the EF process increases costs and greenhouse gas emissions. Advantages of the process include easy control, high efficiency, and good compatibility. Furthermore, the low iron requirement allows the process to be carried out with residual iron present in the wastewater. H₂O₂ can be produced continuously by the electro-Fenton reaction and Fe²⁺ can be continuously regenerated in situ by electrolysis [127,128,131].

Increasing the concentration of iron can increase the concentration of sediment in solution, which affects water quality. The use of inadequate concentrations of reagent can result in high operational costs and difficulty in removing excess reagent to meet effluent standards for disposal or reuse. Although the effect of Fenton’s reagent and catalyst concentration on the degradation kinetics of various pharmaceutical compounds has been studied in several studies, each recommended different optimal dosages. This is because the optimal dose of reagent is highly dependent on the initial concentration of the compound, the aqueous matrix, the reaction time, the pH used, and the chemical structure of the compound [129,131].

Naimi, I. and Bellakhal, N. [132] conducted a study on the removal of oestrogens (i.e., EE2) using an electro-Fenton process [132]. The process was carried out in an aqueous acetonitrile mixture using a carbon felt cathode and a platinum anode. The complete removal of E2 was achieved after 25, 30, and 40 min depending on the initial E1 concentration (

Table 8. Degree of hormone removal in electro-Fenton process; authors’ own elaboration based on [132].

Name of Compound	Initial Concentration (mg/L)	Reactions	Time (min)	Degree of Reduction [%]
EE2	1	pH = 3; Fenton reaction, Fe2+ = 28 mg/L Fe2+:H2O2 = 1:10	180	50
			10	70
			30	90
E2	1	Electro-Fenton reaction, Na2SO4:7.1 g/L Fe2+:11 mg/L pH = 3	25	100
	5		30	100
	10		40	100

) [132]. E2 was removed most effectively regardless of concentration.

2.2.6. Electrolysis Process

The level of elimination of micropollutants from wastewater depends on the type of electrode material used. The most effective but quite expensive is a boron-doped nanodiamond electrode, which achieves up to 90% elimination of xenoestrogens [133]. The electrolysis process for the elimination of oestrogens from wastewater has been very rarely studied. In the case of contaminants in poultry slaughterhouse wastewater, the efficiency level was 33.5–100% depending on the additional processes used (reverse osmosis and ultrafiltration). A significant disadvantage of the electrolysis process is the very high demand for electricity (about 40 kWh/9 L of water), resulting in significant costs [133,134].

2.2.7. Electrocoagulation Process

Electrocoagulation is an advanced process that combines the functions of conventional coagulation, flotation, and electrochemistry. The process consists of three stages, i.e., coagulant formation by dissolving metal ions in the anode electrode, the destabilisation of contaminants and suspended particles, and the de-emulsification and aggregation of insoluble phases and floc formation. Electrocoagulation reduces impurities and suspended particles through floc formation and removal by sedimentation [135]. The cost associated with metal electrocoagulation is five times lower than that for chemical purification [136]. The electrocoagulation technique uses a direct current source between metal electrodes immersed in water. The electric current generated in the water causes the metal plates to dissolve in the water, and these metal ions at different pH can form a wide range of flocculates and metal hydroxides, which readily precipitate and adsorb soluble endocrine-disrupting compounds (EDCs) and aggregate suspended particles present in the water [137]. Aluminium and iron are the most commonly used metals in the electrocoagulation process.

According to [43], all endocrine compounds were removed at similar levels (>60%), except for E3, which is eliminated at a level of 56% (Figure 9).

2.3. Combined Processes

In recent years, the development of wastewater treatment technologies has focused on combining different physical, chemical, and biological methods to increase the removal efficiency of micropollutants, including hormones (e.g., E2, EE2, and E1) and pharmaceuticals.

Table 9. Hybrid technologies used to eliminate hormones and pharmaceuticals from wastewater; authors’ own elaboration based on [31,32,33,34,35,36,41,42,43,138,139,140,141,142,143].

