Treatment system, methods of forming and operating the same

Abstract

Various embodiments may relate to a treatment system for removing pollutants in wastewater. The treatment system may include a tank configured to hold the wastewater, and a bubble generator configured to generate bubbles, each of the bubbles having a diameter of less than 0.1 mm, in the wastewater held in the tank. The treatment system may further include an electrode assembly including a cathode and an anode, the electrode assembly being configured to generate oxidizing agents via electrochemical oxidation at the anode when a direct current (DC) voltage or pulsed current voltage is applied between the cathode and the anode such that the oxidizing agents oxidize the pollutants in the wastewater held in the tank, thereby removing the pollutants from the wastewater. The treatment system may additionally include a power supply configured to apply the direct current (DC) voltage or pulsed current voltage between the cathode and the anode.

Description

TREATMENT SYSTEM, METHODS OF FORMING AND OPERATING THE SAMECROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority of Singapore application No. 10202403469 filed November 7, 2024, the contents of it being hereby incorporated by reference in its entirety for all purposes.TECHNICAL FIELD

[0002] Various embodiments of this disclosure may relate to a treatment system for removing pollutants in wastewater. Various embodiments of this disclosure may relate to a method of forming a treatment system for removing pollutants in wastewater. Various embodiments of this disclosure may relate to a method of operating a treatment system for removing pollutants in wastewater.BACKGROUND

[0003] A lot of wastewater streams, such as industrial wastewater, agricultural and aquacultural wastewaters, domestic wastewater, and landfill leachate, contain nitrogenous pollutants which pose great threat to the environment. Those nitrogenous pollutants can present in various forms including total ammonia nitrogen (TAN), nitrite nitrogen, nitrate nitrogen, etc. The removal of those nitrogenous pollutants is important to maintain their concentrations below the required standard and avoid adverse impact on the environment.

[0004] In particular, excess nitrogen in water can be harmful to aquatic ecosystems by causing depletion of dissolved oxygen and eutrophication of amphibian systems. In a recirculating aquaculture system (RAS), TAN could accumulate in the water and gradually betoxic to the fish species, even at low concentrations of < 5 mg / L in a low fish stocking density condition. Current-state-of-the-art RAS solutions are based on biofilter treatment and circulation / reconditioning accessories. However, biofilter with microorganism species still faces challenges in aquaculture water treatment, and may only function well in a limited fish stocking density. Reasons include (1) the microorganism communities may have limited capacity; (2) the accumulation of TAN bio-oxidation products, such as nitrite and nitrate, may still be harmful to fish, (3) the biofilter needs maintenance and replacement; and (4) the fish stocking density may hardly be further improved when the current biofilter is fully loaded at maximum capacity. These issues in current RAS may result in the need for 5% to 15% of water to be discharged and replaced daily.

[0005] As mentioned above, biofilter may still accumulate high concentrations of nitrite in water. Although nitrate is less toxic than ammonia and nitrite, it can cause stress to fishes at high concentrations and affect their health, growth and reproduction. Conversion of nitrate to nitrogen gas is possible through a biological process called denitrification. However, no existing solutions are fully adequate as 1) denitrification is an anaerobic process and additional setup is required; 2) aquaculture water has low carbon / nitrogen (C / N) ratio and additional carbon source is required for denitrification. Therefore, it may be desirable to convert TAN to N2 gas directly.

[0006] On the other hand, membrane bioreactor (MBR) combines microfiltration or ultrafiltration with activated sludge to reduce the footprint of conventional biological wastewater treatment. However, the retention of time of MBR usually ranges between three to ten hours, making it challenging to adapt to RAS which requires water recirculation rate of 1 - 1.5 times per hour. In addition, fishes produce a lot of sludge daily, and the stress on membrane fouling remains.

[0007] Ozonation relies on in-situ generation of ozone gas by ozone generator using air or concentrated oxygen as feeding gas. However, its energy consumption is high, and an additionalstep is required to offset the toxicity of residual ozone Besides, ozonation of ammonia is a very slow process and proceeds only in an alkaline medium of pH > 8 . Although ozone nanobubbles have been employed to overcome the challenge of slow reaction rate, ammonia is oxidized completely to nitrate, which causes fast accumulation of nitrite, thereby requiring eventual water replacement.SUMMARY

[0008] Various embodiments may relate to a treatment system for removing pollutants in wastewater. The treatment system may include a tank configured to hold the wastewater. The treatment system may also include a bubble generator configured to generate bubbles, each of the bubbles having a diameter of less than 0.1 mm, in the wastewater held in the tank. The treatment system may further include an electrode assembly including a cathode and an anode, the electrode assembly being configured to generate oxidizing agents via electrochemical oxidation at the anode when a direct current (DC) voltage or pulsed current voltage is applied between the cathode and the anode such that the oxidizing agents oxidize the pollutants in the wastewater held in the tank, thereby removing the pollutants from the wastewater The treatment system may additionally include a power supply configured to apply the direct current (DC) voltage or pulsed current voltage between the cathode and the anode

[0009] Various embodiments may relate to a method of forming a treatment system for removing pollutants in wastewater. The method may include providing a tank configured to hold the wastewater. The method may also include providing a nanobubble generator configured to generate nanobubbles in the wastewater held in the tank. The method may further include providing an electrode assembly including a cathode and an anode, the electrode assembly being configured to generate oxidizing agents via electrochemical oxidation at the anode when a direct current (DC) voltage or pulsed current voltage is applied between thecathode and the anode such that the oxidizing agents oxidize the pollutants in the wastewater held in the tank, thereby removing the pollutants from the wastewater. The method may additionally include providing a power supply configured to apply the direct current (DC) voltage or pulsed current voltage between the cathode and the anode.

