JPS588310B2 - Katsusei Odeihou Haisui Shiyori Plant No Seigiyohouhou - Google Patents

Description

Detailed Description of the Invention This invention relates to an automatic control method for wastewater treatment plants using the activated sludge method, especially for small and medium-sized plants. It is being

This type of wastewater treatment method includes the activated sludge method, the trickling filter method, and the oxidation pond (lagoon method). This proves that the activated sludge method is an excellent treatment method for this type of wastewater.

As urban sewage treatment plants have become larger in size, their instrumentation has been strengthened, and the control rooms of sewage treatment plants in large cities now look no different from the control rooms of large-scale chemical factories.

However, if we look at the contents in detail, we can see that current sewage treatment plants are subject to instrumentation management, especially automatic control.
The process control of the activated sludge method itself is not yet subject to automatic control, as the hydraulic characteristic values are the main focus.

This is because the activated sludge method is a relatively large capacity process;
This is partly due to the fact that it requires less effort for manual control compared to general chemical plants, but the fundamental reason is that the activated sludge method utilizes complex biological activities, so it is difficult to apply simple control methods. It is difficult to determine the operating conditions, and it is necessary to make comprehensive judgments based on past operating experience from various operating characteristic values, and these characteristic values are only obtained as a result of laboratory analysis test work. This is probably because there was a lot of work going on.

In recent years, the residential areas of city dwellers have expanded widely to the periphery of cities, and on the other hand, as the destruction of the living environment due to water pollution has become more serious, the living areas have become separated from these traditional urban areas, and therefore urban sewage is becoming increasingly common. The treatment of wastewater generated in areas where connectivity is not possible is becoming a critical issue.

The only practical and rational way to solve this problem is to set up a treatment plant of a size appropriate for each region. For a variety of reasons, it is difficult to have full-time operating personnel like in urban sewage treatment plants, and it is necessary to operate unmanned during normal times, with only regular patrols and management.

In response to the above-mentioned circumstances, the present invention provides an automatic control method applicable to small and medium-sized activated sludge process plants.

Originally, the activated sludge method utilizes the action of aerobic microorganisms, so in order for it to function smoothly, there must be dissolved oxygen (abbreviated as DO) in the water. However, excessive DO will cause acidification of pH due to the activity of nitrifying bacteria, rising sludge phenomenon due to denitrification in the sedimentation tank, and bulking due to the growth of oxygen-loving filamentous fungi.
It is necessary to manage this within a certain range.

Currently, DO measurement can be easily performed using instrumental analysis, and DO can be managed as a control loop independently of other conditions, so in medium-sized or larger activated sludge plants, DO measurement and Management has become common sense, and there are many cases where sewage treatment plants in large cities automatically control DO.

Also in the present invention, one of the conditions is that DO be managed within an optimal range depending on the characteristics of the plant.

Another condition as important as the above-mentioned DO control for the proper operation of the activated sludge process is the presence of sufficient microorganisms to treat the contaminants contained in the raw wastewater.

However, since it is impractical to use microscopic inspection for the daily operation management of activated sludge plants, the concentration of suspended solids in the mixed liquor in the aeration tank is usually
r suspended solid (abbreviated as MLSS) is often managed as an index.
On October 25, 2017, the Director of the Environmental Improvement Division, Environmental Sanitation Bureau, Ministry of Health and Welfare issued a notice to the heads of the waste-related departments (bureaus) of each prefecture and designated city. ``Notes to be noted regarding the use of activated sludge methods'' specifies the range of MLSS that should be adjusted as a target for various activated sludge methods.

Therefore, MLS of the aeration tank is the management method for activated sludge method.
A method of maintaining S at a constant value has been considered, and MLS
Automatic control using an S meter as the detection end has also been devised, but DO
Unlike in the case of , it is often inappropriate to simply control only the MLSS value to a constant value for the reasons described below, so some other method is considered necessary for managing the aeration tank.

If the amount of pollutants in raw wastewater increases, if it is in the form of solids, it will directly increase MLSS, but even if the pollutants are dissolved substances, they will be subject to BOD, that is, microorganisms. If the material is subject to treatment, microorganisms absorb and assimilate it in the aeration tank, resulting in MLSS.
will increase.

