JP2021159844A - Aerobic biological film treatment method and device - Google Patents

Abstract

To provide a method and a device for properly controlling aeration in water waste treatment using an aerobic biological film.SOLUTION: There are provided a method and a device for supplying raw water to an aeration tank 2, and performing aerobic biological treatment to a removal object substance in raw water by a biological film carrier C or a granule filled in the aeration tank 2, in which a relationship between a raw water biological film load being a raw water load per biological film carrier or granule and a corresponding DO target value and/or corresponding aeration strength set value is preset, and according to variation in measurement value of the raw water biological film load and on the basis of the relationship, the DO target value and/or the aeration strength set value is adjusted, to control the aeration device so that the DO becomes the target value or becomes the set aeration strength set value.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 biofilm 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, microorganisms are maintained in a dispersed state in the reaction tank in a state called microbial flocs, and the microorganisms that increase with wastewater treatment are pulled out as excess sludge and maintained in the reaction tank. By maintaining a constant amount of microorganisms, the amount of oxygen consumed due to the self-decomposition process of the microorganisms themselves can be maintained at a constant level. Therefore, the increase or decrease in the amount of oxygen required in the process changes in proportion to the load of raw water, and the amount of oxygen to be supplied is determined by adding a certain offset of oxygen consumption associated with the self-decomposition process of microorganisms to this oxygen consumption. can do. In the same process, microorganisms are typically retained in the form of agglomerates of about 1 mm called flocs, and the contact area between the microorganisms and the bulk water tank is sufficiently secured, so that oxygen permeability in the flocs is increased. Diffusibility is not a major rate-determining factor in oxygen supply. Therefore, it can be considered that the amount of aerated air to be supplied to the device is proportional to the amount of oxygen consumed. For example, Patent Document 1 describes that the load of a pollutant substance is measured by an instrument and the aeration air volume is controlled based on the measurement.

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

However, in methods such as the self-granulation granule method, the fluidized bed carrier method, and the fixed bed carrier method that use a biological membrane, the flow rate per unit time of raw water and the pollution of raw water, which are common indicators of raw water load, are used. Strictly speaking, it is difficult to adjust the appropriate oxygen supply amount based only on the inflow load obtained by the product of the substance concentration and the tank load obtained by dividing the inflow load by the volume of the reaction tank. The reasons for this are as follows.

In the method using a biofilm, there is no means to keep the amount of microorganisms held in the form of a microbial membrane constant in the reaction tank, and as a result, the amount of microorganisms held changes with time. The resulting oxygen consumption also changes. Therefore, in the method using biofilm, the amount of oxygen supplied to the device needs to be determined in consideration of the change in oxygen consumption due to the change in the amount of microorganisms retained in addition to the change in oxygen consumption that changes in proportion to the load of raw water. There is.

Due to these factors, in the treatment method using biofilm, the amount of oxygen required for oxidation of raw water organic matter changes according to load fluctuations, and it is also supplied by the change in the amount of biofilm held in the treatment equipment. The amount of oxygen needed varies. Further, in the biofilm method, a biofilm having a film thickness of 3 mm or more is typically formed, and the contact area with bulk water per retained microorganism is smaller than that in the floating method. Therefore, when supplying oxygen to microorganisms in the biofilm, the diffusion phenomenon of oxygen at the contact surface between the bulk water and the biofilm is a major rate-determining factor in the oxygen supply. It is known that the diffusion rate of oxygen in the biofilm depends on the DO level of bulk water, and it is necessary to adjust the DO level in order to adjust the oxygen supply amount. Further, from the viewpoint of the aeration system, the required aeration air volume changes depending on the difference in DO level even if the oxygen supply amount is the same. It is widely known that when the DO level is high, the required aeration amount increases, and when the DO level is low, the required aeration amount decreases.
Therefore, especially when the load is increased, the amount of oxygen required for oxidation of organic matter in raw water increases, and it is caused by a self-decomposition process that changes according to the change in the amount of microorganisms retained as a biofilm. The amount of oxygen that needs to be supplied is determined in consideration of the amount of oxygen consumption, and the DO of bulk water is adjusted to be higher according to the increase in the amount of oxygen that needs to be supplied, and the amount of aerated air to achieve the target DO. Also need to be increased. Conversely, when the load is reduced, the amount of oxygen required to oxidize organic matter in the raw water is reduced, and oxygen consumption due to the self-decomposition process that changes according to the change in the amount of microorganisms retained as a biofilm. The amount of oxygen that needs to be supplied is determined in consideration of the amount, and the DO of bulk water can be kept low according to the decrease in the amount of oxygen that needs to be supplied, and the amount of aerated air to achieve the target DO is also Can be reduced.

