CN115335333A

CN115335333A - Aerobic biofilm treatment method and device

Info

Publication number: CN115335333A
Application number: CN202180025019.XA
Authority: CN
Inventors: 大月孝之; 中野达马
Original assignee: Kurita Water Industries Ltd
Current assignee: Kurita Water Industries Ltd
Priority date: 2020-03-31
Filing date: 2021-03-04
Publication date: 2022-11-11
Also published as: WO2021199885A1; KR20220150285A; JP7017165B2; JP2021159844A

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 an apparatus for biofilm treatment of wastewater containing a pollutant capable of biological oxidation by self-granulated particles, fluidized bed carriers, fixed bed carriers, or the like, and particularly to aeration intensity control thereof. In the present invention, the drainage water present outside the biofilm subjected to the microbial treatment is referred to as bulk water.

Background

As a method for treating wastewater containing pollutants capable of biological oxidation, in addition to an activated sludge method using floating sludge, there are biofilm methods in which microorganisms such as a self-granulation method, a fluidized bed carrier method, and a fixed bed carrier method are treated in a form of aggregation and proliferation called biofilm.

In the activated sludge process using the former floating sludge, microorganisms are maintained in a dispersed state in a reaction tank in a form called microorganism floc. The amount of microorganisms maintained in the reaction tank is maintained constant by an operation of removing excess sludge of microorganisms increased by the drainage treatment, so that the amount of oxygen consumption by the self-decomposition process of the microorganisms themselves can be maintained at a constant level. Therefore, the increase and decrease of the oxygen demand in the process are changed in proportion to the load of the raw water. The amount of oxygen consumed to be supplied can be determined by adding a certain amount of oxygen consumption compensation accompanying the self-decomposition process of the microorganism to the oxygen consumption. In this process, the microorganisms are typically held in the form of micro aggregates of about 1mm called flocs, and the contact area between the microorganisms and the bulk water tank is sufficiently ensured. Thus, the permeability and diffusivity of oxygen within the floe are not the main rate-limiting factors in oxygen supply. Therefore, the amount of aeration air to be supplied to the apparatus is considered to be proportional to the amount of oxygen consumption. Patent document 1 describes that the load of pollutants is measured by an instrument, and the aeration air volume is controlled based on the load.

In an activated sludge process and a biofilm process (a self-granulation process, a fluidized bed carrier process, a fixed bed carrier process, and the like) using floating sludge, a so-called DO control system is widely used which performs air volume control for keeping a dissolved oxygen concentration (hereinafter referred to as DO) in a liquid constant as a method for easily adjusting an oxygen supply amount in proportion to a load of raw water.

Patent document 2 describes that in the self-granulation method and the fluidized bed carrier method, when the BOD volume load is less than a predetermined value, the fluidization of the microorganism carriers is used as a criterion, and when the BOD volume load is greater than the predetermined value, the aeration amount of the wastewater is controlled by using the oxygen demand of the wastewater as a criterion.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2001-353496.

Patent document 2: japanese patent laid-open No. 63-256185.

In the method of treating with a biofilm, such as the self-granulation method, the fluidized bed carrier method, and the fixed bed carrier method, it is strictly speaking difficult to perform appropriate adjustment of the oxygen supply amount only based on the inflow load obtained by the product of the flow rate per unit time of normal raw water and the contaminant concentration of raw water, which is an index of the raw water load, and the tank load obtained by dividing the inflow load by the volume of the reaction tank. The reason is as follows.

In the method using a biofilm, since there is no mechanism for keeping the amount of the microorganism retained in the form of a microbial film in the reaction tank constant, as a result, the amount of the retained microorganism changes with time, and therefore, the amount of oxygen consumed by the self-decomposition process of the microorganism itself also changes. Therefore, in the method using the biofilm, it is necessary to determine the oxygen supply amount to the apparatus in consideration of the change in oxygen consumption accompanying the change in the amount of retained microorganisms in addition to the change in oxygen consumption amount which changes in proportion to the load of raw water.

