Aerobic biofilm treatment method and device

Abstract

This invention provides an aerobic biofilm treatment method and apparatus, which involves supplying raw water to an aeration tank (2) and performing aerobic biological treatment on target substances in the raw water using a biofilm holding carrier (C) or particles filled in the aeration tank (2). The method and apparatus are characterized by pre-setting a relationship between the raw water biofilm load (as a unit raw water load of the biofilm holding carrier or particles) and its corresponding target dissolved oxygen concentration and / or its corresponding aeration intensity setting value. The target dissolved oxygen concentration and / or the aeration intensity setting value are adjusted according to the relationship in response to changes in the measured value of the raw water biofilm load. The aeration device is controlled to ensure that the dissolved oxygen concentration reaches the target value or becomes the set aeration intensity setting value.

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, microorganisms are maintained in a dispersed state in the reactor as microbial flocs. By removing the microorganisms that increase with the wastewater treatment as excess sludge, the amount of microorganisms maintained in the reactor is kept constant, thereby maintaining the oxygen consumption caused by the self-decomposition process of the microorganisms at a fixed level. Therefore, the increase or decrease in the required oxygen in this process varies proportionally to the raw water load. The amount of oxygen to be supplied can be determined by adding a certain amount of oxygen consumption to compensate for the oxygen consumption accompanying the self-decomposition process of the microorganisms. In this process, the microorganisms are typically maintained in the form of micro-aggregates of about 1 mm, called flocs, which sufficiently ensures the contact area between the microorganisms and the bulk water tank. Therefore, the permeability and diffusion of oxygen in the flocs are not the main rate-limiting factors in oxygen supply. Therefore, the aeration air volume to be supplied to the device is considered to be proportional to the oxygen consumption. Patent Document 1 describes measuring the load of pollutants with an instrument and controlling the aeration air volume based on this.

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

[0005] Patent document 2 describes that in the self-granulation particle method and fluidized bed carrier method, when the BOD volumetric load is less than the specified value, the fluidization of the microbial carrier is used as the judgment criterion, and when the BOD volumetric load is greater than the specified value, the oxygen demand of the wastewater is used as the judgment criterion to control the aeration rate 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, it is strictly difficult to adjust the oxygen supply based solely on the inflow load (calculated by multiplying the flow rate of raw water per unit time, a typical indicator of raw water load, by the concentration of pollutants in the raw water) and the tank load (calculated by dividing the inflow load by the volume of the reaction tank). The reasons are as follows.

[0011] In biofilm-based methods, since there is no mechanism to maintain a fixed amount of microorganisms in the reaction tank in the form of a biofilm, the amount of microorganisms maintained varies over time. Consequently, the oxygen consumption due to the self-decomposition process of the microorganisms also varies. Therefore, in biofilm-based methods, in addition to considering the changes in oxygen consumption proportional to the raw water load, it is also necessary to consider the changes in oxygen consumption accompanying changes in the amount of microorganisms maintained to determine the oxygen supply to the device.

[0012] Due to these factors, in biofilm-based treatment methods, the amount of oxygen required for the oxidation of organic matter in the raw water varies with load changes, and changes in the amount of biofilm maintained within the treatment unit also lead to changes in the required oxygen supply. Furthermore, biofilm methods typically form biofilms with a thickness of 3 mm or more, resulting in a smaller contact area between the unit of microorganisms and the bulk water compared to planar methods. Therefore, when supplying oxygen to the microorganisms within the biofilm, oxygen diffusion at the contact surface between the bulk water and the biofilm becomes the primary rate-limiting factor in oxygen supply.

[0013] The rate of oxygen diffusion in biofilms depends on the dissolved oxygen (DO) level in the bulk water; therefore, the DO level needs to be adjusted to regulate the oxygen supply. Furthermore, from the perspective of the aeration system, even with the same oxygen supply, the required aeration volume will vary depending on the DO level. It is well known that higher DO levels require higher aeration volumes, and lower DO levels require lower aeration volumes.

