JPH0824885A - Biological treatment of waste water - Google Patents

Abstract

PURPOSE:To treat even bulking sludge with the effective use of a biological waste water treatment method by causing an active sludge in which filiform microbes are predominant to come into contact with waste water by mixing, and filtering the mixture by a precision filtration membrane. CONSTITUTION:Waste water 1 discharged from a refreshing drink manufacturing plant is stored once in an aeration tank 2 containing seed sludge in which filiform microbes are predominant. Next, the sludge mixed with the water 1 is aerated by blowing in air from the bottom of the aeration tank 2, and N salt 7 and P salt 8 are added to and mixed with an obtained mixed liquid 9. After that, the mixed liquid 9 is sucked or decompressed through a precision filtration membrane 11 immersed in the aeration tank 2, and is discharged as a treated water 4 after filtration. In this case, the concentration of dissolved oxygen in the mixed liquid is 1mg/L or less or at least 3mg/L, and if the waste water is in a nutrient-poor state, it is treated by maintaining a nutritive balance of the waste water at the BOD:N:P of 100:<=1:>=0.1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biological treatment method for wastewater such as industrial wastewater, sewage and night soil, and a biological treatment method for wastewater in purification of closed system such as lakes and river water.

[0002]

2. Description of the Related Art As a conventional biological treatment method for wastewater, an activated sludge method using a settling sludge tank as shown in FIG. 2 has been widely put into practical use. The biological treatment method of wastewater according to the prior art will be described with reference to FIG. 2. 1 is industrial wastewater or wastewater such as sewage and night soil, 5 is air for mixing and stirring (hereinafter referred to as “aeration”), and 2 is an aeration tank. By blowing air 5 from the lower part, a tank for aeration and mixing contact of the waste water 1 with the agglomerates of aggregates of microorganisms called activated sludge (hereinafter referred to as “floc”) is brought into contact. 7 and 8 are N salt and P salt to be injected into the aeration tank 2, 3 is a settling tank for precipitating and separating the treated water 4 and the activated sludge after aeration in the aeration tank 2, and 6 is an activated sludge settled in the settling tank 3. The sludge is returned to the aeration tank 2 and is used again for contact with the wastewater 1.

N added during biological treatment of wastewater
Most of P and P remain in the treated water, which promotes eutrophication at the discharge destination, and N and P must be reduced as much as possible. On the other hand, when N and P are reduced,
There is a dilemma of promoting the generation of bulking sludge. Therefore, the conventional biological treatment method always requires an apparatus for removing N and P by a nitrification denitrification method or a condensation precipitation method as a post-treatment.

In the conventional activated sludge method, bulking is often one of the causes of serious damage. The term "bulking" is used here in a broad sense to refer to "a condition in which the settling property of activated sludge deteriorates and it cannot be separated by natural settling". Has deteriorated. "

Therefore, if activated sludge cannot be separated from water and recovered, it cannot be used in a biological treatment method of wastewater. Therefore, if bulking occurs once, a serious obstacle to the treatment will occur. Is brought.

By the way, there have been many studies on the cause of the bulking and its countermeasure, but the causes of the phenomenon are roughly classified into three types due to poor condensability, decrease in specific gravity and decrease in compaction. it can. In many cases, the phenomenon of poor condensability and deterioration of settling property due to decrease in specific gravity is relatively easy to determine and easy to deal with. However, the cause of the decrease in compaction compared to these is very complicated because the microorganisms are directly involved, and a fundamental solution has not been found.

There are two types of "decrease in compaction" phenomenon, filamentous bulking and non-filamentous bulking, and "filamentous bulking" is the flora of activated sludge injection (of various microorganisms). It means that the filamentous microorganisms have become predominant due to the change of (the proportion of each bacterium).
"Non-filamentous bulking" means floc-forming bacteria (Zoogl
It is produced when a large amount of highly viscous polysaccharide is accumulated as a metabolite of (ea).

However, the causes of bulking are diverse, and because they are intricately related to each other, they have not yet been sufficiently clarified and it is difficult to prevent them. Therefore, if bulking occurs once,
There is no fundamental deciding factor to remove bulking, and currently there is no alternative but to replace bulking sludge with normal activated sludge. In addition, due to the characteristics of wastewater, bulking is likely to occur again when replaced with normal activated sludge.

