JPS63175696A - Method for controlling bulking by using svi - Google Patents

Abstract

PURPOSE:To maintain good water quality by comparting an aeration tank into a plurality of parts to form the aeration tank for performing step aeration and specifying factors for changing the amount and the injection point of sewage introduced into the aeration tank. CONSTITUTION:An aeration tank 1 is comparted into 1A-1E to permit step aeration. A controlling device 4 performs prescribed operation on the basis of value measured with respective measuring equipments to process its output into both disvergence signals of valves 5A-5E provided to change the injection point of water introduced into the aeration tank 1 and the on-off signal of an excess sludge pump 15 for controlling the amount of excess sludge. The controlling algorithm in the controlling device 4 consists of both algorithm for deciding injection of water introduced into respective circuits 1A-1E and algorithm for controlling SRT. The algorithm for deciding injection is determined by the amount Qs of sewage to be introduced, turbidity Tbi of introduced water and sludge volume SVI.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a method for controlling water quality in an activated sludge process.

B0 Summary of the Invention The present invention is an activated sludge treatment method that divides the aeration tank into the first number, and divides the inflow sewage volume, inflow water turbidity, and sludge landscape index into three groups.
This system is designed to change the inflow point of sewage into individual aeration tanks, which are classified based on factors.

In addition, considering the interaction of the above three factors, the bulking phenomenon is suppressed by combining inflow water injection amount injection point control and sludge retention time control.

C0 Conventional technology As a means of treating wastewater that contains a large amount of organic matter, such as urban sewage and food factory wastewater, inflow water is injected into an aeration tank, and after being appropriately aerated, it flows into a final settling tank to collect sludge. An activated sludge method is used in which sedimentation is performed and the supernatant water is discharged.

D0 Problems to be Solved by the Invention The organisms involved in treatment by the activated sludge method are mostly microorganisms such as bacteria and protozoa, and are a mixed culture system in which there are many types. A mixed culture system can be regarded as a single microbial ecosystem in which complex interactions exist between biological species. In order to maintain good water quality, these microbial ecosystems must be kept as stable as possible, and appropriate management and control must be carried out. However, depending on conditions such as inflow substrate composition and water temperature, microbial Quantities change dynamically, and bulking is one of them. What is bulking?
This is a phenomenon in which filamentous microorganisms occur in large quantities in sludge, deteriorating the settling characteristics of activated sludge.As a result, solid-liquid separation in the final settling tank deteriorates, leading to sludge flowing into the treated water. Become. In order to suppress this bulking phenomenon, that is, to reduce or eradicate the amount of filamentous microorganisms, many countermeasures have been proposed in the past, such as chlorine sterilization of returned sludge and changing the dissolved oxygen concentration (Do) level. However, they all have poor reproducibility. One of the reasons for this is that mixed culture systems have not been sufficiently analyzed, and there are many types of filamentous microorganisms that appear during bulking, and each type has different appropriate environmental conditions. Even if a certain method is effective for some types of bulking, it has the problem that it is not effective for other types of bulking.

Therefore, the purpose of the present invention is to establish a method that has not been established in the past for predicting the occurrence of bulking or returning bulked sludge to normal sludge, and to prevent the occurrence of bulking based on this method. The aim is to provide a control method that is very precise.

Means for Solving E0 Problems The first invention is a method for treating wastewater with activated sludge, in which the aeration tank is divided to enable step aeration, and the injection point of inflow water is determined by inflow sewage t (Qs), inflow sewage t (Qs), inflow Water turbidity (Tb
t) and the sludge capacity index 111 (SVI).

In addition, the reference value for change is QB (QsO), 8
VI (El'/I.'l is used, but since each factor varies independently, a basic single value determination method is adopted that takes into account the interaction of each factor.

The second invention further combines the injection water injection point control based on the first invention with sludge retention time (SRT) control.

