JPH05154496A - Controlling method for operation in anaerobic and aerobic activated sludge treating equipment - Google Patents

Abstract

PURPOSE:To remove organic substance and nitrogen contained in waste water with high efficiency by using an anaerobic and aerobic activated sludge treating equipment. CONSTITUTION:Densitometers 12, 13 of dissolved oxygen are equipped to an anaerobic tank 1 and an aerobic tank 2. Moreover an oxygen utilization speed meter 14 is arranged to the aerobic tank 2 in order to decide the proceeding status of nitrification. The proceeding status of the nitrifying reaction of the aerobic tank 2 is judged by detecting the concentration of dissolved oxygen and the oxygen utilization rate accompanied with progress of anaerobic and aerobic activated sludge treatment by the densitometers 12, 13 of dissolved oxygen and the oxygen utilization speed meter 14. The mixed liquor suspended solid concentration(MLSS), dissolved oxygen concentration (DO concentration) and the reflux ratio of nitrification liquid of the anaerobic tank 1 and the aerobic tank 2 are automatically controlled by a controlling circuit 15 from the judged result. Thereby the efficiency for removing organic substance and nitrogen contained in waste water is enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an operation control method for removing organic matter and nitrogen in wastewater with high efficiency by using an anaerobic-aerobic activated sludge treatment device.

[0002]

2. Description of the Related Art Conventionally, various methods have been proposed for efficiently removing organic substances in wastewater such as sewage and removing nitrogen and phosphorus which are considered to be the causative substances of eutrophication. This eutrophication refers to an increase in the concentration of nutrient salts such as N and P in the water area, which activates biological activities using these nutrients as nutrients and changes the ecosystem. In particular, it is known that the above-mentioned eutrophication rapidly progresses when a large amount of domestic wastewater or industrial wastewater flows into lakes and the like.

Although physicochemical methods and biological methods have been proposed as means for removing nitrogen and phosphorus in wastewater, physicochemical methods are not widely used because of the high cost. For example, a phosphorus removal method that has been put into practical use as a physicochemical method includes a coagulation precipitation method and a crystallization method, but this method has drawbacks in terms of cost and maintenance.

On the other hand, as a method for biologically removing nitrogen and phosphorus simultaneously, an anaerobic method is a modification of the conventional activated sludge method.
Aerobic activated sludge method is drawing attention. (See, for example, Water Pollution Research, Vol. 12, No. 7, 441-448, 1989.) In this method, the biological reaction tank is divided into an anaerobic tank and an aerobic tank, and the effluent water from the first settling tank is first divided into the anaerobic tank. Then, denitrifying by denitrifying bacteria in activated sludge in anoxic condition, and then aerating by aeration in an aerobic tank, oxidative decomposition of organic matter by activated sludge and ammonia by nitrifying bacteria in the presence of oxygen. Nitrification is performed. A part of the nitrification solution is circulated to the anaerobic tank and used for promoting denitrification.

By using such an anaerobic-aerobic activated sludge treatment method, an effect comparable to the organic matter removal effect achieved by the ordinary activated sludge method can be obtained, and nitrogen and phosphorus are higher than those by the activated sludge method. A removal rate is achieved.

[0006]

However, in the case of the method for removing organic matter and nitrogen in wastewater using such a conventional anaerobic-aerobic activated sludge treatment device, the operation of the anaerobic-aerobic activated sludge treatment device is performed. It cannot be said that the control method is sufficiently established, and there is a problem that it is difficult to improve processing efficiency and accuracy.

[0007] Generally, in order to purify organic wastewater using a biological treatment method, environmental conditions for maintaining the survival and growth of microorganisms appropriately are necessary. And the following 6 items can be mentioned as main control factors of the above anaerobic-aerobic activated sludge treatment method.

(1) Sludge average retention time (sludge retenti
on time, hereinafter abbreviated as SRT).

(2) Concentration of suspended matter in activated sludge (mixed liquor
suspended solid, hereinafter abbreviated as MLSS).