[0014] Therefore, with increased load, the amount of oxygen required for the oxidation of organic matter in the raw water increases. The required oxygen supply is determined by considering the oxygen consumption resulting from the self-decomposition process, which varies based on changes in the amount of microorganisms maintaining the biofilm. Adjusting the dissolved oxygen (DO) in the bulk water to increase the required DO also necessitates increasing the aeration volume to achieve the target DO.

[0015] Conversely, with reduced load, the amount of oxygen required for the oxidation of organic matter in the raw water decreases. The required oxygen supply was determined by considering the oxygen consumption resulting from the self-decomposition process, which varies according to the amount of microorganisms maintaining the biofilm. The reduced required oxygen supply allows for maintaining a lower dissolved oxygen (DO) level in the bulk water, and also reduces the aeration air volume needed to achieve the target DO level.

[0016] For this reason, in order to maintain a high volumetric water DO and oxygen supply even under high load conditions, constant air volume operation is required when there is excessive aeration air volume, without adjusting and controlling the operation according to the load.

[0017] When operating at high loads with a constant airflow rate maintaining the required high DO (displacement) level, the lack of airflow suppression corresponding to the reduction in oxygen consumption when the load decreases results in wasted energy. Even assuming high-load oxygen supply and DO control with a set high DO target value, the biofilm treatment unit can reduce the DO level when the load decreases. Therefore, lowering the target DO level allows for further limitation of the aeration airflow. However, since this airflow suppression based on the DO target reduction is not performed in normal DO control, energy is still wasted.

[0018] For this reason, energy waste is particularly noticeable under conditions of large load fluctuations. However, even when such energy waste exists, existing technologies struggle to adjust airflow to match the target DO level with the treated water quality without causing deterioration, thus making the airflow level appropriate for the operating conditions. Previously, even at low loads, operators often set excessive DO levels and aeration to allow for additional oxygen supply as needed, even with appropriate airflow adjustments. This frequently results in energy waste.

[0019] If conventional flow rate and tank load are used as indicators of raw water load, the impact of changes in the biomass maintained in the biofilm cannot be considered. Furthermore, the influence of the contact area between the biofilm and the bulk water cannot be taken into account, making appropriate aeration management difficult. Therefore, in the past, oxygen consumption was typically set based on the assumption of a high biomass, without considering the impact of the contact area between the biofilm and the bulk water, resulting in excessively high aeration airflow settings. This often leads to energy waste. Summary of the Invention

[0020] The problem that the invention aims to solve

[0021] The purpose of this invention is to provide a method and apparatus for properly controlling aeration in wastewater treatment using aerobic biofilms.

[0022] Methods for solving problems

[0023] The aerobic biofilm treatment method of the present invention involves supplying raw water to an aeration tank, aerating it using an aeration device, and using a biofilm carrier or particles filled in the aeration tank to perform aerobic biological treatment of the target substances in the raw water. The method is characterized by pre-setting a relationship between the raw water biofilm load (as a unit of raw water load per unit of the carrier or particles) and its corresponding DO target value and / or its corresponding aeration intensity setting value; adjusting the DO target value and / or aeration intensity setting value according to the relationship in response to changes in the measured value of the raw water biofilm load; and controlling the aeration device to ensure that the DO reaches the target value or becomes the set aeration intensity setting value.

[0024] The aerobic biofilm treatment device of the present invention comprises an aeration tank for supplying raw water, an aeration device for aeration of the aeration tank, a biofilm-bearing carrier or particles filled in the aeration tank, and a controller for controlling the aeration device. The aerobic biofilm treatment device is characterized by: a mechanism for pre-setting a relationship between the raw water biofilm load (as a unit raw water load of the carrier or particles) and its corresponding DO target value and / or its corresponding aeration intensity setpoint; and a mechanism for adjusting the DO target value and / or the aeration intensity setpoint according to the relationship in response to changes in the measured value of the raw water biofilm load. The controller controls the aeration device to make the DO reach the target value or to make it reach the set aeration intensity setpoint.

[0025] According to one aspect of the present invention, the raw water biofilm load is any one of the following: the target substance removal load per unit filling volume of the carrier, the target substance removal load per unit total surface area of ​​the carrier group, the target substance removal load per unit filling volume of the particles, and the target substance removal load per unit total surface area of ​​the particle group.

