JPH0155913B2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to a control method for a sewage purification treatment device,
In particular, the present invention relates to a control device for a fixed-bed sewage purification system that nitrates ammonia nitrogen in sewage through the action of microorganisms grown on the surface of a contact material.

[Prior art and its problems]

A fixed bed method has been known as one of the methods for purifying wastewater using the action of microorganisms.
In this fixed bed method, a contact material made of plastic corrugated plates, nets, tubes, etc. is housed in a septic tank, and wastewater is allowed to flow into it. Oxygen is added to the wastewater in the tank through aeration or mechanical stirring. This is a method for purifying wastewater by dissolving and stirring at the same time, and bringing the microorganisms grown on the surface of the contact material into contact with the circulating wastewater.

When ammonia nitrogen (hereinafter referred to as NH ₄ -N) in wastewater is nitrified to nitrite or nitrate nitrogen (hereinafter referred to as NO _x -N) by the action of nitrifying bacteria, the surface of the contact material in the septic tank is The aerobic fixed bed method is preferred because it can retain nitrifying bacteria for a long period of time. FIG. 7 shows this type of conventional sewage purification equipment. Inside the septic tank 1, a contact material 2 formed of a corrugated plastic plate or tube is placed along the side wall. A stirring chamber 3 is formed in the center of the contact material 2, and an aeration pipe 4 is installed in the stirring chamber 3. The septic tank 1 is configured such that wastewater W to be purified is introduced through an inflow pipe 5 and purified water flows out through an outflow pipe 6. The air diffuser pipe 4 is connected to an air outlet of an air diffuser blower 8 via an air supply pipe 7, and an air diffuser valve 9 is installed on the air supply pipe 7. Furthermore, septic tank 1
A sludge drain pipe 10 is connected to the center of the bottom plate, and a sludge drain valve 11 is provided on the pipe. Further, a backwashing air diffuser pipe 12 is installed below the contact material 2, and these pipes and the air supply pipe 7 are connected by a backwashing air supply pipe 13, and a backwash valve is installed on this pipe. 1
4 is included. Next, the nitrification process in the fixed-bed sewage purification apparatus having the above-described structure will be described. The sewage W that has undergone secondary treatment, mainly BOD removal, flows into the septic tank 1 through the inflow pipe 5. In the septic tank 1, the wastewater W is given dissolved oxygen by the air diffused from the aeration pipe 4, and at the same time is circulated and agitated within the septic tank 1 as shown by the arrow due to the air lift effect. In this process, _NH4 in septic tank 1
-N is oxidized to NO _x -N by the action of nitrifying bacteria growing on the surface of the contact material 2, and the nitrified water is discharged from the outflow pipe 6 as treated water.

By the way, if such treatment is carried out continuously for several months, the thickness of the biofilm will increase due to the accumulation of suspended solids in the wastewater W and the proliferation of microorganisms themselves, and eventually the biofilm itself will be deposited on the surface of the contact material 2. There is a problem in that it can no longer be supported by the water and peels off, contaminating the treated water and causing deterioration of the treated water. To solve this problem, backwashing has conventionally been performed periodically. During backwashing, the air diffuser valve 9 is fully closed, the backwash valve 14 is opened, and air is blown through the backwash air diffuser pipe 12 installed below the contact material 2 to remove air bubbles and fill the gaps in the contact material 2. This process removes the thickened biofilm. The biofilm separated in this manner is deposited at the bottom of the septic tank 1 and is removed by opening the sludge valve 11.

In order to perform the above-mentioned nitrification treatment in a stable condition,
It is necessary to take sufficient measures against fluctuations in water temperature and nitrogen load within the septic tank 1.
The activity of nitrifying bacteria is affected by temperature, and it is said that it decreases by about 8% when the water temperature decreases by 1℃.As a result, nitrification efficiency decreases in winter when the water temperature decreases, and NH ₄ -N There was a problem that treated water containing

On the other hand, if the nitrogen load fluctuates greatly and a temporary excessive NH ₄ -N load is applied, the nitrification capacity is relatively insufficient and NH ₄ -N is likely to be contained in the treated water and leaked out. There was a problem.

