WASTEWATER TREATMENT SYSTEM AND METHOD FOR THE REMOVAL OF EMERGING ORGANIC CONTAMINANTS

Abstract

The present invention relates to a wastewater treatment system for the removal of emerging organic pollutants, characterized in that it comprises: at least one reactor configured for the removal of emerging organic pollutants from wastewater by means of a reaction between the wastewater and a photocatalyst added to the reactor, and an external treated water storage unit connected to the treated water outlet of the reactor. The invention also relates to a method for treating wastewater for the removal of emerging organic pollutants using said system.

Description

WASTEWATER TREATMENT SYSTEM AND METHOD FOR THE ELIMINATION OF EMERGING ORGANIC CONTAMINANTS FIELD OF INVENTION The present invention pertains to the technical field of wastewater treatment. More specifically, the present invention relates to a tertiary / quaternary wastewater treatment system for the removal of emerging organic pollutants, characterized by the efficient combination of at least one open tank-type reactor with solar-activated heterogeneous photocatalysis. BACKGROUND OF THE INVENTION The growing concern surrounding emerging organic contaminants (EOCs) stems from the continuous increase in water demand for agricultural, industrial, and domestic uses, with water reclaimed from wastewater treatment plant effluents being one of the sources with the greatest potential for growth. This entails significant risks that EOCs pose to human health and wildlife [1]. In current wastewater treatment plants, the persistence of emerging organic contaminants and pathogens in treated effluents presents a critical challenge to maintaining the quality of water bodies and ensuring the safety of reused water for humans, animals, and ecosystems [2, 3, 4]. Traditional treatment methods, such as activated sludge (secondary treatment) and tertiary processes, including filtration and disinfection, generally fail to effectively remove many COEs. These systems are primarily designed to remove conventional contaminants in accordance with current regulations; as a result, many COEs persist in aquatic ecosystems and in reclaimed water used for irrigation. Recently, significant scientific efforts have been made to develop processes for removing COEs from water, employing various techniques such as adsorption, advanced oxidation processes, and photocatalytic methods, among others. Many of these studies have been carried out with individual contaminants in the laboratory, while others have focused on the removal of COEs in real-world wastewater scenarios, especially in urban wastewater treatment plants (WWTPs) [5, 6, 7]. In the field of advanced wastewater treatment, there are several developments that incorporate photocatalysis technologies for the removal of COEs. One example is ES2577904A2, which describes a closed tubular system incorporating UV lamps and removable catalyst carriers for contaminant removal. This solution focuses on a controlled environment with a closed configuration, which limits its scalability and energy efficiency compared to technologies based on direct solar energy use. WO1997037936A1 describes a photocatalytic reactor designed for wastewater purification using semiconductor catalysts in colloidal or immobilized form. This system is based on a closed tubular design, where process activation occurs using UV radiation lamps. Although efficient in certain contexts, its closed configuration and dependence on artificial energy represent a barrier in terms of scalability and energy efficiency. Another relevant solution is patent WO2017192101A1, which describes a photoelectrochemical cell for wastewater treatment. This invention employs optically permeable materials and a specific light source to induce controlled photoactive reactions. While this technology introduces a hybrid approach with potential, its implementation requires specialized components and greater operational complexity, limiting its applicability in large-scale treatment environments such as wastewater treatment plants. Similarly, patent WO2020146813A1 proposes a photocatalytic reactor system optimized using light management and thermal efficiency techniques, including plasmonic photocatalysis elements. This technology focuses on maximizing the absorption of specific wavelengths and utilizing natural or artificial light sources integrated into closed cells with high energy efficiency. However, as in the previous cases, the closed design, the use of complex technologies, and the limited adaptability to existing infrastructure restrict its practical integration into conventional wastewater treatment systems. WO2024074646A1 refers to a wastewater treatment system. The system comprises a wastewater tank, a transparent tube, a dosing system for a particulate photocatalyst (zinc oxide or graphitic carbon nitride), a solar reflector to concentrate sunlight onto the tube, and a screen downstream of the tube to retain the particulate photocatalyst while allowing water to pass through, so that the particulate photocatalyst is recovered in a cartridge of the dosing system. The system recycles the catalyst used in the purification process, ensuring that it can be reused multiple times, making it efficient and environmentally friendly. However, it does not appear to overcome the scaling challenges inherent in this type of system. Therefore, in view of the state of the art solutions, the need has been identified to solve problems such as clogging, mechanical complexity, energy dependence of internal lamps and scaling limitations characteristic of the systems currently employed. DESCRIPTION OF THE INVENTION The present invention solves problems present in the prior art by providing a wastewater treatment system for the removal of emerging organic pollutants. This system comprises an open