JPH0457398B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a sludge management device used when treating water by an activated sludge process.

Generally, in water treatment using the activated sludge process, the water to be treated is first introduced into a settling tank, then mixed with activated sludge in an aeration tank and aerated there, and then solid-liquid separated in the final settling tank. The clear water is discharged as treated water and used for water treatment.

In such processes, in order to obtain good treated water, the flow rate of return sludge returned from the final settling tank to the aeration tank and the flow rate of sewage flowing into the aeration tank are controlled, but these controls are not conventional methods. This is done with SVI in mind. This SVI is called a sludge capacity index expressed as the ratio of the sludge volume after 30 minutes of settling (SV ₃₀ ) and the activated sludge suspended solids concentration (MLSS). It is determined by sampling water into a sedimentation tube and performing a batch sedimentation test.

By the way, in sludge management using SVI, there is no information on sludge settling control that can be obtained from the progress of sludge settling, so detailed sludge properties cannot be grasped. It was unclear how to control the surface loading rate of the final settling tank in order to prevent sludge from appearing or flowing into the effluent water. Also, if the sludge properties differ, the SV ₃₀ and MLSS values will differ.
Since SVI is the ratio of these values, it may be the same value even if the sludge properties are different. For these reasons, sophisticated sludge management has been difficult, for example, it has been difficult to control the outflow of sludge in effluent water.

Purpose of the Invention The present invention was made under the above circumstances, and an object of the present invention is to provide a sludge management device that can improve sludge management.

Summary of the invention In addition to the SVI meter, the present invention includes a turbidity meter that detects the turbidity of supernatant water obtained by solid-liquid separation of a sampled water mixture, and receives SVI signals from the SVI meter and the turbidity meter, respectively. The present invention is characterized in that the sludge and turbidity signals are input to the calculation section, where a setting signal for the return sludge flow rate is determined, and the return sludge pump is controlled based on this setting signal.

Example Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of the present invention. Reference numeral 1 denotes an aeration tank, into which sewage flows from a first settling tank (not shown) via a sewage inflow pump P ₁ and a pipe 11. 2 is a final settling tank, which separates the liquid mixture sent from the aeration tank 1 through the pipe line 12 into solid and liquid, and discharges the supernatant water through the discharge pipe line 13.
3 is a turbidity meter for effluent water for measuring the turbidity of effluent water. 14 is a return sludge pipe, and the sludge deposited in the final settling tank 2 is returned to the aeration tank 1 via this return sludge pipe 14 by a return sludge pump _P2 . 4 is an SVI meter, which measures the SVI of the mixed liquid sampled near the outlet of the aeration tank 1. 5 is SVI
This is a turbidity meter attached to the meter, and measures the turbidity of the sampled mixed liquid. 40 is turbidity meter 5
The entire device (hereinafter referred to as SVI meter with turbidity meter) attached to SVI meter 4 is shown. 6 is an arithmetic unit;
Based on the turbidity signal from the turbidity meter 5, the SVI signal from the SVI meter, and the turbidity signal from the effluent water turbidity meter 3, a return sludge flow rate setting signal and a sewage flow rate setting signal into the aeration tank 1 are sent. Calculate and find. Reference numeral 7 denotes a control unit, which controls the sewage inflow pump P ₁ and the return sludge pump P ₂ based on the setting signal determined by the calculation unit 6 and the turbidity signal from the effluent water turbidity meter 3.

The structure of the SVI meter 40 with a turbidity meter will be explained with reference to FIG. 2, but the structure of an SVI meter without a turbidity meter is well known. 41 is a sludge settling pipe, 42 is a test water injection pipe, and 43 is an air lift pump whose lower end is immersed in the aeration tank 1. 44A and 44B are a light projector and a light receiver, respectively, and are attached to a support member 45, and this support member 45 is combined with a lifting mechanism (not shown) including a lifting motor. The lift motor is controlled based on the output from the light receiver 44B to move the light receiver 44B up and down while following the interface. Reference numeral 46 denotes an SVI measurement circuit section, which includes a potentiometer etc. attached to the rotating shaft of the lifting motor, and obtains an electric signal corresponding to the solid-liquid interface position within the sedimentation tube 41. Note that since the cross-sectional area of the settling tube 41 is constant, this electric signal has a size corresponding to the sludge volume. In this example, an interface position detection section for detecting the solid-liquid interface in the sedimentation tube 41 is configured by the light emitter 44A, the light receiver 44B, the lifting mechanism, the potentiometer, and the like. 47 is an MLSS detector, the output signal of which is input to the SVI calculation unit 48. A protrusion 51 is provided at the upper part of the sedimentation tube 41, and a turbidity detection sensor 52 is housed within the protrusion 51. 53 is a conversion unit that converts the signal from the turbidity detection sensor 52 into an electric signal, and together with the turbidity detection sensor 52 constitutes the turbidity meter 5. 49 is a drain port, 491 is an air solenoid valve for stirring, and 492 is a blower. In the SVI turbidity meter having such a configuration, a mixed liquid of sewage and activated sewage is injected into the sludge settling pipe 41 via the air lift pump 43. The injected mixture is
Solid-liquid separation occurs as the sludge settles. The interface position between the sludge and the supernatant water is detected by the interface position detection section, and the SV measurement circuit section 46 obtains an electric signal corresponding to the interface position and the sludge volume. and
From the SV measurement circuit section 46 and the MLSS detector 47,
The ratio of the sludge volume after settling for 30 minutes to the initial sludge volume (SV ₃₀ ) and the MLSS signal are calculated by the SVI calculation unit 4.
8, where the SVI signal is obtained.

