JP4295190B2 - How to determine the operating conditions of the oxidation ditch - Google Patents

Description

  The present invention relates to a method for determining operating conditions of an oxidation ditch.

  As a small-scale sewage treatment system, the oxidation ditch (OD) method has attracted attention. In this OD method, a mixture of sewage and activated sludge flowing into an endless circulation channel is stirred and aerated with an impeller to generate an aerobic zone and an anaerobic zone in the OD, and a nitrification reaction is performed in each zone. , Denitrification reaction, or processing in the OD is provided with aerobic time zone and anaerobic time zone in time, nitrification reaction and denitrification reaction are performed in each time zone, organic matter treatment, denitrification Process.

An example of such an OD is disclosed in Patent Document 1. In this OD, the amount of dissolved oxygen is adjusted while controlling the flow rate of the liquid mixture by controlling the immersion depth and rotation speed of the impeller, thereby achieving good sewage treatment during extremely low load operation.
JP 2001-269691 A

  However, in the above-described conventional method, setting of operation conditions such as the impeller immersion depth and the number of revolutions is determined by a skilled driver depending on intuition, and is not efficient.

  The present invention has been made in view of the above circumstances, and provides an operating condition determining method for an oxidation ditch capable of efficiently determining operating conditions such as the immersion depth and rotation speed of an impeller. With the goal.

  The present invention is a method for determining an operating condition of an oxidation ditch provided with an endless circulating water channel and an impeller that stirs and aerates a mixed liquid of sewage and activated sludge flowing into the circulating water channel. In this method, V = a · X + b · Y + c · Z + d, where V is the flow rate of the liquid mixture, X is the immersion depth of the impeller, Y is the power input density, and Z is the sludge concentration (MLSS). Based on the relational expression (a, b, c, d are predetermined constants), the impeller immersion depth and power input density are determined from the flow rate of the mixed liquid and the sludge concentration.

  The present inventor has found that the flow velocity V of the mixed solution can be expressed by a polynomial expression of impeller immersion depth X, power input density Y, and sludge concentration (MLSS) Z. Therefore, based on this relational expression, it is possible to efficiently determine the impeller immersion depth and power input density from the flow rate and sludge concentration of the desired mixed liquid.

  In the method for determining the operating condition of the oxidation ditch according to the present invention, the amount of oxygen supplied to the liquid mixture by the impeller is obtained based on the determined immersion depth and power input density, and the aeration time is determined based on the amount of oxygen supplied. This may be a feature. In this way, it is possible to prevent over-aeration and insufficient aeration and to perform a good process.

  In the operating condition determination method of the oxidation ditch according to the present invention, the above relational expression includes a plurality of data sets including a flow rate, an impeller immersion depth, a power input density, and a sludge concentration in a predetermined part in the circulation channel by changing the conditions. It may be characterized by being obtained by multiple regression of the immersion depth X, power input density Y, and sludge concentration Z with respect to the flow velocity V based on these data sets. If it does in this way, the said relational expression can be obtained easily.

  The present invention is a method for determining an operating condition of an oxidation ditch provided with an endless circulating water channel and an impeller that stirs and aerates a mixed liquid of sewage and activated sludge flowing into the circulating water channel. In this method, a plurality of data sets including the flow velocity, impeller immersion depth, power input density, and sludge concentration at a predetermined site in the circulation channel are acquired under different conditions. Multiple regression of immersion depth X, power input density Y, and sludge concentration Z, V = a · X + b · Y + c · Z + d (a, b, c, d are predetermined constants) The process of calculating | requiring is included.

  Based on the relational expression thus obtained, it is possible to efficiently determine the impeller immersion depth and power input density from the flow rate and sludge concentration of the desired mixed liquid.

  The present invention is a method for determining an operating condition of an oxidation ditch provided with an endless circulating water channel and an impeller that stirs and aerates a mixed liquid of sewage and activated sludge flowing into the circulating water channel. In this method, a plurality of data sets including the flow velocity, impeller immersion depth, power input density, and sludge concentration at a predetermined site in the circulation channel are acquired under different conditions. Multiple regression of the immersion depth X, power input density Y, sludge concentration Z, and the term of synergy between the immersion depth and power input density (XY), V = a · X + b · Y + c · Z + d + The method includes a step of obtaining a relational expression of e · XY (a, b, c, d, and e are predetermined constants).