Due to these factors, in the treatment method using the biofilm, the amount of oxygen required for oxidation of organic matter in raw water changes according to load fluctuation, and the amount of oxygen required to be supplied also changes due to a change in the amount of the biofilm held in the treatment apparatus. In addition, in the biofilm method, a biofilm having a thickness of 3mm or more is typically formed, and the contact area between the retained unit microorganisms and the bulk water is smaller than that in the planktonic method. Therefore, when oxygen is supplied to microorganisms in the biofilm, the phenomenon of oxygen diffusion at the contact surface between bulk water and the biofilm becomes a main rate-limiting factor in oxygen supply.

The diffusion rate of oxygen in the biofilm depends on the DO level of bulk water, and therefore, the DO level needs to be adjusted to adjust the oxygen supply amount. From the viewpoint of the aeration system, the required aeration air volume varies depending on the DO level even if the oxygen supply amount is the same. It is well known that the amount of aeration required increases when the DO level is high and decreases when the DO level is low.

Therefore, when the load is increased, the amount of oxygen required for oxidizing the organic substances in the raw water is increased. The amount of oxygen required for supply is determined in consideration of the amount of oxygen consumed by the self-decomposition process that varies according to the amount of microorganisms maintained as a biofilm. Adjustment of the DO level of bulk water to be raised in response to an increase in the oxygen demand for supply requires an increase in the aeration air volume to achieve the target DO level.

In contrast, when the load is reduced, the amount of oxygen required for oxidation of organic matter in raw water is reduced. The amount of oxygen to be supplied is determined in consideration of the amount of oxygen consumed by the self-decomposition process that varies according to the change in the amount of microorganisms held as a biofilm. By reducing the oxygen demand for supply, the DO of the bulk water can be maintained low, and the aeration air volume for achieving the target DO is also reduced.

For this reason, when the operation is not performed in accordance with the load of the aeration air volume and the control is not performed, it is necessary to perform the air volume constant operation in a state where the aeration air volume is excessive in order to maintain the high bulk water DO and the oxygen supply volume even at the time of high load.

In the constant air flow rate operation capable of maintaining the required high DO at the time of high load, the air flow rate suppression corresponding to the reduction of the oxygen consumption amount at the time of load reduction is not performed, and therefore, waste of energy consumption occurs. Even when the DO control is performed with a high DO target value set on the assumption of oxygen supply at a high load, the biofilm treatment device can reduce the DO level at the time of load reduction, and therefore if the target DO level of the DO control is reduced, the aeration air volume can be further limited. However, since such suppression of the air volume decreased according to the DO target is not performed in the normal DO control, energy consumption is also wasted.

For this reason, waste of energy consumption is particularly significant when load fluctuations are large. However, even if such waste of energy consumption occurs, it is difficult in the related art to perform air volume adjustment matching the operation target DO level by adjusting the DO level that does not deteriorate the treated water quality in accordance with the load fluctuation. In the case where the operator performs the appropriate air volume adjustment, conventionally, even with a low load, excessive DO level setting and aeration are often performed so as to allow a certain degree of margin for oxygen supply more than necessary. Therefore, waste of energy is often generated.

If the normal flow rate load and tank load are used as the indicators of the raw water load, the influence of the change in the amount of microorganisms retained in the biofilm cannot be considered. Further, the influence of the contact area between the biofilm and the bulk water cannot be considered, and it is difficult to appropriately control the aeration amount. Therefore, conventionally, it has been generally assumed that oxygen consumption is assumed to be maintained in a large amount of microorganisms, and a large amount of aeration air volume is set without considering the influence of the contact area between the biofilm and the bulk water. Energy is also often wasted for this reason.

Disclosure of Invention

Problems to be solved by the invention

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

Means for solving the problems

An aerobic biofilm treatment method according to the present invention is a method for supplying raw water to an aeration tank, aerating the raw water by using an aeration apparatus, and aerobically treating a target substance to be removed in the raw water by biofilm-retaining carriers or pellets filled in the aeration tank, wherein a relationship between a raw water biofilm load as a unit of a raw water biofilm load of the carriers or pellets and a DO target value corresponding thereto and/or an aeration intensity set value corresponding thereto is set in advance, the DO target value and/or the aeration intensity set value is adjusted in accordance with a fluctuation in a measurement value of the raw water biofilm load based on the relationship, and the aeration apparatus is controlled so that DO reaches the target value or becomes the set aeration intensity set value.

