WO2019187698A1 - Method for controlling addition of flocculant, control device, and water treatment system - Google Patents

Abstract

A method for controlling addition of flocculant in which a flocculant is added to water to be treated, turbidity in spaces between flocs in the flocculant-treated water is measured with a flocculant sensor, and the addition of flocculant is controlled on the basis of the measurement results, wherein a warning is issued or the amount of flocculant added is regulated when a flocculant sensor measurement value exceeds a prescribed reference value.

Description

Flocculant addition control method, control device, and water treatment system

The present invention relates to a control method and apparatus for determining an optimum amount of a flocculant when aggregating various industrial wastewater and industrial water. Moreover, this invention relates to the water treatment system which has this control apparatus.

In the pretreatment of various wastewater and water, a coagulation treatment is used to remove turbidity and organic matter. As the aggregating agent used in the aggregating treatment, iron-based aggregating agents such as iron chloride and polyaluminum chloride and aluminum-based inorganic aggregating agents are generally used. The coagulation treatment used together is also performed.

It is necessary to add an appropriate amount of the flocculant depending on the quality of the water to be treated. If the amount of chemical is insufficient, the removal of turbidity and organic substances contained in the water to be treated becomes insufficient, resulting in deterioration of the quality of the treated water. On the other hand, if the amount of the chemical is excessive, the chemical leaks to the subsequent stage, which may cause an increase in load and contamination in the subsequent process.

In order to determine the optimal amount of chemicals, it is common to perform a jar test, but it takes a lot of work. It is not practical to perform a jar test every time the quality of treated water changes, because it is not possible to immediately respond to fluctuations in actual water treatment.

In Patent Documents 1 to 5, in order to set optimal aggregation conditions such as pH, flocculant dosage, and stirring conditions, the treatment state of the water to be treated during the aggregation treatment is monitored in real time, and the SS aggregation state A method for monitoring is described.

In Patent Documents 1 and 2, laser light is irradiated on the water to be treated to receive scattered light from particles in the water to be treated, and after AM (Amplitude modulation) detection is performed on the received light signal, the signal intensity is measured. It is described that the minimum value is obtained, and the flocculant dosage is obtained from this minimum value. In this aggregation monitoring, the minimum value of the signal intensity of the scattered light is obtained, and the scattered light from the unaggregated suspension is detected from the scattered light from the aggregate in the water to be treated.

In Patent Documents 3 to 5, there is a chemical injection system that measures the concentration of SS that is not taken into flocs that are generated in the coagulation treatment of water to be treated, and controls the chemical injection amount of the coagulant based on this measured value. Are listed. In the SS concentration measurement, laser light is irradiated to the measurement area of the water to be treated, scattered light from the measurement area is received, and a measurement value representing the SS concentration is obtained from a signal level obtained by photoelectrically converting the scattered light. .

JP 2002-195947 A JP 2005-241338 A JP 2003-154206 A Japanese Unexamined Patent Publication No. 2016-3974 JP 2017-72404 A

An object of the present invention is to provide a flocculant addition control method and apparatus that can satisfactorily perform flocculation treatment even when there is a change in water quality, and a water treatment system including the flocculant addition control apparatus.

In the flocculant addition control method of the present invention, a flocculant is added to the water to be treated, and the turbidity between flocculated flocs in the flocculated water (hereinafter referred to as inter-floc turbidity) is measured by a flocculence sensor. In the flocculant addition control method for controlling flocculant addition based on the measurement result, when the floc turbidity measurement value of the floc sensor exceeds a predetermined reference value, an alarm is issued and / or the amount of flocculant added It is characterized by adjusting.

In one aspect of the present invention, the turbidity of the water to be treated is further measured, and if the ratio of the turbidity measurement value between flocs to the turbidity of the water to be treated exceeds 0.7 to 1, an alarm is issued. And / or adjusting the amount of flocculant added.

