JP2013233527A - Water treatment method by agitation control - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such a problem that formation of a micro flock becomes defective in a mixing basin at a low water temperature particularly in winter, and to provide a water treatment method capable of efficiently removing contaminant by flocculation precipitation even when the temperature of the water to be treated decreases.SOLUTION: A water treatment method in water treatment facilities is provided. In the water treatment facilities having a mixing basin provided with an agitator, when performing initial mixing by adding flocculant to raw water in the mixing basin, an optimal stirring G value in the raw water to be treated and the flocculant used is found beforehand. The temperature of the raw water in the mixing basin is measured when performing the mixing of the flocculant, and the agitation speed of the agitator of the mixing basin is controlled so that the stirring G value of the mixing basin calculated on the basis of the temperature agrees with the optimal stirring G value. Preferably, the flocculant is an iron-based polymer flocculant or an aluminum-based polymer flocculant.

Description

  In the present invention, when water is treated with a flocculant in a mixing pond in a water treatment facility such as a water purification facility, the flocculant is admixed using an index called a stirring G value relating to the stirring state of the mixing pond to cause coagulation precipitation. The present invention relates to a water treatment method.

  In water treatment facilities of waterworks, etc., water treatment using a flocculant is generally performed in order to effectively remove turbidity in raw water from the water within a limited site. In such a water treatment facility, in general, a flocculant is first added to raw water, and the flocculant is uniformly mixed by rapid stirring in a mixing basin equipped with a stirring device. Then, flocs are formed by the flocculant, and the flocs formed by standing in a sedimentation basin are precipitated and separated to obtain purified water.

  In this mixing basin, the flocculant is injected into the raw water, and the flocculant and the fine particles in the raw water are uniformly mixed by a stirrer to form micro flocs first. The fine particles in the raw water usually have negative (−) electricity on the surface and repel each other, so that they are dispersed in water. The flocculant reacts with alkaline components in water to form positive (+) electrically charged metal hydroxides, which mix with negatively charged fine particles and cause electrical neutralization. By eliminating repulsion, a microflock is formed. This micro floc forms a floc that is a large aggregate by aggregating a large number of micro flocs in the floc formation pond in the next step. By forming such a large floc, the floc is efficiently precipitated and separated from the water in the sedimentation basin in the next step, so that the clarified water can be efficiently clarified.

  In particular, with the recent deterioration of raw water quality, it is necessary to remove soluble organic components represented by the index E260 as a treatment target in water purification facilities. There is a demand for further enhancement.

  Conventionally, aluminum sulfate or the like has been used as a flocculant to achieve a target in a water treatment facility. Aluminum sulfate had no problem with its viscosity even when it became a flocculant solution, and its mixing operation was simple. For example, there are operations for mixing by bringing the flocculant into direct contact with the flow point of the raw water, and simple mixing operations for promoting mixing by colliding the aggregated water of the flocculant and raw water against the plate surface with the pump pressure. However, a method is generally employed in which a uniform stirring operation is performed while injecting the flocculant into the mixing basin, and the flocculant is simply uniformly dispersed in water.

  However, in recent years, with the demand for more advanced water treatment such as removal of soluble organic components in water, flocculants with higher flocculation effect than flocculants such as iron-based polymer flocculants, aluminum-based flocculants Polymer flocculants have been developed. In such a flocculant having a high flocculating effect, the chemical reaction related to the flocculating action is not uniform depending on the contact state when the raw water first contacts the flocculant, and the initial mixing state of the flocculant and the raw water is not uniform. It has been found that it has a great influence on the aggregating action. However, in general water purification equipment, no special consideration is given to the state of initial mixing of the flocculant and raw water, and the specifications of the conventional equipment are changed for this purpose. The current situation is not.

  In the winter water purification facilities, even when the turbidity of the raw water is low, the quality of the treated purified water deteriorates and the filter pond is blocked by a short operation. This is because the kinematic viscosity coefficient of water increases as the water temperature decreases, so stirring in the mixing pond is insufficient, electrical neutralization with the flocculant is not performed sufficiently, and good micro flocs are not formed. Responsible. In the case where good micro flocs are not formed in the mixing pond, floc formation by slow stirring is not sufficiently performed in the floc forming pond in the next step, and floc formation is poor. As a result, the precipitation and separation / removal of flocs in the sedimentation basin were not performed effectively, so that the quality of the purified water deteriorated and the filtration basin was blocked during a short operation.

