WO2025088011A1

WO2025088011A1 - Water treatment method with regeneration of activated carbon particles by uv light

Info

Publication number: WO2025088011A1
Application number: PCT/EP2024/080026
Authority: WO
Inventors: Maria Concepcion OVIN ANIA; Carlos Macias GALLEGO
Original assignee: Cm Biolab 2020 SL; Centre National de la Recherche Scientifique CNRS
Current assignee: Cm Biolab 2020 SL; Centre National de la Recherche Scientifique CNRS
Priority date: 2023-10-27
Filing date: 2024-10-24
Publication date: 2025-05-01
Anticipated expiration: 2026-04-27

Abstract

The invention relates to a water treatment method, said water (84) containing organic pollutants, the method including : - a step of adsorption of the organic pollutants on activated carbon particles (82); then - a step of regeneration of the activated carbon particles (82) by degrading the adsorbed organic pollutants. The step of regeneration of the activated carbon particles (82) includes exposing the activated carbon particles to UV light.

Description

Water treatment method with regeneration of activated carbon particles by UV light

The present invention relates to a water treatment method, said water containing organic pollutants, the method including : a step of adsorption of the organic pollutants on activated carbon particles ; then a step of regeneration of the activated carbon particles by degrading the adsorbed organic pollutants.

Depollution of water by using adsorption on activated carbon particles is a known method, disclosed for example in document EP3153475.

Currently, the regeneration of the activated carbon particles, after saturation with organic pollutant, involves heat treatments at very high temperatures. The transport of the saturated carbon particles from a water treatment plant to a regeneration site is timeconsuming and increases the costs of the water treatment methods by carbon adsorption. The cost of regenerating saturated carbon is also high, making it unfeasible and uneconomical for small water circuits.

For example, the document US 5,087,374 relates to a method of regenerating activated carbon adsorbent containing organic pollutants by exposing the activated carbon particles to high power ultrasounds (1 to 100 kHz) in the presence of a surface active agent (which concentration is 20 to 250 ppm). The sonication induces the desorption of the organic compounds from the activated carbon, and then in a second step, ozone is used to destroy these compounds. The UV irradiation is also applied to the water containing the desorbed compounds.

The document WO 95/21794 relates to a single process for the adsorption and degradation of the organic pollutants on activated carbon. The degradation is induced by the reaction of UV light with ozone and hydrogen peroxide (H2O2) to form radical species. The document WO 95/21794 also includes the use of a solid photocatalyst impregnated in the activated carbon particles.

The document ON 207 091 047 relates to the regeneration of activated carbon using hydrogen peroxide (5% concentration) and UV (combined) to decompose the organic matter. As in the case of the document WO 95/21794, radicals are formed by the reaction of UV with H2O2.

On the purpose of overcoming such issues, the invention relates to a water treatment method of the aforementioned type, wherein the step of regeneration of the activated carbon particles is carried out in one single step which includes or consists of exposing the activated carbon particles to UV light, without the need of further ultrasounds, ozone, H2O2, photocatalyst impregnated in the activated carbon particles or any other reactive, as seen in prior art methods. The step of regeneration of the method of the present invention uses the activated carbon particles as photocatalysts themselves to induce self- regeneration due to the fact that they produce radical species that react and decompose the organic molecules retained inside the porosity of the activated carbon particles.

According to the invention, the regeneration of the activated carbon particles may be carried out entirely on-site, namely the adsorption of pollutants on the activated carbon and the regeneration of those activated carbon particles can be carried out in the same installation. This means that the carbon particles can be regenerated without having to be collected and transported elsewhere. The regeneration of the activated carbon particles onsite according to the invention avoids costs to regeneration facilities.

According to preferred embodiments, the water treatment method may include one or more of the following features, considered alone or in any technically possible combination:

- the step of regeneration of the activated carbon particles includes or consists of exposing a water dispersion of the activated carbon particles to at least one UV lamp providing the UV light ;

- during the exposure of the water dispersion to the UV lamp, said UV lamp is at least partially immersed in the water dispersion ;

- during the exposure of the water dispersion to the UV lamp, a gas flux containing oxygen (e.g. air) is provided in the water dispersion ;

- during the exposure of the water dispersion to the UV lamp, a temperature of the water dispersion is comprised between 10°C to 50 °C and preferably comprised between 25 and 30°C ;

