JPS6345639B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Industrial Application] The present invention relates to a method for treating wastewater containing organic matter and phosphorus, such as domestic sewage, industrial wastewater, and similar organic wastewater. This is related to the improvement of dephosphorization technology. [Prior art] In general, the anaerobic-aerobic activated sludge method, which is a biological treatment process, is a biological treatment process in which dissolved oxygen (DO), nitrate radicals, or nitrite radicals (NO ) in an anaerobic state (hereinafter referred to as an anaerobic tank),
Here, the liquid to be treated and the returned sludge are mixed, and then this mixed liquid is led to the aerated zone in the latter stage (hereinafter referred to as the aerobic tank) for aeration treatment, and then solid-liquid separation is performed in the settling tank. It's technology. Specifically, as shown in FIG. 3, the liquid to be treated 1, which is an organic waste liquid such as domestic sewage, is separated from the primary sedimentation tank sludge 3 in the primary sedimentation tank 2, and the supernatant liquid 4 is
is introduced into the anaerobic tank 5 together with the final sedimentation tank sludge 13 that has been separated and returned in the final sedimentation tank 11, and is subjected to anaerobic treatment while being mixed by the stirrer 6. Here, activated sludge releases phosphorus and BOD in the liquid to be treated.
ingest a portion of Next, this anaerobic tank effluent mixed liquid 7 is led to an aerobic tank 8, where residual BOD components and other organic matter are oxidized and decomposed by aeration by an aerator 9, and at the same time, soluble phosphorus in the liquid is absorbed into activated sludge. The aerobic tank effluent mixed liquid 10 in which BOD and soluble phosphorus have been reduced in the aerobic tank 8 is sent to the final settling tank 11 and separated into a treated liquid 12 and a final settling tank sludge 13. This final settling tank sludge 13 is
A portion is returned to the anaerobic tank 5 as returned sludge, but the remainder is transferred to the initial settling tank 2 as surplus sludge 14, and concentrated in the initial settling sludge thickening tank 15 together with the initial settling tank sludge 3, etc., to concentrate the initial settling sludge. The tank supernatant liquid 16 is treated together with the liquid to be treated 1, the concentrated initial settling sludge 17 is treated with a dehydrator 18 etc. to which a dewatering aid is added, and the separated liquid 19 is mixed into the liquid to be treated 1. The process structure of the anaerobic-aerobic activated sludge method, which has these characteristics, produces activated sludge with a higher phosphorus uptake capacity than the activated sludge produced by the standard activated sludge method, making it easier to remove pollutants such as BOD and SS. At the same time, most of the soluble phosphorus present in the liquid to be treated can be absorbed into the activated sludge. [Problems to be solved by the invention] The activated sludge (final settling tank sludge 13) produced by such an anaerobic-aerobic activated sludge method has a higher phosphorus content than the sludge produced by the standard activated sludge method. If the rate is high and the sludge is placed in an anaerobic state, phosphorus will be re-released from the sludge, resulting in a high concentration of phosphorus being contained in the separated liquid produced in the sludge treatment process for excess sludge. Therefore, this separated liquid also needs to be treated, and is returned to the inlet end of the treatment system and treated together with the liquid to be treated. However, returning this separated liquid increases the amount of phosphorus that flows into the treatment system, lowers the phosphorus removal performance in the anaerobic-aerobic activated sludge process, and makes it unstable. It was necessary to reduce the phosphorus concentration of In addition, in the treatment of sludge generated from the conventional anaerobic-aerobic activated sludge method, excess sludge is transferred to the initial settling tank, and all of the sludge generated in the system is concentrated via the initial settling tank, and then dewatered. It was being processed. However, with this method, although the BOD concentration of the liquid to be treated flowing into the first settling tank is high, most of the polyphosphorus (60 to 80%) in the excess sludge transferred to the first settling tank is
%) is released into the liquid, and the P/BOD ratio in the liquid is:
0.06 or higher, a high concentration of phosphorus will remain in the final treatment liquid of the anaerobic-aerobic activated sludge method.
The disadvantage was that biological phosphorus removal was virtually impossible. The purpose of the present invention is to provide a method that eliminates these problems of the conventional anaerobic-aerobic activated sludge method, prevents an increase in the phosphorus load in the treatment system, and always performs stable phosphorus removal. It is something to do. [Means for Solving the Problems] The present invention first performs sedimentation separation on the liquid to be treated in a settling tank, and then separates the separated liquid and returned sludge into dissolved oxygen, nitric acid,
After mixing in an anaerobic state in which nitrous acid is not substantially present, aeration treatment is performed, and the aerated mixture is separated by sedimentation in a final settling tank, a part of the settled sludge is used as the return sludge, and the remainder is In a biological treatment method for organic wastewater that uses surplus sludge, the surplus sludge from the initial settling tank and the final settling tank are concentrated separately, and both thickened sludges are mixed at the same time or immediately after mixing. A salt compound is added as iron in an amount of 1 to 5% per sludge solid, and its pH is 6.
This is a method for treating organic waste liquid, which is characterized in that slaked lime is added and mixed to a concentration of ~8, and then dehydrated. [Function] To explain the embodiment of the present invention based on the drawings, in the first illustrated example, the liquid to be treated 1, which is an organic waste liquid such as domestic sewage, is separated from the first sedimentation tank sludge 3 in the first sedimentation tank 2, The supernatant liquid 4 is sent to the final settling tank 11.
The sludge is introduced into the anaerobic tank 5 together with the final settling tank sludge 13 returned from the sludge, mixed by the stirrer 6, and subjected to anaerobic treatment. Activated sludge hydrolyzes the high molecular phosphorus compound (polyphosphorus) stored in its cells and releases it into the solution, and uses the energy obtained at this time to remove some of the BOD contained in the liquid to be treated. is taken into cells and used as intracellularly stored organic matter. The scale of the anaerobic tank 5 that performs this anaerobic treatment reaction varies depending on the composition and concentration of the supernatant liquid 4 of the initial settling tank 2 flowing into it, but when domestic sewage is used as the liquid to be treated, The inflow amount may be 0.5 to 2.5 hours. In this way, soluble phosphorus increases and BOD
