Aerobic biological treatment method and device

Abstract

This invention provides an aerobic biological treatment method and apparatus, which involves supplying raw water to an aeration tank and using a biofilm filled in the aeration tank to maintain a carrier or particles for aerobic biological treatment of the target substances in the raw water to obtain treated water. The method and apparatus are characterized by alternating strong and weak aeration under low load conditions below a specified value. The strong aeration intensity is set to a specified value that allows the carrier or particles to flow, while the weak aeration intensity is set to less than the specified value or aeration is stopped.

Description

Technical Field

[0001] This invention relates to a method and apparatus for biofilm treatment of wastewater containing pollutants capable of biological oxidation using self-granulating particles, fluidized bed carriers, fixed bed carriers, etc., and particularly to the control of aeration intensity. In this invention, the wastewater existing outside the biofilm undergoing microbial treatment is referred to as bulk water. Background Technology

[0002] In addition to the activated sludge process that uses floating sludge, other treatment methods for wastewater containing pollutants capable of biological oxidation include self-granulation granulation, fluidized bed carrier process, fixed bed carrier process, and other biofilm methods that treat wastewater by means of the aggregation and proliferation of microorganisms, which are called biofilms.

[0003] In the activated sludge process using the former type of floating sludge, the contact area between the microorganisms and the bulk aqueous phase is sufficiently ensured within and outside the typical 1mm-sized microbial flocs, known as microbial flocs. Therefore, the oxygen content, pollutant permeability, and diffusion within the flocs are not the primary rate-limiting factors for pollutant removal speed. Patent Document 1 describes measuring the pollutant load with an instrument and controlling the aeration volume proportionally to it.

[0004] In activated sludge processes using floating sludge, as well as biofilm processes such as self-granulation granulation, fluidized bed carrier, and fixed bed carrier, a so-called DO control system is widely used as a simple method to adjust the oxygen supply in proportion to the raw water load. This system controls the airflow to keep the dissolved oxygen concentration (hereinafter referred to as DO) in the liquid constant.

[0005] Regarding the self-granulation particle method and fluidized bed carrier method, Patent Document 2 describes a wastewater treatment method and apparatus that uses the fluidization of the microbial carrier as a criterion when the biochemical oxygen demand (BOD) volumetric load is less than a specified value, and uses the oxygen demand of the wastewater as a criterion when the BOD volumetric load is greater than the specified value, to control the aeration of the wastewater.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2001-353496;

[0009] Patent Document 2: Japanese Patent Application Publication No. 63-256185.

[0010] In biofilm-based treatment methods such as self-granulation, fluidized bed, and fixed bed methods, it is practically difficult to adjust the oxygen supply solely based on the inflow load, which is typically calculated as the product of the raw water flow rate per unit time and the pollutant concentration, or the tank load, which is calculated by dividing the inflow load by the tank volume. The reasons are as follows.

[0011] That is, even if the raw water load is the same and the amount of oxygen required to oxidize the organic matter in the raw water is the same, in the biofilm method, the amount of microorganisms maintained in the reaction tank in the form of biofilm will change over time. Therefore, the amount of oxygen consumed due to the self-decomposition process of the microorganisms will change. Therefore, the amount of oxygen supplied to the device also needs to take this factor into account when determining it.

[0012] Due to these factors, the amount of oxygen required for the oxidation of organic matter in the raw water varies with load changes, and the required oxygen supply also varies depending on the amount of biofilm maintained within the treatment unit. In the case of biofilm methods where oxygen supply depends on diffusion, the dissolved oxygen (DO) in the bulk water needs to be adjusted according to the amount of oxygen to be supplied to the biofilm, and the aeration airflow used to maintain the DO in the bulk water also needs to be adjusted.

[0013] In particular, with increased load, the amount of oxygen required for the oxidation of organic matter in the raw water increases, and with an increase in the amount of biofilm maintained in the treatment unit, the amount of oxygen required to be supplied also increases.

[0014] In biofilm processes where oxygen supply depends on diffusion, when the amount of oxygen to be supplied to the biofilm increases, it is necessary to increase the dissolved oxygen (DO) in the bulk water and also increase the aeration air volume used to increase the DO in the bulk water.

[0015] For this reason, when not adjusting and controlling the operation according to the aeration volume load, it is necessary to operate with a fixed aeration volume under the condition of increasing the aeration volume in order to maintain a high DO in the bulk water and maintain the oxygen supply even under high load.

[0016] When maintaining a constant airflow rate with the required high DO at high loads, energy is wasted because airflow suppression corresponding to the reduction in oxygen consumption when the load decreases. Furthermore, assuming high-load oxygen supply and DO control with a set high target DO value, the DO level can be reduced even when the load decreases in the biofilm treatment unit. Therefore, lowering the target DO level can further reduce aeration airflow. However, since this airflow suppression based on the target DO value is not performed in normal DO control, energy is also wasted.

[0017] For this reason, energy waste is particularly noticeable when there are large load variations.

[0018] On the other hand, in aerobic biofilm treatment utilizing self-granulated particles or carriers with attached microorganisms, when aeration is controlled according to the raw water load, the airflow per unit bottom area decreases when the raw water load is low. Therefore, insufficient mixing of the water within the aeration tank fails to maintain the flow of the carriers or particles, causing them to accumulate at the bottom of the tank for extended periods. Consequently, the reduced contact area with the bulk water leads to decreased treatment efficiency, or the bottom of the tank becomes an anaerobic environment, resulting in sludge putrefaction and foul odors, especially in the case of treating sulfur-containing wastewater, producing sulfur-based odorous gases such as hydrogen sulfide, causing odor problems. Furthermore, the temporarily accumulated carriers or particles at the bottom of the tank clump together, accumulating nitrogen generated during denitrification or anaerobic gases generated during putrefaction, becoming lighter than the bulk water and floating near the surface. This makes it difficult to stably maintain the carriers or particles within the treatment tank, leading to problems related to carrier leakage or reduced treatment capacity.