An aerobic biofilm treatment apparatus according to the present invention is an aerobic biofilm treatment apparatus including an aeration tank to which raw water is supplied, an aeration apparatus to aerate the aeration tank, carriers or pellets with biofilm filled in the aeration tank, and a controller to control the aeration apparatus, the aerobic biofilm treatment apparatus including: a means for presetting a relationship between a raw water biofilm load, which is a raw water load per carrier or granule, and a DO target value and/or an aeration intensity set value corresponding thereto; and a means for adjusting the DO target value and/or the aeration intensity set value in accordance with the relationship in response to a change in the measured value of the raw water biofilm load, wherein the controller controls the aeration device so that DO reaches the target value or so that the DO reaches the set aeration intensity set value.

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

According to an aspect of the present invention, the removal target substance is an organic substance, a nitrogen compound, or an ammonium ion, and 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 substance, a measured value of raw water flow rate, and a measured value or a calculated value of a packing volume or a surface area of the carrier or the particle.

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

According to one aspect of the present invention, the relationship is set using any one of experimental results, actual performance, and a mechanism model in which the diffusivity of oxygen in the biofilm is taken into consideration.

ADVANTAGEOUS EFFECTS OF INVENTION

In the present invention, sufficient oxygen supply required for the carrier and pellet properties in the aeration tank that change with time is estimated using the raw water biofilm load without using the flow rate load and the volume load, and the control is performed by changing the target DO value and the set value of the aeration intensity itself, so that the aeration can be appropriately controlled.

Drawings

FIG. 1 is a schematic diagram of a biological treatment apparatus 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 view showing the structure of a biological treatment apparatus to which the present invention is applied.

Detailed Description

The wastewater to be treated (raw water) is introduced into an aeration tank 2 through a pipe 1. The aeration tank 2 is filled with a carrier C carrying a biofilm. An air diffuser 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 is taken out as treated water from the pipe 6 through the screen 2 a.

In this biological treatment apparatus, as measuring means, a flow meter 7 and a concentration meter 8 for measuring the flow rate and the concentration of the material to be treated of the raw water flowing through the pipe 1, a DO meter 9 for measuring the DO in the tank 2, and an air flow meter 10 for measuring the amount of air supplied from the blower 4 to the air diffusion pipe 3 are provided, and detection values thereof are inputted to a controller 11. The blower 4 is controlled by the controller 11 to control the aeration intensity.

Examples of the concentration meter 8 include a total organic carbon meter, an ammonia nitrogen meter, and a UV absorptiometer (obtaining total organic carbon/N).

The present inventors have made various studies and found that when a flow rate load or a tank load is used as a raw water load, it is sometimes difficult to perform appropriate aeration control because the state of carriers or particles filled in an aeration tank changes, although the raw water load is the same.

For example, when an aeration tank filled with fluidized bed carriers is operated for a long period of time, the carriers may be cut to have a smaller particle size and flow out of the aeration tank through the gaps of the screen, thereby decreasing the carrier filling rate in the aeration tank, decreasing the carrier filling rate in the tank, and decreasing the contact area between the biofilm surface and the bulk water, which may result in a decrease in the treatment performance.

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

In the case of an aeration tank provided with an expanded bed using a sedimentable carrier, which is one type of fixed bed treatment, it is necessary to periodically backwash to discharge excess sludge and SS between carriers. In this case, the carriers are abraded by collision and shearing force of the carriers, so that the filling rate of the carriers is gradually decreased, the filling rate of the carriers in the tank is decreased, and the contact area between the surface of the biofilm and the bulk water is decreased, thereby deteriorating the treatment performance.

