JP7347304B2 - Aerobic biofilm treatment method and device - Google Patents

Description

The present invention relates to a method and apparatus for biofilm treatment of wastewater containing biologically oxidizable pollutants using self-granulating granules, fluidized bed carriers, fixed bed carriers, etc., and particularly relates to control of aeration intensity. In the present invention, wastewater existing outside the biofilm that undergoes microbial treatment is referred to as bulk water.

Treatment methods for wastewater containing pollutants that can be biologically oxidized include the activated sludge method using suspended sludge, the self-granulation granule method, the fluidized bed carrier method, and the fixed bed carrier method, which allow microorganisms to form biofilms. The biofilm method, which treats bacteria in a state where they accumulate and proliferate, is used.

In the former activated sludge method, which uses suspended sludge, there is sufficient contact area between microorganisms and the bulk aqueous phase inside and outside of aggregates of microorganisms, typically around 1 mm in diameter, called microbial flocs. The permeability and diffusivity of oxygen and pollutants are not the main rate-limiting factors for pollutant removal rate. Patent Document 1 describes that the load of pollutants is measured with a meter and the aeration air volume is controlled in proportion to this.

In activated sludge methods using suspended sludge, and biofilm methods such as self-granulation granule methods, fluidized bed carrier methods, and fixed bed carrier methods, as a method to easily adjust the oxygen supply amount in proportion to the load of raw water, BACKGROUND ART A so-called DO control system that performs air volume control to maintain a constant dissolved oxygen concentration (hereinafter referred to as DO) in a liquid 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 a predetermined value, fluidization of the microbial carrier is used as a criterion, and when the BOD volume load is larger than the predetermined value. A wastewater treatment method and apparatus are described in which the amount of aeration of wastewater is controlled based on the oxygen demand of the wastewater.

At various water treatment plants, operation management personnel manage the amount of electricity received at the power receiving and substation panels and the amount of chemicals purchased, and understand the status of costs and basic units from the balance of the water treatment plant as a whole (patent References 3-6).

Japanese Patent Application Publication No. 2001-353496 Japanese Unexamined Patent Publication No. 63-256185 Japanese Patent Application Publication No. 9-318665 Japanese Patent Application Publication No. 2000-339002 Japanese Patent Application Publication No. 2002-86131 Japanese Patent Application Publication No. 2006-260519

In treatment methods that utilize biofilm, such as the self-granulation granule method, fluidized bed carrier method, and fixed bed carrier method, 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 appropriately adjust the oxygen supply amount based only on the inflow load obtained by multiplying the inflow load by the concentration or 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 the organic matter in the raw water is the same, in the method using a biofilm, the microorganisms retained in the reaction tank in the form of a biofilm As the amount changes over time, the amount of oxygen consumed due to the autolysis process of the microorganism itself changes. Therefore, the amount of oxygen supplied to the device must be determined by taking this factor into consideration.

(ii) Treatment methods using biofilms require oxygen to diffuse into the biofilm where microorganisms are accumulated. The main factors that affect the diffusivity of oxygen into the biofilm include the contact area between the microbial film and bulk water, the level of DO in the bulk water, the concentration of sludge retained in the microbial film, and the concentration of accumulated inorganic components. It is known that in the self-granulation granulation method, the amount of granules retained and the granule size change, so the contact area between microorganisms and 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 microorganisms attached inside and outside the carrier. In particular, if the carrier has a structure with voids and biofilm grows in the voids, the amount of biofilm adhering to the carrier will increase, and if all the voids are blocked, contact between bulk water and the biofilm will increase. The area is significantly reduced.

(iv) Such changes in the contact area between bulk water and biofilms have a significant effect on oxygen diffusivity into biofilms. For example, if the contact area between bulk water and biofilm decreases, it is necessary to increase the DO of bulk water even if the same amount of oxygen is supplied into the biofilm, increasing the dissolved oxygen concentration of bulk water. This requires a larger flow rate of air blowing. Furthermore, when the load of raw water increases, the amount of oxygen consumed increases. Therefore, in order to supply the necessary oxygen into the biofilm through a diffusion phenomenon, it is necessary to increase the dissolved oxygen concentration in 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 that needs to be supplied changes depending on the amount of microbial film retained in the treatment equipment. In the case of the biofilm method, which relies on diffusion phenomena 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 amount of aeration air to maintain the DO of the bulk water must also be adjusted. Need to adjust.

In addition, when operating without adjusting or controlling the aeration air volume according to the load, the aeration air volume must be excessively increased so that the DO of bulk water can be maintained high and the oxygen supply amount can be maintained even during high loads. It is necessary to operate at a constant air volume.

