METHOD FOR ENHANCED BIO-TREATMENT OF REFRACTORY ORGANIC POLLUTANTS WITH PHOTO-EXCITED HOLES AS ELECTRON ACCEPTORS

Abstract

The present invention relates to the technical field of wastewater treatment, and discloses a method for enhanced bio-treatment of refractory organic pollutants with photo-excited holes as electron acceptors. The method comprises the following steps: 1) placing a composite semiconductor-coated carrier material into a reactor, introducing wastewater into the reactor inoculated with anaerobic sludge, and allowing the composite semiconductor-coated carrier material to be immersed in the wastewater, wherein the composite semiconductor-coated carrier material comprises a conductive carrier and composite semiconductor materials loaded on the conductive carrier; 2) carrying out habituated culture on the anaerobic sludge for a period of time, and loading a biological membrane on the surface of the composite semiconductor materials, to construct a photo-excited hole enhanced bioreactor; and 3) treating the refractory pollutants in the wastewater by utilizing the reactor under irradiation.

Claims

1. A method for enhanced bio-treatment of refractory organic pollutants with photo-excited holes as electron acceptors, comprising the following steps: 1-1) placing a composite semiconductor-coated carrier material into a reactor, introducing wastewater into the reactor inoculated with anaerobic sludge, and allowing the composite semiconductor-coated carrier material to be immersed in the wastewater, wherein the composite semiconductor-coated carrier material comprises a conductive carrier and composite semiconductor materials loaded on the conductive carrier; 1-2) carrying out habituated culture on the anaerobic sludge for a period of time, and loading a biological membrane on the surface of the composite semiconductor materials, to construct a photo-excited hole enhanced bioreactor; and 1-3) treating the refractory pollutants in the wastewater by utilizing the reactor under irradiation.

2. The method for enhanced bio-treatment of refractory organic pollutants with photo-excited holes as electron acceptors according to claim 1, wherein the composite semiconductor material comprises any one of BiVO.sub.4/FeOOH, CdS/g-C.sub.3N.sub.4 or BiVO.sub.4/g-C.sub.3N.sub.4.

3. The method for enhanced bio-treatment of refractory organic pollutants with photo-excited holes as electron acceptors according to claim 1, wherein the conductive carrier comprises carbon paper or carbon felt, and/or the reactor comprises a quartz reactor or a glass reactor.

4. The method for enhanced bio-treatment of refractory organic pollutants with photo-excited holes as electron acceptors according to claim 3, wherein the composite semiconductor coated carrier material comprises any one of BiVO.sub.4/FeOOH, CdS/g-C.sub.3N.sub.4@GF, or BiVO.sub.4/g-C.sub.3N.sub.4@GF.

5. The method for enhanced bio-treatment of refractory organic pollutants with photo-excited holes as electron acceptors according to claim 4, wherein the BiVO.sub.4/FeOOH@CP is prepared through a method comprising: preparing BiOI@CP by electrodeposition, converting BiOI@CP into BiVO.sub.4@CP, immersing BiVO.sub.4@CP in a solution of FeCl.sub.3.6H.sub.2O for a period of time, and rinsing with deionized water, to obtain BiVO.sub.4/FeOOH@CP.

6. The method for enhanced bio-treatment of refractory organic pollutants with photo-excited holes as electron acceptors according to claim 5, wherein the sludge is inoculated at a concentration of about 3.0-6.0 g/L, and the anaerobic sludge is subjected to habituated culture for at least 30 days.

7. The method for enhanced bio-treatment of refractory organic pollutants with photo-excited holes as electron acceptors according to claim 5, wherein the electrodeposition comprises the following steps: 7-1) dissolving Bi(NO.sub.3).sub.3.5H.sub.2O and KI in deionized water; adjusting the pH with nitric acid, and mixing the solution with a solution of p-benzoquinone in ethanol for a period of time, to obtain a mixture; and 7-2) adding the mixture to a three-electrode system, and electrodepositing at a cathodic potential for a period of time, to deposit BiOI onto carbon paper, so as to form BiOI@CP.

8. The method for enhanced bio-treatment of refractory organic pollutants with photo-excited holes as electron acceptors according to claim 7, wherein the BiOI@CP is converted into BiVO.sub.4@CP through steps comprising: 8-1) coating a VO(acac).sub.2/DMSO solution onto BiOI@CP, heating to a certain temperature at a certain heating rate and holding for a period of time; and 8-2) treating with NaOH to remove excess V.sub.2O.sub.5, to obtain BiVO.sub.4@CP.