  Based on the relational expression thus obtained, it is possible to efficiently determine the impeller immersion depth and power input density from the flow rate and sludge concentration of the desired mixed liquid. This relational expression is effective when the influence of the synergistic effect between the immersion depth and the power input density is large.

  ADVANTAGE OF THE INVENTION According to this invention, the operating condition determination method of the oxidation ditch which can determine operating conditions, such as the immersion depth and rotation speed of an impeller efficiently, is provided.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a partially broken perspective view of an oxidation ditch (OD). FIG. 2 is a plan view showing the configuration of the OD. The OD operating condition determination method according to the present embodiment can be preferably implemented in this OD1.

  As shown in FIGS. 1 and 2, the OD 1 includes an endless circulating water channel 8 and an impeller 3 that stirs and aerates the mixed liquid 2 of sewage and activated sludge flowing into the circulating water channel 8. Yes. The circulating water channel 8 has a so-called horseshoe-shaped structure in which a U-shaped partition wall is provided in a U-shaped water storage tank. A J-shaped rectifying wall 9 is provided in the flow channel inside the circulation water channel 8. On the side wall of the circulation water channel 8, an inflow port 10 into which dirty water flows and an exhaust port 11 through which treated water is discharged are provided. As shown in FIG. 3, the discharge port 11 is provided with an overflow gate 12, and the treated water treated at OD <b> 1 is discharged beyond the upper end of the overflow gate 12. The overflow gate 12 is driven by a motor 13 to move up and down. When the overflow gate 12 rises, the amount of overflowing water decreases and the water level of the mixed liquid in the circulating water channel 8 rises. On the other hand, when the overflow gate 12 is lowered, the amount of overflowing water is increased, and the water level of the mixed liquid in the circulating water channel 8 is lowered. The overflow gate 12 may be manually moved up and down.

  As shown in FIG. 2, a pair of impellers 3 are provided at the top of a U-shaped water tank. As shown in FIGS. 4 and 5, the impeller 3 forms a water inlet 15 between the stirring blades 14 arranged at equal intervals around the central rotating shaft 4 and the central rotating shaft 4. And a cone-like plate 16 disposed between the stirring blades 14. The upper part of each stirring blade 14 is bent in the same direction, and a bent portion 14a is provided. As shown in FIGS. 1 and 6, the impeller 3 is connected to a motor 6 via a rotating shaft 4 and a speed reducer 5. The speed reducer 5 and the motor 6 are arranged on a gantry 7. The diameter d of the impeller 3 is normally set in the range of 1000 mm to 4000 mm. As shown in FIG. 6, the relationship between the impeller 3 and the water level is set so that the water surface comes to the upper end of the cone-shaped plate 16 at the design water level. At this time, the immersion depth is zero, and the direction in which the water level increases more than this is defined as the positive direction of the immersion depth.

  In this OD1, when the motor 6 is operated and the impeller 3 is rotationally driven, the liquid mixture 2 in the circulating water channel 8 is pumped by the pump action of the impeller 3. A part of the pumped liquid mixture 2 passes through the water inlet 15, passes through the upper surface side of the cone-shaped plate 16, is accelerated by the bent portion 14 a of the stirring blade 14, and is discharged into the atmosphere. Further, the other part of the mixed liquid 2 is accelerated by the lower part of the stirring blade 14 while flowing along the lower surface of the cone-like plate 16 and is discharged in the rotation direction.

  The mixed liquid 2 discharged into the atmosphere descends after colliding with air and is combined with the flow in the rotational direction of the impeller 3, and a spiral swirl flow is generated in the circulation water channel 8. In the above process, oxygen in the air is efficiently dissolved in the liquid mixture, and upper and lower stirring and mixing in the circulation water channel 8 are sufficiently performed. Further, a circulating flow is generated in the circulating water channel 8 by this spiral swirling flow. An aerobic zone is formed by the dissolved oxygen and the nitrification reaction is accelerated. In addition, an anaerobic zone is formed in a place away from the impeller 3 in the OD 1 with a small amount of dissolved oxygen, and nitrogen that causes eutrophication is removed by the denitrification reaction.

  Here, in order to form an anaerobic zone and an aerobic zone with suitable distribution, or to provide an anaerobic time zone and an aerobic time zone, it is necessary to control the amount of oxygen dissolved in the liquid mixture 2 by the impeller 3. . The OD operating condition determination method according to this embodiment is for efficiently determining the operating conditions such as the immersion depth and the rotational speed of the impeller 3 for that purpose.