Under constant air volume operation that can maintain the required high DO during high loads, energy is wasted because the air volume is not suppressed in accordance with the decrease in oxygen consumption when the oxygen consumption decreases when the load decreases.
In addition, even if aeration control is performed with a high DO target value assuming oxygen supply during high loads, the biofilm treatment equipment can reduce the DO level to maintain load reduction, so the aeration control target DO Although it is possible to further reduce the aeration air volume by lowering the level, normal aeration control does not suppress the air volume by reducing the DO target value, so energy consumption will still be wasted.

Even when performing general air volume control with a constant DO, it is necessary to set the DO with a view to ensuring a sufficient amount of oxygen diffusion into the biofilm during high loads. Therefore, during low load, the DO setting is maintained at a DO level or higher required to maintain the required oxygen supply amount. As a result, the amount of aeration air required to maintain the DO is greater than the required amount, resulting in wasted energy consumption.

Therefore, wasteful energy consumption becomes particularly noticeable when load fluctuations are large.

Furthermore, even if appropriate aeration control is carried out according to load fluctuations, when biological treatment equipment that utilizes biofilm continues to operate for a long period of time, the amount of biofilm retained in the treated water tank tends to increase. When the retained amount of biofilm increases, the contact area between the biofilm and bulk water decreases, oxygen permeability decreases, the amount of oxygen supplied to the biofilm decreases, and the quality of treated water deteriorates. When the quality of biofilm treated water deviates from a predetermined value due to an increase in the amount of biofilm retained, it is determined that the amount of biofilm retained in the aeration tank has increased more than necessary, and the amount of biofilm retained on the carrier is reduced. It is conceivable to carry out treatment to reduce the amount of biofilm retained, such as treatment or partial dismantling treatment of granules. However, the biofilm retention amount reduction treatment itself requires time and effort to decide whether to implement it and costs to implement it.

An object of the present invention is to provide an aerobic biofilm treatment method and device that compares the power costs when performing and not performing biofilm retention amount reduction treatment and selects the one with lower power cost. .

The aerobic biofilm treatment method of the present invention is a method in which raw water is supplied to an aeration tank, and a substance to be removed in the raw water is treated with an aerobic biofilm using a biofilm retention carrier or granules filled in the aeration tank. Calculate the aeration power cost A within the subsequent predetermined period when the membrane retention amount reduction treatment is not performed, and calculate the aeration power cost B and biofilm within the subsequent predetermined period when the biofilm retention amount reduction treatment is performed. Calculate the total cost (B + C) with the retained amount reduction treatment cost C, compare (B + C) and A, and if (B + C) is smaller than A, determine that the biofilm retained amount reduction treatment is suitable. It is characterized by doing.

The aerobic biofilm treatment device of the present invention comprises an aeration tank to which raw water is supplied, a biofilm holding carrier or granules filled in the aeration tank, and an aeration device for aerating the aeration tank. In a membrane treatment device, means for calculating aeration power cost A within a subsequent predetermined period when biofilm retention amount reduction processing is not performed, and within a subsequent predetermined period when biofilm retention amount reduction processing is performed. A means for calculating the total cost (B+C) of the aeration power cost B and biofilm retention amount reduction processing cost C, and comparing (B+C) and A, and if (B+C) is smaller than A, the biofilm The method is characterized by comprising means for determining whether retention amount reduction processing is appropriate.

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

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

In one aspect of the present invention, the cost of the biofilm retention reduction treatment includes the cost of performing the biofilm retention reduction treatment of the carrier or the partial disassembly treatment of the granules, and the cost of treating the discharged sludge generated by the operation. including costs.

In one aspect of the present invention, the power consumption per unit time H is calculated from the aeration power consumption in a specified period before the cost calculation time, and after the calculation time, the power consumption per unit time H is determined according to a preset increasing pattern. The aeration power cost A is calculated by the product of the increased unit time power consumption H', the predetermined period, and the power unit price, and the unit time power consumption H' is calculated in advance. α・H′ multiplied by the set specified ratio α (α < 1) is regarded as the unit time power consumption after the biofilm retention amount reduction treatment, and α・A is the aeration power cost B. do.

In one aspect of the present invention, a mathematical model that calculates the amount of power used for aeration power from the DO target value and/or aeration intensity set value in the aeration tank, unit price data corresponding to the amount of power used, and 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 Depending on the variation in the measured value of the oxygen consumption rate (including that calculated from the actual measured value of another measurement item), the DO target value and/or aeration corresponding to the measured value is determined based on one of the correlations. Aeration control is performed by adjusting the intensity setting value.

