A terramycin wastewater treatment method based on algal-bacterial symbiotic granular sludge

Abstract

The application relates to the technical field of wastewater treatment, and discloses a terramycin wastewater treatment method based on algal-bacterial symbiotic granular sludge, which comprises the following steps: (1) performing electro-catalytic oxidation treatment on terramycin wastewater; (2) performing photo-catalytic treatment on the terramycin wastewater subjected to the electro-catalytic oxidation treatment; and (3) treating the terramycin wastewater subjected to the photo-catalytic treatment by using algal-bacterial symbiotic granular sludge. In the application, the terramycin can be effectively removed through the synergistic effect of the three processes of catalytic oxidation, photo-catalysis and algal-bacterial symbiosis, so that efficient and deep treatment of terramycin wastewater is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wastewater treatment, and particularly relates to a terramycin wastewater treatment method based on algal-bacterial symbiotic granular sludge. BACKGROUND

[0002] As a broad-spectrum antibiotic, terramycin is widely used in livestock breeding and human medicine, resulting in a large amount of terramycin entering the water environment. Terramycin has persistence in the water environment and is difficult to degrade naturally, posing a potential threat to aquatic organisms and human health. Traditional terramycin wastewater treatment methods, such as activated sludge method, have limited removal effect on terramycin. Algal-bacterial symbiotic granular sludge technology, as an emerging biological treatment technology, has the advantages of high treatment efficiency, low sludge yield and low operation cost, and shows certain potential in terramycin wastewater treatment. However, the pure algal-bacterial symbiotic granular sludge technology faces many challenges in practical application.

[0003] Firstly, the algal-bacterial symbiotic system has limited treatment capacity for high-concentration terramycin wastewater. High-concentration terramycin can inhibit the activity of algae and bacteria, resulting in reduced biological activity and treatment efficiency. Algae and bacteria have different tolerances to terramycin, and high-concentration terramycin may destroy the symbiotic relationship between algae and bacteria, leading to system collapse.

[0004] Secondly, terramycin has stable molecular structure and is difficult to biodegrade, and some degradation products may have potential toxicity. The algal-bacterial symbiotic system may not completely degrade terramycin into non-toxic and harmless small molecules, and the residual terramycin may cause secondary pollution to the environment.

[0005] Thirdly, the settling performance of algal-bacterial symbiotic granular sludge directly affects the solid-liquid separation efficiency of the system. Poor settling performance will lead to sludge loss, affecting biomass and treatment effect. Sludge loss will also cause deterioration of effluent quality and increase the difficulty of subsequent treatment.

[0006] Therefore, the prior art still needs to be improved and developed. SUMMARY

[0007] In view of the deficiencies of the prior art, the purpose of the present application is to provide a terramycin wastewater treatment method based on algal-bacterial symbiotic granular sludge, aiming to improve the treatment efficiency of terramycin wastewater.

[0008] The technical scheme of the present application is as follows:

[0009] A terramycin wastewater treatment method based on algal-bacterial symbiotic granular sludge, comprising the following steps:

[0010] (1) performing electro-catalytic oxidation treatment on terramycin wastewater;

[0011] (2) performing a photocatalytic treatment on the oxytetracycline wastewater subjected to the electro-catalytic oxidation treatment;

[0012] (3) treating the oxytetracycline wastewater subjected to the photocatalytic treatment by using algal-bacterial symbiotic granular sludge.

[0013] The oxytetracycline wastewater treatment method based on algal-bacterial symbiotic granular sludge, wherein the preparation method of the algal-bacterial symbiotic granular sludge comprises the following steps:

[0014] The biochar is dispersed in an ammonia water solution, CuSO4·5H2O is added as a catalyst, and the reaction is stirred in a 45-55℃ water bath for 5-7 hours; after the reaction is completed, the reaction product is washed with deionized water until it is neutral, and then dried at 70-90℃ until the weight is constant to obtain the modified biochar;

[0015] The modified biochar is mixed with an algal-bacterial symbiotic culture medium, and the mixture is stirred at a speed of 100-140 rpm for 7-14 days under the conditions of a light intensity of 2800-3200 Lux, a temperature of 25-30℃, a pH value of 6.8-7.2, and dissolved oxygen maintained at 5-7 mg / L to form the algal-bacterial symbiotic granular sludge;

[0016] wherein 8-12 mL of the ammonia water solution with a mass concentration of 5-15% is used per 1 g of the biochar, and 0.3-0.7 g of the CuSO4·5H2O is added per 1 L of the ammonia water solution;

[0017] The algal-bacterial symbiotic culture medium comprises chlorella vulgaris and bacillus licheniformis.

[0018] The oxytetracycline wastewater treatment method based on algal-bacterial symbiotic granular sludge, wherein the initial concentration of the chlorella vulgaris in the algal-bacterial symbiotic culture medium is 100-120 cells / mL, and the initial concentration of the bacillus licheniformis is 100-120 cells / mL;

[0019] The chlorella vulgaris is chlorella vulgaris FACHB-21, and the bacillus licheniformis is bacillus licheniformis ATCC14580.

