CA2825752C

CA2825752C - Flocculation magnetic separator

Info

Publication number: CA2825752C
Application number: CA2825752A
Authority: CA
Inventors: Shigeki Terui; Manabu Yamada
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 2011-01-27
Filing date: 2012-01-26
Publication date: 2016-01-12
Anticipated expiration: 2032-01-26
Also published as: RU2553100C2; WO2012102324A1; MX2013008646A; CA2825752A1; JP2012152708A; RU2013135306A

Abstract

Provided is a flocculation magnetic separator which reduces the used amounts of magnetic powder as well as the collected flocs thus recovered, without using a chemical such as hydrochloric acid.
The flocculation magnetic separator comprises a return and addition unit (18) which returns the collected flocs discharged from a magnetic separation unit (16) to a raw water supply pipe (12) at an upstream position of a rapid stirring tank (26) and at an upstream position where a flocculant is added. This process for returning the collected flocs to the raw water supply pipe (12) enables the collected flocs to be recycled without using a chemical such as hydrochloric acid. Further, this process also enables the magnetic powder contained in the collected flocs to be recycled, resulting in the reduction of the used amounts of brand-new magnetic powder.

Description

FLOCCULATION MAGNETIC SEPARATOR
BACKGROUND OF THE INVENTIION
FIELD OF THE INVENTION
[0001]
The present invention relates to a flocculation magnetic separator of flocculating plankton and bacteria contained in ballast water and separating the flocs thus collected by magnetic force.
DESCRIPTION OF THE RELATED ART

[0002]
According to the International Convention for the Control and Management of Ship's Ballast Water adopted by the International Maritime Organization (IMO) in 2004, the ships are demanded to be equipped with a system of removing or sterilizing plankton and bacteria contained in ballast water. This convention was adopted aiming to prevent microorganisms from moving through ballast water (or sea water), the ecosystem from being destructed via the diffusion of the microorganisms, and a health hazard from being caused by the microorganisms.
At present, technologies for treating ballast water are actively developed by combining a variety of water treatment technologies, including a chemical treatment using sodium hypochlorite or the like, an ozonation, ultra-violet irradiation, heat treatment, and magnetic separation or the like.

[0003]
Here, a flocculation magnetic separator disclosed in Patent Document 1 is operated by the steps of: adding magnetic powder and a flocculant to ballast water (or raw water); stirring the resulting mixture to form magnetic flocs containing microorganisms and bacteria mixed in the ballast water;
separating the magnetic flocs from the ballast water by a magnetic separation device; and collecting relatively large solid materials unable to be flocculated by themselves (for example, small fishes each with a several millimeters size, and seaweeds) by a dram type filter.
When the flocculation magnetic separator is operated, the used flocculant is highly safety agent that is also used for the treatment of tap water. Further, such a water treatment using a flocculant is less risky than a treatment using chemicals such as chlorine. In other words, the flocculation treatment has less liability to secondarily contaminate the environment by the chemicals remained in the ballast water at the discharging time and related by-products.
Moreover, the flocculation magnetic separator flocculates not only microorganisms and bacteria but also sand and sludge included in the ballast water, thereby to simultaneously separate and remove all the materials. This allows the flocculation magnetic separator to have a secondary effect of preventing the sand and sludge from being accumulated on a bottom of a ballast tank.

[0004]
However, there are the following issues arising in the flocculation magnetic separator disclosed in Patent Document 1.
One issue is that the used amounts of the expensive magnetic powder should be reduced, with keeping the cleaning performance of ballast water. The other issue is that the total amounts of the collected flocs should be reduced.

[0005]
Namely, with respect to a flocculation magnetic separator, magnetic powder thus added should become uniformly contained in all the flocs as much as possible, when the magnetic flocs are formed. Hereby, should be used the magnetic powder composed of the particles each having an extremely small particle size in several microns as well as an equal particle size.

[0006]
However, it should be noted that such magnetic powder is very expensive, resulting in the increase in the running costs of a flocculation magnetic separator. Therefore, it is demanded to reduce the used amounts of magnetic powder as much as possible.
Further, assuming a flocculation magnetic separator is installed in a ship, reduced amounts of the magnetic powder allows a storage tank of the magnetic powder to be downsized.

4)45 This advantage provides a great merit with the installation of the flocculation magnetic separator into the inside of the ship having a limited space for arranging various devices.
Simultaneously, this advantage allows a frequency of the operations for supplying the magnetic powder into the inside of the ship to be reduced, resulting in the reduction of the burden of sailors.

[0007]
In the meantime, the collected flocs discharged from the magnetic separator have to be stored in a tank and treated as an industrial waste. Thus, it is strongly demanded that the collected flocs should be recycled as much as possible to reduce the total amounts thereof, thereby to downsize a storage tank thereof, achieve space saving, and reduce the costs of treating industrial wastes.

[0008]
From the viewpoints as mentioned above, it is noted that Patent Document 2 discloses a magnetic separation cleaner having the following feature. That is, the magnetic separation cleaner is operated in the steps of: adding hydrochloric acid to collected flocs with stirring the mixture; decomposing a polymer flocculant thereby to be separated into a decomposed flocculant which contains an oil and treated water, and a magnetic powder component; and returning the decomposed flocculant and magnetic powder into raw water so as to recycle those materials.

PRIOR ART DOCUMENTS
PATENT DOCUMENTS

[0009]
Patent Document 1: JP H09-117618 Patent Document 2: JP 2006-718 DISCLOSURE OF INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION

[0010]
In Patent Document 2, hydrochloric acid is used for recycling magnetic powder. Herein, it should be noted that the use of hydrochloric acid in a ship needs to file proof documents with the IMO; the documents demonstrating the safety of installing a treatment system using hydrochloric acid, that is, a strong acid.
Further, needed are additional proof documents to be filed with the IMO; the documents demonstrating the reliability in the process of neutralizing treated materials.
Accordingly, such extremely complicated procedures are required to use such a treatment system in which hydrochloric acid is used.

