Method for conditioning and dewatering sludge by cooperating with anaerobic digestion

Abstract

The invention discloses a synergistic anaerobic digestion sludge conditioning and dewatering method which comprises the following steps: (1) adding polysilicate aluminum ferric into synergistic anaerobic digestion sludge, and stirring and mixing; then adding polyacrylamide, and stirring and mixing to obtain conditioned sludge; (2) carrying out dehydration treatment on the conditioned sludge; the polysilicate aluminum ferric is prepared by the method comprising the following steps: a, mixing a sodium metasilicate solution and dilute sulphuric acid, and controlling the pH value of the mixed solution to be 2.0-4.0; then, activating the obtained mixed solution to obtain a polysilicic acid solution; the activation time is 40 to 70 hours; and b, adding Al2 (SO4) 3.18 H2O and Fe2 (SO4) 3 into the polysilicic acid solution, uniformly mixing, and then heating to obtain the polysilicate aluminum ferric. According to the invention, polysilicic acid is introduced into aluminum ferric sulfate to generate a new polysilicate aluminum ferric conditioner, and after conditioning, the structure and strength of sludge floc cooperating with anaerobic digestion can be improved, and dehydration is facilitated.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of sludge treatment, and more particularly relates to a method for conditioning and dewatering of co-digestion sludge. BACKGROUND

[0002] Municipal sludge is a byproduct of the sewage treatment process, and its efficient dewatering is a key step to realize sludge reduction and resource utilization. High-level anaerobic digestion sludge is a kind of municipal sludge, that is, the sludge after being treated by the "thermal hydrolysis + anaerobic digestion" process (i.e., the high-level anaerobic digestion process). Through research, it is found that the high-level anaerobic digestion sludge has characteristics such as small particle size and large specific surface area, and has the characteristics of being difficult to dewater compared with residual sludge, and generally needs to use flocculation conditioning technology to improve its dewatering performance. In order to improve the biogas production and the comprehensive treatment level of urban organic garbage, the co-digestion technology of thermal hydrolysis sludge and kitchen garbage has been widely concerned and applied. The conditioning and dewatering of co-digestion sludge generally uses the conditioning mode of "aluminum sulfate-iron + polyacrylamide (PAM)", and it is found in the actual conditioning process that the dewatering performance of the sludge after co-digestion becomes worse. In order to solve the problem of conditioning and dewatering of co-digestion sludge, it is necessary to select and optimize the existing conditioning reagents to develop green conditioning reagents that can destabilize the sludge system and cause flocculation. SUMMARY

[0003] The purpose of the present application is to provide a method for conditioning and dewatering of co-digestion sludge, which is applied to the conditioning and dewatering of co-digestion sludge. The inventors have found that, due to the low polymerization degree of conventional aluminum sulfate-iron reagent (polyaluminum iron), the present application introduces polysilicic acid (PSA) into aluminum sulfate-iron to generate a new polysilicic acid aluminum iron (PSAF) conditioning agent. The new polysilicic acid aluminum iron conditioning agent has good adsorption net trapping performance and also has the effect of electric neutralization, and can improve the flocculation structure and strength of co-digestion sludge after conditioning, which is beneficial to dewatering. At the same time, the use of polysilicic acid aluminum iron can reduce the use of aluminum iron and PAM conditioning agents, and does not introduce chloride ions into the sludge, making the sludge treatment process more green and efficient.

[0004] In order to achieve the above-mentioned purpose, the present application provides a method for conditioning and dewatering of co-digestion sludge, which comprises the following steps: (1) adding polysilicic acid aluminum iron to the co-digestion sludge and stirring and mixing, then adding polyacrylamide (PAM) and stirring and mixing to obtain conditioned sludge; (2) dewatering the conditioned sludge; The polysilicic acid aluminum iron is prepared by a method comprising the following steps: a. mixing a sodium metasilicate solution and dilute sulfuric acid, controlling the pH of the mixed solution to be 2.0-4.0; then, activating the obtained mixed solution to obtain a polysilicic acid solution; wherein the activation time is 40-70h, preferably 40-50h; b. adding Al2(SO4)3.18H2O and Fe2(SO4)3 into the polysilicic acid solution, mixing uniformly, and then heating to obtain the polyaluminum ferric silicate.

