JPH09122682A - Method for treating waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To highly purify waste water such as sewage water and to decrease the amt. of generation of excess sludge by a method wherein after a raw sludge separated before biological treatment or the raw sludge and a biological sludge extracted from a biological treatment process is methane-fermented, it is oxidized with ozone and is returned to an anaerobic part. SOLUTION: At first, solid-liq. separation of sewage water 7 is performed in a sedimentation tank 8 and methane fermentation of the precipitated raw sludge 1 is performed in an anaerobic digestion part 2 to reduce biologically the vol. of the sludge and then, the digested residue 3 is oxidized with ozone in an ozone oxidation part 4. The biological sludge is solubilized by an action destroying the cell walls of a fungi and making org. substances into low mol.wt. to make the cell walls of the fungi and the org. substances into BOD. On the other hand, the SS-removed water in the sedimentation tank at the beginning is made to flow into an anaerobic tank 5, where biological denitrification is performed and a part 13 of nitrification-treated water processed once to an aerobic tank 9 is circulated into the anaerobic tank 5 and after water to be treated in the denitrification tank 5 is made to flow into the aerobic tank 9, the active sludge is separated by sedimentation in the final sedimentation tank 10 to obtain a treated water 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biological treatment technology capable of highly purifying sewage such as sewage and significantly reducing the amount of excess sludge generated.

[0002]

2. Description of the Related Art A large amount of excess biological sludge generated from biological treatment processes and raw sludge separated from wastewater such as sewage are increased by subjecting sewage and other sewage to biological treatment such as activated sludge. How to treat these surplus biological sludge and raw sludge is the biggest problem of biological treatment at present. Conventionally, these sludges are dehydrated by a dehydrator and then incinerated after adding a dehydrating auxiliary such as a polymer. However, with the increase in the amount of these sludges, the cost of the dehydrating aid, the cost of adding the dehydrating aid, the addition and enlargement of the dehydrator, and the large scale of the incinerator are becoming a heavy burden. In addition, much of the ash after incineration of sludge and the disposition of it is difficult.

Conventionally, there is a methane fermentation method which is an anaerobic digestion method as a sludge weight reduction method, but the sludge weight reduction effect is inferior in comparison with the long retention time required in the methane fermentation tank. Also,
A method of ozone-oxidizing surplus biological sludge from a biological treatment process, solubilizing it, and then supplying it to an aerobic biological treatment tank to reduce the amount is described in JP-A-7-116685.
Ozone cost is high and it is not practical. Further, the above-mentioned Japanese Patent Application Laid-Open No. 7-116685 does not disclose any method for reducing the volume of raw sludge produced in excess of excess biological sludge.

[0004]

DISCLOSURE OF THE INVENTION The present invention can effectively reduce the volume of both raw sludge and biological sludge generated from a facility for treating organic wastewater such as sewage, and improve the quality of treated wastewater. The challenge is to provide possible new technologies.

[0005]

The present invention combines biological anaerobic digestion method and solubilization of sludge by ozone oxidation in a novel manner to effectively reduce the volume of both raw sludge and excess sludge. It is a completed sewage treatment method by finding a new technology that can be applied. That is, (1) after separating the organic SS of wastewater,
Biological treatment by anaerobic aerobic activated sludge method, in the sewage treatment method of obtaining a biologically treated water solid-liquid separation of the activated sludge from the biological treatment step, the raw sludge separated before the biological treatment,
Alternatively, the raw sludge and the biological sludge withdrawn from the biological treatment step are methane-fermented and then ozone-oxidized,
A sewage treatment method comprising returning to the anaerobic part of the biological treatment step.

The anaerobic / aerobic activated sludge method in the present invention means a method of circulating activated sludge between an anaerobic part and an aerobic part to bring wastewater into contact with the activated sludge. This corresponds to three methods of suppressing the generation of filamentous fungi in the anaerobic part and preventing bulking of activated sludge, the biological nitrification denitrification method or the biological dephosphorization method. Here, the anaerobic part means a zone of an anaerobic atmosphere in which the gas containing oxygen is not aerated. For example, the denitrification part in the biological nitrification denitrification method is the anaerobic part, or the anaerobic phosphorus discharge part in the biological dephosphorization method corresponds to the anaerobic part. In the following description, the portion of the anaerobic part where methane fermentation is performed is an anaerobic digestion part, which is distinguished from the denitrification part in the biological nitrification and denitrification method and the anaerobic part in the biological dephosphorization method.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The principle of operation will be described with reference to FIG. 1 by taking a biological nitrification and denitrification method by an anaerobic aerobic method of sewage as an example. In FIG. 1, the sewage 7 is first subjected to solid-liquid separation in a settling tank 8 and the precipitated raw sludge 1 is first subjected to methane fermentation in the anaerobic digestion section 2 to biologically reduce the volume of the sludge, and then the anaerobic microbial bacteria. Digestion residue 3 consisting of undigested residue of body and raw sludge
By ozone-oxidizing the
By destroying the cell wall of the microbial cell and lowering the molecular weight of the organic matter, the biological sludge is solubilized, and the cell wall of the microbial cell and the organic matter are converted into BOD. The solubilized sludge containing the BOD component is used in the anaerobic part of the activated sludge method that suppresses the generation of filamentous fungi in the anaerobic part and prevents bulking of the activated sludge, or in the denitrification part of the biological nitrification and denitrification method. Alternatively, it is the technical idea of the present invention that the biological treatment supplies the phosphorus discharge reaction section in the biological dephosphorization method.

