Method for removing refractory phosphorus in inflow water of high-efficiency sedimentation tank

Abstract

The invention relates to the technical field of sewage treatment, in particular to a method for removing refractory phosphorus in inflow water of an efficient sedimentation tank. According to the method disclosed by the invention, when the refractory phosphorus in the inlet water is abnormal, the refractory phosphorus in the inlet water is effectively removed by adding excessive coagulant, and in the process, the composite coagulant is adopted, so that a relatively beneficial technical effect can be achieved, the composite coagulant is formed by compounding an inorganic high-molecular coagulant and an organic high-molecular flocculant, and comprises the steps that polyferric sulfate and polyacrylamide are compounded according to a certain mass ratio, and the obtained composite coagulant is added excessively when the content of phosphorus in inflow water difficult to degrade of an efficient sedimentation tank is abnormal, so that the content of phosphorus in the inflow water difficult to degrade of the efficient sedimentation tank is abnormal. The removal rate of phosphorus difficult to degrade can reach 90% or above, the quality of discharged water can reach the first-level A standard of pollutant discharge of a municipal sewage treatment plant, and a positive and effective effect is achieved for guaranteeing the quality of the discharged water.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and particularly relates to a method for removing refractory phosphorus in the influent of a high-efficiency sedimentation tank. Background Art

[0002] Sewage treatment is a process of purifying sewage to meet the water quality requirements for discharging into a certain water body or reusing it, and is widely applied in various fields such as construction, agriculture, transportation, energy, petrochemical, environmental protection, urban landscape, medical treatment, and catering.

[0003] The existing municipal sewage treatment mostly adopts a three-stage treatment method, that is, a treatment method of mechanical treatment + biological treatment + advanced treatment. Among them, for advanced treatment, a high-efficiency sedimentation tank is commonly used to further remove phosphorus from the effluent of biological treatment. During the process, a coagulant is added. Traditional coagulants include polyaluminum chloride, etc. By adding polyaluminum chloride, phosphorus in the form of orthophosphate in the influent of the high-efficiency sedimentation tank forms insoluble orthophosphate, thereby realizing further removal of phosphorus in the influent of the high-efficiency sedimentation tank, and further achieving the purpose of further removing phosphorus from the effluent of biological treatment.

[0004] However, during the actual operation of the process, there is still some phosphorus in the sewage that is difficult to biodegrade, including organic phosphorus, etc. This part of phosphorus cannot be removed in the form of forming orthophosphate in principle; in the existing operation process, the content of this part of refractory phosphorus is generally small, so it is often not particularly considered. However, due to the variability of the sewage treatment influent, especially when there is a large amount of sewage from fields such as food processing and machinery manufacturing in the influent of the sewage treatment plant, this part of refractory phosphorus cannot be ignored, but there is currently a lack of effective means to remove this part of refractory phosphorus.

[0005] Therefore, through production exploration, the present application proposes an effective removal means for the high content of refractory phosphorus in the influent of a high-efficiency sedimentation tank, aiming to provide an effective treatment idea for the existing situation when the content of refractory phosphorus in the high-efficiency sedimentation tank is too high. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for removing refractory phosphorus in the influent of a high-efficiency sedimentation tank to solve the problem that traditional process means cannot effectively remove refractory phosphorus when the existing influent refractory phosphorus is too high.

[0007] To achieve the above purpose, the present invention adopts the following technical scheme: A method for removing refractory phosphorus in the influent of a high-efficiency sedimentation tank, comprising the following steps:

[0008] S1. Compound an inorganic polymer coagulant and an organic polymer flocculant to obtain a compound coagulant;

[0009] S2. Excessively add the composite coagulant obtained in S1 to the water inlet of the high-efficiency sedimentation tank, and the removal of refractory phosphorus in the influent of the high-efficiency sedimentation tank can be achieved.

[0010] Further, in the above-mentioned S1, the composite coagulant is a composite ferric salt coagulant.

[0011] Further, the inorganic polymer coagulant is polyferric sulfate with a basicity of 8-16%; the organic polymer flocculant is polyacrylamide with a molecular weight of 12-16 million.

[0012] Further, the composite ferric salt coagulant is a reddish-brown transparent liquid with an iron content of 7-11%; the mass fraction of polyacrylamide is 2.0-5.0%.

[0013] Further, in the above-mentioned S2, the dosage of the composite coagulant relative to the influent of the high-efficiency sedimentation tank is 200-500 mg / L.

[0014] Further, in the high-efficiency sedimentation tank, the rotation speed of the stirrer in the rapid mixing zone is 80-120 rpm, and the rotation speed of the stirrer in the flocculation zone is 10-20 rpm.

[0015] Further, the sludge return pump at the bottom of the sedimentation zone of the high-efficiency sedimentation tank is always open, the sludge is returned to the flocculation zone, the sludge return ratio is 5-7%, the concentration of the returned sludge is controlled at 2000-3000 mg / L, and the excess sludge is discharged.

