JP2005262016A - Air lift aeration tank suitable for batch activated sludge process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air lift aeration tank suitable for a batch activated sludge process which can sufficiently cope with wastewater having a high nitrogen load, namely high nitrogen content wastewater, for example, wastewater of a food plant, by enabling the control of a liquid circulation quantity in an aeration tank without being influenced by the water level of treated liquid in the aeration tank even if the water level fluctuates. <P>SOLUTION: This air lift aeration tank comprises (1) two partition plates for partitioning the inside of the aeration tank, consisting of (i) a first partition plate for vertically partitioning the tank up to a fixed height so as to leave a fixed space between it and the bottom of the aeration tank, and (ii) a second partition plate for vertically partitioning the tank up to a fixed height so as to leave a fixed space above the first partition plate, (2) an air blowing means installed on the bottom or in the vicinity of the bottom of one side of the aeration tank partitioned by the partition plates, (3) a wastewater introduction means installed in the other side of the aeration tank partitioned by the partition plates, and (4) an aeration tank having an inclined plane, preventing sludge in the tank from depositing, in the vicinity of the bottom of the aeration tank to which the wastewater introduction means is attached. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an airlift aeration tank suitable for a batch activated sludge method.

  According to Non-Patent Document 1, Hano et al. (1992) proposed a method of performing biological nitrogen removal by using a double-tube airlift bubble column in the same apparatus in which an anaerobic region and an aerobic region coexist. ing. According to Non-Patent Document 2, the present inventors have proposed techniques for improving the air lift bubble column in terms of apparatus engineering. Further, according to Non-Patent Document 3, these techniques are applied to a rectangular aeration tank. is suggesting. In addition, according to Non-Patent Document 4, the present inventors have also examined the circulating flow rate of the processing liquid which is a dominant factor in these apparatuses.

  In any of these devices, the anaerobic region and aerobic region can coexist, but in the case of the standard liquid batch type, the liquid height in the aeration tank changes greatly when the wastewater flows in, and one tank is adjusted. In the standard liquid batch system, which plays the role of a tank, aeration tank, and precipitation tank, there is a time zone when the wastewater flows into the tank, followed by a time zone during which aeration is performed. There is a problem that the mixed state of the liquid is remarkably bad because aeration is not performed at the time of drainage inflow (anaerobic state).

Hano, T .; Three other authors, Chem. Eng. Sci. 47, 3737-3744 (1992) Bando, Y .; Four authors, J. Chem. Eng. Japan, 32, 770-775 (1999) Bando, Y .; Two other authors, J.M. Chem. Eng. Japan, 37, in press (2004) Bando Oga, 3 authors, Fluid Thermal Engineering Research, 38, 45-54 (2003)

  The object of the present invention is to increase the nitrogen load by allowing the liquid circulation amount in the tank to be controlled without being substantially affected even if the water level of the processing liquid in the aeration tank fluctuates up and down. In other words, it is to provide an airlift aeration tank suitable for the batch activated sludge method that can sufficiently cope with wastewater with a high nitrogen content, for example, wastewater from a food factory.

In the present invention, (1) (i) the first partition plate vertically partitions a certain height with a certain gap between the bottom of the aeration tank and the partition plate, and (ii) The second partition plate is a partition plate that partitions the inside of the aeration tank vertically with a certain gap directly above the first partition plate up to a certain height,
(2) Air blowing means provided at the bottom of one side of the aeration tank partitioned by the partition plate or in the vicinity thereof,
(3) Drainage introduction means provided on the other side of the aeration tank partitioned by the partition plate,
And (4) an aeration tank in which the vicinity of the bottom of the aeration tank where the drainage introducing means is installed has an inclined surface that does not accumulate sludge in the tank,
It is related with the airlift aeration tank characterized by comprising.

  As shown in FIG. 1, the conventional standard batch activated sludge method is a method in which the entire aeration tank is in an anaerobic state for a certain period of time and an aerobic state in the next period of time. The anaerobic state is maintained until the end (about 10 hours), and the aerobic state is maintained from the start to the end of the aeration (about 10 hours). The sedimentation separation (about 4 hours) is also performed in an anaerobic state. Usually, the maximum liquid volume (at the time of aeration) is 3 to 4 times the daily drainage volume, and 1/3 to 1/4 of the maximum liquid volume is replaced every day.

  When a single partition plate is inserted into the aeration tank in the standard batch activated sludge method as shown in FIG. 2 and aeration is started from the start of inflow, the aerobic and anaerobic areas always coexist in the aeration tank, and the nitrogen removal performance However, the liquid cannot be circulated until the liquid level reaches the upper end of the partition plate.