In one aspect of the present invention, a calculated value of the amount of power used for the current aeration power per unit period is obtained from the DO target value or its actual value of the selected correlation and/or the aeration intensity setting value or its actual value. Assume that the aeration power for the predetermined period in the future is constant at the calculated value, or calculate the predicted value of the future aeration power using a mathematical model that predicts the increase in aeration power over time, and calculate the calculated value or Calculating the power cost A based on the predicted value and unit price data of power usage, and selecting a correlation with relatively better oxygen permeability than the correlation that was being used from the correlation group; The cost B for the future predetermined period is calculated based on the aeration effect in this correlation.

In one aspect of the present invention, the biofilm retention amount reduction treatment is performed by any one or two of strong agitation using a rotating stirring blade or backwashing, strong aeration, high-flow circulation, and passing water in the tank to a crushing pump. Perform the above steps.

In one aspect of the present invention, the biofilm retention amount reduction treatment 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), a period until cost A and cost (B+C) become equal is determined.

According to the present invention, when the aeration power efficiency per raw water load decreases, energy savings can be achieved through maintenance work such as proposing measures to improve the performance of the fluidized bed carrier, updating the carrier, and strong backwashing of the fixed carrier. It is possible to quantitatively demonstrate the effectiveness and cost-effectiveness of maintenance costs.

1 is a configuration diagram of a biological treatment device to which the present invention is applied. 1 is a configuration diagram of a biological treatment device to which the present invention is applied. 1 is a configuration diagram of a biological treatment device to which the present invention is applied. FIG. 2 is a configuration diagram of a biological treatment device. FIG. 2 is a configuration diagram of a biological treatment device.

In the present invention, if it is determined that the electricity cost is cheaper to perform the biofilm retention amount reduction treatment at this point than to perform the biofilm retention amount reduction treatment after a predetermined period of time, the biofilm retention amount of the carrier It is determined that reduction treatment (e.g., detachment of biofilm from the carrier, partial disassembly of granules, etc.) is appropriate.

In other words, the cost of continuing the current aeration control without performing biofilm retention reduction treatment (Cost A: The current unit time power consumption multiplied by the power unit price, accumulated over a predetermined period of time) (Cost B: Cost calculated based on the amount of electricity used per unit time when the oxygen permeability index is better than the current one) and the cost of continuing aeration control after performing biofilm retention reduction treatment (Cost B: The cost (B+C) is calculated by adding the biofilm retention amount reduction treatment 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 magnitude of the cost A and the cost (B+C) is compared to determine whether or not to execute the biofilm retention amount reduction process based on the cost merit.

In addition, in order to find the period until cost (B + C) falls below cost A, we use a predetermined period as a variable and compare the length of the period until cost A and cost (B + C) become equal (or the difference becomes small). The cost benefit may be determined by

As operations for biofilm peeling and partial granule disassembly, operations that forcefully reduce sludge by applying shearing force as shown in (1) to (4) below are suitable.
(1) Strongly stir using rotating stirring blades or backwashing.
(2) Strong aeration.
(3) High flow rate circulation.
(4) Pass the tank water to the crushing pump inside or outside the tank.

In addition, the sludge generated by partially dismantling the biofilm 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 (coagulation sedimentation, coagulation pressure flotation, coagulation filtration, etc.) After treatment, it is discharged from the system.

The biofilm stripping means and partial disassembly means may be temporarily installed when stripping or partial disassembly is performed, or may be installed as permanent equipment.

The biofilm retention amount reduction processing cost includes unit price data for additionally used parts, labor cost data for processing work, pump power cost, power cost for blower reinforcement during strong aeration, etc.

Hereinafter, the configuration of an aerobic biological treatment apparatus equipped with a means for removing attached biofilm from a fluidized bed carrier or a means for partially dismantling self-granulating granules will be explained with reference to the drawings.

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

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

In this biological treatment equipment, the granules and carriers in the aeration tank 2 are pulled out with a suction pump 11, and are introduced into a stirring water tank 12, and strongly stirred with an agitator 13 to partially dismantle the granules or remove the biofilm attached to the carrier. After the stripping is carried out, it is returned to the aeration tank 2 through the piping 14.

The degree of partial disassembly of the granules or peeling of the biofilm attached to the carrier is adjusted by the following (a), (b), (c), etc.
(a) Adjust the discharge amount of the suction pump 11 to adjust the residence time in the stirring water tank 12.
(b) Adjust the rotational speed of the stirrer 13 to adjust the intensity of biofilm disassembly/peeling.
(c) Adjust the above two together.

Note that instead of providing the stirring water tank 12 and the stirrer 13, an underwater crushing pump may be installed instead.

