JP4978002B2 - Ballast water treatment method - Google Patents

Description

  The present invention relates to an apparatus and method for efficiently killing harmful aquatic organisms and microorganisms contained in ballast water loaded in a ballast tank of a ship.

In general, a ship with an empty load or a small load carries water injection of ballast before leaving the port because of the necessity of ensuring the depth of submersion of the propeller and ensuring safe navigation during empty loading. Conversely, when loading in the port, the ballast water is discharged.
By the way, when ballast water is poured and drained by a ship that goes back and forth between loading and unloading ports in different environments, there is a concern that it may adversely affect the coastal ecosystem due to the difference in microorganisms contained in the ballast water. Has been.
Therefore, an international convention for the regulation and management of ship ballast water and sediment was adopted in February 2004 at an international conference on ship ballast water management, which required the treatment of ballast water.

The standard established by the International Maritime Organization (IMO) as a standard for the treatment of ballast water is that the number of organisms (mainly zooplankton) of 50 μm or more contained in the ballast water discharged from the ship is less than 10 in 1 m ³ , 10 μm or more The number of organisms less than 50 μm (mainly phytoplankton) is less than 10 in 1 ml, the number of Vibrio cholerae is less than 1 cfu in 100 ml, the number of E. coli is less than 250 cfu in 100 ml, and the number of enterococci is 100 cfu in 100 ml It is less than.

Many ballast water treatment technologies are currently under development, but as a conventional technology, harmful algal cysts are killed by mixing chlorine-based disinfectant or hydrogen peroxide into the ballast water poured into the ballast tank. A method of sterilizing the paste has been proposed (see, for example, Patent Document 1).
And in the method of patent document 1, when discharging ballast water, air is blown into ballast water with an aeration apparatus, and residual chlorine is made harmless.
JP-A-4-322788

In Patent Document 1, sterilization of harmful algae is killed by mixing a chlorine-based disinfectant into ballast water. Residual chlorine is blown into the ballast water by an aeration apparatus when discharging the ballast water. Is supposed to be harmless.
However, in the method described in Patent Document 1, a chlorine-based disinfectant is mixed in ballast water to kill harmful algal cysts, and then residual chlorine reacts with organic matter in the ballast water to generate harmful trihalomethanes. However, in Patent Document 1, no consideration is given to this trihalomethane. This trihalomethane has a problem that even if air is blown into the ballast water by an aeration apparatus, most of the gas is transferred to the gas phase, but most of it remains and is not harmed, so it is discharged together with the ballast water and adversely affects the environment. .

  In view of such circumstances, an object of the present invention is to provide a ballast water treatment apparatus and treatment method that can surely kill plankton and bacteria in ballast water and prevent discharge of harmful substances.

  In view of the above-mentioned problems, the present inventors, when removing and killing plankton and bacteria contained in ship ballast water, suppress the production of trihalomethane in the case of using a chlorine-based disinfectant, thereby adversely affecting the environment. As a result of intensive studies to provide a ballast water treatment device and a treatment method that are not given, the present invention has been completed. Specifically, the present invention has the following configuration.

(1) A ballast water treatment apparatus according to the present invention is supplied with a chlorine disinfectant supply device that supplies chlorine disinfectant to seawater poured into a ballast tank of a ship and / or seawater discharged from a ballast tank, and a chlorine disinfectant. And a chlorine reducing agent supply device that supplies a chlorine reducing agent to the seawater that is provided downstream of the retention tank and stays in the retention tank for a predetermined time. It is what.

  A chlorine disinfectant is supplied into sea water to kill plankton and bacteria, but the chlorine disinfectant remaining after sterilization of bacteria reacts with organic matter in seawater to produce trihalomethane. FIG. 4 shows an example of the change over time in the concentration of trihalomethane in seawater after the chlorination agent is injected. FIG. 4 shows a case where 20 mg / l of chlorine disinfectant is injected. The amount of trihalomethane produced increases as the concentration of organic matter in seawater increases and the amount of chlorine disinfectant supplied increases.

As shown in FIG. 4, the production of trihalomethane continues until there is no residual chlorine, and the trihalomethane concentration increases with time. In the example shown in FIG. 4, the amount of trihalomethane produced is about 1/10 of the total amount produced one minute after adding the chlorine disinfectant. From this, the production of trihalomethane can be suppressed by supplying a chlorine reducing agent immediately after supplying the chlorine disinfectant and reducing the residual chlorine by performing a reduction treatment.
On the other hand, in order to kill plankton of 50 μm or more together with bacteria by the chlorine disinfectant, effective chlorine must remain in seawater for a certain period of time.

Therefore, in the present invention, in order to kill plankton and bacteria with a chlorine disinfectant, the residual time of effective chlorine is appropriately secured and the generation of trihalomethane due to the long-term remaining of chlorine is suppressed. After supplying the bactericidal agent, a retention tank is provided to retain the seawater for a predetermined time required for the killing of plankton and bacteria with effective chlorine, and the chlorine reducing agent is added to the seawater discharged from the retention tank. It is supplied to reduce residual chlorine and expire it to suppress the production of trihalomethane.
That is, after supplying a chlorine disinfectant to seawater, the seawater in which effective chlorine remains is retained for a time sufficient to kill plankton and bacteria, and for a time that can suppress the production of trihalomethane, and then the residual In order to reduce chlorine, a chlorine reducing agent is supplied to reduce residual chlorine and expire it, thereby suppressing the generation of trihalomethane.
Retention means that seawater does not flow at all and flow at a low speed in order to secure a sterilization time with the chlorine disinfectant before supplying the chlorine reducing agent.
Note that sodium hypochlorite, calcium hypochlorite, and chlorine gas are used as the chlorine disinfectant, and all exist as effective chlorine in the form of hypochlorous acid or hypochlorite ions in seawater.
As the chlorine reducing agent, sodium sulfite, sodium thiosulfate or hydrogen peroxide water is used.