- a wavelength of the UV light is comprised between 200 nm and 400 nm, the wavelength of the UV light being preferably of 254 nm ;

- the activated carbon particles (82) are activated carbon granulates ;

- a granulometry of the activated carbon granulates is comprised between 1000 pm and 3000 pm ;

- the water containing the organic pollutants has a salinity superior to 10 mS/cm and preferably comprised between 10 mS/cm and 50 mS/cm ;

- the step of exposing the activated carbon particles to UV light is carried out during a time comprised between 1 h and 120h ;

- the step of adsorption of the organic pollutants on activated carbon particles and the step of regeneration the activated carbon particles are carried out in a same installation.

The invention also relates to an installation for carrying out a water treatment method as described above, the installation comprising a first reactor, the first reactor comprising : a first container defining a first inner space ; a UV-light device able to provide UV light in the inner space ; a first water inlet ; a first water outlet ; a gas inlet ; and a gas outlet. According to preferred embodiments, the installation may include one or more of the following features, considered alone or in any technically possible combination:

- the installation also comprises a second reactor, the second reactor comprising : a second container defining a second inner space ; a second water inlet ; and a second water outlet ;

- the installation also comprises a connecting pipe, connecting the second water outlet to the first water inlet ;

- the first reactor and the second reactor operate in tandem or independently of one another ;

- the installation is modular, portable and can be coupled with other exchangeable technologies.

The invention will be easier to understand in view of the following description, provided solely as an example, and with reference to the appended drawings, wherein :

- Figure 1 is a schematic view of an installation according to an embodiment of the invention;

- Figure 2 is a schematic representation of a water treatment method according to an embodiment of the invention, carried out by means of the installation of Figure 1 ;

- Figure 3 shows the Specific Surface Area (SBET in m²/g) of a series of activated carbon with increasing saturation degree (AC1 , AC2, AC3, respectively) after regeneration during 8 hours (a) and 12 hours (b) of exposure to UV light. Conditions: 0.250 g/L solids in water; UV 254 nm; and

- Figure 4 shows the recovery of Specific Surface Area (0/1) of a series of activated carbon with increasing saturation degree (AC1 , AC2, AC3, respectively) after regeneration during 8 hours (a) and 12 hours (b) of exposure to UV light. The dotted line is a guide for the eye to indicate the specific surface area of the corresponding saturated activated carbon (before regeneration). Conditions: 0.250 g/L solids in water; UV 254 nm.

Figure 1 shows an installation 10 according to an embodiment of the invention.

The installation 10 comprises a first reactor 12. In the embodiment of Figure 1 , the installation 10 also comprises a second reactor 14 and a water piping system 16.

The first reactor 12 comprises: a first container 20; a UV-light device 22; a first water inlet 24; a first water outlet 26; a gas inlet 28; and a gas outlet 30. Preferably, the first reactor 12 also comprises a manometer 31 .

The first container 20 comprises a first wall 32 defining a closed, first inner space 34. In the embodiment of Figure 1 , the first wall 32 comprises: a top wall 36; a bottom wall 38; and a lateral wall 40, joining the top 36 and bottom 38 walls. In the following description, it is considered that the top wall 36 and the bottom wall 38 are disposed substantially horizontally; and that the lateral wall 40 extends substantially vertically.

Preferably, an inner surface of the first wall 32 is designed for being in contact with salty water, such as sea water. In particular, the inner surface of the first wall 32 is preferably treated against corrosion.

The UV-light device 22 comprises at least one UV lamp 42 extending in the first inner space 34 of the first container 20. Preferably, the UV lamp 42 has an elongated shape and extends substantially vertically from the top wall 36. More preferably, a vertical length of the UV lamp 42 represents more than 50% of a vertical length of the first inner space 34.

In the embodiment of Figure 1 , the UV-light device 22 comprises several UV lamps 42, substantially identical to each other, extending in the first inner space 34 from the top wall 36.

The first water inlet 24 opens in the first inner space 34. Preferably, the first water inlet is situated on the top wall 36 or on an upper part of the lateral wall 40.

In the embodiment of Figure 1 , the first reactor 12 also comprises a first water nozzle 44, disposed in the first inner space 34 and connected to the first water inlet 24.

The first water outlet 26 opens in the first inner space 34. Preferably, the first water outlet 26 is situated on the bottom wall 38 or on a lower part of the lateral wall 40.

