JP2017154038A - Organic waste water treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic waste water treatment method capable of suppressing fouling in accordance with the deterioration of sludge properties by a relatively simple means so as to stably drive a membrane separation active sludge method, when organic waste water such as living waste water and industrial waste water is treated by a membrane separation activated sludge method.SOLUTION: In an organic waste water treatment method where organic waste water containing organic components is fed to a biological reaction tank, the organic waste water is subjected to active sludge treatment in the biological reaction tank and is subjected to membrane filtration treatment by a membrane separation device, and purified water is discharged, while measuring the amount of poor hairs included in the active sludge liquid within the biological reaction tank, the concentration of dissolved oxygen in the biological reaction tank is controlled to 1.5 mg/L or lower, or, the amount of the poor hairs is measured, and, in accordance with the measured result, the concentration of the dissolved oxygen is reduced to 1.5 mg/L or lower.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for treating organic wastewater that can be suitably used for treating organic wastewater such as domestic wastewater and industrial wastewater by a membrane separation activated sludge method.

  In recent years, instead of the conventional activated sludge method, the membrane separation activated sludge method is becoming widespread. In the conventional activated sludge method, organic matter in organic wastewater is sorbed and ingested into the activated sludge by supplying air from the air diffuser in the biological reaction tank, and the ingested organic matter is oxidized by microorganisms in the activated sludge. Decompose, transfer the liquid in the biological reaction tank to the sedimentation tank, separate and settle the supernatant, discharge the supernatant, and return a part of the precipitated solid (activated sludge) to the biological reaction tank to replenish microorganisms. Yes. In contrast, in the membrane separation activated sludge method, the liquid biologically treated in the biological reaction tank is separated by filtration with a membrane separation device.

  In the conventional activated sludge method, it is necessary to set the activated sludge concentration (MLSS) in the biological reaction tank at 2000 to 6000 mg / L on the principle of sedimentation separation, whereas in the membrane separated activated sludge method, MLSS is 20 at the maximum. , 000 mg / L. Therefore, the capacity of the biological reaction tank can be reduced to about 1/10 to 1/3 of that of the conventional one, and a settling tank is unnecessary, so that the installation space can be drastically reduced. In addition, when activated sludge is bulked with the conventional activated sludge method, separation by natural sedimentation becomes difficult, and there is a problem that the sludge flows out into the treated water. The sludge does not flow into the treated water even if it is a sludge, and the operation can be continued.

  On the other hand, in the membrane separation activated sludge method, a membrane clogging (fouling) of the membrane is indispensable for membrane separation of the activated sludge having a high concentration. In the membrane separation activated sludge method, the membrane separator is always washed with the air blown from the diffuser, and the membrane filtration process and the membrane filtration pause process (washing process) are repeated at regular intervals, thereby fouling components adhering to the membrane surface. A method of suppressing fouling by peeling off the film in the cleaning step is common. However, even if such operation is performed, depending on the raw water condition, operating conditions, etc., the properties of the activated sludge deteriorate, fouling progresses, and membrane chemical cleaning is often required.

  As an operation method for avoiding such troubles, for example, in Patent Documents 1 and 2, a lower limit value of the dissolved oxygen concentration in the biological reaction tank is set, and the dissolved oxygen concentration is controlled to be equal to or higher than this value. Is disclosed. This is because if the dissolved oxygen concentration is too low, fouling is more likely to proceed due to an increase in the amount of organic matter that accumulates undecomposed, refinement of sludge flocs due to the growth of anaerobic bacteria, and an increase in viscosity. is there. The lower limit value of the dissolved oxygen concentration is set at about 0.5 to 2 mg / L.

