JP2021169062A - Aerobic biological membrane treatment method and apparatus - Google Patents

Abstract

To provide a method and an apparatus to improve a processing performance when the amount of a biofilm held in a processing device increases, by continuously operating aerobic biofilm treatment with self-granulation granules and biofilm-attached carriers for a long period of time.SOLUTION: There is provided a method in which raw water is supplied to an aeration tank and a substance to be removed in the raw water is treated with an aerobic biofilm using a biofilm-retaining carrier or granule filled in the aeration tank, and when a specified water quality item for treated water deviates from a specified range when a calculated value of an oxygen diffusivity index, an average particle size of the granule, the amount of biofilm attached (weight) per carrier, and an aeration air volume per raw water load are predetermined upper limits, or when a predetermined time has passed since a start of operation or the above processing, biofilm exfoliation treatment from carrier or partial decomposition treatment of granules is performed.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method and an apparatus for treating wastewater containing a pollutant that can be biologically oxidized with a biological membrane using a self-granulation granule, a fluidized bed carrier, a fixed bed carrier, or the like, and particularly relates to an aeration intensity control thereof. In the present invention, wastewater existing outside the microorganisms to be treated with microorganisms is referred to as bulk water.

Microorganisms are called biofilms, such as the activated sludge method using suspended sludge, the self-granulation granule method, the fluidized bed carrier method, and the fixed bed carrier method, as methods for treating wastewater containing pollutants that can be biologically oxidized. A biofilm method or the like is used in which treatment is performed in a state of accumulation and proliferation.

In the former activated sludge method using suspended sludge, the contact area between the microorganisms and the bulk aqueous phase is sufficiently secured inside and outside the agglutination of microorganisms, which is typically about 1 mm, which is called microbial flocs. The permeability and diffusivity of oxygen and pollutants in the plant are not the main rate-determining factors for the treatment performance of the pollutant removal rate. Patent Document 1 describes that the load of a pollutant substance is measured by an instrument and the aeration air volume is controlled in proportion to the load.

In the activated sludge method using suspended sludge and the biological membrane method such as the self-granulation granule method, the fluidized bed carrier method, and the fixed bed carrier method, as a method for easily adjusting the oxygen supply amount in proportion to the load of raw water, A so-called DO control system that controls the air volume to keep the dissolved oxygen concentration in the liquid (hereinafter referred to as DO) constant is widely used.

Regarding the self-granulation granule method and the fluidized bed carrier method, Patent Document 2 states that when the BOD volume load is smaller than the predetermined value, the fluidization of the microbial carrier is used as a criterion, and the BOD volume load is larger than the predetermined value. In some cases, a wastewater treatment method and an apparatus for controlling the amount of aeration to wastewater based on the oxygen demand of wastewater are described.

Japanese Unexamined Patent Publication No. 2001-335496 JP-A-63-256185

In methods such as the self-granulating granule method, the fluidized bed carrier method, and the fixed bed carrier method, which use a biological membrane, the flow rate per unit time of raw water, which is a common index of the amount of pollutants flowing in, is used. Strictly speaking, it is difficult to adjust the appropriate oxygen supply amount based only on the raw water load obtained by multiplying the product with the pollutant concentration of the raw water and the tank load obtained by dividing the raw water load by the volume of the reaction tank. be. The reasons for this are as follows.

(i) Even if the raw water load is the same and the amount of oxygen required to oxidize organic substances in the raw water is the same, in the method using the biofilm, the microorganisms are retained in the reaction tank in the form of a biofilm. Since the amount changes with time, the amount of oxygen consumed due to the self-decomposition process of the microorganism itself changes. Therefore, it is necessary to determine the amount of oxygen supplied to the device in consideration of the same factor.

(ii) In the treatment method using biofilm, it is necessary to diffuse oxygen in the biofilm where microorganisms are accumulated. The main factors that affect the diffusivity of oxygen into the biofilm are the contact area between the biofilm and bulk water and the high and low DO of bulk water. As the amount of granule retained and the size of the granule change, the contact area between the microorganism and bulk water changes.

(iii) In the fluidized bed carrier method, the contact area between the biofilm and bulk water changes due to changes in the amount of microbial adhesion inside and outside the carrier. In particular, when the biofilm grows in the void in a structure having voids inside the carrier, the amount of the biofilm attached to the carrier increases, and when all the voids are closed, the bulk water comes into contact with the biofilm. The area is significantly reduced.

(iv) Such a change in the contact area between bulk water and the biofilm has a great influence on the oxygen diffusivity to the biofilm. For example, when the contact area between the bulk water and the biofilm is reduced, it is necessary to increase the DO of the bulk water even when the same amount of oxygen is supplied into the biofilm, and the dissolved oxygen concentration of the bulk water is increased. For that purpose, a larger flow rate of air is required. In addition, when the load of raw water increases, oxygen consumption increases. Therefore, in order to supply the necessary oxygen into the biofilm by the diffusion phenomenon, it is necessary to increase the dissolved oxygen concentration of the bulk water.

In this way, the amount of oxygen required for oxidation of raw water organic matter changes according to load fluctuations, and the amount of oxygen required to be supplied changes depending on the amount of biological membrane held in the treatment equipment. In the case of the biological membrane method that relies on the diffusion phenomenon, it is necessary to adjust the DO of the bulk water according to the amount of oxygen to be supplied to the biological membrane, and the amount of exposed air to maintain the DO of the bulk water is also adjusted. There is a need.