(2) Further, a chlorine disinfectant supply device for supplying a chlorine disinfectant to seawater poured into the ballast tank of a ship and / or seawater discharged from the ballast tank, and retention for retaining the seawater supplied with the chlorine disinfectant for a predetermined time. A tank and an activated carbon treatment apparatus that is provided on the downstream side of the retention tank and that receives the supply of seawater retained in the retention tank for a predetermined time to treat the seawater with activated carbon are provided.

In order to invalidate residual chlorine in seawater, activated carbon treatment is performed instead of the above reduction treatment. That is, after adding a chlorine disinfectant to seawater, the seawater in which effective chlorine remains is retained for a time sufficient to kill plankton and bacteria, and as short as possible to suppress trihalomethane production, and then activated carbon Seawater is passed through the treatment equipment, and residual chlorine is reduced and decomposed with activated carbon to suppress the production of trihalomethane, and the produced trihalomethane is adsorbed and removed.
As the activated carbon treatment apparatus, an apparatus in which activated carbon is gently flowed in a tank or an apparatus filled with activated carbon can be used. Further, instead of activated carbon, a treatment material capable of adsorbing trihalomethane together with reductive decomposition of residual chlorine may be used.
Further, instead of the activated carbon treatment apparatus, an adsorption tank provided with an adsorbent that adsorbs trihalomethane may be provided, and a chlorine reducing agent may be supplied to seawater retained in the retention tank for a predetermined time. Residual chlorine is reduced by a chlorine reducing agent and expired, and trihalomethane produced by the adsorbent in the adsorption tank is adsorbed. A resin-based adsorbent can be used as the adsorbent.

(3) Moreover, the activated carbon processing apparatus as described in said (2) is characterized by being formed by providing activated carbon in a ballast tank.

  By using activated carbon in a part of the ballast tank as an activated carbon treatment device, it is not necessary to newly provide an activated carbon treatment device, it can be easily applied to existing ships, and equipment costs can be reduced.

(4) Moreover, the retention tank of said (1) is characterized by being able to retain for 0.5 to 20 minutes from supplying a chlorine disinfectant to supplying a chlorine reducing agent. Is.

(5) Moreover, the retention tank as described in said (2) or (3) is that the residence from the supply of a chlorine disinfectant to the activated carbon treatment being 0.5 to 20 minutes is possible. It is a feature.

The residence time should be sufficient to kill plankton and bacteria and be as short as possible to suppress trihalomethane production.
Authorization testing standards ballast water treatment system of IMO, processing plankton of more than 50μm before it is possible to 10 ⁵ individuals / m ³ or more in a raw water after treatment 10 individual / m ³ or less is demanded.
Therefore, the relationship between the residual chlorine concentration in seawater required to satisfy this standard and the contact time between plankton and residual chlorine was determined. FIG. 5 is a log-log graph showing the relationship between the residual chlorine concentration in seawater and the contact time between plankton and residual chlorine.

As shown in the graph of FIG. 5, for example, if the contact time is 10 minutes, the residual chlorine concentration needs to be 11.6 mg / l. When the residual chlorine concentration is 50 mg / l, the contact time is about 1 minute.
Considering the method of procurement, storage and supply of chlorine disinfectant, it is preferable to supply the chlorine disinfectant so that the residual chlorine concentration is 5 to 100 mg / l, so plankton of 50 μm or more is killed to the processing standard The contact time required for this is 0.5 to 20 minutes. The time from supplying the chlorine disinfectant to supplying the chlorine reducing agent or supplying the chlorine disinfectant until the activated carbon treatment is performed so that the contact time can be 0.5 to 20 minutes. By providing a residence tank capable of residence with a residence time of 0.5 to 20 minutes, plankton of 50 μm or more can be killed to the processing standard.

Fig. 6 shows changes over time in the concentration of trihalomethane in seawater after chlorinating agent injection for five cases of chlorinating agent injection rates of 5 mg / l, 10 mg / l, 20 mg / l, 50 mg / l, and 100 mg / l. The vertical axis is the trihalomethane concentration, and the horizontal axis is the elapsed time.
As shown in FIG. 6, when the residual chlorine concentration is in the range of 5 to 20 mg / l, the trihalomethane concentration produced is 0.1 mg / liter, which is the standard for drinking water in Japan, if the residence time is 20 minutes or less. It is 1/2 or less of l. Even if the residual chlorine concentration is 50 to 100 mg / l, it is 0.1 mg / l or less, which is the Japanese drinking water standard, if the residence time is 20 minutes or less.
In this way, the residence tank has a residence time in the range of 0.5 to 20 minutes. By controlling the residence time and sterilizing with a chlorine disinfectant, plankton and bacteria can be sufficiently killed, and trihalomethane can be produced. Can be suppressed.

  In the graph of FIG. 6, white circles are added to the time during which plankton of 50 μm or more can be killed to the treatment standard at each residual chlorine concentration. Looking at the concentration of trihalomethane corresponding to the white circles, all are 0.05 mg / l or less. If the residence time is controlled according to the residual chlorine concentration, plankton of 50 μm or more is killed to the treatment standard, and the trihalomethane concentration is It can be seen that can be suppressed to be extremely small.

(6) The residence tank described in the above (1) to (5) is formed in a ballast tank.

  By using a part of the ballast tank as a retention tank, it is not necessary to newly provide a retention tank, it is easy to apply to existing ships, and equipment costs can be reduced.

