JPH11347599A - Flocculant injection amount determining apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the subject apparatus rapidly corresponding to the alteration of properties of supplied sludge to automatically determine the optimum injection amt. of a flocculant. SOLUTION: A flocculant injection amt. determining apparatus is an apparatus for determining the injection amt. of a flocculant to a flocculating and mixing tank for flocculating sludge and equipped with a measuring tank 1, a separated soln. supply part 2 for supplying a dehydrated and separated soln. obtained by dehydrating flocculated sludge to the measuring tank in a constant flow rate, a drainage part 5 keeping the liquid amt. in the measuring tank constant, a measuring part 4 measuring the amt. of floc present in the dehydrated and separated soln. supplied to the measuring tank and a control means determining the injection amt. of the flocculant minimizing the amt. of floc based on the measured data of the amt. of flock by the measuring part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coagulant injection amount determining apparatus for properly and automatically determining a coagulant injection amount in a sewage sludge dewatering step.

[0002]

2. Description of the Related Art Conventionally, in the case of sewage treatment, a muddy substance formed by precipitation of pollutants in water (hereinafter referred to as sludge).
And sludge drying is performed by solar drying or mechanical drying. Solar drying requires a lot of time and land area, and the odor spreads to the surrounding area. Therefore, at present, a mechanical drying method using a sludge dryer is generally used.

By the way, sewage sludge is mainly composed of colloidal fine particles, and the surface of the sludge particles is negatively charged and repels each other. Therefore, it is difficult to mechanically dewater the sludge as it is. Therefore, as shown in FIG. 5, a process for performing sludge conditioning (sludge aggregation) is provided as a pre-process of mechanical dewatering of sludge in a water treatment facility.

FIG. 5 is a schematic diagram for explaining a schematic configuration of an apparatus for performing sludge conditioning (sludge aggregation) in a sludge dewatering step of a sewage treatment plant. The sludge refining process using this apparatus includes the following steps. That is, a step of putting sludge discharged in the water treatment facility 50 into the coagulation mixing tank 55 via the sludge input pump 51 and the sludge flow rate control valve 52, and a stirring and mixing in the coagulation mixing tank 55 to form a mixture of the sludge particles. A step of forming and growing an aggregate (hereinafter simply referred to as a floc) of sludge particles by making the water contained in the sediment easily dehydrated;
Sending a so-called floc suspension to a sludge dewatering facility (not shown) connected via a flocculated sludge valve 53. Here, the floc refers to a large lump of fine particles in water agglomerated by the aggregating agent. Therefore, the purpose of the sludge conditioning process using the apparatus shown in FIG. 5 is to form and grow flocs in the presence of a flocculant in the flocculation and mixing tank 55, so that solid-liquid separation in the subsequent mechanical dewatering process is performed. It is to improve. Therefore, the proper injection of the coagulant in the coagulation mixing tank 55 is an important factor for maintaining good sludge dewatering properties after mechanical dewatering.

[0005] By the way, a method and an apparatus for measuring the coagulation state applicable to the above-mentioned sludge conditioning process are not known at present. Therefore, it is very difficult for a person skilled in the art to quantitatively grasp the state of sludge aggregation. Therefore, conventionally, a method of determining the injection rate of the coagulant in a state where the actual coagulation state is hardly reflected is adopted. Hereinafter, a conventional method of determining the coagulant injection rate by the sludge dry solid constant ratio formula will be described.

(1) Method for confirming optimum coagulation point by jar test A certain amount of supplied sludge is collected in several beakers. Next, a coagulant is added to the collected sludge. At this time, the coagulant injection rate is changed stepwise for each beaker, and the stirring speed is changed from rapid stirring to slow stirring. An agglutination reaction is caused in each beaker, and the flocculation property is determined to be the best, or the turbidity of the supernatant liquid is determined to be the optimum aggregation point with the lowest injection rate. further,
At this time, the drainage of the floc generated under each condition is measured, and the final determination of the optimal aggregation point may be made (for example, the one having the maximum separation water filtration speed when the generated floc is filtered is optimal).