[0009]

The present invention can effectively use bulking sludge that cannot be fundamentally removed once it is generated, and can effectively use the bulking sludge that has been artificially generated. It is an object of the present invention to provide a biological treatment method of wastewater which is actively used and has better water quality than general activated sludge treated water in which floc-forming bacteria are dominant.

[0010]

[Means for solving the problem] "Bulking sludge" is
Although it causes serious obstacles to the operation of natural sedimentation separation, the quality of the supernatant water of bulking sludge is much more transparent and has less suspended solids (SS) than that of general activated sludge treatment.
Very little D and COD. The present inventors focused their attention on the excellent characteristics of bulking sludge, which has hitherto been regarded as the greatest problem in biological treatment, and as a result of earnest research, they have completed a method of positively utilizing it. In order to solve the above-mentioned problems in the biological treatment method of wastewater, the present invention comprises mixing activated sludge in which filamentous microorganisms are dominant and contacting wastewater, and contacting the mixture with a microfiltration membrane. Characterize.

[0011]

In the biological treatment method for wastewater according to the present invention, as described above, the wastewater is mixed and brought into contact with activated sludge in which filamentous microorganisms generated naturally or artificially are dominant. The following effects occur.

(1) N and P are put into an oligotrophic state, and /
Alternatively, the dissolved oxygen concentration of the mixed solution (hereinafter referred to as “DO”)
Filamentous microorganisms proliferate predominantly by aeration to a microaerobic state of 0.1 to 0.5 mg / l or over-aeration of 3.0 mg / l or more. (2) Activated sludge, in which filamentous microorganisms have become the dominant species, is contained in its matrix (aggregate in which microorganisms are entwined with each other).
Entraps fine suspended matter and filamentous microorganisms in wastewater.

(3) The filamentous microorganisms promote autooxidation by placing the aeration mixture in an aerobic atmosphere. Also, by placing N and P as nutrient sources in an extremely low oligotrophic state, autooxidation is further promoted. (4) The MLSS concentration (suspended substance concentration) of the mixed solution is 60 because the growth rate of filamentous microorganisms and the autooxidation rate are almost balanced.
Equilibrium is reached at 00-15000 mg / l.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 showing a system diagram of an embodiment of the present invention.
It will be specifically described based on. Here, as a representative example, the case where the wastewater is an industrial wastewater of a soft drink will be described, but the present invention is not limited to this, and the wastewater of the food industry such as dairy industry, brewing, canned seafood, and petrochemicals such as ethylene and butanol The same applies to wastewater such as.

1 is waste water discharged from the soft drink factory. The wastewater 1 is once stored in the aeration tank 2 but the aeration tank 2
The seed sludge 13 in which the filamentous microorganisms are predominant is put in and mixed (not shown in FIG. 1) in advance, and air 5 is blown from the lower part of the aeration tank 2 to aerate to prepare a mixed solution 9. Further, N salt 7 and P salt 8 are added to and mixed with the mixed solution 9, and then filtered by suction or reduced pressure with a filtration pump 10 through a microfiltration membrane 11 immersed in the aeration tank 2, Treated water 4 is obtained. Here, 12 is a timer used for controlling the start / stop of the filtration pump 10.

The waste water 1 has a volumetric load of 0.5 to 1.5 kg / m ³
Inject it into the aeration tank 2 so that it becomes a day. This is because in recent soft drink factories, due to the production of many kinds of beverages with the diversification of consumers' tastes, the components of wastewater pollutants (BOD and COD, etc.) are changed from single to complex. It has been changing, and its BOD concentration is 1000-2000 mg / l
As a result, it tends to be relatively higher than in the past, which is one of the reasons why bulking easily occurs.

Here, in order to artificially generate the bulking sludge, BOD: N: P = 100: 1 to 0.5: 0.1 to 0.05 of poor nutrition for at least 4 to 7 days after the start of the passage of the wastewater 1. It is necessary to inject the N salt 7 and the P salt 8 into the aeration tank 2 so as to be in the state. Naturally, it is not necessary to add N and P to industrial wastewater, sewage, etc. in which N and P as nutrient sources are contained in the above proportions.

