Method for treating picoplankton-containing water to be treated and treatment device for picoplankton-containing water to be treated

Abstract

To provide a processing method of treated water containing picoplankton and a processor of treated water containing picoplankton capable of safe and efficient removal of picoplankton in treated water with high removal ratio.SOLUTION: A processing method of treated water containing picoplankton is characterized by that: picoplankton concentration in treated water is measured, and based on a measurement result of the picoplankton concentration, dilution water having lower picoplankton concentration than the treated water is mixed with the treated water having a picoplankton concentration of a reference value or over for a dilution treatment; a coagulant for reduction of picoplankton concentration in the treated water is added to the treated water after the dilution treatment; and the treated water containing the coagulant is solid-liquid separated.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for treating water containing picoplankton and an apparatus for treating water containing picoplankton, and in particular to a method for treating water containing picoplankton that is suitable for water purification treatment and an apparatus for treating water containing picoplankton. [Background technology]

[0002] Recently, there have been frequent outbreaks of microplankton due to eutrophication in tap water sources all over the country. Microplankton leak from rapid filtration basins and cause the turbidity of the filtered water to rise to 0.1 degrees or more, so water utilities are struggling with treatment measures. The Ministry of Health, Labor and Welfare has instructed that filtered water turbidity be maintained at 0.1 degrees or less in response to infectious diseases caused by Cryptosporidium transmitted through tap water (see Non-Patent Document 1), and water utilities in each region have positioned constant management of filtered water turbidity at 0.1 degrees or less as one of the most important water quality management items.

[0003] Picoplankton is a plankton with a size of 0.2 to 2.0 μm, and it has been reported that it is a factor in increasing the turbidity of filtered water (see Non-Patent Document 2). Picoplankton are classified into two groups based on the mechanism of nutritional intake. One is heterotrophic picoplankton mainly composed of bacteria that decompose organic matter and use it as a nutrient source, and the other is phytopicoplankton that performs photosynthesis. Such picoplankton has pigments such as chlorophyll a. Therefore, by irradiating it with an excitation wavelength of green (G) or blue (B) using an epifluorescence microscope, the autofluorescence can be observed, and the presence of picoplankton in the raw water or treated water can be confirmed.

[0004] Picoplankton is a type of suspended solid that originates from living organisms, and so in the past, the effective means of removing it was through the injection of chlorine. However, chlorine injection generates trihalomethanes as a by-product, which are carcinogenic and cause health problems, so a safer method of removing it is needed.

[0005] Japanese Patent No. 5430788 (Patent Document 1) describes that biological particles that can be detected (counted) by a biological particle counter are biological particles with a particle size of 0.1 to several hundreds of μm, algae, and phytoplankton. It also describes that the injection of chemicals such as coagulants and chlorine can be controlled according to the counting results of the biological particle counter, making it possible to efficiently purify water and monitor water quality.

[0006] Japanese Patent No. 5473560 (Patent Document 2) describes a continuous control system for a water purification process that determines whether or not poor water purification is caused by filtration problems due to microplankton, based on information on sediment turbidity and filtrate turbidity obtained from an automatic continuous water purification process monitoring device, and automatically injects a flocculant in the post-coagulation treatment process when it is determined that filtration problems are due to microplankton.

[0007] JP 2017-6902 A (Patent Document 3) describes an example of a water treatment system in which raw water containing heavy metals is diluted with physically treated water or fresh water, and the COD of the raw water is reduced to 160 mg / L or less by dilution. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 5430788 [Patent Document 2] Patent No. 5473560 [Patent Document 3] JP 2017-6902 A [Non-patent literature]

[0009] [Non-Patent Document 1] Ministry of Health, Labor and Welfare Notification, Yakuseisuihatsu 0529 No. 1, "Guidelines for Countermeasures against Cryptosporidium, etc. in Water Supply," Appendix 2, page 3, May 29, 2019 [Non-Patent Document 2] Japan Water Works Association, Water Purification Treatment Guide to Prevent Biological Hazards, p. 57, March 2006 Summary of the Invention [Problem to be solved by the invention]

[0010] However, none of the above-mentioned conventional techniques are sufficient as a measure for efficiently removing picoplankton from the water to be treated with a high removal rate. For example, in conventional water treatment, treated water obtained in a later stage of treatment may be circulated as return water to a previous stage of treatment. In this case, if picoplankton remains in a high concentration in the return water, the picoplankton gradually accumulates and becomes concentrated in the water purification system due to the circulation of the return water. If the concentration of picoplankton in the treated water in the water purification system becomes too high, it becomes difficult to remove the picoplankton using a flocculant, which increases the turbidity of the filtered water, making it difficult to maintain the turbidity of the filtered water below the standard value.

