JP2001079583A - Excess sludge control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably remove the organic matter of effluent by controlling an excess sludge pump according to the preset amount of the amount of excess sludge and controlling the excess sludge so as to increase the same in a time zone where the amount of inflow water is little in an activated sludge process for biologically treating municipal sewage, etc. SOLUTION: The inflow sewage 10 is subjected to settlement and removal of bulky dust, sand, etc., in an initial settling basin 15 and is then introduced to an aeration tank 20 where the sewage is agitated and mixed with the activated sludge withdrawn from a final settling basin 30 by a return sludge pump 60. The liquid mixture composed of the activated sludge and the sewage is introduced to the final settling basin 30 where the activated sludge is gravity settled. The return rate of the amount of the return sludge is set 300 and the amount of the return sludge is computed 310 from the product of the inflow sewage flow rate measured by a flow meter 201 and the return rate. An excess sludge pump 90 is driven at the previously stored withdrawal start time by an excess sludge management means 400 and at this time, the preset amount of the excess sludge is so controlled as to be increased in the time zone when the amount of the inflow sewage is little.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for biologically treating municipal sewage, industrial effluent, or tap water raw water, and more particularly to controlling the amount of excess sludge to stably reduce pollutants in influent water. The present invention relates to a method for controlling excess sludge that can be removed.

[0002]

2. Description of the Related Art In an activated sludge process at a sewage treatment plant, microorganisms called activated sludge take up and remove pollutants such as organic matter from inflowing sewage, and sediment the microorganisms in a sedimentation basin to discharge the supernatant. Organic matter has been removed by oxidative decomposition with dissolved oxygen (DO) and consumption as an organic source for the growth of microorganisms. The activated sludge is withdrawn from the final sedimentation basin and supplied to the aeration tank as return sludge.
On the other hand, in order to discharge the microorganisms grown in the aeration tank to the outside of the system, a part of the activated sludge is drawn out of the final sedimentation basin as surplus sludge outside the process. Unless the balance between organic matter and microorganisms in the aeration tank is properly controlled by the amount of returned sludge, the amount of air sent, and the amount of excess sludge, stable effluent quality cannot be obtained. In particular, it is important that the organic matter and the activated sludge in the aeration tank are maintained at an appropriate ratio. However, the reliability of the sludge densitometer is low, and the measurement of the organic matter concentration relies on manual analysis, so that the ratio of organic matter to activated sludge cannot be automatically controlled. A method has been proposed in which both the sludge amount and concentration of returned sludge are measured to control the amount of sludge solids flowing into the aeration tank, but this is not feasible at present because the concentration measurement means is not reliable. . Therefore, the control of the amount of returned sludge and the amount of excess sludge in the sewage treatment plant are operated based on highly reliable flow measurement values.

[0003] The amount of sewage flowing into a sewage treatment plant depends on human life and natural phenomena, and there is difficulty in operation in that it cannot be controlled artificially. Usually, the amount of returned sludge is controlled so as to have a constant ratio to the amount of inflow sewage. The ratio of the amount of returned sludge to the amount of inflow sewage is called the return rate. Since the flow rate and the water quality of the inflowing sewage depend on human life patterns and show large fluctuations in a 24-hour cycle, the return sludge amount also greatly changes in proportion to the inflowing sewage amount when the return rate constant control is performed. On the other hand, since the returned sludge is once settled in the final sedimentation basin and then withdrawn, the concentration of the returned sludge depends on the structure of the final sedimentation basin, the scraping device, the drawing device and the like, and does not show a constant value.

The amount of surplus sludge is generally about 1% of the amount of inflow sewage. As a surplus sludge amount control method, a method of intermittently withdrawing a constant withdrawal amount (preset amount) using a timer or the like is widely used.

