A microbial flocculant and preparation method thereof

Abstract

The invention belongs to the technical field of sewage treatment, and specifically relates to a microbial flocculant and a preparation method thereof, wherein the microbial flocculant comprises a zinc skeleton, oligodextrose polymerized on the zinc skeleton, and microorganisms colonized on the zinc skeleton and the oligodextrose. The microbial flocculant of the invention immobilizes microorganisms and can be recycled and reused.

Description

Technical Field

[0001] The invention belongs to the technical field of sewage treatment, and specifically relates to a microbial flocculant and a preparation method thereof. Background Art

[0002] Textile dyeing wastewater has high COD content, large chroma and is difficult to treat. Many scholars at home and abroad have studied its treatment. Microbial flocculants have multiple functions such as flocculation and adsorption. They have the advantages of high efficiency and no secondary pollution in removing the chroma and COD of printing and dyeing wastewater. However, the large amount of microbial flocculants and their high price limit their widespread application in large-scale production and industry. Summary of the invention

[0003] In order to solve the deficiencies in the prior art, the present invention mainly provides a preparation method with low microbial loss and simple process. The specific scheme is as follows:

[0004] A microbial flocculant comprises a zinc skeleton, oligodextrose polymerized on the zinc skeleton and microorganisms colonized on the zinc skeleton and the oligodextrose.

[0005] Furthermore, the microorganism is Klebsiella.

[0006] A method for preparing the above-mentioned microbial flocculant comprises the following steps:

[0007] a. Prepare a zinc skeleton by taking a zinc salt and 2-methylimidazole;

[0008] b. Add glucose to the zinc skeleton, add an acid catalyst after it is fully dissolved, adjust the system temperature to 40-50°C, and distill under reduced pressure until the solid-liquid ratio in the system is 1:1; continue stirring until the weight of the system no longer changes; heat the remaining solid in the system and vacuum dry it at 90-100°C for 2-3h to obtain a carrier;

[0009] c. Disperse the carrier in water to obtain a 10-20 g / L dispersion, add dipotassium hydrogen phosphate to the dispersion, and adjust the pH of the system to 5.5-7; add a nitrogen source to the system, mix thoroughly, add microorganisms, and ferment on a shaking table for 24-36 hours; after separation, take the solid for pretreatment and then dry to obtain the product.

[0010] Furthermore, the acid catalyst in step b is one of malic acid, citric acid or chloroacetic acid; and the mass ratio of glucose to zinc skeleton in step b is 1:4-6.

[0011] Furthermore, the nitrogen source in step c is one or more of urea, beef extract, ammonium sulfate, peptone, yeast powder or ammonium sulfide; and the mass ratio of the nitrogen source to the carrier is 1:200-250.

[0012] Furthermore, the shaking fermentation temperature in step c is 25-40° C. and the fermentation speed is 160-200 r / min.

[0013] Furthermore, the drying in step c is performed by forced air drying or vacuum drying at 30-40° C. for 10-20 hours.

[0014] Furthermore, the drying in step c is precooled at 4° C. for 12 hours and then transferred to a -80° C. refrigerator for freezing for 24 hours.

[0015] Furthermore, the pretreatment in step c is to mix the separated solid with starch and whey powder in a mass ratio of 1: (0.05-0.15): (0.1-0.15).

[0016] Furthermore, the preparation of the zinc skeleton comprises the following steps:

[0017] Dissolve zinc salt and 2-methylimidazole in a mixed solvent of dimethyl sulfoxide and water at a molar ratio of 1:4-6 to obtain a zinc solution and a 2-methylimidazole solution; mix the zinc solution and the 2-methylimidazole solution, and stir them thoroughly for 8-10 hours to obtain a zinc skeleton; the zinc salt is one of zinc nitrate and zinc acetate.

[0018] By adopting the above scheme, the method of the present invention has the following advantages:

[0019] 1. The present invention combines polysaccharide-producing microorganisms with good flocculation effect on printing and dyeing wastewater with immobilized carriers, which can improve the precipitation performance of flocs through the carriers, and can also achieve good precipitation effects when the flocs are small.