In FIG. 1, the water from the suction pump 11 is directly supplied to the stirring water tank 12, but as shown in FIG. Alternatively, only carriers and granules with a large amount of biofilm retained and a high sedimentation rate may be selectively supplied to the stirring water tank 12 to perform partial disassembly of the granules or biofilm peeling treatment. Carriers and granules that have a small amount of biofilm retained and a low sedimentation rate are returned to the aeration tank 2 through the pipe 16.

FIG. 3 shows a biological treatment device that uses strong aeration to partially dismantle granules or peel off biofilms attached to carriers.

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

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

This biological treatment equipment is provided with a DO meter 19 that measures the DO in the aeration tank 2, and an air flow meter 20 that measures the amount of air supplied from the blower 4 to the piping 5, and these detected values are sent to the controller. 21. The aeration intensity is controlled by controlling the blower 4 by the controller 21.

When partially dismantling the granules or peeling off the biofilm attached to the carrier, the blower 17 is operated to provide strong aeration.

<Oxygen diffusivity index>
In the case of biofilm treatment that uses self-granulating microbial granules or biofilm attached to a fluidized bed or fixed bed carrier to remove pollutants, compared to the floating method, the microorganisms come into contact with the fluidized liquid phase. To biodegrade pollutants, it is necessary for oxygen and pollutants to diffuse into the biofilm (in the thickness direction), and the speed of this diffusion and osmosis process depends on the growth rate and oxygen consumption of microorganisms. The diffusion-osmosis process is one of the main factors determining treatment performance because it is slow compared to the speed.

The surface area of biofilm contact with bulk water is a factor that influences the diffusion-osmosis process. When the surface area becomes narrower, even if the DO of the bulk water is the same, the total amount of oxygen diffused into the biofilm will be relatively reduced, the treatment performance will decrease, and the quality of the treated water will tend to deteriorate. Conversely, as the surface area increases, even if the DO of the bulk water is the same, the total amount of oxygen diffused into the biofilm will relatively increase, the treatment capacity will increase, and the quality of the treated water will tend to improve. In addition, sufficient processing performance can be achieved even at low DO, and the amount of aeration and electric power involved in aeration can be reduced.

In the case of equipment that uses self-granulating microbial granules, if the granules enlarge due to long-term operation, the specific surface area of the self-granulating microbial granules in contact with bulk water per filling volume decreases, and the surface area in contact with bulk water is reduced.

In the case of a device that uses a carrier, especially when using a carrier with a structure that has voids inside the carrier, if the amount of biofilm retained by the carrier increases due to long-term operation, the void space inside the carrier will become larger than the microbial film itself. The contact area between bulk water and biofilm decreases due to blockage due to non-biologically active solids such as scale components. As a result, the specific surface area in contact with bulk water per carrier filling volume decreases, and the surface area in contact with bulk water per aeration tank volume decreases. In addition, regardless of the presence or absence of voids inside the carrier, if it is operated for a long period of time, the sludge density within the biofilm will increase, or the solids in the microbial film may increase due to the accumulation of non-biologically active solids such as scale components. As the physical density increases, the oxygen diffusion rate decreases.

Furthermore, in the case of a treatment that utilizes biofilm attached to fixed carriers, over a long period of operation, there is a tendency for excessive biofilm to be retained in the spaces between the carriers. In such a situation, the capacity of the bulk aqueous phase decreases relatively as the biofilm retention increases. Furthermore, if this condition progresses further, the spaces between the carriers become blocked by biofilms, creating spaces into which bulk water cannot flow. As a result, the contact area between the bulk water phase and the biofilm gradually decreases, and the permeability of oxygen and pollutants to the biofilm tends to decrease over time.

<Example of control logic construction>
As an aeration control method used in the present invention, a case will be described in which general DO control is performed at high loads, and so-called intermittent aeration is combined, in which weak aeration and strong aeration are alternately repeated at low loads. In the intermittent aeration of this example, a weak aeration process in which the aeration volume is suppressed at a minimum constant air volume for a predetermined time period, and a strong aeration process in which DO control is performed for the remaining time are repeated every fixed time cycle. In the explanation of intermittent aeration in this example, the total process time of the control cycle consisting of the weak aeration process is called the cycle time, and the process time of the weak aeration process is called the weak aeration process time, and the process time of the strong aeration process. is called the strong aeration process time.

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

In Table 1 below, five control tables (correlation tables) are shown in order from the top. Each table has been created assuming different conditions for oxygen diffusivity in biofilms, with the first table being created under conditions with the highest oxygen diffusivity, the oxygen diffusivity decreasing sequentially, and the fifth table being created under conditions with the highest oxygen diffusivity. The table assumes the worst oxygen diffusivity. Each table represents the relationship between TOC carrier volume load, DO target value, and weak aeration process time setting value.

