JP5925005B2 - Coagulation precipitation filtration system - Google Patents

Description

  The present invention is a method of injecting a flocculant into raw water such as river water and groundwater, and flocculating suspended solids contained in the raw water to perform precipitation separation, and then aggregating to obtain purified water by filtering the agglomerated sedimentation treated water with a filtration facility. It relates to a precipitation filtration system.

  Conventionally, as shown in FIG. 4, the chemical injection equipment 101 for injecting the flocculant into the raw water and the suspended substance contained in the raw water by mixing the flocculant injected into the raw water with a rapid rotating stirrer 106. The agitation equipment 102 that agglomerates and forms fine flocs and the slow flocter 107 that rotates slowly agitate the fine flocs contained in the raw water to promote the coupling of the fine flocs to form a floc. A coagulation sedimentation filtration system comprising a rapid stirring equipment 103, a precipitation equipment 104 for precipitating and separating flocs contained in raw water to obtain coagulated sedimentation treated water, and a filtration equipment 105 for filtering the coagulation sedimentation treated water to obtain purified water. In 100, the turbidity of the supernatant water obtained by injecting the coagulant into the test water collected directly from the coagulated sediment treated water and / or raw water obtained by the sedimentation facility 104 and carrying out the coagulation test is determined according to a predetermined target. It controlled the injection rate of the coagulant to be injected with a chemical injection facility 101 so as to approach.

  Furthermore, in the rapid agitation equipment 102 and the slow agitation equipment 103, the flocculant injected into the raw water is mixed and agitated to promote the suspension material to floc. In the rapid agitation equipment 102 and the slow agitation equipment 103 in which the fine flocs are combined to make the flocs, the rotational speeds of the rapid agitator 106 and the slow agitator 107 are related to the quality of raw water and the injection rate of the flocculant. It was always constant without doing. In particular, in the slow stirring facility 103, it is known that if the stirring is performed rapidly, the floc is destroyed. In order to prevent the rotational speed of the slow stirring device 107 from being increased, the rotational speed is kept constant. It was.

  However, the turbidity of the supernatant water obtained by injecting the flocculant into the test water collected directly from the coagulation-precipitation treated water and / or the raw water and carrying out the coagulation test with the injection rate of the flocculant injected by the chemical injection equipment 101. Is used as an index to agglomerate the suspended solids into fine flocs in the rapid agitation equipment 102 and promote the coupling of the fine flocs into flocs in the slow agitation equipment 103, and the combined flocs to the precipitation equipment In order to obtain the coagulation precipitation treated water after precipitating and separating as much as possible in 104, there was a problem that the injection rate of the coagulant tends to increase.

  In addition, the turbidity of the coagulated sediment treated water obtained by separating and precipitating flocs in the precipitation facility 104 and the turbidity of the purified water filtered by the filtration facility 105 are not necessarily correlated. As an index, the injection rate of the flocculant tends to increase, and the excessively injected flocculant component carries over from the precipitation facility 104 and flows into the filtration facility 105, causing the filter blockage in the filtration facility 105. Thus, there is a problem that the frequency of cleaning the filtration equipment 105 increases.

  Furthermore, since the rotation speeds of the rapid stirrer 106 and the slow stirrer 107 are constant, the unreacted state is obtained at low water temperature when the reaction between the suspended substance and the flocculant is slow, and when the injection rate of the flocculant is increased. The coagulant component carried over from the precipitation facility 104 flows into the filtration facility 105, which causes a filtration blockage in the filtration facility 105 and increases the frequency of cleaning of the filtration facility 105.

  In Patent Document 1 below, the suction filtration time ratio (hereinafter referred to as “STR”) in the water to be treated at the stage where the fine flocking step is completed is 4.0 or less, preferably 2.5 or less. It is disclosed to control the coagulant injection rate. However, in the water to be treated at the stage where the fine flocking process has been completed, there are a mixture of flocs that are separated by precipitation separation means in the subsequent process and fine flocs that carry over to the filtration equipment without being separated by precipitation. It is not appropriate to control the flocculant injection rate using the STR of the water to be treated at the inlet of the flocking means.

Japanese Patent No. 4316671

  The present invention has been made to solve the above-mentioned problems, and the object of the present invention is to optimize the injection rate of the flocculant and to control the rotation speed of the stirrer. It is an object of the present invention to provide a coagulation sedimentation filtration system capable of preventing chemicals from carrying over from a precipitation facility and flowing into the filtration facility.