[0020] 2. The present invention can realize the recovery of flocculating microorganisms by recycling the carrier, thereby reducing the amount of flocculant used and effectively reducing the cost of use without increasing secondary pollution, thus achieving a win-win goal of economic and environmental benefits.

[0021] 3. The present invention ensures that the carrier is light and has good adsorption properties, while enabling Klebsiella to be deeply colonized on the carrier, and has strong mass transfer performance and permeability.

[0022] 4. In the flocculant of the present invention, the oligodextrose on the surface of the carrier and wrapped inside and the unpolymerized glucose serve as carbon sources that can ensure the flocculation activity of Klebsiella. During the fermentation and colonization process, Klebsiella is attracted to colonize on the surface and inside of the carrier, so that Klebsiella is in firm contact with the carrier, reducing the loss of the flocculant during recovery.

[0023] 5. The present invention introduces an immobilized carrier into the microbial flocculant, which can not only improve the sedimentation performance of the flocs without adding chemical flocculants and reduce secondary pollution, but also ensure that the flocculating microorganisms are not lost with the effluent. After precipitation, they can be recovered with the carrier and subjected to corresponding regeneration treatment, thereby reducing the application cost of the microbial flocculant and facilitating its promotion. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] Embodiment 1:

[0026] (1) dissolving zinc nitrate and 2-methylimidazole in a mixed solvent of dimethyl sulfoxide and water at a molar ratio of 1:5, respectively, to obtain a zinc solution and a 2-methylimidazole solution; mixing the zinc solution and the 2-methylimidazole solution, stirring and reacting for 8 to 10 hours, to obtain a zinc skeleton;

[0027] (2) Glucose was added to the zinc skeleton, and after it was fully dissolved, an acid catalyst was added, the system temperature was adjusted to 45° C., and vacuum distillation was performed until the solid-liquid ratio in the system was 1:1; stirring was continued until the weight of the system no longer changed; the remaining solid in the system was heated and vacuum dried at 90° C. for 2 h to obtain a carrier;

[0028] (3) dispersing the carrier in water to obtain a 10 g / L dispersion, adding potassium hydrogen phosphate to the dispersion to adjust the pH of the system to 6; adding yeast powder to the system, mixing thoroughly, adding activated Klebsiella at an inoculum rate of 6%, and fermenting on a shaker for 24 hours; and obtaining a solid after separation;

[0029] (4) The separated solid was mixed with starch and whey powder in a mass ratio of 1:0.1:0.1, precooled at 4°C for 12 hours, and then transferred to a -80°C refrigerator for freezing for 24 hours.

[0030] Embodiment 2:

[0031] (1) dissolving zinc nitrate and 2-methylimidazole in a mixed solvent of dimethyl sulfoxide and water at a molar ratio of 1:5, respectively, to obtain a zinc solution and a 2-methylimidazole solution; mixing the zinc solution and the 2-methylimidazole solution, stirring and reacting for 8 to 10 hours, to obtain a zinc skeleton;

[0032] (2) Glucose was added to the zinc skeleton, and after it was fully dissolved, an acid catalyst was added, the system temperature was adjusted to 45° C., and vacuum distillation was performed until the solid-liquid ratio in the system was 1:1; stirring was continued until the weight of the system no longer changed; the remaining solid in the system was heated and vacuum dried at 100° C. for 2 h to obtain a carrier;

[0033] (3) dispersing the carrier in water to obtain a 10 g / L dispersion, adding potassium hydrogen phosphate to the dispersion to adjust the pH of the system to 6; adding yeast powder to the system, mixing thoroughly, adding activated Klebsiella at an inoculum rate of 6%, and fermenting on a shaker for 24 hours; and obtaining a solid after separation;

[0034] (4) The separated solid was mixed with starch and whey powder in a mass ratio of 1:0.1:0.1, precooled at 4°C for 12 hours, and then transferred to a -80°C refrigerator for freezing for 24 hours.

