JP2002096092A - Method of controlling grain size of floc as well as water treating method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently carry out the operation to separate solid from liquid by controlling the grain size of the floc formed by microorganisms in a denitrification treating vessel. SOLUTION: Aeration treatment is effected into denitrification treating vessel for removing nitrogen by the anaerobic microorganisms, by which the grain size of the floc formed by the anaerobic microorganisms is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the particle size of floc and a method and apparatus for treating water, and more particularly, to a method for controlling the particle size of floc generated when performing denitrification by anaerobic microorganisms. The present invention relates to a method and an apparatus for efficiently performing solid-liquid separation of water.

[0002]

BACKGROUND OF THE INVENTION As a method for removing nitrate and nitrite nitrogen present in water,
Anaerobic treatment using denitrifying bacteria, which are anaerobic microorganisms, is widely performed. Denitrifying bacteria breathe using molecular oxygen in the aerobic state where dissolved oxygen exists, and breathe using oxygen such as nitrate nitrogen instead of molecular oxygen in the anaerobic state where dissolved oxygen does not exist. . Therefore, when the denitrifying bacteria breathe, the dissolved oxygen is consumed and the state becomes anaerobic, and the nitrate nitrogen is reduced to nitrogen gas, and the nitrogen content is removed from the water.

However, if the anaerobic state is maintained for a long time, micro floc formation of microorganisms occurs, and solid-liquid separation of treated water becomes difficult. For example, when solid-liquid separation is performed using a separation membrane, clogging due to fine flocs is likely to occur, and it has been necessary to frequently wash the separation membrane. For this reason, for example, in the method for separating a suspension described in JP-A-6-76870, the suspension extracted from the suspension tank for performing the microorganism treatment is first concentrated and separated by centrifugation or the like. Clogging of the separation membrane is reduced by performing the membrane separation step after lowering the SS component concentration in the step.

In the case of a water treatment method in which anaerobic treatment and aerobic treatment are alternately performed by intermittent aeration, for example, Japanese Patent Application Laid-Open No. H11-3
In the membrane separation method described in Japanese Patent No. 47550, an aeration device is installed below the separation membrane, air is aerated from the aeration device during aerobic treatment, and inside an airtight treatment tank during anaerobic treatment. The separation membrane is aerated and cleaned by circulating a gas containing almost no oxygen and aeration from the aeration apparatus to eliminate clogging of the separation membrane.

[0005] In any case, the microbial flocculation of microorganisms in an anaerobic state can be reduced by reducing the load on the separation membrane by performing a concentration separation step or by continuously performing aeration and washing of the separation membrane. No study has been made on the micro floc formation of microorganisms.

In the former method, a centrifugal separator is separately required, and in the latter method, piping and a mist separator for circulating the gas in the processing tank to the aeration device are separately required. It was difficult to apply to general water treatment equipment.

[0007] When nitrification and denitrification are performed in a single treatment tank by intermittent aeration as in the latter case, an aerobic state and an anaerobic state are alternately repeated, and an anaerobic state occurs. Because of the short duration, the effect of micro-flocculation of microorganisms is relatively small compared to a denitrification treatment tank that exclusively performs denitrification in an anaerobic state.

[0008] Accordingly, the present invention provides a method for controlling the size of flocs, which makes it possible to perform a solid-liquid separation operation efficiently by suppressing the formation of microscopic flocs of the microorganisms and controlling the particle size of the flocs formed by the microorganisms. Provide a method,
It is an object of the present invention to provide a water treatment method and apparatus capable of performing effective denitrification processing and membrane separation processing with a simple apparatus configuration using the control of the particle size of flocs.

[0009]

Means for Solving the Problems To achieve the above object, the method for controlling the particle size of floc of the present invention comprises the steps of aerating the inside of a denitrification tank for removing nitrogen by anaerobic microorganisms. It is characterized by controlling the particle size of the floc formed by the microorganism.

Further, the floc particle size control method of the present invention measures the floc particle size generated in the denitrification tank, compares the measurement result with a preset optimal particle size range, The amount of the aeration process is adjusted based on the comparison result, and the aeration process is performed by sequence control based on a preset aeration condition.

In the water treatment method of the present invention, an anaerobic treatment is performed in a denitrification treatment tank to remove nitrogen, and an anaerobic treatment in which the particle size is controlled by performing aeration treatment in the denitrification treatment tank. Forming flocs of microorganisms and performing a membrane separation process on the treated water containing the flocs, thereby separating the flocs, and in particular, membrane filtration water subjected to the membrane separation process in the next step. It is characterized in that the concentrated water is sent out and returned to the denitrification tank.

Further, the water treatment apparatus of the present invention comprises: a denitrification treatment tank for performing a denitrification treatment by an anaerobic microorganism under an anaerobic condition;
Particle size measuring means for measuring the particle size of floc generated in the denitrification treatment tank, aeration means for supplying oxygen into the denitrification treatment tank, and floc particles measured by the particle size measurement means It is characterized by comprising an aeration control means for controlling the amount of aeration treatment of the aeration means on the basis of a diameter, and a membrane separation means for performing solid-liquid separation of treated water extracted from the denitrification treatment tank.

