JPH0691293A - Control method of aerobic-anaerobic active sludge process - Google Patents

Abstract

PURPOSE:To maintain the reaction rate of nitrification and to downsize a nitrification tank in an aerobic-anaerobic active sludge process by attaching a thermometer and a pH meter to the nitrification tank and increasing the pH value set as the temperature in the nitrification tank decreases. CONSTITUTION:A thermometer 20 and a pH meter 9 are attached to the upstream part of a nitration tank 2, and the reaction rate of nitration is determined by a reaction rate arithmetic unit 21 corresponding to the temperature measured by the thermometer. The relationship between the temperature and the reaction rate is determined in advance, and the temperature is regulated so that a desirable reaction rate can be maintained. The pH value is set by a pH setting unit 22 corresponding to the reaction rate determined. The reaction rate is affected by pH which in general decreases with the progress of the reaction and concurrently causes a decrease in the reaction rate. When the pH value decreases remarkably, an alkaline agent 12 is added to restore the value to around 6 to control the reaction rate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for stabilizing and controlling a nitrification reaction against changes in water temperature and inflow load in an anaerobic aerobic activated sludge method.

[0002]

An anaerobic aerobic activated sludge method has been put into practical use as a method for biologically removing nitrogen in waste water. As shown in FIG. 2, this method has an anaerobic tank 1, a nitrification tank 2 and a final settling tank 3, and is a first stage 1/3 to 1 of the aeration tank (nitrification tank) which is a biological reaction tank of the standard activated sludge method. / It is characterized by stopping aeration of the 2nd place and driving in an anaerobic state.

The nitrogen component in the waste water flowing into the reaction tank is oxidized by the action of nitrifying bacteria in the aeration nitrifying tank 2. Part of the oxidized nitrogen is again in the nitrification solution circulation pump 5
It is returned to the anaerobic tank 1 through the anaerobic tank 1, and in this anaerobic tank, the denitrifying bacteria act in an anaerobic state to consume the organic matter of the inflowing water and reduce it to nitrogen gas for removal.

[0004]

In order to remove nitrogen efficiently, the nitrification reaction must be carried out sufficiently. However, since this nitrification reaction is much slower than the BOD oxidation reaction, a reaction tank (nitrification tank) larger than the standard activated sludge method is required.

A method for calculating the volume of the nitrification tank for nitrification will be described below.

Inflow TN (total nitrogen) C _N mg / l Inflow Q m ³ / d where nitrification reaction rate K _N

[0007]

[Equation 1]

(T is the water temperature in ° C), and the sludge concentration MLSS in the reaction tank is M (g / l), the volume V _{N of the} nitrification tank is

[0009]

[Equation 2]

[0010]

Therefore, the nitrification tank volume is inversely proportional to the nitrification rate. Nitrification rate When the water temperature decreases, the rate decreases significantly, so the nitrification tank volume is calculated based on the low water temperature.

Now, assuming that the water temperature is 13 ° C., K _N = 0.67
(MgN / g.MLSS _· h) and the inflow C _N is 25 (mg / l) MLSS
Is 3 (g / l) and the residence time t in the nitrification tank is

[0013]

[Equation 3]

[0014]

As described above, in the anaerobic aerobic activated sludge method, when the nitrification tank and the denitrification tank (anaerobic tank) are combined, the volume required is about 2 to 3 times that of the aeration tank in the standard activated sludge method. For this reason, in cities where there is not enough installation space, there are few examples of introduction even though the effect is recognized. Increasing the MLSS is also effective in reducing the nitrification reaction tank, but SS components easily flow out in the final settling tank 3, so
It is said that the limit is about 3 g / l.

In FIG. 2, 6 is a blower for sending air for aerating the nitrification tank 2. 7 is a returning sludge pump, 8 is a pump for extracting excess sludge, and 9 is a pH meter, which detects the pH of the nitrification tank 2 and controls the controller 10 according to the detected value to nitrify the alkaline agent 12 via the pump 11. Add to tank 2.

Therefore, an object of the present invention is to provide a control method of this kind which can increase the efficiency of nitrification reaction and reduce the required volume of the reaction vessel.

[0018]

According to the present invention, in the anaerobic aerobic activated sludge method, a pH meter and a water thermometer are provided in the nitrification tank, and the set pH value is increased to operate in response to the decrease in the water temperature of the nitrification tank. It is the one.

[0019]

[Function] As shown in the equation (1), the nitrification rate is greatly affected by the water temperature.