(7) In the above-described (1) to (6), a filtration device that filters seawater and captures aquatic organisms is provided upstream of the chlorine disinfectant supply device.

Since the filtration device captures and removes relatively large aquatic organisms such as zooplankton in seawater, it can reduce the supply amount of chlorine disinfectant compared to the case of simply supplying and killing chlorine disinfectant. Production can be further suppressed to reduce the influence on the environment, the supply amount of the chlorine reducing agent can be reduced, and the residence tank and the activated carbon treatment apparatus can be made smaller.
In addition, as a filtration apparatus, it is preferable to use a thing with an opening of 10-200 micrometers, and it is especially preferable to use a thing with an opening of about 50 micrometers especially because the capture rate and the backwashing frequency can be set optimally.

(8) In the ballast water treatment method according to the present invention, a chlorine disinfectant supply step of supplying a chlorine disinfectant to seawater poured into a ballast tank of a ship and / or seawater discharged from the ballast tank, and a chlorine disinfectant are supplied. A retention step of retaining seawater in which effective chlorine remains and a chlorine reducing agent supply step of supplying a chlorine reducing agent to the retained seawater, reducing residual chlorine and causing it to expire to suppress generation of trihalomethane,
Corresponding to the residual chlorine concentration of the retained seawater , the residence time for retaining the seawater in which effective chlorine remains in the retention step corresponds to the residual chlorine concentration of the retained seawater, and the number of planktons of 50 μm or more before treatment is 10 ⁵ individuals / m ³ or more. Is controlled to a time during which the raw water is killed to a treatment standard of 10 individuals / m ³ or less after treatment, and the concentration of trihalomethane produced is suppressed to 0.1 mg / l or less ,
The control of this residence time was obtained in advance,
The relationship between elapsed time and trihalomethane concentration in seawater in which chlorine disinfectants remain at multiple concentrations with different residual chlorine concentrations,
This is performed based on the relationship between the residual chlorine concentration and the time required for killing the plankton to the processing standard .

(9) In addition, a chlorine disinfectant supply step for supplying chlorine disinfectant to seawater poured into the ballast tank of the ship and / or seawater discharged from the ballast tank, and retention for retaining the seawater supplied with the chlorine disinfectant for a predetermined time And an activated carbon treatment step of treating the seawater retained for a predetermined time with activated carbon.

(10) The activated carbon treatment step in (9) above is characterized in that the activated carbon treatment time is 0.5 to 20 minutes.

  Seawater (residual chlorine concentration 15 mg / l), which was supplied with a chlorine disinfectant and killed bacteria in a retention tank, was introduced into the activated carbon treatment equipment. The activated carbon treatment time (horizontal axis) and the trihalomethane concentration in the seawater (vertical axis FIG. 7 shows a graph obtained by measuring the relationship with (). Trihalomethane is generated by residual chlorine in the chlorine disinfectant in the residence tank, and when introduced into the activated carbon treatment device, the trihalomethane concentration is about 0.03 mg / l, but after 10 minutes the activated carbon treatment time is 0.01 mg / l. It decreases to the following, and almost reaches the adsorption equilibrium after 20 minutes.

Residual chlorine is reduced and decomposed by activated carbon and expires to stop generation of trihalomethane, and trihalomethane generated in the residence tank is also adsorbed. The time required for reductive decomposition of residual chlorine and adsorption removal of trihalomethane differs depending on the amount of chlorine disinfectant supplied to the retention tank, but the activated carbon treatment time is 0 within the practical supply amount of chlorine disinfectant. Residual chlorine can be reduced and decomposed in a range of 0.5 to 20 minutes to suppress generation of trihalomethane, and trihalomethane generated in the residence tank can be adsorbed and removed.
If the activated carbon treatment time is shorter than 0.5 minutes, the trihalomethane cannot be sufficiently adsorbed, and if the activated carbon treatment time is longer than 20 minutes, the activated carbon treatment device becomes too large to be mounted on a ship. In addition, the time for supplying the ballast water to the ballast tank becomes long and becomes a problem.

(11) Moreover, the residence process in said (8) is characterized by performing residence which makes time from supplying a chlorine disinfectant to supplying a chlorine reducing agent 0.5 to 20 minutes. is there.

(12) Further, the retention step in the above (9) or (10) is characterized in that retention is performed for 0.5 to 20 minutes from the supply of the chlorine disinfectant to the treatment with activated carbon. It is.

(13) Further, in the above (8) to (12), a filtration step of filtering seawater and capturing aquatic organisms is provided before the chlorine disinfectant supply step. .

(14) Further, in the above (8) to (13), a chlorine disinfectant is supplied so that the weight concentration of effective chlorine content in seawater is 5 to 100 mg / l. It is.

By supplying a chlorine disinfectant so that the weight concentration of effective chlorine in seawater is 5 to 100 mg / l, the quality of seawater (concentration of organic matter, etc.) and the type and quantity of plankton and bacteria that live are different. However, not only bacteria but also plankton of 50 μm or more can be killed to the treatment standard.
In addition, if a chlorine disinfectant is supplied and the weight concentration of effective chlorine in seawater is less than 5 mg / l, effective chlorine will not react with reducing substances or organic substances in water and remain, and bacteria and plankton cannot be killed. On the other hand, if it exceeds 100 mg / l, the amount of trihalomethane produced increases, and there are problems such as corrosion problems, the cost of the chlorine disinfectant, the problem that the chlorine disinfectant storage tank becomes large, and the cost increases.

(15) Further, in the above (8) to (14), an acid supply step is provided before the chlorine disinfectant supply step.

(16) In the above (15), the pH of the seawater to which the chlorine disinfectant is supplied is set to 5-7.

