SE2251224A1

SE2251224A1 - Water purification involving an electro-peroxone process

Info

Publication number: SE2251224A1
Application number: SE2251224A
Authority: SE
Inventors: Daniel Ragnvaldsson; Majid Mustafa; Sten Fernerud
Original assignee: Chemox I Umeaa Ab
Priority date: 2022-10-19
Filing date: 2022-10-19
Publication date: 2024-04-20
Also published as: FI20236156A1; DE102023128362A1

Abstract

Abstract The invention relates to a system and a method for purification of water suitable for large scale water purification, utilizing ozonation in combination with in situ electrochemical formation of hydrogen peroxide to form an electro-peroxone process, wherein the process design is configured to result in scalable, efficient and durable water purification with use of oxygen, water and electricity, and without addition of liquid Hﬁb. The system comprises a reaction vessel and a separate electrochemical cell, the cell comprising a cathode, an anode and a solid-state electrolyte as well as an inlet for clean water.

Description

Technical Field of the Invention The invention relates to the technical field of water purification. More specifically, the present invention relates to a system and a method for water purification comprising addition of ozone and hydrogen peroxide generated by a process involving electricity, oxygen and clean water.

Background Occurrence of micropollutants (MPs) including pharmaceuticals, biocides, personal care products and industrial chemicals in wastewaters is a major challenge which poses a potential threat to aquatic ecosystems as well as to humans. Occurrence of MPs in different water systems including surface water, sea water and drinking water (if surface water is used as a source of drinking water) is mainly related to the discharge from wastewater treatment plants (WWTPs). This is because conventional WWTPs are not designed to remove MPs. The low concentration and diverse nature of MPs complicate their removal at WWTPs. There is an imperative need for a treatment process capable of removing MPs of complex and diverse nature from wastewaters and other contaminated waters.

Advanced oxidation processes (AOPs) have gained interest in the last two decades due to their effectiveness for removal of MPs in various waters. One advantageous AOP is the ozonation process due to the selective nature of ozone for removing MPs and the possibility to handle large volumes of wastewater. MPs are oxidized by ozone and hydroxyl radicals (°OH) during ozonation. Ozone is a selective oxidant and transforms MPs into other small molecular weight compounds by oxidizing their double bonds and other electron rich moieties, selectively. -OH have higher oxidizing potential (2.8 eV) than ozone (2.l eV) and oxidatively degrades almost all organic MPs present in the water non-selectively at very high rate. However, formation of -OH in ozonation is dependent upon ozone reaction with dissolved organic matter (DOM) and other water constituents and often -OH formation is slow for ozonation. This leads to poor removal of ozone-resistant MPs that lack double bonds or electron rich moieties for electrophilic ozone attack as these ozone-resistant MPs are oxidized by -OH. Thus, accelerating formation of -OH is advantageous and required for achieving better water quality by removing ozone-resistant MPs.

For effective removal of ozone-resistant MPs, ozonation can be upgraded to another process called peroxone, where hydrogen peroxide (Hﬁb) is provided externally together with ozone to accelerate the formation of -OH. However, providing Hﬁb externally is not always practically feasible, involves risky handling of liquid Hﬁb and increases the cost substantially. Continuous transportation of Hﬁb on-site and its handling are big challenges in application. To overcome these challenges, an electrochemical advanced oxidation process, called electro- peroxone is developed. In the electro-peroxone process, Hﬂb is generated in-situ electrochemically at cathode via oxygen reduction reaction. Generated Hﬂb mixes homogeneously in the solution and enhances transformation of ozone (by reacting with it) into -OH. As a result, formation of -OH is accelerated which improves the removal of ozone-resistant MPs.

Removal of resistant MPs via effective formation of -OH in a continuous industrial and large scale electro-peroxone process requires a correct system design as well as appropriate electrode materials for robust electrochemical generation of Hﬂb, which has been lacking in previous works.

US 2020/0055754A1 discloses a reaction vessel where ozone is injected from the bottom of the reaction vessel whereas cathode and anode electrodes are suggested to be placed in the upper part of the same reaction vessel in the main water flow. Ozone generator effluent which consists of ozone and oxygen Mb/Og) gas can be guided to the electrodes using a current plate below the electrolysis electrodes pair for generation of H2O2.

Bulk in situ electrochemical generation of Hﬁb in the electro- peroxone process is a key step which depends on the mass transfer of O2 to the cathode for oxygen reduction reaction. In a traditional setting with submerged electrodes, the electrodes are directly submerged in electrolytes and these electrolytes are aerated with oxygen gas (in the reaction vessel). Due to the low solubility of oxygen in water, the mass transfer of oxygen to the submerged electrodes is low which in turn limits the achievable current density to a few mA/cm? and limited generation of Hﬁb. One way of solving this problem is using an electrochemical cell with small water flow (separated from the main water flow) which enables high mass transfer of O2 to the cathode, using for instance gas diffusion electrodes. High mass transfer of oxygen to the cathode enables it to use high current densities for oxygen reduction reaction, in turn high concentration of Hﬁb can be achieved in a smaller liquid volume and injected into the main water stream.

(Yang Li, Yixin Zhang, Guangshen Xia, Juhong Zhan, Gang Yu, Yujue Wang. 2021, Evaluation of the technoeconomic feasibility of electrochemical hydrogen peroxide production for decentralized water treatment. Front. Environ. Sci. Eng. 2021, l5(l): l) used a similar approach with gas diffusion electrodes and achieved current density as high as 400 mA/cm2. This study used liquid electrolyte in an electrochemical cell for generation of H2O2.

EP 3430182 Bl discloses an electrochemical cell with improved properties for production of Hﬂb and suggested to incorporate the Hﬁb with ozone addition. However, no information is provided of the reactor design including the wastewater flows for treatment and ozone and hydrogen peroxide addition.