For this reason, when operating without adjusting or controlling the aeration air volume according to the load, the aeration air volume is excessively increased so that the DO of the bulk water can be maintained high and the oxygen supply amount can be maintained even under a high load. It is necessary to operate with a constant air volume in this state.

Under constant air volume operation that can maintain the required high DO under high load, energy consumption is wasted because the air volume is not suppressed according to the decrease in oxygen consumption when the load is reduced. In addition, even when DO control is performed by assuming oxygen supply at high load and setting a high DO target value, the biofilm treatment device can reduce the DO level when the load is reduced, so the target DO level of DO control can be set. If it is lowered, the aeration air volume can be further reduced, but in normal DO control, the air volume is not suppressed due to such a decrease in the DO target, so that energy consumption is still wasted.

For this reason, the waste of energy consumption becomes particularly noticeable when the load fluctuation is large. However, even in such a situation where energy consumption is wasted, the operation of adjusting the DO level that does not deteriorate the treated water quality according to the load fluctuation and the adjustment of the air volume according to the target DO level are performed by the conventional technology. It is difficult, and even if the operator adjusts the air volume as appropriate, in the past, even with a low load, excessive DO level setting and aeration are often performed to supply more oxygen than necessary with a certain margin, and energy The reality is that waste often occurs.

In addition, if the flow load or tank load, which are common indicators of raw water load, are used, the effect of changes in the amount of microorganisms retained in the biofilm cannot be taken into consideration, and the effect of the contact area between the biofilm and bulk water cannot be taken into consideration. It is difficult to properly manage the amount of aeration. Therefore, conventionally, it is common to set a large amount of aeration air without considering the influence of the contact area between the biofilm and bulk water on the premise of oxygen consumption assuming a situation where a large amount of microorganisms is retained. For these reasons, energy is often wasted.

An object of the present invention is to provide a method and an apparatus for appropriately controlling aeration in wastewater treatment using an aerobic biological membrane.

In the aerobic biological membrane treatment method of the present invention, raw water is supplied to an aeration tank, aerated by an aeration device, and the substance to be removed in the raw water is treated with an aerobic biological membrane by a biological membrane holding carrier or granule filled in the aeration tank. In this method, the relationship between the raw water biological membrane load, which is the raw water load per carrier or granule, and the corresponding DO target value and / or the corresponding aeration intensity setting value is set in advance, and the raw water biological membrane is used. The DO target value and / or the aeration intensity set value is adjusted based on the relationship according to the fluctuation of the measured value of the load so that the DO becomes the target value or the set aeration intensity set value. In addition, it is characterized in that the aeration device is controlled.

The aerobic biological membrane treatment apparatus of the present invention comprises an aeration tank to which raw water is supplied, an aeration device that aerates the aeration tank, a carrier or granule with a biological membrane filled in the aeration tank, and the aeration device. In an aerobic biological treatment apparatus having a control controller, the relationship between the raw water biological membrane load, which is the raw water load per carrier or granule, and the corresponding DO target value and / or the corresponding aeration intensity setting value. Is provided in advance and means for adjusting the DO target value and / or the aeration intensity set value based on the relationship according to the fluctuation of the measured value of the raw aquatic biological membrane load, and the controller is provided with the means. It is characterized in that the aeration device is controlled so that the DO becomes the target value or the set aeration intensity set value.

In one aspect of the present invention, the raw water biological membrane load is the load of the substance to be removed per the filling volume of the carrier, the load of the substance to be removed per the total surface area of the carrier group, the load of the substance to be removed per the filling volume of the granule, and the granule. It is one of the substances to be removed per total surface area of the group.

In one aspect of the present invention, the substance to be removed is an organic substance, a nitrogen compound or an ammonium ion, and the calculated value of the concentration obtained by converting the raw water biological membrane load from the measured value of the concentration of the object to be removed or the measured value of absorbance. And the measured value of the raw water flow rate, and the measured value or the calculated value of the filling volume or surface area of the carrier or the granule.

In one aspect of the present invention, the aeration intensity is controlled by controlling the aeration air volume, the aeration stop time, or the aeration suppression time.