When the aeration air volume is not controlled, it is often the case that the bulk water DO is maintained at an excessively high level assuming a high load.

When aeration is performed at a constant air volume without aeration control in order to maintain the DO excessively high, the air is constantly aerated at an air volume that matches the maximum load, resulting in waste of energy consumption.

Further, even when performing general DO constant air volume control, it is necessary to perform DO setting on the assumption that a sufficient amount of oxygen diffusion into the biofilm is secured at the time of high load. Therefore, when the load is low, the DO level is maintained at the DO level or higher required to maintain the required oxygen supply amount. As a result, the amount of aerated air for maintaining DO becomes larger than the required amount, resulting in waste of energy consumption.

However, the quality of treated water may fluctuate even when the raw water load and the operation items of the reaction tank are constant, or even when appropriate operation control is performed according to the raw water load. This tends to occur especially when the biological treatment equipment is operated for a long period of time.

The cause of this is that in processing devices that utilize spherical biofilms such as self-granulating microbial granules or biofilms attached to fluidized beds or fixed bed carriers, the amount of biofilm retained increases over time. As a result, the amount of oxygen consumed due to the self-decomposition process of the microorganism itself changes, and the contact area between the biofilm and bulk water decreases, which reduces the diffusion rate of oxygen into the biofilm, resulting in the biofilm. It is conceivable that the processing performance will decrease over time.

Therefore, even though the aeration intensity is determined according to the load fluctuation and the aeration is controlled, when the treated water quality deviates from the predetermined value due to continuous operation, the amount of biofilm retained in the aeration tank increases. It is conceivable to change the aeration conditions by judging that the amount has increased and the processing performance has decreased.

Specifically, when the treated water quality is not reduced to the target value and the water quality deteriorates, it is judged that the oxygen diffusivity is reduced due to the increased retention of the biological membrane and the oxygen supply amount is insufficient. Change to the control logic of the aeration condition where the aeration intensity is stronger than the control logic of.

However, there is a problem that the required aeration power increases when an aeration condition with a strong aeration intensity is applied. Further, if an aeration system capable of aerating more than a predetermined value has not been constructed in the first place, the aeration intensity cannot be increased to recover the treated water quality.

The present invention provides a method and an apparatus for improving the treatment performance when the retention amount of the biofilm increases by continuously operating the aerobic biofilm treatment with a self-granulation granule or a biofouling carrier for a long period of time. The purpose is.

The aerobic biological membrane treatment method of the present invention is a method for treating an aerobic biological membrane of a substance to be removed in raw water with a biological membrane-retaining carrier or granule filled in the aerobic tank in an aerobic tank to which raw water is supplied. , When any one or more of the following is satisfied, the carrier's biological film retention reduction treatment or the granule partial decomposition product treatment is performed.
i) The calculated value of the oxygen diffusivity index is below the predetermined lower limit.
ii) The average particle size of the granule exceeds the predetermined upper limit.
iii) The amount (weight) of the biofilm attached per carrier exceeds the predetermined upper limit.
iv) The specified water quality item of treated water exceeds the specified target value in the situation where the aeration air volume per raw water load exceeds the specified upper limit value.
v) A predetermined time has elapsed since the start of operation or the previous processing.

The aerobic biological membrane treatment apparatus of the present invention is an aerobic organism having an aeration tank to which raw water is supplied, a biological membrane holding carrier or granule filled in the aeration tank, and an aeration device that aerates the aeration tank. The membrane treatment apparatus includes a means for reducing the amount of biological membrane retained in the carrier or a means for treating a partially decomposed granule, which operates when any one or more of the following is satisfied.
i) The calculated value of the oxygen diffusivity index is below the predetermined lower limit.
ii) The average particle size of the granule exceeds the predetermined upper limit.
iii) The amount (weight) of the biofilm attached per carrier exceeds the predetermined upper limit.
iv) The specified water quality item of treated water exceeds the specified target value in the situation where the aeration air volume per raw water load exceeds the specified upper limit value.
v) A predetermined time has elapsed since the start of operation or the previous processing.

In one aspect of the present invention, the carrier biological film retention amount reduction or granule part decomposition product treatment is performed by strong stirring by a rotary stirring blade or backwash, strong aeration, high flow velocity circulation, and water flow to a crushing pump of water in the tank. It is performed by any one or two or more of.

In one aspect of the present invention, the aeration tank is filled with a biofilm-retaining carrier, and a new carrier and / or a biofilm-attached carrier that has been subjected to biofilm peeling treatment is used in the aeration tank to reduce the amount of the carrier biofilm retained. Or by replacing the carrier in the aeration tank.

According to the present invention, when the control item deviates from a predetermined value, the partial decomposition product of the self-granulating microbial granule, the peeling of the biofilm adhering to the carrier, or the peeling removal of the biofilm held between the carriers is performed. By doing so, the oxygen diffusion performance of the self-granulating microbial granule or the carrier can be improved, and the energy saving performance of the power related to aeration can be improved.

In particular, when biofilm treatment using a carrier is operated for a long period of time, a dense biofilm with low processing capacity tends to be deposited inside the carrier, which deteriorates the oxygen diffusivity inside the carrier and tends to reduce the treatment performance. However, by detecting the biofilm deposited inside the carrier and peeling the biofilm, the oxygen diffusivity inside the carrier can be restored and the processing performance can be improved.

It is a block diagram of the biological processing apparatus to which this invention is applied. It is a block diagram of the biological processing apparatus to which this invention is applied. It is a block diagram of the biological processing apparatus to which this invention is applied. It is a block diagram of a biological processing apparatus. It is a block diagram of a biological processing apparatus.

