System for the treatment of wastewater and corresponding process

Abstract

The present invention relates to a system (1) for the treatment of wastewater comprising organic compounds and / or inorganic or ionic compounds, optionally deriving from the agri-food or livestock supply chain, said system comprising a first bioelectrochemical reactor (2) and a second photocatalytic reactor (3) connected in series, wherein: the first bioelectrochemical reactor (2) is intended to receive the wastewater to be treated and comprises an anode (22) and a cathode (23) connected to each other by means of an external electrical circuit (24) in which an electrical load (25) is present, the anode (22) being a carbon-based material, preferably in the form of granules, pellets, plates or blocks, and the cathode (23) being floating on the surface (27) of the wastewater (21), and the second photocatalytic reactor (3) is intended to receive the water exiting the first bioelectrochemical reactor (2) and comprises a photocatalyst (32) loaded on an inert support (33), said inert support (33) being suspended in water (31) inside the second photocatalytic reactor (3).

Description

SYSTEM FOR THE TREATMENT OF WASTEWATER AND CORRESPONDINGPROCESSDescription

[0001] Field of the invention

[0002] The present invention relates to a system for the treatment of wastewater and a corresponding process. In particular, the present invention relates to a system for the purification and the valorisation of wastewater and a corresponding process.

[0003] State of the art

[0004] The agricultural and livestock fields contribute significantly to the pollution of air and water, being responsible for the release into the environment of species such as persistent organic substances and nutrients, due to phenomena of leaching of nitrates and phosphates and emissions of ammonia into the atmosphere. This results from poor management of the wastewater deriving from the agri-food and livestock supply chain, which is not appropriately treated. Such wastewater, on the contrary, is often discharged into water bodies, where it causes eutrophication, and into the soil, causing pollution. At the same time, useful and valuable species such as nutrients are lost, which could instead be reused for soil fertilisation.

[0005] Indeed, another problem affecting the agricultural field concerns the availability of fertilisers, whose cost is constantly increasing and whose availability is not always guaranteed. Over the years, several processes have been proposed to recover nutrients necessary for the production of fertilisers and, thus, to overcome the aforementioned problem. Some of these are ammonia stripping and filtration processes. However, they are very expensive and highly energy-consuming.

[0006] Therefore, need is strongly felt to provide a method for the treatment of wastewater that allows the recovery of the nutrients contained therein, without thesebeing dispersed into the environment or degraded by the process itself, which would represent both a loss of value and a significant source of pollution.

[0007] Moreover, the agricultural and livestock fields represent the main global water footprint and the demand for water is rapidly increasing worldwide. Therefore, it is highly desirable to have a method for treating wastewater which is capable of removing even substances that are recalcitrant to the most common methods of treatment and which also allows the reuse of water in the agricultural and livestock fields.

[0008] Therefore, the problem underlying the present invention is to provide a method for treating wastewater, especially deriving from the agri-food or livestock supply chain, which is capable of removing the contaminants present therein as well as recovering the water and the micro- and macronutrients contained therein.

[0009] Summary of the invention

[0010] The above-mentioned problem is solved by a system for the treatment of wastewater and a corresponding process, as defined in the appended claims, the definitions of which form an integral part of the present description.

[0011] A first object of the present invention is a system for the treatment of wastewater comprising organic compounds and / or inorganic or ionic compounds, optionally deriving from the agri-food or livestock supply chain, said system comprising a first bioelectrochemical reactor and a second photocatalytic reactor connected in series, wherein: the first bioelectrochemical reactor is intended to receive the wastewater to be treated and comprises an anode and a cathode connected to each other by means of an external electrical circuit in which an electrical load is present, the anode being a carbon-based material, preferably in the form of granules, pellets, plates or blocks,and the cathode being floating on the surface of the wastewater, and the second photocatalytic reactor is intended to receive the water exiting the first bioelectrochemical reactor and comprises a photocatalyst loaded on an inert support, said inert support being suspended in water inside the second photocatalytic reactor.

[0012] A second object of the present invention is a process for the treatment of wastewater comprising organic compounds and / or inorganic or ionic compounds, optionally deriving from the agri-food or livestock supply chain, wherein said process is conducted in the above-mentioned system and comprises the following steps: a) subjecting the wastewater to a bioelectrochemical process in the first bioelectrochemical reactor, said process being conducted in the presence of a microbiological load, obtaining at least partially treated wastewater; b) subjecting the at least partially treated wastewater exiting the first bioelectrochemical reactor to a photocatalytic process in the second photocatalytic reactor.

[0013] Advantageously, the system of treatment according to the present invention and the corresponding process allow the decontamination of the wastewater subjected to treatment, reducing both the organic load and the bacterial content, as well as removing recalcitrant organic substances possibly present such as drugs, pesticides and herbicides.

[0014] Advantageously, the system of treatment according to the present invention and the corresponding process allow the recovery of micronutrients (for example, iron, zinc, manganese, copper) and macronutrients (for example, nitrogen, phosphorus, potassium, calcium) contained in the wastewater subjected to treatment and of which the wastewater deriving from the agri-food supply chain is particularly rich. These can therefore be reused, for example as fertilisers or soil conditioners.

[0015] At the same time, the system of treatment according to the present invention and the corresponding process ensure a level of purification of the water such that it can be reused for multiple purposes, for example as process water or for irrigation, depending on the composition of the initial wastewater.

[0016] Advantageously, the system of treatment according to the present invention and the corresponding process do not produce sludge, which would constitute special waste.

[0017] Advantageously, the anode of the bioelectrochemical reactor, at the end of the wastewater treatment process, can be used in agriculture as a soil conditioner enriched with micro- and macronutrients.

[0018] Advantageously, the cathode of the bioelectrochemical reactor, at the end of the wastewater treatment process, can be scraped for the recovery of nutrients, which can advantageously be formulated together with the anode enriched with micro- and macronutrients. Advantageously, the cathode of the bioelectrochemical reactor, after scraping the nutrients accumulated on it during the wastewater treatment process, can be reused in subsequent processes, as it is not disposable.

[0019] Moreover, the system according to the present invention and the corresponding process exploit spontaneous reactions, generating electrical energy, which can be accumulated and used, for example, for monitoring the process itself.

[0020] To better understand the invention and appreciate its advantages, some exemplary and non-limiting embodiments thereof will be described below, making reference to the accompanying figures.