  Next, before explaining a specific method for determining operating conditions, the background to the idea of the present invention will be described.

  In the sewage treatment plant adopting OD1 as described above, the accumulation of sludge in the circulating water channel 8 was reported. Therefore, in the A, B, C, and D cross sections shown in FIG. 7, the width as shown in FIG. The deposition state was measured at points in directions 1 to 4. As a result, accumulation of sludge was hardly confirmed in the sections A, C, and D, and accumulation of sludge having a height of 50 cm to 150 cm was confirmed in the B section, particularly B-1. Therefore, after the T-shaped rake forcedly applied an external force to the deposit, which was difficult to wind up due to long-term consolidation, the flow velocity was measured at the design water level.

  FIG. 9 shows a case where the rotational speed of the impeller is measured by adjusting to three stages of low speed L (FIG. 9A), medium speed M (FIG. 9B), and high speed H (FIG. 9C). , The flow velocity at each point of the A cross section is shown. Further, FIG. 10 shows the measurement when the impeller rotation speed is adjusted to three stages of low speed L (FIG. 10 (a)), medium speed M (FIG. 10 (b)), and high speed H (FIG. 10 (c)). The flow velocity at each point of the B cross section is shown.

  As shown in FIGS. 9 and 10, both the A cross section and the B cross section are outlets of the water channel corners, and the flow tends to be biased outward due to centrifugal force. In the section A, the inner flow velocity is kept fast due to the effect of the rectifying wall 9. When the rotation of the impeller 3 is at a low speed L, A-2-L (where A-2-L indicates the position of 2-L in the cross section A in FIGS. 7 and 8. The same applies hereinafter. .) And B-1-L, the bottom flow velocity is less than 0.1 m / sec, but no sludge was confirmed in A-2. This is thought to be because A-2-L is surrounded by A-1-L and A-3-L, which are relatively fast in flow.

  On the other hand, in B-1-L in contact with the water channel wall surface, the flow velocity gradually decreases toward the wall surface and becomes zero on the wall surface. In the region where the flow velocity between the wall surface and B-1-L is less than 0.1 m / sec, it is considered that the deposition of sludge started and the deposition region grew downstream. Therefore, it was decided to study the conditions for producing a flow velocity of 0.1 m / second or higher at B-1-L where the flow velocity was slow and sludge accumulation was remarkable.

  First, the relationship between the rotational speed of the motor and the power consumption was obtained at the above OD1. FIG. 11 shows the result. As shown in FIG. 11, at the same immersion depth, the rotational speed of the motor and the power consumption are in a linear relationship. However, if the immersion depth X is different even at the same OD, the power consumption is different even at the same rotational speed. Therefore, the concept of power input density is introduced.

  The power input density is expressed by the following formula (1).

Power input density [W / m ³ ] = Power consumption [W] ÷ Mixed liquid amount [m ³ ] (1)

Liquid mixture amount [m ³ ] = tank area [m ² ] × (design water depth [m] + immersion depth [m]) (2)

  If this power input density is used, the relationship between the rotational speed of the motor and the power input density as shown in FIG. 12 can be obtained. Although the relational expression between the number of rotations and the power input density was obtained for each immersion depth, there was almost no difference due to the difference in immersion depth. Therefore, the relationship between the rotational speed of the motor and the power input density employs the following formula (3), and in the following examination, the power input density is used instead of the rotational speed of the motor.

Power input density [W / m ³ ] = α × motor rotation speed [rpm] + β (α and β are predetermined constants) (3)

The inventor made (flow rate [m / sec], immersion depth [mm], power input density [W / m ³ ], sludge concentration [mg] at the location of B-1-L where accumulation in the circulation channel 8 occurred. / L]) data sets were obtained by changing the conditions (variably changing the immersion depth, power input density, and sludge concentration as parameters). Based on these data sets, the immersion depth X, power input density Y, and sludge concentration Z are subjected to multiple regression with respect to the flow velocity V.

V = a * X + b * Y + c * Z + d (a, b, c, d are predetermined constants) (4)
Was obtained.