[0019] Patent Document 2 proposes the following countermeasures: when the BOD volumetric loading is less than a specified value, the fluidization of the microbial carrier is used as the criterion; when the BOD volumetric loading is greater than the specified value, the oxygen demand of the wastewater is used as the criterion, and the aeration rate of the wastewater is controlled. However, when using this method for aeration control, especially in biofilm treatment where both nitrification and denitrification reactions within the biofilm are to be promoted simultaneously, particularly under reduced loading conditions, excessive oxygen supply to the biofilm prevents the maintenance of a so-called anaerobic state where only nitrate remains within the biofilm, resulting in the denitrification reaction within the biofilm not proceeding. Consequently, the NO3-N concentration in the treated water increases, and the amount of alkaline reagent required to neutralize NO3-N increases. Summary of the Invention

[0020] The problem the invention aims to solve

[0021] The purpose of this invention is to provide an aerobic biological treatment method and apparatus utilizing a biofilm, which can ensure the treatment capacity under high loads, a characteristic of biofilm processes, and suppress energy loss under low loads, thereby avoiding problems related to the accumulation of granular sludge or carriers, and also mitigating the problem of reduced nitrogen treatment performance.

[0022] means for solving problems

[0023] The aerobic biological treatment method of the present invention involves supplying raw water to an aeration tank and using a biofilm filled in the aeration tank to maintain a carrier or particles for aerobic biological treatment of the target substances in the raw water to obtain treated water. The method is characterized by alternating strong and weak aeration under low-load conditions below a specified value. The strong aeration intensity is set to a specified value that allows the carrier or particles to flow, while the weak aeration intensity is set to less than the specified value or aeration is stopped.

[0024] The aerobic biological treatment device of the present invention comprises an aeration tank for supplying raw water, a biofilm holding carrier or particles filled in the aeration tank, and an aeration device for aeration of the aeration tank. The aerobic biological treatment device is characterized by having an aeration control mechanism that alternates between strong aeration and weak aeration under low-load conditions (below a specified value). The strong aeration sets the aeration intensity to a specified value that allows the carrier or particles to flow, while the weak aeration sets the aeration intensity to less than the specified value or stops aeration.

[0025] According to one aspect of the invention, the low load condition below the specified condition in the preceding paragraph refers to a low load that satisfies any one of (a) to (d) below.

[0026] (a) The measured value of the raw water load is below the specified value;

[0027] (b) The measured value of the oxygen consumption rate in the aeration tank is below the specified value;

[0028] (c) The target value for DO concentration controlled under high load conditions where the load is greater than the specified value is below the specified value;

[0029] (d) The aeration intensity setting under high load conditions where the load is greater than the specified value is below the specified value.

[0030] According to one aspect of the invention, each of the specified values ​​in (a) to (d) is a value for the aeration volume when the aeration volume during weak aeration is between 1 / 2 and 1 / 5 of the minimum aeration volume.

[0031] According to one aspect of the invention, the raw water load is any one of the inflow load, tank load, and carrier volumetric load.

[0032] According to one aspect of the invention, the aeration intensity is controlled by the aeration volume, the aeration stop time, or the aeration inhibition time.

[0033] According to one aspect of the invention, there is no mechanical stirring mechanism or draft tube for the water in the mixing tank.

[0034] The effects of the invention

[0035] According to the present invention, the bottom of the tank is prevented from becoming an anaerobic environment, thus enabling highly efficient biological treatment. Furthermore, in the case of treatment aimed at nitrification, even under low-load conditions, the denitrification reaction in the weak aeration process can be promoted. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of a biological treatment device.

[0037] Figure 2 This is a schematic diagram of the biological treatment device using the present invention. Detailed Implementation

[0038] <Control based on raw water load as a management indicator>

[0039] According to one aspect of the invention, continuous aeration is performed under high load conditions (above a predetermined value), and aeration control, commonly referred to as intermittent aeration, is performed under low load conditions (below a predetermined value). Specifically, an aeration control mechanism includes repeatedly performing weak aeration and strong aeration cycles, wherein the weak aeration cycle involves stopping or suppressing aeration for a specified time, and the strong aeration cycle periodically sets the aeration intensity to a predetermined intensity or higher for a specified time. The following describes the use of... Figure 1 The calculation method for the volumetric load of the raw water carrier under this condition is explained.

[0040] [Method for calculating raw water load based on Total Organic Carbon (TOC) and flow rate]

[0041] Figure 1 The biological treatment device shown performs aeration control based on the raw water load using measurements of the total organic carbon concentration of the raw water.

[0042] exist Figure 1 In the biological treatment device, the treated wastewater (raw water) is introduced into the aeration tank 2 via pipe 1. The aeration tank 2 is filled with a carrier C loaded with biofilm. An air diffuser 3 is installed at the bottom of the aeration tank 2, and air is supplied from the blower 4 via pipe 5 for aeration.

[0043] Water that has undergone aerobic biological treatment via a biofilm is extracted as treated water from pipe 7 through screen 6.

