Method for treating sewage by jointly using Fe-C / N magnetic powder and activated sludge

Abstract

The invention discloses a method for treating sewage by jointly using Fe-C / N magnetic powder and activated sludge, which comprises the following steps: (1) premixing activated sludge and Fe-C / N magnetic powder to obtain magnetically loaded activated sludge; (2) the magnetically-loaded activated sludge is placed in an aeration tank, sewage is treated by adopting a water inlet-aeration-precipitation-drainage process, and the volume ratio of the sewage inlet volume to the magnetically-loaded activated sludge is 1: (0.5-2); the preparation method of the Fe-C / N magnetic powder comprises the following steps: (i) adding an iron source precursor and carbon nitride into deionized water, stirring and evaporating, drying in vacuum after evaporating to dryness, and grinding into powder; the mass of the iron source precursor is metered by the mass of the iron element, and the mass ratio of the iron source precursor to the carbon nitride is 1: (0.1-10); and (ii) calcining the powder obtained in the step (i) for 1-5 hours under the protection of inert gas, and cooling to obtain the Fe-N / C composite catalyst, the calcining temperature is 500-700 DEG C; the method provided by the invention not only improves the removal rate of COD and total nitrogen, but also improves the utilization rate of the magnetic powder.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and particularly relates to a method for treating sewage by jointly using Fe-C / N magnetic powder and activated sludge. Background Art

[0002] The core of the activated sludge process is to degrade organic matter by using the biochemical activity of activated sludge (microbial flocs). Activated sludge itself is a floc composed of microorganisms such as bacteria, fungi, and protozoa and organic / inorganic substances in sewage. Oxygen is provided through aeration to promote the metabolism of organic matter by microorganisms.

[0003] The activated sludge process mainly includes the conventional activated sludge process (traditional plug flow), the sequencing batch reactor (SBR) process, the oxidation ditch process, etc.

[0004] The sequencing batch reactor (SBR) process is an activated sludge sewage treatment technology that operates in an intermittent aeration mode. Its main feature is the orderly and intermittent operation in operation. The core of the SBR technology is the SBR reaction tank, which integrates functions such as equalization, primary sedimentation, biodegradation, and secondary sedimentation in one tank and has no sludge return system. It is particularly suitable for occasions with insufficient construction space, intermittent discharge, and large flow variations.

[0005] The activated sludge process is one of the main methods in biological sewage treatment. The activated sludge process is widely used, but the activated sludge process has the following disadvantages:

[0006] (1) Poor adaptability to shock loads: When there are large fluctuations in the quantity and quality of sewage, such as a sudden increase in the influent concentration or a sharp increase in the water volume, the activated sludge system may be impacted, resulting in a decrease in treatment efficiency, and even situations such as sludge disintegration and reduced activity;

[0007] (2) Prone to sludge bulking: Under certain conditions, such as excessive growth of filamentous bacteria, the structure of the sludge becomes loose and difficult to settle, affecting the solid-liquid separation effect in the secondary sedimentation tank, leading to deterioration of the effluent quality, and even sludge loss;

[0008] (3) Poor sludge sedimentation performance: The floc structure of traditional activated sludge is not tight enough, and the sedimentation speed in the secondary sedimentation tank is slow. A larger sedimentation tank volume is required to ensure sufficient sedimentation time, which increases the floor area and construction cost of sewage treatment facilities to a certain extent.

[0009] The magnetic-loaded activated sludge process is an improvement of the traditional activated sludge process, which can solve the above problems to a certain extent. The magnetic-loaded activated sludge process is based on the traditional activated sludge process, adding magnetic powder and coagulant to the sewage. The magnetic powder carries a positive charge, while the surface of the sludge flocs usually carries a negative charge. The two are combined through electro-neutralization. This combination makes the structure of the sludge flocs more compact, thus enhancing the sedimentation performance of the sludge and improving the sewage treatment efficiency.

[0010] Magnetite (Fe3O4) is a common magnetic powder material. It has good magnetic properties and chemical stability, can play a stable role in the sewage treatment process, and has relatively low cost, easy to obtain and use.

