JP2021000607A - Operational method of biological treatment apparatus - Google Patents

Abstract

To provide an operation method of a biological treatment apparatus capable of easily discharging condensed water from a gas dissolving film and maintaining high gas dissolving efficiency for a long period of time.SOLUTION: Gas dissolving membrane modules 1 to 4 are arranged in parallel in a reaction tank 11. During normal operation, gas is uniformly supplied from a blower 12 to each gas dissolving membrane module 1 to 4. When the gas supply pressure increases more than a predetermined value compared to the normal operation, some valves, for example, two valves are closed and others are opened to increase the gas supply to the gas dissolving membrane modules 1, 2 or 3, 4 connected to the other valves to discharge the condensate.SELECTED DRAWING: Figure 1

Description

The present invention relates to an operation method of a biological treatment apparatus for biologically treating organic wastewater using a gas dissolution membrane, and particularly aerobic biological treatment by aerating an oxygen-containing gas through the gas dissolution membrane and supplying oxygen through the membrane. The present invention relates to a method for operating a biological treatment apparatus suitable for application to a biological treatment apparatus for performing biological denitrification treatment by aerating a methane-containing gas through a gas dissolution membrane and supplying methane through the membrane.

Since aerobic organism treatment methods are inexpensive, they are often used as treatment methods for organic wastewater. In this method, it is necessary to dissolve oxygen in the water to be treated, and aeration is usually performed by an air diffuser.

Aeration with an air diffuser has a low dissolution efficiency of about 5 to 20%. In addition, it is necessary to aerate at a pressure higher than the water pressure applied to the water depth where the air diffuser is installed, and a large amount of air is blown at a high pressure, so that the power cost of the blower is high. Usually, more than two-thirds of the electricity costs in aerobic biotreatment are used for oxygen dissolution.

A membrane aeration bioreactor (MABR) that performs aerobic biological treatment by adhering a biofilm to the outside of a hollow fiber membrane and supplying oxygen from the inside can dissolve oxygen without generating bubbles. In MABR, since it is sufficient to ventilate air having a pressure lower than the water pressure applied to the water depth, the required pressure of the blower is low and the oxygen dissolution efficiency is high.

In the MABR type wastewater treatment apparatus using a hollow fiber membrane, condensed water is generated inside the membrane and obstructs the flow of air. This causes a phenomenon in which sufficient oxygen (or methane, etc.) does not dissolve in the reaction vessel. In particular, it is difficult to remove condensed water from a thin film having a large specific surface area due to capillarity.

Normally, condensed water is continuously generated, so it is necessary to drain the condensed water regularly to eliminate the condensed water.

The above-mentioned problems are not limited to aerobic biological treatment, but are common problems in biological treatment of a method of supplying electron carriers (electron donors, electron acceptors) used for biological treatment through a gas dissolution membrane immersed in a reaction vessel. Is.

Patent Document 2 describes an aerobic biological treatment apparatus in which an oxygen-permeable hollow fiber membrane is arranged in the vertical direction, an oxygen-containing gas is allowed to flow upward, and condensed water is easily evaporated.

JP-A-2006-87310 JP-A-2018-89564

An object of the present invention is to provide a method for operating a biological treatment apparatus in which condensed water is easily discharged from the gas dissolution membrane and high gas dissolution efficiency can be maintained for a long period of time.

In the operation method of the biological treatment apparatus of the present invention, a reaction tank through which organic wastewater is passed, a gas dissolution film module installed in the reaction tank, and a gaseous electron transmitter are provided in the gas dissolution film module. A method of operating a biological treatment apparatus including a gas supply means for supplying a gas containing an electron transmitter and an exhaust gas pipe for discharging a gas not dissolved in the gas dissolution film from the gas dissolution film module to the outside of the reaction vessel. The present invention is characterized in that a condensed water discharge step is performed in which the supply amount of the electron transmitter-containing gas is increased as compared with the normal operation and the condensed water is discharged to the outside of the gas dissolution film module.

In one aspect of the present invention, the gas supply means includes a blower, and in the condensed water discharge step, the amount of air blown by the blower is increased as compared with the normal operation.