[0044] In this biological treatment device, as measuring mechanisms, there are flow meters 22 and total organic carbon meters 23 for measuring the flow rate and total organic carbon concentration of the raw water flowing in the piping 1, a DO meter 19 for measuring the DO concentration in the aeration tank 2, and an air volume meter 20 for measuring the amount of air supplied from the blower 4 to the aeration pipe 3. These measured values ​​are input to the controller 21. The controller 21 controls the aeration intensity by controlling the motor speed of the blower 4.

[0045] The flow rate of raw water is measured using flow meter 22, and the total organic carbon concentration of raw water is measured using total organic carbon meter 23. The TOC load is then calculated as the raw water load.

[0046] <Raw Water Load>

[0047] The raw water load can be calculated using the following formula.

[0048] Load = Q·concentration / 1000

[0049] Load: Raw water load [kg / d]

[0050] Q: Raw water flow rate [m] 3 / d]

[0051] Concentration: Raw water concentration [kg / m³] 3 ]

[0052] As an example of raw water concentration, the concentration of TOC·N can be calculated based on total organic carbon, ammonia nitrogen, and UV absorbance.

[0053] <Carrier Volumetric Load>

[0054] The volumetric load of the carrier can be calculated using the following formula.

[0055] load 载体容积 =Load / V 载体

[0056] load 载体容积 Carrier volumetric load [kg / (m³)] 3 ·d)].

[0057] V 载体 : Carrier filling volume in the aeration tank [m 3 ].

[0058] <Carrier Surface Area Load>

[0059] The surface load of the carrier can be calculated using the following formula.

[0060] load 载体表面积 =Load / S 载体

[0061] load 载体表面积 : Carrier surface area load [kg / (m²)]2 ·d)].

[0062] S 载体 The total surface area of ​​the carrier group in the aeration tank [m²] 2 ].

[0063] It should be noted that in the aeration tank, the raw water load sometimes changes rapidly over time, sometimes on a minute-by-minute basis, while the properties 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 relatively slowly over time, on a daily to monthly basis. Therefore, it is preferable to update the calculated raw water load value frequently. Furthermore, for the carrier filling volume in the aeration tank or the total surface area of ​​the carrier group in the aeration tank, it is sufficient to periodically sample and analyze the carrier (e.g., approximately once every 1 to 3 months) and update the carrier filling volume and total surface area data accordingly.

[0064] [Control based on oxygen consumption rate as a management indicator]

[0065] [Methods for estimating oxygen consumption rate]

[0066] According to one aspect of the invention, the oxygen consumption rate is used as a management indicator for the raw water load for aeration control. That is, under low load conditions where the oxygen consumption rate is below a specified value, the aeration intensity is set to a specified intensity or higher. Thus, using... Figure 2 This section explains the method for calculating oxygen consumption rate when oxygen consumption rate is used as a management indicator.

[0067] exist Figure 2 In the biological treatment device, the treated wastewater (raw water) is introduced into the aeration tank 2 via pipe 1. The aeration tank 2 is filled with a carrier C on which a biofilm is loaded. At the bottom of the aeration tank 2, air diffusers 3a, 3b, and 3c are installed, and air is supplied from the blower 4 via pipe 5 and branch pipes 5a, 5b, and 5c for aeration. The aeration tank 2 is equipped with a top cover 2r.

[0068] Water that has undergone aerobic biological treatment via a biofilm is extracted as treated water from pipe 7 through screen 6.

[0069] In this biological treatment device, as a measuring mechanism, there is an exhaust meter 24 for measuring the oxygen concentration in the gas phase of the upper part of the aeration tank 2 and the lower side of the top cover 2r, a DO meter 19 for measuring the DO concentration in the aeration tank 2, and an air volume meter 20 for measuring the amount of air supplied from the blower 4 to the air distribution pipes 3a to 3c.

[0070] <Scenario 1: Method for calculating oxygen consumption rate based on air volume meter and exhaust gas meter>

[0071] Measure the aeration air volume and the oxygen concentration in the exhaust gas, and directly calculate the oxygen consumption rate qO2 using the following formula.

[0072] Mathematical Formula 1

[0073]

[0074] Mathematical formula 2

[0075]

[0076] OTE: Oxygen transport efficiency [-]

[0077] Z0: Mole fraction of oxygen in the blown air [-]

[0078] Z: Mole fraction of oxygen in exhaust gas [-]

[0079] qO2: Oxygen consumption rate [kg / d]

[0080] Gν: Standard state converted aeration air inflow rate [Nm] 3 / d]

[0081] ν m Specific volume of oxygen [Nm] 3 / kg]

[0082] <Scenario 2: Method for calculating oxygen consumption rate based on DO meter and aeration air volume>

[0083] By measuring the aeration air volume and dissolved oxygen (DO), the oxygen consumption rate qO2 can be indirectly estimated.

[0084] (i) (Preparation before installation of control device) Calculate the oxygen solubility index required for estimating oxygen consumption rate according to the following formula.

[0085] Mathematical Formula 3

[0086]

[0087] Mathematical expression 4

[0088]

[0089] OTE: Oxygen transport efficiency [-]

[0090] Z0: Mole fraction of oxygen in the blown air [-]

[0091] Z: Mole fraction of oxygen in exhaust gas [-]

[0092] Oxygen solubility index [m]

[0093] ν m Specific volume of oxygen [Nm] 3 / kg]

[0094] h: Water depth of the aeration device [m]

[0095] Cs: Concentration of saturated dissolved oxygen [kg / m³] 3 ]

[0096] C: Concentration of dissolved oxygen in the mixture [kg / m³] 3 ]

[0097] (ii) (While the device is in operation) Continuously measure the rate of oxygen consumption over time.