  In order to deal with such problems and to obtain stable and good quality purified water, conventionally, the precipitating failure measures have been taken by increasing the flocculant injection rate or increasing the frequency of backwashing the filter basin. As However, injection of excess flocculant not only increases the chemical cost, but aluminum-based polymer flocculants have the problem of increased aluminum in the treated water, and also increase the frequency of backwashing of the filter basin. There was a problem that it caused a reduction in water treatment capacity.

  In addition, the revision of the tap water quality standard value in April 2003 introduced the first standard value for aluminum, and the water quality management target value was set at half the standard value. In water purification facilities that use chemicals, there is also a problem that it is difficult to take measures against agglomeration defects due to excessive injection of aluminum-based polymer flocculant in winter.

  The present invention solves the problem that the formation of micro flocs becomes poor at low water temperatures in the mixing pond of a water treatment facility such as a water purification facility, particularly in the winter, and the stirring speed when mixing the flocculant is increased. By appropriately controlling, even if the temperature of the water to be treated is lowered, a water treatment method is provided that can more efficiently coagulate and remove the suspended matter.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors paid attention to the initial mixing of water to be treated and the flocculant in the mixing pond of the water treatment facility, and the stirring G value was determined in this initial mixing. The present invention was completed by finding that the above-mentioned object can be achieved by using the index.

That is, the present invention has the following contents.
(1) In a water treatment facility having a mixing pond equipped with a stirrer, when an agglomerating agent is added to the raw water in the mixing pond and initial mixing is performed, the optimum agitation G value for the raw water to be treated and the coagulant to be used is obtained in advance. In addition, when mixing the flocculant, the temperature of the raw water in the mixing pond or the preceding landing well is measured, and the mixing G value of the mixing pond calculated based on the temperature coincides with the optimum mixing G value. A water treatment method in a water treatment facility, wherein the stirring speed of a stirrer in a mixing pond is controlled so that

(2) The optimum agitation G value was obtained by measurement using a simulation test apparatus in a state approximated to the operation method of the mixing pond using the raw water to be treated and the flocculant to be used. The water treatment method in the water treatment facility according to (1), which is characterized in that

(3) The water treatment method in a water treatment facility according to (1) or (2) above, wherein the flocculant is either an iron flocculant or an aluminum flocculant.

(4) The water treatment method in a water treatment facility according to any one of (1) to (3), wherein the flocculant is either polysilica iron or polyaluminum chloride.

  According to the method of the present invention, for example, in a water treatment facility having a mixing pond equipped with a stirrer such as a water purification plant, even when the temperature of water to be treated decreases in winter, the stirring G in the mixing pond By using the value as an index, it is possible to control the mixing speed of the mixing basin to an optimum condition. As a result, even when the temperature of the raw water is lowered, water treatment can be performed under optimum conditions, and deterioration of water quality can be prevented. For this reason, excessive addition of the flocculant for preventing deterioration of water quality can be avoided.

It is a graph which shows the relationship between the temperature of water, and a kinematic viscosity coefficient. It is explanatory drawing which shows the symbol of each site | part of the stirrer in the calculation formula of stirring G value. It is a schematic diagram of the test apparatus used for the jar test in the Example. It is a schematic diagram of the siphon tube used for the collection of the sample in the jar test of the example. It is a graph of the change of the supernatant water turbidity with respect to the flocculant injection rate when the raw water turbidity obtained by the jar test of the Example is 2 and PSI is injected as the flocculant. It is the graph of the change of the supernatant water turbidity with respect to the flocculant injection rate at the time of the raw | natural water turbidity obtained by the jar test of the Example being 2, and injecting PAC as a flocculant. It is a graph of the change of the supernatant water turbidity with respect to the flocculant injection rate when the raw water turbidity obtained by the jar test of the Example is 5 and PSI is injected as the flocculant. It is the graph of the change of the supernatant water turbidity with respect to the flocculant injection | pouring rate at the time of the raw | natural water turbidity obtained by the jar test of the Example 5 and injecting PAC as a flocculant. It is a schematic diagram of the testing apparatus used for the continuous water treatment test in the examples. It is a graph which shows the time-dependent change of the supernatant water turbidity when the raw | natural water turbidity obtained by the continuous water treatment test of the Example is 2, and PSI is inject | poured as a flocculant. It is a graph which shows the turbidity residual rate in the case of FIG. 10 in the continuous water treatment test of an Example. It is a graph which shows the E260 residual rate in the case of FIG. 10 in the continuous water treatment test of an Example. It is a graph which shows the time-dependent change of the supernatant water turbidity when the raw | natural water turbidity obtained by the continuous water treatment test of the Example is 2, and PAC is inject | poured as a flocculant. It is a graph which shows the turbidity residual rate in the case of FIG. 13 in the continuous water treatment test of an Example. It is a graph which shows the E260 residual rate in the case of FIG. 13 in the continuous water treatment test of an Example. It is a graph which shows the aluminum residual rate in the case of FIG. 13 in the continuous water treatment test of an Example. It is a graph which shows the time-dependent change of the supernatant water turbidity when the raw | natural water turbidity obtained by the continuous water treatment test of the Example is 5, and PSI is inject | poured as a flocculant. It is a graph which shows the turbidity residual rate in the case of FIG. 17 in the continuous water treatment test of an Example. It is a graph which shows E260 residual rate in the case of FIG. 17 in the continuous water treatment test of an Example. It is a graph which shows the time-dependent change of the supernatant water turbidity when the raw | natural water turbidity obtained by the continuous water treatment test of the Example is 5, and PAC is inject | poured as a flocculant. It is a graph which shows the turbidity residual rate in the case of FIG. 20 in the continuous water treatment test of an Example. It is a graph which shows E260 residual rate in the case of FIG. 20 in the continuous water treatment test of an Example. In the continuous water treatment test of an Example, it is a graph which shows the aluminum residual rate in the case of FIG.