KR 20l90l20837 A discloses an electro-peroxone based water treatment device. The wastewater is first mixed with ozone and then treated in a reactor comprising electrodes to generate hydrogen peroxone and then circulated again to the system.

US 2020262723 Al discloses a method for removing contaminants in a water treatment process by introducing a mixture of 02 and 03 gas into an ozone reaction column in which electrodes are disposed at the bottom.

Summary of the invention One object of the present invention is to obviate at least some of the problems in the prior art and provide a system and a method for purification of water that can handle large flows of water.

More specifically, the invention relates to a system and a method for purification of water suitable for large scale water purification, utilizing ozonation in combination with in situ electrochemical formation of hydrogen peroxide to form an electro-peroxone process, wherein the process design is configured to result in scalable, efficient and durable water purification with use of oxygen, water and electricity, and without addition of liquid Hﬁb.

According to a first aspect, there is provided a water treatment system for purification of water, said system comprising: a. a reaction vessel 110 comprising - a first vessel inlet 113 for water to be treated to enter said reaction vessel 110, - a first vessel outlet 111 for treated water to exit said reaction vessel 110, - a second vessel outlet 112 for gas to exit said reaction vessel 110, said second outlet 112 being located in an upper part of said reaction vessel 110, and - a second vessel inlet 121 for supplying 03 to the reaction vessel 110, said second inlet 121 being located in a lower part of said reaction vessel 110, b. a main water line 150 leading from a main inlet 118 for water to be treated to said first vessel inlet 113, and c. an electrochemical cell 130 for Hﬂb generation comprising at least one cathode, at least one anode and a solid-state electrolyte, said electrochemical cell 130 having an oxygen inlet 131 and a clean water inlet 132, said electrochemical cell 130 being adapted to be connected with a source of electricity 133, and said electrochemical cell having an outlet enabling said electrochemical cell 130 to be in fluid connection with said reaction vessel 110 through at least one Hﬁb inlet point 115.

According to a second aspect, there is provided a method for purification of water, the method comprising the steps of: - supplying clean water, oxygen and electricity to at least one electrochemical cell 130, said at least one electro- chemical cell 130 comprising of at least one cathode, at least one anode and a solid-state electrolyte, whereby Hﬂb is generated in situ electrochemically when oxygen undergoes an oxygen reduction reaction on the surface of the at least one cathode, - supplying water comprising Hﬂb from said electrochemical cell 130 into a reaction vessel 110, - supplying water to be treated into the reaction vessel 110 through a water main line 150 which enters the reaction vessel 110 through a first vessel inlet 113, - introducing O3 into a lower part of said reaction vessel 110, - releasing gas from said reaction vessel 110, and - releasing treated water from said reaction vessel 110.

An advantage of using an electrochemical cell 130 for Hﬁb generation which is separate from the reaction vessel 110 is an improved ability to provide availability of oxygen to the at least one cathode and thereby use of high current densities. As a result, high concentration of Hﬂb can be achieved in a smaller volume of water before injecting it into the water to be treated.

Another advantage of the electrochemical cell 130 being separate from the reaction vessel 110 and having a clean water inlet 132 through which clean water is supplied to the electrochemical cell 130 is that the Hﬁb generation takes place using clean water, thereby avoiding formation of potential toxic byproducts which usually form during electrochemical processes when using e.g. wastewater as a SOUICG .

By using a solid-state electrolyte, handling of liquid electrolytes is avoided.

Brief description of the drawings Aspects and embodiments will be described with reference to the following drawings in which: Figure 1 is an overview of a specific embodiment of a water purification system wherein ozone is injected into a reaction vessel 110 through diffusers 114.

Figure 2 is an overview of a specific embodiment of a water purification system wherein ozone is injected into a first flow path 151 for water through a venturi injector, wherein the first flow path 151 has a source of water other than that of a main water line 150.

Figure 3 is an overview of a specific embodiment of a water purification system wherein ozone is injected into a first flow path 151 for water through a venturi injector, wherein the source of water for the first flow path 151 is the main water line 150 for water to be treated.

Figure 4 is an overview of a specific embodiment of a water purification system wherein ozone is injected into a first flow path 151 for water through a venturi injector, wherein the source of water for the first flow path 151 is the main water line 150 for water to be treated, and wherein the water comprising Hﬂb is injected to the water main line 150 at an Hﬂb inlet point 115 via a second flow path 152 using a venturi injector.

Figure 5 is an overview of a specific embodiment of a water purification system wherein ozone is added both through a venturi injector into a first flow path 151 which enters the main water line 150 and also through diffusers 114 which are located in a lower part of the reaction vessel 110, and wherein the water comprising Hﬁb is injected to the water main line 150 at an Hﬂb inlet point 115 via a second flow path 152 using a venturi injector.

Detailed description Before the invention is disclosed and described in detail, it is to be understood that this invention is not limited to particular configurations, process steps and materials disclosed herein as such configurations, process steps and materials may vary somewhat. It is also to be understood that the terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting since the scope of the present invention is limited only by the appended claims and equivalents thereof.

It will be apparent to those skilled in the art that various modifications and variations can be made to the system and method of the present disclosure without departing from the scope of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the system and method disclosed herein. The features of the different embodiments which are compatible may be combined in different ways that are not specifically disclosed by example. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalent.

It must be noted that, as used in this specification and the \\ \\ a", an l/ appended claims, the singular forms and “the” include plural referents unless the context clearly dictates otherwise.

If nothing else is defined, any terms and scientific terminology used herein are intended to have the meanings commonly understood by those of skill in the art to which this invention pertains.

As used throughout the claims and the description, the term “reaction vessel” denotes a device where an electro-peroxone reaction is intended to take place. The vessel has a volume where water comprising hydrogen peroxide can react with O3in the water. In some embodiments of the invention, such a reaction also takes place at locations in the system outside of the reaction vessel.