[0020] 5-15 g of the modified biochar is mixed with 100 g of the algal-bacterial symbiotic culture medium.

[0021] The oxytetracycline wastewater treatment method based on algal-bacterial symbiotic granular sludge, wherein the algal-bacterial symbiotic culture medium uses a BG11 culture medium and adds vitamin C to make the concentration of the vitamin C 0.1 g / L.

[0022] The method for treating terramycin wastewater based on algal-bacterial symbiotic granular sludge, wherein, in step (1), a boron-doped diamond electrode is used as an anode, a stainless steel electrode is used as a cathode, the electrode spacing is set to 0.9-1.1 cm, and the current density is set to 18-22 mA / cm 2 , and the reaction time is 50-70 minutes.

[0023] The method for treating terramycin wastewater based on algal-bacterial symbiotic granular sludge, wherein, in step (2), a photocatalyst is filled in the photocatalytic reactor, the loading amount is 3-5 g / L terramycin wastewater, ultraviolet light is used for irradiation, the light intensity is set to 2.5-3.5 mW / cm 2 , and the reaction time is 50-70 minutes.

[0024] The method for treating terramycin wastewater based on algal-bacterial symbiotic granular sludge, wherein, the photocatalyst is a Cu-doped TiO2 photocatalyst, and the doping amount of Cu is 0.5-2%.

[0025] The method for treating terramycin wastewater based on algal-bacterial symbiotic granular sludge, wherein, in step (3), 3-7 g of the algal-bacterial symbiotic granular sludge is added to 1 L of the terramycin wastewater, the temperature is controlled to be between 25-30 DEG C, the light intensity is set to be 2800-3200 Lux, the dissolved oxygen is controlled to be between 5-7 mg / L through intermittent light irradiation, and the hydraulic retention time is 24-48 hours.

[0026] The method for treating terramycin wastewater based on algal-bacterial symbiotic granular sludge, wherein, the preparation process of the biochar comprises the following steps:

[0027] The straw is crushed to a particle size of less than 2 mm, washed several times with deionized water, and dried to a constant weight at 50-70 DEG C;

[0028] The dried straw is heated to 450-550 DEG C at a heating rate of 8-12 DEG C / min under N2 atmosphere, and carbonized at constant temperature for 0.8-1.7 hours to obtain the biochar.

[0029] The method for treating terramycin wastewater based on algal-bacterial symbiotic granular sludge, wherein, the straw is corn straw.

[0030] Compared with the prior art, the present application has the following beneficial effects:

[0031] In the scheme, the three processes of catalytic oxidation, photocatalysis and algal-bacterial symbiosis can work together to more effectively remove terramycin and achieve efficient and deep treatment of terramycin wastewater. The electro-catalytic oxidation reduces the toxicity of terramycin and improves the efficiency of subsequent photocatalysis and biodegradation; the photocatalysis degrades part of the terramycin; and the algal-bacterial symbiotic system uses small-molecule organic matter degraded by photocatalysis as nutrition to further remove terramycin and pollutants in terramycin wastewater. DETAILED DESCRIPTION

[0032] To facilitate the understanding of the present application, the present application is illustrated by the following examples. Those skilled in the art should understand that the examples are only to help understand the present application and should not be regarded as specific limitations of the present application.

[0033] The molecular structure of terramycin is stable and difficult to biodegrade, and some degradation products may have potential toxicity. The algal-bacterial symbiotic granular sludge technology alone may not be able to completely remove terramycin, and there is a risk that the effluent quality cannot meet the standard. In addition, the existing algal-bacterial symbiotic system has limited treatment capacity for high-concentration terramycin wastewater, and the treatment efficiency needs to be further improved. The present application provides a terramycin wastewater treatment method based on algal-bacterial symbiotic granular sludge, which can effectively treat terramycin and improve the treatment efficiency of terramycin wastewater. In the scheme, terramycin wastewater refers to wastewater containing terramycin.

[0034] The present application provides a terramycin wastewater treatment method based on algal-bacterial symbiotic granular sludge, comprising the following steps:

[0035] (1) The terramycin wastewater is subjected to electro-catalytic oxidation treatment.

[0036] Specifically, the terramycin wastewater is introduced into an electro-catalytic oxidation reactor for electro-catalytic oxidation treatment, wherein a boron-doped diamond (BDD) electrode is used as an anode and a stainless steel electrode is used as a cathode, the electrode spacing is set to 0.9-1.1 cm, the current density is set to 18-22 mA / cm 2 , and the reaction time is 50-70 minutes.

[0037] The boron-doped diamond (BDD) electrode has a high oxidation potential and good chemical stability, which can effectively oxidize and break the terramycin molecules, reduce their toxicity, and convert them into small-molecule organic matter that is easier to biodegrade. In this step, the current density is set to 18-22 mA / cm 2 to ensure the rate of electro-catalytic oxidation reaction, and the reaction time of 50-70 minutes can ensure the sufficient oxidation of terramycin.

[0038] (2) The terramycin wastewater is subjected to photocatalysis treatment.

