A method for inhibiting fouling of a post-treatment pipeline for anaerobically digested kitchen waste sludge

Abstract

The present application relates to sludge treatment technical field, specifically to inhibition method of anaerobic digestion kitchen waste liquid sludge post-treatment pipeline scale formation, in the method, through flocculation, aeration treatment to anaerobic digestion sludge, no large particle scale formation body is produced in anaerobic digestion sludge, fine particle scale formation body in sludge is effectively separated when dewatering, so, in the sludge conveying pipeline after dewatering, no large particle scale formation body, no pipeline scale formation phenomenon appears, and in the supernatant of sludge dewatering, scale ion content is reduced, at this time, the pH of supernatant is regulated, which can avoid pipeline scale formation, and due to the reduction of scale ion content, the amount of pH reagent is reduced, which is helpful to reduce the treatment cost, the method is simple, through flocculation, aeration treatment to digestion sludge, on the one hand, sludge pipeline scale formation is avoided, on the other hand, the treatment of supernatant also plays a positive role, which is convenient for use in anaerobic digestion sludge treatment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sludge treatment, and particularly relates to a method for inhibiting pipeline fouling in post-treatment of anaerobic digestion of kitchen waste liquid sludge. BACKGROUND

[0002] In modern sewage treatment plants, the purpose of sludge treatment is to achieve "four changes", i.e. reduction, stabilization, harmlessness and resource utilization. In order to achieve stabilization, most sludge treatment plants in China currently use the method of anaerobic digestion for sludge stabilization treatment. In the initial stage of anaerobic digestion, due to cell death, orthophosphate, potassium ions, magnesium ions and the like in the cells are released into the digestion liquid; with the progress of anaerobic digestion, under the action of hydrolysis and fermentation bacteria, carbohydrates, proteins and fats are hydrolyzed and fermented to convert into monosaccharides, amino acids, fatty acids and the like, and amino acids are further converted into ammonia nitrogen and the like. In order to increase the gas production of anaerobic digestion and ensure long-term stable operation, some sewage treatment plants will use kitchen waste liquid to cooperate with anaerobic digestion to treat sludge; the kitchen waste liquid is mainly composed of carbohydrates, proteins and oils, and can be fermented with residual sludge in an anaerobic digestion device to increase the production of biogas in anaerobic digestion.

[0003] Mg 2+ , NH4 + , PO4 3- formed in the process of sludge anaerobic digestion will form fine particle fouling bodies, and Ca 2+ in the sludge will form calcium carbonate fouling bodies with carbon dioxide produced in anaerobic digestion. Under normal circumstances, the content of particles is low, and it is not easy to form large block fouling bodies in pipeline equipment. However, after the addition of kitchen waste liquid into the anaerobic digestion system, the content of ammonia nitrogen in the anaerobic digestion liquid increases, and the formed particles increase. When the sludge after anaerobic digestion flows out of the anaerobic digestion system, the fine particle fouling bodies formed will adhere to the inner wall of the pipeline or equipment, especially when passing through the supernatant pipeline of the subsequent dewatering equipment, with the continuous flow of fine particle fouling bodies in the supernatant, the fine particle fouling bodies on the pipeline gradually grow, and finally become larger block fouling bodies, which block the pipeline and even the entire water section, and seriously affect the operation of the subsequent equipment.

[0004] Therefore, a method capable of inhibiting pipeline fouling of anaerobic digestion sludge is a necessary technical means to ensure the stable operation of sludge treatment and equipment. SUMMARY

[0005] The purpose of the present application is to provide a method for inhibiting pipeline fouling in post-treatment of anaerobic digestion of kitchen waste liquid sludge, so as to solve the problem of easy fouling in the pipeline for post-treatment of anaerobic digestion sludge, which affects the stability of sludge treatment and equipment operation.