[0011] In view of the above problems, the present invention provides a method for treating water containing picoplankton, which can safely and efficiently remove picoplankton from the water at a high removal rate, and an apparatus for treating water containing picoplankton. [Means for solving the problem]

[0012] As a result of extensive investigations by the present inventors to solve the above problems, it was discovered that it is effective to carry out a specific treatment on water to be treated that has a high picoplankton concentration.

[0013] In one aspect, the present invention, which was completed based on the above findings, is a method for treating water containing picoplankton, which includes measuring the picoplankton concentration in the water to be treated, diluting the water to be treated in which the picoplankton concentration is equal to or higher than a predetermined standard value based on the measurement results of the picoplankton concentration by mixing dilution water having a lower picoplankton concentration than the water to be treated, adding a coagulant to the water to be treated after the dilution treatment to reduce the picoplankton concentration in the water to be treated, and performing solid-liquid separation of the water to be treated containing the coagulant.

[0014] According to one embodiment of the present invention, based on the measurement results of the picoplankton concentration, the treated water, whose picoplankton concentration is equal to or higher than a standard value, is introduced from a first treatment tank containing the treated water to a second treatment tank, in which dilution treatment and addition of a coagulant are performed, at least a portion of the treated water in the second treatment tank is returned to the first treatment tank as return water, and the treated water including the return water in the first treatment tank is subjected to solid-liquid separation.

[0015] According to another embodiment of the present invention, the picoplankton concentration in the treated water after dilution treatment is 1×10 7 This includes adding dilution water to achieve a concentration of 0.1% or less per mL.

[0016] According to yet another embodiment of the present invention, the picoplankton concentration is 1×10 5 This includes using dilution water with less than 1000 / mL.

[0017] According to yet another embodiment of the present invention, the method includes measuring the picoplankton concentration in the return water returned to the first treatment tank, and controlling the dilution ratio of the dilution water based on the measurement results of the picoplankton concentration in the return water.

[0018] In another aspect, the present invention provides an apparatus for treating water containing picoplankton, comprising a first treatment tank capable of separating the water to be treated into solid and liquid, a measuring means for measuring the picoplankton concentration of the water to be treated, a second treatment tank connected to the first treatment tank, a water to be treated introducing means for introducing at least a portion of the water to be treated in the first treatment tank into the second treatment tank when the picoplankton concentration of the water to be treated in the first treatment tank becomes equal to or higher than a reference value based on the measurement results of the measuring means, a dilution water introducing means for introducing dilution water having a lower picoplankton concentration than the water to be treated into the second treatment tank, a chemical injection means for adding a coagulant to the second treatment tank to reduce the picoplankton concentration of the water to be treated, and a return means for returning the water to be treated in the second treatment tank to the first treatment tank.

[0019] According to one embodiment of the present invention, a control means is provided for controlling at least one of the amount of water to be treated introduced into the second treatment tank by the water to be treated introduction means, the dilution ratio of the dilution water, and the amount of coagulant added when the measurement result of the picoplankton concentration in the water to be treated is equal to or higher than a standard value. Effect of the Invention

[0020] According to the present invention, it is possible to provide a method for treating water containing picoplankton, which can safely and efficiently remove picoplankton from the water at a high removal rate, and an apparatus for treating water containing picoplankton. [Brief description of the drawings]

[0021] [Figure 1] 1 is a schematic diagram showing an example of a treatment apparatus for picoplankton-containing water to be treated according to a first embodiment of the present invention. [Diagram 2] FIG. 4 is a schematic diagram showing an example of a treatment apparatus for picoplankton-containing water to be treated according to a second embodiment of the present invention. [Diagram 3] FIG. 11 is a schematic diagram showing an example of a treatment device for picoplankton-containing water to be treated according to a modified example of the second embodiment of the present invention. [Figure 4]1 is a graph showing the relationship between the PAC injection rate and the picoplankton removal rate when sample water 1 was diluted and when it was not diluted. [Diagram 5] This is a graph showing the relationship between the increase in picoplankton when test water 1 (undiluted) and test water 5 (diluted) are returned to the receiving well of the water purification plant. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are given the same or similar reference numerals. Note that the embodiments shown below are examples of devices and methods for embodying the technical idea of ​​the present invention, and do not limit the technical idea of ​​the present invention or the structure and arrangement of the components to those described below.

[0023] (First embodiment) The method for treating water to be treated that contains picoplankton in the first embodiment includes measuring the picoplankton concentration in the water to be treated, diluting the water to be treated in which the picoplankton concentration is equal to or higher than a predetermined standard value based on the measurement results of the picoplankton concentration by mixing dilution water having a lower picoplankton concentration than the water to be treated, adding a coagulant to the water to be treated after the dilution treatment to reduce the picoplankton concentration in the water to be treated, and performing solid-liquid separation of the water to be treated containing the coagulant.