[0011]
From the circumstance as described hereinbefore, it has been demanded to develop a flocculation magnetic separator which is capable of reducing the amounts of the collected flocs as well as the used amounts of the magnetic powder; the flocculation magnetic separator being capable of physically removing microorganisms and bacteria included in ballast water as described in Patent Document 1.

[0012]
Here, a problem caused by a process of reducing the used amounts of the magnetic powder and the amounts of the collected flocs without using a chemical such as hydrochloric acid for treating raw water, is not limited to only the treatment case of ballast water. The same problem is raised in the case of raw water which is treated onshore.

[0013]
The present invention has been developed in the light of the problems as described above. Therefore, an object of the present invention is to provide a flocculation magnetic separator capable of reducing the used amounts of magnetic powder without using a chemical such as hydrochloric acid, as well as the amounts of the collected flocs, so as to treat raw water.
MEANS FOR SOLVING THE PROBLEMS

[0014]
Accordingly, the present invention has been made in order to achieve the above mentioned object. In accordance with an aspect there is provided a flocculation magnetic separator comprising:
a first stirring tank connected with a raw water supply pipe which supplies raw water, for stirring at a first stirring rate the raw water added with a flocculant and magnetic powder which , 6a/45 is supplied from a magnetic powder supply device, thereby to form magnetic microflocs containing the magnetic powder;
a second stirring tank for stirring, at a second stirring rate slower than the first stirring rate, treated water to which a polymer flocculant is added, thereby flocculating the magnetic microflocs, the treated water containing the magnetic microflocs and being discharged from the first stirring tank;
a magnetic separation device for separating the flocculated magnetic microflocs by a magnetic filter from the treated water discharged from the second stirring tank to collect the flocculated magnetic microflocs on the magnetic filter, and scraping the collected flocculated magnetic microflocs off the magnetic filter by a scraper;
a collected floc receiver tank storing the flocculated magnetic microflocs scraped by the scraper; and a return and addition device for recycling magnetic powder contained in the flocculated magnetic microflocs by returning by a pump the flocculated magnetic microflocs stored in the collected floc receiver tank to the raw water supply pipe upstream of the first stirring tank and at a first position upstream of where the flocculant is added, thereby to add the collected microflocs to the raw water.
That is, provided is a flocculation magnetic separator including: a first stirring tank _________________________________ of forming magnetic microflocs containing magnetic powder; and a second stirring tank of enlarging the magnetic microflocs via stirring the water to be treated to which a polymer flocculant has been added.
Herein, the first stirring tank is connected with a raw water supply pipe of supplying raw water, and the magnetic microflocs are formed by rapidly stirring the raw water to which magnetic powder and a flocculant have been added. Such magnetic powder is supplied from a magnetic powder supply device. Further, the raw water to be treated in the second stirring tank contains the magnetic microflocs discharged from the first stirring tank. The second tank is stirred at a lower rotational rate than the first tank.
Further, the flocculation magnetic separator including: a magnetic separation device of collecting the enlarged flocks by magnetic force; and a return and addition device of returning the flocs thus collected by the magnetic separation device to the raw water supply pipe located at an upstream position of the first stirring tank and at an upstream position where the flocculant is added to the raw water. Then, the return and addition device adds the collected flocs to the raw water.

[0015]
Here, the flocculation magnetic separator of the present invention includes the return and addition device of returning the flocs discharged from the magnetic separation device to the raw water supply pipe at the upstream position of the first stirring tank and at the upstream position where the flocculant is added. The collected flocs discharged from the magnetic separation device are once stored in a collected floc receiver tank. Then, the collected flocs are returned to the raw water supply pipe by the return and addition device.
Accordingly, the magnetic powder contained in the collected flocs is recycled in the present invention. This recycling process allows the used amounts of the magnetic powder to be reduced without using a chemical such as hydrochloric acid or the like, and further the amounts of the collected flocs to be reduced.
Moreover, this recycling process allows a complicated separation and extraction treatment of the magnetic powder to be unnecessary.
Note the collected flocs which are not returned are allowed to overflow from the collected floc receiver tank as excess of the collected flocs, thereby to be separately stored in a collected floc storage tank.

[0016]
The flocculation magnetic separator of the present invention preferably includes a concentration detection device of detecting concentration of suspended solids in the raw water at the upstream position where the magnetic powder, the flocculant and the collected flocs are added.
Further, the flocculation magnetic separator preferably includes a control device of controlling the return amounts of the collected flocs conducted by the return and addition device together with the addition amounts of the magnetic powder conducted by the magnetic powder supply device.
Herein, the control device performs the above described operation based on both the concentration of suspended solids detected by the concentration detection device and the maximum suspended solids concentration in raw water set in advance.

[0017]
The control device of the present invention controls the return amounts of the collected flocs conducted by the return and addition device and the addition amounts of the magnetic powder conducted by the magnetic supply device.
Herein, the control unit performs the operation based on both the concentration of suspended solids detected by the concentration detection device and the maximum suspended solids concentration in raw water set in advance (or designed value of the flocculation magnetic separator).
According to the present invention, the concentration of suspended solids in raw water is detected, and subsequently it is confirmed that the detected concentration is lower than the maximum suspended solids concentration in raw water. This procedure allows a complicated separation and extraction treatment to be unnecessary, and therefore the collected flocs to be recycled by a simple and low cost system structure.
Moreover, the recycling process of the magnetic powder contained 10)45 in the collected flocs enables the used amounts of brand-new magnetic powder to be reduced. Hereby, this also allows the generated amounts of the collected flocs derived from the brand-new magnetic powder to be further reduced.

