JP3493783B2 - Aerobic treatment of organic wastewater - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for biologically treating an organic effluent in the presence of biological sludge containing aerobic microorganisms, and more particularly, to a method for treating waste water in an aerobic biological treatment system. The present invention relates to a biological treatment method for organic wastewater capable of reducing sludge volume. [0002] An aerobic biological treatment method, such as an activated sludge treatment method, in which an organic effluent is treated under aerobic conditions by utilizing the action of an aerobic microorganism has a low treatment cost and a low treatment performance. Is widely used because of its superiority, but it generates a large amount of excess sludge capable of dewatering. This excess sludge is treated BOD
As much as about 30-60% of the volume, its processing is difficult.
Conventionally, such excess sludge has been dumped and disposed of. However, it is difficult to secure a disposal site and sludge volume reduction is required. [0003] To reduce the volume of sludge, Japanese Patent Publication No. 5-619
No. 94 describes a method for treating organic wastewater in which excess sludge is solubilized at a pH of 2.5 or less and a temperature of 50 ° C. or more, and then returned to an aeration tank. [0004] However, although the volume of sludge can be reduced by such a conventional method, organic matter that is hardly biodegradable is generated, and the chromaticity and COD _{Mn of the} processing solution are reduced. And the quality of treated water deteriorates. [0005] An object of the present invention is to solve the above problems by reducing the volume of sludge and proposing an aerobic treatment method for organic wastewater that can prevent deterioration of treated water quality. is there. According to the study of the present inventor, the cause of the deterioration of the water quality of the treatment liquid in the conventional method is the poor biodegradability generated when the pH at the time of solubilizing the sludge is too low or the temperature is too high. Was found to be due to organic matter. And by heat treatment at a weak acidity and relatively low temperature, without producing hard biodegradable organic matter,
It has been found that the above object can be achieved, and the present invention has been completed. [0007] The present invention is a method for treating aerobic organic wastewater in an aeration tank in the presence of biological sludge containing aerobic microorganisms. Is introduced into the aeration tank, and an aerobic biological treatment step in which aerobic biological treatment is performed in the presence of biological sludge containing aerobic microorganisms, and the mixture in the aeration tank is solid-liquid separated, and the separated liquid is discharged as a processing liquid. , A solid-liquid separation step of returning at least a part of the separated sludge to the aeration tank, and extracting a part of the mixed liquid or the separated sludge in the aeration tank,
Without adding catalyst and oxidizing agent to this drawn sludge ,
pH 2.8 ~ 5, temperature 40 ~ 90 ° C for 15 minutes ~
An aerobic treatment method for organic effluent, comprising: a solubilization treatment step of performing solubilization treatment for 2 hours and then returning to an aeration tank. The organic effluent to be treated in the present invention is an effluent containing an organic substance which is treated by a usual aerobic biological treatment method, but contains an organic substance or an inorganic substance which is hardly biodegradable. You may. Such organic effluents include sewage, night soil, food factory effluents and other industrial effluents. In the aerobic biological treatment of the present invention, the organic effluent is subjected to aerobic biological treatment in the presence of biological sludge containing aerobic microorganisms. In such treatment, the organic wastewater is mixed with activated sludge in an aeration tank and aerated, the mixed liquid is separated into solid and liquid by a solid-liquid separator, and a part of the separated sludge is returned to the aeration tank. Aerobic biological treatment in the sludge treatment method is general, but other treatments modified from this may be used. In the present invention, a part of the biological sludge is extracted from the treatment system in such aerobic biological treatment, and the extracted sludge is solubilized. When extracting biological sludge, it is preferable to extract a part of the separated sludge separated by the solid-liquid separator, but it may also be possible to extract the mixed sludge from the aeration tank. When extracting from the separated sludge, part or all of the part discharged as excess sludge can be extracted as extracted sludge,
In addition to the excess sludge, it is preferable to further extract and solubilize a part of the sludge returned to the aeration tank as return sludge.In this case, the amount of excess sludge generated can be reduced, and depending on conditions, the excess sludge may be reduced. Sludge generation can be reduced to zero. This will be described in detail later. [0011] In the present invention, the solubilization treatment is performed under milder conditions as compared with the conventional method, that is, pH 2.8 to 5, preferably 3
4, at a temperature of 40 to 90 ° C, preferably 60 to 80 ° C,
It is carried out for 15 minutes to 2 hours, preferably for 30 minutes to 1 hour.
