JP2952282B1 - Wastewater treatment control method - Google Patents

Abstract

Abstract: [PROBLEMS] In wastewater treatment using aerobic microorganisms,
Provided is a wastewater treatment control method capable of achieving energy saving by optimizing aeration air amount, early detection of abnormal wastewater inflow, labor saving of operation management work, and the like. SOLUTION: The wastewater during the aeration treatment is sampled, the dissolved oxygen in the wastewater and the change (curve) in which the dissolved oxygen decreases with the inflow of new wastewater stopped, and then air is aerated to the wastewater. Increase in dissolved oxygen (curve)
Is measured, and the sludge activity, untreated BOD concentration, and information on excess / deficiency of the aeration air obtained from the measurement are compared with the target data / curve patterns to obtain the aeration air amount. In the wastewater treatment control method that issues a signal that instructs or controls the increase or decrease of the concentration, etc., when measuring with the flow of new wastewater stopped, if the dissolved oxygen concentration is low, the dissolved oxygen concentration is linearized by aerating for a short time during the measurement. The rate of decrease in dissolved oxygen is measured by increasing the rate to a point at which the rate decreases.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the operation of a wastewater treatment method using aerobic microorganisms.

[0002]

2. Description of the Related Art As a wastewater treatment method, a biological treatment method using an aerobic microorganism is a widely used wastewater treatment method. A typical process is an activated sludge treatment method. In addition, the activated sludge treatment method depends on the shape of the aeration tank, the method of injecting raw wastewater and the method of applying load, etc.
Oxidation rich, step aeration method,
There are various variations such as complete mixing. The treatment principle is common, and aerobic microorganisms capture the pollutants in wastewater and obtain oxygen for the supply of oxygen to decompose, thereby obtaining energy for biological activities, and decompose and synthesize pollutants in wastewater. Purification of wastewater by highly concentrating the biological activities of the natural world that maintain and proliferate their own organisms. Therefore, whether wastewater can be treated efficiently and cleanly
It depends on how active the aerobic microorganisms are.

[0003] The BOD decomposition rate of activated sludge in the activated sludge treatment can be expressed as follows. When the activity of sludge is defined as the ability of a unit amount of activated sludge to decompose BOD in a unit time when supplied with an appropriate amount of BOD substance and oxygen, BOD decomposition rate = f (BOD concentration, dissolved oxygen concentration, ML
SS × sludge activity). Here, BOD is the biochemical oxygen demand, and MLSS is the sludge concentration of the aeration tank mixture. The sludge activity is an index indicating the power of sludge per unit to decompose pollutants, and is affected by various factors as described later.

[0004] Therefore, in order to operate the activated sludge treatment apparatus properly, it is necessary to: 1. There is an appropriate amount of decomposable pollutants (= BOD load). 2. Decompose pollutants and supply oxygen required for microbial respiration. It is necessary to ensure that the amount of contaminants and the type and amount of microorganisms in the substrate are appropriate, and that the environment suitable for each treatment method is dedicated to the growth of microorganisms. As the operation management index for this, 1. Chemical oxygen demand (COD), pH, etc. as an alternative index of BOD of raw water Dissolved oxygen concentration in the aeration tank (DO
Value) 3. 3. MLSS value, pH, temperature, salt concentration, sludge volume index (SVI), returned sludge concentration, etc. There are COD, visibility, suspended solids concentration (SS), pH, etc. as management indexes of treated water.

FIG. 1 shows a basic flow chart of a standard activated sludge treatment apparatus. 1 is a raw water pump, 2 is a raw water flow control valve, 3 is an aeration tank, 4 is an aeration blower, 5 is an inverter for adjusting the output of the blower, 6 is a diffuser pipe, 7 is a final sedimentation tank, 8 Is a return sludge pump, 9 is a return sludge flow control valve, and 10 is an excess sludge extraction valve. The normal operation of the activated sludge treatment apparatus performs the following operations with reference to the above management index. 1. The raw water control valve is operated to adjust the treated water amount and the BOD load (concentration × water amount) based on the BOD of the raw water, the amount of wastewater to be treated, and the quality of the treated water. 2. The air volume of the aeration blower is adjusted by the inverter based on the BOD load and the DO value to adjust the aeration air volume. 3. Adjusting the amount of excess sludge withdrawn and returning sludge flow rate
Maintain LSS at a constant level. Automatic management of the activated sludge treatment device is theoretically possible if the management index is managed by an automatic analysis instrument or management instrument, and the signal is calculated by a computer to control the above operation amount. Few examples have been put to practical use in operations. The causes can be summarized in the following two points. 1. There is no automatic instrument that can perform reliable measurement in a short time so that the BOD can be directly reflected in driving operation. Automatic instruments that can quickly measure COD, which is an alternative index of BOD, are practically used. However, in actual operation, the BOD of raw water is composed of various components, and the composition and concentration vary greatly.
The value of BOD cannot always be estimated from the value of OD or the like. 2. In an actual operation, the activity of sludge fluctuates under the influence of various factors, but there is no simple means for judging the activity useful for the actual operation. For this reason, the automatic operation method as described above is limited to the case of a very special wastewater in which the substrate of the wastewater hardly changes.