In the present invention, when the control item deviates from a predetermined value, it is determined that the amount of biofilm retained is excessively increased, particularly in the case of self-granulating microbial granule, the granule is enlarged, and the carrier is used. Either the biofilm retention amount is reduced (for example, the biofilm is peeled off from the carrier) or the granule is partially decomposed.

Specifically, when any one or more of the following i) to v) is obtained, the carrier biofilm retention amount such as peeling of the biofilm from the carrier is reduced, and the granule is partially decomposed.
i) When the calculated value of the oxygen diffusivity index falls below a predetermined lower limit value, the oxygen diffusivity index is the amount of biological membrane retained per packed volume of the carrier (mg / m ³ ) and the contact area of the biological membrane with bulk water. However, since it is difficult to directly measure these indexes with an actual machine, they are estimated by simulation calculation from the changes in the treated water quality with respect to the raw water load and aeration conditions per carrier filling volume.
ii) When the average particle size of the granule exceeds the predetermined upper limit value The average particle size of the granule is measured visually or optically by sampling the water in the tank from the air-exhaust tank in a completely mixed state with a Bandoon water sampler or the like. Confirm by measuring the average particle size.
iii) When the amount (weight) of the biofilm attached to the carrier exceeds the predetermined upper limit value The weight of the biofilm attached to the carrier during stable operation is measured in advance, and the value obtained by adding the predetermined width to this value is calculated as " A predetermined upper limit value ".

The weight of the attached biofilm is determined by drying a certain amount of the bioadherent carrier sampled with a Bandoon water sampler and measuring the weight difference from the new carrier, or by burning this carrier to obtain an organic suspended solid. Calculated by measuring (VSS).
iv) When the predetermined water quality item of the treated water exceeds the predetermined target value when the aeration air volume per raw water load exceeds the predetermined upper limit value What is the "predetermined upper limit value" for the aeration air volume per raw water load? , Set the upper limit of the aeration air volume per raw water load from the viewpoint of energy saving, or determine it because the treated water quality cannot be maintained even with the maximum aeration air volume on the facility even though the raw water load is within the design maximum value. This is the set value.
v) When a predetermined time has passed since the start of operation or the previous treatment The elapsed operation time until the biofilm enlarges is estimated experimentally or by simulation, and is defined as the "predetermined time".

In addition, even when an abnormality is not detected in the control items of ii) to iv), the oxygen diffusivity index may decrease. Therefore, it is more preferable to manage in i).

As a means for peeling the biofilm or decomposing the granule part, a means for forcibly reducing the biofilm by applying a shearing force as described in (1) to (4) below, a new carrier, or a biofilm in use is used. Means for additional addition of the adherent carrier or replacement with the carrier in the tank are suitable.
(1) Strongly stir with a rotary stirring blade or backwash.
(2) Strong aeration.
(3) Circulate at high flow velocity.
(4) Pass the water in the tank through the crushing pump inside or outside the tank.

The biofilm generated by the peeling of the biofilm from the carrier and the partial decomposition product of the granule is discharged as SS to the outside of the tank together with the treated water, and is treated with solid-liquid separation (aggregation precipitation, aggregation pressure flotation, aggregation filtration, etc.). After that, it is discharged from the system.

The biofilm peeling means and the partially decomposed body means may be temporarily installed at the time of peeling or processing of the partially decomposed body, or may be installed as permanent equipment.

Hereinafter, the configuration of an aerobic biological treatment apparatus provided with a means for exfoliating the adhered biofilm from the fluidized bed carrier or a means for decomposing a self-granulated granule part will be described with reference to the drawings.

In the biological treatment apparatus of FIG. 1, the wastewater to be treated (raw water) is introduced into the aeration tank 2 through the pipe 1. The aeration tank 2 is filled with a carrier C carrying a granule or a biofilm. An aeration pipe 3 is installed at the bottom of the aeration tank 2, and air is supplied from the blower 4 through the pipe 5 to perform aeration.

The water that has been aerobically treated by the biofilm passes through the screen 6 and is taken out as treated water from the pipe 7.

In this biological treatment apparatus, as a means for peeling the biological film, the granule or carrier of the aeration tank 2 is pulled out by the suction pump 11, introduced into the stirring water tank 12, and strongly stirred by the stirrer 13 to adhere to the granule decomposition product or the carrier. After the biological film is peeled off, it is returned to the aeration tank 2 through the pipe 14.

The degree of exfoliation of the partially decomposed granule or the carrier-attached biofilm is adjusted by the following (a), (b), (c) and the like.
(A) The discharge amount of the suction pump 11 is adjusted to adjust the residence time of the stirring water tank 12.
(B) The rotation speed of the stirrer 13 is adjusted to adjust the strength of disassembly / peeling of the biofilm.
(C) Adjust both of the above.

Instead of providing the stirring water tank 12 and the stirring machine 13, a submersible crushing pump can be installed instead.

In FIG. 1, the water supply from the suction pump 11 is supplied to the stirring water tank 12 as it is, but as shown in FIG. 2, the water supply from the suction pump 11 is sent to the processing target carrier sorting device 15 based on the sedimentation rate of the cyclone or the like. It is also possible to supply and selectively supply only the carrier or the granule having a large amount of biological film retention and the high sedimentation rate to the stirring water tank 12 to perform the biological film peeling treatment from the partially decomposed product or the carrier of the granule. The carrier or granule having a small amount of biofilm retained and a low sedimentation rate is returned to the aeration tank 2 through the pipe 16.