FIG. 6 is a schematic side view for explaining a schematic configuration of a main part of an apparatus for performing a jar test. First, a plurality of beakers 62 from which an appropriate amount of sludge 61 was collected.
The stirrer 63 is inserted into each (three in the figure). The stirrer 63 has one end to which a stirring blade is attached and a pulley 64.
Are coaxially mounted and the other end is coaxially mounted. A common belt 65 applied to each pulley 64 is rotated by driving a motor 67 that is driven and controlled by a rotation speed controller 66. At this time, the stirring speed of the sludge 61 in each beaker 62 can be changed by controlling the rotation speed of the motor 67 using the rotation speed controller 66.

(2) Method for confirming the optimum coagulation point by measuring the flow current The flow current value of the sludge dewatered and separated liquid is measured and the value is close to 0 (electrically neutralized) or the flow current with respect to the coagulant injection rate. When the value history is the coagulant injection rate at which the inflection point is reached, it is determined as the optimum coagulation point.

(3) Method for Determining Optimal Coagulant Injection Rate by Empirical Constant Ratio Formula The optimum coagulant injection rate is determined by previously confirming the optimal coagulation point in the jar test of (1), and the sludge used in the test is determined. The ratio between the sludge dry solid content and the optimal injection rate is defined as the optimal ratio. Therefore, in the actual process, the sludge dry solid amount is estimated from the solid amount based on the supplied sludge supply amount and the measured value of the in-line type sludge densitometer, and the sludge dry solid amount and the coagulant injection rate are calculated. The coagulant injection rate is determined such that the ratio always maintains the previously determined optimum ratio.

[0010]

However, the above-mentioned conventional methods for confirming the optimum aggregation point and the method for determining the injection rate of the flocculant have the following problems.

In the method (1), since the test is troublesome, it is impossible to follow the change with time of the sludge property. Further, since it is relatively difficult to finely set the coagulant injection rate, it is not sufficient to confirm the optimum coagulation point in detail.

In the method (2), it is possible to confirm up to the electrical neutralization point on the sludge particle surface. However, since the subsequent aggregation mechanism is basically based on the collision (electrical coupling / adsorption) of the particles, it is difficult to measure the final aggregation state of the flocs by this method. In addition, depending on the type of organic substance or flocculant contained in the sludge, the optimum flocculation point and the electrical neutralization point may not match.

In the above method (3), a target value (ratio between the amount of dried sludge solids and the coagulant injection rate) is basically determined in advance by the method (1). Therefore, it has the same problem as the above (1). There is also a problem in the reliability of the in-line sludge concentration meter in the actual process. Further, it is necessary to correct a target value due to a change in sludge properties due to a difference in water temperature or a season or weather, and there is a problem that the target value is not universal.

As described above, the conventional method hardly reflects the actual state of aggregation. Therefore, at present, there is no known in-line coagulation state measuring method or apparatus applicable to sewage treatment.

Therefore, the present invention solves the above problems,
It is an object of the present invention to provide a device which can promptly respond to a change in the property of supplied sludge and automatically determines an optimal injection amount of a flocculant.

[0016]

In order to solve the above-mentioned problems, a coagulant injection amount determining apparatus according to the present invention is an apparatus for determining a coagulant injection amount into a coagulation mixing tank for coagulating sludge. A measurement tank, a separation liquid supply unit for supplying a dehydration separation liquid obtained by dehydrating the coagulated sludge to the measurement tank at a constant flow rate, and a drain unit for maintaining a constant liquid amount in the measurement tank. A measuring unit for measuring the volume ratio of floc present in the dehydrated separated liquid supplied to the measuring tank, and the coagulant injection amount at which the amount of floc is minimized based on the measurement data of the amount of floc by the measuring unit. Control means for determining. The control unit may be a control computer having a program for automatically adjusting the coagulant injection amount based on the measured data of the floc amount so as to minimize the floe enemy rate. The measuring tank is in addition to the above,
A stirring device capable of changing the rotation speed is provided.

Since the coagulant injection amount determining apparatus of the present invention is configured as described above, the amount of the residual floc of the dewatered separation liquid is set as the control amount, and the optimum chemical injection amount at which a good sludge dewatering property is obtained is determined by the floc The amount can be determined automatically with a minimum.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on embodiments.

