JP2001087789A - Method and apparatus for treating organic waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for treating waste water which increases consumption rate of alkali when solubilized by alkali and improves the decreasing effect on the volume of sludge. SOLUTION: In this method for treating organic waste water 1, the apparatus for treating activated sludge has a biological reaction vessel 7 and a sedimentation basin 11 and a part of the activated sludge in the biological reaction vessel 7 is extracted from the sedimentation basin 11 or the biological reaction vessel 7 and is supplied to two or more alkali reaction vessels 13 and 17 disposed in series. In the first alkali reaction vessel 13, the amount of alkali agent to be added is controlled so as to be pH 10.5-11.5, in the second and succeeding alkali reaction vessels 17, the amount of sludge to be supplied is controlled so as to be pH 8.0-10.5 and the sludge treated in the final alkali reaction vessel is returned to a controlling vessel 2 at the preceding step to the biological reaction vessel or the biological reaction vessel 7. The amount of the activated sludge to be supplied to the alkali reaction vessel is preferably made to be 5-20% of the amount of the sludge in the biological reaction vessel 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the treatment of organic wastewater, and more particularly to reducing the volume of excess sludge generated when treating organic wastewater such as organic industrial wastewater or domestic wastewater with activated sludge. A possible processing method and apparatus.

[0002]

2. Description of the Related Art Conventionally, in the treatment of wastewater with activated sludge, methods for treating and disposing of excess sludge accompanying the treatment include drawing,
Processes such as concentration, dehydration, and incineration must be obtained and discharged outside the system. The cost was rather enormous, leading to an increase in overall running costs. Furthermore, even in the sludge dewatering treatment, the complexity of maintenance associated with management of an appropriate chemical injection rate and the like remains. Recently, as sludge volume reduction treatment combined with activated sludge treatment, sludge with an excess amount of excess sludge is withdrawn from a sedimentation basin or biological reaction aeration tank, introduced into a separate ozone reaction tank into which ozone is injected, and treated. It is known that when the sludge thus received is returned to the biological reaction aeration tank again, a part of the ozone-treated sludge is decomposed by the biological treatment in the aeration tank (Japanese Patent Application Laid-Open No. 6-2060888).
Further, as a method of solubilizing sludge by adding alkali, a part of returned sludge is returned to a separate alkali treatment tank, and after solubilizing sludge, returned to an aeration tank without neutralization. The method is known (Japanese Patent Publication 6-61)
550).

However, in the process of solubilizing sludge by injecting ozone, not only is it necessary to newly install an ozone gas generator, but also it becomes necessary to perform ozone discharge treatment. In addition, in the sludge solubilization treatment by adding an alkali, if the pH of the alkali reaction tank is excessively high, the decomposition of the alkali-treated sludge in the aeration tank becomes insufficient, and the deterioration of the treated water quality, the increase in pH and the decrease in the volume reduction effect are reduced. Invite. In addition, when only one alkali reaction tank is used, the alkali consumption rate contributing to the solubilization of the sludge in the added alkali agent is reduced, the amount of liquefied alkali-treated sludge is reduced, and the sludge volume reduction effect is reduced. Dots remain.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, and increases the alkali consumption rate when solubilizing with alkali, thereby improving the sludge solubilization effect of organic wastewater. It is an object to provide a method and an apparatus.

[0005]

According to the present invention, there is provided a method for treating organic wastewater in an activated sludge treatment apparatus having a biological reaction tank and a sedimentation pond, comprising the steps of: Is withdrawn from a sedimentation basin or a biological reaction tank, and supplied to two or more alkaline reaction tanks arranged in series. The first alkaline reaction tank has a pH of 10.5-1.
The amount of the alkali agent added was controlled to 1.5,
After the alkali reaction tank, the supply amount of the sludge is controlled so that the pH becomes 8.0 to 10.5, and the treated sludge in the final alkali reaction tank is returned to the pre-adjustment tank or the biological reaction tank of the biological reaction tank. It was decided that. In the treatment method, the amount of activated sludge supplied to the alkaline reaction tank is preferably set to 5 to 20% of the amount of sludge in the biological reaction tank.

