Preparation of anaerobic ammonia oxidation hydrogel embedding body loaded photocatalyst coupling material and application thereof in wastewater treatment

Abstract

The application discloses a preparation of an anaerobic ammonia oxidation hydrogel embedding body loaded with a photocatalyst coupling material and application thereof in wastewater treatment. The photocatalyst and anaerobic ammonia oxidation bacteria are prepared into a composite material of photocatalysis and microorganisms through a phase inversion method according to a hydrogel and a film material, metabolic activity of anaerobic ammonia oxidation in an adverse environment is improved through hydrogel embedding and dissolved oxygen domestication. The problem of insufficient nitrite supply in anaerobic ammonia oxidation is solved through setting a light-dark ratio, and synchronous removal of ammonia nitrogen and nitrate nitrogen is realized. The application has the functions of photocatalysis and anaerobic ammonia oxidation nitrogen metabolism, and can realize removal of ammonia nitrogen and nitrate nitrogen without additional addition of nitrite, thereby providing a new application scene for nitrogen removal in wastewater.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of coupling material preparation and sewage treatment, and particularly relates to a preparation method of an anaerobic ammonia oxidation hydrogel embedding body loaded with a photocatalyst coupling material and application thereof in wastewater treatment. BACKGROUND

[0002] Excessive ammonia nitrogen and nitrate nitrogen discharged into natural water bodies due to intensive human activities (such as overuse of nitrogen fertilizer in the process of agricultural production and discharge of industrial and aquaculture wastewater) will cause water body eutrophication and further destroy the ecological balance if not properly treated. Studies have shown that when the ammonia nitrogen concentration in the water body exceeds 5 mg / L, it will seriously affect the health of aquatic organisms such as fish, shrimp and even humans.

[0003] The traditional biological method for treating nitrogen-containing wastewater has a long start-up time, large sludge yield, unstable treatment efficiency, and is limited by environmental parameters such as temperature, alkalinity, dissolved oxygen and salinity fluctuations, and the removal effect is unstable. Compared with the traditional biological method, the photocatalytic method for degrading nitrogen-containing wastewater has a fast rate, is less affected by environmental factors, and has good stability. At present, photocatalytic technology has been studied for nitrate reduction or ammonia oxidation. Due to the high valence band oxidation potential of the photocatalyst, it is easy to produce by-products of nitrate and nitrite, and the nitrogen conversion efficiency needs to be further improved, which cannot achieve complete denitrification. Anaerobic ammonia oxidation technology converts ammonia nitrogen to nitrogen gas with nitrite as the electron acceptor, and is widely considered as an economical and efficient wastewater denitrification process. However, the slow growth of ammonia oxidation bacteria (AOB) makes it difficult to enrich, which leads to a lack of nitrite, which hinders the widespread application of anaerobic ammonia oxidation process.

[0004] Considering that the by-products of photocatalytic treatment of ammonia nitrogen and nitrate nitrogen contain nitrite, and anaerobic ammonia oxidation bacteria can directly convert ammonia nitrogen and nitrite to nitrogen gas, and studies have reported that microorganisms can utilize photo-generated electrons produced by photocatalysis for metabolic activity. Therefore, how to prepare a coupling material that can couple anaerobic ammonia oxidation with photocatalytic technology to remove ammonia nitrogen and nitrate nitrogen in wastewater has great research significance. SUMMARY

[0005] In view of this, the purpose of the present application is to use hydrogel and polyvinylidene fluoride as carriers to embed and immobilize anaerobic ammonia oxidation bacteria and photocatalysts respectively, to prepare an anaerobic ammonia oxidation hydrogel embedding body loaded with a photocatalyst coupling material, and to treat ammonia nitrogen and nitrate nitrogen in wastewater by adjusting visible light irradiation of the coupling carrier material.

[0006] The preparation method of the anaerobic ammonia oxidation hydrogel embedding body loaded with a photocatalyst coupling material of the present application comprises the following steps:

[0007] Step 1: 5 g of polyvinyl alcohol and 2 g of sodium alginate were weighed and dissolved in 100 mL of deionized water, heated to complete dissolution in a water bath, and then naturally cooled. An equal volume of anaerobic ammonia oxidation sludge was added, stirred uniformly, and then transferred to a flat plate. The mixture was immersed in a saturated boric acid solution containing 1% CaCl2 and a 0.5M potassium dihydrogen phosphate solution, respectively, and finally washed with normal saline to obtain an anaerobic ammonia oxidation hydrogel embedding body.