[0018]
Further, according to the present invention, if the concentration of suspended solids detected by the concentration detection device is determined to be equal to the maximum suspended solids concentration in raw water, preferably the control device stops the returning process of the collected flocs conducted by the return and addition device. Simultaneously, preferably the control device controls the addition amounts of the magnetic powder conducted by the magnetic powder supply device, thereby to increase the returning amounts of the collected flocs conducted by the return and addition device, as the concentration of suspended solids becomes lower than the maximum suspended solids concentration in raw water. Further, preferably the control device controls the addition amounts of the magnetic powder conducted by the magnetic powder supply device such that the addition amounts thereof are to be decreased.
Accordingly, the above mentioned procedure of the present invention enables treatment performance of the flocculation magnetic separator to be more stabilized, regardless of the concentration of suspended solids in the raw water.

[0019]

In the meantime, according to the present invention, if the concentration of suspended solids in the raw water becomes higher than the maximum suspended solids concentration in raw water, the collected flocs cannot be returned to the raw water supply pipe.
However, in order to return the collected flocs so as to recycle the magnetic powder included in the collected flocs even in the above mentioned case, the returning process needs to extract only the magnetic powder component from the collected flocs and remove other suspended solid components.

[0020]
From the viewpoints as described hereinbefore, in the present invention, a magnetic powder extraction device is provided with a return pipeline located between the return and addition device and the raw water supply pipe.
The magnetic powder extraction device includes: a crush device of crushing the collected flocs by shearing force; an extraction device of selectively extracting only the magnetic powder from the collected flocs thus crushed by magnetic force; and a return device of returning the extracted magnetic powder to the raw water supply pipe.

[0021]
The magnetic powder extraction device of the present invention conducts the steps of: extracting the magnetic powder component from the collected flocs; and removing other suspended solid components, through the steps in two stages as mentioned 12)45 below.

[0022]
In the steps of the first stage, the collected flocs are crushed by applying physical force thereto. Note the collected flocs are formed by tight flocculation of magnetic powder and other suspended solid components via the aid of an inorganic flocculant and a polymer flocculant. Therefore, the crushing step of the tight flocculation is conducted by a supersonic wave crusher, a line mill or a ball mill in order to crush the tight flocculation.
That is, the collected flocs are crushed by only physical force without using a chemical such as hydrochloric acid. This allows risk in the step caused by leakage of a chemical to be lower, providing a highly safety feature with the step. As a result, when the magnetic powder extraction unit is installed in a ship, this safety feature facilitates the approval proceedings of the installation by the IMO to be conducted more simply.

[0023]
Next, in the steps of the second stage, the crushed flocs comprised of magnetic powder are extracted from the original collected flocs by an extraction device using magnetic force.
Other suspended solid components are thus removed from the extracted flocs. Then, the extracted collected flocs are returned to the raw water supply pipe by a return device.
Note the suspended solid components other than magnetic powder have been removed from the collected flocs which are to be returned. Hereby, the collected flocs comprised of magnetic powder which are to be returned are highly pure. Accordingly, the collected flocs can be returned to the raw water supply pipe, even though the suspended solids concentration in raw water is high.

[0024]
In the present invention, it is preferable to arrange a sterilization device of sterilizing plankton and bacteria contained in the collected flocs, in a return passage of the collected flocs. Herein, the returning process is conducted by the return and addition device.

[0025]
When the flocculation magnetic separator of the present invention is applied to a ballast water treating system installed in a ship, plankton and bacteria contained in the collected flocs are sterilized by a sterilization device. Then, the collected flocs thus sterilized are returned to a raw water supply pipe.
This procedure can suppress another burden, loaded on the raw water by the collected flocs.
EFFECT OF THE INVENTION

[0026]
The flocculation magnetic separator of the present invention enables the used amounts of magnetic powder to be reduced without using a chemical such as hydrochloric acid, and further the used amounts of the collected flocs to be reduced.
BRIEF DESCRIPTION OF DRAWINGS

[0027]
FIG.1 is a diagram showing a whole construction of a flocculation magnetic separator in an embodiment.
FIG. 2 is a schematic block diagram showing a base body of the flocculation magnetic separator including no magnetic powder extraction unit. Note FIG. 1 shows the separator equipped with the magnetic powder extraction unit.
FIG. 3 is a schematic block diagram of the flocculation magnetic separator in FIG. 1.
FIG. 41s a graphic diagram showing return rates of collected flocs in the flocculation magnetic separator in FIG. 2.
FIG. 5 is a graphic diagram showing return rates of collected flocs in the flocculation magnetic separator in FIG. 3.
FIG. 6 is a graphic diagram showing a relationship between concentration of added magnetic powder and a removal rate of flocs.
FIG. 7 is a graphic diagram showing a relationship between SS (suspended solids) concentration in raw water and a return rate of flocs.
EMBODIMENTS FOR CARRING OUT THE INVENTION

15d45

[0028]
Hereinafter, preferable embodiments of the flocculation magnetic separator in the present invention will be explained in detail referring to the attached drawings.

[0029]
FIG. 1 is a diagram showing a whole construction of the flocculation magnetic separator 10 in an embodiment. The flocculation magnetic separator 10 includes: a raw water supply pipe 12; a flocculation unit 14; a magnetic separation unit (or magnetic separation device) 16; a return and addition unit (or returning and adding device) 18; a magnetic powder extraction unit (or magnetic powder extraction device) 20; a heat sterilization unit (or sterilization device) 22; and a control unit (or control device) 24.

[0030]
Note the flocculation magnetic separator 10 in the present embodiment is applied to a ballast water treating system installed in a ship. Hereby, the separator 10 is equipped with a heat sterilization unit 22. However, when such a flocculation magnetic separator is arranged on shore, the heat sterilization unit 22 is not an essential component of the separator 10.
Further, if the flocs collected by the magnetic separation unit 16 are directly returned to the raw water supply pipe 12 through the return and addition unit 18, the magnetic powder extraction unit 20 also is not an essential component of the separator 10.