[0016] Advantages of the present invention:

[0017] 1. The present invention can effectively remove refractory phosphorus in the sewage treatment process, effectively avoid abnormal effluent caused by the difficulty in removing refractory phosphorus, and at the same time provides an idea for the treatment of refractory phosphorus, indicating the direction for the treatment of refractory phosphorus in sewage treatment, and has broad application prospects. Description of the drawings

[0018] Figure 1 is the structural diagram of the existing high-efficiency sedimentation tank involved in the present invention.

[0019] Names corresponding to each mark in the figure:

[0020] 1. Rapid mixing zone; 11. Inlet pipe; 2. Flocculation zone; 21. Sludge return pipe; 3. Sedimentation zone; 4. Filtration zone. Specific embodiments

[0021] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention.

[0022] As Figure 1As shown in the figure, the present invention relates to an efficient sedimentation tank, which sequentially includes a rapid mixing zone 1, a flocculation zone 2, a sedimentation zone 3, and a filtration zone 4 along the water inlet direction; an inlet pipe 11 is arranged at the front end of the rapid mixing zone 1, and the effluent from the secondary sedimentation tank enters the efficient sedimentation tank through the inlet pipe 11, and enters from the bottom of the rapid mixing zone 1 through overflow. A phosphorus removal agent is added in the rapid mixing zone 1. Under the action of the stirrer in the rapid mixing zone 1, the phosphorus removal agent is rapidly mixed with the sewage and flows into the flocculation zone 2. In the flocculation zone 2, the sewage enters from the bottom of the draft tube. The returned sludge in the corresponding sedimentation zone 3 also enters the bottom of the draft tube from the sludge return pipe 21 and flows out from the upper part of the draft tube, and then enters the sedimentation zone 3. In the sedimentation zone 3, the flocculated sludge precipitates, part of it is refluxed through the sludge return pipe 21, and the remaining sludge is discharged. The water outlet from the upper part of the sedimentation zone 3 is filtered by the fiber rotary disc filter in the filtration zone 4.

[0023] Example 1

[0024] In this example, the municipal sewage A of a sewage treatment plant 2 from the secondary sedimentation tank of the AO treatment process was detected. After detection, the content of orthophosphate in the effluent of this secondary sedimentation tank was 0.57 mg / L, the total phosphorus content was 2.03 mg / L, that is, the content of refractory phosphorus was 1.46 mg / L.

[0025] In this example, the composite coagulant of the present invention was used to treat the effluent of this secondary sedimentation tank. In this example, the composite coagulant was prepared by compounding polyferric sulfate and polyacrylamide. The basicity of polyferric sulfate was 15%, and the average molecular weight of polyacrylamide was 14 million. They were compounded at a mass ratio of polyferric sulfate: polyacrylamide: water = 36:4:60. The obtained composite coagulant was a reddish-brown transparent liquid, with an iron content of 10.84% and a mass fraction of PAM of 4%.

[0026] The composite coagulant of this example was added to the rapid mixing zone of the efficient sedimentation tank at a dosage of 300 mg / L. The rotation speed of the stirrer in the rapid mixing zone was 80 rpm. At the same time, the rotation speed of the stirrer in the flocculation zone was 12 rpm, and the sludge return ratio in the sedimentation zone was 6%.

[0027] After the process operation was stable, the effluent of the fiber rotary disc filter in the filtration zone was sampled and detected. After detection, the content of orthophosphate in the effluent was 0.01 mg / L, and the total phosphorus content was 0.14 mg / L, which could meet the first-class A standard for pollutant discharge from urban sewage treatment plants. During the process, 0.13 mg / L of refractory phosphorus remained in the effluent, and the removal rate of refractory phosphorus reached 91.10%.

[0028] Example 2

[0029] In this embodiment, the content of orthophosphate in the secondary sedimentation tank effluent is 0.97 mg / L, the content of total phosphorus is 3.03 mg / L, that is, the content of refractory phosphorus is 2.06 mg / L.

[0030] In this embodiment, the same composite coagulant as in Example 1 is used, the dosage of the composite coagulant is 400 mg / L, and the subsequent process parameters are the same as those in Example 1.

[0031] After detection, the content of orthophosphate in the effluent of the fiber rotary disk filter is 0.07 mg / L, and the content of total phosphorus is 0.35 mg / L, which can meet the first-class A standard for pollutant discharge from urban sewage treatment plants. During the process, 0.28 mg / L of refractory phosphorus remains in the effluent, and the removal rate of refractory phosphorus reaches 86.41%.

