JP2021159860A - Aerobic biological film treatment method and device - Google Patents

Abstract

To provide aerobic biological film treatment method and device for comparing electrical power expense in the case of performing biological film holding amount reduction treatment with that in the case of not performing the biological film holding amount reduction treatment, and selecting one of the cases in which electrical power expense is low.SOLUTION: There is provided a method for supplying raw water to an aeration tank and subjecting a removal object substance in the raw water to an aerobic biological film treatment by a biological film carrier or a granule filled in an aeration tank. The method calculates an aeration electrical power expense A in a subsequent predetermined period when biological film holding amount reduction treatment is not performed, and then calculates a total expense (B+C) of a subsequent aeration electrical power expense B and a biological film holding amount reduction treatment expense C in a subsequent prescribed period when the biological film holding amount reduction treatment is performed, then compares (B+C) and A, and determines that the biological film holding amount reduction treatment is preferable if the (B+C) is smaller than A.SELECTED DRAWING: Figure 1

Description

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

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

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

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

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

In various water treatment plants, operation management workers manage the amount of power received by the substation and the amount of chemicals purchased, and grasp the cost and basic unit status from the balance of the entire water treatment plant (patent). Documents 3 to 6).

Japanese Unexamined Patent Publication No. 2001-335496 JP-A-63-256185 Japanese Unexamined Patent Publication No. 9-318665 Japanese Unexamined Patent Publication No. 2000-339002 Japanese Unexamined Patent Publication No. 2002-86131 Japanese Unexamined Patent Publication No. 2006-260519

In methods such as the self-granulation granule method, fluidized bed carrier method, and fixed bed carrier method 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. Strictly speaking, it is 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.

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

(ii) In the treatment method using biofilm, it is necessary to diffuse oxygen in the biofilm where microorganisms are accumulated. The main factors that affect the diffusivity of oxygen into the biofilm are the contact area between the microbial membrane and bulk water, the high and low DO of bulk water, the sludge retention concentration in the microbial membrane, and the accumulation concentration of inorganic components. It is known that in the self-granulation granule method, the amount of granule retained and the size of the granule change, so that the contact area between the microorganism and the bulk water changes.

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

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

Due to these factors, the amount of oxygen required to oxidize raw water organic matter changes according to load fluctuations, and the amount of oxygen required to supply changes depending on the amount of microbial membrane held in the treatment equipment, especially. In the case of the biological membrane method that relies on the diffusion phenomenon for oxygen supply, it is necessary to adjust the DO of bulk water according to the amount of oxygen to be supplied to the biological membrane, and the amount of blast air to maintain the DO of bulk water is also Need to be adjusted.

When operating without adjusting or controlling the aeration air volume according to the load, the aeration air volume should be excessively increased so that the DO of the bulk water can be maintained high and the oxygen supply amount can be maintained even at a high load. It is necessary to operate with a constant air 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 aeration control is performed by assuming oxygen supply at high load and setting a high DO target value, the target DO of aeration control can be lowered to maintain the load reduction with the biological membrane treatment device. Although it is possible to further reduce the aeration air volume by lowering the level, energy consumption is still wasted because the normal aeration control does not suppress the air volume due to such a decrease in the DO target value.

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

Therefore, the waste of energy consumption becomes particularly remarkable when the load fluctuation is large.

Furthermore, even if appropriate aeration control is performed according to load fluctuations, the amount of biofilm retained in the treated water tank tends to increase when the biofilm-based biofilm is operated for a long period of time, and the biofilm tends to be retained. When the retention amount of the biofilm increases, the contact area between the biofilm and the bulk water decreases, the oxygen permeability decreases, the amount of oxygen supplied to the biofilm decreases, and the treated water quality deteriorates. When the treated water quality of the biofilm deviates from the predetermined value due to the increase in the biofilm retention amount, it is determined that the biofilm retention amount in the aeration tank has increased more than necessary, and the biofilm retention amount of the carrier is reduced. It is conceivable to perform treatment or treatment for reducing the amount of biofilm retained, such as treatment of a partially decomposed product of granules. However, the biofilm retention reduction treatment itself also requires time and effort to determine the implementation and costs for implementation.

An object of the present invention is to provide an aerobic biofilm treatment method and apparatus for comparing the power costs of the case where the biofilm retention reduction treatment is performed and the case where the treatment is not performed and selecting the one with the lower power cost. ..