Also, it is known that sludge flocs become finer during the period when the water temperature falls, such as in winter, and fouling is likely to progress. In that case, a flocculant that increases the sludge floc size may be added. . Patent Document 3 discloses a method in which a flocculant is added when the moving average temperature difference between the water temperature in the biological reaction tank and the temperature of the installation environment has increased by 4 ° C. or more.
As another method for adding a flocculant, in Patent Document 3, the flocculant is filtered when the filtration flow rate of the sludge in the biological reaction tank is 10 mL / 5 min or less, or the sugar concentration in the sludge is 30 mg / L or more. Is added when the soluble organic carbon concentration (DOC) or the dissolved chemical oxygen demand (S-COD) in the sludge in the biological reaction tank rises above a predetermined value in Patent Document 4. The method of adding a coagulant is disclosed in Patent Document 5, in which the amount of extracellular ATP in activated sludge or the increase rate of the amount of extracellular ATP in activated sludge exceeds the predetermined value. Is disclosed.

JP-A-4-330993 JP 2001-25769 A JP 2006-55766 A JP 2010-12362 A Japanese Patent Laid-Open No. 2014-193452

However, for example, the method of adding a flocculant disclosed in Patent Document 3 based on the difference between the water temperature and the air temperature is suitable for the winter when the air temperature is lowered, but is not applicable to troubles in other periods. Is possible. In addition, the method for measuring the sugar concentration in sludge disclosed in Patent Document 3 and the method for measuring the amount of extracellular ATP disclosed in Patent Document 5 are not water quality analysis items in normal wastewater treatment, but on-site Considering the burden on workers, it is not easy to apply.

  And the biggest problem is that there are still cases where activated sludge deteriorates and fouling progresses even if the above operation is performed, and this problem is the root cause of sludge deterioration. This is due to the fact that the components and organisms are not elucidated. The present inventors believe that elucidating this will lead to the solution of the problem, and as a result of intensive studies, fouling progresses rapidly when micrometazoans belonging to oligochaetes grow in activated sludge. I found out. Then, by suppressing the growth of the oligochaete, the inventors have found a method of suppressing fouling and stably operating the membrane separation activated sludge method.

In order to solve the above problems, the organic wastewater treatment method of the present invention has any of the following configurations.
(1) Organic wastewater treatment that supplies organic wastewater containing organic components to the biological reaction tank, treats the organic wastewater in the biological reaction tank, treats it with activated sludge, and removes purified water through membrane filtration using a membrane separator. In the method, the dissolved oxygen concentration in the biological reaction tank is controlled to 1.5 mg / L or less while measuring the amount of the oligochaete contained in the activated sludge liquid in the biological reaction tank, or An organic wastewater treatment method, wherein the dissolved oxygen concentration is reduced to 1.5 mg / L or less according to the measurement result.
(2) Organic wastewater treatment that supplies organic wastewater containing organic components to a biological reaction tank, treats the organic wastewater in the biological reaction tank, treats it with activated sludge, and removes purified water by membrane filtration using a membrane separator. In the method, an organic wastewater treatment method characterized by measuring the amount of oligochaete contained in the activated sludge liquid in the biological reaction tank and adding a flocculant to the biological reaction tank according to the measurement result .
(3) The organic wastewater treatment method according to (1) or (2), characterized in that the amount of veneer earthworms (Aeolosoma) is measured among the oligochaetes.

According to the present invention, when organic wastewater such as domestic wastewater and industrial wastewater is treated by the membrane separation activated sludge method, fouling associated with deterioration of sludge properties can be suppressed by relatively easy means, thereby The membrane separation activated sludge method can be operated stably.

It is the schematic which shows an example of the organic wastewater treatment method of this invention. It is the schematic which shows another example of the organic wastewater treatment method of this invention.

  Hereinafter, the present invention will be described in detail with reference to FIGS. 1 and 2, but the contents of the present invention are not limited to the embodiments shown in the drawings.

  As shown in FIGS. 1 and 2, the organic wastewater treatment method of the present invention supplies organic wastewater 1 containing an organic component to a biological reaction tank 2, and the organic wastewater is activated sludge in the biological reaction tank. This is carried out in a membrane separation activated sludge treatment method in which the purified water is extracted by membrane filtration using the membrane separation device 3.

