JP2001000996A - Operation method of membrane separation type septic tank and membrane separation type septic tank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently perform denitrification, in supplying air to a nitrification tank (membrane separation tank) from an air feeder, by performing a denitrification process for supplying a low vol. of air, a nitrification process for supplying a medium vol. of air and a membrane separation process for supplying a large vol. of air so as to change over them. SOLUTION: When an operation condition repeatedly performing operations of denitrification, nitrification and membrane separation modes is inputted to a controller 7 at time intervals t1, t2, t3, air is supplied to a membrane separation tank E2 in low vol. of such a degree that the concn. of DO is received in a range fitted to denitrification during the time t1 and denitrification treatment is applied by anaerobic bacteria while water to be treated is stirred. Succeedingly, a medium vol. of air is supplied for the time t2 to transfer the environment in the membrane separation tank E2 to aerobic environment and water to be treated is properly nitrified by aerobic bacteria. A membrane separation apparatus M is operated for the time t3 while supplying air in large vol. sufficient to clean a flat membrane 1 to take water to be treated out of a membrane separation type septic tank.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air supply device in which a membrane separation device and an air diffusion device for supplying air bubbles to the film separation device are installed in a nitrification tank, and air is supplied to the air diffusion device. The present invention relates to a method of operating a membrane separation type septic tank provided.

[0002]

2. Description of the Related Art Heretofore, as a membrane separation type septic tank of this type, there is known a type in which the air supply device can be switched between a stopped state and a high-capacity air supply state by intermittent aeration. Here, as an operation method of such a membrane separation type septic tank, it is known that the operation state of the air supply device is set to the stop state at the time of denitrification, and to the high capacity air supply state at the time of nitrification. Accordingly, at the time of denitrification, the denitrification reaction by anaerobic bacteria (hereinafter, referred to as "denitrifying bacteria") living in the nitrification tank is maintained, and at the time of nitrification, a large volume of air is supplied. Thus, while the nitrification reaction by the aerobic bacteria is promoted, bubbles are brought into contact with the surface of the flat membrane provided in the membrane separation device to clean the membrane surface.

[0003]

However, during the nitrification, if the air supply device is continuously operated at a high capacity in order to perform solid-liquid separation while maintaining the above-mentioned film surface cleaning action, the dissolved oxygen (hereinafter, referred to as "dissolved oxygen") will be described. The supply of “DO”) may be excessive, and the nitrification reaction by the aerobic bacteria may proceed excessively. The treated water that has become excessively nitrified has to be neutralized in order to discharge it to the outside of the membrane separation type septic tank because the pH is inclined to acidic, and the nitrification reaction and the denitrification reaction are performed in the septic tank. Is repeatedly performed, in the high-volume air supply state, the acidity is likely to increase due to excessive air supply, whereby an excessive load is applied to the denitrifying bacteria, and the denitrification reaction is inhibited. There was a problem. In particular, in a membrane separation type septic tank equipped with a small-capacity denitrification tank, the supply of DO to the membrane separation tank tends to be excessive, so that the denitrification efficiency is reduced and the denitrification capacity of the membrane separation type purification tank is reduced. There was a problem that it was easy to do.

[0004] Accordingly, an object of the present invention is to provide a method of operating a membrane separation type septic tank in which denitrification is sufficiently performed in view of the above-mentioned drawbacks.

[0005]

In order to achieve the above object, a method of operating a membrane separation type septic tank according to the present invention is characterized in that a membrane separation apparatus and an air diffuser for supplying air bubbles to the membrane separation apparatus are provided in a nitrification tank. In the method for operating a membrane separation type septic tank equipped with an air supply device for supplying air to the diffuser, the denitrification reaction is performed when air is supplied from the air supply device to the nitrification tank. A denitrification step of supplying low-volume air that can proceed and stir the water to be treated, and supply a medium-volume air that is higher in volume than the amount supplied in the denitrification step and that allows the nitrification reaction to proceed. The point is that the nitrification step and the membrane separation step of supplying a high volume of air that is higher in volume than the amount supplied in the nitrification step and that can operate the membrane separation apparatus are performed by switching. In order to achieve this object, the membrane separation type septic tank of the present invention has a characteristic configuration in which a nitrification tank is provided with a membrane separation device and an air diffuser for supplying air bubbles to the membrane separation device. In a membrane separation type septic tank equipped with an air supply device for supplying air to the device, the air discharge amount of the air supply device can be reduced to allow a denitrification reaction to proceed and to stir the water to be treated, and a nitrification reaction can proceed. An air supply device control mechanism that operates by switching to a medium capacity or a high capacity that can operate the membrane separation device is provided. And these effects are as follows.