As used throughout the claims and the description, the term “electrochemical cell” denotes a device where Hﬂb is generated, having at least one cathode and at least one anode which are connected to a voltage supply to supply a suitable current. The electrodes are provided with oxygen and water.

The oxygen supplied to the electrochemical cell may be in the form of O2 (oxygen gas) or air. Oxygen gas may be preferred as it is generally more efficient to use, while air may be preferred as it is convenient to use due to availability.

The term “water line” or “flow path” denotes a path of connected volumes such as the inner volumes of pipes, chambers and so on in a device where water can flow in a certain direction from one part to another part. Examples include pipes, tubes, and chambers.

The term “upstream” denotes a location situated in the opposite direction from that in which liquid flows, referring to the intended direction of water in the flow path. A position upstream is nearer to the source of the liquid, compared to a given location and following the flow path. In the system there are intended paths for water along which water is designed to flow. Such a path may be divided to several paths which may then optionally rejoin to fewer paths.

Upstream is always opposite the direction of the flow. 11 The term “clean water” denotes water other than water intended to be purified, i.e. not comprising high content of DOC and contaminants intended to be removed through the treatment process. Examples of clean water include DI water, drinking water, tap water, or high quality water.

The terms “upper” and “lower” denote locations in the system as it is intended to be oriented when the system is in position for use. An upper part is situated in a physical position vertically above a lower part with regards to the direction of the gravitational force.

In a first aspect, there is provided a water treatment system for purification of water, said system comprising: a. a reaction vessel 110 comprising - a first vessel inlet 113 for water to be treated to enter said reaction vessel 110, - a first vessel outlet 111 for treated water to exit said reaction vessel 110, - a second vessel outlet 112 for gas to exit said reaction vessel 110, said second outlet 112 being located in an upper part of said reaction vessel 110, and - a second vessel inlet 121 for supplying 03 to the reaction vessel 110, said second inlet 121 being located in a lower part of said reaction vessel 110, b. a main water line 150 leading from a main inlet 118 for water to be treated to said first vessel inlet 113, and c. an electrochemical cell 130 for Hﬂb generation comprising of at least one cathode, at least one anode and a solid-state electrolyte, 12 said electrochemical cell 130 having an oxygen inlet 131 and a clean water inlet 132, said electrochemical cell 130 being adapted to be connected with a source of electricity 133, and said electrochemical cell having an outlet enabling said electrochemical cell 130 to be in fluid connection with said reaction vessel 110 through at least one Hﬁb inlet point 115.

Placing the electrodes directly in the reaction vessel 110, which contains a volume larger than the electrolysis cell 130, would require a very large cathode, or several cathodes, to generate sufficient Hﬁb for substantially high flows of industrial- and full-scale plants. Using larger electrodes in the reaction chamber would also limit the mass transfer of oxygen to the cathode due to low solubility of oxygen in the water, hence low production of Hﬂb and fast deterioration of cathodes. Instead using a separate electrochemical cell 130 with a small water flow enables high mass transfer of oxygen to the cathode, which enables usage of high current densities for oxygen reduction reaction, obtaining a high Hﬁb production rate. A high concentration of Hﬁb can thus be efficiently achieved before being injected into the main water stream. In such a system, small electrodes are sufficient to generate required H2O2.

An advantage of the disclosed system is that the electrochemical cell 130, being separate from the reaction vessel 110, has an inlet 132 where clean water can be supplied. The Hﬁb generation can thereby take place using clean water, thus avoiding formation of potential toxic by- products from electrochemical reactions which usually form 13 during electrochemical processes when using wastewater as a source for Hﬂb generation.

Another advantage is that by using a solid-state electrolyte, handling of liquid electrolytes is avoided. Liquid electrolytes require addition of chemicals for conductivity of the electrochemical cell as well as demand extensive handling and continuous supply. Moreover, if wastewater is used as an electrolyte for generation of Hﬁb, a potential toxic by- product i.e., perchlorate of electrochemical process can be formed which is under strict regulation in many countries. Solid-state electrolytes such as ion exchange membranes can replace liquid electrolytes due to its convenience for practical applications. Using a solid-state electrolyte will also reduce the energy consumption of Hﬁb production, thus, decrease in overall cost.

The reaction vessel llO is adapted to provide sufficient treatment time for reaction between O3 and Hﬂb introduced into the vessel llO for efficient treatment of water. The treatment time depends on the water quality, disinfection to be achieved and contaminants to be removed. For example, wastewater at a sewage treatment plant might require up to 45 minutes of treatment. Oil contaminated water might require a few hours of treatment and drinking water usually requires a few minutes of treatment. The reaction vessel volume is designed based on specific water to be treated to provide sufficient time for treatment.

The outlet ll2 for gas is suited for the release of gasses such as 03. 14 In one embodiment, the system further comprises a source 120 of 03 for providing 03to the system, the source 120 being in fluid connection with the reaction vessel 110 at least via the second vessel inlet 121. It is conceived that the source of 03 may not generate 100% pure ozone, and that there may be a mixture further comprising 02 as well as other gases. The source 120 of 03 is adapted to suit the system. The source 120 of 03 is in one embodiment an 03 generator. The source 120 of 03 is in one embodiment an 03 gas tank.

The 03 enters the reaction vessel 110 in a lower part of the reaction vessel 110, resulting in an upward flow of 03 through the reaction vessel 110 (Fig 1-5). The upward flow allows the 03 to react with water comprised in the reaction vessel 110 before exiting the reaction vessel 110 through the second vessel outlet 112. The lower part is in one embodiment the lower 1/3, 1/4, 1/8 or 1/16 part of the reaction vessel 110.

The outlet 112 for gas is in one embodiment located in the upper 1/4, 1/8 or 1/16 part of the reaction vessel 110, such that gasses (e.g., 03) can exit from the reaction vessel 110 after flowing upwards.