[0026] According to one aspect of the invention, the target substance to be removed is organic matter, nitrogen compounds, or ammonium ions, and the raw water biofilm load is calculated based on a calculated value of concentration converted from a measured value of the concentration of the target substance to be removed or a measured value of absorbance, a measured value of the raw water flow rate, and a measured or calculated value of the filling volume or surface area of ​​the carrier or particles.

[0027] According to one aspect of the invention, the aeration intensity is controlled by controlling the aeration volume, the aeration stop time, or the aeration inhibition time.

[0028] According to one aspect of the invention, the relationship is established using any one of experimental results, actual operational performance, or a mechanism model that takes into account the diffusivity of oxygen in the biofilm.

[0029] The effects of the invention

[0030] In this invention, instead of using flow load or volume load, the raw water biofilm load is used to estimate the sufficient oxygen supply required to suit the properties of the carrier and particles in the aeration tank that change over time. The target value of DO and the set value of aeration intensity are changed to control the aeration. Therefore, aeration can be appropriately controlled. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the biological treatment device using the present invention.

[0032] Figure 2 This is a graph showing the results of the embodiments and comparative examples.

[0033] Figure 3 This is a graph showing the results of the embodiments and comparative examples.

[0034] Figure 4 This is a graph showing the results of the embodiments and comparative examples.

[0035] Figure 5 This is a graph representing the total organic carbon (TOC) load of the raw water.

[0036] Figure 6 This is a schematic diagram showing the configuration of a biological treatment device using the present invention. Detailed Implementation

[0037] Figure 1 This is a schematic diagram of the biological treatment device using the present invention.

[0038] The treated wastewater (raw water) is introduced into the aeration tank 2 through 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 through pipe 5 for aeration.

[0039] Water treated by aerobic biological processes using a biofilm is taken out from pipe 6 as treated water through screen 2a.

[0040] In this biological treatment device, as measuring mechanisms, there are flow meters 7 and concentration meters 8 for measuring the flow rate of raw water flowing in piping 1 and the concentration of the substances being treated, a DO meter 9 for measuring DO in tank 2, and an air volume meter 10 for measuring the amount of air supplied from blower 4 to aeration pipe 3. These measured values ​​are input into controller 11. The aeration intensity is controlled by controlling blower 4 through controller 11.

[0041] Examples of concentration meters include total organic carbon meters, ammonia nitrogen meters, or UV absorbance meters (which calculate total organic carbon / N).

[0042] Through various studies, the inventors have discovered that when using flow load and tank load as raw water load, even if the raw water load is the same, one of the reasons why it is sometimes difficult to carry out proper aeration management is that the state of the carrier and particles filled in the aeration tank changes.

[0043] For example, when an aeration tank filled with fluidized bed carriers is operated for a long time, the carriers may be cut into smaller particles and flow out of the aeration tank through the gaps in the screen. This reduces the carrier filling rate in the aeration tank, and the reduced contact area between the biofilm surface and the bulk water, thus reducing the treatment performance.

[0044] During long-term operation, there is an increase in the amount of microorganisms remaining on the carrier and an increase in oxygen consumption due to the self-decomposition of microorganisms.

[0045] In the case of an aeration tank using an expanded bed with settling carriers as a type of fixed-bed treatment, periodic backwashing is required to remove excess sludge and suspended solids (SS) between the carriers. At this time, the carriers experience wear and tear due to collisions and shear forces, leading to a gradual decrease in carrier filling rate. This reduced carrier filling rate within the tank decreases the contact area between the biofilm surface and the bulk water, thus reducing treatment performance.

[0046] During long-term operation, there is an increase in the amount of microorganisms remaining in and between the carriers, as well as an increase in oxygen consumption due to the self-decomposition of microorganisms.

[0047] In biological treatment tanks using self-granulated granules, the number and size of the granules change over time, and the amount of biofilm in the aeration tank increases or decreases. As a result, the contact area between the biofilm and the bulk water changes, and thus the diffusivity of oxygen to the biofilm changes. Therefore, even with the same organic load, the aeration volume required for wastewater treatment varies.

[0048] In this invention, the relationship between the raw water biofilm load and its corresponding DO target value and / or its corresponding aeration intensity setting value is preset, and the corresponding DO target value and / or aeration intensity setting value is adjusted according to the relationship based on the change in the measured value of the raw water biofilm load.