In one aspect of the present invention, a plurality of the gas dissolution membrane modules are installed in the reaction vessel, and the gas supply means contains an electron carrier to a part of the gas dissolution membrane modules in the condensed water discharge step. By reducing the gas supply or stopping the electron carrier-containing gas supply, the electron carrier-containing gas supply to the other gas-dissolved membrane module is increased and the condensed water is discharged from the other gas-dissolved membrane module. I do.

In one aspect of the present invention, the gas dissolution membrane module that reduces or stops the electron carrier-containing gas supply amount is sequentially switched.

In one aspect of the present invention, the amount of hydrogen carrier-containing gas supplied to the gas dissolution membrane module that performs the condensed water discharge step is 2 to 20 times the amount of hydrogen carrier-containing gas supplied during normal operation.

In one aspect of the present invention, the condensed water discharge step is performed when the gas supply pressure containing an electron carrier to the gas dissolution membrane module becomes higher than a predetermined value during the normal operation.

In the operation method of the biological treatment apparatus of the present invention, the condensed water discharge step of increasing the amount of the gas containing the electron carrier to the gas dissolution film module and discharging the condensed water is performed, so that the condensed water is quickly discharged from the gas dissolution film. It is discharged to the outside of the reaction tank. Therefore, the electron carrier dissolution efficiency of the gas dissolution membrane can always be maintained high.

It is a vertical sectional view of the biological processing apparatus which concerns on embodiment. It is a graph which shows the experimental result. It is a vertical sectional view of the biological treatment apparatus used in the embodiment.

Hereinafter, the present invention will be described in more detail with reference to the drawings.

FIG. 1 is a vertical cross-sectional view of the aerobic organism treatment apparatus 10 according to the embodiment. The aerobic biological treatment apparatus 10 includes a reaction tank (tank body) 11 and a plurality of oxygen dissolution membrane modules (corresponding to gas dissolution membrane modules) 1, 2, 3 and 4 arranged in the reaction tank 11. ing.

In each of the oxygen dissolution film modules 1 to 4, air is supplied from the blower 12 as an oxygen-containing gas (corresponding to an electron carrier-containing gas) to the pipe 13, the pipes 21, 22, 23, 24 and the valve 31 branched from the pipe 13. It is supplied via 32, 33, 34. The exhaust gas that has passed through the oxygen dissolution membrane modules 1 to 4 flows out of the reaction tank 11 through the pipes 41, 42, 43, 44 and the merging pipe 45 (corresponding to the exhaust gas pipe).

In FIG. 1, the reaction vessel 11 is not filled with a fluidized bed carrier, and the oxygen dissolution membrane acts as a MABR. That is, the biofilm adheres to the surface of the oxygen-dissolved membrane, and the oxygen dissolved and supplied from the primary side of the oxygen-dissolved membrane is consumed by the biofilm on the secondary side to perform aerobic biological treatment. However, the reaction vessel 11 is filled with a fluidized bed carrier so that the adhesion of the biofilm to the surface of the oxygen dissolution film is suppressed by the shearing force due to the flow of the carrier so that most of the biofilm adheres to the fluidized bed carrier. At this time, the oxygen dissolving membrane may be used only for the purpose of supplying oxygen.

In FIG. 1, a non-porous (non-porous) oxygen-dissolving film is used as the oxygen-dissolving film, oxygen-containing gas is ventilated from the blower 12 to the primary side of the oxygen-dissolving film through pipes 13, 21 to 24, and the exhaust is piped. It is configured to be discharged to the outside of the tank through 41 to 45. Therefore, the oxygen-containing gas is aerated through the oxygen dissolving membrane at low pressure, oxygen is passed between the constituent atoms of the oxygen dissolving membrane as oxygen molecules (penetrates into the membrane), and is brought into contact with the water to be treated as oxygen molecules (water). Since it dissolves directly in oxygen, no bubbles are generated), so to speak, the treatment using the mechanism of molecular diffusion by the concentration gradient is performed, so that the air diffusion by the air diffuser or the like becomes unnecessary as in the conventional case.

Further, it is preferable to use a hydrophobic material as the oxygen dissolving membrane because it is difficult for water to enter the membrane, but even if it is hydrophobic, a small amount of water is unavoidable, so the use of the present invention is preferable.

The oxygen dissolution membrane modules 1 to 4 may use a hollow fiber membrane as the oxygen dissolution membrane. In particular, the problem of the present invention becomes remarkable when it is composed of a hollow yarn having an inner diameter of 0.1 to 2 mm. The hollow fiber membranes are arranged in the vertical direction, the upper end of each hollow fiber membrane is connected to the upper header, the lower end is connected to the lower header, and the inside of the hollow fiber membrane is connected to the upper header and the lower header, respectively. Is preferable.

