JPH06312200A - Injection control of polymeric flocculant - Google Patents

Abstract

PURPOSE:To develop a rapid polymer injection control method enabling the optimum injection of an ionic polymeric flocculant (polymer) in a process injecting the polymer in sludge to flocculate and dehydrate sludge. CONSTITUTION:In a polymer injection control method, the flow current value corresponding to either one of the bending point A (1) present in the relation between a polymer injection amt. and a flow current meter measured value, the bent point B (2) present in the relation between the polymer injection amt. and the change quantity of a flow current value and the max. value (3) present in the relation between the polymer injection amt. and the change quantity of the flow current value is set to the control objective value of a flow current meter so as to hold the flow current meter measured value of a sludge dehydrated separation soln. to a predetermined value to inject a polymer.

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 injection amount of an ionic polymer coagulant in a sludge dewatering process using an ionic polymer coagulant.

[0002]

2. Description of the Related Art Sludge is dehydrated when treating sludge generated by wastewater treatment, etc. However, since sludge is extremely difficult to dehydrate, a flocculant is usually added to facilitate the dehydration. The means to do is adopted. Among the aggregating agents, ionic polymer aggregating agents are widely used because of their excellent aggregating properties.

By the way, when this ionic polymer flocculant (hereinafter referred to as polymer) is used, the effect is not improved as the injection amount is increased, and the injection amount has an optimum value. In other words, it is impossible to dehydrate with an under injection amount,
On the contrary, if the injection amount is too large, the dewatering property is deteriorated, and phenomena such as an increase in the water content of the dehydrated cake and a decrease in the processing speed occur, and moreover the coagulant consumption increases. Therefore, it is necessary to properly control the polymer injection amount. In order to determine the amount of polymer injection so that sludge dewatering can be performed appropriately, conventionally, a feedback method has been used in which the operating state of the dehydrator is observed and the amount of polymer injection is adjusted appropriately. For the adjustment, a belt press is used as an index by observing the liquid surface position of the gravity filtration section, the cake protrusion in the dehydration section, and the peelability of the cake. In the centrifugal dehydrator, the turbidity of the separated liquid or the motor torque was used as an index. However, all the indicators were not always clear because the target value for achieving a good dehydration state changed depending on the sludge properties.

As an optimal control method of the polymer injection amount in the sludge dewatering process, the injection amount is controlled so that the value measured by the flow ammeter of the dehydrated separated liquid of sludge (hereinafter referred to as the flow current value) is used as an index. A method has been proposed. (Japanese Patent Application Laid-Open No. 4-83600) This method has the best dehydration property of sludge, such as a decrease in water content of the dehydrated cake and an increase in solids recovery rate at a polymer injection amount at which the streaming current value is close to zero. The control method was invented because the phenomenon that Compared with the solids proportional control method that has been widely used so far, this control method can control the polymer injection amount to the optimum amount for the sludge property, so that the operating condition of the dehydrator is always maintained in good condition and the polymer consumption is controlled. This is an excellent method that has the effect of preventing waste of quantity.

However, it has recently become clear that this method has the following two problems. One of them is the problem of control destabilization due to fluctuations in sludge properties.
That is, the above control method can obtain the above effect on the assumption that the flow current value can always be maintained near zero even if there is a change in the sludge property, but a large change occurs in the sludge property in the actual sludge treatment process. , The flowing current value cannot be maintained near zero, the flowing current value fluctuates extremely, and the hunting phenomenon that the amount of polymer injection fluctuates greatly occurs, the operation of the dehydrator becomes unstable and the amount of polymer consumption increases. However, in extreme cases, it will be inoperable.

The second problem is the problem of control failure due to the zero point of the flow ammeter and the shift of the sensitivity over time. That is, if the flow ammeter is continuously used for a long time, the zero point of the flow ammeter moves with time due to wear or contamination of the probe portion, or the sensitivity changes with time. Even if the polymer injection amount was controlled by setting the value to "zero", the dehydrated cake could not always be maintained in a good dehydrated state. In this case, it is necessary to change the control target value while observing the operation status of the dehydrator.
The frequency of changing the target value varies depending on the case, but when it is remarkable, it is once a day and considerably troublesome. Therefore, a control method that does not require changing the target value is desired.

