Patent Application
20120305468
This invention relates to a water treatment apparatus which adds a flocculant to water to be treated, such as industrial water, city water, well water, river water, lake water or industrial waste water, for flocculation, and then performs solid-liquid separation such as filtration or membrane separation.
Methods for treating water to be treated, such as industrial water, city water, well water, river water, lake water or industrial waste water, include methods which comprise, for example, adding an inorganic flocculant and a polymer flocculant of anionic nature or the like to the water to be treated, thereby performing flocculation to adsorb or coagulate suspended matter or the like contained in the water to be treated, followed by carrying out solid-liquid separation, such as sand filtration, dissolved air floatation, filtration using a fibrous filter (filter medium), or membrane separation, to remove the suspended matter (see Patent Documents 1 to 3).
With flocculation, however, a flocculation tank of an open type, namely, one in which the water to be treated is exposed to the atmosphere, is generally used for coarsening flocculated matter (flocs). A liquid feeding means, such as a pump, is necessary when feeding the water to be treated to an apparatus in a subsequent stage which performs solid-liquid separation. The flocs are destroyed by the pump or the like, posing the problem that clear treated water is difficult to obtain.
Patent Document 4 describes closed type flocculation in which water to be treated is held without being exposed to the atmosphere. With this Patent Document 4, however, an apparatus for stirring in an open type flocculation tank basically having a stirrer is provided in a stage succeeding a flocculation means, so that the destruction of flocs by a pump or the like may occur.
The present invention has been accomplished in the light of the above-mentioned circumstances. It is an object of the invention to provide a water treatment apparatus which performs solid-liquid separation after flocculation, and which can reliably obtain clear treated water.
An aspect of the present invention, designed to solve the above-mentioned problems, lies in a water treatment apparatus comprising: mixing means having a mixing tank in which water to be treated is mixed with a flocculant added thereto to form flocs; flocculation means having a cylindrical flocculation tank into which the water to be treated after discharge from the mixing means is introduced, and in which the water to be treated is kept unexposed to the atmosphere, a for-treatment water inlet which introduces the water to be treated into the flocculation tank from a lower part of the flocculation tank in a tangential direction so as to produce a swirl flow, and a for-treatment water outlet, provided in an upper part of the flocculation tank, for discharging the water to be treated from the upper part of the flocculation tank; and solid-liquid separation means into which the water to be treated after discharge from the flocculation means is introduced from the flocculation means without being exposed to the atmosphere, and in which the water to be treated is subjected to solid-liquid separation.
The for-treatment water outlet may be provided so as to discharge the water to be treated from the upper part of the flocculation tank in a tangential direction.
The solid-liquid separation means is preferably filtration means comprising a filter charged into a filtration tank such that the void content of a filtration portion during water passage becomes 50 to 95%, the filter having string-shaped suspended matter trapping portions.
Preferably, the mixing means keeps the water to be treated in such a state as not to be exposed to the atmosphere, the water to be treated is introduced from the mixing means into the flocculation means without being exposed to the atmosphere, and liquid feeding means for feeding the water to be treated is provided in a stage preceding the mixing means.
The water treatment apparatus is configured to have the mixing means for mixing the flocculant and the water to be treated to form flocs such as suspended matter; the flocculation means for introducing the mixed water to be treated into the cylindrical flocculation tank, where the water to be treated is kept unexposed to the atmosphere, so as to produce a swirl flow, thereby coarsening the flocs; and the solid-liquid separation means into which the flocculated water to be treated is introduced, without being exposed to the atmosphere, whereby it is subjected to solid-liquid separation. Because of this configuration, coarse flocs formed by the flocculation means can be conveyed to the solid-liquid separation means in the subsequent stage without the use of a liquid feeding means such as a pump. As a result, the destruction of the coarse flocs can be suppressed. Thus, the water treatment apparatus enables clear treated water to be obtained.
a) and 2(b) are a top view and a side view, respectively, showing the configuration of a flocculation means.
a) to 4(f) are top views, side views and schematic views showing other configuration examples of the flocculation means.
The water treatment apparatus of the present invention is a water treatment apparatus in which a flocculant is added to water to be treated, thereby flocculating the water, and then solid-liquid separation, such as sedimentation, dissolved air floatation, filtration or membrane separation, is carried out.