In one aspect of the present invention, the relationship is set using any of the experimental results, the operating results of the actual machine, and the mechanism model considering the diffusivity of oxygen in the biofilm.

In the present invention, the necessary and sufficient oxygen supply suitable for the properties of the carrier and granule in the aeration tank, which changes with time, is estimated by using the raw water biomembrane load instead of the flow rate load and volume load, and the target of DO is Since the value and the set value of the aeration intensity itself are changed and controlled, the aeration can be appropriately controlled.

It is a block diagram of the biological processing apparatus to which this invention is applied. It is a graph which shows the result of an Example and a comparative example. It is a graph which shows the result of an Example and a comparative example. It is a graph which shows the result of an Example and a comparative example. It is a graph which shows the TOC load of raw water. It is a block diagram of the biological processing apparatus to which this invention is applied.

FIG. 1 is a block diagram of a biological treatment apparatus to which the present invention is applied.

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 2a and is taken out as treated water from the pipe 6.

In this biological treatment apparatus, as measuring means, a flow meter 7 and a concentration meter 8 for measuring the flow rate of raw water flowing through the pipe 1 and the concentration of the substance to be treated, a DO total 9 for measuring DO in the tank 2, and a blower 4 are used. An air flow meter 10 for measuring the amount of air supplied to the air diffuser pipe 3 is provided, and these detected values are input to the controller 11. The aeration intensity is controlled by controlling the blower 4 by the controller 11.

Examples of the densitometer 8 include a TOC meter, an ammoniacal nitrogen meter, and a UV absorbance meter (for obtaining TOC / N).

As a result of various studies by the present inventor, when a flow rate load or a tank load is used as the raw water load, one of the causes that appropriate aeration management may be difficult even though the raw water load is the same is one of the causes of the aeration tank. It was found that this was due to changes in the state of the carrier and granules packed inside.

For example, when an aeration tank filled with a fluidized bed carrier is operated for a long period of time, the carrier is scraped to reduce the particle size and flow out of the aeration tank through a gap in the screen, the carrier filling rate in the aeration tank decreases, and the inside of the tank becomes smaller. The carrier filling factor is lowered, and the contact area between the biological film surface and the bulk water is lowered, so that the physical performance may be lowered.
In addition, during long-term operation, the amount of microorganisms retained on the carrier may increase, and the amount of oxygen consumed due to autolysis of microorganisms may increase.

Further, in the case of an aeration tank provided with an expansion bed using a sedimentable carrier, which is a kind of fixed bed treatment, it is necessary to periodically backwash to discharge excess sludge and SS between the carriers. At this time, the carriers are worn due to collisions and shearing forces between the carriers, and the carrier filling rate gradually decreases, the carrier filling rate in the tank decreases, and the contact area between the biological film surface and the bulk water decreases. Processing performance may decrease.
In addition, during long-term operation, the amount of microorganisms retained in and between the carriers may increase, and the amount of oxygen consumed due to autolysis of microorganisms may increase.

In a biological treatment tank that uses self-granulation granules, the number and particle size of self-granulation granules fluctuate over time, and the amount of biological membrane in the aeration tank increases or decreases, resulting in biological membrane and bulk water. Since the oxygen diffusivity to the biological membrane changes due to the change in the contact area, the aeration air volume required for wastewater treatment changes even if the organic matter load is the same.

In the present invention, the relationship between the raw water biofilm load and the corresponding DO target value and / or the corresponding aeration intensity setting value is set in advance, and the relationship is described according to the fluctuation of the measured value of the raw water biofilm load. Adjust the corresponding DO target value and / or aeration intensity setting value based on.

Then, the aeration device is controlled so that the DO becomes the target value or the set aeration intensity set value.

As the raw water biological membrane load, the substance load to be removed per packed volume of the carrier (carrier volume load), the substance load to be removed per total surface area of the carrier group (all carriers in the tank) (carrier surface area load), and granulation. The material load to be removed per charge volume (granule volume load) or the substance load to be removed per total surface area of the granule group (all granules in the tank) (granule surface area load) is suitable.

<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 ]
Examples of the raw water concentration include TOC, ammoniacal nitrogen, and TOC / N concentration estimated from UV absorbance.

<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 ]

In the aeration tank, the raw water load 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) over time. Changes change relatively slowly from day to month. Therefore, it is preferable to update the calculated value of the raw water load frequently. 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.