[0021] Brief description of the figures

[0022] Figure 1 is a perspective view of the system for the treatment of wastewater according to an embodiment of the present invention.

[0023] Figure 2 is a schematic front view of the first bioelectrochemical reactor of the system of treatment of Figure 1 , according to a first embodiment of the present invention.

[0024] Figure 3 is a schematic front view of the first bioelectrochemical reactor of the system of treatment of Figure 1 , according to a second embodiment of the present invention.

[0025] Figure 4 is a schematic front view of the second photocatalytic reactor of the system of treatment of Figure 1 , according to an embodiment of the present invention.

[0026] Figure 5 is a diagram showing the trend of cell potential (Eceii), cathode potential (Ecat), redox potential (Eredox) and water temperature (Temp) inside the first bioelectrochemical reactor during the operating phase.

[0027] Figure 6 shows a comparison between the EDS analysis (“Energy-dispersive X-ray spectroscopy”) carried out on pristine biochar (above) and the same EDS analysis carried out on biochar after its use as an anode in the first bioelectrochemical reactor (below).

[0028] Figure 7 shows the scanning electron microscopy (SEM) micrographs of the photocatalytic system consisting of BiOBr loaded on loofah sponge before (A, C) and after (B, D) its use in the second photocatalytic reactor.

[0029] Detailed description of the invention

[0030] An object of the present invention is a system for the treatment of wastewater, comprising a first bioelectrochemical reactor and a second photocatalytic reactor connected in series, and the corresponding process.

[0031] It has been surprisingly found that the coupling of said two reactors offers systemic synergy and dual valorisation of wastewater, in particular deriving from the agri-food or livestock supply chain, allowing for the efficient recovery of the micro- andmacronutrients contained therein and, at the same time, efficient remediation of the water itself for its possible reuse. Advantageously, in the first bioelectrochemical reactor organic substances are eliminated which are potentially harmful for the photocatalyst present in the second photocatalytic reactor.

[0032] The expression “treatment of wastewater” relating to the system and the process in accordance with the invention denotes both the purification of the wastewater entering the system and subjected to the corresponding process, and the recovery of micro- and macronutrients contained therein, which can be reused, for example in agriculture, as soil conditioners or fertilisers.

[0033] The wastewater fed to the system of treatment according to the invention and subjected to the corresponding process contains one or more organic compounds and / or one or more inorganic or ionic compounds.

[0034] By way of example, said inorganic or ionic compounds include one or more of: phosphates, nitrites, nitrates, ammonium salts, alkali metals (for example, Na), alkaline earth metals (for example, Mg and Ca), heavy metals.

[0035] By way of example, said organic compounds include one or more of: primary metabolites, secondary metabolites and their intermediates, for example polysaccharides, peptides, simple sugars, amino acids, phenols, urea, acetates, pyruvates, and other organic salts; drugs, for example diclofenac, ibuprofen, amoxicillin; pesticides, for example isoproturon; herbicides. In particular, drugs, pesticides and herbicides fall within the category of recalcitrant organic substances.

[0036] According to an embodiment, the wastewater fed into the above-mentioned system and subjected to the corresponding process is wastewater deriving from the agri-food or livestock supply chain. Advantageously, said wastewater does not contain suspended or precipitated solid material. According to an embodiment, thewastewater deriving from the agri-food or livestock supply chain is filtered to remove the solid material contained therein before being fed into the system of treatment according to the invention. According to an alternative embodiment, the wastewater deriving from the agri-food or livestock supply chain is filtered within the system of treatment according to the invention, in particular inside the first bioelectrochemical reactor, which may comprise a grid with mesh size suitable for removing the solid material contained in the wastewater.

[0037] According to an embodiment, the wastewater fed into the system of treatment according to the invention and subjected to the corresponding process has a COD (“chemical oxygen demand") that can reach up to several tens or hundreds of thousands of units, for example up to 100.000 mg eqO2 / L. According to some embodiments, said wastewater has COD values up to 90,000 mg eqO2 / L, or up to 80,000 mg eqO2 / L, or up to 70,000 mg eqO2 / L, or up to 60,000 mg eqO2 / L, or up to 50,000 mg eqO2 / L, or up to 40,000 mg eqO2 / L, or up to 30,000 mg eqO2 / L, or up to 20,000 mg eqO2 / L, or up to 10,000 mg eqO2 / L, or up to 1 ,000 mg eqO2 / L. For example, said wastewater has COD values between 300 and 10,000 mg eqO2 / L.

[0038] Advantageously, the wastewater fed into the system of treatment according to the invention and subjected to the corresponding process comprises a microbiological load.

[0039] According to an embodiment, said microbiological load is naturally present in the wastewater fed into the system of treatment according to the invention.

[0040] According to another embodiment, a microbiological load, preferably in the form of a microbial consortium, is specifically inoculated into the wastewater to be treated either before it is fed into the bioelectrochemical reactor or inside the bioelectrochemical reactor itself.

[0041] Advantageously, said microbiological load comprises microorganisms capable of exploiting the extracellular electron transfer (EET) mechanism.

[0042] Preferably, said microbiological load is a bacterial load. Advantageously, said bacterial load comprises bacteria capable of exploiting the extracellular electron transfer (EET) mechanism.

[0043] Advantageously, the process of treatment according to the present invention provides for the degradation and / or removal from the wastewater of the organic compounds and / or inorganic or ionic compounds contained therein, as well as at least partial removal of the microbiological load present therein and the recovery of micronutrients and macronutrients.

[0044] The system for the treatment of wastewater according to an embodiment of the present invention is described below with reference to the accompanying figures, by way of example only.

[0045] The system for the treatment of wastewater is generally denoted by the reference number 1 and comprises a first bioelectrochemical reactor 2 and a second photocatalytic reactor 3.

[0046] The first bioelectrochemical reactor 2 and the second photocatalytic reactor 3 are connected in series.

[0047] The wastewater to be treated is fed into the first bioelectrochemical reactor 2 through a feed pipe 4 connected to a suction pump 5.

[0048] The at least partially treated wastewater exits the first bioelectrochemical reactor 2 and is fed into the second photocatalytic reactor 3 through a feed pipe 6 which is, in turn, connected to a suction pump 7.

[0049] According to the embodiment illustrated in the figure, the first bioelectrochemical reactor 2 is provided with a tap 8 for discharging the at leastpartially treated water, and a collection tank (not shown) is optionally connected to said tap.