[0024] The water to be treated is not particularly limited as long as it contains picoplankton. For example, river water, lake water, reservoir water, rainwater, subsurface water, groundwater, and well water, which are used as raw water for water supply, can be used as the water to be treated. Furthermore, it is also preferable to target treated water generated in a water purification system in which a predetermined water purification process such as sedimentation, coagulation sedimentation, or filtration is performed on these raw water for water supply. The turbidity of the raw water is not limited to the following, but is typically 100 degrees or less, more typically 25 degrees or less, and even more typically about 2 to 10 degrees. The raw water is typically subjected to coagulation treatment through a grit chamber or a receiving well.

[0025] Picoplankton includes microplankton, phytoplankton, small plankton, small algae, and algae biological particles, and typically refers to plankton with a cell diameter of 0.2 μm to 2.0 μm. In particular, phytopicoplankton that photosynthesizes are known to exist in raw water for water supply, such as river water, lake water, and reservoir water. When the cell count of phytopicoplankton increases, the effect of reducing the turbidity of the filtered water by adding a flocculant becomes limited, and water purification problems may occur.

[0026] In particular, the picoplankton concentration in the treated water is approximately 1×10 7 If the concentration exceeds 100 picoplankton / mL, it becomes difficult to remove the picoplankton from the water to be treated even if the amount of flocculant added is increased to perform coagulation and precipitation. In this embodiment, the concentration of picoplankton in the water to be treated is measured, and if the measurement result exceeds a standard value that could cause a disruption to water purification treatment due to a large-scale outbreak of picoplankton, treatment is performed to reduce the picoplankton concentration in the water to be treated.

[0027] The standard value for the picoplankton concentration in the treated water may be changed depending on various factors such as the size of the water purification facility, the equipment configuration, and the equipment conditions. Typically, the standard value is 1×10 7 / mL, and even 1×10 6 / mL, or even 5×10 6 It can be set to pieces / mL.

[0028] Picoplankton concentration can be evaluated by the number of picoplankton (cell count) per mL of treated water, and the number of picoplankton with cell diameters of 0.2 μm to 2.0 μm is counted. A method for extracting only picoplankton with a size of 0.2 μm to 2.0 μm from fine particles of all sizes contained in the treated water can be carried out by passing raw water or filtered water through a filter with an opening size of 0.2 μm and a filter with an opening size of 2.0 μm.

[0029] The method for measuring the picoplankton concentration is not particularly limited. For example, the picoplankton concentration can be measured by fluorescence measurement using a fluorescence microscope. In the fluorescence measurement, the number of picoplankton present is confirmed by measuring the fluorescence emitted by chlorophyll contained in the picoplankton. Furthermore, the number of picoplankton present confirmed by the fluorescence measurement is counted by a counter. The picoplankton concentration can be measured using a commonly available picoplankton measuring device in addition to the above-mentioned fluorescence measurement using a fluorescence microscope.

[0030] If the measurement of the picoplankton concentration shows that the picoplankton concentration in the water to be treated is equal to or higher than the reference value, a treatment is carried out to reduce the picoplankton concentration in the water to be treated. Specifically, the water to be treated is mixed with dilution water to be diluted, and a flocculant is added to the diluted water to be treated. Furthermore, by subjecting the water to be treated containing the flocculant to solid-liquid separation, the picoplankton captured in the flocs can be separated by settling and removed from the system as treated sludge.

[0031] As the dilution water, water having a picoplankton concentration lower than that of the water to be treated is used. As such dilution water, it is preferable to use water having a picoplankton concentration lower than that of the water to be treated by 1 / 100 or more, or even 1 / 1000 or more. Typically, the picoplankton concentration is 1×10 5 Dilution water with a picoplankton concentration of less than 1000 / mL is used. For example, water generated during water purification, such as surface washing water, backwash drainage, and sand filtration water, is used as dilution water, which is desirable in that it allows for effective use of the water generated during water purification. Treated water such as groundwater, well water, or supernatant water generated within a water purification system, which has a relatively low picoplankton concentration, may also be used.

[0032] If the dilution ratio of the dilution water to the water to be treated is too large, a large amount of dilution water is required, and a treatment tank with a large capacity is required for the dilution treatment. As a result, the device becomes large, and efficient treatment may not be possible. The dilution ratio is preferably 20 times or less, and more preferably 15 times or less. The dilution ratio is typically about 1 to 10 times, and more typically about 5 to 10 times.

[0033] It is preferable to mix the dilution water with the water to be treated and control the picoplankton concentration in the water to be treated after the dilution treatment so that the picoplankton concentration in the water to be treated after the dilution treatment is equal to or lower than a reference value. For example, if the picoplankton concentration in the water to be treated after the dilution treatment is 1×10 7 By controlling the dilution ratio of the dilution water and adding the dilution water so that the number of picoplankton is reduced to less than 1 / mL, the effect of adding the coagulant described below can be fully exerted. This makes it possible to efficiently remove picoplankton from the water to be treated at a high removal rate.

