JP2002316182A - Method for treating organic waste liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method for treating organic wastewater which can treat the wastewater stably with the quality of treatment water and solid-liquid separation properties improved by keeping biological treatment efficiency high even when sludge in an amount larger than the amount of increased sludge is modified to be easily biodegradable and returned and can reduce the amounts of a chemical necessary for the modification, energy, etc., to be consumed by increasing the volume reduction ratio of the sludge. SOLUTION: In the treatment method in which organic waste liquid is subjected to aerobic biological treatment by a biological treatment system 1 including an aerator 2, and the sludge is modified to be easily biodegradable in a modification apparatus 11 and supplied to an aerator 1 to reduce the volume of the sludge, the amount of the sludge to be extracted including the amount of the sludge to be modified and the amount of the sludge to be discharged outside the system is adjusted to be 1/10 or below of the amount of the sludge in the biological treatment system so that the retention time of living bacteria sludge is made to be at least ten days for the treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating an organic effluent with an aerobic biological treatment, and more particularly to a treatment method for reducing the volume of sludge by modifying the sludge to be easily biodegradable.

[0002]

2. Description of the Related Art In a method of aerobic biological treatment of an organic wastewater, sludge is extracted from a biological treatment system, and is subjected to a biodegradable treatment by ozone treatment or the like, and the modified sludge is supplied to the biological treatment system. A treatment method for reducing the volume of sludge by performing the treatment has been proposed. (For example, see JP-A-6-206)
No. 088). In this method, sludge that has been discharged outside the system as surplus sludge is converted to BOD and returned to the treatment system as a load.
This is a method to reduce the amount of sludge discharged as surplus sludge by assimilating it with living organisms. In the above method, biological sludge, which is biologically stable and has a limit in volume reduction in ordinary biological treatment, is easily assimilated into living organisms by reforming treatment such as ozone treatment to easily degrade it. This makes it possible to reduce the volume of sludge by biological treatment.

However, in such a processing method,
By reforming a larger amount of sludge than the surplus sludge, the cells in the sludge are killed and returned. In this case, the sludge multiplication that is discarded as surplus sludge is unnecessary for the original treatment, so there is no problem with the reforming treatment, but the sludge that is larger than the multiplication is the sludge originally required for biological treatment. However, when this is modified, the amount of sludge required for the treatment is reduced, and the biological treatment efficiency is reduced. Although the amount of sludge required for biological treatment is reduced in this way, the load increases because the reformed sludge is supplied to the aeration tank as a load, and the reformed sludge contains a hardly decomposable component. There is a problem that the treatment efficiency is lowered and the quality of the treated water is deteriorated.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to maintain a high biological treatment efficiency even when sludge of a quantity larger than the amount of multiplied sludge is returned to be easily biodegradable and returned. An organic wastewater treatment method that can perform stable treatment by increasing solid-liquid separation properties, increase sludge volume reduction rate, and reduce the amount of chemicals and energy required for reforming. It is to get.

[0005]

The present invention is the following method for treating organic waste water. (1) Organic wastewater that undergoes aerobic biological treatment of organic effluent in a biological treatment system including an aeration tank and sludge is reformed to be easily biodegradable and supplied to the aeration tank to reduce the volume of sludge. In the treatment method of (1), the amount of sludge to be subjected to the reforming treatment and the amount of the extracted sludge including the amount of the sludge discharged to the outside of the system are set at 1/10 or less of the sludge in the biological treatment system, so that the residence time of the viable bacterial sludge is 10 or less. A method for treating organic effluent, wherein the treatment is performed for at least one day. (2) Increase the MLSS of the aeration tank to 1,000 to 20,000.
The method according to the above (1), wherein the treatment is carried out at mg / L. (3) The amount of sludge to be reformed in the amount of drawn sludge is 10 to
The method according to the above (1) or (2), wherein the method is 100%.

The organic effluent to be treated in the present invention may be any one containing a component that can be decomposed by aerobic biological treatment using biological sludge, and includes organic substances such as sewage, human waste, and industrial wastewater. In addition to wastewater, there are sludge such as surplus sludge and digested sludge, garbage, livestock manure and the like. The organic effluent may contain only organic substances, or may contain inorganic substances such as nitrogen and phosphorus in addition to organic substances.