[0005]

It is desirable to keep the activated sludge concentration (MLSS) in the aeration tank as stable as possible. This is because fluctuations in MLSS disrupt the balance between organic matter and microorganisms, destabilizing organic matter removal performance and deteriorating treated water quality. In addition, the amount of dissolved oxygen required for respiration of living organisms also fluctuates due to fluctuations in MLSS, which complicates the control of the amount of air supply to always maintain appropriate dissolved oxygen, and requires maintenance of air supply equipment. The cost increases. Therefore, it is very important in a sewage treatment plant to suppress extreme rise and fall and maintain as stable as possible, even if MLSS cannot be controlled to be constant.

The MLSS can be adjusted to some extent by adjusting the amount of returned sludge and the amount of excess sludge. Under the condition of constant return rate control that is now common, the only option is to control the MLSS by controlling the amount of excess sludge. To adjust the amount of excess sludge so that the MLSS is maintained at a constant level, grasp the amount of returned sludge and the concentration of returned sludge, increase the amount of excess sludge when the concentration of returned sludge is high, and reduce the amount of excess sludge when the concentration of sludge is low. And the amount of sludge returned to the aeration tank must be adjusted. Specifically, the present invention is to appropriately set the preset amount of the excess sludge and the extraction time timer based on the returned sludge concentration. Conventionally, the preset amount of the excess sludge amount and the setting of the timer are empirically determined.
For example, there is a method in which the total amount of excess sludge generated in one day is assumed, the total amount is divided into 24, the preset amount is set, and the timer is set to one hour interval. To cope with the dynamic fluctuation of MLSS, the fluctuation of returned sludge concentration must be reflected in the control of excess sludge, but the automatic measurement value of returned sludge concentration is poor in reliability, and the frequency of once a day is calculated by hand analysis. Control is difficult under the current situation where measurement can only be performed by a computer.

As described above, in the operation of the activated sludge process, it is necessary to appropriately control the preset amount and the timer of the excess sludge amount by reflecting the returned sludge concentration. The fact is that it is operated in Even better, MLSS is based on automated measurements.
No control is performed to stabilize the fluctuations of.

The present invention has been made in view of the above-mentioned prior art, and has as its object to predict MLSS in an aeration tank by predicting return sludge concentration using a reliable flow measurement value. An object of the present invention is to provide a surplus sludge amount control method capable of stabilizing and removing organic matter of discharged water stably.

[0009]

In order to achieve the above object, the present invention is directed to a surplus sludge managing means for managing a preset amount of surplus sludge and a withdrawal time, and a means for controlling a surplus sludge pump in accordance with the managing means. Be composed.

Further, it may be constituted by a means for measuring the amount of returned sludge, a means for managing a preset amount of excess sludge and a withdrawal time, and a means for controlling the excess sludge pump according to the management means.

Further, there is provided a means for measuring the amount of inflowed sewage and a means for carrying out constant return rate control. The means comprises a means for managing a preset amount of excess sludge and a removal time, and a means for controlling the excess sludge pump in accordance with the management means. You may.

The present inventors faced the problem that the treated water quality was not stable due to rapid change of the MLSS in the sewage treatment plant where the daily fluctuation of the inflow sewage flow rate was large. This is due to the phenomenon that the concentration of the extracted sludge increases when the amount of the sludge extracted from the wastewater is small. Furthermore, the activated sludge that has flowed in is settled by gravity,
In the case of a sedimentation basin with a structure that can be pulled up by pulling, the sludge concentration increases when the extraction amount is small, and the sludge concentration decreases when the extraction amount is large, based on numerical analysis of the sedimentation tank model and experimental data. The return sludge concentration was extremely high during the period when the return sludge flow rate was extremely small, and it was found that the MLSS of the aeration tank also became high due to the effect, leading to the present invention. In other words, the amount of returned sludge extracted from the sedimentation basin is measured, and if the amount of excess sludge is extracted during the period when the amount of returned sludge is small, MLSS
MLSS fluctuation can be kept small.