The organic waste water 1 is waste water containing an organic component to be treated with activated sludge, and generally indicates domestic waste water or industrial waste water. This is supplied to the biological reaction tank 2. The biological reaction tank 2 contains sludge containing microorganisms, and these microorganisms act as organic matter-degrading bacteria to perform biological treatment. Microorganisms contained in sludge contribute to the decomposition of organic substances such as bacteria, yeasts, fungi including fungi, and are obtained from the natural world by accumulation culture and acclimatization, such as soil, compost, and sludge. It is also possible to isolate and use the main microbial group involved in the degradation from this conditioned solution.
The biological reaction tank 2 must contain other components necessary for the growth of microorganisms. Therefore, for example, when nitrogen, phosphorus, potassium, sodium, magnesium and other metal salts are not contained in the wastewater, they are added to the biological reaction tank 2 as necessary.
As the membrane separation device 3 provided in the biological reaction tank 2, a module formed using a microfiltration membrane, an ultrafiltration membrane, a nanofiltration membrane, a reverse osmosis membrane, or the like can be used. From the economical point of view, a module using a microfiltration membrane or an ultrafiltration membrane that has a high filtration rate and can be made compact and is easy to maintain is preferable. The membrane may be a flat membrane, a hollow fiber membrane or the like. The form of the module is also not limited to the immersion type or the outside installation type, but in the case of the immersion type, it is preferable that the fouling substance can be successfully removed by combination and arrangement with an aeration apparatus or a stirring apparatus. . Moreover, as a filtration method in the membrane separator 2, there are a cross flow method and a whole amount filtration method, but there is no particular limitation.

  As a method for taking out purified water, a method using a suction pump 4 as shown in FIGS. 1 and 2 is generally used. However, gravity filtration may be performed using a water head difference.

  In order to perform activated sludge treatment in the biological reaction tank 2, it is necessary to supply oxygen necessary for microorganisms to decompose organic substances. In general, as shown in FIGS. 1 and 2, air is supplied through a biological reaction air diffuser 6 using a biological reaction blower 5. In the immersion type membrane separation apparatus, air is further supplied from the lower part of the membrane separation apparatus through the membrane cleaning air diffuser 8 using the membrane cleaning blower 7. This air is not only used by microorganisms for decomposing organic substances, but also used for peeling fouling components adhering to the film. As a specific operation method, the membrane separation device is always washed with the air blown from the membrane cleaning air diffuser 8 and the membrane surface is obtained by repeating the membrane filtration step and the membrane filtration pause step (washing step) at regular intervals. Generally, a method of suppressing fouling by peeling a fouling component adhering to the surface in a cleaning step.

  In the present invention, in such an organic wastewater treatment method, the dissolved oxygen concentration in the biological reaction tank 2 is adjusted to 1.5 mg / L while measuring the amount of oligochaete contained in the activated sludge liquid in the biological reaction tank 2. Control is performed below, or the amount of the oligochaete is measured, and the dissolved oxygen concentration is reduced to 1.5 mg / L or less according to the measurement result. An oligochaete is a general term for a class belonging to the annelid protozoa, and generally refers to a kind of earthworm. The body is generally an elongated cylinder and consists of many annular segments of approximately the same shape. A segment with a body cavity follows the head (anterior lobe), and finally the anus is open. Appearing in the activated sludge is a class of minute metazoans, such as veneer earthworms (Aeolosoma), earthworms (Nais), prickly earthworms (Dero), and prickly earthworms (Pristina). The veneer earthworm (Aeolosoma) is a thick, long earthworm-like worm that has a heart-shaped head. It is characterized by red, yellow and green oil droplets scattered throughout the worm body. There are two pairs of bristle bundles along the nodes. The size of the insect body is about 50 μm in width and about 500 to 2000 μm in length. The earthworm (Nais) is a thick, long earthworm-like worm that has a sharp head. There are long bristle bundles along the nodes on the dorsum. The size of the insect body is about 50 μm in width and about 2000 to 4000 μm in length. The prickly earthworm (Dero) is a thick, long earthworm-like worm that has a fan-shaped tail. There are long bristle bundles along the nodes on the dorsum. The size of the insect body is about 50 μm in width and about 2000 to 3000 μm in length. Pristina is a thick, long earthworm-like worm that resembles the earthworm (Nais) but has a snout that grows in a hook shape. There are bristle bundles along the nodes on the dorsum. The size of the insect body is about 50 μm in width and about 2000 to 4000 μm in length. These minute metazoans belonging to the oligochaetes proliferate in the activated sludge by feeding on sludge flocs and filamentous fungi that are smaller than the body width of the insect body. When the micrometazoans belonging to these oligochaetes grow in activated sludge, the inventors release extracellular macromolecular components (Extracellular Polymeric Substances, EPS) containing predated sludge flocs and filamentous fungi in the periphery. It has been found that fouling progresses rapidly when these components block the membrane. Further, it was found that by suppressing the dissolved oxygen concentration in the biological reaction tank 2 to 1.5 mg / L or less, the growth of oligochaetes can be suppressed and fouling can be suppressed.