9. The method for enhanced bio-treatment of refractory organic pollutants with photo-excited holes as electron acceptors according to claim 3, wherein the wastewater comprises refractory organic pollutants, Na.sub.2HPO.sub.4.12H.sub.2O, KH.sub.2PO.sub.4, MgSO.sub.4.7H.sub.2O, CaCl.sub.2, and a mixed solution of trace elements.

10. The method for enhanced bio-treatment of refractory organic pollutants with photo-excited holes as electron acceptors according to claim 9, wherein the refractory organic pollutants comprise nitrogen-containing heterocyclic organic compounds, chlorinated organic compounds and antibiotic organic compounds.

11. The method for enhanced bio-treatment of refractory organic pollutants with photo-excited holes as electron acceptors according to claim 2, wherein the conductive carrier comprises carbon paper or carbon felt, and/or the reactor comprises a quartz reactor or a glass reactor.

12. The method for enhanced bio-treatment of refractory organic pollutants with photo-excited holes as electron acceptors according to claim 6, wherein the electrodeposition comprises the following steps: 7-1) dissolving Bi(NO.sub.3).sub.3.5H.sub.2O and KI in deionized water; adjusting the pH with nitric acid, and mixing the solution with a solution of p-benzoquinone in ethanol for a period of time, to obtain a mixture; and 7-2) adding the mixture to a three-electrode system, and electrodepositing at a cathodic potential for a period of time, to deposit BiOI onto carbon paper, so as to form BiOI@CP.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] FIG. 1 schematically shows the structure of a photo-excited hole enhanced bioreactor;

[0040] FIG. 2 shows the removal effect on pyridine in different experimental groups;

[0041] FIG. 3 shows the removal effect on total organic carbon (TOC) in different experimental groups;

[0042] FIG. 4 shows the formation of ammonia nitrogen in different experimental groups;

[0043] FIG. 5 shows the effect of different scavengers on the degradation effect of the photo-excited hole enhanced biological system; and

[0044] FIG. 6 shows the removal effect of the photo-excited hole enhanced biological system for different concentrations of pyridine.

[0045] In the figure, 1. LED light; 2. quartz reactor; 3. biological membrane; 4. BiVO.sub.4/FeOOH composite semiconductor material; 5. carbon paper.

DETAILED DESCRIPTION

[0046] The present invention will be further described below with reference to specific examples.

Example 1

[0047] In this example, the method for enhanced bio-treatment of refractory organic pollutants with photo-excited holes as electron acceptors comprises the following steps.

[0048] FIG. 1 schematically shows the structure of a photo-excited hole enhanced bioreactor. In the enhanced biological system, carbon paper immobilized and loaded with BiVO.sub.4/FeOOH composite semiconductor material was immersed in a quartz reactor 2, having a specification of 4.5×4.5×7.5 cm, and a volume of 150 mL.

[0049] In the present invention, the BiVO.sub.4/FeOOH composite semiconductor material 4 was immobilized on carbon paper carrier (CP, 4×4 cm) by using the immobilization technology of semiconductor materials, to form BiVO.sub.4/FeOOH@CP. Then, anaerobic sludge was inoculated into the reactor, and a biological membrane 3 was loaded on the surface of the, BiVO.sub.4/FeOOH composite semiconductor by habituated culture of sludge, to construct the photo-excited hole enhanced system.

[0050] The specific steps were as follows.

[0051] 1) Preparation of BiOI@CP: 1.94 g of Bi(NO.sub.3).sub.3.5H.sub.2O and 6.64 g of KI were dissolved in 100 mL of deionized water. The pH was adjusted to 1.7 with nitric acid, and then the solution was mixed with 40 mL of a solution of p-benzoquinone in ethanol (0.23 M) for 5 min. The mixture was added to a three-electrode system, and electrodeposited for 10 min at a cathodic potential of −0.1 V (vs. Ag/AgCl), to electrodeposit BiOI onto CP, so as to form BiOI@CP.

[0052] 2) Preparation of BiVO.sub.4@CP: 1 mL of VO(acac).sub.2/DMSO solution was coated onto BiOI@CP, and heated to 450° C. at a heating rate of 2° C./min for 2 hrs; and excess V.sub.2O.sub.5 was removed by treatment for 30 min with 10 M NaOH, to obtain BiVO.sub.4@CP.

[0053] 3) Preparation of BiVO.sub.4/FeOOH@CP: The prepared BiVO.sub.4@CP was further immersed in 5 mM FeCl.sub.3.6H.sub.2O solution for 12 hrs, and rinsed with deionized water.