[0008] Step 2: The anaerobic ammonia oxidation hydrogel embedding body obtained in step 1 was placed in a solution containing 20 mg / L of ammonia nitrogen and 26.4 mg / L of nitrite nitrogen, and then gradually increased the dissolved oxygen concentration in the solution. The dissolved oxygen concentration gradient was 0, 3, and 5 mg / L, and the dissolved oxygen acclimation was performed for 30 days.

[0009] Step 3: 13 g of polyvinylidene fluoride and 3 g of polyvinylpyrrolidone were mixed and dissolved in 80 mL of dimethylacetamide solvent. The bottom liquid was prepared by mechanical stirring at 60°C water bath for 24 hours until complete dissolution. Then 4 g of photocatalyst material was added to the bottom liquid and uniformly dispersed to form the casting liquid.

[0010] Step 4: The obtained casting liquid was uniformly coated on a clean glass plate using a film applicator, with a coating thickness of 1 mm. When it was not completely solidified, a layer of anaerobic ammonia oxidation hydrogel embedding body acclimated in step 2 was placed on top of it. Then the coupled material was immersed in water, and after completely falling off the glass plate, the excess solvent was washed away with deionized water to obtain an anaerobic ammonia oxidation hydrogel embedding body loaded with photocatalyst coupled material.

[0011] In step 1, the microorganisms embedded in the anaerobic ammonia oxidation hydrogel embedding body are anaerobic ammonia oxidation bacteria, which are gram-negative bacteria.

[0012] In step 3, the photocatalyst material is a semiconductor material that can excite electrons under natural light wavelength range, selected from at least one of modified titanium dioxide, cadmium sulfide and graphite-like carbon nitride composite photocatalyst, titanium dioxide and carbon quantum dot composite photocatalyst.

[0013] The modified titanium dioxide is prepared by a method comprising the following steps:

[0014] (1) 8 mL of acetic acid was added to a mixture consisting of 50 mL of tetrabutyl titanate and 100 mL of anhydrous ethanol, and the pH of the solution was adjusted to <3. Then 2.3 g of tourmaline powder was added;

[0015] (2) 40 mL of anhydrous ethanol was mixed with 100 mL of distilled water and added dropwise to the system of step (1) to obtain a TiO2-TM sol;

[0016] (3) The obtained TiO2-TM sol was placed in a 100 °C oven for 4 h, then placed in a 400 °C muffle furnace for 3 h, dried, cooled to room temperature and ground to obtain a TiO2-TM composite material;

[0017] (4) 1 g of the TiO2-TM composite material and 12.5 mg of CuSO4 were added to a beaker containing 450 mL of deionized water and 50 mL of ethanol, stirred at 500 rpm and irradiated with a mercury lamp (20 W) with a wavelength of 254 nm as a light source for 1 h; the mixed solution after reaction was filtered, washed and dried to obtain a modified titanium dioxide, i.e. TiO2-TM-Cu photocatalyst material.

[0018] The cadmium sulfide and graphitic carbon nitride composite photocatalyst is prepared by a method comprising the following steps:

[0019] (1) 5 g of melamine was weighed into a crucible, heated to 550 °C at a heating rate of 10 °C / min in a muffle furnace, maintained at this temperature for 4 hours, and cooled to room temperature to obtain graphitic carbon nitride (g-C3N4);

[0020] (2) 1 g of g-C3N4 was dispersed in 50 mL of dimethyl sulfoxide, then 1.43 mL of cadmium acetate was added, stirred for 60 min, then transferred to a polytetrafluoroethylene-lined stainless steel autoclave, heated at 180 °C for 12 h; after natural cooling to room temperature, the precipitate was washed with anhydrous ethanol and deionized water and dried in a 60 °C vacuum oven to obtain a cadmium sulfide and graphitic carbon nitride composite photocatalyst CdS@g-C3N4.

[0021] The titanium dioxide and carbon quantum dot composite photocatalyst is prepared by a method comprising the following steps:

[0022] (1) 4.5 g of citric acid and 4.5 g of urea were mixed with 15 g of deionized water, the mixed solution was poured into a polytetrafluoroethylene-lined stainless steel autoclave, and heated at 180 °C for 6 hours, the reaction liquid was centrifuged and dried to obtain carbon quantum dots (CQDs);

[0023] (2) 4.26 mL of tetrabutyl titanate was mixed with 20 mL of ethanol and stirred for 45 min, then 0.01 g of CQDs was added and ultrasonically treated for 30 min, the mixture was poured into a 25 mL polytetrafluoroethylene container, then the above container was placed in a 150 mL polytetrafluoroethylene container, and 6 mL of ultrapure water was added, and the titanium dioxide and carbon quantum dot composite photocatalyst TiO2@CQDs was obtained by reacting in a 150 °C stainless steel autoclave for 10 hours.