  Therefore, in the present invention, as shown in FIG. 3, the two partition plates are considered to be installed with a gap. In this case, the lower partition plate, that is, the upper end of the first partition plate is set to the position of the liquid level of the minimum liquid amount (after discharge), and the upper partition plate (second partition plate) is installed with a little space. By doing so, when aeration is performed before and after the liquid level reaches the upper end of the first partition plate, the liquid level also moves up and down, so that a liquid circulation flow has already occurred at this stage, In addition, the aerobic region and the anaerobic region coexist with each other, and the mixing of the activated sludge and the waste water becomes good.

  The cross section of the aeration tank in the present invention can take any shape such as a quadrangle (for example, a rectangle) or a circle, but a rectangle is most preferable from the viewpoint of ease of setting a partition plate and ease of scale-up. [Refer FIG.4 (b)]. When the cross section is a quadrangle, the partition plate has a flat plate shape. When the cross section is circular, the partition plate may have a flat plate shape, but it may have a circular shape (may be concentric or eccentric). The aeration tank is not particularly limited, such as metal, resin or concrete. The inclined surface provided near the bottom of the aeration tank needs to be an inclined surface that does not accumulate sludge in the tank, and this angle can be easily obtained from the repose angle of the sludge. It is not a new matter.

The role of the partition plate is to create a region where many bubbles are present and a region where few bubbles are present in the apparatus. As a result, a low-density portion and a high-density portion of the gas-liquid mixed phase are generated in the apparatus, and a liquid circulation flow is generated using this density difference as a driving force. Naturally, the region with a lot of bubbles becomes an upward flow (riser), the region with almost no bubbles becomes a downward flow (downcomer), and the liquid circulates through the partition plate. Blowing a gas to create a region with a lot of bubbles and forming an upward flow in this region is called air lift in the chemical engineering field. In order to form such a circulating flow, it is necessary that the partition plate is open at the top and bottom of the liquid (L ₁ and L ₃ have corresponding dimensions).

Further, in the present invention, the most important point is that the partition plate is separated into two plates, a first partition plate and a second partition plate, and a gap is provided between the two partition plates.
Thereby, even when the amount of liquid is small, the liquid can be satisfactorily stirred by the air lift, and the anaerobic region and the aerobic region can coexist. The aerobic region is naturally on the air blowing side (riser side), and the anaerobic region is on the opposite downcomer side.

In designing the apparatus of the present invention, it is preferable to carry out the following procedure.
(1) The daily aeration volume {Q [m ³ / day (hereinafter abbreviated as d)]} of the factory and the average dwell time (t [d], usually 3 to 4 d) of the aeration tank (V = Q Xt).
(2) When a blower is used for aeration, the maximum liquid height (L _MAX ) is normally set to 5 to 6 m. Therefore, the floor area (A) of the aeration tank is determined (A = V / L _MAX ).
(3) The floor shape of the aeration tank (whether it is a square close to a square or an elongated square) is determined by the topographic conditions for installing the aeration tank, but an elongated square is desirable for this method. Here, let W be the tank width in the direction perpendicular to the partition plate in the aeration tank.
* In the above design, L _MAX and W correspond to the maximum liquid height and tank width of this equipment.
(4) A partition plate is installed at a position corresponding to 1/4 of W, and an air diffuser is installed from the wall to the bottom surface of the partition plate portion (this portion becomes a riser. Riser width W _R = W / 4. ). By installing the partition plate in this way, it is easy to control the liquid circulation flow in the aeration tank.
(5) Regarding the height of the first partition plate, the position of the upper end is set to the lowest liquid height (the liquid height when the treated water is discharged), and the distance between the lower end and the bottom surface is the riser width (W _R ). 1/2 to 1 times. On the other hand, the upper end of the second partition plate is slightly lower (about the riser width) than the maximum liquid height (the liquid height when the inflow of drainage is completed and aerated).
(6) Here, the most important is the distance between the upper end of the first partition plate and the lower end of the second partition plate. Optimum liquid circulation flow rate (optimal liquid circulation flow rate that allows activated sludge to circulate smoothly in the aeration tank. The higher the liquid circulation flow rate, the smoother the circulation and mixing of activated sludge. However, if the liquid circulation flow rate is too high, downcoma This distance should be determined so that dissolved oxygen is supplied to the bottom and there is no anaerobic region. In the wastewater treatment experiment of the example, this distance is set to 0.01 m.