FIG. 3 shows a biological treatment apparatus in which a partially decomposed product of granule or a biofilm attached to a carrier is peeled off by strong aeration.

In the biological treatment apparatus of FIG. 3, the wastewater to be treated (raw water) is introduced into the aeration tank 2 through the pipe 1. The aeration tank 2 is filled with a carrier C carrying a granule or a biofilm. An aeration pipe 3 is installed at the bottom of the aeration tank 2, and air is supplied from the blower 4 through the pipe 5 to perform aeration. Air can also be supplied to the pipe 5 from the blower 17 for strong aeration.

The water that has been aerobically treated by the biofilm passes through the screen 6 and is taken out as treated water from the pipe 7.

In this biological treatment apparatus, a DO meter 19 for measuring the DO concentration in the aeration tank 2 and an air volume meter 20 for measuring the amount of air supplied from the blower 4 to the pipe 5 are provided, and these detected values are controlled. It is input to the vessel 21. The aeration intensity is controlled by controlling the blower 4 by the controller 21.

When the partially decomposed product of granule or the biofilm attached to the carrier is peeled off, the blower 17 is operated to strongly aerate.

<Oxygen diffusivity index>
In the case of biological film treatment using a self-granulating microbial granule or a biological film attached to a fluidized bed or fixed bed carrier to remove pollutants, the liquid phase in a fluid state and the microorganisms come into contact with each other as compared with the floating method. The surface area is small, and in order to biodecompose pollutants, oxygen and pollutants must diffuse and permeate inside the biological membrane (in the thickness direction), and the rate of this diffusion permeation process is the growth rate of microorganisms and oxygen consumption. Due to its slowness compared to its speed, the diffusion infiltration process is one of the major determinants of processing performance.

The surface area of the biofilm in contact with bulk water is a factor affecting the diffusion osmosis process. When the surface area is narrowed, even if the DO of the bulk water is the same, the total amount of oxygen diffused into the biofilm is relatively reduced, the treatment performance is deteriorated, and the quality of the treated water tends to be deteriorated. On the contrary, when the surface area is widened, even if the DO of the bulk water is the same, the total amount of oxygen diffusion to the biofilm is relatively increased, the treatment capacity is increased, and the treated water quality tends to be good. Further, even if the DO is low, sufficient processing performance can be exhibited, and the amount of aeration and the electric power related to aeration can be reduced.

In the case of equipment using self-granulating microbial granules, if the granules are enlarged due to long-term operation, the specific surface area in contact with bulk water per filling volume of self-granulating microbial granules will decrease, and the specific surface area in contact with bulk water will decrease. The surface area in contact with bulk water is reduced.

In the case of a device using a carrier, especially when a carrier having a structure having voids inside the carrier is used, when the amount of the biofilm retained by the carrier increases due to long-term operation, the void space inside the carrier becomes the biofilm. The contact area between the bulk water and the biofilm is reduced because it is blocked by itself and non-biologically active solids such as scale components. As a result, the specific surface area in contact with bulk water per carrier volume decreases, and the surface area in contact with bulk water per aeration tank volume decreases. In addition, regardless of the presence or absence of voids inside the carrier, when the biofilm is operated for a long period of time, the density of the biofilm in the biofilm increases, or the accumulation of non-bioactive solids such as scale components causes the biofilm to accumulate. As the solids density increases, the oxygen diffusion rate decreases.

In particular, in the case of a treatment using a biofilm attached to a fixed carrier, an excess biofilm tends to be retained in the space between the carriers over a long period of operation. In such a situation, the volume of the bulk aqueous phase decreases relatively as the biofilm retention increases. Further, when this state is further advanced, the space between the carriers is blocked by the biofilm, and a space where bulk water cannot flow in is generated. As a result, the contact area between the bulk aqueous phase and the biofilm gradually decreases, and the permeation permeability of oxygen and pollutants into the biofilm tends to decrease over time.

<Example of control logic construction>
As a method of aeration control used in the present invention, a case will be described in which general DO control is performed at a high load and so-called intermittent aeration in which weak aeration and strong aeration are alternately repeated at a low load is combined. In the intermittent aeration of this case, the weak aeration process in which the air volume is suppressed with the minimum constant air volume for a predetermined time and the strong aeration process in which the DO control is performed for the remaining time are repeated at regular time cycles. In the explanation of intermittent aeration in this case, the total process time of the control cycle consisting of the weak aeration process and the strong aeration process is referred to as the cycle time, and the process time of the weak aeration process is referred to as the weak aeration process time and the process of the strong aeration process. The time is referred to as the strong aeration process time.

The correlation between the raw water load and the oxygen consumption rate of the reaction tank and the appropriate values of the DO target value and the aeration intensity set value (in this case, the set value of the weak aeration process time) is created in advance using a plurality of oxygen diffusivity indexes. .. The correlation between the raw water load, the DO target value, and the weak aeration process time will be described using Table 1 below as an example, in which the correlation between the raw water load and the weak aeration process time is arranged in a control table.

In Table 1, five control tables (correlation tables) are shown in order from the top. Each table is prepared assuming the condition that the oxygen diffusivity in the biofilm is different, the first table is prepared under the condition that the oxygen diffusivity is the highest, the oxygen diffusivity is gradually decreased, and the fifth table is prepared. The table is based on the assumption that oxygen diffusivity is the worst. Each table shows the relationship between the TOC carrier volume loading and the DO target value and the weak aeration process time setting value.