As shown in FIG. 1, the operation means for realizing these is composed of an oligochaete monitoring means 9 and a dissolved oxygen concentration meter 10. Specifically, it is convenient and preferable that the oligochaete monitoring means 9 collects a part of the activated sludge in the biological reaction tank 2 and confirms by a microscope whether or not the oligodendrome is present therein. . Originally, minute metazoans are larger than general activated sludge flocs (about 100 μm), and their presence can be easily confirmed with a microscope. And it is also easy to confirm the presence or absence of the oligochaete based on the characteristics of the oligochaetum described above. Microscopic observation of activated sludge is generally performed at sewage treatment plants, and it does not lead to a significant increase in the burden on workers. As for the monitoring frequency of oligochaeta, it can be said that the more the better, the better. However, considering the burden on the worker, about once a day or two is more realistic and preferable. About the control method of dissolved oxygen concentration, it is always controlled to 1.5 mg / L or less so that the poor hair does not grow, and the operation is performed while confirming that the poor hair has not grown by the measurement of the poor hair. Or, the normal dissolved oxygen concentration is set to 1.5 mg / L or more (for example, 3 mg / L), and when the appearance of oligochaetes is confirmed, the dissolved oxygen concentration is set to 1.5 mg / L. If it is decreased to L or less and poor hair is no longer confirmed, the dissolved oxygen concentration may be returned to the normal value. The dissolved oxygen concentration is adjusted by immersing the dissolved oxygen concentration meter 10 in the biological reaction tank 2 and adjusting the flow rate of the biological reaction blower 5 while measuring the dissolved oxygen concentration in the biological reaction tank 2. This is because the amount of air required for membrane cleaning is generally kept constant, and the air volume of the membrane cleaning blower 7 is generally not changed.
Moreover, in this invention, the quantity of the oligochaete contained in the activated sludge liquid in a biological reaction tank is measured, and a flocculant is added to a biological reaction tank according to this measurement result. By adding a flocculant, the size of the sludge floc increases, and the dispersal bacteria present around the filamentous fungi and sludge floc are entangled in the floc floc, and sludge floc that can be eaten by poor hair. It is estimated that this is because the number of microorganisms decreases.
As shown in FIG. 2, the operation means for realizing these is composed of the oligochaete monitoring means 9 and the flocculant addition means 11. The oligochaetes are monitored by the method described above, and when the appearance of oligochaetes is confirmed, the coagulant is added using the coagulant adding means 11. The flocculant has the effect of increasing the sludge floc size by agglomeration, and includes inorganic flocculants such as polyaluminum chloride (PAC) and aluminum sulfate (sulfuric acid band), and aminoalkyl (meth) acrylate quaternary salts. Cationic polymer flocculants such as (co) polymer, polyaminomethylacrylamide salt, chitosan, acrylamide / sodium acrylate copolymer, acrylamide / sodium acrylate / AMPS copolymer, polyacrylic soda There are non-ionic polymer flocculants such as molecular flocculants and polyacrylamide. The amount of flocculant added varies depending on the type of flocculant, sludge conditions, etc., but some activated sludge is collected in advance, and several kinds of flocculant added are set in lab tests such as jar tests. Thus, the addition amount may be determined. At that time, the amount of addition is such that it can be confirmed visually or by a microscope that the sludge floc size is increased. The means for adding the flocculant is not particularly limited as long as the flocculant can be added to the biological reaction tank, and examples thereof include a method of adding using a pump.
Moreover, in this method, it is more preferable to monitor the presence or absence of the veneer earthworm (Aeolosoma) among the oligochaetes. This is because, in general, the frequency of appearance of veneer earthworms (Aeolosoma) is high, and it is practical to monitor veneer earthworms (Aeolosoma).