[Control using oxygen consumption rate as a management index]
[Calculation method of oxygen consumption rate]
In one aspect of the present invention, the oxygen consumption required to be supplied by the processing apparatus is calculated as the sum of the oxygen requirement for oxidizing the organic substance in the raw water and the oxygen consumption derived from the microbial self-oxidation held in the biological membrane. As an index to monitor, the oxygen consumption rate of the processing device is monitored and the exposure intensity is controlled based on the oxygen consumption rate. That is, under low load conditions where the oxygen consumption rate is equal to or less than the predetermined value, the aeration intensity is set to the specified intensity or more in order to maintain the stirring intensity in the treated water tank, and when the oxygen consumption rate is equal to or more than the predetermined value, the oxygen consumption level. Adjust the aeration intensity according to the above. A method of calculating the oxygen consumption rate when the oxygen consumption rate is used as a control index will be described with reference to FIG.

In the biological treatment apparatus of FIG. 6, 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. Air diffusers 3a, 3b, 3c are installed at the bottom of the aeration tank 2, and air is supplied from the blower 4 through the pipe 5 and the branch pipes 5a, 5b, 5c to perform aeration. The aeration tank 2 is provided with a canopy 2r.

The water that has been aerobically treated by the biofilm passes through the screen 2a and is taken out as treated water from the pipe 6.

In this biological treatment apparatus, as measuring means, an exhaust gas meter 24 for measuring the oxygen concentration in the gas phase portion gas above the aeration tank 2 and below the canopy 2r, and a DO total 19 for measuring the DO in the aeration tank 2 are used. An air volume meter 20 for measuring the amount of air supplied from the blower 4 to the aeration pipes 3a to 3c is provided.

<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: Method of calculating 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 / h]
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]

[Relationship between DO target value or aeration intensity setting value according to raw water biofilm load]
In the mode of the present invention, the oxygen consumption rate (qO ₂ ) is regarded as the raw water load (Load), the "carrier volume load" or the "carrier surface area load" is calculated, and the calculation result is referred to as the "raw water biological membrane load". Assuming that, from the prediction or actual results of the treated water quality when the DO target value or aeration intensity is changed, the appropriate DO target value or aeration intensity setting value is found, and the appropriate DO target value or aeration intensity according to the raw water biological membrane load is found. Find out the relationship between the set values and utilize it in the control system.
The relationship between the raw water biological membrane load and the DO target value or the aeration intensity set value is determined by using 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. Set.

The method of expressing the relationship between the raw water biological membrane load and the DO target value or the aeration intensity set value is a functional expression (an approximate function that obtains an appropriate DO target value or an appropriate aeration intensity according to the raw water biological membrane load) and a control table. (The relationship between the raw water biological membrane load and the appropriate DO target value or the appropriate aeration intensity is arranged in a table format) or the like.

[Biofilm mechanism model for creating the relationship between raw water biofilm load and DO target value and / or aeration intensity setting value]
As one method for finding the relationship between the raw water biofilm load and the DO target value and / or the aeration intensity setting value, pollution when the biofilm comes into contact with the bulk aqueous phase in a fluid state containing pollutants and oxygen. A kinetic model (hereinafter sometimes referred to as a biofilm mechanism model) that estimates the decrease in substances and the increase / decrease in the amount of activated sludge cells in the biofilm can be used. Such a kinetic model is based on the situation where bacterial cell growth and pollutant consumption / oxygen consumption occur simultaneously in the biological membrane, and oxygen is transferred to the bulk water by diffusion of dissolved oxygen in the bulk aqueous phase into 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 kinetic models for biofilm utilization processing, it is necessary to mathematically model these phenomena. Since such a phenomenon originally occurs in a three-dimensional space, the model formula is complicated, but the increase / contraction of the biological membrane should be expressed by a one-dimensional model formula that considers changes only in the thickness direction. The simulation can be performed 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 [Reference 1] can be used. [Reference 2] and the like can be used as an example of a mathematical model for a biofilm.
[Reference 1] M Henze; IWA. Task Group on Mathematical Modeling for Design and Operaton of Biological Wastewater Treatment; et al
[Reference 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 a mathematical model, 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 it is possible to simulate the dynamic behavior of the target process using numerical integration software for the simultaneous differential equations. can. For example, it is possible to predict the treated water quality according to the DO situation of the bulk aqueous phase, which changes depending on a specific device configuration, load assumption, and aeration intensity.