[0049] Furthermore, the aeration device is controlled to ensure that the DO reaches the target value or becomes the set aeration intensity value.

[0050] As the raw water biofilm load, the preferred load is the target substance removal load per unit filling volume of the carrier (carrier volume load) or the target substance removal load per unit total surface area of ​​the carrier group (all carriers in the tank) (carrier surface area load), the target substance removal load per unit filling volume of the particles (particle volume load) or the target substance removal load per unit total surface area of ​​the particle group (all particles in the tank) (particle surface area load).

[0051] <Raw Water Load>

[0052] The raw water load can be calculated using the following formula.

[0053] Load = Q·concentration

[0054] Load: Raw water load [kg / d].

[0055] Q: Raw water flow rate [m] 3 / d].

[0056] Concentration: Raw water concentration [kg / m³] 3 ].

[0057] As an example of raw water concentration, the concentration of total organic carbon / N can be calculated from total organic carbon, ammonia nitrogen, and UV absorbance.

[0058] <Carrier Volumetric Load>

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

[0060] load 载体容积 =Load / V 载体

[0061] load 载体容积 Carrier volumetric load [kg / (m³)] 3 ·d)].

[0062] V_carrier: The carrier filling volume in the aeration tank [m] 3 ].

[0063] <Carrier Surface Area Load>

[0064] The surface load of the carrier can be calculated using the following formula.

[0065] load 载体表面积 =Load / S 载体

[0066] load 载体表面积 : Carrier surface area load [kg / (m²)] 2 ·d)].

[0067] S 载体 The total surface area of ​​the carrier group in the aeration tank [m²] 2 ].

[0068] In aeration tanks, the raw water load can sometimes fluctuate rapidly over time, sometimes on a minute-by-minute basis, while the properties of the carriers (the carrier filling volume or the total surface area of ​​the carrier group within 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 values ​​frequently. Furthermore, for the carrier filling volume or the total surface area of ​​the carrier group within the aeration tank, it is sufficient to periodically sample and analyze the carriers (e.g., approximately once every 1 to 3 months) and update the carrier filling volume and total surface area data accordingly.

[0069] [Control based on oxygen consumption rate as a management indicator]

[0070] [Methods for estimating oxygen consumption rate]

[0071] According to one aspect of the invention, the oxygen consumption rate of the treatment device, which is an indicator of the oxygen consumption required to oxidize the organic matter in the raw water and the oxygen consumption caused by the auto-oxidation of microorganisms maintained on the biofilm, is monitored as the total amount. The aeration intensity is controlled based on the oxygen consumption rate. Specifically, under low-load conditions where the oxygen consumption rate is below a predetermined value, the aeration intensity is set to a predetermined intensity or higher to maintain the stirring intensity in the treatment tank; when the oxygen consumption rate is above a predetermined value, the aeration intensity is adjusted to correspond to the level of oxygen consumption. As described above, using... Figure 6 This paper explains the method for calculating oxygen consumption rate when oxygen consumption rate is used as a management indicator.

[0072] exist Figure 6 In the biological treatment device, the treated wastewater (raw water) is introduced into the aeration tank 2 through pipe 1. The aeration tank 2 is filled with a carrier C loaded with biofilm. Aeration pipes 3a, 3b, and 3c are installed at the bottom of the aeration tank 2, supplying air from the blower 4 through pipe 5 and branch pipes 5a, 5b, and 5c for aeration. A top cover 2r is installed in the aeration tank 2.

[0073] Water treated by aerobic biological processes using a biofilm is taken out from pipe 6 as treated water through screen 2a.

[0074] 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 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.

[0075] <Scenario 1: Method for estimating oxygen consumption rate based on air volume meter and exhaust gas meter>

[0076] Measure the aeration air volume and the oxygen concentration in the exhaust gas, and directly calculate the oxygen consumption rate qO2 according to the following formula.

[0077] Mathematical Formula 1

[0078]

[0079] Mathematical formula 2

[0080]

[0081] OTE: Oxygen transport efficiency [-].

[0082] Z0: Mole fraction of oxygen in the blown air [-].