(3) Dissolved oxygen,
Hereinafter, abbreviated as DO concentration).

(4) Hydrogen ion concentration (pH).

(5) Reflux ratio of nitrification solution.

(6) Volume ratio of anaerobic tank and aerobic tank (hereinafter A /
Abbreviated as O ratio).

Since the control factors of the above six items are often controlled at a constant rate, there is a problem that they are easily affected by changes in the processing state such as changes in flow rate and changes in water quality. That is,
In order to remove nitrogen efficiently by anaerobic-aerobic activated sludge treatment, it is required to maintain denitrification in the anaerobic tank and nitrification in the aerobic tank under optimum operating conditions. Therefore, the nitrification step must be performed well in order to perform good nitrogen removal.

Further, it is known that the nitrification of ammonia nitrogen by nitrifying bacteria greatly depends on the DO concentration in the nitrification tank, and when this DO concentration rises to 2.0 mg / l or more, the nitrification of ammonia nitrogen is performed. Is said to be almost complete.

Further, all of the above-mentioned control factors affect the nitrification reaction and denitrification reaction, but in particular (2) MLSS and (3) D
The O concentration and (5) the reflux ratio of the nitrification solution have a large influence. ML
SS is usually used as an index of the amount of microorganisms in the biological treatment reaction tank, and can be determined from the weight (mg / l) after washing and drying after separating the suspended matter in the reaction tank by centrifugation or filtration. Normally, MLSS is set around 2000 (mg / l).

The above DO concentration is the amount of O ₂ dissolved in water, and when this DO concentration decreases, anaerobic bacteria appear and anaerobic respiration is performed. Further, the growth rate of nitrifying bacteria and the reduction rate of ammonia nitrogen are largely dependent on the DO concentration. The ammonia nitrogen reduction rate of this nitrifying bacterium is R _L , and the maximum nitrification rate is R _Lmax (mgN / gss · hr)
Then, RL = _RLmax · DO / (KO ₂ '+ DO) (1) (KO ₂ ': DO saturation constant, mg / l) .. In formula (1), the value of KO ₂ 'is 0.15 to 0.42
Although values such as (mg / l) or 2.0 (mg / l) have been reported, in the nitrogen removal process design manual of EPA, when the MLDO concentration rises to about 2 mg / l, nitrification of ammoniacal nitrogen occurs. Is almost complete,
1.3 mg / l is used. (Refer to the technical data of the single-stage type and the two-stage type activated sludge circulation modification method, the Japan Sewer Enterprises Technology Development Department, the Sewer Enterprises Business Extension Association, published in June 1990).

On the other hand, if the DO concentration at the outlet of the nitrification tank is low, ammonia nitrogen remains in the treated water and oxygen is consumed by the nitrification reaction, so even if the aeration amount in the nitrification tank is increased, the DO concentration in the tank is increased. Does not rise, and the DO concentration rises when ammonia nitrogen is almost exhausted. However, considering that the denitrification reaction in the denitrification tank is hindered as oxygen is supplied from the nitrification tank to the denitrification tank by circulating the nitrification liquid,
It is important to manage the control factors and monitor the nitrification reaction so that the DO concentration in the nitrification tank does not become higher than necessary.

The present invention has been made in view of the above, and an operation for highly efficiently removing organic matter and nitrogen in wastewater by controlling the main control factors of the above anaerobic-aerobic activated sludge treatment method. It is intended to provide a control method.

