JP3449864B2 - Method and apparatus for reducing organic sludge - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a weight reduction method and a weight reduction apparatus capable of completely decomposing and eliminating organic sludge such as surplus activated sludge generated from biological treatment processes such as activated sludge treatment of organic wastewater.

[0002]

2. Description of the Related Art A large amount of excess sludge is generated from sewage activated sludge treatment facilities and the like, and the treatment and disposal of this sludge is currently the biggest problem. Excess sludge is difficult to dehydrate, so add a large amount of dehydration aid (polymer, etc.)
After dewatering to about 0%, heavy oil is incinerated as an auxiliary fuel, but if there is a large amount of sludge, the cost of dewatering aid and heavy oil will be high, and the dehydrator and incinerator will be large-scale equipment costs.
The maintenance cost is very high. Disposing of incinerated ash is also a challenge.

In order to solve such a problem, a "sludge reduction method using ozone" is disclosed in JP-A-6-206088. This method uses equipment having a configuration as shown in FIG. That is, the organic sewage 1 is supplied to the biological treatment process 22 such as an activated sludge treatment facility and biologically treated. The biologically treated organic wastewater is subjected to solid-liquid separation in a solid-liquid separation step 23 into a liquid content and a solid content, the liquid content is discharged as treated water 4, and a part of the solid content is supplied to the ozone oxidation step 27. It is the excess sludge 25 that is removed, and the rest is the return sludge 26 that is returned to the biological treatment process 22. Ozone-oxidizing sludge 2 treated in ozone-oxidizing step 27
8 is returned to the biological treatment step 22.

However, the present inventor has found that the following serious problems have been found as a result of additional testing of the processing method disclosed in the above publication. With the reduction of sludge, phosphorus cannot be removed inevitably, and the phosphorus concentration of treated water deteriorates. If the sludge is reduced by 100%, the phosphorus removal rate will be zero. Along with the ozone treatment of sludge, a large amount of persistent COD is produced from the sludge, and the COD of biologically treated water deteriorates. Since the sludge is ozone-oxidized and converted into a BOD substance and supplied to the biological treatment process of wastewater to biologically oxidize and decompose the sludge, the BOD load of the aeration tank tends to be high. When the load becomes high, the excess sludge generation rate naturally increases, and as a result, a vicious cycle in which the amount of ozone added increases increases.

At present, when eutrophication of public water areas is a serious problem, it is a fatal drawback of the prior art to cause deterioration of phosphorus and COD of treated sewage water.

[0006]

The present invention has been made in view of the above problems, and provides a new technique for completely solving the above problems. That is, an object of the present invention is to reduce sludge to a large extent, reliably prevent deterioration of phosphorus concentration of treated water, and prevent BOD load of biological treatment process of organic wastewater from becoming high. A method and apparatus for reducing organic sludge are provided.

[0007]

The above object of the present invention is to subject a surplus sludge generated from a biological treatment step of organic wastewater to ozone treatment, or aeration in an aeration tank separate from the biological treatment step as it is, The slurry flowing out from the aeration tank is subjected to solid-liquid separation, and the separated sludge or a part of the sludge inside the aeration tank is returned to the ozone treatment step, and a polymer flocculant is added to the water separated in the solid-liquid separation step. Is added to perform coagulation separation, and phosphorus contained in the coagulation-separated water is removed by a chemical means. This can be achieved by a method for reducing the amount of organic sludge. In the method for reducing the amount of organic sludge according to the present invention, the coagulation-separation sludge obtained by coagulating and separating after adding the polymer coagulant can be returned to the aeration tank in the ozone treatment step.