Examples of the water to be treated are water containing humic acid-based or fulvic acid-based organic substances, water containing biological metabolites such as sugars produced by algae, etc., and water containing synthetic chemical substances such as surface active agents. Concrete examples are industrial water, city water, well water, river water, lake water, and industrial waste water (particularly, bioremediation water resulting after bioremediation of waste water from factories). However, they are not limitative. Humus refers to humic substances occurring upon degradation of plants, etc. by microorganisms, and includes humic acid and so on. Water containing humus has humus and/or humus-derived soluble COD components, suspended matter, or chromatic components.
Using
As shown in
As shown in
The flocculation means 4, as shown in
The size of the flocculation tank 11 is not limited, but its inner diameter may be of the order of 2 m as the upper limit, and inner diameter:height may be of the order of 1 to 5:3 to 10. Nor is any limitation imposed on the position where the for-treatment water inlet 12 or the for-treatment water outlet 13 is provided. However, the central position of a cross section in the water passage direction of the for-treatment water inlet 12 may, for example, be within the radius of the for-treatment water inlet 12 plus 2 m upwardly from the bottom of the flocculation tank 11, while the central position of a cross section in the water passage direction of the for-treatment water outlet 13 may, for example, be within the radius of the for-treatment water outlet 13 plus 2 m downwardly from the ceiling of the flocculation tank 11. Nor are there any limitations on the amount of water passage, the dwell time, or the G-value, of the water to be treated. However, the amount of water passage of the water to be treated may, for example, be such that the initial flow velocity (flow velocity at the for-treatment water inlet) is 0.5 to 2.0 [m/s]. The dwell time may, for example, be 0.1 to 10 minutes, preferably 2 to 5 minutes, and the average G-value of the flocculation tank may, for example, be 20 to 200 [m/s].
The mixing means 3, for example, has a mixing tank 16 introducing the water to be treated and having an open top, a rapid stirrer 17 for stirring the water to be treated to mix the flocculant and the water to be treated, and a temporary storage tank 18 for temporarily storing the mixed water to be treated, as shown in
The solid-liquid separation means 5 is not limited, as long as it can carry out solid-liquid separation for removing flocs including suspended matter, such as sedimentation, dissolved air floatation, filtration or membrane separation. In the present embodiment, however, the solid-liquid separation means 5 is a filtration apparatus 20 having string-shaped (fibrous) filter elements for trapping flocs formed from the flocculant and the suspended matter or the like contained in the water to be treated (details of the filtration apparatus will be described later). The sedimentation or dissolved air floatation can be performed, because pH adjustment using caustic soda, slaked lime or sulfuric acid is made in adding the flocculant to the water to be treated, and the suspended materials are finally converted into flocs with the use of an organic polymer flocculant. If desired, an organic coagulant may be used concurrently. Examples of the membrane for membrane separation are a microfiltration membrane (MF membrane), an ultrafiltration membrane (UF membrane), a nano-filtration membrane (NF membrane), and a reverse osmosis membrane (RO membrane).
With the water treatment apparatus 1 configured as above, the flocculant is introduced by the flocculant introduction means 6 into piping, through which the water to be treated (raw water) that has been stored in a raw water tank 2 is passed, to add the flocculant to the water to be treated. The water to be treated which has the flocculant added thereto is introduced into the mixing tank 16 of the mixing means 3, and is stirred by the stirrer 17 relatively rapidly to mix the water to be treated and the flocculant. By this treatment, suspended matter or the like contained in the water to be treated and the flocculant form flocs. Then, the water to be treated which has flocks formed therein is stored in the temporary storage tank 18. The water to be treated which has been stored in the temporary storage tank 18 is fed by the pump P2, and is introduced into the lower part of the flocculation tank 11 through the for-treatment water inlet 12 provided in the lower part of the flocculation tank 11 of the flocculation means 4 in the tangential direction. When the water to be treated is so introduced into the for-treatment water inlet 12 provided in the tangential direction in the lower part of the flocculation tank 11, a swirl flow as indicated by an arrow in
The water to be treated which has been discharged from the for-treatment water outlet 13 after flocculation is passed through piping connecting the for-treatment water outlet 13 and the solid-liquid separation means 5. As described above, the feeding pressure of the pump P2 is maintained even in the water to be treated which is discharged from the for-treatment water outlet 13. Furthermore, the piping is provided from the flocculation means 4 up to the solid-liquid separation means 5 such that the water to be treated is passed without being exposed to the atmosphere. That is, the for-treatment water outlet 13 of the flocculation means 4 and the inlet for introducing the water to be treated into the solid-liquid separation means 5 are connected by the piping. Even if a liquid feeding means, such as a pump, for passing the water to be treated to the solid-liquid separation means 5 is not provided between the flocculation means 4 and the solid-liquid separation means 5, therefore, the water to be treated is fed to the solid-liquid separation means 5. In this manner, the destruction of the coarsened flocs by a liquid feeding means such as a pump can be prevented. Hence, the flocs can be removed satisfactorily by the solid-liquid separation means 5, and clear treated water can be obtained reliably.
