CN115335333A - Aerobic biofilm treatment method and device - Google Patents

Abstract

A method and an apparatus for aerobic biofilm treatment in which raw water is supplied to an aeration tank (2) and target substances to be removed from the raw water are aerobically treated by biofilm carriers (C) or pellets filled in the aeration tank (2), characterized in that a relationship between a raw water biofilm load as a raw water load per biofilm carrier or pellet and a dissolved oxygen concentration target value corresponding thereto and/or an aeration intensity set value corresponding thereto is set in advance, the dissolved oxygen concentration target value and/or the aeration intensity set value is adjusted in accordance with a change in a measured value of the raw water biofilm load in accordance with the relationship, and the aeration apparatus is controlled so that the dissolved oxygen concentration reaches the target value or becomes the set aeration intensity set value.

Description

Aerobic biofilm treatment method and device

technical field

The present invention relates to a method and device for biofilm treatment of wastewater containing pollutants capable of biological oxidation through self-granulating particles, fluidized bed carriers, fixed bed carriers, etc., and particularly relates to its aeration intensity control. In the present invention, the waste water present outside the biofilm subjected to microbial treatment is referred to as bulk water.

Background technique

As a treatment method for wastewater containing pollutants capable of biological oxidation, in addition to the activated sludge method using floating sludge, there are microorganisms such as the self-granulation granulation method, the fluidized bed carrier method, and the fixed bed carrier method. Biofilm method, etc., to treat the form of accumulation and proliferation of biofilm.

In the activated sludge method using the former floating sludge, microorganisms are maintained in a dispersed state in a reaction tank in a form called microbial floc. The amount of microorganisms maintained in the reaction tank can be kept constant by removing the microorganisms that increase with wastewater treatment as excess sludge, and the oxygen consumption due to the self-decomposition process of the microorganisms can be maintained at a constant level. . Therefore, the increase or decrease in the amount of oxygen required in this process changes in proportion to the raw water load. The amount of oxygen consumption to be supplied can be determined by adding to this oxygen consumption the compensation for a certain amount of oxygen consumption accompanying the self-decomposition process of microorganisms. In this process, microorganisms are typically held in the form of microaggregates of about 1 mm called flocs, and a sufficient contact area between microorganisms and the bulk water tank is ensured. Therefore, the permeability and diffusivity of oxygen within the floc is not the main rate-limiting factor in oxygen supply. Therefore, the aeration air volume that should be supplied to the device is considered to be proportional to the oxygen consumption. Patent Document 1 describes measuring the load of pollutants with an instrument and controlling the aeration air volume based on this.

In the activated sludge method and biofilm method (self-granulation granule method, fluidized bed carrier method, fixed bed carrier method, etc.) As a method, a so-called DO control system that performs air volume control to keep the concentration of dissolved oxygen in a liquid (hereinafter referred to as DO) constant is widely used.

In Patent Document 2, it is described that in the self-granulation granule method and the fluidized bed carrier method, when the BOD volume load is less than a specified value, the fluidization of the microbial carrier is used as a criterion for judgment, and when the BOD volume load is greater than the specified value , taking the oxygen demand of the wastewater as the criterion to control the aeration of the wastewater.

prior art literature

patent documents

Patent Document 1: Japanese Unexamined Patent Publication No. 2001-353496.

Patent Document 2: Japanese Patent Application Laid-Open No. 63-256185.

Strictly speaking, in methods using biofilms such as the self-granulation granulation method, the fluidized bed carrier method, and the fixed bed carrier method, it is difficult to use only the flow rate per unit time of ordinary raw water as an index of raw water load and The inflow load obtained by multiplying the concentration of pollutants in the raw water and the tank load obtained by dividing the inflow load by the volume of the reaction tank are used to adjust the oxygen supply amount appropriately. The reasons for this are listed below.

In the method using biofilm, since there is no mechanism to keep the amount of microorganisms held in the form of a microbial film in the reaction tank fixed, the amount of microorganisms held will change with time, and therefore, due to the self-decomposition process of the microorganisms themselves, The resulting oxygen consumption will also vary. Therefore, in the method using biofilm, in addition to the change in the oxygen consumption that changes in proportion to the raw water load, it is also necessary to consider the change in the oxygen consumption accompanying the change in the amount of microorganisms held in order to determine the oxygen supply to the device. .