  In the method of the present invention, a flocculant is first mixed with raw water in a mixing pond to microfloc the turbidity, then a floc in which these aggregates are formed in a flocking pond, and then agglomerates of pollutants in a sedimentation pond. It is applied to a water treatment facility consisting of a process of precipitation and separation.

  The mixing pond of this water treatment facility is equipped with a stirrer, and raw water and the injected flocculant are mixed by this stirrer. At this time, in order to form micro flocs with good turbidity, it is important that the raw water and the flocculant are in good contact with each other and mixed, and therefore the stirring state of the stirrer in this mixing pond is important. It is important to control the state in accordance with this.

  In the method of the present invention, in such a water treatment facility, even when there is a temperature change such as a decrease in the temperature of the raw water using the “stirring G value” in the mixing pond as an index, By controlling the rotational speed of the agitator in the mixing basin so as to match the optimum agitation G value, it is possible to maintain the optimum agitation state for the formation of the micro floc of the flocculant used.

  The “stirring G value” used in the present invention is represented by the following formula (I), and depends on the capacity of the mixing pond, the shape and stirring speed of the stirrer provided, the kinematic viscosity coefficient of the treated water, and the like. It is a numerical value specific to the operating state of each mixing pond determined, and is a numerical value representing the stirring state and stirring strength in the mixing pond.

Here, the symbols in the formula (I) mean the following. The symbols for the stirrer are the parts shown in FIG.
G: G value of stirring (1 / s)
C _D : Resistance coefficient 1.5 (1 / s)
A: Stirring blade area (B × L × n) (m ² )
k: coefficient 0.85 (-)
ΦD: Stirring blade diameter (m)
V: Mixing pond capacity (m ³ )
R: Stirring speed (rpm)
γ: Kinematic viscosity coefficient of water (m ² / s)

  The stirring G value varies depending on the mixing tank capacity (V) and the shape of the stirrer provided therein (A and ΦD), but even if these values are constant, It varies depending on the rotational speed (R) and the kinematic viscosity coefficient (γ) of water. As shown in FIG. 2, the kinematic viscosity coefficient of water varies greatly depending on the temperature of the water, and increases as the temperature decreases. Therefore, even if the mixing basin capacity and the shape of the agitator are constant, the agitation G value changes as the temperature of the water to be treated changes, and the agitation G value decreases as the water temperature decreases.

  On the other hand, in a mixing pond equipped with a stirrer such as a water treatment facility, there is an “optimum stirring G value” that forms a micro floc most effectively when a flocculant is added to form a micro floc. This optimum agitation G value is a numerical value influenced by the quality of the water to be treated, the injection rate of the coagulant to be added, the residence time in the relaxation pond, etc., and is actually treated in advance by a simulation test called a jar test in advance. It can be determined using the raw water to be used and the flocculant to be used.

