Preparation method of composite flocculant for limiting phosphorus removal of low turbidity water

Abstract

The present application relates to a kind of preparation method of composite flocculant for low turbidity water limit phosphorus removal, belong to water treatment technical field.The operation steps are as follows: (1) the sludge obtained by sewage plant or water supply plant is prepared into biochar;(2) biochar is sieved, pickled, and respectively reacted with ferric chloride and sodium hydroxide to prepare biochar fixed with hydrated iron oxide;(3) the biochar fixed with hydrated iron oxide and polyaluminum flocculant solution are reacted by heating, dried, and the composite flocculant is prepared;The mass fraction of hydrated iron oxide in composite flocculant is 4.4%-14.3%, the mass fraction of biochar is 22.1%-28.6%, and the mass fraction of polyaluminum flocculant is 57.1%-73.5%.When used for limit phosphorus removal treatment of low turbidity tail water or low turbidity sewage, the composite flocculant is added to the water body to be treated at an amount of 50-200 mg / L, the flocculation reaction is 10-20 minutes, at the same time, air flotation method is needed to blow off the floc to realize the separation of floc and water body, or magnetic material is added at the bottom of the sedimentation zone, and finally the limit phosphorus removal of water body is realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of water treatment, and particularly relates to a composite flocculant based on modified biochar of hydrated iron oxide fixed for limiting phosphorus removal of low-turbidity water and a preparation method and application thereof. BACKGROUND

[0002] Phosphorus is a key environmental factor leading to water eutrophication and exacerbating black and odorous water bodies. At present, the phosphorus removal processes mainly include biological phosphorus removal and chemical phosphorus removal. The phosphorus removal limit of the biological phosphorus removal method is 90%, and the total phosphorus concentration in the effluent is generally 1.0 mg / L-3.0 mg / L. The chemical phosphorus removal method has the advantages of fast reaction speed, simple operation, small land occupation, and easy-to-meet-standard effluent, and is widely used. However, for low-turbidity tail water of sewage treatment plants and industrial parks, the use of traditional flocculants not only requires large dosages, but also generates small and difficult-to-separate alum flowers from water bodies. Therefore, it is difficult to achieve limiting phosphorus removal of low-turbidity sewage treatment plant tail water and the like using traditional flocculants. SUMMARY

[0003] In view of the difficulty of limiting phosphorus removal of traditional flocculants for low-turbidity sewage plant tail water, the application provides a preparation method of a composite flocculant for limiting phosphorus removal of low-turbidity water.

[0004] The preparation operation steps of the composite flocculant for limiting phosphorus removal of low-turbidity water are as follows:

[0005] (1) Preparation of biochar

[0006] (1.1) Alkaline substances are added to sludge obtained by treatment of a sewage plant or sludge obtained by treatment of a water supply plant and stirred uniformly to obtain alkaline sludge with a pH value of 9.0-12.0, which is dried and broken into sludge particles;

[0007] (1.2) The sludge particles are burned at high temperature under aeration to prepare biochar; the aeration gas is nitrogen or other inert gas.

[0008] (2) Preparation of biochar fixed with hydrated iron oxide

[0009] (2.1) The biochar is washed with deionized water for 3-4 times, dried, ground through a 20-50 mesh sieve to obtain 20-50 mesh biochar;

[0010] (2.2) The 20-50 mesh biochar is added into a 5.0% hydrochloric acid solution for constant-temperature acid washing and oscillation to obtain oscillation biochar; the oscillation biochar is washed with deionized water until neutral, dried, and obtained as acid-washed biochar;

[0011] (2.3) The acid-washed biochar is added to the ferric chloride (FeCl3) solution with a concentration of 16.2 g / L according to the mass ratio of ferric chloride to acid-washed biochar of 0.2-0.5:1.0, and is shaken in a constant-temperature water bath shaker at 35℃ for 24 hours. The biochar is filtered out and dried to obtain dried biochar;

[0012] (2.4) The dried biochar is added to the sodium hydroxide (NaOH) solution with a concentration of 5% according to the mass ratio of sodium hydroxide to dried biochar of 0.3-0.8:1.0, and the pH value is adjusted to 10.0. The reaction is carried out in a constant-temperature water bath shaker at 35℃ for 24 hours to generate hydrated iron oxide precipitate on the surface of the biochar. The solid material obtained by fixing the hydrated iron oxide biochar is filtered, washed with deionized water until neutral, and dried to obtain the biochar fixed with hydrated iron oxide.