In one embodiment, (Fig. 1 and 5) of the water treatment system, said second vessel inlet 121 is in fluid connection with said reaction vessel 110 through at least one diffuser 114, said at least one diffuser 114 being located in a lower part of the reaction vessel 110. The source 120 of 03 thereby introduces 03 into a lower part of reaction vessel 110 through at least one diffuser 114, resulting in an upward flow of 03 through the reaction vessel 110.

In one such embodiment (Fig. 1), the first vessel inlet 113 is located in an upper part of the reaction vessel 110, for example the upper 1/4, 1/8 or 1/16 part of the reaction vessel 110 and the first vessel outlet 111 is located in a lower part of the reaction vessel 110, for example the lower 1/4, 1/8 or 1/16 part of the reaction vessel 110, resulting in a downward flow of water to be treated comprising Hﬁb through the reaction vessel 110. The upward flow of the 03 and the simultaneous downward flow of the water comprising Hﬁb results in Hﬂb reacting with dissolved 03 to produce the desired °OH. The at least one diffuser 114 is in one embodiment a plurality of diffusers 114 spread out at different horizontal locations in the lower part, such as at the lower 1/3, 1/4, 1/8 or 1/16 part of the reaction vessel 110. In this embodiment, Hﬁb enters the reaction vessel 110 in an upper part. In one embodiment, this occurs as the Hﬁb inlet point 115 is located at a point on the main water line 150 and the main water line 150 leads into the reaction vessel 110 through first vessel inlet 113 which is located in an upper part of the reaction vessel 110 (as in Fig. 1). In another embodiment, the Hﬂb inlet point 115 is located at a point directly leading into the upper part of the reaction vessel 110, separately from the main water line 150. This setup allows the water to be treated to react with ozone without presence of Hﬁb in the reaction vessel 110 for an adaptable time period to achieve water disinfection by ozonation before Hﬂb is added and the peroxone reaction takes place. 16 In another such embodiment, the first vessel inlet 113 is located in a lower part of the reaction vessel 110, for example the lower 1/4, 1/8 or 1/16 part of the reaction vessel 110 and the first vessel outlet 111 is located in an upper part of the reaction vessel 110, for example the upper 1/4, 1/8 or 1/16 part of the reaction vessel 110. Features regarding how the Hﬁb and ozone may enter the main water line 150 which will described below may when suitable (such as when the main water line 150 enters the reaction vessel 110 through first vessel inlet 113 at an upper part of the vessel 110) be combined with the presence of at least one diffuser 114. In one embodiment, ozone can thereby be added to the reaction vessel 110 both via the main water line 150 (optionally through a venturi injector and optionally via a first flow path 151 which will be described further below) and is also added to the reaction vessel 110 via at least one diffuser 114 located in a lower part of the reaction vessel 110. One such embodiment is shown in Fig. 5. In one such embodiment, a major part of the ozone is added via the main water line 150 and a smaller part is added via the at least one diffuser 114. In one embodiment, the system is configured such that ozone may be added from these sources at least in part simultaneously. In one embodiment, the system is configured such that ozone may be added from these sources at different time points.

In one embodiment, (Fig. 2-5), the water treatment system further comprises at least one injection site 140 for injecting 03 into at least one first flow path 151 for water, said at least one first flow path 151 being in fluid connection with the reaction vessel 110 and having at least one first flow path inlet 116 upstream of said at least one injection site 140 and at least one first flow path outlet 119 downstream of said at least one injection site 140, 17 said at least one injection site 140 optionally comprising a venturi injector.

In one embodiment, the cross-sectional area of the narrowest passage of the at least one first flow path 151 is smaller than the cross-sectional area of the narrowest passage of main water line 150 (Fig. 2-5).

A venturi injector allows more ozone to be added per volume of water compared to addition of gas bubbles. Injecting ozone via a venturi injector using a side stream with a lower flow (such as the first and second flow paths 151, 152) than the main water line 150 is advantageous because injecting ozone via a venturi injector requires certain pressure which is easily managed for low flow using a small pump. Injecting the ozone into the full flow of the main water line 150 which would require a more powerful pump and higher energy.

In one embodiment (Fig. 2), the at least one first flow path outlet 119 is located at a lower part of said reaction vessel 110, said first vessel inlet 113 is located in an upper part of the reaction vessel 110, said first vessel outlet 111 is located in a lower part of the reaction vessel 110, and said Hﬂb inlet point 115 is located at a point on the main water line 150 or at an upper part of the reaction vessel 110.

In one embodiment, the at least first flow path outlet 119 coincides with second vessel inlet 121. In one embodiment, the 18 at least one first flow path outlet 119 is located inside the reaction vessel 110. In one embodiment, a plurality of first flow path outlets 119 are spread out at different horizontal locations in the reaction vessel 110. In one embodiment, the plurality of first flow path outlets 119 are spread out at different horizontal locations in the lower 1/3, 1/4, 1/8 or 1/16 part of the reaction vessel 110. In one embodiment, the plurality of first flow path outlets 119 are spread out at different horizontal locations located below the first vessel outlet 111 (Fig. 2).

In one embodiment (Fig. 3-5), the at least one first flow path 151 is in fluid connection, through said first flow path inlet 116, either with said main water line 150 at a point A on the main water line 150 or with a separate source of water, said at least first flow path outlet 119 is in fluid connection with said main water line 150 at a point B on the main water line 150, point B is located downstream of point A in the intended flow direction of the water in said at least one first flow path 151, said first vessel inlet 113 is located in the lower part of said reaction vessel 110, and said first vessel outlet 111 is located in the upper part of said reaction vessel 110.

In other words, the first flow path 151 can have as a source of water either the water in main water line 150 or a separate source of water. The water in first flow path 151 enters the main line 150 at a point upstream of first vessel inlet 113. 19 This setup enables addition of ozone to the water to be treated before introduction of Hﬁb into that water.