[0034] A flocculant is added to the water to be treated in order to reduce the picoplankton concentration in the water. A "flocculant" refers to an agent that has a cross-linking ability to neutralize the charge of suspended particles and colloidal substances in the water, agglomerate them, and form flocs. For example, inorganic flocculants can be used as such flocculants. For example, polyaluminum chloride (PAC), aluminum sulfate (alum sulfate), polyferrous sulfate, etc. can be used as inorganic flocculants. These can be used alone or in combination of two or more.

[0035] In particular, a polyaluminum chloride (PAC) solution with a basicity of 60% or more is preferably used as a flocculant for reducing the number of picoplankton. The higher the basicity of the PAC solution used to remove picoplankton, the higher the charge neutralization ability in the water to be treated can be, and the more the effect of capturing fine particles can be improved. In addition, when maintaining the same treatment capacity, the higher the basicity of the PAC solution, the lower the addition rate can be, which improves treatment efficiency and is economically advantageous. In this embodiment, it is preferable to use a PAC solution with a basicity of 65% or more, more preferably 70% or more, and even more preferably 75% or more as a flocculant to be added to the water to be treated.

[0036] The amount of flocculant added is appropriately selected depending on the type of flocculant selected, but is usually 1 to 400 mg / L, preferably 50 to 300 mg / L, and more typically 100 to 200 mg / L, and the amount and type of flocculant added can be controlled within this range.

[0037] In order to more efficiently remove picoplankton from the water to be treated, a flocculation aid (also called a flocculation auxiliary) may be added to the water to be treated. The term "flocculation auxiliary" refers to a chemical that is added together with a flocculant to improve the flocculation and settling properties of flocs during flocculation treatment and the capture properties in rapid sand filters, and to form large, dense, and strong flocs.

[0038] Examples of the flocculation aid include various flocculation aids such as floc formation aids, alkaline agents such as slaked lime, sodium hydroxide, and soda ash, inorganic substances such as active silicic acid and bentonite, organic flocculation aids, polymer flocculants, flocculation improvers, etc. In particular, as a flocculation aid for improving the flocculation and settling properties of hard-to-flocculate fine particles such as picoplankton, it is preferable to use an agent containing granular material that can become the nucleus of flocs.

[0039] It is preferable to use a polymer flocculant selected from among cationic polymer flocculants, anionic polymer flocculants, and nonionic polymer flocculants, taking into consideration the surface charge of particles in the liquid, and the like.

[0040] The organic flocculation aid may be alginate, poly(meth)acrylate, CMC, polyglutamic acid, gum arabic, xanthan gum, guar gum, chitosan, or polyvinyl alcohol. The alginate may be alginic acid, sodium alginate, calcium alginate, or magnesium alginate. An alginate ester may also be used. The poly(meth)acrylate may be polyacrylic acid, sodium polyacrylate, potassium polyacrylate, ammonium polyacrylate, polymethacrylic acid, sodium polymethacrylate, potassium polymethacrylate, or ammonium polymethacrylate, but it is more preferable to use sodium polyacrylate.

[0041] The aggregation improver may be fine sand having a particle size distribution in which the mass ratio of particles having a particle size of 100 μm or more is 5% or less and the mass ratio of particles having a particle size of 10 μm or less is 30% or less, and a specific gravity of 2.0 to 4.0. It is more preferable that such fine sand is insoluble in water and has a zeta potential of -30 mV to -60 mV when added to the water to be treated.

[0042] As the flocculation aid, it is also preferable to add particles with good flocculation and settling properties, such as inorganic particles or clay particles, either alone or in combination with the above-mentioned flocculation aid. The inorganic particles may be any granular material that has a specific gravity in the range of 2.0 to 4.0 and is insoluble in water. Specific examples of the granular material include sand, activated carbon, and kaolin, and among these, sand is preferred. Furthermore, the main component is SiO 2 More preferably, the particles have a particle size distribution in which the weight ratio of particles of 105 μm or less is 95% or more.

[0043] Inorganic particles or clay particles are also contained in sludge or washing wastewater generated in water purification treatment. Therefore, by using the return sludge from the coagulation treatment or the washing wastewater from the filtration treatment as a coagulation aid, resources generated in the water purification treatment can be effectively utilized without using additional chemicals for the coagulation treatment of particles containing picoplankton. Specific examples of wastewater or washing wastewater generated in water purification treatment that contain inorganic particles or clay particles include sludge from a settling tank (purified water sludge), sand washing wastewater, and washing wastewater. By returning the sludge from a settling tank or the backwash wastewater from a filtration tank to the raw water as a substitute for commercially available coagulation aids, the proportion of inorganic particles in the raw water can be increased, and the removal rate of picoplankton can be further improved.