[0010] Various embodiments may relate to a method of operating a treatment system for removing pollutants in wastewater The method may include supplying the wastewater to a tank. The method may also include using a bubble generator to generate bubbles. Each of the bubbles may have a diameter of less than 0.1 mm, in the wastewater held in the tank. The method may further include applying a direct current (DC) voltage or pulsed current voltage between a cathode and an anode of an electrode assembly using a power supply, the electrode assembly being configured to generate oxidizing agents via electrochemical oxidation at the anode when the direct current (DC) voltage or pulsed current voltage is applied between the cathode and the anode such that the oxidizing agents oxidize the pollutants in the wastewater held in the tank, thereby removing the pollutants from the wastewater.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily drawn to scale, emphasis instead generally being placed upon illustrating the principles of various embodiments. In the following description, various embodiments of the invention are described with reference to the following drawings.FIG. 1 shows a general illustration of a treatment system for removing pollutants in wastewater according to various embodimentsFIG. 2 shows a general illustration of a method of forming a treatment system for removing pollutants in wastewater according to various embodiments.FTG. 3 shows a general illustration of a method of operating a treatment system for removing pollutants in wastewater.FIG. 4 shows a schematic of a setup or system for hybrid electrochemical oxidation - bubble treatment according to various embodiments.FIG. 5 shows a table illustrating the percentage of total ammonia nitrogen (TAN), nitrate nitrogen and nitrite nitrogen to initial nitrogen (0.02 M) after 3-hours (hr) treatment of wastewater of about pH 7 by dissolving ammonium bicarbonate (NH4HCO3) and sodium chloride (NaCl) using a setup or system including an iridium ruthenium oxide (Ir-Ru-O) anode and a platinum coated titanium cathode according to various embodiments.FIG. 6 shows a table illustrating the percentage of total ammonia nitrogen (TAN), nitrate nitrogen and nitrite nitrogen to initial nitrogen (0.02 M) after 3-hours (hr) treatment of wastewater of about pH 7 by dissolving ammonium bicarbonate (NH4HCO3) and sodium chloride (NaCl) using a setup or system including a boron doped diamond (BDD) anode and a platinum coated titanium cathode according to various embodiments.FIG. 7 shows a table illustrating the percentage of total ammonia nitrogen (TAN), nitrate nitrogen and nitrite nitrogen to initial nitrogen (0.02 M) after 3-hours (hr) treatment of wastewater of about pH 5 by dissolving ammonium bicarbonate (NH4HCO3) and sodium chloride (NaCl) using a setup or system including an iridium ruthenium oxide (Ir-Ru-O) anode and a platinum coated titanium cathode according to various embodiments.FIG. 8 shows a table illustrating the percentage of total ammonia nitrogen (TAN), nitrate nitrogen and nitrite nitrogen to initial nitrogen (0.02 M) after 3-hours (hr) treatment of wastewater of about pH 9 by dissolving ammonium bicarbonate (NH4HCO3) and sodium chloride (NaCl) using a setup or system including an iridium ruthenium oxide (Ir-Ru-O) anode and a platinum coated titanium cathode according to various embodiments.FTG. 9 shows a table illustrating the percentage of total ammonia nitrogen (TAN), nitrate nitrogen and nitrite nitrogen to initial nitrogen (0.02 M) after 3 -hours (hr) treatment of wastewater prepared by dissolving ammonium bicarbonate (NH4HCO3) and sodium sulphate (NazSC ) using a setup or system including an iridium ruthenium oxide (Ir-Ru-O) anode and a platinum coated titanium cathode according to various embodiments.FTG. 10A shows (a) a schematic illustrating a top planar view of a first Recirculating Aquaculture System (RAS #1) according to various embodiments; and (b) a schematic illustrating a perspective view of the Recirculating Aquaculture System (RAS #1) according to various embodiments shown in (a).FIG. 10B shows a schematic of a portion of the first Recirculating Aquaculture System (RAS #1) according to various embodiments as illustrated in FTG. 10 A.FIG. TOC shows (a) a schematic illustrating a perspective view of a holder of an electrode assembly according to various embodiments; and (b) a schematic illustrating a side view of the holder of the electrode assembly according to various embodiments.FIG. 10D shows a plot of concentration (in particles per milliliter (ml)) as a function of size (in nanometers or nm) illustrating the distribution of different sizes of bubbles generated by the nanobubble generator according to various embodiments, with an inset showing a microscopy image of two nanobubbles according to various embodiments.FIG. HA shows (a) a schematic illustrating a top planar view of a second Recirculating Aquaculture System (RAS #2), and (b) a schematic illustrating a perspective view of the Recirculating Aquaculture System (RAS #2) shown in (a).FIG. 1 IB shows a schematic of yet another recirculating aquaculture system (RAS) including a biofilter.FIG. 12A shows a table illustrating results of water quality, water exchange rate, power and feed conversion rate of the first Recirculating Aquaculture System (RAS #1) according tovarious embodiments and the second Recirculating Aquaculture System (RAS #2) during 21 - day fish production period.FIG. 12B shows a table showing the power consumptions of the energy consuming components of the first Recirculating Aquaculture System (RAS #1) according to various embodiments and the second Recirculating Aquaculture System (RAS #2).FIG. 12C illustrates the combination of electrochemical oxidation, nanobubble treatment and prefiltration / activated carbon treatment leading to synergistic effects according to various embodiments.FIG. 12D shows a table illustrating results of water quality, water exchange rate, power and feed conversion rate of the treatment system according to various embodiments and a conventional biofilter recirculating aquaculture system (RAS).DESCRIPTION

[0012] The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized, and structural, logical, and electrical changes may be made without departing from the scope of the invention. The various embodiments are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments.

[0013] Features that are described in the context of an embodiment may correspondingly be applicable to the same or similar features in the other embodiments. Features that are described in the context of an embodiment may correspondingly be applicable to the other embodiments, even if not explicitly described in these other embodiments. Furthermore, additions and / orcombinations and / or alternatives as described for a feature in the context of an embodiment may correspondingly be applicable to the same or similar feature in the other embodiments.

[0014] In the context of various embodiments, the articles “a”, “an” and “the” as used with regard to a feature or element include a reference to one or more of the features or elements.

[0015] In the context of various embodiments, the terms “about” or “approximately” as applied to a numeric value encompasses the exact value and a reasonable variance, e g. within 10% of the specified value.

[0016] As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0017] By “comprising” it is meant including, but not limited to, whatever follows the word “comprising” Thus, use of the term “comprising” indicates that the listed elements are required or mandatory, but that other elements are optional and may or may not be present.

[0018] By “consisting of’ is meant including, and limited to, whatever follows the phrase “consisting of’. Thus, the phrase “consisting of’ indicates that the listed elements are required or mandatory, and that no other elements may be present.

[0019] As summarized above, current limitations of state-of-the-art include the following: (1) biofilter requires long time (> 2 months) for the inoculation of microorganism; (2) biofilter requires large volume of sump tank to build up the desired amount of microorganism; (3) biofilter treatment leads to nitrite generation as the first step of nitrification, and nitrite may be toxic to the fishes even at a low concentration of < 10 mg / L; (4) biofilter treatment also leads to nitrate accumulation as the final product of nitrification, and a high concentration of nitrate (> 500 mg / L) may cause stress to the fishes, making them more susceptible to disease and inhibit their growth and reproduction; (5) optimal pH for biofilter is between 7 to 8, and metabolism of the fishes may result in the drop in water pH, thereby requiring regular pH adjustment using sodium bicarbonate, resulting in additional costs; and (6) performance ofbiofilter may be difficult to be pushed further when they reach the maximum capacity, limiting the concentration of fish stock.

[0020] Various embodiments may address or overcome the abovementioned limitations using an alternative approach. Various embodiments may be biological free, and may have lower chemical and energy consumption for removing nitrogenous compounds in wastewater.

[0021] FIG. 1 shows a general illustration of a treatment system for removing pollutants in wastewater according to various embodiments. The treatment system may include a tank 102 (e g., sump tank) configured to hold the wastewater. The treatment system may also include a bubble generator 104 configured to generate bubbles, each of the bubbles having a diameter of less than 0.1 mm (also referred to as “fine bubbles”), in the wastewater held in the tank 102. The treatment system may further include an electrode assembly 106 including a cathode 106a and an anode 106b, the electrode assembly 106 being configured to generate oxidizing agents via electrochemical oxidation at the anode 106b when a direct current (DC) voltage or pulsed current voltage is applied between the cathode 106a and the anode 106b such that the oxidizing agents oxidize the pollutants in the wastewater held in the tank 102, thereby removing the pollutants from the wastewater. The treatment system may additionally include a power supply 108 configured to apply the direct current (DC) voltage or pulsed current voltage between the cathode 106a and the anode 106b.