[0031]
The flocculation unit 14 includes a high speed stirring tank (or first stirring tank) 26 and a low speed stirring tank (or second stirring tank) 28. The flocculation unit 14 produces magnetic microflocs from water to be treated (or sea water) which has been supplied through the raw water supply pipe 12. For this operation, the raw water supply pipe 12 is equipped with a magnetic powder supply unit (or magnetic powder supplier) 30 and a flocculant addition unit 32.
Further, a polymer flocculant addition unit 36 is arranged at a pipeline 34 through which the water to be treated is supplied from the high speed stirring tank 26 to the low speed stirring tank 28.

[0032]
The magnetic powder supply unit 30 has a magnetic powder injection pump 38.
A rotational rate of the magnetic powder injection pump 38 is controlled by the control unit 24.
This mechanism controls the addition amounts of brand-new magnetic powder added to the raw water supply pipe 12.

[0033]
Further, an SS (Suspended Solids: hereinafter referred to as SS) concentration meter 40 (or turbidimeter) which detects concentration of suspended solids is attached to an upstream position of the raw water supply pipe 12. The SS concentration data detected by the SS concentration meter 40 are outputted to =
/

the control unit 24. Then, based on the SS concentration data, the control unit 24 controls a rotational rate of the magnetic powder injection pump 38 as well as a rotational rate of a collected floc return pump 42 which is a component of the return and addition unit 18.
Based on the above mentioned mechanism, brand-new magnetic powder and collected flocs are added to raw water which flows through the raw water supply pipe 12. Herein, note the attachment position of the SS concentration meter 40 is not limited to the raw water supply pipe 12. In this regard, any attachment position may be preferable as long as the attachment position is located at the upstream region to which the magnetic powder, the flocculant and the collected flocs are added.
For example, the SS concentration meter 40 may be attached to a tank of temporarily storing the raw water.

[0034]
Here, as magnetic powder, triion tetraoxide powder may be preferably used. As a flocculant, a water soluble inorganic flocculant such as poly aluminum chloride, iron (III) chloride, and iron (III) sulfate may be preferably used. Further, as a polymer flocculant, an anionic flocculant and a non-ionic flocculant may be preferably used.

[0035]
The high speed stirring tank 26 has a stirring blade (not shown in FIG. 1) which rapidly rotates so as to stir a mixture of raw water, magnetic powder, a flocculant and the collected flocs which have been added to the raw water. The raw water to which magnetic powder, a flocculant and the collected flocs have been added is rapidly stirred by the stirring blade. This operation allows extremely small magnetic microflocs each having a several tens m size to be formed in the high speed stirring tank 26. When the magnetic microflocs are formed, microorganisms and bacteria in the raw water are adsorbed on the magnetic powder which works as an adsorption core since the microorganisms and bacteria are electrically charged, thereby to be taken in the magnetic microflocs.

[0036]
The low speed stirring tank 28 is constructed as a multistage stirring tank comprised of a series of multiple tanks. A stirring tank at each stage is equipped with a stirring blade (not shown in FIG. 1). As to the stirring tank 28 constructed in a multistage form, a stirring speed at each tank is set so that the stirring speed is stepwise decreased from an upstream stirring tank to a downstream stirring tank. Hereby, water to be treated of containing the magnetic microflocs and the polymer flocculant which has been added to the water to be treated are supplied to the slow speed stirring tank 28 from the high speed stirring tank 26. As a result, the stirring speed is stepwise lowered along with from the upstream stirring tank to the downstream tank.
This mechanism facilitates the magnetic microflocs to be grown up, thereby to become enlarged flocs. Further, since the stirring speed at each tank is stepwise lowered, there is little chance that the enlarged flocs are broken by the respective stirring blades.

[0037]
The magnetic separation unit 16 collects the enlarged flocs from the water to be treated, comprising: a magnetic separation tank 44, a magnetic filter 46, a scraper (not shown in FIG. 1) and a conveyer system 48. Water to be treated containing enlarged flocs is supplied from the low speed stirring tank 28 to the magnetic separation tank 44. The magnetic filter 46 has, for example, a shape of a rotational drum, and at least a part of the filter 46 is immersed in the water to be treated in the magnetic separation tank 44. Hereby, the magnetic separation filter 46 collects enlarged flocs which drift in the magnetic separation tank 44 filled with the water to be treated.
Then, the enlarged flocs thus collected (or collected flocs) are lifted up from the magnetic separation tank 44 associated with the rotational movement of the magnetic filter 46. The lifted enlarged flocs are scraped from the magnetic filter 46 by the scraper. After that, the collected flocs thus scraped are conveyed to a collected floc receiver tank 50 by the conveyer system 48 such as a screw conveyer. The collected flocs thus conveyed are temporarily stored in the tank 50.

[0038]

The collected flocs stored in the collected floc receiver tank 50 are sent to a heat sterilization unit 22 by a collected floc return pump 42. The heat sterilization unit 22 sterilizes microorganisms and bacteria contained inside the collected flocs by the heat treatment of the collected flocs.
Note the collected flocs are in a slurry form. Therefore, it is preferable to use a positive displacement pump such as a tube pump or a single axis screw type pump, as a collected floc return pump 42. A heating temperature for sterilizing bacteria or the like is set in the range from 75 to 80 C, and a heating time is set in about three minutes.

[0039]
In the meantime, the magnetic powder extraction unit 20 includes: crush units (or crush devices) 52 and 54 of crushing the collected flocs by shearing force; an extraction unit (or extraction device) 56 of selectively extracting a magnetic powder component from the crushed collected flocs by magnetic force; and a pump (or return device) 58 of returning the extracted magnetic powder component to the raw water supply pipe 12.

[0040]
As mentioned hereinbefore, the flocculation magnetic separator 10 shown in FIG. 1 represents an embodiment in which the heat sterilization unit 22 is arranged at the upstream position of the collected floc return passage which is included in the return and addition unit 18. Further, in the embodiment, , the magnetic powder extraction unit 20 is arranged at the downstream position of the return passage.