26 Effects Even when the inflow load increases or in a bulking state where BVr is large, by changing the injection point of the inflow sewage volume, the specific gravity of the sludge volume in the aeration tank relative to the final sedimentation tank is increased, and the sludge volume is transferred from the aeration tank to the final sedimentation tank. Reduce the amount of sludge flowing into
Prevent sludge from flowing into treated water.

In addition, in the case of quantitative extraction of sludge, the concentration of returned sludge (the concentration of surplus sludge is also approximately the same) changes as the injection point changes, and the amount of sludge extracted as surplus sludge (kg/a) per day changes, resulting in a change in the SR. 'r cannot be maintained constant. Therefore, by combining injection point change control KSRT control, even if the injection point is changed, S
RT can be controlled to be constant.

G. Example An embodiment of the present invention will be described in detail below based on the drawings.

FIG. 1 shows a case where the present invention is applied to a typical activated sludge treatment flow for urban sewage.

In the same figure, l is an aeration tank, and this aeration tank l is ]A~IN
In Figure C, it is divided into IE) and step aeration is possible. 2 is a Q meter installed on the inflow path side of the aeration tank 1, and 3 is the same <Tbt meter, and the Q6 value and 'rbt value measured by these measuring devices are output to the control device 4. 5A to 5E are gates or pulps (the pulp will be explained below), and each pulp 5A to 5E is a sectional aeration tank IA.
~Motor 6A for opening/closing, provided corresponding to each IE~
Adjust the flow rate to each circuit (section aeration tank) via 6E. 7 is a sludge volume (SV) meter, and 8 is an activated sludge suspended solids concentration (MLSS) meter, each of which is installed on the outflow side of the aeration tank 1 (in this case, 1E), and the measured sv value and MLSS value are SVI It is output to the arithmetic unit 9 and the SVI value is determined by the following equation.

(Here, S V t is the Bv value of the wave after the start of SV measurement, t is usually 30 minutes, and ML8B is the MLaE1 concentration of the sampled sludge at the time of sludge sump for SV measurement.)
The VI value is output to the control device 4, but since the SVI value is measured intermittently, the current value is held until the next value is output. Also, one of the MLSS values is directly controlled by the control device 4.
is also output. 10 is a final settling tank, and 11 is a return sludge pump, which is a pump for returning sludge from the final settling tank 10 to the aeration tank 1. 12 is a return sludge concentration (CR) meter;
13 is the return sludge flow rate (QR) meter, 14 is the excess sludge flow rate (
Qw), and each individual measured by each of these measuring instruments is output to the control device 4, respectively. In addition, CB total 12 and Q
The W total 14 may be any one of the following.

15 is a surplus sludge pump.

The operation of the device as described above will be explained.

In the aeration tank 1, moderate aeration is performed on the inflowing wastewater, but in general, the inflow water is divided into 1 aeration tank per person.
In the case of the step aeration method adopted in the present invention, compared to the standard activated sludge method in which 00% water is introduced, the amount of sludge remaining in the entire aeration tank increases, but on the contrary, the final settling tank 10 The amount of sludge remaining in the tank is reduced by the step aeration method. In the case of the step aeration method, this phenomenon occurs because the amount (or concentration) of activated sludge flowing out from the aeration tank 1 to the final settling tank 1O decreases.

In the present invention, such a step aeration method is adopted, but the control device wt, 4 performs predetermined calculations based on the values measured by each measuring device, and the output is determined by the injection of inflow water into the aeration tank 1. Pulp 5A provided for changing the point
5E opening signal and surplus sludge pump 150 turned on to control the amount of surplus sludge.

Off signal (or surplus sludge pump rotation speed control signal)
The control algorithm in the control device 4 can be roughly divided into the inflow water injection point determination algorithm for each circuit IA to Ig and the SRT control algorithm, but the inflow water injection point determination algorithm is Q a * Tb L e B
” Determined by the engineer.

Below, we will specifically describe how each of these factors affects the state quantity of the process.

