JPH07275888A - Nitration accelerating method of activated sludge circulation modified method - Google Patents

Abstract

PURPOSE:To enhance the nitration efficiency in an aerobic tank and the denitrification effect in an anaerobic tank in the nitration accelerating method of an activated sludge circulation modified method. CONSTITUTION:In an activated sludge circulation modified method containing a process denitrifying raw water 3 in an anaerobic tank l by denitrifying bacteria, a process performing nitration in an aerobic tank 2 by nitrifying bacteria and a process performing solid-liquid separation in a sedimentation tank 7 to discharge a supernatant soln. as treated water 11, a first pH meter 15 and a measuring device 16 measuring a value wherein the oxygen consumption speed accompanied by nitration reaction is subtracted from the total oxygen consumption speed are arranged to the first stage aerobic tank 2a among a plurality of aerobic tanks. A second pH meter 21 is arranged to the final stage aerobic tank 2d among the aerobic tanks and the nitration speed in the aerobic tank is estimated from the measured pH values of the respective aeration tanks and the oxygen consumption amt. based on nitration reaction and, corresponding to the estimated value, pH control by injecting alkali 25 into the initial and final stage aerobic tanks is executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for promoting nitrification in a system for highly efficiently removing organic matter and nitrogen in wastewater by using a modified anaerobic-aerobic activated sludge circulation method.

[0002]

2. Description of the Related Art Various methods have conventionally been proposed for efficiently removing organic matter in wastewater such as sewage and removing nitrogen and phosphorus which are considered to be the causative agents of eutrophication in closed water areas. . This eutrophication refers to an increase in the concentration of nutrient salts such as N, 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.

Recently, it has been required to increase the removal rate of nitrogen, and it is expected that the regulations on nitrogen will be stricter. Therefore, the number of facilities adopting an advanced treatment process capable of removing this will increase. it is conceivable that.

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 which has been put into practical use as a physicochemical method includes a coagulation precipitation method and a crystallization method, but this method has a drawback in terms of cost and maintenance.

On the other hand, as a biological biological method for simultaneously removing nitrogen and phosphorus, an anaerobic method is a modification of the conventional activated sludge method.
The aerobic activated sludge method is drawing attention. The anaerobic-aerobic activated sludge method is, for example, as shown in FIG. 2, a biological reaction tank is an anaerobic tank 1a in which dissolved oxygen (hereinafter abbreviated as DO) does not exist,
1b and multi-stage aerobic tanks 2a, 2b, 2c where DO exists
And the anaerobic tanks 1a and 1b are used to agitate the inflowing raw water 3 by an agitation mechanism 10 under anoxic conditions to denitrify by denitrifying bacteria in the activated sludge, and then the aerobic tank 2
By supplying air from the blower 5 to the air diffuser 4 arranged inside a, 2b, and 2c, oxidative decomposition of organic matter by activated sludge and nitrification of ammonia by nitrifying bacteria are performed in the presence of oxygen by aeration. Then, the nitrification solution in the last-stage aerobic tank 2c is transferred to the anaerobic tank 1a using the nitrification solution circulation pump 6.
By feeding the anaerobic tanks 1a and 1b, the denitrification effect of the anaerobic tanks 1a and 1b is promoted.

Since the activity of the above nitrifying bacteria decreases as the DO concentration decreases, the DO of the last aerobic tank 2c is measured and D
It is customary that the O controller 12 controls the drive of the blower 5.

The denitrifying bacterium is a bacterium that reduces N0 ₂ -N and N0 ₃ -N to N ₂ and NO ₂ by respiration of nitric acid under anaerobic conditions. Also, phosphorus in raw water is anaerobic tanks 1a and 1b.
It is released inside and is taken in and removed by the activated sludge in the aerobic tanks 2a, 2b and 2c. Reference numeral 7 denotes a final settling basin, and the supernatant of the final settling basin 7 is discharged as treated water 11 after passing through a disinfection tank or the like not shown in the figure, and a part of sludge settled in the final settling basin 7. Is returned to the anaerobic tank 1a by the sludge return pump 8, and other sludge is sent from the excess sludge drawing pump 9 to an excess sludge treatment device (not shown) for treatment.

By using such an anaerobic-aerobic activated sludge treatment method, the same effect as the organic substance removal effect achieved by the normal standard activated sludge method can be obtained, and nitrogen and phosphorus are more effective than the activated sludge method. A high removal rate is achieved.