In one embodiment of the present invention, the flow potential of the flocculated water to which the flocculant is added is measured with a flow potential meter, and the amount of flocculant added is controlled based on the measured value of the flow potential.

In one embodiment of the present invention, an oxidizing agent is added to the water to be treated so that the ORP value of the water to be treated is 300 mV or more.

The flocculant addition control device of the present invention includes an adding means for adding a flocculant to the water to be treated, an agglomeration sensor for measuring turbidity between flocs in the agglomerated water, and addition of the flocculant based on the measurement result of the agglomeration sensor. A flocculant addition control device having a control means for performing control, characterized by comprising an alarm notification means for issuing an alarm when the measured value of the aggregation sensor exceeds a predetermined reference value It is.

In one aspect of the present invention, a flow potential meter that measures the flow potential of water to be treated or flocculated water to which a flocculant has been added, and a calculation means for determining the amount of flocculant added based on the measured value of the flow potential meter Have

The water treatment system of the present invention includes the flocculant addition control device of the present invention and solid-liquid separation means for solid-liquid separation of the flocculated water.

In one embodiment of the present invention, there are provided a means for measuring the ORP value of the water to be treated and an adding means for adding an oxidizing agent to the water to be treated so that the ORP value of the water to be treated is 300 mV or more.

In the present invention, the turbidity between flocs in the flocculated water is measured, and if the turbidity between flocs exceeds a predetermined reference value, it is determined that the flocculation is defective and an alarm is issued or the amount of flocculant added is determined. Control. Thereby, the continuation of the aggregation failure can be prevented.

FIG. 1 is a configuration diagram of a flocculant injection control device according to an embodiment. FIG. 2 is a graph showing experimental results. FIG. 3 is a graph showing experimental results. FIG. 4 is a graph showing experimental results.

Hereinafter, embodiments will be described with reference to the drawings.

FIG. 1 is a block diagram showing a control device according to the first embodiment.

Raw water is introduced into the raw water tank 1, and if necessary, an oxidizing agent is added by the ORP meter 2 and the raw water tank chemical injection control device 4 provided in the raw water tank 1 so that the ORP becomes 300 mV or more. As the oxidizing agent, hypochlorite or chlorine dioxide compounds can be used.

When it is necessary to adjust the pH to a certain level before adding the flocculant, a form in which the pH meter 3 is installed in the raw water tank 1 and the pH adjusting tank 1a is provided in the previous stage of the raw water tank 1 may be employed. As a pH adjuster, sodium hydroxide, slaked lime, hydrochloric acid, sulfuric acid and the like can be used.

When measuring the ratio of inter-floc turbidity to turbidity of treated water, install an optical turbidity meter in the raw water tank.

The raw water in the raw water tank 1 is then introduced into the coagulation tank 5 and after the cationic polymer flocculant is added, it is introduced into the coagulation tank 11 and the inorganic flocculant is added. In the flocculation tank 11, a pH adjuster is added to adjust the pH of the flocculated water detected by the pH meter 12 to be constant. The addition amount of the coagulant to the coagulation tanks 5 and 11 is controlled by the coagulant injection control device 10.

Cationic polymer flocculants include poly (diallyldimethylammonium chloride), poly (2-dimethylaminoethyl methacrylate), polydimethylaminoethyl methacrylate benzyl quaternary salt, polyethyleneimine, polyallylamine, polyvinylamine, poly ( (Methacrylic acid 2-dimethylaminoethyl), poly (2-vinyl-1-methylpyridinium), dialkylamine-epichlorohydrin polycondensate, polylysine, chitosan, diethylaminoethyldextran and the like.

Inorganic flocculants include ferrous chloride, ferric sulfate, polyferric chloride, polyferric sulfate, and other iron-based inorganic flocculants, and aluminum chloride, polyaluminum chloride, sulfate bands, aluminum hydroxide, and aluminum oxide. Aluminum-based inorganic flocculants such as

A mixture of two or more types of cationic polymer flocculants may be used as the cationic polymer flocculant. A mixture of two or more inorganic flocculants may be used as the inorganic flocculant.