There may be a case in which a liquid feeding means, such as a pump, for passing the water to be treated to the solid-liquid separation means 5 needs to be provided between the flocculation means 4 and the solid-liquid separation means 5. With a water treatment apparatus in which the top of the flocculation tank of the flocculation means is open and the water to be treated is exposed to the atmosphere, or with a water treatment apparatus in which the water to be treated becomes exposed to the atmosphere in a region from the flocculation means to the solid-liquid separation means, for example, the use of the liquid feeding means such as a pump results in the destruction of the flocks, which have been coarsened by flocculation, to very small sizes. The flocs so destroyed cannot be removed satisfactorily by the solid-liquid separation means in the subsequent stage, and clear treated water is difficult to obtain. If an apparatus for relatively rapid stirring by a stirrer or the like after flocculation is provided, the flocks are destroyed, making it similarly difficult to obtain clear treated water.
The example shown in
Concretely, as shown in
In the water treatment apparatus shown in
In the above-mentioned example, the flocculant is added to the water to be treated before being introduced into the mixing means 3. However, the flocculant may be added to the mixing means 3 into which the water to be treated has been introduced, namely, the mixing tank 16. Moreover, a plurality of mixing tanks or line mixers may be provided, and different types of flocculants may be added for the respective mixing tanks or line mixers. A water treatment apparatus configured to add different types of flocculants for different line mixers, that is, to pass water through a line mixer each time a different type of flocculant is added, will be described using
As shown in
In the water treatment apparatus shown in
There may be constructed a water treatment apparatus in which each time a flocculant of a different type is added, water is passed through a line mixer and flocculation means 4 in this order. Such a water treatment apparatus, as shown in
In the water treatment apparatus shown in
In the present embodiment, the solid-liquid separation means 5 is a filtration means, and has a fibrous filter. For example, it is preferred that a filter having string-shaped (fibrous) suspended matter trapping portions be charged into a filtration tank such that the void content of a filtration portion during water passage is 50 to 95%. A concrete example of such a filtration means is a filtration apparatus shown in
As shown in
The filter 22 is charged into the filtration tank 21 such that the void content of a filtration portion when passed through by the water to be treated is 50 to 95%, preferably 60 to 90%, more preferably 50 to 80%. The void content is a value obtained from the equation indicated below. The filtration portion refers to a region where the suspended matter, etc. in the water to be treated are trapped by the filter 22, namely, a region remaining after excluding a part, which does not contribute to filtration (the part corresponding to the core material 23 in
Void content (%)=[(volume of filtration portion−volume of suspended matter trapping portions)/volume of filtration portion]×100 [Equation 1]
When the water to be treated is passed through the filtration apparatus 20 of the above-described configuration, the water to be treated passes through the respective string-shaped suspended matter trapping portions 24 and the slits 25 provided in the suspended matter trapping portions 24. During this course, the suspended matter, etc. contained in the water to be treated are trapped by the string-shaped suspended matter trapping portions 24 and the slits 25, and the water to be treated which has been deprived of the suspended matter is discharged from the filtration tank 21. Since the filter 22 is charged such that the void content of the filtration portion during water passage is 50 to 93%, water passage is not impeded, and the trapping of the suspended matter, etc. is satisfactory. In the present invention, in particular, the water to be treated which is introduced into the filtration apparatus 20 is prevented from involving the destruction of flocs formed from the suspended matter, etc. and the flocculant and coarsened. Thus, the suspended matter, etc. can be trapped satisfactorily by the filtration apparatus 20.
