JPH0246279B2 - CHITSUSOGANJUHAISUISHORISOCHI - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <<Industrial Application Field>> The present invention relates to an apparatus for nitrifying and denitrifying human waste and other nitrogen-containing wastewater.

<<Prior art>> Conventionally, as a means of treating nitrogen-containing wastewater, there is a treatment device using an intermittent injection method (Japanese Patent Application Laid-Open No. 1982-
No. 152598).

In other words, this treatment equipment has a means for intermittently introducing nitrogen-containing wastewater (hereinafter referred to as "raw water") into a single treatment tank, a means for discharging treated water that has been subjected to nitrification and denitrification, an aeration means, and an agitation means. It is set up and configured.

To treat raw water with this treatment device, raw water is put into a treatment tank, aerated using an aeration means for a predetermined period of time to simultaneously advance nitrification and denitrification reactions, and then the raw water is stirred and mixed using a stirring means. Anaerobic treatment is performed to denitrify the water, and the nitrification-denitrification treated water is discharged to the outside of the treatment tank by a discharge means.

<<Problems to be solved by the invention>> However, in the above conventional processing device,
In order to make the raw water have the quality of treated water as initially designed in a single treatment process consisting of aeration and anaerobic treatment processes, there is the inconvenience that the amount of air supplied in the aeration process, that is, the amount of air blown, must be strictly controlled. It was hot.

This is because if the amount of air blown is less than the specified amount, nitrification will be insufficient and ammonia nitrogen will remain, and if it is too much, the dissolved oxygen concentration (hereinafter referred to as "DO") value will increase and denitrification will not occur. This is because the amount of foaming caused by aeration increases, resulting in an increase in the amount of antifoaming agent injected, and the power consumption of the blower is wasted due to the over-aeration.

By the way, the air flow rate control in the above aeration process is
If you try to use a DO meter, the DO value will be 0 until the nitrification of the raw water is almost complete, so control using this is impossible.

It is also possible to control the amount of air flow using an oxidation-reduction potential (ORP) meter, but this cannot be applied due to a sensitivity problem.

Therefore, in conventional equipment, the aeration (process) time, anaerobic (process) time, and aeration air flow rate during one treatment process are determined in advance based on the average quality of raw water, and the operation is performed accordingly. It's getting old.

However, since the quality of raw water is not uniform and varies, when aeration treatment is performed at a predetermined amount of air each time for a specified period of time, the above-mentioned excess or deficiency of aeration will occur, and the initial treated water quality will deteriorate. The problem was that I couldn't get it.

<Object of the Invention> The present invention has been made to solve the above problems, and its purpose is to correct the amount of air supplied in the aeration process for each treatment process so that there is no excess or deficiency. An object of the present invention is to provide a nitrogen-containing wastewater treatment device capable of performing aeration treatment.

<Means for Solving the Problems> In order to achieve the above object, the present invention includes a means for intermittently introducing nitrogen-containing wastewater, a means for discharging treated water subjected to nitrification and denitrification, and an aeration means. a treatment tank; an air supply means for supplying aeration air to the aeration means; an air supply amount detection means for detecting the supply amount of the supplied air; and a dissolved oxygen detector for detecting the dissolved oxygen concentration in the treatment tank. Inputting the concentration meter, the detection signal of the air supply amount detection means and the dissolved oxygen concentration meter, and calculating the air supply amount so that the aeration time in the next treatment step approximates a preset standard aeration time, and arithmetic control means for controlling the air supply means so as to achieve the calculated air supply amount.

<<Operation>> The present invention has the above configuration, and the calculation control means corrects the air supply amount for the next aeration so that the next aeration time becomes the standard aeration time.

<<Description of Examples>> This example will be described below based on the illustrated example.

FIG. 1 is a block diagram schematically showing a nitrogen-containing wastewater treatment apparatus according to the present invention. In the figure, 1 is a vertically long treatment tank, and an aerator 2 is provided at the bottom of the treatment tank.

The diffuser 2 is connected to an air supply means 3 having a blower driven by a motor whose rotation speed is adjustable, and a flow meter 5 as an air supply amount detection means is provided in the communication passage 4. ing.

In addition, 6 in the figure has a sensor in the processing tank 1.
It is a DO meter, and its detection signal is input to the calculation section 7a of the calculation control means 7 together with the detection signal of the airflow meter 5.

The calculation control means 7 is provided with a control section 7b for adjusting the amount of air supplied by the air supply means 3 based on the calculation result of the calculation section 7a. This control section 7b includes a conversion section 8 for adjusting the rotation speed of the motor of the air supply means 3 by voltage/frequency control.
It is designed to send control signals to the

Next, in order to facilitate understanding of the operation of this embodiment, the nitrogen removal effect when human waste is used as raw water will be explained using FIG. 2.

