JP2003053363A - Method and apparatus for treating organic-containing water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the MLSS concentration in a membrane immersion tank in the treatment of water containing organic matter by a submerged membrane activated sludge method, and therefore, to increase the aeration time in the membrane immersion tank. Without causing deterioration of the aeration efficiency
BOD per unit area of aeration tank by increasing sludge load
Improve processing capacity. SOLUTION: Three or more aeration tanks 51 to 55 are arranged in series, and at least one of them is a membrane immersion tank 55. The nominal separation hole diameter of the immersion membrane of the immersion membrane module 59 is set to 0.01 to 0.4 μm, the water temperature of the liquid in the aeration tanks 51 to 55 is 20 to 37 ° C., and the BOD sludge load is 0.15 to 0.40.
kg-BOD / kg-VSS / day, and the MLSS concentration in the membrane immersion tank 55 is 5,000 to 20,000 mg / L.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for removing organic matter in wastewater by the biological action of activated sludge, and in particular, it is possible to obtain an organic matter removing effect equivalent to or better than that of the conventional method in a small aeration tank. The present invention relates to a method and an apparatus for treating organic matter-containing water.

[0002]

2. Description of the Related Art Conventionally, as a method for treating activated sludge containing organic matter-containing water, a membrane module is immersed in an aeration tank containing the activated sludge, and a diffusing pipe for supplying aeration air is arranged below the membrane module. A submerged membrane activated sludge method is applied in which treated water is taken out from the activated sludge by filtering the liquid in the tank while stirring the surface with aerated air and accompanying rising water flow. As the immersion membrane, a microfiltration membrane (MF membrane) or an ultrafiltration membrane (UF membrane) is used, and the shape of the membrane is a hollow fiber membrane,
A flat membrane, a tubular membrane or the like is used. As the material of the film, various materials such as polyethylene, polysulfone, polyether sulfone, polyvinylidene fluoride, cellulose acetate and derivatives thereof can be applied.

A water tank (membrane immersion tank) in which the immersion membrane module is immersed is usually provided with an aeration section and a non-aeration section to generate a swirling flow due to an air lift action. Baffle plates are often used to partition the aerated and non-aerated parts to promote swirling flow. The submerged membrane module is installed above the air diffusing tube of the aeration unit, whereby bubbles and swirling flow can effectively hit the membrane surface, and the membrane surface can be efficiently stirred.

A feature of such a submerged membrane type activated sludge method is that, because the treated water is filtered out of the submerged membrane of the MF membrane or the UF membrane, clear treated water with a low concentration of suspended solids (SS) is used. Obtained; unlike the conventional activated sludge method, solid-liquid separation between activated sludge flocs and treated water by gravity settling is not performed, so it is stable without being affected by changes in sludge settling property, which was a conventional problem. Can be treated; sludge concentration (MLSS
(Concentration) can be increased to 5,000 to 30,000 mg / L as compared to the conventional method of 2,000 to 5,000 mg / L, and thus the treatment capacity per volume of the water tank can be increased. Can be mentioned.

On the other hand, as a drawback of the immersion membrane type activated sludge method,
The dip membrane is expensive and the membrane needs to be replaced regularly, which increases the operating cost. That is, when the membrane is contaminated and can no longer exhibit the predetermined filtration capacity, the contaminants are removed by physical cleaning or chemical cleaning and the membrane is repeatedly used. However, these cleaning methods cannot restore the predetermined filtering ability, and it becomes difficult to perform stable continuous operation of the submerged membrane type activated sludge treatment device. Therefore, it is necessary to replace the submerged membrane. Such membrane replacement is usually performed once every 3 to 5 years.

Further, in the immersion membrane type activated sludge method, if the frequency of cleaning the membrane with chemicals is too high, the cost of cleaning chemicals increases,
Since the number of operations of the operator is increased and the deterioration of the membrane is accelerated, the operating condition that does not cause excessive membrane fouling is usually selected. Specifically, the membrane fouling is prevented by setting the permeation flux (flux) of the membrane low or increasing the amount of aerated air from the lower portion of the membrane. The degree of contamination of the membrane can be understood by measuring the filtration resistance of the membrane, and normally, when water is passed with the design flux, it is 5 to 40 k compared to the new membrane.
Physical cleaning or chemical cleaning is performed when the filtration resistance increases by about Pa. Chemical cleaning interval is 2 months to 9 months
Once a month is common.

On the other hand, the operating condition for biological treatment is that the sludge concentration is MLSS concentration of 5,000 to 20,000 mg.
Although a large amount of / L is used, the higher the sludge concentration, the more easily the sludge is concentrated on the film surface and becomes a dehydrated cake, which is strongly adhered (clogging). When clogging occurs, the filtration pressure for obtaining the necessary membrane flux rises extremely, and in many cases it becomes impossible to operate within a few days, so it is necessary to avoid it as much as possible. To avoid crogging, keep the MLSS concentration low,
It is important to maintain a large amount of aeration from the lower part of the membrane. This aeration amount is ^{30 to} 250 Nm ³ / bottom area of the submerged membrane module or per membrane immersion tank aeration section bottom area (m ² ).
hr is commonly adopted.

[0008]

As described above, in the submerged membrane type activated sludge method, it is desired to maintain a large amount of aeration from the lower portion of the membrane in order to prevent membrane contamination. According to the results, the increase in the amount of aeration from the lower part of the membrane is caused by the fluctuation of the membrane, the rubbing of the membranes, the load of repeated stress on the adhesion part of the membrane to the support, the activated sludge itself and the contaminants in the activated sludge. It promotes a phenomenon such as physical contact with the membrane, which causes the membrane to peel from the support and fail to exhibit a predetermined SS separation performance; the strength of the membrane deteriorates and the membrane breaks; The structure that forms the pores of the membrane is deformed, the number and area of the pores that open on the membrane surface decrease, and the filtration pressure becomes high, and it becomes easy to be affected by membrane contaminants. To be done. From this, an increase in the amount of aeration leads to a decrease in film life.

Therefore, from the viewpoint of the life of the film, it is effective to reduce the aeration amount as much as possible, but the reduction of the aeration amount causes clogging.

Further, as the MLSS concentration is increased, the viscosity of the activated sludge is increased and the fluidity is lowered, the efficiency of dissolving oxygen in the aerated air in the sludge (dissolution efficiency) is deteriorated, and oxygen is absorbed by the microorganisms. There is also a problem that a large amount of aeration is required to supply the gas.

From the viewpoints of preventing clogging and the efficiency of oxygen dissolution, it is desirable to keep the MLSS concentration low. In this case, however, it is clear from the following equation that the same BOD volume load is applied to the sludge. BOD load (=
BOD sludge load; here, the ratio of BOD and VSS, B
OD / VSS load) is also high. BOD sludge load [kg-BOD / kg-VSS / da
y] = BOD volume load [kg-BOD / m ³ / day]
÷ MLVSS concentration [mg / L] × 1000

From the above, in the conventional submerged membrane type activated sludge method, the BOD / VSS load condition is 0.03.
.About.0.1 kg-BOD / kg-VSS / day or less is often adopted, and almost no case has been reported in which the BOD sludge load is taken higher than this.

The ratio of MLVSS to MLSS varies depending on the property of wastewater, but is usually 0.6 to 0.9 [g-V].
SS / g-SS] ratio. Therefore, increasing the MLSS concentration is synonymous with increasing the MLVSS.