The anaerobic tank effluent mixed liquid 7 in which the anaerobic tank has been reduced is led to an aerobic tank 8 which is partitioned in a continuous or communicating state. This aerobic tank 8 supplies air and other oxygen-containing gases to an aeration chamber 9.
The activated sludge contained in the anaerobic tank outflow mixed liquid 7 takes in the BOD components that could not be taken up in the anaerobic tank 5 and is oxidized and decomposed, and the organic matter stored in the cells is also oxidized and separated. . In addition, the activated sludge utilizes part of the energy generated during the oxidation of organic matter to absorb soluble phosphorus that exists outside the cells into the cells, while also ingesting polymeric phosphorus compounds into the cells. Contains (polyline). At this time, an amount of soluble phosphorus greater than that released in the anaerobic tank 5 is ingested, and the soluble phosphorus concentration in the mixed liquid becomes lower than that in the liquid to be treated 1. In order to completely remove soluble phosphorus, the daily average P/BOD ratio of the liquid to be treated must be 0.06 or less, and most domestic sewage satisfies this condition. in this case,
In order to complete the oxidative decomposition of BOD and the removal of soluble phosphorus, the BOD sludge loading F/M ratio of aerobic and anaerobic 8 should be adjusted to 0.05 to 0.7 (1/day), preferably 0.3 to 0.5 (1/day).
day). The aerobic tank effluent mixed liquid 10 generated in the aerobic tank 8 and reduced in BOD and soluble phosphorus is sent to the final settling tank 11, where it is mixed with the treated liquid 12 and the final settling tank sludge 1.
Solid-liquid separation is carried out in 3 steps. A part of this final settling tank sludge 13 is returned to the anaerobic tank 5 as return sludge, and the remainder is transferred to the surplus sludge thickening tank 20 as surplus sludge 14, and separated into surplus sludge thickening tank supernatant liquid 21 and concentrated surplus sludge 22. be done. Further, the first settling tank sludge 3 separated in the first settling tank 2 is concentrated in the first settling sludge concentration tank 15. The degree of concentration of these sludges is preferably such that both sludge concentrations are 1% or more. Next, the concentrated initial settling sludge 17 and the concentrated excess sludge 22 are mixed in a mixing tank 23. When both thickened sludges are mixed, a large amount of phosphorus in the thickened excess sludge 22 is released in a short period of time, so in order to prevent phosphorus release, an iron salt compound 24 is added and mixed, and at the time of mixing.
Add 25% of slaked lime so that the pH becomes 6-8. The amount of iron salt compound 24 added varies depending on the properties of the sludge, but it is necessary to mix 1 to 5% iron based on the solid matter of sludge, and the addition and mixing of iron salt compound 24 and slaked lime 25 is It is preferable to start at the same time as the mixing of the thickened sludge, but if it is within one hour after mixing, the difference in the effect of phosphorus fixation is small, so it is sufficient to start within one hour after mixing. The method for mixing the iron salt compound 24 and the slaked lime 25 is not limited to mixing them in the mixing tank 23, but also a mixer may be provided in the transfer line of the mixing tank thickened sludge 26 to mix them with the thickened sludge. As the iron salt compound 24, it is preferable to use ferrous chloride, ferric chloride, and ferrous sulfate. Moreover, in order to adjust the amount of slaked lime 25 added so that the pH becomes 6 to 8, the slaked lime injection pump 27 may be controlled by the PH meter 28. Next, the mixing tank concentrated sludge 26 mixed with the iron salt compound 24 and slaked lime 25 is introduced into the dehydrator 18, dehydrated, and taken out as a dehydrated cake 29. When dewatering the mixing tank thickened sludge 26, if the sludge is left for a long time, phosphorus will be re-released from the sludge.
It is effective to dehydrate the iron salt compound 24 and slaked lime 25 within 5 hours after addition and mixing, since the phosphorus concentration in the separated liquid 19 can be reduced. As the dehydrator 18 used, a normal dehydrator such as a belt press dehydrator or a centrifugal dehydrator can be used. The dehydrated cake 29 is normally disposed of by drying, incineration, etc. The separated liquid 19 flowing out from the dehydrator 18 is returned and mixed with the liquid to be treated 1 or the supernatant liquid 4 of the initial settling tank 2. The phosphorus concentration in the separated liquid 19 has become low, and the separated liquid 19 is returned to the liquid to be treated 1.
Even if mixed with phosphorus, the inflow phosphorus load will not increase. The second illustrated example is basically the same as the first illustrated example, but a denitrification tank 30 is provided between the anaerobic tank 5 and the aerobic tank 8, and the anaerobic tank outflow mixed liquid 7 of the anaerobic tank 5, A part of the aerobic tank effluent mixed liquid 10 is introduced into the denitrification tank 30 and mixed and stirred to reduce the amount of water contained in the liquid.
While NOx is denitrified, a portion of the soluble phosphorus contained in the anaerobic tank outflow mixed liquid 7 is absorbed into the sludge. Therefore, in the second illustrated example,
Not only can BOD and phosphorus be removed, but nitrogen can also be removed. As described above, in the present invention, the initial settling tank sludge in the first stage of the anaerobic-aerobic activated sludge process and the surplus sludge generated in the anaerobic-aerobic activated sludge process are separately separated and concentrated, and then Simultaneously or immediately after mixing the silted sludge and thickened excess sludge, an iron salt compound is mixed in the range of 1 to 5% iron based on the solids of the mixed sludge, and slaked lime is added so that the pH at the time of mixing is 6 to 8. By mixing and then dehydrating the
This reduces the phosphorus concentration in the separated liquid during dewatering, reduces the amount of phosphorus returned from these sludge treatment systems, and reduces the anaerobic
This prevents an increase in the phosphorus load in the water treatment system of the aerobic activated sludge method, and allows stable phosphorus removal at all times. [Example] Next, an example of the present invention will be shown. Example 1 Domestic sewage discharged from a housing complex was treated as the liquid to be treated by the method shown in the first example. The specifications of each device were as follows. Initial settling tank 2: circular clarifaria water volume 4
m ³ Anaerobic tank 5: Double cylindrical stirring tank Water volume: 4 m ³ Aerobic tank 8: 4-compartment rectangular tank Water volume: 7 m ³ Final settling tank 11: Circular clarifier Water volume:
7m ³ Initial settling sludge thickening tank (gravity type) 15: Circular clarifier Water volume 0.6m ³ Water area 0.15m ² Excess sludge thickening tank (gravity type) 20: Circular clarifier Water volume 0.6m ³ Water area 0.3m ² Dehydrator 18 : Centrifugal separator Processing amount: 10Kg/h Using such facilities, the amount of liquid to be processed is 55m ³ /
When the returned sludge 13 was treated at a flow rate of 15.4 m ³ /d, a treated liquid as shown in Table 1 was obtained.

