Wastewater treatment equipment and wastewater treatment methods.

Abstract

A wastewater treatment device 10 is provided which controls the amount of dissolved oxygen DO in a nitrification zone and the oxidation redox potential ORP in a denitrification zone so as to enable stably performing nitrification and denitrification.　This wastewater treatment device 10 is provided with a reaction vessel 1, and the reaction vessel 1 comprises partition plate 2 which separates a nitrification region D1 where nitrification is performed and a denitrification region D2 where denitrification is performed, and a circulation plate 5 which is arranged in the nitrification region D1; the partition plate 2 has an overflow opening 2c where the treated water overflows from the nitrification region D1 to the denitrification region D2, and a return opening 2d where the treated water returns from the denitrification region D2 to the nitrification region D1. Treated water in the nitrification region D1 circulates through the circulation plate 5 and moves via the overflow opening 2c to the denitrification region D2, and treated water in the denitrification region D2 returns to the nitrification region D1 via the return opening 2d.

Description

Wastewater treatment device and wastewater treatment method

[0001] The present invention relates to a wastewater treatment device and a wastewater treatment method.

[0002] Conventionally, wastewater treatment equipment has been known that performs, in a single reaction tank, a nitrification reaction in which nitrifying bacteria, which are organic sludge containing microorganisms (hereinafter referred to as "activated sludge"), convert ammonia contained in wastewater into nitrite and nitrate in the presence of oxygen, and a denitrification reaction in which denitrifying bacteria, which are activated sludge, convert the nitrite and nitrate into nitrogen in the absence of oxygen (see, for example, Patent Document 1). In the wastewater treatment equipment of Patent Document 1, the reaction tank is equipped with a partition plate that divides the reaction tank into a nitrification reaction region where the nitrification reaction occurs and a denitrification reaction region where the denitrification reaction occurs, and the nitrification reaction region has a membrane separation device that separates and removes solids contained in wastewater that has undergone the nitrification and denitrification reactions (hereinafter referred to as "treated water"), and an air diffuser that cleans the surface of the membrane separation device or diffuses air bubbles to supply the air necessary for the nitrification reaction.

[0003] When the wastewater level is higher than the top of the partition, the wastewater overflows the partition and moves from the nitrification reaction zone to the denitrification reaction zone, and from the denitrification reaction zone back to the nitrification reaction zone. This creates a circulation flow that circulates around the partition. Therefore, the nitrite and nitrate produced in the nitrification reaction zone move to the denitrification reaction zone, where they are converted to nitrogen. On the other hand, when the wastewater level is lower than the top of the partition, the wastewater does not overflow the partition. Therefore, no circulation flow is formed, and nitrite and nitrate are produced in the nitrification reaction zone, while the nitrite and nitrate that previously moved from the nitrification reaction zone to the denitrification reaction zone are converted to nitrogen in the denitrification reaction zone.

[0004] The dissolved oxygen (DO), which indicates the amount of oxygen dissolved in the wastewater in the nitrification reaction region, and the oxidation-reduction potential (ORP), which indicates the oxidation-reduction power in the denitrification reaction region, are used as indicators of whether the nitrification reaction and the denitrification reaction are being carried out properly. The dissolved oxygen (DO) in the nitrification reaction region is controlled to, for example, 1.5 mg / L or more, and the oxidation-reduction potential (ORP) in the denitrification reaction region is controlled to, for example, -200 mV to -100 mV, thereby allowing the nitrification reaction and the denitrification reaction to be carried out properly.

[0005] JP 2018-103129 A

[0006] However, the size of the circulation flow varies depending on the water level of the wastewater in the reaction tank and the amount of air diffused from the air diffuser, and as a result, the amount of dissolved oxygen (DO) in the nitrification reaction zone and the oxidation-reduction potential (ORP) in the denitrification reaction zone fluctuate depending on the size of the circulation flow. Therefore, the amount of dissolved oxygen (DO) in the nitrification reaction zone and the oxidation-reduction potential (ORP) in the denitrification reaction zone cannot be controlled within a certain range, and there is a risk that the nitrification reaction and the denitrification reaction will not be carried out properly.