[0044] The amount of the flocculation aid to be added is appropriately selected, but is usually 4 to 40 mg / L relative to the amount of raw water, and the addition of the flocculation aid can be controlled within this range. The order of addition of the flocculation aid and the flocculation aid is appropriately changed depending on the type of the flocculation aid and the flocculation aid. Usually, after adding the flocculation aid and the flocculation aid, the diluted water to be treated is mixed with the flocculation aid and the flocculation aid to form flocs, and the flocs are separated into solid and liquid by settling or the like. Since the picoplankton concentration of the treated water obtained by the solid-liquid separation is sufficiently reduced, even if the treated water is returned to any treatment process of the water purification treatment, an increase in the picoplankton concentration in the water purification treatment system due to the introduction of the returned water can be suppressed.

[0045] According to the method for treating water containing picoplankton relating to the first embodiment of the present invention, high-concentration water to be treated, which has a high concentration of picoplankton, is diluted with dilution water until the picoplankton concentration reaches a level at which the coagulant can effectively exert its coagulation treatment effect on the picoplankton, thereby reducing the picoplankton concentration, so that the coagulation treatment effect of the coagulant can be efficiently exerted with a small amount of coagulant, thereby improving the removal rate of picoplankton.

[0046] 1 shows an example of a treatment apparatus for water to be treated to which the method for treating water to be treated containing picoplankton according to the first embodiment of the present invention can be applied. The treatment apparatus for water to be treated includes a first treatment tank 1 capable of performing solid-liquid separation of the water to be treated, a measuring means 2 for measuring the picoplankton concentration of the water to be treated, a second treatment tank 3 connected to the first treatment tank 1, a water to be treated introduction means 4 for introducing at least a part of the water to be treated in the first treatment tank 1 into the second treatment tank 3 when the picoplankton concentration of the water to be treated in the first treatment tank 1 is equal to or higher than a reference value based on the measurement result of the measuring means 2, a dilution water introduction means 5 for introducing dilution water into the second treatment tank 3, a chemical injection means 6 for adding a flocculant to reduce the picoplankton concentration of the water to be treated into the second treatment tank 3 to which the dilution water has been introduced, and a return means 7 for returning the water to be treated in the second treatment tank 3 to the first treatment tank 1.

[0047] The first treatment tank 1 is not particularly limited as long as it can store the water to be treated for a certain period of time. For example, in addition to raw water tanks, thickening tanks, and settling tanks, structures such as moats, reservoirs, and waterways, and puddles that can store the water to be treated with a high picoplankton concentration for a long period of time can also be included as the first treatment tank 1. As the measurement means 2, a fluorescent microscope, a picoplankton measuring device, etc. that can measure the number of picoplankton with a cell diameter of 0.2 μm to 2.0 μm can be used.

[0048] The second treatment tank 3 may be a coagulation tank for mixing the water to be treated introduced from the first treatment tank 1 with dilution water and adding a coagulant. The water to be treated introducing means 4 may include an introduction pipe 41 connecting the first treatment tank 1 and the second treatment tank 3, and an introduction pump 42. The introduction pump 42 is connected to a control means 8 for controlling the amount of water to be treated introduced. Based on a control signal from the control means 8, the start and stop of the introduction pump 42 and the flow rate of the water to be treated are controlled.

[0049] The dilution water introducing means 5 includes a dilution water tank 50 for storing dilution water, an introduction pipe 51 for introducing dilution water from the dilution water tank 50 to the second treatment tank 3, and an introduction pump 52 for draining dilution water from the dilution water tank 50 and introducing it into the second treatment tank 3. The introduction pump 52 is connected to a control means 8 for controlling the amount of dilution water introduced into the second treatment tank 3. The operation and stopping of the introduction pump 52 and the flow rate of the dilution water are controlled based on a control signal from the control means 8. The dilution water tank 50 contains water having a lower picoplankton concentration than the water to be treated introduced into the second treatment tank 3, typically a picoplankton concentration of 1×10 5 Water is retained at levels of less than 1 / mL.

[0050] The chemical injection means 6 includes a supply pipe 61 for supplying a flocculant and a flocculation aid. The return means 7 returns the water to be treated (or treated sludge) in the second treatment tank 3 from the second treatment tank 3 to the first treatment tank 1. The return means 7 may be connected to a measurement means 2 for measuring the picoplankton concentration in the returned water. The measurement means 2 measures the picoplankton concentration in the returned water returned to the first treatment tank 1, and can control the dilution ratio of the dilution water based on the measurement result of the picoplankton concentration in the returned water. This allows the water to be treated in the second treatment tank 3 to be adjusted to a picoplankton concentration suitable for the addition of the flocculant and the flocculation aid, thereby further enhancing the effect of adding the flocculant and the flocculation aid.

[0051] Based on the measurement results of the picoplankton concentration of the water to be treated by the measurement means 2, when the measurement results are equal to or above a standard value, the control means 8 outputs a control signal to control at least one of the amount of water to be treated introduced into the second treatment tank 3 by the water to be treated introduction means 4, the dilution ratio of the dilution water introduced from the dilution water tank 50 to the second treatment tank 3, and the amount of coagulant added.

