JP6673390B2 - Coagulant addition control method, control device and water treatment system - Google Patents

Description

  The present invention relates to a control method and an apparatus for determining an optimal amount of a coagulant for coagulating various types of industrial wastewater or industrial water. The present invention also relates to a water treatment system having the control device.

  In the pretreatment of various kinds of wastewater and water, coagulation treatment is used to remove suspended matter and organic matter. As the coagulant used for the coagulation treatment, iron-based coagulants such as iron chloride and polyaluminum chloride and aluminum-based inorganic coagulants are generally used. The coagulation treatment used in combination is also performed.

  It is necessary to add an appropriate amount of the coagulant according to the quality of the water to be treated. If the amount of chemicals is insufficient, the removal of turbid and organic substances contained in the water to be treated becomes insufficient, and the quality of the treated water deteriorates. 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 processing.

  In order to determine the optimal amount of chemicals, it is common to perform a jar test, but it takes a lot of time and effort to perform a jar test every time the quality of the water to be treated fluctuates. In this case, it is not practical to respond immediately to the change.

  In Patent Documents 1 to 5, in order to set optimum coagulation conditions such as pH, coagulant injection amount, stirring conditions, etc., the treatment state of water to be treated during coagulation treatment is monitored in real time, and the coagulation state of SS The method of monitoring is described.

  Patent Literatures 1 and 2 disclose that the water to be treated is irradiated with a laser beam to receive scattered light due to particles in the water to be treated, AM (Amplitude Modulation: Amplitude Modulation) detection is performed on the received light signal, and the signal intensity is reduced. It is described that a minimum value is determined, and a flocculant injection amount is determined from the minimum value. In this aggregation monitoring, the minimum value of the signal intensity of the scattered light is obtained, so that the scattered light due to the unaggregated suspension is detected separately from the scattered light due to the aggregate in the water to be treated.

  Patent Literatures 3 to 5 disclose a chemical dosing system that measures the concentration of SS not taken into flocs generated in the flocculation treatment of water to be treated, and controls the dosing amount of a flocculant based on the measured value. Are listed. In the SS concentration measurement, a laser beam is applied 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 JP-A-2006-3974 JP 2017-72404 A

  An object of the present invention is to provide a method and an apparatus for controlling the addition of a flocculant capable of favorably performing a flocculation treatment even when there is a fluctuation in water quality, and an object of the present invention to provide a water treatment system provided with the control apparatus for a flocculant addition.

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

  In one embodiment of the present invention, the turbidity of the water to be treated is further measured, and an alarm is issued when the ratio of the turbidity value between the flocs to the turbidity of the water to be treated exceeds 0.7 to 1. And / or the addition amount of the flocculant is adjusted.

  In one embodiment of the present invention, the flow potential of the flocculated water to which the flocculant has been added is measured by a streaming potentiometer, and the amount of the 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, a flocculant sensor for measuring turbidity between flocs in the flocculant water, and a flocculant addition based on a measurement result of the flocculant sensor. A coagulant addition control device having control means for performing control, comprising: alarm issuing means for issuing an alarm when a measured value of the agglutination sensor exceeds a predetermined reference value. It is.

  In one embodiment of the present invention, a streaming potentiometer for measuring the flow potential of the water to be treated or the coagulation treatment water to which the coagulant has been added, and a calculation means for determining the amount of the coagulant to be added based on the measurement value of the streaming potentiometer Having.

  The water treatment system of the present invention is a water treatment system having a coagulant addition control device, and has solid-liquid separation means for performing solid-liquid separation of coagulation treatment water.

  One embodiment of the present invention includes 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 flocculation treatment water is measured, and when 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 the flocculant added is determined. Control. Thereby, the continuation of the aggregation failure can be prevented.

It is a lineblock diagram of a flocculant injection control device concerning an embodiment of the invention. It is a graph which shows an experimental result. It is a graph which shows an experimental result. It is a graph which shows an experimental result.

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

  FIG. 1 is a configuration diagram showing a control device according to the first embodiment. The 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 a chlorine dioxide compound can be used.

  When it is necessary to adjust the pH to a constant value before adding the flocculant, a configuration may be adopted in which a pH meter 3 is installed in the raw water tank 1 and a pH adjusting tank 1a is provided in a stage preceding the raw water tank 1. Sodium hydroxide, slaked lime, hydrochloric acid, sulfuric acid and the like can be used as the pH adjuster.

  When measuring the ratio of turbidity between flocs to turbidity of the water to be treated, 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 coagulant is added, is introduced into the coagulation tank 11 and the inorganic coagulant is added. In the coagulation tank 11, a pH adjuster is added to adjust the pH of the coagulation water detected by the pH meter 12 to a constant value. The amount of the coagulant added to the coagulation tanks 5 and 11 is controlled by the coagulant injection control device 10.