Due to these factors, in the treatment method using biofilm, the amount of oxygen required to oxidize organic matter in raw water changes according to load fluctuations, and changes in the amount of biofilm held in the treatment device also lead to changes in the amount of oxygen that needs to be supplied. Furthermore, in the biofilm method, typically, a biofilm having a film thickness of 3 mm or more is usually formed, and the contact area between the retained unit microorganism and the bulk water is smaller than that in the planktonic method. Therefore, when oxygen is supplied to the microorganisms in the biofilm, the oxygen diffusion phenomenon on the interface between the bulk water and the biofilm becomes the main rate-limiting factor in the oxygen supply.

The diffusion rate of oxygen in the biofilm depends on the DO level of the bulk water, therefore, it is necessary to adjust the DO level to adjust the oxygen supply. In addition, from the point of view of the aeration system, even if the oxygen supply is the same, the required aeration air volume will vary due to the different DO levels. It is well known that increased aeration is required at high DO levels and decreased at low DO levels.

Therefore, in the case of increased load, the amount of oxygen required for the oxidation of organic matter in raw water increases. The amount of oxygen required for supply is determined in consideration of the amount of oxygen consumption due to the self-decomposition process that varies according to the change in the amount of microorganisms held as a biofilm. According to the increase of the required oxygen supply to increase the DO of the bulk water, it is also necessary to increase the aeration air volume to achieve the target DO.

On the contrary, when the load is reduced, the amount of oxygen required for the oxidation of organic matter in raw water is reduced. The amount of oxygen that needs to be supplied is determined in consideration of the amount of oxygen consumption due to the self-decomposition process that varies according to the change in the amount of microorganisms held as a biofilm. By reducing the amount of oxygen required for supply, the DO of the bulk water can be kept low, and the aeration air volume used to achieve the target DO is also reduced.

For this reason, when the operation is not adjusted and controlled according to the load of the aeration air volume, in order to maintain a high bulk phase water DO and maintain the oxygen supply at high loads, it is necessary Constant air volume operation is performed in a state of high volume.

In the constant air volume operation capable of maintaining the required high DO at high load, the air volume is not suppressed in response to the decrease in oxygen consumption when the load decreases, resulting in wasteful energy consumption. Assuming the oxygen supply at high load and performing DO control with a high DO target value set, the biofilm treatment device can also reduce the DO level when the load decreases. Therefore, if the target DO level of DO control is lowered, it can Further limit the aeration air volume. However, in normal DO control, since such air volume reduction according to the DO target is not performed, wasteful energy consumption also occurs.

For such reasons, the waste of energy consumption is particularly noticeable when the load fluctuates greatly. However, even if such wasteful energy consumption occurs, conventionally it is difficult to adjust the air volume to match the operation target DO level to adjust the DO level without deteriorating the treated water quality according to the load fluctuation. With proper air volume adjustments by the operator, in the past, even at low loads, excessive DO level settings and aeration were often performed to allow some degree of leeway for more than needed oxygen supply. Therefore, waste of energy often occurs.

If the usual flow load and tank load are used as indicators of the raw water load, the influence of changes in the amount of microorganisms held in the biofilm cannot be considered. In addition, the influence of the contact area between the biofilm and the bulk water cannot be considered, and it is difficult to manage the appropriate aeration amount. Therefore, conventionally, a large amount of aeration air volume is generally set on the premise that the amount of oxygen consumption assumed to maintain a large amount of microbial biomass is assumed, and the influence of the contact area between the biofilm and the bulk water is not considered. Energy is often wasted for this reason as well.

Contents of the invention

The problem to be solved by the invention

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

means to solve the problem

In the aerobic biofilm treatment method of the present invention, raw water is supplied to an aeration tank, aeration is performed using an aeration device, and the removal target substance in the raw water is carried out through the biofilm holding carrier or particles filled in the aeration tank The method for aerobic biological treatment is characterized in that the relationship between the raw water biofilm load and the corresponding DO target value and/or the corresponding aeration intensity set value is preset as the raw water load of the carrier or particle, Adjusting the DO target value and/or the aeration intensity setting value according to the relationship corresponding to the variation of the measured value of the raw water biofilm load, and controlling the aeration device so that DO reaches the target value or becomes Set the aeration intensity setpoint.