1) The aeration tank of the present invention in which two partition plates are installed through a certain gap allows coexistence of anaerobic and aerobic regions regardless of changes in liquid height.
2) The liquid circulation flow rate in the aeration tank of the present invention is determined by the size of each position. In other words, the liquid circulation flow rate can be controlled by the gap between the first and second partition plates and the distance between the second partition plate and the liquid surface.
3) In the aeration tank of the present invention, high nitrogen removal performance can be obtained.

  Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto.

電磁流速計を用いて槽内の液循環流量Ｑ_Ｌを求めた。溶存酸素濃度がゼロになっている領域を嫌気領域とし、その濃度分布から槽全体（Ｖ）に対する嫌気領域（Ｖ_ＡＮ）の割合Ｖ_ＡＮ／Ｖを算出した。 Example 1
When a partition plate is installed parallel to one side of the floor area, the liquid flow in the direction parallel to the partition plate during aeration is small, and the liquid circulation flow in the depth direction and the direction perpendicular to the partition plate is dominant.
Therefore, an experiment was conducted using the apparatus shown in FIG. In addition, when the liquid velocity in three directions was measured with this apparatus, it was clear that the velocity component in the direction parallel to the partition plate was extremely small compared to the other two directions (depth direction and direction perpendicular to the partition plate). became.
The aeration tank was made of a transparent acrylic resin having a width of 0.32 m, a depth of 0.12 m, and a height of 2.50 m. A partition plate (first partition plate 2) with a length of 1.20m is installed at a position of 0.08m from the left wall and 0.05m from the bottom, with a gap of 0.01m above it and a length of 0.54m The tank in which the partition plate (second partition plate 3) was installed was used.
As the activated sludge, sludge collected at a food factory and conditioned for 2 months with model waste water was used. The composition of the model wastewater is shown in Table 1 [BOD (biological oxygen demand): TN (total nitrogen content): TP (total phosphorus content) = 100: 10: 1]. One cycle of wastewater treatment was set to 24 hours, and continuous operation of one cycle per day was repeated every day. Model waste water was supplied over 11 hours (the position of the liquid level changed from the position of the upper end of the first partition plate to 0.06 m above the upper end of the second partition plate). Aeration was performed for 22 hours from the start of drainage supply. After 22 hours, aeration was stopped, and after sedimentation, the supernatant liquid was discharged in the same amount as the inflow amount (both the discharge amount and the inflow amount in one cycle were 1/3 of the total liquid amount). MLSS (sludge concentration in the aeration tank) was adjusted to 3.0 kg / m ³ . One cycle of the process is shown in FIG. For comparison, an experiment was also conducted in an aeration tank [comparative example (standard solution batch type)] without a partition plate. In the comparative example, model waste water was supplied in the same manner as in Example 1, and aerated for 11 to 22 hours after the end of waste water supply. The operation after aeration is the same as in Example 1. The aeration flow rate in Example 1 was half that of the comparative example. The same wastewater treatment experiment was repeated over two months, and COD (chemical oxygen demand) and TN (total nitrogen amount) of the discharged water (treated water) were analyzed, and the respective removal rates were calculated.
COD removal rate (%)
= 100 x (COD concentration in influent water-COD concentration in effluent water) / COD concentration TN removal rate in inflow water (%)
= 100 x (total nitrogen concentration in influent water-total nitrogen concentration in effluent water) / total nitrogen concentration in influent water

The liquid circulation flow rate Q _L in the tank was determined using an electromagnetic current meter. A region where the dissolved oxygen concentration is zero was defined as an anaerobic region, and a ratio V _AN / V of the anaerobic region (V _AN ) to the entire tank (V) was calculated from the concentration distribution.

In FIG. 4, the height of the aqueous solution in the aeration tank is L, the vertical length of the first partition plate is L _P1 , the vertical length of the second partition plate is L _P2 , the bottom of the aeration tank and the first 1 of the distance between the partition plate lower end (lower end opening height) L _B, the distance between the first partition plate upper end and a second partition plate bottom (intermediate opening height) L _1, The distance between the upper end of the second partition plate and the liquid surface (upper open part height) is L ₃ , the width of the aeration tank is W, the width of the downcomer (lowering part) in the aeration tank is W _D , and the riser of the aeration tank ( When the width of the raised portion) and W _R, the distance between the aeration tank bottom and the first partition plate lower end (lower end opening height) L _B is 1/2 to the width W _R of the riser (rising portion) 1 time, the distance (L ₃ ) between the upper end of the second partition plate and the maximum liquid height is not more than the tank width (W), preferably not more than half of the tank width (W), most preferably the riser width (W _R ) About half good. Further, the gap between the first partition plate and the second partition plate should be set so as to be the lowest liquid circulation flow rate at which activated sludge circulates smoothly, and is at most 50 mm or less, preferably 10 to 30 mm, Most preferably, it should be about 10 mm. These distances are completely independent of the length of both partition plates and the amount of drainage. Also, if this distance is too small, the gap between the first partition plate and the second partition plate due to the adhering activated sludge is feared. On the other hand, if this distance is too large, the amount of liquid circulation becomes too large, and the downcomer Since the upper part of becomes an aerobic area | region, it is not preferable.