[0007] An object of the present invention is to provide a wastewater treatment device and a wastewater treatment method that can stably carry out nitrification and denitrification reactions by controlling the amount of dissolved oxygen (DO) in the nitrification reaction region and the oxidation-reduction potential (ORP) in the denitrification reaction region.

[0008] In order to achieve the above object, a wastewater treatment device of the present invention performs a nitrification reaction in which ammonia contained in wastewater is converted into nitrite or nitrate in the presence of oxygen, and a denitrification reaction in which the nitrite or nitrate produced by the nitrification reaction is converted into nitrogen in an oxygen-free state, and is characterized by comprising: a partitioning means for partitioning a nitrification reaction zone in which the nitrification reaction is performed and a denitrification reaction zone in which the denitrification reaction is performed; a membrane separation device disposed in the nitrification reaction zone for separating and removing solids contained in wastewater that has been subjected to the nitrification reaction and the denitrification reaction; a first aeration device for diffusing air bubbles into the membrane separation device; a second aeration device for diffusing air bubbles outside the membrane separation device; a first aeration zone through which the air bubbles diffused by the first aeration device pass; a second aeration zone through which the air bubbles diffused by the second aeration device pass; and circulation plates disposed between the first aeration zone and the second aeration zone, and between the first aeration zone and the partitioning means.

[0009] In order to achieve the above object, the wastewater treatment method of the present invention performs a nitrification reaction in which ammonia contained in wastewater is converted into nitrite or nitrate in the presence of oxygen, and a denitrification reaction in which the nitrite or nitrate produced by the nitrification reaction is converted into nitrogen in an oxygen-free state, and includes a dividing means for dividing a nitrification reaction area into a nitrification reaction area in which the nitrification reaction is performed and a denitrification reaction area in which the denitrification reaction is performed, a membrane separation device that is disposed in the nitrification reaction area and separates and removes solids contained in wastewater that has been subjected to the nitrification reaction and the denitrification reaction, a first air diffuser that diffuses air bubbles into the membrane separation device, and a second air diffuser that diffuses air bubbles into a region other than the membrane separation device. a second aeration device configured to diffuse bubbles into the first aeration zone; a first aeration zone through which bubbles diffused by the second aeration device pass; a second aeration zone through which bubbles diffused by the second aeration device pass; and a circulation plate disposed between the first aeration zone and the second aeration zone and between the first aeration zone and the dividing means. The method for treating wastewater is characterized by comprising: a circulation step in which the wastewater is circulated through the circulation plate based on the aeration by the first aeration device into the first aeration zone; and a transfer step in which the wastewater is transferred from the nitrification reaction zone to the denitrification reaction zone.

[0010] According to the present invention, the amount of dissolved oxygen (DO) in the nitrification reaction region and the oxidation-reduction potential (ORP) in the denitrification reaction region can be controlled to stably carry out the nitrification reaction and the denitrification reaction.

[0011] Fig. 1 is a plan view schematically showing a wastewater treatment device according to an embodiment of the present invention. It is a cross-sectional view taken along line A-A in Fig. 1, and is a diagram used to explain a circulation plate. It is a cross-sectional view taken along line B-B in Fig. 1, and is a diagram used to explain a partition plate. It is a flowchart showing the procedure of wastewater treatment performed by the wastewater treatment device of Fig. 1.

[0012] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0013] FIG. 1 is a plan view schematically showing a wastewater treatment device 10 according to an embodiment of the present invention.

[0014] The wastewater treatment device 10 in FIG. 1 includes a reaction tank 1 connected to a raw water tank (not shown). The reaction tank 1 includes a partition plate 2 (dividing means), a membrane separation device 3, an aeration device 4, a circulation plate 5, an agitator 6, and an oxidation-reduction potentiometer 7. A pump (not shown) is connected to the membrane separation device 3, and a blower (not shown) is connected to the aeration device 4. Raw water stored in the raw water tank is supplied to the reaction tank 1. The partition plate 2 divides the reaction tank 1 into a nitrification reaction zone D1, in which nitrifying bacteria convert ammonia to nitrite and nitrate in the presence of oxygen, and a denitrification reaction zone D2, in which denitrifying bacteria convert the nitrite and nitrate generated from ammonia into nitrogen in anoxic conditions. The membrane separation device 3, the aeration device 4, and the circulation plate 5 are disposed in the nitrification reaction zone D1, and the agitator 6 and oxidation-reduction potentiometer 7 are disposed in the denitrification reaction zone D2.