During long-term operation, the amount of microorganisms held in and between carriers may increase, and the amount of oxygen consumed by the self-decomposition of microorganisms may increase.

In a biological treatment tank using self-granulated particles, the number of self-granulated particles and the particle size vary with time, and the amount of biofilm in the aeration tank increases and decreases, whereby the contact area between the biofilm and the bulk water changes, and the oxygen diffusivity to the biofilm changes, so that the aeration air volume required for the drainage 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 set value is set in advance, and the corresponding DO target value and/or the aeration intensity set value is adjusted according to the relationship in accordance with the fluctuation of the measured value of the raw water biofilm load.

Then, the aeration apparatus is controlled so that the DO reaches a target value or a set aeration intensity value.

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

< raw Water load >

The raw water load was calculated from the following formula.

Load = Q · concentration

Loading: raw water load [ kg/d ].

Q: flow rate of raw water [ m ³ /d]。

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

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

< Carrier volume load >

The volume loading of the support was calculated according to the following equation.

Load(s) _{Volume of carrier} = load/V _Carrier

Load(s) _{Volume of carrier} : volume load of carrier [ kg/(m) ³ ·d)]。

V vector: volume [ m ] of carrier packed in aeration tank ³ ]。

< surface area loading of support >

The surface area loading of the support was calculated according to the following formula.

Load(s) _{Surface area of support} = load/S _Carrier

Load(s) _{Surface area of support} : surface area load of support [ kg/(m) ² ·d)]。

S _Carrier : in an aeration tankTotal surface area of support group [ m ² ]。

In the aeration tank, the raw water load may rapidly change in units of minutes over time, but the change over time in the properties of the carrier (the carrier-packed volume in the aeration tank or the total surface area of the carrier groups in the aeration tank) changes relatively slowly in units of days to months. Therefore, it is preferable to frequently update the calculated value of the raw water load. The volume of the packed carriers in the aeration tank or the total surface area of the group of carriers in the aeration tank may be periodically sampled and analyzed (for example, at a frequency of about 1 time every 1 to 3 months) to update the data on the volume of the packed carriers and the total surface area of the group of carriers.

[ control with oxygen consumption Rate as a control index ]

[ method for estimating oxygen consumption Rate ]

According to one aspect of the present invention, the total of the oxygen demand required for oxidizing the organic substances in the raw water and the oxygen consumption amount by autoxidation of the microorganisms retained on the biofilm is monitored for the oxygen consumption rate of the treatment apparatus, which is an index for monitoring the oxygen consumption that the treatment apparatus needs to supply, and the aeration intensity is controlled in accordance with the oxygen consumption rate. That is, under a low load condition where the oxygen consumption rate is equal to or less than a predetermined value, the aeration intensity is adjusted in accordance with the level of oxygen consumption when the aeration intensity is equal to or more than the predetermined intensity and the oxygen consumption rate is equal to or more than the predetermined value in order to maintain the stirring intensity in the treatment water tank. 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 with reference to fig. 6.

In the biological treatment apparatus of fig. 6, treated wastewater (raw water) is introduced into an aeration tank 2 through a pipe 1. The aeration tank 2 is filled with a carrier C carrying a biofilm.

Air diffusing pipes

3a, 3b, and 3c are provided at the bottom of the aeration tank 2, and air is supplied from a blower 4 through a pipe 5 and

branch pipes

5a, 5b, and 5c to perform aeration. A top cover 2r is provided in the aeration tank 2.

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

< case 1: method for estimating oxygen consumption rate from air gauge and exhaust gas gauge

The aeration air quantity and the oxygen concentration in the exhaust gas are measured, and the oxygen consumption rate qO is directly calculated according to the following formula ₂ 。

Mathematical formula 1

Mathematical formula 2

OTE: oxygen transfer efficiency (- ]).