A preset amount setting means and a time setting means set a surplus sludge withdrawal schedule in the surplus sludge management means so as to increase the surplus sludge during a time period in which the amount of returned sludge decreases. When the set time comes, the surplus sludge management means transmits a pull-out start command and a surplus sludge preset amount to the surplus sludge pump control device. The surplus sludge pump control device starts the surplus sludge pump, stops the surplus sludge pump after extracting a predetermined amount of the sludge, and then stops the surplus sludge pump.

The excess sludge removal schedule may be set in advance, or may be automatically set from the measured value of the returned sludge flow rate.

[0015] When the return sludge amount control is the inflow sewage flow rate ratio control, a schedule for extracting the excess sludge amount from the inflow sewage flow rate may be automatically set.

As a method of increasing or decreasing the amount of excess sludge withdrawn, the preset amount of excess sludge may be changed, or the frequency of withdrawal of the preset amount may be increased under certain conditions.

[0017]

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

FIG. 1 shows an example of application to a sewage treatment plant including a first settling tank, an aeration tank, and a final settling tank. 10 is an inflow sewage, 15 is a first settling tank, 20 is an aeration tank, 30 is a final settling tank, 60 is a return sludge pump, 90 is an excess sludge pump, 110 is a blower for blowing air, and 201 is a flow meter. The inflow sewage 10 discharged from homes and factories first settles and removes foreign matters such as coarse dust and sand in the sedimentation basin 15. The sewage that first flows out of the sedimentation basin 15 is guided to the aeration tank 20. Returned sludge, which is a group of microorganisms called activated sludge drawn out from the final sedimentation tank 30 by the returned sludge pump 60, is supplied to the aeration tank 20 through a sludge return pipe 70.

The inflow sewage and the returned sludge are stirred and mixed in the aeration tank 20. An air diffuser 40 is provided at the bottom of the aeration tank 20, and a blower 110 is provided.
From the air through the air pipe 130
The air is diffused into the aeration tank 20 by 0, agitating the mixed liquid composed of sewage and activated sludge in the aeration tank 20 and supplying oxygen. The dissolved oxygen dissolved in the aeration tank 20 is measured by a dissolved oxygen meter 202.
It is measured by. Returned sludge, that is, activated sludge, is a lump (floc) having a particle size of about 0.1 to 1.0 mm in which microorganisms are aggregated.
Contains dozens of microorganisms. The pollutants of the mixed liquid in the aeration tank 20 are treated by activated sludge activated by oxygen supply. For example, activated sludge adsorbs organic matter, absorbs dissolved oxygen from the supplied air, and oxidizes and decomposes the organic matter to carbon dioxide and water. In addition, ammonia nitrogen (NH4-N) is oxidized to nitrate (NO3-N) or nitrite nitrogen (NO2-N). In addition, these organic substances,
Some of the pollutants such as ammonia nitrogen are also used for growing activated sludge. The mixture of the activated sludge and the sewage is guided to the final sedimentation basin 30, where the activated sludge settles by gravity. The supernatant of the final sedimentation basin 30 is usually subjected to chlorine sterilization treatment and then discharged into a river or sea. On the other hand, high-concentration activated sludge settled in the final sedimentation basin 30 is collected at the bottom of the entrance of the final sedimentation basin by the scraper 31, and is pulled out by the return sludge pump 60 or the excess sludge pump 90. Most of the extracted sludge is returned to the aeration tank 20 as return sludge by the sludge return pump 60, and a part of the activated sludge corresponding to the microbial growth is discharged from the sludge discharge pipe 80 as excess sludge by the excess sludge pump 90 outside the system. And treated through sludge treatment processes such as dehydration and incineration. In this activated sludge process, the effluent from the final sedimentation basin 30 is intended to have a water quality that does not consume dissolved oxygen in the effluent water area and does not cause pollution. It is important to remove the material.