[0006] To achieve the above object, the present application adopts the following technical scheme: an anaerobic digestion kitchen waste liquid sludge post-treatment pipeline scale inhibition method, comprising the following steps:

[0007] S1, a dewatering front tank is arranged between a sludge anaerobic digestion system and a sludge dewatering device, and polyaluminum chloride is added to the dewatering front tank under stirring conditions;

[0008] S2, an aeration pipeline is arranged at the bottom of the S1 dewatering front tank, and the sludge from the anaerobic digestion system is aerated and then transported to the sludge dewatering device for dewatering;

[0009] S3, a buffer tank is arranged at the supernatant outlet of the sludge dewatering device in S2, a stirrer and a pH meter are installed in the buffer tank, and an electric valve is installed on the supernatant outlet pipeline of the buffer tank;

[0010] S4, a formic acid adding pump is arranged beside the buffer tank in S3, and the formic acid adding pump is linked with the pH meter, and the pH of the supernatant in the buffer tank is controlled to be lower than 7.45.

[0011] Further, in S1, the basicity of the polyaluminum chloride is not less than 75%, and the addition amount is 10-30 mg / L.

[0012] Further, in S2, the aeration intensity in the dewatering front tank is 8-16 m 3 air / m 3 sludge.

[0013] Further, in S2, the sludge from the anaerobic digestion system is in a plastic state after being dewatered by the sludge dewatering device, and the water content of the sludge is 65-80%.

[0014] Further, in S3, for a single sludge dewatering device, the length of the supernatant outlet pipeline is not greater than 2.0 m, the inner wall of the pipeline is smooth, and the connection part is a flange connection.

[0015] Further, in S4, the hydraulic retention time in the buffer tank is 20-40 min.

[0016] Further, in S3, the supernatant outlet of the supernatant outlet pipeline is located at the upper part of one side of the buffer tank, the buffer tank outlet pipeline is located at the bottom of the other side of the buffer tank, a partition wall is arranged between the supernatant outlet pipeline and the buffer tank outlet pipeline in the buffer tank, and a liftable electric weir gate is installed at the partition wall.

[0017] Further, in S3, the stirrer and the pH meter are both installed in the tank body of the buffer tank between the supernatant outlet pipeline and the partition wall.

[0018] Further, in the S4, when pH < 7.45, the electric valve on the buffer tank outflow pipe is in the open state; when pH ≥ 7.45, the electric valve on the buffer tank outflow pipe is closed, the formic acid adding pump pumps formic acid into the tank body until the pH value is lower than 7.45, and the duration is greater than 2 min, at this time, the electric valve is opened.

[0019] Further, in the S4, the adding point of formic acid is located at the bottom of the buffer tank, and the mass fraction of the formic acid solution is 0.85%.

[0020] The beneficial effects of the present application are:

[0021] 1. The digestion sludge is treated by adopting the flocculation and aeration mode, the fine particle scale body in the digestion sludge is removed, and the scale body nucleation is avoided. On the one hand, the subsequent sludge is in a plastic state after dewatering, and the scale phenomenon does not occur in the sludge conveying pipeline; on the other hand, the pH value of the treated sludge is lowered, so that the sludge is not easy to form scale body when the sludge and water are separated in the dewatering equipment, and the scale of the dewatering equipment is avoided; in addition, the content of scale-forming ions in the supernatant after sludge dewatering is reduced to a certain extent, which is convenient for the treatment of the supernatant after sludge dewatering, and also plays a positive role in inhibiting the scale of the supernatant conveying pipeline.

[0022] 2. By adjusting the pH of the supernatant in the buffer tank, the pH in the buffer tank is controlled to be less than 7.45, so that the scale control of the buffer tank outflow pipe is realized, the use amount of formic acid is effectively reduced, and the treatment cost is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0023] Fig. 1 is a process flow diagram of the present application;

[0024] Fig. 2 is a structure diagram of the buffer tank.

[0025] Corresponding names of various marks in the figure are as follows:

[0026] 1. Buffer tank; 11, partition wall; 111, electric weir gate; 12, supernatant outflow pipe; 13, buffer tank outflow pipe; 131, electric valve; 14, stirrer; 15, formic acid adding pump; 16, pH meter. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be clearly and completely described in combination with the drawings in the embodiments of the present application.

[0028] As Figs. 1-2As shown in the technical scheme of the present application, the sludge produced by the anaerobic digestion system is transported to a dewatering device after being treated in a dewatering pre-pool, wherein the sludge is flocculated and settled in the dewatering pre-pool by adding polyaluminum chloride, and is aerated by an aeration device, and the dewatering device is an existing one, such as a centrifugal dewatering machine.