As the flocculant, both the cationic polymer flocculant and the inorganic flocculant may be added, or only the inorganic flocculant may be added. When both the cationic polymer flocculant and the inorganic flocculant are added, each flocculant may be added to the separate flocculant tanks 5 and 11 as shown in the figure, or added to the same flocculant tank although not shown in the figure. You may do it. As for the order of addition, either may be added first or at the same time.

The agglomerated water in the agglomeration tank 11 is then introduced into the agglomeration sensor tank 13. The aggregation sensor tank 13 includes a fine particle sensor 14. As the fine particle sensor 14, a light scattering fine particle sensor (for example, Patent Document 3) provided with a light emitter for emitting laser light for measuring inter-floc turbidity and a probe for detecting scattered laser light. Etc.) can be used.

When the inter-floc turbidity measured by the fine particle sensor 14 is increased, the addition amount of the two coagulants is insufficient or excessive with respect to the water quality fluctuation, or the ratio of the addition amount of the cationic polymer flocculant and the inorganic flocculant is It is considered that a poor aggregation occurs for any reason in the case of inappropriateness. Therefore, an alarm is issued and / or the amount of flocculant added is controlled.

As shown in Example 1 described later, since there is a correlation between the value of the turbidity between flocs and the differential pressure increase rate in the subsequent turbidity removal membrane treatment, depending on the use conditions such as the chemical cleaning frequency of the turbidity removal membrane, A reference value for inter-floc turbidity can be established to send an alarm and / or a signal to adjust the amount of flocculant added.

* Instead of inter-floc turbidity, the ratio of inter-floc turbidity to the turbidity of water to be treated may be used as a reference value. In this case, as shown in Example 2 described later, when the ratio of the turbidity between flocs to the turbidity of the water to be treated exceeds the range of 0.7 to 1, the rate of increase in the differential pressure of the subsequent turbidity removal membrane is increased. To increase. Therefore, this value can be set as a reference value for transmitting an alarm and / or a signal for adjusting the amount of flocculant added. When calculating the ratio of turbidity between flocs to the turbidity of the water to be treated, take into account the difference in residence time between the raw water tank where the optical turbidimeter is installed and the aggregation sensor tank where the fine particle sensor is installed. Is desirable.

The agglomerated treated water in the agglomeration sensor tank 13 is sent to the solid-liquid separation treatment facility via the treated water pump 15. Examples of the solid-liquid separation treatment include membrane separation treatment, sand filtration treatment, precipitation treatment, and pressurized flotation treatment.

In this embodiment, a part of the flocculated water from the flocculation sensor tank 13 is received through the valve 9, the flow potential is measured by the flow potential meter 8, and the water after the measurement is returned to the flocculation sensor tank 13. A sampling cell 6 is installed in In the sampling cell 6, a certain volume of flocculated water is sealed, and the flow potential value of the flocculated water is measured by the flow potential meter 8. For the calculation of the addition amount of the flocculant, the optimum value of the flow potential value of the flocculated water obtained by the preliminary evaluation is required.
It is desirable to employ a stopped flow method in which the agglomerated water is passed through the sampling cell 6 for a certain period of time and then the flow is temporarily stopped by a valve 9 attached to the agglomerated water side of the sampling cell 6. In addition, it is desirable to be able to introduce a cleaning solution into the sampling cell 6 so that the measurement part of the flow potential meter 8 and the inside of the sampling cell 6 can be periodically cleaned. As the cleaning liquid, it is desirable to use one or more of acids, alkalis and oxidizing agents depending on the quality of the water to be treated.

The automatic adjustment of the flocculant addition amount based on the measured value of the flow potential meter 8 may be set to be performed at regular intervals, or set to be performed when the inter-floc turbidity measured by the fine particle sensor 14 is increased. You may do it.