In order to achieve the above object, a coagulation sedimentation filtration system according to claim 1 of the present invention mixes a chemical injection facility for injecting a coagulant into raw water and the coagulant injected into the raw water with a rapid rotating stirrer. And agitation of the fine flocs contained in the raw water with a rapid stirring facility for agglomerating suspended substances contained in the raw water to form fine flocs and a slow rotating slow agitator. A slow agitation facility that promotes the binding of the flocs to form flocs, a precipitation facility that precipitates and separates the flocs contained in the raw water to obtain agglomerated sedimentation treated water, In the coagulation sedimentation filtration system comprising the filtration equipment to obtain, the rotational speed of the slow-speed stirrer is variable, the injection rate of the flocculant injected in the chemical injection equipment and the rotational speed of the slow-speed stirrer, Coagulated sediment treated water and Or infusion speed and the aggregating agent in the STR (suction filtration time ratio) of the supernatant water obtained by carrying out agglutination tests by injecting coagulant into the test water taken directly from the raw water and the slow stirrer Based on the relationship with the rate, the STR (suction filtration time ratio) is controlled to be a predetermined target value .

  The coagulation sediment filtration system according to the present invention performs the coagulation test by injecting the coagulant into the coagulation sediment treatment water and / or test water directly collected from the raw water. Since it is controlled by the STR of the supernatant water obtained by carrying out, it is possible to prevent the injection amount of the flocculant from becoming excessive. Therefore, it prevents the excessively injected flocculant component from carrying over from the sedimentation facility and flowing into the filtration facility, causing a filter blockage in the filtration facility, and preventing the frequency of cleaning of the filtration facility from increasing. be able to.

  Furthermore, the rotation speed of the stirrer of the slow stirring equipment is controlled by the STR of the supernatant water in which the flocculant was injected by injecting the flocculant into the coagulated sediment treated water and / or the test water collected directly from the raw water. Therefore, unreacted flocculant components carry over from the precipitation facility and flow into the filtration facility, such as when the water temperature is low, where the reaction of the flocculant slows, or when the injection rate of the flocculant increases. It is possible to prevent the filter from becoming clogged and prevent the frequency of cleaning of the filtration equipment from increasing.

Schematic explanatory diagram of the coagulation sediment filtration system according to the present invention 1 A graph showing the relationship between the slow stirring speed, the flocculant injection rate, and the STR Graph showing the relationship between the coagulant injection rate and turbidity or STR Schematic illustration of a conventional coagulation sedimentation filtration system

  Hereinafter, with reference to the drawings, a water treatment system according to an embodiment of the present invention will be described by way of example.

  FIG. 1 is a schematic explanatory diagram of a coagulation sediment filtration system according to the first aspect of the present invention. The coagulation sedimentation filtration system 1 according to the present invention includes a chemical injection facility 10, a rapid stirring facility 20, a slow stirring facility 30, a precipitation facility 40, and a filtration facility 50.

  The chemical injection facility 10 stores chemicals such as a flocculant, a pH adjuster for an acid agent and an alkaline agent, and one or two of a flocculant, an acid agent and an alkaline agent that need to be injected into raw water. Or everything is injected into the rapid stirring equipment 20 described later. As for the flocculant, the flocculant is injected into test water collected directly from the coagulated sediment treated water and / or raw water and injected at an injection rate based on the STR of the supernatant water subjected to the flocculation test. Here, STR (Suction Filtration Time Ratio) is an abbreviation for Suction Time Ratio, agglomerated sediment treated water or supernatant water, and the same amount of distilled water at the same temperature, and the same filter paper is aspirated by the same degree of suction. In this case, the ratio expressed by Ta / Tb, where Ta is the suction time of the coagulated sediment treated water or supernatant water, and Tb is the suction time of distilled water.

  The rapid agitation equipment 20 agitate the flocculant, acid agent, and alkali agent injected from the chemical injection equipment 10 into raw water such as river water and groundwater that has flowed into the rapid agitation equipment 20 from a raw water tank (not shown) with the rapid agitator 21. The mixture is mixed with the raw water and the suspended substances contained in the raw water are agglomerated by the action of the flocculant to form fine flocs.

  The slow stirring facility 30 slowly stirs the raw water sent from the rapid stirring facility 20 with a slow rotating stirrer 31 that rotates slowly, and combines the fine flocks contained in the raw water to form a flock. The rotational speed of the slow agitator 31 is variable, and the rotational speed is controlled based on the STR of the coagulation sedimentation treated water and / or the coagulation test supernatant water.

  The sedimentation facility 40 precipitates and separates flocs contained in the raw water sent from the slow stirring facility 30 to obtain coagulated sedimentation treated water.

  The filtration facility 50 is a sand filtration facility, and filters the coagulated sediment treated water sent from the sedimentation facility 40 into purified water.

  Next, in the coagulation sedimentation filtration system 1 having the above-described configuration, the coagulant is injected into the raw water and mixed and stirred, and the suspended matter contained in the raw water is floculated by the action of the coagulant to precipitate and separate the coagulated sediment. A flow for obtaining water will be described.