[0052] It is preferable to use solid-liquid separation tanks as the first treatment tank 1 and the second treatment tank 3. The solid-liquid separation treatment in the first treatment tank 1 and the second treatment tank 3 may be either continuous or batchwise. For example, when the picoplankton concentration in the water to be treated in the first treatment tank 1 is very high and it is difficult to reduce the picoplankton concentration in the water to be treated below the reference value even if the dilution ratio is increased, batchwise treatment is performed in the second treatment tank 3. Then, the flocs (treated sludge) that have settled in the second treatment tank 3 are returned to the raw water tank, and the supernatant water is sent to the dilution water tank 50. By performing such an operation, it is possible to prevent the device from becoming large, and to perform a more efficient treatment to reduce the picoplankton concentration.

[0053] The picoplankton concentration of the water to be treated contained in the first treatment tank 1 is measured by the measuring means 2. When the measurement result of the picoplankton concentration of the water to be treated in the first treatment tank 1 is equal to or higher than a preset reference value, the water to be treated introducing means 4 separates at least a part of the water to be treated from the first treatment tank 1 and introduces it as separated water into the second treatment tank 3. In the second treatment tank 3, dilution treatment is performed by the dilution water introducing means 5 and addition of a flocculant is performed by the chemical injection means 6. Then, at least a part of the water to be treated in the second treatment tank 3 is returned to the first treatment tank 1 via the returning means 7 as return water, and the water to be treated including the return water is subjected to solid-liquid separation in the first treatment tank 1.

[0054] According to the treatment device for picoplankton-containing water to be treated according to the first embodiment of the present invention, the picoplankton concentration is reduced to a level at which the effect of adding a flocculant can be fully obtained by mixing the water to be treated, which has a high picoplankton concentration, with dilution water in the second treatment tank 3. This maximizes the effect of adding the flocculant, thereby enabling safe and efficient removal of picoplankton from the water to be treated at a high removal rate.

[0055] The water to be treated in the first treatment tank 1 is introduced into the second treatment tank 3 and diluted there, and the diluted water to be treated is returned as return water from the return means 7, gradually reducing the picoplankton concentration. Therefore, even if the clear water obtained by solid-liquid separation in the first treatment tank 1 is returned to a treatment upstream of the first treatment tank 1, the circulation of the return water can prevent picoplankton from gradually accumulating and becoming concentrated in the water purification system.

[0056] (Second embodiment) 2 shows an example in which the method for treating water containing picoplankton according to the embodiment of the present invention is applied to a typical water purification apparatus. The water purification apparatus can basically include a receiving well 101 for introducing raw water, a coagulation tank 102 for adding a coagulant and a coagulation aid to the raw water introduced from the receiving well 101, a sedimentation tank 103 for settling and separating the coagulated water in the coagulation tank 102, a filtration tank 104 for filtering the supernatant water of the sedimentation tank 103, and a primary thickening tank 1a for thickening the sludge generated in the sedimentation tank 103 and the filtration tank 104. In the second embodiment, the primary thickening tank 1a in FIG. 2 corresponds to the first treatment tank 1 in FIG. 1, and the second treatment tank 3a in FIG. 2 adjacent to the primary thickening tank 1a in FIG. 2 corresponds to the second treatment tank 3 in FIG. 1.

[0057] Raw water taken from a water source is introduced into the receiving well 101, and the amount of raw water is adjusted and the water quality is monitored. In the example of FIG. 2, a coagulation tank 102 and a sedimentation tank 103 are provided, but the present invention is not limited to this example. For example, the coagulation tank 102 may include a mixing tank for mixing the raw water with a coagulant and a coagulation aid, a flocculation tank for sufficiently forming flocs, and a sedimentation tank 103 for settling and removing the flocs. Alternatively, the coagulation tank 102 may include a coagulation settling device that performs coagulation and settling in a single tank. As the filtration tank 104, typically, a sand filtration device can be used, but other known filtration devices such as a membrane filtration device can also be used.

[0058] The primary thickening tank 1a is a treatment tank capable of performing solid-liquid separation of the water to be treated, and is connected to a measuring means 2a that measures the picoplankton concentration of the water to be treated in the primary thickening tank 1a. The primary thickening tank 1a is connected to a water to be treated introducing means 4a that draws out at least a portion of the water to be treated in the primary thickening tank 1a based on the measurement results of the measuring means 2a and introduces the water to be treated into a second treatment tank 3a connected to the primary thickening tank 1a.

[0059] The second treatment tank 3a is connected to a dilution water introduction means 5a for introducing dilution water into the second treatment tank 3a, and a chemical injection means 6a for adding a flocculant to reduce the picoplankton concentration in the water to be treated into the second treatment tank 3a to which the dilution water has been introduced. A return means 7a for returning the water to be treated in the second treatment tank 3a from the second treatment tank 3a to the primary thickening tank 1a is connected between the second treatment tank 3a and the primary thickening tank 1a.