  Examples of the cationic polymer coagulant include poly (diallyldimethylammonium chloride), poly (2-dimethylaminoethyl methacrylate), polydimethylaminoethyl methacrylate benzyl quaternary salt, polyethyleneimine, polyallylamine, polyvinylamine, poly ( 2-dimethylaminoethyl methacrylate), poly (2-vinyl-1-methylpyridinium), dialkylamine-epichlorohydrin polycondensate, polylysine, chitosan, diethylaminoethyldextran and the like. Examples of the inorganic coagulant include iron-based inorganic coagulants such as ferric chloride, ferric sulfate, polyferric chloride, and ferric polysulfate, aluminum chloride, polyaluminum chloride, sulfate bands, aluminum hydroxide, and aluminum oxide. And aluminum-based inorganic flocculants. A mixture of two or more cationic polymer coagulants may be used as the cationic polymer coagulant, or a mixture of two or more inorganic coagulants may be used as the inorganic coagulant.

  As the coagulant, both a cationic polymer coagulant and an inorganic coagulant may be added, or only an inorganic coagulant may be added. When both the cationic polymer flocculant and the inorganic flocculant are added, each flocculant may be added to separate flocculation tanks 5 and 11 as shown in the figure, or is added to the same flocculation tank although not shown. You may. Regarding the order of addition, either one may be added first or the two may be added simultaneously.

  The coagulated water in the coagulation tank 11 is then introduced into the coagulation sensor tank 13. The agglutination sensor tank 13 includes a particle sensor 14. As the fine particle sensor 14, a light scattering type fine particle sensor provided with a light emitting device for emitting laser light for measuring turbidity between flocs and a probe for detecting scattered laser light (for example, Patent Document 3) Etc.) can be used.

  When the inter-floc turbidity measured by the fine particle sensor 14 increases, the addition amount of the coagulant two agents is insufficient or excessive with respect to water quality fluctuation, or the ratio of the addition amount of the cationic polymer coagulant and the inorganic coagulant is It is considered that coagulation failure has occurred for any reason in the inappropriate case. Therefore, an alarm is issued and / or the amount of the coagulant added is controlled.

  As shown in Example 1 below, there is a correlation between the value of the turbidity between flocs and the rate of increase in the differential pressure in the subsequent stage of the opaque membrane treatment. A reference value for inter-floc turbidity can be established for issuing a signal to control an alarm and / or the amount of coagulant added.

  Instead of the inter-floc turbidity, the ratio of the inter-floc turbidity to the turbidity of the water to be treated may be used as the 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 rise in the differential pressure of the subsequent turbidity membrane increases. To increase. Therefore, this value can be set as a reference value for issuing a signal for adjusting a warning and / or a coagulant addition amount. When calculating the ratio of the turbidity between flocs to the turbidity of the water to be treated, the ratio was calculated by taking into account the difference in the residence time between the raw water tank equipped with the optical turbidity meter and the flocculation sensor tank equipped with the particle sensor. It is desirable to do.

  The coagulation treatment water in the coagulation sensor tank 13 is sent to the solid-liquid separation treatment equipment via the treatment water pump 15. Examples of the solid-liquid separation treatment include a membrane separation treatment, a sand filtration treatment, a precipitation treatment, and a pressure flotation treatment.

  In this embodiment, the sampling cell 6 receives a part of the coagulation treatment water from the coagulation sensor tank 13, measures the streaming potential with the streaming electrometer 8, and returns the water after this measurement to the coagulation sensor tank 13. is set up. In the sampling cell 6, a fixed volume of raw water is sealed, and the streaming potential value of the flocculated water is measured by the streaming potentiometer 8. For the calculation of the coagulant addition amount, the optimum value of the streaming potential value of the coagulation treatment water obtained by the preliminary evaluation becomes practical. In addition, it is desirable to adopt a stopped flow method in which the raw water is passed through the sampling cell for a certain period of time, and then the flow is temporarily stopped by a valve attached to the raw water side of the sampling cell. Further, it is desirable that a cleaning liquid can be introduced into the sample cell so that the inside of the sample cell and the measuring section of the streaming electrometer can be periodically cleaned. As the cleaning liquid, one or more of an acid, an alkali, and an oxidizing agent are desirably used depending on the quality of the water to be treated.

  The automatic adjustment of the coagulant addition amount based on the measurement value of the streaming electrometer 8 may be set to be performed at regular intervals or / and / or the turbidity between flocs measured by the fine particle sensor 14 may be adjusted. It may be set to be performed at the time of ascent.