For example, in the third table from the top, the carrier filling volume per TOC load ^{[kgC / (m 3 · d} ), below, may be omitted units. ] Is set to 3.1 mg / L for the TOC load in the strong aeration step when the TOC load is 0.1 or more and less than 0.6, and the weak aeration step when the TOC load is 0.1 or more and less than 0.2. The time is 110 minutes every 2 hours, the weak aeration process is 90 minutes every 2 hours when the TOC load is 0.2 or more and less than 0.3, and the weak aeration process is when the TOC load is 0.3 or more and less than 0.4. The time is 80 minutes every 2 hours, the weak aeration process time is 60 minutes every 2 hours when the TOC load is 0.4 or more and less than 0.5, and the weak aeration process is when the TOC load is 0.5 or more and less than 0.6. The time is set to 40 minutes every 2 hours as an appropriate value, and when the TOC load is 0.6 or more and less than 0.7, the DO target value in the strong aeration process is 3.8 mg / L, and the weak aeration process time. For 20 minutes every 2 hours, if the TOC load is 0.7 or more, no intermittent aeration is performed (weak aeration time is 0 minutes), and if the TOC load is 0.7 or more and less than 0.9, the DO target value is set to 3. 9. When the TOC load is 0.9 or more and less than 1.0, the DO target value is set to 4.4, and when the TOC load is 1.0 or more, the DO target value is set to 4.8 as appropriate values. The same applies to the other tables.

When the treated water quality (for example, TOC concentration) is good over a predetermined time, the table moves up one level, and conversely, when the treated water quality is poor over a predetermined time, the table moves down one level. For example, if the quality of treated water deteriorates even though aeration control has been continued appropriately using the standard control table (third table from the top), it is considered that the oxygen diffusivity has deteriorated, and the oxygen diffusivity is considered to have deteriorated. Switch to aeration control using the side control table (fourth table from the top). On the contrary, when the treated water quality becomes excessively good, it is considered that stable treatment can be performed even if the aeration is weakened, and the aeration control is switched to the one above the control table (the second table from the top). By applying this control procedure, a control table assuming oxygen diffusivity according to the state of the biofilm of the actual machine will be automatically selected, and as a result, the oxygen diffusivity index will be estimated.

Although it is difficult to directly measure the oxygen diffusivity index with an actual machine, it is possible to estimate it from normal operation data by the above operation.

If the quality of the treated water is higher than the TOC upper limit of the control target when the control table (the bottom table in Table 1) is selected and controlled assuming the situation where the treatment performance has deteriorated, it is higher than that. However, since a control table with an increased aeration intensity has not been set, the performance is restored by performing a peeling treatment on the partially decomposed product of the granule or the biofilm attached to the carrier.

Even at the stage where the processing performance is slightly deteriorated (for example, the state of the fourth control table from the top), in consideration of the energy efficiency and cost of aeration enhancement, the partially decomposed product of the granule or the carrier-attached biofilm The performance may be recovered by peeling.

<Control management index>
The calculation method of the raw water carrier load when the raw water load is used as a control index will be described below with reference to FIG.

[Method of calculating raw water load from TOC meter and flow meter]
The biological treatment apparatus shown in FIG. 4 performs aeration control based on the raw water load using the measured value of the TOC concentration of the raw water.

In the biological treatment apparatus of FIG. 4, the wastewater to be treated (raw water) is introduced into the aeration tank 2 through the pipe 1. The aeration tank 2 is filled with a carrier C supporting a biofilm. An aeration pipe 3 is installed at the bottom of the aeration tank 2, and air is supplied from the blower 4 through the pipe 5 to perform aeration.

The water that has been aerobically treated by the biofilm passes through the screen 6 and is taken out as treated water from the pipe 7.

In this biological treatment apparatus, as measuring means, a flow meter 22 and a TOC total 23 for measuring the flow rate and TOC concentration of raw water flowing through the pipe 1, a DO total 19 for measuring the DO concentration in the aeration tank 2, and a blower 4 An air flow meter 20 for measuring the amount of air supplied to the aeration pipe 3 is provided, and these detected values are input to the controller 21. The aeration intensity is controlled by controlling the blower 4 by the controller 21.

The TOC load is calculated as the raw water load by measuring the raw water flow rate with the flow meter 22 and measuring the TOC concentration of the raw water with the TOC total 23.

<Raw water load>
The raw water load is calculated by the following formula.

Road = Q ・ Conc
Road: Raw water load [kg / d]
Q: Raw water flow rate [m ³ / d]
Conc: Raw water concentration [kg / m ³ ]
The raw water concentration is not limited to TOC, and other indexes may be used depending on the treatment purpose as long as it is the concentration of the substance to be oxidized by the microorganism. Typically, it is possible to utilize the concentration of a specific chemical substance such as _{COD Cr} , COD _{Mn, nitrite nitrogen, ammoniacal nitrogen, and organic amines.}

<Carrier volume loading>
The carrier volume load is calculated by the following equation.

_{Road CarrierVol} = Road / V _Carrier
Load _CarrierVol: support volume loading ^{[kg / (m 3 · d} )]
V _Carrier : Carrier filling volume in the aeration tank [m ³ ]

<Carrier surface area load>
The carrier surface area load is calculated by the following equation.