As described above, although the need for automatic driving is high, in an actual operation in which fluctuations are severe, it is general that the judgment of the operation amount from the management index depends on the skill of the operator.
If the quality of the treated water such as BOD is constantly maintained at a certain value or less, it is difficult to predict the fluctuation of the wastewater and the fluctuation of the activity of the sludge. This means that the original capacity of the processing apparatus is not sufficiently utilized, and that the power of the aeration blower is wasted.

The present inventor has proposed a method according to Japanese Patent Application No. 8-205359 "Wastewater Treatment Control Method and Apparatus" as a means for solving this problem (hereinafter referred to as a 3-Step DO control method). The outline of the method is shown below. In the 3Step DO control method, in wastewater treatment using aerobic microorganisms, wastewater during aeration treatment is sampled, and dissolved oxygen (DO1) in the wastewater is measured.
After that, while the inflow of new sampling wastewater is stopped, the change (DO2 change curve) of decreasing dissolved oxygen is measured,
Thereafter, the wastewater is aerated with air to measure the increase in dissolved oxygen (DO3 change curve), or a liquid containing a known amount of BOD substance is added to the wastewater as data in place of the DO3 change curve. The air is aerated to measure the increasing change in dissolved oxygen (DO3 'change curve). From the shapes of the DO1 and DO2 change curves and the DO3 or DO3' change curves, at least the sludge activity, untreated BOD concentration, Identify information on excess or deficiency of the aeration air amount, compare it with the target sludge activity, untreated BOD concentration and the target inspection DO curve pattern, and compare the operating conditions such as the amount of aeration air and the processing amount. Output a control signal and an alarm signal.

[0008]

Basic data in the 3-Step DO control method are DO1, DO2 change curves, DO
3 change curve or DO3 'change curve, and its collection method is described in Japanese Patent Application No. 8-205359, but data collection is as quick as possible and as much information as possible is obtained. Needless to say, an accurate judgment can be made, and the present invention makes it possible to efficiently collect data which is an improvement over Japanese Patent Application No. 8-205359.

[0009]

In the three-step DO control method, when measuring the DO2 change curve, the dissolved oxygen concentration in the waste liquid at the start of the measurement of the DO2 change curve is set to a preset value.
When it is lower than the aeration limit value , the waste liquid is aerated for a short time at the start of the measurement, the dissolved oxygen concentration at the start is increased to a degree that decreases linearly in advance, and then the decrease of the dissolved oxygen is measured. The rate of decrease in the DO2 change curve is the BOD addition limit value.
Larger, smaller than preset second half BOD addition limit
If it is within the range, the first half from the start is aerated with air to measure the increasing change in dissolved oxygen, and in the second half the liquid containing a known amount of BOD substance is added to the wastewater and the air is aerated. The DO3 ″ change curve of dissolved oxygen is measured
The rate of decrease of the change curve is larger than the latter half BOD addition limit value
In this case, a DO3 change curve is measured.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the principle of the 3Step DO control method will be briefly described. The activity of the aerobic microorganisms can be estimated by measuring respiration (oxygen consumption rate). 3Step DO
In the control method, the change in the dissolved oxygen concentration (DO) in the following three steps is measured, and information required for activated sludge treatment is obtained by data processing by a computer, and is reflected in operating conditions. In the first step (referred to as Step 1), DO in the aeration tank is measured by sampling the liquid mixture in the aeration tank. In the second step (referred to as Step 2), sampling is stopped, the supply of oxygen is cut off, and the curve of DO decreasing is measured.
In a third step (referred to as Step 3), the mixture is aerated and D
The increasing change in O is measured. Alternatively, if the rate at which DO decreases in the second step is small, a known amount of a readily decomposable BOD substance is added, followed by aeration, and the change in DO is measured (referred to as Step 3 '). FIG. 2 shows a typical DO change. BO that can be easily decomposed into sampled mixture
When the substance D is present, a two-step curve as shown in FIG. 3 is obtained in Step 3, and an area surrounded by a dotted line and a solid line corresponds to the BOD of the mixed solution as described later. From Step 1, information on the balance between the amount of aerated air in the aeration tank and the amount of oxygen required for BOD decomposition, St
Information on the BOD decomposition power of the sludge is obtained from ep2, and information on the processing state (or information on the activity of the sludge) is obtained from Step 3. St
This cycle is repeated by setting Step 3 (or Step 3 ') from ep1 as one cycle, and the computer comprehensively judges such information.