  In this way, the inventor has found that the flow velocity V of the mixed liquid 2 can be expressed by a polynomial expression of an immersion depth X of the impeller 3, a power input density Y, and a sludge concentration (MLSS) Z. And based on this relational expression, it turned out that the immersion depth and power input density of the impeller 3 can be determined from the flow velocity and sludge density | concentration of the liquid mixture 2. FIG. If the power input density is determined, the rotational speed of the motor 6 can be obtained based on the above equation (3).

Further, the relationship between the immersion depth, power input density, and oxygen supply amount can be obtained by measuring in advance under fresh water conditions. For example, when the oxygen supply amount when the immersion depth is 0 [mm] and the power input density is ω [W / m ³ ] is 100%, the oxygen supply amount when the immersion depth and the power input density are changed respectively. P [%] is obtained as shown in FIG.

  Therefore, when the oxygen supply amount P is determined based on the immersion depth and power input density,

Aeration time T1 = U [h / day] × i [%] × 10 ⁻² × 100 [%] / P [%] (5)
The required aeration time T1 can be calculated based on the relational expression. Here, U indicates the aeration capability of the impeller 3 to be used, and is the time required to supply oxygen necessary for the planned sewage inflow, and i is the ratio of the inflow sewage amount to the planned sewage amount. .

  The OD operating condition determination method according to the present embodiment is based on the findings described above. Next, a specific OD operation condition determination method will be described.

  In particular, a method for determining operating conditions for preventing sedimentation in the circulating water channel 8 at the initial use stage of OD1 will be described here. In such a sewage treatment system equipped with OD1, it takes time to develop the sewage network, but it is unlikely that the system will be operated after the sewage network is completed. It is common to construct a plant first and to gradually develop a sewer network connected to it. Therefore, in the initial stage of use of the plant, operation is performed with a load much lower than the design processing capacity. However, in such an extremely low load operation state, even if the impeller 3 is operated at a low speed or intermittent operation to the limit necessary to prevent sedimentation of the activated sludge in the mixed liquid, it is excessively aerated by the gas-liquid contact promoted by this. As a result, the microorganism in OD1 undergoes auto-oxidation or the nitrification reaction proceeds, so that the pH in OD1 decreases, the sludge concentration does not increase, and the treatment capacity decreases. In order to prevent over-aeration, if the impeller 3 is stopped for a longer time, the sludge settles and the amount of dissolved oxygen does not decrease, and the treatment capacity also decreases. After that, there is also a problem of giving off odor. Therefore, in such an initial stage of using OD1, a method for efficiently and suitably determining operating conditions is important.

First, at the site where the accumulation in the circulation channel 8 occurs (B-1-L in FIG. 7), (flow velocity [m / sec], immersion depth [mm], power input density [W / m ³ ], sludge concentration [ mg / l]) data sets are acquired by changing the conditions (variably changing the immersion depth, power input density, and sludge concentration as parameters). Next, based on these data sets, multiple regression of immersion depth X, power input density Y, and sludge concentration Z with respect to flow velocity V, V = a · X + b · Y + c · Z + d ( The relational expression (4) of a, b, c, and d is obtained. Further, as shown in the above equation (3), the relationship between the power input density [W / m ³ ] and the motor rotation speed [rpm] is obtained in advance.

  Next, the immersion depth and power input density are determined from the desired flow rate and sludge concentration based on the above relational expression (4). Then, the necessary number of rotations of the motor 6 is obtained from the expression (3) representing the relationship between the power input density and the number of motor rotations.

  Further, the relationship between the immersion depth, power input density, and oxygen supply amount is obtained in advance. Then, an oxygen supply amount P is obtained from the determined immersion depth and power input density. Then, based on the equation (5), the aeration time T1 is determined from the obtained oxygen supply amount.

In this way, the immersion depth X [mm], power input density Y [W / m ³ ], that is, the rotational speed [rpm] of the motor 6 and the aeration time T1 [h / day] at the time of aeration can be obtained. .

  Although it is conceivable to stop driving the impeller 3 except during aeration, it is necessary to secure a constant flow rate in order to prevent the accumulation of sludge, so the mixed liquid is agitated except during aeration.