The sampling cell 6 may introduce the coagulated water from the coagulation tank 11 or may be installed after the solid-liquid separator to introduce the solid-liquid separated water. When solid-liquid separation treated water is introduced, it is necessary to obtain an optimum value of the flow potential value of the solid-liquid separation treated water by preliminary evaluation.

The optimum value of the flow potential value of the flocculated water can be obtained from the result shown in FIG.

FIG. 2 shows the relationship between the amount of the inorganic flocculant added, the flow potential value, and the water quality of the agglomerated water evaluated by a prior desktop test, and the agglomerated water quality is represented by the MFF value.

The measuring method of the MFF value is as follows.
The MF membrane was set in a suction filtration device, and after measuring the permeation time T0 of 150 mL of the soluble polymer substance and fine particle-free reference water under a reduced pressure of −67 kPa, the first flow time T1 of the measurement sample (150 mL), Measure the second water passage time T2. MFF value = T2 / T1.

When the MFF value becomes good, the streaming potential shows a specific value, and this value is the optimum streaming potential value of the flocculated water (about -300 mV here). A correlation diagram between the amount of the inorganic flocculant added and the flow potential value is recorded in the flocculence control device, and the inorganic flocculant concentration and the flow potential value indicated by the actual flow potential value of the flocculated water are optimum values. The insufficient concentration (A) of the inorganic flocculant is calculated from the difference in the flocculant concentration (here, about 200 mg / L).

When only the inorganic flocculant is used as the flocculant, it is desirable to adjust and set the additional addition amount within the range of A × 0.5 to A × 1. When two types of flocculants, a cationic polymer and an inorganic flocculant, are used, depending on the quality of the water to be treated and the type of inorganic flocculant used, the additional amount of the inorganic flocculant is A × 0. It is desirable to adjust and set to be within the range of 1 to A × 0.9, and the additional amount of the cationic polymer depends on the quality of the water to be treated and the type of the cationic polymer to be used. It is desirable to adjust and set to be within the range of A × 0.001 to A × 0.008.

If the actual flow potential value of the coagulation treated water is higher than the optimum value of the flow potential value of the coagulation treated water, there is a high possibility that the cationic polymer is excessive. The value needs to be reviewed.

[Example 1]
The test water and reagents used in Example 1 are as follows.

Test water: Biologically treated water from factory wastewater A (ORP: 100-200 mV)
Cationic polymer: poly (diallyldimethylammonium chloride)
Inorganic flocculant: ferric chloride (38%)
Oxidizing agent: Sodium hypochlorite

<Test method>
In the configuration of the flocculant injection control system shown in FIG. 1, an oxidizing agent is added to the raw water tank so that the ORP of the raw water tank is within the range of 325 ± 25 mV, and the above flocculants are added to perform the flocculation process. Then, a membrane separation process (PVDF, pore diameter 0.02 μm, operation conditions: operation flux 2-4 m / D, backwash interval 10-28 min) was performed as a solid-liquid separation process at the latter stage of the system. Further, the floc turbidity during continuous water passage was measured by the light scattering fine particle sensor 14 provided in the aggregation sensor tank 13.

The relationship between the floc turbidity and the increase rate of the transmembrane pressure difference in the membrane separation treatment was measured. The results are shown in FIG.

As shown in FIG. 3, it was found that when the turbidity between flocs increased, the differential pressure increase rate increased and a strong correlation was observed. The increase in turbidity between flocs is due to the fact that the quality of the water to be treated has fluctuated rapidly and the occurrence of coagulation failure has occurred, or the quality of the water to be treated has fluctuated extremely greatly, This is considered to be caused by inappropriate adjustment settings for the amount of flocculant added automatically.

Therefore, when the turbidity between flocs rises above a certain value, a new method is set to adjust the flocculant addition amount automatically by measuring the flow potential meter, and the automatic flocculant addition amount adjustment setting A method of resetting to a value can be considered. in this way. The particle sensor provided in the aggregation sensor tank can be used as an alarm sensor for confirming whether or not an aggregation failure has occurred.