In the conventional submerged membrane type activated sludge method, BOD /
The VSS load condition is 0.03 to 0.1 kg-BOD / k
In most cases, g-VSS / day or lower is adopted, and few cases in which the BOD sludge load is higher than that have been reported. Even if there is a case where the volume load is taken high, it is usually dealt with by increasing the MLSS concentration while keeping the BOD / VSS load within the above range.

However, according to the inventor's consideration, MLS
Since increasing the S concentration has the above-mentioned disadvantages, keeping the MLSS concentration as low as possible while maintaining the BOD / VS
Increasing the S load increases the BOD processing capacity per volume, that is, the BOD volume load, and thus the reaction tank can be efficiently downsized.

However, according to the study by the present inventor,
If the BOD / VSS load is increased under inappropriate conditions, the contamination of the film with a different form from the above-mentioned clogging will progress rapidly, and it will be necessary to set the chemical cleaning interval within one month, and within one week depending on the conditions. It was found that it was not practical.

The present invention solves the above problems, and in the treatment of organic matter-containing water by the immersion membrane type activated sludge method, BOD
An object of the present invention is to provide a method and apparatus for treating organic matter-containing water, which can prevent contamination of a submerged film and reduce the frequency of chemical cleaning while taking a high sludge load.

[0018]

The method for treating organic matter-containing water according to the present invention comprises a biological treatment step of mixing raw water containing organic matter with activated sludge to form a mixed solution, and treating the treated water from the mixed solution with an immersion membrane. In the method for treating organic matter-containing water, which comprises a separation membrane separation step for separating, in the biological treatment step, raw water is passed through at least three treatment tanks arranged in series, and the water temperature of the mixed solution is 20 to 37. It is characterized in that activated sludge treatment is performed by adjusting the temperature to ℃.

According to a second aspect of the present invention, in the method for treating organic matter-containing water according to the first aspect, the immersion membrane has a nominal separation pore diameter of 0.01 to.
It is characterized by being 0.4 micrometer.

The method for treating water containing organic matter according to claim 3 is the method according to claim 1 or 2, wherein the BOD sludge load of the activated sludge treatment is 0.15 to 0.40 kg-BOD / kg-VSS / d.
It is characterized as ay.

The method for treating organic matter-containing water according to claim 4 is the method according to any one of claims 1 to 3, wherein the MLSS in the submerged membrane separation step is performed.
The concentration is 5,000 to 20,000 mg / L.

The method for treating organic matter-containing water according to claim 5 is characterized in that, in any one of claims 1 to 4, an antifoaming agent is added to at least one of the treatment tanks.

A method for treating organic matter-containing water according to a sixth aspect is characterized in that, in the first to fifth aspects, the concentration of ammonia nitrogen in the treated water is 0 to 3 mg / L.

The method for treating organic matter-containing water according to claim 7 is characterized in that, in claims 1 to 6, the ratio of the SS concentration to the BOD concentration of the raw water (SS / BOD) is 0 to 0.5.

The method for treating organic matter-containing water according to claim 8 is the method according to any one of claims 1 to 7, characterized in that at least one treatment tank holds a microorganism-attached carrier.

According to a ninth aspect of the present invention, there is provided an apparatus for treating organic matter-containing water, comprising at least three treatment tanks for retaining activated sludge arranged in series, and treated water immersed in at least one of the treatment tanks. What is claimed is: 1. A treatment apparatus for organic substance-containing water, comprising a submerged membrane module for separation and raw water supply means for supplying raw water containing organic matter to the treatment tank, wherein at least a part of the submerged membrane incorporated in the submerged membrane module is nominally separated. The pore size is 0.01 to 0.4 μm, and the effective total volume of the treatment tank satisfies 1.3 to 4 kg-BOD / m ³ / day with respect to the BOD (planned value) of the raw water supplied. It is characterized in that it is a volume.

A treatment apparatus for organic matter-containing water according to claim 10 is:
In Claim 9, it has a means for adjusting the temperature of the raw water or the liquid in the treatment tank.

An apparatus for treating water containing organic matter according to claim 11 is:
Claim 9 or 10 is characterized in that at least one treatment tank holds a microorganism-attached carrier.

In order to treat a large amount of BOD without increasing the sludge concentration as much as possible in the submerged membrane activated sludge method, the present inventor applied a BOD / VSS load of 0.15 to 0.40 kg-
BOD / kg-VSS / day was set to a high value, and continuous tests were conducted under various conditions. Depending on the conditions, film contamination rapidly progressed, and the chemical cleaning interval was within 1 month, and even 1
Needed to be within a week. Then, at this time, when the surface of the film where the film was contaminated was observed, the above-mentioned clogging was hardly generated, but a slight slime was observed on the film surface. That is, there was observed a phenomenon that the filtration differential pressure was increased, or the filtration differential pressure was increased by covering the membrane surface with a gel-like contaminant, although the contaminant was not found on the membrane surface.

These phenomena often occur when colloid-like organic matter is generated from the activated sludge, or when dispersed bacteria which do not become activated sludge flocs and grow in a dispersed state are generated. It was presumed that the filtration resistance of the membrane was increased by condensing in the form of a gel and that the membrane was contaminated. And part of the resulting gel is easy to peel off,
Part of the filtration resistance is recovered by stopping filtration and performing air aeration, or by taking out the membrane and washing it with water, but part of it is difficult to peel off and penetrates inside the pores of the membrane, resulting in a pore structure of the membrane. It was thought that they were trapped inside the and increased the filtration resistance.

As a method for avoiding such gel contamination, it is conceivable to carry out the above-mentioned air aeration, washing with water, or backwashing, but a filtration treatment can be carried out during these recovery operations. However, in the case of backwashing, there is a problem that the water used for backwashing is mixed with activated sludge and the amount of water to be treated increases, resulting in an increase in the membrane area required for treatment and an increase in membrane cost. Because it was not realistic.
In particular, when gel contamination becomes severe, air aeration and backwashing are required very frequently, the required membrane area further increases, and there is a problem that the progress of contamination that cannot be recovered by these means becomes severe. It was Furthermore, the means of washing with water is
Since it is necessary to take out the film and wash it with a spray or a sponge, there is a problem that contamination that is not realistic and difficult to remove cannot be recovered even by such water washing.

In the present invention, the production itself of such colloidal substances and dispersed bacteria is suppressed by the following action mechanism,
Further, by promoting the decomposition of the colloid-like substance once produced, the above-mentioned gel contamination and pore contamination are prevented.

Effect of arranging three or more treatment tanks (aeration tanks) in series By providing aeration tanks in multiple stages in series, a tank for ingesting a substrate and a tank for metabolizing the ingested substrate in the microbial cells Can be clearly divided. Then, because the activated sludge sequentially passes through these tanks, the time period when the activated sludge ingests the substrate and the time period when the ingested substrate metabolizes and proliferates by microbial cell synthesis are alternately created. Become. Further, when such a growth cycle is passed, the amount of colloid-like substance produced outside the bacterial cells is reduced, and the membrane contamination by the colloid-like substance is suppressed. Considered as a mechanism. However, the details of this metabolic mechanism have not been clarified.