In order to solve these problems, it is possible to increase the nitrification capacity by increasing the capacity of the nitrification tank and the amount of contact material filled. period and NH ₄ −N
During periods of low load, there is no choice but to overcapacity,
The drawback is that the equipment cost is high, leading to waste in operating costs for the diffuser blower.

In addition, in order to suppress fluctuations in NH ₄ −N load,
One possible method is to provide a regulating tank to equalize the water quantity and quality before the fixed bed method to keep the NH ₄ -N load constant. However, this method has a problem in that the capacity of the regulating tank needs to be 40 to 50% of the amount of sewage that normally flows in each day, which increases the equipment cost.

[Purpose of the invention]

SUMMARY OF THE INVENTION Therefore, the purpose of the present invention is to solve the problems of the above-mentioned conventional techniques, and to
It is an object of the present invention to provide a control method for a sewage purification treatment device that can adjust the nitrification capacity in response to changes in the NH ₄ -N load.

[Key points of the invention]

In order to achieve the above object, the present invention installs a contact material on which microorganisms are attached and grown in waste water in a septic tank, and contacts the waste water by supplying air sent from a diffuser blower into the waste water in the septic tank. Temperature measuring means for measuring the temperature of sewage in a septic tank in a sewage purification device that generates a circulating flow that passes through the surface of a material to nitrify ammonia nitrogen in sewage into nitrite nitrogen or nitrate nitrogen. , an air flow rate measuring means for measuring the flow rate of air sent from the aeration blower into the septic tank, and output signals from the temperature measuring means and air flow rate measuring means and pre-input water temperature, circulation speed and nitrification rate. and a means for controlling the flow rate of air sent from the aeration blower according to an output signal from the arithmetic control means, and adjusting the aeration agitation capacity in the septic tank. This method is characterized in that the nitrification ability is controlled by this method.

In addition, another invention of the present application is to install a contact material on which microorganisms have grown attached to the surface of the contact material in waste water in a septic tank, and to supply air from a diffuser blower into the waste water in the septic tank to surface the contact material. In a sewage purification device that generates a circulating flow that passes through the septic tank and nitrifies ammonia nitrogen in the sewage into nitrite nitrogen or nitrate nitrogen, a temperature measuring means for measuring the temperature of the sewage in the septic tank; an air flow rate measuring means for measuring the flow rate of air sent from the aeration blower into the septic tank; a means for measuring the nitrogen load contained in the wastewater to be treated in the septic tank; and the temperature measuring means; arithmetic control means for comparing and calculating the output signals from the air flow rate measuring means and the nitrogen load measuring means with the relationship between water temperature and circulation speed input in advance; The septic tank is characterized in that it includes means for controlling the flow rate of air sent out, and the nitrification capacity is controlled by adjusting the air diffusion capacity within the septic tank.

[Embodiments of the invention]

Embodiments of the method for controlling a sewage purification apparatus according to the present invention will be described below.

Before explaining specific embodiments of the present invention, the principle of the present invention will be explained first.

In general, when the NH ₄ -N load is constant or fluctuates at regular intervals such as daily fluctuations, the nitrification rate of the sewage purification system is determined by the temperature of the sewage in the septic tank and the circulating flow rate of the sewage passing through the surface of the contact material ( It is known that the flow rate depends on the circulation flow rate (hereinafter referred to as the circulation flow rate). Regarding water temperature, it is known that the nitrification rate changes by 8% per 1°C of change in water temperature.

The present inventors conducted an experiment to investigate the effect of circulation flow rate on nitrification rate under a constant water temperature, and found that
The results shown in the figure were obtained. As can be seen from this diagram, it can be seen that as the circulating flow rate increases, the nitrification rate also tends to increase. This trend can be explained as follows. In other words, when the circulation flow rate of sewage flowing through the contact material increases and the thickness of the film of sewage formed on the surface of the contact material becomes thinner, NH ₄ −
The rate at which N moves to the nitrifying bacteria film on the surface of the contact material also increases, promoting the nitrification reaction.