Further, the above object of the present invention is to provide ozone treatment means for ozone-treating excess sludge generated from the biological treatment step of organic wastewater, aeration means having a treatment system different from the biological treatment step, and the aeration. A solid-liquid separation means for solid-liquid separating the outflow slurry from the means, and a return system for returning a part of the sludge in the separation sludge or the aeration means to the ozone treatment step,
The solid-liquid separation means is provided with an adding means for adding a polymer coagulant to the separated water, and a phosphorus removing means for chemically removing phosphorus contained in the separated water discharged from the solid-liquid separating means. This can also be achieved by an organic sludge weight reduction device characterized by the above. The present invention is
In the organic sludge reduction apparatus, the return system for coagulating and separating the treated water after the addition of the polymer coagulant by coagulating and separating means, and sending the coagulated and separated sludge to the aeration means of the ozone treatment step. It can be a provided embodiment.

In the above-mentioned present invention, the amount of sludge larger than the amount of excess sludge from the biological treatment process of wastewater is not ozone-treated and returned to the aeration tank of the biological treatment process of wastewater, but the amount of excess sludge is equivalent. Is aerobically treated in an aeration tank separate from the aeration tank for wastewater, and sludge is supplied from this aerobic treatment step to the ozone oxidation step to reduce excess sludge, and the phosphorus produced from this step is removed by chemical means. By doing
It is possible to highly reduce the amount of sludge and extremely effectively prevent the deterioration of the phosphorus concentration in the treated water of biologically treated water. And
In particular, by adding a polymer flocculant and performing coagulation separation before chemical phosphorus removal, colloidal bacterial cells can be subjected to aeration treatment and ozone treatment again, and sludge elimination treatment can be made more effective. .

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A preferred embodiment of the present invention will be described in detail below with reference to FIG. Note that FIG.
FIG. 1 is a diagram showing an overall configuration of an organic sludge weight reduction device of the present invention and a flow of processing steps.

In this embodiment, as shown in FIG. 1, the organic sewage A1 is supplied to a biological treatment step 22 such as an activated sludge treatment facility for biological treatment. The organic wastewater biologically treated in the biological treatment step 22 is solid-liquid separated into a liquid content and a solid content in a solid-liquid separation step 23 such as a settling tank, and the liquid content is discharged as treated water A2. The solid content is returned to the biological treatment process 22 as return sludge 26. In addition, a part of the returned sludge 26 is supplied as excess sludge 25 to the excess sludge treatment device 10 described below.

The excess sludge treatment device 10 shown in FIG. 1 is an ozone oxidation tank 2 which is an ozone treatment means for treating the excess sludge 25 generated from the biological treatment process of organic wastewater with ozone.
An aeration tank 3 which is an aeration means having a treatment system different from that of the biological treatment step, a solid-liquid separation tank 4 which is a solid-liquid separation means for separating the outflow slurry from the aeration tank 3 into a solid-liquid separation tank, and a solid-liquid separation tank The separation systems 5 and 7 for returning the separated sludge from 4 or a part of the sludge in the aeration tank 3 to the ozone oxidation tank 2 and phosphorus contained in the separated water discharged from the solid-liquid separation tank 4 by a chemical means. And a phosphorus removing means 8 for removing the phosphorus.

The sewage treatment process by the treatment apparatus of this embodiment shown in FIG. 1 will be described in detail. Excessive sludge 25 discharged from the biological treatment process of organic wastewater such as sewage (activated sludge treatment facility, etc.) is ozone-oxidized, or supplied as it is to the aeration tank 3 separate from the biological treatment process of wastewater to contain oxygen. Ozone-oxidizing sludge is aerated with gas (air, etc.) in the presence of aerobic microorganisms for biological treatment. Since the sludge that has been ozone-oxidized in this biological treatment process has improved biodegradability, about 40% is decomposed into carbon dioxide gas and water by aerobic microorganisms, and about 60% is converted into activated sludge again.

After that, the slurry flowing out of the aeration tank 3 is subjected to solid-liquid separation in a solid-liquid separation tank 4 such as precipitation or membrane separation, and a part of the separated sludge is supplied to the ozone oxidation tank 2 via a return system 5 which is composed of an appropriate pipe. (The amount of solid sludge 25 to be supplied is about 2 to 3 kg · s when the solid matter inflow amount is 1 kg · ss / day.
s / day) Ozone oxidation. A part of the other part of the sludge separated from the solid-liquid separation tank 4 can be returned to the aeration tank 3 via the return system 6.