[0050] According to the embodiment illustrated in the figure, the treated water exits the second photocatalytic reactor 3 through a discharge tap 9, to which a collection tank (not shown) is optionally connected.

[0051] According to the embodiment illustrated in the figure, an aeration blower 10 is connected to the second photocatalytic reactor 3, supplying air to the reactor itself through a feed pipe 11.

[0052] According to an embodiment, the first bioelectrochemical reactor 2 comprises a reaction vessel 12 and a lid 13 for said reaction vessel 12. Preferably, there are special spacers 14 between the reaction vessel 12 and the lid 13, which ensure that the lid 13 does not rest on the reaction vessel 12, but is instead slightly raised above it, ensuring the presence of a passage 15 between the reaction vessel 12 and the lid 13. The term “spacers” denotes mechanical elements intended to keep an appropriate distance between parts between which they are interposed, preventing contact between them; for example, said spacers are threaded spacers. This configuration is intended to ensure the entry, through the passage 15, of the air necessary for the bioelectrochemical process to take place, and to prevent the entry of external agents into the bioelectrochemical reactor 2.

[0053] According to an embodiment, visible in Figure 1 , the second photocatalytic reactor 3 is open at the top so that the water contained therein is exposed to solar radiation.

[0054] According to an alternative embodiment (not shown), the second photocatalytic reactor 3 comprises a reaction vessel and a lid for said reaction vessel, wherein said lid is transparent to sunlight, allowing solar radiation to pass through it.Preferably, there are special spacers between the reaction vessel and the lid, which ensure that the lid does not rest on the reaction vessel, but is instead slightly raised above it, ensuring the presence of a passage between the reaction vessel and the lid. The term “spacers” denotes mechanical elements intended to keep an appropriate distance between parts between which they are interposed, preventing contact between them; for example, said spacers are threaded spacers. This configuration is such as to hinder the entry of external agents into the photocatalytic reactor 3 and to prevent the generation of overpressure in the reactor itself. Furthermore, this configuration ensures that the water contained inside the reactor 3 is exposed to solar radiation.

[0055] The first bioelectrochemical reactor 2 according to an embodiment of the present invention is shown in greater detail in Figure 2 and Figure 3, where the wastewater contained therein is denoted by the reference number 21 .

[0056] Said reactor 2 comprises an anode 22 and a cathode 23 connected to each other by means of an external electrical circuit 24 in which an electrical load 25 is present, for example a resistance. The anode 22 may consist of a single electrode or a plurality of electrodes appropriately connected. Similarly, the cathode 23 may consist of a single electrode or a plurality of electrodes appropriately connected.

[0057] The anode 22 is a carbon-based material, preferably in the form of granules, pellets, plates or blocks. Preferably, the carbon-based material constituting the anode 22 has a size between 1 and 50 mm, for example between 10 and 20 mm. Advantageously, said size ensures that the carbon-based material constituting the anode 22 is conductive and, at the same time, easy to recover at the end of the process for subsequent applications (for example, spreading on soil for soil fertilisation or storage for subsequent spreading on soil for soil fertilisation). A materialwith a smaller size, if not properly treated, could disperse and settle at the bottom of the reactor, potentially causing clogging of the taps and difficulty in recovery; conversely, a material with a larger size could cause reduced effectiveness of the anodic process due to an unfavourable surface-to-volume ratio and, consequently, a smaller contact area with the wastewater to be treated and a reduced inter-particle contact area (greater electrical resistance). Advantageously, the carbon-based material constituting the anode 22 does not include powders, granules, pellets, plates or blocks of micro- or nanometric size.

[0058] According to some embodiments, said carbon-based material is selected from the group consisting of: graphite, biochar, activated carbon, graphene, carbon fabric, conductive material derived from biomass pyrolysis. Advantageously, the anode 22 of the bioelectrochemical reactor 2 of the system of the invention is not a boron-doped porous diamond film electrode (BDD) generally used in known systems.

[0059] According to a preferred embodiment, the anode 22 consists of biochar, preferably in the form of granules, pellets, plates or blocks, preferably with a size between 1 and 50 mm, for example between 10 and 20 mm. Advantageously, the biochar is such as to ensure both the conduction of electrons and the growth of microorganisms and the development of an electrochemically active biofilm on its surface.

[0060] According to the embodiment illustrated in Figure 2, the carbon-based material constituting the anode 22, for example biochar, is housed inside a bag 26 made of a filtering and water-permeable material, for example a jute bag.

[0061] According to the embodiment illustrated in Figure 3, the carbon-based material constituting the anode 22, for example biochar, is housed inside cartridges 40. Preferably, the cartridges 40 are made of a non-conductive material. Preferably, thecartridges 40 are made of a material inert to the wastewater. By way of example, the cartridges 40 are made of a metal material, for example steel, or a plastic material. Advantageously, the cartridges 40 are provided with holes and / or meshes (not shown in the figure) of a size smaller than that of the anodic material so that, advantageously, the latter does not escape but, at the same time, water can pass through. Advantageously, the cartridges 40 are mechanically and chemically stable in water. According to an embodiment, the anodic material is pressed inside the cartridge 40, resulting in increased contact between the granules and, therefore, increased electrical conductivity. Advantageously, at the end of the process, the cartridges 40 can be easily removed from the reactor 2 and handled for the recovery of the anodic material contained therein and for its reuse, for example as a soil conditioner enriched with micro- and macronutrients.

[0062] The cathode 23 is floating on the surface 27 of the wastewater 21. The fact that the cathode 23 is floating on the water surface implies that one of its faces (or surfaces) is directly in contact with the air above the surface 27 of the water, while one of its faces (or surfaces) is in contact with the wastewater, in particular with the surface 27 of the wastewater contained in the reactor. Therefore, the cathode 23 is understood as an “air cathode”. The fact that the cathode 23 is floating implies, advantageously, that its face (or surface) in contact with the air remains dry even after electrical wiring, that is, even after connection to the external circuit that allows electrical continuity with the anode.

[0063] The term “floating” denotes that the cathode 23 is “self-floating” or that the cathode 23 is made floating by attachment to a floating element or to a specific floatation system. The term “floating” referred to the cathode 23 also denotes that the cathode 23 is positioned on the surface 27 of the wastewater 21 , therefore even inthe event of variation in the water level.