The biological treatment in the present invention is an aerobic biological treatment in which a biological treatment system including an aeration tank is used to aerobically treat the above-mentioned organic effluent in the presence of biological sludge. The decomposition of organic substances includes a reaction in which heterotrophic microorganisms decompose organic substances by assimilation, a nitrification reaction by ammonia oxidizing bacteria in the case of ammonia, and a denitrification reaction by nitrate reducing bacteria in the case of nitric acid. The biological treatment system can be provided with a solid-liquid separation tank and the like in addition to the aeration tank.

According to the present invention, a part of the biological sludge is extracted from the biological treatment system in such aerobic biological treatment, and the sludge in the biological treatment system is modified to be easily biodegradable to convert the modified sludge into the biological treatment system. Perform the reforming process to supply to the aeration tank. When extracting biological sludge, it is preferable to extract a part of the separated sludge separated by the solid-liquid separator, but the mixed solution may be extracted from the aeration tank. When extracting from the separated sludge, in addition to excess sludge, a part of the returned sludge returned to the aeration tank as returned sludge can be further extracted and reformed,
As a result, the amount of excess sludge discharged out of the system can be reduced, and in some cases, can be reduced to zero.

[0009] As a reforming treatment method for modifying the extracted sludge into a property easily decomposed by living organisms, any method can be used as long as it is a method for modifying the extracted sludge to be easily biodegradable by adding a chemical and / or energy. Can be adopted. For example, reforming treatment by ozone treatment, reforming treatment by hydrogen peroxide treatment, reforming treatment by acid treatment, reforming treatment by alkali treatment, reforming treatment by heat treatment, high pressure pulse discharge treatment, ball mill, colloid mill, etc. A grinding treatment by a mill, a modification treatment combining these, and the like can be employed. Among these, the reforming treatment by ozone treatment is preferable because the treatment operation is simple and the treatment efficiency is high.

In the ozone treatment as the reforming treatment, the sludge extracted from the biological treatment system may be brought into contact with ozone, and the sludge is reformed to be easily biodegradable by the oxidizing action of ozone. When the ozone treatment is performed in an acidic region having a pH of 5 or less, the efficiency of oxidative decomposition increases. At this time, the pH is adjusted by adding an inorganic acid such as sulfuric acid, hydrochloric acid or nitric acid to the biological sludge as a pH adjuster, or adjusting the biological sludge by acid fermentation,
Alternatively, it is preferable to carry out the treatment in combination. When a pH adjuster is added, the pH is preferably adjusted to 3 to 4, and when an acid fermentation treatment is performed, the pH is preferably adjusted to 4 to 5.

The ozone treatment can be carried out by adjusting the pH of the extracted sludge or acid fermentation treatment solution to pH 5 or less as it is or by concentrating it with a centrifugal separator or the like, if necessary, and bringing it into contact with ozone. As a contact method, a method of introducing sludge into an ozone treatment tank and blowing ozone, a method of mechanical stirring, a method of using a packed bed, and the like can be adopted. As the ozone gas, an ozone-containing gas such as ozonized oxygen and ozonized air can be used. Ozone is used in an amount of 0.1 to 10% by weight, preferably 1.5 to 5% by weight, based on the sludge solid to be treated.
It is desirable that the content be% by weight. The biological sludge is oxidatively decomposed and converted into a BOD component by the ozone treatment.

In the hydrogen peroxide treatment as the reforming treatment, the extracted sludge extracted from the biological treatment system is led to a reforming tank and mixed with the hydrogen peroxide. The amount of hydrogen peroxide used is 0.001-0.
And _{2g-H 2 O 2 / g} -SS. At this time, it is preferable to add an acid such as hydrochloric acid to the extracted sludge to adjust the pH to 3 to 5. In this case, the amount of hydrogen peroxide used is 0.001 to 0.
Preferably between _{07g-H 2 O 2 / g} -SS. To promote the reaction, heating or addition of a catalyst such as ferrous ion may be performed.

In the acid treatment as a reforming method, the extracted sludge extracted from the biological treatment system is led to a reforming tank, and a mineral acid such as hydrochloric acid or sulfuric acid is added thereto.
What is necessary is just to keep for a predetermined time under acidic conditions of 2. The residence time is, for example, 5 to 24 hours. At this time, it is preferable to heat the sludge, for example, to 50 to 100 ° C., since the reforming is promoted. The sludge becomes easily biodegradable by the treatment with the acid, and can be easily decomposed and removed by returning the sludge to the biological reaction tank.