On the other hand, as a means to suppress MLSS to a constant value,
There is no other way than to reduce the amount of returned sludge containing microorganisms that is separated from treated water in the settling tank and sent back to the aeration tank.

On the other hand, most of the types of medium-sized or larger aeration tanks targeted by the present invention are of the plug-flow type, so the liquid in the tank is not completely mixed. Reducing the amount of returned sludge that opens near the inlet of raw wastewater in order to suppress the amount of pollutants increases, which means that the amount of microorganisms must also increase to treat this. This goes against the principle of the sludge method.

For the above reasons, the control method of simply maintaining the MLSS value at a constant value seems to have problems in reality.

Next, the amount of pollutants contained in the raw wastewater flowing into the aeration tank (
To be precise, the amount of food that is edible for microorganisms in it) (hereinafter referred to as F
The ratio F/M between the amount of microorganisms (hereinafter referred to as M) and the amount of microorganisms used to treat this sludge, that is, the amount of microorganisms in the returned sludge (hereinafter referred to as M) that is returned from the settling tank to the aeration tank as activated sludge, is kept constant. There are ways to maintain it, and it is currently the most widely applied or the subject of consideration before application.

In this case, F is the product of the flow rate of the raw wastewater and the total organic carbon concentration, or TOC, in the raw wastewater.
OD must be used, but since it takes five days to measure BOD, it cannot be used for control purposes, so TOC is used instead.

) Furthermore, as M, the product of the return sludge flow rate and the suspended organic carbon concentration, ie, SSOC, is often used.

(SSOC is TOC minus dissolved organic carbon concentration.

) The above method is an excellent method in that it solves the drawbacks of the method using MLSS as a control target, and as mentioned above, it is currently considered to be a promising method.
In addition to the fact that measuring the /M ratio is time-consuming and difficult to control automatically, there are the following problems.

It is generally recognized that the mechanism of the activated sludge method follows the following steps.

(1) Among the organic pollutants in the raw wastewater that flowed into the aeration tank, solid ones come into contact with microorganisms (activated sludge) and are collected by their biological flocculation, and then by the action of their enzymes. It is dissolved and absorbed into the microbial body.

On the other hand, dissolved organic pollutants come into contact with microorganisms and are absorbed by the microorganisms as stored materials prior to the above-mentioned treatment of the solid matter.

(2) The substances absorbed and stored in the microbial bodies in the previous paragraph are assimilated by the microorganisms and become constituent elements of the microbial bodies, and the microbial bodies multiply to generate new microbial bodies that become the center of activity of activated sludge.

(3) As microorganisms age, they first consume stored substances and then self-digest cell substances, gradually losing activity.

The inactivated old microorganisms and the microorganisms that were initially collected but could not be decomposed by the microorganisms combine to accumulate inactive substances in the sludge.

As described above, the amount of inert substances gradually increases in the sludge returned from the settling tank.
Even if M is kept constant, the proportion of active moieties in M decreases, in other words, the proportion of microorganisms decreases, resulting in insufficient collection of organic pollutants, and the quality of the treated water decreases. The result is that it gets worse.

In order to compensate for the above-mentioned deficiencies, it is necessary to renew the sludge stored in the sedimentation tank by extracting a portion of the sludge as surplus sludge from the system and putting it out of business.

When extracting excess sludge for the above reasons, the most easily considered method is to determine in advance the appropriate range of the MLSS of the aeration tank (for example, the value specified in the above-mentioned notification from the Environmental Maintenance Division Manager, or to select a value within that range according to the characteristics of the plant. There is a method of determining the MLSS value) and then removing excess sludge so that the MLSS value does not exceed that value, but the drawbacks of this method are:
Since MLSS also increases when the amount of raw wastewater and pollutant concentration increases (hereinafter referred to as "when the pollution load increases"), extracting excess sludge at this point will lead to a shortage of activated sludge when the pollution load increases. This is the result.

Another method for removing excess sludge that anyone can think of, and which is already in use in some cases, is to measure the level of sludge at the bottom of the settling tank, and to determine whether the level of sludge is based on the characteristics of the plant. This method involves pulling out excess sludge when it reaches a predetermined height.