When aeration tanks are provided in multiple stages in series, each stage has activated sludge that passes in a time shorter than the average residence time and activated sludge that stays for a relatively long time. The more the number of aeration tanks, the more preferable it is because this cycle can be produced more reliably. However, since the structure becomes more complicated and the cost increases as the number of aeration tanks increases, it is most preferable that the number of aeration tanks is 4 to 6 in the present invention. preferable.

The repetition of the substrate intake step and the substrate metabolism step by providing the aeration tanks in multiple stages is also effective in suppressing dispersed bacteria. This is because the disperse bacteria have a high sludge load and grow a lot when soluble BOD is abundant in the liquid, but when an environment in which a substrate is abundant and an environment in which a substrate is not abundant are repeated as in the present invention, It is presumed that this is due to the existence of a mechanism that is more advantageous for the growth of ordinary activated sludge flocs than the dispersed bacteria. The reason for this may be, for example, an improvement in the cohesiveness between the disperse bacteria, and a possibility that the activated sludge flocs are changed to a property in which the disperse bacteria are easily taken in. The effect of suppressing such dispersed bacteria is also higher as the number of aeration tanks arranged in series is larger, but for the same reason as above,
The aeration tank is preferably 4 to 6 tanks.

The effect of setting the water temperature to 20 to 37 ° C. The activated sludge produces a colloid-like substance, and the fact that it grows in a dispersed state is closely related to the water temperature. Particularly, the lower the water temperature, the more the colloid-like substance is produced. , And dispersal bacteria also increase. On the other hand, by setting the water temperature to a relatively high value of 20 to 37 ° C., it is possible to prevent the production of the colloidal substance and the growth in the dispersed state, and to prevent the membrane contamination.

Effect of setting the nominal separation pore size (hereinafter, simply referred to as “pore size”) of the submerged membrane to 0.01 to 0.4 micrometer (μm) has an effect of removing suspended matter by membrane filtration. , The action of sieving SS that is coarser than the pore size of the membrane surface on the membrane surface, and the action of trapping fine particles of the same size as the pore size of the membrane in the intricate channel inside the membrane In particular, it is considered that the contamination generated inside the latter film is the main cause of irrecoverable contamination. Further, in the case of an MF membrane having a relatively large pore size, it is presumed that bacteria that have proliferated in a dispersed state also invade the inside of the membrane and are captured, resulting in irrecoverable contamination.

As described above, the substance that enters the inside of the membrane and causes irrecoverable contamination is
It is considered that it penetrates deeper. When clogging occurs in the deep part of the membrane, colloidal substances with a relatively small molecular weight that had permeated through the pores of the membrane and flowed out to the treated water side,
Since the flow path inside the pores is narrowed by the clogging substance,
It will not be able to permeate through the pores of the membrane and will also be trapped within the pores and become a new clogging material. The agitated flow on the membrane surface due to aeration from the lower part of the submerged membrane does not reach the inside of such pores, so a so-called dead-end filtration state occurs inside the pores, and the substances clogged in the pores are separated. It accumulates without any action and rapidly progresses to irrecoverable membrane fouling.

The membrane pore size is 0.4 μm or less, preferably 0.
By setting the thickness to 3 μm or less, and more preferably 0.2 μm or less, it is possible to prevent such a colloidal substance in a portion relatively close to the surface layer of the film and prevent it from entering the inside of the pores. For this reason, the probability that even once clogged colloidal substances and dispersed bacteria are separated by the agitation flow on the membrane surface is increased. Further, as described above, even if the dead-end filtration occurs inside the pores, since it occurs relatively close to the surface layer of the membrane, the area where the clogging substance can enter is limited to the surface layer of the membrane. It becomes possible to suppress an increase in filtration pressure due to these clogging substances to a small extent.

Effect of Retaining Carrier for Adhering Microorganisms in Treatment Tank (Aeration Tank) A part of the colloid-like substance which is a problem in the present invention is decomposed by microorganisms grown in an environment having a long SRT (sludge retention time). Activated sludge, which mainly treats inflowing organic matter,
SRT is usually 5 to 2 due to high sludge load
It will be 0th day. On the other hand, the microorganisms that adhere to the surface of the carrier and grow are not extracted together with the suspended activated sludge, and thus microorganisms having a slow growth rate can also grow. By growing microorganisms with a slow growth rate on the carrier surface in this way, it becomes possible to grow microorganisms capable of decomposing colloidal substances that cannot be decomposed by suspended activated sludge, and to prevent membrane contamination by colloidal substances. It can be reduced.

A large amount of B is added to the tank in which the carrier is put.
When OD constantly flows in, a large amount of BOD-degrading bacteria grow on the surface of the carrier, and bacteria that grow above a certain level are separated from the surface of the carrier. Therefore, microorganisms having a slow growth rate are also peeled off from the carrier surface at the same time, and the effect of adding the carrier is diminished. To avoid this situation,
The load of soluble BOD flowing into the water tank containing the carrier is 0 to the amount of VSS retained in this water tank.
0.1 kg-BOD / kg-VSS / day, more preferably 0-0.05 kg-BOD / kg-VSS / da.
It is good to say y. However, when the carriers are loaded in a plurality of aquariums, at least a part of the carriers only need to play this role, so it is acceptable that there are carriers loaded in other aquariums with a high load. Absent.

Further, such a carrier also has an effect of suppressing dispersed bacteria. This effect is considered to be due to the fact that the dispersed bacteria are adsorbed in the structure of the carrier or in the biofilm on the surface of the carrier.
Therefore, the carrier is more preferably porous so that such dispersed bacteria can be trapped inside the carrier structure.

[0043]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the method and apparatus for treating organic matter-containing water of the present invention will be described in detail below.

In the present invention, three or more treatment tanks (aeration tanks) for holding activated sludge are arranged in series to treat raw water. The number of aeration tanks arranged in series is 3 to 8 stages. Is preferable, and it is particularly preferable that the number of stages is 4 to 6. In the present invention, upstream of the n-th stage aeration tank in series,
There are (n-1) aeration tanks arranged in series, and a plurality of n-th aeration tanks may be provided in parallel. It is preferable that the aeration tank volume of each stage (the total volume of the aeration tanks arranged in parallel in the stage where the aeration tanks are arranged in parallel is close to) is equal to the average value of the aeration tank volume of each stage. When compared,
The volume of the aeration tank in each stage is preferably 0.6 to 1.4 times, particularly 0.8 to 1.2 times the average value. However, p
Small water tanks provided for the purpose of H adjustment, pump pits, distribution tanks, etc. are not considered.

Of these aeration tanks, the membrane immersion tank for immersing the membrane does not have to be at the last stage, and the immersion membrane may be installed at any stage, but a water tank other than the water tank into which raw water mainly flows. Is preferable, and it is more preferable to provide the water tank downstream of the second and subsequent stages of the water tank into which the raw water mainly flows, that is, to the water tank at the stage subsequent to the water tank into which the raw water flows. Further, an anaerobic tank for the purpose of denitrification or dephosphorization may be provided.

The water temperature in the aeration tank is preferably 20 to 37 ° C, and more preferably 25 to 35 ° C. This temperature range is extremely important for solving the problem that when the sludge load applied to the activated sludge is higher than before, dispersal bacteria grow and the colloid-like organic matter increases and the membrane becomes clogged. is there.