[0022] In other words, various embodiments may relate to a treatment system including an electrode assembly 106 in electrical connection with a power supply 108, as well as a bubble generator 104. The power supply 108 may be a direct current (DC) power supply (for providing the direct current (DC) voltage) or a pulsed current power supply (for providing the pulsed current voltage).

[0023] For avoidance of doubt, FIG. 1 is intended to illustrate features of the treatment system according to various embodiments, and is not intended to limit, for instance, the shape,dimensions, arrangement, orientation etc. of the various embodiments For instance, while FIG. 1 shows the cathode 106a and the anode 106b on the left of the tank 102, the cathode 106a and the anode 106b may be arranged at any suitable positions. Likewise, while FIG. 1 shows the bubble generator 104 on the right, the bubble generator may be arranged at any suitable position. Various embodiments may have flexibility in the positioning of the electrodes.

[0024] The bubbles may be generated in the same tank 102 in which the electrode assembly 106 is immersed.

[0025] In various embodiments, the bubble generator 104 may be in electrical connection with the power supply 108, or may be in electrical connection with another power supply. In various other embodiments, the bubble generator 104 may include a power source, e.g., a battery or batteries WhileFIG. 1 shows the bubble generator 104 within the tank 102, in various embodiments, a main body of the bubble generator 104 may be provided external to the tank 104, and channels or pipes may carry the bubbles generated by the main body to the wastewater held in the tank 102.

[0026] In various embodiments, the bubbles may include or be microbubbles (i.e. bubbles each having a diameter of 200 nm to 10 pm) and / or nanobubbles (i.e. bubbles each having a diameter of less than 200 nm).

[0027] In various embodiments, the bubbles generated may increase efficiency of generating the oxidizing agents, improve conversion rate of pollutants and / or provide a cleaning effect to the cathode and the anode. The stability of bubbles in the wastewater may help to reduce energy consumption by requiring less efforts in aeration

[0028] In various embodiments, the anode 106b may include any material selected from a group consisting of a metal oxide, mixed metal oxides, a conductive diamond material, a carbon material, platinum, a platinum-based alloy, titanium and a titanium-based alloy. An example ofthe mixed metal oxides may be iridium ruthenium oxide (Tr-Ru-O) An example of the conductive diamond material may be boron doped diamond (BDD).

[0029] The oxidizing agents may be reactive chlorine species such as chlorine (Ch), hypochlorous acid / hypochlorite anion (HC1O / C1O"), chlorine dioxide (CIO2) and other chlorine radicals. The pollutants may be or may include nitrogenous pollutants, organic pollutants, sulfite, phosphorous compounds, and / or arsenic compounds. An example of nitrogenous pollutants may be total ammonia nitrogen (TAN).

[0030] The oxidizing agent (e.g., chlorine) generated at the anode 106b may oxidize the TAN present in the wastewater to nitrogen gas, which may be able to escape and be removed from the wastewater. The wastewater may include an oxidizing agent precursor (e g., chloride ions), and the application of the DC voltage between the cathode and the anode may generate the oxidizing agents (e g., reactive chlorine species such as Ch, HC1O / C1O", CIO2 and other chlorine radicals) from the oxidizing agent precursor (e.g., chloride ions) via electrochemical oxidation of the oxidizing agent precursor (e.g., chloride ions) at the anode 106b. The oxidizing agent precursor (e.g., chloride ions) may be added to the wastewater.

[0031] In various embodiments, the treatment system may be also configured to generate a further oxidizing agent, the further oxidizing agent being hydroxyl radicals. The bubbles generated may increase a lifetime of the hydroxyl radicals by providing an oxygen-rich environment for reducing a probability of recombination of the hydroxyl radicals to generate oxygen gas, and by improving a stability of the hydroxyl radicals in the wastewater.

[0032] Further, the bubbles may provide better efficiency for generation of the oxidizing agent (e.g., chlorine), reduce nitrate generation, improve conversion rate to nitrogen gas and / or provide cleaning effect for surfaces of the anode 106b and the cathode 106a.

[0033] In various embodiments, the cathode 106a may include a metal oxide, mixed metal oxides, a conductive diamond material, titanium, a platinum coated titanium, a titanium-basedalloy, aluminum, an aluminum-based alloy, iron, an iron-based alloy, a carbon material, or any other suitable material(s).

[0034] In various embodiments, the electrode assembly 106 may include one or more further pairs of cathodes and anodes. The one or more further pairs of cathodes or anodes may be in electrical connection with the power supply 108, or may be in electrical connection with one or more additional power supplies. The electrode assembly 106 may be configured to generate oxidizing agents via electrochemical oxidation at the one or more further anodes (of the one or more further pairs of cathodes and anodes) when corresponding direct current (DC) voltage(s) or pulsed current voltage(s) are applied between each further pair of cathodes and anodes (of the one or more further pairs of cathodes and anodes), such that the oxidizing agents oxidize the pollutants in the wastewater held in the tank 102.

[0035] In various embodiments, a pH of the wastewater may be selected from a range from 3 to 11.

[0036] In various embodiments, the treatment system may also include a prefiltration filter including a layer of activated glass and a layer of activated carbon. The layer of active carbon of the prefiltration filter may be over the layer of activated glass of the prefiltration filter. The treatment system may be configured such that the wastewater flows through the layer of activated glass of the prefiltration filter before flowing through the layer of activated carbon of the prefiltration filter. In various embodiments, the prefiltration filter may have a backwash function. The activated glass layer of the prefiltration filter may be replaced by layer including additional or alternative materials such as polymers, sands and / or ceramics to achieve similar filtration performance.

[0037] In various embodiments, the treatment system may further include an activated carbon filter including one or more layers (e g., three layers) of activated carbon. The one or more layers of activated carbon may include a plurality of layers of activated carbon. Anaverage particle size of an overlying layer of the plurality of layers of activated carbon of the activated carbon filter may be smaller than an average particle size of a middle layer of the plurality of layers of activated carbon of the activated carbon filter. The average particle size of the middle layer of the plurality of layers of activated carbon of the activated carbon filter may be smaller than an average particle size of an underlying layer of the plurality of layers of activated carbon of the activated carbon filter. The treatment system may be configured such that the wastewater flows through the underlying layer before flowing through the middle layer to the overlying layer. In various embodiments, the activated carbon filter may have a backwash function.

[0038] The activated carbon present in the layer of activated carbon of the prefiltration filter, and in the layers of the activated carbon filter may help to remove T AN by oxidation in addition to adsorption. It may be observed that when the electrochemical oxidation is stopped in the tank, the activated carbon in the prefiltration filter and the activated carbon layer may reduce an amount of TAN. The activated carbon may also play a role in removing toxic by-products generated during electrochemical oxidation. In other words, the activated carbon may not only reduce toxic by-products from electrochemical oxidation of TAN, but may also help to oxidize TAN which is not degraded by electrochemical oxidation. In various embodiments, after the activated carbon filter has reached the maximum dechlorination capacity, replacement of activated carbon may be required to maintain the proper performance of the system. This may be addressed by regular replacement of activated carbon, and / or using mild electric current condition to reduce active chlorine generation. Various embodiments may not reach maximum dechlorination capacity even after more than a month of fish production. The prefiltration filter and / or the activated carbon filter may also trap particulates / particles in the wastewater. The biofouling of activated carbon may be reduced or minimized due to disinfection of the wastewater by electrochemical oxidation.