On the other hand, the circulation flow rate of wastewater in the septic tank 1 is also affected by the air flow rate supplied into the air diffuser pipe 4 by the air diffuser blower, and the relationship is as shown in Fig. 6. If it increases, the circulation flow rate also increases.

The circulation flow rate of the fixed bed method targeted by the present invention is 0.2
~2 m/min (laminar flow), which represents a part of the low-velocity region of the relationship between the wide circulation flow velocity and the nitrification rate, including the turbulent region. From these considerations, since the target area is narrow, it is considered that there is virtually no problem in approximating the relationship between circulation flow rate and nitrification rate using the following linear equation.

Vnt=alv+b...(1) However, Vnt: Nitrification rate at t°C Lv: Circulating flow rate a, b: Constants obtained experimentally Considering the influence of water temperature, the general formula is as follows.

It is expressed as Vnt=(aLv+b)θt ^-to ...(2).

However, Vnt: Nitrification rate θ: Constant (1.08) to: Reference temperature t: Water temperature Equation (2) above shows that if the water temperature and circulation flow rate are determined, the nitrification rate can be determined, so change the circulation flow rate. In other words, the nitrification rate can be controlled by controlling the air flow rate.

Next, a specific embodiment of the present invention will be described with reference to FIGS. 1 to 4, in which the same parts as in FIG. 7 are denoted by the same reference numerals.

In this embodiment, a thermometer 15 for measuring the temperature of the waste water is set in the waste water in the septic tank 1, and a temperature detection signal 16 from the thermometer 15 is input to an arithmetic and control unit 17. Further, an air flow meter 18 is incorporated on the air supply pipe 7 on the downstream side of the air diffuser 9 to measure the amount of supply air flowing in the pipe. The flow rate detection signal 19 is input to the arithmetic and control unit 17. The design nitrification rate Vnd and the relationship between the air flow rate and the circulation flow rate are input into the arithmetic and control unit 17 in advance. Based on the measured wastewater temperature and the designed nitrification rate Vnd, the arithmetic and control unit 17 determines the necessary circulation flow rate from the above equation (2) as Vn=Vnd, and sets the necessary air flow rate. An output signal 20 from the arithmetic and control device 17 is input to an inverter 21 that controls the rotation speed of the diffuser blower 8 . In this way, the fixed bed can be operated with an appropriate air flow rate depending on the temperature of the wastewater. Note that the most appropriate method for determining the values of a, b, Lv, and Vnt in equation (2) above is to conduct an experiment using an actual machine under actual usage conditions, but they can also be determined using a small experimental device. There is no practical problem. In addition, the actual circulation flow rate is determined by measuring the flow rate in the circumferential direction in the upper part of the stirring chamber 3 or the rising flow rate in the stirring chamber 3 using a current meter, and calculating the flow rate as the product of the respective flow path cross-sectional areas. Furthermore, this value is obtained by dividing this value by the horizontal filling cross-sectional area of the contact material 2.

FIG. 2 shows another embodiment of the present invention, which differs from the embodiment shown in FIG. This is the point where 24 is provided. The control method in this embodiment is basically the same as the example shown in FIG. 1, but there is a difference in the method of setting the nitrogen load. That is, the sewage flow rate signal 25 measured by the sewage flow meter 23 is input to the arithmetic and control unit 17, and the nitrogen concentration in the sewage is measured by the total nitrogen analyzer 24, and the product of the sewage flow rate and the nitrogen concentration is calculated. Metered as nitrogen load. Once the size of the nitrogen load has been determined in this way, the optimal value for the circulation flow rate is determined by taking that value into account.
1, the amount of air supplied from the diffuser blower 8 is feedback-controlled. In addition, for wastewater where the ratio of total nitrogen concentration to NH ₄ -N concentration is relatively stable, such as secondary treated water, an NH _{4 -N} analyzer is used instead of a total nitrogen analyzer.
-N analyzer can be used.