[0041]
A crush unit 52 is a line mill which generates strong shearing force by rapidly rotating the stirring blade 60 having a special shape. In contrast, another crush unit 54 is a supersonic wave crusher (frequency= about 20 kHz) which generates shearing force with a liquid 64 by immersing a rod shaped vibrator 62 vibrating at the frequency of the supersonic wave, in the liquid 64.
Note in the present embodiment, two crush units 52 and 54 are arranged, while either of the units may be arranged.
Alternatively, a ball mill 65 may be used as a crush unit (or crush device).

[0042]
Then, the collected flocs crushed by the crush units 52 and 54 are supplied to an extraction unit 56. The extraction unit 56 extracts a magnetic powder component from the crushed collected flocs by magnetic force. To such an extraction unit 56, applied is a system using a magnetic disk or a magnetic drum, permanent magnets being embedded in the disk and the drum.
This construction enables the magnetic powder component to be extracted from the collected flocs, and SS substances other than the magnetic powder component to be discharged.

[0043]

Here, a discharged content of the SS substances other than the magnetic powder component is about 0.2% of the throughput of the flocculant magnetic separator 10. Accordingly, the extraction unit 56 in the present embodiment may be smaller than the magnetic separation unit 16 which is a main component.
The collected flocs, of which extraction treatment for extracting the magnetic powder component has been finished, are stored in a collected floc storage tank (not shown in FIG. 1) as .
separated and collected flocs. This process is similar to the process conducted for an excess of the collected flocs which are generated in the collected floc receiver tank 50. Note the magnetic powder component extracted by magnetic force has a low water content, resulting in a low flowability. Hereby, the magnetic powder component is supplied to a tank 68 of storing clear water 66, thereby to be diluted therein. After that, the magnetic powder component thus diluted with clear water 66 is returned to the raw water supply pipe 12 by a pump 58. This process enables magnetic powder in a high purity to be added to the water to be treated which flows through the raw water supply pipe 12.
Herein, in the raw water supply pipe 12, a return position of the collected flocs and an addition position of the magnetic powder are located at a downstream region of the SS concentration meter 40, at an upstream region of the high speed stirring tank 26, and at an upstream region of the place where a flocculant is added. Note the rotational rate of the pump 58 is controlled by the control unit 24 based on the SS concentration date measured by the SS concentration meter 40.

[0044]
Next, the effects of the flocculation magnetic separator 10 constructed as mentioned hereinbefore will be explained in detail.

[0045]
FIG. 2 is a schematic block diagram showing a base body of a flocculation magnetic separator 10. This base body of a flocculation magnetic separator 10 represents a separator constructed by removing the magnetic powder extraction unit 20 from the flocculation magnetic separator 10 shown in FIG. 1.
That is, the flocculation magnetic separator 10 in FIG. 2 represents an embodiment in which only the heat sterilization unit 22 is arranged in the return passage of the collected flocs.
Herein, the return process is conducted by the return and addition unit 18.

[0046]
In the flocculation magnetic separator 10 in FIG. 2, arranged is the return and addition unit 18 which returns and adds the collected flocs discharged from the magnetic separation unit 16 to an upstream region of the position where a flocculant is added, in the raw water supply pipe 12. The collected flocs discharged from the magnetic separation unit 16 are temporally stored in a collected floc receiver tank 50 (see FIG. 1). Then, the resulting collected flocs are returned to the raw water supply pipe 12 by a collected floc return pump 42 included in the return and addition unit 18.
In contrast, the non-returned collected flocs are separately stored in a collected flock storage tank (not shown in FIG. 2) by overflowing the flocs from the collected floc receiver tank 50 as an excess of the flocs.

[0047]
As mentioned above, the returning procedure of the collected flocs to the raw water supply pipe 12 allows the collected flocs to be recycled without using a chemical such as hydrochloric acid. As a result, the magnetic powder component contained in the collected flocs, allowing the used amounts of brand-new magnetic powder to be reduced. Further, this also allows the total amounts of the collected flocs thus generated due to the addition of the brand-new magnetic powder to be reduced.

[0048]
Meanwhile, the control unit 24 controls return amounts of collected flocks conducted by the return and addition unit 18 and addition amounts of brand¨new magnetic powder conducted by the magnetic powder supply unit 30. Herein, this controlling operation is conducted based on the SS concentration detected by the SS concentration meter 40 and the maximum SS concentration in raw water, the maximum SS concentration in raw water having been set in advance.

[0049]
That is, when the SS concentration detected by the SS
concentration meter 40 is equal to the maximum SS concentration in raw water, the control unit 24 stops the returning operation of the collected flocs conducted by the return and addition unit 18. Simultaneously, the control unit 24 controls the addition amounts of brand-new magnetic powder conducted by the magnetic powder supply unit 30.
At that time, as the SS concentration becomes lower than the maximum SS concentration in raw water, the control unit 24 increases the return amounts of the collected flocs conducted by the return and addition unit 18. Simultaneously, the control unit 24 reduces the addition amounts of brand-new magnetic powder conducted by the magnetic powder supply unit 30.

[0050]
The above mentioned procedure allows the treatment performance of the flocculation magnetic separator 10 in FIG. 2 to be stabilized without being influenced by the SS concentration in raw water. Note a unit with the reference numeral 70 represents a filter. The filter 70 separates treated water and washing water from the water to be treated which has been separated by the magnetic separation unit 16. Then, the washing water is returned to the raw water supply pipe 12 through the pipeline 72.

[0051]
Next, more specifically, a control method conducted by the control unit 24 will be explained in detail.

[0052]
First, note the return amounts of the collected flocs are controlled by the rotational rate of the collected floc return pump 40, which is controlled by the control unit 24. Herein, the rate in the return amounts of the collected flocs are adjusted in the range from 0 to 100% of the total discharged amounts of the collected flocs.

[0053]
Secondly, note the return amounts of the collected flocs are controlled by the control unit 24 based on the SS concentration in raw water detected by the SS concentration meter 40 together with the maximum SS concentration in raw water set in advance.