[0039] Tn various embodiments, the treatment system may also include a water quality monitoring system. The water quality monitoring system may be configured to monitor parameters of the wastewater, such as pH, temperature, dissolved oxygen, and / or conductivity. The water quality monitoring system may include a plurality of sensors, such as a pH sensor, a temperature sensor, a dissolved oxygen sensor, and / or an electrical conductivity sensor, for monitoring the parameters of the wastewater.

[0040] The wastewater may be aquaculture water. Various embodiments may be applicable to brackish water or seawater. The wastewater may require some conductivity so that the electrochemical oxidation could take place. In addition, the presence of chloride in the wastewater may be required for generation of active chlorine to remove TAN effectively. For brackish water or seawater, both the conductivity and chloride concentration may be sufficient.

[0041] The concentration of chloride in wastewater may be required to be at or above a sufficient level, e.g., at or above 0.05 M. For other wastewaters in which chlorides are absent or have an insufficient level of chloride, chloride (via a salt such as sodium chloride) may be introduced into the wastewater prior to electrochemical oxidation.

[0042] FIG. 2 shows a general illustration of a method of forming a treatment system for removing pollutants in wastewater according to various embodiments. The method may include, in 202, providing a tank configured to hold the wastewater. The method may also include, in 204, providing a nanobubble generator configured to generate nanobubbles in the wastewater held in the tank. The method may further include, in 206, providing an electrode assembly including a cathode and an anode, the electrode assembly being configured to generate oxidizing agents via electrochemical oxidation at the anode when a direct current (DC) voltage or pulsed current voltage is applied between the cathode and the anode such that the oxidizing agents oxidize the pollutants in the wastewater held in the tank, thereby removing the pollutants from the wastewater. The method may additionally include, in 208, providing apower supply configured to apply the direct current (DC) voltage or pulsed current voltage between the cathode and the anode.

[0043] In other words, various embodiments may relate to forming a treatment system for removing pollutants in wastewater. The method may include providing / arranging a tank, a bubble generator, an electrode assembly and a power supply. The method may include electrically connecting the power supply to the electrode assembly.

[0044] For avoidance of doubt, FIG. 2 seeks to illustrate steps of a method of forming a treatment system, and is not intended to limit the sequence of the various steps.

[0045] In various embodiments, the bubbles generated may increase efficiency of generating the oxidizing agents, improve conversion rate of pollutants and provide a cleaning effect to the cathode and the anode.

[0046] In various embodiments, the treatment system may be also configured to generate a further oxidizing agent, the further oxidizing agent being hydroxyl radicals. The bubbles generated may increase a lifetime of the hydroxyl radicals by providing an oxygen-rich environment for reducing a probability of recombination of the hydroxyl radicals to generate oxygen gas, and by improving a stability of the hydroxyl radicals in the wastewater.

[0047] In various embodiments, the anode may include any material selected from a group consisting of a metal oxide, mixed metal oxides, a conductive diamond material, a carbon material, platinum, a platinum-based alloy, titanium and a titanium-based alloy. An example of the mixed metal oxides may be iridium ruthenium oxide (Ir-Ru-O). An example of the conductive diamond material may be boron doped diamond (BDD)

[0048] The oxidizing agents may be reactive chlorine species. The pollutants may be or may include nitrogenous pollutants, organic pollutants, sulfite, phosphorous compounds, and / or arsenic compounds. An example of nitrogenous pollutants may be total ammonia nitrogen (TAN).

[0049] Tn various embodiments, the electrode assembly may include one or more further pairs of cathodes and anodes.

[0050] In various embodiments, a pH of the wastewater may be selected from a range from3 to 11.

[0051] In various embodiments, the method may include providing a prefiltration filter including a layer of activated glass and a layer of activated carbon.

[0052] In various embodiments, the layer of active carbon of the prefiltration filter may be over the layer of activated glass of the prefiltration filter. The treatment system may be configured such that the wastewater flows through the layer of activated glass of the prefiltration filter before flowing through the layer of activated carbon of the prefiltration filter.

[0053] In various embodiments, the prefiltration filter may have a backwash function.

[0054] In various embodiments, the method may also include providing an activated carbon filter including one or more layers of activated carbon.

[0055] The one or more layers of activated carbon may include a plurality of layers of activated carbon. An average particle size of an overlying layer of the plurality of layers of activated carbon of the activated carbon filter may be smaller than an average particle size of a middle layer of the plurality of layers of activated carbon of the activated carbon filter. The average particle size of the middle layer of the plurality of layers of activated carbon of the activated carbon filter may be smaller than an average particle size of an underlying layer of the plurality of layers of activated carbon of the activated carbon filter. The treatment system may be configured such that the wastewater flows through the underlying layer before flowing through the middle layer to the overlying layer.

[0056] In various embodiments, the activated carbon filter may have a backwash function.

[0057] In various embodiments, the method may also include providing a water quality monitoring system. The water quality monitoring system may be configured to monitorparameters of the wastewater, such as pH, temperature, dissolved oxygen, and / or conductivity. The water quality monitoring system may include a plurality of sensors, such as a pH sensor, a temperature sensor, an oxygen sensor, and / or an electrical conductivity sensor, for monitoring the parameters of the wastewater.

[0058] FIG. 3 shows a general illustration of a method of operating a treatment system for removing pollutants in wastewater. The method may include, in 302, supplying the wastewater to a tank. The method may also include, in 304, using a bubble generator to generate bubbles. Each of the bubbles may have a diameter of less than 0.1 mm, in the wastewater held in the tank. The method may further include, in 306, applying a direct current (DC) voltage or pulsed current voltage between a cathode and an anode of an electrode assembly using a power supply, the electrode assembly being configured to generate oxidizing agents via electrochemical oxidation at the anode when the direct current (DC) voltage or pulsed current voltage is applied between the cathode and the anode such that the oxidizing agents oxidize the pollutants in the wastewater held in the tank, thereby removing the pollutants from the wastewater.

[0059] In other words, various embodiments may relate to removing pollutants in wastewater. The method may include holding wastewater in a tank, generating bubbles in the wastewater, and applying a DC voltage or pulsed current voltage to generate oxidizing agents to oxidize the pollutants in the wastewater.

[0060] For avoidance of doubt, FIG. 3 seeks to illustrate steps of a method of operating a treatment system, and is not intended to limit the sequence of the various steps. In various embodiments, step 304 and step 306 may occur at the same time and after step 302.

[0061] In various embodiments, the method may include using a pump to pump the wastewater from the tank to a prefiltration filter such that the wastewater flows through a layer of activated glass of the prefiltration filter before flowing through a layer of activated carbon of the prefiltration filter. The prefiltration filter may be in fluidic connection with an activatedcarbon filter such that the wastewater from the prefiltration filter flows through an underlying layer of the activated carbon filter before flowing through a middle layer of the activated carbon filter to an overlying layer of the activated carbon filter.

[0062] Various embodiments may relate to a method and system for removing aqueous nitrogenous pollutants. Various embodiments may be based on synergistic effects of electrochemical oxidation and nanobubble treatment, verified by lab investigation. Experiments for degradation of artificial ammonium wastewater were conducted under different conditions, and the results are discussed herein. A recirculating aquaculture system (RAS) may be developed to extend the application of various embodiments to water management in aquaculture. The RAS is benchmarked with another RAS having biofilter, and the performance comparison of the two RAS systems are illustrated herein.

