JP7014258B2 - Aerobic organism treatment methods and equipment - Google Patents

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 biological membranes, 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. The biological membrane method, which treats sludge in an accumulated and proliferated manner, is used.

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

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

Regarding the self-granulation granule method and the fluidized bed carrier method, Patent Document 2 describes 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. 2001-353496 Japanese Unexamined Patent Publication No. 63-256185

In the self-granulation granule method, fluidized bed carrier method, fixed bed carrier method, and other methods that use biological membranes, the flow rate per unit time of raw water and pollutants in raw water are common indicators of raw water load. It is actually difficult to adjust the appropriate oxygen supply amount based only on the inflow load obtained by the product of the 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.

That is, even if the raw water load is the same and the amount of oxygen required to oxidize the organic matter in the raw water is the same, in the method using the biofilm, the amount of microorganisms held in the reaction tank in the form of the biofilm is large. Since it changes with time, the amount of oxygen consumed due to the self-decomposition process of the microorganism itself changes. Therefore, it is necessary to determine the amount of oxygen supplied to the device in consideration of the same factor.

Due to these factors, the amount of oxygen required for oxidation of organic matter in raw water changes according to load fluctuations, and the amount of oxygen required to be supplied changes depending on the amount of biofilm held in the treatment apparatus. In the case of the biomembrane method that relies on the diffusion phenomenon for oxygen supply, it is necessary to adjust the DO of the bulk water according to the amount of oxygen to be supplied to the biofilm, and the aeration air volume for maintaining the DO of the bulk water is also. Need to be adjusted.

In particular, when the load increases, the amount of oxygen required to oxidize organic matter in the raw water increases, and even when the amount of biofilm held in the treatment device increases, the amount of oxygen that needs to be supplied increases. The amount increases.

In the case of the biofilm method in which the oxygen supply depends on the diffusion phenomenon, when the amount of oxygen to be supplied to the biofilm increases, it is necessary to increase the DO of the bulk water, and the DO of the bulk water is increased. It is also necessary to increase the amount of aerated air.

For this reason, when operating without adjusting or controlling the aeration air volume according to the load, the aeration air volume is 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 aeration volume.

Under constant air volume operation that can maintain the required high DO under high load, energy 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 setting a high DO target value assuming oxygen supply at the time of high load, the DO level can be lowered to maintain the load reduction in the biofilm treatment device, so the target DO of DO control is performed. Although it is possible to further reduce the aeration air volume by lowering the level, energy consumption is still wasted because the air volume is not suppressed by such a decrease in the DO target value in normal DO control.

For this reason, the waste of energy consumption becomes particularly remarkable when the load fluctuation is large.

On the other hand, in aerobic biological membrane treatment using self-granulation granules or carrier-adhered microorganisms, when aeration is controlled according to the raw water load, the air volume per unit bottom area decreases when the raw water load is low. Therefore, the mixing and stirring action of the water in the tank due to aeration is insufficient, the fluid state of the carrier and granule cannot be maintained, and the carrier and granule are deposited on the bottom of the tank for a long period of time. As a result, the treatment efficiency decreases due to the decrease in the contact area with bulk water, and the bottom of the tank becomes an anaerobic atmosphere, which causes putrefactive odor due to sludge putrefaction, especially hydrogen sulfide when treating sulfur-containing wastewater. Sulfur-based odorous gas such as is generated and causes odor problem. In addition, the carrier and granule once deposited on the bottom of the tank are agglomerated, and the nitrogen gas generated by the denitrification reaction and the anaerobic gas generated by the putrefaction reaction are accumulated inside, so that the specific gravity becomes lighter than that of bulk water. As it floats near the surface of the water, it becomes difficult to stably maintain the carrier and granules in the treatment water tank, and problems related to leakage of the carrier to the outside of the device and deterioration of the treatment capacity occur.