61 is a recorder for recording turbidity and interface position; 62 is a data analysis section such as a computer that analyzes the data recorded on the recorder; and 63 is a printer. The data analysis unit 62 has a sludge settling curve storage processing function, a function of determining parameters such as initial settling rate, Roberts constant, compaction density, final sludge interface, etc. based on the sludge settling curve, and a noise filtering function of turbidity data. It also has turbidity data storage and processing functions. The above parameters represent changes in sludge properties and sludge settling characteristics, and once determined, they can be used for operational control such as selecting the optimal surface load rate in the final settling tank. Further, while measuring the turbidity of supernatant water, the turbidity instantaneously increases and noise is generated, so if the data analysis section 62 is provided with a noise filter function to cut out the noise, stable measurement results can be obtained. Note that the calculation section 6 in FIG. 1 incorporates an analysis function, a turbidity noise filter function, and the like. Regarding data processing, the data may be recorded only using the recorder 61, or the data may be analyzed directly by the data analysis unit 62 without recording the data, or even as described above. Both data recording and data analysis may be performed. In other words, a flexible system can be created depending on the situation. By constantly detecting turbidity and recording the data, it is possible to predict changes in SVI and sludge properties, as described below. Further, as will be described later, since there is a correlation between the turbidity of supernatant water and SVI, SV, etc., the above-mentioned parameters can be determined by measuring the turbidity, and a sedimentation curve can be obtained.

Reference numeral 100 in FIG. 2 is a cleaning brush, which has the function of cleaning the inner wall of the sludge settling pipe 41 and the surface of the turbidity detection sensor 52. This can prevent biofilm etc. from adhering to the wall surface.

As the turbidity detection sensor 52, it is preferable to use, for example, a near-infrared type sensor because it is easy to attach and stable turbidity detection can be performed. The standard measurement span is 0 to 200 mg/.

Here, we will discuss the relationship between turbidity, sludge properties, and sludge settling characteristics. FIG. 3 is a graph showing the relationship between the supernatant water turbidity TU _SV in the sedimentation tube 41 (the value when the turbidity at the top of the mixed liquid has settled down after the start of solid-liquid separation) and SV ₃₀ using a double logarithmic graph. , Figure 4 shows TU _SV and
FIG. 3 is a graph showing the relationship with SVI using a log-log graph. As you can see from these figures, TU _SV and
There is a high correlation with SV ₃₀ and SVI. Figures 5A and 5B are graphs showing changes in sea level position H _t and changes in supernatant water turbidity TU with respect to settling time, respectively.The points are the curves representing the changes in H _t (sludge settling curves), and the solid lines are the curves representing the changes in TU. This is a curve showing changes. Fifth
As can be seen from Figures A and B, there is a certain degree of correspondence between the turbidity reduction pattern and the sedimentation pattern. By measuring the time it takes for the turbidity to reach 50mg/or less and the value at which the turbidity has settled down, the turbidity reduction pattern can be determined and used to predict changes in sludge properties. FIG. 6 is a logarithmic graph of the relationship between the sedimentation velocity ISV and TU _SV , and if the consolidation start times t _c are the same, ISV and TU _SV have a high correlation. Experiments have shown that t _c has a correlation with SVI, so in the end it can be calculated from SVI and TU _SV .
ISV can be predicted. As can be seen from FIG. 6, activated sludge flocs with a large ISV have a large difference in settling speed depending on the size of the floc diameter, so the activated sludge with a small ISV remains in the upper part of the settling tube 41, and the TU _SV is large. On the other hand, if the ISV is small
SVI is large and filamentous fungi (Sphaerotilus natans)
The flocs are connected to each other by filamentous fungi, and the minute flocs are surrounded by other flocs and settle as a group, so the TU _SV is small. i.e. TU _SV
When TU SV is large, the overall sedimentation rate is high, and when TU _SV is small, the overall sedimentation rate is low. FIG. 7 is a diagram showing the relationship between the frequency of occurrence of filamentous fungi and SVI, and it can be seen from the figure that the larger the SVI, the higher the frequency. However, CC appears in extremely large amounts, C appears in large amounts, + appears normally, r appears slightly,
rr means that it appears very rarely, and ND means that it does not appear. As described above, the turbidity of the supernatant water is a factor that is greatly related to the sludge properties and sedimentation characteristics, and the present invention performs operation control taking this turbidity into account.