The return rate setting means 300 sets the ratio of the amount of returned sludge to the amount of inflow sewage (return rate). The returned sludge amount calculating means 310 calculates the returned sludge amount from the product of the inflow sewage flow rate measured by the flow meter 200 and the return rate, for example. The returned sludge pump control device 320 is provided with the returned sludge amount calculating means 31.
The number and the number of rotations of the returned sludge pump 60 are controlled so that the returned sludge amount output from 0 is withdrawn from the final sedimentation basin 30. The ratio between the amount of sewage flowing into the aeration tank 20 and the amount of returned sludge is constantly controlled to the set return rate.

The surplus sludge management means 400 stores a surplus sludge withdrawal start time and a withdrawal amount (preset amount) as a surplus sludge withdrawal schedule. The time setting unit 401 can set the surplus sludge withdrawal start time and the preset amount setting unit 402 can set the preset amount corresponding to the withdrawal start time with the surplus sludge management unit 400. The surplus sludge management means 400 sends a start command of the surplus sludge pump 90 to the surplus sludge pump control device 410 at the time of starting the drawing. The surplus sludge pump control device 410 stops the surplus sludge pump 90 after extracting a predetermined amount of surplus sludge from the final sedimentation basin 30.

FIG. 2 is a diagram showing an example of fluctuation of the amount of inflow sewage. As shown in FIG. 2, the flow rate and water quality of the inflowing sewage vary greatly in a 24-hour cycle depending on human life patterns. Normally, the inflow flow rate of the sewage treatment plant for municipal sewage reaches a peak at around 3:00 to 6:00, and peaks at around 10:00 and around 21:00 when wastewater from homes increases. The ratio of the maximum value of the inflow rate to the minimum value may be several times.

FIG. 3 is a diagram showing the fluctuation of the MLSS flowing into the aeration. In the MLSS 500 of FIG. 3, the return sludge amount calculation means 310 performs the return rate constant control, and the setting of the surplus sludge management means 400 sets the pulling start time from 0:00 to 23:
An example of variation when the excess sludge preset amount is set to the same amount for 24 times is shown 24 times / day every hour until 00.
The amount of returned sludge is withdrawn from the final sedimentation basin at a constant ratio of the amount of inflow sewage, so that the amount of inflow sewage becomes the lowest during the minimum time of 3:00 to 6:00. If the withdrawal amount from the final sedimentation basin 30 is small, the sludge with a high concentration that has settled out is withdrawn, so that the concentration of returned sludge becomes very high. The MLSS 500 at the entrance 20 also shows a high value. On the other hand, the MLSS 501 in FIG. 3 shows the fluctuation when the amount of excess sludge is controlled according to the present invention. In the MLSS 501 of FIG. 3, the return sludge amount calculation means 310 performs return rate constant control, and the excess sludge management means 4
The setting of 00 sets the extraction start time from 0:00 to 23:00.
MLSS fluctuations when the excess sludge preset amount is set higher than other time zones from 3:00 to 6:00 from 24 times / day every hour until 0. The MLSS rise can be suppressed even during the period of 3 to 6 o'clock when the amount of returned sludge is small.
SS has kept the fluctuation range small throughout the day. FIG. 4 shows an embodiment of the surplus sludge management means 400. FIG. 4 shows an embodiment of a surplus sludge schedule set in the surplus sludge management means 400 in a sewage treatment plant operated under constant return rate control. The drawing start time is set by the time setting means 401, and the surplus sludge preset amount is set by the preset amount setting means 402. The excess sludge flow from 3 o'clock to 6 o'clock when the inflow sewage flow becomes low is increased to a maximum of 40, and the remaining time is kept at 10 constant. As described above, the excess sludge preset amount is changed in response to the fluctuation of the inflow sewage flow rate.

FIG. 5 shows an example of the relationship between the amount of sludge extracted from the final sedimentation tank 30 and the concentration. Sludge and treated water are mixed in the amount withdrawn from the final sedimentation basin 30. When the amount of withdrawal is small, the ratio of the sludge of high concentration that has settled is large, and therefore, the concentration of returned sludge is high.