Regarding the Ialfi inlet water injection point determination algorithm, first regarding factor Q8, as the amount of inflowing sewage Qs increases, the interfacial area load in the final settling tank IO generally increases, and the amount of sludge carried over from the treated water increases. Therefore, the Q8 value is measured at Qf3 total 2, and when the amount of inflowing sewage increases and exceeds a certain predetermined condition, the control device 4 generates a deposit output and changes the injection point of the inflowing water to the circuit. Change from front stage to rear stage. That is, until now valve 5A
The one that was injected 100% into the circuit IA by opening the
Depending on a certain condition, the motor 6BK command is issued to open the pulp 5B, and IA and IB are changed to step aeration of 50% and 50%, respectively, and the step aeration of IA to IE is similarly performed for each condition. The concentration of MLBB flowing out from the final settling tank 10 is reduced. As a result, the amount of sludge carried into the treated water from the final settling tank can be reduced.

Next is the factor TbI, which is used in place of the biochemical oxygen demand (BOD) and chemical oxygen consumption (COB) of the inflow water, and is used when the inflow water increases,
This will be a factor in deciding when to switch the injection point during increase. Generally, the inflow characteristics during rainfall are such that the inflow turbidity increases rapidly at the beginning of the rain, this state continues for several tens of minutes, and then it rapidly decreases. When the amount of inflow wastewater is the same, inflow water turbidity Tbt
(or BOD, COD, total organic carbon T○C, etc.), the longer the residence time (reaction time) of the inflow water in the aeration tank is advantageous. Therefore, the 'rbt value is measured by the 'X'bt meter 3, and this Tbi value is used as a factor for advancing or delaying the change timing of the inflow water injection point when the inflow water increases or when the SVI increases. The higher the inflow turbidity, the longer the reaction time for each aeration tank must be lengthened; however, in such a case, the change timing is delayed.

Next, regarding the SVI signal, as the BVI value increases, the sedimentation rate of sludge in the final settling tank IO decreases, and as a result, the carryover of sludge from the final settling tank increases. Therefore, in the same way as when the amount of inflow spring water increases, when the SVX increases, the injection point of the injected water is changed to the later stage of the circuit when the 8V engineering value exceeds a certain condition to prevent carryover of sludge from the final settling tank. 0 or more, which is a factor that causes
If the value or the like decreases, an operation is performed to return the injection point to the previous stage. Further, in the above, the amount of inflowing sewage and SVX have been explained separately, but in an actual plant, since they each vary independently, for example, the amount of inflowing sewage and SVI may both increase. In this case of 5,
One or more points that require the timing of changing the inflow water injection point to be earlier than when the timing is increased by each factor - 10,000 are summarized as follows.

As a factor for changing the inflow water injection point, the inflow fresh water amount value,
Influent water turbidity Hz Use SVI value. In addition, the standard value for change is the amount of inflow sewage (Q, 0) SVI (8VI.)
However, since each factor varies independently, the reference value of each factor for modification is determined by considering the interaction of each factor.

Figure 2 shows an example of this standard value determination method.
For example, this shows the case where Tbi is constant, and it can be seen that as SVI increases, the reference value of Q5 decreases.

This indicates that as the SVI increases, it is necessary to lower the standard value of Qs and change the injection point early. Preparing such a standard value as a table in the control device 4 makes it possible to make predictions. Control.

Regarding the lbl S RT control algorithm, the fa1
By changing the injection point of inflow sewage, the ratio of sludge in the aeration tank to the final settling tank can be increased, even when the inflow load increases or when the SV works is in a large bulking state. It is possible to reduce the amount of sludge flowing into the final sedimentation, and as a result, prevent the sludge from flowing into the treated water.

By the way, when the sludge to be withdrawn from the final settling tank is quantitatively withdrawn, the return sludge concentration changes as the injection point changes, and the amount of sludge to be withdrawn as surplus sludge (division/d') changes, resulting in SRT.
cannot be maintained constant.