  Specifically, the optimum stirring G value is determined as follows by, for example, a jar test. First, grasp the operating conditions such as the tank capacity of the mixing pond in the actual water purification plant, the stirring blade area, the stirring speed (rotation speed), the temperature of the water to be treated. Next, the water (raw water) of the actual water purification plant to be purified is collected and the flocculant added thereto at various injection rates is used as the water to be treated, for example, in a jar test as shown in FIG. Using a simulation test apparatus (jar tester), the rotation speed of the stirrer is changed to perform a coagulation treatment, and the turbidity of the supernatant portion of the obtained treated water is measured to evaluate the quality of the treated water. By changing the number of revolutions of the stirrer, the stirring G value in this jar tester can be obtained by the above formula (I). A graph of the change in turbidity of water is obtained. From this result, the stirring G value with the greatest decrease in the numerical value of turbidity is the “optimum stirring G value” in the water to be treated.

  Jar testers generally dispense 1 liter of raw water into a 1 liter beaker for testing. The area of the stirring shaft and stirring blade of the jar tester is assumed to stir about 1 liter of water, and the rotation speed can be changed in the range of about 0 to 180 rpm. This jar test approximates the operation method of the mixing basin in order to reproduce the stirring G value of the mixing basin of the water purification plant by the jar test, and corresponds by adjusting the stirring speed of the jar tester. First, in this jar tester, the stirrer is rapidly stirred at various stirring speeds for a length of time corresponding to the residence time of the water purification plant mixing basin, and then only for the length of time corresponding to the residence time of the floc formation pond. After slow stirring, the mixture is allowed to stand for a length of time corresponding to the residence time of the sedimentation basin, and then the supernatant water in the beaker is collected and its turbidity is measured.

  The stirring blade of the jar tester is preferably the same as that used in an actual mixing pond, and a two-blade pitched paddle is common. The type of the agitating blade may be either a pitched paddle or a pitched turbine, or may be an inclined agitating blade, but any type of agitating blade diameter as shown in FIG. (ΦD), stirring blade area (A) is obtained.

  Thus, the optimum agitation G value corresponding to the actual raw water of the water treatment plant to be treated and the type of the flocculant used there is determined. Next, the temperature of the raw water in the mixing pond of the actual water purification plant, the tank capacity (V) of the mixing pond, the area of the stirring blade provided in the mixing pond (B × L × n), and the diameter of the stirring blade (ΦD) By determining the kinematic viscosity coefficient (γ) of the water at the stirring speed (R) and the temperature of the raw water in the mixing pond, the stirring G value in the actual operation state can be obtained from the above equation (I). When the stirring G value obtained here is smaller than the optimum stirring G value obtained as described above, the stirring speed (rotation speed) of the stirrer is increased so that the stirring G value becomes the optimum stirring G value. Control the operating conditions to get closer. Thus, by operating in the mixing pond of an actual water purification plant in the state of the optimal stirring G value, the flocculant injected in the mixing pond can be brought into contact with the raw water in an optimal state and mixed. Micro flocs can be formed.

  In the winter season, the temperature of the raw water decreases and the temperature of the mixing pond in the water treatment facility also decreases. As mentioned above, there was a problem that the water quality of the mixing pond deteriorated in winter and the quality of the purified water deteriorated or the filtration pond closed up after a short period of operation. This was because the initial mixing was not achieved.

  In the present invention, in response to such a problem, when a flocculant is added in this mixing basin to form a turbid micro floc, the actual water in the mixing basin is actually measured using the above-mentioned optimum stirring G value as an index. The stirring speed of the stirrer in the mixing pond is controlled so that the stirring G value calculated based on the temperature of the mixing tank matches the optimum stirring G value. As the actual temperature of the raw water in the mixing pond, the temperature of the raw water in the mixing pond or the landing well provided in the preceding stage is measured.

  For example, when the actual temperature of the mixing pond decreases in the winter, etc., the stirring G value at that temperature in the mixing pond of the actual water purification plant is calculated by the above formula (I), and this value is the mixing pond. If it does not coincide with the optimum stirring G value, the mixing pond can be brought into an optimal stirring state for the formation of micro flocs by the flocculant by adjusting the stirring speed of the mixing pond stirrer.

  In the method of the present invention, various flocculants can be used to form turbid micro flocs in the mixing pond. As the flocculant for this purpose, various conventionally used flocculants can be used. For example, various flocculants such as aluminum sulfate, ferric chloride, polyferric sulfate, polyaluminum chloride, and polysilica iron. An aggregating agent can be used. Among these flocculants, the use of high-performance flocculants such as polyaluminum chloride (PAC) and polysilica iron (PSI) is more effective.