[0064] According to an embodiment, the cathode is self-floating, meaning that it is inherently buoyant, and therefore does not require to be attached to a specific floatation system to remain on the surface 27 of the wastewater. According to this embodiment, advantageously, the cathode is made of a material which is lightweight and / or low-density and / or hydrophobic and / or not wettable by water, properties which preserve its buoyancy over time.

[0065] According to another embodiment, the cathode 23 is made floating by attachment to a specific floating element or floatation system, made for example of solid foam (for example, polyurethane or polystyrene foam) or an organic or inorganic sponge. According to this embodiment, preferably, said floating element or floatation system is of the passive type, being intended to ensure that the cathode 23 floats on the surface 27 of the water autonomously and without any external intervention (neither manual nor automated), that is, without requiring control or adjustment to modulate the degree of buoyancy. For example, said floating element or floatation system is such that it does not require an airbag to be inflated or deflated, nor does it require confinement within sleeves that adapt to the height of the surrounding liquid. By way of example only, said floating element or floatation system is made in the form of a frame specifically shaped to the shape of the cathode and sealed thereto so as to constitute a single element integral with the cathode; preferably, said frame is made of a material which is low-density and not wettable by water, preferably non-porous.

[0066] According to an embodiment, the cathode 23 has at least one flat surface. Preferably, the cathode 23 is configured as a 2D (two-dimensional) material. The term “2D material” denotes that the cathode 23 has a thickness much smaller (for example, two orders of magnitude) than the extent of the other two coplanar geometricdimensions (width and length). According to this embodiment, preferably, the cathode 23 has two flat faces (or surfaces), one of which is directly in contact with the air above the surface 27 of the wastewater, while the other is in contact with the wastewater, in particular with the surface 27 of the wastewater contained in the reactor. Advantageously, this embodiment allows for easier recovery of nutrients from the cathode by simple scraping.

[0067] According to an embodiment, the cathode 23 is made of a carbon-based material. According to some embodiments, the cathode 23 consists of carbon paper or carbon felt or carbon fabric, on which a layer 28 of carbon-based ink is preferably deposited, said layer being conductive and hydrophobic.

[0068] According to a preferred embodiment, the cathode 23 comprises or consists of a carbon fabric floating on the surface 27 of the wastewater 21. Preferably, a layer 28 of carbon-based ink is deposited on said carbon fabric, said layer being conductive and hydrophobic.

[0069] Advantageously, the cathode 23 of the bioelectrochemical reactor 2 of the system of the invention is not a boron-doped porous diamond film electrode (BDD) generally used in known systems.

[0070] Advantageously, the cathode 23 can be employed in subsequent processes, as it is not disposable.

[0071] Advantageously, both the anode 22 and the cathode 23 are made of materials suitable for the recovery of micronutrients and / or macronutrients present in the wastewater entering the bioelectrochemical reactor 2.

[0072] Advantageously, both the anode 22 and the cathode 23 are made of materials that are benign to the environment and human health, not containing metals or metalloids (such as boron) that could be released into the treated water and not beingsources of micro- and nanoparticles that could pollute the water and have a significant ecotoxicological impact.

[0073] According to an embodiment, the first bioelectrochemical reactor 2 comprises one or more measurement sensors (not shown in Figures 2 and 3), for example one or more sensors selected from the group consisting of: temperature, pH, electrical conductivity, redox potential, cathode potential, COD (“chemical oxygen demand’) sensors. Advantageously, said sensors are in contact with the wastewater 21 contained in the first bioelectrochemical reactor 2, preferably they are immersed in the wastewater 21. According to an embodiment, said sensors are fixed to a special rack. Preferably, said sensors are continuous and in-line measurement sensors.

[0074] According to some embodiments, the external electrical circuit 24 is made of copper, or stainless steel, or titanium, or a combination of two or more thereof. Advantageously, the wires of the electrical circuit are appropriately electrically insulated from the outside by means of suitable insulating sheaths.

[0075] Advantageously, the anode 22 is positioned below the surface 27 of the wastewater 21 contained in the first bioelectrochemical reactor 2, preferably it is positioned at the bottom of the bioelectrochemical reactor 2 or close to the bottom of the bioelectrochemical reactor 2, since it is not floating.

[0076] Advantageously, the anode 22 and the cathode 23 of the first bioelectrochemical reactor 2 are arranged according to a vertical electrode geometry. In particular, the cathode 23 floats on the surface 27 of the wastewater 21 , while the anode 22 is placed below, preferably at the bottom of the first bioelectrochemical reactor 2; in accordance with this embodiment, the anode confined in such a position is made non-floating.

[0077] Advantageously, the anode 22 and the cathode 23 of the firstbioelectrochemical reactor 2 of the system according to the present invention are not separated by a membrane, for example an ion-exchange or proton-exchange membrane. Advantageously, the first bioelectrochemical reactor 2 of the system according to the present invention is a single-compartment reactor, wherein the anode 22 and the cathode 23 are not placed in two chambers compartmentalised by a physical separator, such as a membrane, for example an ion-exchange or protonexchange membrane, but they are positioned in a single chamber. Advantageously, the bioelectrochemical reactor 2 of the system according to the present invention does not comprise a pumping system to push the water from the anode to the cathode. Said configuration advantageously allows the free migration of ions as well as the deposition of micro- and / or macronutrients on the anode and cathode, thereby enabling their recovery and, consequently, reuse. Furthermore, the absence of physical separators between anode and cathode, as well as the absence of a water pumping system between anode and cathode, ensure simpler construction, lower costs, easier maintenance, longer lifespan and lower probability of malfunction, hence higher production efficiency.

[0078] The second photocatalytic reactor 3 according to an embodiment of the present invention is illustrated in greater detail in Figure 4, where the wastewater contained in the second photocatalytic reactor 3 is denoted by the reference number 31. Advantageously, the photocatalytic reactor 3 is not a photoelectrocatalytic reactor (i.e., a reactor combining electrochemistry with photocatalysis, using electrical energy and light to stimulate reactions), but an exclusively photocatalytic reactor (i.e., a reactor that uses only light to activate a catalyst). Advantageously, the photocatalyst 32 is neither a photoelectrode nor a photoelectrocatalyst; therefore, it does not require either a constant external potential for its operation or a conductive support.

