JPH10156381A - Method for reducing volume of organic sludge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To diminish the org. sludge to be discharged outside the system to zero by extracting a part of the sludge generated from the biological stage of org. sewage, bringing the extracted sludge into contact with ozone, then aerating the sludge, subjecting the sludge to solid-liq. separation, adding an inorg. flocculant to the separated water and separating the floc from the water. SOLUTION: The sludge 12 from a biological treating stage 1 is subjected to a solid-liq. separation stage 2, the separated excess sludge 13 is introduced into an ozone oxidation stage 3, the sludge 13 is oxidized with ozone and decomposed therein, and the sludge 14 is converted into a BOD component. The sludge 14 is then supplied to an aeration stage 4 and biologically treated, and a part of the sludge 14 is decomposed into carbon dioxide and water. Subsequently, the sludge 15 discharged from the aeration stage 4 is separated in a solid-liq. separation stage 5, and the separated sludge 18 is supplied to the biological treating stage 1 and utilized as activated sludge. Meanwhile, an inorg. flocculant 22 is added to the separated water 16, the floc is separated in the flocculation and separation stage 6, the separated water 17 is supplied to the biological treating stage 1, and the flocculated and separated sludge 19 is sent to a sludge dehydrating stage and disposed of.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a novel process for biologically treating organic sewage such as sewage and industrial wastewater, which can reduce the amount of excess sludge generated from the biological treatment process and does not deteriorate the quality of biologically treated sewage. About technology.

[0002]

2. Description of the Related Art A large amount of organic sludge (excess sludge, raw sludge, etc.) is generated daily from activated sludge treatment facilities such as sewage, industrial wastewater, human waste, and landfill wastewater. Surpass. The treatment and disposal of this excess sludge is the biggest problem. Since organic sludge is dewaterable, a large amount of dehydration aid (polymer, etc.) is added and dewatered with a sludge dewatering machine to about 85% water, and the dewatered cake is landfilled or incinerated. There are many problems such as dehydration aid costs, insufficient landfill for dewatered cakes, insufficient disposal sites for incinerated ash, high incineration equipment costs, and high cost of heavy oil for incineration. In order to solve such a problem, a "sludge reduction method using ozone" is disclosed in JP-A-6-206088.
No. 6,086,045. This technique is a method in which a larger amount of activated sludge than the amount of surplus sludge is extracted from the activated sludge treatment step of wastewater, ozone oxidized, and returned to the activated sludge treatment step as it is.

[0003]

However, when the present inventor re-tested this technique, the following problems occurred and the vehicle could not be operated satisfactorily. The higher the sludge reduction rate, the worse the phosphorus concentration in the sewage treatment water. Since phosphorus is removed in the form of being taken into activated sludge, unless the sludge that has taken in phosphorus is actively discharged out of the system as excess sludge, the material balance of phosphorus is not established and a high phosphorus removal rate cannot be obtained. . Therefore, if any measure is taken to reduce the amount of excess sludge generated, the phosphorus concentration in the treated water will necessarily increase, and if the sludge reduction rate is set to 100%, the phosphorus removal rate will be zero. As a result of the ozone oxidation, hardly biodegradable COD is generated from the activated sludge cells, and the COD concentration of the treated water is deteriorated. Since the sludge is oxidized with ozone and converted into BOD components and returned to the aeration tank in the sewage treatment process, the aeration BOD load becomes high. When the load becomes high, the excess sludge generation rate increases, and as a result, the required amount of ozone increases, leading to an increase in running costs, thereby causing a vicious cycle.

[0004] At present, eutrophication of public water bodies has become a major problem.
Is worse for environmental protection.
It is not ideal unless the technology is capable of obtaining a high quality of treated water while reducing the amount of sludge to a high degree. An object of the present invention is to provide a new system capable of reducing the amount of organic sludge discharged to the outside of the system to zero and satisfying the contradictory requirement that the phosphorus and COD removal rates in the wastewater biological treatment process do not deteriorate.

[0005]

The present inventor has found that the above object can be achieved by combining a novel method of sludge oxidation with chemical phosphorus, COD, and ozone. That is, in the present invention, after a part of the sludge generated from the biological treatment step of the organic wastewater is withdrawn and brought into contact with ozone, it is aerated in a separate aeration step from the aeration step of the biological treatment step. The method is characterized in that the sludge flowing out is subjected to solid-liquid separation, the solid-liquid separated sludge is supplied to the biological treatment step, and an inorganic coagulant is added to the solid-liquid separation water for coagulation separation.

[0006]

FIG. 1 shows a configuration example of the present invention, and the configuration and operation of the present invention will be described in detail. A part of the sludge is withdrawn from the biological treatment step 1 of the organic sewage (hereinafter simply referred to as sewage) 11 and introduced into the “sludge elimination step 7” of the present invention. That is, a part of the extracted sludge (hereinafter, also referred to as excess sludge 13) obtained by solid-liquid separation of the sludge 12 discharged from the biological treatment step 1 in the solid-liquid separation step 2 is led to the ozone oxidation step 3, and the sludge 13 is oxidized by the ozone 21. Decompose and sludge 14
Is converted into BOD components that can be assimilated by microorganisms.