For example, in the third table from the top, TOC load per carrier filling volume [kgC/(m ³ d). Below, units may be omitted. ] is 0.1 or more and less than 0.6, the DO target value in the strong aeration process is set to 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 set to 2. 110 minutes per hour, if the TOC load is 0.2 or more and less than 0.3, the weak aeration process time is 90 minutes every 2 hours, and if the TOC load is 0.3 or more and less than 0.4, the weak aeration process time is 2 hours. 80 minutes per hour, if the TOC load is 0.4 or more and less than 0.5, the weak aeration process time is 60 minutes every 2 hours, and if the TOC load is 0.5 or more and less than 0.6, the weak aeration process time is 2 hours. 40 minutes is set as the appropriate value for each hour, and if the TOC load is 0.6 or more and less than 0.7, the DO target value in the strong aeration process is set to 3.8 mg/L every 2 hours during the weak aeration process. If the TOC load is 0.7 or more, do not perform intermittent aeration (weak aeration time is set to 0 minutes), and if the TOC load is 0.7 or more and less than 0.9, set the DO target value 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. The same applies to other tables.

When the quality of the treated water (for example, TOC concentration) is good for a predetermined period of time, the control table moves to the next higher control table, and conversely, when the quality of the treated water is poor for a predetermined period of time, the control table moves to the next lower control table. . For example, if the quality of the treated water deteriorates despite continued appropriate aeration control using the standard control table (third table from the top), it is assumed that the oxygen diffusivity has deteriorated, and the level is lowered. Switch to aeration control using the side control table (fourth table from the top). On the other hand, when the quality of the treated water becomes excessively good, it is assumed that stable treatment can be achieved even if the aeration is weakened, and the aeration control is switched to using the control table one level above (the second table from the top). By applying this control procedure, a control table that assumes oxygen diffusivity according to the state of the actual biofilm 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, the above operation makes it possible to estimate it from normal operation data.

If the TOC of the treated water is higher than the TOC upper limit value of the control target when controlling by selecting the control table assuming the situation where the treatment performance has deteriorated the most (the lowest control table in Table 1), However, since no control table has been set for increasing the aeration intensity, performance is restored by performing biofilm retention reduction treatment.

Even if the treatment performance is at a stage where it has slightly decreased (for example, the state shown in the fourth control table from the top), performance can be improved by performing biofilm retention reduction treatment, taking into consideration the energy efficiency and cost of strengthening aeration. It may be possible to recover the .

<Control management indicators>
A method of calculating the raw water carrier load when the raw water load is used as a management index will be explained next using FIG. 4.

[How to calculate 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 shown in FIG. 4, wastewater to be treated (raw water) is introduced into an aeration tank 2 through a pipe 1. The aeration tank 2 is filled with a carrier C carrying a biofilm. An aeration pipe 3 is installed at the bottom of the aeration tank 2, and air is supplied from a blower 4 through a pipe 5 to perform aeration.

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

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

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

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

Load=Q・Conc
Load: 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, but other indicators may be used depending on the purpose of treatment as long as it is the concentration of a substance to be oxidized by microorganisms. Typically, concentrations of specific chemical substances such as COD _Cr , _CODMn , nitrite nitrogen, ammonia nitrogen, organic amines, etc. can be utilized.

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

Load _{Carrier Vol} = Load/V _Carrier
Load _CarrierVol : Carrier volume load [kg/( ^m3・d)]
V _Carrier : carrier filling volume in the aeration tank [m ³ ]

<Surface area load of carrier>
The carrier surface area loading is calculated by the following formula.

Load _CarrierSurf = Load/S _Carrier
Load _CarrierSurf : Carrier surface area load [kg/( ^m2・d)]
S _Carrier : Total surface area of the carrier group in the aeration tank [m ² ]

In addition, in an aeration tank, the raw water load may change rapidly on a minute-by-minute basis over time, but the characteristics of the carrier (the carrier filling volume in the aeration tank or the total surface area of the carrier group in the aeration tank) change over time. Changes occur relatively slowly, from days to months. Therefore, it is preferable to update the calculated raw water load frequently. In addition, the carrier filling volume in the aeration tank or the total surface area of the carrier group in the aeration tank is determined by sampling and analyzing the carriers periodically (for example, once every 1 to 3 months). , the total surface area data of the carrier group may be updated.