When the BOD volume load is smaller than the predetermined value, the fluidization of the microbial carrier is used as the criterion, and when the BOD volume load is larger than the predetermined value, the oxygen demand of the wastewater is used as the criterion to control the aeration amount of the wastewater. Is proposed in Patent Document 2. However, when aeration is controlled by this method, especially in biofilm treatment intended to promote both nitrification and denitrification reactions in the biofilm at the same time, the biofilm is affected, especially when the load is reduced. Since the oxygen supply is excessive, the so-called anoxic state in which there is no oxygen and only nitric acid remains cannot be maintained even inside the biofilm, and a situation occurs in which the denitrification reaction inside the biofilm does not proceed. As a result, there arises a problem that the concentration of NO ₃ -N in the treated water increases and the amount of the alkaline chemical required for neutralizing NO ₃ -N increases.

The present invention ensures nitrogen treatment under high load conditions, which is a characteristic of biofilm processes, suppresses energy loss under low load conditions, and avoids problems related to granule sludge or carrier deposition. It is an object of the present invention to provide an aerobic biological treatment method and an apparatus using a biofilm that can reduce the problem of performance deterioration.

The aerobic biological treatment method of the present invention is a method in which raw water is supplied to an aeration tank and the substance to be removed in the raw water is aerobically treated with a biological membrane holding carrier or granule filled in the aeration tank to obtain treated water. In low load conditions where the load is less than or equal to a predetermined value, the aeration intensity is set to a predetermined value at which the carrier or granule can flow, and the aeration intensity is set to less than the predetermined value or the aeration is stopped. It is characterized by alternating weak aeration.

The aerobic biological treatment apparatus of the present invention comprises an aeration tank to which raw water is supplied, a biological membrane holding carrier or granule filled in the aeration tank, and an aeration device for aerating the aeration tank. In the apparatus, the aeration intensity is set to a predetermined value at which the carrier or granule can flow under a low load condition where the load is a predetermined value or less, and the aeration intensity is set to a value less than the predetermined value or the aeration is stopped. It is characterized by being provided with an aeration control means that alternately performs weak aeration.

In one aspect of the present invention, the low load condition equal to or less than the predetermined condition in the preceding paragraph is a low load satisfying any one of the following (a) to (d).
(A) The measured value of the raw water load is below the specified value (b) The measured value of the oxygen consumption rate of the aeration tank is below the specified value (c) The target value of the DO concentration controlled under high load conditions where the load exceeds the specified value is Less than or equal to the specified value (d) The set value of the aeration intensity controlled under high load conditions where the load exceeds the specified value is less than or equal to the specified value.

In one aspect of the present invention, each of the predetermined values (a) to (d) is set so that the aeration air volume at the time of weak aeration is between 1/2 and 1/5 of the minimum aeration air volume. It is a numerical value at the time of

In one aspect of the invention, the raw water load is either an inflow load, a tank load, or a carrier volume load.

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

In one aspect of the present invention, there is no mechanical stirring means or draft tube for stirring the water in the tank.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to prevent the bottom portion of the tank from becoming an anaerobic atmosphere, and biological treatment is efficiently performed. Further, in the case of the treatment for the purpose of nitrification denitrification, the denitrification reaction in the weak aeration step can be promoted even under low load conditions.

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

<Control using raw water load as a management index>
In one aspect of the present invention, continuous aeration is performed under a high load condition with a load of a predetermined value or more, and aeration control generally called intermittent aeration is performed under a low load condition with a load of a predetermined value or less. Specifically, it is provided with an aeration control means that repeats a weak aeration step of stopping or suppressing aeration for a designated time and a strong aeration step of periodically setting the aeration intensity for a designated time to a predetermined intensity or higher. The method of calculating the volumetric load of the raw water carrier in this case will be described below with reference to FIG.

[Method of calculating raw water load from TOC meter and flow meter]
The biological treatment apparatus shown in FIG. 1 performs aeration control based on the raw water load using the measured value of the TOC concentration of the raw water.

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

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

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

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

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

Load = Q ・ Conc / 1000
Load: 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 the concentration of TOC / N estimated from UV absorbance.

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

_{Road CarrierVol} = Road / V _{Carrier
LoadCarrierVol} : Carrier volumetric load [kg / ⁽ m3 ・ 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 carrier periodically (for example, once every 1 to 3 months) and analyzing the carrier filling volume. , 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, aeration control is performed using the oxygen consumption rate as a control index for the raw water load. That is, the aeration intensity is set to be equal to or higher than the specified intensity under a low load condition in which the oxygen consumption rate is equal to or less than a predetermined value. As described 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. 2, 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 the carrier C supporting the 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 6 and is taken out as treated water from the pipe 7.