The biological sludge 6 extracted from the biological treatment process is digested together with the raw sludge 1 in the anaerobic digestion section 2, or the biological sludge 6 is the anaerobic digestion residue 3 of the raw sludge.
At the same time, the ozone is oxidized in the ozone oxidation unit 4. Since the biological sludge 6 is less likely to be anaerobically digested than the raw sludge 1, it may be mixed with the anaerobic digestion residue 3 of the raw sludge 1 for ozone oxidation 4.

On the other hand, the sewage 7 is first SS in the sedimentation tank 8.
Or to remove the SS by filtration by providing a coarse filter medium packed layer before the denitrification section 5, the SS-removed water flows into the anaerobic section 5 and is biologically denitrified. Further, a part 13 of the nitrification-treated water that has once advanced to the aerobic part 9 is also circulated to the anaerobic part 5. The water to be treated in the denitrification section 5 then flows into the aerobic section 9, is biologically nitrified, and then the activated sludge is settled and separated in the final settling tank 10 to obtain treated water 11.

Ozone has a strong oxidative effect and destroys the cell wall of microbial cells, lowers the molecular weight of organic SS and turns it into BOD. Therefore, the effluent from the step of passing from the anaerobic digestion section 2 to the ozone oxidation section 4, that is, the anaerobic digestion residue 3, is subjected to ozone oxidation of the anaerobic digested raw sludge and biological sludge to be solubilized, and thus the BOD component. Is contained in a high concentration (however, it is a suspension containing non-solubilized microbial cells SS), so that it is supplied to the anaerobic part 5 of the biological treatment process, and a hydrogen donor for biological denitrification. Is used to accelerate the denitrification reaction. When the biological treatment step is a biological dephosphorization method, the anaerobic digestion residue is used for promoting the phosphorus discharge reaction for biological dephosphorization.

According to the experiments conducted by the present inventor, it was found that when the anaerobic digestion residue or a mixture of the anaerobic digestion residue and the biological sludge is subjected to ozone oxidation, the sludge overflows violently in the ozone oxidation tank to overflow the tank. In order to prevent this vigorous foaming, it has been found that it can be effectively prevented by making powdered activated carbon coexist in sludge and oxidizing it with ozone. When powdered activated carbon is added to the sludge flowing into the anaerobic digestion tank, the activated carbon adsorbs the anaerobic digestion inhibitor and the anaerobic digestion effect is improved.
A double effect is exhibited, which is preferable. Moreover, since the effluent of the ozone treatment process coexisting with the powdered activated carbon flows into the biological treatment process, the powdered activated carbon adsorbs the hardly biodegradable COD in the sewage, and the treated water COD can be reduced.

Since the biodegradability of SS in the effluent water from the ozone oxidation step is enhanced by the action of ozone, it is returned to the anaerobic section 5, and the order of anaerobic section 5 → aerobic section 9 → precipitation tank 10 → anaerobic section 5 is given. When it is circulated, the SS biologically decomposes into carbon dioxide and water in this process. As a result, the amount of raw sludge and biological sludge generated can be significantly reduced, and can be reduced to almost zero depending on the conditions. In FIG. 1, reference numeral 12 is a discharge pipe for inorganic SS such as sand and silt and a small amount of sludge left undecomposed.

The present invention does not directly oxidize raw sludge and biological sludge by ozonolysis, but anaerobically digests sludge, and the sludge assimilated by anaerobic microorganisms (methane fermenting bacteria, sulfate reducing bacteria, etc.) is methane, After decomposing it into hydrogen, carbon dioxide, and water and biologically decomposing and reducing most of the sludge (about 70%),
Since ozone is oxidized, the amount of ozone added can be greatly reduced. In the present invention, it was found that the anaerobic microorganisms grown in the anaerobic digestion step are solubilized by ozone oxidation and converted into BOD. Heretofore, there has been no research example of ozone oxidation of anaerobic microorganisms, and it is a new finding that the anaerobic microorganisms are solubilized by ozone oxidation and become BOD. The required amount of ozone added for effectively causing sludge solubilization is 10 to 30% based on the weight of solid matter, but it is determined experimentally to be exact.

Anaerobic digestion of raw sludge and biological sludge causes a problem that phosphorus is eluted from the sludge under anaerobic conditions. Therefore, it is preferable to add phosphorus compounds such as magnesium compounds, lime, ferric chloride and PAC to the anaerobic digested sludge for dephosphorization. For example, when magnesium ions are added, a crystalline precipitate of magnesium ammonium phosphate (abbreviated as MAP) is generated, whereby phosphorus can be removed and at the same time phosphorus can be recovered as a valuable resource with high purity. In addition, when lime is added, a calcium phosphate precipitate is generated and phosphorus is removed. As a result, even if the sludge volume is almost completely reduced, it is possible to prevent the phosphorus concentration of the treated water from increasing due to the phosphorus eluted from the sludge. Further, as another method for solving the problem of elution of phosphorus due to the reduction of sludge volume, a method of biological treatment after adding iron or aluminum coagulant to sewage and separating generated flocs and a biological treatment step Alternatively, a method of adding an iron- or aluminum-based coagulant before the final settling tank is recommended.