  In the water treatment method of the present invention, the raw water not only treats purified water such as tap water, but also treats various types of wastewater such as domestic wastewater, wastewater from urban sewage, agricultural wastewater, and various industrial wastewater. It can also be used in water treatment facilities.

  According to the method of the present invention for controlling the stirring G value in the mixing basin to the optimum value, even if the quality of the raw water to be applied is different, the stirring G value is determined after determining the optimum stirring G value for the raw water. By controlling so as to approach the value, good micro floc can be formed, so turbidity of supernatant water, E260 which is an indicator of soluble organic matter, insoluble aluminum and other water quality expected to be removed by micro floc formation Those items to be evaluated can be improved.

  The flocculant used in the water treatment facility in the present invention is particularly preferably polysilica iron (PSI), which is an iron-based polymer flocculant, or polyaluminum chloride (PAC), which is an aluminum-based polymer flocculant. In the method of the present invention, when any flocculant is used, a good micro floc can be obtained by determining the optimum stirring G value for the flocculant used and controlling the stirring G value to approach this value. Since it can be formed, turbidity of the supernatant water, E260 which is an indicator of soluble organic matter, insoluble aluminum and other items that evaluate the water quality expected to be removed by micro flocation can be improved. it can.

  In addition, for example, even if the water treatment facility has different design specifications for the mixing time of the continuous treatment equipment for the simulation test and the actual water treatment facility, the residence time of the flock formation pond and the water area load of the sedimentation pond, By determining the G value and controlling the stirring G value so as to approach this value, a good micro floc can be formed. Therefore, the turbidity of the supernatant water, E260 which is an indicator of soluble organic matter, insoluble aluminum, Other items that evaluate the water quality expected to be removed by micro-flocing can be improved.

  In addition, about the turbidity of water for evaluating the quality of the water to process, E260 which is a parameter | index of a soluble organic substance, and aluminum, what was measured with the following method is used.

The turbidity of water is obtained by integrating sphere photoelectric photometry, which measures the amount of light scattered by turbid particles in water using an integrating sphere, and at the same time, measures the amount of transmitted light that passes through water and determines the ratio of these amounts. . In other words, the turbidity D test water, the amount of scattered light I _R, when the quantity of transmitted light and I _T, is calculated by the following equation. K is a proportionality constant determined from a calibration curve using a turbidity standard solution.

  Since organic substances having unsaturated bonds in water absorb in the ultraviolet region, the absorbance in the wavelength range of 250 to 260 nm is measured to evaluate the state of organic contamination of water and the water treatment performance in the water purification treatment process. Can do. The absorbance of water in the wavelength region of 260 nm, which is the ultraviolet region, is measured with a spectrophotometer. This is expressed as “E260” and used as a value indicating the amount of soluble organic matter in water. For details, it is described in “Water Supply Test Method 2011 Version II. Physical Chemistry” published by Japan Water Works Association.

  The concentration of aluminum and its compound in water is determined by measuring the emission intensity at a wavelength of 396.152 nm or 309.271 nm by inductively coupled plasma (ICP) emission spectroscopy. Details are described in “Water Supply Test Method 2011 Version III. Metals” published by Japan Water Works Association.

As for these water quality evaluation items, in the jar test for obtaining the optimum stirring G value, there are cases where the suspended turbidity in water is measured and the total value including insoluble components is obtained. Therefore, when evaluating the component of a dissolved state, the sample collected is filtered with a 1 micrometer membrane filter, and said evaluation is performed about this filtered water.
About said water quality evaluation item, as shown in following Table 1, the presence or absence of filtration is distinguished according to test water and an evaluation item.

  The turbidity is not filtered to evaluate the turbidity of the whole water, and E260 is filtered to evaluate the soluble component. For aluminum, simulated raw water is not filtered to know the total value of insoluble aluminum and soluble aluminum, and treated water is filtered. The reason is that without filtration, the fluctuation of the value is difficult to evaluate due to the presence or absence of floc remaining in the supernatant water. Generally, in water purification facilities and wastewater treatment facilities, a sand filtration process is provided after the coagulation sedimentation process. In addition, filtering with a 1 μm membrane filter has the same filtration effect as sand filtration. Therefore, by measuring the aluminum content of the filtrate, the scavenging ability of insoluble aluminum due to good floc formation should be evaluated. Can do.