Further, in the present invention, a raw water regulating tank, a biological reaction tank, a sedimentation pond, and two or more alkaline reaction tanks arranged in series for treating activated sludge from the biological reaction tank and / or the sedimentation pond. In the treatment apparatus for treating activated organic sludge having activated sludge having the following, an introduction route for supplying activated sludge extracted from the biological reaction tank and / or the sedimentation basin to each of the alkaline reaction tanks is provided, and the first alkali reaction tank is provided with: Has an adjusting means for adjusting the pH to 10.5 to 11.5 by adding an alkali agent, and the reaction tanks after the second alkali reaction tank have p.
A control means for controlling the supply amount of the sludge so that H becomes 8.0 to 10.5 is provided, and a route for returning the treated sludge of the final alkaline reaction tank to the raw water adjusting tank or the biological reaction tank is provided. An organic wastewater treatment apparatus characterized in that:

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the present invention, in an activated sludge treatment apparatus comprising a biological reaction tank and a sedimentation tank, a part of the activated sludge is supplied from the sedimentation tank or the biological reaction tank to the first alkaline reaction tank, When an alkali agent is added so that the pH of the tank becomes 10.5 to 11.5, the organic matter in the sludge can be effectively reduced within a relatively short time in the first alkali reaction tank at a high OH ^- concentration. Is hydrolyzed to lower molecular weight, thereby promoting the liquefaction effect of sludge. If the pH is set to 11.5 or more in the first alkaline reaction tank, microorganisms in the activated sludge will be killed. Further, the processing solution passed through the first alkali reaction tank is supplied to the second alkali reaction tank, and the pH of the second and subsequent alkali reaction tanks is adjusted to 8.0 to 10.
Sludge is supplied to be 5, remains in the first alkaline reaction tank OH ^- is in contact with the activated sludge to be newly supplied, the organic matter in the sludge is hydrolysis, increase liquefaction of sludge more I do. Similarly, the mixed solution of the second and subsequent alkaline reaction tanks is supplied to the subsequent alkaline reaction tank, and the residual OH ^- is contacted and mixed with the newly introduced activated sludge to hydrolyze the organic matter in the sludge, The amount of sludge liquefied further increases.

As a result, the consumption rate of the alkali contributing to the liquefaction of the sludge is high, and the pH of the treated sludge can be kept lower than before. By supplying the alkali-treated sludge obtained as described above to, for example, a raw water adjusting tank in the former stage of the biological reaction tank, the anaerobic state of the adjusting tank is promoted, and acid fermentation of the liquefied organic matter of the inflowing raw water and the alkali-treated sludge is performed. In addition to being promoted, the pH fluctuation in the adjusting tank is small, and the lack of required alkalinity accompanying acid fermentation can be replenished by the alkalinity of the alkali-treated sludge. Furthermore, the liquefied organic matter of the alkali-treated sludge improves the decomposition efficiency in the biological reaction tank, hardly remains in the treated water, and can maintain the quality of the treated water well.

Further, even if supply alkaline treated sludge to the biological reaction tank, residual OH of the alkali treatment sludge ^- is less, because of high biodegradability of the liquefied organic, almost no increase in pH bioreactor In the biological reaction tank, liquefied organic matter is decomposed and removed with high efficiency. In addition, if the amount of the biological alkali-treated sludge is 5 to 20% of the total sludge amount of the biological reaction tank,
The increase in organic matter load on the biological reaction tank due to the increase in liquefied organic matter is small, and the organic matter decomposition ability in the biological reaction tank is sufficiently maintained, and the liquefied organic matter in raw water and alkali-treated sludge is efficiently biologically decomposed and removed. However, by partially decomposing it into CO ₂ and H ₂ O, the amount of sludge generated in the system can be suppressed, and the quality of treated water can be maintained well.

Next, the present invention will be described in detail with reference to the drawings. FIG. 1 is a flowchart showing an example of the method for treating organic wastewater of the present invention. As shown in FIG.
Is once introduced into the raw water adjusting tank 2, into which the alkali-treated sludge 9 from the second alkali reaction tank 17 is also introduced, and is uniformly mixed with the raw water by the adjusting tank stirring pump 3, and in the anaerobic state, the raw water and the alkali-treated sludge are mixed. The acid fermentation of the organic matter inside proceeds. The alkali required for the alkali consumption accompanying the acid fermentation can be replenished from the alkali-treated sludge, the fluctuation of the pH of the adjusting tank is small, and the pH of the raw water 4 at the outlet of the adjusting tank can be maintained at about neutral. The raw water 4 from the regulating tank outlet is introduced into the biological reaction tank 7, the organic matter in the raw water is decomposed and removed by the activated sludge, and the mixed liquid is introduced into the sedimentation basin 11 via the biological reaction tank outlet 10 to be separated into a solid and a liquid. Get 20.