As the sludge to be supplied to the ozone oxidation tank 2, the sludge may be extracted from the aeration tank 3 and supplied to the ozone oxidation tank 2 via the return system 7. As a result, the sludge that has not been decomposed in the aeration tank 3 is subjected to ozone treatment again to improve the biodegradability, so that when it flows into the aeration tank 3, it is decomposed again into carbon dioxide gas and water, and the surplus sludge finally supplied. 25 is completely biodegraded. Then, the amount of sludge discharged to the outside of the treatment system of the excess sludge treatment device 10 becomes zero. As an aeration tank for ozone-oxidized sludge, it is needless to say that a part of the aeration tank of the biological treatment process 22 for wastewater may be partitioned by a partition wall and that part may be used. (Do not let sewage flow into this section).

As described above, the ozone-oxidized sludge is biologically oxidatively decomposed in the aeration tank 3, and as a result, the biodegradable C
Although OD and phosphorus are eluted and produced, in the present invention, since the ozone-treated sludge is not returned to the aeration tank of the wastewater treatment system, the amount of water is extremely small (equal to the flow rate of the surplus sludge 25 supplied), and therefore, for example, extremely small aggregates. Phosphorus and COD can be easily removed by chemical means only by providing a settling tank.

Further, as a phosphorus removing means, a coagulation treatment (as the aggregating agent, lime, aluminum sulfate, ferric chloride, etc. are applied. Among them, lime recovers phosphorus as apatite which is highly dehydratable and has a fertilizer value. Therefore, it is possible to apply either a crystallization dephosphorization method using hydroxyapatite as a seed crystal or an adsorptive dephosphorization method (using activated alumina, zirconium oxide or the like as a phosphorus adsorbent).

The "crystallization dephosphorization method" requires phosphorus ore, bone charcoal, etc. as seed crystals for crystallizing phosphorus, but since the amount of treated water is extremely small in the present invention, the required amount of seed crystals is significantly reduced. The construction cost and operation cost of the dephosphorization equipment can be extremely reduced. Further, in the crystallization dephosphorization method, it is necessary to add an acid to the raw water in advance to lower the pH for decarboxylation treatment, but in the present invention, the amount of water is small, so the decarboxylation cost can be greatly reduced.

The "adsorption dephosphorization method" is characterized in that no sludge is generated, but since the adsorbent such as activated alumina is expensive, the adsorbent filling amount becomes enormous when the amount of water to be treated is large, resulting in a large initial cost. However, in the present invention, since the amount of water is small, such an obstacle does not occur and the adsorptive dephosphorization method can be easily carried out. Although the treated water 9 from which phosphorus has been removed can be discharged as it is, it may be supplied to the aeration tank of the sewage treatment system if necessary.

In comparison with the present invention, in the prior art (method of performing biodegradation of ozone-oxidizing sludge in an aeration tank in the biological treatment process of wastewater), the biological treated water itself having a large amount of water (equal to the raw water flow rate) in FIG. As the water quality (COD, phosphorus) deteriorates,
For example, if COD and phosphorus are removed by coagulation / sedimentation treatment, a very large facility is required as a coagulation / sedimentation apparatus. On the other hand, when the present invention is applied to sewage treatment, the amount of water discharged from the settling tank after the aeration tank of ozone-oxidized sludge is remarkably small at about 1/80 of the amount of sewage, so various chemical dephosphorization means are used. Easy to apply. Further, contrary to the prior art, the present invention does not return the ozone-oxidizing sludge to the biological treatment process of the wastewater, so that there is no drawback that the wastewater treatment process has a high BOD load and the excess sludge production rate increases.