The gas inlet 28 opens in the first inner space 34. Preferably, the gas inlet 28 is situated on the bottom wall 38. In the embodiment of Figure 1 , the gas inlet 28 comprises a plurality of gas nozzles 46, situated on the bottom wall 38.

In the installation 10, the gas inlet 28 is preferably connected to a compressed air source (not shown).

The gas outlet 30 opens in the first inner space 34. In the embodiment of Figure 1 , the gas outlet 30 comprises a venting valve disposed on the top wall 36.

The second reactor 14 comprises: a second container 50; a second water inlet 54; and a second water outlet 56.

The second container 50 comprises a second wall 58 defining a closed, second inner space 60.

The second water inlet 54 opens in the second inner space 60. Preferably, the second water inlet 54 is situated on an upper part of the second wall 58.

In the embodiment of Figure 1 , the second reactor 14 also comprises a second water nozzle 62, disposed in the second inner space 60 and connected to the second water inlet 54.

The second water outlet 56 opens in the second inner space 60. Preferably, the second water outlet 56 is situated on a lower part of the second wall 58. The water piping system 16 comprises pipes connected to the first water inlet 24 and outlet 26 and to the second water inlet 54 and outlet 56. In the embodiment of Figure

1 , the water piping system 16 comprises a connecting pipe 64 connecting the second water outlet 56 to the first water inlet 24.

A water treatment method 100 according to a first embodiment of the invention will now be described. The water treatment method 100 is schematically represented on Figure

2.

The water treatment method 100 comprises an adsorption step 102 and a regeneration step 104.

The adsorption step 102 will now be described.

In a first sub-step 106 of the adsorption step, a bed 80 of activated carbon particles 82 is formed in the second inner space 60 of the second reactor 14.

Preferably, the activated carbon particles are activated carbon granulates. More preferably, a granulometry of the activated carbon granulates is comprised between 1000 pm and 3000 pm. Alternatively, the activated carbon particles are activated carbon powder.

In a second sub-step 108 of the adsorption step, a flux of polluted water 84 is sent to the second inner space 60 through the second water nozzle 62. The polluted water 84, intended to be treated, contains organic pollutants.

In an embodiment, the polluted water 84 has a salinity superior to 10 mS/cm and preferably comprised between 10 mS/cm and 50 mS/cm. For example, the polluted water 84 is sea water.

The polluted water 84 passes through the bed 80 due to a driving force. In the disclosed embodiment, the driving force comprises a pressure gradient, provided for example by a pump. In another embodiment, the driving force is gravity.

As the polluted water 84 passes through the bed, the organic pollutants are adsorbed on the activated carbon particles 82. A flux 86 of carbon-treated water is recovered at the bottom of the second reactor 14.

In an optional third sub-step 110 of the adsorption step, a first part 88 of the flux 86 is directed to another treatment unit (not shown), for example a nanofiltration unit, for further treatment of the carbon-treated water.

The second sub-step 108 of the adsorption step 102 may be carried out until the activated carbon particles 82 of the bed 80 are saturated with organic pollutants coming from the polluted water 84.

The regeneration step 104 will now be described.

In a first sub-step 112 of the regeneration step, the activated carbon particles 82 of the bed 80, partially or completely saturated with organic pollutants, are transferred to the first container 20 of the first reactor 12. In a second sub-step 114 of the regeneration step, a water dispersion 90 of the activated carbon particles 82 is formed in the first inner space 34, by sending a water flux to the first water inlet 24. In an embodiment, the water dispersion 90 is formed by sending a second part 92 of the flux 86 of carbon-treated water to the first water inlet 24, through the connecting pipe 64.

Preferably, the water dispersion 90 of the activated carbon particles 82 is formed so that at least a part of the UV lamps 42 is immersed in the water.

In a third sub-step 116 of the regeneration step, the water dispersion 90 of the activated carbon particles 82 is exposed to UV light from the UV lamps 42. Preferably, a wavelength of the UV light is comprised between 200 nm and 400 nm, the wavelength of the UV light being preferably of 254 nm.

Simultaneously, a gas flux containing oxygen, preferably an air flux, is sent into the first inner space 34 through the gas inlet 28.

The UV illumination of the activated carbon particles 82 dispersed in water promotes the photocatalytic degradation of the organic pollutants adsorbed inside said carbon particles in the water dispersion 90. The activated carbon particles 82 are thus regenerated.