  The stirring time is calculated from the following formula (6):

Agitation time T2 = 24 [h / day] −Aeration time T1 [h / day] (6)
On the basis of During stirring, it is necessary to reduce the oxygen supply amount so as not to cause excessive aeration. On the other hand, in order to prevent sludge accumulation, it is necessary to secure a flow rate of 0.1 [m / sec] or more. Therefore, based on the above formula (4), the immersion depth and power input density are determined under the condition that the flow velocity is lower than that during aeration. At this time, it is preferable to confirm that the oxygen supply amount at the determined immersion depth and power supply density is sufficiently small from the relationship between the immersion depth, power input density, and oxygen supply amount.

In this way, the immersion depth X [mm] during stirring, the power input density Y [W / m ³ ], that is, the rotational speed [rpm] of the motor 6 and the stirring time T2 [h / day] can be obtained.

  As described above, in the initial stage of use of OD1, it is possible to efficiently and suitably determine the operating conditions during aeration and stirring.

  The present invention is not limited to the above-described embodiment, and various modifications can be made. For example, in the above-described embodiment, the circulating water channel 8 is described as a horseshoe type, but the present invention is not limited to this, and the circulating water channel 8 may be of other types such as an oval type.

  In the above-described embodiment, the method for determining the operating condition in the initial use stage of OD1 has been described. However, the present invention can also be applied to the determination of the operating condition in another stage.

  Further, in the above-described embodiment, the intermittent operation in which the aerobic time zone and the anaerobic time zone are provided in time and the nitrification reaction and the denitrification reaction are performed in each time zone has been described. The present invention is also applicable to zone operation in which an aerobic zone is provided for processing.

In the above-described embodiment, the description has been made on the premise that the synergistic effect X · Y of the immersion depth X and the power input density Y with respect to the flow velocity V is negligible. Second], immersion depth [mm], power input density [W / m ³ ], sludge concentration [mg / l]), and increase the number of data sets acquired. X, Y of power input density, sludge concentration Z, and the term of the synergistic effect of immersion depth and power input density (XY),

V = a * X + b * Y + c * Z + d + e * XY * (a, b, c, d, e are predetermined constants) (4a)
The impeller immersion depth and power input density may be determined from the flow rate of the mixed liquid and the sludge concentration based on the relational expression (4a). This is effective when the influence of the synergistic effect between the immersion depth and the power input density is large.

  Note that it is preferable to simplify the equation while ignoring the term that has the least influence on the flow velocity V so that the equation (4) can be obtained by ignoring the XY term in the equation (4a).

  Hereinafter, although an example is described, the present invention is not limited to this example.

  In this example, in the initial stage of use of OD, the operating conditions for preventing sedimentation in the circulation channel were determined. The aeration capacity U [h / day] by the impeller was able to supply oxygen necessary for the planned sewage inflow in 12 hours. Furthermore, the inflow amount i of sewage at the initial use stage of the OD was set to 10 [%] with respect to the planned sewage amount. Further, the immersion depth of the impeller can be changed in the range of 300 mm to -100 mm.

First, a data set of (flow velocity [m / sec], immersion depth [mm], power input density [W / m ³ ], sludge concentration [mg / l]) at the site where sedimentation occurs in the circulation channel of OD. , I acquired multiple items under different conditions. Based on these data sets, multiple regression of immersion depth X, power input density Y, and sludge concentration Z with respect to flow velocity V, V = a · X + b · Y + c · Z + d (a, b , C, d are predetermined constants). In this example,

V = 0.0369 + 0.000266X + 0.00710Y + 0.000010Z (7)
The relational expression represented by is obtained. In addition, as a formula showing the relationship between the motor rotation speed and power input density,

Y [W / m ³ ] = 0.0072 × motor rotation speed [rpm] −3.61 (8)
Got.

  Next, the initial value of the aeration time was set. In order not to cause accumulation in the circulation channel, the flow velocity needs to be 0.1 [m / sec] or more. Here, the flow velocity V was set to 0.15 [m / sec] so as to satisfy this condition. Moreover, the period when the inflow amount is about 10% corresponds to immediately after the start of service, and the sludge concentration is almost equal to zero, so the sludge concentration Z is set to zero.

These values were substituted into the equation (7), and the immersion depth X and the power input density Y were determined. At this time, since the amount of sludge that flows in during the initial operation is extremely small, it is preferable to operate the impeller at a deep position so as not to cause excessive aeration. Therefore, the immersion depth X was determined to be the deepest 300 [mm], and the power input density Y was determined to be about 5 [W / m ³ ]. Since the power input density Y was determined to be 5 [W / m ³ ], the rotational speed of the motor was determined to be about 1200 [rpm] according to the equation (8).