[0054]
For example, it is premised that the flocculation magnetic separator 10 is designed to have the maximum SS concentration in raw water of 50 mg/L. In that case, it is assumed that the raw water having the SS concentration of 50 mg/L flows into the raw water supply pipe 12. If 100% of the collected flocs return to the raw water, this means that the SS in the amounts corresponding to the SS concentration of 50 mg/L is returned to the raw water.
Accordingly, the SS concentration in the raw water flowing into the high speed stirring tank 26 is represented by the following formula: 50 + 50 - 100 mg/L. Hereby, the SS concentration in the raw water having a value of 100 mg/L is higher than the maximum SS concentration in raw water which represents the marginal ability performed by the flocculation magnetic separator 10.

[0055]
On the other hand, when the raw water having the SS
concentration of 10 mg/L flows into the raw water supply pipe 12, the flocculation magnetic separator 10 has enough treatment ability for treating the raw water by room of the ability of treating the raw water with the SS concentration of 40 mg/L
compared to the raw water with the maximum SS concentration of 50 mg/L.
As a result, it is no problem to return the amount of the collected flocs corresponding to the remaining room of the treating ability of the flocculation magnetic separator 10.

[0056]
In a trial calculation, when the flocculation magnetic separator 10 in FIG. 2 is used for the treatment of raw water, the relationship among the SS concentration in raw water (A) (mg/L), the returnable amount of the collected flocs (B) (return rate (%) of the collected floc amount per the discharged floc amount), and the addition amount of the brand-new magnetic powder (C) (mg/L) is shown in a graphic diagram of FIG. 4, and in Table 1 listed below.
Herein, the graphic diagram in FIG. 4 and Table 1 show a returnable amount of the collected flocs when the maximum designed SS concentration in raw water is 50 mg/L.

28)45

[0057]
In the graphic diagram of FIG. 4, the vertical axis represents a rate of the magnetic powder contained in the flocs at the just prior time to be returned to the magnetic separator unit 16. The horizontal axis represents a return rate of the collected flocs per the discharged amount.
Further, the lowest limited value of the magnetic powder rate in the flocs is set in 31.4%. Here, the return rate of the flocs and the addition amount of the brand-new magnetic powder are set so that the magnetic powder rate becomes 31.4% or more in order to effectively perform the magnetic separation by the magnetic separation unit 16.

[0058]
Note the return rate of the flocs and the addition amount of the brand-new magnetic powder are set in 31.4% in the present embodiment. More specifically, as shown in Table 1, when the SS
concentration in raw water is 50 mg/L, the flocculation magnetic separator 10 does not return the collected flocs, while the separator 10 adds only brand-new magnetic powder by the concentration of 30 mg/L. The SS concentration in raw water is detected by the SS concentration meter 40, and the flocculation magnetic separator 10 controls the return rate of the collected flocs and the addition amount of the brand-new magnetic powder corresponding to the detected data thus measured as shown in Table 1.

[0059]
Further, when the flocculation magnetic separator 10 is applied to a treatment of ballast water, the maximum SS
concentration in raw water is designed to have a value of 50 mg/L, following the regulations of the IMO. However, since the actual SS concentration in seawater often has a value less than 10 mg/L, the return process of the collected flocs to the raw water supply pipe 12 as set as mentioned above allows the used amounts of the brand-new magnetic powder to be reduced.
This also enables the storage amounts necessary for the brand-new magnetic powder to be reduced, resulting in greatly advantageous merits to a ship of which inside space for arranging multiple devices is significantly limited. Note plankton and bacteria (viable individual) are set for a removal target in a treatment of ballast water. Therefore, when the collected flocs are returned to the raw water supply pipe 12, a heat sterilization unit 22 is arranged in a return pipeline, thereby to return the collected flocs as sterilizing the plankton and bacteria.

[0060]
Table 1.
A
50 0 (NOT RETURNABLE) 30

[0061]
On the other hand, the injection amounts of the brand-new magnetic powder are controlled by the control unit 24 through adjusting the rotational rate of the magnetic powder injection pump 38. Herein, the control operation is conducted in the range from 0 to 100%, in which a rate of 100% (that is, 30 mg/L) calculated by the injection amount of the brand-new magnetic powder represents a case that no collected flocs are returned to the raw water supply pipe 12. The injection amounts of the brand-new magnetic powder are determined by the return amounts of the collected flocs. For example, when the return amount of the collected flocs per discharged amount is 47%, the magnetic powder which flows into the high speed stirring tank 26 is to be returned in 47% thereof. Hereby, the injection amounts of the brand-new magnetic powder may be set in about 53% (or 16 mg/L).
The return amounts of the collected flocs are detected by a flowmeter 74 which is arranged in the return pipeline for the collected flocs. Based on the measurement results of the flowmeter 74, the control unit 24 adjusts the rotational rate of the pump 38, thereby to adjust the injection amounts of the brand-new magnetic powder.

[0062]
Here, the flocculation magnetic separator 10 in FIG. 2 cannot return the collected flocs, if the SS concentration in raw water is larger than the maximum designed SS concentration in raw water. Therefore, even in such a case, in order to return the collected flocs thereby to recycle the magnetic powder component in the collected flocs, it is needed to extract only a magnetic powder component from the collected flocs and remove other SS
components, in the return process.

[0063]
Next, the flocculation magnetic separator 10 in FIG. 3 shows an arrangement of the units. Herein, a magnetic powder extraction unit 20 is arranged at a downstream position of a magnetic separation unit 16 and a heat sterilization unit 22 is arranged at a downstream position of the magnetic powder extraction unit 20.

[0064]
That is, the flocculation magnetic separator 10 in FIG. 3 represents an embodiment in which the magnetic powder extraction unit 20 is arranged at an upstream position in a return passage of the magnetic flocs; the return process being conducted by the return and addition unit 18, while the heat sterilization unit 22 is arranged at a downstream position in the return passage.