[0015] The membrane separation device 3 is a long housing having a plurality of hollow fiber membranes, and when installed in the reaction tank 1, its longitudinal direction extends along the vertical direction. Treated water, which is obtained by subjecting the wastewater to be treated (hereinafter referred to as "water to be treated") stored in the reaction tank 1 to nitrification and denitrification reactions, contains solids. The membrane separation device 3 separates and removes the solids from the treated water using hollow fiber membranes, and the treated water from which the solids have been separated and removed is discharged outside the reaction tank 1. The blower supplies air to the aeration device 4, which diffuses a large amount of minute air bubbles, for example, with an air diameter of 20 μm to 500 μm, into the nitrification reaction region D1. The aeration device 4 consists of an aeration device 4a (first aeration device) located directly below the membrane separation device 3 and an aeration device 4b (second aeration device) located in a region other than directly below the membrane separation device 3.

[0016] The air diffuser 4a diffuses a large amount of tiny bubbles into the membrane separation device 3. This prevents the bubbles diffused from the air diffuser 4a from colliding with the surfaces of the hollow fiber membranes constituting the membrane separation device 3, resulting in the adhesion of solids separated and removed from the treated water to the surfaces of the hollow fiber membranes, thereby suppressing fouling. However, even if the air diffuser 4a diffuses a large amount of tiny bubbles, the bubbles diffused from the air diffuser 4a coalesce and become larger as they pass through the membrane separation device 3 while colliding with the surfaces of the hollow fiber membranes. Since these larger bubbles are less likely to dissolve in the water being treated, the required dissolved oxygen amount DO in the nitrification reaction zone D1 cannot be ensured. To address this issue, the air diffuser 4b is arranged to supply tiny bubbles to a dissolved oxygen control zone DZ (second air diffusion zone), which is a region other than the membrane aeration zone MZ (first air diffusion zone) through which the bubbles diffused by the air diffuser 4a pass.

[0017] The circulation plate 5 is disposed between the membrane aeration zone MZ and the dissolved oxygen control zone DZ. A dissolved oxygen meter is disposed in the dissolved oxygen control zone DZ, and the dissolved oxygen amount DO in the nitrification reaction zone D1 is controlled based on the dissolved oxygen meter. The dissolved oxygen amount DO in the nitrification reaction zone D1 may be controlled using at least one dissolved oxygen meter. For example, if the nitrification reaction zone D1 is divided into two zones, aeration zone A and aeration zone B, and a dissolved oxygen meter DO1 is installed in aeration zone A and a dissolved oxygen meter DO2 is installed in aeration zone B, the dissolved oxygen amount DO in the nitrification reaction zone D1 can be adjusted with higher accuracy in the aeration airflow rate than when a single dissolved oxygen meter is used, and maintenance can be improved. This embodiment assumes that dissolved oxygen meters DO1 and DO2 are disposed in the dissolved oxygen control zone DZ. Therefore, the amount of dissolved oxygen DO in the nitrification reaction region D1 is controlled based on the dissolved oxygen meters DO1 and DO2. For example, when the dissolved oxygen meters DO1 and DO2 indicate a value less than 1.5 mg / L, the aeration device 4b increases the amount of aeration to increase the amount of dissolved oxygen DO, and when the dissolved oxygen meters DO1 and DO2 indicate a value greater than 1.5 mg / L, the aeration device 4b reduces the amount of aeration to reduce power consumption.