As described above, water passage is not impeded, and the trapping of the suspended matter, etc. is rendered satisfactory, by charging the filter 22 such that the void content of the filtration portion during water passage is 50 to 95%. Thus, the effects are exhibited that clogging of the filtration apparatus 20 can be suppressed, and clear treated water is obtained. If the void content is higher than 95%, water passage becomes satisfactory and fast filtration is easily achieved, but the turbidity of treated water is markedly high. If the void content is lower than 50%, the trapping of the suspended matter is satisfactory, but water passage is so insufficient that clogging occurs in the filtration apparatus or a membrane separation means provided optionally in a subsequent stage, whereupon the rate of increase in the differential pressure becomes markedly high. Particularly when the filtration operation is performed at a high speed of, say, 100 m/h or above, or when the water to be treated which has a high turbidity (e.g., 20 degrees or higher) is treated, the problem tends to occur that the turbidity of resulting treated water rises, or that the apparatus clogs. By using the filtration apparatus 20 charged with the filter 22 such that the void content is 50 to 95%, on the other hand, clogging can be suppressed, and clear treated water is obtained, even in the case of the high speed operation or the highly turbid water to be treated. Even when low speed treatment is carried out or the low turbidity water to be treated is treated, it goes without saying that clogging can be suppressed, and clear treated water is obtained. Since the void content is preferably uniform, it is preferred that the suspended matter trapping portions 24 be charged up to sites near both ends in the water passage direction of the filtration tank 21. It is also preferred that the suspended matter trapping portions 24 be charged up to sites near the inner wall surface of the filtration tank 21. Furthermore, the volume of the filtration portion preferably does not change between states, namely, between the time of water passage of the water to be treated and other state such as the time of backwash to be described later or the time of stoppage of filtration. The change rate of the volume of the filtration portion is preferably 30% or less, more preferably 10% or less. By setting such a range, the filtration apparatus can be rendered compact.
In the filtration apparatus of
Examples of the material for the core material 23 or the suspended matter trapping portion 24 are synthetic resins such as polypropylene, polyester and nylon. The core material 23 may be given strength by knitting up synthetic fibers, such as polypropylene, polyester or nylon, during the manufacturing process. Alternatively, like a twisted brush, an example may be adopted in which a wire formed from SUS or a resin-coated metal free from corrosion is used as the core material 23, the suspended matter trapping portions 24 are arranged uniformly, and then the metal is twisted to construct the filter 22 having the suspended matter trapping portions 24 spread radially. By so enhancing the strength of the core material 23, the core material 23 does not bend any more, and the ends of the filter 22 are easily fixed thereto. Thus, replacement work for the filter 22 is facilitated.
The sizes of the core material 23 and the suspended matter trapping portion 24 are not restricted. For example, the size can be such that the thickness is 0.05 to 2 mm, the width is 1 to 50 mm, and the length (the distance from the core material when the water to be treated is passed) is of the order of 10 to 500 mm, preferably, the thickness is 0.3 to 2 mm, the width is 1 to 20 mm, and the length is of the order of 50 to 200 mm.
In
In
By performing such mixing, flocculation and solid-liquid separation, clear treated water is obtained, but there may further be deionization such as ion exchange treatment. By such treatment, pure water or ultrapure water can be obtained. Treatment for purification of the water to be treated, such as decarboxylation or activated carbon treatment, may be further carried out.
If desired, a pH adjustor, a coagulant, a microbicide, a deodorizer, an anti-foaming agent, an anti-corrosive, etc. may be added. Furthermore, ultraviolet irradiation, ozone treatment, or bioremediation may be concurrently used, if desired.
The present invention will now be described in further detail based on Example and Comparative Example, but is in no way limited by these examples.
As water to be treated (raw water), industrial water (turbidity 5 to 7 degrees) was treated by the water treatment apparatus shown in
<Mixing Means>
Two line mixers (model 1/2-N50-171-1, produced by NORITAKE CO., LTD.) were connected in series for use as a mixing means. Ahead of the first line mixer in the water passage direction of the water to be treated, polyaluminum chloride (PAC: 10% by weight as Al2O) was added in an amount of 60 mg/L with respect to the water to be treated. The dwell time in the zone from the outlet of the first line mixer until the inlet of the second line mixer was of the order of 10 seconds. Directly before the second line mixer, an amphoteric polymer flocculant (Kuribest E851, produced by Kurita Water Industries Ltd.) was added in an amount of 4 mg/L with respect to the water to be treated.