[0007]

SUMMARY OF THE INVENTION The present invention solves the problems of the conventional method, and provides a highly stable and rapid injection control method that enables optimal injection of polymer in the sludge dewatering process. To develop.

[0008]

The above objects can be achieved by the method for controlling the injection of a polymer flocculant according to the present invention. That is, 1) In the sludge dewatering method in which the polymer injection amount is controlled so that the flowing current value of the sludge dewatering separated liquid maintains a predetermined value, it corresponds to the inflection point A existing in the relationship between the polymer injection amount and the flowing current value. A method for controlling injection of an ionic polymer flocculant, characterized in that the flowing current value to be set is set as a control target value of the flowing ammeter. 2) In the sludge dewatering method in which the polymer injection amount is controlled so that the flowing current value of the sludge dewatering separated liquid maintains a predetermined value, at the bending point B existing in the relationship between the polymer injection amount and the changing amount of the flowing current value. A method for controlling injection of a polymer flocculant, characterized in that a corresponding flow ammeter measurement value is used as a control target value of the flow ammeter. 3) In the sludge dewatering method of controlling the injection amount of the ionic polymer coagulant so that the measured value of the sludge dewatering separated liquid flow current meter maintains a predetermined value, the injection amount and the streaming current of the ionic polymer coagulant are measured. A method for controlling injection of a polymer flocculant, wherein a flow ammeter measurement value corresponding to a maximum point existing in a relationship with a change amount of a constant value is set as a control target value of the flow ammeter. Is.

In the polymer injection control method described in the above 1) of the present invention, in the step of adding the polymer to the sludge and dehydrating it, the flow corresponding to the bending point A existing in the relationship between the polymer injection amount and the flowing current value. The current value is used as the control target value of the flow ammeter to control the polymer injection amount. Here, the inflection point A that exists in the relationship between the polymer injection amount and the streaming current value is shown in the graph of FIG. 1 in that when the polymer injection amount increases, the method of increasing the value of the streaming current meter sharply decreases. It is the inflection point A entered, and when the polymer is injected with the flowing current value corresponding to this point as the control target value of the flowing ammeter, the polymer injection amount becomes the point a entered in the graph of FIG.

Further, in the polymer injection control method described in the above 2) and 3) of the present invention, the amount of change in the flowing current value is mainly a certain polymer injection amount in the coagulation and dehydration step of sludge by polymer injection. , The flow current value of the sludge dewatering separated liquid in response to the polymer injection amount at two points before and after the close fixed interval is observed, and the difference between the flow current values is taken as the change amount of the flow current value in the central polymer injection amount. , Found in the relationship between the polymer injection amount and the change amount of the streaming current value (this relationship is a differential function relationship of the polymer injection amount of the polymer injection amount and the measurement value of the streaming ammeter). It is intended to control the polymer injection amount by setting the maximum value or the flowing current value for the bending point B as the control target value of the flowing ammeter.

Here, the inflection point B existing in the relationship between the polymer injection amount and the change amount of the streaming current value is that the change amount of the streaming current meter value becomes very small when the polymer injection amount increases,
It is the inflection point B entered in the graph of FIG. 2, and when the polymer is injected with the flowing current value at the polymer injection amount corresponding to this point as the control target value of the flowing ammeter, the amount of polymer injection is plotted even if the sludge property changes. It can be maintained at point a entered in the graph of 2. (This point a coincides with point a in FIG. 1.) Since the difference in the fluctuation of the streaming current value is used to determine the control target value by this control, even if the zero point or sensitivity of the streaming ammeter changes, it is affected by it. The sludge can be properly dehydrated continuously without being subjected to the above. In actual sludge dewatering, it is preferable to inject a little more than the polymer injection amount at the bending points A and B obtained as the control target value, preferably about 2 to 5% of the obtained polymer injection amount.