Combined Processes	Mechanism of Action	Hormone Removal [%]	Pharmaceutical Removal [%]	By-Product Details	Advantages	Disadvantages
MBR + adsorption (AC, MOF)	Biodegradation + adsorption of residuals	85	80	None or minimal–CO2 and H2O; adsorption does not generate by-products	High efficiency, resistant to variable loads	Adsorbent cost, regeneration needed
Photocatalysis (TiO2) + UV-C	•OH degrade organic molecules	85	80	Oxidised compounds: carboxylic acids, aldehydes, alcohols, phenols, and quinones	Complete mineralisation, no secondary sludge	High energy cost, catalyst requirement
Ozonation + GAC	Oxidation by ozone + adsorption of by-products	90	85	Aldehydes, ketones, organic acids, and brominated organics (e.g., bromoform)	Good efficiency, EDC reduction	Intermediate products, ozonation cost
Ultrasound + AOP (UV/H2O2)	Cavitation enhances oxidation and degradation	88	80	Short-lived radicals (•OH, O2•⁻), molecular fragments–aldehydes, ketones, and fatty acids	Effective against persistent compounds	High energy use, complex setup
Coagulation + UF/MF	Aggregation + physical membrane separation	50	40	Non-significant physical removal of particles; possible sludge with sorbed micropollutants	Low-cost preliminary step, protects downstream processes	Low micropollutant removal
MBR + AOP (ozonation/UV)	Biodegradation + oxidation of residuals	90	85	Intermediates: Aldehydes, phenols, alcohols, carboxylic acids, and brominated compounds	Comprehensive removal, reduced toxicity	Operational cost, AOP control
NF + UV/ozonation	Membrane retention + degradation in effluent	92	90	Oxidation by-products (aldehydes and acids), high concentration of retentate—needs further treatment	High efficiency, water recovery	Membrane fouling, operating cost
RO + AOP	Pressure separation + oxidation in concentrate or permeate	99	98	High metabolite concentrations of retentate; AOP can form toxic by-products (e.g., THMs and HAAs)	Highest efficiency, water reuse	Very high cost, retentate disposal required
AOP + BAC (bioactive carbon)	Oxidation + biodegradation in biofiltration bed	85	80	Oxidised by-products biodegradable in BAC—minimal final toxicity	Toxicity reduction, metabolite degradation	Media regeneration, microbial sensitivity
Plasma + adsorption (AC/MOF)	Plasma radicals + adsorption by carbon or MOF	90	85	Short-lived radicals (•OH, NO• and H2O2), aromatic fragments; possible nitrated products (with air plasma)	Innovative, fast, chemical-free method	Complexity, installation cost
Photocatalysis + membrane separation	Photodegradation of micropollutants on membrane surface coated with photocatalyst; membrane simultaneously filters pollutants and retains catalyst	~85–90% (e.g., EE2, E2)	>90% (e.g., ibuprofen and paracetamol)	Short-chain organic acids identified; most found to be non-toxic [1]	High efficiency, continuous operation, catalyst retention, reduced secondary contamination	Potential for membrane fouling, higher material and operational costs
Photocatalysis + photothermal evaporation	Simultaneous photothermal water evaporation and photocatalytic degradation of micropollutants; solar energy converted to heat and catalyst activated	~80–85% (e.g., E1, E2)	85–90% (e.g., sulfamethoxazole)	Minor intermediate by-products; some phenolic compounds, mostly undergoing further degradation [2]	High removal and desalination efficiency, off-grid operation, environmentally friendly	Limited by sunlight availability, more difficult to scale, longer processing times

shows the different configurations of the combined processes along with their mechanisms of action, removal efficiencies, benefits, limitations, and potential by-products. The highest removal efficiencies of both hormones (up to 99%) and pharmaceuticals (up to 98%) are shown by advanced combinations such as reverse osmosis (RO) with AOPs. Combinations of nanofiltration (NF) with ozonation or UV, as well as MBR (biological membrane reactor) with adsorption or AOP, also show efficiencies above 90%. Processes such as photocatalysis (TiO₂ with UV-C) or ultrasound combined with AOP provide good removal efficiencies but have the disadvantages of high energy costs and the need for catalysts. In contrast, methods based on coagulation and membrane filtration (UF/MF) show much lower efficiency in the elimination of micropollutants but are cheap and can protect further purification steps [31,32,33,34,35,36,41,42,43,138,139,140,141]. As far as by-products are concerned, the most undesirable effects occur when using oxidation processes (ozonation and AOP), which can lead to the formation of aldehydes, ketones, carboxylic acids, brominated compounds, and trihalomethanes. It is therefore important to select combinations of technologies to ensure both high purification efficiency and the minimisation of harmful by-products. The advantages of many combination methods are their ability to remove difficult-to-degrade contaminants and the stability of operation under varying wastewater loads. Disadvantages tend to be operational costs, plant complexity, and the need for the regeneration of materials (e.g., activated carbon and MOF).

Photocatalysis, as an advanced oxidation process (AOP), plays a key role in modern technologies for the treatment of the aquatic environment, especially in the context of the removal of organic micropollutants such as pharmaceuticals, plant protection products, or endocrinically active compounds. However, under real-world conditions, the effectiveness of conventional photocatalytic systems can sometimes be limited due to the short life of electron–hole pairs, the low availability of UV/vis light in the environment, and problems with the separation and recovery of the photocatalyst. In response to these challenges, integrated, multifunctional hybrid systems that combine photocatalysis with other physicochemical processes to increase purification efficiency and improve the operational properties of reaction systems have been developed in recent years [142,143].