[0024] The application of the anaerobic ammonia oxidation hydrogel embedding body loaded photocatalyst coupling material in wastewater treatment can simultaneously remove ammonia nitrogen and nitrate nitrogen in wastewater.

[0025] Specifically, the following steps are included: the anaerobic ammonia oxidation hydrogel embedding body loaded photocatalyst coupling material is added into wastewater containing ammonia nitrogen and nitrate nitrogen to be treated, and alternating and repeated under visible light irradiation and in the dark.

[0026] Further, the light-dark ratio is 1:2.

[0027] Further, the alternating process is performed after irradiation under visible light for 8 hours and cultivation in the dark for 16 hours, and the process is continued for 12 days.

[0028] Compared with the prior art, the beneficial effects of the application are reflected in:

[0029] The application combines photocatalysis and microbial treatment technology, uses the hydrogel and polyvinylidene fluoride to fix the anaerobic ammonia oxidation bacteria and the photocatalyst in the same system, and the denitrification effect of the coupling material is significantly greater than that of photocatalysis or microbial denitrification alone. As strict anaerobic bacteria, the embedding and fixing mode can weaken the toxic effect of dissolved oxygen on anaerobic ammonia oxidation bacteria, create an anoxic microenvironment for microorganisms, and at the same time, can maximize the avoidance of the adverse effects of light on anaerobic ammonia oxidation bacteria.

[0030] The anaerobic ammonia oxidation hydrogel embedding body loaded photocatalyst coupling material can provide a more stable metabolic environment for the synergistic process of photocatalysis and anaerobic ammonia oxidation reaction. The photocatalysis continuously converts ammonia nitrogen and nitrate nitrogen into nitrite nitrogen, providing nitrite nitrogen supply for anaerobic ammonia oxidation, and converting ammonia nitrogen and nitrite nitrogen into nitrogen gas for removal. At the same time, the anaerobic ammonia oxidation bacteria can use the photogenerated electrons produced by photocatalysis for denitrification, and can simultaneously remove ammonia nitrogen and nitrate nitrogen in wastewater. In addition, through the dissolved oxygen acclimation experiment of the anaerobic ammonia oxidation hydrogel embedding body, the environmental adaptability of the coupling material is further improved, and through the light-dark alternating treatment design, the removal efficiency is maximized. The preparation and denitrification method of the coupling material can provide a new solution and technical guidance for deep denitrification of wastewater. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to facilitate the understanding of those skilled in the art, the application will be further described below with reference to the accompanying drawings.

[0032] Figure 1 The preparation method of the anaerobic ammonia oxidation hydrogel embedding body loaded photocatalyst coupling material of the application is shown in the figure.

[0033] Figure 2 The SEM image of the anaerobic ammonia oxidation hydrogel embedding body of the application is shown in the figure. Figure 2It can be seen from the figure that anaerobic ammonia oxidation is embedded in the hydrogel, and there are many gaps in the inner layer of the embedding body, and it is connected by filaments. This is conducive to the transportation of nutrients and metabolites.

[0034] Figure 3 The figure shows the effect of the photocatalytic, microbial and coupled materials of the application on the removal of ammonia nitrogen and nitrate nitrogen. From Figure 3 It can be seen from the figure that the photocatalytic and microbial groups alone have low removal efficiency of ammonia nitrogen and nitrate nitrogen, and the coupled material group successfully removes 95.5 and 85% of ammonia nitrogen and nitrate nitrogen. DETAILED DESCRIPTION

[0035] The technical solutions of the application will be further described in detail below in combination with the drawings and specific implementation cases. Example 1

[0036] The photocatalyst coupled material of the anaerobic ammonia oxidation hydrogel embedding body of the application is prepared by the following method, and the preparation steps are shown in the schematic diagram Figure 1 as shown:

[0037] 1. Select a semiconductor material that can excite electrons under natural light wavelength irradiation, prepare it into nanoparticles as a photocatalyst, and take TiO2-TM-Cu, CdS@g-C3N4 and TiO2@CQDs photocatalysts as examples.