FIG. 1 is a schematic diagram showing a schematic configuration of a main part of a coagulant injection amount determining apparatus according to the present invention. In the figure, the parts shown by dotted lines are the main components of the device.

The coagulant injection amount determining apparatus comprises a measuring tank 1 and a separating liquid supply unit 2 for supplying a predetermined amount of dehydrated separating liquid to the measuring tank.
And a stirrer 3 for stirring the dehydrated separated liquid supplied to the measuring tank 1, a measuring unit 4 for measuring the amount of residual floc present in the dehydrated separated liquid, and constantly measuring the amount of the dehydrated separated liquid in the measuring tank 1. A drain section 5 for keeping the temperature constant is provided as a main component.

The dewatering / separation liquid 10 is supplied to a machine in a sludge dewatering facility (not shown) which is a latter stage of a sludge conditioning process (formation and growth of flocs in the presence of a flocculant in a flocculation mixing tank) using the apparatus shown in FIG. Occurs during solid-liquid separation in the mechanical dehydration process.

The separated liquid supply unit 2 sends the dehydrated separated liquid 10 sent from the sludge dewatering equipment to the measuring tank 1 via the liquid sending pipe 6. At this time, the manual valve 7 provided in the separation liquid supply unit 2
The supply amount of the dehydrated separation liquid 10 is adjusted by the method.

The stirring device 3 inserted into the measuring tank 1 has a motor 8 and a stirring blade 9 rotated by driving the motor 8. The number of rotations of the stirring blade 9 is such that the residual floc in the dehydrated separation liquid 10
The G value (determined by the shape of the stirring blade and the number of rotations) may be set so as not to be re-agglomerated by the residual coagulant therein.

The drain section 5 includes an overflow port 11 located at a predetermined height from the bottom of the measuring tank 1 so that the dehydrated separated liquid 10 stored in the measuring tank 1 does not exceed a predetermined amount. Drainage weir 1 that receives dewatered separated liquid 10 flowing out of outlet 11
Consists of two. A drain pipe 13 communicates with the bottom of the drain weir 12. The drain pipe 13 is configured such that the amount per unit time of the dewatered separation liquid 10 flowing out from the overflow port 11 is the amount per unit time of the dewatered separation liquid 10 discharged from the drain weir 12 through the drain pipe 13. It has a sufficiently large diameter that it is much less than.

The measuring section 4 includes a dehydrated separated liquid 10 in the measuring tank 1.
Is provided with a sensor 14 for measuring the amount of the residue flocs contained in the. The sensor 14 is connected to the drainage section 5 in the measuring tank 1.
Is immersed in the vicinity of the overflow port 11. The output of the measurement value of the measurement unit 4 can be input to the computer 16 via the signal line 15. The computer 16 is a control computer having a program for automatically adjusting the coagulant injection amount so as to minimize the amount of floc based on the measurement data of the residual floc volume ratio.

Here, the sensor 14 of the measuring section 4 applies the absorbance fluctuation analysis method described in Japanese Patent Application Laid-Open No. 4-366750, for example, to determine the floc particle size from the measurement results of the average absorbance and the absorbance standard deviation. It is sufficient to use a sensor capable of calculating the concentration and the number concentration, and the amount of floc can be replaced with a floc volume ratio (an index proportional to the amount of floc) calculated from the particle diameter and the number concentration. The computer 16
The coagulant injection amount output from is supplied to the existing coagulant injection pump control device via a signal line 17. At this time, the computer 16 determines the coagulant injection amount such that the amount of floc measured by the measuring unit 4 is minimized. Based on this determination, the computer 16 controls the driving of the coagulant injection pump 54 as shown in FIG. Is optimized.

The coagulant injection amount determining apparatus according to the present invention is configured based on the following theory.

Originally, the floc in the flocculation mixing tank (FIG. 5, reference numeral 55) directly reflects the flocculation state. However, in the case of sewage sludge, in-line measurement of the coagulation state in the coagulation mixing tank is very difficult. Then, the present inventors paid attention to measuring the amount of residual floc (for example, the volume ratio of residual floc) of the dewatered separated liquid after sludge aggregation.