FIG. 1 shows a specific example in the case where the 3-Step DO control method is installed in an activated sludge treatment apparatus. 11 is 3Step DO
It is a control part of the control method. The main device of the control unit is a personal computer. Reference numeral 12 denotes a measurement unit for the 3-Step DO control method. Reference numeral 13 denotes a sampling pump which is a part of the measuring unit. 3Step
In the DO control method, a mixed solution is pumped up from an aeration tank by a sampling pump according to a command from the control unit, a series of processes are inspected by a measurement unit, and the change data of the DO is transmitted to the control unit and analyzed by the control unit. Then, the control signal obtained as a result is output to operation equipment such as a blower of the activated sludge treatment apparatus, a raw water pump, and a return sludge pump. In the case of standard activated sludge, the sampling pump is usually installed slightly before the outlet of the aeration tank.

Next, the meaning of each step will be described in detail. Step 1 is a step of measuring DO in the aeration tank. In Step 1, first, the previous sample liquid in the measurement container is drained, and at the same time, the sample liquid is pumped from the aeration tank into the measurement container by the sampling pump to measure DO. The last value of Step 1 in which the sample liquid is sufficiently replaced is a valid value as the DO value (DO1) in the aeration tank. D in the aeration tank
The O value is a value that balances the supply and consumption of oxygen. In formula, G · η · (DOsat-DO) = V · (ASact + BODact) (2.1) Formula: Activated sludge from aeration device breathes and supplies oxygen (left) Oxygen consumed by BOD decomposition (right) Where DOsat: oxygen concentration of dissolved oxygen DO: oxygen concentration of dissolved oxygen in the aeration tank ASact: consumption rate of oxygen by respiration of activated sludge (oxygen consumption) BODact: consumption rate of oxygen that activated sludge decomposes BOD components ( G: Aeration air volume V: Aeration tank capacity η: Oxygen absorption efficiency (coefficient determined by aeration method, diffuser shape, etc.) The DO value in the aeration tank is about 0.5 mg / l. Is the most efficient,
Normally, 1 mg / l to 2 mg / l is adopted as a control value in consideration of variations in the aeration tank and contaminants. What is known in Step 1 is the excess or deficiency of the amount of aerated air in the aeration tank. However, the cause of excess or deficiency is that BOD with fast decomposition increases (BODact is large). BO to be disassembled
Did D disappear (BODact small) and air became excessive? Did the sludge become less active, reduce oxygen consumption by breathing (ASact small), and air become relatively excessive? ,
For example, the cause cannot be specified only by the information in Step 1.

In Step 2, the sampling pump is stopped,
The supply of oxygen is cut off, and the rate at which the DO of the sample liquid decreases is measured. This curve is called a DO2 change curve. The inclination of the reduction curve in FIG. 3 corresponds to this. In terms of the formula, The DO2 change curve generally decreases as shown in Fig. 2-2. (A) It decreases linearly in the range of DO> 0.5 mg / l. (B) It decreases toward 0 in the exponential curve when DO <0.5 mg / l. . (a) shows that the right side (ASact + BODact) of the equation (2.2) is constant. (b) is the right-hand side of equation (2.2) (ASact + BODac
t) is a function of DO. Also (ASact
+ BODact) = β, β represents the oxygen consumption rate of the activated sludge, and a large β is evidence that the sludge is active. Conversely, when β is small, sludge activity is slow. Hereinafter, β is referred to as sludge activity.

ASact is the rate of consumption of oxygen by the basic respiration of sludge. Because it is basal respiration, it is not directly related to the BOD component and is almost constant within the measurement time. However, even in the case of basic respiration, changes in sludge state (logarithmic growth phase, decay growth phase, endogenous respiration phase, etc.) in a slightly longer range To increase or decrease. In the short term, the state of this sludge is drug inflow, environmental change (water temperature change, p
H, salt concentration, etc.), the composition of raw water, fluctuations, etc., and in the long term, changes due to nutritional balance (P, N), shortage and overaeration of BOD, prolonged sludge age, etc. In general, active extraction of surplus sludge results in young active sludge.