  Hereinafter, the present invention will be specifically described, but the present invention is not limited only to the embodiment.

(Comparative Example 1)
A schematic structure of the membrane filtration device is shown in FIG. The membrane filtration device is a submerged membrane separation activated sludge device, and is a wastewater treatment device that treats organic wastewater 1 mainly composed of acetic acid. The organic wastewater 1 was intermittently charged into the biological reaction tank 2 having an average capacity of 2.5 m ³ / d and an effective capacity of 1 m ³ . The biological reaction tank 2 contains activated sludge. The membrane separation device 3 is immersed in the biological reaction tank 2, and a membrane cleaning air diffuser 8 is installed below the membrane separation device 3. The air diffusing tube 8 is structured to be supplied with air from a membrane cleaning blower 7 as a cleaning means. That is, in this apparatus, the air supplied from the membrane cleaning air diffuser tube 8 comes into contact with the membrane surface, and the flow of activated sludge due to aeration also occurs at the same time. Will be obtained. The aeration air volume was set at 100 L / min. In addition, since only the air supplied from the membrane cleaning blower 7 cannot cover the amount of air necessary for the microorganisms in the activated sludge, the biological reaction blower 5 and the biological reaction air diffuser 6 were provided to supply air. The water temperature was operated at 25 ° C. The membrane separator 3 was a flat membrane type microfiltration membrane (effective membrane area 4.2 m ² ) made of PVDF (polyvinylidene fluoride). Moreover, about filtration, it performed using the suction pump 4 installed in the membrane filtration water side. Moreover, filtration was performed continuously for 9 minutes, and after that, it stopped for 1 minute and repeated this. The average membrane filtration flux was set at 0.6 m / day.

And as a result of operating in such a membrane filtration device, after about 2 weeks have passed since the start of operation, fouling rapidly proceeds, the transmembrane pressure difference reaches the critical pressure difference, and chemical cleaning is performed. It became. At this time, when a part of the activated sludge in the biological reaction tank 2 was collected and observed with a microscope, a large amount of oligochaetes (Aeolosoma, Nais, etc.) was observed. After that, although the operation was continued, the transmembrane pressure difference reached the critical pressure difference immediately, and the chemical cleaning was frequently performed. During this period, the dissolved oxygen concentration in the biological reaction tank was 1.9 to 2.5 mg / L.
Example 1
In the same membrane filtration apparatus, a part of the activated sludge in the biological reaction tank 2 was collected regularly (once every 1 to 2 days) and observed with a microscope. As a result, the appearance of veneered earthworms (Aeolosoma) was confirmed in the activated sludge when about 10 days had elapsed after the start of operation. Therefore, the air flow of the biological reaction blower 5 was adjusted to reduce the dissolved oxygen concentration in the biological reaction tank 2 to 1.5 mg / L or less, and the operation was continued. Two days after the dissolved oxygen concentration was reduced, a portion of the activated sludge in the biological reaction tank 2 was collected and microscopically observed, and no veneer earthworm (Aeolosoma) was observed. Therefore, when the dissolved oxygen concentration was returned to the previous value (1.9 to 2.5 mg / L) and the operation was continued, the appearance of veneered earthworm (Aeolosoma) was confirmed after about 2 weeks. As a result, when the dissolved oxygen concentration was reduced to 1.5 mg / L or less and the operation was continued, 3 days after the decrease of the dissolved oxygen concentration, no veneer earthworm (Aeolosoma) was observed. By continuing such an operation method, a stable operation could be performed without increasing the transmembrane pressure difference for about 3 months.