[0013] (3) Preparation of composite flocculant

[0014] (3.1) The polyaluminum flocculant is dissolved in water according to the mass ratio of 0.05-0.1:1.0 to obtain a polyaluminum flocculant solution;

[0015] (3.2) The biochar fixed with hydrated iron oxide is added to the polyaluminum flocculant solution according to the mass ratio of 0.3-0.5:1.0, mixed, heated and stirred, and dried to obtain the composite flocculant modified by the biochar fixed with hydrated iron oxide.

[0016] The mass ratio of the composite flocculant is 4.4%-14.3% for hydrated iron oxide, 22.1%-28.6% for biochar, and 57.1%-73.5% for polyaluminum flocculant.

[0017] When the composite flocculant is used for the limit phosphorus removal treatment of low-turbidity tail water in a sewage treatment plant or low-turbidity sewage in an industrial park, the composite flocculant is added to the treated water body in an amount of 50-200 mg / L, and the flocculation reaction is carried out for 10-20 minutes. At the same time, air flotation method is used to blow off the flocculation to separate the flocculation from the water body, or magnetic material is added at the bottom of the sedimentation zone to enhance the settling speed of the magnetic flocculation and accelerate the separation of the flocculation from the water body, so as to finally realize the limit phosphorus removal of the water body.

[0018] The further defined technical solutions are as follows:

[0019] In step (1.1), the alkaline substance is potassium hydroxide or urea.

[0020] In step (1.1), the particle size of the sludge particles is 0.5-1.0 cm.

[0021] In step (1.2), the high-temperature firing is performed at a temperature of 300-800 DEG C for 2.0-6.0 hours.

[0022] In step (2.1), the drying is performed in an oven at a temperature of 110 DEG C for 4 hours.

[0023] In step (2.2), the oscillation is performed at a temperature of 20-35 DEG C at a speed of 100-200 r / min for 5 hours.

[0024] In step (2.2), the drying is performed in a blast drying machine at a temperature of 110 DEG C for 2-10 hours.

[0025] In step (2.3), the oscillation is performed at a temperature of 20-35 DEG C at a speed of 100-200 r / min for 24 hours.

[0026] In step (2.3), the drying is performed in an oven at a temperature of 110 DEG C for 4 hours.

[0027] In step (2.4), the oscillation is performed at a temperature of 20-35 DEG C at a speed of 100-200 r / min for 24 hours.

[0028] In step (2.4), the drying is performed in an oven at a temperature of 110 DEG C for 12 hours.

[0029] In step (3.1), the polymeric aluminum flocculant is polyaluminum chloride or polyaluminum sulfate.

[0030] In step (3.2), the drying is performed in an oven at a temperature of 45-55 DEG C for 2-5 hours.

[0031] The beneficial technical effects of the present application are embodied in the following aspects:

[0032] 1. The present application prepares a composite flocculant based on hydrated iron oxide fixed biochar modification, which can be used for the flocculation of municipal sewage plant tail water, industrial park tail water and other various sewage, has the advantages of small dosage, fast flocculation speed, high stability and easy separation, and is especially suitable for the micro-flocculation treatment of low-turbidity water for extreme phosphorus removal.

[0033] 2. The polymeric aluminum has good coagulation performance for conventional surface water or sewage, and the generated alum flower is large and has good settling performance, but for low turbidity sewage plant tail water or industrial park tail water, the conventional flocculant not only has large dosage, but also generates small alum flower, and it is difficult to separate from the water body. In the present application, the polymeric aluminum flocculant is modified by using the biochar fixed with hydrated iron oxide. First, after adding the modified flocculant, the turbidity of the water body is increased, so as to enhance the flocculation effect of the polymeric aluminum flocculant and increase the size of the alum flower. Second, the hydrated iron oxide fixed on the biochar has high selectivity for phosphate in the water body, and can form a coordination complex with the phosphate. At the same time, the biochar can quickly adsorb and fix the coordination complex generated by the hydrated iron oxide on the surface and the phosphate ions, and rely on the alum flower floc formed by the polymeric aluminum flocculant to perform the net capture and sweeping movement, further adsorb the phosphorus in the water, and finally realize the ultimate phosphorus removal by separating the floc from the water body.