The embodiments where the ozone is injected into the main water line 150 before entering the vessel 110 are configured such that the main water line 150 enters in the lower part so that ozone enters into the reaction vessel 110 from the lower part. In these embodiments, the water flows upwards through the reaction vessel 110 as the first vessel outlet 111 is located in an upper part of the reaction vessel 110. As can be seen in Fig. 3-4, the second vessel inlet 121 for supplying 03 to the vessel and the first vessel inlet 113 for water to be treated to enter the vessel 110 may coincide. In Fig. 5, 03 is added both this way and through a separate path leading to diffusers 114.

In one embodiment, (Fig. 4-5), the water treatment system further comprises a second flow path 152 for water, said Hﬂb inlet point 115 being located at a point on said second flow path 152, said second flow path 152 having a second flow path inlet 122 upstream of said Hﬁb inlet point 115 and a second flow path outlet 123 downstream of said Hﬂb inlet point 115, said Hﬁb inlet point 115 optionally comprising a venturi injector, said second flow path 152 being in fluid connection, through said second flow path inlet 122, with said main water line 150 at a point C on the main water line 150 or with a separate source of water, said second flow path outlet 123 being in fluid connection with said main water line 150 at a point D on the main water line 150, and point D being located downstream of point C in the intended flow direction of the water in said second flow path 152.

Such a second flow path 152 may be present in all embodiments where Hﬂb is introduced into the main water line 150, allowing water comprising Hﬁb to be introduced into a smaller stream first.

In one embodiment, where there also is a first flow path 151 and a point B present, point C is located on said main water line 150 at a location downstream of point B in the intended flow direction of the water in said main water line 150.

This setup also allows the water to be treated to react with ozone without presence of Hﬂb in the main water line 150 for an adaptable time period to achieve water disinfection by ozonation before the Hﬁb enters and a peroxone reaction takes place. In this embodiment, the main water line 150 enters the reaction vessel in a lower part of the reaction vessel. The lower part is in one embodiment the lower 1/3, 1/4, 1/8 or 1/16 part of the reaction vessel 110. The ozone enters the main water line 150 upstream of first vessel inlet 113, either directly or through at least one separate first flow path 151 for water configured as in the embodiments described above. In one embodiment, the ozone enters a first flow path 151 through a dosing pump. In one embodiment, the ozone enters a first flow path 151 through a venturi injector. 21 The ozone thereby enters the reaction vessel 110 in a lower part of the reaction vessel 110. The first vessel outlet 111 for treated water to exit said reaction vessel 110 is located in the upper part of the reaction vessel 110. The second vessel outlet 112 for gas to exit said reaction vessel 110 is located in the upper part of said reaction vessel 110. This results in an upward flow of 03 through the reaction vessel 110.

The same characteristics apply for the second flow path 152 as for first flow path 151: the separate second flow path 152 may be a narrower flow path with a lesser water stream than the main water line 150. It may have the main water line 150 as a source of water, or have a separate source of water, and enter the main water line 150 upstream of the first vessel inlet 113. This is suitable when there is a high flow and pressure in the main water line 150. In one embodiment, the water comprising Hﬂb is introduced into the second flow path 152 using a dosing pump. In another embodiment, the Hﬂb inlet point 115 comprises a venturi injector.

The different ways of introducing 03 and Hﬂb to the reaction vessel 110 may be combined when compatible in ways that produce additional embodiments. For example, there could be multiple paths for 03 leading into the reaction vessel 110, directly or via the main water line 150. This facilitates introducing 03 at more than one location and at more than one time point when performing water purification. In one embodiment, there is more than one first flow path 151 into which 03 is injected. 22 In one embodiment, the water treatment system further comprises at least one static mixer 160 located in at least one of the main water line 150, or when present, a first flow path 151 and a second flow path 152. In one embodiment, the water treatment system further comprises at least one static mixer 160 located between the at least one Hﬂb inlet point 115 and the first vessel inlet 113. In one embodiment, the water treatment system further comprises at least one static mixer 160 located between point B and the at least one Hﬁb inlet point 115. Between, in this context, refers to a location between two points with respect to the flow or water.

In one embodiment, the water treatment system further comprises UV lamps in the reaction vessel 110.

In one embodiment, at least one of the at least one cathode and the at least one anode is a gas diffusion electrode. In one embodiment, the cathode is carbon-based. In one embodiment, the cathode is modified by catalysts. In one embodiment, the anode is comprised of carbon or metal based.

In one embodiment, the cathode is selected from the group consisting of a graphite electrode, a glassy carbon electrode, a carbon fibre electrode and a gas diffusion electrode.

In one embodiment, the cathode is a gas diffusion electrode selected from the group consisting of a carbon paper/cloth/felt-polytetrafluoroethylene electrode, activated carbon-polytetrafluoroethylene electrode, carbon black- polytetrafluoroethylene electrode, carbon nanotube- 23 polytetrafluoroethylene electrode, and graphene- polytetrafluoroethylene electrode.

In one embodiment, the cathode is shaped flat in gas diffusion electrode configuration.

In one embodiment, the at least one anode comprises at least one material selected from the group consisting of carbon cloth, BDD, Pt, Ru, and Ti/RuO2.

In one embodiment, the at least one anode is at least one selected from the group consisting of a Pt electrode, a boron- doped diamond electrode, a Pt/C electrode, a titanium rhodium- plated electrode, a titanium platinized electrode, a titanium based ruthenium dioxide electrode, a stainless steel electrode, a nickel electrode and an alloy electrode containing two or more transition metals, an aluminum alloy electrode, a titanium alloy electrode, a copper alloy electrode, a zinc alloy electrode, a carbon paper- polytetrafluoroethylene, a carbon cloth and a carbon black- polytetrafluoroethylene electrode.

In one embodiment, the solid-state electrolyte comprises an ion exchange membrane. In one embodiment, it is coated with a catalyst.