Specific examples of the N salt 7 include urea and ammonium sulfate. Ammonium salts such as ammonium chloride and aqueous ammonia are used. As the P salt 8, specifically, phosphates such as dipotassium phosphate, disodium phosphate, monopotassium phosphate, monosodium phosphate, and ammonium phosphate can be used, in which case water-soluble salts are used. Preferably.

The sewage or wastewater treatment facility which is already in operation is mixed in advance with the aeration tank 2 as activated sludge so that the MLSS concentration in the aeration tank 2 is 500 to 1000 mg / l. In order to obtain filamentous bulking sludge as soon as possible, it is better to use bulking sludge, which is already predominantly filamentous microorganisms, as seed sludge. In general, the sludge has an SVI (sludge volume index) of 200 ml / g or more, and the sludge can be selected on the basis of the value. At that time, it is preferable to confirm the sludge form by a microscope.

The DO of the mixed liquid 9 of wastewater 1 and activated sludge is 1.
0 mg / l or less (microaerobic state) or 3.0 to 7.5 mg /
1 (overaeration state), preferably 0.1-0.5 mg / l
Alternatively, aerate and mix with air 5 so that the concentration becomes 4.0 mg / l or more. By maintaining this condition, bulking sludge can be obtained relatively quickly.

This is for the following reason. That is, the surface area of the filamentous microorganism with respect to its volume is significantly larger than that of floc-forming bacteria. In general, when DO, where the respiration rate of microorganisms is oxygen-limited, is maintained at 0.5 mg / l or less under microaerobic conditions for a long time, oxygen uptake becomes much more advantageous than floc-forming bacteria, and relatively filamentous microorganisms Is becoming dominant. In addition, many filamentous microorganisms easily grow even under aerobic or aerobic anaerobic conditions, and they are less damaged than floc-forming bacteria.

On the other hand, when the DO was 3.0 mg / l or more, floc-forming bacteria were likely to disassemble the flocs to cause autooxidation, whereas filamentous microorganisms were more likely to undergo autooxidation, but flocs were more likely to undergo autooxidation. There is no phenomenon such as dismantling. The mixed liquid 9 is filtered by operating a filtration pump 10 that sucks or reduces pressure through a microfiltration membrane 11 immersed in the aeration tank 2 to obtain treated water 4.

As the microfiltration membrane 11, for example, a porous hollow filtration membrane or the like is used. In order to suppress the increase in the clogging of the microfiltration membrane 11 and the increase in the filtration differential pressure to reduce the backwashing frequency, it is preferable to increase the switching frequency between the stop time and the operating time of the filtration pump 10. However, the capacity of the filtration pump 10 and the area of the microfiltration membrane 11 must be increased in order to secure a predetermined amount of permeated water per unit time.

Considering these advantages and disadvantages, the filtration speed of the filtration pump 10 is set to 250 to 700 l / m ² day, and the timer 12 for operating the filtration pump 10 for sucking or depressurizing the microfiltration membrane 11 is operated for 5 minutes or more. Intermittent operation is preferably set for 5 to 25 minutes to 5 minutes. In the present embodiment, the microfiltration membrane 11 is immersed in the mixed liquid 9 in the aeration tank 2 as described above, but the microfiltration membrane 11 and the filtration pump 10 are installed at these locations. It is not limited, and it may be installed inside or outside the tank within a range that can satisfy the filtration condition, and can be appropriately selected in consideration of the mutual arrangement of the devices. By the way, although the wastewater 1 varies depending on the type, in the case of wastewater from a soft drink factory,
The SVI of the mixture 9 is 7 to 10 days after the start of the flow of the wastewater 1.
It becomes 00 ml / g and comes to have a bulking state.
At this stage, filamentous microorganisms become dominant, so aeration tank 2
Keep DO aerobic (1.0 mg / l or more).

After that, when the supply of the wastewater 1 is continued, the MLSS concentration of the mixed solution 9 reaches 6000 to 15000 mg / l, and the equilibrium state in which neither increase nor decrease is reached. This is because the auto-oxidation rate of filamentous microorganisms of high bacterial age is balanced with the rate at which other filamentous microorganisms take up organic carbon, N and P, which are disintegrated as nutrients, and grow. is there. At this time, the N of the nutrient source is within a range that does not deteriorate the water quality of the treated water 4.
It is also possible to intermittently stop the supply of salt 7 and P salt 8.