First, a predetermined amount of raw water and return sludge are put into the treatment tank 1, and the air supply means is driven to aerate air from the diffuser 2. When the aeration process begins, the DO value initially indicates that oxygen is consumed due to nitrification. Therefore, the value of DO total 6 shows 0 (see the upper row of Figure 2), but as the aeration process continues, the nitrification of ammonia nitrogen progresses.
Start detecting DO. Furthermore, if you continue aeration, the DO value will gradually rise, so stop the aeration process when the value is in the range of 0.4 to 1.2 mg/, for example 0.6 mg/, and add methanol as necessary to keep it constant. When anaerobic treatment is carried out while stirring the mixed liquid in the treatment tank 1 while keeping it in an anaerobic state for a while, nitrous acid or nitric acid is reduced to _N2 gas by the action of denitrifying bacteria, thereby completing one treatment step.

In the above aeration process, as is clear from the lower part of Figure 2, not only the nitrification reaction but also the denitrification reaction is progressing. That is, in the treatment tank 1, both nitrifying bacteria and denitrifying bacteria are active. In order to allow nitrification and denitrification to proceed simultaneously during the aeration process, it is necessary to aerate at a predetermined air flow rate based on the quality of the raw water, etc. This is because excessive aeration inhibits denitrification, and insufficient aeration results in insufficient nitrification.

The operation of this embodiment will be described below with reference to the graph shown in FIG. 3 showing the change in DO over time.

Now, when a predetermined amount of human waste and a predetermined amount of return sludge, which are raw water, are put into treatment tank 1 and one treatment process is to be processed in three hours, based on the average quality of the raw water, a predetermined air flow rate is required. When aerated for 135 minutes, the DO value at that time became 0.6 mg/, and after that, it was kept in an anaerobic state for 45 minutes, and the mixed liquid in the treatment tank 1 was stirred for 45 minutes using a stirring means (not shown) for anaerobic treatment.
It has been experimentally determined in advance that treated water of a predetermined quality can be obtained. For this reason, each of the above-mentioned times is set in a programmable controller (not shown) by using the processing times of these processing steps as standard times.

Therefore, the programmable controller controls the air supply means 3 to alternately ventilate and pause at the above-mentioned times, and also controls supply of raw water, return sludge, discharge of treated water, etc.

However, the quality of raw water is not necessarily uniform in each treatment process due to factors such as the proportion of septic tank sludge mixed in. Although this difference does not show a large difference in successive processing steps, it can become large in separate processing steps.

For example, if aeration is performed with the same amount of air each time, the third
As shown in A of the figure, nitrification may be completed 135 minutes before the standard aeration time and the DO value may exceed the specified value, and conversely, as shown in B, nitrification may not be sufficient even after the standard aeration time. may occur.

Therefore, as mentioned in A above, before the end of the standard aeration time, a DO value higher than the predetermined value, for example 0.6 mg/
When this value is reached, the aeration process is normally shifted to the anaerobic process. In this case, anaerobic treatment is performed for a longer time than the predetermined standard anaerobic time. However, if the DO value reaches the predetermined value significantly earlier than the standard aeration time, it is preferable to continue aeration without stopping the aeration until it reaches the predetermined time before the standard aeration time. This ensures a minimum aeration time.

On the other hand, as shown in B above, the standard aeration time has passed,
And even if the specified time has elapsed from the standard aeration time, the specified
If the DO value is not reached, in order to ensure the shortest denitrification time, after a predetermined time has elapsed from the standard time, the air supply means 3 is forcibly stopped and the process shifts to the anaerobic process.

In this way, it is preferable to set an aeration adjustment time that ensures the shortest aeration process or anaerobic process, that is, a maximum allowable anaerobic time and a minimum allowable anaerobic time, before and after the standard aeration time. The aeration adjustment time varies depending on the raw water quality, the time required for the whole process, etc., but can be set, for example, to 10 to 15 minutes before and after the standard aeration time.

By the way, above A shows a tendency for overaeration in which nitrification progresses quickly due to the large amount of air blown due to the raw water quality.
In addition, B shows a tendency toward insufficient nitrification due to insufficient aeration.

For this reason, in the arithmetic control means 7 of this embodiment, if the current treatment step shows the above-mentioned tendency (a), the amount of air blown in the next treatment step is reduced and the next aeration time is set to the standard aeration time. Control as follows.

On the other hand, if there is insufficient aeration in the current treatment step as in (B) above, the amount of air blown in the next treatment step is increased and the next aeration time is controlled to be the standard aeration time.

The controlled air flow rate, that is, the air flow rate in the next processing step, can be determined using the following formula.

Q(i)=Q(i-1)+Q(i-1) ×(ΔT _STD −ΔT(i−1)/ΔT _STD ) ×(|ΔT _STD −ΔT(i−1)|/ΔT _STD )〓 Q(i): Next air volume Q(i-1): Current air volume ΔT _STD : Standard setting anaerobic time (1 treatment process time - standard aeration time) ΔT(i-1): Current actual anaerobic time ( (1 treatment process time - actual aeration time) α: correction coefficient Therefore, the calculation section 7a of the calculation control means 7 calculates the above equation.