[0083] Z: Mole fraction of oxygen in exhaust gas [-].

[0084] qO2: Oxygen consumption rate [kg / d].

[0085] Gv: Standard-condition converted aeration air inflow rate [Nm] 3 / d].

[0086] v m Specific volume of oxygen [Nm] 3 / kg).

[0087] <Scenario 2: Method for calculating oxygen consumption rate based on DO meter and aeration air volume>

[0088] By measuring the aeration air volume and dissolved oxygen (DO), the oxygen consumption rate qO2 can be indirectly estimated.

[0089] (i) Calculate the oxygen solubility index φ required for estimating the oxygen consumption rate (preparation before control device installation) according to the following formula.

[0090] Mathematical Formula 3

[0091]

[0092] Mathematical expression 4

[0093]

[0094] OTE: Oxygen transport efficiency [-].

[0095] Z0: Mole fraction of oxygen in the blown air [-].

[0096] Z: Mole fraction of oxygen in exhaust gas [-].

[0097] φ: Oxygen solubility index [m].

[0098] v m Specific volume of oxygen [Nm] 3 / kg).

[0099] h: Water depth of the aeration device [m].

[0100] Cs: Concentration of saturated dissolved oxygen [kg / m³] 3 ].

[0101] C: Concentration of dissolved oxygen in the mixture [kg / m³] 3 ].

[0102] (ii) Continuously measure the rate of oxygen consumption over time (while the device is in operation).

[0103] Based on continuous measurement data of DO meter and aeration air volume, and the pre-calculated oxygen solubility index φ, the oxygen consumption rate qO2 is continuously calculated using the following formula.

[0104] Mathematical formula 5

[0105]

[0106] qO2: Oxygen consumption rate [kg / d].

[0107] Gv: Standard-condition converted aeration air inflow rate [Nm] 3 / h).

[0108] h: Water depth of the aeration device [m].

[0109] Cs: Concentration of saturated dissolved oxygen [kg / m³] 3 ].

[0110] C: Concentration of dissolved oxygen in the mixture [kg / m³] 3 ].

[0111] φ: Oxygen solubility index [m].

[0112] [Relationship between DO target value or aeration intensity setpoint and the raw water biofilm load]

[0113] In an embodiment of the present invention, the oxygen consumption rate (qO2) is regarded as the raw water load (load), and then the "carrier volume load" or "carrier surface load" is calculated. The calculation result is regarded as the "raw water biofilm load". Based on the prediction or actual results of the treated water quality under the condition of changing the DO target value or aeration intensity, the appropriate DO target value or aeration intensity setting value is found, and the relationship between the appropriate DO target value or aeration intensity setting value corresponding to the raw water biofilm load is found, which is effectively utilized in the control system.

[0114] The relationship between raw water biofilm load and DO target value or aeration intensity setpoint is determined using preliminary experimental data, actual operational performance data, and simulation results of a mechanism model that considers the diffusivity of oxygen in the biofilm.

[0115] The relationship between the raw water biofilm load and the DO target value or aeration intensity setpoint can be expressed by any of the following methods: a function (an approximate function that yields an appropriate DO target value or appropriate aeration intensity based on the raw water biofilm load), a control table (a table that summarizes the relationship between the raw water biofilm load and the appropriate DO target value or appropriate aeration intensity), etc.

[0116] [A biofilm mechanism model used to establish the relationship between raw water biofilm loading and target DO values ​​and / or aeration intensity setpoints]

[0117] As a method for discovering the relationship between raw water biofilm loading and target DO values ​​and / or aeration intensity setpoints, a kinetic model (hereinafter sometimes referred to as a biofilm mechanism model) can be used to estimate the decrease of pollutants and the increase or decrease of activated sludge cell mass in the biofilm when the biofilm comes into contact with a bulk water phase containing pollutants and oxygen in a flowing state. This kinetic model also needs to consider the simultaneous occurrence of cell proliferation and pollutant consumption and oxygen consumption within the biofilm, the diffusion of dissolved oxygen from the bulk water phase to the biofilm, and the phenomenon of oxygen dissolving in the bulk water due to aeration. Furthermore, the increase and decrease of biofilm size are caused by the increase and decrease in the volume of the cell population accompanying cell proliferation and death, the attachment of cells from the bulk water phase, and the detachment of cells from the bulk water 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, the model formulas become complex. However, by using a one-dimensional model formula that only considers changes in the thickness direction to represent the increase and decrease of the biofilm, simulation can be performed more easily. As mathematical models for simulating wastewater treatment using activated sludge, a series of mathematical models proposed by the International Water Association (IRA) task force can be effectively utilized (Reference 1). As examples of mathematical models focusing on biofilms, (Reference 2) can be used, etc.