The aerobic biofilm treatment device of the present invention has an aeration tank for supplying raw water, an aeration device for aerating the aeration tank, carriers or particles with biofilms filled in the aeration tank, and The aerobic biological treatment device of the controller that controls the aeration device is characterized in that the aerobic biofilm treatment device has: the raw water biofilm load and the raw water load that are preset as the raw water load of the carrier or particle A mechanism for the relationship between the corresponding DO target value and/or its corresponding aeration intensity setting value; and adjusting the DO target value and/or aeration according to the relationship corresponding to the variation of the measured value of the raw water biofilm load Intensity setting value mechanism, the controller controls the aeration device to make DO reach the target value or set the aeration intensity setting value.

According to an aspect of the present invention, the raw water biofilm load is the removal target substance load per unit filling volume of the carrier, the removal target substance load per unit total surface area of the carrier group, the removal target substance load per unit filling volume of the particles, and the removal target substance load per unit filling volume of the particles. Any one of the removal target substance loads per unit total surface area of the group.

According to one aspect of the present invention, the removal target substance is organic matter, nitrogen compound or ammonium ion, according to the calculated value of the concentration converted from the measured value of the concentration of the removed target substance or the measured value of absorbance, the measured value of the raw water flow and the carrier Or the measured or calculated value of the packing volume or surface area of the particles to calculate the raw water biofilm load.

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

According to one aspect of the present invention, the relationship is set using any one of experimental results, actual operating results, and a mechanism model that considers the diffusivity of oxygen in the biofilm.

The effect of the invention

In the present invention, instead of using flow load and volume load, raw water biofilm load is used to estimate sufficient oxygen supply suitable for the characteristics of carriers and particles in the aeration tank that changes over time, and the target value of DO is changed. , The setting value of the aeration intensity itself is controlled, so the aeration can be properly controlled.

Description of drawings

Fig. 1 is a configuration diagram of a biological treatment device to which the present invention is applied.

FIG. 2 is a graph showing the results of Examples and Comparative Examples.

FIG. 3 is a graph showing the results of Examples and Comparative Examples.

FIG. 4 is a graph showing the results of Examples and Comparative Examples.

Fig. 5 is a graph showing the total organic carbon (TOC) load of raw water.

Fig. 6 is a diagram showing the configuration of a biological treatment device to which the present invention is applied.

Detailed ways

Fig. 1 is a configuration diagram of a biological treatment device to which the present invention is applied.

The waste water to be treated (raw water) is introduced into the aeration tank 2 through the pipe 1 . The carrier C carrying the biofilm is filled in the aeration tank 2 . A diffuser pipe 3 is provided at the bottom of the aeration tank 2, and air is supplied from a blower 4 through a pipe 5 to perform aeration.

The water subjected to aerobic biological treatment by the biofilm passes through the screen 2a and is taken out from the pipe 6 as treated water.

In this biological treatment device, as measuring means, a flow meter 7 and a concentration meter 8 for measuring the flow rate of raw water flowing in the piping 1 and the concentration of the substance to be treated, a DO meter 9 for measuring DO in the tank 2, and a flow meter for measuring the concentration of the substance to be treated are provided. The air volume meter 10 of the air volume supplied by the blower 4 to the diffuser pipe 3 is input to a controller 11 . The blower 4 is controlled by the controller 11 so as to control the aeration intensity.

Examples of the concentration meter 8 include a total organic carbon meter, an ammonia nitrogen meter, or a UV absorbance meter (to determine total organic carbon/N) and the like.

The present inventors have conducted various researches and found that when the flow load and the tank load are used as the raw water load, although the raw water load is the same, one of the reasons why it is sometimes difficult to perform appropriate aeration management is the density of the carrier and particles filled in the aeration tank. Status changes.

For example, when the aeration tank filled with the fluidized bed carrier is operated for a long time, the carrier is cut and the particle size is reduced, and it flows out of the aeration tank from the gap of the screen, the carrier filling rate in the aeration tank is reduced, and the tank The carrier filling rate in the biofilm decreases, the contact area between the surface of the biofilm and the bulk water decreases, and the treatment performance decreases.