[0034] 3. The surface functional groups of the hydrated iron oxide will exhibit different forms under the influence of the pH value in the environment, such as FeOH 2 + , FeOH, FeO - . The pH value of natural water body and sewage plant tail water is neutral condition, and the hydrated iron oxide mainly exists in the form of FeOH. The hydrated iron oxide can form a coordination complex with phosphate ions, and the biochar can quickly adsorb and fix the coordination complex generated by the hydrated iron oxide on the surface and the phosphate ions. At the same time, the biochar fixed with the hydrated iron oxide relies on the floc formed by the polymeric aluminum flocculant to further capture and sweep the particulate phosphorus in the water, and finally realizes the ultimate phosphorus removal by separating the floc from the water body. In the present application, the hydrated iron oxide, biochar and polymeric aluminum flocculant in the composite flocculant realize the ultimate removal of phosphorus in the water body by forming a coordination complex, adsorbing and fixing, and net capture and sweeping, respectively.

[0035] 4. The conventional polymeric aluminum flocculant has large dosage and generates small alum flower for low turbidity sewage plant tail water, and cannot be effectively removed by the conventional coagulation and sedimentation method. In the present application, the composite flocculant modified by the biochar fixed with the hydrated iron oxide contains the hydrated iron oxide with magnetic function, so that the generated floc also has magnetism. Therefore, the magnetic adsorption device is added in the sedimentation zone or the air flotation zone, so as to realize the rapid separation of the floc from the water body.

[0036] 5. The composite flocculant in the present application can realize more than 90% removal rate of total phosphorus in low turbidity water with total phosphorus of 0.5 mg / L in the raw water, and the total phosphorus in the effluent is controlled to be less than 0.05 mg / L, so as to realize the ultimate phosphorus removal in the low turbidity water. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 Figure for comparison of the ultimate phosphorus removal effect of the flocculants before and after modification in the laboratory beaker experiment.

[0038] Figure 2 Figure for phosphorus removal effect of the conventional flocculant coupled with the integrated air flotation device.

[0039] Figure 3 Figure for phosphorus removal effect of the modified composite flocculant coupled with the integrated air flotation device. DETAILED DESCRIPTION

[0040] In order to more clearly illustrate the present application, to have a more clear understanding of the technical features, objects and beneficial effects of the present application, the technical solutions of the present application are described in detail as follows, but cannot be understood as limiting the scope of the present application.

[0041] Example 1

[0042] The preparation operation steps of the composite flocculant based on the modified biochar fixed with hydrated iron oxide are as follows:

[0043] (1) Preparation of biochar

[0044] (1.1) 20 g of potassium hydroxide was added to 100 g of sludge obtained by treatment in a sewage plant and stirred uniformly to obtain alkaline sludge with pH value of 12.0, which was dried and broken into sludge particles with particle size of 0.5-1.0 cm;

[0045] (1.2) The sludge particles were calcined at high temperature under the condition of nitrogen gas by using a tube furnace, and the calcination temperature was 800℃ and the time was 2.0 hours to prepare biochar; the biochar was cooled in an oxygen-free environment for 24 hours and stored at room temperature.

[0046] (2) Preparation of biochar fixed with hydrated iron oxide

[0047] (2.1) The biochar was washed with deionized water for 3-4 times. It was dried in an oven at 110℃ for 4 hours. It was ground through a 20-50 mesh sieve to obtain 20-50 mesh biochar;

[0048] (2.2) The 20-50 mesh biochar was added to a conical flask containing a hydrochloric acid solution with a concentration of 5.0%, and constant temperature acid washing was performed under the condition of temperature 25℃ and speed 100 r / min for 5 hours. It was washed with deionized water until neutral. It was dried in a forced air drying machine at 110℃ for 4 hours to obtain acid-washed biochar;

