METHOD OF VISIBLE-LIGHT PHOTOCATALYSIS COMBINED WITH CLO2 OXIDATION FOR HIGHLY EFFICIENT REMOVAL OF ORGANIC POLLUTANTS IN WASTEWATER

Abstract

A method of visible-light photocatalysis combined with ClO.sub.2 oxidation for high efficient removal of organic pollutants in the wastewater, includes that i) the pH of the organic wastewater is adjusted to a constant value; the visible light photocatalysts are added to wastewater with full stirring to reach the adsorption equilibrium; (ii) turning on the Xenon lamp and adjust the distance between the light source and the liquid surface; chlorite is added to the system to reach a concentration and the reaction remained at a constant temperature with adequate stirring to achieve the degradation of organic pollutants.

Claims

1. A method of visible-light photocatalysis combined with ClO.sub.2 oxidation for high efficient removal of organic pollutants in wastewater comprising the following steps: i) adjusting the pH of the wastewater to a constant value; ii) adding the visible light photocatalysts to the wastewater which is stirred in dark for 60 min until adsorption reached equilibrium; iii) turning on a Xenon lamp and adjusting the distance between a light source and a liquid surface; and iv) adding a chlorine-containing salt to reach a certain concentration and keeping reaction at a constant temperature with adequate stirring to achieve the degradation of the organic pollutants.

2. The method according to claim 1, characterized in that, adjusting the pH by an acidic regulator or an alkaline regulator in pH 3-11 which is optionally pH 5-9.

3. The method according to claim 2, characterized in that, the acid regulator is selected from the group consisting of hydrochloric acid, acetic acid, or nitric acid, and the alkaline regulators are NaOH and ammonium hydroxide.

4. The method according to claim 1, characterized in that, the visible light photocatalyst is selected from the group consisting of Ag/TiO.sub.2, BiVO.sub.4, and C.sub.3N.sub.4; and is optionally BiVO.sub.4.

5. The method according to claim 1, characterized in that, the concentration of the visible light photocatalysts is 10-50 mg/L.

6. The method according to claim 1, characterized in that, the organic pollutants are one or more than two selected from the group consisting of norfloxacin, sulfadiazine, bisphenol A and imidacloprid; and the wastewater is selected from the group consisting of tap water, surface water, domestic sewage, printing & dyeing wastewater, medical wastewater, and seawater.

7. The method according to claim 1, characterized in that, the optical power density of the light source is 100-300 mW/cm.sup.2 and the distance between the light source and the surface of the wastewater is 10-50 cm.

8. The method according to claim 1, characterized in that, the chlorine-containing salt is selected from the group consisting of hypochlorites, chlorites, chlorates and perchlorates.

9. The method according to claim 1, characterized in that, the concentration of the chlorine-containing salt is 0.1-1.0 mmol/L.

10. The method according to claim 1, characterized in that, in the step iv), a stirring time is 30-60 min and the constant temperature is 25-45° C.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0035] FIG. 1 shows a schematic diagram of the double-walled reactor with an interlayer;

[0036] In FIG. 1, 1—light source, 2—sealing lid, 3—gas outlet, 4—liquid inlet, 5—sample outlet, 6—cooling water inlet, 7—gas inlet, 8—cooling water outlet, 9—wastewater, 10—catalyst.

[0037] FIG. 2 shows the comparison of the performance of visible light photocatalysis-ClO.sub.2 oxidation combined process mediated by different visible light photocatalysts in the treatment of norfloxacin organic wastewater as described in the embodiments 1-3 of the present invention.

[0038] FIG. 3 shows the performance of visible light photocatalysis-ClO.sub.2 oxidation combined process composed of different concentrations of chlorine-containing precursors in the treatment of norfloxacin organic wastewater.

[0039] FIG. 4 shows the effect of pH on the performance of visible light photocatalysis-ClO.sub.2 oxidation combined process in the treatment of norfloxacin organic wastewater as described in the embodiments 7 of the present invention.

[0040] FIG. 5 shows the effect of inorganic and organic substances on the performance of visible light photocatalysis-ClO.sub.2 oxidation combined process in the treatment of norfloxacin organic wastewater as described in the embodiments 8-12 of the present invention.

[0041] FIG. 6 shows the effect of actual water matrices on the performance of visible light photocatalysis-ClO.sub.2 oxidation combined process in the treatment of norfloxacin organic wastewater as described in the embodiments 13-18 of the present invention.

DETAILED EMBODIMENTS

[0042] The present invention is further described by the specific embodiments and figures, but the protection scope of the present invention is not limited to the following embodiments.