[Table] At this time, the MLSS concentration in the returned sludge was 1.2%, and the MLSS concentration in the aerobic tank was 2800 mg/. In addition, the surplus sludge 14 is introduced into the 410/d surplus sludge thickening tank 20, and the sludge 2 drawn from the thickening tank is
When the amount of sludge 2 was set as 205/d, the sludge interface in the thickening tank was almost constant at 1000 mm below the water surface, and the concentration of thickened surplus sludge 22 was 2.4%. On the other hand, the first settling tank sludge 3 is transferred to the first settling sludge thickening tank 15.
The sludge with a concentration of 3% was introduced as thickened sludge 17.
312/d was obtained. Next, these concentrated excess sludge 22 and concentrated initial settling sludge 17 are introduced into the mixing tank 23, and ferric chloride 24 is injected in an amount of 2.5% as iron per solid sludge.
Inject 25% of slaked lime to make the pH within 15%.
Immediately after mixing for a minute, dehydration was performed using a centrifuge 18. The amount of slaked lime 25 added is 4 per solid sludge.
It was %. The results were as shown in Table-2. Comparative Example The excess sludge in Example 1 was returned to the initial settling tank, and the entire amount was introduced into the initial settling sludge thickening tank to concentrate and reduce the concentration.
A 2.5% concentrated initial settled sludge of 570/d was obtained. Next, this thickened sludge was introduced into a mixing tank, ferric chloride was injected at 2.5% as iron per sludge solids, slaked lime was injected so that the pH in the mixing tank became 7.5, and after mixing for 15 minutes, It was immediately dehydrated using a centrifuge. The results are also shown in Table-2.