[0009]

However, in the case of such a conventional activated sludge circulation modification method, it is difficult to establish an efficient operation control method. Particularly, in the aerobic tank, the nitrification efficiency and the anaerobic tank associated therewith are difficult to establish. There is a problem that it is difficult to sufficiently enhance the denitrification effect.

That is, the operation mode in the anaerobic-aerobic activated sludge method can be roughly classified into a denitrification reaction in the anaerobic tanks 1a and 1b and a nitrification reaction in the aerobic tanks 2a, 2b and 2c. The latter, that is, the nitrification reaction, is the rate-determining reaction. In particular, in order to remove nitrogen efficiently by the anaerobic-aerobic activated sludge treatment method, it is required to maintain denitrification in the anaerobic tank and nitrification in the aerobic tank under the optimum operating conditions, and the nitrogen removing step. Is highly affected by the nitrification process, so that the nitrification process must be performed well in order to perform good nitrogen removal.

This nitrification reaction is caused by the nitrifying bacteria as described above. The activity of the nitrifying bacteria is
It is known that it is easily affected by subtle changes such as water temperature. In addition, in order to obtain sufficient aeration time, it is necessary to increase the volume of the biological reaction tank by a factor of 2 to 3 compared with the standard activated sludge method, and under conditions where it is difficult to secure land for urban areas. There is a problem that it is difficult to adopt.

When the nitrification progresses satisfactorily, the quality of the denitrification reaction affects the nitrogen removal rate. Therefore, in order to maintain a high nitrogen removal rate, a good balance between the nitrification reaction and the denitrification reaction should be maintained. Required to do so.

Therefore, the present invention solves the problems of such anaerobic-aerobic activated sludge treatment, estimates the nitrification rate in the aerobic tank, and increases the nitrification rate in the aerobic tank by controlling the pH. Furthermore, it is an object of the present invention to provide a nitrification rate method which is a modified method of operating activated sludge circulation that can enhance the denitrification reaction in an anaerobic tank.

[0014]

In order to achieve the above object, the present invention performs a step of denitrifying raw water with denitrifying bacteria in an anaerobic tank, and nitrifying with nitrifying bacteria in a plurality of aerobic tanks. In the modified activated sludge circulation process including the steps of solid-liquid separation in a settling tank and discharging the supernatant as treated water, the first aerobic tank in the first aerobic tank of the above plurality of aerobic tanks is And a measuring instrument for measuring the value obtained by subtracting the oxygen consumption rate associated with the nitrification reaction from the total oxygen consumption rate, and installing a second pH meter in the final aerobic tank of the multi-stage aerobic tank. The nitrification rate in the aerobic tank is estimated from the measured pH value of each aerobic tank and the oxygen consumption based on the nitrification reaction, and alkali is injected into the aerobic tank at the first and last stages according to the value. Provided is a method for promoting nitrification, which is a modified activated sludge circulation method, in which pH control is performed.

[0015]

[Operation] According to the nitrification accelerating method of the modified activated sludge circulation method, the raw water is denitrified in the anaerobic tank or the anaerobic condition, and the aeration in the aerobic tank or the aerobic condition and the nitrification based on the effect of nitrifying bacteria While being performed, the pH of the sample sampled from the first and last aerobic tanks is measured and the ATU
-Rr meter measures oxygen consumption rate [Nt
-Rr] is measured, the actual nitrification rate associated with the nitrification of activated sludge in the aerobic tank is estimated, and pH control for injecting alkali into each aerobic tank is performed.

When it is necessary to enhance the nitrification reaction, alkali is injected into the first-stage aerobic tank based on pH control to increase the pH value to promote nitrification, while when the nitrification rate increases, the alkali The pH of the aerobic tank at the final stage was stopped by stopping the injection and further consuming the alkalinity accompanying the nitrification reaction.
When the value decreases, the pH is controlled based on the pH control by injecting alkali into the final aerobic tank to raise the pH value.