[0049] (2.3) 16.2 g of the pickling biochar was added into 500 mL of 16.2 g / L ferric chloride (FeCl3) solution (mass ratio of ferric chloride to pickling biochar was 0.5:1.0), and oscillated in a constant temperature water bath shaker at 35°C and 200 r / min for 24 hours. Subsequently, the biochar was filtered out, and dried in a blast drying machine at 110°C for 12 hours to obtain dried biochar;

[0050] (2.4) The dried biochar was further added into 300 mL of 5% sodium hydroxide (NaOH) solution (mass ratio of sodium hydroxide to dried biochar was 0.8:1.0), and the pH value was adjusted to 10.0. Then, the mixture was oscillated in a constant temperature water bath shaker at 35°C and 200 r / min for 24 hours to form iron oxide hydrate precipitate on the surface of the biochar. The above reaction obtained the solid material of biochar fixed with iron oxide hydrate, which was suction filtered, washed with deionized water until neutral, and dried in a blast drying machine at 110°C for 12 hours to obtain biochar fixed with iron oxide hydrate.

[0051] (3) Preparation of composite flocculant

[0052] (3.1) The polyaluminum chloride flocculant was dissolved in water at a mass ratio of 0.05:1.0 to obtain a polyaluminum flocculant solution;

[0053] (3.2) The biochar fixed with iron oxide hydrate was added into the polyaluminum flocculant solution at a mass ratio of 0.5:1, and stirred and mixed uniformly. Then, the mixture was dried in an oven at 55°C for 5 hours, and cooled at room temperature to obtain the composite flocculant modified by biochar fixed with iron oxide hydrate.

[0054] The mass ratio of iron oxide hydrate in the composite flocculant of Example 1 was 14.3%, the mass ratio of biochar was 28.6%, and the mass ratio of polyaluminum flocculant was 57.1%.

[0055] Example 2

[0056] The preparation operation steps of the composite flocculant modified by biochar fixed with iron oxide hydrate are as follows:

[0057] (1) Preparation of biochar

[0058] (1.1) 20 g of urea was added into 100 g of sludge obtained by treatment in a water supply plant, and stirred uniformly to obtain alkaline sludge with a pH value of 9.0. The sludge was dried and broken into sludge particles with a particle size of 0.5-1.0 cm;

[0059] (1.2) The sludge particles were high-temperature calcined by using a tube furnace under the condition of nitrogen gas, and the calcination temperature was 800°C and the time was 2 hours to obtain biochar. The biochar was cooled in an oxygen-free environment for 24 hours, and stored at room temperature.

[0060] (2) Preparation of biochar immobilized with hydrated iron oxide

[0061] (2.1) Wash the biochar with deionized water for 3-4 times. Dry in an oven at 110℃ for 4h. Grind through a 20-50 mesh sieve to obtain 20-50 mesh biochar;

[0062] (2.2) Add the 20-50 mesh biochar into a conical flask containing a 5.0% hydrochloric acid solution, and perform constant temperature acid washing and oscillation at a temperature of 25℃ and a speed of 100r / min for 5h. Wash with deionized water until neutral. Dry in a forced air drying machine at 110℃ for 4h to obtain acid-washed biochar;

[0063] (2.3) Add 40.5g of the acid-washed biochar into 500mL of a 16.2g / L ferric chloride (FeCl3) solution (mass ratio of ferric chloride to acid-washed biochar is 0.2:1.0), and oscillate in a constant temperature water bath shaker at a temperature of 35℃ and a speed of 200r / min for 24h. Then, filter out the biochar and dry in a forced air drying machine at 110℃ for 12h to obtain dried biochar;

[0064] (2.4) Further add the dried biochar into 300mL of a 5% sodium hydroxide (NaOH) solution (mass ratio of sodium hydroxide to dried biochar is 0.3:1.0), and adjust the pH value to 10.0. Then, oscillate in a constant temperature water bath shaker at a temperature of 35℃ and a speed of 100r / min for 24h to form a hydrated iron oxide precipitate on the surface of the biochar. The solid material of the biochar immobilized with hydrated iron oxide obtained by the above reaction is suction filtered, washed with deionized water until neutral, and then dried in a forced air drying machine at 110℃ for 12h to obtain biochar immobilized with hydrated iron oxide.