On the other hand, a part of the returned sludge from the sedimentation basin 11 is introduced into the first alkali reaction tank 13 as sludge 12 flowing into the alkali reaction tank, and the pH of the first alkali reaction tank 15 is measured by the pH meter 15.
NaOH is injected from the NaOH injection pump 14 so that H10.5 to 11.5. The first alkali-treated sludge 16 that has undergone hydrolysis in the first alkali reaction tank 13 and is liquefied is introduced into the second alkali reaction tank 17. In the second alkali reaction tank 17, return sludge is injected from the second alkali reaction tank sludge injection pump 18 so that the pH of the second alkali reaction tank pH meter 19 becomes 8.0 to 10.5. OH remaining in the treated sludge 16 in the reactor ^- the sludge hydrolysis is promoted by reaction with the liquefied sludge proceeds further. The alkali-treated sludge 9 obtained from the second alkali reaction tank 17 is sent to the raw water adjustment tank 2.

The present invention will be described below in more detail with reference to examples. Example 1 Processing was performed according to the flow chart of the present invention shown in FIG.
First, the alkali treatment of the separated sludge will be described. ML
SS 11000 mg / L, pH 7.5, SM alkalinity 220 mg / L, S-COD 15 mg / L,
As a result of supplying the returned sludge having an S-BOD of 5 mg / L or less to the first alkali reaction tank and injecting NaOH to adjust the pH to 10.8 and treating for about 2 hours, at the outlet of the first alkali reaction tank,
MLSS dropped to 9200 mg / L, while S-CO
D was increased to 450 mg / L and S-BOD was increased to 430 mg / L, and solubilization of organic matter in sludge was observed. Incidentally, S-P- alkalinity remaining 620 mg / L, OH in the addition NaOH ^- it is deemed not sufficiently consumed.

Then, the treated sludge from the first alkali reaction tank is added to the second alkali reaction tank without adding NaOH, and the returned sludge is added so that the pH of the reaction tank becomes 10 or more. Processed in time. As a result, the MLSS was 900 mg / L at the outlet of the second alkali reaction tank, which was about 18% lower than the inflow sludge. Further, the pH was lowered to 9.8 and the SP alkalinity was 310 mg / L.
From what has been reduced to, OH in the addition NaOH ^- it was consumed in the second alkaline reaction vessel. Thereby, S-COD becomes 480 mg / L, S-BOD becomes 520 mg / L,
In each case, the increase was larger than that in the first alkaline reaction tank, and it is recognized that the solubilization of the organic matter in the sludge was further advanced. Table 1 shows the processing conditions and results of the alkaline reaction tank. The results are the numerical values at the outlet of each reactor.

[0013]

[Table 1]

Next, the treatment of the raw water in the adjusting tank will be described. Raw water of the quality described in Table 3
³ / d, 100 m ³ / d of the treated sludge having the properties shown in Table 1 from the second alkaline reaction tank were introduced. As a result, about 1
At a residence time of 0 hours, the water quality at the outlet of the control tank was lower than the pH at the inlet of the control tank from 9.0 to 7.1, while the total organic acid was increased from 10 mg / L to 150 mg / L. The progress of acid fermentation was observed in the adjustment tank. In addition, since the S-BOD / S-COD ratio at the inlet was about 1.2, but increased at the outlet to 2.0, it is considered that the biodegradability of organic matter was improved.

Table 2 shows the conditions of the raw water regulating tank and changes in water quality.

[Table 2]

Next, the raw water subjected to the anaerobic treatment in the regulating tank was treated in the biological reaction tank. BOD sludge load of biological reaction tank is 0.14kg / kg · d, MLSS in tank is 6100mg
/ L, the BOD of the influent raw water is about 720 mg / L, whereas the BOD of the treated water is 5.8 mg / L,
The biological treatment was found to be good. Table 3 shows the treatment conditions of the biological reaction tank and the quality of raw water and treated water.