Therefore, the present invention provides EI to further improve control efficiency.
It combines RT control, and the control algorithm is shown below.

First, calculate the amount of sludge remaining in the treatment system.

Here, the inside of the treatment system mainly refers to the aeration tank 1 and the final settling tank 1.
0, but if there is another sludge storage tank or if the amount of sludge stagnant in the return circuit cannot be ignored, this value is added. The amount MA of sludge in a 14-air tank is calculated by the following regression formula using, for example, the measured values of a total of 8 ML8Bs installed in one aeration tank.

MA= f(ML[381-az)=[2+(- For example, MA(kg)=aI+ a, -MLSBE(where t=1xn, z=1~m, at, a,
: regression coefficient, MLSBE: MLS installed in circuit lE
Output of S meter) Also, the final settling tank sludge 1tM8 is calculated using, for example, the following regression formula.

MS(kg)=:f(QB-QR-MSLLB-8Vr
)++t++ The amount Mw of sludge to be extracted as surplus sludge on the f311th day is determined by the following formula.

However, if the inflow water injection point is changed, the sludge distribution in the aeration tank changes, so it is necessary to change the regression coefficient of the regression equation shown in equation (2). For this purpose, it is necessary to obtain regression coefficients corresponding to each injection method in advance and input them to the control device 4. In addition, in the case of the final settling tank, it is not necessary because factors such as SvZ * Qs and QB are included in the formula.

By combining such SRT control, even if the injection point is changed, 8RT can be controlled to be constant.

H1 Effects of the Invention The present invention improves SV by changing the injection point of the amount of inflow sewage by the factor of ``Q B + Tb L a SV''.
Even when X is large or the inflow load increases, it is possible to increase the sludge volume ratio in the aeration tank, reduce the amount of sludge flowing from the aeration tank to the final settling tank, and prevent sludge from flowing into the treated water. It is something. Further, by further combining SRT control with this injection point change control, effects such as improved quality control in the activated sludge method are achieved.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of the present invention, and FIG. 2 is an explanatory diagram for determining a reference value when changing an injection point. l...Aeration tank, 2...Inflow water turbidity meter, 3...Inflow water turbidity meter, 4...Control device, 7...Sludge capacity meter, 8.
...Activated sludge suspended solids concentration meter, 9...Sludge capacity index calculation unit, lO...Final settling tank.

Claims (3)

[Claims] (1) Install an inflow sewage volume (Q_s) meter and inflow water turbidity (T_b_i) meter on the inflow side of the aeration tank, and install a sludge volume (SV) meter and activated sludge suspended solids concentration (MLSS) meter in the aeration tank. , and an SVI calculation unit that calculates a sludge volume index (SVI) based on the SV value and the MLSS value, and in activated sludge treatment in which water quality is controlled by introducing the values measured by each of these measuring instruments into a control device, respectively, The aeration tank is divided into a plurality of step aeration tanks, and the Q_s, T_b_i, and SVI are used as changing factors for the injection point of the amount of sewage flowing into the divided aeration tank. Bulking control method. (2) A patent claim characterized in that Q_s, T_b_i and SVI are stored in the control device as reference values based on mutual interaction, and the inflow sewage amount injection point change control is performed based on the stored reference values. Range of S described in item 1
Bulking control method using VI. (3) A Q_s meter and a T_b_i meter are provided on the inflow side of the aeration tank, an SV meter and an MLSS meter are provided in the aeration tank, and an SVI calculation unit that calculates SVI based on the SV value and the MLSS value is provided, and each of these In activated sludge treatment in which water quality is controlled by introducing values measured by measuring instruments into respective control devices, the aeration tank is divided into a plurality of step aeration aeration tanks, and the inflow sewage amount injection point into the divided aeration tank is The change control is carried out by using the Q_s, T_b_i, and SVI, and the inflow sewage amount injection point change control and the sludge retention time control which controls the sludge retention time are controlled in combination. bulking control method.