[0098] Based on continuous measurement data of DO meter and aeration air volume, and the pre-calculated oxygen solubility index The oxygen consumption rate qO2 can be continuously calculated using the following formula.

[0099] Mathematical formula 5

[0100]

[0101] qO2: Oxygen consumption rate [kg / d]

[0102] Gν: Standard state converted aeration air inflow rate [Nm] 3 / h]

[0103] h: Water depth of the aeration device [m]

[0104] Cs: Concentration of saturated dissolved oxygen [kg / m³] 3 ]

[0105] C: Concentration of dissolved oxygen in the mixture [kg / m³] 3 ]

[0106] Oxygen solubility index [m]

[0107] [Relationships among management indicators used in control]

[0108] When the raw water load and oxygen consumption rate are high, and the load index is above the specified value, continuous aeration is set and DO control is applied. The target value of DO concentration in the aeration tank is increased according to the load. When the load is below the specified value, the time of the weak aeration process of intermittent aeration is shortened, that is, the time of the strong aeration process is extended. The correlation between the raw water load or oxygen consumption rate and the corresponding target value of DO concentration or the time of the weak aeration process is pre-established using preliminary experimental data, actual operational data, and simulation results of a mechanism model that considers the diffusivity of oxygen in the biofilm.

[0109] As a method to realize this correlation in the control system, it can be any of the following: a method that records the correlation between the raw water load and the appropriate value of the DO target value or the appropriate value of the weak aeration time or a combination of both; or a method that uses a control table or the like.

[0110] [A biofilm mechanism model used to create control tables]

[0111] As a method for constructing control tables, a kinetic model (hereinafter sometimes referred to as a biofilm structure model) can be used to estimate the decrease of pollutants and the increase or decrease of activated sludge bacteria in the biofilm when the biofilm comes into contact with a flowing bulk aqueous phase containing pollutants and oxygen. This kinetic model also needs to consider the simultaneous occurrence of bacterial proliferation and pollutant consumption and oxygen consumption within the biofilm, the diffusion of dissolved oxygen from the bulk aqueous phase to the biofilm, and the dissolution of oxygen in the bulk aqueous phase due to aeration. Furthermore, the increase or decrease in biofilm size is caused by the increase or decrease in the volume of bacterial colonies accompanying bacterial proliferation and death, or by the attachment of bacteria from the bulk aqueous phase and the detachment of bacteria from the bulk aqueous phase. When using a kinetic model in biofilm utilization treatment, these phenomena need to be mathematically modeled. Since these phenomena originally occur in three-dimensional space, modeling becomes complex; however, by using a one-dimensional model that only considers changes in the thickness direction to represent the increase and decrease of the biofilm, simulation can be performed relatively easily. As mathematical models for simulating wastewater treatment using activated sludge, a series of mathematical models proposed by the International Water Association's task group (Report 1 below) can be effectively utilized. As an example of a mathematical model focusing on biofilms, Report 2 below is reported.

[0112] 1.M Henze; ​​IWA.Task Group on Mathematical Modeling for Design andOperaton of Biological Wastewater Treatment; et al.

[0113] 2. Boltz, JP, Johnson, BR, Daigger, GT, Sandino, J., (2009a). "ModelingIntegrated Fixed-FilmActivated Sludge and Moving Bed Biofilm Reactor Systems I: Mathematical Treatment and Model Development". Water Environment Research, 81(6), 555-575.

[0114] By utilizing the mathematical models described above, such as those for fluidized bed carriers, it is possible to construct mathematical models. Typically, these mathematical models are expressed in the form of simultaneous ordinary differential equations, which can be used to simulate the dynamic behavior of the process using numerical integration software. For example, it is possible to anticipate the treated water quality corresponding to the DO (dissolved oxygen) conditions in the bulk aqueous phase, which vary depending on the specific device structure, load assumptions, and aeration intensity.

[0115] By utilizing the mathematical model described above, it is possible to predict, for example, the total organic carbon concentration of the treated water under various loading conditions and aeration intensities for different oxygen diffusivity conditions in various biofilms. A table summarizing the simulation results has been created and can be effectively used in the control system of this invention.

[0116] [Control of aeration intensity]

[0117] Aeration intensity can be controlled, for example, by changing the aeration volume (air supply flow rate) and the duration of the weak aeration phase at fixed time intervals. The weak aeration phase performs aeration at a specified volume less than the minimum flow rate, while the strong aeration phase performs aeration at a volume greater than the minimum flow rate or DO control at the target DO value that ensures that volume.

[0118] The aeration volume, aeration stop time, and aeration inhibition time are controlled continuously or in stages according to the raw water load.

[0119] [Minimum aeration airflow rate, longest aeration stop time, or longest weak aeration time]

[0120] The minimum aeration air volume in the embodiments of the present invention is the minimum aeration air volume required to ensure the overall flow state of the carrier in the fluidized bed carrier device, prevent the carrier from accumulating at the bottom of the aeration tank, promote the contact between the carrier and the bulk water, and suppress the problems of sludge putrefaction, hydrogen sulfide odor, and floating of lumpy carriers that accompany the accumulation of the carrier at the bottom.