(Example 2)
In the same membrane filtration apparatus, the air flow of the biological reaction blower 5 was adjusted so that the dissolved oxygen concentration in the biological reaction tank 2 was always kept at 1.5 mg / L or less. Moreover, a part of activated sludge in the biological reaction tank 2 was extract | collected regularly (once every 1-2 days), and the microscope observation was performed. As a result, the appearance of oligochaete was not confirmed, and the transmembrane pressure difference did not increase rapidly for about 3 months, and stable operation was possible.

(Example 3)
In the same membrane filtration apparatus, a part of the activated sludge in the biological reaction tank 2 was collected regularly (once every 1 to 2 days) and observed with a microscope. As a result, the appearance of veneered earthworms (Aeolosoma) was confirmed in the activated sludge when about 10 days had elapsed after the start of operation. Therefore, the coagulant is added using the coagulant adding means 11. As the flocculant, polyaluminum chloride (PAC), an inorganic flocculant, was used and supplied to the biological reaction tank 2 using a pump. In addition, in order to determine the flocculant addition concentration, a part of the activated sludge was collected in advance, and the amount of flocculant added was set to several types, and a jar test was performed. At that time, it was decided to add at the minimum addition amount (1.0% per activated sludge weight) that the sludge floc size could be confirmed visually. This is because if the amount added is too large, the cost of the flocculant is increased. Three days after the addition of the flocculant, a part of the activated sludge in the biological reaction tank 2 was collected and observed under a microscope, and no veneer earthworm (Aeolosoma) was observed. After that, when the operation was continued, the appearance of veneer earthworms (Aeolosoma) was confirmed after about 6 weeks, and when the same amount of flocculant was added, the flocculant was added 4 After a day, the veneer earthworm (Aeolosoma) disappeared. By continuing such an operation method, a stable operation could be performed without increasing the transmembrane pressure difference for about 3 months.

  The present invention can be suitably used for treating organic wastewater such as domestic wastewater and industrial wastewater by the membrane separation activated sludge method.

DESCRIPTION OF SYMBOLS 1 Organic waste water 2 Biological reaction tank 3 Membrane separation device 4 Suction pump 5 Blower for biological reaction 6 Aeration tube for biological reaction 7 Blower for membrane cleaning 8 Aeration tube for membrane cleaning 9 Poor hair monitoring means 10 Dissolved oxygen concentration meter 11 Aggregation Agent addition means

Claims (3)

In the organic wastewater treatment method of supplying organic wastewater containing organic components to the biological reaction tank, treating the organic wastewater in the biological reaction tank with activated sludge, and performing membrane filtration with a membrane separator to extract purified water, While measuring the amount of poor hair contained in the activated sludge liquid in the biological reaction tank, the dissolved oxygen concentration in the biological reaction tank is controlled to 1.5 mg / L or less, or the amount of the said poor hair is An organic wastewater treatment method characterized by measuring and reducing the dissolved oxygen concentration to 1.5 mg / L or less according to the measurement result. In the organic wastewater treatment method of supplying organic wastewater containing organic components to the biological reaction tank, treating the organic wastewater in the biological reaction tank with activated sludge, and performing membrane filtration with a membrane separator to extract purified water, An organic wastewater treatment method characterized by measuring the amount of poor hair contained in the activated sludge liquid in a biological reaction tank and adding a flocculant to the biological reaction tank according to the measurement result. The organic wastewater treatment method according to claim 1 or 2, wherein the oligochaete is veneer earthworm (Aeolosoma).

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