Generally, the water temperature of the organic substance-containing water to be treated may fluctuate, so it is preferable to provide an adjusting tank of an appropriate capacity in front of the first aeration tank to mitigate the fluctuation of the water temperature. When the resulting water temperature is lower than 20 ° C, it is heated by using steam, a heater or a heat exchanger, and when it exceeds 37 ° C, it is cooled by using a cooling tower or a heat exchanger. . These heating and cooling may be performed on the raw water or the activated sludge in the aeration tank.

A water temperature outside the above range is temporarily allowed,
In particular, when the inflowing BOD load is low, a lower water temperature is allowed, but in the case where, for example, 75% or more of the design capacity is processed, the period of deviation from the water temperature of the present invention is within 30% of one month. More preferably, it should be within 15%, and the period of continuously deviating from the water temperature of the present invention is within 7 days, and more preferably within 3 days.

In each aeration tank, a means for adjusting the amount of aeration is required so that dissolved oxygen (DO) can be detected without excess or deficiency, and a flow rate adjusting valve and a flow meter are usually used. At this time, the amount of oxygen required at each stage changes depending on the operating conditions, so it is necessary to periodically measure the DO of each stage of the aeration tank and adjust the amount of aeration. Therefore, it is preferable to install the air diffuser in each stage of the aeration tank with a sufficient capacity, and the total maximum oxygen supply capacity of the air diffusers in each stage of the aeration tank is more than that in the case where the present invention is not used. It is preferable to design so that the capacity is 10 to 80% larger, and more preferably 20 to 50% larger. However, since the total amount of required air does not change and only the distribution ratio changes, the capacity of the blower does not need to be particularly larger than the originally required air supply capacity.

The organic substance-containing water to be treated may be configured to flow into any stage of the aeration tanks arranged in series.
Usually, it is made to flow into the uppermost aeration tank. However, by partially injecting part of the raw water into the aeration tanks of the second and subsequent stages, the capacity of the air diffuser placed in the first stage is reduced, and the air diffuser with the optimal capacity for dissolution efficiency and construction is installed. You can also do it.

When such a split injection is carried out, as will be described later, the sludge concentrated and separated in the membrane dipping tank and returned to the aeration tank in a state before being mixed with the raw water and completely diluted. Since it becomes possible to retain the sludge, compared to the case where the entire amount of raw water is flown into the first aeration tank, the sludge concentration in the membrane immersion tank is kept the same while the sludge retention in the entire system is maintained. The amount can be kept high. As a result, there is also an effect of increasing the BOD volume load on the entire system without increasing the BOD sludge load.

When performing such split injection of raw water,
It is desirable to provide raw water supply means to the aeration tank of the second and subsequent stages, as well as means for adjusting the flow rate, a flow meter, and the like.

The sludge is usually returned from the last stage aeration tank to the first stage aeration tank, but the returned sludge may be divided and returned to the second and subsequent aeration tanks. The sludge returning means may be any means such as using a pump or utilizing a water level difference. The amount of sludge returned is about 0.5 to 10 times that of the inflowing raw water as is conventionally done, but the sludge concentration in each aeration tank is made as uniform as possible, while the power required for sludge return is increased. From the viewpoint of saving, it is preferable that the sludge return amount is 2 to 5 times the inflowing raw water amount.

In the present invention, the BOD sludge load is 0.15
It is preferably 0.40 kg-BOD / kg-VSS / day, particularly 0.20 to 0.35 kg-BOD / k.
It is preferably g-VSS / day. When the load is lower than this range, the conventional immersion membrane type activated sludge method can be used without adopting the present invention. If the load exceeds this range, the effects of the present invention will be exceeded, and dispersal bacteria or colloidal substances will be generated, causing membrane contamination.

A BOD sludge load outside the range of the BOD sludge load is also allowed if it is temporary, and a particularly low BOD sludge load has no adverse effect. However, when the low BOD sludge load continues for a long period of time, the sludge generation amount decreases, and the sludge concentration tends to decrease due to the progress of self-extinguishing of the activated sludge. In such a case, it is preferable to maintain the sludge concentration as much as possible, for example, by stopping the extraction of sludge and performing intermittent aeration to suppress self-extinguishing.

On the other hand, it is preferable that the sludge load exceeding the BOD sludge load range does not exceed 10 days or more, particularly preferably 4 days or more. Dispersed bacteria and colloid-like substances generated under high sludge load increase in quantity a few days after the sludge load increases, and when the high sludge load continues thereafter, the amount of generation tends to increase even more. is there. Therefore, if the sludge load of the present invention is returned to the range of the sludge load in the early stage when these membrane contaminants start to be generated, serious membrane contamination is often prevented.

In the present invention, the MLSS concentration in the membrane dipping tank is preferably 5,000 to 20,000 mg / L, and particularly preferably 8,000 to 15,000 mg / L.

As described above, the concentration of activated sludge on the membrane surface is prevented by increasing the amount of aeration from below the submerged membrane,
It is possible to achieve a higher sludge concentration, but in this case, as described above, the membrane swings or the membranes rub against each other, repeated stress is applied to the adhesive part of the membrane, the activated sludge itself or the activated sludge. Phenomena such as physical contact between the foreign matter and the film are promoted, the film cannot be separated from the support to exhibit the predetermined SS separation performance, or the strength of the film deteriorates and the film breaks, Deformation of the structure that forms the pores of the membrane reduces the number and area of pores that open on the surface, increasing the filtration pressure and increasing the sensitivity to the effects of membrane contaminants. The life is shortened.

On the other hand, in the present invention, such a problem that occurs when a method of increasing the MLSS concentration is adopted in order to aim at a device having a higher load and a lower construction cost, and the MLSS concentration is reduced. It provides a way to achieve high loads without raising. As a result, it is possible to prevent a reduction in the film life as described above, while achieving a device smaller than the conventional one.

When the MLSS concentration is lower than the above range, it does not directly cause the membrane fouling, so that the MLSS concentration below the above range is acceptable, but in this case, the amount of VSS retained in the entire system. And the sludge load tends to increase. As long as the sludge load is within the above range, a temporary low MLSS concentration does not cause any inconvenience.

Even when the MLSS concentration exceeds the above range, if the aeration blower has a margin, temporarily increase the amount of aeration from the lower part of the submerged film or increase the frequency of chemical cleaning. However, if such an operation is continued for a long time, the life of the membrane is shortened and the effect of the present invention is lost.
The period of operation at LSS concentration is preferably 2 in one year.
Within a month, more preferably within 3 weeks.

The present invention is effective by keeping the MLSS concentration in the membrane dipping tank low while keeping the sludge load high, but it is effective for removing organic matter when a large amount of SS flows in from the raw water. SS other than simple microorganisms stay in the system,
It will increase the MLSS concentration in the membrane immersion tank. There are inorganic SS and VSS in the SS that accumulates like this,
In particular, when such an inactive VSS flows in, it becomes difficult to distinguish the VSS derived from the microorganism effective for the original treatment by analysis. As described above, when VSS that is not effective for treatment is accumulated in the system, the proportion of microorganisms effective for treatment in the substances measured as VSS in the aeration tank decreases. Therefore, even if operated within the above sludge load range, VS that is effective for treatment
Since the sludge load on S is high, the sludge load limit is low.

Further, even when the inflowing SS is an inorganic SS, the limit of the MLSS concentration in the membrane dipping tank is almost the same although there is a tendency that a slightly higher value is allowed, while the sludge VSS is increased. Since the / SS ratio decreases, in order to maintain the same sludge load as compared with the case where such SS does not flow, the inflowing BOD load must be lowered, and in this case, the device according to the present invention is used. The miniaturization of can not be achieved.