In the alkali treatment as a sludge reforming method, the extracted sludge extracted from the biological treatment system is led to a reforming tank, and alkali such as sodium hydroxide and potassium hydroxide is added to the sludge by 0.1 to 0.1%. What is necessary is just to add 1% by weight and to stay for a predetermined time. The residence time is about 0.5 to 2 hours, and the sludge is reformed to be easily biodegradable. At this time, it is preferable to heat the sludge, for example, to 5 to 100 ° C. because the reforming is promoted.

The heat treatment as a reforming method can be performed alone, but is preferably performed in combination with an acid treatment or an alkali treatment. When heat treatment is performed alone, for example, the temperature may be 70 to 100 ° C. and the residence time may be 2 to 3 hours.

The high-voltage pulse discharge process is performed with an electrode interval of 3 to
Sludge is present between a positive electrode of 10 mm, preferably 4 to 8 mm such as a tungsten / thorium alloy, and a negative electrode of stainless steel or the like, and the applied electricity is 10 to 50 kV, preferably 20 to 50 kV.
40 kV, pulse interval 20-80 Hz, preferably 40
Pulse discharge is performed at 〜60 Hz, and the treatment can be performed while the sludge is circulated sequentially.

The sludge thus modified to be easily biodegradable is introduced into an aeration tank of a biological treatment system, subjected to aerobic biological treatment, and assimilated by microorganisms to be decomposed. When the sludge is reformed and returned to the aeration tank as described above, the sludge volume required for the treatment decreases, the load increases, and the reformed sludge is hardly degradable. Since the water deteriorates, in the present invention, the amount of the extracted sludge including the amount of the sludge to be reformed and the amount of the sludge discharged outside the system is 1/10 or less of the sludge in the biological treatment system, preferably 1/10 to 1/30. The treatment is performed with the residence time (hereinafter, referred to as LSRT) of the viable sludge being 10 days or more, preferably 10 to 30 days. By increasing the LSRT in this way, the amount of sludge retained in the biological treatment system increases, thereby increasing the treatment efficiency, increasing the quality of treated water, and increasing the sludge volume reduction rate. The residence time of viable sludge is determined by the ratio of the amount of sludge to be reformed and the amount of withdrawn sludge including the amount of sludge discharged outside the system to the amount of sludge in the biological treatment system. If the capacity is relatively large compared to the capacity, the amount of sludge in the biological treatment system can be conveniently set as the amount of sludge in the aeration tank, ignoring the sludge held in the settling tank and the sludge in the piping.

In general, in aerobic biological treatment, the sludge retention time (SRT) is about 5 to 7 days. It is known that the longer the SRT, the higher the sludge concentration and the quality of the treated water, as well as the higher the self-digestion rate of the sludge and the lower the amount of excess sludge generated. However, as the sludge concentration increases, the solid-liquid separation property deteriorates, and separation cannot be performed by ordinary sedimentation. Therefore, the SRT is not set to 10 days or more in aerobic treatment in a normal load range. In the case of performing a reforming treatment such as an ozone treatment, the SRT is set to about 5 to 7 days from the same concept.

However, when a reforming treatment such as an ozone treatment is performed, the rate of increase in the sludge concentration when the LSRT is lengthened is smaller than in the case of a normal treatment without the reforming treatment, and the LSRT is reduced by 10 days. Above, preferably 10 to 30
Even for days, it was found that the separation can be sufficiently performed by ordinary solid-liquid separation means. This is because, in ordinary treatment, the rate of increase in the sludge concentration is large due to accumulation of the hardly biodegradable components contained in the sludge, whereas when the reforming treatment is performed, the hardly bioseparable components are converted to easily biodegradable components. This is presumed to be due to the fact that the rate of increase in the sludge concentration is reduced due to the assimilation and assimilation. Therefore, the amount of extracted sludge is set to 1/10 or less of the total amount of sludge, and L
Even when the SRT is set to 10 days or more, preferably 10 to 30 days, the increase in the sludge concentration is smaller than that in the case of only pulling out, and biological treatment can be performed by a usual apparatus.

Further, increasing the LSRT means reducing the amount of sludge withdrawn from the treatment system, and thus reducing the amount of sludge to be reformed. As a result, the amount of the reformed sludge returned to the aeration tank as a load decreases, and the load decreases. Further, the longer the LSRT, the higher the self-digestion rate of the sludge. Therefore, the amount of the proliferating sludge is reduced, and the load as the modified sludge is also reduced. On the other hand, the sludge concentration in the treatment and the like increases, so that the treatment efficiency increases and the treated water quality improves.

