JPH06170392A - Control method in anaerobic and aerobic activated sludge method - Google Patents

Abstract

PURPOSE:To provide a control method accelerating the nitrification speed of sludge to reduce the necessary volume of a reaction tank in an anaerobic and aerobic activated sludge method introducing flowing water in a nitrification tank where aeration is performed through an anaerobic tank to discharge the same as treated water through a final sedimentation basin. CONSTITUTION:A pH meter 9 and a water temp. meter 20 are provided to a nitrification tank 2 and the nitrification speed corresponding to water temp. is calculated by a nitrification speed operation part 21. A pH value is set corresponding to the calculated nitrification speed by a pH setting part 22 and carbonate 13 is injected into the nitrification tank 2 through a pump 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method for increasing the nitrification rate in an anaerobic aerobic activated sludge method.

[0002]

2. Description of the Related Art In recent years, it has been required to remove nitrogen and phosphorus for the purpose of preventing eutrophication in closed water areas. Moreover, it is considered that regulations on nitrogen and phosphorus will become more and more important in the future, and the number of treatment facilities adopting advanced treatment processes capable of removing them is increasing.

An anaerobic / aerobic activated sludge method capable of removing nitrogen / phosphorus, which is a modification of the conventional standard activated sludge method, is currently receiving attention. This divides the biological reaction tank into an anaerobic tank in which dissolved oxygen (DO) does not exist and an aerobic tank in which it exists. First, the effluent of the sedimentation basin is introduced into the anaerobic tank to release phosphorus from the activated sludge and denitrification by denitrifying bacteria. In addition to absorption, oxidative decomposition of organic substances and nitrification of ammonia by nitrifying bacteria are performed.

The anaerobic / aerobic activated sludge method is a method of removing organic substances to the same degree as that achieved by the standard activated method, and removing nitrogen / phosphorus higher than that of the standard activated sludge method.

FIG. 2 shows an apparatus configuration for carrying out the anaerobic aerobic activated sludge method. In FIG. 2, 1 is an anaerobic tank, 2
Is a nitrification tank, 3 is a final settling tank, and is 1/3 to 1/2 in front of the aeration tank (nitrification tank) which is a biological reaction tank of the standard activated sludge method.
Stop aeration in the lower part and drive 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.

In FIG. 2, 6 is a blower,
The air for aerating the nitrification tank 2 is sent. Reference numeral 7 is a return sludge pump, and 8 is a pump for extracting excess sludge. Reference numeral 9 denotes a pH meter, which detects the pH of the nitrification tank 2 and controls the controller 10 according to the detected value to feed the alkaline agent 12 into the nitrification tank 2 via the pump 11.

[0008]

In order to achieve efficient nitrogen removal by the anaerobic aerobic activated sludge method, it is important to maintain denitrification in the anaerobic tank and nitrification in the aerobic tank under optimum operating conditions. Is. In particular, nitrogen removal often affects the nitrification process, and in order to obtain good nitrogen removal, it is first of all necessary to achieve good nitrification. Nitrification is greatly affected by the activity of nitrifying bacteria, but the growth rate of nitrifying bacteria is affected by pH and water temperature, and it is often observed that the nitrification rate decreases and nitrogen removal deteriorates in the low water temperature period. Therefore, it is necessary to have an operation method that does not reduce the nitrification rate even in the low water temperature period.

Since the nitrification reaction is much slower than the organic matter removal reaction, the anaerobic aerobic activated sludge method requires a larger reaction tank than the standard activated sludge method. Therefore, unless measures are taken to increase the nitrification rate, the reaction tank would have to be made larger, making it difficult to adopt the anaerobic and aerobic sludge method in urban treatment plants where it is difficult to secure a site.

The method of calculating the capacity of the nitrification tank for nitrification is shown below.

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

[0012]

[Equation 1]

(Where T is water temperature ° C) and the reaction tank sludge concentration MLSS is M (g / l), the nitrification tank volume V
_N is

[0014]

[Equation 2]

[0015]

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.

If the water temperature is now 13 ° C., K _N = 0.6
7 (mgN / g.MLSS.h), the inflow C _N was 25 (mg / l) MLSS was 3 (g / l), and the residence time t in the nitrification tank was

[0018]

[Equation 3]

It becomes

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 for making the nitrification reaction tank smaller, but it is said that the SS component is likely to flow out in the final settling tank 3, so that the limit is about 3 g / l.

The present invention has been made in view of the above points, and an object thereof is to provide a control method of this type which can increase the efficiency of the nitrification reaction and reduce the required volume of the reaction tank.

[0022]

The present invention provides (1) an anaerobic aerobic sludge activation method in which inflow water is introduced into a nitrification tank which is aerated through an anaerobic tank and is discharged as treated water through a final settling tank. In the above, the water temperature meter and the pH meter are provided in the nitrification tank, and the set pH value is increased according to the decrease in the water temperature of the nitrification tank to operate, and carbonate is added to the nitrification tank,
(2) The pH control is characterized in that it is carried out simultaneously with the start of the nitrification reaction.

[0023]

[Function] Nitrification is greatly affected by the activity of nitrifying bacteria, but the growth rate of nitrifying bacteria is affected by water temperature. If the nitrification reaction decreases during low water temperature periods or high loads, increase the set pH value and add carbonate. This addition increases the growth of nitrifying bacteria, which accelerates the nitrification rate.