In the case wherein carbon-treated water from the adsorption step 102 is used for forming the water dispersion 90, the third sub-step 116 also allows organic pollutants, remaining in the carbon-treated water, to be degraded by the UV light.

In the case the pollutants are desorbed from the carbon particles 82 to the water during the regeneration sub-step 116, they are degraded by the UV light.

The photocatalytic degradation consumes some of the oxygen of the gas flux. Meanwhile, said gas flux generates a stirring of the water dispersion 90, accelerating the photocatalytic degradation.

Preferably, during the third sub-step 116, a temperature of the water dispersion is comprised between 10°C and 50 °C and preferably comprised between 25°C and 30°C.

Preferably, the third sub-step 116 of the regeneration step 104 is carried out during a time comprised between 1 h and 120 h of irradiation, and preferably below 8 h.

In a fourth sub-step 118 of the regeneration step, a flux 94 of UV-treated water is recovered at the first water outlet 26. Optionally, said flux 94 of UV-treated water is directed to another treatment unit (not shown), for example a nanofiltration unit, for further treatment.

In a fifth sub-step 120 of the regeneration step, the regenerated activated carbon particles 82 are reintroduced in the second reactor 14 so as to re-form the bed 80. Said bed is thus regenerated for another adsorption step 102.

A water treatment method (not shown) according to a second embodiment of the invention will now be described. According to the second embodiment, the water treatment method comprises an adsorption step similar to the adsorption step 102 described above, but carried out in the first reactor 12.

In other terms, the bed 80 of activated carbon particles 82 is formed in the first reactor 12 and the flux of polluted water 84 is sent to the first inner space 34 through the first water nozzle 44. The flux 86 of carbon-treated water is recovered at the first water outlet 26.

According to the second embodiment, the water treatment method further comprises a regeneration step wherein the bed 80 of activated carbon particles 82 is expanded by means of the gas flux sent into the first inner space 34 through the gas inlet 28. Simultaneously, water from the flux 86 is re-introduced in the first reactor 12 by the first water inlet 24, for forming the water dispersion 90 of activated carbon particles 82.

Alternatively, the water from the flux 86 is re-introduced in the first reactor 12 by a third water inlet (not shown), situated on the bottom wall 38.

The remaining sub-steps of the regeneration step of the second embodiment are similar with the regeneration step 104 described above.

The water treatment method according to the second embodiment avoids the handling of the activated carbon particles 82 between the first 12 and second 14 reactors.

The water treatment method according to the invention involves a simple and non- expensive installation, easy to settle near a place of water extraction. The invention thus improves the efficiency of water treatment methods involving carbon adsorption. The invention is also compatible with the treatment of salty waters.

For saturation assays, granular activated carbon (3 mm) was introduced in a stainless steel column (total mass 5 g) and saturated by flowing an aqueous solution with an initial concentration of 5 mg of organic carbon per liter. The solution was composed of a mixture of organic aromatic pollutants (phenol and acetaminophen) and diluted for reaching an initial concentration of the mixture of 5 ppm C (parts per million of organic carbon, determined by Total Organic Carbon). The solution was passed through the column (flow rate 2 ml/min) until saturation of the activated carbon at three increasing stages: samples AC1 (3 hours), AC2 (5 hours), AC (7 hours).

For regeneration assays, the saturated granular activated carbon was introduced in a 500 mL reactor filled with distilled water (total solids loading 0.25 g/L). An air flow was continuously fed to the dispersion. A 254 nm lamp (provided with a pyrex jacket to prevent heating of the dispersion) was vertically introduced in the reactor and the dispersion was exposed to UV light for 8 hours (test a) and 12 hours (test b). After the irradiation, the granular activated carbon was filtered and dried at 60°C for 12 hours for further characterization. For characterization, to evaluate the efficiency of the UV-assisted regeneration, the porosity of the initial saturated carbon and the regenerated carbons in the different conditions were characterized by nitrogen adsorption at 77 K (standard method recommended by IIIPAC). For this, about 200 mg of the samples were outgassed under vacuum at 373 K for 12 hours, and the nitrogen adsorption isotherms were measured in a volumetric instrument. From the gas adsorption isotherm the specific surface area was estimated using the BET equation.