  A flocculant, an acid agent, and an alkali agent are injected from the chemical injection facility 10 into raw water such as river water and groundwater from the raw water tank that has flowed into the rapid stirring facility 20. The injection rate of the flocculant is controlled by using the STR value of the supernatant water obtained by injecting the flocculant into the test water collected directly from the raw water and performing the flocculence test. For example, the current operating status is that the flocculant is injected from the chemical injection facility 10 to the rapid stirring facility 20 at a coagulant injection rate of 60 mg / L, and the rotation speed of the slow agitator 31 in the slow stirring facility 30 is 30 rpm. When the target value is set to STR3.0, the STR measurement result of the supernatant water obtained by injecting the flocculant into the test water collected directly from the raw water at a coagulant injection rate of 60 mg / L is 5.5. Then, changing the flocculant injection rate and / or the rotational speed of the slow agitator 31 to be injected into the rapid agitation equipment 20 is examined so that the STR becomes a predetermined target value. The graph of FIG. 2 which shows the relationship between slow stirring rotation speed, the coagulant injection rate, and STR is calculated | required by the coagulation test, and coagulant injection rate so that STR may be set to 3.0 which is target value from this graph FIG. Is changed to 50 mg / L, and the rotation speed of the slow agitator 31 is changed to 50 rpm.

  Next, after changing to the above-described conditions, after the passage of time when raw water is obtained as coagulation-precipitated treated water in the precipitation facility 40 via the rapid stirring facility 20 and the slow stirring facility 30, the coagulating sedimentation treatment is performed from the precipitation facility 40. Collect water and measure STR. As a result, when the STR has reached the target value, the injection rate of the flocculant injected into the rapid stirring equipment 20 and the rotation speed of the slow stirring machine 31 of the slow stirring equipment 30 are maintained as they are without adjustment. .

  However, when the STR value measured by collecting the above-described coagulation sedimentation treated water does not reach the target value, the coagulant injection rate is adjusted so that the STR becomes the target value of 3.0 by the same method as described above. And / or the rotation speed of the slow agitator 31 is changed. Thereafter, the same method is repeated until the STR reaches the target value. If the target value is reached once and the STR deviates from the target value due to fluctuations in the quality of the raw water after a certain period of time, the same method is repeated.

  In the above description, the STR measured with the supernatant of the coagulation test is used. However, the STR measured with the coagulated sediment treated water may be used. Whether to use coagulated sediment treated water or coagulation test supernatant water is determined in consideration of the environment, climate, etc. of the water treatment plant. In general, when STR is measured using supernatant water, it can be measured in a short time. Therefore, it is preferably used when the quality of raw water is suddenly changed.

  As described above, the coagulation sediment filtration system according to the present invention is a test in which the injection rate of the coagulant injected by the chemical injection facility 10 is directly collected from the coagulation sediment treated water obtained from the precipitation facility 40 and / or the raw water. Since the flocculant is injected at the current flocculant injection rate injected from the chemical injection equipment 10 into the rapid stirring equipment 20 into the water, it is controlled by the STR of the supernatant water that has been subjected to the flocculation test. As shown, when STR is used as an index, the amount of flocculant injected when STR, which is the minimum value of STR, is 2.5 is 50 mg / L, and turbidity, which is the minimum value of turbidity, is measured using turbidity as an index. Compared with the coagulant injection amount of 70 mg / L at 0.03 degrees, the coagulant injection amount can be reduced by 20 mg / L. Accordingly, it is possible to prevent the amount of the flocculant injected from becoming excessive, and it is possible to prevent the excessively injected flocculant component from carrying over from the precipitation facility 40 and flowing into the filtration facility 50. Become. Therefore, it becomes possible to prevent the cleaning frequency of the filtration equipment 50 from increasing.

DESCRIPTION OF SYMBOLS 1 Coagulation sedimentation filtration system 10 Chemical injection equipment 20 Rapid stirring equipment 21 Rapid stirring equipment 30 Slow stirring equipment 31 Slow stirring equipment 40 Precipitation equipment 50 Filtration equipment

Claims (1)

Chemical injection equipment for injecting flocculant into raw water,
A rapid stirring facility for mixing the flocculant injected into the raw water with a fast rotating rapid stirrer to agglomerate suspended substances contained in the raw water to form fine flocs;
Slow stirring equipment that stirs the fine flocs contained in the raw water with a slow rotating slow stirrer and promotes the coupling of the fine flocs to form flocs;
A precipitation facility for separating and separating the flocs contained in the raw water to obtain coagulated sediment treated water;
In a coagulation sedimentation filtration system comprising filtration equipment for filtering the coagulation sedimentation treated water to obtain purified water,
The rotational speed of the slow agitator is variable,
The injection rate of the flocculant injected by the chemical injection facility and the rotation speed of the slow agitator are determined by injecting the flocculant into the test water collected directly from the coagulation sedimentation treated water and / or the raw water. Based on the relationship between the suction filtration time ratio of the supernatant water obtained by performing the test, the rotational speed of the slow agitator and the injection rate of the flocculant, the suction filtration time ratio is set to a predetermined target value. And a coagulation sediment filtration system characterized by controlling.

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