_{Road CarrierSurf} = Road / S _{Carrier
Road CarrierSurf} : Carrier surface area load [kg / (m ² · d)]
S _Carrier : Total surface area of the carrier group in the aeration tank [m ² ]

[Case 1: How to calculate the oxygen consumption rate from the air volume meter and the exhaust gas meter]
The aeration air volume and the oxygen concentration in the exhaust gas are measured, and the oxygen consumption rate qO ₂ is directly calculated by the following equation.

OTE: Oxygen transfer efficiency [-]
Z ₀ : Oxygen mole fraction in blown air [-]
Z: Mole fraction of oxygen in exhaust gas [-]
qO ₂ : Oxygen consumption rate [kg / d]
Gν: Blow-in flow rate of aerated air converted to standard state [Nm ³ / d]
ν _m : Specific volume of oxygen [Nm ³ / kg]

[Case 2: How to calculate oxygen consumption rate from DO meter and aeration air volume]
The aeration air volume and DO are measured, and the oxygen consumption rate qO ₂ is indirectly estimated.
(I) (Preparation before mounting the control device) Calculate the oxygen solubility index φ required for estimating the oxygen consumption rate by the following formula.

OTE: Oxygen transfer efficiency [-]
Z ₀ : Oxygen mole fraction in blown air [-]
Z: Mole fraction of oxygen in exhaust gas [-]
φ: Oxygen solubility index [m]
ν _m : Specific volume of oxygen [Nm ³ / kg]
h: Water depth of the air diffuser [m]
Cs: Saturated dissolved oxygen concentration [kg / m ³ ]
C: Dissolved oxygen concentration in the mixture [kg / m ³ ]

(Ii) (During equipment operation) Continuously measure changes in oxygen consumption rate over time.

_{The oxygen consumption rate qO 2} is continuously estimated by the following formula from the DO meter, the continuous measurement data of the aeration air volume, and the oxygen solubility index φ obtained in advance.

qO ₂ : Oxygen consumption rate [kg / d]
Gν: Blow-in flow rate of aerated air converted to standard state [Nm ³ / d]
h: Water depth of the air diffuser [m]
Cs: Saturated dissolved oxygen concentration [kg / m ³ ]
C: Dissolved oxygen concentration in the mixture [kg / m ³ ]
φ: Oxygen solubility index [m]

[Correlation between raw water load or oxygen consumption rate and DO target value or aeration intensity setting value]
The correlation between the raw water load or oxygen consumption rate and the DO target value or the aeration intensity setting value is the result data of the preliminary experiment, the operation record data of the actual machine, the simulation result of the mechanism model considering the diffusivity of oxygen in the biological membrane, etc. Is set using.

In the aeration tank, the raw water load or oxygen consumption rate may fluctuate rapidly in minutes over time, but the properties of the carrier (carrier filling volume in the aeration tank or total surface area of the carrier group in the aeration tank). ) Changes with time from day to month relatively slowly. Therefore, it is preferable to frequently update the calculated values of the raw water load or the oxygen consumption rate. The carrier filling volume in the aeration tank or the total surface area of the carrier group in the aeration tank is analyzed by sampling the carriers periodically (for example, once every 1 to 3 months), and the carrier filling volume is analyzed. , The total surface area data of the carrier group may be updated.

[Correlation between raw water load or oxygen consumption rate and appropriate value of DO target value and / or aeration intensity setting value]
In the uniform state of the aeration control method used in combination with the present invention, the raw water load or oxygen consumption rate per unit volume or unit surface area of the carrier or granule of the aeration tank, and the DO target value and / or weak aeration time for this. A plurality of correlations with appropriate values are set in advance according to the difference in oxygen diffusivity, and the corresponding correlation is based on the above correlation assuming the oxygen diffusivity of the characteristics according to the fluctuation of the measured value of the oxygen consumption rate. Set an appropriate value for the DO target value or other aeration intensity setting value.

The combination of the raw water load or oxygen consumption rate and the appropriate value of the DO target value and / or the weak aeration time set value is the result data of the preliminary experiment, the operation record data of the actual machine, or the mechanism considering the diffusivity of oxygen in the biological membrane. It is set using the simulation result of the model.

As a method of implementing this correlation in the control system, it is implemented by a functional formula that describes the correlation between the raw water load or oxygen consumption rate and the appropriate value of the DO target value and / or weak aeration time, or a control table is used. It may be any of the methods of expressing.

[Biofilm mechanism model for creating control tables]
One method for constructing a control table is to reduce the amount of pollutants and increase or decrease the amount of activated sludge cells in the biofilm when the biofilm comes into contact with the bulk aqueous phase in a fluid state containing pollutants and oxygen. An estimated kinetic model (hereinafter sometimes referred to as a biofilm mechanism model) can be used. In such a kinetic model, bacterial cell growth and pollutant consumption / oxygen consumption occur simultaneously in the biological membrane, and oxygen is converted to bulk water volume by diffusion of dissolved oxygen in the bulk aqueous phase to the biological membrane and aeration. It is necessary to consider the melting phenomenon. In addition, the increase or contraction of the biofilm occurs due to the increase or decrease in the volume of the bacterial cell group accompanying the growth and death of the bacterial cell, the attachment of the bacterial cell from the bulk water, and the exfoliation of the bacterial cell into the bulk water. When using a kinetic model for biofilm utilization processing, it is necessary to mathematically model these phenomena. Since such a phenomenon originally occurs in a three-dimensional space, modeling is complicated, but by expressing the increase / contraction of the biological membrane with a one-dimensional model that considers changes only in the thickness direction. The simulation can be done relatively easily. As a mathematical model for simulating wastewater treatment with activated sludge, for example, a series of mathematical models proposed by the Task group of the International Water Association can be used (report 1 below). The following report 2 and the like have been reported as examples of mathematical models for biofilms.