[0121] In fluidized bed carrier devices employing intermittent aeration with repeated aeration and aeration stop, the longest aeration stop time or longest weak aeration time in embodiments of the present invention refers to the maximum time for a weak aeration process involving repeated aeration stop or aeration suppression at fixed time intervals. In the weak aeration process, assuming that the minimum aeration airflow cannot be guaranteed for fluidization, the airflow suppression is achieved. Compared to treatment devices that perform continuous aeration through this airflow adjustment, this process further suppresses the average aeration intensity and also suppresses related power consumption. Therefore, during this process, a fixed proportion of carrier accumulates at the bottom of the device. By limiting the time of this process to a fixed period, the accumulated carrier is re-fluidized during the remaining cycle time by ensuring an airflow above the minimum aeration airflow (referred to as the airflow in the strong aeration process in the present invention). This results in suppressing sludge putrefaction problems and hydrogen sulfide odor generation that accompany long-term carrier accumulation at the bottom. The longest aeration stop time or longest weak aeration time is set for this purpose.

[0122] The optimal minimum aeration volume or maximum aeration stop time is determined based on preliminary experimental data and actual operational data. In the installation example of this invention, under high load conditions, intermittent aeration operation with repeated weak and strong aeration is not performed; instead, continuous aeration is performed to maximize the utilization of the aeration device's capacity. Under reduced load conditions, a lower DO target value is set according to the control table, and the aeration volume is suppressed. However, when the aeration volume reaches the minimum aeration volume, the aeration mode is switched to intermittent aeration operation. The aeration volume, which serves as the criterion for switching from continuous aeration operation to intermittent aeration operation, can also be directly measured and managed. Control can be performed as follows: by monitoring any one of the indicators (a) to (d) below and evaluating the relationship between the indicator value and the volume in advance, the aeration volume is estimated based on the indicator. Continuous aeration is performed when the aeration volume is ≥ the minimum aeration volume, and intermittent aeration is performed when the aeration volume is < the minimum aeration volume.

[0123] (a) The measured value of the raw water load is below the specified value;

[0124] (b) The measured value of the oxygen consumption rate in the aeration tank is below the specified value;

[0125] (c) Under high load conditions (continuous aeration), the target value of the DO concentration controlled by the load is below the specified value;

[0126] (d) Under high load conditions (continuous aeration), the set value of the aeration intensity (including the aeration volume) controlled by the load is below the specified value.

[0127] The raw water load in (a) above is preferably any one of the following: inflow load, tank load, carrier volume load, and carrier surface area load.

[0128] Biological treatment other than fluidized bed

[0129] exist Figure 2 The invention describes how biological treatment using fluidized bed carriers can also be implemented using the same method when using fixed bed carriers or particles.

[0130] [Aeration management based on factors other than total organic carbon]

[0131] In this embodiment, the application of aerobic biofilm treatment with accompanying aeration to treat wastewater containing organic matter has been described. However, the same method can also be used in biological treatment processes, such as biological nitrification denitrification using a biofilm, which includes aerobic treatment steps using a biofilm in an aeration tank. Therefore, the water quality value of the treated water is not limited to total organic carbon, but can also be NH4-N·NO3-N, NO2-N, the concentration of specific chemical substances, or combinations thereof.

[0132] According to one aspect of the invention, in an aeration tank without stirring using a mechanical stirring mechanism or other power source, the airflow rate in the weak aeration process is set to the minimum necessary to maintain agitated contact between the biofilm and the bulk water while achieving water treatment performance. The airflow rate in the strong aeration process is set to at least the minimum flowable aeration airflow rate. Furthermore, when DO control is performed in the strong aeration process, DO control is also performed with an aeration airflow rate at least the minimum flowable aeration airflow rate. In the weak aeration operation process, since airflow suppression cannot guarantee the minimum flowable aeration airflow rate, the average aeration intensity can be further suppressed compared to a treatment device that maintains the minimum flowable aeration airflow rate at a minimum while performing continuous aeration. However, during this weak aeration process, while minimum agitated contact between the biofilm and the bulk water is maintained, a fixed proportion of carriers accumulates at the bottom of the device. By limiting the time of this process to a fixed period, aeration is carried out with a fluidized air volume during the remaining cycle time, i.e., the strong aeration process time, thereby achieving reflow of the accumulated carrier. As a result, the problem of sludge putrefaction and the generation of hydrogen sulfide odor that accompany the long-term accumulation of the carrier to the bottom are suppressed. The longest weak aeration time is set to ensure the maximum weak aeration process time that reliably induces reflow; in other words, it is set to ensure the minimum strong aeration process time that reliably induces reflow.

[0133] According to one aspect of the invention, at low loads, intermittent aeration that can periodically maintain the fluidity of the carrier is performed, thereby suppressing the long-term accumulation of carriers or particles at the bottom of the aeration tank. As a result, the generation of anaerobic gases or the generation of odors such as hydrogen sulfide during the treatment of sulfur-containing wastewater can be suppressed, and the clumping of carriers or particles temporarily accumulated at the bottom of the tank can be suppressed. Because nitrogen generated in the internal denitrification reaction or anaerobic gases generated in the putrefaction reaction are lighter than the bulk water and float to the vicinity of the water surface, it is difficult to stably maintain the carriers or particles in the treatment tank, resulting in problems related to carrier leakage outside the reaction tank or reduced treatment capacity.

[0134] In nitrification denitrification, intermittent aeration with periodic, weak aeration avoids problems related to carrier or particle accumulation. Compared to continuous aeration, by reducing the average aeration intensity, an anaerobic environment within the biofilm can be maintained primarily during the weak aeration phase, sustaining the denitrification reaction and suppressing the rise in nitrate nitrogen concentration in the treated water. As a result, the problem of failing to achieve nitrogen treatment targets due to increased nitrate nitrogen concentration in the treated water under low-load conditions is mitigated; costs associated with suppressing the addition of alkaline chemicals required for pH adjustment based on nitrate nitrogen are reduced; and the ion load in downstream water treatment processes such as RO is decreased.