In order to avoid such a phenomenon and to realize a small-sized apparatus, it is desirable that SS derived from raw water is not allowed to flow in as much as possible, and the ratio of SS to soluble BOD in raw water is 0 to 0.5 g-. It is preferably SS / g-BOD, more preferably 0 to 0.2 g-SS / g-BOD.
In order to achieve such a raw water SS / BOD ratio, prior to the activated sludge treatment, if necessary, coagulation treatment or the like is performed, and then SS in the raw water is separated and removed by means such as sedimentation or pressure floating. Is preferred.

In the present invention, the material of the dipping membrane used in the membrane dipping tank is not particularly limited, and various materials such as conventionally known polyethylene, polysulfone, polyether sulfone, polyvinylidene fluoride, cellulose acetate and derivatives thereof can be used. Applicable. Among these, from the viewpoint of the membrane separation performance and the effect of preventing membrane contamination, polyethylene, chlorinated polyethylene, and polyolefin that are hydrophilized are particularly preferable. The shape of the membrane may be any conventionally known shape such as a hollow fiber membrane, a tubular (tubular) membrane, or a flat membrane.

The separation performance (pore size) of the separation membrane is preferably 0.01 to 0.4 μm, more preferably 0.02 to 0.2 μm for the above-mentioned reason.

The effective film area of the dipping film is calculated based on the flux suitable for the film to be used, but the flux is generally 0.1 to 1.5 m ³ / m ² / day, and particularly, ^{2 to} 0.7 m ³ / m ² / day is good.

As in the conventional case, the amount of aerated air in such a submerged membrane is preferably ^{30 to} 250 Nm ³ / hr per bottom area of the membrane module or bottom area (m ² ) of the aeration section of the membrane immersion tank, and particularly 40. -100 Nm < ³ > / hr is suitable. The air diffusing tube provided in the lower part of the immersion membrane may be a perforated pipe, a fine air bubble diffusing tube, or any other conventionally known diffusing tube, but normally a 10 to 50 mmφ pipe with a 3 to 10 mmφ hole is used, and a diffusing tube is also used. A suitable air diffuser cleaning mechanism is provided to prevent pore clogging.

As in the conventional case, the membrane dipping tank is preferably of a type in which a swirl flow is generated by an air lift action by providing an aeration part and a non-aeration part. Particularly, in order to promote the swirl flow, the aeration part and the non-aeration part are preferably used. It is preferable to partition the part with a baffle plate.

In the present invention, the permeated water of such an immersion membrane is taken out as treated water. There is no particular limitation on the method of taking out the treated water, and it may be withdrawn by a pump.
You may take out using the water pressure in a membrane immersion tank. When taking out the membrane-permeated water, any of a continuous taking-out method, an intermittent taking-out method, a method of intermittently back-flowing fresh water or a chemical solution during membrane filtration and back-washing, etc. may be used. The intermittent filtration method in which a filtration stop time of 1 to 3 minutes is provided every time filtration is continued for 5 to 30 minutes is preferable.

The method for cleaning the immersion membrane is as follows: the membrane module is lifted from the membrane immersion tank and moved to a chemical cleaning water tank to perform chemical cleaning, as described in JP-A No. 11-28468. After extracting the sludge, a method of introducing a cleaning chemical solution into the membrane dipping tank for chemical cleaning, a method of performing a membrane cleaning by allowing the cleaning chemical solution to flow backward from the permeate side while the membrane module is immersed in the activated sludge, etc. Any known method can be used.

In the present invention, the prevention of film contamination results in
In general, the chemical cleaning of such a membrane can be performed once every 2 to 6 months for stable treatment.

In the present invention, it is preferable that at least one of the plurality of aeration tanks holds the microorganism-attached carrier in terms of the growth of the above-mentioned microorganisms and the suppression of dispersed bacteria.

The carrier used here is a cube,
Regardless of the shape such as cylindrical, spherical, gear, etc., the material is nylon, urethane, PVA (polyvinyl alcohol), PE
Any known material such as G (polyethylene glycol) and cellulose may be used. The specific gravity of the carrier is preferably about 1.0 to 1.1 in order to improve the stirring in the aeration tank, but is not particularly limited. As for the size of the carrier, the long side or the diameter is 1-2.
Those having a diameter of 0 mm can be used, and those having a diameter of 2 to 6 mm are particularly preferably used.

It is desirable that the raw water does not flow into the aeration tank into which the carrier is fed as much as possible, but it is not necessary to completely prohibit the introduction of the raw water, and therefore a raw water inflow means may be provided.

The amount of the carrier to be charged is based on the total amount of the aeration tank.
The apparent volume is preferably 1 to 50%, 2 to 20
% Is more preferable.

The aeration tank containing the carrier is provided with a carrier separating means in order to prevent the carrier from flowing out.

As a means for separating the carrier, it is effective to use a wedge wire screen having an opening smaller than that of the carrier. In order to prevent the carrier from blocking the wedge wire screen, this screen is preferably installed at a place where the flow is strong such as the upper part of the swirling flow, or aeration is performed from the lower part of the screen. The activated sludge from which the carrier has been removed through this screen is sent to the aeration tank of the next stage.

As described above, the load of soluble BOD flowing into the aeration tank to which this carrier is added is 0 to 0.1 kg-B with respect to the VSS amount held in this aeration tank.
OD / kg-VSS / day, more preferably 0 to 0.
It is preferably set to 05 kg-BOD / kg-VSS / day.

In the present invention, foaming tends to occur more easily than in the conventional method. This is because the sludge load is higher than that in the conventional method, and the load is higher than average in the water tank into which raw water mainly flows. It is likely due to the microbial effects that occur. Further, the foaming amount in the multistage aeration tank is often different. For this reason, it is desirable to provide means for efficiently defoaming any aeration tank. For example, a defoaming agent injection means is provided in the aeration tank, or the upper part of the aeration tank is covered with the exhaust parts of all the aeration tanks concentrated in one section.
It is desirable to provide a mechanical defoaming means such as a defoaming blade, a spray, or a heat ray in the exhaust portion. When providing an antifoaming agent injection means, it is desirable to easily select an aeration tank to which an antifoaming agent is added to each aeration tank, and to have a structure in which the antifoaming agent can be concentrated in an aeration tank with severe foaming, For example, it is preferable to use a means such as injecting an antifoaming agent through a flexible pipe such as a vinyl hose, or making it possible to easily switch the injection destination of the antifoaming agent with a valve.

However, since the degree of foaming differs depending on the water quality of the raw water, the defoaming means is not always necessary and may be unnecessary in the present invention. Examples of wastewater species that require defoaming include wastewater containing proteins and oils, especially food factory wastewater.

The quality of the treated water obtained in the present invention, that is, the water quality of the membrane permeated water taken out from the immersion membrane, is as follows.
The ammoniacal nitrogen concentration is preferably 0 to 3 mg-N / L.

In the conventional submerged membrane activated sludge method, the sludge retention time is, for example, 15 in order to operate with a relatively low sludge load.
Since the cells that have been grown for a long time or more in the aeration tank do not flow out into the treated water, an environment in which nitrifying bacteria having a slow growth rate can easily grow is provided. For this reason, organic nitrogen and ammonia nitrogen in raw water were often oxidized to nitrate nitrogen.