[0032] Comparative Example 1

[0033] In this comparative example, the effluent of the secondary sedimentation tank in Example 1 was sampled, and polyaluminum chloride (basicity 60%, mass fraction 30%) was used to treat the effluent of the secondary sedimentation tank in the laboratory. During the process, the dosage of polyaluminum chloride was 300 mg / L. After stirring and mixing evenly, precipitation and filtration were carried out, and the treated sewage was detected. After detection, the content of orthophosphate in the treated sewage is 0.03 mg / L, the content of total phosphorus is 0.61 mg / L, which cannot meet the first-class A standard for pollutant discharge from urban sewage treatment plants. During the process, 0.58 mg / L of refractory phosphorus remains in the effluent, and the removal rate of refractory phosphorus reaches 60.27%.

[0034] Comparative Example 2

[0035] In this comparative example, the effluent of the secondary sedimentation tank in Example 1 was sampled, and polyaluminum chloride (basicity 60%, mass fraction 30%) was used to treat the effluent of the secondary sedimentation tank in the laboratory. During the process, the dosage of polyaluminum chloride was 400 mg / L. After stirring and mixing evenly, precipitation and filtration were carried out, and the treated sewage was detected. After detection, the content of orthophosphate in the treated sewage is 0.03 mg / L, the content of total phosphorus is 0.55 mg / L, which cannot meet the first-class A standard for pollutant discharge from urban sewage treatment plants. During the process, 0.52 mg / L of refractory phosphorus remains in the effluent, and the removal rate of refractory phosphorus reaches 64.38%.

[0036] Although the method of adding excessive polyaluminum chloride can also remove some refractory phosphorus in Comparative Examples 1-2, when using polyaluminum chloride for treatment, even if the dosage of polyaluminum chloride is increased, it is difficult for the effluent to meet the standard, and the treatment effect is inferior to that of the composite coagulant of the present invention.

[0037] Comparative Example 3

[0038] In this comparative example, samples were taken from the effluent of the secondary sedimentation tank in Example 2. In the laboratory, the composite coagulant in Example 1 of the present invention, polyferric sulfate (basicity 15%, mass fraction 36%), and polyaluminum chloride (basicity 60%, mass fraction 30%) were used for treatment respectively, but the dosage of each chemical agent was 50 mg / L. The obtained data are shown in the following table:

[0039] Table 1 Comparison table of the treatment effects of various chemical agents.

[0040]

[0041] It can be seen that when the dosage of each chemical agent is at a general level, the removal of orthophosphate in the sewage can be achieved, but the removal of refractory phosphorus is not obvious, which are 8.25%, 2.43%, and 4.85% respectively, and the effect of removing refractory phosphorus cannot be achieved.

[0042] The present invention is not limited to the above best implementation mode. Anyone can obtain various other forms of products under the inspiration of the present invention. However, no matter what changes are made in its shape or structure, as long as it has the same or similar technical solutions as this application, it falls within the protection scope of the present invention.

Claims

1. A method for removing refractory phosphorus in the influent water of an efficient sedimentation tank, characterized in that, It includes the following steps: S1. Compound an inorganic polymer coagulant and an organic polymer flocculant to obtain a compound coagulant; S2. Excessively add the compound coagulant obtained in S1 to the water inlet of the high-efficiency sedimentation tank, and the removal of refractory phosphorus in the influent water of the high-efficiency sedimentation tank can be achieved.

2. The method for removing refractory phosphorus in the influent of an efficient sedimentation tank according to claim 1, characterized in that: In the above S1, the compound coagulant is a compound iron salt coagulant.

3. The method for removing refractory phosphorus in the influent water of an efficient sedimentation tank according to claim 2, characterized in that: The inorganic polymer coagulant is polyferric sulfate with a basicity of 8-16%; the organic polymer flocculant is polyacrylamide with a molecular weight of 12-16 million.

4. The method for removing refractory phosphorus in the influent of an efficient sedimentation tank according to claim 3, characterized in that: The compound iron salt coagulant is a reddish-brown transparent liquid with an iron content of 7-11%; the mass fraction of polyacrylamide is 2.0-5.0%.

5. The method for removing refractory phosphorus in the influent of the high-efficiency sedimentation tank according to any one of claims 1-4, characterized in that: In the above S2, the dosage of the compound coagulant relative to the influent water of the high-efficiency sedimentation tank is 200-500 mg / L.

6. The method for removing refractory phosphorus in the influent water of the high-efficiency sedimentation tank according to claim 5, characterized in that: In the high-efficiency sedimentation tank, the rotation speed of the stirrer in the rapid mixing zone is 80-120 rpm, and the rotation speed of the stirrer in the flocculation zone is 10-20 rpm.

7. The method for removing refractory phosphorus in the influent of the high-efficiency sedimentation tank according to claim 6, characterized in that: The sludge return pump at the bottom of the sedimentation zone of the high-efficiency sedimentation tank is always open, the sludge is returned to the flocculation zone, the sludge return ratio is 5-7%, the concentration of the returned sludge is controlled at 2000-3000 mg / L, and the excess sludge is discharged externally.

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