[0015] BODact is the rate of consumption of oxygen by which sludge decomposes BOD components. BODact is a substance whose BOD component is easily biodegradable, whether the sludge is adapted to the substance, the state of the sludge (logarithmic growth phase, decay growth phase, endogenous respiration phase), water temperature, pH, salt concentration It changes depending on the habitat environment. Normally, the average of ASact vs. BODact in the entire aeration tank is 1: 1-3.

[0016] When there is an influx of toxic substances or a sudden change in habitat, both ASact and BODact are sharply reduced by a shock. And β
(= ASact + BODact) is proportional to biomass (MLSS). Generally, β changes according to the degree of progress of the processing. In the early stage of treatment, decomposable substances in wastewater are decomposed, so the decomposition rate is high, BODact is large, and β takes a large value. In the middle stage of the treatment, the decomposition rate of the substance having a moderate degree of decomposability is slightly reduced, and β becomes smaller than the initial stage. At the end of the treatment, the decomposition rate is reduced because the hardly decomposable substance remains, and β is a small value slightly larger than ASact.
The 3Step DO device is installed near the exit of the aeration tank,
The state of progress of the process can be roughly inferred from the size of. However,
For the estimation, it is assumed that the state of the sludge is normal. However, if β is small, it is not possible to judge whether the state of the sludge is normal only from the data in Step 2. Regarding the matters found in Step 2, the state of treatment can be roughly estimated. In particular, when β is large, there is a high possibility that the treated water itself has not been treated, but it can be determined that the activity state of the sludge is normal. On the other hand, if β is small, it is impossible to judge from the data in Step 2 alone, whether the processing is completed and the decomposable BOD has disappeared, or the inflow of toxic substances or the like has slowed down the biological activity and the consumption rate of oxygen has decreased. .

In Step 3, the mixed solution of Step 2 is aerated using an aeration device of the 3 Step DO control method. DO rises in the mixed solution due to aeration, and the rising curve is called a DO3 change curve, and the DO3 change curve has the following characteristics depending on the sludge and the treatment state. When this process is expressed by an equation, Here, Kabs is the overall mass transfer coefficient based on the liquid phase, and is a constant determined by the characteristics of the aerator such as the shape of the aspirator and the strength of the water flow and the properties such as the temperature and viscosity of the mixed solution. Right side second
The term (ASact + BODact) is replaced by the constant β obtained in Step 2 when DO> 0.5 mg / l, Equation (2 · 4) becomes the following exponential curve. DO = α + (α−DO ₀ ) exp (−Kabs · t) Equation (2,5) where α = DOsat−β / Kabs If there is a BOD that can be easily decomposed, β = large and β in FIG. It becomes a curve. When there is almost no easily decomposable BOD from the beginning, β = small, and the curve becomes a high curve in FIG. When there is a small amount of BOD that can be easily decomposed and the decomposition is completed in the middle of aeration, the curve becomes a two-stage curve in FIG. As shown in FIG. 5, DOsat: saturated dissolved oxygen concentration highDO: final DO value of the upper stage of the two-stage curve lowDO: final DO value of the lower stage of the two-stage curve, DOsat = lowDO + β / Kabs BODact = Kabs (highDO-lowDO) There is a relationship of β = ASact + BODact, and if the dotted line in FIG. 5 is a rising curve when β is small (when there is no BOD), it is surrounded by a solid measurement curve and a dotted line. If the area of the range is S, Sx Kabs is BO
This is the oxygen consumption required for the decomposition of the D substance, and this value corresponds to the BOD of the mixture. In Step 3, since the sampling liquid is simply aerated, the matter found out in Step 3 is that the BOD of the treated water can be estimated as described above. However
If β is small in Step 2, the DO3 change curve immediately becomes D
The curve of FIG. 4b in which O increases is shown in FIG. 4. In step 3, it is determined whether the cause is that there is no degradable BOD serving as bait or the sludge activity is decreasing due to inflow of toxic substances or the like. Can not.

When β is small, the process is completed if there is no decomposable BOD and the BOD is small, but if the activity is reduced, it is dangerous for operation management. Computer is Step 2
If it is determined that β is small, it is not the normal Step 3
The process automatically shifts to Step 3 ', and aeration is performed after a prescribed amount of easily decomposable BOD substance is added at the beginning of Step 3. The DO change curve obtained here is referred to as a DO3 'curve. If the DO3' curve simply has no decomposable BOD and the activity is good, the DO3 'curve is obtained until the decomposition of the added BOD substance of the formula (2.3) is completed. Since the BODact becomes large, the curve becomes a two-step curve in FIG. 6C, and the BOD value obtained by calculation should match the added BOD value. Conversely, if the curve is a low one stage in a of FIG. 6, the decomposition power is weak, and if the curve is a high one stage in b, the activity is considerably reduced, and it can be determined that the state is dangerous. If the value of β is small in Step 3 ′, it can be determined whether the cause is that there is no degradable BOD or that the sludge activity is reduced due to the inflow of toxic substances.