<Flocculation Means>
Size of the flocculation tank: Inner diameter 100 mm×height 510 mm
Position of the for-treatment water inlet: The central position of a cross section in the water passage direction thereof was the radius thereof +20 mm upwardly from the bottom of the flocculation tank.
Position of the for-treatment water outlet: The central position of a cross section in the water passage direction thereof was the radius thereof +20 mm downwardly from the ceiling (top surface) of the flocculation tank.
Amount of water passage of the water to be treated: Initial flow velocity (flow velocity at the for-treatment water inlet): 1.33 [m/s]
Dwell time of the water to be treated: 1 minute
Stirring speed (rotational speed of the swirl flow): 20 to 30 rpm
Average G-value of the flocculation tank: 121.07 [l/s]
<Filtration Apparatus>
Size of the filtration tank: Tubular column of acrylic resin with a diameter of 200 mm and a height of 500 mm
Filter: The filter 22 comprising the core material 23 and the string-shaped suspended matter trapping portions 24. The core material had a volume of 250 mL, and each suspended matter trapping portion 24 was woven in a loop form into the core material such that its thickness was 0.5 mm, its width was 2 mm, and its length (distance of its loop end from the core material when the water to be treated was passed) was 100 mm. The void content of the filtration portion (the remainder after subtracting the volume of the core material 23 from the volume of the interior of the filtration tank 21) during water passage was 60%. Both ends of the core material 23 of the filter 22 were fixed to the plates placed above and below.
LV=250 m/h
The diameter of flocs in the flocculation tank, and the turbidities at the inlet and outlet of the filtration apparatus were measured. The results are shown in Table 1. The turbidity decrease rate obtained as (turbidity at inlet of filtration apparatus−turbidity at outlet of filtration apparatus)/turbidity at inlet of filtration apparatus×100, and the time after start of water passage (described as “elapsed time after water passage”) through the filtration apparatus are also shown in Table 1. The turbidity was determined by the transmission/scattering measurement method using a formazin standard solution.
The same procedure as in Example 1 was performed, except that the flocculation means had a flocculation tank and a stirrer and was configured such that the water to be treated was held exposed to the atmosphere, and that a pump for feeding the water to be treated was provided between the flocculation means and the filtration apparatus. In Comparative Example 1, the dwell time of the flocculation means was 10 minutes, and the stirring speed was 30 rpm.
As shown in Table 1, the floc diameter in the flocculation tank was nearly comparable in Example 1 and Comparative Example 1, but treated water discharged from the filtration apparatus was much clearer in Example 1 than in Comparative Example 1. In Example 1, it is presumed that flocs were coarsened in the flocculation tank, and these coarse flocks were introduced into the filtration apparatus without being destroyed by the pump or the like, with the result that very clear water as compared with Comparative Example 1 was obtained. In Comparative Example 1 in which the pump for liquid feeding needed to be provided between the flocculation tank and the filtration apparatus, on the other hand, it is presumed that water to be treated which was introduced into the filtration apparatus underwent destruction of flocs, thereby forming fine flocs, which could not be trapped by the filtration apparatus.
Reference example showing the effects of the filtration apparatus 20 will be indicated below.
(Relation between the void content and the increase in the differential pressure as well as the turbidity of treated water in the filtration apparatus)
As water to be treated (raw water), industrial water having turbidity of 20 degrees was treated for a week at LV 200 m/h by use of the water treatment apparatus 30 shown in
It was found that with the filtration apparatus having the filter charged such that the void content of the filtration portion during water passage would become 50 to 95%, the differential pressure increase rate and the treated water turbidity were markedly low as compared with that having avoid content outside the range of 50 to 95%, clear treated water was obtained, and clogging could be suppressed.
1 Water treatment apparatus, 2 Raw water tank, 3 Mixing means, 4 Flocculation means, 5 Solid-liquid separation means, Flocculant introduction means, 7 PH adjustor introduction means, 11 Flocculation tank, 12 For-treatment water inlet, 13 For-treatment water outlet, 16 Mixing tank, 17 Stirrer, 20 Filtration apparatus, 21 Filtration tank, 22 Filter, 23 Core material, 24 Suspended matter trapping portion, 26 Plate
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-079591 | Mar 2010 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2011/058003 | 3/30/2011 | WO | 00 | 8/9/2012 |