[0135] Furthermore, under high load conditions, by stopping intermittent aeration and implementing continuous aeration, high-load treatment can be carried out to maximize the oxygen supply capacity of the aeration device. In nitrification denitrification, even without intermittent aeration, an anaerobic environment can be formed deep within the biofilm through oxygen diffusion and organic matter diffusion within the biofilm, as well as the oxidation process involving nitrification using microorganisms, maintaining denitrification performance. Therefore, with proper aeration control, the denitrification reaction can proceed well simply by adjusting conditions such as the organic matter load. Continuous aeration under DO control provides the oxygen supply required for the nitrification of ammonia and the oxidation of untreated organic matter in the denitrification reaction, and maximizes the denitrification reaction within the biofilm, thereby achieving energy savings and ensuring nitrogen removal performance.

[0136] Example

[0137] [Example 1]

[0138] exist Figure 2 In the aerobic biological treatment device with the fluidized bed carrier shown, wastewater 1 or wastewater 2 with the following water quality was treated under the conditions shown below and in Table 1.

[0139] <Water quality of drainage>

[0140] Types of drainage:

[0141] Organic wastewater from electronics manufacturing plants

[0142] Under high load:

[0143] Raw water concentration range: total organic carbon 115–150 mg C / L, ammonia nitrogen 15–30 mg N / L

[0144] Approximately twice a day, with a half-day cycle.

[0145] The raw water volume is fixed.

[0146] At low load:

[0147] Raw water concentration range: total organic carbon 60–90 mgC / L, ammonia nitrogen 7–15 mgN / L

[0148] Approximately twice a day, with a half-day cycle.

[0149] <Processing device method>

[0150] Fluidized bed aerobic biofilm treatment

[0151] 3mm angular cube polyurethane foam carrier

[0152] 40% fill rate

[0153] <Processing Conditions>

[0154] High load: 0.7~1.0kgC / (carrier m 3 ·d)

[0155] Low load: 0.4~0.6kgC / (carrier m 3 ·d)

[0156] Aeration-based stirring and mixing

[0157] Minimum aeration air volume for fluidization: 7m³ 3 / (base m) 2 ·h)

[0158] Processing time: 0.5 days

[0159] Aeration control conditions when applying this invention

[0160] Aeration cycle time during intermittent aeration control: 120 minutes

[0161] Air volume per unit bottom area in the weak aeration process: 2.6m³ 3 / (base m) 2 ·h)

[0162] Target values ​​for DO control in the forced aeration process:

[0163] The aeration rate is set to the target DO value that is above the minimum aeration rate for fluidization based on the load.

[0164] Using the multiple control tables in Table 1, adjust the aeration conditions according to the load;

[0165] The control table used is the third "standard" control table in this embodiment, selected by comparing the actual measured values ​​of the treated water quality with the target water quality.

[0166] <Target values ​​for treated water quality>

[0167] Total organic carbon 5-10 mg C / L

[0168] Nitrate nitrogen concentration 5-10 mgN / L

[0169] It should be noted that in Table 2, "low load" means that the water quality under "low load" in the above <Water Quality of Drainage> is set to the "low load" condition in the above <Treatment Conditions>, and "high load" means that the water quality under "high load" in the above <Water Quality of Drainage> is set to the "high load" condition in the above <Treatment Conditions>.

[0170] Under the following conditions, the aeration control method and control conditions are changed to evaluate the power consumption per unit of carbon in the raw water load (referred to as the raw power unit) and the treated water quality.

[0171] Example 1:

[0172] Under low load conditions, aeration control is implemented based on the "standard" control table.

[0173] Under low load conditions, in order to repeatedly perform intermittent aeration control of weak aeration and strong aeration processes, the time of weak aeration process is controlled between 60 and 20 minutes, and the target value of DO in strong aeration process is controlled between 3.1 and 3.8 mg / L, depending on the load.

[0174] Comparative Example 1:

[0175] Under low load conditions, in order to maintain the flow of the carrier, a fixed aeration volume is controlled at the minimum flow aeration volume.

[0176] Comparative Example 2:

[0177] Under low load conditions, with the aim of reducing aeration air volume, the target DO value is controlled at approximately the average value of the actual DO value in Example 1, which is 3.0 mg / L.

[0178] Comparative Example 3:

[0179] Under low load conditions, assuming that the aeration is always operated at a fixed DO value regardless of the load conditions, and under high load conditions, aeration is also controlled at the DO control target of 4.8 mg / L to achieve good total organic carbon treatment of the water.

[0180] Comparative Example 4:

[0181] Under low load conditions, assuming no change in load, aeration is always performed with a fixed airflow. Under high load conditions, an aeration airflow of 14 m³ / s per unit bottom area is maintained to achieve good total organic carbon treatment of the water. 3 / (m 2 Aeration under h).

[0182] Example 2:

[0183] Under high load conditions, aeration control based on the "standard" control table is implemented according to the aeration control method of this patent. Under high load conditions, continuous aeration based on DO control is performed, and the target DO value is controlled between 3.9 mg / L and 4.8 mg / L, depending on the load.

[0184] Comparative Example 5:

[0185] Under high load conditions, assuming that the aeration is always operated at a fixed DO value regardless of the load conditions, the aeration is also controlled at the DO control target of 4.8 mg / L to achieve good total organic carbon treatment water quality under high load conditions.