When acid is supplied to seawater to which chlorine disinfectant is supplied and the pH of the seawater is adjusted to 5 to 7, the form of free residual chlorine in seawater to which chlorine disinfectant is supplied is mostly hypochlorous acid (HOCl). It is preferable because of its high bactericidal efficacy. When the pH of seawater is lower than 5, the form of free residual chlorine is hypochlorous acid and Cl _{2. When the} pH is higher than 7, the form of free residual chlorine is hypochlorous acid and hypochlorite ion (OCl ⁻ ). In either case, the proportion of hypochlorous acid having a sterilizing effect which is 100 times higher than the others is reduced, and the sterilizing effect is lowered. Moreover, when the pH of seawater is 5-7, there is also an effect of suppressing the production of trihalomethane.
Hydrochloric acid or sulfuric acid is used as the acid to be supplied.

  It should be noted that an alkaline agent such as sodium hydroxide is neutralized to the treated ballast water that has been subjected to the killing process of the microorganisms, so that no trouble occurs even if the ballast water is discharged to the surrounding sea area.

  In the present invention, a chlorine disinfectant is supplied to the seawater poured into the ballast tank of the ship and / or the seawater discharged from the ballast tank, and retained for a predetermined time, and then supplied with a chlorine reducing agent or activated carbon treatment. As a result, plankton and bacteria in the seawater can be killed, seawater that does not contain pests that meet the ballast water treatment standards set by IMO can be supplied as ballast water, and the production of trihalomethanes by chlorine disinfectants can be achieved. Can be suppressed.

[Embodiment 1]
Hereinafter, an example of the best mode of the ballast water treatment apparatus according to the present invention will be specifically described with reference to the drawings.
FIG. 1 is a view showing a ballast water treatment apparatus according to the present embodiment. As shown in FIG. 1, the ballast water treatment apparatus according to the present embodiment is a seawater intake line 1 for taking seawater into a ship, and a coarse filtration apparatus that removes coarse substances in seawater taken by the seawater intake line 1. 2. Planktons present in the seawater from which coarse substances have been removed by the coarse filter device 2 for pumping in the seawater or pumping the ballast water in the ballast tank 10 described later to the filter device 4 described later Filter device 4, a chlorine disinfectant supply device 6 for supplying a chlorine disinfectant to kill bacteria in seawater filtered by the filter device 4, and a chlorine disinfectant supply device 6 for supplying filtered water filtered by the filter device 4 Diffuser 5 for diffusing the chlorinated disinfectant, retention tank 7 for retaining the seawater to which the chlorine disinfectant has been added for a predetermined time, and chlorine return for supplying the chlorine reducing agent to the seawater derived from the retention tank 7 Agent supply device 8, treated water feed line 9 for feeding treated water to which a chlorine reducing agent has been added to a ballast tank 10, which will be described later, and ballast tank 10 for storing treated water or untreated water fed from the treated water feed line 9. It is equipped with.
Hereinafter, each device will be described in more detail.

1. Coarse filter device Coarse filter device 2 receives water from a sea chest (seawater inlet) provided on the side of the ship and is taken by seawater intake line 1 by pump 3 and contains various small and large contaminants and aquatic organisms. Among them, coarse materials of about 10 mm or more are removed.
As the coarse filtration device, a cylindrical strainer (strainer) having a hole of about 10 mm, a hydrocyclone that separates coarse matter in the water flow by the difference in specific gravity, a device that captures and collects the coarse matter with a rotating screen, etc. are used. be able to.

2. Filtration device The filtration device 4 removes planktons present in the seawater from which coarse substances have been removed by the coarse filtration device 2, and has a mesh size of 10 to 200 μm.
The reason why the mesh opening is 10 to 200 μm is to reduce the frequency of backwashing and shorten the ballast water treatment time in the port of call while keeping the capture rate of zooplankton and phytoplankton at a certain level. In other words, if the mesh size is larger than 200 μm, the capture rate of zooplankton and phytoplankton is remarkably reduced. If the mesh size is smaller than 10 μm, the frequency of backwashing increases and the ballast water treatment time at the port of call becomes longer. Therefore, it is not preferable. In particular, it is preferable to use one having an opening of about 50 μm because the capture rate and the backwashing frequency can be set optimally.
Moreover, the filtration device 4 is preferably 1 day 200 meters ³ or more filtration rate per filtration area 1 m ² is obtained. However, there is no particular limitation when the size can be further reduced by integrating the filtration modules.

As a specific example of the filtration device 4, it is preferable to use a notch wire filter or a wedge wire filter.
A notch wire filter is a cylindrical element in which a wire with a notch (protrusion) is wound around a frame and the distance between the wires is maintained by the notch so that the size of the filtration passage is 10 to 200 μm. , Provided with valves and piping for water supply and backwashing. A specific example of this notch wire filter is a notch wire filter manufactured by Kanagawa Kikai Kogyo.
Japanese Laid-Open Patent Publication No. 2001-170416 discloses a plurality of notch wire filters as filtration elements and backwashing means. By attaching a small ultrasonic vibrator to the filtration element assembly substrate and each filtration element and adding ultrasonic vibration during backwashing, the backwashing effect is increased and the backwashing interval is extended to increase the filtration efficiency. Can do.
A wedge wire filter is a tubular element that has a triangular cross-section wound around a frame and adjusts the distance between the wires to maintain a filtration passage size of 10 to 200 μm in the casing. A valve and piping are provided. As a specific example of this wedge wire filter, there is a wedge wire filter manufactured by Toyo Screen Industries.