Next, the operation of the embodiment shown in FIG. 1 will be described. The mixed liquid in the aeration tank 1 is injected into the settling tube 41 of the SVI meter 40 with a turbidity meter, where SVI and TU _SV are detected. The SVI signal and the TU _SV signal are then input to the calculation unit 6 along with the turbidity signal from the effluent turbidity meter 3, where the set value Q _R of the return sludge flow rate and the setting value for the aeration tank 1 are determined based on these input signals. A set value Q _S of the inflow sewage flow rate is calculated. Q _R , Q _S and the turbidity signal from the effluent turbidity meter 3 are input to the control unit 7, which controls the sewage inflow pump P ₁ and return sludge pump P ₂ based on these input signals. now
If TU _SV is large, SVI is small, and as shown in Figure 6, the sedimentation velocity ISV is large, so
The effect of concentrating the sludge in the final settling tank 2 is promoted, and the concentration of returned sludge increases. Therefore, the flow rate of return sludge is decreased so as to keep the MLSS in the aeration tank 1 constant, and the flow rate of inflow sewage is increased accordingly. On the other hand, when TU _SV is small,
Since the SVI is large and the sedimentation rate ISVI is small, the effect of concentrating the sludge in the final settling tank 2 is reduced, and therefore the concentration of returned sludge is reduced. Therefore, the flow rate of returned sludge is increased, and the flow rate of inflow sewage is decreased accordingly. Figure 8 is a diagram showing an example of such control. When TU _SV is small (less than TU ₁ ), the return sludge flow rate set value Q _R is large as Q _R1 , and the sewage inflow rate setting is The value Q _S is small as Q _S1 . and if TU _SV is between TU ₁ and TU ₂ , then Q _R
becomes smaller corresponding to the value of TU, and Q _S becomes larger corresponding to the value of TU. Furthermore, when TU _SV exceeds TU ₂ , Q _R becomes small as Q _R2 , and Q _S becomes large as Q _S1 .

In this embodiment, the turbidity of the water discharged from the final sedimentation tank 2 is detected and the operation is controlled by feeding back the turbidity signal. The residence time of the final settling tank 2 (V _F /Q _S +Q _R , V _F ; final settling tank volume) is controlled so as to keep it low, that is, to suppress the outflow of sludge into the effluent water. Furthermore, since the sewage inflow pump _P1 is also controlled in consideration of TU _SV ,
More appropriate operation control is possible.

Effects of the Invention As described above, in the present invention, the turbidity of the supernatant water obtained by solid-liquid separation of the mixed liquid sampled from the aeration tank 1 is
Based on the discovery that there is a high correlation with SV, SVI, sedimentation rate, etc., and that there is a deep relationship between sedimentation characteristics and sludge properties, in addition to the SVI meter, we have developed a turbidity meter to detect the turbidity described above. Using a detector, SVI
Since the signal and the turbidity signal are used as input signals for controlling the return sludge pump, the operation control takes into consideration the sludge properties and sedimentation characteristics. Therefore, proper operation control is performed and sludge management becomes sophisticated.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram showing an embodiment of the present invention, Figure 2 is an explanatory diagram showing an SVI meter with a turbidity meter added and its output signal line, and Figure 3 is a diagram showing the relationship between SV ₃₀ and supernatant water turbidity. Graph showing the relationship, Figure 4 is a graph showing the relationship between SVI and supernatant water turbidity, Figure 5 A and B are sedimentation curves and graphs showing the relationship between supernatant water turbidity and settling time, and Figure 6 is a graph showing the relationship between SVI and supernatant water turbidity. Figure 7 is a graph showing the relationship between sedimentation rate and supernatant water turbidity, Figure 7 is a graph showing the relationship between SVI and filamentous fungus occurrence frequency, and Figure 8 is a graph showing the relationship between supernatant water turbidity, return sludge flow rate setting, and inflow sewage. It is a graph showing an example of the relationship with a flow rate setting value. 1... Aeration tank, 2... Final settling tank, 3... Turbidity meter for effluent water, 4... SVI meter, 5... Turbidity meter, 40
...SVI meter with turbidity meter, 41 ...Sludge settling pipe, 46
...SV measurement circuit section, 47...MLSS detector, 4
8...SVI calculation unit, 52...Turbidity detection sensor, 5
3... Conversion unit, 6... Calculation unit, 7... Control unit,
P ₁ ... Sewage inflow pump, P ₂ ... Return sludge pump.

Claims (1)

[Claims] 1. A sludge capacity index meter for determining the sludge capacity index of a mixed liquid of activated sludge and sewage sampled from the aeration tank in an activated sludge process, and the turbidity of supernatant water obtained by solid-liquid separation of the mixed liquid. A turbidity meter for detecting sludge, a sludge capacity indicator signal from the sludge capacity indicator, and a turbidity signal from the turbidity meter are input, and based on the input signals, the sludge is returned from the final settling tank to the aeration tank. 1. A sludge management device comprising: a calculation unit that calculates a setting signal for a return sludge flow rate; and a control unit that controls a return sludge pump based on the output signal of the calculation unit.