[0060] The control means 8a is connected to the dilution water introduction means 5a, the chemical injection means 6a, and the measurement means 2a (not shown), and when the measurement results of the picoplankton concentration of the water to be treated by the measurement means 2a are equal to or higher than a reference value, the control means 8a can output a control signal to control at least one of the amount of water to be treated introduced by the water to be treated introduction means 4a, the dilution ratio of the dilution water introduced from the dilution water introduction means 5a to the second treatment tank 3a, and the amount of coagulant added supplied from the chemical injection means 6a.

[0061] FIG. 2 shows an example in which at least a portion of the water to be treated in the primary concentration tank 1a is removed and introduced into the second treatment tank 3a to perform a treatment to reduce the picoplankton concentration. However, the treatment tank from which the water to be treated is removed is not limited to the primary concentration tank 1a, and any treatment tank in the water purification system can be used as long as the picoplankton concentration is expected to increase. In this case, a small coagulation tank for dilution is newly installed near the treatment tank from which a portion of the water to be treated is removed, and dilution treatment and coagulant addition treatment are performed in the coagulation tank. By improving the existing equipment by installing a small coagulation tank, picoplankton concentration can be reduced more efficiently with simpler equipment.

[0062] By using water to be treated containing picoplankton generated at high concentrations as return water, the picoplankton concentration in the water purification system may increase, and the standard value of turbidity of the filtered water may not be achieved. According to the water treatment device and treatment method of the second embodiment of the present invention, the picoplankton concentration of the water to be treated in the primary concentration tank 1a in the water purification system can be reduced with a high removal rate. As a result, even if the water to be treated (sludge) in the primary concentration tank 1a is returned to a treatment tank in a stage preceding the primary concentration tank 1a, for example, the receiving well 101, the water purification treatment can be performed more efficiently while suppressing the inflow of a large amount of picoplankton into the receiving well 101.

[0063] (Modification) Fig. 3 shows an example of a treatment method and treatment device for reducing the picoplankton concentration in the water to be treated in the settling tank 103 in Fig. 2. As shown in Fig. 3, the treatment device for water to be treated containing picoplankton according to a modified example of the second embodiment of the present invention includes a concentration tank 1b for concentrating the treated water obtained in the settling tank 103, a coagulation tank 3b for mixing the concentrated treated water obtained in the concentration tank 1b with dilution water and adding a coagulant and a coagulation aid to the diluted concentrated treated water, and a settling tank 3c for performing solid-liquid separation of the coagulated treated water in the coagulation tank 3b.

[0064] Thickening tank 1b in Fig. 3 corresponds to the first treatment tank 1 in Fig. 1, and coagulation tank 3b in Fig. 3 corresponds to the second treatment tank 3 in Fig. 1. Coagulated sludge obtained in coagulation tank 3b is returned into thickening tank 1b via return means 7b. Treated sludge obtained in settling tank 3c is returned to thickening tank 1b via return means 7c. Supernatant water obtained in settling tank 3c can be reused as dilution water for coagulation tank 3b via return means 9.

[0065] Although the present invention has been described with reference to the above embodiment, the description and drawings forming a part of this disclosure should not be understood as limiting the present invention. In other words, the present disclosure is not limited to the above embodiment, and it is of course possible to combine and modify the components to embody the present disclosure without departing from the spirit of the present disclosure. EXAMPLES

[0066] Examples of the present invention will be described below together with comparative examples. These examples are provided for a better understanding of the present invention and its advantages, and are not intended to limit the invention.

[0067] We obtained water samples suspected to contain high concentrations of picoplankton and examined treatment methods. The following water samples 1 to 5 were prepared. Sample 1: Supernatant water from the primary thickener tank of a water purification plant Water sample 2: Raw water from water purification plant Test water 3: Test water 1 was prepared by injecting PAC as a coagulant at an injection rate of 200 mg / L without dilution and filtering through 5A filter paper. Test water 4: Water prepared by diluting test water 1 by 10 times with test water 2 Test water 5: Test water 1 was diluted 10 times with test water 2, PAC was added as a coagulant at an injection rate of 200 mg / L, and the water was filtered through 5A filter paper.

[0068] The change in picoplankton concentration before and after dilution treatment is shown in Table 1. The picoplankton concentration was measured using a picoplankton measuring device, and the number of particles with diameters of 0.5 to 2.0 μm contained in sample waters 1, 3, 4, and 5 was measured.