[0065] (3) Preparation of a composite flocculant

[0066] (3.1) Dissolve the polyaluminum chloride flocculant in water at a mass ratio of 0.1:1.0 to obtain a polyaluminum flocculant solution;

[0067] (3.2) Add the biochar immobilized with hydrated iron oxide into the polyaluminum flocculant solution at a mass ratio of 0.3:1.0, and mix uniformly by stirring. Dry in an oven at 55℃ for 5h, and cool at room temperature to obtain a modified composite flocculant of biochar immobilized with hydrated iron oxide.

[0068] The composite flocculant of this embodiment 1 has a mass ratio of hydrated iron oxide of 4.4%, a mass ratio of biochar of 22.1%, and a mass ratio of polyaluminum flocculant of 73.5%.

[0069] Example 3

[0070] Laboratory beaker experiment

[0071] Using laboratory 1L beaker and six coagulation mixer test, using potassium dihydrogen phosphate, sludge powder to adjust the TP concentration in water to 0.5 mg / L, SS is 50 mg / L. In two beakers, respectively, add conventional flocculant polyaluminum chloride 75 mg / L (control group) and the composite flocculant of the application 75 mg / L (experimental group), the mixer is fast stirring at 200 r / min for 2 min, then add the corresponding dose of coagulant polyacrylamide 1 mg / L, slow stirring at 50 r / min for 10 min, after the formation of flocs, precipitate for 20 min. Take the supernatant, measure its total phosphorus concentration.

[0072] See Figure 1 , the total phosphorus concentration of raw water is 0.51 mg / L, add conventional flocculant polyaluminum chloride after coagulation and sedimentation, the total phosphorus concentration of effluent is 0.058 mg / L (more than 0.05 mg / L), the total phosphorus removal rate is 88.6%. Add the composite flocculant of the application, after coagulation and sedimentation, the total phosphorus concentration of effluent is 0.027 mg / L (much less than 0.05 mg / L), the TP removal rate is as high as 94.6%, which can achieve the effect of ultimate phosphorus removal.

[0073] Example 4

[0074] Laboratory pilot test

[0075] Using laboratory pilot test, the reactor uses coagulation and air flotation integrated device, the reactor operating parameters are HRT=25 min, gas solubility: 200 L / h, using potassium dihydrogen phosphate, sludge powder to adjust the TP concentration in 500 L experimental barrel to about 0.5 mg / L, the experiment respectively dissolves polyaluminum chloride, the composite flocculant of the application and polyacrylamide in the dosing barrel, through the metering pump to control the polyaluminum chloride solution added in the reactor is 75 mg / L (control group), the composite flocculant of the application is 75 mg / L (experimental group), the coagulant polyacrylamide added in the two groups is 1 mg / L. After the coagulation and air flotation integrated device runs for 100 min, take out water every 25 min to determine the total phosphorus concentration.

[0076] See Figure 2 , add conventional flocculant polyaluminum chloride to coagulation and air flotation integrated device, after treatment, the total phosphorus removal rate is 77.7%, 77.4%, 82.6% and 81.6% respectively, the total phosphorus concentration of effluent is 0.120, 0.122, 0.094 and 0.099 mg / L respectively, the total phosphorus concentration of effluent is more than 0.05 mg / L, which fails to achieve the effect of ultimate phosphorus removal.

[0077] SeeFigure 3 After adding the composite flocculant to the integrated coagulation and air flotation device, the total phosphorus removal rates were 89.7%, 90.3%, 92.4% and 91.0% respectively, and the total phosphorus concentrations in the effluent were 0.061, 0.057, 0.045 and 0.052 mg / L respectively. The total phosphorus concentration in the effluent was controlled at about 0.05 mg / L, and the limit phosphorus removal was basically achieved.