Further, by making the LSRT longer, the amount of sludge to be reformed is reduced due to an increase in self-digestion, and the amount of sludge to be reformed is reduced. When the reduced sludge is reformed and returned to the aeration tank, the load is reduced, and the amount of the sludge caused by the reformed sludge is also reduced. Therefore, the sludge volume reduction rate is higher than when the LSRT is short. In addition, since the amount of sludge to be subjected to the reforming treatment is reduced, the amount of chemicals such as ozone or energy required for the reforming can be reduced.

In the above biological treatment system, the same device as the conventional one can be used for the aeration tank. The sludge concentration MLSS in the aeration tank varies depending on the properties of the water to be treated and the like, but can be generally 1,000 to 20,000 mg / l, preferably about 4,000 to 6,000 mg / l. Solid-liquid separation means such as a solid-liquid separation tank can be provided in addition to the aeration tank. The solid-liquid separation tank requires a large capacity as the sludge concentration increases, but sludge can be separated by ordinary sedimentation. In the solid-liquid separation tank, or in place of the solid-liquid separation tank, a membrane separation device may be provided to separate the treated water.

In the present invention, the whole amount of the sludge extracted from the biological treatment system may be reformed. Alternatively, a part of the sludge may be reformed and a part of the sludge may be discharged out of the system as surplus sludge. Even when a part is reformed, the volume of sludge can be reduced. Generally, sludge to be reformed for the entire drawn sludge is 10 to 100.
%, Preferably 50 to 95%.

[0024]

According to the present invention, the sludge having a larger amount than the propagation sludge is reformed to be easily biodegradable by reforming the extracted sludge and returning the sludge to the aeration tank with the LSRT being 10 days or more. Even when returned, the biological treatment efficiency can be maintained at a high level, thereby improving the quality of treated water and solid-liquid separation for stable treatment, increasing the sludge volume reduction rate, and improving the chemicals and energy required for reforming. Etc. can be reduced.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a flowchart showing a method for treating an organic waste liquid according to the embodiment.

In FIG. 1, 1 is a biological treatment system,
An aeration tank 2 and a solid-liquid separation tank 3 are included. In the biological treatment system 1, the liquid to be treated is introduced from the liquid passage 4 to be treated, the returned sludge is introduced and mixed from the returned sludge passage 5, air is supplied from the diffuser 6, and aeration is performed to perform aerobic biological treatment. Then, the aeration liquid is introduced into the solid-liquid separation tank 3 from the transfer path 7 to perform solid-liquid separation, the separated liquid is discharged from the processing liquid path 8 as a processing liquid, and the separated sludge is taken out from the sludge take-out path 9 and a part thereof is removed. The water is returned to the aeration tank 2 through the return sludge passage 5.

Reference numeral 11 denotes a reformer, which is a drawn sludge passage 12
At least a part of the extracted sludge from the sludge is introduced from the reformed sludge passage 13 and is reformed to be easily biodegradable by a reforming treatment such as ozone treatment. 2 is provided. The entire amount of the drawn sludge may be subjected to the reforming treatment, but a part of the drawn sludge may be discharged from the surplus sludge passage 15 outside the system. In order to prevent the accumulation of hardly degradable sludge such as inorganic sludge which cannot be reformed because it is easily biodegradable even when the reforming treatment is performed, it is preferable to partially discharge the sludge.

In the above treatment method, the amount of the extracted sludge to be withdrawn from the biological treatment system 1 through the extraction sludge passage 12 is set to be 1/10 or less of the total amount of sludge retained in the biological treatment system 1 so that the biological treatment can be carried out. The LSRT of system 1 is 10 days or more. Then, the non-reformed sludge of the biological treatment system 1, which is at least a part of the extracted sludge, is supplied to the aeration tank 1 by the reformer 11, and assimilated into the biological sludge.

By setting the LSRT to 10 days or more,
A larger amount of sludge will be retained in the biological treatment system than in the case of the conventional LSRT for 5 to 7 days, thereby improving the efficiency of treatment, stabilizing the treated water quality with high water quality, and self-digestion and easy biodegradation of sludge. The biodegradation of the modified sludge that has been modified to a low level greatly reduces the amount of multiplication sludge. Therefore, even if the sludge concentration in the biological treatment system 1 becomes high, the solid-liquid separation in the solid-liquid separation tank 3 is easy, and the outflow of sludge into the treated water is reduced. In addition, the amount of sludge to be reformed is reduced, and the amount of chemicals, energy, and the like for reforming the amount of ozone used is also reduced.