[0063] FIG. 4 shows a schematic of a setup or system for hybrid electrochemical oxidation - bubble treatment according to various embodiments. The setup or system may include a tank or reaction chamber 402 of 1 liter (L) volume, a DC power supply 408, a pair of electrodes 406a, 406b in electrical connection with the DC power supply 408, and a nanobubble generator 404 connected to the bottom of the tank or reaction chamber 402. The pair of electrodes 406a, 406b may each have a surface area of about 50 cm2and may be kept at about 1 cm distance from each other.

[0064] When the chamber is filled with wastewater, the nanobubble generator 404 may provide fine bubbles (size of < 0.1 mm) including microbubbles (size of 200 nm to 10 pm) and nanobubbles (size of < 200 nm) into the water, and may drive the wastewater recirculation at 1.5 L / min. The DC power supply 408 may maintain the electric current for reactions to take place.

[0065] Example 1

[0066] Tn this example, iridium ruthenium oxide (Tr-Ru-O) was used as the anode and platinum coated titanium was used as the cathode. 1 liter (L) of artificial wastewater was prepared by dissolving ammonium bicarbonate (NH4HCO3) and sodium chloride (NaCl) in ultrapure water to make their concentrations at 0.02 M and 0.1 M respectively. The initial pH was adjusted to 7 by adding 0.01 M sodium hydroxide (NaOH) dropwise. The current was set at 0.5 A. Agitation of the wastewater was provided by water recirculation with nanobubbles, magnetic stirring at 350 revolutions per minute (rpm), or 3L / min aeration with compressed air. All the experiments were duplicated. After 3-hours (hr) treatment, the quality of the wastewater was summarized in FIG. 5. FIG. 5 shows a table illustrating the percentage of total ammonia nitrogen (TAN), nitrate nitrogen and nitrite nitrogen to initial nitrogen (0.02 M) after 3-hours (hr) treatment of wastewater of about pH 7 by dissolving ammonium bicarbonate (NH4HCO3) and sodium chloride (NaCl) using a setup or system including an iridium ruthenium oxide (Ir- Ru-O) anode and a platinum coated titanium cathode according to various embodiments. As seen from FIG. 5, when combining electrochemical oxidation and nanobubbles, highest TAN removal rate of 74. 17% and lowest nitrate nitrogen accumulation of 0.67% of initial nitrogen were observed. No nitrite was detected after the treatment.

[0067] Example 2

[0068] The experiments in Example 1 were repeated, except for using boron doped diamond (BDD) as the anode. After 3 -hr treatment, the quality of the wastewater was summarized in FIG. 6. FIG. 6 shows a table illustrating the percentage of total ammonia nitrogen (TAN), nitrate nitrogen and nitrite nitrogen to initial nitrogen (0.02 M) after 3-hours (hr) treatment of wastewater of about pH 7 by dissolving ammonium bicarbonate (NH4HCO3) and sodium chloride (NaCl) using a setup or system including a boron doped diamond (BDD) anode and a platinum coated titanium cathode according to various embodiments. As seen from FIG. 6, Ir-Ru-O may be more effective compared to BDD in removing TAN in the wastewater Also, the accumulation of nitrate nitrogen in wastewater by using BDD anode may be substantial.

[0069] Example 3

[0070] The experiments in Example 1 were repeated, except for adjusting pH to 5 by adding 0.01 M hydrochloric acid (HC1) dropwise. After 3-hr treatment, the quality of the wastewater was summarized in FIG. 7. FIG. 7 shows a table illustrating the percentage of total ammonia nitrogen (TAN), nitrate nitrogen and nitrite nitrogen to initial nitrogen (0.02 M) after -hours (hr) treatment of wastewater of about pH 5 by dissolving ammonium bicarbonate (NH4HCO3) and sodium chloride (NaCl) using a setup or system including an iridium ruthenium oxide (Ir- Ru-O) anode and a platinum coated titanium cathode according to various embodiments. As seen from FIG. 7, when combining electrochemical oxidation and nanobubbles, highest TAN removal rate of 76.76% and lowest nitrate nitrogen accumulation of 0.91 % of initial nitrogen was observed.

[0071] Example 4

[0072] The experiments in Example 1 were repeated, except for adjusting pH to 9 by adding 0.01 M sodium hydroxide (NaOH) dropwise. After 3-hr treatment, the quality of the wastewater was summarized in FIG. 8. FIG. 8 shows a table illustrating the percentage of total ammonia nitrogen (TAN), nitrate nitrogen and nitrite nitrogen to initial nitrogen (0.02 M) after 3 -hours (hr) treatment of wastewater of about pH 9 by dissolving ammonium bicarbonate (NH4HCO3) and sodium chloride (NaCl) using a setup or system including an iridium ruthenium oxide (Ir- Ru-O) anode and a platinum coated titanium cathode according to various embodiments. As can be seen from FIG. 8, when combining electrochemical oxidation and nanobubbles, highest TAN removal rate of 64.98% and lowest nitrate nitrogen accumulation of 0.23% of initial nitrogen was observed.

[0073] Example 5

[0074] The experiments in Example 1 were repeated, except for 1 L of artificial wastewater was prepared by dissolving ammonium bicarbonate (NH4HCO3) and sodium sulphate (Na2SO4) in ultrapure water to make their concentrations at 0.02 M and 0.05 M respectively. After 3-hr treatment, the quality of the wastewater was summarized in FIG. 9. FIG. 9 shows a table illustrating the percentage of total ammonia nitrogen (TAN), nitrate nitrogen and nitrite nitrogen to initial nitrogen (0.02 M) after 3-hours (hr) treatment of wastewater prepared by dissolving ammonium bicarbonate (NH4HCO3) and sodium sulphate (Na2SC>4) using a setup or system including an iridium ruthenium oxide (Ir-Ru-O) anode and a platinum coated titanium cathode according to various embodiments. As can be seen from FIG. 9, when using sodium sulphate to prepare artificial wastewater, the TAN may not be effectively removed at all the conditions. The presence of chlorides in the wastewater may be required for TAN removal from wastewater via electrochemical oxidation.

[0075] Design of Recirculating Aquaculture System (RAS)

[0076] The RAS may involve (1) electrochemical oxidation of nitrogenous compounds (NH3, NH4+, NO2") through electrogenerated active chlorine, (2) filtration of particulate substances and removal of active chlorine by pre-filtration filter with activated glass material and activated carbon as dual medium bed; and (3) reduction of residual active chlorine and adsorption of toxic by-products by activated carbon filter. FIG. 10A shows (a) a schematic illustrating a top planar view of a first Recirculating Aquaculture System (RAS #1) according to various embodiments, and (b) a schematic illustrating a perspective view of the Recirculating Aquaculture System (RAS #1) according to various embodiments shown in (a).

[0077] As shown in FIG. 10A, each fish tank 1010a, 1010b of the RAS may have a water capacity of 1 metric ton (t). In a water recirculation cycle, the water in the fish tanks 1010a, 1010b may overflow (i.e., via one or more one or more interconnecting pipes) to the sump tank 1002 with electrode assembly 1006 and nanobubble generator 1004, which may removenitrogenous pollutants generated during fish production The sump tank 1002 may have a water capacity of 0.42 t. The nanobubble generator 1004 may be connected to a DC power supply 1008.