reactor containing a suspended photocatalyst and utilizing solar energy as the primary activation source, significantly reducing operating costs and environmental impact. This contrasts with traditional advanced treatment systems that require closed facilities, expensive pressurized reactors, or the intensive use of chemicals. The system of the present invention uses open, raft-type reactors without concentrators, where the photocatalyst operates in suspension and is kept homogeneously dispersed by bubbling aeration from the bottom and lateral recirculation. Catalyst / water separation is achieved by gravity settling at the end of the cycle, with photocatalyst capture by closing an internal platform, requiring only a protective filter in the discharge line. The system is modular and incorporates perimeter UV-Vis irradiation when solar irradiance is insufficient, sizing the operating depth according to Beer-Lambert's law (2-3 m in clear water), which allows for the treatment of a much larger volume of water. This configuration eliminates screens, cartridges, and conveyors, reduces clogging and operating costs, prevents overpressure, expands photocatalyst compatibility, and facilitates integration into wastewater treatment plants with standard equipment. In one aspect, the present invention relates to a wastewater treatment system for the removal of emerging organic contaminants, characterized in that it comprises: (i) at least one open reactor connected to a wastewater inlet (influent) and to an outlet of the treated water (effluent), configured for the removal of emerging organic contaminants in wastewater by means of a reaction between the wastewater and a photocatalyst that is added inside the reactor, wherein at least one reactor comprises inside: - an aeration stirring system located at the bottom of the reactor comprising a plurality of holes configured to introduce air in the form of bubbles; - at least one recirculation means located in one of the internal walls of the reactor; and - a separation element comprising an open position in which the separation element is entirely outside the reactor during the reaction and a closed position in which the separation element is inside the reactor after the reaction and divides the reactor into a lower chamber and an upper chamber in which the treated water outlet is arranged, the chambers being isolated from each other; and ii) an external treated water storage unit that is connected to the treated water outlet of the reactor. In a second aspect, the present invention relates to a method for the treatment of wastewater for the removal of emerging organic contaminants by means of a system as described above, characterized in that it comprises the steps of: a) introduce wastewater through the reactor inlet; b) add a photocatalyst to the reactor and activate the aeration stirring system by producing bubbles and at least one recirculation means to keep the photocatalyst in suspension and promote contact between the contaminants present in the water and the photocatalyst so that the reaction takes place for a period of at least 4 hours; c) deactivate the aeration stirring system and at least one recirculation means and allow the photocatalyst to settle to the bottom of the reactor by gravity; d) activate the separation element to move from an open position to a closed position, leaving the photocatalyst in the lower chamber and the treated water in the upper chamber; and e) extract the treated water from the upper chamber through the outlet and transfer it to the treated water storage unit. The use of photocatalysts allows for the degradation of pollutants when activated by light. The reaction consists of the ability of these materials to convert triplet oxygen from the air (3O2, the ground state of molecular oxygen) into singlet oxygen (1O2) through energy transfer, thanks to the photosensitization effect of sunlight or a radiation source such as a UV-Vis lamp. Singlet oxygen is a highly reactive compound that produces oxidation reactions in highly resistant organic compounds, including COE. The photocatalyst is selected from the group consisting of TiO₂, TiO₂ doped with transition metals selected from palladium (Pd), gold (Au), silver (Ag), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), molybdenum (Mo), vanadium (V), manganese (Mn) and chromium (Cr), TiO₂ doped with rare earths selected from cerium (Ce), lanthanum (La), neodymium (Nd), europium (Eu), gadolinium (Gd) and samarium (Sm), or combinations thereof. The photocatalysts that can be used in the system and method of the present invention are both inorganic and organic and in all cases must be in suspension in the treated aqueous medium. The inorganic heterogeneous photocatalysts suitable for the system and method of the present invention are selected from the group consisting of titanium dioxide (TiO), anatase, rutile, or mixed-phase TiO, nitrogen-doped TiO (TiO-N), platinum-doped TiO (TiO-Pt), transition-metal-doped TiO selected from palladium (Pd), gold (Au), silver (Ag), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), molybdenum (Mo), vanadium (V), manganese (Mn), and chromium (Cr), non-metal-doped TiO selected from carbon (C), sulfur (S), phosphorus (P), fluorine (F), boron (B), and co-doped TiO with combinations of metals and non-metals such as TiO-NF, TiO-Mo-N, TiO-VN, TiO-NS, TiO-CN, TiO doped with rare earths selected from cerium (Ce) , lanthanum (La) , neodymium (Nd) , europium (Eu) , gadolinium (Gd) and samarium (Sm) , and TiO modified with carbon quantum dots or graphene-derived materials. Other suitable photoactive inorganic materials are metal oxides such as zinc oxide (ZnO), tungsten trioxide (WO), iron oxide (FeO), tin oxide (SnO), bismuth oxide (BiO), cadmium oxide (CdO); complex compounds selected from bismuth vanadate (BiVO), nickel ferrite (NiFeO), doped