[0186] Comparative Example 6:

[0187] Under high load conditions, assuming that aeration is always performed at a constant airflow regardless of load conditions, an aeration airflow of 14 m³ / s per unit bottom area is maintained to achieve good total organic carbon treatment of the water even under high load conditions. 3 / (m 2 Aeration under h).

[0188] Table 1

[0189] High oxygen diffusivity TOC carrier volumetric load <![CDATA[[kgC / (m 3 ·d)]]]> 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 =Excellent processing performance DO target value [mg / L] 2.8 2.8 2.8 2.8 2.8 3.2 3.3 3.3 3.3 3.7 Weak aeration time setting value [minutes / 2 hours] 110 90 80 60 40 20 0 0 0 0

[0190] Slightly higher oxygen diffusivity TOC carrier volumetric load <![CDATA[[kgC / (m 3 ·d)]]]> 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 =Good processing performance DO target value [mg / L] 2.9 2.9 2.9 2.9 2.9 3.5 3.6 3.6 3.9 4.2 Weak aeration time setting value [minutes / 2 hours] 110 90 80 60 40 20 0 0 0 0

[0191] oxygen diffusivity TOC carrier volumetric load <![CDATA[[kgC / (m 3 ·d)]]]> 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 =Processing performance standards DO target value [mg / L] 3.1 3.1 3.1 3.1 3.1 3.8 3.9 3.9 4.4 4.8 Weak aeration time setting value [minutes / 2 hours] 110 90 80 60 40 20 0 0 0 0

[0192] Slightly poor oxygen diffusivity TOC carrier volumetric load <![CDATA[[kgC / (m 3 ·d)]]]> 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 = Slightly lower processing performance DO target value [mg / L] 4.0 4.0 4.0 4.0 4.0 4.0 4.2 4.4 4.9 5.5 Weak aeration time setting value [minutes / 2 hours] 110 90 80 60 40 20 0 0 0 0

[0193]

[0194]

[0195] Table 2

[0196]

[0197] As shown in Table 2, the carrier flow state, aeration power unit, and treated water quality under each aeration condition are as follows.

[0198] Example 1:

[0199] In the weak aeration stage, aeration power is suppressed by decreasing the airflow, while in the strong aeration stage, a minimum aeration airflow is ensured. This re-fluidizes the settled carriers from the weak aeration stage, thereby preventing carrier accumulation at the bottom and the generation of odor. The treated water quality is 6 mgC / L for total organic carbon and 8 mgN / L for nitrate nitrogen, meeting the target values. The aeration power unit is 4 kWh / kgC.

[0200] Comparative Example 1:

[0201] By consistently maintaining a minimum aeration airflow, the odor problem associated with carrier accumulation is avoided. The treated water quality is 4 mg C / L for total organic carbon, below the target value. However, the nitrate nitrogen is 11 mg N / L, higher than the target value. The rationale is that by prioritizing carrier flow and increasing the aeration volume, although carbonaceous pollutants are treated well, the denitrification reaction within the carrier is suppressed when aeration is inhibited, thus failing to promote nitrogen treatment and leading to an increase in nitrate concentration. Furthermore, the aeration power unit is 6 kWh / kgC, which is 2 kWh / kgC higher than in Example 1.

[0202] Comparative Example 2:

[0203] By setting the operation to always suppress DO, the aeration power unit was 3 kWh / kgC, which is 1 kWh / kgC lower than in Example 1, but the minimum specific flow aeration air volume of 7 m³ / kg was always maintained. 3 / (m 2 •h) Aeration volume of 2-3 m³ / h per unit bottom area 3 / (m 2 As a result, the carrier fluidity deteriorates, leading to carrier accumulation at the bottom and causing odor problems. The treated water quality was 11 mg C / L total organic carbon, which fails to meet the target value, and 6 mg N / L nitrate nitrogen, which is within the target range. The deterioration in total organic carbon is presumably due to carrier accumulation, which substantially reduces the surface area of ​​the biofilm in contact with the bulk water, reduces the amount of oxygen diffusing into the biofilm, and decreases the oxidation capacity of carbonaceous organic matter.

[0204] Comparative Example 3:

[0205] Aeration was performed under high load to maintain the required dissolved oxygen (DO) value. As a result, although aeration volume was suppressed according to the load, a higher DO value was maintained under low load conditions. Therefore, the kinetic energy unit was 7 kWh / kgC, which is 3 kWh / kgC higher than in Example 1. The treated water quality was 4 mgC / L total organic carbon, below the target value. Additionally, nitrate nitrogen was 15 mgN / L, higher than the target value and higher than in Comparative Example 1. This is believed to be because although excessive aeration allowed for good treatment of carbonaceous pollutants, the denitrification reaction within the carrier was suppressed during aeration suppression, failing to promote nitrogen treatment and leading to an increase in nitrate concentration.

[0206] Comparative Example 4:

[0207] Aeration was maintained at the required air volume under high load conditions. As a result, an excessive aeration air volume was maintained under low load conditions. Therefore, the power unit was 14 kWh / kgC, which is 10 kWh / kgC higher than that of Example 1. The treated water quality was 3 mgC / L total organic carbon, which is below the target value. In addition, the nitrate nitrogen was 20 mgN / L, which is higher than the target value and higher than that of Comparative Example 3.

[0208] Example 2:

[0209] Based on the DO target value set according to the load variation, the aeration power unit is 4 kWh / kgC, which is the same as the aeration power unit under low load conditions. The treated water quality is 7 mgC / L total organic carbon and 4 mgN / L nitrate nitrogen, which meets the target values.