[0005] The commonly used conditioning dewatering agent for municipal sludge is aluminum ferrite and PAM, and a large amount of aluminum ferrite will increase the conductivity and salinity of the sludge, which is not conducive to subsequent disposal such as sludge land use. The PAM monomer has certain toxicity, which also increases the risk of sludge treatment and disposal. The present application aims at the disadvantages of existing agents and limited conditioning effect, and develops a green chlorine-free polyaluminum ferric silicate conditioner and a use method. After the new polyaluminum ferric silicate is generated by the polymerization reaction of polysilicic acid and aluminum ferrite, the polymerization degree of aluminum ferrite is increased, the polyaluminum ferric silicate agent with adsorption net capture and electric neutralization effect is formed, the sludge flocculation structure and strength are improved, the use of aluminum ferrite and PAM is reduced to a certain extent, and no chloride ion is introduced into the sludge, so that the sludge treatment and disposal are more green and efficient.

[0006] According to the present application, preferably, in the preparation method of the polyaluminum ferric silicate, The sodium metasilicate solution is an aqueous sodium metasilicate solution, and the concentration of the sodium metasilicate solution is 0.3-1 mol / L; The volume percentage of the dilute sulfuric acid is 15-25% (v / v); In the polyaluminum ferric silicate, the molar ratio of the sum of aluminum and iron to silicon is (3-5):1; the molar ratio of aluminum to iron is 1:(1-3); The heating temperature is 28-35℃, and the time is 0.5-2h.

[0007] According to the present application, preferably, the synergistic anaerobic digestion sludge is prepared by a method comprising the following steps: synergistically anaerobically digesting the thermally hydrolyzed sludge and kitchen waste to obtain the synergistic anaerobic digestion sludge.

[0008] According to the present application, preferably, the thermal hydrolysis temperature is 150-180℃, and the time is 25-35min; The dry solid weight ratio of the thermally hydrolyzed sludge to the kitchen waste is (2-11):1; The synergistic anaerobic digestion temperature is 39-41℃, and the time is 15-25d.

[0009] According to the present application, preferably, the capillary water absorption time (CST) of the synergistic anaerobic digestion sludge is 1100-2700s; The D of the synergistic anaerobic digestion sludge is 0.5-0.6% of the dry weight of the synergistic anaerobic digestion sludge 50 The particle size is 17-21 μm.

[0010] According to the application, preferably, the dosage of the polyaluminum ferric silicate is 4.5-5.5% of the dry weight of the synergistic anaerobic digestion sludge; The dosage of the polyacrylamide is 0.7-0.8% of the dry weight of the synergistic anaerobic digestion sludge; The sum of the dosages of the polyaluminum ferric silicate and the polyacrylamide is 5.2-6.3% of the dry weight of the synergistic anaerobic digestion sludge.

[0011] According to the application, preferably, in step (1), after the polyaluminum ferric silicate is added, the stirring speed is 500-800 rpm, and the stirring time is 30-50 min.

[0012] According to the application, preferably, in step (1), after the polyacrylamide is added, the stirring speed is 50-200 rpm, and the stirring time is 5-10 min.

[0013] According to the application, preferably, in step (2), the dewatering treatment adopts suction filtration dewatering or plate-and-frame filter pressing dewatering.

[0014] In the application, preferably, the plate-and-frame filter pressing dewatering comprises: firstly performing pressing in a plate-and-frame machine, then feeding the pressed sludge into a sludge feeding pump, and performing manual compression treatment to complete the dewatering treatment; further preferably, the pressure of the pressing is 6-8 bar; and the pressure of the manual compression treatment is 20-30 Mpa.