The aerobic biological membrane treatment method of the present invention is a method in which raw water is supplied to an aerobic tank and the substance to be removed in the raw water is treated with an aerobic biological membrane by a biological membrane holding carrier or granule filled in the aerobic tank. The aerobic power cost A within the subsequent predetermined period when the membrane retention reduction treatment is not performed is calculated, and the aerobic power cost B and the biological membrane within the subsequent predetermined period when the biological membrane retention reduction treatment is performed. The total cost (B + C) with the retention amount reduction treatment cost C is calculated, (B + C) and A are compared, and if (B + C) is smaller than A, it is determined that the biological membrane retention reduction treatment is suitable. It is characterized by doing.

The aerobic biological membrane treatment apparatus of the present invention is an aerobic organism having an aeration tank to which raw water is supplied, a biological membrane holding carrier or granule filled in the aeration tank, and an aeration device that aerates the aeration tank. In the membrane treatment apparatus, a means for calculating the aeration power cost A within the subsequent predetermined period when the biological membrane retention amount reduction treatment is not performed, and within the subsequent predetermined period when the biological membrane retention amount reduction treatment is performed. The means for calculating the total cost (B + C) of the aeration power cost B and the biological membrane retention reduction processing cost C is compared with (B + C) and A, and if (B + C) is smaller than A, the biological membrane It is characterized by having a means for determining that the holding amount reduction treatment is suitable.

In one aspect of the present invention, the calculations and comparisons of A and (B + C) are performed periodically or when an execution command is given.

In one aspect of the present invention, when the (B + C) is smaller than A by a predetermined amount or more, it is determined that the biofilm retention reduction treatment is suitable.

In one aspect of the present invention, the biofilm retention reduction treatment cost includes the cost of performing the biofilm retention reduction treatment of the carrier or the partial decomposition product treatment of the granule, and the waste sludge generated by the operation. Including costs.

In one aspect of the present invention, the unit-time power consumption H is obtained from the exposed power consumption in the specified period before the cost calculation, and after the calculation, the unit-time power consumption follows a preset gradual increase pattern. Is gradually increased, the aerated power cost A is calculated from the product of the gradually increased unit time power consumption H', the predetermined period, and the power unit price, and the unit time power consumption H'is set in advance. Α · H'multiplied by the set specified ratio α (where α <1) is regarded as the unit time power consumption after the biological membrane retention reduction treatment, and α · A is defined as the aerated power cost B. do.

In one aspect of the present invention, a mathematical model for calculating the amount of power used for aeration power from the DO target value and / or the set value of aeration intensity in the aeration tank, unit price data corresponding to the amount of power used, raw water load, or Two or more correlation groups determined by relating the correlation between the oxygen consumption rate and the DO target value and / or the aeration intensity setting value to the quality of oxygen permeability are set, and the raw water load or Based on one of the above correlations, the DO target value and / or aeration corresponding to the measured value depends on the fluctuation of the measured value of the oxygen consumption rate (including the one calculated from the measured value of another measurement item). Aeration is controlled by adjusting the intensity setting value.

In one aspect of the present invention, the calculated value of the amount of power used for the aeration power per current unit period is calculated from the selected DO target value of the correlation or the actually measured value thereof, and / or the aeration intensity set value or the actually measured value thereof. Is determined, and the aeration power for the predetermined period in the future is constant at the calculated value, or the predicted value of the future aeration power is obtained by a mathematical model that predicts the increase of the aeration power over time, and the calculated value or The power cost A is calculated based on the predicted value and the unit price data of the power consumption, and a correlation having a relatively better oxygen permeability than the correlation used is selected from the correlation group. Based on the aeration action in this correlation, the cost B for the predetermined period in the future is calculated.

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

In one aspect of the present invention, the biofilm retention reduction processing cost C is set as a constant.

In one aspect of the present invention, when the cost A is smaller than the cost (B + C), the period until the cost A and the cost (B + C) become equal is determined.

According to the present invention, when the aeration power efficiency per raw water load decreases, the energy saving obtained by the proposal of implementation of the performance improvement measure of the fluidized bed carrier, the renewal of the carrier, and the maintenance work such as strong backwashing of the fixed carrier. It is possible to quantitatively show the effect and the cost-effectiveness for the maintenance cost.