[0039] Specifically, the oxytetracycline wastewater after electro-catalytic oxidation is introduced into a photocatalytic reactor for photocatalytic treatment, wherein the photocatalytic reactor is filled with a photocatalyst, the loading amount is 3-5 g / L of the oxytetracycline wastewater, ultraviolet light is used for irradiation, the light intensity is set to 2.5-3.5 mW / cm 2 , and the reaction time is 50-70 minutes. The photocatalyst can be a Cu-doped TiO2 photocatalyst.

[0040] The loading amount of 3-5 g / L of the oxytetracycline wastewater means that 3-5 g of the Cu-doped TiO2 photocatalyst is used for treating 1 liter of the oxytetracycline wastewater.

[0041] The Cu-doped TiO2 photocatalyst can improve the visible light response of the photocatalyst and improve the photocatalytic efficiency. The Cu-doped TiO2 photocatalyst generates an electron-hole pair under ultraviolet light irradiation, and the hole oxidizes water or hydroxyl ions into hydroxyl radicals (·OH), and the electron reacts with dissolved oxygen to generate superoxide radicals (O 2- ·). These free radicals can further degrade the oxytetracycline into non-toxic and harmless small molecular substances such as CO2 and H2O. In this step, the light intensity is set to 2.5-3.5 mW / cm 2 , which can ensure the rate of photocatalytic reaction, and the reaction time of 50-70 minutes can ensure the sufficient degradation of the oxytetracycline.

[0042] The Cu-doped amount of the Cu-doped TiO2 photocatalyst can be 0.5-2%, and in the embodiment of the present application, the Cu-doped amount is 1.5%, and the Cu-doped TiO2 photocatalyst is purchased from Nanjing Baokete New Material Co., Ltd.

[0043] (3) The oxytetracycline wastewater is treated by using algal-bacterial symbiotic granular sludge.

[0044] Specifically, the oxytetracycline wastewater after photocatalytic treatment is introduced into an algal-bacterial symbiotic granular sludge reactor, 3-7 g of algal-bacterial symbiotic granular sludge is added per 1 L of the oxytetracycline wastewater, the temperature is controlled to be between 25-30℃, the light intensity is set to be 2800-3200 Lux, the dissolved oxygen is controlled to be between 5-7 mg / L by intermittent light, and the hydraulic retention time (HRT) is 24-48 hours.

[0045] The algal-bacterial symbiotic granular sludge can use the small molecular organic matter after photocatalytic degradation as nutrition to further remove the pollutants in the oxytetracycline wastewater. In this step, controlling the temperature to be between 25-30℃ is beneficial to the growth and metabolism of algae and bacteria, setting the light intensity to be 2800-3200 Lux can ensure the photosynthesis of algae, and the hydraulic retention time of 24-48 hours can ensure the sufficient degradation of the oxytetracycline.

[0046] In the scheme of the present application, through the synergistic effect of the three processes of catalytic oxidation, photocatalysis and algal-bacterial symbiosis, the terramycin can be more effectively removed, and the efficient and deep treatment of terramycin wastewater is realized. The electro-catalytic oxidation reduces the toxicity of terramycin, improves the efficiency of subsequent photocatalysis and biodegradation; the photocatalysis degrades part of the terramycin; the algal-bacterial symbiotic system uses the small molecular organic matter degraded by photocatalysis as nutrition to further remove terramycin and pollutants in terramycin wastewater.

[0047] Compared with the prior art, the process flow has the following advantages:

[0048] Compared with the simple algal-bacterial symbiotic granular sludge technology, the process flow can more effectively remove terramycin, realize efficient and deep treatment of terramycin wastewater, and improve the effluent water quality;

[0049] Compared with the traditional terramycin wastewater treatment method, the process flow has the advantages of high treatment efficiency, low operation cost, and low sludge yield;

[0050] The electro-catalytic oxidation process reduces the toxicity of terramycin, protects the algal-bacterial symbiotic system, and improves the stability of the system;

[0051] The Cu-doped TiO2 photocatalyst can improve the visible light response of the photocatalyst and improve the photocatalytic efficiency.

[0052] The traditional algal-bacterial symbiotic granular sludge has poor settling performance due to low density and loose structure. Slow settling speed can lead to sludge loss, reduce treatment effect, and increase operation cost. Moreover, the existing preparation method lacks consideration of the long-term stability of the algal-bacterial symbiotic system. Imbalance of the ratio of algae and bacteria, loss of EPS (extracellular polymeric substance), and death of microorganisms can cause the disintegration of sludge particles and affect the persistence of treatment effect. As a porous material, biochar has the advantages of adsorbing pollutants and providing microbial attachment sites, but the influence of its surface properties and pore structure on the algal-bacterial symbiotic system has not been fully studied. Unmodified biochar may have strong surface hydrophobicity and pore blockage, limiting its application in the algal-bacterial symbiotic system.

[0053] Further, in the scheme of the present application, the preparation method of the algal-bacterial symbiotic granular sludge comprises the following steps:

[0054] (a) straw pretreatment:

[0055] The straw is crushed to a particle size of less than 2 mm, washed several times with deionized water to remove surface impurities and soluble sugars, and dried to constant weight in an oven at 50-70°C.