[0029] After the sludge is dewatered by the dewatering device, the obtained supernatant is sent to a buffer pool 1, and is mixed into the sewage pipe network of the plant area after pH control in the buffer pool 1 (the pipe in the pipe network is thicker, and the supernatant is diluted by other sewage in the pipe network, and is in a turbulent state, and thus does not form a scaling body), wherein a partition wall 11 is arranged in the buffer pool 1, a liftable electric weir door 111 is installed at the partition wall 11, a supernatant outlet pipe 12 is located at the upper part of one side of the buffer pool 1, a buffer pool outlet pipe 13 is located at the lower part of the other side of the buffer pool 1, a stirrer 14 and a pH meter 15 are installed in the pool body between the supernatant outlet pipe 12 and the partition wall 11, and the outlet of a formic acid adding pump 15 extends into the pool body, and the formic acid adding pump 15 is arranged beside the buffer pool 1.

[0030] The principle of the present application is as follows:

[0031] Polyaluminum chloride is added to the dewatering pre-pool, and the polyaluminum chloride can improve the performance of the sludge produced by the anaerobic digestion, wherein the addition amount of the polyaluminum chloride is 10-30 mg / L, and the salt base degree needs to be more than 75%; the addition of the polyaluminum chloride can effectively improve the flocculation effect of the sludge, and the fine particle scaling body in the sludge is adsorbed and flocculated into the sludge, which is convenient for dewatering and separation in the subsequent treatment; the sludge produced by the anaerobic digestion is aerated in this process, and the aeration intensity is maintained at 8-16 m 3 air / m 3 sludge, which prevents the sludge from being blown away, and also prevents the fine particle scaling body from forming a nucleus.

[0032] Through experiments, when the aeration intensity is more than 16 m 3 air / m 3 sludge, the sludge is easy to be blown away, which is not conducive to the sludge dewatering process itself; when the aeration intensity is less than 8 m 3 air / m 3 sludge, the calcium ions contained in the fine particle scaling body are easy to be converted into calcium carbonate crystal nuclei, and other Mg 2+ , NH4 + , PO4 3- take the crystal nuclei as cores to form large scaling bodies, which are attached to the inner wall of the pipeline to form scaling; therefore, the aeration intensity is preferably maintained at 8-16 m 3 air / m 3 sludge (the dissolved oxygen content is not more than 0.5 mg / L).

[0033] Through the flocculation and aeration operation of the sludge, the fine particle scale body in the sludge is effectively separated in the subsequent dewatering equipment, on the one hand, the pipe wall scale caused by the formation and adhesion of the large particle scale body is avoided, on the other hand, the pH value of the treated sludge is reduced, so that the sludge is not easy to form scale body when the sludge and water are separated in the dewatering equipment, and the dewatering equipment is prevented from scaling; in addition, the amount of scale-forming ions in the supernatant after the sludge is dewatered is reduced, which plays a positive role in inhibiting the scale of the supernatant pipe.

[0034] The sludge treated by the above method is transported to the dewatering equipment for dewatering, and the water content is reduced to 65-80% during the process, at this time, the sludge is in a plastic state, and no large particle scale body is formed, so that the scale body is not formed on the inner wall of the pipe during transportation; when the sludge is dewatered, the supernatant is generated, and the supernatant is transported to the buffer tank 1 through the supernatant outlet pipe 12; in the technical scheme of the present application, the supernatant outlet pipe 12 is as short as possible, preferably not more than 2.0m for a single sludge dewatering equipment, and the pipe adopts a smooth inner wall material, so as to effectively prevent scaling; in addition, the connection is flange connection, which is easy to disassemble, clean and replace when scaling occurs.