[Table 3]

Comparative Example 1 As Comparative Example 1, a processing example in which only one alkali reaction tank is used is shown. First, in the alkaline reaction tank, the amount of NaOH added and the amount of supplied sludge were 80
kg / d and 1000 kg / d and the residence time was 2.0 hours, the inflow sludge MLSS was 10200
mg / L, MLSS of alkali-treated sludge
Was 9700 mg / L, a reduction rate of only 4.9%, which was 13 points lower than in Example 1. Also, S
-Both COD and S-BOD are lower than Example 1, and SP-
The alkalinity was higher than in Example 1, and it was recognized that the alkali treatment was not effectively performed.

Table 4 shows the treatment conditions and results of the alkali reaction tank of Comparative Example 1.

[Table 4]

FIG. 2 shows the progress of the amount of sludge in the system under the condition that the excess sludge is not discharged in the system. In about two months, the amount of sludge in the system of Example 1 can be maintained almost constant, and even if there is no discharge of excess sludge, there is almost no increase in the amount of sludge in the system, and the example in which the alkali reaction tank is two-staged The sludge volume reduction effect by the alkali injection of No. 1 was remarkable. On the other hand, in Comparative Example 1,
When the amount of sludge in the system gradually increases with the progress of the treatment and the excess sludge is not withdrawn, the amount of sludge in the system after two months has elapsed is about 1.4 times the initial amount, and the sludge volume reduction effect is higher than in Example 1. Is recognized as low.

Comparative Example 2 Table 5 shows the same treatment flow as in Example 1 except that the set pH of the alkaline treatment tank was different from that of Example 1.
The processing result when pH is set to 7.5 in the second tank is shown.

[Table 5]

As shown in Table 5, in Comparative Example 2, the amount of sludge supplied to the alkaline tank was 19.2% of the total amount of sludge in the system.
g / d, and the amount of sludge supplied to the first alkaline reaction tank is 15
00 kg / d and residence time was 2 hours. As a result, the first
The MLSS at the inlet of the alkali reaction tank was 11,000 mg / L, whereas the MLSS at the outlet was 10500 mg / L, a decrease of only 4.5%, which was about 1% lower than that of Example 1.
Two points lower. The S-COD at the exit is 18
0 mg / L, S-BOD was limited to 80 mg / L, and S-COD was 270 mg / L, S-BO compared to Example 1.
D decreased by 350 mg / L, and it was recognized that the solubilization of sludge was insufficient. Also in the second alkaline reaction tank, the MLSS at the inlet and the outlet was hardly changed,
It became 00 mg / L.

Also, S-COD and S-BOD were reduced to 120 mg / L and 52 mg / L, respectively, and rather decreased. This is to return the sludge to the second alkaline reaction tank at 1000k.
g / d, the concentration was reduced by the dilution effect, and no solubilizing effect was observed. The progress of the amount of sludge in the system in Comparative Example 2 is also shown in FIG. In contrast, the amount of sludge in the system of Comparative Example 2 also gradually increased with the progress of the treatment, and the amount of sludge in the system after two months passed was about 1.4 times the initial value when the excess sludge was not extracted. It is recognized that the sludge volume reduction effect is lower than in Example 1.

[0023]

As described above, according to the present invention, in an activated sludge treatment apparatus comprising a biological reaction tank and a sedimentation tank,
Part of the activated sludge from the sedimentation basin or the biological reaction tank, pH 1
Is supplied to the first alkaline reaction vessel for adding an alkaline agent such that from 0.5 to 11.5, in the first alkaline reaction vessel, OH ^- relatively short time organic medium to the sludge with high concentration state The liquefaction effect of the sludge is promoted by effectively hydrolyzing and reducing the molecular weight in the inside. Further, the treatment liquid that has left the first alkali reaction tank is supplied to the second alkali reaction tank, and the OH ⁻ remaining in the first alkali reaction tank is brought into contact with the newly supplied activated sludge to adjust the pH to 8.0. -10.
The organic matter in the sludge is hydrolyzed so as to be 5, and the liquefied amount of the sludge further increases. Similarly, the mixed liquid of the second and subsequent alkaline reaction tanks is supplied to the latter reaction tank,
The residual OH ^- is mixed with the activated sludge to be newly introduced, and the organic matter in the sludge is hydrolyzed by adjusting the pH to 8.0 to 10.5 to further increase the liquefied amount of the sludge. As a result, the consumption rate of the alkali contributing to the liquefaction of the sludge is high, and the pH of the treated sludge can be kept lower than before.