In FIG. 5, the flow state at the time of the waste_water | drain inflow of Example 1 is shown. Regardless of the change in liquid height, a liquid circulation flow is generated in the tank, and the waste water and activated sludge are well mixed.
6 and 7 show the influence of the gas velocity and the distance of each position on the liquid circulation flow rate in the first embodiment. FIG. 6 is a result of measuring the liquid circulation flow rate by changing L _T (distance from the upper end of the lower partition plate to the liquid level) under the conditions of L ₁ = 0.01 m and L _P2 = 0.54 m. ₆ the liquid level in either of the gas superficial velocity as seen in _{(L 1 = 0.01m, L P2} = liquid circulation flow rate when changing the _{L T} in 0.54 m) is higher than the first partition plate upper end In a range that is high and does not reach the upper end of the second partition plate (L _T = 0.01 to 0.55 m), the liquid flows out from the gap between the partition plates and circulates, and the liquid circulation flow rate becomes substantially constant. When the liquid level is higher than the second partition plate upper end (although the liquid also flows out from the gap between both partition plates) liquid flow exceeds a second partition plate upper end dominant becomes, liquid circulation flow, the L _T increases with increasing, constant and equal to or greater than a certain L _T.
In FIG. 7, when L _T -L ₁ = 0.2 m (the distance from the lower end of the second partition plate to the liquid level is constant at 0.2 m), L ₁ and gas that affect the liquid circulation flow rate (Q _L ) The effect of the superficial velocity U _G (mm / s) was examined. In this experiment, the liquid level is always 0.34 m lower than the upper end of the upper partition plate, and no liquid circulation occurs here. Higher becomes even longer L ₁ at any of the gas superficial velocity, the liquid circulation rate is increased.
Thus, it can be seen that the liquid circulation flow rate is strongly governed by the distance of each position. As described above, the upper end of the first partition plate is determined from the wastewater treatment conditions (treatment flow rate and average residence time of wastewater). The gap between the first partition plate and the second partition plate should be set so as to be the lowest liquid circulation flow rate at which activated sludge circulates smoothly, and is at most 50 mm or less, preferably 10 to 30 mm, most preferably Should be about 10 mm. The distance between the second partition plate and the maximum liquid height is not more than the tank width, preferably not more than half the tank width, and most preferably about half the riser width.

FIG. 8 shows the change with time (θ) in one cycle of the liquid circulation flow rate (Q _L ) and the ratio of the anaerobic region in Example 1. Since the liquid height is changed by the drainage supply, the liquid circulation flow rate and, as a result, the anaerobic region changes with time, but it can be seen that the anaerobic region exists until about 18 hours.
Further, in FIG. 8, L ₁ = 0.01 m, wastewater treatment experiment using activated sludge (liquid flows in at a constant flow rate during the period of 0 to 11 hours, and the amount of liquid in the aeration tank is between 11 and 22 hours. constant become. that L _T is increased in the first half, at constant become) in the second half, the liquid circulation flow rate (Q _L), shows the time course of the rate V _{aN / V} anaerobic region for the aeration tank total volume .
Similar to FIG. 6, the liquid circulation flow rate is substantially constant at a low value during a period (θ = 0 to 10 hours) where the liquid level is higher than the upper end of the lower partition plate and does not reach the upper end of the upper partition plate. When the liquid level becomes higher than the upper end of the upper partition plate (θ = 10 to 11 hours), it rapidly increases, and thereafter (θ = 11 to 22 hours) becomes substantially constant at a high value. On the other hand, the ratio V _AN / V of the anaerobic region is high during a period when the liquid circulation flow rate is low (θ = 0 to 10 hours), and rapidly decreases as the liquid circulation flow rate rapidly increases (θ = 10 to 11 hours). When the liquid circulation flow rate becomes high (θ = 18 to 22 hours), zero, that is, the entire aeration tank becomes an aerobic region. That is, as described above, it can be understood that the ratio of the anaerobic region is strongly governed by the liquid circulation flow rate, and L ₁ and L ₃ are important factors for the liquid circulation.
In this case, the temporal average value of the anaerobic region ratio over one cycle was about 45%. In order to obtain a high nitrogen removal rate, it is extremely important to set the temporal average value to about 50%.