Z ₀ : oxygen mole fraction in blown air [ -]。

Z: the oxygen mole fraction in the exhaust gas-.

qO ₂ : oxygen consumption Rate [ kg/d]。

Gv: aeration air blowing flow rate [ Nm ] converted in standard state ³ /d]。

v _m : specific volume of oxygen [ Nm ³ /kg]。

< case 2: method for calculating oxygen consumption rate based on DO meter and aeration air volume

Measuring aeration air quantity and DO, indirectly calculating oxygen consumption speed qO ₂ 。

(i) The oxygen solubility index φ required for estimating the oxygen consumption rate is calculated from the following equation (preparation before installation of the control device).

Mathematical formula 3

Mathematical formula 4

OTE: oxygen transfer efficiency-.

Z ₀ : oxygen mole fraction in blown air [ -]。

Z: the oxygen mole fraction in the exhaust gas-.

Phi: oxygen solubility index [ m ].

v _m : specific volume of oxygen [ Nm ³ /kg]。

h: the water depth [ m ] of the air diffusing device.

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

C: concentration of dissolved oxygen in the liquid mixture [ kg/m ] ³ ]。

(ii) The change in the oxygen consumption rate with time was continuously measured (while the apparatus was running).

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

Mathematical formula 5

qO ₂ : oxygen consumption Rate [ kg/d]。

Gv: aeration air blowing flow rate [ Nm ] converted in standard state ³ /h]。

h: the water depth [ m ] of the air diffuser.

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

C: concentration of dissolved oxygen in the mixture solution [ kg/m ] ³ ]。

Phi: oxygen solubility index [ m ].

[ relationship between DO target value or aeration intensity set value corresponding to raw water biofilm load ]

In the present inventionIn the illustrated embodiment, the oxygen consumption rate (qO) ₂ ) The "carrier volume load" or the "carrier surface area load" is calculated as the raw water load (load), the calculation result is regarded as the "raw water biofilm load", an appropriate DO target value or an aeration intensity set value is found based on the prediction or actual result of the treated water quality when the DO target value or the aeration intensity is changed, and the relationship between the appropriate DO target value or the aeration intensity set value corresponding to the raw water biofilm load is found, and the calculation result is effectively used in the control system.

The relationship between the raw water biofilm load and the DO target value or the aeration intensity set value is set using the result data of the preliminary experiment, the actual operation result data, the simulation result of the mechanism model in which the diffusivity of oxygen in the biofilm is taken into consideration, and the like.

The expression method of the relationship between the raw water biofilm load and the DO target value or the aeration intensity setting value may be any of a functional formula (an approximate function in which an appropriate DO target value or an appropriate aeration intensity is obtained from the raw water biofilm load), a control table (a table in which the relationship between the raw water biofilm load and an appropriate DO target value or an appropriate aeration intensity is arranged), and the like.

[ biofilm mechanism model for establishing relationship between raw water biofilm load and DO target value and/or aeration intensity set value ]

As one method for finding the relationship between the raw water biofilm load and the DO target value and/or the aeration intensity set value, a kinetic model (hereinafter, sometimes referred to as a biofilm mechanism model) can be used which estimates the reduction of pollutants and the increase and decrease of the amount of activated sludge bacteria in a biofilm when the biofilm is in contact with a bulk water in a flowing state containing pollutants and oxygen. The kinetic model is constructed in consideration of the simultaneous occurrence of cell growth and contaminant consumption and oxygen consumption in the biofilm, diffusion of dissolved oxygen in the bulk aqueous phase to the biofilm, and dissolution of oxygen in the bulk water by aeration. The increase and decrease in the biofilm are caused by the increase and decrease in the volume of the cell mass accompanying the growth and death of the cells, the adhesion of the cells to the bulk water from the bulk water, and the detachment of the cells from the bulk water. When a kinetic model is used in the biofilm utilization process, it is necessary to mathematically model these phenomena. Since this phenomenon is a phenomenon that originally occurs in a three-dimensional space, the model formula becomes complicated, but the increase and decrease of the biofilm can be expressed by a one-dimensional model formula considering only the change in the thickness direction, and the simulation can be performed relatively easily. As a mathematical model for simulating the wastewater treatment using activated sludge, for example, a series of mathematical models proposed by a task group of International Water Association (reference 1) can be effectively used. As an example of a mathematical model for a biological membrane, there can be used (reference 2) and the like.