Oxygen-containing gas such as air supplied to the upper part of the oxygen dissolution membrane modules 1 to 4 flows from the upper header through the hollow fiber membrane to the lower header, and during this time, oxygen permeates the hollow fiber membrane and enters the reaction tank 11. Dissolves in water.

In the embodiment of FIG. 1, the oxygen dissolved membrane modules 1 to 4 are installed in parallel, and the air supplied by the blower 12 is evenly supplied to the oxygen dissolved membrane modules 1 to 4 during normal operation. .. Water to be treated (organic wastewater) is supplied to the reaction tank 11, and the treated water treated with aerobic organisms flows out from the reaction tank 11.

When performing the condensed water discharge step, some of the valves 31 to 34 are closed, the air supply to the oxygen dissolution film module to which the some valves are connected is stopped, and the air supply to the other oxygen dissolution film modules is performed. Increase the amount.

In the present invention, the amount of air supplied in the condensed water discharge step is preferably twice or more, particularly 2 to 20 times, particularly 2 to 5 or more in the normal operation. When doubling the air supply amount, for example, by first closing the valves 31 and 32 and leaving the valves 33 and 34 open, the air supply amount to the oxygen dissolution membrane modules 3 and 4 is set to 2 during normal operation. Double. After this state is maintained for a predetermined time, the valves 33 and 34 are closed and the valves 31 and 32 are opened, so that the amount of air supplied to the oxygen dissolution membrane modules 1 and 2 is doubled during normal operation. After a lapse of a predetermined time, all valves 31 to 34 are opened to return to normal operation.

When the amount of air supplied in the condensed water discharge process is four times that in normal operation, for example, by opening only the valve 31 and closing the other valves 32 to 34, the amount of air supplied to the oxygen dissolution film module 1 Is four times that during normal operation. Only the valves 32, 33, and 34 are opened in sequence, and the condensed water is discharged by the oxygen dissolution membrane modules 2, 3 and 4.

In FIG. 1, four oxygen dissolution membrane modules 1 to 4 are installed in parallel, but the number of oxygen dissolution membrane modules installed is arbitrary. However, when the air supply amount is switched by opening and closing the valve as in the present embodiment, the number of installed oxygen dissolution membrane modules needs to be 2 or more.

The condensed water discharge step may be performed periodically, and when the air supply pressure in the pipe 13 becomes higher than the predetermined pressure (for example, when the pressure becomes 1.2 times or more the pressure during normal operation) or the air supply It may be performed when the amount becomes less than a predetermined amount.

Condensed water is usually discharged once every 1 to 2 weeks, and it is sufficient to discharge the condensed water once per oxygen-dissolved membrane module for about 1 to 30 minutes.

<Estimated mechanism of action>
When the reaction tank in which the oxygen dissolution film module is immersed is continuously operated for a long period of time, the case where the condensed water discharge according to the present invention is not carried out and the case where the condensed water discharge according to the present invention is carried out periodically FIG. 2 shows an example of the change over time in the oxygen dissolution film module internal pressure (ventilation pressure loss).

When the condensed water is not discharged, the number of hollow fibers that are blocked due to the accumulation of the condensed water gradually increases, and the ventilation resistance of the oxygen dissolution membrane module increases accordingly, so that the internal pressure gradually increases. It is presumed to be (Δ in Fig. 2).

On the other hand, it is presumed that by discharging the condensed water, the number of closed hollow fibers is reduced and the internal pressure of the oxygen dissolution membrane module is lowered to a predetermined value or less. By periodically discharging the condensed water, the internal pressure of the oxygen dissolution membrane module can be maintained below a predetermined value for a long period of time, and a stable oxygen supply becomes possible (◯ in FIG. 2).

In the above description, the valves 31 to 34 are switched between opening and closing, but instead of the closing operation, the amount of air supplied to the other oxygen dissolution membrane module may be increased by performing an operation of narrowing the opening. Good.

Further, instead of opening / closing (or adjusting the opening degree) the valve, the condensed water may be discharged by increasing the supply air volume by increasing the output of the blower or increasing the number of operating units. Blower air volume increase and valve operation may be combined.