The inventors have empirically obtained the knowledge that the nitrification reaction proceeds excessively if a large volume of air sufficient to clean the surface of the flat membrane is continuously supplied to the nitrification tank during the nitrification reaction. Was. As a result of intensive research, the DO concentration contained in the water to be treated was reduced by setting the amount of air discharged from the air supply device during the nitrification reaction to be lower than that during the operation of the membrane separation device. Thus, the present inventors have conceived to slow down the progress of nitrification and to eliminate the excessive tendency of nitrification of the liquid to be treated. That is, a membrane separation device and a diffuser for supplying air bubbles to the membrane separator are installed in a nitrification tank, and a membrane separation type purification tank equipped with an air supply for supplying air to the diffuser is operated. In supplying the air from the air supply device to the nitrification tank, in the denitrification step, a small amount of air is supplied to the nitrification tank so that the carry-in of DO is not a problem. Since the water to be treated is stirred, the deposition of impurities contained in the water to be treated can be prevented, and the progress of the denitrification reaction can be promoted. Then, the membrane separation and the nitrification reaction, which have conventionally proceeded simultaneously, are temporally separated into a separate step. In the membrane separation step, a high volume of air is supplied to the air diffuser as in the past, and the flat membrane The solid-liquid separation is performed while cleaning the surface, and in the nitrification step, the nitrification reaction is controlled by reducing the amount of air supply compared to the membrane separation step, so that the water to be treated becomes excessively nitrified. Suppress. In this way, by operating the air supply device in combination with the three types of air supply conditions according to the characteristics of the membrane separation type septic tank and the state of the water to be treated, the denitrification of the water to be treated is performed. The balance between the reaction and the nitrification reaction can be easily adjusted. Therefore, by adopting the operation method according to the present invention, when it is difficult to purify the water to be treated, for example, when the nitrification tank has a small capacity, or when the raw water containing a high concentration of organic matter is treated. However, the total nitrogen amount of the water to be treated discharged from the membrane separation type septic tank can be kept low.

Further, a membrane separation device and an air diffuser for supplying air bubbles to the membrane separation device are installed in a nitrification tank.
In a membrane separation type septic tank equipped with an air supply device for supplying air to the air diffusion device, an air supply device control mechanism that operates by switching the air discharge amount of the air supply device to low capacity, medium capacity or high capacity. By providing, in a low volume supply state, the denitrification reaction proceeds while the air supplied to the membrane separation tank stirs the water to be treated, and in a medium volume supply state, the nitrification reaction proceeds, In a high-volume air supply state, solid-liquid separation can be performed while cleaning the flat membrane surface.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 2 and FIG. 3, the membrane separation type septic tank according to the present invention comprises a sedimentation separation tank N from the upstream side.
1. A flow control tank E1 and a membrane separation tank E2 are provided in the stated order so that the water to be treated flows.

The sedimentation separation tank (contaminant removal tank) N1 comprises:
Receiving the raw water of the water to be treated flowing into the septic tank from the inflow port I, the water to be treated is anaerobically treated by anaerobic bacteria living therein while sedimentation and removal of impurities in the water to be treated are carried out. Through the flow control tank E1.

The flow rate adjusting tank (denitrification tank) E1 is used for anaerobic treatment of the water to be treated having a relatively low solid component concentration flowing from the sedimentation separation tank N1 with denitrifying bacteria, and is temporarily stored to adjust the amount of the water to be treated. I do. The flow rate adjusting tank E1 is provided with a transfer pump P for pumping up the water to be treated and transferring it to the membrane separation tank E2. Is transferred to the membrane separation tank E2. In addition, a return pipe 5 for circulating the overflow water from the membrane separation tank E2 is disposed in the flow rate adjustment tank E1, so that the water level in the membrane separation tank E2 does not rise more than a certain level.

