JPS6231633B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for purifying wastewater by removing harmful substances from domestic wastewater such as sewage, human waste, and wastewater containing organic substances and phosphoric acid contained in industrial wastewater. Generally, various types of wastewater discharged into natural water systems include:
Orthophosphates, various condensed phosphates, and organic phosphates exist in various states as organic substances and inorganic phosphates that are sources of BOD and COD, and these substances exist in lakes and inland seas. It is a factor that induces the occurrence of blue water and red tide in closed waters such as inner bays or stagnant waters.Furthermore, when water is used for various purposes, biological slime may form inside equipment and piping, which can lead to accidents. It is a serious cause. Therefore, various methods have been studied and proposed to remove the pollutants contained in these wastewaters. Activated sludge is a typical conventional method for removing organic substances, but this method uses floc-like biological growth that has a purifying function and is constantly circulated in a biological reaction system as needed. , the aeration tank is artificially operated so that the ratio of organic matter components (BOD) and purifying microorganisms is always constant, and the organic components and microorganisms are brought into contact in the presence of dissolved oxygen, resulting in aerobic decomposition. It's a process. However, with this method, the floc-like sludge produced during the biological treatment process does not necessarily have good settling, thickening, and dewatering properties, and the settling pond for settling the sludge is spread over a vast area. requires
Furthermore, in order to improve the concentration and dehydration properties, large amounts of chemicals such as polymers and water glass are required, which is considered a problem. In addition, the phosphorus that flows into the biological treatment process is only removed at a roughly constant ratio to the BOD removed, and phosphorus may leak into the biologically treated water, or in the process of treating sludge, it can become highly concentrated in the separated liquid. There was a problem when phosphorus leaked out. On the other hand, a typical method for removing phosphorus from wastewater is the coagulation-sedimentation method, which removes it as insoluble phosphate by adding a coagulant to the liquid.
The biggest drawback of this method is that it uses a large amount of chemicals and produces a large amount of sludge with poor thickening and dewatering properties, which poses problems in the treatment and disposal of this sludge. As a method for improving this coagulation-sedimentation method, there is a method (hereinafter referred to as "catalytic dephosphorization method") in which wastewater is brought into contact with a granular solid containing calcium phosphate (hereinafter referred to as "phosphorus removal material"). Although this method does not generate sludge,
By continuing the treatment, organic substances contained in the liquid are often incorporated onto the phosphorus removal material during the reaction process, resulting in a decrease in performance, or 5Ca ²⁺ +7OH ^- +3H ₂ PO ₄ ^- → Ca ₅ (OH) (PO ₄ ) ₃ +6H ₂ O... As shown in the reaction of the formula, apatite precipitates and becomes enlarged, leading to problems such as insufficient cleaning when necessary. . The present invention aims to solve these problems, and when a dephosphorization step is provided after a biological treatment process such as activated sludge, in which compounds are brought into contact with a phosphorus removal material, the compounds precipitated on the surface of the phosphorus removal material are continuously removed.
Alternatively, the biological treatment process and the catalytic dephosphorization process can be organically combined by intermittently peeling and returning the peeled material to the biological treatment process (sedimentation tank, thickening tank, return sludge, sludge dewatering process, etc.). The purpose of this invention is to provide a method for efficiently purifying organic wastewater. One of the important features of the method of the present invention is that it removes the compounds precipitated on the surface of the phosphorus removal material and mixes the removed compounds with the sludge produced in the biological treatment process, which improves concentration, sedimentation, and dewatering properties. In addition, it is possible to suppress the outflow of phosphorus during the sludge treatment process, and in the catalytic dephosphorization process in which the material is brought into contact with the phosphorus removal material, compounds that are generated on the surface of the phosphorus removal material are removed intermittently or continuously. The aim is to prevent deterioration of water quality due to long-term operation. That is, the present invention provides a method in which wastewater is treated by a biological method and then subjected to contact treatment in a reaction tank filled with granular solids containing calcium phosphate, in which compounds formed on the surface of the granular solids are continuously or intermittently treated. This is a wastewater treatment method in which the compound is exfoliated and the exfoliated compound is returned to the preceding biological treatment process. Next, one embodiment of the present invention will be described with reference to FIG. 1. In sewage 1 such as so-called raw sewage, relatively large suspended matter is settled and removed in a first settling tank 2, and the outflow from this first settling tank is Water 3 is introduced into an aeration tank 4 under aerobic conditions, that is, an aeration tank 4 in which air 5 is diffused, and organic substances in the liquid are oxidized and removed by the action of aerobic microorganisms. Floating matter in the outflow water from the aeration tank 4 is settled and removed in the final settling tank 6, and the settled sludge is led out from the final settling tank 6 and divided into return sludge 7 and surplus sludge 10, and the returned sludge is The sludge 7 is returned to the aeration tank 4, and the MLSS concentration in the aeration tank 4 is
Maintain at 2000-3000mg/. On the other hand, surplus sludge 10
The sludge is transferred to a thickening tank 8 and then passed through a sludge dewatering step 9 using a mechanical dehydrator or the like, and then led to a drying and incineration step 20 for treatment. The outflow water 6' from the final settling tank 6 is sent to the adjustment tank 1.