[0035] Embodiment 3:

[0036] (1) dissolving zinc nitrate and 2-methylimidazole in a mixed solvent of dimethyl sulfoxide and water at a molar ratio of 1:5, respectively, to obtain a zinc solution and a 2-methylimidazole solution; mixing the zinc solution and the 2-methylimidazole solution, stirring and reacting for 8 to 10 hours, to obtain a zinc skeleton;

[0037] (2) Glucose was added to the zinc skeleton, and after it was fully dissolved, an acid catalyst was added, the system temperature was adjusted to 45° C., and vacuum distillation was performed until the solid-liquid ratio in the system was 1:1; stirring was continued until the weight of the system no longer changed; the remaining solid in the system was heated and vacuum dried at 90° C. for 3 h to obtain a carrier;

[0038] (3) dispersing the carrier in water to obtain a 10 g / L dispersion, adding potassium hydrogen phosphate to the dispersion to adjust the pH of the system to 6; adding yeast powder to the system, mixing thoroughly, adding activated Klebsiella at an inoculum rate of 6%, and fermenting on a shaker for 24 hours; and obtaining a solid after separation;

[0039] (4) The separated solid was mixed with starch and whey powder in a mass ratio of 1:0.1:0.1, precooled at 4°C for 12 hours, and then transferred to a -80°C refrigerator for freezing for 24 hours.

[0040] Embodiment 4:

[0041] (1) dissolving zinc nitrate and 2-methylimidazole in a mixed solvent of dimethyl sulfoxide and water at a molar ratio of 1:5, respectively, to obtain a zinc solution and a 2-methylimidazole solution; mixing the zinc solution and the 2-methylimidazole solution, stirring and reacting for 8 to 10 hours, to obtain a zinc skeleton;

[0042] (2) Glucose was added to the zinc skeleton, and after it was fully dissolved, an acid catalyst was added, the system temperature was adjusted to 45° C., and vacuum distillation was performed until the solid-liquid ratio in the system was 1:1; stirring was continued until the weight of the system no longer changed; the remaining solid in the system was heated and vacuum dried at 90° C. for 2 h to obtain a carrier;

[0043] (3) dispersing the carrier in water to obtain a 20 g / L dispersion, adding potassium hydrogen phosphate to the dispersion to adjust the pH of the system to 6; adding yeast powder to the system, mixing thoroughly, adding activated Klebsiella at an inoculum rate of 6%, and fermenting on a shaker for 24 hours; and obtaining a solid after separation;

[0044] (4) The separated solid was mixed with starch and whey powder in a mass ratio of 1:0.1:0.1, precooled at 4°C for 12 hours, and then transferred to a -80°C refrigerator for freezing for 24 hours.

[0045] Embodiment 5:

[0046] (1) dissolving zinc nitrate and 2-methylimidazole in a mixed solvent of dimethyl sulfoxide and water at a molar ratio of 1:5, respectively, to obtain a zinc solution and a 2-methylimidazole solution; mixing the zinc solution and the 2-methylimidazole solution, stirring and reacting for 8 to 10 hours, to obtain a zinc skeleton;

[0047] (2) Glucose was added to the zinc skeleton, and after it was fully dissolved, an acid catalyst was added, the system temperature was adjusted to 45° C., and vacuum distillation was performed until the solid-liquid ratio in the system was 1:1; stirring was continued until the weight of the system no longer changed; the remaining solid in the system was heated and vacuum dried at 90° C. for 2 h to obtain a carrier;

[0048] (3) dispersing the carrier in water to obtain a 10 g / L dispersion, adding potassium hydrogen phosphate to the dispersion to adjust the pH of the system to 7; adding yeast powder to the system, mixing thoroughly, adding activated Klebsiella at an inoculum rate of 6%, and fermenting on a shaker for 24 hours; and obtaining a solid after separation;

[0049] (4) The separated solid was mixed with starch and whey powder in a mass ratio of 1:0.1:0.1, precooled at 4°C for 12 hours, and then transferred to a -80°C refrigerator for freezing for 24 hours.