[0011] However, magnetite is combined with the sludge flocs through electro-neutral adsorption, and this combination method is easily affected by the external environment, having the defect of low utilization rate of magnetic powder. Summary of the Invention

[0012] The present invention provides a method for treating sewage by jointly using Fe-C / N magnetic powder and activated sludge, which not only improves the removal rates of COD and total nitrogen, but also improves the utilization rate of magnetic powder.

[0013] The technical solution of the present invention is as follows:

[0014] A method for treating sewage by jointly using Fe-C / N magnetic powder and activated sludge, comprising:

[0015] (1) Pre-mixing activated sludge with Fe-C / N magnetic powder to obtain magnetic-loaded activated sludge;

[0016] (2) Placing the magnetic-loaded activated sludge in an aeration tank, and treating the sewage by adopting the process of influent-aeration-sedimentation-drainage. The volume ratio of the sewage influent to the volume of the magnetic-loaded activated sludge is 1:0.5-2;

[0017] The preparation method of the Fe-C / N magnetic powder includes:

[0018] (i) Adding an iron source precursor and carbon nitride to deionized water, stirring and evaporating, vacuum drying after evaporation to dryness, and grinding into powder; the mass of the iron source precursor is calculated by the mass of iron element, and the mass ratio of the iron source precursor to carbon nitride is 1:0.1-10;

[0019] (ii) Calcining the powder obtained in step (i) for 1-5 h under the protection of inert gas, and cooling to obtain the Fe-N / C composite catalyst; the calcining temperature is 500-700 °C.

[0020] The described Fe-C / N magnetic powder is nitrogen-doped graphite-coated iron nitride carbide particles, and its main components are Fe3C, Fe3N, C, and unreacted carbon nitride (C3N4). The Fe-C / N material structure is a unique core-shell structure, which uses porous carbon as the skeleton carrier, and Fe3N and C 0.08 Fe 1.92 are distributed on the porous carbon. This substance has high adsorption characteristics. Due to the existence of the pore structure of the porous carbon, this material has better adsorption performance than Fe3O4. The Fe-C / N magnetic powder is more sensitive to the magnetic field. Different from the Fe3O4 magnetic powder that binds and adsorbs to sludge flocs in an electrically neutral manner, the Fe-C / N magnetic powder physically adsorbs and binds to sludge flocs through the outer layer of iron carbide coating and the pore structure of the porous carbon carrier, avoiding the defect that the electrically neutral binding method is easily affected by the external environment and results in low utilization rate of magnetic powder.

[0021] In the present invention, Fe-C / N is combined with the activated sludge method, which improves the removal rates of COD and total nitrogen.

[0022] In step (1), based on 1 L of activated sludge, the dosage of Fe-C / N magnetic powder is 500-1000 mg; further preferably 800-1000 mg.

[0023] In step (1), mechanical stirring is used for premixing, the stirring speed is 100-200 r / min, and the stirring time is 10-20 min. The mixing situation of the magnetic powder and the sludge is observed through a microscope. If there is no magnetic powder deposition at the bottom of the sludge, it is regarded as complete mixing.

[0024] In step (2), during the aeration stage, the aeration time is 10-20 h, the aeration flow rate is 0.1-0.5 L / min, and the dissolved oxygen concentration is 2-5 mg / L.

[0025] Further preferably, in step (2), during the aeration stage, the aeration time is 10-20 h, the aeration flow rate is 0.1-0.3 L / min, and the dissolved oxygen concentration is 2-5 mg / L.

[0026] In step (2), during the aeration stage, disk aeration is used, and mechanical stirring is carried out simultaneously.

[0027] The mechanical stirring is a pushing flow effect, which can ensure the uniform flow of the sludge in the aeration tank, avoid sludge deposition, and make the dissolved oxygen diffuse evenly in the aeration tank.

[0028] Preferably, the stirring speed during the aeration stage is 200-250 r / min.