[Control using oxygen consumption rate as a management index]
[How to calculate oxygen consumption rate]
In one aspect of the present invention, aeration control is performed using the oxygen consumption rate as a management index. That is, under low load conditions where the oxygen consumption rate is below a predetermined value, the aeration intensity is set to be above the specified intensity. A method of calculating the oxygen consumption rate when the oxygen consumption rate is used as a management index in this way will be explained using FIG. 5.

In the biological treatment apparatus shown in FIG. 5, wastewater to be treated (raw water) is introduced into an aeration tank 2 through a pipe 1. The aeration tank 2 is filled with a carrier C carrying a biofilm. Aeration pipes 3a, 3b, and 3c are installed at the bottom of the aeration tank 2, and air is supplied from the blower 4 through the pipe 5 and branch pipes 5a, 5b, and 5c, and aeration is performed. 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 from the pipe 7 as treated water.

In this biological treatment device, as measurement means, an exhaust gas meter 24 that measures the oxygen concentration in the gas phase gas above the aeration tank 2 and below the canopy 2r, and a DO meter 19 that measures DO in the aeration tank 2. An airflow meter 20 is provided to measure the amount of air supplied from the blower 4 to the diffuser pipes 3a to 3c.

<Case 1: Method of calculating oxygen consumption rate from airflow meter and 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 using the following equation.

OTE: Oxygen transfer efficiency [-]
Z ₀ : Oxygen molar fraction in blown air [-]
Z: Oxygen mole fraction in exhaust gas [-]
qO ₂ : Oxygen consumption rate [kg/d]
Gν: Aeration air blowing flow rate converted to standard conditions [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 to indirectly estimate the oxygen consumption rate _qO2 .
(i) (Preparation before installing the control device) Calculate the oxygen solubility index φ necessary for estimating the oxygen consumption rate using the following formula.

OTE: Oxygen transfer efficiency [-]
Z ₀ : Oxygen molar fraction in blown air [-]
Z: Oxygen mole fraction 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 mixed liquid [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, continuous measurement data of the aeration air volume, and the oxygen solubility index φ determined in advance using the following equation.

qO ₂ : Oxygen consumption rate [kg/d]
Gν: Aeration air blowing flow rate converted to standard conditions [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 mixed liquid [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 aeration intensity setting value is determined based on preliminary experiment result data, actual operating performance data, and a mechanistic model that takes into account the diffusivity of oxygen in biofilms. It is set using simulation results, etc.

This correlation is organized and utilized in a functional formula or a control table that describes the functional relationship between the raw water load and the DO target value and/or the appropriate value of the aeration intensity setting value.

[Biofilm mechanism model for creating control table]
One method for constructing a control table is to measure the decrease in pollutants and the increase or decrease in the amount of activated sludge bacteria in the biofilm when the biofilm comes into contact with the bulk water phase in a fluid state containing pollutants and oxygen. A dynamic model to estimate (hereinafter sometimes referred to as a biofilm mechanism model) can be used. Such a dynamic model assumes a situation in which bacterial growth, contaminant consumption, and oxygen consumption occur simultaneously within a biofilm, and a situation in which dissolved oxygen in the bulk water phase diffuses into the biofilm and oxygen increases in bulk water volume due to aeration. It is necessary to consider the phenomenon of dissolution when constructing the system. Furthermore, the increase or shrinkage of the biofilm occurs due to an increase or decrease in the volume of a bacterial group due to proliferation and death of bacterial cells, adhesion of bacterial cells from bulk water, or detachment of bacterial cells to bulk water. When using a dynamic model for biofilm treatment, it is necessary to mathematically model these phenomena. Since such phenomena originally occur in three-dimensional space, modeling is complicated, but it is possible to express the increase and shrinkage of biofilms using a one-dimensional model that takes into account changes only in the thickness direction. Simulations can be performed relatively easily. As a mathematical model for simulating wastewater treatment using activated sludge, for example, a series of mathematical models proposed by the International Water Association's Task Group can be used (Report 1 below). As an example of a mathematical model targeting biofilms, the following paper 2 has been reported.

1. M Henze; IWA. Task Group on Mathematical Modeling for Design and operation 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 described in the previous section, for example, a mathematical model of a fluidized bed carrier can be constructed. Generally, such mathematical models are often described in the form of simultaneous ordinary differential equations, and the dynamic behavior of the same process can be simulated using numerical integration software for simultaneous ordinary differential equations. For example, it is possible to predict the quality of treated water according to the DO conditions of the bulk water phase, which vary depending on the specific equipment configuration, load assumption, and aeration intensity.

By using a mathematical model such as that described in the previous section, it is possible to predict, for example, the TOC concentration of treated water when treatment is performed at various aeration intensities under various load conditions. A table organizing the simulation results can be created and utilized as a control table used in the control system of the present invention.