[0013]

FIG. 1 is a system diagram showing one embodiment of a water treatment apparatus to which a method for controlling the particle size of flocs of the present invention is applied. This water treatment apparatus includes a denitrification treatment tank (anaerobic tank) 11
And a cross-flow type membrane separation device 12, which performs a biological denitrification treatment with anaerobic microorganisms under anaerobic conditions in the denitrification treatment tank 11 and an anaerobic treatment in the membrane separation device 12. By separating floc of germ-free microorganisms from the treated water, nitrate nitrogen contained in the raw water is removed to perform a denitrification treatment of the raw water.

The denitrification tank 11 has a stirrer 13 for stirring the microorganism-mixed water and an oxidation-reduction potentiometer (ORP) for measuring the oxidation-reduction potential (ORP) of the microorganism-mixed water.
14) and an aerator 15 for supplying oxygen to the microorganism-mixed water, and mixes raw water and microorganisms flowing through the path 16 to biologically reduce nitrate nitrogen to nitrogen. Perform processing.

The membrane separation device 12 has a pump 18 for pressurizing the treated water extracted from the denitrification treatment tank 11 to the path 17.
And a path 19 for sending the membrane filtered water subjected to the solid-liquid separation processing (filtration processing) to the next step, and a path 20 for returning the concentrated water to the denitrification treatment tank 11. In addition to the filtration treatment, flocs attached to the membrane surface are separated by treated water flowing along the inner surface of the hollow fiber membrane to suppress the accumulation of flocs.

In the water treatment apparatus thus formed, in the denitrification treatment tank 11, fine flocs of anaerobic microorganisms are generated due to long-lasting anaerobic state in the tank. When the fine flocs are generated, the fine flocs penetrate into the fine holes provided in the hollow fiber membrane of the membrane separation device 12 and close the fine holes. Therefore, the particle size of the flocs generated in the denitrification treatment tank 11 is made sufficiently larger than the fine pores of the hollow fiber membrane to prevent the flocs from entering the fine pores, thereby suppressing blockage of the fine pores. This makes it possible to remove the flocs attached to the membrane surface by the treatment water flowing in the hollow fiber membrane.

The generation of fine flocs occurs when microorganisms take in oxygen of nitrate nitrogen and breathe under anaerobic conditions.
This is due to reduced excretion of protoplasm. In other words, a suitable amount of molecular oxygen is given to microorganisms to cause oxygen respiration, thereby facilitating excretion of the protoplasm, thereby forming a floc having a large particle size in a state where the respective microorganisms are put together by the protoplasm.

On the other hand, the determination of the anaerobic state can be known by measuring the oxidation-reduction potential of the mixed water of microorganisms. For example, in the case of normal intermittent aeration, the oxidation-reduction potential is about +100 mV in an aerobic state during aeration, and about -100 mV in an anaerobic state in which aeration is stopped. Further, if the anaerobic state is maintained as it is in the denitrification treatment tank 11, the oxidation-reduction potential often reaches −300 to −400 mV, and in such a case, the fine flocs easily occur.

The oxidation-reduction potential varies depending on the properties of the raw water flowing in (content of nitrate nitrogen, content of organic substances, etc.), residence time, types of microorganisms, etc., but is generated in advance in the denitrification treatment tank 11. By examining the relationship between the particle size of the floc and the oxidation-reduction potential of the microbial mixed water, it is possible to control the particle size of the floc by adjusting the oxidation-reduction potential.

That is, by maintaining the oxidation-reduction potential at a high level within a range that does not impair the denitrification treatment in the denitrification treatment tank 11, it is possible to form flocs having an appropriate particle size by discharging the protoplasm by the oxygen respiration of microorganisms. it can. The oxidation-reduction potential that does not impair the denitrification treatment is usually +100 to −1
The range of 00 mV is appropriate, and the redox potentiometer 14
The oxidation-reduction potential of the microbial mixed water is measured continuously, and the aeration process is performed so that the measured value falls within a predetermined oxidation-reduction potential range in which flocs having an appropriate particle size are formed. Flock generation can be suppressed.

In the aeration treatment, it is sufficient that oxygen can be supplied to the microorganisms, and the stirring effect and the membrane washing effect need not be considered at all. Therefore, not only the appropriate position in the denitrification treatment tank 11 but also
The path 16, the path 17, and the path 20 through which the water flowing into the denitrification tank 11 flows can be provided. Further, the gas for aeration only needs to contain oxygen, and usually air may be used, but oxygen gas can also be used.

Further, the aeration treatment may be performed so as to form a floc having an optimum particle size range set in advance. For example, the opening degree of the valve 15a of the aeration device 15 is adjusted in accordance with the oxidation-reduction potential of the microorganism-mixed water. Aeration is performed continuously, or the valve 15a is opened when the measured value is lower than a predetermined oxidation-reduction potential, and the valve 15a is closed when the measurement value is higher than a predetermined oxidation-reduction potential. By adjusting the aeration time and the amount of aeration by sequence control based on a preset aeration condition, the entire denitrification treatment tank 11 can be made uniform.