Next, the ozone oxidized sludge 14 flows into an aeration step 4 different from the aeration step of the biological treatment step 1 of the sewage 11, and is biologically treated in the presence of activated sludge having BOD removal activity. Part of sludge (30 whose biodegradability by microorganisms is improved by the oxidizing action of ozone) 14 (30
~ 40%) is decomposed into carbon dioxide and water by activated sludge (aerobic microorganisms). It is preferable that the sludge is circulated from the aeration tank 4 to the ozone oxidation step 3 through the path 23 because the amount of hardly biodegradable COD is reduced. Thereafter, aeration step 4 and sludge 15 flowing out are subjected to solid-liquid separation in solid-liquid separation step 5, and solid-liquid separation sludge 1
8 has BOD removal activity like ordinary activated sludge, and is supplied to the biological treatment step 1 and used as activated sludge for biological treatment. On the other hand, solid-liquid separation water (containing high concentration of phosphorus and COD eluted from sludge during ozone treatment → aeration treatment)
An inorganic coagulant 22 of calcium, aluminum, iron or the like is added to the mixture 16 and the mixture is subjected to coagulation and separation in the coagulation separation step 6. The coagulated and separated water 17 flows into the activated sludge aeration tank in the biological treatment step 1. The flocculated and separated sludge 19 is sent to a sludge dewatering step (not shown) and disposed.

The biological treatment step 1 used in the present invention
As a typical example, the activated sludge method is a typical method. Alternatively, the wastewater treatment can be performed by a biological dephosphorization method or a biological nitrification denitrification method. Phosphorus and COD eluted from the sludge due to the sludge disappearance phenomenon due to the combined action of the ozone oxidation step 3 and the aeration step 4 are calcium-based,
Iron or aluminum based inorganic coagulant (eg, slaked lime, iron chloride, polyiron, sulfate band, PAC, etc.) 22 is insolubilized and removed as calcium phosphate, iron phosphate, aluminum phosphate and the like. Of these, slaked lime is most suitable because calcium phosphate sludge with good dehydration properties is generated. At this time, the hardly biodegradable COD is also effectively coagulated and removed. Of course, a polymer flocculant may be used in combination to promote sedimentation and separation. The solid-liquid separation sludge 18 may be returned to the aeration step 4.

[0009]

The effects of the present invention can be clarified by the embodiments of the present invention. However, the present invention is not limited by the following embodiments of the present invention. EXAMPLE A verification test of the present invention was performed on sewage (average water quality is shown in Table 1) according to the process shown in FIG. Table 2
Shows the test conditions.

[0010]

[Table 1]

[0011]

[Table 2]

As a result of the experiment, the average value of the treated water quality of the coagulation sedimentation tank 6 after the sedimentation tank 5 of the ozone oxidized sludge aeration tank 4 was obtained after the treatment state became stable two months after the start of the treatment. 3 As shown in the first column, phosphorus, COD and BOD were highly removed. Therefore, the deterioration of the quality of the sewage treated water when the coagulated sediment treated water 19 is supplied to the aeration tank for sewage treatment is shown in Table 3.
Little was observed as in column 2. The third column in Table 3 shows the sewage treatment water quality when sludge reduction is not performed.
Although the sludge was not pulled out of the system during the 6-month test, the MLVSS in the aeration tank for the sewage treatment activated sludge was maintained at the initially set 3500 to 3700 mg / l. It was found that no organic sludge was generated. On the other hand, the amount of surplus sludge generated by the ordinary activated sludge method to which the present invention was not applied was 100 to 120 g.ss / m ³ of sewage.

[0013]

[Table 3]

[0014]

[Effects of the Invention] As a result of combining a method of removing sludge by the action of ozone and microorganisms and a method of removing chemical phosphorus and COD with a new concept,
The amount of organic sludge out of the system can be reduced to almost zero, and a high degree of COD and phosphorus removal can be performed stably. Further, COD generated by the ozone treatment of the sludge is also removed. Ozone-treated sludge is aerated in the presence of activated sludge in a tank separate from the aeration tank for sewage treatment to reduce the volume of sludge, then separated into surface liquids and the separated sludge is supplied to the aeration tank in the biological treatment process for sewage. Therefore, the wastewater biological treatment process does not have a high BOD load and the excess sludge generation rate does not increase.

[Brief description of the drawings]

FIG. 1 is a view schematically showing a method for reducing organic sludge of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Biological treatment process 2 Solid-liquid separation process 3 Ozone oxidation process 4 Aeration process 5 Solid-liquid separation process 6 Agglomeration separation process 7 Sludge annihilation process 11 Organic wastewater 12 Outflow sludge 13 Excess sludge 14 Ozone oxidation sludge 15 Aeration process outflow sludge 16 Solid Liquid separation water 17 Coagulation separation water 17 Settling sludge 18 Solid-liquid separation sludge 19 Solid-liquid separation sludge 21 Ozone 22 Inorganic coagulant 23 Circulating sludge

Claims (1)

[Claims] Claims: 1. A part of sludge generated from a biological treatment step of an organic wastewater is withdrawn and brought into contact with ozone, and then aerated in a separate aeration step from the aeration step of the biological treatment step. A method wherein the sludge flowing out is subjected to solid-liquid separation, the separated sludge is returned to the wastewater biological treatment step, and an inorganic coagulant is added to the solid-liquid separation water for coagulation separation.