JPH1133598A - Method for biological treatment of organic wastewater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new technology which scarcely discharges excess sludge outside a biological wastewater treatment system, almost without increasing COD of the treated water. SOLUTION: In a method for biological treatment of organic wastewater, sludge in a larger amount than that of excess sludge is extracted from a process 11 in which organic wastewater 1 is purified by a biological aerobic treatment method, circulated between an ozone oxidation process 13 and a sludge aeration process 14 installed separately from the biological aerobic treatment process 11, and subjected to solid-liquid separation, and the separated water and part of sludge aerated in the aeration process 14 are returned to the biological treatment process 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention can eliminate the generation of excess sludge in the process of biologically treating organic wastewater such as sewage and industrial wastewater, and hardly deteriorate the COD of wastewater biologically treated water. Related to new 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 hardly dewaterable, a large amount of a dehydration aid (such as a polymer) is added thereto, and the sludge is dewatered to about 85% by a sludge dewatering machine, and the dewatered cake is landfilled or incinerated. However, there are many problems such as dehydration aid cost, insufficient landfill for dewatered cake, insufficient disposal of incinerated ash, high incineration equipment cost, and high cost of heavy oil for incineration.

In order to solve such a problem, "Sludge reduction method using ozone" as shown in FIG.
06088. According to this technique, organic sludge (hereinafter also simply referred to as sewage) 1 is drawn directly from an activated sludge treatment step 11 or through a solid-liquid separation step 12 to draw out (pull out) an amount of activated sludge about three times larger than the amount of excess sludge generated. This is a method of returning sludge (also called ozone oxidized sludge) 3 after being treated in the ozone oxidation step 13 to the activated sludge treatment step 11.

[0004]

However, the inventor of the present invention has conducted additional tests of this technique and found that there are the following major drawbacks. If the ozone oxidized sludge is returned to the aeration tank in the sewage biological treatment process and is biologically treated, part of the ozone oxidized sludge will surely be eliminated. Poorly biodegradable COD is generated, which significantly deteriorates the COD concentration of the treated water. According to the experiment of the present inventor, it was confirmed that about 100 g of the non-biodegradable COD was generated per 1 kg-SS of sludge disappeared.

[0005] Since the sludge is oxidized with ozone to be converted into a BOD component and returned to the aeration tank in the sewage treatment process, the BOD load of the aeration tank becomes high when the capacity of the aeration tank is insufficient. When the load becomes high, the excess sludge generation rate in the sewage biological treatment process increases, and as a result, a vicious cycle occurs in which the required amount of ozone increases and the running cost increases. At present, when eutrophication of public water bodies has become a major problem, it is a major drawback of the prior art that treated water COD is greatly deteriorated with sludge reduction. It is not ideal unless the technology can reduce sludge to a high degree and obtain good treated water quality. An object of the present invention is to overcome the drawbacks of the conventional technology and to provide a new technology that can reduce the excess sludge discharged to the outside of the system to zero and that the COD of the sewage biological treatment water hardly deteriorates.

[0006]

According to the present invention, it has been found that the above-mentioned object can be achieved by combining a method of oxidizing sludge with ozone and a biological treatment of ozone-treated sludge in a novel manner. That is, the present invention relates to a process for purifying organic wastewater by an aerobic biological treatment method, extracting more sludge than the amount of excess sludge, and performing an ozone oxidation process and a sludge aeration process provided separately from the aerobic biological treatment process. And then separating the separated water and a part of the sludge aerated in the sludge aeration step to the biological treatment step.

[0007]

FIG. 1 shows a configuration example of the present invention. Activated sludge treatment step of purifying organic sewage 1 with aerobic microorganisms (may be a step provided with an anaerobic part such as a biological dephosphorization method or a biological nitrification denitrification method; hereinafter, also simply referred to as an aerobic biological treatment step) ) 11 directly or through a solid-liquid separation step 12 such as a final sedimentation basin, etc.
It is not necessary to withdraw three times the amount of excess sludge as in the prior art;
And is introduced into the sludge eliminating step 10 of the present invention.