Reference 1: m Henze; task Group on physical modeling for Design and Operaton of Biological Water Treatment; e tal.

Reference 2: boltz, j.p., johnson, b.r., daiger, g.t., sandino, j., (2009 a). "modulated Integrated Fixed-Film Activated Sludge and Moving Bed Biofilm reader Systems I: (iii) physical Treatment and Model Development ". Water Environment Research,81 (6), 555-575.

By using a mathematical model, for example, a mathematical model of the fluidized bed carrier can be constructed. In general, such a mathematical model is often described in the form of simultaneous ordinary differential equations, and the dynamic behavior of the target process can be simulated by numerical integration software that targets the simultaneous ordinary differential equations. For example, the quality of the treated water can be predicted based on the DO state of the bulk-aqueous phase that varies depending on a specific apparatus configuration, load assumption, and aeration intensity.

By using the mathematical model, it is possible to predict, for example, the total organic carbon concentration of the treated water when the treatment is performed under various aeration intensities for various load conditions. From the simulation results, the adjustment of the DO target value and the aeration intensity, which are minimum values for preventing the degradation, are examined, and a table in which the simulation results are arranged is created, and the table can be effectively used as a control table used in the control system of the present patent.

[ control of aeration intensity ]

The aeration intensity can be controlled by changing, for example, 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 means a time during which aeration is stopped for a predetermined period of time in so-called intermittent aeration. The aeration control time is a time during which the weak aeration operation is repeated alternately in the strong aeration operation and the weak aeration operation.

The aeration air quantity, the aeration stop time and the aeration inhibition time are continuously or periodically controlled according to the raw water load.

[ biological treatment other than fluidized bed ]

In FIG. 1, the biological treatment using the fluidized bed carrier is described, and the present invention can be carried out by the same method even in the case of using the fixed bed carrier or the particles. For example, in the case of raw water particle loading, the volume or surface area of the carrier or carrier group may be set to the volume or surface area of the particle or particle group in the formulae (2) and (3).

In the present embodiment, the case of using the aerobic biofilm treatment accompanied by aeration for treating the wastewater containing organic matter has been described, and the present invention can be carried out in the same manner also in the case of performing a biological treatment including an aerobic treatment step using a biofilm in an aeration tank, such as a biological nitrification/denitrification treatment using a biofilm.

Examples

< device Structure >

An example of a method for controlling the DO weak aeration time by monitoring the raw water load for the carrier volumetric load of total organic carbon for fluidized bed carriers using the apparatus of fig. 1 will be described below.

The controller 11 includes a mechanism for adjusting the aeration rate to achieve a DO value corresponding to the DO target value and an intermittent aeration mechanism for periodically performing weak aeration with a predetermined air flow rate.

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

< biofilm mechanism model >

In fact, the phenomenon of diffusion of pollutants and oxygen generated between the inside of the carrier having a three-dimensional structure and the bulk water is represented by a one-dimensional simple model composed of a model assuming a total of 4 layers of complete mixing compartments of three layers of bulk water and biofilm.

The cells proliferate by consuming substrates, i.e., contaminants and oxygen, in the bulk aqueous phase and in the biofilm, and self-decompose at a predetermined ratio. The proliferated cells are attached to and detached from each other depending on the difference in cell concentration between the bulk and aqueous phases. Generally, since the cell concentration in the biofilm is higher than that in the bulk-phase aqueous phase, the amount of cell desorption occurring in the biofilm and growing in the biofilm is modeled as being larger than the amount of cell adhering to the biofilm in the aqueous phase.

The substrate, i.e., the pollutant to be treated, was supplied from the influent wastewater, a part of the pollutant flowed out together with the treated water, and the remaining part diffused to the biofilm by the concentration difference between the bulk aqueous phase and the biofilm, thereby modeling the state in which the pollutant was reduced by oxidative decomposition with the growth of the microorganisms in the bulk aqueous phase and the biofilm. The rate of oxidative decomposition of the contaminants with the proliferation of the microorganisms is modeled to decrease with the decrease in the oxygen concentration and the substrate, i.e., the contaminant concentration.