By performing the solubilization treatment under such conditions, it is possible to suppress the generation of the hardly biodegradable organic substance and convert the sludge into BOD. The solubilization treatment can be performed in a batch system or a continuous system. In the case of the continuous system, the treatment time is a retention time.
In order to adjust the pH, an inorganic acid such as hydrochloric acid, sulfuric acid, and nitric acid can be used. When the pH is out of the above range due to the continuation of the solubilization treatment, the above acid is further added and the pH is adjusted to a predetermined value.
H can be maintained, but when the treatment is performed for a predetermined time within the above-mentioned pH range, further treatment may be performed outside the above-mentioned pH range. The treated sludge that has been solubilized is neutralized with an alkali such as sodium hydroxide or potassium hydroxide.
Alternatively, it is introduced into an aeration tank in an aerobic biological treatment step without neutralization to perform aerobic biological treatment. Thereby, the components converted into BOD by the solubilization treatment are inorganicized into carbon dioxide gas or the like and removed, and the amount of excess sludge discharged from the entire system is reduced. In this case, since the generation of the hardly biodegradable organic matter in the solubilization treatment is suppressed, the chromaticity and COD _Mn are low, and high treated water quality can be obtained. In the above treatment, the treatment is carried out at a weak acidity and at a relatively low temperature.
The danger to work is reduced. In addition, the amount of alkali required for neutralization after the solubilization treatment is also reduced, and can be usually neutralized by the alkalinity (carbon dioxide) of the aeration tank. Therefore, it is possible to return to the aeration tank without neutralization. is there. In the above treatment, as the amount of sludge to be solubilized increases, the sludge volume reduction rate increases. However, since the sludge multiplies when biodegrading organic matter in the solubilized sludge, excess sludge cannot be reduced to zero simply by solubilizing the excess sludge, but the amount of sludge that grows is apparent. When the excess sludge is withdrawn and solubilized so as to be zero, the amount of excess sludge generated from the entire system can be reduced to zero. In this case, when the amount of the sludge to be solubilized increases, the biological treatment performance may decrease.In such a case, a carrier for supporting the sludge is provided in the aeration tank, and a fixed amount of the sludge is supplied. By keeping the biological treatment performance, high biological treatment performance can be maintained. The principle of sludge volume reduction in the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram for explaining the principle of sludge volume reduction. In the figure, 1 is an aerobic biological treatment system,
2 is a solubilization treatment system. The aerobic biological treatment system 1 is a treatment system in which an organic effluent is brought into contact with biological sludge to decompose aerobically, such as an activated sludge treatment device, and an aeration tank and a solid-liquid separation device are separately provided. However, it is illustrated as an entire processing system including these. The solubilization treatment system 2 is illustrated as a treatment system for solubilizing drawn sludge that is drawn in a state of a mixed solution or a concentrated solution. Sludge is hydrolyzed by the solubilization treatment and becomes a BOD source. The aerobic biological treatment system 1 of FIG. 1 holds a certain amount of biological sludge 3a for performing aerobic biological treatment. When the liquid 4 to be treated is introduced into the aerobic biological treatment system 1 and subjected to the aerobic biological treatment, the BOD contained in the liquid 4 to be treated is assimilated into the biological sludge 3a, and the sludge 3b is newly generated by the multiplication thereof. Is generated. On the other hand, biological sludge 3a in the system
The self-decomposition part 3c disappears by self-decomposition. Therefore, in a steady state, the difference between the generated sludge 3b and the self-decomposed component 3c multiplies as multiplication sludge 3d. The case where the sludge 3d is treated as excess sludge in the solubilization treatment system 2 is shown by a broken line 5 in FIG.
When the proliferating sludge 3d is solubilized and returned to the aerobic biological treatment system 1, the BOD generated by the solubilization process is converted into sludge, and another generated sludge 3e is generated. And must be discharged as excess sludge. On the other hand, a larger amount of the extracted sludge 3f than the multiplication sludge 3d is extracted from the aerobic biological treatment system 1, and the solubilization treatment system 2
To convert it to BOD, and return the solubilized sludge 6 to the aerobic biological treatment system 1, whereby another 3 g of generated sludge is generated from the BOD generated by the solubilization treatment. In this case, the difference between the extracted sludge 3f and the generated sludge 3g is the mineralized portion 3h.
It becomes. Here, a larger amount of the extracted sludge 3f than the multiplied sludge 3d is solubilized and converted to BOD,
As compared with the case where only the proliferating sludge 3d is solubilized, the amount of mineralized parts increases, and the sludge volume reduction rate increases. Proliferating sludge 3
d so as to make the mineralized portion 3h equal to d.