In the above processing method, the aeration tank 2 may be a standard aeration tank or a modified aeration tank. Further, other solid-liquid separation means such as a membrane separation device may be provided in the solid-liquid separation tank 3 or instead. As the reforming device 11, other reforming devices such as a heating device can be used in addition to the ozone treatment device.

[0031]

Embodiments of the present invention will be described below. In each case,% is% by weight.

Comparative Examples 1-4, Examples 1-2 In the method shown in FIG. 1, a system was operated by simply pulling out without performing the reforming treatment (Comparative Examples 1-3), and an ozone treatment was performed as a reforming apparatus. Using the apparatus, the system was operated for a system (Comparative Example 4, Examples 1 and 2) in which the entire amount of the extracted sludge was subjected to a biological treatment by a reforming treatment. As a liquid to be treated, synthetic wastewater containing peptone and yeast extract as main components was used, and the COD concentration was adjusted to about 340 mg / L. This wastewater was passed through a 2 L aeration tank at a tank load of 1.0 kg / m ³ / d. In the system where the extraction was performed, the sludge was continuously extracted so as to have a predetermined SRT (Comparative Example 1: 5 days, Comparative Example 2: 10 days, Comparative Example 3: 10 days), and in the system where the reforming treatment was performed, Predetermined LS
RT (Comparative Example 4: 5 days, Example 1: 10 days, Example 2:
30 days) continuously withdraw sludge, p before the ozone reaction
H to 3 and 1.5 to
It was reacted with 2.0% by weight of ozone and continuously returned to the aeration tank. The sludge was not pulled out of the system at all. The pH-reduced sludge after the ozone treatment was returned to the aeration tank as it was, but the aeration tank had a pH controller using an alkali, and the pH in the aeration tank was maintained at about 7.0. The results of Comparative Examples 1 to 3 are shown in Table 1, and the results of Comparative Example 4 and Examples 1 and 2 are shown in Tables 2 to 4 and FIG.

[0033]

[Table 1]

[0034]

[Table 2]

Tables 1 and 2 show that in the reforming systems of Examples 1 and 2, sludge treatment is also carried out in the aeration tank, so that the sludge concentration is higher than in the pull-out operation of Comparative Examples 1 to 3. Alternatively, there was a difference in the sludge concentration that increased when the LSRT was changed. Further, since the sludge concentration in the aeration tank increases, the quality of the treated water (soluble COD) can be improved as shown in FIG. Further, as shown in Table 3, the SS concentration of the treated water did not fluctuate much.

[0036]

[Table 3] In addition, the amount of sludge to be reformed is also reduced.
As shown in the figure, the amount of ozone required for reforming was small and good.

[0037]

[Table 4]

From the above results, it can be seen that when the LSRT is increased, the quality of the treated water is improved, and the amount of ozone required for reducing the amount of sludge can be significantly reduced. Further, the results of the treated water quality show that if the LSRT is at least 10 days or more, the deterioration of the treated water quality can be minimized while the excess sludge is significantly reduced.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a method for treating an organic wastewater according to an embodiment.

FIG. 2 is a graph showing the quality of treated water in Examples and Comparative Examples.

[Explanation of symbols]

 Reference Signs List 1 biological treatment system 2 aeration tank 3 solid-liquid separation tank 4 liquid path to be treated 5 return sludge path 6 diffuser 7 transfer path 8 treatment liquid path 9 sludge take-out path 11 reformer 12 pull-out sludge path 13 reformed sludge path 14 Reformed sludge path 15 Excess sludge path

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D028 BD00 BD11 CA05 CA12 CB02 CB03 CD02 4D059 AA01 AA05 AA07 AA23 BC02 BF02 BF12 BF14 BK11 BK12 CA28 DA01 DA32 DA33 DA43 DA44 EB02

Claims (3)

[Claims] 1. An organic wastewater treatment system comprising an aerobic biological treatment of an organic effluent in a biological treatment system including an aeration tank, a sludge reforming treatment for easy biodegradability, and a supply of the sludge to the aeration tank to reduce the sludge volume. In the wastewater treatment method, the amount of the extracted sludge including the amount of the sludge to be reformed and the amount of the sludge discharged outside the system is reduced to 1/10 of the amount of the sludge in the biological treatment system.
A method for treating organic effluent, wherein the treatment is performed with the residence time of viable sludge being 10 days or more by the following. 2. The aeration tank has an MLSS of 1,000 to 20,
The method according to claim 1, wherein the treatment is performed at 000 mg / L. 3. The method according to claim 1, wherein the amount of sludge to be subjected to the reforming treatment in the amount of the extracted sludge is 10 to 100%.