In other words, once raw water has been input into the treatment tank 1, aeration has started, and one treatment process has started, the elapsed time from that point is measured based on the internal clock signal, and the DO value of the DO total 6 is determined as the predetermined value. The time it takes to reach the value is measured. Furthermore, the actual anaerobic time T(i-1) in the current treatment process is calculated by subtracting that time from the one treatment process time. Further, since the air flow rate Q(i-1) for the current processing step from the airflow meter 5 is input to the calculation unit 7a, the calculation unit 7a calculates the airflow amount Q(i-1) for the next processing step from the above equation. ) can be calculated.

Based on the calculated air blowing amount Q(i) for the next processing step, a control signal is sent from the control section 7b to the conversion section 8, and the rotation speed of the motor (not shown) of the air supply means 3 is controlled.

In addition, outside the certain range where the standard aeration time is reached, DO
When the value reaches a certain value, for example, in the example shown in Figure 3, when the maximum allowable anaerobic treatment time T _MAX of 48 minutes is exceeded, that is, when the aeration time becomes shorter than 132 minutes, the Actual aeration time ΔT
(i-1) uses the maximum allowable anaerobic time T _MAX .

In addition, the minimum allowable anaerobic time T _MIN of the anaerobic treatment time
If the DO value reaches the predetermined value later, the anaerobic treatment process will be forcibly started when the minimum allowable anaerobic time T _MIN (36 minutes in the example in Figure 3) is reached, that is, 144 minutes after the start of aeration. However, the minimum allowable anaerobic time T _MIN is used as the actual anaerobic time ΔT (i-1) at this time.

Note that the correction coefficient α in the above calculation formula is a value determined by the raw water quality, the size of the treatment tank, the oxygen dissolution efficiency, etc., and is specifically determined experimentally for each wastewater treatment device. However, normally α is
It is set in the range of 0.1 to 2.

However, with the device of this embodiment, the standard aeration time was 130
When the treatment process was performed four times in a row with the standard anaerobic time set to 50 minutes, the average aeration time was
The time was 130.7 minutes, which did not exceed the allowable range of anaerobic time, and the aeration process could always be performed in a time close to the standard aeration time.

As described above, according to this embodiment, the air flow rate is set by correcting it based on the previous air flow rate and the anaerobic process time. It can be divided into process and anaerobic process times.

Therefore, in the aeration process, nitrification and denitrification proceed simultaneously as initially, and in the denitrification process, denitrification also proceeds as initially, so that treated water as good as initially can be obtained.

In the above-mentioned embodiment, an aerator is placed at the bottom of the processing tank and aeration is performed using a blower. A circulating aeration method may also be used in which air is supplied by an ejector midway. In this case, the rotational speed of the circulation pump is used as a means for detecting the air supply amount. That is, since the amount of air supplied by suction to the circulating fluid is approximately proportional to the flow rate of the circulating fluid, the amount of air supplied can be determined by detecting the rotational speed of the circulation pump. Therefore, in the case of the circulation aeration method, the rotation speed of the circulation pump is used as the air supply amount detection means, and the value is input to the arithmetic control section to control the rotation speed of the circulation pump.

In addition, the aeration may be performed using a gas with a high oxygen concentration, instead of using air, so-called oxygen aeration. Therefore, when referring to air in the present invention, it must be understood that it also includes gases with a high oxygen concentration.

<<Effects>> In the present invention, the amount of air blown in the aeration process is determined by correcting it based on the previous amount of air blown and the anaerobic process time or the aeration time, so the times of the aeration process and the anaerobic process can be brought closer to the initial standard time.

Therefore, the nitrification reaction and the denitrification reaction proceed efficiently and simultaneously in the aeration step, and the denitrification reaction proceeds efficiently in the anaerobic step, resulting in the effect that good treated water can be obtained.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the configuration of the nitrogen-containing wastewater treatment device according to the present invention, Figure 2 is an explanatory diagram showing changes in DO and nitrogen concentration in the treatment tank in the intermittent feeding method, and Figure 3 is a diagram showing changes in DO and nitrogen concentration in the treatment tank in the intermittent feeding method. FIG. 3 is an explanatory diagram showing changes in DO over time. 1... Processing tank, 3... Air supply means, 5... Air flow meter, 6... DO meter (dissolved oxygen concentration meter), 7...
Arithmetic control means.

Claims (1)

[Scope of Claims] 1. A treatment tank having means for intermittently introducing nitrogen-containing wastewater, means for discharging nitrified and denitrified treated water, and aeration means, and supplying aeration air to the aeration means. Air supply means; Air supply amount detection means for detecting the supply amount of the supplied air; Dissolved oxygen concentration meter for detecting the dissolved oxygen concentration in the processing tank; The air supply amount detection means and the dissolved oxygen concentration. The air supply means calculates the air supply amount so that the aeration time in the next treatment process approximates the preset standard aeration time, and the air supply means A nitrogen-containing wastewater treatment device comprising: arithmetic control means for controlling; and a nitrogen-containing wastewater treatment device.