The above is the basic data sampling method in the 3-Step DO control method. The present invention, in addition to the above, adds the following means to enable more efficient data collection. The first is that in the measurement of Step 2, Step 2
In the case where the concentration of dissolved oxygen at the start of is already low. As explained by the equation (2.2), DO is approximately 0.5.
If the concentration is not less than mg / l, the analysis is easy because the decrease curve of Step 2 decreases substantially linearly. However, if the concentration is less than 0.5 mg / l, the decrease curve becomes a function of DO, and the analysis becomes practically impossible.
Therefore, if DO at the start of Step 2 is low, Step 2
The analysis is performed only on the straight line portion at the initial stage, but there is a risk that the error may increase. Therefore, in the present invention, Step 2
If the DO at the start of step 2 is small, the mixed solution is previously aerated for a short time at the start of Step 2 to increase DO to a degree at which a linear decrease can be obtained before measurement. Whether or not to perform aeration in advance is automatically determined by comparing with a numerical value stored as a preliminary aeration limit value by the computer. The pre-aeration limit is generally about 1 mg / l to 2 mg / l.
If the aeration time is too long, the process proceeds and the value of β changes, or the measurement error in Step 3 occurs. Therefore, the aeration time should be minimized. Usually, it is preferably about 2 minutes or less. It is preferable that the computer stop the aeration at the time when the temperature rises to as low as possible, so that the time is as short as possible. FIG. 7 is a view showing a typical DO change of the 3 Step DO control method when aeration is performed in advance in Step 2 according to the present invention.

The second aspect of the present invention relates to a data collecting method in the third step. Conventionally, from the measurement result of β in Step 2, if β is larger than the BOD addition limit value,
Perform ep3 to measure the BOD of the mixture. Β is B
If it is smaller than the OD addition limit value, Step 3 'is performed to test the sludge activity. The present invention is a data collection method applicable when β is in a range from the BOD addition limit value to a little larger than the BOD addition limit value (hereinafter referred to as the latter half BOD addition limit value). By measuring the BOD in the medium and adding a known amount of BOD which can be easily decomposed in the latter half of Step 3, the activity of the sludge can be determined in the latter half. This curve is
The O3 "change curve is referred to as a" DO3 "change curve.
If the inspection time of the step is set to 22 minutes, the computer determines that the result β of Step 2 is within this range, and determines that
The amount of DO increase was measured by simple aeration, and a known amount of easily decomposable BOD substance was added at the 15th minute.
Measure the change. Since β is not a very large value, the rise curve of the DO3 ″ change curve rises to a high level in a relatively short time. Therefore, as shown in FIG. 8, the BOD of the sample solution was extrapolated to the solid line in the first half. Even if it is calculated from the dotted line, the error is small, and the sludge activity cannot be measured completely in a short time, but if the sludge is normal, the normal size BODact corresponding to the degradable BOD substance will not be obtained. Since it is supposed to occur, it can be determined by showing a DO decrease of a magnitude corresponding to h = highDO−lowDO = BODact / Kabs derived from the equation (2.5).
The DO3 ″ change curve makes it possible to simultaneously determine the BOD of the mixed solution and the activity of the sludge. In the actual operation control of the activated sludge treatment apparatus, if the treatment is normal, β as shown in a pattern legend 1 described later. Is around the BOD addition limit,
If the method of collecting the DO3 ″ change curve data according to the present invention is added, the conventional DO3 change curve or DO3 ′ change curve 2 data can be obtained.
Much more information can be collected compared to data collection methods,
It is significant in the judgment of the computer. FIG. 8 shows the D of the present invention.
This is a typical DO change diagram of the O3 ″ change curve. When β is smaller than the BOD addition limit value, the DO3 ′ change curve is measured, and when β is larger than the latter half BOD addition limit value, the DO3 change curve is measured. Is as before.

Next, the data collection method of the present invention is added to add
A specific example of the determination of the epDO control method will be described.