[0043] Unless otherwise specified, the raw materials used in the embodiment are conventional commercial products.

[0044] The double-walled reactor with an interlayer in embodiments is composed of a reactor body with a reaction cavity enclosed by an inner wall and an interlayer between the inner wall and outer wall. There are air inlet and outlet on the inner wall and the air inlet is connected to the intake pipe, which extends to the bottom of the reaction cavity. There are liquid inlet and sample outlet on the inner wall, which separately pass through the outer wall. There are cooling water inlet and outlet on the outer wall, which connect with the interlayer. There is a sealing lid at the opening of the inner wall.

Embodiment 1

[0045] The steps of a method of visible-light photocatalysis combined with ClO.sub.2 oxidation for highly efficient removal of organic pollutants in wastewater are as follows:

[0046] (1) The pH of organic wastewater containing organic contaminants was adjusted to 7. Then, 30 mg of visible light photocatalyst BiVO.sub.4 was added into the wastewater and stirred for 60 min until the adsorption equilibrium;

[0047] (2) Turn on the Xenon lamp and adjust the distance between the light source and liquid surface by 30 cm. Sodium hypochlorite, as the precursor of ClO.sub.2, was added to the system to reach a concentration of 1.0 mmol/L with a constant reaction temperature and full stirring to achieve the degradation of contaminants.

Embodiment 2

[0048] Similar to the method of visible-light photocatalysis combined with ClO.sub.2 oxidation for highly efficient removal of organic pollutants in the wastewater as described in embodiment 1, the difference is that the visible light photocatalyst was selected as Ag/TiO.sub.2 and the other information was the same as Embodiment 1.

Embodiment 3

[0049] Similar to the method of visible-light photocatalysis combined with ClO.sub.2 oxidation for highly efficient removal of organic pollutants in the wastewater as described in embodiment 1, the difference is that the visible light photocatalyst was selected as C.sub.3N.sub.4 and the other information was the same as Embodiment 1.

Embodiment 4

[0050] Similar to the method of visible-light photocatalysis combined with ClO.sub.2 oxidation for highly efficient removal of organic pollutants in the wastewater as described in embodiment 1, the difference is that the precursor of ClO.sub.2 was selected as sodium chlorite and the other information was the same as Embodiment 1.

Embodiment 5

[0051] Similar to the method of visible-light photocatalysis combined with ClO.sub.2 oxidation for highly efficient removal of organic pollutants in the wastewater as described in embodiment 1, the difference is that the precursor of ClO.sub.2 was selected as sodium chlorate and the other information was the same as Embodiment 1.

Embodiment 6

[0052] Similar to the method of visible-light photocatalysis combined with ClO.sub.2 oxidation for highly efficient removal of organic pollutants in the wastewater as described in embodiment 1, the difference is that the precursor of ClO.sub.2 was selected as sodium perchlorate and the other information was the same as Embodiment 1.

Embodiment 7

[0053] Similar to the method of visible-light photocatalysis combined with ClO.sub.2 oxidation for highly efficient removal of organic pollutants in the wastewater as described in embodiment 1, the difference is that the pH of wastewater was adjusted to 3, 5, 7, 9, 11 before adding BiVO.sub.4 photocatalysts and the other information was the same as Embodiment 1.

Embodiment 8

[0054] Similar to the method of visible-light photocatalysis combined with ClO.sub.2 oxidation for highly efficient removal of organic pollutants in the wastewater as described in embodiment 1, the difference is that 10.0 mmol/L of Cl.sup.− was dosed into the solution at the same time as adding the precursor of ClO.sub.2 and the other information was the same as Embodiment 1.

Embodiment 9

[0055] Similar to the method of visible-light photocatalysis combined with ClO.sub.2 oxidation for highly efficient removal of organic pollutants in the wastewater as described in embodiment 1, the difference is that 10.0 mmol/L of SO.sub.4.sup.2- was dosed into the solution at the same time as adding the precursor of ClO.sub.2 and the other information was the same as Embodiment 1.

Embodiment 10

[0056] Similar to the method of visible-light photocatalysis combined with ClO.sub.2 oxidation for highly efficient removal of organic pollutants in the wastewater as described in embodiment 1, the difference is that 10.0 mmol/L of HCO.sub.3.sup.− was dosed into the solution at the same time as adding the precursor of ClO.sub.2 and the other information was the same as Embodiment 1.

Embodiment 11

[0057] Similar to the method of visible-light photocatalysis combined with ClO.sub.2 oxidation for highly efficient removal of organic pollutants in the wastewater as described in embodiment 1, the difference is that 1.0 mmol/L of ClO.sub.3.sup.− was dosed into the solution at the same time as adding the precursor of ClO.sub.2 and the other information was the same as Embodiment 1.