[0038] Synthesis steps of photocatalyst TiO2-TM-Cu:

[0039] (1) 8 mL of acetic acid is added to a mixture composed of 50 mL of tetrabutyl titanate and 100 mL of anhydrous ethanol, stirred for 30 minutes, then ultrasonicated for 20 minutes, the solution pH is adjusted to <3, then 2.3 g of tourmaline powder is added;

[0040] (2) 40 mL of anhydrous ethanol is mixed with 100 mL of distilled water, also stirred for 30 minutes, then ultrasonicated for 20 minutes, slowly added to the solution of step (1), to obtain TiO2-TM sol;

[0041] (3) After gelation, place it in room temperature for 6 hours, then place it in a 100℃ oven for 4 hours, then place it in a 400℃ muffle furnace for 3 hours, dry it, cool it to room temperature and grind it, to obtain TiO2-TM composite photocatalyst;

[0042] (4) 1 g of TiO2-TM composite photocatalyst and 12.5 mg of CuSO4 were weighed into a beaker containing 450 mL of deionized water and 50 mL of ethanol, the mixed solution was stirred at 500 rpm and a mercury lamp (20 W) with a wavelength of 254 nm was used as a light source to irradiate the mixed solution for 1 hour; the mixed solution after reaction was filtered and washed three times, and finally the powder was dried to obtain a TiO2-TM-Cu photocatalyst.

[0043] Synthesis steps of photocatalyst CdS@g-C3N4:

[0044] (1) 5 g of melamine was weighed into a crucible and placed in a muffle furnace to heat to 550°C at a heating rate of 10°C / min, maintained at this temperature for 4 hours, and cooled to room temperature to obtain graphite-like carbon nitride (g-C3N4);

[0045] (2) 1 g of g-C3N4 was dispersed in 50 mL of dimethyl sulfoxide. Then, 1.43 mL of cadmium acetate was added to the above suspension, stirred for 60 min, and then transferred to a polytetrafluoroethylene-lined stainless steel autoclave and heated at 180°C for 12 h. After natural cooling to room temperature, the precipitate was washed with anhydrous ethanol and deionized water and dried in a vacuum oven at 60°C to obtain CdS@g-C3N4.

[0046] Synthesis steps of photocatalyst TiO2@CQDs:

[0047] (1) 4.5 g of citric acid and 4.5 g of urea were mixed with 15 g of deionized water. Then, the solution was poured into a polytetrafluoroethylene-lined stainless steel autoclave and heated at 180°C for 6 hours. The mixed solution was centrifuged and dried to obtain carbon quantum dots (CQDs);

[0048] (2) 4.26 mL of tetrabutyl titanate was mixed with 20 mL of ethanol and stirred for 45 minutes. Then, 0.01 g of CQDs was added and ultrasonically treated for 30 minutes. The mixture was poured into a 25 mL polytetrafluoroethylene container. Then, the above container was placed in a 150 mL polytetrafluoroethylene container, and 6 mL of ultrapure water was added, and then it was placed in a stainless steel autoclave at 150°C for 10 hours to obtain TiO2@CQDs.

[0049] 2. 5 g of polyvinyl alcohol and 2 g of sodium alginate were weighed and dissolved in 100 mL of deionized water in a 90°C water bath until completely dissolved, and then sterilized at 121°C for 30 minutes. After natural cooling, an equal volume of anaerobic anammox sludge was added, stirred uniformly, and then transferred to a flat plate and immersed in a saturated boric acid solution containing 1% CaCl2. After crosslinking for 1 hour, the mixture was washed three times with deionized water, then placed in a 0.5M potassium dihydrogen phosphate solution for 1 hour of phosphatization, and finally washed with physiological saline to obtain an anaerobic anammox hydrogel embedding body. The SEM image of the embedding body is shown in FIG. 1. Figure 2

[0050] 3. The anaerobic anammox hydrogel embedding body was placed in a solution containing 20 mg / L of ammonia nitrogen and 26.4 mg / L of nitrite nitrogen, and the dissolved oxygen concentration in the solution was gradually increased. The dissolved oxygen concentration gradient was 0, 3, and 5 mg / L, and the dissolved oxygen acclimation was performed for 30 days.