[0054] 4) Before the reactor was put into use, anaerobic sludge was inoculated into the quartz reactor, at a mixed liquor suspended solid (MLSS) concentration of 3.0-6.0 g/L, and the semiconductor material was immersed and immobilized in the reactor. After two days, the supernatant was removed, and 125 mL of freshly prepared simulated wastewater was added to the reactor to start a new batch. After at least 30 days of habituated culture, a biological membrane was grown and enriched on the surface of the semiconductor material, and excess suspended sludge in the reactor was removed.

[0055] A 150 W LED light 1 was used as a visible light source, and the refractory organic compounds in wastewater were treated by the above enhanced system under irradiation.

[0056] The simulated wastewater comprises the following components: organic pollutants, Na2HPO.sub.4.12H.sub.2O 3.06 g/L, KH.sub.2PO.sub.4 0.76 g/L, MgSO.sub.4.7 H.sub.2O 0.2 g/L, CaCl.sub.2 0.05 g/L, and 1 mL/L mixed solution of trace elements, including ZnSO.sub.4.7H.sub.2O 0.01 g/L, MnCl.sub.2.4H.sub.2O 0.003 g/L, H.sub.3BO.sub.3 0.03 g/L, CoCL.sub.2.6H.sub.2O 0.02 g/L, CuCl.sub.2.2H.sub.2O 0.001 g/L, NiCl.sub.2.6H.sub.20.002 g/L, and Na.sub.2MoO.sub.4.2H.sub.2O 0.003 g/L, EDTA 0.5 g/L, and FeSO.sub.4.7H.sub.2O 0.2 g/L. The carbon and nitrogen needed for microbial growth and metabolism in the photo-excited hole enhanced biological system are provided by organic pollutants.

Example 2

[0057] This example was substantially the same as Example 1. In actual use, pyridine simulated wastewater was added to the photo-excited hole enhanced biological system, and sequencing batch degradation was performed for a period of two days. The pyridine simulated wastewater contains pyridine, a buffer solution, inorganic salts, and trace elements, etc.

[0058] Different reactors were configured according to the method in Example 1, and different experimental groups were set. The reactor configured with blank carbon paper having no biological membrane loaded and configured to run under irradiation was designated as R.sub.con. The reactor configured with blank carbon paper having a biological membrane loaded and configured to run under irradiation was designated as R.sub.bio. The reactor configured with a semiconductor material having no biological membrane loaded and configured to run under irradiation was designated as R.sub.pho. The reactor configured with a semiconductor material having a biological membrane loaded and configured to run without irradiation was designated as R.sub.pho-bio-dark. The reactor configured with a semiconductor material having a biological membrane loaded and configured to run under irradiation was designated as R.sub.pho-bio.

[0059] As shown in FIG. 2, R.sub.con and R.sub.bio have almost no degradation on pyridine, and the pyridine concentration is only reduced from 150 mg/L to 133 and 137 mg/L. This means that pyridine will not degrade by itself under irradiation, and the biological degradation of pyridine is also negligible. R.sub.pho shows obvious removal effect on pyridine, and the pyridine concentration is reduced from 150 mg/L to 100 mg/L. This shows that the semiconductor material BiVO.sub.4/FeOOH used in the present invention has a degradation effect on pyridine under irradiation, but the effect is much less than the removal effect of R.sub.pho-bio. After two days of degradation, no pyridine is detected in R.sub.pho-bio, showing that the photo-excited hole enhanced biological system has a significant removal effect on pyridine, due to the synergistic effect between the semiconductor materials and the microorganisms. Therefore, the degradation effect of the enhanced system on pyridine is greatly enhanced. Notably, the pyridine removal effect in R.sub.pho-bio-dark is the same as that in R.sub.bio, suggesting that in the absence of light, the semiconductor material fails to promote the significant degradation of pyridine by microorganisms. This also proves that there is a synergistic effect in the enhanced system.

[0060] FIG. 3 shows the removal effect on total organic carbon (TOC) in different experimental groups. The reactor configured with blank carbon paper having no biological membrane loaded and configured to run under irradiation was designated as R.sub.con. The reactor configured with blank carbon paper having a biological membrane loaded and configured to run under irradiation was designated as R.sub.bio. The reactor configured with a semiconductor material having no biological membrane loaded and configured to run under irradiation was designated as R.sub.pho. The reactor configured with a semiconductor material having a biological membrane loaded and configured to run without irradiation was designated as R.sub.pho-bio-dark. The reactor configured with a semiconductor material having a biological membrane loaded and configured to run under irradiation was designated as R.sub.pho-bio.