As described above, the position of the upper end of the first partition plate (lower partition plate) is determined from the minimum liquid height, and the position of the upper end of the second partition plate (upper partition plate) is determined from the maximum liquid height. The distance (L ₁ ) between the two partition plates is determined from the required liquid circulation flow rate (low liquid flow rate at which activated sludge circulates smoothly) as shown in FIG. Do not depend.

表２に実施例１と比較例の両曝気槽を用いて行なった排水処理実験の結果を示す。ＣＯＤ除去率はいずれの槽でも高く、両槽の差異は見られない。一方、窒素除去率は実施例１がかなり高く、嫌気・好気領域の良好な共存および液循環流の効果が認められる。ＣＯＤと全窒素量のそれぞれの除去率η_ＣＯＤ（％）とη_ＴＮ（％）は、曝気槽からの排出水（処理水）中のＣＯＤ（化学的酸素要求量、本来ならばＢＯＤを測定すべきであるが、簡略のためにＣＯＤを測定した）およびＴＮ（全窒素量）を滴定および発色分光法によって分析し、以下の式からそれぞれの除去率を算出した。
ＣＯＤ除去率（％）
＝１００×（流入水中ＣＯＤ濃度−排出水中ＣＯＤ濃度）／流入水中ＣＯＤ濃度
ＴＮ除去率（％）
＝１００×（流入水中全窒素濃度−排出水中全窒素濃度）／流入水中全窒素濃度

Table 2 shows the results of the wastewater treatment experiment conducted using both the aeration tanks of Example 1 and Comparative Example. The COD removal rate is high in both tanks, and there is no difference between the two tanks. On the other hand, the nitrogen removal rate is considerably high in Example 1, and good coexistence of anaerobic / aerobic regions and the effect of liquid circulation flow are recognized. The removal rates η _COD (%) and η _TN (%) of COD and total nitrogen, respectively, measure COD (chemical oxygen demand, originally BOD) in the discharged water (treated water) from the aeration tank. Although, for simplicity, COD was measured) and TN (total nitrogen) were analyzed by titration and color spectroscopy and the respective removal rates were calculated from the following equations.
COD removal rate (%)
= 100 x (COD concentration in influent water-COD concentration in effluent water) / COD concentration TN removal rate in inflow water (%)
= 100 x (total nitrogen concentration in influent water-total nitrogen concentration in effluent water) / total nitrogen concentration in influent water

It is a figure explaining the aeration cycle of a day (24 hours) and the inflow / discharge cycle of a liquid in the aeration tank used for the conventional standard batch type activated sludge method. It is a figure explaining the aeration cycle of a day (24 hours) and the inflow / discharge cycle of a liquid when one partition plate is put into the aeration tank used for the conventional standard batch type activated sludge method. It is a figure explaining the aeration cycle of a day (24 hours) and the inflow / discharge cycle of a liquid in the aeration tank used for the present invention. It is a figure which shows one example of the aeration tank used for this invention, (a) is sectional drawing of a perpendicular direction, (b) is sectional drawing of a horizontal direction (only an aeration tank), (c) is the process of 1 cycle Indicates. It is a figure which shows the flow state at the time of (a) drainage inflow start, (b) drainage inflow, (c) drainage inflow completion in this invention aeration tank, respectively. It is a diagram showing the effect of height L _T and the gas superficial velocity from the first partition plate upper end on liquid circulation flow rate (Q _L) in Example 1 to the liquid surface (U _G). Shows the influence of the gap L ₁ and the gas superficial velocity (U _G) between the first partition plate and second partition plate on the liquid circulation flow rate (Q _L) in the first embodiment. Shows a liquid circulation flow rate in Example 1 (Q _L) and aging theta (h = hour) anaerobic area ratio.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Aeration tank 2 1st partition plate 3 2nd partition plate 4 Gas disperser 5 Artificial drainage tank DO Probe Dissolved oxygen measuring device

Claims (1)

(1) (i) The first partition plate vertically partitions up to a certain height with a certain gap between the tank bottom of the aeration tank and the partition plate, and (ii) the second partition The plates are two partition plates that partition the inside of the aeration tank, with a certain gap directly above the first partition plate and vertically partitioning up to a certain height,
(2) Air blowing means provided at the bottom of one side of the aeration tank partitioned by the partition plate or in the vicinity thereof,
(3) Drainage introduction means provided on the other side of the aeration tank partitioned by the partition plate,
And (4) an aeration tank in which the vicinity of the bottom of the aeration tank where the drainage introducing means is installed has an inclined surface that does not accumulate sludge in the tank,
An airlift aeration tank characterized by comprising:

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