During long-term operation, the amount of microorganisms held on the carrier increases and the oxygen consumption due to self-decomposition of microorganisms may increase.

In the case of installing an aeration tank with an expanded bed using a settling carrier as one of the fixed bed treatments, it is necessary to periodically backwash to discharge excess sludge and SS between the carriers. At this time, the carrier may be worn out due to the mutual collision and shear force of the carriers, and the carrier filling rate may gradually decrease, the carrier filling rate in the tank may decrease, the contact area between the surface of the biofilm and the bulk water may decrease, and the treatment performance may decrease.

During long-term operation, the amount of microorganisms held in and between carriers increases, and the amount of oxygen consumption due to self-decomposition of microorganisms may increase.

In the biological treatment tank using self-granulating particles, the number and particle size of self-granulating particles change with time, and the amount of biofilm in the aeration tank increases and decreases, thereby reducing the contact area between biofilm and bulk water. As a result, the diffusibility of oxygen to the biofilm changes, so even if the organic matter load is the same, the aeration air volume required for wastewater treatment also changes.

In the present invention, the relationship between the raw water biofilm load and the corresponding DO target value and/or the corresponding aeration intensity set value is preset, and according to the variation of the measured value of the raw water biofilm load, according to the The relationship adjusts the corresponding DO target value and/or aeration intensity setting value.

Moreover, the aeration device is controlled so that DO reaches a target value or a set aeration intensity setting value.

As raw water biofilm load, the removal target substance load per unit filling volume of the carrier (carrier volume load) or the removal target substance load per unit total surface area of the carrier group (all carriers in the tank) (carrier surface area load), the unit of particles The removal target substance load (particle volume load) of the filling volume or the removal target substance load per unit total surface area of the particle group (all particles in the tank) (particle surface area load).

＜Raw water load＞

Calculate the raw water load according to the following formula.

Load = Q Concentration

Load: raw water load [kg/d].

Q: Raw water flow rate [m ³ /d].

Concentration: raw water concentration [kg/m ³ ].

The concentration of raw water includes the concentration of total organic carbon/N estimated from total organic carbon, ammonia nitrogen, and UV absorbance.

＜Carrier Volume Load＞

The carrier volume load was calculated from the following formula.

Load _{carrier volume} = load/V _carrier

Load _{carrier volume} : carrier volume load [kg/(m ³ ·d)].

V carrier: the carrier filling volume in the aeration tank [m ³ ].

＜Carrier Surface Area Load＞

The carrier surface area load was calculated from the following formula.

Load _{carrier surface area} = load/S _carrier

Load _{carrier surface area} : carrier surface area load [kg/(m ² ·d)].

S _carrier : the total surface area [m ² ] of the carrier group in the aeration tank.

In the aeration tank, the raw water load sometimes changes rapidly with time in minutes, but the time-dependent change of the properties of the carrier (carrier filling volume in the aeration tank or the total surface area of the carrier group in the aeration tank) is measured in days. Months change relatively slowly. Therefore, it is preferable to frequently update the calculated value of the raw water load. In addition, for the carrier filling volume in the aeration tank or the total surface area of the carrier group in the aeration tank, it is only necessary to periodically sample and analyze the carrier (for example, at a frequency of about once every 1 to 3 months), and update the carrier filling. Volume and total surface area data of the carrier group are sufficient.

[Control with oxygen consumption rate as management index]

[How to estimate oxygen consumption rate]

According to one aspect of the present invention, as the sum of the oxygen demand required for the oxidation of organic substances in raw water and the oxygen consumption caused by the autoxidation of microorganisms held on the biofilm, the oxygen consumption required to be supplied as a monitoring treatment device is monitored. The oxygen consumption rate of the treatment device of the index and the control of the aeration intensity according to the oxygen consumption rate. That is, under low-load conditions where the oxygen consumption rate is below the specified value, in order to maintain the agitation intensity in the treatment water tank, the aeration intensity is set to be above the specified intensity, and when the oxygen consumption rate is above the specified value, the oxygen consumption level Corresponding aeration intensity adjustment. As described above, the method of estimating the oxygen consumption rate when the oxygen consumption rate is used as the management index will be described using FIG. 6 .