Another preferred specific example of the filtration device 4 is a laminated disk type filter. A laminated disk type filter is a ring-shaped disk formed by pressing doughnut-shaped disks having a plurality of oblique grooves formed on both sides in an axial direction to form a ring, and a gap formed by grooves of adjacent disks. The aquatic organisms are filtered through the water. By appropriately setting the size of the oblique grooves, the openings are set to 10 to 200 μm and filtered.
In the laminated disk type filter, the disk pressure is released during backwashing to increase the gap and remove the filtration residue. A specific example of this laminated disk type filter is Spin Klin Filter Systems manufactured by Arkal Filtration Systems.

  In addition to the two types of filtration devices described above, other various filtration devices such as a sealed sand filter, a filter cloth filter, and a metal fiber filter can be used as the filtration device 4.

3. Chlorine disinfectant supply device The chlorine disinfectant supply device 6 supplies chlorine disinfectant that kills bacteria to the seawater that is filtered by the filtration device and supplied to the diffuser 5. As the chlorine disinfectant to be supplied, sodium hypochlorite, calcium hypochlorite and chlorine gas can be used.

In addition, it is preferable to supply a chlorine disinfectant so that the weight concentration of the amount of effective chlorine in seawater may be 5-100 mg / l.
The reason for this is that if chlorine disinfectant is supplied and the weight concentration of effective chlorine in seawater is less than 5 mg / l, effective chlorine does not remain after reacting with reducing substances and organic substances in the water. It cannot be killed, and if it exceeds 100 mg / l, the amount of trihalomethane produced will increase, and there will be problems such as corrosion problems, the cost of chlorinated disinfectants and the increased cost of chlorinated disinfectant storage tanks. It is.

The chlorine disinfectant is supplied upstream of the diffuser 5 and / or to the diffuser 5. In the case of using a venturi pipe, which will be described later, as the diffuser 5, the chlorine disinfectant is supplied to the upstream side of the venturi pipe and / or the throat of the venturi pipe.
When supplying the chlorine disinfectant to the upstream side of the venturi pipe, the chlorine disinfectant is diffused to some extent in the flow path until reaching the throat of the venturi pipe where cavitation occurs. Mixing can be further promoted to further promote the penetration of the chlorine disinfectant into bacteria, thereby promoting the killing effect of the chlorine disinfectant.
In order to supply the chlorine disinfectant to the upstream side of the venturi pipe, an inlet for the chlorine disinfectant may be provided in the flow path upstream of the venturi pipe.
Further, when supplying the chlorine disinfectant to the throat of the venturi tube, the chlorine disinfectant supply pump is not necessary because it is self-primed by the ejector action of the venturi tube.

4). Diffuser It is preferable to use a Venturi tube as a diffuser that diffuses the chlorine disinfectant into the seawater filtered by the filtration device 4.
The Venturi tube diffuses the chlorine disinfectant into the seawater and damages or kills the plankton that has passed through the filtration device 4 by cavitation generated by the Venturi tube.
The Venturi pipe is composed of a throttle part where the pipe cross-sectional area gradually decreases, a throat part which is the minimum cross-sectional area part, and a widened part (diffuser part) where the pipe cross-sectional area gradually increases. Cavitation bubbles are generated due to a sudden drop in static pressure accompanying a rapid increase in flow velocity at the throat, and cavitations that cause the cavitation bubbles to grow rapidly collapse due to a sudden increase in pressure due to a decrease in flow velocity at the spreading portion are generated. To do.

Cavitation rapidly diffuses the chlorine disinfectant into seawater and promotes the bactericidal action of bacteria by the chlorine disinfectant. In this way, diffusing action of cavitation promotes mixing of chlorine disinfectant into seawater, so the supply amount of chlorine disinfectant can be reduced compared to simply injecting chlorine disinfectant. Thus, the supply amount of the chlorine reducing agent for detoxification can be reduced, and the production amount of trihalomethane can be reduced to reduce the environmental impact.
In addition, aquatic organisms in seawater are damaged or destroyed and killed by the action of OH radicals with strong impact pressure, shearing force, high temperature and strong oxidizing power due to the collapse of cavitation bubbles. According to the venturi cavitation, the protozoan having a relatively hard shell, the outer shell of zooplankton, can be destroyed, and the penetration of the chlorine disinfectant can be promoted to be surely killed.

In addition, when supplying seawater to a venturi pipe, it is preferable to feed seawater so that the flow rate of seawater at the throat of the venturi pipe is 10 to 40 m / sec.
The reason for this is that when a ballast water treatment device is installed in the middle of a pipe that takes seawater and passes it to the ballast tank, the flow rate of seawater in the pipe is usually 2 to 3 m / s at the venturi pipe entrance. If the flow velocity at the throat of the tube is less than 10 m / sec, the rate of increase in the flow velocity at the throat is not sufficient, and the rapid decrease in static pressure associated therewith is not sufficient, so cavitation does not occur even under atmospheric pressure, If the flow velocity at the throat of the venturi pipe is higher than 40 m / s, the cavitation phenomenon will occur excessively, the pressure loss associated with the passage of the venturi pipe will be excessive, and the energy consumed for water supply will be excessive, resulting in excessive pump power. This is because the cost is high.

Moreover, when supplying seawater to a venturi pipe, it is preferable to feed seawater so that the pressure loss head of the venturi pipe is 5 to 40 m.
The reason for this is that if the head loss is less than 5 m, cavitation cannot be generated, and if it is greater than 40 m, the large flow pump used as a ballast water pump provided in the ship cannot cope with the problem. is there.

  As a diffuser, you may use the stirrer which rotates the static mixer and stirring blade which produce a stirring flow other than a venturi pipe | tube in a seawater flow path.