[0118] Reference 1: M Henze; ​​IWA.Task Group on Mathematical Modeling for Design and Operaton of Biological Wastewater Treatment; et al.

[0119] Reference 2: Boltz, JP, Johnson, BR, Daigger, GT, Sandino, J., (2009a). "Modeling Integrated Fixed-Film Activated Sludge and Moving Bed BiofilmReactor Systems I: Mathematical Treatment and Model Development". WaterEnvironment Research, 81(6), 555-575.

[0120] By utilizing mathematical models, such as those for fluidized bed carriers, it is possible to construct mathematical models. Typically, these mathematical models are expressed as simultaneous ordinary differential equations, which can be used to simulate the dynamic behavior of the target process using numerical integration software focused on simultaneous ordinary differential equations. For example, it is possible to predict the treated water quality based on the dissolved oxygen (DO) status of the bulk aqueous phase, which varies due to specific device structure, load assumptions, and aeration intensity.

[0121] By utilizing mathematical models, it is possible to predict, for example, the total organic carbon concentration of treated water under various load conditions and aeration intensities. Based on the simulation results, the minimum target DO value for non-deterioration and the adjustment of aeration intensity were studied, and a table summarizing the simulation results was created, which can be effectively used in the control system of this patent.

[0122] [Control of aeration intensity]

[0123] Aeration intensity can be controlled, for example, by changing the aeration volume (air supply flow rate), the aeration stop time per specified time cycle, or the aeration inhibition time (the duration of weak aeration). The aeration stop time refers to the period during which aeration ceases within a specified time cycle in so-called intermittent aeration. The aeration inhibition time refers to the duration of weak aeration during alternating strong and weak aeration operations.

[0124] The aeration volume, aeration stop time, and aeration inhibition time are controlled continuously or in stages according to the raw water load.

[0125] Biological treatment other than fluidized bed

[0126] exist Figure 1 The invention describes biological treatment using a fluidized bed carrier, and the same method can be used when using a fixed bed carrier or particles. For example, when the raw water is under particle loading, the volume or surface area of ​​the carrier or carrier group can be set to the volume or surface area of ​​the particles or particle group in equations (2) and (3).

[0127] In this embodiment, the case of treating wastewater containing organic matter by aerobic biofilm treatment with aeration is described. In addition, the present invention can also be implemented in the same way when performing biological treatments such as biological nitrification denitrification treatment using biofilm, which includes aerobic treatment steps using biofilm in aeration tank.

[0128] Example

[0129] <Device Structure>

[0130] The following instructions use Figure 1 This is an example of a device for monitoring raw water load and controlling DO weak aeration time using the total organic carbon carrier volumetric load of a fluidized bed carrier.

[0131] The controller 11 has a mechanism for adjusting the aeration volume to achieve a DO value corresponding to the target DO value, and an intermittent aeration mechanism for periodically performing weak aeration with a specified air volume.

[0132] As carrier C, a cubic polyurethane foam with one side length of 3mm is used as the carrier.

[0133] <Model of Biomembrane Structure>

[0134] In fact, a one-dimensional simplified model is used to represent the diffusion of pollutants and oxygen between the interior of a carrier with a three-dimensional structure and the bulk water. This one-dimensional model consists of a model of a completely mixed compartment with a total of four layers, assuming three layers of bulk water and biofilm.

[0135] Bacterial cells consume substrates (pollutants) and oxygen to proliferate within both the bulk aqueous phase and the biofilm, and then self-decompose according to a prescribed ratio. The proliferating bacteria attach and desorb based on the concentration difference between the bulk and aqueous phases. Typically, because the bacterial concentration in the biofilm is higher than in the bulk aqueous phase, a model is developed to handle cases where the amount of bacteria desorbed from the biofilm is greater than the amount of bacteria attached to the biofilm in the aqueous phase.