The temperature of the raw water of the mixing pond or the preceding landing well is measured, and the optimum stirring G value is achieved as a system for matching the mixing G value of the mixing pond calculated based on the temperature with the optimal stirring G value. Therefore, a feedback control system can be constructed by using the stirring speed obtained using the formula (I) as a control variable.
The feedback control is a mechanism for calculating the deviation of the control variable from the target value and adjusting the value of the manipulated variable so that the deviation is eliminated. In order to eliminate the deviation, this is a method in which control variable measurement, target value and control variable comparison (deviation calculation), and operation variable change procedures are repeated. In the method of the present invention, the operating variable is calculated from the deviation between the target stirring speed and the measured stirring speed by using the formula (I) and setting the stirring speed for achieving the optimum stirring G value as the target value of the control variable. Since the calculation formula can be built into the general-purpose sequencer, it is possible to follow the stirring speed of the stirrer toward the stirring speed corresponding to the optimal stirring G value without introducing a dedicated controller for feedback control. Therefore, an inexpensive control system can be provided by constructing the stirring G value control system with a general-purpose sequencer and a general-purpose touch panel.

  Conventionally, operations to increase the amount of flocculant injected in order to stabilize the treatment capacity have been carried out as a general maintenance management method against the increase in raw water load due to the increase in turbidity of raw water due to heavy rain etc. Yes. However, feedback control to follow the injection amount of the flocculant corresponding to the increase in turbidity of the raw water is because the controller is manually changing the flocculant injection amount because the controller is expensive. Currently. In contrast, by the method of the present invention using a general-purpose sequencer that has a built-in arithmetic expression for calculating the manipulated variable from the deviation, the optimum coagulant injection can be performed without purchasing a dedicated controller for feedback control. Because the injection amount of the flocculant injection pump can be made to follow the injection amount of the flocculant leading to the rate, the feedback control of the flocculant injection amount with respect to the raw water flow rate and raw water turbidity should be constructed with a general-purpose sequencer and a general-purpose touch panel And an inexpensive control system can be provided.

(1) Determination of optimum agitation G value by simulation test First, simulated raw water adjusted to a predetermined turbidity by adding kaolin to tap water was prepared. In order to determine the optimum stirring G value, a jar tester having eight bowl-shaped stirrers as shown in FIG. 3 is prepared, and this simulated raw water is used as a jar test with the stirring G value of the stirrer as a parameter. Carried out.

  One liter of simulated raw water is sampled in a 1 L beaker, and each beaker containing the simulated raw water is installed in the jar tester of FIG. 3 to correspond to the process of “mixing of flocculant-floc formation-precipitation separation” in the water treatment facility. Thus, a water purification treatment test was carried out by batch operation under the stirring conditions of “rapid stirring—slow stirring—standing”. As shown in Table 2, the stirring conditions were as follows: rapid stirring corresponding to mixing pond stirring was performed with three types of stirrer rotation speeds of 115 rpm, 150 rpm and 180 rpm, and slow stirring corresponding to the flock formation pond was set to 40 rpm. The stirring time was 3 minutes for rapid stirring, 10 minutes for slow stirring, and 10 minutes for standing time. The stirring G value of the simulation test by this jar tester was determined by the above formula (I). Table 2 shows the value of the stirring G value.

  Two types of simulated raw water were used, one adjusted to turbidity 2 ° and the other adjusted to turbidity 5 °. In addition, the flocculant was poured into the beaker immediately before the rapid stirring corresponding to the mixing pond and subjected to rapid stirring for 3 minutes. As the flocculant, two kinds of flocculants, polyaluminum chloride (PAC) and polysilica iron (PSI), were used. The injection rate of the flocculant was varied in the range of 0 to 50 (mg / L) for PSI and 0 to 40 (mg / L) for PAC.

  As an evaluation method of the rapid stirring process corresponding to this mixing pond, the turbidity of the supernatant water after 10 minutes of the jar test standing process was employed. Since the sample for measuring the turbidity of the supernatant water needs to be collected from a certain depth, the siphon tube shown in FIG. 4 was installed in a 1 L beaker at the same time as the slow stirring was completed, and 10 minutes of the stationary process passed. Later, water was collected from a predetermined depth shown in FIG. 4, and the turbidity was measured using this. In this simulation test, the temperature of the simulated raw water was constant at 25 ° C.