5. Retention tank Retention tank 7 is for contacting chlorine generated from a chlorine disinfectant with plankton and bacteria for a time sufficient to kill them and as short as possible so as to suppress the production of trihalomethane. It retains the diffused seawater with the addition of a chlorine disinfectant. The size and shape of the retention tank 7 are determined and flowed at a predetermined speed so as to stay for a predetermined time until the residual chlorine is expired by supplying a chlorine reducing agent.
For example, a long flow path may be formed by providing a plurality of partitions in the tank to ensure the residence time in the tank.
Alternatively, the retention tank 7 may be a simple storage tank that opens the discharge gate or discharges the seawater when the predetermined time has elapsed after storage.

6). Chlorine reductant supply device Chlorine reductant supply device 8 supplies chlorine reductant to seawater that has been added with a chlorine disinfectant and stays in the retention tank 7 for a predetermined time to reduce and expire the effective chlorine remaining in the seawater, It suppresses the generation of trihalomethane. In order to supply the chlorine reducing agent, an inlet for the chlorine reducing agent may be provided in the flow path for discharging seawater from the retention tank 7.
As the chlorine reducing agent to be supplied, it is desirable to use sodium thiosulfate, sodium sulfite, or sodium bisulfite from the viewpoints of cost and ease of handling. Further, hydrogen peroxide water may be used as the chlorine reducing agent.

The operation of the present embodiment configured as described above will be described.
By operating the pump 3, seawater is taken into the ship from the seawater intake line 1. At that time, the coarse filter 2 removes large and small contaminants and aquatic organisms of about 10 mm or more from seawater.
Seawater from which coarse substances have been removed is supplied to the filtration device 4, and zooplankton, phytoplankton, and the like having a size corresponding to the opening of the filtration device 4 are removed.
Aquatic organisms and the like captured by the coarse filtration device 2 and the filtration device 4 are washed away by backwashing the filters of the coarse filtration device 2 and the filtration device 4 and returned to the sea. Even if aquatic organisms captured by the filtration device 4 are returned to the sea, the ecosystem is not adversely affected because they are in the same sea area. That is, in this example, since the treatment is performed when the ballast water is loaded, the backwash water of the coarse filtration device 2 and the filtration device 4 can be discharged as it is.

The seawater filtered by the filtration device 4 is supplied with a chlorine disinfectant from the chlorine disinfectant supply device 6, and the seawater supplied with the chlorine disinfectant is supplied to a venturi pipe serving as the diffuser 5.
In the Venturi tube, cavitation is generated by the above-described mechanism, and the diffusion of the chlorine disinfectant into the seawater is promoted to enhance the bacteria killing effect. Furthermore, OH radicals with strong impact pressure, shearing force, high temperature, and oxidizing power act on aquatic organisms in seawater by cavitation, damaging or destroying aquatic organisms and killing them.

  Seawater in which the chlorine disinfectant is diffused in the Venturi tube is guided to the retention tank 7 and stays for a predetermined time, and plankton and bacteria are killed by the effective chlorine generated from the chlorine disinfectant. The residence time for retaining the seawater in the residence tank 7 is set in the range of 0.5 to 20 minutes so that the large plankton is sufficiently killed during the residence and trihalomethane generated by the residual chlorine is as little as possible.

  A chlorine reducing agent supply device 8 supplies chlorine reducing agent to the seawater that has been retained and discharged from the residence tank 7 for a predetermined time to cause the residual chlorine to expire and suppress the generation of trihalomethane. 9 is stored in the ballast tank 10.

In the above example, the chlorine disinfectant is supplied to the upstream side of the venturi pipe and / or the throat of the venturi pipe, but may also be supplied to the downstream side of the venturi pipe. When supplying to the downstream side of the venturi tube, bacteria attached to plankton and the like are peeled off by cavitation. Therefore, by supplying a chlorine disinfectant downstream of the venturi tube, The effect of killing bacteria can be promoted by the action of a chlorine disinfectant on the species.
In addition, the sterilization of plankton that does not die while damaging the outer shell due to cavitation can penetrate the chlorinated fungicide and promote the killing effect of the chlorinated fungicide. It can be killed with a small amount of added chlorine disinfectant compared with the treatment with a chlorine disinfectant alone.

In addition, although said example is a case where a process is performed when seawater is loaded into a ballast tank, when a seawater is loaded into a ballast tank, it may process, when discharging from a ballast tank, without processing. In this case, untreated ballast water is supplied from the ballast tank to the filtration device 4, and thereafter the same processing as described above is performed. However, in this case, since the ballast water to which the chlorine disinfectant is added upstream of the venturi pipe is drained to the sea, it is necessary to completely detoxify the chlorine disinfectant. Therefore, in this case, the amount of the chlorine reducing agent supplied by the chlorine reducing agent supply device 7 is different from the case of supplying the treated water to the ballast tank, and the remaining chlorine disinfectant is reduced and the ballast water is discharged. It is necessary to make it an amount that does not affect the environment of the port.
Moreover, you may make it perform the killing process of the aquatic organism in ballast water both when loading seawater into a ballast tank, and when discharging | emitting from a ballast tank. In that case, the treatment at the time of discharging the ballast water may be light.

  As described above, in the present embodiment, zooplankton and phytoplankton having a size of 10 to 200 μm or more are removed by the filtration device 4, and the plankton and bacteria are removed by supplying a chlorine disinfectant and retaining the plankton for a predetermined time. Since it was killed and the residual chlorine was reduced and expired, the treatment of ballast water that reliably meets the ballast water standard set by IMO can be realized, and the production of trihalomethane generated from the residual chlorine can be suppressed.

  In addition, although the example shown in FIG. 1 assumes that the detoxification treatment of ballast water is performed at the time of water intake, the timing at which the treatment is performed at the time of water intake, at the time of drainage, or both, It can be determined by the amount of microorganisms inhabiting the sea area and the operating conditions of the ship.