According to a second aspect, there is provided a method for purification of water, the method comprising the steps of: 24 - supplying clean water, oxygen and electricity to at least one electrochemical cell 130, said at least one electro- chemical cell 130 comprising at least one cathode, at least one anode and a solid-state electrolyte, whereby Hﬂb is generated electrochemically when oxygen undergoes an oxygen reduction reaction on the surface of the cathode, - supplying water comprising Hﬂb from said electrochemical cell 130 into a reaction vessel 110, - supplying water to be treated into the reaction vessel 110 through a water main line 150 which enters the reaction vessel 110 through a first vessel inlet 113, - introducing O3 into a lower part of said reaction vessel 110, - releasing gas from said reaction vessel 110, and - releasing treated water from said reaction vessel 110.

An advantage of supplying clean water, oxygen and electricity to at least one electrochemical cell 130, is the resulting Hﬂb generation which takes place separate from the reaction vessel 110 where an electro-peroxone reaction takes place. This gives an improved ability to provide availability of oxygen to the at least one cathode and thereby use of high current densities using small size electrodes.

Another advantage of the method is that Hﬂb generation takes place using clean water, thereby avoiding formation of potential toxic by-products which usually form during electrochemical processes when using Wastewater as a source.

By using a solid-state electrolyte in the method, handling of liquid electrolytes is avoided.

The flow velocity of the water entering the reaction vessel llO is adapter to provide sufficient treatment time in the reaction vessel llO for reaction between O3 and H2O2.

In one embodiment, the water comprising Hﬂb is supplied into the reaction vessel llO by being introduced into the main water line 150 in which the water to be treated flows.

In one embodiment, the water comprising Hﬂb is supplied into the reaction vessel llO by being introduced into the reaction vessel llO separately from the main water line 150 in which the water to be treated flows.

In all embodiments, the step of introducing O3 into the reaction vessel llO is performed such that O3 and Hﬁb is at some point present in the reaction vessel llO at the same time. In one embodiment, the step of introducing O3 occurs at least in part simultaneously as introducing the water comprising H2O¿ In one embodiment, the step of introducing O3 into the reaction vessel llO commences prior to introducing the water comprising Hﬁb. It may vary from a few seconds to a few minutes. In one embodiment, O3 is introduced at more than one time point and/or through more than one inlet.

In one embodiment, the method further comprises: water to be treated comprising Hﬂb entering said reaction vessel llO in an upper part of said reaction vessel llO, and treated water exiting through the first vessel outlet lll located in a lower part of said reaction vessel llO, such that 26 a downward flow of water occurs within said reaction vessel 110, and introducing O3 into a lower part of said reaction vessel 110, such an upward flow of O3occurs within said reaction vessel 110.

The upward flow of the 03 and the simultaneous downward flow of the water comprising Hﬂb results in Hﬂb reacting with dissolved 03 to produce the desired °OH.

In one embodiment, the step of introducing 03 into said reaction vessel 110 comprises introducing 03 to said reaction vessel 110 through at least one diffuser 114 located in a lower part of said reaction vessel 110.

In one embodiment, the method comprises: introducing O3 into at least one first flow path 151 for water through at least one injection site 140, optionally through a venturi injector, and water with 03 entering from said at least one first flow path 151 into said reaction vessel 110 through at least one first flow path outlet 119 located in a lower part of said reaction vessel 110.

In one embodiment, the method comprises: introducing O3 into at least one first flow path 151 for water through at least one injection site 140, optionally through a venturi injector, 27 water entering said at least one first flow path 151 through at least one first flow path inlet 116 and exiting through at least one first flow path outlet 119, said first flow path inlet 116 being located such that water to be treated enters the at least one first flow path 151 from a point A on the main water line 150 or from a separate source of water, said at least one first flow path outlet 119 being located such that water exits from the at least one first flow path 151 and enters the main water line 150 at a point B, point B being located downstream of point A and upstream of first vessel inlet 113 in the intended flow direction of the water, said first vessel inlet 113 being located in the lower part of said reaction vessel 110, and said first vessel outlet 111 being located in the upper part of said reaction vessel 110.

In one embodiment, 03 is introduced to the water to be treated at a time point 0-5 minutes before being mixed with water comprising Hﬂb. In one embodiment, 03 is introduced into the water to be treated at at least one more time point after this first mixing of water comprising 03 and with water comprising H2O2.

In one embodiment, 03 is introduced to the water to be treated both through diffusers 114 located in a lower part of the reaction vessel 110 and through the water main line 150, optionally through a venturi injector. 28 In one embodiment, the content of the at least one first flow path 151 is mixed before entering said reaction vessel 110, at a location downstream and/or upstream of said at least one injection site 140.

In one embodiment of the method, the impurities to be removed from the water to be treated comprises at least one selected from the group consisting of ibuprofen, diclofenac, diazepam, iopromide, methotrexate, primidone, chloranilic acid, 2-(methylthio)-benzothiazole (MTBT), cetirizine, clindamycin, ranitidine, diclofenac, sulfamethoxazole, carbamazepine, trimethoprim, terbutaline, erythromycin, naproxen, norfloxacin, ciprofloxacin, clotrimazole, codeine, clarithromycin, bisoprolol, atorvastatin, flecainide, fexofenadine, tramadol, metoprolol, atenolol, mirtazapine, citalopram, methyl-benzotriazole, miconazole, propiconazole, metronidazole, ketoconazole, bupropion, 1H-benzotriazole, pentamidine, loratadine, irbesartan, oxazepam, fluconazole, and other pharmaceuticals, quaternary ammonium compounds, 2- methylisoborneol, geosminbenzoic acids, clofibric acid, oxalic acid,1,4-dioxane, bezafibrate, phthalates, petroleum products, polycyclic aromatic hydrocarbon , polychlorinated biphenyls , dyes, hydrocarbons, tolune, pesticides, surfactants, biocides, solvents, tetrachloroethylene, tricholoroethylene, benzene, phenols, xylene, ethyl benzene, pathogens.