[0029] Preferably, in step (2), the volume ratio of the sewage inflow to the volume of the magnetic carrier activated sludge is 1:1. It can maintain an appropriate sludge load and avoid sludge aging and sludge disintegration.

[0030] During the whole operation period, keep the pH value of the sewage at 6.5 - 7.5. A neutral environment can maintain the activity of microorganisms and is beneficial for sludge flocs to wrap magnetic powder. If the pH is too low, it will cause the magnetic powder to react and dissolve in the acidic environment, resulting in the inactivation of microorganisms and the inability of the magnetic powder to combine with sludge flocs.

[0031] During the whole operation process, regularly monitor the sludge concentration in the sewage and adjust the supplementary dosage of magnetic powder according to the sludge growth amount.

[0032] Preferably, in step (i), based on the mass of iron element in the iron source precursor, the mass ratio of the iron source precursor to carbon nitride is 1:1 - 3; the iron source precursor is ferrous oxalate or ferrous oxalate dihydrate.

[0033] Preferably, in step (ii), the calcination temperature is 500 - 600 °C.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] The Fe-C / N magnetic powder of the present invention has good adsorption performance, which improves the speed of magnetic powder attaching to activated sludge flocs, makes the sludge floc structure gradually change from loose to compact, is beneficial for the metabolism of microorganisms, and further improves the biochemical effect of activated sludge. Compared with Fe3O4 magnetic powder, the combined application technology of the Fe-C / N magnetic powder of the present invention and the activated sludge technology reduces the use of coagulants, saves economic costs, and improves the operation efficiency. Specific Embodiments

[0036] The following further describes the present invention in detail with reference to embodiments. It should be noted that the following embodiments are intended to facilitate the understanding of the present invention and do not limit it in any way.

[0037] Example 1:

[0038] Preparation of Fe-C / N material:

[0039] (1) Weigh 10 g of melamine in an alumina crucible, calcine it in a muffle furnace at 550 °C for 4 h, collect the obtained pale yellow carbon nitride solid after cooling to room temperature, and grind it into powder for standby;

[0040] (2) Weigh 1.61 g of ferrous oxalate dihydrate (FeC2O4·2H2O) and 1 g of the carbon nitride (g-C3N4) obtained in step (1) into a 100 mL beaker, add 10 mL of deionized water, and stir and evaporate to dryness in a water bath at 50 °C;

[0041] (3) The mass ratio of the precursor Fe-MOF and g-C3N4 is 1:0.5. The evaporated yellow solid is transferred to a vacuum drying oven and dried at 60 °C for 4 h, and then the solid is ground into powder. It is calcined at 550 °C for 2 h under N2 protection. After cooling to room temperature, the obtained black powder is collected, which is the Fe-N / C material.

[0042] The above Fe-C / N material has a unique core-shell structure. This structure uses porous carbon as the skeleton carrier, and Fe3N and Fe3C are distributed on the porous carbon. This substance has high adsorption characteristics. Due to the existence of the pore structure of the porous carbon, this material has better adsorption performance than Fe3O4. In the hysteresis loop test, the saturation magnetization intensity of this material is 52.18 emu / g, proving that this material is more sensitive to the magnetic field. Different from the electro-neutral binding of Fe3O4 magnetic powder to sludge flocs, this magnetic powder combines with sludge flocs through the physical adsorption of the outer layer of iron carbide and the pore structure of the porous carbon carrier, avoiding the defect that the electro-neutral binding method is easily affected by the external environment and results in low utilization rate of magnetic powder. The present invention combines this Fe-C / N material with the activated sludge method, which not only improves the removal rates of COD and total nitrogen, but also improves the anti-load capacity of the activated sludge.

[0043] The Fe-N / C material used in the following examples is the Fe-N / C material prepared in Example 1.

[0044] In the following examples and comparative examples, the analysis method for COD in the water sample is the potassium dichromate method (HJ828-2017), and the analysis method for total nitrogen in the water sample is the Nessler reagent spectrophotometry (HJ 535-2009).