In the present invention, since the sludge load is increased and the operation is performed, the SRT may decrease, nitrifying bacteria may not grow sufficiently, and ammonia nitrogen may remain. If ammonia nitrogen remains in this way, when measuring the BOD of the treated water, B as so-called N-BOD is obtained.
The BOD value of the treated water may increase due to detection in the OD. Usually, for 1 mg-N / L of ammonia nitrogen,
BOD is detected up to 4.6 mg / L.

On the other hand, when the immersion membrane type activated sludge method, which is more expensive than the ordinary activated sludge method, is adopted, a higher quality of treated water is often required, and the guaranteed value of the treated water BOD is usually It is often 20 mg / L or less, and further 10 mg / L or less, or 5 mg / L or less, which is a water quality that cannot be handled by the ordinary activated sludge method.

Therefore, residual ammoniacal nitrogen in the treated water is not preferable because there is a risk that the treated water BOD will exceed the guaranteed value.

From the above, in the present invention, it is preferable that the concentration of ammonia nitrogen in the treated water is adjusted to 0 to 3 mg-N / L by favorably promoting the nitrification reaction.
Therefore, the pH is adjusted to the range of 7 to 8.5, the water temperature is kept high within the range of the present invention, and the DO of each part of the aeration tank is set to 1 mg / L or more, preferably 2 mg / L or more,
It is preferable to promote the nitrification reaction by incorporating an operation of keeping the SRT for 5 days or longer, more preferably 8 days or longer, if necessary. However, if SRT is lengthened, M in the aeration tank
Care must be taken that the MLSS concentration does not exceed the scope of the present invention as the LSS concentration increases.

In the present invention, the organic substance-containing water to be treated is all industrial effluent that can be treated with activated sludge, such as industrial effluent, sewage, and human waste. According to the present invention,
Such organic substance-containing water can be efficiently treated under a high load.

The apparatus for treating organic matter-containing water of the present invention will be described below with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of the organic substance-containing water treatment apparatus of the present invention.

In the treatment apparatus of FIG. 1, raw water is introduced through a pipe 31, heated to a predetermined water temperature by a heat exchanger 50, and then fed into an aeration tank (first aeration tank) 51 at the most upstream stage. It In FIG. 1, the raw water is heated by exchanging heat with the heating steam from the pipe 32 in the heat exchanger 50, but the steam may be blown directly into the raw water introducing pipe 31 to heat the raw water. Further, in FIG. 1, the raw water pipe 31 and the first aeration tank 51 are provided with thermometers 31T and 51T, and the raw water after heating and the water temperature of the first aeration tank 51 are measured, but only one of them is measured. It may be a temperature measurement. 31F is a flow meter, 32V ₁ is a flow rate adjusting valve, and 32V ₂ is an automatic valve.

The aeration tank is composed of five stages, and the last stage aeration tank (fifth aeration tank) 55 is a membrane dipping tank. The membrane dipping tanks 55 are provided in parallel in four tanks so that they can be switched during chemical cleaning. That is, there are three more membrane dipping tanks not shown,
It is provided in parallel with the membrane immersion tank 55.

From the first aeration tank 51 to the second aeration tank (second
Aeration tank) 52, third aeration tank (third aeration tank) 53, 4
Up to the aeration tank (fourth aeration tank) 54 of the stage, the water level difference is 50 to
Sludge is transferred by overflow at a drop of about 500 mm to prevent backflow of sludge. Each aeration tank 51-55
The air diffusers 51S, 52S, 53S, 54S, 55 respectively.
S is provided, but the first aeration tank to the fourth aeration tank 51 to
The diffuser tubes 51S to 54S of 54 facilitate the distribution of the diffused air amount by making the water depths substantially the same. Each air diffuser 5
1S, 52S, 53S, 54S, 55S, pipe 40
And 41, 42, 43, 44, 45 for supplying aeration air. 41V, 42V, 43V, 44V, 45V
Is a flow control valve, 41F, 42F, 43F, 44F, 45
F is a flow meter.

A pH meter 51P is provided in the first aeration tank 51, and an acid or alkali is manually or automatically added as necessary to keep the pH at 7 to 8.5, for example.

A 3 mm square sponge carrier 56 is put into the third aeration tank 53, and a wedge wire screen 57 having a 1 mm opening is provided at the outlet of the third aeration tank 53 to prevent the carrier 56 from flowing out. ing. In order to prevent the carrier 56 from clogging the screen 57 and preventing water from flowing under the screen 57, a dedicated diffuser pipe 57S is provided so that the screen 57 is constantly aerated. In addition, a level switch 53L is provided in this water tank in order to cope with the case where the screen is blocked, and an interlock is incorporated to emergencyly stop the inflow of the raw water and the returned sludge when the water level rises abnormally.

In the fourth aeration tank 54, a pump 33P, a flow meter 33F and an automatic valve 33V for withdrawing excess sludge.
The sludge extraction pipe 33 is provided.
This is because when the sludge in the first and second aeration tanks 51 and 52 is drawn out, the substrate that has not been sufficiently oxidized and decomposed is often accumulated inside the bacterial cells, and thus the decomposition easily progresses in the sludge storage tank or the like. Is. On the other hand, when the membrane is soaked in the membrane dipping tank 55, the sludge cannot be drawn out while the membrane is being cleaned with chemicals. Therefore, the excess sludge is drawn out from the fourth aeration tank 54 immediately before the membrane soaking tank 55. The extracted excess sludge is transferred to a sludge storage tank or dehydrator.

The fourth aeration tank 54 is provided with an underwater pump 54P and an air lift pump for transferring the sludge to the membrane immersion tank 55, and the sludge from the fourth aeration tank 54 is connected to the pipe 3
4, pipes 35A, 35B, 35C, 3 through the distribution tank 58
From 5D, it is distributed and transferred to each film immersion tank 55 at a predetermined flow rate. 35V _A , 35V _B , 35V _C and 35V _D are automatic valves.

In the membrane dipping tank 55, the dipping membrane module 59 is provided.
Is dipped, and an air diffuser 55S is provided below the dipped membrane module 59. Further, a baffle plate 60 is provided around the submerged membrane module 59, and the inside of the tank is partitioned into an aeration part and a non-aeration part.

In the membrane immersion tank 55, a predetermined amount of membrane permeated water is taken out as treated water and discharged from the pipe 36. The amount of sludge transferred from the fourth aeration tank 54 is larger than the amount of discharged treated water, and the sludge not discharged as treated water is concentrated and returned to the first aeration tank 51 through the pipe 39 due to overflow. . Since the water level in the membrane immersion tank 55 is almost constant in this way, the water level in the fourth aeration tank 54 changes mainly when the amount of water in the entire system increases or decreases. For this reason,
The fourth aeration tank 54 is provided with a level switch 54L,
When the water level in the fourth aeration tank 54 is lowered, the membrane filtration is stopped until the water level is restored, and when the water level is raised, the raw water input is stopped until the water level is restored. There is.

As the pump 36P for discharging the membrane-treated water, a self-priming spiral pump or the like is used. When air or the like is mixed into the suction side of the pump, a predetermined capability cannot be exhibited, so that the automatic valve 36V ₂ on the suction side is closed so that the air or the like does not flow backward when the pump is stopped.
36PI is a pressure gauge, 36V ₁ is a flow rate adjusting valve, and 36F is a flow meter.

