JPH10165964A - Flocculation and sedimentation of turbid water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently sediment a suspended substance having a small particle size without using a conventional flocculant. SOLUTION: In a method for flocculating and sedimenting turbid water, turbid water and seawater are charged in a sedimentation basin 1 in a mixed state to be allowed to stand for a predetermined time in this state. By this constitution, a suspended substance contained in turbid water, mainly, colloidal particles of clay contained therein is neutralized in surface potential by cations in seawater and electrostatic repulsive force between particles becomes weak and the colloidal particles are flocculated in a floc state to be sedimented on the bottom of the sedimentation basin 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating turbid water and muddy water generated during construction work by coagulation and sedimentation.

[0002]

2. Description of the Related Art Turbid water and muddy water generated during construction and civil engineering work contain a large amount of insoluble suspended solids (SS). It is necessary to remove suspended substances in advance based on regulations such as the Water Pollution Control Law so as not to have any adverse effects.

[0003] The removal treatment of such suspended substances is regarded as an important item of the turbid water treatment together with the pH adjustment. When considering mainly the removal of SS, a natural precipitation method using no flocculant and a method using a flocculant are used. Flocculation and precipitation method.

Here, the natural sedimentation method does not use a flocculant, and thus does not require a stirrer or a flocculant injection pump, and is the simplest in terms of equipment. However, it is a method of sedimentation by gravity. For example, fine clay particles having a particle size of about 5 μm sediment only about 6 cm per hour. Therefore, it is not very suitable for turbid water containing a large amount of suspended matter having a small particle size.

On the other hand, in the coagulation sedimentation method, a suspended substance is formed into a large floc by a flocculant and the floc is settled in a sedimentation tank or a thickener, so that even suspended particles having a small particle size can be efficiently sedimented. Can be.

[0006]

Here, in an area where the importance of environmental conservation is high, it may not be appropriate to use a coagulant as a drug. In such a case, it is difficult to employ not only the coagulation sedimentation method but also centrifugal sedimentation and sand filtration which require the use of a coagulant. As a result, the natural sedimentation method must be employed.

However, as described above, the sedimentation speed of fine particles in turbid water is extremely slow, and the natural sedimentation method cannot hardly precipitate suspended substances having a small particle size. In the worst case, there is a problem that untreated turbid water overflowing from the sedimentation basin may flow into rivers and the sea and deteriorate water quality.

The present invention has been made in view of the above-mentioned circumstances, and provides a method for coagulating and sedimenting turbid water capable of efficiently precipitating a suspended substance having a small particle size without using a conventional coagulant. The purpose is to provide.

[0009]

According to a first aspect of the present invention, there is provided a method for coagulating and sedimenting turbid water, the method comprising: mixing turbid water with seawater; The substance is to coagulate and precipitate.

[0010] In the method for coagulating and sedimenting turbid water according to the present invention, a sedimentation basin is formed in or near a turbid water generation area, and when turbid water is generated in the area, the turbid water is generated. Is stored in the sedimentation basin in a state of being mixed with seawater, and the suspended solids contained in the turbid water are coagulated and settled in the sedimentation basin.

Further, the method for coagulating and sedimenting turbid water according to the present invention creates an inland water area which is cut off from an outer water area by installing a predetermined partition body in a coastal area, and uses the inner water area as the sedimentation pond. It is.

In the method for coagulating sedimentation of turbid water according to the present invention, the suspended substance contained in the turbid water, mainly clay colloid particles, is neutralized in surface potential by cations in seawater and electrostatic repulsion between the particles is achieved. Are weakened and easily flocculate. That is, seawater acts as a coagulant similarly to, for example, conventionally used PAC (polyaluminum chloride).

Conventional coagulants neutralize the surface potential of colloidal particles with polyvalent cations such as aluminum ions, iron ions, magnesium ions, and zinc ions. However, the present applicant is a monovalent cation. It was discovered that seawater containing a large amount of sodium ions had a sufficient coagulation effect, and this was confirmed by experiments.

Here, turbid water means all solutions containing insoluble suspended and suspended substances, and in a narrow sense generated by rain falling on excavated soil such as an exposed portion of the scalp surface or a tunnel by a cutting work. In addition to turbid water, it shall also include stabilizing liquid for stabilizing perforated walls used in cast-in-place pile method, underground continuous wall method, muddy water shield method, etc.

The proportion of seawater to be added to the turbid water may be appropriately set according to the type of suspended substance contained in the turbid water, the turbidity, etc. In the case of turbid water generated by rain falling on the ground,
If the mixed amount of seawater is 5 to 10% of turbid water, a remarkable coagulation effect can be obtained.

Further, in the method for coagulating and sedimenting turbid water according to the present invention, a sedimentation basin is formed in advance in or near the turbid water generation area, and suspended substances contained in the turbid water are sedimented and settled in the sedimentation basin.

That is, when turbid water is generated in the above-mentioned area due to, for example, rainfall, the turbid water is stored in a sedimentation basin in a state of being mixed with seawater. In this way, as described above, the seawater acts as a coagulant, and the suspended substances contained in the turbid water are coagulated and settled in the sedimentation basin.

The place where the sedimentation basin is installed is arbitrary, but one place where turbid water is easily stored is one standard. That is, in the case where turbid water is generated by rainfall, for example, turbid water can be allowed to flow naturally into the sedimentation basin by being installed on the downstream side of the development area which is a turbid water generation area,
In the case where turbid water is generated as a stabilizing liquid, install in a place that is easily transported via a pump or the like.