[0136] The substrate, i.e., the pollutants to be treated, is supplied by the inflow and outflow. A portion flows out with the treated water, while the remainder diffuses into the biofilm based on the concentration difference between the bulk aqueous phase and the biofilm. A model is constructed to represent the oxidative decomposition and reduction of pollutants within both the bulk aqueous phase and the biofilm as microorganisms proliferate. This model shows that the rate of pollutant oxidative decomposition decreases with decreasing oxygen concentration and substrate (pollutant) concentration as microorganisms proliferate.

[0137] Most of the oxygen is supplied to the bulk aqueous phase via aeration devices, with some also supplied as oxygen in the inflow and outflow. Additionally, a portion of the supplied oxygen flows out with the treated water, and the remainder diffuses into the biofilm based on the oxygen concentration difference between the bulk aqueous phase and the biofilm. A model was developed to represent the oxygen consumed by microorganisms during proliferation and self-decomposition within both the bulk aqueous phase and the biofilm. The model shows that the rate of decrease in oxygen consumption due to microbial proliferation, which becomes pollutant, decreases with decreasing oxygen concentration and substrate (pollutant) concentration.

[0138] <Relationship between raw water biofilm loading and DO target value and / or aeration intensity setpoint>

[0139] Using the mathematical formula of the constructed one-dimensional diffusion model of the biofilm, the treated water quality under the treatment conditions was predicted by numerical integration simulation. The appropriate control conditions were explored and summarized in the control table below.

[0140] In this embodiment, the control table in Table 1 is used to show the relationship between the target DO value and / or the set value of aeration intensity corresponding to the biofilm load in the raw water.

[0141] Table 1

[0142]

[0143] In this control table, for example, the total organic carbon carrier volumetric loading (kg C / (m³)) 3 •d), where units are sometimes omitted below, the target value for DO is 3.1 mg / L when the concentration is above 0.1 and below 0.6; 3.8 mg / L when the concentration is above 0.6 and below 0.7; 3.9 mg / L when the concentration is above 0.7 and below 0.9; 4.4 mg / L when the concentration is above 0.9 and below 1.0; and 4.8 mg / L when the concentration is above 1.0. These values ​​should be set to appropriate values ​​respectively.

[0144] When the total organic carbon carrier volumetric loading is above 0.1 and below 0.2, the weak aeration time setting is set to 110 minutes every 2 hours; 90 minutes every 2 hours when above 0.2 and below 0.3; 80 minutes every 2 hours when above 0.3 and below 0.4; 60 minutes every 2 hours when above 0.4 and below 0.5; and 20 minutes every 2 hours when above 0.5 and below 0.6. These values ​​are set appropriately, and the total organic carbon carrier volumetric loading is 0.6 (kg C / (m³)). 3 When d)) or above, set the weak aeration time setting to zero (i.e., do not perform intermittent aeration).

[0145] [Example 1]

[0146] Total organic carbon load as Figure 5The raw water shown is set as the drainage object to be treated.

[0147] Based on the 2-hour moving average of the carrier volumetric load, the DO target value is adjusted every 2 hours according to the control table in Table 1, and the weak aeration time is set to a fixed low air volume (3m³ / h) during weak aeration. 3 / (base area m) 2 For periods other than weak aeration, control the motor speed of the blower to achieve the set DO target value.

[0148] The variation of the duration of weak aeration over time is shown in the figure. Figure 2 The change of DO over time is shown in Figure 3 In addition, the change in the power consumption of the blower over time is shown in... Figure 4 .

[0149] [Comparative Example 1]

[0150] The target DO value was set to a fixed value of 3.5 mg / L, and the weak aeration time was maintained at a fixed value of 10 minutes / 2 hours. Otherwise, it was the same as in Example 1. The results are shown below. Figures 2-4 .