[0015]

【Example】

Example 1 Based on the process of FIG. 1, according to the present invention by a biological nitrification denitrification method provided with a sludge volume reduction bypass step for ozone-oxidizing an anaerobic digestion residue or a mixture of this and a biological sludge for sewage. Sewage was treated. Table 1 shows the water quality of the sewage used for the treatment.

[0016]

[Table 1]

Table 2 shows the treatment conditions of the biological nitrification and denitrification method in the present invention.

[0018]

[Table 2]

Also, the treatment conditions of the sludge volume reduction bypass step of the anaerobic digestion residue or the mixture of the anaerobic digestion residue and the biological sludge are set forth in the third.
It is shown in the table. Here, regarding the amount of ozone oxidation of biological sludge, the amount of MLSS in the aerobic tank 9 (nitrification tank) is 3000 to 3500 m.
The amount of biological sludge drawn from the aerobic tank 9 is controlled and determined so as to satisfy the condition of g / liter. Here, the test was conducted under the condition that powdered activated carbon was added to prevent vigorous foaming in the ozone oxidation tank during ozone oxidation. Table 3 shows the treatment conditions for the sludge volume reduction bypass process.

[0020]

[Table 3]

As a result of treatment for one year under the above conditions, the average water quality of the treated water is as shown in Table 4.

[0022]

[Table 4]

The amount of surplus sludge discharged outside the system was about 6 to 7 g · ss per month, which was extremely small.

Comparative Example 1 The same conditions were used except that the sludge volume reduction bypass step consisting of the anaerobic digestion tank and the ozone oxidation tank was omitted from the step of FIG. 1, and the treatment conditions were the same as those in Tables 2 and 3. A comparative test was conducted. As a result, the amount of sludge generated was approximately 50 g / g for raw sludge.
The amount of surplus biological sludge was about 20 g / month, which was a large amount of about 70 g / month in total. This corresponds to 10 times the sludge generation amount of the present invention. The SVI of the activated sludge was 190 to 250 high, which was in a bulking state. The average water quality of the treated water is shown in Table 5.

[0025]

[Table 5]

Comparative Example 2 When the raw anaerobic digestion tank was omitted from the process of FIG. 1 and the raw sludge and the biological sludge were directly ozone-oxidized, the required ozone amount was 3 to 4 times that of the present invention, and the running cost was practically used. It was not the target.

[0027]

According to the present invention, raw sludge and biological sludge from sewage and the like are subjected to methane fermentation and then ozone-oxidized. (1) Both sludges are effectively solubilized by a small amount of ozone, and then biologically reduced. It can be installed and the conventional sludge dewatering process becomes unnecessary or can be remarkably reduced in scale. (2) The conventional sludge incineration process becomes unnecessary or can be remarkably reduced in size. (3) Almost no sludge incineration ash is generated, and depending on conditions, it can be completely eliminated. (4) The effect of the denitrification step can be enhanced by adding BOD generated by the solubilization of both sludges to the anaerobic part of the biological nitrification and denitrification step. (5) The biological dephosphorization effect can be promoted by adding the BOD to the anaerobic part of the anaerobic aerobic activated sludge method for sludge treatment. (6) The vigorous foaming in the ozone oxidation step can be solved by the method of the present invention in which the activated carbon powder is added to the sludge flowing into the anaerobic digester. (7) When filamentous fungi such as spherocillus are anaerobically retained in a state where the BOD of the liquid is high, their growth is suppressed, and thus they are culled by normal activated sludge fungi (Zugeraea, etc.) that grow fast. Therefore, no accident such as bulking will occur, and good biological treatment will proceed steadily. (8) By the method of the present invention, it is possible to prevent deterioration of the phosphorus concentration of the treated water due to the sludge solubilization by ozone.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an example of a flow of a nitrification denitrification method of organic wastewater of the present invention.

[Explanation of symbols]

 1 Raw sludge 2 Anaerobic digester 3 Digestion residue 4 Ozone oxidation tank 5 Anaerobic tank 6 Biological sludge 7 Sewage 8 First settling tank 9 Aerobic tank 10 Final settling tank 11 Treated water 12 Sludge discharge pipe 13 Nitrified water

Claims (1)

[Claims] 1. A sewage treatment method for obtaining biologically treated water by subjecting biologically treated anaerobic and aerobic activated sludge method to biological treatment after separating organic SS of the sewage, to obtain biologically treated water by solid-liquid separation. The raw sludge separated before biological treatment, or the biological sludge and the biological sludge extracted from the biological treatment step, after methane fermentation, ozone oxidation, to return to the anaerobic part of the biological treatment step. Characteristic sewage treatment method.