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

In the present invention, if it is determined that the biofilm retention reduction treatment at present is cheaper than the biofilm retention reduction treatment after a lapse of a predetermined period, the biofilm retention of the carrier It is determined that the reduction treatment (for example, biofilm peeling from the carrier, partial decomposition product of granule, etc.) is appropriate.

That is, the cost of continuing the current exposure control without performing the biological membrane retention reduction treatment (cost A: the current unit-time power consumption multiplied by the power unit price is accumulated for a predetermined period of time. (Cost calculated by It is compared with the cost (B + C) obtained by adding the biological membrane retention reduction processing cost C to the cost calculated by accumulating the power cost per unit time multiplied by the power unit price for a predetermined period.

Then, the size of the cost A and the cost (B + C) are compared, and the necessity of executing the biofilm retention reduction treatment is determined based on the cost merit.

In addition, in order to obtain the period until the cost (B + C) falls below the cost A, the predetermined period is set as a variable, and the length of the period until the cost A and the cost (B + C) become equal (or the difference becomes small) is compared. You may judge the cost merit.

As the operation of biofilm exfoliation and granule decomposition product, it is preferable to apply shearing force to forcibly reduce sludge as described in (1) to (4) below.
(1) Strongly stir with a rotary stirring blade or backwash.
(2) Strong aeration.
(3) Circulate at high flow velocity.
(4) Pass the water in the tank through the crushing pump inside or outside the tank.

The sludge generated by partially decomposing the biological film and granules peeled off from the carrier is discharged as SS to the outside of the tank together with the treated water, and solid-liquid separation (aggregation precipitation, aggregation pressure flotation, aggregation filtration, etc.) After processing, it is discharged from the system.

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

The biological membrane retention reduction processing cost includes unit price data of additional materials used, labor cost data of processing work, pump power cost, power cost for boosting the blower during strong aeration, and the like.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

For example, in the third table from the top, the carrier filling volume per TOC load ^{[kgC / (m 3 · d} ). Hereinafter, the unit may be omitted. ] Is 0.1 or more and less than 0.6, the DO target value in the strong aeration process is 3.1 mg / L, and when the TOC load is 0.1 or more and less than 0.2, the weak aeration process time is 2. 110 minutes per hour, 90 minutes every 2 hours when the TOC load is 0.2 or more and less than 0.3, and 2 weak aeration process times when the TOC load is 0.3 or more and less than 0.4. 80 minutes per hour, weak aeration process time every 2 hours when TOC load 0.4 or more and less than 0.5, weak aeration process time 2 when TOC load 0.5 or more and less than 0.6 40 minutes is set as an appropriate value for each hour, and when the TOC load is 0.6 or more and less than 0.7, the DO target value in the strong aeration process is 3.8 mg / L and the weak aeration process time is every 2 hours. If the TOC load is 0.7 or more, intermittent aeration is not performed (weak aeration time is 0 minutes), and if the TOC load is 0.7 or more and less than 0.9, the DO target value is set to 3.9. When the TOC load is 0.9 or more and less than 1.0, the DO target value is set to 4.4, and when the TOC load is 1.0 or more, the DO target value is set to 4.8 as appropriate values. The same applies to the other tables.

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

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

If the TOC of the treated water is higher than the TOC upper limit of the control target when the control table (the control table at the bottom in Table 1) is selected and controlled assuming the situation where the processing performance is the lowest, it is higher than that. However, since the control table with increased aeration intensity has not been set, the performance is restored by performing the biofilm retention reduction treatment.

Even at the stage where the processing performance is slightly deteriorated (for example, the state of the fourth control table from the top), the performance is performed by performing the biofilm retention reduction treatment in consideration of the energy efficiency and cost of aeration enhancement. May be restored.

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

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

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

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

In this biological treatment apparatus, as measuring means, a flow meter 22 and a TOC total 23 for measuring the flow rate and TOC concentration of raw water flowing through the pipe 1, a DO total 19 for measuring DO in the aeration tank 2, and a blower 14 disperse. An aeration meter 20 for measuring the amount of air supplied to the trachea 13 is provided, and these detected values are input to the controller 21. The aeration intensity is controlled by controlling the blower 14 by the controller 21.