Particularly, the destabilization of the nitrification reaction is prevented in the entire aerobic tank due to the decrease in the activity of the nitrifying bacteria in the first stage of the aerobic tank, the nitrification reaction in the aerobic tank is promoted, and by extension, anaerobic The effect of improving the nitrogen removal rate in the tank is obtained.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the operation control method of the modified activated sludge circulation method according to the present invention will be described in detail below with reference to the drawings, in which the same components as those of the conventional components are designated by the same reference numerals. . In FIG. 1, 1a and 1b are anaerobic tanks for denitrifying wastewater, and 2a, 2b, 2c and 2d are aerobic tanks having a plurality of stages for performing nitrification. The anaerobic tanks 1a, 1b and aerobic tanks are aerobic. Tank 2a,
The same biological reaction tanks as 2b, 2c and 2d are divided by a partition plate 13 and divided.

The anaerobic tanks 1a, 1b have a stirring mechanism 10,
10, air diffusers 4, 4, 4 and 4 as an air blowing mechanism are arranged in the aerobic tanks 2a, 2b, 2c and 2d, and a blower for supplying air to each of the above diffusers outside. 5 are deployed. 6 is a nitrification solution circulation pump.

The first aerobic tank 2a in the aerobic tanks 2a, 2b, 2c and 2d has a first pH meter 15 and ATU-Rr.
A total 16 is installed, and the [Nt-Rr] value 17 calculated based on the pH value measured by the first pH meter 15 and the value measured by the ATU-Rr meter 16 is used as the control mechanism 1.
8 is input. Then, the pH control 19 of the aerobic tank 2a is performed by the output signal of the control mechanism 18, and the alkali 25 (NaOH) is injected into the aerobic tank 2a by driving the first alkali injection pump 20.

Further, a second pH meter 21 is installed in the last-stage aerobic tank 2d of the aerobic tanks 2a, 2b, 2c, 2d, and the second pH meter 21 measures the pH. The pH value is input to the control mechanism 18. The pH signal 22 of the aerobic tank 2d is implemented by the output signal of the control mechanism 18, and the aerobic tank 2 is driven by driving the second alkali injection pump 23.
Alkali 25 (NaOH) is injected into d.

Reference numeral 7 is a final sedimentation pond, and this final sedimentation pond 7
A stirring mechanism 14 is provided in the. Reference numeral 8 is a sludge return pump for returning a part of the sludge to the anaerobic tank 1a, and reference numeral 9 is a surplus sludge drawing pump for sending another sludge to a surplus sludge treatment device (not shown). A timer is usually attached to the excess sludge removal pump, and the excess sludge removal pump is set to perform a removal operation of the excess sludge at every predetermined time.

In this example, from the measured values of the nitrification rate at pH 7 and pH 8 in the preliminary experiment based on the modified activated sludge circulation method, the measured value at pH 7 was 0.68 (mg-N / g.
It was 0.93 at pH 8 while it was ss · hr).
(Mg-N / g · ss · hr), and it is based on the finding that controlling the pH of the liquid to be treated to pH 8 accelerates the nitrification rate. Therefore, as described above, the first and second pH meters 15 and 21 are installed in the first-stage aerobic tank 2a and the last-stage aerobic tank 2d, respectively, to perform pH control in the aerobic tank. It is the main focus.

The basic operation of such a device is as follows. As shown in FIG. 1, first, raw water 3 as waste flows into the anaerobic tanks 1a and 1b, and the stirring mechanism 10,
Based on the stirring action of 10 and the action of denitrifying bacteria, NO ₃ −
Reduction of N, NO ₂ —N ions to N ₂ , that is, denitrification, is performed. Next, raw water 3 flows into aerobic tanks 2a, 2b, 2c, 2d, and air diffuser 4 is driven as blower 5 is driven. , _{4, 4, 4} are aerated by aeration, and based on the action of nitrifying bacteria, ammoniacal nitrogen NH ₄ -N is converted to NO ₂ -N or N _2.
Oxidation to O ₃ -N, that is, nitrification is performed.

[0025] Thus nitrification reaction is oxidation of ammonium nitrogen by nitrifying bacteria, nitrification rate can be expressed as an increase rate of decreasing speed or NO _X -N ammoniacal nitrogen _{(NO 2 -N + NO 3 -N} ) .

The other denitrification reaction can be expressed as 2NO ₃ ⁻ +5 (H ₂ ) → N ₂ ↑ + 2OH ⁻ + 2H ₂ O.