The sludge elimination step referred to in the present invention means that the extracted sludge 2 is supplied to an ozone oxidation step 13 and the sludge is chemically oxidized by ozone 4 to improve the biodegradability of the sludge. This is a step of flowing into a separately provided sludge aeration step 14 for aeration and biodegrading the ozone-treated sludge 3. Part of the sludge aerated in the sludge aeration step 14 is circulated to the ozone oxidation step 13. The circulation amount may be set to about three times the weight of the excess sludge SS generated in the activated sludge treatment step 11. Note that the extracted sludge 2 may be supplied first to the sludge aeration step.

Ozone injection rate is 40-50g-ozone / 1kg-s
s Sludge is appropriate. When the ozone oxidized sludge is aerated, a part of the ozone oxidized sludge (biodegradability by microorganisms is improved by the oxidizing action of ozone) (30 to 40% of SS)
Is decomposed into carbon dioxide and water by activated sludge (aerobic microorganisms) and disappears. The sludge flowing out of the sludge aeration step 14 is subjected to solid-liquid separation in a solid-liquid separation step 15 such as centrifugation, membrane separation, and precipitation. Most of the separated sludge is returned to the sludge aeration step 14 as the concentrated sludge 5, and the separated water is sent to the activated sludge treatment step 11.
Is circulated to the aeration section.

If a part of the sludge is operated from the sludge aeration step 14 for a long time without being supplied to the activated sludge treatment step 11, an increase in inorganic SS occurs in the sludge aeration step 14, VSS decreases, and the sludge reduction effect is reduced. It turned out to be worse. As a countermeasure, it is important to supply a part of the sludge from the sludge aeration step 14 to the activated sludge treatment step 11. By doing so, it was found that the accumulation of the inorganic SS and the deterioration of the sludge decomposition activity in the sludge aeration step 14 could be prevented, and the predetermined sludge reduction effect was stably maintained.

In the configuration shown in FIG. 1, the hardly biodegradable COD component generated when the ozone oxidized sludge 3 is aerated and biologically disintegrated and decomposed is ozone-oxidized again, and the hardly biodegradable COD is oxidized by ozone. It is considered that as a result of the action of being converted to biodegradable COD by the action many times, the hardly biodegradable COD is highly degraded biologically in the sludge aeration step 14. In the method of the present invention, the amount of COD generated per kg-SS of sludge that has disappeared is about 1/7 that of the conventional method.
It was confirmed experimentally that the weight was significantly reduced to 15 g.

In the prior art shown in FIG. 2, the ozone oxidized sludge 3 is returned to the aeration section of the activated sludge treatment step 11 as it is. Sex COD is generated,
Since the treated water 6 flows out as it is through the solid-liquid separation step 12 of the final sedimentation basin or the like, it was recognized that the COD of the treated sewage significantly deteriorated. That is, in the prior art, the hardly decomposable COD component in the liquid flows out to the treated water 6 through the solid-liquid separation step 12 such as a final sedimentation basin without being oxidized again by ozone, whereas the present invention relates to sludge aeration. After the hardly decomposable COD component generated in the step 14 undergoes ozone oxidation again to improve the biodegradability, the process returns to the sludge aeration step 14 where COD is removed, and this is repeated many times. As a result, according to the present invention, it was experimentally confirmed that the amount of hardly decomposable COD produced was reduced to about 1/7 that of the conventional technique.

[0013]

EXAMPLES The method of the present invention will be described in more detail by way of examples, which should not be construed as limiting the invention. EXAMPLE A proof test of the present invention was conducted on wastewater in accordance with the process shown in FIG. Table 1 shows the average quality of sewage.

[0014]

[Table 1]

Table 2 shows the test conditions.