The results obtained from these simulation tests are shown in FIGS. 5 to 8 with the stirring G value as a parameter for the turbidity of 2 degrees and 5 degrees turbidity of the simulated raw water.
That is, FIG. 5 shows the injection of PSI with a rapid stirring G value of 200, 300, 400 (1 / s) as a parameter when PSI is used as a flocculant for turbidity of 2 degrees of simulated raw water with a water temperature of 25 ° C. It is a measurement result of the supernatant water turbidity with respect to a rate of 0 to 50 (mg / L). Similarly, FIG. 6 shows the measurement results of the supernatant water turbidity when the PAC injection rate is 0 to 40 (mg / L) when PAC is used as the flocculant. 7 and 8 show the measurement results of the supernatant water turbidity when PSI and PAC are used as flocculants for the turbidity of the simulated raw water of 5 degrees, respectively.

  From these test results, when PSI was used as the flocculant, the flocculant was injected when the stirring G value was 300 (1 / s) in both cases of the turbidity of the simulated raw water being 2 degrees and 5 degrees. The supernatant turbidity at the low injection rate of 30 to 45 (mg / L) is the most improved. Similarly, when PAC is used as the flocculant, the stirring G value is 300 (1 / s). Occasionally, it was found that the supernatant water turbidity was most improved at a low injection rate of 15 to 25 mg / L. Therefore, from this result, it was found that the optimum stirring G value for the simulated raw water was 300 (1 / s).

(2) Test by continuous treatment apparatus Next, as shown in FIG. 9, “cooling pond—corresponding to a water purification treatment process consisting of“ mixing of flocculant—floc formation—separation of precipitate ”with raw water having a constant load. Using a continuous water treatment simulation test device consisting of a coagulant flocculation pond-floc formation pond-sedimentation pond ", the mixing rate of the mixing pond stirrer is increased with respect to the raw water at low water temperature, and the stirring G value is optimized. A continuous treatment experiment was conducted for the purpose of evaluating the impact of water quality improvement.

  Table 3 shows the quality of simulated raw water having turbidity of 2 and 5 degrees used in this continuous treatment experiment. The initial temperature of the simulated raw water was 25 ° C. Table 4 shows the raw water flow rate (L / min), the capacity (L), the residence time (min), and the stirring speed (rpm) of the equipped stirrer for each of the mixing pond, flock formation pond and sedimentation pond.

  In addition, when using either PSI or PAC as the flocculant, it is desired to maintain a pH at the time of aggregation in a weakly acidic range (about pH 6.8) to exert a high coagulation effect. Using sodium, the pH of the simulated raw water was adjusted to a predetermined pH according to the flocculant used.

  This continuous treatment system is scaled down in line with an actual water purification facility, and the coagulant injection rate, the mixing pond residence time, and the water area load of the settling basin are values based on general design specifications. . However, the residence time of the floc formation pond was set to be shorter than the actual water purification facility value, and the treatment water quality by PSI and PAC was enhanced to further clarify the difference in applying the stirring G value.

  As for the stirring speed of the mixing pond stirrer, the optimum stirring G value for the simulated raw water, which is the result of the jar test, is adopted, and numerical values such as the tank capacity of the mixing pond and the stirring blade area are input to the formula (I), The stirring speed required to maintain the optimum stirring G value for this water temperature was calculated. As a result, the stirring speed of the stirrer required to maintain the optimum stirring G value 300 (1 / s) in this mixing pond was 150 rpm when the water temperature was 25 ° C., and 180 rpm when the water temperature was 5 ° C. .

  Next, in the continuous simulation test apparatus shown in FIG. 9, the simulated raw water was stored in the raw water storage tank, and the raw water was transferred to the cooling pond at a constant flow rate by the raw water pump. And the time of flowing into the mixing pond from the cooling basin overflow was set as the start of the continuous treatment experiment, and at the same time, the injection of the flocculant into the mixing value was started. At the start of the experiment, the mixing pond, the flock formation pond and the settling pond were filled with tap water. Raw water is mixed and agglomerated in a mixing basin to form micro flocs, and flocs are formed in the floc forming ponds by slow stirring. The formed floc was separated and removed in the sedimentation basin, and the supernatant water was discharged from the overflow dam.

In order to evaluate the influence of the water quality improvement of the method of the present invention when the temperature of the raw water was lowered, the raw water was cooled in the cooling device simultaneously with the start of the experiment. Table 4 shows the experimental conditions.
Here, “G value application” means that when the raw water temperature is lowered from 25 ° C. to 5 ° C., the stirring speed of the mixing pond is increased from 150 rpm to 180 rpm and the stirring G value is set to 300 (1 / s This is the case of the conditions maintained in (1). The “control system” is a case where the stirring speed is kept constant at 150 rpm even when the temperature of the raw water is lowered from 25 ° C. to 5 ° C., and the stirring G value is 300 to 236 ( This is the case of the condition reduced to 1 / s).