3, slaked lime 11 and gypsum 12 are added to adjust the pH and Ca concentration. This PH adjusted water 1
3' flows downward into the dephosphorization tank 14, and the dephosphorization tank 1
The treated water 19 is brought into contact with the phosphorus removing material 15 filled in the tank 4, and is caused to flow out from the bottom of the tank as treated water 19. The phosphorus removal material 15 in the tank is continuously or intermittently backwashed with backwash water 17 in the tank, or in combination with this, air 18 is introduced from the bottom of the tank to remove the phosphorus by water and air currents. By backwashing, compounds generated on the phosphorus removal material 15 are peeled off and removed. Note that the backwash wastewater 16 containing separated substances from the dephosphorization tank 14 is returned to one or more of the biological treatment process, such as the final settling tank 6, aeration tank 4, sludge thickening tank 8, or sludge dewatering process 9, and is recycled. It is processed. In the embodiment described above, the activated sludge method was used as an example of the biological treatment process, but other methods such as a trickling filter method, a catalytic oxidation method, and a granular media biological treatment method may also be used. In addition, when adjusting the pH of biologically treated water, the removal rate of phosphates decreases significantly on the acidic side, so it is necessary to adjust the pH to 6.0 or higher. In such a case, the pH should be 6.0 as it may precipitate on the surface of the phosphorus removal material in the dephosphorization tank and reduce its surface activity.
It is best to adjust to ~11.0, more preferably 8.5~
9.5 is good. Calcium chloride, slaked lime, gypsum, etc. can be used as calcium agents to be added, but the amount should be in the Ca/ _PO4 molar weight ratio of 1 to 5, and the injection point should be placed so that the calcium agent becomes ionic. The dephosphorization tank 14 is designed to flow into the dephosphorization tank 14 as it is. Further, the calcium phosphate-containing solid as the phosphorus removing agent 15 used in the present invention includes various phosphate rocks containing calcium phosphate, bone charcoal, coral sand, etc.
Sand, anthracite, or the like supported on calcium phosphate can be selected as appropriate. The compound formed on the surface of the phosphorus removal material can be peeled off and removed by water flow in the dephosphorization tank 14, or by backwashing using a combination of water and air flow. Either a mixing method or a so-called rubbing method in which the phosphorus removing material is placed in a container and rubbed together to separate the materials may be used. The compounds resulting from these peeling operations are easily peeled off, flow out of the tower along with the backwash wastewater, and can be easily separated from the liquid by simple physical operations.