[0061] The removal for total organic carbon (TOC) has the similar trend to that for pyridine removal. As shown in FIG. 3, the removal of TOC by R.sub.con, R.sub.bio, and R.sub.pho-bio-dark is almost negligible. R.sub.pho shows a certain removal effect on TOC, and the TOC concentration is reduced from 110 mg/L to 80 mg/L. R.sub.pho-bio shows the most excellent effect in TOC removal, and after two days of degradation, the TOC concentration is reduced from 110 mg/L to 13 mg/L, with a removal efficiency of TOC of up to 88%. This shows that the photo-excited hole enhanced biological system can not only completely remove pyridine, but also maintain a significant mineralization ability.

[0062] FIG. 4 shows the formation of ammonia nitrogen in different experimental groups. The reactor configured with blank carbon paper having no biological membrane loaded and configured to run under irradiation was designated as R.sub.con. The reactor configured with blank carbon paper having a biological membrane loaded and configured to run under irradiation was designated as R.sub.bio. The reactor configured with a semiconductor material having no biological membrane loaded and configured to run under irradiation was designated as R.sub.pho. The reactor configured with a semiconductor material having a biological membrane loaded and configured to run without irradiation was designated as R.sub.pho-bio-dark. The reactor configured with a semiconductor material having a biological membrane loaded and configured to run under irradiation was designated as R.sub.pho-bio.

[0063] The complete degradation of pyridine is usually accompanied by the formation of ammonia nitrogen. Therefore, the formation efficiency of ammonia nitrogen can be used as an important index for the complete degradation of pyridine. As shown in FIG. 4, no formation of ammonia nitrogen is detected during the entire degradation process in R.sub.con, R.sub.bio, R.sub.pho-bio-dark, and R.sub.pho, further confirming that the degradation effect of R.sub.con, R.sub.bio, R.sub.pho-bio-dark, and R.sub.pho is poor. Under irradiation, although the semiconductor can remove pyridine to some extent, the low mineralization rate and incomplete degradation are the main causes limiting its use. After two days of degradation, the concentration of ammonia nitrogen in R.sub.pho-bio is up to 23 mg/L, with a formation efficiency of ammonia nitrogen of as high as 84%, indicating that the photo-excited hole enhanced biological system can completely degrade pyridine.

[0064] In summary, the photo-excited hole enhanced biological system has a significant removal effect on pyridine, and also maintains a very high mineralization capacity. The photo-excited hole enhanced biological system can completely degrade pyridine, and also overcome the defects of low mineralization efficiency in traditional semiconductor photocatalytic technology and low load and slow degradation in traditional biotechnology. The semiconductor immobilization technology adopted in the present invention solves the problems of high cost and difficult catalyst recovery.

Example 3

[0065] In this example, different scavengers were used to explore the effects of photo-excited holes, superoxide radicals and hydroxyl radicals in the photo-excited hole enhanced biological systems.

[0066] Upon excitation under irradiation, the semiconductor material generates photo-excited electron-hole pairs, and the photo-excited electron-hole pairs can produce superoxide radicals and hydroxyl radicals through reaction with oxygen and water. As shown in FIG. 5, different scavengers were used to explore the effects of photo-excited holes, superoxide radicals and hydroxyl radicals in the photo-excited hole enhanced biological systems. Methanol (MET) and isopropanol (IPA) acted as scavengers for photo-excited holes and hydroxyl radicals, respectively. To explore the effect of superoxide radicals in the photo-excited hole enhanced biological systems, the solution was purged with nitrogen (N.sub.2) for 15 min to ensure the removal of potentially dissolved oxygen from the system. After removing the dissolved oxygen in the system, the effect of the photo-excited hole enhanced biological system on the degradation of pyridine was not suppressed, and the pyridine removal rate and ammonia nitrogen formation were almost unchanged. This indicates that superoxide radicals do not play a role in the photo-excited hole enhanced biological system. When isopropanol was added to the photo-excited hole enhanced biological system, both pyridine removal and ammonia nitrogen generation in the system were slightly inhibited, but the effect was not obvious. This indicates that hydroxyl radicals do not play a main role in the photo-excited hole enhanced biological system. When methanol was added to the photo-excited hole enhanced biological system, both pyridine removal and ammonia nitrogen formation were significantly inhibited, and the pyridine removal rate dropped to 79%. This indicates that the photo-excited hole is an important factor affecting the degradation of pyridine in the photo-excited hole enhanced biological system. Notably, after methanol was added to the photo-excited hole enhanced biological system, no ammonia nitrogen was detected in the system. This indicates that compared to pyridine removal, the photo-excited hole has a higher influence on the formation of ammonia nitrogen (that is, the complete degradation of pyridine). This also indicates that the photo-excited hole is not reacted directly with pyridine. Considering the fact that the biological membrane is loaded on the surface of the semiconductor material, pyridine comes into contact with the biological membrane firstly. In the process of microbial degradation of pyridine, the photo-excited hole acts as an electron acceptor to receive electrons generated during the microbial degradation of pyridine, thereby promoting the degradation of pyridine by microorganisms.