Any ionic polymer flocculant can be applied to the flocculant used in the present invention. As an example, first, as the cationic organic polymer flocculant, N, N '
Of cations such as dimethylaminoalkyl acrylate or methacrylate acid salts, vinylbenzyltrimethylammonium acid salts, acrylamide cation modified acid salts, vinylpyridine and its substituted derivatives, acrylamine and its substituted derivatives. Examples include homopolymers and copolymers. In addition, copolymers of the above cationic monomers with monomers such as acrylamide, acrylonitrile, and alkyl acrylate, as well as polyvinyl imidazoline acid salts, chitosan acid salts, and starch cationization products are also used. it can.

As the anionic organic polymer flocculant, acrylic acid, methacrylic acid and alkali metal salts thereof, sulfomethylated acrylamide and alkali metal salts thereof, vinylbenzenesulfonic acid, styrenesulfonic acid and alkali metal salts thereof, vinyl Sulfonic acid and its alkali metal salts, and homopolymers and copolymers such as maleic anhydride are used. Further, copolymers of the above anionic monomers with monomers such as acrylamide, acrylonitrile and alkyl acrylate, as well as sodium alginate and anion-modified chitin can be used. In some cases, an inorganic flocculant such as PAC, sulfuric acid band, ferric chloride, ferrous sulfate, or lime may be used together with these organic polymer flocculants. Furthermore, a combination of a Mannich modified product of a polyacrylamide polymer and an anion polymer; a combination with a cationic polymer, an anionic polymer, an acid or an acidic sodium salt (powder); a combination with a cationic polymer, an anionic polymer, an alkaline agent; a cationic monomer, an anion An amphoteric polymer flocculant such as a copolymer of a monomer or a nonionic monomer alone or PAC, van sulphate,
It can also be used in combination with an inorganic salt such as iron chloride.

[0014]

In recent research, it has been clarified that the change of the streaming current value of the sludge dewatering separated liquid in response to the polymer injection amount has a tendency as shown in FIG. That is, in the illustrated range of the polymer injection amount, there is a region where the flowing current value of the sludge dewatered separation liquid shows a large change and a region where the flow current value of the sludge dehydrated separation liquid shows little change in response to the change of the polymer injection amount, and there is a boundary between them. Has the above-mentioned bending point A (indicated by point A in the figure).

In a state where the flow ammeter is operated with the control target value being zero, for example, due to the property of sludge (as in the state shown in FIG. 1), the current value before and after the current value of the flow ammeter is zero ( The flow current value / polymer injection amount) gradient is large, so even if the polymer injection amount is slightly increased, the flow current value changes significantly, and polymer injection is performed to keep the flow current value constant at zero. It becomes difficult to control the quantity.

On the other hand, when the control target value of the flow ammeter is set to a region having a small (flow current value / polymer injection amount) gradient after the inflection point (point A) shown in FIG. 1, the flow with respect to changes in the polymer injection amount is determined. Since the change in the current value is extremely small, even a slight change in the flowing current value increases the adjustment amount of the polymer injection amount and is difficult to control. If (flow current value / polymer injection amount) rapidly changes from a large gradient region to a very small gradient region, this region (this is the bending point A shown in FIG. 1).
It is understood that it becomes easy to control the polymer injection amount by controlling the polymer injection amount by setting the control target value of the streaming ammeter to (4).

Next, how to obtain the flowing current value corresponding to the bending point A will be described. FIG. 3 is a flow sheet of a control system of the present invention in which a flowing ammeter is used as a sensor and a flowing current value of a sludge dewatered separated liquid is sent to a controller as a signal from the sensor, and the controller controls the polymer injection amount, for an example of sewage sludge. It is the figure which showed. How to control the polymer injection amount by the control system of the present invention depends on the function of the controller. (1) The controller of the control system of the present invention in FIG. 3 inputs at least a specific flowing current value. A function to set the control target value. (Setting function) A function to control an external device such as a pump according to the control target value. If it has (control function), change the polymer injection amount in advance for sewage sludge and measure the flowing current value corresponding to each injection amount,
The relationship curve between the flowing current value and the polymer injection amount is obtained, the bending point A is determined from the relationship curve, and the flowing current value corresponding to the bending point A is input to the controller as the control target value. The polymer injection pump can be controlled by the control target value.