When cleaning the immersed membrane module 59 of the membrane immersion tank 55, the inflow of sludge from the distribution tank 58 is stopped, and then the sludge in the corresponding membrane immersion tank 55 is drawn out, and rinsed if necessary, and then piped. A chemical solution is added from 37, and cleaning is performed while aeration is also used as necessary. After the cleaning is completed, the chemical solution is drawn out from the membrane immersion tank 55 through the pipe 38, rinsed if necessary, and then the inflow of sludge from the distribution tank 58 is restarted, and after reaching a predetermined water level, the membrane filtration is restarted. 37
V and 38V are automatic valves.

[0102]

EXAMPLES The present invention will be described more specifically with reference to Examples, Comparative Examples and Experimental Examples below.

Example 1 As shown in FIG. 1, three aeration tanks were provided in series, and the treatment apparatus in which the immersion membrane module 6 was immersed in the last-stage aeration tank (membrane immersion tank) 5 was used to treat organic substance-containing water. I went. The volumes of the aeration tanks 1 to 3 are as shown in Table 1, and the pore size of the separation membrane of the submerged membrane module 6 is as shown in Table 1.

In this treatment apparatus, raw water is introduced from the pipe 11 into the aeration tank (first aeration tank) 1 at the front stage and aerated, and after being treated with activated sludge, it flows into the second aeration tank 2 and further aerated. The activated sludge is treated and transferred to the membrane immersion tank 5 through the pipe 12. The permeated water that has undergone membrane separation in the membrane immersion tank 5 in the immersion membrane module 6 is taken out as treated water from the pipe 13, and the sludge separated and concentrated is returned to the first aeration tank 1 via the pipe 14. Excess sludge is extracted from the second aeration tank 2 through the pipe 15 as needed.

The first aeration tank 1, the second aeration tank 2 and the membrane immersion tank 5 are provided with air diffusion tubes 1S, 2S, 5S for air aeration, respectively, and the air diffusion tubes 1S, 2S are provided with pipes 16, 1 respectively.
Air is sent from 7,18. Further, air is supplied from the pipe 21 to the air diffuser 5S.

In the membrane immersion tank 5, an air diffuser 5S is provided below the immersion membrane module 6, and a baffle plate 7 is provided around the immersion membrane module 6 to partition the inside of the tank into an aeration part and a non-aeration part. ing. The bottom areas of the aerated part and non-aerated part were made equal. Further, the opening areas above and below the baffle plate 7 are set so as not to disturb the flow of the swirling flow circulating in the aeration section and the non-aeration section.
It was made equal to the bottom area of the aeration section.

In FIG. 2, P ₁ is a raw water pump, P ₂ is a treated water pump (self-contained pump), P ₃ is a sludge return pump, and P ₄ is a sludge drawing pump. Also, 13F, 17F, 1
8F and 21F are flow meters, 13P is pressure gauges, 17V and 18
V and 21V are flow rate adjusting valves.

As raw water, a synthetic wastewater mainly containing fish meat extract and liquid sugar was used. The quality of this synthetic wastewater is BOD1,
000-1,500 mg / L, and the SS / BOD concentration ratio is 0-0.05. The water temperature is 20 to 25 ° C, and the sludge load is 0.3 kg-BOD / kg-VSS as shown in Table 1.
/ Day, and the MLSS concentration in the membrane dipping tank was set to around 11,000 mg / L as shown in Table 1. Since the sludge of 4 times the amount of raw water was returned from the membrane immersion tank 5 to the first aeration tank 1, the MLSS concentration other than the membrane immersion tank 5 was about 80% of the MLSS concentration of the membrane immersion tank 5. Sludge removal is performed from the second aeration tank 2 and the sludge concentration in the membrane immersion tank 5 is 14,000 mg.
/ L or less. Further, the aeration in the aeration section of the membrane dipping tank 5 is 75 to 100 Nm per aeration section bottom area.
^{3 -air} / ^{m 2} - and the bottom surface / hr.

The permeated water side of the immersed membrane was sucked by a self-contained pump P ₂ , and after performing filtration for 8 minutes, intermittent filtration was performed in which it was stopped for 2 minutes. A pressure gauge 13P was provided in the treated water pipe 13, and the pressure difference between when the filtration was performed and when the filtration was stopped was measured as the filtration differential pressure of the membrane. The average flux is 0.4 m ³ / m ² / d
ay and the obtained filtration resistance is flux 0.4 m ³ /
It was corrected to m ² / day and a water temperature of 25 ° C.

The filtration pressure difference increased almost linearly. The increase rate (kPa / day) of the filtration differential pressure was determined as the membrane fouling rate, and the results are shown in Table 1. Moreover, the filtration differential pressure is 15 kPa.
It is assumed that the chemical cleaning is performed when the temperature rises, and the chemical cleaning interval is predicted and shown in Table 1.

The average water quality of the obtained treated water was as shown in Table 1.

The synthetic wastewater was mixed with 0.1 kg-BOD.
Foaming does not occur particularly when the same treatment is carried out with a sludge load of about / kg-VSS / day, whereas foaming was observed in this test, so a higher alcohol antifoamer was added to the raw water. In contrast, foaming was suppressed by adding 1 to 10 ppm.

Example 2 As shown in FIG. 3, five aeration tanks were provided in series, and the treatment apparatus in which the immersion membrane module 6 was immersed in the last aeration tank (immersion tank) 5 was used and the conditions shown in Table 1 were used. Then, the same synthetic wastewater treatment as in Example 1 was performed, and the membrane fouling rate, chemical cleaning interval, and treated water quality were examined, and the results are shown in Table 1.
The processing conditions other than those shown in Table 1 are the same as those in the first embodiment.

In this embodiment, the raw water is the first aeration tank 1 and the second aeration tank.
After being sequentially treated in the aeration tank 2, the third aeration tank 3 and the fourth aeration tank 4, the membrane separation tank 5 performs membrane separation, the permeated water is taken out, and the concentrated separation sludge is returned to the first aeration tank 1. It
Moreover, the excess sludge is drawn out from the fourth aeration tank 4.

In FIG. 3, members having the same functions as those shown in FIG. 2 are designated by the same reference numerals, and their description will be omitted. 3S and 4S are air diffusers, 19 and 20 are these air diffusers 3
It is a pipe for sending air to S, 4S, 19F, 20F
Is a flow meter, and 19V and 20V are flow rate adjusting valves.

COMPARATIVE EXAMPLE 1 As shown in FIG. 4, only the membrane dipping tank 5 was provided, and the treatment apparatus for performing activated sludge treatment and membrane separation in one aeration tank was used under the conditions shown in Table 1 in Example 1. The same synthetic wastewater treatment as the treated one was conducted, and the membrane fouling rate, chemical cleaning interval and treated water quality were examined, and the results are shown in Table 1. The processing conditions other than those shown in Table 1 are the same as those in the first embodiment.

In FIG. 4, members having the same functions as those shown in FIG. 2 are designated by the same reference numerals, and their description will be omitted.

[0118]

[Table 1]

As is clear from Table 1, in Comparative Example 1 in which the aeration tank is one tank, chemical cleaning is required once every two months, but in Example 1 in which three aeration tanks are provided, In Example 2 in which five aeration tanks are provided, the cleaning may be performed once every about 3.5 months, and the chemical cleaning may be performed once every about 5.5 months to prevent the membrane from being contaminated. Can be significantly reduced.