One of the most promising approaches is the integration of photocatalysis with membrane processes, enabling the simultaneous degradation of contaminants and their physical separation. Such hybrid systems combine the high selectivity and separation efficiency of membranes with the oxidation potential of photocatalysts, leading to an increase in the overall removal efficiency of micropollutants. Additionally, the use of the membrane as a catalyst carrier can significantly reduce catalyst losses and facilitate system operation and regeneration. In reference [142], an integrated photocatalytic membrane system was used, and the use of a composite membrane with embedded semiconductor photocatalyst nanoparticles enabled a significant increase in micropollutant degradation efficiency under continuous flow conditions. The authors showed that the synergistic action of these two processes translated into more than a 90% reduction in model contaminants in short retention times, confirming the high utility of this approach in environmental engineering practice [142]. Equally innovative and promising is the combination of photocatalysis with photothermal evaporation, which uses materials capable of converting solar energy into heat. Such systems allow not only the degradation of pollutants, but also the intensification of water evaporation, which can be particularly beneficial in wastewater treatment or water recovery systems in water-scarce conditions. In another study [143], a composite material combining photothermal and photocatalytic properties was developed that enabled the simultaneous treatment and desalination of water containing organic micropollutants. Thanks to the synergy of photothermal and photocatalytic effects, it was possible to achieve both a high evaporation rate (exceeding 1.6 kg m⁻² h⁻¹) and the efficient degradation of micropollutants (more than 85% removal within 2 h of exposure). These results indicate significant potential for the integration of photothermal processes with photocatalysis in the context of advanced water purification, especially in regions with high insolation [143].

Both integration with membrane separation and photothermal processes exemplify a new generation of hybrid technologies that can effectively address the limitations of conventional photocatalysis processes. The implementation of such solutions can not only increase treatment efficiency but also contribute to the development of more sustainable and energy-efficient environmental technologies that respond to the challenges of wastewater treatment and water resource recovery in a changing climate.

3. Conclusions

Pharmaceuticals and steroid hormones are among the most significant micropollutants present in wastewater, posing a serious threat to the aquatic environment and public health. Steroid hormones are among the most studied pollutants due to their widespread use in hormone therapy and their natural secretion by living organisms. The occurrence of these compounds in watercourses not only affects aquatic organisms (causing endocrine disruption, for example), but also humans and plants.

This article presents current methods for removing pharmaceuticals and hormones from wastewater. Although many of them, such as advanced oxidation processes (AOPs), adsorption on activated carbon, membrane filtration, and hybrid systems, show high efficiencies (often >90%), there are still important limitations. The main gaps concern the cost-effectiveness of large-scale implementation, the sustainability of the technology, the risk of secondary contamination, and the environmental impact. In particular, broad-spectrum purification methods are not sufficiently developed as most existing studies focus on a limited number of selected pharmaceuticals and steroid hormones. It is necessary to extend analyses to other classes and subclasses of these compounds to obtain a more complete picture of efficacy and risk. Based on the literature review and the current state of knowledge, the following conclusions are made:

• The effectiveness of classical wastewater treatment plants is limited—many drugs, such as carbamazepine, ibuprofen, antibiotics, and beta-blockers, pass through biological systems virtually unchanged.
• There is a lack of standardised analytical methods and environmental standards for many pharmaceuticals, making it difficult to monitor their presence and disposal efficacy
• The efficiency of conventional treatment plants is insufficient for the elimination of pharmaceuticals and hormones—it is necessary to implement advanced technologies and integrate them into hybrid systems.
• Most of the research was limited to laboratory and pilot scales, so further research should be carried out on a larger scale, i.e., the technical scale.
• Most of the methods were applied only using steroid hormones as a single contaminant in aqueous solution. However, wastewater is a complex mixture, and research should focus on the efficiency of removal in both synthetic and real wastewaters in the presence of other organic and inorganic contaminants.
• Most studies have focused on the clearance of oestrogen hormones compared to progesterone and androgens. No new purification processes for progesterone and androgens have been studied.
• Membrane systems remove hormones with greater efficiency. However, in this case, the hormones are transferred to the brine, and another step is required to remove them from the brine before discharge. Therefore, future research should focus on the complete removal of hormones from wastewater rather than transferring them to another phase.
• Although advanced treatment technologies, such as AOP, membrane technologies, or adsorption, effectively remove steroid hormones, they have many disadvantages. These drawbacks make them uneconomical and environmentally unfriendly. Therefore, research should focus not only on the efficiency of steroid hormone removal, but also on cost analysis, benefits, system cycle, and environmental aspects.
• Modern sorption and catalytic materials (e.g., biochar, MOFs, and nanoparticles) have the potential to increase purification efficiency at lower operating costs.
• Researchers are focusing mainly on advanced purification techniques. However, they should also focus on increasing the efficiency of steroid hormone removal from existing conventional wastewater treatment plants by redesigning, changing operational parameters, or upgrading.
• There is a lack of research involving techno-economic analysis, so more work needs to be performed in this area as it is a major focus for investors, engineers, industry, and policy makers.
• The development of monitoring and analytical methods (including methods for determining trace concentrations) is crucial for effective water quality control and the assessment of treatment effectiveness.
• Regulatory, educational, and systemic actions are needed, reducing emissions at the source and supporting the responsible management of pharmaceuticals and hormonal waste.
• Research needs to be extended to less well-studied active substances—both synthetic and natural—in order to develop purification methods with a broader spectrum of action.