[Embodiment 2]
FIG. 2 is an explanatory diagram of the second embodiment of the present invention, and the same parts as those of the first embodiment are denoted by the same reference numerals.
This embodiment is different from the first embodiment in that an activated carbon treatment tank 11 is arranged downstream of the retention tank 7, and the seawater in which the chlorine disinfectant is diffused in the retention tank 7 is retained for a predetermined time. This is the point that seawater is introduced into the activated carbon treatment tank 11 after killing the species. With such an arrangement, residual chlorine in seawater can be reduced and decomposed by activated carbon in the activated carbon treatment tank 11 to suppress generation of trihalomethane, and trihalomethane generated in the retention tank 7 can be adsorbed and removed. Seawater treated with activated carbon in the activated carbon treatment tank 11 is stored in a ballast tank.
As the activated carbon treatment tank 11, one in which the shape and size are set so that the activated carbon is gently flowed in the tank and the flow rate of seawater to be introduced is adjusted, or one filled with activated carbon can be used. If granular activated carbon is used, it can be made to flow gently by the flow through the activated carbon treatment tank 11 and can be easily replaced.
The activated carbon treatment time in the activated carbon treatment tank 11 is adjusted within a range of 0.5 to 20 minutes depending on the amount of chlorine disinfectant supplied to the seawater so that residual chlorine can be sufficiently reduced and decomposed and the generated trihalomethane can be adsorbed and removed. Is set.

In the present embodiment, as shown in FIG. 2, the chlorine reducing agent supply device 8 is used in combination and the chlorine reducing agent is also supplied to the seawater retained in the retention tank 7 for a predetermined time. In addition, the residual chlorine can be reliably expired, the activated carbon treatment tank 11 can be downsized, and the amount of activated carbon used can be reduced.
However, the activated carbon treatment tank 11 may be used alone without using the chlorine reducing agent supply device 8.
Further, instead of the activated carbon treatment tank, an adsorption tank provided with an adsorbent that adsorbs trihalomethane may be provided, and a chlorine reducing agent may be supplied to seawater retained in the retention tank for a predetermined time. Residual chlorine is reduced by chlorine reducing agent and expired, and trihalomethane produced by the adsorbent is adsorbed in the adsorption tank. A resin-based adsorbent can be used as the adsorbent.

FIG. 3 is an explanatory diagram of a modification of the second embodiment of the present invention, and the same reference numerals are given to the same parts as those of the second embodiment.
This modification is different from the second embodiment in that the residence tank 7 and the activated carbon treatment tank 11 are partly modified from the ballast tank 10. By using a part of the ballast tank 10 as the retention tank 7 and the activated carbon treatment tank 11, there is no need to newly provide the retention tank 7 and the activated carbon treatment tank 11, and it is easy to apply to existing ships and reduce equipment costs. it can.

  In addition, you may provide the chlorine disinfectant supply amount control means which controls the quantity of the chlorine disinfectant supplied from the chlorine disinfectant supply apparatus 6 of said embodiment. As an example of a chlorine disinfectant supply amount control means, a chlorine disinfectant supply for measuring the redox potential of seawater supplied with a chlorine disinfectant and adjusting the chlorine disinfectant supply amount based on the measured value of the redox potential Provide a quantity control device.

Although the chlorine disinfectant supplied to kill bacteria is consumed by reducing substances in the seawater, seawater taken as ballast water has different water quality depending on the sea area, and the content of reducing substances is also different. For this reason, in order to sufficiently kill bacteria, it is necessary to adjust the supply amount of the chlorine disinfectant to an amount suitable for the water quality.
Therefore, in order to adjust the supply amount of the chlorine disinfectant to an amount suitable for the water quality, the oxidation-reduction potential of seawater supplied with the chlorine disinfectant is measured, and the oxidation-reduction potential is 800 mV or more with respect to the silver / silver chloride electrode. Adjust so that. By setting the oxidation-reduction potential to 800 mV or higher, the concentration of chlorine remaining in the seawater can be made sufficient to kill bacteria.
As described above, by adjusting the supply amount of the chlorine disinfectant according to the amount of the reducing substance in the seawater or filtered water, it is possible to surely kill the aquatic organisms and to prevent excessive supply of the chlorine disinfectant.

  As another example of the chlorine disinfectant supply amount control means, the residual chlorine concentration is measured by measuring the residual chlorine concentration of the seawater supplied with the chlorine disinfectant discharged from the retention tank and killed by the living organisms. A chlorine disinfectant supply amount control device that adjusts the chlorine disinfectant supply amount based on the above may be provided. In this way, the supply amount of the chlorine disinfectant can be adjusted to an amount suitable for the water quality.

  In the above embodiment, it has been described that the chlorine disinfectant supplied by the chlorine disinfectant supply device 6 may be sodium hypochlorite. In this case, the seawater is directly electrolyzed to reduce hypoxia. Cost can be reduced by using an apparatus for generating sodium chlorate.

In addition, since sodium hypochlorite may decompose at a high temperature of 30 ° C. or higher and the concentration may decrease, hypochlorite is prevented in the sodium hypochlorite storage tank in order to prevent decomposition of sodium hypochlorite. It is preferable to provide a temperature rise prevention means for preventing the temperature of sodium chlorate from rising.
Thereby, decomposition | disassembly of sodium hypochlorite can be prevented, the consumption of sodium hypochlorite can be suppressed, and the processing expense of ballast water can be suppressed.
As a specific example of the temperature rise prevention means, for example, there is a storage tank heat insulating device for insulating a sodium hypochlorite solution storage tank to prevent the temperature of sodium hypochlorite in the storage tank from rising during navigation. .
In addition, if the sodium hypochlorite solution is cooled in advance and stored in a storage tank equipped with a storage tank heat insulating device, temperature control of sodium hypochlorite can be ensured, and sodium hypochlorite Can be more reliably prevented.
Moreover, the cooling heat exchanger which is provided in a storage tank and cools the sodium hypochlorite solution in a storage tank as another example of a temperature rise prevention means is mentioned. In the cooling heat exchanger, cooling water can be used as a refrigerant, but if seawater is used as the refrigerant, the operating cost for cooling can be suppressed.