[0016]

[Table 2]

As a result of the experiment, the average value of the quality of the treated water in the final sedimentation basin, which is the solid-liquid separation step 12 after the activated sludge treatment step 11, is shown in FIG. As shown in the first column of FIG. 3, COD and BOD were highly removed. The second column in Table 3 shows the sewage treatment water quality when sludge reduction is not performed. In the method of the present invention, even if the excess sludge is completely eliminated, COD deterioration of the sewage treatment water is hardly recognized. Sludge was not drawn out of the system during the 6-month test, but M in the aeration section of the activated sludge treatment process 11 was not removed.
Since the LVSS maintained the initially set value of 3500 to 3700 mg / liter, there was no excess sludge to be discarded outside the system of the present invention.

On the other hand, ordinary activated sludge to which the present invention is not applied
The amount of excess sludge generated by the method is 1 m of sewage. ^Three55-60g per
-ss. The VSS / MLSS ratio of the sludge aeration tank is
It is 0.86 at the start of operation and the value after 6 months is 0.85
Met. From this fact, the present invention shows that the sludge aeration tank
It was found that there was no accumulation of inorganic SS in the mud. Sludge weight loss
The rate is 32% at the start of operation and 33% after 6 months.
The sludge decomposition activity of the sludge aeration tank (process) is low.
It was confirmed that the temperature was maintained at a constant level.

[0019]

[Table 3]

[Comparative Example] The same sewage and the same biological treatment process as in the present invention were used, and the operation was carried out according to the process diagram of the prior art (FIG. 2). The operating conditions of the prior art are disclosed in JP-A-6-20608.
According to the description of JP-A No. 8-3, three times the amount of surplus activated sludge generated is withdrawn from the final sedimentation basin, which is the solid-liquid separation step 12, and subjected to ozone oxidation (ozone absorption of 0.05 to 0.08 g-ozone).
/ g-ss), which is returned to the activated sludge treatment tank (process) as it is. COD of conventional sewage biological treatment water
Deteriorated remarkably as shown in the third column of Table 3. If the sludge from the sludge aeration tank is not supplied to the wastewater biological treatment process,
A month later, the VSS / MLSS ratio in the sludge aeration tank dropped to 0.68, and the sludge weight loss rate also worsened to 23%.

[0021]

The following effects can be obtained by the method of the present invention. Sludge extracted from the aerobic biological treatment process of organic wastewater (it is important to extract more sludge than excess sludge, not excess sludge) As a result of biodegrading the ozone oxidized sludge and circulating this aerated sludge to the ozone oxidation step, the amount of organic sludge discharged outside the system can be reduced to almost zero, and the amount of hardly decomposable COD generated is reduced. .

The ozone-treated sludge is aerated in a sludge aeration step to decompose the sludge and then supply the sludge to an aeration section (biological treatment tank) in a biological treatment step. A vicious cycle of high BOD load and a large excess sludge generation rate does not occur. Since part of the sludge is returned to the biological treatment step from the sludge annihilation step, accumulation of inorganic SS in the sludge aeration step can be prevented, and the biodegradation activity of the ozone-treated sludge does not deteriorate.

[Brief description of the drawings]

FIG. 1 is a process chart showing one example of the method of the present invention.

FIG. 2 is a process diagram showing an example of a conventional sludge volume reducing method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Organic wastewater 2 Extraction sludge 3 Ozone oxidation sludge 4 Ozone 5 Condensed sludge 6 Treated water 10 Sludge annihilation process 11 Activated sludge treatment process 12 Solid-liquid separation process 13 Ozone oxidation process 14 Sludge aeration process 15 Solid-liquid separation process

Claims (1)

[Claims] 1. A process for purifying organic sewage by an aerobic biological treatment method, wherein sludge larger than the amount of excess sludge is extracted, and a process is performed between an ozone oxidation process and a sludge aeration process provided separately from the aerobic biological treatment process. And then separating the separated water and a part of the sludge aerated in the sludge aeration step into the biological treatment step.