In the biological treatment device of FIG. 6 , waste water to be treated (raw water) is introduced into an aeration tank 2 through a pipe 1 . The carrier C carrying the biofilm is filled in the aeration tank 2 . Diffuser pipes 3a, 3b, 3c are installed at the bottom of the aeration tank 2, and air is supplied from the blower 4 through the piping 5 and branch pipes 5a, 5b, 5c to perform aeration. A top cover 2r is installed in the aeration tank 2 .

The water subjected to aerobic biological treatment by the biofilm passes through the screen 2a and is taken out from the pipe 6 as treated water.

In this biological treatment device, as measuring means, an exhaust meter 24 for measuring the oxygen concentration in the gas phase part of the upper part of the aeration tank 2 and the lower side of the top cover 2r, and a DO meter for measuring DO in the aeration tank 2 are provided. 19 and an air flow meter 20 for measuring the amount of air supplied from the blower 4 to the diffuser pipes 3a to 3c.

<Case 1: Method of estimating oxygen consumption rate from air flow meter and exhaust meter>

Measure the aeration air volume and the oxygen concentration in the exhaust, and directly calculate the oxygen consumption rate qO ₂ according to the following formula.

Mathematical formula 1

Mathematical formula 2

OTE: Oxygen transfer efficiency [-].

Z ₀ : Oxygen mole fraction [-] blown into the air.

Z: Oxygen mole fraction in exhaust gas [-].

qO ₂ : Oxygen consumption rate [kg/d].

Gv: blowing flow rate [Nm ³ /d] of the aeration air converted from the standard state.

v _m : Specific volume of oxygen [Nm ³ /kg].

<Case 2: Method for calculating oxygen consumption rate from DO meter and aeration air volume>

Measure the aeration air volume and DO, and indirectly calculate the oxygen consumption rate qO ₂ .

(i) Calculate (preparation before installation of the control device) the oxygen solubility index φ necessary for the estimation of the oxygen consumption rate from the following formula.

Mathematical formula 3

Mathematical formula 4

OTE: Oxygen transfer efficiency [-].

Z ₀ : Oxygen mole fraction [-] blown into the air.

Z: Oxygen mole fraction in exhaust gas [-].

φ: Oxygen solubility index [m].

v _m : Specific volume of oxygen [Nm ³ /kg].

h: water depth of the diffuser [m].

Cs: concentration of saturated dissolved oxygen [kg/m ³ ].

C: Concentration of dissolved oxygen in the mixed solution [kg/m ³ ].

(ii) Continuous measurement (while the device is running) of the oxygen consumption rate over time.

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

Mathematical formula 5

qO ₂ : Oxygen consumption rate [kg/d].

Gv: blowing flow rate [Nm ³ /h] of the aeration air converted from the standard state.

h: water depth of the diffuser [m].

Cs: concentration of saturated dissolved oxygen [kg/m ³ ].

C: Concentration of dissolved oxygen in the mixed solution [kg/m ³ ].

φ: Oxygen solubility index [m].

[Relationship between DO target value or aeration intensity setting value corresponding to raw water biofilm load]

In the embodiment of the present invention, the oxygen consumption rate (qO ₂ ) is regarded as the raw water load (load), and then the "carrier volume load" or "carrier surface area load" is calculated, and the calculation result is regarded as the "raw water biofilm load" According to the prediction or actual performance of the treated water quality under the condition of changing the DO target value or aeration intensity, find the appropriate DO target value or aeration intensity setting value, and find the appropriate DO target value corresponding to the raw water biofilm load or The aeration intensity set point relationship is effectively utilized in the control system.

The relationship between raw water biofilm load and DO target value or aeration intensity setting value is set using the result data of the preliminary experiment, actual operation performance data, and the simulation results of the mechanism model considering the diffusion of oxygen in the biofilm.