[0045] Example 2:

[0046] The Fe-C / N magnetic powder and activated sludge are used in combination to treat sewage:

[0047] (1) Based on 1 L of activated sludge, 900 mg / L of Fe-C / N magnetic powder is added in batches, and the mixture is premixed at a stirring speed of 150 r / min for 15 min. The mixing situation of the magnetic powder and the sludge is observed through a microscope. If there is no magnetic powder deposition at the bottom of the sludge, it is regarded as complete mixing;

[0048] The 1 L of activated sludge solution containing Fe-C / N magnetic powder after premixing is placed in the aeration tank.

[0049] (2) Using simulated wastewater as the object, the SBR process is adopted. The reaction device operates according to the process of influent water - aeration - sedimentation - drainage. The volume ratio of influent water to sludge is maintained at 1:1, and the pH is maintained at 6.5 - 7.5 during the whole operation period. Among them, the aeration time is 14 h, and the sedimentation time is 1 h. During the aeration stage, disk aeration is used, the aeration flow rate is 0.2 L / min, the DO is maintained at 2 - 5 mg / L, and mechanical stirring is used as the pushing flow effect.

[0050] (3) After the operation cycle is completed, samples are taken from the supernatant of the drained water to analyze the COD and total nitrogen of the water sample.

[0051] Comparative Example 1:

[0052] Treating sewage with activated sludge alone:

[0053] (1) For 1 L of blank activated sludge solution, mechanical stirring is adopted, with a stirring speed of 150 r / min and a stirring time of 15 min.

[0054] (2) Using simulated wastewater as the object, the SBR process is adopted. The reaction device operates according to the process of influent water - aeration - sedimentation - drainage. The volume ratio of influent water to sludge is maintained at 1:1. Among them, the aeration time is 14 h, and the sedimentation time is 1 h. During the aeration stage, disk aeration is used, the aeration flow rate is 0.2 L / min, the DO is maintained at 2 - 5 mg / L, and mechanical stirring is used as the pushing flow effect.

[0055] (3) After the operation cycle is completed, samples are taken from the supernatant of the drained water to analyze the COD and total nitrogen of the water sample.

[0056] The COD removal rates of Example 2 and Comparative Example 1 are shown in Table 1.

[0057] Table 1

[0058]

[0059] The total nitrogen removal rates of Example 2 and Comparative Example 1 are shown in Table 2.

[0060] Table 2

[0061]

[0062] Example 3:

[0063] Treating sewage by using Fe - C / N magnetic powder and activated sludge jointly:

[0064] (1) Based on 1 L of activated sludge, 900 mg / L of Fe - C / N magnetic powder is added in batches, and premixing is carried out by stirring at a stirring speed of 150 r / min for 15 min. The mixing situation of the magnetic powder and the sludge is observed through a microscope. If there is no deposition of magnetic powder at the bottom of the sludge, it is regarded as complete mixing;

[0065] Place 1 L of the pre-mixed activated sludge solution containing Fe-C / N magnetic powder in the aeration tank.

[0066] (2) Using actual wastewater as the object, adopt the SBR process. The reaction device operates according to the process of influent water - aeration - sedimentation - drainage. The volume ratio of influent water to sludge is maintained at 1:1. Among them, aeration lasts for 14 h, sedimentation lasts for 1 h. During the aeration stage, disk aeration is adopted, the aeration flow rate is 0.2 L / min, DO is maintained at 2 - 5 mg / L, and mechanical stirring is used as the pushing flow effect.

[0067] (3) After the operation cycle is completed, sample the supernatant of the drained water to analyze the COD and total nitrogen of the water sample.

[0068] Comparative Example 2:

[0069] In step (1), the sludge does not contain magnetic powder, and the rest is the same as in Example 3.

[0070] Comparative Example 3:

[0071] In step (1), the Fe-C / N magnetic powder is changed to Fe3O4 magnetic powder, and the rest is the same as in Example 3.

[0072] Example 4:

[0073] In step (2), the aeration time is 16 h, and the rest is the same as in Example 3.

[0074] Example 5:

[0075] In step (2), the aeration flow rate is 0.4 L / min, and the rest is the same as in Example 3.