In the present invention, the residence time in the ozone oxidation tank is about 1 to 2 hours, the residence time in the aeration tank for ozone oxidation sludge is about 24 to 48 hours, and the installation area is small because the amount of water is small. Also, even if the residence time is set to such a long time, the amount of water is small, so the aeration tank can be small, and since ozone treatment and biological treatment are repeated many times on the liquid, it is difficult to decompose in the liquid. It was observed that the COD removal rate was significantly improved. According to the experiment conducted by the present inventor, in the excess sludge treatment device 10, the separated water treated in the solid-liquid separation tank 4 on the downstream side of the aeration tank 3 for ozone-oxidized sludge contains fine colloidal microbial bacteria. It was found that the body contained SS in a considerably large amount of about 500 to 1000 mg / liter. This is because when the sludge is ozone-oxidized, the floc structure of the activated sludge is destroyed and the sludge is dispersed.

Therefore, a particularly important point in the present invention is
Before the separated water treated in the solid-liquid separation tank 4 is subjected to the chemical phosphorus removal treatment by the phosphorus removal means 8, a means for adding the above-mentioned colloidal bacterial cells, for example, a polymer flocculant such as a cationic polymer or an amphoteric polymer 11 is added and coagulated and separated by the coagulating and separating means 12 (the coagulating and separating means can be composed of a coagulating and separating tank or the like). Then, chemical phosphorus is removed from the separated clear treated water, while the colloidal bacterial cells separated by the polymer flocculant are returned to the return system 1.
3 (connected to the return systems 5 and 6) is sent to the aeration tank 3 through the ozone oxidation tank or directly, and is processed again and decomposed and eliminated.

[0023]

The effects of the present invention can be clarified by the following examples of the present invention. [Example] A verification test was conducted on excess sludge discharged from an activated sludge treatment facility of sewage.

Sludge reduction process supply sludge solid concentration 8 g / liter Sludge treatment amount 10 liters / day (80 g.ss / day) Ozone oxidation tank volume 1 liter Ozone oxidizing sludge amount 240-300 g.ss / day Ozone supply amount 10 〜15g ・ ozon / day Aeration tank volume 15 liters (air is aerated to maintain the dissolved oxygen at 5-6mg / liter) Temperature 25 ℃ Sludge concentration in aeration tank 6-7g / liter Solid-liquid separation of aeration tank outflow sludge Method Precipitation Separation water SS 670 mg / liter Soluble phosphorus 32 mg / liter Solubility COD 295 mg / liter Return sludge amount from settling tank to ozone oxidation tank 160-190 g · ss / day

Coagulation and Separation Process of Solid-Liquid Separation Water with Polymer Flocculant Polymer Type Cationic Polyacrylamide Injection Rate 12 mg / L Aggregate Separation Water Quality SS 12 mg / L Soluble Phosphorus 32 mg / L Soluble COD 53 mg / L Phosphorus Chemical Removal process Coagulation sedimentation tank Sedimentation separation speed 30 m / day Coagulant type Slaked lime (combined with anion polymer 1 mg / liter) Coagulant injection rate 600 mg / liter Treated water phosphorus 0.34 mg / liter COD 32 mg / liter

As a result of continuing the test for 6 months under these conditions, the total weight of sludge (14 kg) supplied was completely decomposed and disappeared, and the amount of discharged organic sludge outside the system was zero. It was found that even if the treated water of the chemical phosphorus removal step is mixed with the biologically treated water of the sewage and discharged, the water quality is not deteriorated.

[Comparative Example 1] The same treatment as in Example was carried out except that the chemical phosphorus removing step was omitted. As a result, the phosphorus concentration in the treated water was 32 mg / liter, which was extremely poor. [Comparative Example 2] The same treatment as in Example was carried out except that the aggregation / separation step using a polymer flocculant was omitted. As a result, the amount of organic sludge discharged outside the treatment system was a large amount of 1.2 kg in 6 months.