[Control of aeration intensity]
As one aspect of the implementation of this patent, a case will be described in which general DO control is performed at high loads, and so-called intermittent aeration is performed in which weak aeration and strong aeration are alternately repeated at low loads. In the intermittent aeration in this case, a weak aeration process in which the aeration air volume is suppressed or aeration is stopped at a constant minimum required air volume for a predetermined time period is repeated every fixed time cycle, and a strong aeration process in which DO control is performed for the remaining time. . The aeration stop time indicates the time during which aeration is stopped within a certain time cycle in so-called intermittent aeration. The aeration suppression time is the time for weak aeration in an operation in which strong aeration and weak aeration are alternately repeated. 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 cycle time, and the process time of the weak aeration process is called the weak aeration process time, and the process time of the strong process is called the cycle time. This is called 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 depending on 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 weak aeration process time are controlled continuously or stepwise depending on the raw water load.

[Cost comparison]
In the present invention, the electric power cost and the biofilm retention amount reduction processing cost are compared between the case where the biofilm retention amount reduction process is performed at the present time and the case where it is not performed at the present time and is performed after a predetermined period f has passed.

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

[Calculation of electricity cost (cost) A when biofilm retention amount reduction treatment is not performed]
In order to predict the amount of electricity used in the case where biofilm retention amount reduction treatment is not performed at the present time, it is necessary to calculate the amount of electricity per unit time based on the actual electricity consumption in a specified period between the present moment and the past specified time from the present moment. The consumption amount H (average actual value in the specified period) is determined.

The first prediction method for predicting the power consumption from the current moment to the subsequent predetermined period f is to assume 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 for 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 for the predetermined period f.

The second prediction method assumes that power consumption per unit time increases gradually during a predetermined period f according to a preset increasing pattern.

This increasing pattern may be a mathematical model, or may be a pattern in which the power consumption per unit time increases at an average rate of increase determined from the operational history of the biological treatment device.

Regardless of the increasing pattern, the electric power cost A for the predetermined period f is calculated by multiplying the cumulative electric power predetermined period for the predetermined period f by the electric power unit price a.

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

The extent to which the power consumption is reduced depends on how many levels the control table is shifted to by the biofilm retention amount reduction process. Therefore, it is preferable to determine in advance how many stages the control table should be shifted by the biofilm retention amount reduction process based on the operational history of the biological treatment device.

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

[Biofilm retention amount reduction treatment cost C]
The biofilm retention amount reduction processing cost C includes unit price data of members used in the processing work, labor cost data for the processing work, power cost for the pump, power cost for increasing the blower during strong aeration, etc.

Although these data can be known from the actual data, it is sufficient to initially set them as the sum of the predicted values of each cost.

[Comparison 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 amount reduction treatment is suitable, and this treatment is performed. Note that if the cost (B+C) is lower than the cost A by a predetermined amount or more, it may be determined that the biofilm retention amount reduction process is suitable, and this process may be performed.

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

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

[Biological treatment other than fluidized bed]
In FIG. 1, biological treatment using a fluidized bed carrier has been described, but the present invention can be carried out in a similar manner when using a fixed bed carrier or granules.

In this embodiment, it has been explained that it is used when wastewater containing organic matter is treated by aerobic biofilm treatment accompanied by aeration. The present invention can also be carried out using the same method when performing biological treatment including an aerobic treatment step using biofilm.

[Example 1]
The above costs will be compared for the case of using an aerobic biological treatment device using a fluidized bed carrier shown in FIG. 1 and having the following structural conditions. Note that 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 × carrier filling rate 50% = 1000 m ³
Average TOC load: 1000kgC/specific TOC carrier volume load
= TOC load 1000 [kgC/day] ÷ carrier filling volume 1000 [m ³ ]
=1.0[kgC/( ^m3・d)]
Control table used: Tables 2 and 3 below

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

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

By performing biofilm retention reduction treatment, the air volume per bottom area is reduced from 20.0 m ³ /(m ² ·h) to 14.0 m at a carrier volume load of 1.0 kgC/(m ³ ·d). ³ / (m ² · h).

Assuming that the power consumption per air volume of 1N- ^m3 is 0.017 [kWh/air volume ^m3 ] and that the raw water load remains constant for the next one year, as shown in Table 4, the amount of biofilm retention is currently being reduced. In this case, the annual power consumption will be reduced from 1.19 GWh/year to 0.83 GWh/year compared to the case where the biofilm retention amount reduction treatment is not performed for one year.