[0020]

[Means for Solving the Problems] In order to achieve the above object, a step of denitrifying wastewater such as sewage with denitrifying bacteria in an anaerobic tank, and nitrifying ammoniacal nitrogen with nitrifying bacteria in an aerobic tank. The steps of performing and solid-liquid separation in the settling tank, returning part of the settled sludge to the anaerobic tank and sending the rest to the excess sludge treatment device for processing, and discharging the supernatant of the settling tank as treated water. In an anaerobic-aerobic activated sludge treatment device including a step of refluxing a part of the nitrification liquid in the aerobic tank to the anaerobic tank to accelerate the denitrification reaction, the anaerobic tank and the aerobic tank have a concentration meter for dissolved oxygen. And an oxygen utilization rate meter for determining the progress of nitrification in the aerobic tank, and the progress of anaerobic-aerobic activated sludge treatment is performed by the concentration meter of dissolved oxygen and the oxygen utilization rate meter. The concentration of dissolved oxygen and the oxygen utilization rate are detected to detect the glass in the aerobic tank. The progress of the reaction is judged, and from the judgment results, the concentration of suspended solids in the anaerobic tank and aerobic tank, the dissolved oxygen concentration, and the reflux ratio of the nitrification solution are automatically controlled to improve the efficiency of removing organic matters and nitrogen in the wastewater. Provided is an operation control method for an anaerobic-aerobic activated sludge treatment device.

[0021]

According to the operation control method of the anaerobic-aerobic activated sludge treatment device, the wastewater is first denitrified in the anaerobic tank, and then aerated in the aerobic tank. Nitrification of nitrogen takes place. 1 of the nitrification liquid in this aerobic tank
The part is returned to the anaerobic tank to promote denitrification in the anaerobic tank.
The liquid discharged from the aerobic tank flows into the settling tank for solid-liquid separation,
A part of the settled sludge returns to the anaerobic tank again, the rest of the sludge is treated as excess sludge, and the supernatant of the settling tank is discharged as treated water.

At the time of the above treatment, the progress of the nitrification reaction is judged based on the data obtained from the dissolved oxygen concentration meter provided in the anaerobic tank and the aerobic tank as an index and the oxygen utilization rate meter installed in the aerobic tank. Based on the result of the judgment, the concentration of suspended solids in the anaerobic tank and the aerobic tank, the dissolved oxygen concentration, and the reflux ratio of the nitrification solution can be automatically controlled to improve the efficiency of removing organic matters and nitrogen in wastewater. Become.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The anaerobic of the present invention will be described below with reference to the drawings
An embodiment of the operation control method of the aerobic activated sludge treatment device will be described.

FIG. 1 is a schematic diagram showing a basic embodiment of the present invention. Reference numeral 1 is an anaerobic tank for denitrifying wastewater, and 2 is an aerobic tank for nitrification. 1 and aerobic tank 2
And the same biological reaction tank are divided by a partition plate 3. Underwater agitators 4 and 4 are arranged at the inner bottom of the anaerobic tank 1. Further, at the bottom of the aerobic tank 2, the air blowing member 5,
5, 5 are arranged, and a blower 6 for supplying air is provided outside. Further, the aerobic tank 2 is provided with a nitrification solution circulation pump 7 for returning a part of the nitrification solution to the anaerobic tank 1 and a return pipe line 8.

Reference numeral 9 is a final settling tank as a settling tank, and a sludge return pump 11 is arranged in the middle of a pipe 10 extending from the bottom of the final settling tank 9. Reference numeral 20 denotes a sludge distribution tank. The sludge distribution tank 20 has a function of returning a part of sludge to the anaerobic tank 1 again and sending the remaining sludge as excess sludge 23 to an excess sludge treatment device (not shown).

Further, in the present embodiment, the anaerobic tank 1 is provided with a dissolved oxygen concentration meter 12, and the aerobic tank 2 is also provided with a similar dissolved oxygen concentration meter 13.

Further, the aerobic tank 2 is provided with an oxygen utilization speedometer 14 for judging the progress of nitrification. 15
Is a control circuit, and the data detected by the dissolved oxygen concentration meters 12 and 13 and the oxygen utilization speed meter 14 is the control circuit 1.
5, and a drive signal is output from the control circuit 15 to the nitrification solution circulation pump 7, the blower 6 and the sludge return pump 11 based on these input data.