The expression method of the relationship between the raw water biofilm load and the DO target value or the set value of the aeration intensity can be a function formula (an approximate function of the appropriate DO target value or the appropriate aeration intensity is obtained according to the raw water biofilm load), a control table (The relationship between the raw water biofilm load and the appropriate DO target value or the appropriate aeration intensity is arranged in the form of a table), etc. Any one of them.

[A biofilm mechanism model for the relationship between raw water biofilm load and DO target value and/or aeration intensity setting]

As one method for discovering the relationship between raw water biofilm load and DO target value and/or aeration intensity set point, it is possible to use the putative biofilm pollutants when they are in contact with the bulk water phase in the flow state containing pollutants and oxygen. The kinetic model of the reduction and the increase and decrease of the amount of activated sludge cells in the biofilm (hereinafter sometimes referred to as the biofilm mechanism model). This kinetic model also needs to take into account the simultaneous occurrence of bacterial growth and consumption of pollutants and oxygen consumption in the biofilm, the diffusion of dissolved oxygen in the bulk water phase to the biofilm, and the dissolution of oxygen in the bulk phase due to aeration. Phenomena in water to construct. In addition, the increase and shrinkage of biofilms are caused by the increase and decrease in the volume of the bacterial cell group accompanied by the proliferation and death of the bacterial cells, the attachment of the bacterial cells from the bulk water, and the detachment of the bacterial cells to the bulk water. When utilizing kinetic models in biofilm utilization processes, mathematical modeling of these phenomena is required. Since this phenomenon occurs in a three-dimensional space, the model formula becomes complicated, but by expressing the growth and shrinkage of the biofilm with a one-dimensional model formula that only considers changes in the thickness direction, it can be relatively easily to simulate. As a mathematical model for simulating wastewater treatment using activated sludge, for example, a series of mathematical models proposed by a task force of the International Water Association (Reference 1) can be effectively used. As an example of a mathematical model for biofilms, (Reference Document 2) and the like can be used.

Reference 1: M Henze; IWA. Task Group on Mathematical Modeling for Design and Operaton of Biological Wastewater Treatment; et al.

Reference 2: Boltz, J.P., Johnson, B.R., Daigger, G.T., Sandino, J., (2009a). "Modeling Integrated Fixed-Film Activated Sludge and Moving Bed Biofilm Reactor Systems I: Mathematical Treatment and Model Development". WaterEnvironment Research, 81(6), 555-575.

By using a mathematical model, for example, a mathematical model of a fluidized bed carrier can be constructed. Usually, this kind of mathematical model is mostly recorded in the form of simultaneous ordinary differential equations, and the dynamic behavior of the target process can be simulated by numerical integration software with simultaneous ordinary differential equations as the object. For example, it is possible to predict the treated water quality based on the DO status of the bulk water phase which changes due to a specific device structure, load assumption, and aeration intensity.

By using a mathematical model, it is possible to predict, for example, the total organic carbon concentration of treated water when treatment is performed at various aeration intensities for various load conditions. Based on the simulation results, the minimum DO target value and the adjustment of the aeration intensity to prevent deterioration of the treatment were studied, and a table was prepared to organize the simulation results, which can be effectively used for the control table used in the control system of this patent.

[Control of Aeration Intensity]

The aeration intensity can be controlled by, for example, changing the aeration air volume (air supply flow rate), the aeration stop time per predetermined time period, or the aeration suppression time (weak aeration time). The aeration stop time indicates the time at which the aeration is stopped within a prescribed period of time in so-called intermittent aeration. The aeration suppression time means the time to alternately repeat the strong aeration and the weak aeration in the weak aeration operation.

According to the raw water load, the aeration air volume, aeration stop time, and aeration inhibition time are controlled continuously or periodically.

[Biological treatment other than fluidized bed]

In FIG. 1 , the biological treatment using a fluidized bed carrier is explained, but the present invention can be implemented in the same way when using a fixed bed carrier or granules. For example, in the case of raw water particle loading, it is only necessary to set the volume or surface area of the carrier or carrier group to the volume or surface area of particles or particle group in the formulas (2) and (3).

In this embodiment, the case where the wastewater containing organic matter is treated by the aerobic biofilm treatment accompanied by aeration is described. In addition, the biological nitrification and denitrification treatment using the biofilm, etc. are included in the aeration process. The present invention can also be carried out by the same method in the biological treatment of the aerobic treatment step using a biofilm in a tank.