Although this method can provide somewhat satisfactory results, as can be seen from practical examples, it is not the best method for the following reasons.

The settling tank is originally intended to settle the activated sludge that flows out of the aeration tank to obtain clear treated water, but at the same time, the bottom part also serves to store and thicken the settled sludge.

Since this thickening effect is based on the weight of the sludge accumulated at the bottom, it is controlled by the height of the sludge level, but at the same time it is also influenced by the residence time of the sludge at the bottom of the settling tank.

That is, if the amount of activated sludge that settles during a unit time is large, the estimated level of activated sludge will be higher than the absolute amount of activated sludge.

Therefore, managing the extraction of excess sludge by mechanically maintaining the sludge level in the settling tank will cause the tank to lose its function as an activated sludge storage tank, and excess sludge will be extracted when the pollution load is high. As a result, the returned sludge becomes diluted, and in order to compensate for this, it becomes necessary to increase the flow rate of the returned sludge, which inevitably increases the flow rate passing through the aeration tank and shortens the residence time in the aeration tank. This will bring about results that are contradictory to load countermeasures.

Based on the above recognition regarding the control of the activated sludge method, the present inventor has devised a method that solves the above-mentioned problems with a system as simple as possible regarding the control of the activated sludge method and enables automatic control. This invention was obtained as a result of extensive research and repeated pilot plant tests and trials using small-scale equipment.

The gist of this invention is to adjust the amount of aeration using an automatic control method so that the dissolved oxygen concentration in the aeration tank is maintained within a predetermined range, and to adjust the amount F of organic pollutants flowing into the aeration tank and the amount of aeration from the settling tank. Adjust the amount of returned sludge so that the ratio F/M to the amount of microorganisms M in the sludge returned to the tank maintains a predetermined value, and
In this method, excess sludge is extracted from the settling tank so that the concentration of suspended matter MLSS in the mixed liquid in the aeration tank maintains a predetermined standard fluctuation pattern.

The structure of the present invention will be explained below using a flow sheet showing an embodiment of the present invention.

1 is an equalization pond into which raw wastewater flows through a waterway 21.

2 is an aeration tank into which raw wastewater flows from the equalization pond 1 through a waterway 22.

3 is a sedimentation tank, into which the mixed liquid flows through waterway 23;
4, clear treated water is released.

Reference numeral 4 denotes a DO regulator, which is connected to a DO detection end 5 in the aeration tank 2, and controls an air volume adjustment valve 6 in the air pipe 28 based on the detected value.

The air pipe 28 is led to the bottom of the aeration tank 2, and releases air from a number of holes drilled in the part led to the bottom to supply oxygen.

7 is a flow meter connected to a detection end 8 provided in the water channel 22.

A turbine pump 9 sucks return sludge from the bottom of the settling tank 3 through a conduit 25 and returns it to the aeration tank 2 through a conduit 26.

10 is a return sludge MLSS meter connected to the detection end 11 in the conduit 26, and 12 is an arithmetic unit that receives signals from the flow meter 7 and the return sludge MLSS meter 10 and calculates the resulting value. The flow rate of the conduit 26 is regulated by a regulating valve 14 connected to the flow regulator 13 .

15 is an MLSS meter connected to the detection end 16 near the terminal of the aeration tank 2; 17 is a fluctuation pattern setting device that sets a pattern of MLSS fluctuations that occur over time in the aeration tank 2; The ML is calculated based on the expected load fluctuation of aeration tank 2 and test run results.
Determine and set the standard SS fluctuation pattern.

This fluctuation pattern may be a continuous curve with time as the horizontal axis, but for further simplicity, one day may be divided into several time periods and a standard value of MLSS may be set for each time period.

18 is an aeration tank MLSS control device, and the MLSS of the aeration tank at that point is M according to the signal from the MLSS meter 15.
ML set in the LSS fluctuation pattern setting device 17
When the MLSS of the aeration tank 2 is higher than the standard value of SS, the opening degree of the excess sludge discharge valve 19 is increased and the MLS of the aeration tank 2 is increased.
S acts to maintain the standard pattern.