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 concentration 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 air diffusers 3a to 3c is provided.

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

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

<Case 2: How to calculate the oxygen consumption rate from the DO meter and the aerated 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 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 from the DO meter, the continuous measurement data of the aerated air volume, and the oxygen solubility index φ obtained in advance by the following equation.

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 air diffuser [m]
Cs: Saturated dissolved oxygen concentration [kg / m ³ ]
C: Dissolved oxygen concentration in the mixture [kg / m ³ ]
φ: Oxygen solubility index [m]

[Correlation of management indicators used for control]
When the raw water load and oxygen consumption rate are large, if the load index is above the specified value, continuous aeration is applied and DO control is applied to raise the DO concentration target value in the aeration tank according to the load, and the load is below the specified value. In the case of, the time of the weak aeration step of the intermittent aeration is shortened, that is, the time of the strong aeration step is lengthened. The correlation between this raw water load and oxygen consumption rate and the corresponding DO concentration target value or the time of the weak aeration process is determined by considering the preliminary experiment result data, the actual operation record data, and the diffusivity of oxygen in the biological membrane. Build in advance using the simulation results of the model.

As a method of implementing this correlation in the control system, a method of implementing by a functional expression describing the correlation between the raw water load and the appropriate value of the DO target value or the weak aeration time or the appropriate value of the combination of both, or the control. Any method of expressing using a table or the like may be used.

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

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

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

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

[Control of aeration intensity]
The aeration intensity can be controlled, for example, by changing the aeration air volume (supply air flow rate) and the weak aeration process time for each fixed time cycle. In the weak aeration step, aeration is performed with a designated aeration volume smaller than the fluidized minimum aeration air volume, and in the strong aeration step, aeration above the fluidized minimum aeration air volume or DO control with a DO target value that can secure the same air volume is performed.

The aeration air volume, aeration stop time, and aeration suppression time are controlled continuously or stepwise according to the raw water load.

[Minimum fluidization air volume, longest aeration stop time or longest weak aeration time]
The minimum fluidized aeration air volume in the examples of the present invention ensures the fluid state of the entire carrier in the fluidized bed carrier device, prevents the carrier from accumulating on the bottom of the aeration tank, promotes contact between the carrier and bulk water, and at the same time. The minimum amount of aeration required to suppress the problems of sludge decay and hydrogen sulfide odor caused by the accumulation on the bottom of the carrier and the problem of floating of the massive carrier after the accumulation.

In the fluidized bed carrier device adopting the intermittent aeration method in which aeration and aeration stop are repeated, the longest aeration stop time or the longest weak aeration time in the embodiment of the present invention means that the aeration stop or the aeration suppression operation is repeated at regular time cycles. Refers to the maximum time of the weak aeration process. In the weak aeration process, it is assumed that the minimum aeration air volume for fluidization is not secured, and the average aeration intensity is further suppressed and related to the processing device that performs continuous aeration by adjusting the air volume. It has the characteristic that it can also suppress the power consumption. This causes a certain percentage of carrier deposits on the bottom of the device during this step. By limiting the time of the same process within a certain period of time and securing the air volume equal to or higher than the minimum aeration air volume (referred to as the air volume in the strong aeration step in the present invention), the deposited carrier can be refluidized. As a result, the problem of sludge decay and the generation of hydrogen sulfide odor caused by long-term deposition on the bottom of the carrier are suppressed. The longest aeration stop time or the longest weak aeration time is set for this purpose.