FIG. 6 shows an example of application to a sewage treatment plant. 202 is a flow meter for measuring the amount of returned sludge. The surplus sludge management means 400 changes a preset pulling start time and a preset surplus sludge amount based on the returned sludge flow rate data from the flow meter 202. Thus, even if the return sludge flow rate pattern changes, the excess sludge withdrawal schedule can be automatically corrected.

[0026]

According to the present invention, since the fluctuation range of the MLSS in the aeration tank can be reduced, there is an effect that the quality of treated water can be maintained stably.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a sewage treatment plant showing one embodiment of the present invention.

FIG. 2 is a diagram showing a change in the amount of inflow sewage.

FIG. 3 is a diagram showing a change in MLSS flowing into aeration.

FIG. 4 is a diagram showing an embodiment of surplus sludge management means.

FIG. 5 is a diagram showing the relationship between the amount of returned sludge and the concentration.

FIG. 6 is a schematic configuration diagram of a sewage treatment plant showing one embodiment of the present invention.

[Explanation of symbols]

10 ... inflow sewage, 15 ... first sedimentation basin, 20 ... aeration tank, 30 ... final sedimentation basin, 31 ... scraper, 4
0: diffuser, 60: return sludge pump, 70: sludge return pipe, 80: sludge discharge pipe, 90: excess sludge pump, 110
... blower, 130 ... air pipe, 120 ... air volume control valve, 20
DESCRIPTION OF SYMBOLS 1 ... Flow meter, 202 ... Dissolved oxygen meter, 300 ... Return rate setting means, 310 ... Return sludge amount calculation means, 320 ... Return sludge pump control means, 400 ... Surplus sludge management means, 401 ...
Time setting means, 402... Preset amount setting means, 410
... Excess sludge pump control means.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Ichiro Enbutsu 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside the Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Fumichi Kimura 5-chome, Omika-cho, Hitachi City, Ibaraki Prefecture No. 2 in Hitachi, Ltd. Omika Works (72) Inventor Masakazu Nakanishi 5-2-1, Omika-cho, Hitachi City, Ibaraki Prefecture F-term in Hitachi, Ltd. Omika Works F-term (reference) 4D028 BC18 BD16 CA11 CA12 CB02 CB03 CB08 CC01 CC07 CC12

Claims (6)

[Claims] 1. A biological water treatment process comprising: a surplus sludge managing means for managing a preset amount of surplus sludge and a withdrawal time; and a means for controlling a surplus sludge pump in accordance with a preset amount from the managing means. A surplus sludge amount control method characterized in that the surplus sludge preset amount set in the surplus sludge amount management means is increased during a time period when the amount of inflow water is small. 2. A biological water treatment process comprising: a surplus sludge managing means for managing a preset amount of surplus sludge and a withdrawal time; and a means for controlling a surplus sludge pump in accordance with a preset amount from the managing means. A surplus sludge amount control method, wherein the frequency of withdrawal set in the surplus sludge amount management means is increased during a time period when the amount of inflow water is small. 3. A means for measuring the amount of returned sludge in the biological water treatment process, a means for managing a preset amount of excess sludge and a withdrawal time, and a means for controlling an excess sludge pump according to the preset amount from the management means. Wherein the means for managing the preset amount of excess sludge increases the preset amount of excess sludge during a time period when the amount of returned sludge is small. 4. The surplus sludge amount control method according to claim 3, wherein the surplus sludge amount preset amount management means increases the surplus sludge amount withdrawal frequency during a time period when the returned sludge amount is small. 5. A biological water treatment process, comprising: means for measuring the amount of inflow sewage; means for managing a preset amount of excess sludge and withdrawal time; and means for controlling the excess sludge pump in accordance with the preset amount from the management means. A surplus sludge amount control method, wherein the surplus sludge amount preset amount managing means increases the excess sludge amount preset amount during a time period when the inflow sewage amount is small. 6. The surplus sludge amount control method according to claim 5, wherein said surplus sludge amount preset amount management means increases the surplus sludge amount withdrawal frequency during a time period when the inflow sewage amount is small.