Pattern legend 1 is a specific example in which proper processing is performed. In the case of a standard activated sludge treatment device,
As shown in FIGS. 9 to 11, pattern legends 1-1 to 1-
The computer determines that the state where 3 appears alternately indicates that the processing has been performed extremely properly. Pattern legend 1
In cases 2 and 1-3, the sludge activity can be judged to be good from the DO3 ″ change curve and the DO3 ′ change curve, respectively.
The fact that β is small means that the amount of degradable BOD is small, that is, it can be determined that the treatment is good. The pattern legend 1-1 is DO
The three change curves show that a slight BOD remains. Since the sampling position of the 3Step DO control method is slightly before the outlet of the aeration tank, the processing is just completed at the outlet of the aeration tank. It is in the state.

Pattern legend 2... This is a specific example in the case where processing is abnormal in overload. Legend 2-1 of the pattern in FIG.
As shown in the figure, the DO value in the aeration tank (final value of Step 1) is
If the curve sharply decreases to → and the slope of the decrease curve in Step 2 increases, and the curve in Step 3 changes to → →, the BOD component that is easily decomposed remains unprocessed up to the sampling position of the 3 Step DO control method. Since the BOD decomposition power of sludge is judged to be normal from the magnitude of β in Step 2, the amount of aerated air is insufficient or the amount of BOD in raw water exceeds the treatment capacity in the aeration tank. It is shown that. If the amount of aerated air at this time is the upper limit of the blower capacity, it can be specified that the cause is overload.

Pattern legend 3 is a specific example in the case of over-aeration. In the case of over-aeration, the normal pattern shown in the pattern legend 3-1 in FIG.
From the O3 ″ change curve), since the state of excessive treatment and no BOD substance serving as feed continues, the rate of consumption of oxygen decreases because the respiratory rate of microorganisms decreases and the amount of microorganisms gradually decreases, as shown in FIG. As shown in the pattern legend 3-2, the DO value in the aeration tank (final value in Step 1) increases, β decreases, and the curve in Step 3 changes as in the pattern legend 3-2. Since the slope in Step 2 is small, a DO3 'change curve is obtained, and the sample responds normally to the addition of BOD. However, the decomposition rate decreases, the two-step curve becomes shallow, and the decomposition rate further decreases. The activity of the sludge decreases, and in the case of over-aeration, this change is a gradual change over several days.

Pattern Legend 4—Specific example in the case of processing abnormality due to poisonous substance inflow. If the sludge is damaged by the influx of the poison, the processing speed in the first half of the aeration tank is reduced as shown by the pattern legend 4-1 in FIG. Since the BOD measured in the DO3 change curve in Example 2 deteriorates after the deterioration of the BOD, the DO value in the aeration tank (the final value in Step 1) is reduced as shown by the pattern legend 4-2 in FIG. Rising rapidly, St
The slope of ep2 sharply decreases, and the curve of Step 3 changes as shown in the figure. Step 3 shows a DO3 ″ change curve, but the response after the addition of BOD becomes slow.
Although it is an O3 'change curve, the curve responds little to the addition of BOD, and is above the hypothetical curve without BOD due to respiratory inhibition. Unlike the case of over-aeration, the toxic substance has a rapid change of about several hours.

FIG. 17 is a flowchart showing an example of an apparatus embodying the present invention. 14 is a dissolved oxygen meter. Reference numeral 15 denotes a measuring vessel, in which a sensor of the dissolved oxygen meter is immersed in a sampling liquid in the vessel. The shape of the container is such that the arrangement of the inlet and outlet of the liquid and the accumulation of air do not occur so that the measurement error does not occur due to the dissolution of oxygen from the liquid surface. 16 is a sampling pump. Reference numeral 17 denotes a gas-liquid separation tank for separating coarse bubbles. 18 is an aeration circulation pump, 19 is an aspirator, 20 is an air flow control valve, and 21 is an air flow meter. Numerals 18 to 21 denote systems used for re-aeration in the third step.
The oxygen is dissolved by suction and stirring air from the aspirator. 22, a BOD solution tank; and 23, a BOD addition pump. 22 to 23 are the BOD of a known amount in the third step
Used when adding substances. 24 is a stirring pump,
It is used to secure the flow velocity near the sensor of the dissolved oxygen meter. 25 is a computer. The operation of the inspection operation, the analysis of the measurement data, the command of the operating condition, the alarm and the like of the present invention are all managed by this computer. As the computer used in the present invention, an ordinary personal computer can be used, and in this embodiment, IBM Corp.'s Optiva is used.
Using analog to digital in expansion 1 / O slot,
IBX-3133 and IBX-3325 manufactured by Interface Co., Ltd. are used as a digital-to-analog conversion board, and digital output boards for driving commands of pumps and the like are manufactured by Interface Co., Ltd. IBX-2727 was used. 26 is a relay box. For driving 16, 18, 23 and 24, the relay is operated by a signal from a computer via a digital output board, and the equipment is operated at a necessary timing from the first step to the third (3 ') step. Is turned ON-OFF. 27 is a converter of the dissolved oxygen meter. The signal of 14 dissolved oxygen meters is 27
Is converted to an analog current signal of 4 mA to 20 mA by the converter, and the analog to digital conversion board of 25 computers
And converted into a computer. As a result of the calculation, the computer outputs a digital-to-analog conversion board or digital output of a control signal for controlling the amount of aerated air, raw water treatment, and returned sludge, and an alarm signal for sludge activity abnormality, treatment abnormality, or equipment abnormality. It is output from the 28 control unit terminal board via the board. The hardware for realizing the present invention can use the one shown in Japanese Patent Application No. 8-205359 "Method and Apparatus for Controlling Wastewater Treatment" and is realized by computer software for controlling the hard.