The minimum aeration air volume or the longest aeration stop time for fluidization is preferably determined based on the result data of the preliminary experiment, the actual operation data of the actual machine, and the like. In the implementation example of the present invention, when the load is high, the intermittent aeration operation in which weak aeration and strong aeration are repeated is not performed, and continuous aeration that can fully utilize the capacity of the aeration device is performed. When the load decreases, a lower DO target value is set according to the control table to suppress the aeration air volume, but when the aeration air volume reaches the minimum aeration air volume, the aeration method is switched to intermittent aeration operation. The aeration air volume, which is the criterion for switching from continuous aeration operation to intermittent aeration operation, can be managed by directly measuring the aeration volume, but any of the following indicators (a) to (d) should be monitored and used as the index value. By pre-evaluating the relationship with the air volume, the aeration air volume is estimated based on the index, continuous aeration when the aeration air volume ≥ fluidized minimum aeration air volume, and intermittent when the aeration air volume <fluidized minimum aeration air volume. It is also possible to control aeration.
(A) The measured value of the raw water load is below the specified value (b) The measured value of the oxygen consumption rate of the aeration tank is below the specified value (c) The DO concentration controlled according to the load under high load conditions (under continuous aeration) Target value is below the specified value (d) The set value of the aeration intensity (including aeration air volume) controlled according to the load under high load conditions (under continuous aeration) is below the specified value.

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

[Biological treatment other than fluidized bed]
Although the biological treatment using the fluidized bed carrier has been described in FIG. 2, the present invention can be carried out by the same method when a fixed bed carrier or granule is used.

[Aeration management other than TOC]
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. The present invention can be carried out by the same method when performing biological treatment including an aerobic treatment step using a biological membrane. Therefore, the water quality value of the treated water is not limited to TOC, but may be NH ₄ -N / NO ₃ -N, NO ₂ -N, the concentration of a specific chemical substance, or a combination thereof.

In one aspect of the present invention, in an aeration tank that does not agitate by another power such as a mechanical aeration means or a draft tube, it is necessary that the aeration contact between the biological film and the bulk water is maintained and the water treatment performance can be exhibited. The minimum air volume shall be used, and the air volume in the strong aeration step shall be equal to or greater than the fluidized minimum aeration air volume. Further, even when the DO control is performed in the strong aeration step, the DO control is performed so that the aeration air volume becomes equal to or more than the fluidized minimum aeration air volume. In the weak aeration operation process, the air volume is suppressed so that the minimum fluidized aeration air volume is not secured, so the average aeration intensity is further suppressed compared to the processing device that maintains the minimum fluidized aeration air volume while performing continuous aeration. It becomes possible to do. However, during this weak aeration step, minimal agitation contact between the biofilm and bulk water is maintained, but a certain percentage of the carrier deposits on the bottom of the device. By limiting the time of the same process within a certain period of time and aerating the remaining cycle time, that is, the strong aeration process time with the amount of fluidized air, the deposited carrier is refluidized, resulting in long-term deposition on the bottom of the carrier. Suppress the problem of sludge rot and the generation of hydrogen sulfide odor. The maximum weak aeration time is set to secure the maximum weak aeration process time that can surely cause refluidization, in other words, the minimum strong aeration process time that can surely cause refluidization.

In one aspect of the present invention, intermittent aeration that can maintain the fluidity of the carrier on a regular basis under low load suppresses long-term accumulation of the carrier and granules on the bottom of the aeration tank, and as a result, Suppressing the odor problem associated with the generation of anaerobic gas and the generation of hydrogen sulfide when treating sulfur-containing wastewater, the carrier and granule once deposited on the bottom of the tank are agglomerated, and the nitrogen generated by the denitrification reaction By accumulating gas and anaerobic gas generated by the decay reaction inside, the specific gravity becomes lighter than that of bulk water and floats near the water surface, making it difficult to stably maintain carriers and granules in the treated water tank. It is possible to suppress the problem of leakage of the carrier to the outside of the reaction vessel and the problem of deterioration of the processing capacity.

In the nitrification denitrification treatment, the average aeration intensity is compared with the case where continuous aeration is performed while avoiding the problems related to the deposition of carriers and granules by intermittent aeration in which weak aeration is performed regularly. The anoxic environment in the biological membrane can be maintained mainly in the weak aeration step, the progress of the denitrification reaction can be maintained, and the increase in the concentration of nitrate nitrogen in the treated water can be suppressed. As a result, the problem that the nitrogen treatment target of the treated water cannot be achieved due to the increase in the concentration of nitrate nitrogen in the treated water under low load conditions is alleviated, the cost is reduced by suppressing the addition concentration of alkaline chemicals necessary for adjusting the pH of the nitrate nitrogen, and the latter stage. It is possible to reduce the ion load on water treatment processes such as RO.