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

A = [Annual electricity cost without biofilm retention reduction treatment]
= 1.19GWh/year x electricity unit price B = [annual electricity cost when biofilm retention amount reduction treatment is performed]
= 0.83GWh/year x electricity unit price C = [Biofilm retention amount reduction treatment cost]
B + C = 0.83GWh/year x electricity unit price + [biofilm retention amount reduction treatment cost]

By comparing the total costs calculated in this way, it is possible to know the cost benefit of performing biofilm retention amount reduction treatment, and it is possible to know that implementing biofilm retention amount reduction treatment is preferable from a cost merit perspective. I was able to judge.

2 Aeration tank 3, 3a, 3b, 3c Aeration pipe 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 a substance to be removed in the raw water is treated with an aerobic biofilm using a biofilm retention carrier or granules filled in the aeration tank,
Calculate the aeration power cost A within the subsequent predetermined period in the case where the biofilm retention amount reduction treatment is not performed,
Calculate the total cost (B + C) of aeration power cost B and biofilm retention amount reduction treatment cost C within a subsequent predetermined period when biofilm retention amount reduction treatment is performed,
(B+C) and A are compared, and if (B+C) is smaller than A, it is determined that the biofilm retention amount reduction treatment is suitable. 2. The aerobic biofilm 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 amount reduction treatment is suitable. Claim 1: The biofilm retention amount reduction treatment cost includes the cost of performing the biofilm retention amount reduction treatment of the carrier or the partial disassembly treatment of the granules, and the cost of treating the discharged sludge generated by the operation. The aerobic biofilm treatment method according to any one of ~3. Determine the power consumption H per unit time from the aeration power consumption in a specified period before the time of calculating the cost,
After the calculation, the unit time power consumption shall gradually increase according to the preset increasing pattern,
Calculate the aeration power cost A by the product of this increased unit time power consumption H', the predetermined period, and the power unit price,
The unit time power consumption H' is multiplied by a preset specified ratio α (however, α<1), which is αH', which is regarded as the unit time power consumption after the biofilm retention amount reduction process is performed. , α·A is the aeration power cost B, the aerobic biofilm treatment method according to any one of claims 1 to 4. a mathematical model that calculates the amount of electricity used for aeration power from the target value of DO in the aeration tank and/or the aeration intensity setting value;
Unit price data corresponding to electricity usage,
Two or more correlation groups are set in which the correlation between the raw water load or oxygen consumption rate and the DO target value and/or aeration intensity setting value is determined in relation to the quality of oxygen permeability. ,
In response to fluctuations in the measured value of raw water load or oxygen consumption rate (including those calculated from actual measured values of other measurement items), the target value of DO corresponding to the measured value is determined based on one of the correlations. The aerobic biofilm treatment method according to any one of claims 1 to 5, wherein aeration control is performed by adjusting and/or an aeration intensity setting value. From the selected DO target value or its actual value of the correlation and/or the aeration intensity setting value or its actual value, calculate the calculated value of the amount of electricity used for the current aeration power per unit period,
Assuming that the aeration power for the predetermined period in the future is constant at the calculated value, or calculating a predicted value of the future aeration power using a mathematical model that predicts an increase in the aeration power over time,
Calculating the power cost A based on the calculated value or predicted value and unit price data of power consumption;
A correlation having relatively better oxygen permeability than the correlation that was used is selected from a correlation group, and the cost B for the future predetermined period is calculated based on the aeration effect in this correlation. 6 aerobic biofilm treatment method. Claims 1 to 3 in which the biofilm retention amount reduction treatment is carried out by one or more of strong agitation by rotating stirring blades or backwashing, strong aeration, high flow rate circulation, and passing water in the tank to a crushing pump. 7. The aerobic biofilm treatment method according to any one of 7. The aerobic biofilm treatment method according to claim 1, wherein the biofilm retention amount reduction treatment cost C is set as a constant. The aerobic biofilm treatment method according to any one of claims 1 to 9, wherein when the cost A is smaller than the cost (B+C), a period until the cost A and the cost (B+C) become equal is determined. An aerobic biofilm treatment device having an aeration tank to which raw water is supplied, a biofilm holding carrier or granules filled in the aeration tank, and an aeration device for aerating the aeration tank,
means for calculating the aeration power cost A within a subsequent predetermined period in the case where the biofilm retention amount reduction treatment is not performed;
means for calculating the total cost (B+C) of the aeration power cost B and the biofilm retention amount reduction treatment cost C within a subsequent predetermined period when the biofilm retention amount reduction treatment is performed;
An aerobic biofilm treatment device comprising means for comparing (B+C) and A, and determining that the biofilm retention amount reduction treatment is suitable if (B+C) is smaller than A.

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