Once the amount is determined, the excess sludge will be virtually zero. When the amount of the proliferating sludge 3d is larger than that of the mineralized portion 3h, the difference becomes a substantial increase portion 3i, and is discharged out of the system as excess sludge 7. Reference numeral 8 denotes a treatment liquid of the aerobic biological treatment system 1. In the aerobic biological treatment system 1, the capacity of the aeration tank is V, the biological sludge concentration is X, the sludge yield is Y, the flow rate of the liquid to be treated (the flow rate of the treatment liquid) is Q, and the organic matter concentration of the liquid to be treated is C.
i, the organic matter concentration of the treatment liquid is Ce, the biologically treated organic matter concentration is (Ci-Ce), the sludge self-decomposition constant is Kd, the surplus sludge discharge amount is q, and the withdrawal amount to the solubilization treatment tank is Q '. Assuming that the rate at which the solubilized sludge is converted back to biological sludge is k, the material balance is expressed by the following equation [1]. VdX / dt = YQ (Ci-Ce) -VKdX-qX-Q'X + kQ'X [1] In the formula [1], VdX / dt is an aerobic biological treatment. The amount of change in biological sludge 3a in system 1, YQ (Ci-C
e) is the amount of generated sludge 3b, V Kd X is the amount of self-decomposition 3c, q X is the amount of excess sludge 7 discharged, Q'X is the amount of extracted sludge 3f, and k Q'X is the amount of generated sludge 3g. Is shown. Where Q
(Ci-Ce) / V = LV (tank load), q / v = 1 / SRT (excess sludge residence time ratio), Q '/ V = θ (circulation ratio of biological sludge to the solubilization treatment system), ( If 1−k) = δ (inorganization ratio), in a steady state, the equation [1] is simplified as the following equation [2]. Y LV / X = Kd + 1 / SRT + δθ [2] In a normal aerobic biological treatment system in which the solubilization treatment system 2 does not exist, there is no third term (δθ) in the formula (2). When sludge load is constant, excess sludge (X / S
RT) is determined. On the other hand, in the treatment system combined with the solubilization treatment, the excess sludge is reduced by the value of the third term as is apparent from the equation (2). And the value of the third term is the second
Under conditions comparable to the value of the term, it is possible to set the sludge load to a normal value without discharging excess sludge (1 / SRT = 0). Next, an embodiment of the present invention will be described. FIG.
3 is a system diagram showing an aerobic treatment apparatus according to another embodiment, FIG. 2 is an example of solubilizing the separated sludge of a solid-liquid separation apparatus, and FIG. 3 is a solubilization of a mixed solution in an aeration tank. It shows an example of processing. In FIG. 2, aerobic biological treatment system 1
Is composed of an aeration tank 11 and a solid-liquid separation device 12. The aeration tank 11 communicates with the liquid passage 13 to be treated, the return sludge passage 14 and the solubilized sludge passage 26, and a diffuser 15 is provided at the bottom, and the air supply passage 16 communicates therewith. A communication path 17 communicates from the aeration tank 11 to the solid-liquid separation device 12. The treatment liquid path 18 and the separated sludge discharge path 19 communicate with the solid-liquid separation device 12, and the return sludge path 14 branches off from the separated sludge discharge path 19. Reference numeral 20 denotes a surplus sludge discharge passage provided as needed. The solubilization treatment system 2 is composed of a solubilization treatment tank 21, which is connected to a sludge extraction passage 22 and an acid supply passage 23, and a heater 24 and a stirrer 25 are provided inside. Have been. Further, a solubilization treatment sludge passage 26 is connected from the solubilization treatment tank 21 to the aeration tank 11. In the aerobic biological treatment method for organic effluent by the treatment apparatus shown in FIG. 2, the organic effluent is introduced into the aeration tank 11 from the liquid passage 13 to be treated, and the return sludge returned through the return sludge passage 14 and It mixes with the activated sludge in the aeration tank 11 and diffuses the air supplied from the air supply path 16 from the diffuser 15 to perform aerobic biological treatment. Thereby, the organic matter in the wastewater is decomposed by the biological oxidation reaction. A part of the mixed liquid (reaction liquid) in the aeration tank 11 is introduced into the solid-liquid separator 12 through the communication path 17 and separated into a separated liquid and a separated sludge by sedimentation. The separated liquid is discharged as a processing liquid from the processing liquid path 18 to the outside of the system, and the separated sludge is taken out from the separated sludge discharge path 19.