When the load is high, the intermittent aeration is stopped and continuous aeration is performed to enable high load processing that maximizes the oxygen supply capacity of the air diffuser. In the nitrification denitrification treatment, an oxygen-free environment is formed in the deep part of the microbial membrane due to the diffusion of oxygen and organic substances in the biological membrane and the progress of the oxidation treatment including nitrification by microorganisms without intermittent aeration, and the denitrification performance. If the aeration is properly controlled and the conditions such as the load of organic substances are met, the denitrification reaction will proceed satisfactorily. Nitrogen removal while saving energy by maximizing the denitrification reaction in the biological membrane while continuously aerating under DO control and supplying oxygen necessary for the nitrification of ammonia and the oxidation of organic substances that are not treated by the denitrification reaction. Performance can be ensured.

[Example 1]
In the aerobic biological treatment apparatus for the fluidized bed carrier shown in FIG. 2, the following water quality wastewater 1 or wastewater 2 was treated under the conditions shown in the following and Table 1.

<Water quality of drainage>
Drainage type:
Electronic product manufacturing factory Organic wastewater High load:
Raw water concentration fluctuation range TOC 115-150 mgC / L, ammonia nitrogen 15-30 mgN / L
It fluctuates about twice a day in a half-day cycle. When the amount of raw water is constant and the load is low:
Raw water concentration fluctuation range TOC 60-90 mgC / L, ammonia nitrogen 7-15 mgN / L
Fluctuates about twice a day in a half-day cycle

<Processing device method>
Fluidized bed type aerobic biofilm treatment 3 mm square cubic urethane sponge carrier Filling rate 40%
<Processing conditions>
High load: 0.7-1.0 ^kgC / (carrier m3 ・ d)
Low load: 0.4-0.6 ^kgC / (carrier m3 ・ d)
Stirring and mixing by aeration Minimum aeration air volume of fluidization: 7 m ³ / (bottom surface m ² · h)
Processing time: 0.5 days Conditions for aeration control when applying the present invention Air aeration cycle time during intermittent aeration control: 120 minutes Air volume per bottom area in the weak aeration process: 2.6 m ³ / (bottom m ² · h)
Target value of DO control in the strong aeration process:
Set the DO target value at which the aeration amount is equal to or greater than the fluidized minimum aeration amount according to the load. Use the multiple control tables in Table 1 to adjust the aeration conditions according to the load. In this example, the third “standard” control table was used, which is selected by comparing the treated water quality targets with.

<Target value of treated water quality>
TOC 5-10mg C / L
Nitrate nitrogen concentration 5-10 mgN / L

In Table 2, "low load" refers to the case where the water quality is "low load" in the above <wastewater quality> and the condition is "low load" in the above <treatment conditions>, and is referred to as "high load". Indicates the case where the water quality at the time of "high load" in the above <water quality of wastewater> is the condition of "high load" in the above <treatment condition>.

The aeration control method and control conditions were changed under the following conditions, and the power consumption per carbon amount per raw water load unit (called the power basic unit) and the treated water quality were evaluated.

Example 1:
Aeration control based on the "standard" control table is performed under low load conditions.
Under low load conditions, the weak aeration process and the strong aeration process are repeated, and the weak aeration process is controlled between 60 and 20 minutes depending on the load. The DO target value in the strong aeration process is 3. It was controlled between 1 and 3.8 mg / L.

Comparative Example 1:
In order to maintain carrier flow under low load conditions, constant aeration air volume control was performed with the minimum flow aeration air volume.

Comparative Example 2:
Under low load conditions, the DO target value was controlled at an approximate average value of 3.0 mg / L of the actual DO value of Example 1 for the purpose of reducing the amount of aerated air.

Comparative Example 3:
Under low load conditions, assuming operation where aeration is always constant regardless of load conditions, DO control that provides good TOC treated water quality even under high load conditions. Aeration control at the target of 4.8 mg / L was performed. ..

Comparative Example 4:
Assuming operation in which aeration is always performed with constant wind under low load conditions, aeration air volume per bottom area is 14 m ³ / (m ² · h), which provides good TOC treated water quality even under high load conditions. Was aerated.