[0056] In this step, by removing the impurities and soluble sugars on the surface of the straw, it can avoid excessive tar and gas in the subsequent carbonization process, affecting the quality of the biochar. Drying to constant weight can ensure the stability and consistency of the carbonization process.

[0057] In the embodiment of the present application, the straw used is corn straw, which is widely available, low in price, and has a high cellulose content. In addition, straw can also be used as wheat straw, rice straw and other agricultural waste.

[0058] (b) Preparation of biochar:

[0059] The dried straw is heated to 450-550℃ at a heating rate of 8-12℃ / min under N2 atmosphere, and carbonized at constant temperature for 0.8-1.7 hours to obtain biochar.

[0060] In this step, the organic matter in the straw can be converted into stable carbon structure by high temperature carbonization to form biochar. The carbonization temperature is set to 450-550℃, which can ensure the yield of biochar while obtaining higher specific surface area and porosity. In the carbonization process, N2 atmosphere is introduced to prevent the oxidation of biochar.

[0061] (c) Modification of biochar:

[0062] The biochar is dispersed in an ammonia solution, CuSO4·5H2O is added as a catalyst, and the reaction is stirred in a water bath at 45-55℃ for 5-7 hours; after the reaction is completed, it is washed with deionized water until it is neutral, and dried in an oven at 70-90℃ to constant weight.

[0063] In this step, ammonia water is used as the ammonia source for liquid phase ammoniation modification, which improves the contact area and reaction efficiency of ammonia gas with biochar, improves the utilization rate of ammonia gas, and reduces the escape of ammonia gas. CuSO4 is used as a catalyst to promote the dissolution of ammonia gas in water and accelerate the reaction between ammonia gas and the acidic functional groups on the surface of biochar, forming more nitrogen-containing functional groups, thereby improving the adsorption capacity of biochar for terramycin. These nitrogen-containing functional groups can form hydrogen bonds or electrostatic interactions with the hydroxyl, amino and other groups in the terramycin molecule, enhancing the adsorption effect.

[0064] In this step, 8-12mL of ammonia solution is used per 1g of biochar, and the mass concentration of the ammonia solution can be 5-15%, and 0.3-0.7g of CuSO4·5H2O is added per 1L of ammonia solution.

[0065] In the present application, the modified biochar has the following advantages:

[0066] Higher terramycin removal efficiency: ammonia-modified biochar can significantly improve the adsorption capacity of terramycin, combined with the biodegradation of algal-bacterial symbiotic system, can achieve higher terramycin removal efficiency;

[0067] Stronger stress resistance: modified biochar can adsorb organic matter and salt in terramycin wastewater, reduce its inhibition on microorganisms, and improve the stress resistance of algal-bacterial symbiotic system;

[0068] Lower cost: straw is an agricultural waste, widely available and low in price, which can reduce production cost;

[0069] More environmentally friendly: the process uses environmentally friendly biochar and microorganisms, avoiding the use of chemical agents, and is more environmentally friendly.

[0070] (d) Preparation of algal-bacterial symbiotic granular sludge:

[0071] Mix modified biochar with algal-bacterial symbiotic medium, under the conditions of light intensity of 2800-3200 Lux, temperature of 25-30℃, pH value of 6.8-7.2, dissolved oxygen maintained at 5-7mg / L, stirring culture at 100-140rpm for 7-14 days to form algal-bacterial symbiotic granular sludge.

[0072] In this step, algal-bacterial symbiotic medium contains terramycin and bacillus licheniformis, and the initial concentration of terramycin and bacillus licheniformis can be 100-120 cells / mL respectively. Every 5-15g of modified biochar can be mixed with 100g of algal-bacterial symbiotic medium.

[0073] In this embodiment, terramycin is terramycin FACHB-21, purchased from Freshwater Algae Culture Collection of Institute of Hydrobiology, Chinese Academy of Sciences; bacillus licheniformis is ATCC 14580, purchased from Shanghai Baoluobiotechnology Co., Ltd. Terramycin can produce oxygen through photosynthesis, providing oxygen source for aerobic respiration of bacillus licheniformis; bacillus licheniformis decomposes organic matter, providing CO2 and nutrients for terramycin, this mutualistic symbiotic relationship can improve the activity and stability of algal-bacterial symbiotic system.

[0074] Further, the culture medium used in algal-bacterial symbiotic medium uses BG11 culture medium and adds vitamin C, so that the concentration of vitamin C is 0.1g / L. Vitamin C as an antioxidant can scavenge active oxygen free radicals in terramycin wastewater, reduce its stress on microorganisms, and improve the stress resistance and long-term stability of algal-bacterial symbiotic system.

[0075] In this step, the light intensity, temperature, pH value and dissolved oxygen conditions need to be controlled within the appropriate range to ensure the activity of microorganisms. Maintaining the dissolved oxygen at 5-7 mg / L can promote algal photosynthesis and bacterial aerobic respiration, and improve the activity of the algal-bacterial symbiotic system.

[0076] (e) Sludge particle post-processing:

[0077] The formed algal-bacterial symbiotic granular sludge is collected with a 200 μm mesh screen, washed with deionized water, and the unbound biochar and free microorganisms are removed.