[0078] After nitrogenous pollutants are removed from the water, a water pump may drive the water in sump tank to flow (i.e., via one or more interconnecting pipes) through pre-fdtration filter 1014 and activated carbon filter 1016, before the filtered water is recirculated back to the fish tanks 1010a, 1010b (i.e., via one or more interconnecting pipes). Three aerators 1018 may be deployed to the two fish tanks 1010a, 1010b and sump tank 1002 to maintain the dissolved oxygen in the water. Both the pre-filtration filter 1014 and the activated carbon filter 1016 may have multiple port valves to reverse the direction of water flow for back wash when the filters 1014, 1016 are blocked by big particles. The dissolved oxygen, pH, temperature and conductivity of the fish tanks 1010a, 1010b may be monitored on a real time basis through an online monitoring system 1022.

[0079] The treatment process of the water from fish tanks 1010a, 1010b may be further elaborated in FIG. 10B. FIG. 10B shows a schematic of a portion of the first Recirculating Aquaculture System ( AS #1) according to various embodiments as illustrated in FIG. 10A. Untreated water from the fish tanks 1010a, 1010b may overflows to the sump tank 1002 (dimensions: 0.6 m (L) x 1 m (D) x 0.9 m (H)) by gravity, and electrochemical oxidation reactions may take place on the surface of electrode assembly 1006, where active chlorine is generated to oxidize the TAN in water and microorganisms are deactivated through disinfection The dimension of each electrode of the electrode assembly 1006 may be 0 54 m (L) x 0.3 m (W) with a thickness of 2 mm, and the electrodes may be immersed in the water in sump tank 1002 vertically. The power supply 1008 can be in direct current mode or pulsed current mode. The nanobubble generator 1004 may generate fine air bubbles (size < 0.1 mm) including microbubbles (size of 200 nm to 10 pm) and nanobubbles (size of < 200 nm), and 1may recirculate the water in the tank 1002 with the electrode assembly 1006 to enhance the mass transfer and clean the surface of electrodes. The water may be further circulated to the prefdtration filter 1014 by the centrifugal pump 1012. A first pipe may fluidically connect the sump tank 1002 to the centrifugal pump 1012, and a second pipe may fluidically connect the centrifugal pump 1012 to a bottom portion of the prefiltration filter 1014. The prefiltration filter 1014 may have bedding materials of activated glass material (size: 0.4 - 4 mm) as the support layer 1014a, and coarse granular activated carbon (size: 6 x 12 mesh) as the top layer 1014b. In the prefdtration filter 1014, particulates in the water may be rejected or trapped by both activated glass layer 1014a and activated carbon layer 1014b. In addition, the residual active chlorine in the water may be reduced by activated carbon in the activated carbon layer 1014b. The water may be directed to flow from the bottom activated glass layer 1014a to the activated carbon layer 1014b.

[0080] Another activated carbon filter 1016 after prefdtration filter 1014 may be provided to remove the particulates and active chlorine which are not captured by prefdtration filter 1014. A third pipe may fluidically connect the top portion of the prefdtration filter 1014 to a bottom portion of the activated carbon filter 1016. Granular activated carbon with three different sizes (coarse: 6 x 12 mesh; medium: 8 x 30 mesh; fine: 12 x 40 mesh) may be loaded in descending order in layers 1016a - c to reduce hydraulic loss. In other words, an average size of the carbon particles of the bottommost layer 1016a may be bigger compared to an average size of the carbon particles of the middle layer 1016b, which may in turn be bigger compared to an average size of the carbon particles of the topmost layer 1016c. The water may be directed to flow from the bottommost layer 1016a (via the middle layer 1016b) to the topmost layer 1016b. As the water is disinfected (via electrochemical oxidation and fine bubble treatment) prior to entering prefdtration filter 1012 and the activated carbon filter 1014, biofouling can be avoided.

[0081] FIG. 10C shows (a) a schematic illustrating a perspective view of a holder 1020 of an electrode assembly 1006 according to various embodiments; and (b) a schematic illustrating a side view of the holder 1020 of the electrode assembly 1006 according to various embodiments. The holder 1020 may allow installation of electrodes varying from one pair to six pairs, depending on the number and weight of fishes in the fish tanks 1010a, 1010b. The distance between two neighboring electrodes may be 1 cm The anode(s) and cathode(s) may be connected to current collectors made of copper, and the current collectors may be further connected to the DC power supply 1008. The anode material may be made of metal oxide, mixed metal oxides, conductive diamond material, carbon material, platinum and alloy, titanium and alloy, and the like.

[0082] FIG. 10D shows a plot of concentration (in particles per milliliter (ml)) as a function of size (in nanometers or nm) illustrating the distribution of different sizes of bubbles generated by the nanobubble generator according to various embodiments, with an inset showing a microscopy image of two nanobubbles according to various embodiments. The characterization may be carried out using Nanosight. FIG. 10D shows that the nanobubbles may be stably presented in the water with mean diameter of 1 16 nm and a concentration of around 2 x 108 / ml .

[0083] In order to have a direct comparison between hybrid electrochemical oxidation - nanobubble treatment and conventional biofilter treatment in RAS, another RAS with biofilter is designed involving (1) removal of nitrogenous compounds (NH3, NH4+, NO2-) through nitrification process by biofilter; (2) filtration of particulate substances by pre-filtration filter with activated glass material as medium bed; and (3) disinfection of harmful pathogens by ultraviolet (UV) disinfection, as shown in FIG. 11 A. FIG. 11A shows (a) a schematic illustrating a top planar view of a second Recirculating Aquaculture System (RAS #2); and (b) a schematic illustrating a perspective view of the Recirculating Aquaculture System (RAS #2) shown in (a). As shown in FIG. 11 A, each fish tank 1110a, 1110b of the RAS has water capacityof 1 t. In a water recirculation cycle, the water in the fish tanks 1 1 10a, 1 1 10b may overflow to the sump tank 1102 with biofilter, which provides removal of nitrogenous pollutants generated during fish growth. The sump tank 1102 may have water capacity of 0.92 t. After that, a water pump 1112 may drive the water in sump tank 1102 to flow through the pre-filtration filter 1114 and UV disinfector 1116, before it is recirculated back to the fish tanks 1110a, 1110b. Six aerators 1 1 18 may be deployed to the two fish tanks 1 1 10a, 1 1 10b and sump tank 1 102 to maintain the dissolved oxygen in water. The pre-filtration filter 1114 may have multiple port valves to reverse the direction of water flow for back wash when the filter 1114 is blocked by big particles. The dissolved oxygen, pH, temperature and conductivity of the fish tanks 1110a, 1110b may be monitored on a real time basis through online monitoring system 1122.

[0084] FIG. 1 IB shows a schematic of yet another recirculating aquaculture system (RAS) including a biofilter.

[0085] Example 6

[0086] 8 kg of sodium chloride was added to RAS #1 to make the initial total dissolved solids of water at 3.8 g / L. Jade Perch fishes with an average weight of 31.2 g / fish were deployed to the fish tanks, and the number of Jade Perch was 100 fishes / tank upon deployment. The current was set as 12 A and the DC power supply was switched on from 10 am to next day 8 am. The voltage ranged between 2.9 V to 3.0 V. The nanobubble generator was switched on for 15 minutes per hour from 10 am to 6 pm daily.