[0065]
The magnetic powder extraction unit 20 separately performs the treatment of the collected flocs which have been discharged from the magnetic separation unit 16 through the following two stages of the steps of: extracting the magnetic powder component contained in the collected flocs, and removing other SS components, from the collected flocs.

[0066]
The first stage includes the steps of: crushing collected flocs by applying physical force to the collected flocs. In the collected flocs, a magnetic powder component and other SS
components are tightly agglomerated by an inorganic flocculant and a polymer flocculant. Accordingly, a line mill 52 and/or a supersonic wave crusher 54 are/is used so as to crush such tightly agglomerated flocs.
Note it is experimentally determined that collected flocs thus tightly agglomerated are decomposed to be almost crushed, via a crushing treatment thereof for several 10 seconds to several minutes conducted by the lime mill 52 and/or the supersonic wave crusher 54.

[0067]
Here, a method for adjusting a pH value using a chemical as described in the patent document 2 may be conducted so as to facilitate the collected flocs to be decomposed. However, when the treatment is conducted in a ship, it is preferable to decompose the collected flocs via only a physical method, taking the IMO
regulations or the like in consideration.

[0068]
The second stage includes the steps of: extracting only a magnetic powder component from the collected flocs thus crushed by magnetic force. As an extracting unit 56 (see FIG. 1), a unit using a magnetic disk or a magnetic drum both in which permanent magnets are embedded. Then, the second stage further includes the steps of: diluting the extracted magnetic powder component with clear water 66 (see FIG. 1); and returning the magnetic powder component to the raw water supply pipe 12 (see FIG. 1) by the pump 58 (see FIG. 1).

[0069]
Though the two stages of the steps, the purity of the magnetic powder component to be returned is increased. This increase in the purity allows the collected flocs mainly containing the magnetic powder component to be returned even though the SS concentration in raw water becomes higher.

[0070]
Here, a trial calculation is conducted assuming the case that the SS components other than the magnetic powder component are separated from 30% of the collected flocs. Accordingly, in the case of the flocculation magnetic separator 10 of FIG. 3, the relationships among SS concentration in raw water (A) (mg/L), returnable amounts of the collected flocs (B) (this is represented by the return rate % of the collected flocs per discharged amounts of collected flocs) , and addition amounts of the brand-new magnetic powder (C) (mg/L) , are represented by the graphic diagram in FIG. 5 and Table 2.

[0071]

The above mentioned results demonstrate that the flocculation magnetic separator 10 of FIG. 3 can more increase the return rate of the collected flocs corresponding to the SS
concentration in raw water and reduce the addition amounts of the bran-new magnetic powder than the flocculation magnetic separator 10 having no magnetic powder extraction unit 20 of FIG.
2.

[0072]
Table 2.
A
50 0 (NOT RETURNABLE) 30 [ 0073]
Further, if 30% of the SS components other than the magnetic powder component contained in the collected flocs are separated and removed from collected flocs by the magnetic powder extraction unit 20, this results in the condition that the collected flocs originally contain the SS concentration in raw water of 30 mg/L.
Hereby, this SS concentration allows 42% of the discharged collected flocs to be returned.
Accordingly, it is preferable to arrange the magnetic powder extraction unit 20 in the flocculation magnetic separator , 10, if the SS concentration in raw water is often higher than the maximum designed SS concentration in raw water, or if more amounts of the collected flocs are returned so as to reduce the used amounts of the brand-new magnetic powder to be also reduced.
[0074]
[Additional Remarks]
[Explanation on Optimal Value of Magnetic Powder Rate in Magnetic Flocs]
Here, it is noted that treatment targets for treating ballast water include plankton and bacteria. In addition to this, if a ballast water treatment system is installed in a ship, it is needed to pass a test for checking the treatment performance of the system or regulations, as defined by the regulatory agency.
According to the regulations, the treatment system is demanded to have the performance enough to treat the ballast water containing the suspended solids (SS) such as sand in the ballast water with the maximum concentration of 50 mg/L, with satisfying the discharging criteria on ballast water.
[0075]
In this regard, the present inventors adopt a method for adding mineral based micro particles called kaolin as a simulant of sand or the like in the test for determining conditions in the flocculation magnetic separation of plankton and bacteria.
Hereinafter, more specifically will be explained the test method in detail.

[0076]
First, to sea water containing plankton and bacteria, is added the above mentioned kaolin in the concentration of 50 mg/L.
Then, a flocculation test of the seawater is conducted by setting parameters (or variables) to include the addition rates of magnetic powder, an inorganic flocculant and a polymer flocculant.
After that, formation state of the magnetic flocs is evaluated by visual observation. Next, the seawater containing the magnetic flocs is introduced into a channel in which permanent magnets are placed in order. The sea water was subjected by a contact treatment and an adsorption treatment with the magnets for a predetermined time (or several seconds). Then, the concentration of the magnetic flocs in the sea water discharged from the channel is measured, whereas the removal rate of the magnetic flocs is determined.
[0077]
The results in the evaluation test as mentioned above clearly indicate that plankton and bacteria are sufficiently flocculated under the condition of the addition rates: poly aluminum chloride used as an inorganic flocculant = 5 mg Al/L;
and polymer flocculant = 1 mg/L.
[0078]
Further, as shown in FIG. 6, the removal rate of the magnetic flocs is likely to increase, as the addition rate of the magnetic powder increases. When the addition rate of the magnetic powder becomes 30 mg/L or more, the removal rate is likely to reach a peak. From the viewpoint of costs, it is desirable to decrease the addition rate of the magnetic powder as many as possible.
Hereby, the addition rate of the magnetic powder is determined to be 30 mg/L.
[0079]
If the addition rates of the magnetic powder, the inorganic flocculant and the polymer flocculant are set in the values as mentioned above, the content of the magnetic powder per magnetic flocs may be calculated by the following formula.
[0080]
Content of Magnetic Powder in Magnetic Flocs (%) =
(Addition Rate of Magnetic Powder) / (Addition Rate of Kaolin + Addition Rate of Magnetic Powder + Addition Rate of Inorganic Flocculant + Addition Rate of Polymer Flocculant) x 100 ---(Formula 1) Here, each value is listed as follows. Addition Rate of Magnetic Powder - 30 mg/L; Addition Rate of Kaolin = 50 mg/L;
Addition Rate of Inorganic Flocculant = 5 x (78/27) = 14.4 mg/L;
Addition Rate of Polymer Flocculant = 1 mg/L.
Note poly aluminum chloride added as an inorganic flocculant exists in the form of aluminum hydroxide (Al(OH)3) in the magnetic flocs. Therefore, the addition rate of the poly aluminum chloride is calculated by the formula of: 5 mg Al/L
(addition rate) x 78 (MW of Al(OH)3)/ 27 (AW of Al).