During the above operation, the aerobic tank 2 in the first and last stages
The pH (hydrogen ion concentration) of the sample sampled from a and 2d is measured by the first pH meter 15 and the second pH meter 21, and the ATU-Rr meter 16 measures the oxygen consumption rate [Nt- Rr] 17 is measured, and the pH control 19 of the aerobic tank 2a and the pH control 22 of the aerobic tank 2d are performed based on the measured pH values and the [Nt-Rr] value.

Further, the nitrification solution in the aerobic tank 2d is fed into the anaerobic tank 1a by using the nitrification solution circulation pump 6, whereby the denitrification effect in the anaerobic tank is promoted. Particularly, phosphorus in the wastewater is released in the anaerobic tank, and is taken into and removed by the activated sludge in the aerobic tank.

A part of the sludge settled in the final settling basin 7 is returned to the anaerobic tank 1a by the sludge return pump 8, and the other sludge is sent to the excess sludge treatment device by the excess sludge drawing pump 9 for treatment. The supernatant of the final sedimentation tank 7 is treated water 1
It is discharged after passing through a disinfection tank (not shown) as No. 1.

The ATU-Rr meter 16 is used to monitor the progress of the nitrification reaction in the aerobic tank 2. That is, oxygen utilization rate
respiration (hereinafter abbreviated as Rr) includes the amount of oxygen consumed during oxidative decomposition of organic matter, the amount of oxygen consumed for endogenous respiration of activated sludge, and the amount of oxygen consumed for nitrification reaction.

This value is expressed as a respiratory rate due to removal of organic substances and endogenous respiration, that is, a value obtained by subtracting the oxygen consumption rate associated with the nitrification reaction from the total oxygen consumption rate. Therefore, the progress of the nitrification reaction is based on the difference (ATU-Rr) between Rr and Rr measured by adding N-allylthiourea (chemical formula C ₄ H ₈ N ₂ S, hereinafter abbreviated as ATU), which is a nitrification inhibitor. You can ask.

If the above difference is [Nt-Rr], then [Nt-Rr] = [Rr]-[ATU-Rr] ...
(1) That is, [Nt-Rr] is the oxygen consumption rate associated with nitrification. If this value is small, it can be determined that the nitrification reaction has ended, and if it is large, the nitrification reaction has not ended.

Since the above [Nt-Rr] represents the oxygen consumption amount based on the nitrification reaction, it is possible to estimate the nitrification rate in the aerobic tank 2a from this value.

The values measured by these measuring devices are input to the control mechanism 18, the ideal nitrification rate is calculated from the volume of the aerobic tank and the hydraulic retention time, and the activated sludge of the aerobic tank 2a is calculated. The actual nitrification rate of activated sludge is estimated from [Nt-Rr] 17 and pH value accompanying nitrification, and when the value of [Nt-Rr] in the equation (1) is large and the nitrification reaction must be increased, Based on the control 19, the first alkali injection pump 20 is operated to inject the alkali 25, thereby increasing the pH value of the aerobic tank 2a at the first stage to promote nitrification, and at the same time, the pH is increased with the progress of nitrification. When the value has decreased, the alkali 25 is further injected.

Further, when the nitrification rate becomes high, the aerobic tank 2
When the injection of the alkali 25 into a is stopped and the pH value of the final aerobic tank 2d decreases due to alkalinity consumption accompanying the nitrification reaction, the second alkali injection pump 23 is operated based on the pH control 22. The pH value of the aerobic tank 2d is increased by injecting the alkali 25 into the final aerobic tank 2d. Particularly, since the pH value of the discharged water is regulated to be in the range of 5.8 to 8.6, when the pH value falls below 5.8, the alkaline 25 is immediately added to the final aerobic tank 2d. It must be injected to raise the pH value.

Aerobic tank 2 at high water temperature or by adding chemicals
In order to adjust the nitrification rate that has been excessively promoted with respect to the inflowing ammoniacal nitrogen into a, it is possible to adjust the air flow rate of the blower 5 as appropriate to adjust to the ideal nitrification rate. or,
The amount of the nitrification solution returned from the aerobic tank 2d to the anaerobic tank 1a based on the action of the nitrification solution circulation pump 6 is increased (2 in practical use).
(Up to 00%), the nitrogen removal rate can be increased by increasing the liquid circulation ratio.