[0015] The application has the following beneficial effects: The application introduces polysilicic acid (PSA) into aluminum ferric sulfate to generate a new polysilicic acid aluminum ferric (PSAF) conditioner, the new polysilicic acid aluminum ferric conditioner has good adsorption and trapping performance, and has an electric neutralization effect, and can improve the flocculation structure and strength of the synergistic anaerobic digestion sludge after conditioning, which is beneficial to dewatering. Meanwhile, the use of the polysilicic acid aluminum ferric can reduce the use of aluminum ferric and PAM conditioners, and does not introduce chloride ions into the sludge, so that the sludge treatment process is more green and efficient.

[0016] Other features and advantages of the application will be described in detail in the following specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0017] The above and other objects, features and advantages of the present application will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which like reference characters refer to like parts throughout the several views, and in which:

[0018] Figure 1A microscope observation image of the polysilicic acid prepared according to the preparation example of the present application is shown.

[0019] Figure 2 A microscope observation image of the polysilicic acid prepared according to the comparative preparation example of the present application is shown. DETAILED DESCRIPTION

[0020] The preferred embodiments of the present application will be described in more detail below. Although the preferred embodiments of the present application are described below, it is understood that the present application can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that the present application will be thorough and complete, and will fully convey the scope of the present application to those skilled in the art.

[0021] The present application will be further illustrated below by examples: In the present application, the test method of CST of sludge is as follows: about 2-3 mL of sludge sample is collected by using a 5 mL disposable dropper, and is placed in a 2 cm diameter stainless steel cylinder carried by the CST instrument. The CST is obtained by recording the time required for the wetting radius of the filtrate to increase from 1 cm to 3 cm.

[0022] The test method of the moisture content of sludge cake is to calculate the mass loss before and after drying in a drying oven at 105°C for 2 h.

[0023] D 50 The particle size (median particle size) is tested by using a laser image particle size analyzer (Bettersize 3000 Plus).

[0024] The synergistic anaerobic digestion sludge used in Example 1 and Test Example 1 is taken from a certain reclaimed water plant in Beijing, and the capillary suction time (CST) of the synergistic anaerobic digestion sludge is 1737.4 s, the D 50 The particle size is 20.57 μm; the synergistic anaerobic digestion sludge is prepared by a method comprising the following steps: synergistic anaerobic digestion of thermally hydrolyzed sludge and kitchen waste to obtain synergistic anaerobic digestion sludge; wherein the temperature of the thermal hydrolysis is 160°C, and the time is 30 min; the dry solid weight ratio of the thermally hydrolyzed sludge to the kitchen waste is 4:1; the temperature of the synergistic anaerobic digestion is 40°C, and the time is 20 d.

[0025] The cationic degree of the polyacrylamide used in the following Example 1 and Test Example 1 is 30%, which is purchased from the Aisen Company.

[0026] Preparation Example

[0027] The present preparation example provides a polyaluminum ferric silicate conditioner, and the preparation method thereof is as follows: 1. Mix 0.5 mol / L sodium metasilicate aqueous solution and 20% (v / v) dilute sulfuric acid in a beaker, control the amount of dilute sulfuric acid added so that the pH value of the mixed solution reaches 3.0; place the beaker containing the mixed solution in room temperature (20±5℃) for activation for 48 h, to obtain a polysilicic acid solution. The activated polysilicic acid is petal-shaped.

[0028] 2. Under stirring, add Al2(SO4)3·18H2O powder and Fe2(SO4)3 powder into the PSA solution in sequence (add according to the molar ratio of the sum of aluminum and iron to silicon being 4:1, and the molar ratio of aluminum to iron being 1:2), mix uniformly, and then heat the mixture in a 30°C water bath for 1 h; after the heating polymerization reaction is completed, a polysilicic acid aluminum iron conditioner is obtained.

[0029] Comparative Preparation Example 1

[0030] 1. Mix 0.5 mol / L sodium metasilicate aqueous solution and 20% (v / v) dilute sulfuric acid in a beaker, control the amount of dilute sulfuric acid added so that the pH value of the mixed solution reaches 3.0; place the beaker containing the mixture in room temperature (20±5℃) for activation for 6 h. The activated polysilicic acid is branch-shaped.