When performing the condensed water discharge step, it is preferable to reduce the inflow amount of the water to be treated, but if the condensed water discharge step is short, it is not necessary to reduce it, and if the condensed water discharge step is long. The inflow of water to be treated may be stopped.

In this embodiment, aerobic biological treatment has been described, but the present invention is not limited to this, as long as it is a biological treatment in which an electron carrier used for biological treatment is supplied through a gas dissolution membrane immersed in a biological treatment reaction vessel. The present invention can be preferably used.

For example, in the present embodiment, air, which is an oxygen-containing gas, is aerated to supply oxygen as an electron donor to perform aerobic biological treatment, but methane gas is aerated to supply methane as an electron acceptor. It may be subjected to biological denitrification treatment.

In the method using a gas dissolution film, the electron carrier (electron donor or electron acceptor) needs to be in a gaseous state, and it needs to be a substance capable of molecular diffusion from the surface of the gas dissolution film to the inside. ..

[Example 1]
A test apparatus was prepared in which the oxygen dissolution membrane module 52 was immersed and arranged in a 200 L reaction tank 51 filled with pure water at 25 ° C. shown in FIG. Air was ventilated from the pipe 53 to the oxygen dissolution membrane module 52 at a constant flow rate, and the exhaust gas was discharged from the pipe 54. The air flow rate and pressure were detected by the flow meter 55 and the pressure gauge 56.

Once a week, the air volume was adjusted to double for 10 minutes each time to discharge the condensed water. The pressure P on the inlet side of the oxygen dissolution membrane (value detected by the pressure gauge 56) was initially 10 kPa.

After normal operation for 2 weeks, the pressure P (pressure gauge 56 detection value) on the oxygen dissolution membrane inlet side increased to about 30 kPa. Therefore, the air was ventilated for 10 minutes at a ventilation volume three times that of the normal operation, and then returned to the initial ventilation volume. As a result, the pressure P on the inlet side of the oxygen dissolution membrane (value detected by the pressure gauge 56) decreased to about 10 kPa.

As described above, it was confirmed that the aeration pressure loss was reduced and the high oxygen dissolution efficiency was maintained by performing the condensed water discharge step according to the present invention.

1-4, 52 Oxygen Dissolved Membrane Module 11 Reaction Tank 31-34 Valve

Claims (6)

A reaction tank through which organic wastewater is passed, and
The gas dissolution membrane module installed in the reaction vessel and
A gas supply means for supplying an electron carrier-containing gas containing a gaseous electron carrier to the gas dissolution membrane module, and
In the operation method of the biological treatment apparatus including the exhaust gas pipe for discharging the gas not dissolved in the gas dissolution membrane module from the gas dissolution membrane module to the outside of the reaction vessel.
A method for operating a biological treatment apparatus, which comprises performing a condensed water discharge step of discharging condensed water to the outside of a gas dissolution membrane module by increasing the supply amount of a gas containing an electron carrier as compared with normal operation. The method for operating a biological treatment apparatus according to claim 1, wherein the gas supply means includes a blower, and the amount of air blown by the blower is increased in the condensed water discharge step as compared with the normal operation. A plurality of the gas dissolution membrane modules are installed in the reaction vessel.
In the condensed water discharge step, the gas supply means dissolves another gas by reducing the amount of the hydrogen carrier-containing gas supplied to some of the gas dissolution membrane modules or by stopping the supply of the hydrogen carrier-containing gas. The method for operating a biological treatment apparatus according to claim 1, wherein the amount of gas supplied to the membrane module containing an electron carrier is increased to discharge condensed water from the other gas-dissolved membrane module. The method for operating a biological treatment apparatus according to claim 3, wherein the gas dissolution film module for reducing or stopping the supply amount of the gas containing an electron carrier is sequentially switched. Claims 1 to 4 are characterized in that the amount of the electron carrier-containing gas supplied to the gas dissolution film module performing the condensed water discharge step is 2 to 20 times the amount of the electron carrier-containing gas supplied during normal operation. The operation method of the biological treatment apparatus according to any one of. The invention according to any one of claims 1 to 5, wherein the condensed water discharge step is performed when the gas supply pressure containing an electron carrier to the gas dissolution film module becomes higher than a predetermined value during the normal operation. How to operate the biological processing equipment.

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