If the respective values are substituted in Formula 1, the formula is represented as:
Content of Magnetic Powder in Magnetic Flocs (%) =
30 / (50 + 30 + 14.4 + 1) x 100 = 31.4 (%) The present inventors determine that this calculated rate of the magnetic powder is the optimal value which allows the removal rate of the magnetic flocs to be secured and the treatment costs to be minimized.
[0081]
As mentioned hereinbefore, it should be noted that a recycle method of magnetic powder needs to construct a treatment flow of magnetic powder so as to secure the removal rate of magnetic flocs and maintain the treatment performance thereof, without lowering the content of the magnetic powder less than the value as calculated above.
[0082]
Further, a graphic diagram in FIG. 7 shows a return rate of the collected flocs per SS in raw water (mg/L). A return rate of the collected flocs is set based on the graph.
DESCRIPTION OF REFERENCE NUMERALS
[0083]
10: Flocculation Magnetic Separator 12: Raw Water Supply Pipe 14: Flocculation Unit 16: Magnetic Separation Unit (or Magnetic Separation Device) 18: Return and Addition Unit (or Return and Addition Device) 20: Magnetic Powder Extraction Unit (or Magnetic Powder Extraction Device) 22: Heat Sterilization Unit (or Heat Sterilization Device) 24: Control Unit (or Control Device) 26: High Speed Stirring Tank (or First Stirring Tank) 28 Low Speed Stirring Tank (or Second Stirring Tank) 30: Magnetic Powder Supply Unit (or Magnetic Powder Supply Device) 32: Flocculant Addition Unit 34: Pipeline 36: Polymer Flocculant Addition Unit 38: Magnetic Powder Injection Pump 40: SS Concentration meter (or Concentration Detection Device) 42: Collected Flocs Return Pump 44: Magnetic Separation Tank 46: Magnetic Filter 48: Conveyer 50: Collected Floc Receiver Tank 52: Crush unit (or Crush device: Line Mill) 54 Crush unit (or Crush Device: Supersonic Wave Crusher) 56: Extraction Unit (or Extraction Device) 58: Pump (or Return Device) 60: Stirring Blade 62: Vibrator 64: Liquid 65: Ball Mill (Crush Unit) 66: Clear Water 68: Tank 70: Filter 72: Pipeline 74: Flowmeter

Claims

1. A flocculation magnetic separator comprising:
a first stirring tank connected with a raw water supply pipe which supplies raw water, for stirring at a first stirring rate the raw water added with a flocculant and magnetic powder which is supplied from a magnetic powder supply device, thereby to form magnetic microflocs containing the magnetic powder;
a second stirring tank for stirring, at a second stirring rate slower than the first stirring rate, treated water to which a polymer flocculant is added, thereby flocculating the magnetic microflocs, the treated water containing the magnetic microflocs and being discharged from the first stirring tank;
a magnetic separation device for separating the flocculated magnetic microflocs by a magnetic filter from the treated water discharged from the second stirring tank to collect the flocculated magnetic microflocs on the magnetic filter, and scraping the collected flocculated magnetic microflocs off the magnetic filter by a scraper;
a collected floc receiver tank storing the flocculated magnetic microflocs scraped by the scraper; and a return and addition device for recycling magnetic powder contained in the flocculated magnetic microflocs by returning by a pump the flocculated magnetic microflocs stored in the collected floc receiver tank to the raw water supply pipe upstream of the first stirring tank and at a first position upstream of where the flocculant is added, thereby to add the collected microflocs to the raw water.

2. The flocculation magnetic separator as described in claim 1, further comprising:
a concentration detection device detecting suspended solids concentration in the raw water, at a second position upstream of where the magnetic powder, the flocculant and the collected microflocs are added; and a control device controlling return amounts of the collected microflocs conducted by the return and addition device, and addition amounts of the magnetic powder conducted by the magnetic powder supply device, based on both the suspended solids concentration detected by the concentration detection device and maximum suspended solids concentration in raw water set in advance.

3. The flocculation magnetic separator as described in claim 2, wherein the control device stops a process of returning the collected microflocs conducted by the return and addition device, when the suspended solids concentration detected by the concentration detection device is equal to the maximum suspended solids concentration in raw water, and simultaneously the control device controls addition amounts of the magnetic powder conducted by the magnetic powder supply device; and the control device increases return amounts of the collected microflocs conducted by the return and addition device, as the suspended solids concentration becomes lower than the maximum suspended solids concentration in raw water, and simultaneously the control unit decreases addition amounts of the magnetic powder conducted by the magnetic powder supply device.

4. The flocculation magnetic separator as described in claim 1, further comprising:
a magnetic powder extraction device which is arranged at a return pipeline located between the return and addition device and the raw water supply pipe;
the magnetic powder extraction device comprising:
a crush device crushing the collected microflocs by shearing force;
an extraction device selectively extracting only a magnetic powder component from the collected microflocs thus crushed by using magnetic force; and a return device returning the magnetic powder component thus extracted to the raw water supply pipe.

5. The flocculation magnetic separator as described in claim 1, further comprising a sterilization device sterilizing plankton and bacteria contained in the collected microflocs, arranged in a return pipeline of the collected microflocs conducted by the return and addition device.