[0031] 2. Under stirring, add Al2(SO4)3·18H2O powder and Fe2(SO4)3 powder into the PSA solution in sequence (add according to the molar ratio of the sum of aluminum and iron to silicon being 4:1, and the molar ratio of aluminum to iron being 1:2), mix uniformly, and then heat the mixture in a 30°C water bath for 1 h; after the heating polymerization reaction is completed, a polysilicic acid aluminum iron conditioner is obtained.

[0032] Comparative Preparation Example 2

[0033] Under stirring, add Al2(SO4)3·18H2O powder and Fe2(SO4)3 powder into deionized water in sequence (add according to the molar ratio of aluminum to iron being 1:2), mix uniformly, and then heat the mixture in a 30°C water bath for 1 h; after the heating polymerization reaction is completed, a polyaluminum iron (PAF) conditioner is obtained.

[0034] Microscope observation was performed on the polysilicic acid solutions prepared in the above preparation examples and Comparative Preparation 1, respectively, and the observation results are shown in Figure 1 and Figure 2 As shown in Figure 1 , the polysilicic acid synthesized in the step 1 of the preparation example is petal-shaped; as shown in Figure 2 , the polysilicic acid synthesized in the step 1 of the comparative preparation example 1 is branch-shaped.

[0035] Example 1

[0036] (1) To the synergistic anaerobic digestion sludge, polyaluminum ferric silicate prepared in Preparation Example 1 was added, and after mixing for 40 minutes at 700 rpm, polyacrylamide (PAM) agent was added, and mixing was carried out at 100 rpm for 5 minutes, and then the sludge was fed. The addition amount of the polyaluminum ferric silicate was 5.1% of the dry weight of the synergistic anaerobic digestion sludge, and the addition amount of the polyacrylamide was 0.74% of the dry weight of the synergistic anaerobic digestion sludge.

[0037] (2) The sludge was fed into the plate-and-frame machine, and after the feeding was completed, the pressing was started, and the pressing pressure was 7 bar.

[0038] (3) The discharge was completed, the air compressor and the pressure output valve were closed, the output pipe at the plate-and-frame pressing interface was pulled out and connected to the sludge feeding pump interface. The handle was pressed to 25 MPa, the nut was loosened, and after the pressure was released, the plate-and-frame filter plate was loosened to take out the filtrate.

[0039] The water content of the sludge cake was measured to be 60%, which met the requirement of deep dewatering of sludge.

[0040] Test Example 1

[0041] This test example was used to test the influence of dewatering effect of sludge conditioning with different polyaluminum ferric silicates.

[0042] Sludge conditioning method: 100 milliliters of synergistic anaerobic digestion sludge was first placed in a 400 milliliter beaker, and stirred at 700 rpm for 10 minutes on a magnetic stirrer, and then polyaluminum ferric silicate conditioning agent was added to the stirred sludge, and the addition amount was 5.1% of the dry weight of the sludge. After the addition of the agent, the stirring was continued at 700 rpm for 40 minutes. Then the speed was adjusted to 100 rpm, PAM (the addition amount of PAM agent was 7.4‰ of the dry weight of the sludge) was added to the sludge, and stirring was carried out for 5 minutes, and the conditioning process was completed.

[0043] The polyaluminum ferric silicates prepared in Preparation Example and Comparative Preparation Example 1 and the polyaluminum ferric prepared in Comparative Preparation Example 2 were respectively used to condition the synergistic anaerobic digestion sludge according to the above sludge conditioning method, and then the CST of the conditioned sludge was tested.