Therefore, the nitrogen removal rate is increased and stable treated water is always obtained, and the volume of the reaction tank for nitrification can be reduced.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

The nitrifying bacteria that cause nitrification are autotrophic bacteria. Nitrifying bacteria acquire energy for growth by oxidizing inorganic nitrogen compounds and utilize inorganic carbon for cell synthesis. These are represented as follows.

NH ₄ + 1.86O ₂ + 1.98HCO ₃ ⁻ → 0.021C ₅ H ₇ NO ₂ +1.041 H ₂ O + 0.98NO ₃ ⁻ + 1.88H ₂ CO ₃ [Reference] Sewerage Practice Course 7 “Advanced Treatment And reuse "
Mitsuto Kuribayashi ed. Sankaido Considering the above, the addition of carbonate to activated sludge increases the growth of autotrophic bacteria, which may accelerate the nitrification rate.

Therefore, verification was carried out in the following examples.

The apparatus used for this verification is as shown in FIG.
The 1-liter reaction tank is equipped with a blower device (B), a stirring device (M), an inflow pump, and a drainage pump (P), and each is automatically operated by a sequence controller. Operation pattern is 15 minutes of raw water input, 1 hour of anaerobic (stirring),
Aerobic (aeration) 4 hours, precipitation 30 minutes, discharge 15 minutes (50%
Emission) for a total of 6 hours was set as one cycle, and operation was performed for four cycles per day. As the input raw water, artificial sewage mainly containing meat extract, peptone and sodium acetate was used. 1N for one
Of NaOH (comparative example) and 1 mol / l of Na ₂ CO ₃ (example) were added to the other, and the sludge was acclimated for 5 days.
After acclimatization finished using the two sludges, NO ₃ ^- seeking nitrification rate than the increase in N, it was compared.

The results are shown in Tables 1 and 2.

[0031]

[Table 1]

[0032]

[Table 2]

According to Tables 1 and 2, the addition of Na ₂ CO ₃ gives a nitrification rate of 1.4 compared to the case of adding NaOH.
It can be understood that the nitrification rate of the activated sludge becomes faster by adding the carbonate twice as fast.

Therefore, using this result, when the nitrification rate is lowered and the nitrogen removal is deteriorated, for example, at low water temperature or high load, the nitrification rate can be improved by introducing carbonate into the aeration tank. As a result, the nitrification rate increases and a stable nitrification rate is always obtained, and the nitrogen removal rate can be kept excellent. FIG. 1 shows an example of an apparatus configuration for carrying out the control method of the present invention. The same parts as or corresponding parts to those of the conventional device shown in FIG. .

Reference numeral 20 is a water thermometer, which is installed together with the pH meter 9 in the upstream portion of the nitrification tank 2. Reference numeral 21 denotes a nitrification rate calculation unit, which calculates a 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. Reference numeral 22 denotes a pH setting unit that sets a pH value according to the nitrification rate calculated by the nitrification rate calculation unit 21.

Next, an experimental example will be described.

As shown in the 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 (mg
N / g. MLSS. h), the required residence time in the nitrification tank 2 was 9.93 hours at 13 ° C, but was 7.87 hours at 16 ° C.

On the other hand, the nitrification rate is also influenced by the 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 carbonate 13 is controlled to be injected around pH 6 as a guide.

In the present invention, paying attention to the change in nitrification rate depending on the pH, the nitrification rate is increased 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 C1 was added to the activated sludge in which nitrification had occurred at a concentration of 15 mg / l in 11 flasks, and aeration was carried out to measure the change with time of ammoniacal 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 are three levels of 7.4, 7.9, and 8.4, and the average pH of each is 7.5, 8.0, and 8.5.
The fluctuation range was 0.1. As a result, the nitrification rate was 0.71, 0.96, 1.06 (m
gN / g. MLSS. h) was obtained.

From this, when the nitrification rate complies with the equation (1), the controller 10 starts the injection of the carbonate 13 via the pump 11 when the water temperature becomes 16 ° C. or lower, and the set pH is raised with the decrease of the water temperature. , When the pH is lowered 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 equation showing the nitrification rate due to the change in water temperature is measured in advance with the target activated sludge, and (1)
It is created by changing the constant term of the expression.

The addition to the nitrification tank 2 is not limited to the carbonate 13 and may be bicarbonate.

[0044]

As described above, according to the present invention, when the water temperature is lowered or the nitrogen load is increased, the pH is increased and the carbonate is added to the nitrification tank. The excellent effect is obtained.

(1) A high nitrification rate is obtained, the nitrification rate is increased, and as a result, the nitrogen removal rate is increased.

(2) As the nitrification rate increases,
The volume of the nitrification tank can be reduced, which helps save space.

(3) Even if the nitrification rate is lowered with respect to changes in water temperature and load, the nitrification rate is originally high, so that it does not decrease to the extent that the treatment is impaired, and the treatment is stable.

[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.

FIG. 3 is a block diagram of a batch tank experimental apparatus according to the present invention.

[Explanation of symbols]

 1 ... Anaerobic tank 2 ... Nitrification tank 3 ... Final settling tank 9 ... pH meter 10 ... Controller 11 ... Pump 12 ... Alkaline agent 13 ... Carbonate 20 ... Water thermometer 21 ... Nitrification rate 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 adding a carbonate to a nitrification tank while operating at a high value. 2. The method for controlling the anaerobic aerobic activated sludge method according to claim 1, wherein the pH control is performed simultaneously with the start of the nitrification reaction.