In the case of wastewater containing a sufficient amount of N and P as nutrient sources, it is of course impossible to control the injection rate of such nutrient sources. Therefore, in order to balance the growth rate and the autooxidation rate of filamentous microorganisms, the volumetric load varies from 0.2 to 1.0 kg / m ³ d, depending on the type of wastewater.
ay, preferably 0.2 to 0.5 kg / m ³ day.

(Experimental example) According to the method shown in FIG. 1, activated sludge collected from the wastewater treatment facility of a soft drink factory was added to the aeration tank 2 (effective volume 100 l) so that the MLSS concentration was 1000 mg / l. The soft drink wastewater having the water quality shown in Table 1 was supplied to the aeration tank 2 under the conditions shown in Table 2, and the aeration tank 2 was set at 20 ° C.
For N and P, BOD: N: P = 100:
A solution of urea and dipotassium phosphate was added to the aeration tank 2 so that the ratio became 1: 0.1.

The SVI at this time was 150 ml / g, and the DO in the aeration tank 2 was 4.0 to 6.5 mg / l. The porous hollow filtration membrane is made of polyethylene and has an inner diameter of 270 μm and a pore diameter of 0.1.
μm. The filtration pump uses a metering pump, 600
At a constant flow rate of 1 / m ² day, intermittent suction operation was performed for 25 minutes to 5 minutes of stop. Table 3 shows the changes over time in the differential pressure of the filtration membrane thus obtained.

In the aeration state, the SVI was 200 ml / g on the 7th day from the start of waste water supply, and the state was a bulking state. BOD of treated water after this is 2-5 mg /
1, SS is 1 mg / l or less, TN is 5 mg / l or less, PO ₄
^3-- P was stable at 0.1 mg / l or less. However, when the DO in the aeration tank is in a microaerobic state (0.1 to 0.5 mg / l or less), it takes about 10 days to exhibit the bulking state, and the BOD of the treated water at that time is 10 to 15 mg / l, SS less than 1 mg / l, T-N less than 5 mg / l, PO ₄ ^3-- P 0.1
At mg / l or less, the water quality was slightly inferior to the over-aerated state.

[Table 1]

[Table 2]

[Table 3]

(Comparative Example) Similar to the experimental example, using the waste water of the soft drink waste water having the properties shown in Table 1, the operating conditions shown in Table 2 were tested by the test apparatus shown in FIG. For activated sludge, add sludge from a soft drink wastewater treatment facility where floc-forming bacteria are dominant so that the MLSS concentration in the aeration tank is 1000 mg / l.
Is the conventionally known BOD: N: P = 100: 5: 1
Was added.

That is, the concentration of N added to the wastewater is 50 mg /
The concentration of l and P added was 10 mg / l. Also, the DO of the aeration tank
Was aerated and mixed with air 5 so as to be 1.0 to 2.0 mg / l. In the same manner as in the experimental example, this mixed solution was suction-filtered by a constant flow rate intermittent operation of a filtration pump to obtain treated water.

Five days after passing the wastewater, the SVI of the aeration tank mixture was 150 ml / g, and flocs with good sedimentation were formed, and no filamentous microorganisms were observed under a microscope. Table 3 shows the time-dependent changes in the differential pressure between the filtration membranes thus obtained and the quality of treated water.

The BOD of the treated water during the entire period is 3 to 5 m.
g / l, SS was less than 1 mg / l, T-N was less than 10-15 mg / l, and PO ₄ ^3-- P was less than 1-2 mg / l, but when the operating time reached 500 hours The filtration differential pressure increased. At this time, even if the membrane was backwashed and calcium washed, the filtration pressure difference was 53
The pressure did not drop below kPa, and the filtration differential pressure immediately increased even after restarting filtration. Therefore, the operation after this was stopped because the membrane blockage could not be recovered. As is clear from Table 3, according to the present invention, the activated sludge in which filamentous microorganisms are predominant can significantly reduce the filtration pressure difference, reduce the clogging of the membrane surface, and prolong the life of the membrane.

[0034]

As described above, according to the biological treatment method for wastewater according to claims 1 to 5, the following effects can be obtained. (1) Even if bulking sludge cannot be fundamentally removed once it is generated, it can be effectively used for biological treatment of wastewater, and by actively utilizing the artificially generated bulking sludge, floc-forming bacteria It is possible to obtain a water quality superior to that of general activated sludge treated water, which is dominant. (2) By separating the activated sludge into a membrane, the installation area is smaller than the conventional method using a large-sized sedimentation tank.