In these cases, the stripping operation may be performed within the tower or outside the tower, and in either case, the phosphorus removal material 15
If all the compounds precipitated on the top are stripped off, the amount of peeled substances will be 5 to 10 times the amount of phosphorus removed.If the amount of phosphorus to be removed in the dephosphorization tank is 2g per ^1m3 of raw water, the amount of peeled substances will be 10 to 10 times the amount of phosphorus removed. It will be 20g. Note that it is preferable to reuse the separated material since it is possible to improve the settling properties, thickening properties, and dewatering properties by mixing the separated material into the sludge in the sedimentation basin, thickening tank, or dehydrator. The ratio of this mixing may be 1 to 2% or more on a dry sludge basis. The mixing method may be by adding it to the influent water of each process or directly into the process. The present invention continuously and intermittently peels off the compounds precipitated on the surface of the phosphorus removal material used in the dephosphorization process, thereby preventing the phosphorus removal material from thickening or deteriorating water quality due to organic matter adhesion, for a long period of time. Excellent phosphorus removal performance can be maintained, and the performance of the sludge can be greatly improved by returning the exfoliated material to the sludge treatment process.In other words, when exfoliated material is mixed into the settling tank, the settling properties of the sludge can be improved,
In addition, it is possible to suppress the elution of phosphorus from the sludge that has settled in the settling tank, and when the exfoliated material is mixed into the concentration process, the thickening property of the sludge is improved, and the elution of phosphorus can also be suppressed. When mixed into the process, it acts as a dewatering aid that improves the dewatering properties of sludge, saving the amount of chemicals normally used such as Ca(OH) ₂ and FeCl ₃ , and also removing water from sludge during the dewatering process. It is possible to organically combine the biological treatment process and the catalytic dephosphorization process, such as suppressing the elution of phosphorus into the separated water, and it is possible to efficiently purify organic wastewater, and the operation is stable and easy to control. Next, examples of the present invention will be shown. Example 1 After treating sewage from which coarse solids have been roughly separated using the conventional activated sludge method, the treated liquid was treated with caustic soda (slaked lime had the same effect).
Adjust the pH to around 90, use calcium chloride as a calcium agent, and adjust the molar weight ratio of Ca/PO ₄ according to the concentration of soluble phosphates in the liquid to be treated.
It was added in a range of 1.0 to 1.5. This liquid to be treated is guided into a cylindrical dephosphorization tower with a diameter of 0.5 m and an effective depth of 2.5 m, from the top to the bottom at LV = 2.5
Water was passed through at a flow rate of m/h. North African phosphate rock particle size 0.42 to 0.54 is used as a phosphorus removal material inside the dephosphorization tower.
Filled with mm. A stirrer (blade diameter: 0.2 m) is installed inside the tower, which allows the phosphorus removal material to be stirred and mixed once every day for about 15 minutes, and at the same time washed with water (water flow rate: 0.6 m/min).
The wash water containing the separated solids was returned to the final settling tank of the activated sludge process. As a comparative example, a case was shown in which no peeling operation was performed on the same scale. The processing results are shown in Table 1.

[Table] Table 1 shows the phosphorus concentration in the sludge thickening tank effluent. In the comparative example, the phosphorus concentration during treatment was over 1.2 mg/ml, so the thickening tank effluent was first returned to the settling tank. However, in the present invention, the concentration of effluent phosphorus was 0.35 mg/, which made it possible to considerably suppress the elution of phosphorus that normally occurs at high concentrations. Table 1 also shows the SVI of the final settling tank sludge.
SVI is a scale that expresses the settling and thickening properties of sludge.
Generally, the smaller the SVI, the better the sludge properties. As shown in Table 1, the SVI comparison example of sludge in the final settling tank is 55.0, but according to the present invention, the SVI is 36.5.
It was confirmed that the settling and thickening properties of the sludge were improved. Similarly, Table 1 shows an example in which thickened sludge was dehydrated using a belt press, and the dewatering performance of thickened sludge using the method of the present invention was found to be 20% higher than in the comparative example, and the cake was removed. The water content decreased by 5%, improving the dewaterability of the sludge. When the phosphorus concentration during separation was examined, the phosphorus concentration in the present invention was 1 mg/, which was lower than that in the comparative example, and the elution of phosphorus from the sludge in the escape process was also suppressed. Moreover, the phosphorus concentration in the treated water according to the present invention remained at an average of 0.27 mg/12 months after the start of water flow.
On the other hand, in the comparative method in which stripping was not performed, the phosphorus concentration in the treated water was 1.2 to 1.2 mg/12 months after the start of water flow, and the dephosphorization effect was significantly deteriorated. Example 2 The same equipment as in Example 1 was used. The experimental conditions were as follows: In Example 1, the reaction product on the phosphorus removal material was removed in a column packed with the phosphorus removal material.