[0078] In this step, the unbound biochar and free microorganisms can be removed by the mesh screen to improve the purity and stability of the algal-bacterial symbiotic granular sludge. Further washing with deionized water can remove residual medium components and avoid interference with subsequent processing.

[0079] In the present application, the algal-bacterial symbiotic granular sludge can remove terramycin in terramycin wastewater based on the adsorption of biochar and the biodegradation of microorganisms, and can achieve higher terramycin removal efficiency. Straw-based biochar has a high specific surface area and rich pore structure, which can adsorb terramycin in terramycin wastewater. The nitrogen-containing functional groups introduced on the surface of ammonia-modified biochar can form hydrogen bonds or electrostatic interactions with hydroxyl groups, amino groups and other groups in terramycin molecules, enhancing its adsorption capacity for terramycin. In addition, the pore structure of biochar can also provide attachment sites for algae and bacteria, increasing biomass and activity. Chlorella vulgaris produces oxygen through photosynthesis, providing oxygen source for aerobic respiration of Bacillus licheniformis; Bacillus licheniformis decomposes organic matter, providing CO2 and nutrients for Chlorella vulgaris, which can improve the activity and stability of the algal-bacterial symbiotic system.

[0080] The present application is further described below through specific embodiments.

[0081] Example 1: Preparation of algal-bacterial symbiotic granular sludge

[0082] 1. Straw pretreatment: The collected corn straw was crushed to a particle size of less than 2 mm, washed with deionized water for 3 times, each time for 15 minutes, to remove surface impurities and soluble sugars, and dried to constant weight in an oven at 60°C.

[0083] 2. Biochar preparation: The dried straw was placed in a tube furnace, heated to 500°C at a rate of 10°C / min under N2 atmosphere, and carbonized at constant temperature for 2 hours to obtain biochar.

[0084] 3. Biochar modification: The biochar was dispersed in 10% ammonia solution (purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd.) with a solid-liquid ratio of 1:10 (g / mL), and 0.5 g of CuSO4·5H2O (National Pharmaceutical Group Chemical Reagent Co., Ltd.) was added as a catalyst per 1 L of ammonia solution. The mixture was stirred in a 50°C water bath for 6 hours. After the reaction was completed, the mixture was washed with deionized water until it was neutral, and then dried in an oven at 80°C until the weight was constant.

[0085] 4. Preparation of algae-bacteria symbiotic granular sludge: The BG11 medium was used, and vitamin C was added to make the concentration of vitamin C 0.1 g / L (National Pharmaceutical Group Chemical Reagent Co., Ltd.). The Chlorella vulgaris FACHB-21 (purchased from the Freshwater Algae Culture Collection of the Chinese Academy of Sciences) and Bacillus licheniformis ATCC 14580 (purchased from Shanghai Baoluobiotechnology Co., Ltd.) were mixed at a volume ratio of 1:1, and the initial concentration of each was 106 cells / mL, to obtain an algae-bacteria symbiotic culture medium. The modified biochar was added to the algae-bacteria symbiotic culture medium and mixed at a mass ratio of 10:100. The mixture was then cultured under the following conditions: light intensity of 3000 Lux, temperature of 25°C, pH of 7.0, and dissolved oxygen maintained at 6 mg / L, with stirring at a speed of 120 rpm for 7 days, to form algae-bacteria symbiotic granular sludge.

[0086] 5. Post-treatment of sludge granules: The algae-bacteria symbiotic granular sludge formed was collected using a sieve with a pore size of 200 μm, washed once with deionized water, and the unbound biochar and free microorganisms were removed.

[0087] Specific surface area and pore size analysis: The modified biochar prepared in step 3 was subjected to specific surface area and pore size analysis. The specific surface area of the solid material was determined by gas adsorption BET method according to standard GB / T 19587-2004. Nitrogen adsorption method was used, and a specific surface area analyzer was used to determine the specific surface area of the biochar. Before testing, the biochar sample was vacuum degassed at 300°C for 3 hours. The specific surface area was calculated using the BET (Brunauer-Emmett-Teller) method. The specific surface area of the biochar was 220 m 2 / g.

[0088] Sludge granule settling performance determination: The prepared algae-bacteria symbiotic granular sludge was added to deionized water, and the sludge granule concentration was 10 g / L. The sludge was allowed to settle, and the sludge interface height was recorded every 5 minutes. The sludge settling velocity was calculated. The settling velocity was 1.2 cm / min, indicating that the algae-bacteria symbiotic granular sludge had good settling performance.

[0089] Stability determination of algal-bacterial symbiotic system: The prepared algal-bacterial symbiotic granular sludge was added to the simulated oxytetracycline wastewater, the initial concentration of oxytetracycline was 50 mg / L, and the amount of sludge granules added was 5 g / L. The light intensity was controlled at 3000 Lux, the temperature was controlled between 25-30℃, the dissolved oxygen was controlled at about 6 mg / L by intermittent light, the stirring speed was 120 rpm, and the reaction was continuously operated for 30 days to investigate the stability of the algal-bacterial symbiotic system. During the operation, samples were taken every 7 days to determine the cell density of algae and bacteria and calculate the algal-bacterial ratio. The cell density of algae was determined by fluorescence microscopic counting, and the cell density of bacteria was determined by plate counting method. During the operation, the algal-bacterial ratio (algae:bacteria) was basically stable at about 1:1 in 4 sampling times (1st day, 7th day, 14th day, 28th day), indicating that the algal-bacterial symbiotic system had good stability and could maintain stable operation within 30 days.