FIG. 2 is a schematic diagram in which the floc state of the flocculation mixing tank and the floc state of the dewatered and separated liquid of the flocculated sludge at that time are estimated by the difference in the chemical injection amount. In the case of an insufficient chemical injection amount in the upper stage, floccification does not proceed due to insufficient charge neutralization, and much of the supplied sludge leaks to the separated liquid side due to mechanical dehydration, and the cake dewatering property in this case is extremely poor. In the case of the middle amount,
Since the floc grows and the mechanical strength of the floc is strong, the amount of the residual floc leaking into the separated liquid even after mechanical dehydration is small, and the cake dewatering property is improved. On the other hand, if the amount of chemicals in the lower stage is excessive, small flocs generated by flocculation due to positive charge repulsion along with the growth block increase, and the mechanical strength of the flocs is weak, so that flocs easily leak into the separated solution, and the cake again Dehydration becomes poor. That is,
Amount of residual floc (eg, volume fraction of residual floc)
Is the U that minimizes the appropriate drug pour point for the coagulant injection amount.
It is presumed to draw a character curve.

The above theory invented by the present inventors has been verified by the following examples.

First, the floc volume ratio was used as an index representing the amount of floc. The relationship between the floc volume fraction of the dewatered separation liquid and the dewatering property was calculated by dividing the amount of solids of the flocculant solution injected into the sludge by the solids amount of the sludge to be injected under the combined conditions of various sludges and the flocculant. FIG. 3 and FIG. 4 show an example of a case where the measurement was performed with the apparatus of the present invention while changing the ratio of the measured values by percentage. The sludge used was a standard activated sludge method for water treatment, and a cationic polymer flocculant (hereinafter simply referred to as polymer) was used as a flocculant. Specifically, the polymers used are a strong cationic polymethacrylate coagulant (hereinafter simply referred to as polymer I) and a strong cationic polyacrylate coagulant (hereinafter simply polymer II). These polymers are well known to those skilled in the art. The dehydrator used was a leaf tester assuming a belt press dehydrator, and the water content of the cake was calculated by measuring the cake weight before and after the drying treatment (105 ° C., 12 hours) of the dehydrated cake.

FIG. 3 is a graph plotting the relationship between the floc volume ratio and the water content of the cake with respect to the polymer injection rate when the raw sludge from the A treatment plant is agglomerated with the polymer I. In the range of the drug injection rate of 0.5 to 1.6%, the floc volume ratio showed a tendency to temporarily decrease and then rapidly increase. At this time, the floc volume ratio was a minimum of 0.03% at a chemical injection rate of 0.8%. On the other hand, the cake moisture content showed the same behavior as the floc volume ratio, and reached the minimum value of 89.4% at the same chemical injection rate of 0.8% as the volume ratio.

FIG. 4 is a graph plotting the relationship between the floc volume ratio and the cake moisture content with respect to the polymer injection rate in the case where the sludge digested from the B treatment plant is agglomerated with the polymer II. In the range of the chemical injection rate of 1.0 to 2.2%, the floc volume ratio sharply decreased to the chemical injection rate of 1.6%, where the minimum value was 0.01%. Similarly, the cake moisture content also reached a minimum value of 87.4% at a chemical injection rate of 1.6%.

As described above, the relationship between the residual floc volume fraction in the dehydrated separated liquid and the cake water content was verified by changing the polymer chemical pouring rate. As a result, the minimum value of the floc volume rate relative to the polymer chemical pouring rate and the water content were confirmed. The agreement with the minimum value of the rate was in good agreement, and the validity of the above assumption was verified (universality of various sludges and flocculants other than the above was verified).

From these facts, regardless of the properties and types of sludge, the amount of residual floc in the separated liquid after mechanical dehydration was measured, and the chemical injection amount was adjusted so that the amount of floc at this time was minimized. By automatically determining, it is possible to perform chemical injection control for maintaining good sludge dewatering properties. The present invention is implemented based on the above principle. (1) Since the automatic control can be performed in-line, no trouble is required, and the optimal medicine injection point can be determined finely.

(2) The minimum point of the residual floc volume fraction in the dewatered separation liquid coincides with the minimum point of the moisture content of the dewatered sludge.