(2) Furthermore, as a function of the controller of the control system of the present invention in FIG. 3, a function of storing the measured value of the sensor. (Memory function) Function to compare the stored previous measurement value with the new measurement value and specify the same type of specific value by calculation. (Comparison / calculation function) A function to set a specific measured value as a control target value. (Setting function) A function to control an external device such as a pump according to the control target value. If it has a (control function), it stores the relationship curve between the flow current value and the polymer injection amount for the previous sewage sludge, compares it with the relationship curve for the current sewage sludge, and compares the two relationships with the current relationship curve. The bending point A at is determined by calculation, and the corresponding flowing current value is automatically input as the control target value, and thereafter the method for controlling the polymer injection pump according to the control target value for the current sewage sludge is completely automatic. It is possible to control the polymer injection amount. The storage and comparison functions can be omitted if necessary.

Next, a method for automatically controlling the polymer injection amount by using the amount of change in the flowing current value is proposed. As already described above, for example, when the variation amount of the streaming current value is taken on the vertical axis instead of the relationship curve of the polymer injection amount and the streaming current value shown in FIG. 1, a differential relation curve of the streaming current value with respect to the polymer injection amount is obtained. The curve is as shown in FIG. In this Figure 2,
There are local maxima and inflection points B. Here, the bending point B is a point at which the rate of change (decrease rate) of the flowing current value changes rapidly. In order to measure the differential relation curve of the flowing current value with respect to the polymer injection amount as shown in FIG. 2, in the flow sheet of the control system of the present invention shown in FIG. 3, a differential circuit is provided between the sensor and the controller. You can insert and measure.

The polymer injection amount corresponding to the maximum point in FIG. 2 is the polymer injection amount (b) where the flowing current value in FIG. 1 is zero.
2 corresponds to the polymer injection amount (a) at which the flowing current value in FIG. 1 bends. Therefore, a differential circuit is inserted between the sensor and the controller of the control system of the present invention to differentially transform the measured value of the sensor, and the control target value corresponding to the maximum value or the bending point B can be automatically determined. In this way, obtaining the control target value using the amount of change in the flowing current value is equivalent to using the relative value, that is, the difference in fluctuation of the flowing current value, for control, rather than the absolute value of the flowing current value. Even if the zero point or sensitivity of the meter changes, the polymer injection amount can be determined without being affected by it.

FIG. 4 shows the structure of the flow ammeter 1 which is the sensor of the control system of the present invention. When the sample 4 existing in the gap between the piston 2 and the cylinder 3 is sheared by the vertical movement of the piston, the electric charge of the sample is biased. The minute bias of the electric charge is detected as a voltage or a current by an electric circuit provided outside, and appropriately amplified and displayed. Since there is no physicochemical index that indicates the bias of electric charge, its magnitude is usually determined using the output value of a streaming ammeter. However, it should be noted that the output value does not have a unit and has no absolute meaning, because the electric circuit and the display method differ depending on the manufacturer of the flow ammeter and the measurement range. However, normally, the measurement circuit and the like are set so that zero and its sign of the output of the flow ammeter match the electric charge of the actual sample. In that case, apart from the absolute value, at least zero and the sign will have a physical meaning.

In FIG. 4, the sample is the sample inlet 5
It is further introduced and discharged from the sample outlet 6. The flowing current value is measured by the electrode 7, and a current corresponding to the electric charge of the sample is generated in the AC state in the electrode 7 as the piston moves up and down. This current is amplified and displayed using a suitable amplifier (not shown). The piston 2 is configured to move up and down via the guide 10 by the rotation of the motor 9.

[0023]

EXAMPLES The present invention will be specifically described below with reference to examples. However, the present invention is not limited to this embodiment.