[0035] The hydraulic retention time in the buffer tank 1 is preferably 20-40min, the pH in the buffer tank 1 is controlled by cooperation of the formic acid adding pump 15 and the pH meter 16, and the pH is controlled to be less than 7.45 during the process; it is found through experiments that when the pH is less than 7.45, the pipe inside is basically not scaled, and when the actual operation is greater than or equal to 7.45, the electric valve 131 is closed, the electric weir gate 111 is raised, formic acid is continuously added until the pH value is reduced to less than 7.45, and is maintained for more than 2min, at this time, the electric weir gate 111 is lowered, and the electric valve 131 is reopened.

[0036] At present, the mass concentration of industrial formic acid on the market is mostly about 85%, through experiments, when diluted by 100 times, that is, the formic acid concentration is 0.85%, the pipe and equipment are not corroded and the formation of struvite is effectively inhibited, which is the most suitable concentration, and the addition flow rate Q 甲酸 (L / h) is:

[0037] Q 甲酸 = (measured pH value-7.45)*50Q*1.2

[0038] In the formula, Q is the flow rate of the supernatant, m 3 / h;

[0039] 7.45 is the best pH value for control;

[0040] 50 is an empirical value; the specific calculation is that 1L of supernatant needs 0.05 mL of 85% formic acid for each 0.1 pH reduction, which is converted into 0.85% formic acid, and the formula needs to be multiplied by 50 according to experience;

[0041] 1.2 is a coefficient, and the coefficient is greater than 1 to ensure that the supernatant effluent pH value is within the control range.

[0042] Example 1

[0043] Take 1L of supernatant sample in the buffer tank respectively, and adjust the pH value to 7.00, 7.45, 8.00 and 8.50 respectively. After standing, centrifugation, pouring off the supernatant sample in the bottle, drying, and weighing the bottle body again, the difference between the weight and the empty bottle mass is the mass of the obtained crystalline material. The data are as follows:

[0044] Table 1 Data table of scaling amount of supernatant sample with pH change

[0045]

[0046] It can be seen that when pH > 7.45, the mass of the crystalline material gradually increases with the increase of the pH value, and when the pH value is 8.0, the mass of the crystalline material reaches the maximum in the same time. When the pH value is more than 8.0, the mass of the crystalline material gradually decreases. When the pH value is 8.0, a relatively large amount of precipitate can be formed in 10 min, and the precipitate amount changes little between 20 min and 60 min. After 60 min, the mass of the crystalline material gradually increases with the increase of the standing time.

[0047] When the pH value is 7.45, there is almost no scaling phenomenon between 20 min and 60 min, and a small amount of precipitate is formed after more than 1 hour. When the pH value is less than 7.45, there is almost no scaling phenomenon. It is shown that by adjusting the pH value in the buffer tank, the formation of the pipe scaling body can be effectively inhibited, which plays a positive role in inhibiting the pipe scaling.

[0048] After 60 days of actual production operation, there is no obvious scaling phenomenon on the sludge pipeline and the supernatant pipeline, which shows that the method of the present application plays a positive role in inhibiting the scaling of the anaerobic digestion sludge post-treatment pipeline.

[0049] Comparative Example 1

[0050] After stopping aeration and stopping the addition of polyaluminum chloride for 1 day, take 1L of supernatant sample from the dewatering equipment before the buffer tank, and adjust the pH value to 7.00, 7.45, 8.00 and 8.50 respectively. After standing, centrifugation, pouring off the supernatant sample in the bottle, drying, and weighing the bottle body again, the difference between the weight and the empty bottle mass is the mass of the obtained crystalline material. The data are as follows:

[0051] Table 2 Data table of scaling amount of supernatant sample with pH change

[0052]

[0053] It can be seen that after stopping aeration and stopping polyaluminum chloride dosing, when pH>7.45, with the increase of pH value, the crystalline mass gradually increases, and when the pH value is about 8.50, the crystalline mass reaches the maximum in the same time.

[0054] It can be seen that through aeration and polyaluminum chloride dosing, the pH value of the supernatant sample forming the maximum crystalline mass is increased, which shows that the content of scale-forming ions in the supernatant is increased; that is, through aeration and polyaluminum chloride dosing, on the one hand, it can avoid the formation of large particle scale-forming body in the sludge pipeline after dewatering, effectively avoid the scaling of the sludge pipeline, on the other hand, it can reduce the content of scale-forming ions in the supernatant after sludge dewatering, which is helpful for the treatment of the supernatant and the reduction of the use amount of the reagent, and plays a positive role in inhibiting the scaling of the pipeline.