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

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

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

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

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

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

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

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

[Control using oxygen consumption rate as a management index]
[Calculation method of oxygen consumption rate]
In one aspect of the present invention, aeration control is performed using the oxygen consumption rate as a control index. 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. 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. 5, the wastewater to be treated (raw water) is introduced into the aeration tank 2 through the pipe 1. The aeration tank 2 is filled with a carrier C supporting a biofilm. Air diffusers 3a, 3b, 3c are installed at the bottom of the aeration tank 2, and air is supplied from the blower 4 through the pipe 5 and the branch pipes 5a, 5b, 5c to perform aeration. The aeration tank 2 is provided with a canopy 2r.

The water that has been aerobically treated by the biofilm passes through the screen 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 in the aeration tank 2 are used. An air volume meter 20 for measuring the amount of air supplied from the blower 4 to the aeration pipes 3a to 3c is provided.

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

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

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

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

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

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

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

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

This correlation is organized and used in a functional expression describing the functional relationship between the raw water load and the appropriate value of the DO target value and / or the aeration intensity setting value, or a control table or the like.

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

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

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

By using the mathematical model as described in the previous section, it is possible to predict, for example, the TOC concentration of the treated water when the treatment is performed with various aeration intensities under various load conditions. A table in which the 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]
As a uniform form of the implementation of this patent, an example of combining so-called intermittent aeration in which general DO control is performed at a high load and weak aeration and strong aeration are alternately repeated at a low load will be described. In the intermittent aeration of this case, the weak aeration step of suppressing or stopping the aeration with the minimum required constant air volume for a predetermined time and the strong aeration step of performing DO control for the remaining time are repeated every fixed time cycle. .. The aeration stop time indicates the time for stopping the internal aeration in a fixed time cycle in so-called intermittent aeration. The aeration suppression time is the time of weak aeration in the operation of alternately repeating strong aeration and weak aeration. In the explanation of intermittent aeration in this case, the total process time of the control cycle consisting of the weak aeration process and the strong aeration process is referred to as the cycle time, the process time of the weak aeration process is referred to as the weak aeration process time, and the process time of the bullish process is referred to as the process time of the bullish process. It is called the strong aeration process time. The time of the weak aeration step and the DO target value in the strong aeration step are controlled continuously or stepwise according to the raw water load. The strong aeration process time is automatically determined as the cycle time minus the weak aeration process time. Further, the longest time when adjusting the weak aeration process time is referred to as the longest weak aeration process time.

The DO target value and the weak aeration process time are controlled continuously or stepwise according to the raw water load.

[Cost comparison]
In the present invention, the power cost and the biofilm retention reduction treatment cost are compared between the case where the biofilm retention reduction treatment is performed at the present time and the case where the biofilm retention amount reduction treatment is performed at the present time and after a predetermined period f has elapsed.

[Predetermined period]
The predetermined period f can be arbitrarily set, but is usually preferably selected from 1 month to 36 months, particularly from 12 months to 24 months.

[Calculation of power cost (cost) A when biofilm retention reduction processing is not performed]
In order to predict the amount of power consumption when the biofilm retention reduction process is not performed at the present time, the power consumption per unit time is based on the actual power consumption in the specified period between the current time and the past specified time back from the current time. The consumption amount H (average actual value in the specified period) is calculated.

The first prediction method for predicting the power consumption during the predetermined period f from the present time is to consider that the power consumption per unit time changes at the same H as before during the predetermined period f. .. In this case, the cumulative power consumption in the predetermined period f is calculated as H · f, and H · f · a obtained by multiplying this by the power unit price a becomes the power cost A in the predetermined period f.

The second prediction method considers that the power consumption per unit time gradually increases according to a preset gradual increase pattern during the predetermined period f.

This gradual increase pattern may be a mathematical model, or may be a pattern in which the power consumption per unit time increases at the average increase rate obtained from the operation results of the biological processing apparatus.

Regardless of the gradual increase pattern, the power cost A in the predetermined period f is calculated by multiplying the cumulative power in the predetermined period f by the power unit price a.

[Calculation of power cost (cost) B when biofilm retention reduction processing is performed]
When the biofilm retention reduction treatment is performed, the oxygen diffusivity of the biofilm is improved, so that the TOC can be satisfactorily treated even if the aeration amount is reduced. By reducing the amount of aeration, the blower power consumption is reduced.