[0028]

As described above, according to the present invention, after the excess sludge generated from the biological treatment step of organic wastewater is treated with ozone, or as it is, it is aerated in an aeration tank separate from the biological treatment step, The outflow slurry from the aeration tank is subjected to solid-liquid separation, and the separated sludge or a part of the sludge inside the aeration tank is returned to the ozone treatment step, and a polymer flocculant is added to the separated water in the solid-liquid separation step. Addition is performed for coagulation separation, and phosphorus contained in the separated water in the solid-liquid separation is removed by a chemical means. Further, by adding a polymer coagulant and separating and coagulating, the coagulated product can be bioprocessed again and biodegraded.

Therefore, the following effects can be obtained. 1. Since the excess sludge discharged from the biological treatment process of wastewater can be completely decomposed, a sludge dewatering machine and a sludge incinerator are unnecessary. No need to dispose of dehydrated cake and incinerated ash. 2. Do not return the ozone-treated sludge to the aeration tank of the biological treatment system of the wastewater, and dephosphorize the clear treated water obtained by coagulating and separating the effluent from the sludge erasing process with a polymer coagulant by a chemical phosphorus removal means. Therefore, even if the sludge is reduced by 100%, the phosphorus in the treated water in the sewage treatment system is not deteriorated. 3. Since there is almost no SS flowing into the chemical phosphorus removing means, there are few impurities in the recovered phosphorus (such as hydroxyapatite), and it is easy to reuse as a phosphorus resource with high quality. 4. Since the ozone-treated sludge is not returned to the aeration tank of the wastewater treatment system, the excess sludge generation rate can be suppressed to a low level without causing a high BOD load in the aeration tank of the wastewater treatment system. 5. In the sludge erasing process, the persistent COD in the liquid is also
It is efficiently removed by repeating the ozone treatment → biological treatment a very large number of times. (In the conventional method of FIG. 2, most of the COD in the liquid flows out as it is as treated water.)

[Brief description of drawings]

FIG. 1 is a diagram showing an overall configuration of an organic sludge treatment apparatus of the present invention and a flow of treatment steps.

FIG. 2 is a schematic diagram showing a conventional method for treating organic sludge.

[Explanation of symbols]

1 excess sludge 2 Ozone oxidation tank 3 aeration tank 4 Solid-liquid separation tank 5, 6, 7, 13 Return system 8 phosphorus removal means 9 treated water 10 Surplus sludge treatment equipment 11 Addition means 12 Aggregation / separation means 22 Biological treatment process 23 Solid-liquid separation process (precipitation) 26 Return sludge

Claims (4)

(57) [Claims] 1. Excess sludge generated from a biological treatment process of organic wastewater is subjected to ozone treatment, or is aerated in an aeration tank separate from the biological treatment process as it is, and the slurry discharged from the aeration tank is subjected to solid-liquid separation. Then, the separated sludge or a part of the sludge in the aeration tank is returned to the ozone treatment step, and a polymer flocculant is added to the separated water of the solid-liquid separation step to perform coagulation separation, and the coagulation separation A method for reducing organic sludge, which comprises removing phosphorus contained in water by chemical means. 2. The method for reducing the amount of organic sludge according to claim 1, wherein the coagulated separation sludge coagulated and separated after the addition of the polymer coagulant is returned to the aeration tank of the ozone treatment step. 3. An ozone treatment means for ozone-treating excess sludge generated from a biological treatment step of organic wastewater, an aeration means having a treatment system different from that of the biological treatment step, and a slurry discharged from the aeration means. Solid-liquid separation means for liquid separation, a return system for returning a part of the sludge in the separation sludge or the aeration means to the ozone treatment step, and a polymer flocculant in the separation water flowing out from the solid-liquid separation means. An apparatus for reducing organic sludge, comprising: an addition means for adding and a phosphorus removal means for removing phosphorus contained in the separated water discharged from the solid-liquid separation means by a chemical means. 4. A return system is provided, in which the treated water after the addition of the polymer flocculant is coagulated and separated by coagulation separation means, and the sludge coagulated and separated is sent to the aeration means in the ozone treatment step. The organic sludge weight reducing device according to claim 3.