[0076] The COD removal rates of Example 3, Example 4, Example 5, Comparative Example 2, and Comparative Example 3 are shown in Table 3.

[0077] Table 3

[0078]

[0079] Too large an aeration flow rate will reduce the effective contact time between the activated sludge and oxygen, thereby reducing the oxygen utilization rate.

[0080] The total nitrogen removal rates of Example 3, Example 4, Example 5, Comparative Example 2, and Comparative Example 3 are shown in Table 4.

[0081] Table 4

[0082]

[0083] The above-described embodiments have elaborated in detail the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements, equivalent replacements, etc. made within the scope of the principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for treating sewage by using Fe-C / N magnetic powder and activated sludge in combination, characterized in that, Comprising: (1) Pre-mix activated sludge with Fe-C / N magnetic powder to obtain magnetic-loaded activated sludge; (2) Place the magnetic-loaded activated sludge in an aeration tank, and treat the sewage by the process of influent water - aeration - sedimentation - drainage. The volume ratio of the sewage influent to the volume of the magnetic-loaded activated sludge is 1:0.5 - 2; The preparation method of the described Fe-C / N magnetic powder includes: (i) Add an iron source precursor and carbon nitride to deionized water, stir and evaporate, dry in vacuum after evaporation, and grind into powder; the mass of the iron source precursor is based on the mass of iron element, and the mass ratio of the iron source precursor to carbon nitride is 1:0.1 - 10; (ii) Calcinate the powder obtained in step (i) for 1 - 5 h under the protection of an inert gas, and cool to obtain the described Fe-N / C composite catalyst; the calcination temperature is 500 - 700 °C.

2. The method for treating sewage by using Fe-C / N magnetic powder and activated sludge in combination according to claim 1, characterized in that, In step (1), based on 1 L of activated sludge, the dosage of Fe-C / N magnetic powder is 500 - 1000 mg.

3. The method for treating sewage by using the Fe-C / N magnetic powder and activated sludge in combination according to claim 1, wherein, In step (1), mechanical stirring is used for pre-mixing, the stirring speed is 100 - 200 r / min, and the stirring time is 10 - 20 min.

4. The method for treating sewage by jointly using Fe-C / N magnetic powder and activated sludge according to claim 1, characterized in that In step (2), during the aeration stage, the aeration time is 10 - 20 h, the aeration flow rate is 0.1 - 0.5 L / min, and the dissolved oxygen concentration is 2 - 5 mg / L.

5. The method for treating sewage by using the Fe-C / N magnetic powder and activated sludge in combination according to claim 1 or 4, characterized in that During the aeration stage, disk aeration is used, and mechanical stirring is carried out simultaneously; the stirring speed during the aeration stage is 200 - 250 r / min.

6. The method for treating sewage by using Fe-C / N magnetic powder and activated sludge in combination according to claim 1, characterized in that, In step (2), the volume ratio of the sewage influent to the volume of the magnetic-loaded activated sludge is 1:

1.

7. The method for treating sewage by using Fe-C / N magnetic powder and activated sludge in combination according to claim 1, characterized in that, During the whole operation period, keep the sewage pH value at 6.5 - 7.

5.

8. The method for treating sewage by using the Fe-C / N magnetic powder and activated sludge in combination according to claim 1, characterized in that, During the whole operation process, regularly monitor the sludge concentration in the sewage, and adjust the supplementary dosage of magnetic powder according to the sludge growth amount.

9. The method for treating sewage by jointly using Fe-C / N magnetic powder and activated sludge according to claim 1, characterized in that, In step (i), the mass of the iron source precursor is based on the mass of iron element, and the mass ratio of the iron source precursor to carbon nitride is 1:1 - 3; the described iron source precursor is ferrous oxalate or ferrous oxalate dihydrate.

10. The method for treating sewage by using Fe-C / N magnetic powder and activated sludge in combination according to claim 1, characterized in that, In step (ii), the calcination temperature is 500 - 600 °C.

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