How much the power consumption is reduced depends on how many steps the control table is shifted to by the biofilm retention reduction treatment. Therefore, it is preferable to find out how many steps the control table shifts due to the biofilm retention reduction treatment from the operation results of the biological treatment apparatus.

For example, when the control table shifts to a higher table due to the biological membrane retention reduction process, the average power consumption per unit time when controlled according to the control table after the shift and the control table when controlled according to the control table before the shift. The ratio α to the average power consumption per unit time is obtained from the actual data or set as an expected value. Then, B can be calculated by multiplying the amount of money A by this α (that is, B = α · A).

[Biofilm retention reduction processing cost C]
The biological membrane retention reduction processing cost C includes unit price data of the members used in the processing work, labor cost data of the processing work, power cost of the pump, power cost for enhancing the blower at the time of strong aeration, and the like.

These data can be seen from the actual data, but initially it should be set as the total of the predicted values of each cost.

[Contrast between cost A and cost (B + C)]
When the cost (B + C) is lower than the cost A, it is determined that the biofilm retention reduction treatment is suitable, and this treatment is performed. When the cost (B + C) is lower than the cost A by a predetermined amount or more set in advance, it may be determined that the biofilm retention amount reduction treatment is suitable, and this treatment may be performed.

The controller 21 may perform this comparison and give an operation signal to the biofilm retention reduction processing device such as the pump 11, the stirrer 13, and the blower 17 for strong aeration by performing this comparison. A separately installed cost comparison circuit may output a biofilm retention reduction processing start signal, or the worker may execute the biofilm retention reduction processing operation based on the comparison result.

The calculation and contrast of the costs A and (B + C) may be performed continuously, intermittently, or when the calculation / contrast command signal is given.

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

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

[Example 1]
The above costs are compared in the case of using the aerobic biological treatment apparatus for the fluidized bed carrier shown in FIG. 1 having the following constitutional conditions. The predetermined period f is one year.
Aeration tank capacity: 2000m ³ , water depth 5m, bottom area 400m ²
Carrier filling rate: 50%
Carrier filling volume: Reaction tank volume 2000 m ³ x carrier filling rate 50% = 1000 m ³
Average TOC load: 1000 kgC / ratio TOC carrier volume load
= TOC load 1000 [kgC / day] ÷ carrier filling volume 1000 [m ³ ]
^{= 1.0 [kgC / (m 3} · d)]
Control table to be used: Tables 2 and 3 below

Table 2 is a control table created based on the operating conditions directly extracted from the settings of the current control system.

Table 3 is a control table assuming a situation in which the biofilm retention amount is reduced by the biofilm retention reduction treatment and the oxygen diffusion performance index is high, that is, a situation in which the biofilm retention performance is good.

By performing the biological film retention reduction treatment, the air volume per bottom area ^{is 20.0 m 3} / (m ² · h) to 14.0 m at ^{a carrier volume load of 1.0 kg C / (m 3} · d). It is greatly reduced to ³ / (m ^{2 · h).}

Assuming that the power consumption per 1 N-m ^{3 of} air volume is 0.017 [kWh / air volume m ³ ] and the raw water load is constant for the next year, as shown in Table 4, the biological membrane retention amount is reduced at present. In this case, the annual power consumption is reduced from 1.19 GWh / year to 0.83 GWh / year as compared with the case where the biological membrane retention reduction treatment is not performed for one year.

The total costs when the biofilm retention reduction treatment is not performed and when the biofilm retention reduction treatment is performed are as follows.

A = [Annual power cost when biofilm retention reduction treatment is not performed]
= 1.19 GWh / year x power unit price B = [annual power cost when biofilm retention reduction processing is performed]
= 0.83 GWh / year x power unit price C = [Biofilm retention reduction processing cost]
B + C = 0.83 GWh / year x power unit price + [biofilm retention reduction processing cost]

By comparing the total costs calculated in this way, it is possible to know the cost merit when the biofilm retention reduction treatment is performed, and it is preferable to carry out the biofilm retention reduction treatment from the viewpoint of cost merit. I was able to judge.