Usually, in the inflow water such as sewage flowing into the activated sludge treatment device, most of the ammonia nitrogen passes through the anaerobic tank in the same form. Therefore, nitrification rate control due to a decrease in ammonia nitrogen does not occur in the most upstream part of the aerobic tank in which the Rr meter is installed. This [Nt-Rr]
Has a constant water temperature and 3 (mg / l) ammoniacal nitrogen
It is known that if the above exists, it becomes constant. Therefore, install the ATU-Rr meter as described above [Nt-Rr].
The change in nitrification activity can be directly detected by measuring.

In the present embodiment, particularly the aerobic tanks 2a, 2b, 2
Instability of nitrification reaction is prevented in the aerobic tank as a whole due to the decrease in the activity of nitrifying bacteria in the first-stage aerobic tank 2a portion of c, 2d, and in the aerobic tanks 2a, 2b, 2c, 2d The effect of promoting the nitrification reaction and improving the nitrogen removal rate in the anaerobic tanks 1a and 1b can be obtained.

[0039]

As described in detail above, according to the method for promoting nitrification in the modified activated sludge circulation method according to the present invention,
Raw water is denitrified in the anaerobic tank, and aeration in the aerobic tank and nitrification based on the action of nitrifying bacteria are performed.On the other hand, the pH of the samples sampled from the first and last aerobic tanks and oxygen involved in the nitrification reaction. When the consumption rate is measured, the actual nitrification rate of the activated sludge in the aerobic tank is estimated based on this, and the pH of the aerobic tank is controlled to enhance the nitrification reaction. While injecting alkali to increase the pH value, when the nitrification rate becomes high, the injection of alkali is stopped and when the pH value of the final aerobic tank decreases due to alkalinity consumption accompanying the nitrification reaction, PH control is carried out by injecting alkali into the aerobic tank to raise the pH value. Especially, the nitrification reaction is unstable throughout the year due to a decrease in the activity of nitrifying bacteria in the first stage of the aerobic tank. Aspiration Nitrification reaction in is promoted.

Since the nitrification reaction is stabilized, there is no need to increase the volume of the biological reaction tank as compared with the standard activated sludge method, and it can be used under conditions where it is difficult to secure land for urban areas. There is an advantage to In particular, the amount of electric power and the amount of chemicals used for nitrification can be reduced, which is advantageous in terms of cost.

In order to remove nitrogen efficiently by the anaerobic-aerobic activated sludge treatment method, it is required to maintain denitrification in the anaerobic tank and nitrification in the aerobic tank under optimum operating conditions. Since the nitrification reaction is stabilized in this example, the nitrogen removal rate in the anaerobic tank can be improved accordingly.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of a nitrification promoting method of a modified activated sludge circulation method according to the present embodiment.

FIG. 2 is a schematic diagram showing an example of conventional anaerobic-aerobic activated sludge treatment.

[Explanation of symbols]

 1a, 1b ... Anaerobic tank 2a, 2b, 2c, 2d ... Aerobic tank 4 ... Diffuser pipe 5 ... Blower 6 ... Nitrification liquid circulation pump 7 ... Final sedimentation tank 8 ... Sludge return pump 9 ... Excess sludge extraction pump 13 ... Partition plate 15 ... 1st pH meter 16 ... ATU-Rr meter 18 ... Control mechanism 19,22 ... pH control 20 ... 1st alkali injection pump 21 ... 2nd pH meter 23 ... 2nd alkali injection pump

Claims (1)

[Claims] 1. A step of denitrifying raw water with denitrifying bacteria in an anaerobic tank, a step of nitrifying with nitrifying bacteria in a plurality of aerobic tanks, and solid-liquid separation in a precipitation tank to treat a supernatant. In the modified activated sludge circulation method treatment including the step of discharging as water, the oxygen consumption rate accompanying the nitrification reaction is calculated from the first pH meter and the total oxygen consumption rate in the first-stage aerobic tank of the above-mentioned plurality of aerobic tanks. Is installed and a second pH meter is installed in the final aerobic tank of the multi-stage aerobic tank, and the measured pH value and nitrification reaction of each aerobic tank Based on oxygen consumption based on oxygen consumption, the nitrification rate in the aerobic tank is estimated, and the pH is controlled by injecting alkali into the aerobic tank at the first and last stages according to the value, and the modified sludge circulation method is characterized. Method for promoting nitrification in.