Claims

1. A method for the preparation of a composite flocculant for the limit phosphorus removal of low turbidity water, characterized by, The operation steps are as follows: (1) Preparation of biochar (1.1) Add an alkaline substance to the sludge obtained by sewage treatment or the sludge obtained by water supply plant treatment and stir uniformly to obtain alkaline sludge with a pH value of 9.0-12.0, dry and crush into sludge particles; The alkaline substance is potassium hydroxide or urea; The particle size of the sludge particles is 0.5-1.0 cm; (1.2) High-temperature sintering of sludge particles under aeration to prepare biochar; the aeration gas is nitrogen or other inert gas; (2) Preparation of biochar fixed with hydrated iron oxide (2.1) Wash the biochar with deionized water for 3-4 times, dry, grind through a 20-50 mesh sieve to obtain 20-50 mesh biochar; (2.2) Add 20-50 mesh biochar to a 5.0% hydrochloric acid solution, constant temperature acid washing and oscillation to obtain oscillation biochar; rinse with deionized water until neutral, dry to obtain acid washed biochar; (2.3) According to the mass ratio of ferric chloride to acid washed biochar of 0.2-0.5:1.0, add the acid washed biochar to a 16.2g / L ferric chloride solution, oscillate in a constant temperature water bath shaker at 35℃ for 24 hours, filter out the biochar and dry to obtain dried biochar; (2.4) According to the mass ratio of sodium hydroxide to dried biochar of 0.3-0.8:1.0, add the dried biochar to a 5% sodium hydroxide solution, adjust the pH value to 10.0; oscillate in a constant temperature water bath shaker at 35℃ for 24 hours to generate hydrated iron oxide precipitate on the surface of the biochar, the solid material obtained by the reaction of the biochar fixed with hydrated iron oxide is filtered, the solid material is washed with deionized water until neutral, and dried to obtain biochar fixed with hydrated iron oxide; (3) Preparation of composite flocculant (3.1) Dissolve polyaluminum flocculant in water according to the mass ratio of 0.05-0.1:1.0 to obtain a polyaluminum flocculant solution; The polyaluminum flocculant is polyaluminum chloride or polyaluminum sulfate; (3.2) Add biochar fixed with hydrated iron oxide to the polyaluminum flocculant solution according to the mass ratio of 0.3-0.5:1.0, mix, heat and stir, and dry to obtain a composite flocculant modified by hydrated iron oxide fixed biochar; The mass ratio of hydrated iron oxide in the composite flocculant is 4.4%-14.3%, the mass ratio of biochar is 22.1%-28.6%, and the mass ratio of polyaluminum flocculant is 57.1%-73.5%; When the composite flocculant is used for the limit phosphorus removal treatment of low turbidity tail water of sewage treatment plants or low turbidity sewage of industrial parks, the composite flocculant is added to the water body to be treated at a dosage of 50-200mg / L, and the flocculation reaction is carried out for 10-20 minutes, at the same time, air flotation method is used to blow off the flocculation to separate the flocculation from the water body, or magnetic material is added at the bottom of the sedimentation zone to enhance the settling velocity of the magnetic flocculation and accelerate the separation of the flocculation from the water body, so as to realize the limit phosphorus removal of the water body.

2. The method for preparing a composite flocculant for limiting phosphorus removal from low-turbidity water according to claim 1, characterized in that: In step (1.2), the high-temperature sintering is carried out at a temperature of 300-800℃ for 2.0-6.0 hours.

3. The process as claimed in claim 1, wherein the process for preparation of composite flocculants for limiting phosphorous removal in low turbidity water is characterized by: In step (2.1), the drying is carried out in an oven at 110℃ for 4h.

4. The process as claimed in claim 1, wherein the process for preparation of a composite flocculant for limiting phosphorous removal in low turbidity water is characterized by: In step (2.2), the oscillation is carried out at 20-35℃ at a speed of 100-200r / min for 5h; the drying is carried out in a blast drier at 110℃ for 2-10h.

5. The process as claimed in claim 1, wherein the process for preparation of a composite flocculant for limiting phosphorous removal in low turbidity water is characterized by: In step (2.3), the oscillation is carried out at a speed of 100-200r / min for 24h; the drying is carried out in an oven at 110℃ for 12h.

6. The process as claimed in claim 1, wherein the process for preparation of composite flocculants for limiting phosphorous removal in low turbidity water. In step (2.4), the oscillation is carried out at a speed of 100-200r / min for 24h; the drying is carried out in an oven at 110℃ for 12h.

7. The process as claimed in claim 1, wherein the process for preparation of a composite flocculant for limiting phosphorous removal in low turbidity water. In step (3.2), the drying is carried out in an oven at 45-55℃ for 2-5h.

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