[0079] The second photocatalytic reactor 3 comprises a photocatalyst 32 loaded onto an inert support 33. The inert support 33 is suspended in the water 31 inside the second photocatalytic reactor 3, preferably near the surface 34 of the water 31 inside the second photocatalytic reactor 3, that is, just below the surface 34. The expression “near the surface 34 of the water 31” denotes that the inert support 33 is suspended in the water 31 in a region extending, starting from the surface 34, up to (i.e., not beyond) 35 cm below the surface 34, for example up to 30 cm, or up to 25 cm, or up to 20 cm, or up to 15 cm, or up to 10 cm, or up to 5 cm below the surface 34. Advantageously, when it is suspended in the water near the surface, the photocatalyst maximises the aeration of its surface and the amount of light absorbed, regenerating its surface during operation itself.

[0080] According to various embodiments, the photocatalyst 32 is selected from the group consisting of: BiOBr, BiOCI, BiOl, Bi2O3, or a mixture of at least two of them.

[0081] Preferably, the photocatalyst 32 is immobilised on the inert support 33. The term “immobilised” means that the photocatalyst is not pre-synthesised and then adhered, glued or made to adhere to the inert support using glues, adhesives and / or other substances or compounds. On the contrary, the photocatalyst is directly synthesised on the inert support. For example, it is directly synthesised on the inert support through a process involving the following two steps: 1) spontaneous chemical anchoring of the metal precursor (for example, Bi3+) on the surface of the support (with the formation of strong coordination bonds between polar groups, for example hydroxyl, amino, etc., and the metal), and 2) subsequent growth of the semiconductor through impregnation with a solution based on the corresponding halide (for example, bromide or chloride) and / or alkaline solution and subsequent thermal treatment at 60-80°C.

[0082] Preferably, the photocatalyst 32 can be activated by UV light and / or visible light.

[0083] According to an embodiment, the inert support 33 is a material having a density lower than the density of water. According to this embodiment, the inert support 33 remains naturally suspended in the water 31 inside the second photocatalytic reactor 3.

[0084] According to various embodiments, the inert support 33 is an organic material or an inorganic material or a polymer material (natural or synthetic). Preferably, said organic material is a natural sponge, for example loofah sponge. Preferably, said inorganic material is pumice stone or expanded clay. Preferably, said polymer material is an expanded polymer material, for example expanded polyurethane.

[0085] According to an embodiment, the second photocatalytic reactor 3 comprises a mechanical system 35 for lifting the inert support 33 on which the photocatalyst 32 is loaded so as to keep the inert support 33, and therefore the photocatalyst 32, suspended in the water 31 inside the second photocatalytic reactor 3, preferably near the surface 34 of the water 31. The expression “near the surface 34 of the water 31” is as defined above. Advantageously, said mechanical lifting system 35 is also a system for confining the inert support 33, and therefore the photocatalyst 32. According to the embodiment illustrated in Figure 4, said system 35 is a lifting basket.

[0086] Advantageously, said mechanical lifting system 35 is such as to keep the inert support 33 (on which the photocatalyst 32 is loaded) suspended in the water 31 inside the second photocatalytic reactor 3, more particularly near or below the surface 34 of the water 31 , for example in case of loss of buoyancy of the inert support 33 or in case the inert support 33 is not a “self-floating” material, having, for example, a densityhigher than the density of water.

[0087] Advantageously, said mechanical lifting system 35 also facilitates the removal of the photocatalytic material during maintenance and its regeneration.

[0088] According to an embodiment, the inert support 33 is loaded with an amount of photocatalyst 32 between 1 and 20% by weight, preferably between 2 and 10% by weight.

[0089] According to an embodiment, the second photocatalytic reactor 3 comprises at least one lamp 36 of UV light or visible light or sunlight. Said at least one lamp 36 is such as to be at least partially immersed in the water 31 inside the second photocatalytic reactor 3. Advantageously, said at least one lamp 36 is activated in the event of poor sunlight.

[0090] According to an embodiment, the second photocatalytic reactor 3 comprises one or more measurement sensors (not shown in Figure 4), for example one or more sensors selected from the group consisting of: temperature, redox potential, pH, electrical conductivity, COD (“chemical oxygen demand’) sensors. Advantageously, said sensors are in contact with the water 31 contained in the second photocatalytic reactor 3, preferably they are immersed in the water 31. According to an embodiment, said sensors are fixed to a special rack or to the mechanical lifting system 35 described above. Preferably, said sensors are continuous and in-line measurement sensors.

[0091] As already described above with reference to Figure 1 , according to an embodiment, the second photocatalytic reactor 3 is aerated. In this regard, preferably, the system 1 according to the present invention comprises a blower 10 for the aeration of said second photocatalytic reactor 3.

[0092] Another object according to the present invention is a process for thetreatment of wastewater comprising organic compounds and / or inorganic or ionic compounds, optionally deriving from the agri-food or livestock supply chain, said process being carried out within the system 1 described above with reference to the figures. Said process comprises the following steps: a) subjecting the wastewater to a bioelectrochemical process in the first bioelectrochemical reactor 2, said process being carried out in the presence of a microbiological load, obtaining at least partially treated wastewater; b) subjecting the at least partially treated wastewater exiting the first bioelectrochemical reactor 2 to a photocatalytic process in the second photocatalytic reactor 3.

[0093] According to an embodiment, the microbiological load is inherently contained in the wastewater to be subjected to the treatment process according to the invention. According to an embodiment, the microbiological load is added to the wastewater simultaneously or before being subjected to the bioelectrochemical process within the first bioelectrochemical reactor 2. According to an embodiment, the microbiological load is partly inherently contained in the wastewater to be treated and partly added to the wastewater simultaneously or before being subjected to the bioelectrochemical process.

[0094] According to an embodiment, the process of the invention comprises monitoring one or more parameters of the bioelectrochemical process, said parameters being selected from, but not limited to, temperature, pH, electrical conductivity, redox potential, cell potential / current, cathode potential, COD (“chemical oxygen demand”). Preferably, the monitoring of the parameters of the bioelectrochemical process is continuous and in-line monitoring.

[0095] According to an embodiment, the process of the invention comprisesmonitoring one or more parameters of the photocatalytic process, said parameters being selected from, but not limited to, temperature, redox potential, pH, electrical conductivity, COD (“chemical oxygen demand’). Preferably, the monitoring of the parameters of the photocatalytic process is continuous and in-line monitoring.

[0096] According to an embodiment, the process of the invention comprises a step of irradiating the water inside the second photocatalytic reactor 3 with UV light, sunlight and / or visible light during the photocatalytic process.