The alkali-treated sludge obtained as described above is supplied to, for example, a raw water adjusting tank in the former stage of the biological reaction tank, thereby promoting the anaerobic state of the adjusting tank, and inflowing raw water and acid of the alkali-treated sludge liquefied organic matter. Not only the fermentation is promoted, but also the pH fluctuation in the adjusting tank is small, and the lack of required alkalinity accompanying acid fermentation can be replenished from the alkalinity of the alkali-treated sludge. Furthermore, the liquefied organic matter of the alkali-treated sludge has an improved decomposition efficiency in the biological reaction tank,
There is almost no residue in the treated water, and the treated water quality can be maintained well. Further, even if the alkali-treated sludge is similarly supplied to the biological reaction tank, the residual O
Since H ^- is small and the biodegradability of liquefied organic matter is high,
In the biological reaction tank, there is almost no increase in pH, and in the biological reaction tank, liquefied organic matter is decomposed and removed with high efficiency. In addition, the amount of biological alkali-treated sludge is 5 to 20 times
%, The increase in organic matter load on the biological reaction tank due to the increase in liquefied organic matter is small, the ability to decompose organic matter in the biological reaction tank is sufficiently maintained, and the liquefied organic matter in raw water and alkali-treated sludge can be efficiently converted into biological matter. Can be removed by decomposition
By decomposing into O ₂ and H ₂ O, the amount of sludge generated in the system can be suppressed, and the quality of treated water can be maintained well.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an example of a processing method of the present invention.

FIG. 2 is a graph showing a change in the amount of sludge in the system according to the number of elapsed days.

[Explanation of symbols]

1: Inflow raw water, 2: Raw water adjustment tank, 3: Adjustment tank stirring pump, 4: Adjustment tank outlet raw water, 5: Returned sludge, 7: Biological reaction tank, 8: Aeration line, 9: Treatment in second alkaline reaction tank Sludge, 10: Biological reactor outlet, 11: Sedimentation basin, 12: 1st
Sludge flowing into the alkali reaction tank, 13: first alkali reaction tank,
14: first alkaline reaction tank NaOH injection pump, 15:
First alkali reaction tank pH meter, 16: Sludge treated with first alkali reaction tank, 17: Second alkali reaction tank, 18: Sludge injection pump for second alkali reaction tank, 19: pH meter for second alkali reaction tank, 20: Treatment water

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Akira Watanabe 11-1 Haneda Asahimachi, Ota-ku, Tokyo Inside Ebara Corporation (72) Inventor Kiyomi Arakawa 11-1 Haneda Asahi-cho, Ota-ku, Tokyo EBARA F-term (reference) 4D028 AC03 AC09 BC18 BD00 BD11 BD12 BD16 CA00 CD01

Claims (3)

[Claims] 1. A method for treating organic wastewater in an activated sludge treatment apparatus having a biological reaction tank and a sedimentation pond, wherein a part of the activated sludge in the biological reaction tank is withdrawn from the sedimentation pond or the biological reaction tank and arranged in series. To the two or more alkali reaction tanks, and the first alkali reaction tank has a pH of 10.5 to 1
The amount of the alkali agent added was controlled to 1.5,
Control the supply amount of sludge so that the pH becomes 8.0 to 10.5 after the alkaline reaction tank, and return the treated sludge of the final alkaline reaction tank to the pre-adjustment tank or biological reaction tank of the biological reaction tank. A method for treating organic wastewater. 2. The method according to claim 1, wherein the amount of activated sludge supplied to the alkaline reaction tank is 5 to 20% of the amount of sludge in the biological reaction tank. 3. An organic system comprising a raw water regulating tank, a biological reactor, a sedimentation basin, and two or more alkaline reactors arranged in series for treating activated sludge from the biological reactor and / or the sedimentation basin. In a treatment device for treating activated wastewater with activated sludge,
Providing an introduction path for supplying the activated sludge extracted from the biological reaction tank and / or the sedimentation tank to each of the alkaline reaction tanks,
An alkali agent is added to the first alkali reaction tank to adjust the pH.
Is adjusted to 10.5 to 11.5, and pH is set to 8.0 to 1 in the reaction tanks after the second alkali reaction tank.
An organic means having a control means for controlling the supply amount of the sludge so as to be 0.5 and a path for returning the treated sludge of the final alkaline reaction tank to the raw water adjusting tank or the biological reaction tank. Wastewater treatment equipment.