By using a mathematical model, it is possible to predict, for example, the TOC concentration of treated water when treated with various aeration intensities under various load conditions. Based on the simulation results, the minimum DO target value and aeration intensity adjustment that do not deteriorate the processing can be examined, a table that organizes the simulation results can be created, and it can be used for the control table used in the control system of the present patent.

[Control of aeration intensity]
The aeration intensity can be controlled, for example, by changing the aeration air volume (aeration flow rate), the aeration stop time or the aeration suppression time (weak aeration time) for each fixed time cycle. The aeration stop time indicates the time for stopping aeration within a fixed time cycle in so-called intermittent aeration. The aeration suppression time is the time of weak aeration in the operation of alternately repeating strong aeration and weak aeration.

The aeration air volume, aeration stop time, and aeration suppression time are controlled continuously or stepwise according to the raw water 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. For example, in the case of a raw water granule load, the volume or surface area of the carrier or the carrier group may be the volume or surface area of the granule or the granule group in the equations (2) and (3).

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.

<Device configuration>
An example of a method for controlling the DO / weak aeration time by monitoring the raw water load with the carrier volume load of TOC on the fluidized bed carrier using the apparatus of FIG. 1 will be described below.

The controller 11 includes a mechanism for adjusting the aeration amount in order to obtain a DO value according to the target value of DO, and an intermittent aeration mechanism for periodically performing weak aeration with a designated air volume.

As the carrier C, a cubic urethane sponge carrier having a side length of 3 mm was used.

<Biofilm mechanism model>
Actually, the diffusion phenomenon of pollutants and oxygen generated between the inside of the carrier having a three-dimensional structure and the bulk water is expressed by a one-dimensional simple model, and this one-dimensional model is a bulk water and three layers of biological membranes. It was constructed with a model assuming a completely mixed compartment of all four layers.

The cells grow in the bulk aqueous phase and biofilm by consuming the substrate, that is, pollutants and oxygen, and autolyze at a constant rate. Proliferated cells undergo attachment / detachment according to the difference in cell concentration in the bulk aqueous phase. In general, the cell concentration in the biofilm is higher than the cell concentration in the bulk aqueous phase, so the amount of desorption of the cells grown in the biofilm is such that the cells existing in the aqueous phase become the biofilm. It models a situation where there is more than the amount that adheres.

The substrate, the pollutant to be treated, is supplied from the inflow and effluent, part of which flows out with the treated water, and the rest diffuses into the biofilm according to the concentration difference between the bulk aqueous phase and the biofilm, and the bulk aqueous phase and the organism. It models a situation in which oxidative decomposition occurs and decreases with the growth of microorganisms in the membrane. The rate of oxidative decomposition of pollutants with the growth of microorganisms is a model that decreases as the oxygen concentration and the substrate, that is, the pollutant concentration decrease.

Most of the oxygen is supplied to the bulk aqueous phase by an air diffuser, but part of it is also supplied as oxygen contained in the inflow and effluent. In addition, part of the supplied oxygen flows out together with the treated water, and the rest diffuses into the biofilm according to the difference between the oxygen concentration of the bulk aqueous phase and the oxygen concentration of the biofilm, and microorganisms in the bulk aqueous phase and the biofilm. It models the situation in which it is consumed as it grows and self-decomposes. The rate of decrease in oxygen consumed by the growth of pollutant microorganisms is a model that decreases as the oxygen concentration and the substrate, that is, the pollutant concentration decrease.

<Relationship between raw water biofilm load and DO target value and / or aeration intensity setting value>
Using the mathematical formula of the one-dimensional diffusion model of the constructed biological membrane, the treated water quality for the treatment conditions was predicted by numerical integration simulation, and the appropriate control conditions were searched for, and summarized in the following control table.

In this case, the control table in Table 1 was used as the relationship between the DO target value and / or the aeration intensity setting value according to the raw water biofilm load.

In this control table, for example, TOC carrier volume loading ^{(kgC / (m 3 · d} ), below, may be omitted units.) If there is less than 0.1 or more to 0.6, the target value of the DO 3.1 mg / L,
In the case of 0.6 or more and less than 0.7, the target value of DO is 3.8 mg / L,
In the case of 0.7 or more and less than 0.9, the target value of DO is 3.9 mg / L,
In the case of 0.9 or more and less than 1.0, the target value of DO is 4.4 mg / L,
If it is 1.0 or more, the target value of DO is 4.8 mg / L,
Are set as appropriate values,
When the TOC carrier volume load is 0.1 or more and less than 0.2, the weak exposure time setting value is 110 minutes every 2 hours, and when it is 0.2 or more and less than 0.3, 90 minutes every 2 hours. If it is 0.3 or more and less than 0.4, it is 80 minutes every 2 hours, if it is 0.4 or more and less than 0.5, it is 60 minutes every 2 hours, and if it is 0.5 or more and less than 0.6, it is 2 set as each proper value of 20 minutes per time, TOC carrier volume load in the case of ^{0.6 (kgC / (m 3 ·} d)) or more, and zero weak aeration time set value (i.e. intermittent aeration I didn't do it.)