Most of the oxygen is supplied to the bulk aqueous phase by the gas diffusing means, and a part of the oxygen is also supplied as oxygen contained in the influent wastewater. In addition, a part of the supplied oxygen flowed out together with the treated water, and the remaining part diffused to the biofilm by the difference between the oxygen concentration of the bulk aqueous phase and the oxygen concentration of the biofilm, thereby modeling the consumption of the bulk aqueous phase and the biofilm due to the proliferation and self-decomposition of microorganisms. The rate of decrease of oxygen consumed by the contaminant with the growth of the microorganism is a model in which the oxygen concentration and the substrate, i.e., the contaminant concentration decrease.

< relationship between raw water biofilm load and DO target value and/or aeration intensity set value >

The water quality under the treatment conditions was predicted by numerical integration simulation using the mathematical expression of the constructed one-dimensional diffusion model of the biofilm, and appropriate control conditions were obtained heuristically and summarized in the following control table.

In this example, the control table of table 1 was used as the relationship between the DO target value and/or aeration intensity set value corresponding to the raw water biofilm load.

TABLE 1

In this control table, for example, the total organic carbon carrier volume load (kg C/(m) ³ D), hereinafter, the unit may be omitted) is 0.1 or more and less than 0.6, the target value of DO is 3.1mg/L; when the DO concentration is more than 0.6 and less than 0.7, the target value of DO is 3.8mg/L; when the DO concentration is more than 0.7 and less than 0.9, the DO target value is 3.9mg/L; when the DO concentration is more than 0.9 and less than 1.0, the DO target value is 4.4mg/L; when the DO concentration is 1.0 or more, the DO target value is 4.8mg/L, and each is an appropriate value.

The weak aeration time setting value is set to 110 minutes per 2 hours, 90 minutes per 2 hours when the total organic carbon carrier volume load is 0.1 to less than 0.2, 80 minutes per 2 hours when the weak aeration time setting value is 0.3 to less than 0.3, 60 minutes per 2 hours when the weak aeration time setting value is 0.4 to less than 0.5, and 20 minutes per 2 hours when the weak aeration time setting value is 0.5 to less than 0.6, and the total organic carbon carrier volume load is 0.6 (kg C/(m C)) ³ D)) or more, the weak aeration time set value is set to zero (i.e., no intermittent aeration is performed).

[ example 1]

Raw water whose total organic carbon load varied as shown in fig. 5 was treated as wastewater.

Based on the 2-hour moving average of the carrier volume load, the DO target value was adjusted 1 time every 2 hours according to the control table of Table 1, and the weak aeration time was adjusted for 2-hour period, and the low air volume (3 m) was set to be constant at the time of weak aeration ³ /(base area m) ² Hr)), the motor rotation speed of the blower is controlled to reach the set DO target value for the period other than the weak aeration.

The time-dependent change in the length of the weak aeration time is shown in FIG. 2, and the time-dependent change in DO is shown in FIG. 3. Fig. 4 shows a change in power consumption of the blower with time.

Comparative example 1

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

< investigation >)

In example 1, the DO target value and the weak aeration time were adjusted according to the load per unit carrier, and therefore, the amount of electric power used by the blower was less compared to comparative example 1. That is, the power consumption amount of comparative example 1 was about 1150 kWh/day, whereas the power consumption amount of example 1 was about 950 kWh/day, which was reduced by about 17%.

In addition, there was little difference in the quality of the treated water between example 1 and comparative example 1.

The present invention has been described in detail with reference to the specific embodiments, but it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention.

This application is based on Japanese patent application No. 2020-063031, filed 3/31/2020, the entire contents of which are hereby incorporated by reference.

Description of the reference numerals

2: an aeration tank; 3: a gas dispersing pipe; 4: a blower; 7: a flow meter; 8: a concentration meter; 9: a DO meter; 10: a wind meter; 11: and a controller.

Claims

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.