[0087] Example 7

[0088] The water in RAS #2 had initial total dissolved solids of 1 .2 g / L. Jade Perch fishes with an average weight of 31.2 g / fish were deployed to the fish tanks, and the number of Jade Perch was 100 fishes / tank upon deployment.

[0089] Example 8

[0090] Both systems in Example 6 and Example 7 were operated for a same period of 21 days. The fishes in the four fish tanks may be fed one to three times daily, with 40 g fish food per tank for one feeding. Water samples from the fish tank outlets were collected at the same time every morning for analysis. The average values of the TAN concentration, nitrite concentration, daily nitrate accumulation, dissolved oxygen, water exchange rate, power and feed conversion rate of the fish production period is summarized in FIG. 12A. FIG. 12A shows a table illustrating results of water quality, water exchange rate, power and feed conversion rate of the first Recirculating Aquaculture System (RAS #1) according to various embodiments and the second Recirculating Aquaculture System (RAS #2) during 21 -day fish production period.

[0091] As shown in FIG. 12A, the TAN for RAS #1 was 0.143 mg / L, which is slightly higher than that of RAS #2. However, RAS #1 had moderate to significant improvement in other parameters such as nitrite concentration (26 % decrease), daily nitrate accumulation (47 % decrease) and dissolved oxygen (26 % increase), compared to RAS #2. This has resulted in a better feed conversion rate of 1.35 in RAS #1 than 1.73 in RAS #2. Due to the less surface area of water and less amount of water used for back wash the filters in RAS #1, the water exchange rate was more efficient in RAS #1 , leading to less water consumption. The power of RAS #1 (745 W) was also less than RAS #2 (831 W), with a breakdown of the power of each component provided in FIG. 12B

[0092] FIG. 12B shows a table showing the power consumptions of the energy consuming components of the first Recirculating Aquaculture System (RAS #1) according to various embodiments and the second Recirculating Aquaculture System (RAS #2).

[0093] Generally speaking, RAS #1 may maintain desirable water quality for fish production and may demonstrate advantages in water and energy consumption in comparison to RAS #2.

[0094] Various embodiments may relate to a method for removing aqueous nitrogenous pollutants and a system for effective TAN removal and nitrite control in aquaculture water,including a tank with electrode assembly and nanobubble generator, a pre-filtration filter, an activated carbon filter, a DC power source, two fish tanks and a water quality monitoring system (for monitoring pH, temperature, dissolved oxygen, conductivity etc. of the aquaculture).

[0095] The combination of electrochemical oxidation and nanobubble treatment can achieve synergistic effects in improving the oxidation (for effective TAN removal), reducing accumulation of nitrate and avoiding generation of nitrite, disinfection, and cleaning electrode surface.

[0096] The combination of electrochemical oxidation, nanobubble treatment and prefiltration / activated carbon treatment may also lead to synergistic effects. FIG. 12C illustrates the combination of electrochemical oxidation, nanobubble treatment and prefiltration / activated carbon treatment leading to synergistic effects according to various embodiments. Nanobubbles may improve the energy efficiency of electrochemical oxidation. Nanobubbles and electrochemical oxidation may prevent clogging and fouling of filter and activated carbon through mechanical and electrochemical de-contamination of foulant(s).

[0097] In various embodiments, the holder for electrode assembly may be adjusted from at least one pair of electrodes to six pairs of electrodes to adapt to varying concentrations of nitrogenous compounds in different periods of fish growth.

[0098] In various embodiments, the anode material may be made of metal oxide, mixed metal oxides, conductive diamond material, carbon material, platinum and alloy, titanium and alloy, and the like.

[0099] In various embodiments, the pre-filtration filter may be loaded with dual media bed, where activated glass material serves as support layer and activated carbon serves as top layer. The flocs and big particles can be removed in the support layer and active chlorine can be reduced in the top layer. 1

[0100] Tn various embodiments, the activated carbon filter may be loaded with granular active carbon of same size or different sizes in descending order along the water path to remove toxic by-products and particulate pollutants which are not captured by pre-fdtration filter, and to oxidize TAN which is not degraded by electrochemical oxidation.

[0101] In various embodiments, both the pre-fdtration filter and activated carbon filter may be equipped with back wash function to reduce blockage of filters by sludges in the event of flow rate drop.

[0102] Various embodiments may further extend to removal of other types of pollutants such as organic pollutants, sulfite, phosphorus compounds, arsenic compounds, and the like.

[0103] Various embodiments may have advantages such as easy operation, less energy consumption and / or ease of scaling up. Various embodiments may be used as an intensive recirculating aquaculture system. Various embodiments may be extended to the treatment of other types of wastewater containing nitrogenous pollutants, e.g., agricultural wastewater or industrial wastewater.

[0104] In contrast, a biofilter RAS may involve multiple bacteria species (nitrification, denitrification, etc ), thereby requiring long conditioning time and periodic replacement Also, the biofilter RAS may suffer from filter clogging due to solid particles and biofilms, requiring periodic back wash. There may be a need for continuous air blowing to maintain dissolved oxygen level in fish tank, and may involve energy consumption due to UV disinfection. All these may mean that there is a long payback period, e.g., up to 10 years. FIG. 12D shows a table illustrating results of water quality, water exchange rate, power and feed conversion rate of the treatment system according to various embodiments and a conventional biofilter recirculating aquaculture system (RAS). Various embodiments may have 39% decrease of nitride concentration, 38% decrease of daily nitrate accumulation, 26% increase in dissolved oxygen,better water exchange rate, better feed conversion rate and lower power consumption compared to the conventional biofilter recirculating aquaculture system (RAS).

Claims

Claims1. A treatment system for removing pollutants in wastewater, the treatment system comprising: a tank configured to hold the wastewater; a bubble generator configured to generate bubbles, each of the bubbles having a diameter of less than 0.1 mm, in the wastewater held in the tank; an electrode assembly comprising a cathode and an anode, the electrode assembly being configured to generate oxidizing agents via electrochemical oxidation at the anode when a direct current (DC) voltage or pulsed current voltage is applied between the cathode and the anode such that the oxidizing agents oxidize the pollutants in the wastewater held in the tank, thereby removing the pollutants from the wastewater; and a power supply configured to apply the direct current (DC) voltage or pulsed current voltage between the cathode and the anode.

2. The treatment system according to claim 1, wherein the treatment system is also configured to generate a further oxidizing agent, the further oxidizing agent being hydroxyl radicals; and wherein the bubbles generated increase a lifetime of the hydroxyl radicals by providing an oxygen-rich environment for reducing a probability of recombination of the hydroxyl radicals to generate oxygen gas, and by improving a stability of the hydroxyl radicals in the wastewater.

3. The treatment system according to claim 1 or claim 2,wherein the bubbles generated increase efficiency of generating the oxidizing agents, improve conversion rate of pollutants and provide a cleaning effect to the cathode and the anode.

4. The treatment system according to any one of claims 1 to 3, wherein the anode comprises any material selected from a group consisting of a metal oxide, mixed metal oxides, a conductive diamond material, a carbon material, platinum, a platinum-based alloy, titanium and a titanium-based alloy.