[0051] 4. 13 g of polyvinylidene fluoride and 3 g of polyvinylpyrrolidone were mixed and dissolved in 80 mL of dimethylacetamide solvent, and then stirred mechanically at 60°C for 24 hours until completely dissolved to prepare a base solution. Then 4 g of photocatalyst material was added and uniformly dispersed in the solution. A film applicator was used to evenly apply the casting liquid to a clean glass plate, with a coating thickness of 1 mm. When it had not yet completely solidified, a layer of anaerobic anammox hydrogel embedding body was placed on top, and then the coupling material was immersed in water until it completely detached from the glass plate. After washing away the excess solvent with deionized water, the anaerobic anammox hydrogel embedding body loaded with photocatalyst coupling material was obtained and stored for use. Example 2

[0052] The method for removing ammonia nitrogen and nitrate nitrogen using an anaerobic anammox hydrogel embedding body loaded with photocatalyst coupling material according to the present application comprises the following steps:

[0053] Three groups of schemes were used to study the denitrification effect of different systems: (1) only adding photocatalyst, to evaluate the pollutant removal effect of photocatalysis; (2) only adding anaerobic anammox embedding body, to evaluate the pollutant removal effect of anaerobic anammox; (3) adding anaerobic anammox hydrogel embedding body loaded with photocatalyst coupling material, to evaluate the denitrification effect of the coupling system. The above groups are named as P, B and ICPB groups. At the beginning of the experiment, ammonia nitrogen with a concentration of 20 mg / L and nitrate nitrogen with a concentration of 20 mg / L were placed in beakers, and the pH value of the simulated wastewater was fixed at 7±0.3. Then, different carriers were added to the beakers, and a xenon lamp (250W) with a 380-800 nm cut-off filter was used as a light source to simulate sunlight, with an illumination intensity of 150 mW / cm 2 ​The experiment lasted for 24 hours in each stage, and the light was on for 8 hours and then placed in the dark for 16 hours, for a total of 12 stages. During the experiment, 2 mL of liquid sample was taken at regular intervals, filtered through a 0.22 μm injection filter, and used for subsequent nitrogen concentration analysis. The experimental temperature was maintained at 30±2℃. The denitrification effects of P, B and ICPB groups are shown in Figure 3 .

Claims

1. A preparation method of an anaerobic ammonia oxidation hydrogel-embedded photocatalyst-coupled material, characterized in that It comprises the following steps: Step 1: weigh polyvinyl alcohol and sodium alginate into deionized water, heat in water bath to complete dissolution, after natural cooling, add equal volume of anaerobic ammonia oxidation sludge, stir uniformly, then transfer the mixture to a flat plate and immerse into saturated boric acid solution containing 1% CaCl2 and 0.5M potassium dihydrogen phosphate solution in turn, then wash with normal saline to obtain anaerobic ammonia oxidation hydrogel embedding body; Step 2: place the anaerobic ammonia oxidation hydrogel embedding body obtained in step 1 in a solution containing ammonia nitrogen and nitrite nitrogen, then gradually increase the dissolved oxygen concentration in the solution for dissolved oxygen acclimation; Step 3: mix polyvinylidene fluoride and polyvinylpyrrolidone in dimethylacetamide solvent, mechanically stir at 60℃ water bath until complete dissolution to prepare a bottom solution, then add the photocatalyst material after sufficient drying and grinding to the bottom solution and disperse uniformly, which is the pouring liquid; Step 4: use a film applicator to evenly spread the obtained pouring liquid on a clean glass plate, when it has not completely solidified, lay a layer of anaerobic ammonia oxidation hydrogel embedding body after acclimation in step 2 on its surface, then immerse the coupling material in water, after completely falling off from the glass plate, wash off the excess solvent with deionized water, and the anaerobic ammonia oxidation hydrogel embedding body loaded with photocatalyst coupling material is obtained; In step 1, the microorganism embedded in the anaerobic ammonia oxidation hydrogel embedding body is anaerobic ammonia oxidation bacteria; In step 2, during the dissolved oxygen acclimation, the dissolved oxygen concentration is set in a gradient in the range of 0-5mg / L, and the acclimation time is 30 days; In step 3, the photocatalyst material is selected from at least one of modified titanium dioxide, cadmium sulfide and graphite-like carbon nitride composite photocatalyst.

2. The application of the anaerobic ammonia oxidation hydrogel embedding body loaded with photocatalyst coupling material prepared in claim 1 in wastewater treatment, characterized in that: The anaerobic ammonia oxidation hydrogel embedding body loaded with photocatalyst coupling material is added into wastewater containing ammonia nitrogen and nitrate nitrogen, irradiated under visible light for 8 hours, then cultured in the dark for 16 hours, the light-dark ratio is 1:2, and the process is alternated for 12 days, and the ammonia nitrogen and nitrate nitrogen in the wastewater are removed simultaneously.

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