perovskites; composite materials selected from ZnO / NiFeO, ZnO / FeO, WO / BiVO; and advanced porous materials selected from metal-organic frameworks (MOFs) and mesoporous silica materials. The heterogeneous organic photocatalysts suitable for the system and method of the present invention are selected from the group consisting of compounds formed by a polymer matrix functionalized with covalently anchored organic photosensitizers, wherein the polymer matrix is ​​selected from polystyrene, polyacrylamide, poly(2-hydroxyethyl methacrylate) (polyHEMA), chitosan, porous silicone, polymethyl methacrylate (PMMA), polyethylene glycol (PEG), polyurethane, polyvinyl alcohol (PVA), polyaniline, polypyrrole, polyethylene, polypropylene, polycarbonate, polyamide, polyester, and styrene-butadiene copolymers. Other examples of photocatalysts suitable for use in the system and method of the present invention are organic molecular photocatalysts capable of being anchored in polymeric structures such as Rose Bengal, Methylene Blue, Acridine Yellow, Tetraphenylporphyrin or Phenol Pink, among others. Once the invention has been clearly described, it is noted that the particular embodiments described above are subject to minor modifications provided they do not alter the fundamental principle and essence of the invention. BRIEF DESCRIPTION OF THE FIGURES Next, to facilitate understanding of the invention, an embodiment of the invention will be described by way of illustration but not limitation, which refers to a series of figures. Figure 1 is a schematic diagram of a system with four open reactors for decontaminating wastewater according to an embodiment of the present invention. Figure 2 presents a cross-sectional view of an embodiment of the reactor system of the present invention, highlighting the location of the aeration stirring system and the recirculation means, arranged along the internal walls of the reactor. Figure 3 is a representation of the reactor of the system of the present invention while the reaction between the wastewater and the photocatalyst is taking place, specifically detailing the open position of the separation element, which is completely outside the reactor. Figure 4 presents a cross-sectional view of the reactor according to the present invention after the completion of the reaction between the wastewater and the photocatalyst, showing the closed position of the separation element that delimits a lower chamber and an upper chamber, the latter being provided with the treated water outlet, both chambers being isolated from each other. Figure 5 is a schematic diagram of a system like the one described in Figure 1, which also incorporates two sources of electromagnetic radiation in UV-Vis located at two corners of the reactor and oriented towards the interior of the reactor. These figures refer to a set of elements which are: 1. Wastewater inlet. 2. Open reactor. 2a. Lower chamber. 2b.Upper chamber. 3. Aeration agitation system. 4. Recirculation medium. 5. Treated water outlet. 6. Treated water collection unit. 7. Separation element. 8. Source of electromagnetic radiation in UV-Vis. DETAILED DESCRIPTION OF THE INVENTION The object of the present invention is a wastewater treatment system for the removal of emerging organic contaminants, characterized in that it comprises: ) at least one open reactor (2) connected to a wastewater inlet (1) and to an outlet of the treated water (5), configured for the removal of emerging organic contaminants in wastewater by means of a reaction between the wastewater and a photocatalyst that is added inside the reactor, wherein the at least one reactor (2) comprises inside: - an aeration stirring system (3) located at the bottom of the reactor (2) comprising a plurality of holes configured to introduce air in the form of bubbles; - at least one recirculation means (4) located in one of the internal walls of the reactor; and - a separation element (7) comprising an open position in which the separation element is entirely outside the reactor (2) during the reaction and a closed position in which the separation element (7) is inside the reactor after the reaction and divides the reactor into a lower chamber (2a) and an upper chamber (2b) in which the treated water outlet (5) is arranged, and the chambers (2a, 2b) are isolated from each other; and ii) an external treated water storage unit (6) that is connected to the treated water outlet (5) of the reactor (2). As can be seen in Figure 1, a plurality of open reactors (2) can be arranged. These reactors are not connected to each other but have the same configuration; that is, each one is an identical unit. The possibility of interconnecting several reactors in the same system allows for the creation of a modular structure that adapts to different production capacities. This approach facilitates scalability at an industrial level, since increased demand does not require redesigning the entire process, but simply adding more units (reactors) to the existing system, while maintaining efficiency and operational uniformity. Each of the open reactors (2) has a wastewater inlet (1) and a treated water outlet (5). The treated water outlet (5) is connected to a treated water recovery unit (6). This unit (6) is located outside the reactor but is part of the system. The reactor (2) comprises an internal aeration stirring system (3) located at the bottom of the reactor (2), comprising a plurality of orifices configured to introduce air in the form of bubbles, and at least one recirculation means (4) located in one of the internal walls of the reactor. Figure 2 shows one embodiment in which there are four recirculation means (4), each located in the internal walls of the reactor, and the arrangement of the orifices of the aeration stirring system (3) can be observed. Additionally, the system of the present invention has a