[0018] In the denitrification reaction zone D2, a water flow is generated based on the raw water flowing into the reaction tank 1 and the water to be treated that passes through the overflow opening 2c and the return opening 2d (described later). However, the force of the water flow generated in the denitrification reaction zone D2 is very gentle, for example, with a flow velocity of less than 10 cm / s, and the denitrification reaction zone D2 is not sufficiently agitated by the water flow alone. Therefore, denitrifying bacteria are not dispersed throughout the denitrification reaction zone D2, and the denitrification reaction cannot be carried out efficiently. To address this, an agitator 6 is disposed in the denitrification reaction zone D2 to sufficiently agitate the water to be treated in the denitrification reaction zone D2. This allows denitrifying bacteria to be dispersed throughout the denitrification reaction zone D2, enabling the denitrification reaction to be carried out efficiently.

[0019] The oxidation-reduction potentiometer 7 is disposed in the denitrification reaction zone D2, and the oxidation-reduction potential of the denitrification reaction zone D2 is controlled based on the oxidation-reduction potentiometer 7. For example, when the oxidation-reduction potentiometer 7 indicates −200 mV or less, there is a shortage of nitrite and nitrate necessary for the denitrification reaction, and the water to be treated from the nitrification reaction zone D1 is supplied to the denitrification reaction zone D2. When the oxidation-reduction potentiometer 7 indicates −100 mV or more, oxygen is present in the denitrification reaction zone D2, and the inflow of new raw water to the denitrification reaction zone D2 or the supply of water to be treated from the nitrification reaction zone D1 is restricted.

[0020] FIG. 2 is a cross-sectional view taken along line AA in FIG. 1, and is used to explain the circulation plate 5. As shown in FIG.

[0021] In Figure 2, the circulation plate 5 has an opening 5a (circulation plate opening) near the bottom of the reaction tank 1. When the air diffuser 4a diffuses air into the membrane separation device 3, the air bubbles diffused from the air diffuser 4a move upward in the vertical direction, forming an upward flow, and the water to be treated in the membrane aeration zone MZ flows over the circulation plate 5 and moves to the dissolved oxygen adjustment zone DZ. Furthermore, as the upward flow is formed in the membrane aeration zone MZ, the water to be treated in the dissolved oxygen adjustment zone DZ moves to the membrane aeration zone MZ through the opening 5a. Furthermore, as the water to be treated moves from the dissolved oxygen adjustment zone DZ to the membrane aeration zone MZ, a downward flow is formed in the water to be treated that has overflowed the circulation plate 5 and descends to the bottom of the reaction tank 1. In other words, when the air diffuser 4a diffuses air into the membrane separation device 3, a circulating flow is formed that circulates through the circulation plate 5. The size of the opening 5a (circulation plate opening) formed at the bottom of the circulation plate 5 need only be large enough to form a circulation flow circulating through the circulation plate 5, and the opening 5a may be provided across the entire horizontal width perpendicular to the vertical direction of the circulation plate 5, or may be provided across only a portion of the horizontal width.

[0022] FIG. 3 is a cross-sectional view taken along the line BB in FIG. 1, and is used to explain the partition plate 2. As shown in FIG.

[0023] 3, the partition plate 2 has an upper end 2a near the water surface of the water to be treated and a lower end 2b abutting the bottom of the reaction tank 1. The upper end 2a has an overflow opening 2c (first opening) near the membrane separation device 3, and the lower end 2b has a return opening 2d (second opening) near the dissolved oxygen meter DO1. The overflow opening 2c has an overflow end 2e, and the water level of the water to be treated in the reaction tank 1 is lower than the upper end 2a and higher than the overflow end 2e. The overflow opening 2c and the return opening 2d are preferably located diagonally on the partition plate 2. The water to be treated in the nitrification reaction region D1 moves to the denitrification reaction region D2 via the overflow opening 2c, and the water to be treated in the denitrification reaction region D2 moves to the nitrification reaction region D1 via the return opening 2d.