[0044] The CST of the sludge conditioned according to the above sludge conditioning method with the polyaluminum ferric silicate prepared in Preparation Example was 582.1 s, which was decreased by 1155.3 s compared with that before conditioning. The CST of the sludge conditioned according to the above sludge conditioning method with the polyaluminum ferric silicate prepared in Comparative Preparation Example 1 was 850.6 s, which was decreased by 886.8 s compared with that before conditioning. The CST of the sludge conditioned according to the above sludge conditioning method with the polyaluminum ferric prepared in Comparative Preparation Example 2 was 636.4 s, which was decreased by 1101 s compared with that before conditioning. It can be seen that the CST of the sludge conditioned with the polyaluminum ferric silicate prepared in Preparation Example decreased more, and the dewatering effect of the sludge was better.

[0045] The D50 of the sludge treated by the polyaluminum ferricosilicate prepared in the preparation example and the polyaluminum ferric prepared in the comparative preparation example 2 respectively according to the above sludge conditioning method is as follows: 50 The particle sizes are 53.37 μm and 31.45 μm respectively, so it can be seen that the particle size of the sludge treated by the polyaluminum ferricosilicate is larger and the floc strength is better, which is beneficial to dewatering.

[0046] The above has described various embodiments of the present application, the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes are obvious to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for conditioning and dewatering sludge through synergistic anaerobic digestion, characterized in that, The method includes the following steps: (1) Add polyaluminum iron silicate to the synergistic anaerobic digestion sludge and stir to mix; then add polyacrylamide and stir to mix to obtain conditioned sludge; (2) The conditioned sludge is dewatered; The polyaluminum iron silicate is prepared by a method comprising the following steps: a. A sodium metasilicate solution and dilute sulfuric acid are mixed, and the pH of the mixed solution is controlled to be 2.0-4.0; then, the resulting mixed solution is activated to obtain a polysilicic acid solution; wherein the activation time is 40-70 h, preferably 40-50 h; b. Add Al2(SO4)3·18H2O and Fe2(SO4)3 to the polysilicic acid solution, mix well, and then heat to obtain the polyaluminum iron silicate.

2. The method according to claim 1, wherein, In the preparation method of the aforementioned aluminum iron silicate, The sodium metasilicate solution is an aqueous solution of sodium metasilicate, and the concentration of the sodium metasilicate solution is 0.3-1 mol / L; The volume percentage of the dilute sulfuric acid is 15-25% (v / v). In the polyaluminum iron silicate, the molar ratio of the sum of aluminum and iron to silicon is (3-5):1; the molar ratio of aluminum to iron is 1:(1-3). The heating temperature is 28-35℃, and the time is 0.5-2h.

3. The method according to claim 1, wherein, The co-anaerobic digestion sludge is prepared by a method including the following steps: co-anaerobic digestion of hot hydrolyzed sludge and kitchen waste to obtain co-anaerobic digestion sludge.

4. The method according to claim 3, wherein, The hot water hydrolysis temperature is 150-180℃, and the time is 25-35 min; The dry weight ratio of the sludge from the thermal hydrolysis to the kitchen waste is (2-11):1; The temperature for the synergistic anaerobic digestion is 39-41℃, and the time is 15-25 days.

5. The method according to claim 3, wherein, The capillary water absorption time of the synergistic anaerobic digestion sludge is 1100-2700s; The D of the co-anaerobic digestion sludge 50 The particle size is 17-21 μm.

6. The method according to claim 1, wherein, The dosage of the polyaluminum ferric silicate is 4.5-5.5% of the dry weight of the co-anaerobic digestion sludge; The dosage of the polyacrylamide is 0.7-0.8% of the dry weight of the co-anaerobic digestion sludge; The sum of the dosages of the aluminum ferric silicate and polyacrylamide is 5.2-6.3% of the dry weight of the synergistic anaerobic digestion sludge.

7. The method according to claim 1, wherein, In step (1), after adding polyaluminum ferric silicate, the stirring speed is 500-800 rpm and the time is 30-50 min.

8. The method according to claim 1, wherein, In step (1), after adding polyacrylamide, the stirring speed is 50-200 rpm and the time is 5-10 min.

9. The method according to claim 1, wherein, In step (2), the dehydration process is carried out by vacuum filtration or plate and frame filtration.

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