[0151] <Inspection>

[0152] In Example 1, the target DO value and weak aeration time were adjusted according to the load per unit carrier, resulting in lower power consumption of the blower compared to Comparative Example 1. Specifically, the power consumption of Comparative Example 1 was approximately 1150 kWh / day, while the power consumption of Example 1 was approximately 950 kWh / day, a reduction of approximately 17%.

[0153] Furthermore, there was almost no difference in the treated water quality between Example 1 and Comparative Example 1.

[0154] The present invention has been described in detail using specific embodiments; however, those skilled in the art will recognize that various modifications can be made without departing from the intent and scope of the invention.

[0155] This application is based on Japanese Patent Application No. 2020-063031, filed on March 31, 2020, the entire contents of which are incorporated herein by reference.

[0156] Explanation of reference numerals in the attached figures

[0157] 2: Aeration tank; 3: Air diffuser; 4: Blower; 7: Flow meter; 8: Concentration meter; 9: DO meter; 10: Air volume meter; 11: Controller.

Claims

1. An aerobic biofilm treatment method, comprising supplying raw water to an aeration tank, aerating the water using an aeration device, and using a biofilm carrier or self-granulating particles filled in the aeration tank to perform aerobic biological treatment of the target substances in the raw water, characterized in that... The relationship between the raw water biofilm load (as a unit of raw water load for the carrier or self-granulated particles) and its corresponding target dissolved oxygen concentration and / or its corresponding aeration intensity setting value is preset. Based on the changes in the measured value of the biofilm load in the raw water, the target value of dissolved oxygen concentration and / or the set value of aeration intensity are adjusted accordingly based on the relationship described above. The aeration device is controlled to make the dissolved oxygen concentration reach the adjusted target value or the aeration intensity reach the adjusted set value.

2. The aerobic biofilm treatment method as described in claim 1, wherein, The raw water biofilm load is any one of the following: the target substance removal load per unit filling volume of the carrier, the target substance removal load per unit total surface area of ​​the carrier group, the target substance removal load per unit filling volume of the self-granulating particles, and the target substance removal load per unit total surface area of ​​the self-granulating particle group.

3. The aerobic biofilm treatment method as described in claim 1, characterized in that, The target substance to be removed is organic matter, nitrogen compounds, or ammonium ions. The raw water biofilm load is calculated based on the concentration calculated from the measured concentration or absorbance of the target substance being removed, the measured raw water flow rate, and the measured or calculated filling volume or surface area of ​​the carrier or self-granulating particles.

4. The aerobic biofilm treatment method as described in claim 2, characterized in that, The target substance to be removed is organic matter, nitrogen compounds, or ammonium ions. The raw water biofilm load is calculated based on the concentration calculated from the measured concentration or absorbance of the target substance being removed, the measured raw water flow rate, and the measured or calculated filling volume or surface area of ​​the carrier or self-granulating particles.

5. The aerobic biofilm treatment method according to any one of claims 1 to 4, wherein, The aeration intensity is controlled by adjusting the aeration volume, aeration stop time, or aeration inhibition time.

6. The aerobic biofilm treatment method according to any one of claims 1 to 4, characterized in that, The relationship can be established using any one of the following: experimental results, actual operational performance, or a mechanism model that takes into account the diffusivity of oxygen in the biofilm.

7. The aerobic biofilm treatment method as described in claim 5, characterized in that, The relationship can be established using any one of the following: experimental results, actual operational performance, or a mechanism model that takes into account the diffusivity of oxygen in the biofilm.

8. An aerobic biofilm treatment device, comprising an aeration tank for supplying raw water, an aeration device for aeration of the aeration tank, a biofilm-bearing carrier or self-granulating particles filled in the aeration tank, and a controller for controlling the aeration device, characterized in that, The aerobic biofilm treatment device has the following features: A mechanism that pre-sets the relationship between the raw water biofilm load, which is the raw water load per unit of the carrier or self-granulated particles, and the corresponding target value of dissolved oxygen concentration and / or the corresponding set value of aeration intensity. as well as A mechanism that adjusts the target dissolved oxygen concentration and / or aeration intensity setpoint according to the relationship described above, based on the variation in the measured value of the biofilm load in the raw water. The controller controls the aeration device to make the dissolved oxygen concentration reach the adjusted target value or the aeration intensity reach the adjusted set value.

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