Further, when the oxygen supply amount at an immersion depth of 0 [mm] and a power input density of 11.7 [W / m ³ ] is 100 [%], the immersion depth X and the power input density Y under fresh water conditions The relationship with the oxygen supply amount P was obtained in advance. That is, the relationship as shown in the graph shown in FIG. 13 is obtained in advance. In this example, when the power input density is 10.1-11.7 [W / m ³ ] and the immersion depth is changed to 300-0 [mm], the oxygen supply amount is 34-100 [%]. And changed. On the other hand, when the power input density was 3.4 to 4.6 [W / m ³ ], the oxygen supply amount was almost constant regardless of the immersion depth, and was 12 to 16 [%]. In addition, when the power input density was 1.2 to 2.8 [W / m ³ ], the oxygen supply amount was almost constant regardless of the immersion depth, and was 4 to 7 [%]. From this relationship, the oxygen supply amount was determined to be 17% based on the determined immersion depth and power input density. Based on the formula (5), the aeration capacity U is set to 12 [h / day], the sludge inflow rate i is set to 10 [%], the oxygen supply amount P is set to 17 [%], and the aeration time T1 [h / day]. It was determined.

In this way, the immersion depth X during aeration is 300 [mm], the power input density Y is 5 [W / m ³ ], that is, the rotational speed of the motor is 1200 [rpm], and the aeration time T1 is 7 [h / day]. ] Was determined.

  Next, the initial value of the stirring time was set. At the time of stirring, it is necessary to reduce the oxygen supply amount so as not to cause excessive aeration. On the other hand, in order to prevent sludge accumulation, it is necessary to secure a flow rate of 0.1 [m / sec] or more. Here, the flow velocity V was set to 0.13 [m / sec] so as to satisfy this condition. Moreover, the period when the inflow amount is about 10% corresponds to immediately after the start of service, and the sludge concentration is almost equal to zero, so the sludge concentration Z is set to zero.

By substituting these values into the equation (7), the immersion depth X and the power input density Y were determined. At this time, since the amount of sludge that flows in during the initial operation is extremely small, it is preferable to operate the impeller at a deep position so as not to cause excessive aeration. Therefore, the power input density Y was determined to be about 2 [W / m ³ ] by setting the immersion depth X to the deepest 300 [mm]. Since the power input density Y was determined to be 2 [W / m ³ ], the rotational speed of the motor was determined to be about 780 [rpm] according to the equation (8).

Next, from the relationship between the immersion depth X, the power input density Y, and the oxygen supply amount P, the oxygen supply amount was confirmed based on the determined immersion depth and power input density. Then, the power input density Y was about 2 [W / m ³ ], the oxygen supply amount P was 4 to 7 [%], and it was confirmed that the oxygen supply amount was reduced. And stirring time T2 [h / day] was calculated | required based on (6) Formula.

Thus, the immersion depth X at the time of stirring is 300 [mm], the power input density Y is 2 [W / m ³ ], that is, the rotational speed of the motor is 780 [rpm], and the stirring time T2 is 17 [h / day]. ] Was determined.

  From the above, under the above operating conditions, it was possible to efficiently and suitably determine the operating conditions, such as a cycle of 1.75 hours of aeration and 4.25 hours of stirring as one cycle, and four cycles per day. .

In FIG. 14, the straight line L1 is a straight line based on the above equation (7), and the immersion depth and power input when the flow rate is 0.1 [m / sec] and the sludge concentration is 3063 [mg / l]. The relationship with density is shown. As shown in FIG. 14, in the region above the straight line L1, a flow velocity of 0.1 [m / sec] or more is ensured, and sludge accumulation is suppressed. Therefore, it is preferable to determine the immersion depth and the power input density within the region indicated by the oblique lines in FIG. However, in this embodiment, the power input density is limited to a range of 1 to 12 [W / m ³ ] and the immersion depth of the impeller is limited to a range of −100 to 300 [mm]. If data is acquired by changing the immersion depth range and the same analysis is performed, this is not the case. The act of determining the immersion depth and power input density based on such a diagram is also based on the above equation (7), and the straight line L1 is determined from the flow rate of the mixed liquid and the sludge concentration. Based on the relational expression “V = a · X + b · Y + c · Z + d (a, b, c, d are predetermined constants), the impeller immersion depth is calculated from the flow rate of the liquid mixture and the sludge concentration. And determining the power input density ”. In FIG. 14, points G1 and G2 correspond to the operating conditions during aeration and stirring determined by the above steps, respectively.