In this example, the phosphorus removal material is taken out from the dephosphorization tower once a week and guided to the stripping tank (10), and a stirrer (blade diameter 20 cm, rotation speed 100 r.pm) is installed in the tank.
The reactive substance on the surface was peeled off. The liquid containing the separated substances was stored and returned to the initial settling tank using a metering pump, and the phosphorus removal material was returned to the dephosphorization tower, and a treatment experiment was conducted for about 12 months. As a result, the phosphorus concentration of the treated water after 12 months of water flow was the same as the results shown in Table 1, and the phosphorus concentration of the treated water by the method of the present invention was maintained at 0.3 mg/or less.
Good results were obtained, with no reduction in the dephosphorization effect observed at all. In addition, the settling property of the initial settling sludge was SVI100 in the conventional method, but the settling property of the initial settling sludge mixed with the exfoliated material was SVI50, and the settling property was good. Example 3 Activated sludge 1 containing 2000 mg of MLSS in a measuring cylinder was mixed with the above sludge at a constant ratio of the compound exfoliated from the phosphorus removal material, and the sedimentation properties of the sludge were compared. The measurement results are shown in Figure 2. That is, as shown in FIG. 3, when the addition amount was 1% or more, the sedimentation property was significantly improved. Example 4 500 ml of the activated sludge used in Example 3 was placed in beaker 1, fresh water was poured into the beaker, the top of the beaker was sealed with paraffin, air was blocked for a certain period of time, and then the phosphorus concentration in the fresh water was measured. . Similarly, the above-mentioned activated sludge was mixed with the surface of the phosphorus removing material and the resulting compound removed at a certain ratio, placed in a beaker No. 1, and the same test was conducted. The results are shown in Figure 3. From these results, phosphorus is eluted from the activated sludge when the air is shut off for a certain period of time in a beaker containing activated sludge. It was found that the elution of phosphorus can be prevented by mixing it with phosphorus.

[Brief explanation of the drawing]

Fig. 1 is a flow sheet of one embodiment of the method of the present invention, Fig. 2 is a relational diagram showing the sedimentation property of sludge, and Fig. 3 is a flow sheet of an embodiment of the method of the present invention.
The figure is a phosphorus elution characteristic diagram. 1...Sewage, 2...First settling tank, 3...First settling effluent, 4...Aeration tank, 5...Air, 6...Final settling tank, 7...Return sludge, 8...Sludge thickening tank ,9...
...Dehydrator, 10... Surplus sludge, 11... Slaked lime,
12...Gypsum, 13...PH adjustment tank, 14...Dephosphorization tank, 15...Phosphorus removal material, 16...Backwash drainage,
17... Backwash water, 18... Air, 19... Treated water.

Claims (1)

[Scope of Claims] 1. A method of treating organic wastewater in a biological treatment step and then contacting it with a granular solid phosphorus removal material containing calcium phosphate, in which a compound formed on the surface of the granular solid is removed. A method for treating wastewater, which comprises stripping the waste continuously or intermittently, and returning the stripped material to the biological treatment step for treatment. 2. The method according to claim 1, wherein the stripping operation is performed in a contact reaction tank filled with the granular solid. 3. Claims in which the peeling operation is performed by continuously or intermittently taking out the granular solids out of the reaction tank, and then returning the peeled granular solids to the reaction tank for treatment. The method described in paragraph 1. 4. The biological treatment step is carried out in an activated sludge treatment step consisting of an aeration tank, a final settling tank, a surplus sludge thickening tank, and a sludge dewatering step, and the detached material is treated in at least one of the treatment steps. 3. The method according to claim 1, 2 or 3, wherein the method is returned to a laboratory for processing. 5. Claim 1, wherein the peeling operation is performed using a water stream and/or an air stream.
2. The method according to paragraph 2, paragraph 3, or paragraph 4. 6. Claim 1, wherein the peeling operation is performed by mechanical stirring, agitation, or vibration.
2. The method according to paragraph 2, paragraph 3, or paragraph 4.