There are many other examples of impurities which could be removed using this method, such as those mentioned in the articles (Huijiao Wanga, Majid Mustafa, Gang Yu, Marcus Östman, Yi Chenga, Yujue Wang, Mats Tysklind. Oxidation of emerging biocides and antibiotics in Wastewater by ozonation and the electro-peroxone process. Chemospere, Volume 235, 29 November 2019) and (Jerker Fick, Richard H. Lindberg, Mats Tysklind, D.G. Joakim Larsson. Predicted critical environmental concentrations for 500 pharmaceuticals. Regulatory Toxicology and Pharmacology 58 (2010) 516-523). The articles are incorporated herein in their entirety by reference.

In one embodiment of the method, the water to be treated is at least one selected from sewage after secondary treatment, industrial Wastewater, car wash Wastewater, groundwater, surface water, and drinking water.

In one embodiment of the method, drinking water is produced.

In one embodiment of the method, the water in the reaction vessel 110 is UV treated.

The system is suitable to be used to perform the method described herein.

Claims

l. A water treatment system for purification of water, said system comprising: a. a reaction vessel (llO) comprising - a first vessel inlet (ll3) for water to be treated to enter said reaction vessel (llO), - a first vessel outlet (lll) for treated water to exit said reaction vessel (llO), - a second vessel outlet (ll2) for gas to exit said reaction vessel (llO), said second outlet (ll2) being located in an upper part of said reaction vessel (llO), and - a second vessel inlet (l2l) for supplying O3 to the reaction vessel (llO), said second inlet (l2l) being located in a lower part of said reaction vessel (llO), b. a main water line (l50) leading from a main inlet ll8 for water to be treated to said first vessel inlet (ll3), and c. an electrochemical cell (l30) for Hﬂb generation comprising at least one cathode, at least one anode and a solid-state electrolyte, said electrochemical cell (l30) having an oxygen inlet l3l and a clean water inlet (l32), said electrochemical cell (l30) being adapted to be connected with a source of electricity (l33), and said electrochemical cell having an outlet enabling said electrochemical cell (l30) to be in fluid connection with said reaction vessel (llO) through at least one Hﬁb inlet point (ll5).
2. The water treatment system according to claim 1, wherein said system further comprises a source (120) of O3 for providing O3to the system, the source (120) being in fluid connection with the reaction vessel (110) at least via said second vessel inlet (121).
3. The water treatment system according to any of claims 1-2, wherein said second vessel inlet (121) is in fluid connection with said reaction vessel (110) through at least one diffuser (114), said at least one diffuser (114) being located in a lower part of the reaction vessel (110).
4. The water treatment system according to any of claims 1-3, further comprising at least one injection site (140) for injecting O3 into at least one first flow path (151) for water, said at least one first flow path (151) being in fluid connection with the reaction vessel (110) and having at least one first flow path inlet (116 ) upstream of said at least one injection site (140) and at least one first flow path outlet (119) downstream of said at least one injection site, said at least one injection site (140) optionally comprising a venturi injector.
5. The water treatment system according to claim 4, wherein the cross-sectional area of the narrowest passage of the at least one first flow path (151) is smaller than the cross-sectional area of the narrowest passage of main water line (150).
6. The water treatment system according to any of claims 4-5, said at least one first flow path outlet (119)being located in a lower part of said reaction vessel (110), and said first vessel inlet (113) being located in an upper part of the reaction vessel (110), said first vessel outlet (111) being located in a lower part of the reaction vessel (110), and said Hﬂb inlet point (115) being located at a point on the main water line (150) or at an upper part of the reaction vessel (110).
7. The water treatment system according to any of claims 3-5, said at least one first flow path (151) being in fluid connection, through said first flow path inlet (116 ), either with said main water line (150) at a point A on the main water line (150) or with a separate source of water, said at least one first flow path outlet (119) being in fluid connection with said main water line (150) at a point B on the main water line (150), point B being located downstream of point A in the intended flow direction of the water in said at least one first flow path (151), said first vessel inlet (113) being located in the lower part of said reaction vessel (110), and said first vessel outlet (111) being located in the upper part of said reaction vessel (110).
8. The water treatment system according to any of claims 1-7 further comprising a second flow path (152) for water,said Hﬂb inlet point (115) being located at a point on said second flow path (152), said second flow path (152) having a second flow path inlet (122) upstream of said Hﬁb inlet point (115) and a second flow path outlet (123) downstream of said Hﬂb inlet point (115), said Hﬁb inlet point (115) optionally comprising a venturi injector, said second flow path (152) being in fluid connection, through said second flow path inlet (122), with said main water line (150) at a point C on the main water line (150) or with a separate source of water, said second flow path outlet (123) being in fluid connection with said main water line (150) at a point D on the main water line (150), and point D being located downstream of point C in the intended flow direction of the water in said second flow path (152).
9. The water treatment system according to claim 8 and 7, point C being located downstream of point B in the intended flow direction of the water in said main water line (150).
10. The water treatment system according to any of claims 1-9, further comprising at least one static mixer (160) located in at least one of: the main water line (150), a first flow path (151) and a second flow path (152).
11. The water treatment system according to any of claims 1-19, wherein at least one static mixer (160) islocated between the at least one Hﬁb inlet point (115) and the first vessel inlet (113).
12. The water treatment system according to any of claim 7-11 wherein at least one static mixer (160) is located between point B and the at least one Hﬁb inlet point (115).
13. The water treatment system according to any of claim 1-12, further comprising UV lamps in the reaction vessel (110).
14. The water treatment system according to any of claims 1-13, wherein at least one of the at least one cathode and the at least one anode is a gas diffusion electrode.
15. The water treatment system according to any of claims 1-14, wherein the cathode is selected from the group consisting of a graphite electrode, a glassy carbon electrode, a carbon fiber electrode and a gas diffusion electrode.