It is a partially broken perspective view of OD. It is a top view which shows the structure of OD. It is a figure for demonstrating an overflow gate. It is a perspective view which shows an impeller. It is a figure which shows the state which looked at the impeller from the bottom. It is a figure for demonstrating the relationship between an impeller and a water level. It is a figure for demonstrating the place which measures the flow velocity in OD. It is a figure for demonstrating the location which measures the flow velocity in each A, B, C, D cross section of OD of FIG. When the rotational speed of the impeller is adjusted to three levels of low speed L (FIG. 9 (a)), medium speed M (FIG. 9 (b)), and high speed H (FIG. 9 (c)), It is a figure which shows the flow velocity in each point. When the rotational speed of the impeller is adjusted to three levels of low speed L (FIG. 10 (a)), medium speed M (FIG. 10 (b)), and high speed H (FIG. 10 (c)), It is a figure which shows the flow velocity in each point. It is a graph which shows the relationship between the rotation speed of a motor, and power consumption. It is a graph which shows the relationship between the rotation speed of a motor, and power input density. It is a graph which shows the relationship between immersion depth, power input density, and oxygen supply amount. In an Example, it is a graph which shows the relationship between immersion depth and power input density when a flow rate is 0.1 [m / sec] and a sludge density | concentration is 3063 [mg / l].

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Oxidation ditch, 2 ... Mixed liquid, 3 ... Impeller, 4 ... Rotating shaft, 5 ... Reduction gear, 6 ... Motor, 7 ... Mount, 8 ... Circulating water channel, 9 ... Rectification wall, 10 ... Inlet, 11 ... Discharge port, 12 ... overflow gate, 13 ... motor, 14 ... stirring blade, 14a ... bent portion, 15 ... water inlet, 16 ... cone plate.

Claims (4)

A method for determining operating conditions of an oxidation ditch comprising an endless circulation channel, and an impeller for stirring and aeration of a mixed liquid of sewage and activated sludge flowing into the circulation channel,
When the flow rate of the liquid mixture is V, the impeller immersion depth is X, the power input density is Y, and the sludge concentration (MLSS) is Z,
V = a * X + b * Y + c * Z + d (a, b, c, d are predetermined constants)
Based on the relation of
A value of 0.1 [m / sec] or more is substituted as the flow velocity V of the mixed solution, a sludge concentration value [mg / l] in the oxidation ditch is substituted as the sludge concentration Z, and the impeller immersion depth is substituted. An operation condition determination method for an oxidation ditch , wherein a predetermined value [mm] is substituted as X to determine the power input density Y [W / m ³ ] . The oxygen supply amount for the mixed liquid by the impeller is obtained based on the immersion depth X and the determined power input density Y, and the aeration time is determined based on the oxygen supply amount. The operating condition determination method of the oxidation ditch described in 1. The relational expression is
A plurality of data sets including the flow velocity at the predetermined site in the circulation channel, the immersion depth of the impeller, the power input density, and the sludge concentration are obtained under different conditions, and the immersion depth with respect to the flow velocity V is obtained based on these data sets. The method for determining the operating condition of the oxidation ditch according to claim 1 or 2, wherein X, power input density Y, and sludge concentration Z are obtained by multiple regression. A method for determining the operating conditions of an oxidation ditch comprising an endless circulation channel and an impeller for stirring and aeration of a mixed liquid of sewage and activated sludge flowing into the circulation channel,
When the flow rate of the mixed liquid is V, the immersion depth of the impeller is X, the power input density is Y, the sludge concentration (MLSS) is Z, and the term of the synergistic effect of the immersion depth and the power input density is XY,
V = a * X + b * Y + c * Z + d + e * XY (a, b, c, d, e are predetermined constants)
Based on the relation of
A value of 0.1 [m / sec] or more is substituted as the flow velocity V of the mixed solution, a sludge concentration value [mg / l] in the oxidation ditch is substituted as the sludge concentration Z, and the impeller immersion depth is substituted. Substituting a predetermined value [mm] as X, the power input density Y [W / m ³ ], Determining the operating condition of the oxidation ditch.

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