[0024] The overflow opening 2c may have a water volume adjustment device (changing means) that adjusts the amount of water being treated that moves from the nitrification reaction region D1 to the denitrification reaction region D2. The water volume adjustment device may be, for example, a movable weir that moves from the overflow end 2e relative to the water surface, or a rubber weir that expands with air or water, or an undulating weir that uses a rubber weir. The water volume adjustment device operates to control the amount of water being treated that moves from the nitrification reaction region D1 to the denitrification reaction region D2, and changes the opening range of the overflow opening 2c.

[0025] FIG. 4 is a flowchart showing the procedure of wastewater treatment carried out by the wastewater treatment device 10 of FIG.

[0026] In the wastewater treatment (wastewater treatment method) shown in FIG. 4 , first, the water to be treated is supplied to the reaction tank 1 (S1). At this time, the water level of the water to be treated is lower than the upper end 2a and higher than the overflow end 2e. Next, in the nitrification reaction region D1, the air diffuser 4a disposed in the membrane aeration zone MZ diffuses a large amount of minute bubbles into the membrane separation device 3 to suppress fouling of the hollow fiber membranes constituting the membrane separation device 3. This forms a circulating flow that circulates through the circulation plate 5. Furthermore, the air diffuser 4b disposed in the dissolved oxygen control zone DZ diffuses a large amount of minute bubbles, thereby ensuring the required amount of dissolved oxygen DO in the nitrification reaction region D1 (S2). In this embodiment, whether the amount of dissolved oxygen DO is ensured is determined based on the dissolved oxygen meters DO1 and DO2.

[0027] Next, the water to be treated after the nitrification reaction in the nitrification reaction region D1 moves to the denitrification reaction region D2 via the overflow opening 2c (S3), and the agitator 6 agitates the water in the denitrification reaction region D2 (S4). Whether the denitrification reaction is proceeding properly in the denitrification reaction region D2 is determined based on the oxidation-reduction potential (ORP). The water to be treated after the denitrification reaction in the denitrification reaction region D2 moves to the nitrification reaction region D1 via the return opening 2d (S5). The water to be treated that has moved to the nitrification reaction region D1 in S5 contains solids. The water to be treated is discharged to the outside of the reaction tank 1 via the membrane separation device 3, and the solids are separated and removed by the membrane separation device 3 (S6), completing the treatment.

[0028] 4, the water to be treated after the nitrification reaction in the nitrification reaction region D1 moves to the denitrification reaction region D2 via the overflow opening 2c (S3), and the water to be treated after the denitrification reaction in the denitrification reaction region D2 moves to the nitrification reaction region D1 via the return opening 2d (S5). As a result, the amount of water to be treated circulating through the nitrification reaction region D1 and the denitrification reaction region D2 is controlled to a constant amount, so that the amount of dissolved oxygen (DO) in the nitrification reaction region and the oxidation-reduction potential (ORP) in the denitrification reaction region can be controlled to stably carry out the nitrification reaction and the denitrification reaction.

[0029] In the nitrification reaction region D1, the air diffuser 4a diffuses a large amount of minute bubbles into the membrane separation device 3, forming a circulation flow that circulates through the circulation plate 5 (S2, circulation step). The circulation flow sufficiently agitates the nitrification reaction region D1, so that the nitrification reaction region D1 is sufficiently agitated without requiring additional power. This allows nitrifying bacteria to be dispersed throughout the nitrification reaction region D1, enabling the nitrification reaction to be carried out efficiently.

[0030] Furthermore, the treated water after nitrification in the nitrification reaction zone D1 is transferred to the denitrification reaction zone D2 via the overflow opening 2c (S3, transfer step). In the denitrification reaction zone D2, a water flow based on the inflow of raw water and a water flow of treated water via the overflow opening 2c and return opening 2d are generated. However, the water velocity of these water flows is gentle, and the denitrification reaction zone D2 is not sufficiently agitated by the water flow alone. In response to this, the agitator 6 agitates the treated water in the denitrification reaction zone D2 (S4), dispersing denitrifying bacteria throughout the denitrification reaction zone D2 and enabling efficient denitrification. Incidentally, continuous operation of the agitator 6 increases power consumption by 5%. Intermittent operation of the agitator 6, which alternates between 2-minute on and 7-minute off periods, increases power consumption by 1.5%. Therefore, although the introduction of the agitator 6 requires a certain amount of power, the aeration device 4b is controlled based on the dissolved oxygen meters DO1 and DO2, so the power consumption required for the wastewater treatment device 10 is reduced compared to conventional systems even when the agitator 6 is introduced.