Embodiment 12

[0058] Similar to the method of visible-light photocatalysis combined with ClO.sub.2 oxidation for highly efficient removal of organic pollutants in the wastewater as described in embodiment 1, the difference is that 1.0 mg/L of fulvic acid was dosed into the solution at the same time as adding the precursor of ClO.sub.2 and the other information was the same as Embodiment 1.

Experimental Examples for Application

[0059] The degradation experiments of simulated norfloxacin wastewater were carried out in a double-walled reactor with an interlayer. The initial concentration of norfloxacin in the simulated wastewater is 10 mg/L and the initial volume is 100 mL. The temperature of the reactor was maintained at 25° C. by feeding a thermostatic cooling circulating water to the interlayer of the double-walled reactor. At the same time, the control group without hypochlorite was established. During the degradation of norfloxacin, 1 mL of sample was collected at a certain interval, i.e. 0 min, 5 min, 10 min, 15 min, 30 min, 45 min, 60 min, 90 min, and 120 min, and filtered through a 0.22 μm membrane to further detect the concentration change of norfloxacin by high-performance liquid chromatography.

Experimental Example 1

[0060] The performance of visible light photocatalysis-ClO.sub.2 oxidation combined process mediated by different visible light photocatalysts to treat norfloxacin organic wastewater was shown in FIG. 2.

Experimental Example 2

[0061] The performance of visible light photocatalysis-ClO.sub.2 oxidation combined process composed of different concentrations of chlorine-containing precursors to treat norfloxacin organic wastewater was shown in FIG. 3.

Experimental Example 3

[0062] The effect of pH on the performance of visible light photocatalysis-ClO.sub.2 oxidation combined process to treat norfloxacin organic wastewater was shown in FIG. 4.

Experimental Example 4

[0063] Moreover, in this invention, the single factor experiments on the effect of inorganic and organic matters on the performance of visible light photocatalysis-ClO.sub.2 oxidation combined process to treat norfloxacin organic wastewater was carried out. And the ability of degradation and anti-interference of this process in actual water matrix was investigated. After reaching the adsorption equilibrium, a certain concentration of interfering matters was added to the organic wastewater including inorganic and organic matters. Meanwhile, a certain concentration of chlorine-containing salts was added into the same reactor with full stirring for contaminant degradation and the reaction temperature was controlled by the cooling water. The inorganic matters are one or more than two mixtures of Cl.sup.−, Br.sup.−, ClO.sub.3.sup.−, NO.sub.3.sup.−, SO.sub.4.sup.2-, CO.sub.3.sup.2- or HCO.sub.3.sup.− with a concentration of 0.01-0.10 mmol/L. The organic matters are one or two mixtures of fulvic acid, brown humic acid, or humic acid.

Embodiment 13

[0064] Similar to the method of visible-light photocatalysis combined with ClO.sub.2 oxidation for highly efficient removal of organic pollutants in the wastewater as described in embodiment 1, the difference is that the organic solution was prepared using tap water and the other information was the same as Embodiment 1.

Embodiment 14

[0065] Similar to the method of visible-light photocatalysis combined with ClO.sub.2 oxidation for highly efficient removal of organic pollutants in the wastewater as described in embodiment 1, the difference is that the organic solution was prepared using surface water and the other information was the same as Embodiment 1.

Embodiment 15

[0066] Similar to the method of visible-light photocatalysis combined with ClO.sub.2 oxidation for highly efficient removal of organic pollutants in the wastewater as described in embodiment 1, the difference is that the organic solution was prepared using medical wastewater and the other information was the same as Embodiment 1.

Embodiment 16

[0067] Similar to the method of visible-light photocatalysis combined with ClO.sub.2 oxidation for highly efficient removal of organic pollutants in the wastewater as described in embodiment 1, the difference is that the organic solution was prepared using domestic sewage and the other information was the same as Embodiment 1.

Embodiment 17

[0068] Similar to the method of visible-light photocatalysis combined with ClO.sub.2 oxidation for highly efficient removal of organic pollutants in the wastewater as described in embodiment 1, the difference is that the organic solution was prepared using printing wastewater and the other information was the same as Embodiment 1.

Embodiment 18

[0069] Similar to the method of visible-light photocatalysis combined with ClO.sub.2 oxidation for highly efficient removal of organic pollutants in the wastewater as described in embodiment 1, the difference is that the organic solution was prepared using seawater and the other information was the same as Embodiment 1.