(3) Since the nutrient source required for the filamentous microorganisms is smaller than that of the usual activated sludge of floc-forming bacteria, post-treatment for preventing eutrophication at the discharge destination is unnecessary, and the equipment is not required. The area is also small. (4) Even in bulking sludge for which there is no fundamental solution, sludge and supernatant water can be easily filtered, so operation is simple and maintenance is extremely easy.

(5) Due to the balance between the autooxidation rate and the growth rate of bulking sludge, the amount of excess sludge generated is extremely small, so that the dehydration equipment can be made small or unnecessary. (6) Activated sludge in which filamentous microorganisms have become the dominant species has less clogging on the membrane surface due to SS than activated sludge caused by floc-forming bacteria, so clogging of the membrane surface can be reduced and filtration differential pressure is significantly increased. Is reduced to. As a result, the frequency of backwashing the membrane can be reduced and the life of the membrane can be extended.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of a biological treatment method for wastewater according to the present invention.

FIG. 2 is a system diagram showing a conventional biological treatment method for wastewater.

[Explanation of symbols]

 1 Wastewater 2 Aeration tank 3 Settling tank 4 Treated water 5 Air 6 Return sludge 7 N salt 8 P salt 9 Mixture 10 Filtration pump 11 Microfiltration membrane 12 Timer

[Procedure amendment]

[Submission date] September 9, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0024

[Correction method] Change

[Correction content]

Considering such advantages and disadvantages, the filtration rate of the filtration pump 10 is 250 to 700 l / m ² day.
And then, intermittent operation to be set to stop microfiltration membrane 11 to suction or a timer 12 for 5 minutes driver 5 minutes stopped for filtering pump 10 operated to depressurize the <br/> for 25 minutes operation to 5 minutes, sand
Street operation: Stop intervals are filtered with a relationship of 1 to 5: 1
Preference is. In the present embodiment, the microfiltration membrane 11 is immersed in the mixed liquid 9 in the aeration tank 2 as described above, but the microfiltration membrane 11 and the filtration pump 10 are installed at these locations. But not limited to
It may be installed inside or outside the tank as long as the filtration conditions can be satisfied, and can be appropriately selected in consideration of the arrangement of the devices. By the way, although the wastewater 1 varies depending on the type,
In the case of waste water from a soft drink factory, the SVI of the mixed solution 9 becomes 400 ml / g 7 to 10 days after the start of the flow of the waste water 1, and the bulking state is exhibited. Since the filamentous microorganisms become dominant at this stage, the DO in the aeration tank 2 is kept aerobic (1.0 mg / l or more).

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

FIG.

[Fig. 2]

Claims (5)

[Claims] 1. A biological treatment method for wastewater, characterized in that activated sludge in which filamentous microorganisms are dominant is mixed and brought into contact with the wastewater, and the mixed solution is filtered through a microfiltration membrane to obtain treated water. . 2. The activated oxygen sludge in which the filamentous microorganism is dominant and the waste water are mixed and brought into contact with each other, and the dissolved oxygen concentration in the mixed solution is adjusted to 1
A method for biological treatment of wastewater, which comprises treating the treatment liquid with a filamentous microorganism being dominated and treating the treatment liquid with a microfiltration membrane to obtain treated water at a concentration of mg / l or less or 3 mg / l or more. 3. When the wastewater is in an oligotrophic state, the nutrient balance in the wastewater is BOD: N: P of 100: 1 or less:
Claim 1 and 2 which process and maintain so that it may be 0.1 or more.
The biological treatment method for wastewater according to. 4. Waste water which is separated into solid and liquid by intermittent operation of a filtration pump when the activated sludge in which filamentous microorganisms predominantly mix and contact wastewater and the mixture is filtered through a microfiltration membrane. Biological treatment method. 5. When the activated sludge in which filamentous microorganisms are dominant is mixed and brought into contact with each other, and the mixed solution is filtered through a microfiltration membrane, the operation of the filtration pump during intermittent operation: stop interval The method for biological treatment of wastewater according to claim 4, wherein the water is filtered in a ratio of 1 to 5: 1.