  The sampling cell 6 may introduce coagulated water from the coagulation tank 11 or may be installed at the subsequent stage of the solid-liquid separator to introduce the solid-liquid separated water. However, when the solid-liquid separation treatment water is introduced, it is necessary to obtain the optimum value of the streaming potential value of the solid-liquid separation treatment water by prior evaluation.

  The optimum value of the streaming potential value of the coagulation treatment water can be obtained from the result as shown in FIG. 2, for example.

  FIG. 2 shows the relationship between the amount of the inorganic coagulant added, the streaming potential value, and the water quality of the coagulation treatment water, which was evaluated by a preliminary desk test, and the water quality of the coagulation treatment water is represented by the MFF value.

  The method for measuring the MFF value is as follows. After setting the MF membrane in a suction filtration device and measuring the permeation time T0 of 150 mL of reference water free of soluble polymer substances and fine particles under reduced pressure of -67 kPa, the first water passage time T1 of the measurement sample (150 mL) was measured. The second water passage time T2 is measured. MFF value = T2 / T1.

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

  When only an inorganic coagulant is used as the coagulant, it is desirable to adjust and set the additional amount to be in the range of A × 0.5 to A × 1. When two types of coagulants, a cationic polymer and an inorganic coagulant, are used, the additional amount of the inorganic coagulant is A × 0.1, although it depends on the quality of the water to be treated and the type of the inorganic coagulant used. It is desirable to adjust and set to be in 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 used. , A × 0.001 to A × 0.008.

  If the actual flowing potential value of the flocculated water is higher than the optimal value of the flowing potential value of the flocculated water, it is highly possible that the cationic polymer is excessive, and thus the amount of the flocculant added is large. It is necessary to review the set value of.

[Example 1]
The water to be treated and the reagents used in Example 1 are as follows.

Test water to be treated: biologically treated water of factory wastewater A (ORP: 100 to 200 mV)
Cationic polymer: poly (diallyldimethylammonium chloride)
Inorganic flocculant: ferric chloride (38%)
Oxidizing agent: sodium hypochlorite

<Test method>
In the configuration of the coagulant 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 falls within the range of 325 ± 25 mV, and the above coagulants are added to perform the coagulation treatment. Then, a membrane separation treatment (PVDF, pore size 0.02 μm, operation conditions: operation Flux 2 to 4 m / D, backwash interval 10 to 28 min) was performed as a solid-liquid separation treatment at the latter stage of the system. The turbidity between flocs in continuous water flow was measured by the light scattering type fine particle sensor 14 provided in the aggregation sensor tank 13.

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

  As shown in FIG. 3, it was found that as the inter-floc turbidity increased, the differential pressure increasing rate also increased, and a strong correlation was observed. The rise in the turbidity between flocs indicates that the water quality of the water to be treated fluctuates rapidly and that coagulation failure has occurred, or that the water quality of the water to be treated fluctuates extremely significantly, with respect to the value measured with a streaming electrometer. It is considered that the adjustment setting of the automatic addition amount of the flocculant became inappropriate.

  Therefore, when the turbidity between flocs rises to a certain value or more, a method of setting the automatic adjustment of the amount of the flocculant added by the measurement of the streaming electrometer and a method of adjusting the automatic addition amount of the flocculant are new. A method of resetting to a value can be considered. in this way. The particle sensor provided in the coagulation sensor tank can be used as an alarm sensor for checking whether or not coagulation failure has occurred.

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

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

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

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

  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 increasing the differential pressure tends to increase. Therefore, good or bad agglomeration can be determined based on this value.

  As is clear from the above examples, according to the present invention, even when the water to be treated fluctuates, by detecting the coagulation failure and adjusting the coagulation conditions, it is possible to prevent the contamination of the subsequent treatment due to the coagulation failure. it can.

Reference Signs List 1 Raw water tank 5, 11 Coagulation tank 6 Sampling cell 13 Coagulation sensor tank 14 Particle sensor

Claims (3)

A flocculant is added to the water to be treated, and the turbidity between flocculated flocs in the treated water (hereinafter referred to as floc turbidity) is measured by a flocculation sensor. In the method of controlling the addition of a flocculant,
When the measured value of turbidity between flocs of the coagulation sensor exceeds a predetermined reference value, an alarm is issued and / or the addition amount of the coagulant is adjusted .
Measure the turbidity of the water to be treated,
When the ratio of the measured value of turbidity between flocs to the turbidity of the water to be treated, that is, [turbidity between flocs] / [water turbidity to be treated] exceeds 0.7, an alarm is issued and / or a flocculant is used. A method for controlling the addition of a flocculant, characterized by adjusting the amount of addition of a coagulant. Oite to claim 1, the streaming potential aggregating treatment water with the addition of flocculant was measured with a streaming potential meter, based on the measured value of the flow potentiodynamic, and controlling the amount of flocculant coagulant Addition control method. 3. The method according to claim 1, 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.

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