[0055] The present application is not limited to the above-mentioned best mode of implementation, and anyone can derive other various forms of products under the inspiration of the present application, but regardless of any changes in shape or structure, any technical solution with the same or similar to the present application falls within the protection scope of the present application.

Claims

1. A method for inhibiting scaling in pipelines used for the post-treatment of anaerobic digestion of kitchen waste sludge, characterized in that, Includes the following steps: S1. A pre-dewatering tank is set up between the sludge anaerobic digestion system and the sludge dewatering equipment. Polyaluminum chloride is added to the pre-dewatering tank under stirring conditions. S2. An aeration pipe is installed at the bottom of the pre-dewatering tank of S1 to aerate the sludge discharged from the anaerobic digestion system. After aeration, the sludge is directly transported to the sludge dewatering equipment for dewatering. The aeration intensity in the pre-dehydration tank is 8~16m. 3 air / m 3 Mud; it prevents sludge from being blown away and also prevents fine particles from forming nuclei; S3. Set up a buffer tank at the outlet of the clear liquid outlet pipe of the S2 sludge dewatering equipment, install a stirrer and pH meter in the buffer tank, and install an electric valve on the outlet pipe of the buffer tank. S4. Install a formic acid addition pump next to the S3 buffer tank. The formic acid addition pump is linked to a pH meter to control the pH of the supernatant in the buffer tank to be below 7.

45.

2. The method for inhibiting scaling in pipelines used for the post-treatment of anaerobic digestion of kitchen waste sludge according to claim 1, characterized in that: In S1, the basicity of polyaluminum chloride is not less than 75%, and the addition amount is 10~30 mg / L.

3. The method for inhibiting scaling in pipelines used for the post-treatment of anaerobic digestion of kitchen waste sludge according to claim 1, characterized in that: In S2, the sludge from the anaerobic digestion system is in a plastic state after being dewatered by the sludge dewatering equipment, and the sludge moisture content is 65-80%.

4. The method for inhibiting scaling in pipelines used for the post-treatment of anaerobic digestion of kitchen waste sludge according to claim 1, characterized in that: In S3, for a single sludge dewatering device, the length of the supernatant outlet pipe is no more than 2.0m, the inner wall of the pipe is smooth, and the connection is a flange connection.

5. The method for inhibiting scaling in pipelines used for the post-treatment of anaerobic digestion of kitchen waste sludge according to claim 1, characterized in that: In S4, the hydraulic retention time in the buffer tank is 20-40 minutes.

6. The method for inhibiting scaling in pipelines used for the post-treatment of anaerobic digestion of kitchen waste sludge according to claim 1, characterized in that: In S3, the outlet of the supernatant outlet pipe is located at the upper part of one side of the buffer pool, and the buffer pool outlet pipe is located at the bottom of the other side of the buffer pool. A partition wall is set between the supernatant outlet pipe and the buffer pool outlet pipe in the buffer pool, and a liftable electric weir gate is installed at the partition wall.

7. The method for inhibiting scaling in pipelines used for the post-treatment of anaerobic digestion of kitchen waste sludge according to claim 1, characterized in that: In S3, the stirrer and pH meter are both installed in the buffer tank between the supernatant outlet pipe and the partition wall.

8. The method for inhibiting scaling in pipelines used for the post-treatment of anaerobic digestion of kitchen waste sludge according to claim 1, characterized in that: In S4, when pH < 7.45, the electric valve on the outlet pipe of the buffer tank is in the open state; When pH ≥ 7.45, the electric valve on the outlet pipe of the buffer tank is closed, and the formic acid addition pump pumps formic acid into the tank until the pH value is lower than 7.45 and the duration is greater than 2 minutes. At this time, the electric valve can be opened.

9. The method for inhibiting scaling in pipelines used for the post-treatment of anaerobic digestion of kitchen waste sludge according to claim 1, characterized in that: In step S4, the formic acid is added at the bottom of the buffer tank, and the mass fraction of the formic acid solution is 0.85%.

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