[0090] Oxytetracycline removal rate determination: The simulated wastewater containing oxytetracycline was introduced into the sludge reactor with the algal-bacterial symbiotic granular sludge prepared in Example 1, the initial concentration of oxytetracycline was 50 mg / L, 5 g of algal-bacterial symbiotic granular sludge was added per 1 L of oxytetracycline wastewater, the temperature was controlled at 25-30℃, the light intensity was controlled at 3000 lux, the dissolved oxygen was controlled at about 6 mg / L by intermittent light, and the hydraulic retention time was 24 hours. The treated oxytetracycline wastewater was subjected to oxytetracycline removal rate determination: The concentration of oxytetracycline was determined by Agilent 1200 liquid chromatograph, the chromatographic column was C18 column (4.6 mm x 250 mm, 5 μm), the mobile phase was oxalic acid: acetonitrile: methanol = 80:10:10 (volume ratio), the ultraviolet detector was used, and the analysis wavelength was 260 nm. The oxytetracycline removal rate calculation formula is: removal rate = (C0-C t ) / C0 x 100%, wherein C0 is the initial concentration of oxytetracycline, C t is the concentration of treated oxytetracycline. Results: The oxytetracycline removal rate was 95%.

[0091] Example 2: Treatment of oxytetracycline wastewater

[0092] Source of oxytetracycline wastewater: The oxytetracycline wastewater from a certain veterinary drug production enterprise, the initial concentration of oxytetracycline was 50 mg / L, the COD was 300 mg / L, and the pH was 7.5.

[0093] 1. Electro-catalytic oxidation stage: The oxytetracycline wastewater was introduced into the electro-catalytic oxidation reactor for electro-catalytic oxidation treatment, boron-doped diamond (BDD) electrode was used as anode, stainless steel electrode was used as cathode, the electrode spacing was 1 cm, the current density was 20 mA / cm 2 , and the reaction time was 60 minutes.

[0094] 2. Photocatalysis stage: the oxytetracycline wastewater after electrocatalytic oxidation is introduced into a photocatalytic reactor for photocatalytic treatment, the reactor is filled with Cu-doped TiO2 photocatalyst (Cu doping amount 1.5%, purchased from Nanjing Baokete New Material Co., Ltd.), the loading amount is 4 g / L of oxytetracycline wastewater, ultraviolet light is used for irradiation, the light intensity is 3 mW / cm 2 , and the reaction time is 60 minutes.

[0095] 3. Algal-bacterial symbiosis stage: the oxytetracycline wastewater after photocatalysis is introduced into a sludge reactor in which the algal-bacterial symbiotic granular sludge prepared in Example 1 is put, 5 g of the algal-bacterial symbiotic granular sludge is put for every 1 L of the oxytetracycline wastewater, the temperature is controlled at 25-30°C, the light intensity is 3000 Lux, the dissolved oxygen is controlled at about 6 mg / L through intermittent light, and the hydraulic retention time is 24 hours.

[0096] The removal rate of oxytetracycline in the treated oxytetracycline wastewater is determined: after the electrocatalytic oxidation, photocatalysis and algal-bacterial symbiosis treatment, the concentration of oxytetracycline is reduced to 0.5 mg / L, and the removal rate reaches 99%.

[0097] The removal rate of COD in the treated oxytetracycline wastewater is determined: the COD is determined by the potassium dichromate method, and the standard is “HJ 828-2017 Water Quality-Determination of Chemical Oxygen Demand-Potassium Dichromate Method”. The results are as follows: after the electrocatalytic oxidation, photocatalysis and algal-bacterial symbiosis treatment, the COD is reduced to 38 mg / L, and the removal rate reaches 87.33%.

[0098] Example 3: treatment of oxytetracycline wastewater

[0099] The source of the oxytetracycline wastewater is the oxytetracycline wastewater of a breeding farm, the initial concentration of oxytetracycline is 80 mg / L, the COD is 400 mg / L, and the pH is 7.0.

[0100] 1. Electro-catalytic oxidation stage: the oxytetracycline wastewater is introduced into an electro-catalytic oxidation reactor for electro-catalytic oxidation treatment, a boron-doped diamond (BDD) electrode is used as an anode, a stainless steel electrode is used as a cathode, the electrode spacing is 1 cm, the current density is 20 mA / cm 2 , and the reaction time is 60 minutes.

[0101] 2. Photocatalysis stage: the oxytetracycline wastewater after electro-catalytic oxidation is introduced into a photocatalytic reactor for photocatalytic treatment, the reactor is filled with Cu-doped TiO2 photocatalyst (Cu doping amount 1.5%, purchased from Nanjing Baokete New Material Co., Ltd.), the loading amount is 4 g / L of oxytetracycline wastewater, ultraviolet light is used for irradiation, the light intensity is 3 mW / cm 2 , and the reaction time is 60 minutes.