A part of it is returned to the aeration tank 1 from the returned sludge passage 14 as returned sludge.
1 and a part or all of the remaining part is introduced into a solubilization tank 21 through a drawn sludge passage 22 to perform a solubilization treatment. In the solubilization tank 21, the pH of the solution in the tank is adjusted to the above-mentioned value by adding an acid from the acid supply path 23, and the temperature is maintained at the above-mentioned temperature by heating with the heater 24. To process. Thereby, the sludge is hydrolyzed to BOD. The solubilized sludge is converted to the solubilized sludge channel 26.
To the aeration tank 11 continuously to perform aerobic biological treatment.
Thereby, the BOD component converted by the solubilization treatment is decomposed and removed, and the volume of excess sludge generated from the aerobic biological treatment system 1 is reduced. Excess sludge discharge channel 2 when excess sludge is generated
Discharge from 0 to outside the system. In FIG. 3, a part of the mixed solution in the aeration tank 11 is drawn out from the sludge extraction passage 22 as extracted sludge and introduced into the solubilization treatment tank 21. Acid supply path 23
Is connected to the sludge extraction passage 22. In the treatment method using the apparatus shown in FIG. 3, a part of the mixed solution in the aeration tank 11 is withdrawn from the drawn sludge passage 22 as drawn sludge, and an acid is added to the drawn sludge from the acid supply passage 23 to adjust the pH to the above value. After that, it is introduced into the solubilization tank 21 and solubilized. Other operations are the same as those in FIG. Example 1 Synthetic wastewater containing peptone and yeast extract as main components was subjected to ML
0.2g BOD load in SS 5000mg / l aeration tank
-BOD / g-sludge treated per day, the sulfuric acid is added to the sludge extracted from the aeration tank to adjust the pH to 0.5 to 5,
A solubilization treatment was performed at a temperature of 80 ° C. for 1 hour. B of treated sludge
FIG. 4 shows the OD conversion rate (g-BOD / g-sludge) and the production rate of hardly biodegradable organic matter (g-COD _Mn / g-sludge). From the results shown in FIG. 4, the BOD conversion rate of the treated sludge was 0.47 to 0.6 as the pH decreased from pH 5 to pH 2.
It can be seen that it gradually increases, but is constant at about 0.6 at pH 2 or less. On the other hand, the production rate of the hardly biodegradable organic substance is 0.01 or less in the range of pH 5 to pH 2.8 and almost no formation of the hardly biodegradable organic substance is observed.
As the pH becomes lower than H2.8, it rises rapidly,
It can be seen that a hardly biodegradable organic substance is rapidly generated in a strongly acidic region having a pH of 2.5 or less. From the above, pH
It can be seen that in the range of 2.8 to 5, a high BOD conversion rate can be obtained with almost no formation of hardly biodegradable organic substances. Example 2 The same sludge as in Example 1 was adjusted to pH 2.9 by adding sulfuric acid, and subjected to a solubilization treatment at 20 to 100 ° C. for 1 hour. FIG. 5 shows the BOD conversion rate of the treated sludge and the generation rate of the hardly biodegradable organic matter. From the results shown in FIG. 5, it can be seen that the BOD conversion rate of the treated sludge increases rapidly as the treatment temperature increases to 40 to 60 ° C., and thereafter becomes constant at about 0.6. On the other hand, it can be seen that the production rate of the hardly biodegradable organic matter rapidly increases when the temperature exceeds 90 ° C. From the above, it can be seen that a high BOD conversion rate can be obtained in the temperature range of 40 to 90 ° C. with almost no generation of hardly biodegradable organic substances. Comparative Example 1 In the treatment apparatus shown in FIG. 2, an aerobic biological treatment was performed without performing a solubilization treatment. That is, the wastewater from the food factory (BOD = 1000 ppm, SS = 100 ppm) is 1
In the aeration tank of m ^3, the bath load 1kg-BOD / m ^3, it was treated with sludge load 0.2kg-BOD / kg-MLSS / day. The treated water quality was 20 mg / l as COD _Mn , and 0.4 kg of excess sludge was discharged per day. Example 3 The same wastewater as in Comparative Example 1 was subjected to aerobic biological treatment using the treatment apparatus shown in FIG. That is, under the biological treatment conditions of Comparative Example 1,
0.8 kg of activated sludge is withdrawn daily from the solid-liquid separator.