[0069] [Table 1]

[0070] As shown in Table 1, the picoplankton concentration in sample 1 was 4.2 × 10 7 When a flocculant was added to sample water 1 to perform flocculation treatment, the picoplankton concentration in sample water 3 was 1.2 × 10 7 The picoplankton removal rate was about 70%. On the other hand, sample 4, which was a 10-fold dilution of sample 1 with sample 2 (raw water from the water purification plant), had a picoplankton concentration of 1×10 7 The picoplankton concentration was reduced to less than 5 × 10 5The picoplankton removal rate was 92% when dilution was performed, and the picoplankton removal rate was 90% or more.

[0071] Figure 4 shows a graph of the relationship between the PAC injection rate and the picoplankton removal rate when sample water 1 was diluted and not diluted. As shown in Figure 4, by diluting the sample, a picoplankton removal rate of about 70% was achieved, even when the PAC injection rate was about 100 mg / L. By increasing the PAC injection rate to 200 mg / L, a picoplankton removal rate of about 90% was achieved. It can also be seen that diluting sample water 1 achieves a higher picoplankton removal rate than not diluting sample water 1.

[0072] Figure 5 shows the relationship between the increase in picoplankton when test water 1 (undiluted) and test water 5 (diluted) are returned to the receiving well of the water purification plant. "Raw water without return" in Figure 5 shows the picoplankton concentration in the raw water stored in the receiving well of the water purification plant before test water 1 or 5 was returned to the receiving well. When the supernatant water from the primary thickener tank was returned without dilution, the number of picoplankton increased by 1200% compared to the raw water. On the other hand, when the supernatant water from the primary thickener tank was diluted and test water 5, which had been subjected to coagulation treatment, was returned to the receiving well, the increase was limited to about 45%. [Explanation of symbols]

[0073] 1...First treatment tank 1a…Primary concentration tank 1b…Concentrator tank 2, 2a...Measurement means 3, 3a...Second treatment tank 3b…Flocculation tank 3c…Sedimentation pond 4, 4a…Means for introducing treated water 5, 5a…Dilution water introduction means 6, 6a...Medicine injection means 7, 7a, 7b, 7c, 9…Return method 8, 8a…Control means 41...Inlet pipe 42…Inlet pump 50…Dilution tank 51...Inlet piping 52…Inlet pump 61…Supply pipe 101…Waterfall well 102…Flocculation tank 103…Sedimentation tank 104…Filtration pond

Claims

1. Measure the picoplankton concentration in the treated water, Based on the measurement result of the picoplankton concentration, the treated water having a picoplankton concentration equal to or higher than a predetermined reference value is diluted with dilution water having a picoplankton concentration lower than that of the treated water, A flocculant for reducing a picoplankton concentration in the treated water is added to the treated water after the dilution treatment, The water to be treated containing the flocculant is subjected to solid-liquid separation. Including, Based on the measurement result of the picoplankton concentration, the water to be treated, in which the picoplankton concentration is equal to or greater than the reference value, is introduced from a first treatment tank that contains the water to be treated to a second treatment tank; The dilution treatment and the addition of the coagulant are carried out in the second treatment tank; Returning at least a portion of the water to be treated in the second treatment tank to the first treatment tank as return water; performing solid-liquid separation on the water to be treated including the return water in the first treatment tank; A method for treating water containing picoplankton, comprising:

2. The picoplankton concentration in the treated water after the dilution treatment is 1×10 7 The method for treating water containing picoplankton according to claim 1 , further comprising adding the dilution water so that the picoplankton concentration is less than or equal to 1 / mL.

3. Picoplankton concentration is 1 x 10 5 The method for treating water to be treated according to claim 1 or 2, further comprising using the dilution water having a concentration of less than 1 / mL.

4. Measure a picoplankton concentration in the return water returned to the first treatment tank; Controlling the dilution ratio of the dilution water based on the measurement result of the picoplankton concentration of the return water. The method for treating picoplankton-containing water to be treated according to claim 1 .

5. A first treatment tank capable of performing solid-liquid separation of the water to be treated; A measuring means for measuring the picoplankton concentration in the treated water; a second treatment tank connected to the first treatment tank; a treated water introduction means for introducing at least a portion of the treated water in the first treatment tank into the second treatment tank when the picoplankton concentration in the treated water in the first treatment tank is equal to or greater than a reference value based on the measurement result of the measurement means; A dilution water introduction means for introducing dilution water having a picoplankton concentration lower than that of the water to be treated into the second treatment tank; A chemical injection means for adding a flocculant to the second treatment tank into which the dilution water is introduced to reduce the picoplankton concentration in the water to be treated; a return means for returning the water to be treated in the second treatment tank to the first treatment tank; A treatment device for water to be treated that contains picoplankton.

6. A treatment device for water to be treated containing picoplankton as described in claim 5, further comprising a control means for controlling at least one of the amount of water to be treated introduced into the second treatment tank by the water to be treated introduction means, the dilution ratio of the dilution water, and the amount of coagulant added when the measurement result of the picoplankton concentration of the water to be treated is equal to or higher than the standard value.

Images