[Example 1]
Raw water whose TOC load fluctuates as shown in FIG. 5 was designated as wastewater to be treated.

Based on the 2-hour moving average of the carrier volume load, the DO target value once every 2 hours and the weak aeration time in the 2-hour cycle are adjusted based on the control table in Table 1, and the constant low air volume during weak aeration ( It was set to 3 m ³ / (bottom area m ² · hr)), and the motor rotation speed of the blower was controlled so as to reach the set DO target value during the time zone other than the time of weak aeration.

The time course of the weak aeration time is shown in FIG. 2, and the time course of DO is shown in FIG. Further, FIG. 4 shows a change over time in power consumption due to the blower.

[Comparative Example 1]
The same as in Example 1 except that the target value of DO was fixed at 3.5 mg / L and the weak aeration time was kept constant at 10 minutes / 2 hours. The results are shown in Figures 2-4.

<Discussion>
In Example 1, since the DO target value and the weak aeration time were adjusted according to the load per carrier, the amount of electric power used by the blower was smaller than that in Comparative Example 1. That is, while the power consumption of Comparative Example 1 was about 1150 kWh / day, the power consumption of Example 1 was about 950 kWh / day, which is about 17% less.

There was almost no difference in the treated water quality between Example 1 and Comparative Example 1.

2 Aeration tank 3 Aeration pipe 4 Blower 7 Flow meter 8 Densitometer 9 DO meter 10 Air flow meter 11 Controller

Claims (6)

In a method of supplying raw water to an aeration tank, aerating it with an aeration device, and aerobically treating the substance to be removed in the raw water with a biological membrane-retaining carrier or granule filled in the aeration tank.
The relationship between the raw water biofilm load, which is the raw water load per carrier or granule, and the corresponding DO target value and / or the corresponding aeration intensity setting value is set in advance.
The DO target value and / or the aeration intensity set value is adjusted based on the above relationship according to the fluctuation of the measured value of the raw water biofilm load.
An aerobic biological membrane treatment method comprising controlling the aeration device so that the DO becomes the target value or the set aeration intensity set value. The raw water biological membrane load is the load of the substance to be removed per the filling volume of the carrier, the load of the substance to be removed per the total surface area of the carrier group, the load of the substance to be removed per the filling volume of the granule, and the load of the substance to be removed per the total surface area of the granule group. The aerobic biological membrane treatment method according to claim 1, which is one of the substances to be removed. The substance to be removed is an organic substance, a nitrogen compound or an ammonium ion.
The raw water biofilm load,
The calculated value of the concentration converted from the measured value of the concentration of the object to be removed or the measured value of the absorbance, and
The measured value of the raw water flow rate and
Measured or calculated values of carrier or granule filling volume or surface area,
The aerobic biological membrane treatment method according to claim 1 or 2, wherein the method is calculated from. The aerobic biological membrane treatment method according to any one of claims 1 to 3, wherein the aeration intensity is controlled by controlling the aeration air volume, the aeration stop time, or the aeration suppression time. The aerobic biological membrane according to any one of claims 1 to 4, wherein the relationship is set by using any of the experimental results, the operation results of the actual machine, and the mechanism model considering the diffusivity of oxygen in the biofilm. Processing method. Aerobic biological treatment having an aeration tank to which raw water is supplied, an aeration device that aerates the aeration tank, a carrier or granule with a biological film filled in the aeration tank, and a controller that controls the aeration device. In the device
Means for presetting the relationship between the raw water biofilm load, which is the raw water load per carrier or granule, and the corresponding DO target value and / or the corresponding aeration intensity setting value.
It is provided with a means for adjusting the DO target value and / or the aeration intensity set value based on the above relationship according to the fluctuation of the measured value of the raw water biofilm load.
The controller is an aerobic biological membrane treatment device, which controls the aeration device so that the DO becomes the target value or the set aeration intensity set value.

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