Next, still another embodiment of the present invention will be described with reference to FIG. This embodiment is suitable when the fluctuation pattern of water temperature and the fluctuation pattern of nitrogen load can be predicted in advance. That is, predicted values of the water temperature fluctuation pattern and the nitrogen load fluctuation pattern are input into the arithmetic and control device 17 in advance.

If the above-mentioned embodiment is shown in a block diagram,
The results are as shown in the figure, and although the above example shows an example of a fixed bed in which stirring is performed by aeration,
Similar control is possible for mechanically stirred fixed beds by adjusting the stirring capacity.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the circulating flow rate in the septic tank can be adjusted by measuring or predicting changes in the temperature and nitrogen load of wastewater in the septic tank. It is possible to control the NH ₄ at a level higher than the load.
- It becomes possible to prevent N from flowing out into the treated water. Further, according to the present invention, the diffuser blower is operated via an inverter so that the circulation flow rate can be set in accordance with fluctuations in the nitrogen load in wastewater, so that the diffuser blower can save energy. Furthermore, in winter, it is possible to increase the circulation flow rate to increase the nitrification rate, thereby reducing the capacity of the septic tank.

[Brief explanation of drawings]

FIG. 1 is a control system diagram showing one embodiment of the sewage purification apparatus according to the present invention, FIGS. 2 and 3 are control system diagrams according to other embodiments of the present invention, and FIG. 4 is a control method according to the present invention. Figure 5 is a diagram showing the relationship between flow velocity in the contact material and nitrification rate, Figure 6 is a diagram showing the relationship between air flow rate and flow velocity in the contact material, and Figure 7 is a diagram showing the relationship between air flow rate and flow velocity in the contact material. is a system diagram showing a conventional sewage purification device. 1... Septic tank, 2... Contact material, 3... Stirring chamber,
4... Air diffuser pipe, 7... Air supply pipe, 8... Air diffuser blower, 9... Air diffuser valve, 15... Thermometer, 18...
Air flow meter, 21...inverter, 24...total nitrogen analyzer.

Claims (1)

[Claims] 1. A contact material on which fine particles have grown attached is placed in waste water in a septic tank, and air sent from a diffuser blower is supplied into the waste water in the septic tank to remove the contact material. In a sewage purification device that generates a circulating flow passing through a surface to nitrify ammonia nitrogen in sewage into nitrite nitrogen or nitrate nitrogen, a temperature measuring means for measuring the temperature of sewage in a septic tank; an air flow rate measuring means for measuring the flow rate of air sent from the aeration blower into the septic tank; and a relationship between the output signals from the temperature measuring means and the air flow rate measuring means and pre-input water temperature, circulation speed, and nitrification rate; and means for controlling the flow rate of air sent from the aeration blower based on the output signal from the arithmetic control means, and for adjusting the aeration agitation capacity in the septic tank. A sewage purification device characterized in that the nitrification capacity is controlled. 2. In the sewage purification device according to claim 1, the air flow rate supplied from the diffuser blower to the septic tank is nitrogen gas whose nitrification rate value calculated based on the measured water temperature is set in advance. A sewage purification device characterized in that it is controlled to match the load. 3. A contact material with microorganisms attached and grown on its surface is installed in the wastewater in the septic tank, and air from a diffuser blower is supplied into the wastewater in the septic tank to generate a circulating flow that passes through the surface of the contact material. In a sewage purification device that nitrifies ammonia nitrogen in sewage to nitrite nitrogen or nitrate nitrogen, a temperature measuring means for measuring the temperature of sewage in a septic tank;
an air flow rate measuring means for measuring the flow rate of air sent from the aeration blower into the septic tank; a means for measuring the nitrogen load contained in the wastewater to be treated in the septic tank; the temperature measuring means; arithmetic control means for comparing and calculating the output signals from the flow rate measuring means and the nitrogen load measuring means with the relationship between water temperature and circulation speed input in advance; What is claimed is: 1. A sewage purification device, comprising means for controlling the flow rate of air in the septic tank, and the nitrification ability is controlled by adjusting the aeration ability in the septic tank.