[0210] Comparative Example 5:

[0211] Aeration was performed at a high peak load to maintain the required DO value. As a result, although aeration volume was suppressed according to the load, a high DO value was maintained even under periodic load fluctuations and reductions. Therefore, the kinetic energy unit was 5 kWh / kgC, which is 1 kWh / kgC higher than that of Example 2. The treated water quality was 6 mgC / L total organic carbon and 6 mgN / L nitrate nitrogen, which is within the target range.

[0212] Comparative Example 6:

[0213] Aeration was performed at a peak load to maintain the required airflow. As a result, due to the maintenance of excessive aeration airflow under conditions of periodic load fluctuations and reductions, the power unit was 7 kWh / kgC, 3 kWh / kgC higher than in Example 2. The treated water quality was 5 mgC / L total organic carbon, within the target range, but 12 mgN / L nitrate nitrogen, higher than the target value. Under high load conditions, assuming constant aeration regardless of load conditions, an aeration airflow of 14 m³ / L per unit bottom area was achieved to obtain good total organic carbon treatment water quality even under high load conditions. 3 / (m 2 Aeration under h).

[0214] For the embodiments, it was confirmed that, compared with the comparative examples, under low load conditions, there was no problem of odor caused by the accumulation of the carrier at the bottom and no reduction in treatment capacity. The aeration power unit was suppressed to a low level and the treated water quality was set to the target value range. Under high load conditions, the aeration air volume was also adjusted according to the load, and the aeration power unit was suppressed to a low level and the treated water quality was set to the target value range.

[0215] The present invention has been described in detail using specific embodiments, but those skilled in the art will recognize that various changes can be made without departing from the purpose and scope of the invention.

[0216] This application is based on Japanese Patent Application No. 2020-090648, filed on May 25, 2020, the entire contents of which are incorporated herein by reference.

[0217] Explanation of reference numerals in the attached figures

[0218] 2: Aeration tank;

[0219] 3: Ventilation tube;

[0220] 4: Blower.

Claims

1. An aerobic biological treatment method, comprising supplying raw water to an aeration tank, and utilizing a fluidized bed containing a biofilm carrier filled in the aeration tank to perform aerobic biological treatment on the target substances to be removed from the raw water to obtain treated water, characterized in that, Continuous aeration is performed under high-load conditions where the load exceeds the specified high-load value. Under the following low-load conditions, strong aeration and weak aeration are performed alternately. The strong aeration intensity is set to a specified aeration intensity value that allows the carrier to flow, and the weak aeration intensity is set to less than the minimum flow rate or aeration is stopped. The low load condition is a low load that satisfies any one of the following (a) to (d). (a) The measured value of the raw water load is below the specified measured value; (b) The measured oxygen consumption rate of the aeration tank is below the specified oxygen consumption rate; (c) Under high load conditions where the load is greater than the specified high load value, i.e., under continuous aeration, the target value of the dissolved oxygen concentration controlled according to the load is below the specified dissolved oxygen concentration value; (d) Under high-load conditions where the load exceeds the specified high-load value, i.e., during continuous aeration, the aeration intensity setting controlled according to the load is below the specified intensity value. The specified measurement value in (a), the specified oxygen consumption rate in (b), the specified dissolved oxygen concentration value in (c), and the specified intensity value in (d) are respectively the values ​​of the aeration volume when the aeration volume is set in a manner that the aeration volume during weak aeration is between 1 / 2 and 1 / 5 of the minimum aeration volume during fluidization.

2. The aerobic biological treatment method as described in claim 1, wherein, The raw water load can be any one of the following: inflow load, tank load, and carrier volumetric load.

3. The aerobic biological treatment method as described in claim 1 or 2, wherein, The aeration intensity is controlled by the aeration volume, aeration stop time, or aeration inhibition time.

4. The aerobic biological treatment method as described in claim 1 or 2, wherein, The aeration tank does not have a mechanical stirring mechanism or a guide pipe for stirring the water in the tank.

5. The aerobic biological treatment method as described in claim 3, wherein, The aeration tank does not have a mechanical stirring mechanism or a guide pipe for stirring the water in the tank.

6. An aerobic biological treatment device, comprising an aeration tank for supplying raw water, a fluidized bed containing a biofilm holding carrier filled in the aeration tank, and an aeration device for aerating the aeration tank, characterized in that, The aerobic biological treatment device has an aeration control mechanism. The aeration control mechanism performs continuous aeration under high-load conditions where the load exceeds a specified high-load value, and alternates between strong and weak aeration under the following low-load conditions. The strong aeration intensity is set to a specified aeration intensity value that allows the carrier to flow, while the weak aeration intensity is set to less than the minimum flow rate or aeration is stopped. The low load condition is a low load that satisfies any one of the following (a) to (d). (a) The measured value of the raw water load is below the specified measured value; (b) The measured oxygen consumption rate of the aeration tank is below the specified oxygen consumption rate; (c) Under high load conditions where the load is greater than the specified high load value, i.e., under continuous aeration, the target value of the dissolved oxygen concentration controlled according to the load is below the specified dissolved oxygen concentration value; (d) Under high-load conditions where the load exceeds the specified high-load value, i.e., during continuous aeration, the aeration intensity setting controlled according to the load is below the specified intensity value. The specified measurement value in (a), the specified oxygen consumption rate in (b), the specified dissolved oxygen concentration value in (c), and the specified intensity value in (d) are respectively the values ​​of the aeration volume when the aeration volume is set in a manner that the aeration volume during weak aeration is between 1 / 2 and 1 / 5 of the minimum aeration volume during fluidization.

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