Example

＜Device Structure＞

An example of a method of monitoring the raw water load and controlling the DO weak aeration time with respect to the carrier volume load of the total organic carbon of the fluidized bed carrier using the apparatus of FIG. 1 will be described below.

The controller 11 has a mechanism for adjusting the amount of aeration to achieve a DO value corresponding to a DO target value, and an intermittent aeration mechanism for periodically performing weak aeration with a specified air volume.

As the carrier C, a cube-shaped polyurethane sponge carrier having a length of one side of 3 mm was used.

＜Biofilm Mechanism Model＞

In fact, the diffusion phenomenon of pollutants and oxygen generated between the interior of the carrier with a three-dimensional structure and the bulk water is represented by a one-dimensional simple model. This one-dimensional model consists of a total of four layers assuming three layers of bulk water and biofilm. A model of a fully mixed compartment is constructed.

Bacteria consume substrates, namely pollutants and oxygen in the bulk water phase and biofilm to proliferate and self-decompose in a prescribed proportion. Proliferated bacteria will attach and desorb according to the difference in the concentration of bacteria in the bulk water phase. Generally, since the concentration of bacteria in the biofilm is higher than that of the bulk water phase, the desorption amount of the bacteria proliferating in the biofilm is greater than the amount of bacteria attached to the biofilm existing in the water phase. Many situations are modeled.

The matrix, that is, the pollutants of the treatment object is supplied by the inflow and drainage, part of it flows out with the treated water, and the rest diffuses to the biofilm according to the concentration difference between the bulk water phase and the biofilm. Modeling of the conditions in which the proliferation of oxidative decomposition and reduction is carried out. It becomes a model that the rate of oxidative decomposition of pollutants decreases with the decrease of oxygen concentration and matrix, that is, the concentration of pollutants along with the proliferation of microorganisms.

Most of the oxygen is supplied to the bulk water phase through the diffuser, and a part of the oxygen is also supplied as oxygen contained in the inflow wastewater. In addition, a part of the supplied oxygen flows out together with the treated water, and the remaining part diffuses to the biofilm according to the difference between the oxygen concentration of the bulk water phase and the oxygen concentration of the biofilm, and the growth of microorganisms in the bulk water phase and the biofilm and consumption from self-decomposition were modeled. It becomes a model that the rate of reduction of oxygen consumed by the growth of microorganisms of pollutants decreases as the oxygen concentration and the concentration of substrates, that is, pollutants, decrease.

<Relationship between raw water biofilm load and DO target value and/or aeration intensity setting>

Using the mathematical formula of the one-dimensional diffusion model of the constructed biofilm, the treated water quality under the treatment conditions was predicted by numerical integral simulation, and the appropriate control conditions were exploratoryly obtained, which are summarized in the following control table.

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

Table 1

In this control table, for example, when the volume load of total organic carbon carrier (kg C/(m ³ ·d), the unit is sometimes omitted below) is 0.1 or more to less than 0.6, the DO target value is 3.1 mg/L; 0.6 or more When it is less than 0.7, the target value of DO is 3.8 mg/L; when it is more than 0.7 to less than 0.9, the target value of DO is 3.9 mg/L; when it is more than 0.9 to less than 1.0, the target value of DO is 4.4 mg/L; 1.0 In the above cases, the target value of DO is 4.8 mg/L, and each is set to an appropriate value.

When the total organic carbon carrier volume load is more than 0.1 to less than 0.2, set the weak aeration time setting value to 110 minutes every 2 hours; when it is more than 0.2 and less than 0.3, it is 90 minutes every 2 hours; 80 minutes per 2 hours, 60 minutes per 2 hours when 0.4 or more and less than 0.5, 20 minutes every 2 hours when 0.5 or more and less than 0.6, respectively set to appropriate values, total organic carbon carrier volume load 0.6 (kg When C/(m ³ ·d)) is above, set the weak aeration time setting value to zero (that is, no intermittent aeration).

[Example 1]

The raw water whose total organic carbon load fluctuates as shown in Fig. 5 was set as the treated wastewater.