The basic operation of the anaerobic-aerobic activated sludge treatment device is as follows. First, waste water as waste 2
1 flows into the anaerobic tank 1, and NO ₃ —N and NO ₂ —N ions are reduced to N ₂ , that is, denitrification is performed based on the stirring action of the water agitators 4 and 4 and the action of denitrifying bacteria. .. Next, the wastewater flows into the aerobic tank 2, and aeration by aeration from the air blowing members 5, 5, 5 is performed as the blower 6 is driven,
Based on the action of nitrifying bacteria, ammoniacal nitrogen NH ₄ -N
Is oxidized to NO ₂ —N or NO ₃ —N, that is, nitrification is performed.

Then, a part of the nitrification solution in the aerobic tank 2 is returned from the return pipe 8 to the anaerobic tank 1 by the action of the nitrification solution circulation pump 7.
NO ₃ --N, NO ₂ --N, etc. necessary for denitrification are supplied to the anaerobic tank 1.

The liquid discharged from the aerobic tank 2 flows into the final settling basin 9 for solid-liquid separation, and a part of the sludge that has settled down is transferred from the pipeline 10 through the sludge return pump 11 to the sludge distribution tank 20. The sludge distribution tank 20 returns a part of the sludge to the anaerobic tank 1 together with the wastewater 21, and the rest of the sludge is sent to a surplus sludge treatment device (not shown) for treatment. Further, the supernatant liquid 22 of the final settling basin 9 is discharged as treated water.

In the present embodiment, while such anaerobic-aerobic activated sludge treatment is in progress, nitrification is performed by using the data obtained from the dissolved oxygen concentration meters 12 and 13 and the oxygen utilization speed meter 14 as an index. The main purpose is to improve the efficiency of wastewater treatment by judging the progress of the reaction and controlling the MLSS and DO concentrations and the circulation ratio of the nitrification solution based on the judgment results.

That is, the progress of the nitrification reaction in the aerobic tank 2 is determined by the oxygen utilization rate re
(hereinafter, abbreviated as rr) and N which is a nitrification inhibitor
- allyl thiourea (formula C ₄ H ₈ N ₂ S, hereinafter referred to as ATU) oxygen utilization rate (hereinafter, measured by the addition of AT
U-rr). When the above difference is [N-rr], [N-rr] = [rr]-[ATU-rr] (2)

The oxygen utilization rate rr is the oxygen concentration (mgO ₂ / l · hr) utilized per unit time, and if the aeration of the ordinary aerobic tank 2 becomes excessive, the sludge will be fragmented and the aeration will be insufficient. If so, phenomena such as organic matter remaining in the treated water and spoilage of sewage occur, and the purification performance deteriorates. Therefore, in order to optimally manage the activated sludge, it is necessary to supply oxygen at the oxygen utilization rate of the activated sludge or at a rate higher than that, which is used as an index of aeration.

The above [N-rr] is the oxygen utilization rate associated with nitrification. Therefore, if this value is small, it can be judged that the nitrification reaction has ended, and if this value is large, it can be judged that the nitrification reaction has not yet ended. it can. When the value of [N-rr] is large and the nitrification reaction must be enhanced, the amount of sludge returned from the sludge distribution tank 20 to the anaerobic tank 1 is increased to increase the MLSS, which is an activated sludge suspended matter. or,
The aeration amount by aeration is increased so that the oxygen consumption amount of the aerobic tank 2 does not exceed the oxygen supply amount.
Nitrification is promoted by adjusting the drive of the blower 6 so that the DO concentration at the outlet does not exceed 2.0 mg / l.

When the nitrification is carried out smoothly, the reflux rate of the nitrification solution from the aerobic tank 2 to the anaerobic tank 1 based on the action of the nitrification solution circulation pump 7 is increased (up to 200% in practice), By increasing the circulation ratio of the liquid, the removal rate of nitrogen can be increased.