1. M Henze; IWA. Task Group on Mathematical Modeling for Design and Operaton of Biological Wastewater Treatment; et al
2. Boltz, JP, Johnson, BR, Daigger, GT, Sandino, J., (2009a). “Modeling Integrated Fixed-Film Activated Sludge and Moving Bed Biofilm Reactor Systems I: Mathematical Treatment and Model Development”. Water Environment Research, 81 ( 6), 555-575

By using the mathematical model as in the previous section, for example, a mathematical model of a fluidized bed carrier can be constructed. In general, such mathematical models are often described in the form of simultaneous ordinary differential equations, and the dynamic behavior of the process can be simulated using numerical integration software for simultaneous ordinary differential equations. For example, it is possible to predict the treated water quality according to the DO conditions of the bulk aqueous phase, which changes depending on a specific device configuration, load assumption, and aeration intensity.

By using the mathematical model as in the previous section, the TOC of treated water, for example, when treated with various aeration intensities under various load conditions under oxygen permeable conditions in various biofilms, for example. The concentration can be predicted. A table in which the simulation results are organized can be created and used for creating a control table used in the control system of the present invention.

[Control of aeration intensity]
The aeration intensity can be controlled by, for example, the aeration air volume or the aeration air volume to the blower, the DO target value of DO control, the weak aeration process time in the intermittent aeration operation, or a combination thereof.

The aeration intensity is controlled continuously or stepwise according to the raw water load or the oxygen consumption rate.

[Weak aeration process air volume, minimum carrier aeration air volume, maximum aeration stop time, maximum weak aeration time]
In the present invention, a constant air volume in the weak aeration process is referred to as a weak aeration process air volume. This air volume is the air volume required to maintain the minimum agitation of the liquid phase in the treatment tank in the weak aeration step and maintain the contact between the biofilm and the bulk water. When the aeration is completely stopped in the weak aeration step, the aeration by the aeration is eliminated, so that a mechanical aeration function different from the aeration is required. In this case, it is assumed that the minimum aeration is performed even in the weak aeration process and the aeration is performed by the aeration. The minimum carrier aeration air volume ensures the flow state of the entire carrier in the strong aeration process, especially in equipment using a fluidized bed carrier, prevents the carrier from accumulating on the bottom of the aeration tank, and reduces the biological film and bulk with the accumulation. It is the minimum aeration air volume required to suppress the decrease in contact area with water, the problem of sludge decay caused by the accumulation on the bottom of the carrier, and the generation of hydrogen sulfide odor, and is usually weak aeration. It will be larger than the process air volume. In the strong aeration step, DO control is performed, but the control is performed on the condition that the air volume is always equal to or higher than the minimum carrier aeration air volume.

In the explanation of intermittent aeration in this case, the total process time of the control cycle consisting of the weak aeration process and the strong aeration process is referred to as the cycle time, the process time of the weak aeration process is referred to as the weak aeration process time, and the process time of the bullish process is referred to as the process time of the bullish process. It is called the strong aeration process time. The DO target value in the weak aeration process time and the strong aeration process is controlled continuously or stepwise according to the raw water load. The strong aeration process time is automatically determined as the cycle time minus the weak aeration process time. Further, the longest time when adjusting the weak aeration process time is referred to as the longest weak aeration process time. Therefore, the longest weak aeration process time is shorter than the cycle time.

In a fluidized bed carrier device that employs an intermittent aeration method that repeats aeration and aeration stop, the minimum carrier aeration air volume is not secured in the aeration stop or weak aeration operation process, so that the carrier accumulates on the bottom of the device during this process. do. Refluidization of the deposited carrier by limiting the time of the same process within a certain time and ensuring the remaining cycle time is equal to or greater than the minimum carrier aeration air volume (referred to as air volume in the strong aeration step in the present invention). The problem of sludge rot and the generation of hydrogen sulfide odor caused by long-term deposition on the bottom of the carrier are suppressed.

The minimum carrier aeration air volume or the maximum aeration stop time is preferably determined based on the result data of the preliminary experiment, the actual operation data of the actual machine, and the like. In this case, when the raw water load is high, the intermittent aeration operation that repeats weak aeration and strong aeration is not performed, but continuous aeration that maximizes the capacity of the aeration device is performed. When the raw water load decreases, a lower DO target value is set according to the control table to suppress the aeration air volume, but when the aeration air volume reaches the minimum carrier aeration air volume, the aeration method is switched to the intermittent aeration operation. The operation of switching from continuous aeration operation to intermittent aeration operation can be performed by directly measuring the air volume and using the minimum carrier aeration air volume as a criterion, but the index value is monitored by monitoring any of the following indicators (a) to (d). By pre-evaluating the relationship between and air volume, the aeration air volume is estimated based on the index, continuous aeration when aeration air volume ≥ minimum carrier flow aeration air volume, and continuous aeration when aeration air volume <minimum carrier flow aeration air volume. It is also possible to control the intermittent aeration.
(A) The measured value of the raw water load is below the specified value (b) The measured value of the oxygen consumption rate of the aeration tank is below the specified value (c) The DO target value controlled according to the load under continuous aeration is below the specified value (d) ) The set value of the aeration intensity (including aeration air volume) controlled according to the load under continuous aeration is less than the specified value.

The raw water load in (a) is preferably any of an inflow load, a tank load, a carrier volume load, and a carrier surface area load.