  Each of the above examples is for preventing the decomposition of sodium hypochlorite, but the sodium hypochlorite is obtained by electrolyzing seawater or sodium chloride produced by the decomposition of sodium hypochlorite. By providing an electrolytic device that generates or regenerates, the concentration of sodium hypochlorite reduced by decomposition can be recovered.

Moreover, the killing effect of bacteria can be increased by providing an acid supply step before the chlorine disinfectant supply step and setting the pH of seawater to which the chlorine disinfectant is supplied to 5 to 7.
When acid is supplied to seawater to which chlorine disinfectant is supplied to adjust the pH of the seawater to 5 to 7, the form of free residual chlorine in seawater to which chlorine disinfectant is supplied is mostly hypochlorous acid (HOCl), This is preferable because of its high bactericidal efficacy. When the pH of seawater is lower than 5, the form of free residual chlorine is hypochlorous acid and Cl _{2. When the} pH is higher than 7, the form of free residual chlorine is hypochlorous acid and hypochlorite ion (OCl ⁻ ). In either case, the proportion of hypochlorous acid having a sterilizing effect which is 100 times higher than the others is reduced, and the sterilizing effect is lowered. Moreover, when the pH of seawater is 5-7, there is also an effect of suppressing the production of trihalomethane.
Note that hydrochloric acid or sulfuric acid is used as the acid to be supplied.

Using the ballast water treatment apparatus of Embodiment 2 (using the activated carbon treatment tank 11 alone), an experiment for killing plankton and bacteria in seawater was conducted. Sodium hypochlorite is supplied as a chlorine disinfectant so that the effective chlorine amount is 20 mg / l, and after 10 minutes retention in the retention tank, the activated carbon treatment tank 11 charged with coconut shell granular activated carbon is used for 10 minutes. went.
Plankton inhabited 5 × 10 ⁵ pieces / m ^{3 in} the seawater before treatment, but after the above treatment, the number decreased to 4 pieces / m ³ , and the treatment fulfilled the IMO ballast water standard. In addition, the trihalomethane concentration is as low as about 0.03 mg / l in the seawater at the outlet of the retention tank, and is extremely low at 0.002 mg / L in the seawater at the outlet of the activated carbon treatment tank 11, so there is no problem with environmental impact. Was confirmed.

It is explanatory drawing of the ballast water treatment apparatus which concerns on one embodiment of this invention. It is explanatory drawing of the ballast water treatment apparatus which concerns on other embodiment of this invention. It is explanatory drawing of the modification of other embodiment of this invention. It is a graph which shows the time change of the trihalomethane density | concentration in seawater after chlorine disinfectant injection | pouring. It is a graph which shows the relationship between the residual chlorine density | concentration in seawater required in order to satisfy | fill the standard of IMO, and the contact time of the plankton and effective chlorine which are death targets. It is a graph which shows the time change of the trihalomethane density | concentration in the seawater after chlorinating agent injection | pouring about five cases, when the chlorine disinfectant injection rate is 5 mg / l, 10 mg / l, 20 mg / l, 50 mg / l, and 100 mg / l. . It is a graph which shows the relationship between the activated carbon processing time when the seawater which killed bacteria with the chlorine disinfectant was introduce | transduced into the activated carbon treatment tank, and was made to stay, and the trihalomethane density | concentration in seawater.

Explanation of symbols

  2 Coarse filtration device, 3 pump, 4 filtration device, 5 diffuser, 6 chlorine disinfectant supply device, 7 residence tank, 8 chlorine reducing agent supply device, 10 ballast tank, 11 activated carbon treatment tank.

Claims (3)

A chlorine disinfectant supply step for supplying chlorine disinfectant to seawater poured into the ballast tank of the ship and / or seawater discharged from the ballast tank;
A retention step of retaining seawater in which effective chlorine remains after being supplied with a chlorine disinfectant;
A chlorine reducing agent supply step for supplying a chlorine reducing agent to the retained seawater, reducing residual chlorine and making it expire to suppress the production of trihalomethane,
Corresponding to the residual chlorine concentration of the retained seawater , the residence time for retaining the seawater in which effective chlorine remains in the retention step corresponds to the residual chlorine concentration of the retained seawater, and the number of planktons of 50 μm or more before treatment is 10 ⁵ individuals / m ³ or more. Is controlled to a time during which the raw water is killed to a treatment standard of 10 individuals / m ³ or less after treatment, and the concentration of trihalomethane produced is suppressed to 0.1 mg / l or less ,
The control of this residence time was obtained in advance,
The relationship between elapsed time and trihalomethane concentration in seawater in which chlorine disinfectants remain at multiple concentrations with different residual chlorine concentrations,
A ballast water treatment method, which is performed based on the relationship between the residual chlorine concentration and the time required to kill plankton to the treatment standard .   The ballast water treatment method according to claim 1, further comprising a filtration step of capturing aquatic organisms by filtering seawater before the chlorine disinfectant supply step. 3. The ballast water treatment method according to claim 1, wherein the chlorine disinfectant is supplied so that the weight concentration of the effective chlorine amount in the sea water is 5 to 100 mg / l.

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