(3) Because of the feedback control, the setting of the chemical injection amount following the fluctuation of the property of the injected sludge can be realized. Unprecedented features such as are obtained, and all the problems to be solved by the above-described conventional method are solved.

As is apparent from the above, conventionally, there was no coagulation state measuring apparatus applicable to the sludge dewatering step, and it was difficult to quantitatively grasp the actual coagulation state. The agent injection amount determination device includes a separation liquid supply unit for injecting the dehydrated separation liquid into the measurement tank at a constant flow rate, a drainage unit for keeping the amount of liquid in the measurement tank constant, and a separation liquid in the measurement tank. A measuring unit that measures the amount of floc, and a control computer that has a built-in program that automatically adjusts the coagulant injection amount so that the amount of floc is minimized based on the measured data of the floc amount, and It is equipped with a stirrer that can change the rotation speed in the measurement tank according to
The optimum chemical injection amount can be determined promptly in response to the change in the properties of the supplied sludge, and as a result, the sludge dewatering property can be maintained in a favorable and stable state. In addition, it is obvious that the apparatus of the present embodiment measures the residual floc in the liquid which has been subjected to the mechanical / physical squeezing process and which is subjected to solid-liquid separation, and does not depend on the method of the squeezing process. That is, for example, the present invention can be applied to centrifugal dehydration, screw press dehydration and the like in addition to belt press dehydration, and has been partially proven.

[0039]

As is apparent from the above description, the coagulant injection amount determining apparatus according to the present invention can quickly respond to a change in the properties of supplied sludge and automatically determine the optimum coagulant injection amount. Is possible.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining an example of the configuration of a coagulant injection amount determining device according to the present invention.

FIG. 2 is a schematic diagram for explaining a difference between a flocculation mixing tank and a floc state of a dewatering / separation liquid according to a chemical injection amount.

FIG. 3 is a graph plotting a relationship between a floc volume ratio and a cake water content with respect to a polymer injection rate in a case where raw sludge from the A treatment plant is agglomerated with a polymer I.

FIG. 4 is a graph plotting the relationship between the floc volume ratio and the cake water content with respect to the polymer injection rate when the digestion sludge of the B treatment plant is agglomerated with the polymer II.

FIG. 5 is a schematic diagram for explaining an apparatus configuration for performing general sludge conditioning.

FIG. 6 is a schematic diagram for explaining a configuration of a main part of an apparatus for performing a jar test.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Measurement tank 2 Separation liquid supply part 3 Stirrer 4 Measuring part 5 Drainage part 6 Liquid sending pipe 7 Manual valve 8 Motor 9 Stirrer blade 10 Dehydration separation liquid 11 Overflow port 12 Drain weir 13 Drain pipe 14 Sensor 15 Signal line 16 Computer 17 signal line

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toru Yame 1-1, Tanabe-Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fuji Electric Co., Ltd. (72) Inventor Kenzo Sugaya 1-1-1, Kyobashi, Chuo-ku, Tokyo (72) Inventor Takafumi Omae 483-16 Ejiri-cho, Sakaide-shi, Kagawa Prefecture Inside Ishigaki-Sakaide Plant (72) Inventor Masayoshi Katayama 483-16, Ejiri-cho, Sakaide-shi, Kagawa Prefecture Ishigaki-Sakaide Co., Ltd. Inside the factory (72) Inventor Yoshio Sawada 483-16 Ejiri-cho, Sakaide-shi, Kagawa Inside the Ishigaki-Sakaide factory

Claims (2)

[Claims] An apparatus for determining the amount of coagulant injected into a coagulation mixing tank for coagulating sludge, comprising: a measuring tank; and a dehydration / separation liquid obtained by dehydrating the coagulated sludge, into the measuring tank at a constant flow rate. A separation liquid supply unit supplied at, a drainage unit that keeps the liquid amount in the measurement tank constant, and a measurement unit that measures the amount of floc present in the dehydrated separation liquid supplied to the measurement tank. Control means for determining the flocculant injection amount at which the floc amount is minimized based on the measurement data of the floc amount by the measuring unit. 2. The coagulant injection amount determining device according to claim 1, wherein a stirrer capable of changing a rotation speed is provided in the measuring tank.