Figure 3 and table 1 below show that the Specific Surface Area (SSA) increased significantly after the UV exposure to 8 h. This is also seen in Figure 4 and table 2 below where the recovery of SSA is shown normalized versus the saturated sample. The recovery of SSA was lower for AC3 due to its higher saturation degree (i.e., lower SSA in the saturated sample), but the extension of the UV exposure time from 8 h to 12 h increased the recovery of the SSA (thus, increased the regeneration extent) as seen in the higher SSA values (Figure 3, table 1) and the higher recovery factors (Figure 4, table 2).

Table 1

Figure 4 shows that the increase in the specific surface area (SSA) of the carbons after UV exposure confirms the regeneration of those carbons. The porosity of the saturated carbon is measured using a method well known to the skilled person to evaluate the state of the carbon before and after the regeneration process is applied (in this case expressed as specific surface area determined by gas adsorption). It is used to verify that the carbon has been indeed regenerated, since the porosity is increasing when the UV is applied (compared to the initial saturated state). Indeed in the present case the porosity of the carbons was partially blocked in the saturated carbon due to the adsorption of the pollutants (surface areas of 515, 462 and 435 m²/g). Tables 1 and 2 show that the porosity is recovered after the UV exposure according to the present invention (surface areas of 893, 650/815 and 915/890 m²/g after UV exposure of 8 h/12 h (table 1) ; corresponding to surface area recoveries after regeneration between 1.41 and 2.1 (table 2)).

Table 2

Claims

1 Water (84) treatment method (100), said water (84) containing organic pollutants, the method including :

- a step (102) of adsorption of the organic pollutants on activated carbon particles (82) ; then

- a step (104) of regeneration of the activated carbon particles (82) by degrading the adsorbed organic pollutants ; the method being characterized in that the step (104) of regeneration of the activated carbon particles (82) includes exposing the activated carbon particles to UV light.

2.- Water treatment method according to claim 1 , wherein the step (104) of regeneration of the activated carbon particles includes exposing a water dispersion (90) of the activated carbon particles (82) to at least one UV lamp (42) providing the UV light.

3.- Water treatment method according to claim 2, wherein, during the exposure of the water dispersion to the UV lamp, said UV lamp (42) is at least partially immersed in the water dispersion.

4.- Water treatment method according to claim 2 or 3, wherein, during the exposure of the water dispersion (90) to the UV lamp (42), a gas flux containing oxygen is provided in the water dispersion.

5.- Water treatment method according to any one of claims 2 to 4, wherein, during the exposure of the water dispersion (90) to the UV lamp (42), a temperature of the water dispersion is comprised between 10°C to 50 °C and preferably comprised between 25 and 30°C.

6.- Water treatment method according to any one of the previous claims, wherein a wavelength of the UV light is comprised between 200 nm and 400 nm, the wavelength of the UV light being preferably of 254 nm.

7.- Water treatment method according to any one of the previous claims, wherein the activated carbon particles (82) are activated carbon granulates.

8.- Water treatment method according to claim 6, wherein a granulometry of the activated carbon granulates is comprised between 1000 pm and 3000 pm.

9.- Water treatment method according to any one of the previous claims, wherein the water (84) containing the organic pollutants has a salinity superior to 10 mS/cm and preferably comprised between 10 mS/cm and 50 mS/cm.

10.- Water treatment method according to any one of the previous claims, wherein the step (104) of exposing the activated carbon particles to UV light is carried out during a time comprised between 1h and 120h.

11.- Water treatment method according to any one of the previous claims, wherein the step (102) of adsorption of the organic pollutants on activated carbon particles and the step (104) of regeneration the activated carbon particles (82) are carried out in a same installation.

12.- Installation (10) for carrying out a water treatment method (100) according to any one of the previous claims, the installation comprising a first reactor (12), the first reactor comprising : a first container (20) defining a first inner space (34) ; a UV-light device (22) able to provide UV light in the inner space ; a first water inlet (24) ; a first water outlet (26) ; a gas inlet (28) ; and a gas outlet (30).

13.- Installation according to claim 12, also comprising a second reactor (14), the second reactor comprising : a second container (50) defining a second inner space (60) ; a second water inlet (54) ; and a second water outlet (56).

14.- Installation according to claim 12, also comprising a connecting pipe (64), connecting the second water outlet (56) to the first water inlet (24).