[0031] In this embodiment, the overflow opening 2c and the return opening 2d are formed diagonally on the partition plate 2. This determines the position where the treated water is supplied from the nitrification reaction zone D1 to the denitrification reaction zone D2 and the position where the treated water returns from the denitrification reaction zone D2 to the nitrification reaction zone D1, ensuring a certain amount of time for the denitrification reaction. Furthermore, in this embodiment, the overflow opening 2c has a water flow rate adjusting device that adjusts the amount of treated water moving from the nitrification reaction zone D1 to the denitrification reaction zone D2. This allows for easy control of the amount of treated water moving from the nitrification reaction zone D1 to the denitrification reaction zone D2 in response to the value indicated by the oxidation-reduction potentiometer 7.

[0032] Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments.

[0033] D1 Nitrification reaction zone D2 Denitrification reaction zone MZ Membrane aeration zone DZ Dissolved oxygen control zone 10 Wastewater treatment device 1 Reaction tank 2 Partition plate 2c Overflow opening 2d Return opening 3 Membrane separation device 4, 4a, 4b Aeration device 5 Circulation plate 6 Agitator

Claims

DEPCT6707 / 11 / 25661. Wastewater treatment equipment set for nitrification operations that convert ammonia in wastewater to nitrite and / or nitrate in the presence of oxygen, and denitrification that converts the nitrite and / or nitrate produced by nitrification to nitrogen under oxygen-free conditions. The equipment set includes: a partitioning device for separating the nitrification portion, in which nitrification is carried out, from the denitrification portion, in which denitrification is carried out; a set of... The membrane separation unit is arranged in the nitrification section and separates and removes solid matter in the wastewater that is subjected to nitrification and denitrification; the first air diffuser supplies air bubbles to the membrane separation unit; the second air diffuser supplies air bubbles to areas other than the membrane separation unit; the first supply area where air bubbles are supplied by the first air diffuser through the second supply area where air bubbles are supplied by the second air diffuser;and the recirculating plates arranged between the first and second discharge areas and between the first and second discharge areas and the dividing device; 2. The wastewater treatment equipment according to claim 1 where the agitator is arranged in the denitrification section; 3. The wastewater treatment equipment according to claim 1 or 2 where the recirculating plates have recirculating plate openings in the vicinity of the first aeration head; 4. Any one of the wastewater treatment equipment according to claims 1 to 3 where the dividing device has the first and second openings on its diagonal;And wastewater is transferred from the nitrification section to the denitrification section through the first opening and transferred from the denitrification section to the nitrification section through the second opening.

5. The wastewater treatment equipment according to claim 4, in which the first opening has a mechanism to adjust the opening range of the first opening.

6. The wastewater treatment method performed by the wastewater treatment equipment is to carry out nitrification that converts ammonia in the wastewater to nitrite and / or nitrate in the presence of oxygen and denitrification. The nitrite and / or nitrate produced by nitrification are converted to nitrogen under oxygen-free conditions; a unit of equipment incorporating a partitioning device for separating the nitrification section from the denitrification section; a membrane separation unit arranged in the nitrification section that separates and removes solid matter from the wastewater subjected to nitrification and denitrification; and a primary air inlet for supplying aeration bubbles to the membrane separation unit.A second air diffuser for supplying air bubbles to areas other than the membrane separation unit; the first supply area through which air bubbles are supplied by the first air diffuser; the second supply area through which air bubbles are supplied by the second air diffuser; and recirculating plates arranged between the first and second supply areas and between the first supply area and the separation instrument; characterized by the following assembly method: the recirculation phase of wastewater around the recirculating plates based on the supply of air bubbles by the first air diffuser to the first supply area; and the transfer phase of transferring wastewater from the nitrification section to the denitrification section.