As shown in FIG. 5, the membrane separation tank (nitrification tank) E2 is provided with a membrane separation device M in which a number of flat membranes 1 are juxtaposed, and is provided below the membrane separation device M. Supplies bubbles to the membrane separation device M to prevent sludge and the like from adhering to the membrane surface, and supplies oxygen to the water to be treated while forming a circulating flow in the membrane separation tank E2. A diffuser D is installed, and a water collecting pipe M is provided on each flat membrane 1 of the membrane separator M.
The front end of the water collecting pipe M1 faces the outside in order to take out the water to be treated out of the septic tank. As shown in FIG. 4, the flat membrane 1 sandwiches a filter plate 1B with a nonwoven fabric 1C,
Further, it is formed as a unit sandwiched between the microporous membranes 1A and 1A made of polyolefin from the outside of the nonwoven fabric 1C sandwiching the filter plate 1B. As shown in FIG. I have.

Next, the air diffuser D and its control will be described. As shown in FIG. 5, the air diffusing device D supplies air to the air diffusing pipe 2 arranged in the membrane separation tank E2 by an air supply device 3 arranged on the upper surface of the membrane separation tank E2. It is configured as follows. Here, the air supply device 3 includes an air blower 3 having three air diffusion first, second, and third air discharge units A, B, and C for supplying air to the air diffusion pipe 2. Has adopted.

A control mechanism W for controlling the air diffuser D includes:
It is composed of a circuit composed of a first switch 8 and a second switch 9, and the operation state of the membrane separation tank E2 is classified into denitrification, nitrification, and membrane separation modes, and each operation time and operation order are manually set. Possible controllers 7 are linked. A power supply is directly connected to the first air discharging portion A for air diffusion, and is wired so as to operate constantly. On the other hand, the second and third air discharge units B and C are connected to the first switch 8 and the second switch 9 respectively.
, And are wired so as to be turned on and off by a signal from the controller 7.

When the setting of the controller 7 is in the denitrification mode, the control mechanism W turns off the first switch 8 and the second switch 9 (OFF) and drives only the first air discharge section A, A small volume of air is supplied to the membrane separation tank E2 through the air diffuser D. When the setting of the controller 7 is in the nitrification mode,
The first switch 8 is turned on (ON), the second switch 9 is turned off (OFF), and the first air discharging unit A and the second air discharging unit B are driven, and a medium volume of air is discharged from the membrane separation tank E2. To supply. When the controller 7 is in the membrane separation mode, the first switch 8 and the second switch 9 are both turned on (ON) to drive the first to third air discharge units A, B, and C, and Is supplied to the membrane separation tank E2.

The controller 7 supplies time Δt1, Δt
When the operating conditions for repeatedly performing the denitrification, nitrification, and membrane separation mode operations are input at intervals of 2. and Δt3, as shown in FIG.
A low-volume air is supplied so that the O concentration falls within a range suitable for denitrification, and the water to be treated is subjected to denitrification by anaerobic bacteria while stirring. Subsequently, during the time period Δt2, a medium volume of air is supplied, whereby the membrane separation tank E2 is supplied.
The interior shifts to an aerobic environment, and by the action of the aerobic bacteria,
The water to be treated is appropriately nitrified. Then, during Δt3, the membrane separation device M is operated while supplying a large volume of air sufficient to clean the flat membrane 1, so that the water to be treated is taken out of the membrane separation type purification tank through the water collecting pipe M1. Can be taken out.