【table】

[Table] From Table 2, the phosphorus concentration in the dehydrated solution was 200mg/in the comparative example, while in the case of the present invention,
The total amount of phosphorus in the dehydrated solution is 89.2 g/d and 0.9 g/d, respectively, indicating that the present invention significantly reduces the amount of phosphorus in the dehydrated solution. In addition, the phosphorus concentration of the liquid to be treated is 8.3
mg/cm2, whereas in the comparative example the phosphorus concentration in the final treatment solution was 4.0mg/ ^cm2 , the phosphorus concentration in the final treatment solution of the present invention was as low as 0.7mg/cm2, and stable treatment results were obtained. You can see what you can get. Example 2 The sludge prepared under various conditions by changing the amount of ferric chloride injected into the mixing tank and the PH in the mixing tank in Example 1 was immediately dehydrated using a centrifuge. The treatment results are shown in the table below. 3 and 4 (the mixing time in the mixing tank was 15 minutes and constant).

【table】

[Table] As a result, the phosphorus concentration in the dehydrated liquid is 1 to 5, with the amount of ferric chloride added per solid sludge being iron.
%, it can be seen that good results can be obtained if the mixing treatment is carried out under conditions of pH 6 to 8. Example 3 Table 5 shows the relationship between the sludge storage time until the mixed sludge (mixing time 15 minutes) prepared in Experiment No. 3 in Example 2 is dehydrated using a centrifuge and the phosphorus concentration in the dehydrated liquid. It was as shown in.

[Table] Thus, it is advantageous to perform the dehydration treatment as soon as possible after the mixing treatment (preferably within 5 hours after the mixing treatment).

[Brief explanation of the drawing]

FIG. 1 is a system explanatory diagram showing one embodiment of the present invention, FIG. 2 is a system explanatory diagram showing another embodiment of the present invention, and FIG. 3 is a system explanatory diagram showing a conventional method. 1... Liquid to be treated, 2... First settling tank, 3... First settling tank sludge, 4... Supernatant liquid, 5... Anaerobic tank, 6
...Agitator, 7...Anaerobic tank effluent mixed liquid, 8...Aerobic tank, 9...Aerator, 10...Aerobic tank effluent mixed liquid, 11...Final sedimentation tank, 12...Treatment liquid , 13
...Final settling tank sludge, 14... Surplus sludge, 15...
... Initial settling sludge thickening tank, 16... Initial settling sludge thickening tank supernatant liquid, 17... Concentrated initial settling sludge, 18... Dehydrator, 1
9...separated liquid, 20...excess sludge thickening tank, 21...
... Surplus sludge concentration tank supernatant liquid, 22 ... Thickened surplus sludge, 23 ... Mixing tank, 24 ... Iron salt compound, 25
... Slaked lime, 26 ... Mixing tank thickened sludge, 27 ...
Slaked lime injection pump, 28...PH meter, 29...Dehydration cake, 30...Denitrification tank.

Claims (1)

[Scope of Claims] 1. The liquid to be treated is first separated by sedimentation in a settling tank, and the separated liquid and returned sludge are mixed in an anaerobic state in which dissolved oxygen, nitric acid, and nitrous acid are substantially absent. Afterwards, an aeration treatment is performed, and the aerated mixture is separated by sedimentation in a final settling tank, a part of the settled sludge is used as the return sludge, and the remainder is used as surplus sludge. The sedimentation tank sludge and the surplus sludge from the final sedimentation tank are each concentrated separately, and at the same time or immediately after mixing both of these thickened sludges, an iron salt compound is added as iron in an amount of 1 to 5% based on the sludge solids, and A method for treating an organic waste liquid, which comprises adding and mixing slaked lime so that the pH thereof becomes 6 to 8, and then dehydrating the liquid. 2. The method for treating organic waste liquid according to claim 1, wherein when the excess sludge from the first settling tank sludge and the final settling tank are concentrated separately, the sludge concentration of each is set to 1% or more. . 3. The method for treating organic waste liquid according to claim 1 or 2, wherein dehydration treatment is performed within 5 hours after the mixing treatment of the thickened sludge.