Next, the operation of this invention will be explained.

The detection end 5 detects the DO value in the aeration tank 2, and based on it, the DO value is controlled by the feedback control method.
The regulator 4 operates, and the regulating valve 6 operates to adjust the air volume of the blast pipe 28 from an air supply source (not shown), thereby reducing the DO in the aeration tank 2.
is maintained at a predetermined value.

In this case, instead of using the feedback method, it is also possible to determine in advance a variation pattern of the inflow amount of raw wastewater, with one cycle per day, and adjust the air volume using a timer accordingly.

Since the equalization pond 1 has a capacity sufficient to homogenize the raw wastewater flowing in from the waterway 21, almost homogeneous raw wastewater is sent to the aeration tank 2 through the waterway 22 throughout the day.

In other words, T of the liquid containing organic pollutants flowing through the waterway 22
OC remains approximately constant throughout the day.

Therefore, in this device, the above-mentioned value of F is
can be replaced with the flow rate of

Therefore, in controlling the aforementioned F/M to a predetermined value, it is sufficient to send the value detected by the flow meter 7 by the detection end 8 to the arithmetic unit 12 as the value of F.

On the other hand, assuming that excess sludge is to be removed as described later, the MLSS of the returned sludge sent from the bottom of the settling tank 3 to the conduit 26 via the conduit 25 and the turbine pump 9 can be considered to be proportional to the above-mentioned M, so the detection Sludge MLSS returned by end 11
When the value detected by the total 10 is sent to the calculation device 12, this device 12 calculates it together with the input F mentioned above, issues a flow rate setting signal so that F/M becomes a predetermined value, and sends this to the return sludge. The sludge is sent to the flow rate regulator 13 , and the regulator 13 operates the regulating valve 14 to adjust the flow rate of the return sludge in the conduit 26 and return it to the aeration tank 2 .

Next, the extraction control of excess sludge is detected by the detection end 16 located near the terminal of the aeration tank 2, and a signal corresponding to the MLSS value of the aeration tank 2 measured by the MLSS meter 15 is sent to the aeration tank MLSS control device 18. Here, it is compared with a predetermined standard MLSS fluctuation pattern set in the MLSS fluctuation pattern setting device 17, and if the above-mentioned measured value at that time is high, the control device 18 acts to open the regulating valve 19. The MLSS value of aeration tank 2 is the MLSS at that point in the standard MLSS fluctuation pattern.
Operate to achieve the value.

According to the method of the present invention, the activated sludge method is the most excellent method for treating organic polluted raw wastewater, and the control method for keeping the F/M ratio constant is the most reasonable method for controlling this activated sludge method. The MLSS of the aeration tank is a standard MLSS pattern that matches the load characteristics of this plant. Since the treatment of raw wastewater is carried out well, and the operation is fully automated by the automatic control system, it is a suitable method for medium-sized community wastewater treatment plants. It is.

[Brief explanation of the drawing]

The figure is a flow sheet showing an embodiment of a small and medium-sized wastewater treatment plant used in the present invention. 1... Equalization pond, 2... Aeration tank, 3.
...Sedimentation tank, 4...DO regulator, 7...
...Flowmeter, 9 ...Turbine pump, 10
... Return sludge MLSS meter, 12 ... Arithmetic device, 13 ... Return sludge flow rate regulator, 15.
...MLSS meter, 17...MLSS fluctuation pattern setting device, 18...Aeration tank MLSS control device.

Claims (1)

[Claims] 1. In the operation of wastewater treatment and burial plants using the live sludge method, the amount of aeration is adjusted so that the dissolved oxygen concentration in the aeration tank maintains a predetermined value, and the amount of organic matter F flowing into the aeration tank and the amount of organic matter F from the settling tank are The amount of returned sludge is adjusted so that the ratio F/M to the amount of biological matter M in the returned sludge returned to the aeration tank maintains a predetermined value, and the concentration of suspended solids in the mixed liquid in the aeration concentration is adjusted. A method for controlling an activated sludge wastewater treatment plant, characterized in that the amount of excess sludge drawn is adjusted so as to maintain a standard fluctuation pattern specific to the plant, and each of the above operations is automatically performed.