[0067] FIG. 6 shows the removal effect of the photo-excited hole enhanced biological system for different concentrations of pyridine. As shown in FIG. 6, as the pyridine concentration increases, although the degradation performance of the photo-excited hole enhanced biological system is slightly reduced, when the pyridine concentration is as high as 450 mg/L, the system can still maintain a high degradation performance (with a pyridine removal efficiency of 82%, a TOC removal efficiency of 70% and an ammonia nitrogen formation efficiency of 64%). These results indicate that the photo-excited hole enhanced biological system has excellent load resistance, and the system will not break down even at a high concentration of pyridine, where the highest treatment capability is up to 2.34 mol m.sup.−3.Math.d.sup.−1. The load resistance of the photo-excited hole enhanced biological system allow the system to adapt to the complex and variable industrial wastewater, making it have great potential in the treatment of practical industrial wastewater.

Example 4

[0068] This example was substantially the same as Example 1. In actual use, CdS/g-C.sub.3N.sub.4@AGF was immobilized in a reactor, then chlorophenol simulated wastewater was added to the photo-excited hole enhanced biological system, and sequencing batch degradation was performed for a period of two days. The chlorophenol simulated wastewater contains chlorophenols, a buffer solution, inorganic salts, and trace elements, etc.

[0069] In R.sub.con, R.sub.bio, and R.sub.pho-bio-dark, the removal of chlorophenol and TOC is almost negligible. This indicates that chlorophenol itself can exist stably under light and cannot be biodegraded. The semiconductor material has no effect on the degradation of chlorophenol in the absence of light. The removal rate of chlorophenol in R.sub.pho is up to 84%, suggesting that under the catalysis of semiconductor material, the structure of chlorophenol is destroyed. However, the removal rate of TOC is merely 28%, suggesting that chlorophenol cannot be mineralized by the catalytic effect of the semiconductor material alone, and only organic compounds derived therefrom can be obtained. The removal rates of chlorophenol and TOC in R.sub.pho-bio are as high as 96% and 78%, respectively. This shows that the photo-excited hole enhanced biological system has a significant removal effect on chlorophenols, and also maintains a very high mineralization capacity.

Example 5

[0070] This example was substantially the same as Example 1. In actual use, BiVO.sub.4/g-C.sub.3N.sub.4@GF was immobilized in a reactor, then tetracycline simulated wastewater was added to the photo-excited hole enhanced biological system, and sequencing batch degradation was performed for a period of two days. The tetracycline simulated wastewater contains tetracycline, a buffer solution, inorganic salts, and trace elements, etc.

[0071] The removal rate of tetracycline in R.sub.con is merely 12%, and the TOC concentration keeps unchanged during the degradation process. The mild removal of tetracycline is attributed to the adsorption of tetracycline by the conductive carrier. In R.sub.bio, and R.sub.pho-bio-dark, the removal efficiency of tetracycline are 53% and 55%, respectively, and the removal of TOC is almost negligible. This shows that tetracycline can be biodegraded; however, the efficiency of biodegradation is very limited. The semiconductor material has no effect on the degradation of tetracycline in the absence of light. The removal rate of tetracycline in R.sub.pho reaches 78%, suggesting that under the catalysis of semiconductor material, the structure of tetracycline is destroyed. However, the removal rate of TOC is merely 17%, suggesting that tetracycline cannot be mineralized by the catalytic effect of the semiconductor material alone, and only organic compounds derived therefrom can be obtained. The removal rates of tetracycline and TOC in R.sub.pho-bio are as high as 91% and 68%, respectively. This shows that the photo-excited hole enhanced biological system has a significant removal effect on tetracycline, and also maintains a high mineralization capacity.

[0072] Examples 4 and 5 show that the excellent degradation ability of the photo-excited hole enhanced biological system can adapt to industrial wastewater with complex components. Undoubtedly, it has broad prospects in industrial wastewater treatment.

[0073] The above embodiments are provided to facilitate the understanding of the present invention, instead of limiting the present invention. Apparently, various modifications can be easily made by those skilled in the art to these embodiments, and the general principles illustrated here are applicable to other embodiments without creative efforts. Therefore, any modifications, equivalent replacements, and improvements made without departing from the principle of the present invention are embraced in the protection scope of the present invention.