[0050] Embodiment 6:

[0051] (1) dissolving zinc nitrate and 2-methylimidazole in a mixed solvent of dimethyl sulfoxide and water at a molar ratio of 1:5, respectively, to obtain a zinc solution and a 2-methylimidazole solution; mixing the zinc solution and the 2-methylimidazole solution, stirring and reacting for 8 to 10 hours, to obtain a zinc skeleton;

[0052] (2) Glucose was added to the zinc skeleton, and after it was fully dissolved, an acid catalyst was added, the system temperature was adjusted to 45° C., and vacuum distillation was performed until the solid-liquid ratio in the system was 1:1; stirring was continued until the weight of the system no longer changed; the remaining solid in the system was heated and vacuum dried at 90° C. for 2 h to obtain a carrier;

[0053] (3) dispersing the carrier in water to obtain a 10 g / L dispersion, adding potassium hydrogen phosphate to the dispersion to adjust the pH of the system to 6; adding yeast powder to the system, mixing thoroughly, adding activated Klebsiella at an inoculum rate of 6%, and fermenting on a shaker for 36 hours; and obtaining a solid after separation;

[0054] (4) The separated solid was mixed with starch and whey powder in a mass ratio of 1:0.1:0.1, precooled at 4°C for 12 hours, and then transferred to a -80°C refrigerator for freezing for 24 hours.

[0055] Embodiment 7:

[0056] (1) dissolving zinc nitrate and 2-methylimidazole in a mixed solvent of dimethyl sulfoxide and water at a molar ratio of 1:5, respectively, to obtain a zinc solution and a 2-methylimidazole solution; mixing the zinc solution and the 2-methylimidazole solution, stirring and reacting for 8 to 10 hours, to obtain a zinc skeleton;

[0057] (2) Glucose was added to the zinc skeleton, and after it was fully dissolved, an acid catalyst was added, the system temperature was adjusted to 45° C., and vacuum distillation was performed until the solid-liquid ratio in the system was 1:1; stirring was continued until the weight of the system no longer changed; the remaining solid in the system was heated and vacuum dried at 90° C. for 2 h to obtain a carrier;

[0058] (3) dispersing the carrier in water to obtain a 10 g / L dispersion, adding potassium hydrogen phosphate to the dispersion to adjust the pH of the system to 6; adding yeast powder to the system, mixing thoroughly, adding activated Klebsiella at an inoculum rate of 6%, and fermenting on a shaker for 24 hours; and obtaining a solid after separation;

[0059] (4) The separated solid was mixed with starch and whey powder in a mass ratio of 1:0.15:0.15, precooled at 4°C for 12 hours, and then transferred to a -80°C refrigerator for freezing for 24 hours.

[0060] Example sample test:

[0061] The flocculation effect experiment was conducted on the printing and dyeing wastewater using the flocculants of each embodiment. The flocculants of each embodiment were activated to prepare a flocculant solution with a concentration of 500 mg / L, 100 mL of printing and dyeing wastewater was taken and 5 mL of flocculant was added, and then 1% CaCl2 solution was added as a coagulant, stirred for 3 minutes and then allowed to settle for 30 minutes, and the supernatant was taken to measure its absorbance B at the maximum absorption wavelength of 523 nm, and the absorbance A of the blank group without adding the flocculant solution was used as a control, and the flocculation rate was calculated by the ratio of the difference between A and B and A.

[0062] After standing and flocculating for 30 minutes according to the above steps, the flocculant was separated and washed by water, and then added to a new printing and dyeing wastewater sample. After repeating the flocculation experiment 5 times, the difference in flocculation rate between the first and fifth times was calculated.

[0063] Example First flocculation rate (%) Flocculation rate difference (%) 1 83 1.3 2 78 0.6 3 80 0.5 4 85 0.8 5 74 1.7 6 84 0.3 7 86 1.1