For example, when a membrane separation type purification tank (five-person tank type) provided with a membrane separation tank is operated by a conventional operation method in which a denitrification mode and a membrane separation mode are alternately operated, the total amount of the water to be treated discharged is increased. Nitrogen concentration was below 15 mg / liter. Here, in accordance with the operation method according to the present invention, the membrane separation type septic tank is provided with a low capacity (40 liters / minute), a medium capacity (80 liters / minute), and a high capacity (120 liters / minute).
And a cycle of 5: 1: 1 operation in the stated order with a discharge rate of, and by repeating this cycle, the total nitrogen concentration of the water to be treated discharged from the membrane separation type purification tank Was controlled to 10 mg / liter or less.

[Other Embodiment] Another embodiment will be described below. When operating the membrane separation type septic tank according to the present invention, the denitrification, nitrification, the order and the execution time of the membrane separation mode are not necessarily the same as long as the denitrification / nitrification balance of the water to be treated can be optimized. As in the embodiment,
It is not necessary to repeat the cycle of performing the denitrification, nitrification, and membrane separation modes in the stated order. Therefore, it may be optimized in accordance with the membrane separation type septic tank to be used.
As shown in (a), after the denitrification mode and the nitrification mode are repeated a plurality of times to sufficiently decompose and remove nitrogen compounds in the water to be treated, the mode shifts to the membrane separation mode, and the membrane separation type septic tank is removed. When the nitrification is likely to proceed, and as shown in FIG. 6B, the time for performing the denitrification mode is set to be longer than the time for performing the nitrification mode. Is also good. Here, instead of the controller 7, a configuration may be adopted in which the operation mode of the air supply device is manually switched, or both may be provided together. Then, a mechanism for monitoring the pH value or the DO concentration of the water to be treated is connected to the controller 7, and when the pH value is low or the DO concentration is high, the period of the denitrification mode is extended or the number of times of execution is increased. If it is set to increase, it is easy to maintain the denitrification / nitrification balance. Further, the amount of air supplied to the membrane separation tank E2 is changed to an air supply device having a plurality of blowers 3 instead of a configuration in which the amount of air supplied per blower 3 is increased or decreased. A configuration for controlling may be adopted. Further, instead of forming a circulation flow between the denitrification tank and the nitrification tank, the transfer is performed so that the water to be treated is pumped from the denitrification tank until the water level of the nitrification tank reaches a set water level. A configuration for controlling the pump may be employed.

[Brief description of the drawings]

FIG. 1 is a time chart of an air supply amount to a membrane separation tank by an operation method according to the present invention.

FIG. 2 is a longitudinal sectional view of a membrane separation type septic tank according to the present invention.

FIG. 3 is a cross-sectional view of a membrane separation type septic tank according to the present invention.

FIG. 4 is a perspective view showing a flat membrane structure.

FIG. 5 is a control configuration diagram showing an air diffuser and a membrane separation device.

FIG. 6 is a time chart of an air supply amount to a membrane separation tank by an operation method according to another embodiment.

[Explanation of symbols]

 3 Air supply device (blower) D Air diffuser M Membrane separation device W Air supply device control mechanism E2 Nitrification tank (Membrane separation tank)

Claims (2)

[Claims] 1. A membrane separation type purification tank in which a nitrification tank is provided with a membrane separation device and an air diffusion device for supplying air bubbles to the membrane separation device, and an air supply device for supplying air to the diffusion device is provided. In the operation method, in supplying air from the air supply device to the nitrification tank, a denitrification step of supplying low-volume air capable of allowing a denitrification reaction to proceed and stirring water to be treated, A nitrification step of supplying a medium volume of air that is higher in volume than the supplied amount and in which the nitrification reaction can proceed, the volume is higher than the amount supplied in the nitrification step, and the membrane separation device is operable. A method of operating a membrane separation type septic tank that switches between membrane separation steps for supplying a large volume of air. 2. A membrane separation type purification tank in which a nitrification tank is provided with a membrane separation device and an air diffusion device for supplying air bubbles to the membrane separation device, and an air supply device for supplying air to the diffusion device is provided. In the above, the air discharge amount of the air supply device is set to a low capacity capable of advancing the denitrification reaction and stirring the water to be treated, a medium capacity capable of advancing the nitrification reaction, or a high capacity capable of operating the membrane separation device Septic tank with an air supply device control mechanism that operates by switching to