5. The treatment system according to claim 4, wherein the material is the mixed metal oxides, the mixed metal oxides being iridium ruthenium oxide (Ir-Ru-O).

6. The treatment system according to claim 4, wherein the material is the conductive diamond material, the conductive diamond material being boron doped diamond (BDD).

7. The treatment system according to any one of claims 1 to 6, wherein the oxidizing agents are reactive chlorine species.

8. The treatment system according to any one of claims 1 to 7, wherein the pollutants are nitrogenous pollutants, organic pollutants, sulfites, phosphorous compounds, or arsenic compounds.

9. The treatment system according to claim 8, wherein the pollutants are the nitrogenous pollutants, the nitrogenous pollutants being total ammonia nitrogen (TAN).

10. The treatment system according to any one of claims 1 to 9, wherein the electrode assembly comprises one or more further pairs of cathodes and anodes.

11. The treatment system according to any one of claims 1 to 10, wherein a pH of the wastewater is selected from a range from 3 to 11.

12. The treatment system according to any one of claims 1 to 1 1 , further comprising: a prefiltration filter comprising a layer of activated glass and a layer of activated carbon.

13. The treatment system according to claim 12, wherein the layer of active carbon of the prefiltration filter is over the layer of activated glass of the prefiltration filter; and wherein the treatment system is configured such that the wastewater flows through the layer of activated glass of the prefiltration filter before flowing through the layer of activated carbon of the prefiltration filter.

14. The treatment system according to claim 12 or claim 13, wherein the prefiltration filter has a backwash function.

15. The treatment system according to any one of claims 1 to 14, further comprising: an activated carbon filter comprising one or more layers of activated carbon.

16. The treatment system according to claim 15,wherein the one or more layers of activated carbon comprise a plurality of layers of activated carbon, wherein an average particle size of an overlying layer of the plurality of layers of activated carbon of the activated carbon filter is smaller than an average particle size of a middle layer of the plurality of layers of activated carbon of the activated carbon filter; wherein the average particle size of the middle layer of the plurality of layers of activated carbon of the activated carbon filter is smaller than an average particle size of an underlying layer of the plurality of layers of activated carbon of the activated carbon filter; and wherein treatment system is configured such that the wastewater flows through the underlying layer before flowing through the middle layer to the overlying layer.

17. The treatment system according to claim 15 or claim 16, wherein the activated carbon filter has a backwash function.

18. A method of forming a treatment system for removing pollutants in wastewater, the method comprising: providing a tank configured to hold the wastewater; providing a nanobubble generator configured to generate nanobubbles in the wastewater held in the tank; providing an electrode assembly comprising a cathode and an anode, the electrode assembly being configured to generate oxidizing agents via electrochemical oxidation at the anode when a direct current (DC) voltage or pulsed current voltage is applied between the cathode and the anode such thatthe oxidizing agents oxidize the pollutants in the wastewater held in the tank, thereby removing the pollutants from the wastewater; and providing a power supply configured to apply the direct current (DC) voltage or pulsed current voltage between the cathode and the anode.

19. The method according to claim 18, wherein the treatment system is also configured to generate a further oxidizing agent, the further oxidizing agent being hydroxyl radicals; and wherein the bubbles generated increase a lifetime of the hydroxyl radicals by providing an oxygen-rich environment for reducing a probability of recombination of the hydroxyl radicals to generate oxygen gas, and by improving a stability of the hydroxyl radicals in the wastewater.

20. The method according to claim 18 or claim 19, wherein the bubbles generated increase efficiency of generating the oxidizing agents, improve conversion rate of pollutants and provide a cleaning effect to the cathode and the anode.

21. The method according to any one of claims 18 to 20, wherein the anode comprises any material selected from a group consisting of a metal oxide, mixed metal oxides, a conductive diamond material, a carbon material, platinum, a platinum-based alloy, titanium and a titanium-based alloy.

22. The method according to claim 21, wherein the material is the mixed metal oxides, the mixed metal oxides being iridium ruthenium oxide (Ir-Ru-O).

23. The method according to claim 21, wherein the material is the conductive diamond material, the conductive diamond material being boron doped diamond (BDD).

24. The method according to any one of claims 18 to 23, wherein the oxidizing agents are reactive chlorine species.

25. The method according to any one of claims 18 to 24, wherein the pollutants are nitrogenous pollutants, organic pollutants, sulfite, phosphorous compounds, or arsenic compounds.

26. The method according to claim 25, wherein the pollutants are the nitrogenous pollutants, the nitrogenous pollutants being total ammonia nitrogen (TAN).

27. The method according to any one of claims 18 to 26, wherein the electrode assembly comprises one or more further pairs of cathodes and anodes.

28. The method according to any one of claims from 18 to 27, wherein a pH of the wastewater is selected from a range from 3 to 1 129. The method according to any one of claims 18 to 28, further comprising: providing a prefiltration filter comprising a layer of activated glass and a layer of activated carbon.

30. The method according to claim 29, wherein the layer of active carbon of the prefdtration filter is over the layer of activated glass of the prefdtration filter; and wherein the treatment system is configured such that the wastewater flows through the layer of activated glass of the prefdtration filter before flowing through the layer of activated carbon of the prefdtration filter.

31. The method according to claim 29 or claim 30, wherein the prefdtration filter has a backwash function.

32. The method according to any one of claims 18 to 31, further comprising: providing an activated carbon filter comprising one or more layers of activated carbon.

33. The method according to claim 32, wherein the one or more layers of activated carbon comprise a plurality of layers of activated carbon; wherein an average particle size of an overlying layer of the plurality of layers of activated carbon of the activated carbon filter is smaller than an average particle size of a middle layer of the plurality of layers of activated carbon of the activated carbon filter; wherein the average particle size of the middle layer of the plurality of layers of activated carbon of the activated carbon filter is smaller than an average particle size of an underlying layer of the plurality of layers of activated carbon of the activated carbon filter; andwherein treatment system is configured such that the wastewater flows through the underlying layer before flowing through the middle layer to the overlying layer.

34. The method according to claim 32 or claim 33, wherein the activated carbon filter has a backwash function.

35. A method of operating a treatment system for removing pollutants in wastewater, the method comprising: supplying the wastewater to a tank; using a bubble generator to generate bubbles, each of the bubbles having a diameter of less than 0.1 mm, in the wastewater held in the tank; and applying a direct current (DC) voltage or pulsed current voltage between a cathode and an anode of an electrode assembly using a power supply, the electrode assembly being configured to generate oxidizing agents via electrochemical oxidation at the anode when the direct current (DC) voltage or pulsed current voltage is applied between the cathode and the anode such that the oxidizing agents oxidize the pollutants in the wastewater held in the tank, thereby removing the pollutants from the wastewater.

36. The method according to claim 35, further comprising: using a pump to pump the wastewater from the tank to a prefiltration filter such that the wastewater flows through a layer of activated glass of the prefiltration filter before flowing through a layer of activated carbon of the prefiltration filter.

37. The method according to claim 36,wherein the prefiltration filter is in fluidic connection with an activated carbon filter such that the wastewater from the prefiltration filter flows through an underlying layer of the activated carbon filter before flowing through a middle layer of the activated carbon filter to an overlying layer of the activated carbon filter.

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