10000mg sulfuric acid for 0000mg / l sludge
/ L was added. pH was 2.9. The extracted sludge was kept at 60 ° C. for 1 hour, and was returned to the aeration tank continuously after neutralization. In order to maintain the sludge load in the same manner as in Comparative Example 1, the amount of excess sludge discharged outside the system was 0.12 kg per day, and the amount of excess sludge was about 1/3 of Comparative Example 1. The treated water quality is CO
D _Mn was 22 mg / l, and a treated water quality equivalent to that of Comparative Example 1 in which the sludge volume reduction treatment was not performed was obtained. Example 4 An aerobic biological treatment was carried out in the same manner as in Example 3, except that the conditions for the solubilization treatment were changed. That is, 0.8 kg of activated sludge was withdrawn per day from the solid-liquid separator, and 3000 mg / l of sulfuric acid was added to 10,000 mg / l of sludge. pH was 4.8. The extracted sludge was kept at 80 ° C. for 1 hour, and returned to the aeration tank continuously after neutralization. In order to maintain the sludge load in the same manner as in Comparative Example 1, the amount of excess sludge discharged outside the system was 0.12 kg per day, and the amount of excess sludge was about 1/3 of Comparative Example 1. The treated water quality is 21mg as COD _Mn
Comparative Example 1 in which no sludge volume reduction treatment was performed
The same quality of treated water was obtained. Comparative Example 2 The operation was carried out in the same manner as in Example 3 except that the added sulfuric acid was changed to 50,000 mg / l (pH 2.2). The surplus sludge amount was 0.12 kg per day, and a similar value was obtained. However, the treated water quality was 80 mg / l as COD _Mn , and remarkable deterioration was confirmed. Comparative Example 3 The operation was carried out in the same manner as in Example 3 except that the temperature of the solubilization treatment was changed to 100 ° C. The surplus sludge amount is 0 per day.
The value was 10 kg, and although there was a volume reducing effect, the quality of the treated water deteriorated and the COD _Mn became 120 mg / l.
In addition, sludge bulking became severe, and sedimentation property was extremely deteriorated. According to the present invention , the catalyst and the oxidizing agent are not added to a part of the mixture or the separated sludge in the aeration tank.
Since it is solubilized under mild acidic and heating conditions and returned to the aeration tank, sludge can be reduced in volume without generating non-biodegradable organic substances, and the quality of treated water can be reduced. Higher treated water quality can be obtained by preventing deterioration, the corrosiveness to the apparatus and the danger to work are low, and the amount of alkali for neutralization is also reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram for explaining the principle of sludge volume reduction. FIG. 2 is a system diagram showing an aerobic treatment device of an embodiment. FIG. 3 is a system diagram showing an aerobic treatment device of another embodiment. FIG. 4 is a graph showing the results of Example 1. FIG. 5 is a graph showing the results of Example 2. [Description of Signs] 1 Aerobic biological treatment system 2 Solubilization treatment system 3a Biological sludge 3b, 3e, 3g Produced sludge 3c Self-decomposition 3d Proliferation sludge 3f Extracted sludge 3h Mineralized part 3i Increased part 4 Liquid to be treated 6 Solubilization Processed sludge 7 Excess sludge 8 Processing liquid 11 Aeration tank 12 Solid-liquid separator 13 Liquid to be processed 14 Returned sludge path 15 Air diffuser 16 Air supply path 17 Connection path 18 Processing liquid path 19 Separated sludge discharge path 20 Excess sludge discharge path 21 solubilization tank 22 sludge extraction path 23 acid supply path 24 heater 25 stirrer 26 solubilization treatment sludge path

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C02F 3/12 C02F 11/00-11/20

Claims (1)

(57) [Claims 1] A method for aerobic biological treatment of organic wastewater in an aeration tank in the presence of biological sludge containing aerobic microorganisms, wherein the organic wastewater is aerated. An aerobic biological treatment process in which the mixture is introduced into a tank and aerobic biological treatment is carried out in the presence of biological sludge containing aerobic microorganisms.The mixed liquid in the aeration tank is solid-liquid separated, and the separated liquid is discharged as a processing liquid and separated. A solid-liquid separation step of returning at least a part of the sludge to the aeration tank; extracting a mixed liquid or a part of the separated sludge in the aeration tank; and adding a catalyst and an oxidizing agent to the extracted sludge without adding a catalyst and an oxidizing agent.
Aerobic treatment of an organic effluent, comprising: a solubilization treatment step of performing solubilization treatment at 2.8 to 5 and a temperature of 40 to 90 ° C. for 15 minutes to 2 hours, and then returning to an aeration tank. Method.