  Under each condition, a 4-hour continuous treatment experiment was conducted, and the turbidity of the supernatant water, UV absorbance (E260), which is an indicator of soluble organic matter, and the value of soluble aluminum (Al) were measured. Went. The stirring speed of the stirrer in the flock formation pond was constant at 30 rpm regardless of the water temperature change in each experimental condition. PSI and PAC were used as the aggregating agent, and the injection rate was 45 mg / L and PAC 25 mg / L as the injection rate PSI obtained by the jar test, and the injection rate was constant regardless of the water temperature change in each experimental condition.

  The water quality measurement result in each condition in the continuous treatment experiment of the above simulated raw water is shown in FIGS. That is, FIG. 10 shows the time-dependent change in the turbidity of the supernatant water by the continuous test when the raw water turbidity is 2 degrees and the flocculant is PSI. In FIG. The E260 residual ratio of is shown in FIG. The results when the raw water turbidity is 2 degrees and the flocculant is PAC are similarly shown in FIGS. In addition, when a flocculant is PAC, a soluble aluminum residual rate is shown in FIG. Also, the results when the raw water turbidity is 5 degrees and the flocculant is PSI are similarly shown in FIGS. 17 to 19, and the results when the raw water turbidity is 5 degrees and the flocculant is PAC are similarly shown in FIGS. 20 to 23. . In addition, when a flocculant is PAC, a soluble aluminum residual rate is shown in FIG.

  In the continuous treatment experiment for 4 hours, the residual ratio in the figure means that these values in the raw water of the average value of each of the four analysis values for 2.5 to 4 hours after the start of the experiment when the water temperature and turbidity became steady. Percentage of value.

  In FIG. 11, the turbidity residual value exceeds 100%, which is due to the following circumstances. In the above-mentioned continuous treatment experiment, the floc formation pond residence time was made shorter than the actual water purification plant value in order to clarify the difference in the stirring G value application by increasing the supernatant turbidity as a whole. Responsible. Even though a good micro floc can be formed by “G value application” in the mixing pond, the average residence time in the floc forming pond that promotes floc formation is short, so it was transferred to the sedimentation basin with insufficient floc formation. it is conceivable that. Therefore, the turbidity remaining rate exceeded 100% was limited to this continuous treatment experiment. When PSI was used in an actual water purification facility, the flock formation pond residence time was determined according to general design specifications. Therefore, the residual turbidity can be reduced to a low level by good floc formation.

  Comparing the result of “G value application”, which is the method of the present invention, with the “control system” in which the stirring conditions were not changed even when the temperature of the raw water was lowered, the raw water turbidity was 2 degrees or 5 degrees. On the other hand, it was found that in both the PSI and PAC flocculants, the supernatant water turbidity and the residual rate of E260, which is a soluble organic matter index, were lower when the G value was applied than in the control system. Further, when PAC was used as a flocculant, the residual aluminum residual rate was lower when G value was applied. From these facts, by applying the method of the present invention that controls the stirring G value corresponding to the temperature change of the raw water, a good micro floc can be formed in the mixing pond, and the suspended matter can be effectively separated by precipitation. It was possible to confirm the excellent water quality improvement effect.

  According to the method of the present invention, it is possible to effectively prevent a decrease in water quality due to a decrease in treatment performance due to a decrease in water temperature in winter, etc. in a water treatment facility, which is useful for efficient operation of various water treatment facilities. .

Claims (4)

  In a water treatment facility having a mixing pond equipped with a stirrer, when an initial mixing is performed by adding a flocculant to raw water in the mixing pond, an optimum stirring G value for the raw water to be treated and the flocculant to be used is obtained in advance. When mixing the flocculant, the temperature of the raw water in the mixing pond or the preceding landing well is measured, and the stirring G value of the mixing pond calculated based on the temperature is matched with the optimum stirring G value. A water treatment method in a water treatment facility, characterized by controlling a stirring speed of a stirrer in a mixing pond.   The optimum stirring G value is obtained by measuring using a simulation test apparatus in a state approximate to the operation method of the mixing pond using raw water to be treated and a coagulant to be used. The water treatment method in the water treatment facility according to claim 1.   The water treatment method in a water treatment facility according to claim 1 or 2, wherein the flocculant is either an iron-based flocculant or an aluminum-based flocculant.   The water treatment method in a water treatment facility according to any one of claims 1 to 3, wherein the flocculant is either polysilica iron or polyaluminum chloride.

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