[Example 2]
In Example 2, the following water to be treated and inorganic flocculant were used.

Test water: Factory wastewater B
Inorganic flocculant: ferric chloride (38%)

<Experiment method>
In the system configuration shown in FIG. 1, only the inorganic flocculant was added to perform the agglomeration treatment. In addition, a membrane separation process (PVDF, pore diameter 0.02 μm, operation conditions: operation flux 3.3 m / D, backwash interval 15 min) was performed as a solid-liquid separation process at the latter stage of the system.

FIG. 4 shows the results of measuring the relationship between the ratio of the turbidity between flocs to the turbidity of the water to be treated and the rate of increase in transmembrane pressure difference.

As shown in FIG. 4, it was found that when the ratio of the turbidity between flocs to the turbidity of the water to be treated exceeds the range of 0.7 to 1, the rate of increase in the differential pressure tends to increase. Therefore, if the ratio of turbidity between flocs to turbidity of the water to be treated ([floc turbidity] / [raw water turbidity]) is smaller than the value selected from the range of 0.7 to 1, the aggregation is good. If it is present and larger, it can be determined that the aggregation is poor.

As is clear from the above examples, according to the present invention, even when fluctuations in the water to be treated occur, it is possible to prevent contamination of subsequent processing due to poor aggregation by detecting poor aggregation and adjusting the aggregation conditions. it can.

Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention.
This application is based on Japanese Patent Application No. 2018-064449 filed on Mar. 29, 2018, which is incorporated by reference in its entirety.

DESCRIPTION OF SYMBOLS 1 Raw water tank 5,11 Aggregation tank 6 Sampling cell 13 Aggregation sensor tank 14 Fine particle sensor

Claims (8)

1. A flocculant is added to the water to be treated, and the turbidity between flocculated flocs in the flocculated water (hereinafter referred to as turbidity between flocs) is measured by a flocculence sensor. In the flocculant addition control method to be performed,
   A flocculant addition control method, wherein when the measured value of floc turbidity of the floc sensor exceeds a predetermined reference value, an alarm is issued and / or the amount of flocculant added is adjusted.
2. In claim 1, further, the turbidity of water to be treated is measured,
   When the ratio of the measured value of turbidity between flocs to the turbidity of water to be treated exceeds 0.7 to 1, the alarm is reported and / or the addition amount of the flocculant is adjusted. Addition control method.
3. The flocculant according to claim 1 or 2, wherein the flow potential of the flocculated water to which the flocculant is added is measured with a flow potential meter, and the amount of flocculant added is controlled based on the measured value of the flow potential. Addition control method.
4. 4. The flocculant addition control method according to any one of claims 1 to 3, wherein an oxidizing agent is added to the water to be treated so that the ORP value of the water to be treated is 300 mV or more.
5. An adding means for adding a flocculant to the water to be treated; a flocculence sensor for measuring the floc turbidity in the agglomerated water;
   In a flocculant addition control device having control means for performing flocculant addition control based on the measurement result of the flocculence sensor,
   An aggregating agent addition control device comprising an alarm reporting unit for issuing an alarm when a measured value of the aggregation sensor exceeds a predetermined reference value.
6. In claim 5, a flow potential meter for measuring the flow potential of the water to be treated or the agglomerated treated water to which a flocculant is added,
   A flocculant addition control device comprising a calculating means for determining the amount of flocculant added based on the measured value of the flow potential meter.
7. A water treatment system comprising the flocculant addition control device according to claim 5 or 6,
   A water treatment system comprising solid-liquid separation means for solid-liquid separation of flocculated treated water.
8. 8. The water according to claim 7, comprising means for measuring the ORP value of the water to be treated and means for adding an oxidant to the water to be treated so that the ORP value of the water to be treated is 300 mV or more. Processing system.

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