[0097] According to an embodiment, the process of the invention comprises a step of aerating the second photocatalytic reactor 3 during the photocatalytic process.

[0098] Advantageously, the organic content of the water is at least partially removed within the first bioelectrochemical reactor 2.

[0099] The bioelectrochemical process taking place in the first reactor 2 advantageously exploits the anodic half-reaction of oxidation of the organic substances dissolved in the wastewater by the biofilm developed on the biochar, and the cathodic half-reaction of reduction to water of the oxygen of air dissolved in the wastewater. In other words, the bioelectrochemical process uses the microorganisms of the microbiological load, more specifically bacteria, as biocatalysts for the anodic half-reaction of oxidation of the organic substances and for the production of electric current. The microorganisms perform the conversion of the chemical energy contained in the organic substances into electrical energy.

[0100] Advantageously, inorganic or ionic substances are also removed from the wastewater within the first bioelectrochemical reactor 2, with consequent recovery of micro- and macronutrients, which advantageously enrich the anodic material (for example, biochar), forming a soil conditioner enriched with nutrients that can be directly used, for example, for soil fertilisation, and which deposit on the surface of thecathodic material as well. Therefore, at the end of the process of the invention, the anodic material can be reused in agriculture as a soil conditioner enriched with micro- and macronutrients and the cathodic material can be scraped to recover further nutrients. Advantageously, the anodic material, preferably biochar, is authorised by the European legislation for field dispersion; therefore, the anodic material, after a certain treatment time required to enrich it with micro- and macronutrients, can simply be dispersed in the field, without generating waste or residues.

[0101] Advantageously, the microbiological or bacterial load present in the wastewater is also partially removed within the first bioelectrochemical reactor 2.

[0102] Advantageously, the first bioelectrochemical reactor 2, during its operation, generates an amount of electric current due to the spontaneous progression of the bioelectrochemical process which, although variable and dependent on the nature of the wastewater, can be exploited for the monitoring of the process itself, facilitating the automation of the entire system. Therefore, the first bioelectrochemical reactor 2, by exploiting spontaneous reactions, has significantly low energy consumption.

[0103] Advantageously, within the second photocatalytic reactor 3, the removal of the organic content is completed, recalcitrant substances (for example, drugs, pesticides, herbicides) are degraded, and the microbiological or bacterial load is removed.

[0104] Experimental section

[0105] Wastewater present in the wastewater collection pit of a farm was subjected to a process of treatment within a system comprising a first bioelectrochemical reactor and a second photocatalytic reactor connected in series. The anode of the bioelectrochemical reactor consists of biochar having a size between 10 and 20 mm.The cathode of the bioelectrochemical reactor consists of carbon fabric on which aconductive and hydrophobic carbon-based ink is deposited; the cathode is selffloating. The photocatalyst of the photocatalytic reactor is BiOBr immobilised on loofah sponge, which is activated by sunlight.

[0106] 1) Removal of the organic content of the wastewater

[0107] A continuous monitoring of the parameters of the first bioelectrochemical reactor was carried out using appropriate sensors positioned inside the reactor itself and a multifunction and multichannel measurement device placed externally to the two reactors.

[0108] In particular, the following parameters were monitored: the cell potential (Eceii) by potentiometric measurement with Graphtec GL840 data logger and known (variable) resistance; the cathode potential (Ecat) by potentiometric measurement with Graphtec GL840 data logger and AgCl / Ag reference electrode (in 3M KCI) with KNO3salt bridge; the redox potential (Eredox) of the aqueous solution near the surface by potentiometric measurement with Graphtec GL840 data logger and combined redox electrode; and the temperature (Temp) of the aqueous solution by thermometry with Graphtec GL840 data logger and PT100 Probe.

[0109] The acquisition of the aforementioned parameters was carried out in-line, through continuous in-situ and in-operando monitoring. The results of said monitoring are shown in the graph of Figure 5.

[0110] The current generated by the bioelectrochemical reactor was obtained by dividing the values of cell potential (Eceii) by 200 Q (value of the shunt resistance).From the above-mentioned monitoring, it was observed that the current generated by the bioelectrochemical reactor increased during the two days following the feeding of wastewater into the reactor itself, while starting from the fifth day a substantially constant value of approximately 1 mA was reached.

[0111] In the graph of Figure 5, a correlation of the three electrochemical signals with the variation of water temperature, linked to environmental conditions (as there is no forced thermostating), is observed. In particular, an in-phase trend is highlighted for the daily fluctuations of Eceii and Ecat and an out-of-phase trend for Eredox.

[0112] The sensor of the redox potential was useful for continuously monitoring the relative amount of oxygen present in the aqueous solution as well as the degree of advancement of the oxidative process of the wastewater.

[0113] The results of the above monitoring confirm a significant reduction of COD (“chemical oxygen demand”), which was measured ex-situ following sampling of the treated water at increasing residence time intervals in the reactor. The quantification of COD of each sample was carried out using Hach DR 1900 and 3900 spectrophotometers and Hach LCK 114 (high range) and LCK 314 (low range) kits, pre-emptively performing, where necessary, appropriate sample dilutions with deionised water.

[0114] In particular:- when the bioelectrochemical reactor was filled with the wastewater to be treated, the COD was 920 mg eqo2 / L;- after 3 days of residence of the water in the reactor, the COD was 496 mg eqo2 / L, equivalent to a 46% reduction of the initial organic content;- after 14 days of residence of the water in the reactor, the COD was significantly reduced and reached 102 mg eqo2 / L, corresponding to a reduction of approximately89% of the initial organic content.

[0115] The reduction of the organic content was completed after further treatment in the photocatalytic reactor. After 15 days of treatment of the wastewater in the photocatalytic reactor, indeed, the COD was 73 mg eqo2 / L, equivalent to a 28% reduction of the organic content of the water exiting the bioelectrochemical reactor and a 92% reduction of the initial organic content of the wastewater.

[0116] 2) Determination of the content of nitric nitrogen in the water treated in the bioelectrochemical reactor

[0117] Following a 14-day treatment cycle of the wastewater in the bioelectrochemical reactor, the content of nitric nitrogen, monitored using Hach DR 1900 and 3900 spectrophotometers and Hach LCK 339 kit, was found to be completely removed. The wastewater from the collection pit, used to feed the bioelectrochemical reactor, was found to have a content of nitric nitrogen of 7.77 mg / L. At the end of the aforementioned treatment cycle, the content of nitric nitrogen was <1 mg / L.