[0064] As can be seen from the table above, the first flocculation rate of Example 2, which has a higher temperature for vacuum drying reaction, is lower than that of Example 1, but the difference in flocculation rate after multiple flocculation experiments is significantly smaller than that of Example 1. At the same time, the difference in flocculation rate of Example 3, which has a longer reaction time, is also significantly smaller than that of Example 1, indicating that higher reaction temperature and time are conducive to the polymerization of glucose on the zinc skeleton, and it is closely connected with the zinc skeleton. After multiple flocculations, the Klebsiella attached and colonized thereon is not easy to be lost, and the impact on the flocculation rate is smaller. However, higher reaction temperature and longer time make the first flocculation rate decrease. It may be that the change in reaction conditions makes the polymerization degree of glucose higher, which is more unfavorable for the utilization of Klebsiella, so the Klebsiella colonized by the flocculant itself is less. The concentration of nutrients and carriers in the fermentation system of Example 4 is large, the first flocculation rate is slightly increased, and the difference in flocculation rate is lower than that of Example 1. It may be that higher concentration is more conducive to the deep colonization and growth of Klebsiella. The fermentation system of Example 5 is neutral. In comparison, less potassium dihydrogen phosphate is added than in Example 1, and its first flocculation rate is reduced, indicating that an acidic environment or more phosphorus and potassium is more suitable for the growth of Klebsiella. The increase in the difference in flocculation rate indicates that the increase in pH is not conducive to the colonization of Klebsiella. The first flocculation rate of Example 6 with a longer fermentation time did not change significantly, and the difference in flocculation rate was smaller, indicating that a longer fermentation time is conducive to the colonization of Klebsiella. The amount of starch and whey powder added in Example 7 is higher, and the first flocculation rate of the sample increases, which may be because the combination of more starch and whey powder can better protect the activity of Klebsiella during the freeze-drying process.

[0065] For those skilled in the art, various other corresponding changes and deformations can be made according to the technical solutions and concepts described above, and all of these changes and deformations should fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a microbial flocculant, characterized in that: The microbial flocculant comprises a zinc skeleton, oligodextrose polymerized on the zinc skeleton, and microorganisms colonized on the zinc skeleton and the oligodextrose; and the preparation method comprises the following steps: Taking zinc salt and 2-methylimidazole to prepare a zinc skeleton; Glucose is added to the zinc skeleton, and after it is fully dissolved, an acid catalyst is added, the system temperature is adjusted to 40-50°C, and vacuum distillation is performed until the solid-liquid ratio in the system is 1:1; stirring is continued until the weight of the system no longer changes; the remaining solid in the system is heated to 90-100°C and vacuum dried for 2-3 hours to obtain a carrier; The carrier is dispersed in water to prepare a 10-20 g / L dispersion, dipotassium hydrogen phosphate is added to the dispersion to adjust the pH of the system to 5.5-7; a nitrogen source is added to the system, microorganisms are added after sufficient mixing, and the system is shaken for fermentation for 24-36 hours; after separation, the solid is taken for pretreatment and then dried to obtain the product.

2. The method for preparing a microbial flocculant according to claim 1, characterized in that: The microorganism is Klebsiella.

3. The method for preparing a microbial flocculant according to claim 1, characterized in that: The acid catalyst in step b is one of malic acid, citric acid or chloroacetic acid; the mass ratio of glucose to zinc skeleton in step b is 1:4-6.

4. The method for preparing a microbial flocculant according to claim 1, characterized in that: In step c, the nitrogen source is one or more of urea, beef extract, ammonium sulfate, peptone, yeast powder or ammonium sulfide; the mass ratio of the nitrogen source to the carrier is 1:200-250.

5. The method for preparing a microbial flocculant according to claim 1, characterized in that: In step c, the temperature of the shaking fermentation is 25-40° C. and the fermentation speed is 160-200 r / min.

6. The method for preparing a microbial flocculant according to claim 1, characterized in that: The drying in step c is carried out by forced air drying or vacuum drying at 30-40° C. for 10-20 hours.

7. The method for preparing a microbial flocculant according to claim 1, characterized in that: The drying in step c is performed by precooling at 4°C for 12 h and then freezing in a -80°C refrigerator for 24 h.

8. The method for preparing a microbial flocculant according to claim 1, characterized in that: The pretreatment in step c is to mix the separated solid with starch and whey powder in a mass ratio of 1: (0.05-0.15): (0.1-0.15).

9. The method for preparing a microbial flocculant according to claim 1, characterized in that: The preparation of the zinc skeleton comprises the following steps: Dissolve zinc salt and 2-methylimidazole in a mixed solvent of dimethyl sulfoxide and water at a molar ratio of 1:4-6 to obtain a zinc solution and a 2-methylimidazole solution; mix the zinc solution and the 2-methylimidazole solution, stir and react for 8-10 hours to obtain a zinc skeleton; the zinc salt is one of zinc nitrate and zinc acetate.