Comparative Example 2 In Example 1, the water temperature was set to 15 ° C. to less than 20 ° C.
Sludge load 0.17 to 0.23 kg-BOD / kg-VS
S / day, volume load 1.5-2.0 kg-BOD / m
³ / day, MLSS concentration of membrane dipping tank 10,000 to 1
When the raw water was treated in the same manner as in Example 1 except that the water was passed under the condition of 2,000 mg / L, the membrane fouling progressed violently after 2 to 4 weeks from the start of the operation, and after 1 week. The required speed was one or more washes. The membrane fouling rate was 2.7 kPa / day and the chemical cleaning interval was expected to be 6 days. Therefore, it was judged that it is not practical to apply this sludge load at a water temperature of less than 20 ° C.

Example 4 In Example 2, an apparent volume of 40 L of 3 mm square nylon sponge was added to the third aeration tank 3 as a carrier for adhering microorganisms, and a load of 0.33 to 3 which was higher than the sludge load of Example 2 was added.
Water was passed under the conditions of 0.38 kg-BOD / kg-VSS / day, volume load 2.8-3.5 kg-BOD / m ³ / day, and membrane immersion tank MLSS concentration of 10,000-14,000 mg / L. Raw water was treated in the same manner as in Example 2 except for the above. The volume of the charged carrier is about 6% of the total volume of the aeration tank. At the outlet of the 3rd aeration tank where the carrier is put, a 1m opening is provided to prevent the carrier from flowing out.
A wedge wire screen of m was provided, and a diffusing tube was provided below the screen to aerate, thereby preventing the sponge from condensing and clogging the screen.

As a result, the membrane fouling is effectively suppressed, the membrane fouling rate is 0.1 kPa / day, and the chemical cleaning interval is 150 days ( Once every 5 months).

Experimental Example 1 In order to investigate the effect of the pore size of the immersion membrane, in Comparative Example 1 in which the aeration tank was one, the pore size was 0.03 μm,
Sludge load of 0.1 μm and 0.4 μm was used.
24-0.42 kg-BOD / kg-VSS / day,
Volume load 1.9 to 4.7 kg-BOD / m ³ / day,
Membrane immersion tank MLSS concentration 9,400 to 13,000 mg /
When raw water was treated as L in the same manner as in Comparative Example 1,
The membrane fouling rate and expected chemical cleaning frequency are as shown in Table 2, and the immersion membrane with a pore size of 0.4 μm has a pore size of 0.1 μm.
Contamination progresses at a rate 8 times faster than the immersion film of
It was necessary to wash the chemical more than once. On the other hand, pore size 0.03
In the case of the submerged membrane of μm, almost the same result as that of the submerged membrane of 0.1 μm in pore size was obtained, and it was confirmed that the limit of the membrane pore size applicable to such a high sludge load condition is around 0.4 μm. .

[0124]

[Table 2]

[0125]

As described above in detail, according to the method and apparatus for treating organic matter-containing water of the present invention, in treating organic matter-containing water by the submerged membrane type activated sludge method, the MLSS concentration in the membrane submerged tank is increased. Therefore, it is possible to improve the BOD treatment capacity per unit area of the aeration tank by increasing the sludge load without causing deterioration of the membrane life and reduction of the aeration efficiency due to the increase of the aeration amount in the membrane immersion tank. it can. Therefore, the aeration tank can be downsized, which can reduce the construction cost and the operating cost, and can reduce the installation area.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of a treatment apparatus for organic matter-containing water of the present invention.

2 is a system diagram showing a processing apparatus used in Example 1. FIG.

FIG. 3 is a system diagram showing a processing apparatus used in Example 2.

FIG. 4 is a system diagram showing a processing apparatus used in Comparative Example 1.

[Explanation of symbols]

1st aeration tank 2 Second aeration tank 3rd aeration tank 4th aeration tank 5 membrane immersion tank 6 Immersion membrane module 7 baffle board 1S, 2S, 3S, 4S, 5S Air diffuser 51 First Aeration Tank 52 Second aeration tank 53 Third aeration tank 54 Fourth Aeration Tank 55 Membrane immersion tank 56 carrier 57 screen 58 distribution tanks 59 Immersion Membrane Module 60 baffle board

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4D003 AA12 AB02 BA02 CA07 CA10                       EA14 EA19                 4D006 GA07 HA93 KA01 KA12 KA44                       KB22 KE12R KE13R MA01                       MA02 MA03 MA22 MC18 MC22                       MC26 MC29 MC63 PB08 PC62                 4D028 AA04 AA07 AA08 AC03 BB02                       BC14 BC17 BC26 BD10 BD11                       CA01 CA05 CA06 CA07 CB02                       CC01 CC07 CC09 CD01

Claims (11)

[Claims] 1. A method for treating water containing organic matter, comprising: a biological treatment step of mixing raw water containing organic matter with activated sludge to form a mixed solution; and a submerged membrane separation step of separating treated water from the mixed solution with an immersion membrane. In the biological treatment step, the raw water is passed through at least three treatment tanks arranged in series, and the activated sludge treatment is performed by adjusting the water temperature of the mixed solution to 20 to 37 ° C. A method for treating organic matter-containing water. 2. The submerged membrane has a nominal separation pore size of 0.01-0.
It is 4 micrometers, The processing method of the organic substance containing water of Claim 1 characterized by the above-mentioned. 3. The BOD sludge load of activated sludge treatment is 0.1.
5 to 0.40 kg-BOD / kg-VSS / day is set, The organic substance containing water treatment method of Claim 1 or 2 characterized by the above-mentioned. 4. The method for treating water containing organic matter according to claim 1, wherein the MLSS concentration in the immersion membrane separation step is 5,000 to 20,000 mg / L. 5. The method for treating organic matter-containing water according to claim 1, wherein a defoaming agent is added to at least one of the treatment tanks. 6. Ammonia nitrogen concentration of treated water is 0 to 3
It is mg / L, The processing method of the organic substance containing water of any one of Claim 1 thru | or 5 characterized by the above-mentioned. 7. The ratio of SS concentration to BOD concentration of raw water (SS
/ BOD) is 0 to 0.5, The method for treating organic matter-containing water according to any one of claims 1 to 6, wherein. 8. The method according to any one of claims 1 to 7, wherein at least one treatment tank holds a microorganism-attached carrier.
The method for treating organic matter-containing water according to any one of 1. 9. A treatment tank holding at least three activated sludges arranged in series, a submerged membrane module for separating treated water immersed in at least one of the treatment tanks, and the treatment tank An apparatus for treating water containing organic matter, comprising: raw water supply means for supplying raw water containing organic matter to at least a part of the submerged membrane incorporated in the submerged membrane module, which has a nominal separation pore diameter of 0.01 to 0.4 micrometer. And the effective total volume of the treatment tank is a volume satisfying 1.3 to 4 kg-BOD / m ³ / day with respect to the BOD of the raw water supplied, treatment of water containing organic matter. apparatus. 10. The treatment apparatus for organic matter-containing water according to claim 9, further comprising means for controlling the temperature of the raw water or the liquid in the treatment tank. 11. The method according to claim 9 or 1, wherein at least one treatment tank holds a microorganism-attached carrier.
The organic substance-containing water treatment device according to 0.