On the other hand, the nitrification rate is also affected by the pH, and generally the pH decreases with the progress of the nitrification reaction, and at the same time, the nitrification reaction decreases.

The present invention pays attention to the above-mentioned change in nitrification rate, and raises the nitrification rate by raising the pH value of the nitrification tank.
This is a reduction of the required reaction tank volume at low water temperature.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of a block diagram applied to the control method of the present invention, in which the same parts as the conventional one shown in FIG. The description is omitted.

Reference numeral 20 denotes a water temperature meter, which together with the pH meter 9 has a nitrification tank 2
Will be installed in the upstream part of. Reference numeral 21 denotes a nitrification rate calculation unit, which calculates the nitrification rate according to the water temperature detected by the water temperature gauge 20. At that time, the relationship between the water temperature and the nitrification rate is measured in advance, and output is performed so that an efficient nitrification rate is maintained. 22 sets the pH value according to the nitrification rate obtained by the pH value setting unit.

Next, an experimental example will be described.

As shown in the above equation (1), the nitrification rate is greatly affected by the water temperature. Therefore, the size of the nitrification tank is generally determined by the nitrification rate at the minimum water temperature, for example, 13 ° C. Assuming that the minimum water temperature has changed from 13 ° C to 16 ° C, K _N = 1.06 (mgN / g.MLSS _· h) from the equation (1), and the required residence time in the nitrification tank 2 is 9. What was 93 hours now becomes 7.87 hours at 16 ° C.

On the other hand, the nitrification rate is also affected by pH, but generally the pH decreases with the progress of the nitrification reaction, and at the same time the nitrification rate decreases. Therefore, when the pH is remarkably lowered, the control for injecting the alkaline agent is carried out with a pH of around 6 as a guide.

The present invention pays attention to changes in nitrification rate depending on these pH values, and raises the nitrification rate by increasing the pH of the nitrification tank to reduce the required reaction tank volume at low water temperature. The change in nitrification rate when set to was examined as follows.

NH ₄ Cl was added to the activated sludge in which nitrification had occurred at a concentration of 15 mg / l in a 1-liter flask, and aeration was performed to measure the time-dependent change of ammonia nitrogen. Then, using a pH meter and a controller, when the pH was less than a set value, 1N sodium hydroxide solution was injected.
The set values were three levels of 7.4, 7.9, and 8.4, and the average pH of each was 7.5, 8.0, and 8.5, and all were controlled with a fluctuation range of ± 0.1. As a result, at a water temperature of 13 ° C., nitrification rates of 0.71 _, 0.96, _and 1.06 (mgN / g.MLSS _· h) were obtained, respectively.

From this, when the nitrification rate complies with the equation (1), the controller 10 discloses the injection of the alkaline agent 12 through the pump 11 when the water temperature becomes 16 ° C. or lower, and the set pH is lowered as the water temperature is lowered. When the pH is raised to 13 ° C. and the pH is adjusted to 8.5, the required residence time in the nitrification tank 2 is 7.87 hours.

Here, the formula showing the nitrification rate due to the change in the water temperature is prepared by measuring the target activated sludge in advance and changing the constant term of the formula (1).

[0031]

As described above, according to the present invention, when the water temperature is lowered or the nitrogen load is increased, it is possible to prevent the efficiency of the nitrification reaction from decreasing by operating at a higher pH, and it is necessary to provide a reaction tank for nitrification. The volume can be reduced.

Further, the efficiency of nitrogen removal is improved by applying it to the anaerobic aerobic activated sludge method.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a configuration diagram of a conventional anaerobic / aerobic activated sludge treatment device.

[Explanation of symbols]

 1 ... Anaerobic tank 2 ... Nitrification tank 3 ... Final settling tank 9 ... pH meter 10 ... Controller 11 ... Pump 12 ... Alkaline agent 20 ... Water thermometer 21 ... Nitrification speed calculation unit 22 ... pH setting unit

Claims (2)

[Claims] 1. In an anaerobic aerobic activated sludge method in which inflowing water is introduced into a nitrification tank that is aerated through an anaerobic tank and is discharged as treated water through a final settling tank, a water temperature meter and a pH meter are provided in the nitrification tank. The pH is set according to the decrease in water temperature in the nitrification tank.
A method for controlling the anaerobic aerobic activated sludge process, which is characterized by operating at a high value. 2. The control method in the anaerobic aerobic activated sludge method according to claim 1, wherein the pH control is performed at the same time as the start of the nitrification reaction.