separation element (7), which has two positions: open and closed. In the open position, the separation element (7) is located outside the reactor, as shown in Figure 3. Conversely, in the closed position, the element is inside the reactor and divides the reactor into a lower chamber (2a) and an upper chamber (2b), as can be seen in Figure 4. According to one particular embodiment, the system described above incorporates at least one electromagnetic radiation source (8), which is positioned around the perimeter of the reactor (2). As can be seen in Figure 5, a plurality of electromagnetic radiation sources (8) can be arranged. This arrangement is repeated in each of the reactors. The UV-Vis electromagnetic radiation sources can be lamps or LEDs emitting in the UV-Vis emission range. Another object of the present invention is a method for treating wastewater for the removal of emerging organic contaminants by means of a system described above, characterized in that it comprises the steps of: a) introduce wastewater through the inlet (1) of the reactor (2); b) adding a photocatalyst to the reactor and activating the aeration stirring system (3) by producing bubbles and at least one recirculation means to keep the photocatalyst in suspension and promote contact between the contaminants present in the water and the photocatalyst so that the reaction takes place for a period of at least 4 hours; c) deactivate the aeration stirring system (3) and at least one recirculation means (4) and allow the photocatalyst to settle to the bottom of the reactor (2) by gravity; d) activate the separation element (7) to move from an open position to a closed position, leaving the photocatalyst in the lower chamber (2a) and the treated water in the upper chamber (2b); and e) extract the treated water from the upper chamber (2b) through the outlet (5) and transfer it to the treated water storage unit (6). EXAMPLE Having described the present invention, it is further illustrated with an example. The purpose of the example given below is to illustrate the invention, without limiting its scope. Example 1. Decontamination of water from a WWTP using the system of the present invention using only sunlight. Initially, water from a tertiary treatment effluent of a wastewater treatment plant was introduced into the system of the present invention. In this example, a system was used consisting of two reactors, each equipped with a wastewater inlet and a treated water outlet, an aeration agitation system located at the bottom of the reactor, four recirculation means (one located on the walls of each reactor), and a separation element. In this example, sunlight was used, and no electromagnetic radiation sources were employed. The system was activated by introducing water and turning on the stirring and recirculation systems. Simultaneously, rutile-phase titanium dioxide was added as a photocatalyst at a concentration of 200 grams of TiO2 per cubic meter of water. The system operated for approximately 14 hours. It was then shut down and allowed to settle for about 9 hours to allow the photocatalyst to deposition at the bottom of the reactor. Finally, the closed position of the separation element was activated, leaving the deposited photocatalyst confined in the lower chamber, and the treated water was extracted from the upper chamber through the treated water outlet. Samples were collected at the beginning and end of the process to analyze the effectiveness of the process and the system for removing emerging contaminants present in wastewater. Table 1 shows the data obtained, expressed in ng / L, for each of the compounds present in the reactor influent (the incoming water) and the effluent (the water treated with the system of the present invention). It can be seen that of the 48 emerging contaminants analyzed, only sulfamethoxazole is present in a detectable quantity, specifically 0.8 ng / L, which, when compared to the concentration of this compound in the influent, represents a reduction of 99.85%. The remaining 47 compounds were found in undetectable quantities, that is, below the detection limit of the analytical method used consisting of high-performance liquid chromatography (HPLC), these results being very favorable, especially for COEs such as Losartan or Sitagliptin, which are found in very high concentrations. Table 1. Results obtained by compound nd= not detected BIBLIOGRAPHIC REFERENCES [1] Fabregat V. Unlocking the Potential of Reclaimed Water: Analysis of the Challenges and Market Size as a Strategic Solution for Water Scarcity in Europe. Challenges. 2025 Sep 4;16 (3):43. [2] Arman, N.Z.; Salmiati, S.; Aris, A.; Salim, M.R.; Nazifa, T.H.; Muhamad, M.S.; Marpongahtun, M. A review on emerging pollutants in the water environment: Existences, health effects and treatment processes. Water 2021, 13, 3258. [3] Patel, N.A.V.E.E.N.; Khan, M.D.; Shahane, S.; Rai, D.; Chauhan, D.; Kant, C.; Chaudhar y , V.K. Emerging pollutants in aquatic environment: Source, effect, and challenges in biomonitoring and bioremediation-a review. Pollution 2020, 6, 99-113. [4] Morin-Crini, N.; Lichtfouse, E.; Liu, G.; Balaram, V.; Ribeiro, A.R.L.; Lu, Z.; Crini, G. Worldwide cases of water pollution by emerging contaminants: A review. Environ. Chem. Lett. 2022, 20, 2311-2338. [5] Shahid, M.K.; Kashif, A.; Fuwad, A.; Choi, Y. Current advances in treatment technologies for removal of emerging contaminants from water-A critical review. Coord. Chem. Rev.2021, 442, 213993. [6] Rathi, B.S.; Kumar, P.S.; Show, P.L. A review on effective removal of emerging contaminants from aquatic systems: Current trends and scope for further research. J. Hazard. Mater.2021, 409, 124413. [7] Marin, M.L.; Santos-Juanes, L.; Arques, A.; Amat, A.M.; Miranda, M.A. Organic photocatalysts for the oxidation of pollutants and model compounds. Chem. Rev.2012, 112, 1710-1750.