According to the 2-hour moving average of the carrier volume load, the DO target value and the weak aeration time of the 2-hour cycle are adjusted every 2 hours according to the control table in Table 1, and the weak aeration is set to a fixed low air volume ( ^3m3 /(bottom area m ² ·hr)), for time periods other than weak aeration, control the motor speed of the blower to achieve the set DO target value.

FIG. 2 shows the time-dependent change of the length of the weak aeration time, and FIG. 3 shows the time-dependent change of DO. In addition, the temporal change of the power consumption of the blower is shown in FIG. 4 .

[Comparative example 1]

The DO target value was set at a fixed value of 3.5 mg/L, and the weak aeration time was maintained at a fixed value of 10 minutes/2 hours, except that it was the same as in Example 1. The results are shown in FIGS. 2 to 4 .

＜Survey＞

In Example 1, the DO target value and the weak aeration time were adjusted according to the load per unit carrier, so the power consumption of the blower was smaller than that of Comparative Example 1. That is, the power consumption of Comparative Example 1 was about 1150 kWh/day, whereas the power consumption of Example 1 was about 950 kWh/day, which is about 17% less.

In addition, there was almost no difference in the treated water quality between Example 1 and Comparative Example 1.

Although this invention was demonstrated in detail using the specific embodiment, it is clear to those skilled in the art that various changes can be added without deviating from the intention and range of this invention.

This application is based on Japanese Patent Application No. 2020-063031 filed on March 31, 2020, the entire contents of which are hereby incorporated by reference.

Explanation of reference signs

2: Aeration tank; 3: Diffuser pipe; 4: Blower; 7: Flow meter; 8: Concentration meter; 9: DO meter; 10: Air volume meter; 11: Controller.

Claims (6)

1. A method for aerobic biofilm treatment, comprising supplying raw water to an aeration tank, aerating the raw water with an aerator, and aerobically treating a target substance to be removed in the raw water with biofilm-retaining carriers or granules filled in the aeration tank,

the relationship between the load of raw water biofilm, which is the load of raw water per carrier or granule, and the target dissolved oxygen concentration value and/or aeration intensity set value corresponding thereto is set in advance,

adjusting the dissolved oxygen concentration target value and/or the aeration intensity set value in accordance with the relationship in correspondence with the variation of the measured value of the raw water biofilm load,

the aeration device is controlled so that the dissolved oxygen concentration reaches the target value or a set aeration intensity set value is set.

2. The aerobic biofilm treatment method according to claim 1,

the raw water biofilm load is any one of a removal target substance load per packed volume of the carrier, a removal target substance load per total surface area of the carrier group, a removal target substance load per packed volume of the particles, and a removal target substance load per total surface area of the particle group.

3. The aerobic biofilm treatment method according to claim 1 or 2,

the removal target substance is an organic substance, a nitrogen compound or an ammonium ion,

the raw water biofilm load is calculated from a calculated value of concentration converted from a measured value of concentration or a measured value of absorbance of the removal target, a measured value of raw water flow rate, and a measured value or a calculated value of a filling volume or a surface area of the carrier or the particle.

4. The aerobic biofilm treatment method according to any one of claims 1 to 3,

the aeration intensity is controlled by controlling the aeration air quantity, the aeration stop time or the aeration inhibition time.

5. The aerobic biofilm treatment method according to any one of claims 1 to 4,

the relationship is set using any one of experimental results, actual operation results, and a mechanism model in which the oxygen diffusivity in the biofilm is considered.

6. An aerobic biofilm treatment apparatus comprising an aeration tank to which raw water is supplied, an aeration apparatus for aerating the aeration tank, carriers or granules with biofilm filled in the aeration tank, and a controller for controlling the aeration apparatus,

the aerobic biofilm treatment device comprises:

a means for presetting the relationship between the load of raw water biofilm, which is the load of raw water per carrier or granule, and the target dissolved oxygen concentration value and/or aeration intensity set value corresponding thereto; and

means for adjusting the target dissolved oxygen concentration value and/or the aeration intensity set value in accordance with the relationship in accordance with the change in the measured value of the raw water biofilm load,

the controller controls the aeration device so that the dissolved oxygen concentration reaches the target value or a set aeration intensity set value is set.

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