[0102] 3. Algal-bacterial symbiosis stage: the photocatalyzed oxytetracycline wastewater was introduced into a sludge reactor filled with the algal-bacterial symbiotic granular sludge prepared in Example 1, 5 g of the algal-bacterial symbiotic granular sludge was added per 1 L of the oxytetracycline wastewater, the temperature was controlled at 25-30°C, the light intensity was 3000 Lux, the dissolved oxygen was controlled at about 6 mg / L by intermittent light, and the hydraulic retention time was 24 hours.

[0103] The removal rate of oxytetracycline in the treated wastewater was determined: after the electro-catalytic oxidation, photocatalysis and algal-bacterial symbiosis treatment, the concentration of oxytetracycline was reduced to 0.45 mg / L, and the removal rate reached 99.44%.

[0104] The removal rate of COD in the treated wastewater was determined: after the electro-catalytic oxidation, photocatalysis and algal-bacterial symbiosis treatment, the COD was reduced to 43 mg / L, and the removal rate reached 89.25%.

[0105] Comparative Example 1

[0106] The preparation method of the algal-bacterial symbiotic granular sludge was basically the same as that of Example 1, except that the biochar modification was not performed.

[0107] 1. Straw pretreatment: The collected corn straw was crushed to a particle size of less than 2 mm, washed with deionized water for 3 times, each time for 15 minutes, to remove surface impurities and soluble sugars, and dried to constant weight in an oven at 60°C.

[0108] 2. Biochar preparation: The dried straw was placed in a tube furnace, heated to 500°C at a heating rate of 10°C / min under N2 atmosphere, and carbonized at constant temperature for 2 hours to obtain biochar.

[0109] 3. Preparation of algal-bacterial symbiotic granular sludge: The culture medium was BG11 medium with the addition of vitamin C to make the concentration of vitamin C 0.1 g / L (National Pharmaceutical Group Chemical Reagent Co., Ltd.), and the soil green ball algae FACHB-21 (purchased from Freshwater Algae Culture Collection of Institute of Hydrobiology, Chinese Academy of Sciences) and Bacillus licheniformis ATCC 14580 (purchased from Shanghai Baoluobiotechnology Co., Ltd.) were mixed at a volume ratio of 1:1, and the initial concentration of each was 106 cells / mL to obtain an algal-bacterial symbiotic culture medium. The modified biochar was added to the algal-bacterial symbiotic culture medium for mixing, the mass ratio of modified biochar to algal-bacterial symbiotic culture medium was 10:100, then under the conditions of light intensity of 3000 Lux, temperature of 25°C, pH value of 7.0, and dissolved oxygen maintained at 6 mg / L, the stirring culture was carried out at a speed of 120 rpm for 7 days to form algal-bacterial symbiotic granular sludge.

[0110] 4. Post-treatment of sludge granules: The formed algal-bacterial symbiotic granular sludge was collected with a 200 μm mesh screen, washed once with deionized water to remove unbound biochar and free microorganisms.

[0111] Specific surface area and pore size analysis: The specific surface area of the biochar was 150 m 2 / g, indicating that liquid ammonia-modified straw-based biochar can improve the specific surface area of biochar.

[0112] Sludge granule settling performance determination: The settling speed was 0.8 cm / min, indicating that liquid ammonia-modified straw-based biochar can significantly improve the settling speed of sludge granules.

[0113] Algal-bacterial symbiotic system stability determination: During the operation, four samples were taken (1st day, 7th day, 14th day, 28th day), and the algal-bacterial ratio was basically stable at about 1:1 (algae: bacteria) before the 14th day, but the pH fluctuation was large on the 20th day, and the algal-bacterial symbiotic system was unbalanced.

[0114] Terramycin removal rate determination: The simulated wastewater containing terramycin was introduced into the sludge reactor with the algal-bacterial symbiotic granular sludge prepared by Comparative Example 1, the initial concentration of terramycin was 50 mg / L, 5 g of algal-bacterial symbiotic granular sludge was added per 1 L of terramycin wastewater, the temperature was controlled at 25-30°C, the light intensity was 3000 lux, the dissolved oxygen was maintained at about 6 mg / L by intermittent light control, and the hydraulic retention time was 24 hours. The terramycin removal rate was 70%.

[0115] Comparative Example 2

[0116] The algal-bacterial symbiotic granular sludge prepared by Comparative Example 1 was used to treat the terramycin wastewater in Example 2, and the treatment steps were the same as in Example 2, except that the algal-bacterial symbiotic granular sludge prepared by Comparative Example 1 was used.

[0117] Terramycin removal rate determination was performed on the treated terramycin wastewater: After electro-catalytic oxidation, photocatalysis and algal-bacterial symbiosis treatment, the terramycin concentration was reduced to 0.8 mg / L, and the removal rate was 98.4%.

[0118] COD removal rate determination was performed on the treated terramycin wastewater: After electro-catalytic oxidation, photocatalysis and algal-bacterial symbiosis treatment, the COD was reduced to 60 mg / L, and the removal rate was 80%.