Example 2:
Under high load conditions, aeration control based on the "standard" control table is performed according to the aeration control of this patent. Under high load conditions, continuous aeration was performed by DO control, and the DO target value was controlled between 3.9 and 4.8 mg / L depending on the load.

Comparative Example 5:
Under high load conditions, assuming operation in which the DO value is constantly aerated regardless of the load conditions, aeration control was performed at the DO control target of 4.8 mg / L, which provides good TOC treated water quality even under high load conditions. ..

Comparative Example 6:
Assuming operation in which aeration is always performed with constant wind under high load conditions, aeration air volume per bottom area is 14 m ³ / (m ² · h), which provides good TOC treated water quality even under high load conditions. Was aerated.

As shown in Table 2, the carrier flow state, aeration power intensity, and treated water quality under each aeration condition are as follows.

Example 1:
By suppressing the aeration power by suppressing the aeration power in the weak aeration process, and by securing the aeration air volume of the minimum aeration air volume in the strong aeration process, the carrier that has settled in the weak aeration process is refluidized to make the carrier. It was possible to prevent the odor problem from accumulating on the bottom. The treated water quality can reach the target values of TOC 6 mgC / L and nitrate nitrogen 8 mgN / L, and the aeration power intensity is 4k.
It became Wh / kgC.

Comparative Example 1:
By maintaining the constant flow minimum aeration air volume, the odor problem associated with the accumulation of the carrier did not occur, the treated water quality was TOC 4 mgC / L, which was below the target value, and the nitrate nitrogen was 11 mgN / L, which was the target value. It became higher. By giving priority to carrier flow, the amount of aeration becomes excessive and carbon-based pollutants can be treated well, but the denitrification reaction that occurs in the carrier when aeration is suppressed is suppressed and nitrogen treatment is not promoted. The reason was thought to be the increase in nitric acid concentration. The basic unit of aeration power is 6kWh / kgC, which is 2 more than that of Example 1.
It became a high value of kWh / kgC.

Comparative Example 2:
By operating to suppress DO at all times, the aeration power intensity is 3kWh /
The aeration amount was kgC, which was 1 kWh / kgC lower than that of Example 1, but the aeration amount per bottom area was less than the minimum flow air volume of 7 m ³ / (m ² · h) 2-3 m ³ / (.
As a result of the constant maintenance of ^m2 · h), the fluidity of the carrier deteriorated and the carrier was deposited on the bottom, resulting in an odor problem. The treated water quality is TOC 11mgC
It became / L and the target value could not be achieved, and the nitrate nitrogen was 6 mgN / L, which was within the range of the target value. The deterioration of the TOC value is due to the fact that the surface area of the biofilm in contact with the bulk water is substantially reduced due to the accumulation of the carrier, the amount of oxygen diffused into the biofilm is reduced, and the oxidizing ability of carbon-based organic matter is reduced. It is inferred that.

Comparative Example 3:
As a result of aeration that maintains the required DO value under high load, the aeration air volume was suppressed according to the load, but the high DO value was maintained under low load conditions, so the power intensity was 7kWh / It becomes kgC, and it becomes 3kWh / k from Example 1.
The gC value was high. The treated water quality was TOC 4 mgC / L, which was below the target value, and the nitrate nitrogen was 15 mgN / L, which was higher than the target value and even higher than that of Comparative Example 1. This is because the amount of aeration is excessive and carbon-based pollutants can be treated well, but the denitrification reaction that occurs in the carrier during aeration suppression is suppressed, nitrogen treatment is not promoted, and the nitric acid concentration rises. it was thought.

Comparative Example 4:
As a result of aeration to maintain the required air volume under high load, the excessive aeration air volume was maintained under low load conditions, so the power intensity was 14kWh / kgC, which is significantly higher than Example 1 by 10kWh / kgC. It became a value. The treated water quality was TOC 3 mgC / L, which was below the target value, and the nitrate nitrogen content was 20.
The value was mgN / L, which was higher than the target value and even higher than that of Comparative Example 3.