FIG. 18 is a flowchart of the computer software of the present invention. The portions enclosed by the dotted line 1 and the portions enclosed by the dotted line 2 in the figure are functions added in the present invention. The preliminary aeration limit value and the preliminary aeration increase value are values used in claim 1 of the present invention, and are values which are previously input and stored in a computer. If the pre-aeration limit value at the start of Step 2 (DO1 in the figure) is equal to or less than this value, pre-aeration is performed.
After increasing the O value, the decreasing change of DO is measured, and the value is set from 1 mg / l to 2 mg / l. The pre-aeration rise value is for minimizing the pre-aeration time, and if the DO rises above this value, the pre-aeration is stopped, and the decrease in DO is measured. Usually, the preliminary aeration increase value is set to a value that is about 0.5 mg / l to 1 mg / l higher than the preliminary aeration limit value. BOD
The addition limit value, the second half BOD addition limit value, and the second half addition time are the values used in claim 2 of the present invention, and are values which are previously input and stored in the computer. BOD addition limit value is 3
Although the step DO control method is used, if β is less than this value, a known amount of a solution containing a readily decomposable BOD substance is added to perform aeration, and the change in DO is measured. If β is larger than the latter half BOD addition limit value, aeration is simply performed and the change of DO is measured. The case where β is larger than the BOD addition limit value and smaller than the latter BOD addition limit value is the measurement method of the present invention. In the method from Step 3 to the latter half addition time, only aeration is performed and the change in DO is measured. In the latter half of the addition time, a known amount of a solution containing a readily decomposable BOD substance is added and aeration is performed, and the change in DO is measured. The specific values of the BOD addition limit value and the latter half BOD addition limit value are the BODact and ASac of the activated sludge treatment equipment to be controlled.
Depends on t. Specifically, it differs depending on various conditions such as sludge activity, MLSS, biodegradability of pollutants in raw water, and temperature.
For this reason, the BOD addition limit value and the latter half BOD addition limit value are determined by sampling the mixed liquid at the sampling position of the 3Step DO measurement unit operating in a standard and normal processing state as a reference in the activated sludge treatment to be performed, The supply of oxygen from the outside of the mixture is cut off, and the rate of DO reduction is measured. This value is the BODact + of the activated sludge at the sampling point.
Equivalent to ASact. Further, after the mixed solution is sufficiently aerated to reduce the decomposable BOD in the mixed solution, supply of oxygen from the outside is stopped, and the rate of decrease of DO is measured. This value roughly corresponds to ASact. Bac addition limit is ASac
Preferably, it is set to a value slightly larger than t. The BOD addition limit in the latter half is the BOD addition limit and BODact + ASac
Set to a value between t. In the case of a standard activated sludge treatment device,
BOD addition limit value is about 0.2 to 0.5mg / min.
The D addition limit is often set to about 0.4 to 0.9 mg / min.

[0028]

The 3Step DO control method which is the basis of the present invention can be applied to the treatment of aerobic microorganisms typified by an activated sludge treatment device, and the measurement and analysis functions of the 3Step DO control method have previously made the aeration tank unclear. The active state of activated sludge treatment, which previously could only be roughly set, can be set appropriately by being able to output the activity state of microorganisms in the inside and the treatment state of treated water on a computer screen in a short time of about 30 minutes. Can be improved and stabilized. As a result, great effects are obtained, such as energy saving by optimizing the amount of aerated air, early detection of abnormal wastewater inflow, and labor saving of operation management work. The present invention makes the data sampling method of the 3Step DO control method more powerful. According to the present invention, the 3Step DO control method enables more accurate and accurate output, and the effect of the above 3Step DO control method is improved. .