By performing a predetermined aeration process in this way to form flocs of anaerobic microorganisms having a controlled particle size, the hollow fiber membrane in the membrane separation device 12 for performing a filtration process of the treated water containing the flocs is formed. Clogging can be suppressed, and stable membrane separation can be continued for a long time.

Further, the present invention can be carried out simply by installing a particle size measuring means such as an oxidation-reduction potentiometer 14 and an aerator 15 capable of controlling the amount of aeration treatment in the ordinary denitrification tank 11. It is easy to apply to existing denitrification equipment, and equipment and operating costs are low.

In the present embodiment, the particle size of the floc is indirectly measured by the oxidation-reduction potential as the particle size measuring means, but the particle size can also be measured directly by a particle counter. . Also, the particle size of the floc can be indirectly measured by measuring the dissolved oxygen concentration (DO) of the mixed water of microorganisms. In this case, the optimal dissolved oxygen concentration is 0.5 mg / l.
It is as follows.

The aeration control means for controlling the amount of aeration treatment in the aeration device 15 may open and close the electromagnetic valve directly by an electric signal from a particle size measuring means such as the oxidation-reduction potentiometer 14. The opening and closing of the valve can be controlled by processing the electric signal from the measuring means by a computer or the like, and the aeration amount can be controlled by controlling the operation of the blower that supplies the air for aeration. At this time, the amount of stirring by the stirrer 13 can be adjusted in conjunction with the aeration process.

Further, the type of the membrane separation device as the membrane separation means is not limited, and is not limited to the cross-flow type, but may be a full-filtration type or a combined type, and may be an external pressure type instead of an internal pressure type. it can. The separation of flocs is not limited to membrane separation, and even when solid-liquid separation means such as sand filtration is employed, an efficient filtration process in which blockage by fine flocks is suppressed can be performed.

In addition, an organic carbon source necessary for the respiration of microorganisms may be provided by organic carbonaceous matter in raw water, or a shortage may be added from the outside. In the latter case, denitrification treatment is required. It was necessary to add a little more than the theoretical amount in order to sufficiently perform the treatment, and there was a risk that the BOD of the treated water might increase. However, by performing appropriate aeration, consumption of BOD by microorganisms occurred, Can be prevented from rising.

[0029]

As described above, according to the present invention,
Since generation of fine flocs in the denitrification tank can be suppressed, solid-liquid separation for separating flocs can be efficiently performed. In addition, it can be easily applied to existing denitrification treatment equipment.

[Brief description of the drawings]

FIG. 1 is a system diagram showing one embodiment of a water treatment apparatus to which a floc particle size control method of the present invention is applied.

[Explanation of symbols]

11: denitrification tank, 12: membrane separator, 13: stirrer,
14: redox potentiometer, 15: aeration device, 18: pump

Continued on the front page F term (reference) 4D006 GA02 HA01 KA01 KB22 KB23 MA01 PB08 PC62 4D040 AA22 AA55 AA61 BB07 BB24 BB67 BB91 BB92

Claims (6)

[Claims] 1. A method for controlling the size of flocs formed by anaerobic microorganisms by subjecting a denitrification treatment tank for removing nitrogen by anaerobic microorganisms to an aeration treatment to control the particle size of flocs formed by the anaerobic microorganisms. . 2. The particle size of floc generated in the denitrification treatment tank is measured, the measurement result is compared with a preset optimum particle size range, and the aeration treatment amount is adjusted based on the comparison result. 2. The method for controlling the particle size of floc according to claim 1, wherein: 3. The floc particle size control method according to claim 1, wherein the aeration process is performed by a sequence control based on a preset aeration condition. 4. A water treatment method to which the method for controlling floc particle size according to claim 1, 2 or 3, wherein nitrogen is removed by performing anaerobic treatment in the denitrification treatment tank.
The denitrification treatment tank is subjected to aeration treatment to form flocs of anaerobic microorganisms having a controlled particle size, and the membrane is subjected to a membrane separation treatment for treated water containing the flocs, thereby separating the flocs. Characterized water treatment method. 5. The water treatment method according to claim 4, wherein the membrane filtered water subjected to the membrane separation treatment is sent to the next step, and the concentrated water is returned to the denitrification treatment tank. 6. A denitrification treatment tank for performing a denitrification treatment by an anaerobic microorganism under an anaerobic condition, a particle size measuring means for measuring a particle size of floc generated in the denitrification treatment tank, and a denitrification treatment. Aeration means for supplying oxygen into the tank, aeration control means for controlling the amount of aeration of the aeration means based on the particle size of the floc measured by the particle size measurement means, and extraction from the denitrification treatment tank And a membrane separation means for performing solid-liquid separation of the treated water.