[0119] In summary, the liquid ammonia modified straw-based biochar can significantly improve the removal efficiency of oxytetracycline, the settling velocity and the stability of the algal-bacterial symbiotic granular sludge. Compared with the unmodified biochar, the liquid ammonia modified biochar can significantly improve the performance of the algal-bacterial symbiotic granular sludge. Moreover, the synergistic effect of the three processes of electro-catalytic oxidation, photo-catalysis and algal-bacterial symbiosis in the application can more effectively remove oxytetracycline, and achieve efficient and deep treatment of wastewater.

[0120] It should be understood that the application of the present application is not limited to the above examples, and those skilled in the art can make improvements or changes according to the above description, and all these improvements and changes shall belong to the protection scope of the present application.

Claims

1. A method for treating oxytetracycline wastewater based on algae-bacterial symbiotic granular sludge, characterized in that, Includes the following steps: (1) Electrocatalytic oxidation treatment of oxytetracycline wastewater; (2) The oxytetracycline wastewater that has undergone the electrocatalytic oxidation treatment is subjected to photocatalytic treatment; (3) The oxytetracycline wastewater that has undergone photocatalytic treatment is treated with algae-bacteria symbiotic granular sludge; The method for preparing the algae-bacterial symbiotic granular sludge includes the following steps: Biochar was dispersed in an ammonia solution, and CuSO4·5H2O was added as a catalyst. The mixture was stirred in a water bath at 45-55℃ for 5-7 hours. After the reaction was completed, the mixture was washed with deionized water until neutral and dried at 70-90℃ to constant weight to obtain modified biochar. The modified biochar was mixed with an algae-bacterial symbiotic culture medium and cultured under the conditions of light intensity of 2800-3200 Lux, temperature of 25-30℃, pH of 6.8-7.2, and dissolved oxygen maintained at 5-7 mg / L, and stirred at a speed of 100-140 rpm for 7-14 days to form the algae-bacterial symbiotic granular sludge. In this process, 8-12 mL of the ammonia solution is used for every 1 g of the biochar, the mass concentration of the ammonia solution is 5-15%, and 0.3-0.7 g of CuSO4·5H2O is added to every 1 L of the ammonia solution; The algae-bacterial symbiotic culture medium contains *Chlorella vulgaris* and *Bacillus licheniformis*. The preparation process of the biochar includes the following steps: The straw is crushed to a particle size of less than 2 mm, washed several times with deionized water, and dried at 50-70℃ to constant weight. The dried straw was heated to 450-550℃ at a heating rate of 8-12℃ / min under N2 atmosphere and carbonized at a constant temperature for 0.8-1.7 hours to obtain the biochar.

2. The method for treating oxytetracycline wastewater based on algae-bacterial symbiotic granular sludge according to claim 1, characterized in that, The initial concentration of the terrestrial Chlorella in the algae-bacterial symbiotic culture medium is 100-120 cells / mL, and the initial concentration of the Bacillus is 100-120 cells / mL. The terrestrial green algae is terrestrial green algae FACHB-21, and the Bacillus licheniformis is Bacillus licheniformis ATCC14580; Mix 5-15g of the modified biochar with 100g of the algae-bacteria symbiotic culture medium.

3. The method for treating oxytetracycline wastewater based on algae-bacterial symbiotic granular sludge according to claim 1, characterized in that, The algae-bacteria symbiotic culture medium used is BG11 medium with added vitamin C, so that the vitamin C concentration is 0.1 g / L.

4. The method for treating oxytetracycline wastewater based on algae-bacterial symbiotic granular sludge according to claim 1, characterized in that, In step (1), a boron-doped diamond electrode is used as the anode, and a stainless steel electrode is used as the cathode. The electrode spacing is set to 0.9-1.1 cm, and the current density is set to 18-22 mA / cm². 2 The reaction time is 50-70 minutes.

5. The method for treating oxytetracycline wastewater based on algae-bacterial symbiotic granular sludge according to claim 1, characterized in that, In step (2), the photocatalytic reactor is filled with a photocatalyst with a loading of 3-5 g / L of oxytetracycline wastewater, and is irradiated with ultraviolet light at an intensity of 2.5-3.5 mW / cm². 2 The reaction time is 50-70 minutes.

6. The method for treating oxytetracycline wastewater based on algae-bacterial symbiotic granular sludge according to claim 5, characterized in that, The photocatalyst is a Cu-doped TiO2 photocatalyst with a Cu doping amount of 0.5-2%.

7. The method for treating oxytetracycline wastewater based on algae-bacterial symbiotic granular sludge according to claim 1, characterized in that, In step (3), 3-7g of the algae-bacteria symbiotic granular sludge is added to every 1L of the oxytetracycline wastewater, the temperature is controlled between 25-30℃, the light intensity is set to 2800-3200 Lux, the dissolved oxygen is controlled between 5-7mg / L by intermittent light, and the hydraulic retention time is 24-48 hours.

8. The method for treating oxytetracycline wastewater based on algae-bacterial symbiotic granular sludge according to claim 1, characterized in that, The straw in question is corn stalks.