[0118] 3) Determination of pH, specific conductivity, and redox potential of the water treated in the bioelectrochemical reactor

[0119] The water was characterised by measuring the following physico-chemical parameters: pH, by pH-metry with Amel 2335 potentiometer and combined glass electrode; specific conductivity (k), proportional to the ionic strength and, thus, to the content of dissolved salts, by conductometry with Amel 2131 conductometer and conductivity cell (K = 1 cm); and redox potential (Eredox) by potentiometric measurement with Amel 2335 potentiometer and combined redox electrode.

[0120] The above parameters were measured both on aliquots (50-500 mL) of water samples taken from the surface and on aliquots (50-500 mL) of water samples taken from the bottom of the reactor, at different operating times (3 and 14 days). Analyses were performed within 3 hours of collection in the field or after natural thawing of the sample stored at approximately -18°C.

[0121] The values of the above parameters are reported in Table 1 , together with those of the wastewater present in the collection pit, i.e., before treatment in the bioelectrochemical reactor.Table 1

[0122] The values reported in Table 1 refer to ex-situ measurements, carried out in the laboratory on specifically collected samples.

[0123] From the values reported in Table 1 , the following is highlighted:- a variation in the pH of the solution (linked to electrode and bacterial H+-dependent processes), which desirably remains within a range close to neutrality;- a significant variation in the redox potential of the solution, indicating the occurrence of degradation processes that alter the quantity and type of redox-active species present in the wastewater.

[0124] The increase of the value of the specific conductivity k of the solution recorded after a few days, combined with the subsequent decrease observed at the end of the cycle, is indicative of the degradation of the organic material (already in the first days) and a concurrent, albeit slower, sequestration of the generated ionic species (macro- and micronutrients), mainly by the anode, during the continuation of the cycle.

[0125] 4) Recovery of nutrients present in the wastewater

[0126] As can be seen from Figure 6, which provides a comparison (for purely qualitative purposes) between the EDS analysis performed on pristine biochar and the same analysis performed on biochar used as an anode in the bioelectrochemical reactor, some of the nutrients detectable with this technique (K, P, Ca) and naturally contained in the wastewater, were found to have accumulated on the biochar after a 14-day treatment cycle of the wastewater in the bioelectrochemical reactor.

[0127] Table 2 below reports the quantities of macronutrients present on a biochar sample at time zero and after a 14-day treatment cycle of the wastewater in the bioelectrochemical reactor.Table 2

[0128] The nitrogen (N) concentration was determined through CHN analysis using the Perkin Elemer CHN 2400 analyser. In this case, the solid samples were dried at 130°C for 4 hours, then introduced into the instrument for analysis.

[0129] The concentrations of Na, Mg, P, Ca were determined through ICP-MS analysis using the Agilent 7850 ICP-MS instrument. In this case, the solid samples were appropriately treated to promote leaching of the substances accumulated on their surface, by treatment at room temperature with a 10% w / w citric acid solution overnight (solidJiquid ratio equal to 1g:10mL), and subsequent removal of the suspended material through filtration. The resulting solution was appropriately diluted with 1.3% HNO3(0.3 M), then analysed via ICP-MS. The biochar was also analysed via ICP-MS, after mineralization in 67-69% HNO3using an ANTON PAAR Multivave ECO microwave system.

[0130] 5) Reduction of the bacterial content of the wastewater

[0131] It was verified that during treatment in the bioelectrochemical reactor, the bacterial content of the wastewater was also partially reduced, while during the photocatalytic treatment the bacterial component was completely eliminated.

[0132] The above was demonstrated by analyses carried out on the content of Escherichia Coli and Salmonella, using an M250 TBR Basic incubator by Instruments srl.

[0133] Table 3 shows the results of the analyses conducted on a sample of wastewater from the wastewater collection pit (used to feed the bioelectrochemical reactor), on a water sample after a treatment of 14 days in the bioelectrochemical reactor, and on a water sample after a further treatment of 14 days in the photocatalytic reactor.Table 3

[0134] 6) Removal of recalcitrant organic substances

[0135] In order to verify the effectiveness of the reduction of recalcitrant organic substances, a portion of the wastewater exiting the bioelectrochemical reactor was added with a quantity of an NSAID drug, specifically Diclofenac, up to a concentration of 10 mg / L. The resulting solution was exposed to irradiation with artificial sunlight in the presence of BiOBr immobilized on loofah sponge as a photocatalytic system.

[0136] From an analysis carried out using the Agilent 1100 Series HPLC instrument coupled with an Agilent 1100 series G1315B UV detector, it was possible to verify the complete removal of Diclofenac within 90 minutes. This demonstrates the stability of the photocatalytic system and its efficiency of removing a drug present in wastewater.

[0137] 7) Stability of the photocatalytic system

[0138] Morphological investigations were carried out on the photocatalytic system (BiOBr immobilized on loofah sponge) by means of scanning electron microscopy (SEM) in order to verify its stability.

[0139] These investigations were carried out using the Hitachi TM-1000 tabletop microscope. The solid samples were dried in an oven at 130°C for 4 hours, then placed on a stub on a carbon-based double-sided adhesive, then introduced into theinstrument and analysed.

[0140] As shown by the SEM images illustrated in Figure 7, the BiOBr photocatalyst, in the form of spheroidal aggregates, remains well anchored to the loofah sponge even after several days of use (images B and D), in particular after 90 days of use, demonstrating a high stability of the photocatalytic system under operating conditions.

[0141] It is evident that what has been described is only one particular embodiment of the present invention. The person skilled in the art will be able to make to the invention all those modifications necessary for its adaptation to particular conditions, without however departing from the scope of protection as defined in the appended claims.

Claims

CLAIMS1. A system (1) for the treatment of wastewater comprising organic compounds and / or inorganic or ionic compounds, optionally deriving from the agrifood or livestock supply chain, said system comprising a first bioelectrochemical reactor (2) and a second photocatalytic reactor (3) connected in series, wherein: the first bioelectrochemical reactor (2) is intended to receive the wastewater to be treated and comprises an anode (22) and a cathode (23) connected to each other by means of an external electrical circuit (24) in which an electrical load (25) is present, the anode (22) being a carbon-based material, preferably in the form of granules, pellets, plates or blocks, and the cathode (23) being floating on the surface (27) of the wastewater (21), and the second photocatalytic reactor (3) is intended to receive the water exiting the first bioelectrochemical reactor (2) and comprises a photocatalyst (32) loaded on an inert support (33), said inert support (33) being suspended in water (31) inside the second photocatalytic reactor (3).