The value of [N-rr] becomes extremely small at low load such as at night, and when the removal of organic substances and the nitrification reaction are completely completed and the DO concentration is much higher than 2.0 mg / l. By refluxing the nitrification liquid to the anaerobic tank 1, the DO concentration in the anaerobic tank 1 may be increased, and the denitrification reaction may be hindered, and the nitrogen removal rate may be decreased. In such a case, by reducing the aeration amount in the aerobic tank 2 and reducing the circulation amount of the nitrification solution, or by keeping the MLSS concentration high to increase the consumption amount of dissolved oxygen in the anaerobic tank 1. It is possible to cope with this, and the nitrogen removal rate can be maintained high by implementing both of the above controls.

[0037]

As described above in detail, according to the operation control method of the anaerobic-aerobic activated sludge treatment device of the present invention, the dissolved oxygen concentration meter and the anaerobic tank provided in the anaerobic tank and the aerobic tank are used as indicators. The progress of the nitrification reaction is judged based on the data obtained from the oxygen utilization rate meter installed in the aerobic tank, and based on the judgment results, the concentration of suspended solids in the sludge of the anaerobic tank and the aerobic tank, the dissolved oxygen concentration, and the nitrification liquid. The reflux ratio of is automatically controlled,
It is possible to improve the efficiency of removing organic matters and nitrogen in wastewater. In particular, if the oxygen utilization rate accompanying nitrification is low, it can be judged that the nitrification reaction has ended, and if this value is large, it can be judged that the nitrification reaction has not ended. When enhancing the nitrification reaction, nitrification can be promoted by increasing the activated sludge suspended matter concentration in the anaerobic tank and increasing the aeration amount so that the oxygen consumption amount in the aerobic tank does not exceed the oxygen supply amount. Also, if nitrification is carried out smoothly,
By increasing the circulation ratio of the nitrification liquid from the aerobic tank to the anaerobic tank, the nitrogen removal rate can be increased.

Therefore, according to the present invention, by establishing the operation control method of the anaerobic-aerobic activated sludge treatment device, the great effect that the treatment efficiency and accuracy of wastewater can be enhanced is exhibited.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a basic embodiment of the present invention.

[Explanation of Codes] 1 ... Anaerobic tank, 2 ... Aerobic tank, 4 ... Submersible agitator, 5 ... Air blowing member, 6 ... Blower, 7 ... Nitrification solution circulation pump, 8 ... Return pipe line, 9 ... Final sedimentation site , 11 ... Sludge return pump, 12,
13 ... (dissolved oxygen) concentration meter, 14 ... oxygen utilization rate meter,
15 ... Control circuit, 20 ... Sludge distribution tank, 21 ... Waste water, 22
… Supernatant.

Claims (1)

[Claims] 1. A step of denitrifying wastewater such as sewage with denitrifying bacteria in an anaerobic tank, a step of nitrifying ammoniacal nitrogen with nitrifying bacteria in an aerobic tank, and solid-liquid separation and sedimentation in a settling tank. A part of the sludge is returned to the anaerobic tank and the rest is sent to an excess sludge treatment device for treatment, and the supernatant of the sedimentation tank is discharged as treated water, and part of the nitrification solution in the aerobic tank is anaerobic. In the anaerobic-aerobic activated sludge treatment device including the step of promoting the denitrification reaction by returning to the tank, the concentration of dissolved oxygen is installed in the anaerobic tank and the aerobic tank, and the progress of nitrification in the aerobic tank. An oxygen utilization rate meter for determining the concentration of oxygen is used to detect the concentration of dissolved oxygen and the rate of utilization of oxygen with the progress of anaerobic-aerobic activated sludge treatment by the dissolved oxygen concentration meter and the oxygen utilization rate meter. Judging the progress of the nitrification reaction in the air tank, and Anaerobic-aerobic activity characterized by automatically controlling the concentration of suspended sludge in the air tank and aerobic tank, the dissolved oxygen concentration, and the reflux ratio of the nitrification solution to improve the efficiency of removing organic matters and nitrogen in wastewater. Sludge treatment equipment operation control method.