16. The water treatment system according to any of claims 1-15, wherein the cathode is a gas diffusion electrode selected from the group consisting of a carbon paper/cloth/felt-polytetrafluoroethylene electrode, activated carbon-polytetrafluoroethylene electrode, carbon black- polytetrafluoroethylene electrode, carbon nanotube- polytetrafluoroethylene electrode, and graphene- polytetrafluoroethylene electrode.
17. The water treatment system according to any of claims 1-16, wherein the cathode is shaped flat in gas diffusion electrode configuration.
18. The water treatment system according to any of claims 1-17, wherein the at least one anode comprises at least one material selected from the group consisting of carbon cloth, BDD, Pt, Ru, and Ti/RuO
19. A method for purification of water, the method comprising the steps of: - supplying clean water, oxygen and electricity to at least one electrochemical cell (130), said at least one electro- chemical cell (130) comprising at least one cathode, at least one anode and a solid-state electrolyte, whereby Hﬂb is generated in situ electrochemically when oxygen undergoes an oxygen reduction reaction on the surface of the cathode, - supplying water comprising Hﬂb from said electrochemical cell (130) into a reaction vessel (110), - supplying water to be treated into the reaction vessel (110) through a water main line (150) which enters the reaction vessel (110) through a first vessel inlet (113), - introducing O3 into a lower part of said reaction vessel (110), - releasing gas from said reaction vessel (110), and - releasing treated water from said reaction vessel (110).
20. The method for purification of water according to claim, 19, wherein the water comprising Hﬁb is supplied intothe reaction vessel (110) by being introduced into the main water line (150) in which the water to be treated flows.
21. The method for purification of water according to any of claims 19-20, wherein the water comprising Hﬂb is supplied into the reaction vessel (110) by being introduced into the reaction vessel (110) separately from the main water line (150) in which the water to be treated flows.
22. The method for purification of water according to any of claims 19-21, the method further comprising: - water to be treated comprising Hﬂb entering said reaction vessel (110) in an upper part of said reaction vessel (110), and - treated water exiting through the first vessel outlet (111) located in a lower part of said reaction vessel (110), such that a downward flow of water occurs within said reaction vessel (110), and - introducing 03 into a lower part of said reaction vessel (110), such an upward flow of 03occurs within said reaction vessel (110).
23. The method for purification of water according to any of claims 19-22, wherein the step of introducing 03 into said reaction vessel (110) comprises introducing 03 to said reaction vessel (110) through at least one diffuser (114) located in a lower part of said reaction vessel (110).
24. The method for purification of water according to any of claims 19-22, the method comprising:- introducing O3 into a first flow path (151) for water through at least one injection site (140), optionally through a venturi injector, and - water with O3 entering from said first flow path (151) into said reaction vessel (110) through at least one first flow path outlet (119) located in a lower part of said reaction vessel (110).
25. The method for purification of water according to any of claims 19-23, the method comprising: - introducing O3 into a first flow path (151) for water through at least one injection site (140), optionally through a venturi injector, - water entering said first flow path (151) through at least one first flow path inlet (116 ) and exiting through at least one first flow path outlet (119), said first flow path inlet (116 ) being located such that water to be treated enters the first flow path (151) from at a point A on the main water line (150) or from a separate source of water, said at least one first flow path outlet (119) being located such that water exits from the first flow path (151) and enters the main water line (150) at a point B, point B being located downstream of point A and upstream of first vessel inlet (113) in the intended flow direction of water, said first vessel inlet (113) being located in the lower part of said reaction vessel (110), and said first vessel outlet (111) being located in the upper part of said reaction vessel (110).26. The method for purification of water according to any of claims 19-21 and 23-25, when not dependent on claim 22, wherein 03 is introduced to the water to be treated at a time point 0-5 minutes before being mixed with water comprising
H2O
27. The method according to any of claims 19-26, wherein the content of main water line (150) is mixed before entering said reaction vessel (110), at a location downstream and/or upstream of said at least one injection site (140).
28. The method according to any of claims 24-27, wherein the content of first flow path (151) is mixed before entering said reaction vessel (110), at a location downstream and/or upstream of said at least one injection site (140).
29. The method according to any one of claims 19-28, wherein the impurities comprise at least one selected from the group consisting of ibuprofen, diclofenac, diazepam, iopromide, methotrexate, primidone, chloranilic acid, 2-(methylthio)-benzothiazole (MTBT), cetirizine, clindamycin, ranitidine, diclofenac, sulfamethoxazole, carbamazepine, trimethoprim, terbutaline, erythromycin, naproxen, norfloxacin, ciprofloxacin, clotrimazole, codeine, clarithromycin, bisoprolol, atorvastatin, flecainide, fexofenadine, tramadol, metoprolol, atenolol, mirtazapine, citalopram, methyl-benzotriazole, miconazole, propiconazole, metronidazole, ketoconazole, bupropion, 1H-benzotriazole, pentamidine, loratadine, irbesartan, oxazepam, fluconazole, and other pharmaceuticals, quaternary ammonium compounds, 2- methylisoborneol, geosminbenzoic acids, clofibric acid, oxalic acid,1,4-dioxane, bezafibrate, phthalates, petroleum products,polycyclic aromatic hydrocarbon, polychlorinated biphenyls, dyes, hydrocarbons, tolune, pesticides, surfactants, biocides, solvents, tetrachloroethylene, tricholoroethylene, benzene, phenols, xylene, ethyl benzene, pathogens.
30. The method according to any one of claims 19-29, wherein the water to be treated is at least one selected from sewage after secondary treatment, industrial Wastewater, car wash Wastewater, groundwater, surface water, and drinking water.
31. The method according to any one of claims 19-30, wherein drinking water is produced.
32. The method for purification of water according to any of claims 19-31, wherein the method is performed using a system according to any one of claims 1-
33. The method for purification of water according to any of claims 19-32, wherein the water in the reaction vessel (110) is UV treated.