[Brief description of the drawings]

FIG. 1 is a flowchart showing a basic activated sludge treatment apparatus.

FIG. 2 is a change curve diagram showing a typical change of DO in first to third steps.

FIG. 3 is a change curve diagram showing a decreasing change of DO in a second step.

FIG. 4 is a DO change curve diagram showing a change according to the amount of easily decomposable BOD in a third step.

FIG. 5 is a DO change curve diagram showing an oxygen consumption amount required for decomposing a BOD substance.

FIG. 6 is a change curve diagram showing a change of DO in step 3 ′.

FIG. 7 is a change curve diagram showing a change in DO when aeration is performed in advance in step 2;

FIG. 8 is a diagram showing a DO3 ″ change curve.

FIG. 9 is a diagram illustrating one state of transition of the DO change curve when an appropriate process is performed, and a DO change curve diagram illustrating a state in which a small amount of easily decomposable BOD remains.

FIG. 10 is a diagram illustrating one state of transition of a DO change curve when an appropriate process is performed, and is a change curve diagram illustrating a change in DO when BOD is added in the latter half in step 3;

FIG. 11 is a diagram showing one state of transition of a DO change curve when an appropriate process is performed;
It is a change curve figure which shows the change of DO at the time of adding.

FIG. 12 is a diagram showing transition of a DO change curve diagram in an overload state.

FIG. 13 is a change curve diagram showing a normal change of DO before an over-aeration state.

FIG. 14 is a diagram showing transition of a DO change curve diagram in a case of over-aeration.

FIG. 15 is a diagram showing the first half transition of a DO change curve diagram in the case of poisonous substance inflow.

FIG. 16 is a diagram showing a transition in the latter half of a DO change curve diagram in the case of a poisonous substance inflow.

FIG. 17 is a flowchart showing the apparatus of the present invention.

FIG. 18 is a flowchart of the computer software of the present invention.
It is.

[Explanation of symbols]

14 Dissolved oxygen meter 15 Measurement vessel 1
8 Aeration circulation pump 19 Aspirator 22 BOD solution tank 2
3 BOD addition pump 25 Computer 26 Relay box 2
8 Control terminal board

Claims (2)

(57) [Claims] In wastewater treatment utilizing aerobic microorganisms, wastewater during aeration treatment is sampled, dissolved oxygen (hereinafter referred to as DO1) in the wastewater is measured, and then the inflow of new sampled wastewater is stopped. The change in the amount of dissolved oxygen (hereinafter referred to as the DO2 change curve ) is measured with the supply of oxygen cut off, and the rate of decrease of the DO2 change curve is set in advance.
Value (hereinafter referred to as BOD addition limit value)
The wastewater is aerated with air and the dissolved oxygen increases (hereinafter D).
O3 change curve) from the BOD addition limit
If it is small , a known amount of BOD substance is added to the waste liquid, aeration is performed, and the change in dissolved oxygen (hereinafter referred to as DO3 'change curve) is measured, and the DO1, DO2 change curve, DO3 change curve or DO3' change curve is measured. At least the sludge activity, untreated BOD concentration and target inspection DO
When measuring a DO2 change curve in a wastewater treatment control method (hereinafter, referred to as a 3 Step DO control method) that issues a signal for instructing or controlling at least an increase or decrease in the amount of aerated air as compared with the curve pattern, the DO2 change curve is measured. When the dissolved oxygen concentration in the wastewater at the start is lower than the preset preliminary aeration limit value , the waste oxygen is aerated for a short time at the start of the measurement to linearly decrease the dissolved oxygen concentration at the start in advance. A method for controlling wastewater treatment, wherein the rate of decrease in dissolved oxygen is measured after the temperature has been increased. 2. In the 3Step DO control method,BOD addition
Preset value larger than the limit value
Limit value).After measuring the DO2 change curve,DO
2. The rate of decrease of the change curve is greater than the BOD addition limit value,
If it is in the range smaller than the latter half BOD addition limit value,Star
-The first half of the air is aerated and the dissolved oxygen rises
Measure the change and add a known amount of BOD
Solution containing oxygen and aerating the air to remove dissolved oxygen.change
(Hereinafter referred to as DO3 ″ change curve)And DO2 change
When the decrease rate of the curve is larger than the latter half BOD addition limit value
Measures the DO3 change curveWastewater treatment characterized by the following:
Control method.