[Biological treatment other than fluidized beds]
Although the biological treatment using the fluidized bed carrier has been described in FIG. 1, the present invention can be carried out by the same method when a fixed bed carrier or granule is used.

In the present embodiment, it has been described that wastewater containing organic substances is used when treated by aerobic biological membrane treatment accompanied by aeration, but in addition, an aeration tank such as biological nitrification and denitrification treatment using a biological membrane. The present invention can be carried out by the same method when performing biological treatment including an aerobic treatment step using a biological membrane.

[Example 1]
When operating the aerobic biological treatment apparatus for the fluidized bed carrier shown in FIG. 1, the control table shown in Table 1 is switched according to the degree of treated water quality while appropriately controlling the aeration according to the raw water load at any time. Controlled. In the five types of control tables due to the difference in oxygen diffusivity, each of the upper to lower rows is referred to by the control table names "excellent", "good", "standard", "slightly deteriorated", and "deteriorated". The criterion for switching to the control table with high oxygen diffusivity is the treated water TOC less than 5 mg / L, and the treated water quality in this situation is referred to as "below the target". As a criterion for switching to a control table with low oxygen diffusivity, the treated water TOC is set to be larger than the upper limit of 10 mg / L, and the treated water quality in this situation is called "deterioration". When the treated water TOC is 5 mg / L or more and 10 mg / L or less, the control table is not changed, and the treated water quality in this situation is referred to as “good”. The quality of treated water was confirmed by manual analysis, and the decision to change the control table was carried out once a day. At the start of operation, operation control was started using the fourth "slightly lowered" control table from the top.

90 days after the start of operation, in the aeration control using the "slightly lowered" control table, the treated water TOC became 11 mg / L and the treated water quality became "deteriorated". After 91 days, the treated water TOC recovered to 7 mg / L, which was within the target TOC range, and became "good". Therefore, the aeration control in the "decrease" control table was continued. However, after 180 days, the treated water quality was 11 mg / L even in the aeration control according to the control table "decrease", and the situation was "deteriorated". From the situation where the aeration control by the control table of "decrease" also deviated from the target range of treatment, it was judged that the oxygen diffusivity deviated from the permissible range and decreased, and a temporary strong aeration (air volume 20 m ³ / (reaction tank). The bottom area m2 · hr)) was carried out for 12 hours to peel off the biological film on the surface of the carrier. The exfoliated biofilm was discharged from the aeration tank 2 together with the treated water.

After the peeling treatment, the aeration control was continued while using the "decrease" control table. The following 181 days later, the treated water TOC improved to 3 mg / L and became "below the target", so the control table was changed to "slightly decreased". 182 days later, the treated water TOC was still 3 mg / L and "below the target". Since it was confirmed that the control table was changed to "standard", and after 183 days, it was confirmed that the treated water TOC was "good" at 6 mg / L. Continued. As a result, the control table was switched from "decreased" to "standard" by the biofilm peeling treatment, and it was confirmed that the oxygen diffusivity of the microbial carrier was restored by the biofilm peeling operation of the present invention.

2 Aeration tank 3,3a, 3b, 3c Air diffuser 4,17 Blower 12 Stirring water tank 13 Stirrer 15 Sorting device

Claims (4)

In a method of aerobic biofilm treatment of a substance to be removed in raw water with a biofilm-retaining carrier or granule filled in the aeration tank in an aeration tank to which raw water is supplied.
An aerobic biofilm treatment method, which comprises performing a biofilm retention reduction treatment of a carrier or a partial decomposition product treatment of a granule when any one or more of the following is satisfied.
i) The calculated value of the oxygen diffusivity index is below the predetermined lower limit.
ii) The average particle size of the granule exceeds the predetermined upper limit.
iii) The amount (weight) of the biofilm attached per carrier exceeds the predetermined upper limit.
iv) The specified water quality item of treated water exceeds the specified target value in the situation where the aeration air volume per raw water load exceeds the specified upper limit value.
v) A predetermined time has elapsed since the start of operation or the previous processing. The carrier's biological film retention amount reduction or granule decomposition product treatment is performed by either 1 or 2 of strong stirring by a rotary stirring blade or backwash, strong aeration, high flow velocity circulation, and water flow to a crushing pump of water in the tank. The aerobic biological membrane treatment method according to claim 1, wherein the method is performed as described above. The aeration tank is filled with a biological film-retaining carrier, and a new carrier and / or a biological film-attached carrier that has been subjected to biological film peeling treatment is added to the aeration tank or aeration to reduce the biological film retention amount of the carrier. The aerobic biological membrane treatment method according to claim 1, wherein the method is carried out by replacing the carrier in the tank. In an aerobic biofilm treatment apparatus having an aeration tank to which raw water is supplied, a biofilm holding carrier or granule filled in the aeration tank, and an aeration device for aerating the aeration tank.
An aerobic biofilm treatment apparatus comprising a means for reducing the amount of biofilm retained in a carrier or a means for treating a partially decomposed granule, which operates when any one or more of the following is satisfied.
i) The calculated value of the oxygen diffusivity index is below the predetermined lower limit.
ii) The filling volume ratio of the granule exceeds the predetermined upper limit.
iii) The amount (weight) of the biofilm attached per carrier exceeds the predetermined upper limit.
iv) The predetermined water quality item of the treated water when the aeration air volume per raw water load is the predetermined upper limit value exceeds the predetermined target value.
v) A predetermined time has elapsed since the start of operation or the previous processing.

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