Example 2:
The aeration power intensity is 4kWh / k by setting the DO target value according to the load fluctuation.
It became gC and could be the same as the aeration power basic unit under low load conditions. The treated water quality reached the target values of TOC 7 mgC / L and nitrate nitrogen 4 mgN / L.

Comparative Example 5:
As a result of aeration that maintains the required DO value at the peak value of high load, the aeration air volume was suppressed according to the load, but the high DO value was still maintained when the load fluctuated periodically and decreased. Therefore, the power intensity was 5 kWh / kg C, which was 1 kWh / kg C higher than that of Example 2. The treated water quality is TOC
The water quality was 6 mgC / L and nitrate nitrogen was 6 mgN / L, which was within the target range.

Comparative Example 6:
As a result of aeration to maintain the required air volume at the peak value of high load, the excessive aeration air volume was maintained in the state where the load fluctuated periodically and decreased, so the power source unit was 7kWh / kgC. The value was 3 kWh / kg C higher than that of Example 2. The treated water quality was TOC 5 mgC / L, which was within the target value range.
Nitrate nitrogen was 12 mgN / L, which was higher than the target value.
Assuming operation in which aeration is always performed with constant wind under high load conditions, aeration air volume per bottom area is 14 m ³ / (m ² · h), which provides good TOC treated water quality even under high load conditions. Was aerated.

Compared with the comparative example, the examples do not cause the problem of odor and the decrease in the treatment capacity due to the accumulation on the bottom of the carrier under the low load condition, and the treated water quality can be set within the target value range while keeping the aeration power intensity low. It was confirmed that the aeration air volume can be adjusted according to the load even under high load conditions, and the treated water quality can be kept within the target value range while keeping the aeration power intensity low.

2 Aeration tank 3 Dispersing tube 4 Blower

Claims (7)

In a method of supplying raw water to an aeration tank and aerobic biologically treating a substance to be removed from the raw water with a fluidized bed of a biological membrane-retaining carrier filled in the aeration tank to obtain treated water.
Continuous aeration under high load conditions where the load exceeds the specified high load value,
Under low load conditions where the load is equal to or less than the predetermined low load value, whether to set the aeration intensity to a predetermined aeration intensity value at which the carrier can flow and the aeration intensity to be less than the predetermined aeration intensity value. Alternatively, a method for treating aerobic organisms, which comprises alternately performing weak aeration to stop aeration. The aerobic organism treatment method according to claim 1, wherein the low load condition is a low load satisfying any one of the following (a) to (d).
(A) The measured value of the raw water load is below the specified value (b) The measured value of the oxygen consumption rate of the aeration tank is below the specified low load value (c) The load is above the specified high load value under high load conditions (under continuous aeration ) ), The target value of the DO concentration controlled according to the load is equal to or less than the predetermined DO concentration value (d) The aeration controlled according to the load under high load conditions (under continuous aeration) in which the load exceeds the predetermined high load value. The set value of intensity is less than or equal to the specified aeration intensity value Each of the predetermined values (a) to (d) is a numerical value when the aeration air volume is set so that the aeration air volume during weak aeration is between 1/2 and 1/5 of the fluidized minimum aeration air volume. The aerobic organism treatment method according to claim 1, wherein the aerobic organism is treated. The aerobic biological treatment method according to claim 2 or 3, wherein the raw water load is any one of an inflow load, a tank load, and a carrier volume load. The aerobic biological treatment method according to any one of claims 1 to 4, wherein the aeration intensity is controlled by the aeration air volume, the aeration stop time, or the aeration suppression time. The aerobic biological treatment method according to any one of claims 1 to 5, wherein the aeration tank is not provided with a mechanical stirring means for stirring the water in the tank or a draft tube. In an aerobic biological treatment apparatus having an aeration tank to which raw water is supplied, a fluidized bed of a biological membrane holding carrier filled in the aeration tank, and an aeration device for aerating the aeration tank.
Continuous aeration under high load conditions where the load exceeds the specified high load value,
Under low load conditions where the load is equal to or less than the predetermined low load value, whether to set the aeration intensity to a predetermined aeration intensity value at which the carrier can flow and the aeration intensity to be less than the predetermined aeration intensity value. Alternatively, an aerobic biological treatment apparatus comprising an aeration control means for alternately performing weak aeration to stop aeration.

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