Claims

1. A wastewater treatment system for the removal of emerging organic contaminants, characterized in that it comprises: i) at least one open reactor (2) connected to a wastewater inlet (1) and a treated water outlet (5), configured for the removal of emerging organic contaminants in wastewater by means of a reaction between the wastewater and a photocatalyst added to the reactor, wherein the at least one reactor (2) comprises internally: - an aeration stirring system (3) located at the bottom of the reactor (2) comprising a plurality of orifices configured to introduce air in the form of bubbles; - at least one recirculation means (4) located in one of the internal walls of the reactor; and - a separation element (7) comprising an open position in which the separation element is completely outside the reactor (2) during the reaction and a closed position in which the element1. The system of claim 1, wherein the separation element (7) is located inside the reactor after the reaction and divides the reactor into a lower chamber (2a) and an upper chamber (2b) in which the treated water outlet (5) is arranged, and the chambers (2a, 2b) are isolated from each other; and ii) an external treated water storage unit (6) that is connected to the treated water outlet (5) of the reactor (2).

2. The system according to claim 1, wherein the separation element (7) in its closed position is arranged at a height corresponding to 1 / 3 of the depth of the reactor (2), measured from the bottom of the reactor (2).

3. The system according to claim 1 or 2, wherein the at least one open reactor (2) further comprises at least one electromagnetic radiation source (8) that emits in the ultraviolet and visible regions.

4. The system according to claim 3, wherein the at least one electromagnetic radiation source (8) is located around the perimeter of thereactor (2).

5. The system according to any of claims 1 to 4, wherein the treated water outlet (5) comprises a filter.

6. A method for treating wastewater for the removal of emerging organic contaminants by means of a system according to any of claims 1 to 5, characterized in that it comprises the steps of: a) introducing wastewater through the inlet (1) of the reactor (2); b) adding a photocatalyst to the reactor and activating the aeration stirring system (3) by means of bubble production and at least one recirculation means to keep the photocatalyst in suspension and promote contact between the contaminants present in the water and the photocatalyst so that the reaction takes place for a period of at least 4 hours; c) deactivating the aeration stirring system (3) and at least one recirculation means (4) and allowing the photocatalyst to settle to the bottom of the reactor (2) by gravity;d) activate the separation element (7) to move from an open position to a closed position, leaving the photocatalyst in the lower chamber (2a) and the treated water in the upper chamber (2b); e) extract the treated water from the upper chamber (2b) through the outlet (5) and transfer it to the treated water storage unit (6).

7. The method according to claim 6, wherein the photocatalyst is selected from the group consisting of TiO₂, TiO₂ doped with transition metals selected from palladium (Pd), gold (Au), silver (Ag), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), molybdenum (Mo), vanadium (V), manganese (Mn) and chromium (Cr), TiO₂ doped with rare earths selected from cerium (Ce), lanthanum (La), neodymium (Nd), europium (Eu), gadolinium (Gd) and samarium (Sm), or combinations thereof.

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