2. System (1) according to claim 1, wherein the carbon-based material of the anode (22) is selected from the group consisting of graphite, biochar, activated carbon, graphene, carbon fabric, conductive material derived from biomass pyrolysis, preferably in the form of granules, pellets, plates or blocks, preferably having a size between 1 and 50 mm, for example between 10 and 20 mm, preferably said carbonbased material being housed inside a bag (26) made of a filtering material or inside cartridges (40).

3. A system (1) according to claim 1 or 2, wherein the anode (22) is positioned at the bottom of the first bioelectrochemical reactor (2) or close to the bottom of the first bioelectrochemical reactor (2).

4. A system (1 ) according to any one of the preceding claims, wherein the cathode (23) is self-floating, or the cathode (23) is made floating by attachment to a suitable floating element or floatation system made, for example, of solid polyurethane or polystyrene foam or made of an organic or inorganic sponge.

5. A system (1 ) according to any one of the preceding claims, wherein the cathode (23) is two-dimensional and comprises two flat surfaces, one of said surfaces being in contact with the air above the surface (27) of the wastewater (21) and the other surface being in contact with the wastewater (21).

6. System (1) according to any one of the preceding claims, wherein the cathode (23) is made of a carbon-based material, preferably it consists of carbon paper or carbon felt or carbon fabric, on which a layer (28) of carbon-based ink is preferably deposited, said layer (28) being conductive and hydrophobic.

7. System (1) according to any one of the preceding claims, wherein the first bioelectrochemical reactor (2) is a single-compartment reactor, in which the anode (22) and the cathode (23) are positioned in a single chamber.

8. System (1) according to any one of the preceding claims, wherein said photocatalyst (32) is selected from the group consisting of: BiOBr, BiOCI, BiOl, Bi2O3or a mixture of at least two of them.

9. System (1) according to any one of the preceding claims, wherein said inert support (33) is suspended in water (31) inside the second photocatalytic reactor (3) in a region extending up to 35 cm below the surface (34) of the water (31).

10. System (1) according to any one of the preceding claims, wherein said inert support (33) is a material having a density lower than the density of water, preferably said inert support (33) being an organic material or an inorganic material or a polymer material, preferably, said organic material is a natural sponge, for example loofah sponge; preferably, said inorganic material is pumice stone or expanded clay; preferably, said polymer material is an expanded polymer material, for example expanded polyurethane.

11. System (1) according to any one of the preceding claims, wherein said second photocatalytic reactor (3) comprises a mechanical system (35) for lifting the inert support (33) on which the photocatalyst (32) is loaded so as to keep the inert support (33) suspended in water (31) inside the second photocatalytic reactor (3), preferably in a region extending up to 35 cm below the surface (34) of the water (31), for example said system (35) is a lifting basket.

12. System (1) according to any one of the preceding claims, wherein said inert support (33) is loaded with an amount of photocatalyst (34) between 1 and 20% by weight, preferably between 2 and 10% by weight.

13. System (1) according to any one of the preceding claims, wherein said second photocatalytic reactor (3) comprises at least one lamp (36) of UV light or visible light or sunlight, said at least one lamp (36) being such as to be at least partially immersed in water (31) inside the second photocatalytic reactor (3).

14. System (1) according to any one of the preceding claims, wherein said second photocatalytic reactor (3) is aerated, preferably said system (1) comprises a blower (10) for the aeration of said second photocatalytic reactor (3).

15. System (1) according to any one of the preceding claims, wherein the first bioelectrochemical reactor (2) and the second photocatalytic reactor (3) comprise one or more measurement sensors, preferably, the first bioelectrochemical reactor (2) comprises one or more measurement sensors selected from the group consisting of: temperature, pH, electrical conductivity, redox potential, cathode potential, COD (“chemical oxygen demand’) sensors, preferably, the second photocatalytic reactor (3) comprises one or more measurement sensors selected from the group consisting of: temperature, redox potential, pH, electrical conductivity, COD ^‘chemical oxygen demand’) sensors.

16. System (1) according to any one of the preceding claims, wherein: the first bioelectrochemical reactor (2) comprises a reaction vessel (12) and a lid (13) for said reaction vessel (12), wherein between the reaction vessel (12) and the lid (13) there are special spacers (14) which ensure that the lid (13) does not rest on the reaction vessel (12), with the formation of a passage (15) between the reaction vessel (12) and the lid (13), and / or the second photocatalytic reactor (3) is open at the top, or comprises a reaction vessel and a lid for said reaction vessel, wherein the lid is transparent to sunlight and wherein between the reaction vessel and the lid there are special spacers which ensure that the lid does not rest on the reaction vessel, with the formation of a passage between the reaction vessel and the lid.

17. Process for the treatment of wastewater comprising organic compounds and / or inorganic or ionic compounds, optionally deriving from the agrifood or livestock supply chain, wherein said process is conducted in the system (1) according to any one of the preceding claims and comprises the following steps: a) subjecting the wastewater to a bioelectrochemical process in the first bioelectrochemical reactor (2), said process being conducted in the presence of a microbiological load, obtaining at least partially treated wastewater; b) subjecting the at least partially treated wastewater exiting the first bioelectrochemical reactor (2) to a photocatalytic process in the second photocatalytic reactor (3).

18. Process according to claim 17, wherein the microbiological load is inherently contained in the wastewater to be subjected to the treatment process and / or is added to the wastewater simultaneously or before being subjected to the bioelectrochemical process.

19. Process according to claim 17 or 18, comprising monitoring one or more parameters of the bioelectrochemical process, said parameters being selected from temperature, pH, electrical conductivity, redox potential, cell potential, cathode potential, COD (“chemical oxygen demand”), and monitoring one or more parameters of the photocatalytic process, said parameters being selected from temperature, redox potential, pH, electrical conductivity, redox potential, COD (“chemical oxygen demand’).

20. Process according to any one of claims 17 to 19, comprising a step of irradiating the water inside the second photocatalytic reactor (3) with UV light, sunlight and / or visible light during the photocatalytic process.

21. Process according to any one of claims 17 to 20 comprising a step of aerating the second photocatalytic reactor (3) during the photocatalytic process.

Images