Example 1 A cationic polymer (Ebara Gloss C104G, manufactured by Ebara Infilco Co., Ltd.) was added to mixed raw sludge discharged from an urban sewage treatment plant, and dehydrated by a belt press. The properties of the mixed raw sludge are 1.5 to 3 in SS because the amounts of surplus sludge and initial settled sludge change.
5% (2.5% on average), 60-85% on VSS (7 on average)
5%). When the control target value of the flowing ammeter is operated at zero (conventional method JP-A-4-83600), when the control target value is operated at the inflection point A according to the present invention (invention method 1), and the flowing current value The results shown in Table 1 were obtained by comparing the case where the measured value corresponding to the maximum point of the change amount of 1 was used as the control target value (invention method 2). In the conventional method, the measured value of the streaming ammeter fluctuates, resulting in a so-called hunting state, in which the polymer flow rate fluctuates greatly, and the fluctuation range is about 0.8 to 1.25% in the polymer injection rate, and the average value is It became 0.95%. In addition, the operating state was unstable, such as temporary protrusion in the filtration section of the belt press and poor peelability at the cake outlet.
In the method 1 of the present invention, although the polymer injection rate is slightly high, the fluctuation range is small, and it is clear that the method has extremely stable controllability and good dehydration property. Further, in the method 2 of the present invention, the fluctuation range was small and stable control was possible. The polymer injection rate in Table 1 is the polymer solution injected into the sludge (usually 0.2%).
The amount of solids of the aqueous solution dissolved in the polymer concentration of 1) divided by the amount of solids of the sludge to be injected is expressed as a percentage.

[0025]

[Table 1]

[0026]

EFFECTS OF THE INVENTION According to the present invention, it is possible to always operate the dehydrator stably with respect to changes in the properties of sludge, so that the polymer saving effect is great. Also, since the control operation can be performed by the difference in the fluctuation of the flowing current value without using the absolute value of the flowing current meter, the flowing current value can be a relative value and the disturbance due to the fluctuation of the zero point can be canceled. The maintenance of the sensor is easy because the zero / span adjustment of the meter is unnecessary.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the polymer injection rate of the present invention and the measurement value of a streaming ammeter.

FIG. 2 is a graph showing a relationship between a polymer injection rate of the present invention and a differential value of a measurement value of a streaming ammeter.

FIG. 3 is a diagram showing a flow sheet of the control system of the present invention.

FIG. 4 is a schematic structural diagram of a streaming ammeter of the present invention.

[Explanation of symbols]

 1 Flow ammeter 2 Piston 3 Cylinder 4 Sample 5 Sample inlet 6 Sample outlet 7 Electrode 8 Power supply 9 Motor 10 Guide A Bending point A B Bending point B a Polymer injection amount at bending points A and B b Zero point and maximum point Polymer injection amount in

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kiyoshi Shimizu, Toranomon, 2-3-13, Minato-ku, Tokyo Within the Japan Sewer Works (72) Inventor, Chiaki Igarashi, 1-127, Konan, Minato-ku, Tokyo EBARA IN FILCO Co., Ltd. (72) Inventor Issei Tanaka 1-6-27 Konan, Minato-ku, Tokyo Ebara-IN Filco Co., Ltd. (72) Inventor Kazuo Fujita 1-6-27 Konan, Minato-ku, Tokyo EBARA In Infilco Co., Ltd. (72) Inventor Takeshi Yozomoto 1-6-27 Konan, Minato-ku, Tokyo Ebara Infilco Co., Ltd.

Claims (3)

[Claims] 1. A sludge dewatering method for controlling an injection amount of an ionic polymer coagulant so that a flow ammeter measurement value of a sludge dewatering separated liquid maintains a predetermined value. A method for controlling injection of a polymer flocculant, wherein a flow ammeter measurement value corresponding to a bending point A existing in a relationship with a flow ammeter measurement value is set as a control target value of the flow ammeter. 2. A sludge dewatering method for controlling an injection amount of an ionic polymer coagulant so that a flow ammeter measurement value of a sludge dewatering separated liquid maintains a predetermined value. A method for controlling injection of a polymer flocculant, characterized in that a flow ammeter measurement value corresponding to a bending point B existing in a relationship with a change amount of a flow ammeter measurement value is used as a control target value of the flow ammeter. 3. A sludge dewatering method for controlling an injection amount of an ionic polymer coagulant so that a flow ammeter measurement value of a sludge dewatering separated liquid maintains a predetermined value. A method for controlling injection of a polymer flocculant, wherein a flow ammeter measurement value corresponding to a maximum point existing in a relationship with a change amount of a flow ammeter measurement value is set as a control target value of the flow ammeter.