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

Claims (11)

In a method in which raw water is supplied to an aeration tank and the substance to be removed in the raw water is treated with an aerobic biofilm by a biofilm-retaining carrier or granule filled in the aeration tank.
Calculate the aeration power cost A within the subsequent predetermined period when the biofilm retention reduction treatment is not performed.
The total cost (B + C) of the aeration power cost B and the biofilm retention reduction treatment cost C within the subsequent predetermined period when the biofilm retention reduction treatment is performed is calculated.
A method for treating an aerobic biofilm, which comprises comparing (B + C) and A, and determining that the biofilm retention reduction treatment is suitable if (B + C) is smaller than A. The aerobic biological membrane treatment method according to claim 1, wherein the calculation and comparison of A and (B + C) are performed periodically or when an execution command is given. The aerobic biofilm treatment method according to claim 1 or 2, wherein when the (B + C) is smaller than A by a predetermined amount or more, it is determined that the biofilm retention reduction treatment is suitable. The biofilm retention reduction treatment cost includes the cost of performing the biofilm retention reduction treatment of the carrier or the partial decomposition product treatment of the granule, and the cost of treating the discharged sludge generated by the operation. The method for treating an aerobic biofilm according to any one of 3 to 3. Obtain the unit-time power consumption H from the aerated power consumption in the specified period before the cost is calculated.
After the calculation, the unit time power consumption shall gradually increase according to the preset gradual increase pattern.
The aeration power cost A is calculated from the product of the gradually increased unit time power consumption H', the predetermined period, and the power unit price.
Α · H', which is obtained by multiplying the unit time power consumption H'by a preset specified ratio α (however, α <1), is regarded as the unit time power consumption after the biological membrane retention reduction treatment is performed. , Α · A is the aeration power cost B, and the aerobic biological membrane treatment method according to any one of claims 1 to 4. A mathematical model for calculating the amount of power used for aeration power from the target value of DO in the aeration tank and / or the set value of aeration intensity, and
Unit price data corresponding to power consumption and
Two or more correlation groups determined by relating the correlation between the raw water load or oxygen consumption rate and the DO target value and / or the aeration intensity setting value to the quality of oxygen permeability are set. ,
The target value of DO corresponding to the measured value based on one of the above correlations according to the fluctuation of the measured value of the raw water load or the oxygen consumption rate (including the one calculated from the measured value of another measurement item). And / or the aerobic biological membrane treatment method according to any one of claims 1 to 5, wherein the aeration intensity setting value is adjusted to control the aeration. From the selected target value of DO of the correlation or its actual measurement value, and / or the aeration intensity set value or its actual measurement value, the calculated value of the electric power consumption for the aeration power per unit period is obtained.
It is assumed that the aeration power for the predetermined period in the future is constant at the calculated value, or the predicted value of the future aeration power is obtained by a mathematical model that predicts the increase of the aeration power over time.
The electric power cost A is calculated based on the calculated value or the predicted value and the unit price data of the electric power consumption.
A claim that selects a correlation having a relatively better oxygen permeability than the correlation used and calculates the cost B for the predetermined period in the future based on the aeration action in this correlation. 6. Aerobic biological membrane treatment method. Claims 1 to 1 in which the biological film retention reduction treatment is performed by any one or more of strong stirring by a rotary stirring blade or backwash, strong aeration, high flow velocity circulation, and water flow to a crushing pump of water in a tank. 7. The aerobic biological membrane treatment method according to any one of 7. The aerobic biofilm treatment method according to any one of claims 1 to 8, wherein the biofilm retention reduction treatment cost C is set as a constant. The aerobic biological membrane treatment method according to any one of claims 1 to 9, wherein when the cost A is smaller than the cost (B + C), the period until the cost A and the cost (B + C) become equal is determined. In an aerobic biofilm treatment apparatus having an aeration tank to which raw water is supplied, a biofilm holding carrier or granule filled in the aeration tank, and an aeration device for aerating the aeration tank.
A means for calculating the aeration power cost A within a predetermined period thereafter when the biofilm retention reduction treatment is not performed, and
A means for calculating the total cost (B + C) of the aeration power cost B and the biofilm retention reduction treatment cost C within a predetermined period after the biofilm retention reduction treatment is performed.
An aerobic biofilm treatment apparatus comprising: (B + C) and A, and if (B + C) is smaller than A, a means for determining that the biofilm retention reduction treatment is suitable.

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