On the other hand, the location of the sedimentation basin may be determined on the basis of a place where seawater can be easily transferred. For example, by setting a predetermined partitioning body in the coastal area, the inland water area isolated from the outer water area can be created. If a sedimentation basin is used, the pipeline for transferring seawater and discharging the supernatant water will be shortened, and running costs will be reduced.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the method for coagulating and sedimenting turbid water according to the present invention will be described below with reference to the accompanying drawings.

In the method for coagulating and sedimenting turbid water according to the present embodiment, first, as shown in FIG. 1, turbid water and seawater are charged into a sedimentation basin 1 in a mixed state, and then left for a predetermined time in such a state.

The turbid water includes turbid water in a narrow sense generated by rain falling on a portion where the ground surface is exposed by the cutting work and excavated earth and sand excavated by tunnel construction or the like. It also includes a stabilizing solution for stabilizing the pore wall used in the wall method, the muddy water shield method, and the like, for example, muddy water mainly containing bentonite.

The proportion of seawater added to the turbid water can be appropriately set according to the type of suspended substance contained in the turbid water, the turbidity, and the like. Is preferably 5 to 10% of turbid water, for example.

The turbid water and the seawater are sufficiently stirred in advance before being put into the sedimentation basin 1, and a coagulation stirrer is used if necessary.

When seawater is mixed with turbid water and allowed to stand in this way, the suspended substance contained in the turbid water, mainly colloidal particles of clay, is neutralized in surface potential by cations in the seawater and electrostatic repulsion between the particles is caused. The force weakens and flocculates, and sediments at the bottom of the sedimentation basin 1. The pH of the supernatant water is adjusted if necessary, and then discharged to rivers and the sea.

Next, the effect of the coagulation-sedimentation method according to the present embodiment has been confirmed by experiments, and the outline thereof will be described below.

The experiment was conducted by collecting turbid water generated by rain that had fallen on the ground and collecting it as a sample. The turbid water was allowed to settle as it was, and the seawater equivalent to 10% of turbid water was mixed with the turbid water to settle. It was compared with the case where it was performed.

FIG. 2 is a graph showing the change over time in turbidity at a position 30 cm deep from the water surface. As can be seen from the figure, in the case of only turbid water, the turbidity was 500 to 600 ppm even after 8 hours, and hardly decreased from the beginning. This indicates that the fine particles contained in the turbid water hardly settled over time and remained floating in the water.

On the other hand, when seawater was mixed with the turbid water, the turbidity decreased remarkably within several hours, and after 8 hours, fell below 50 ppm, which is the standard for discharge in areas where environmental regulations are severe. This indicates that the fine particles contained in the turbid water rapidly aggregated and settled under the action of seawater.

It is considered that such coagulation and precipitation of SS by seawater is caused by sodium ions, which are monovalent cations in seawater, neutralizing the surface potential of colloidal particles in turbid water. It has been considered that only polyvalent cations such as iron ion, magnesium ion and zinc ion are effective in neutralizing the surface potential of colloid particles.

The above-mentioned experimental results reverse this conventional idea, and demonstrate that sodium ions, which are monovalent cations, have an effect of sufficiently coagulating suspended substances. The amount of seawater is 5%
An experiment was separately performed, and it was confirmed that a certain result could be obtained even with such an amount.

As described above, according to the method for coagulating and sedimenting turbid water according to the present embodiment, the suspended suspended solids contained in the turbid water, particularly the spontaneous sedimentation velocity, are extremely high only by mixing seawater with the turbid water and allowing it to stand. A small clay component having a slow particle size can be efficiently coagulated and precipitated.

That is, seawater becomes a natural coagulant in place of, for example, PAC (polyaluminum chloride) conventionally used, and it is possible to perform turbid water treatment without minding the diffusion of the artificial agent into the environment. Become. Therefore, it is an extremely effective turbid water treatment method in an area where the regulations for environmental protection are strict. In addition, since there is no cost to procure seawater, which is a flocculant, it can be said that this method is a very economical turbid water treatment method when a large amount of turbid water needs to be treated at a site close to the sea.

In this embodiment, after mixing seawater with turbid water,
Although the sedimentation basin is settled, the sedimentation basin is not necessarily required, and may be settled in a tank or the like.

In this embodiment, the seawater is mixed with the turbid water, and then the flocculated sedimentation tank is allowed to stand for coagulation sedimentation. However, instead of such a sedimentation tank or a combination with a sedimentation tank, a thickener is used. You may use it.

In this embodiment, the location where the sedimentation basin 1 is installed and the location where the turbid water is generated are not particularly mentioned. However, the location may be specifically as shown in FIG. 3 (a). . That is, the creation area 11 as a turbid water generation area
A pit 12 for stirring and a sedimentation basin 1 are arranged adjacent to the downstream side of the vessel, and a seawater pipe (not shown) is connected to the pit 12.

In such a location, the turbid water generated by the rainwater that has fallen into the development area 11 flows in the direction of the arrow in the figure and flows into the stirring pit 12 together with the seawater. Transfer to Pond 1 and allow to stand for a predetermined time.

In this manner, as described above, the suspended substance contained in the turbid water is neutralized by the cations in the seawater to neutralize the surface potential, the electrostatic repulsion between the particles is weakened, and the suspended substances are flocculated. It settles at the bottom of the sedimentation basin 1. The supernatant water may be discharged to the sea after pH adjustment as necessary.

According to this configuration, as described above, the treatment of turbid water can be performed without any concern about the effect on the environment, and the coagulation sedimentation separation can be performed much more efficiently than natural sedimentation. Therefore, even if the area of the formation area 11 is large, the effect that the scale of the sedimentation basin 1 can be small can be obtained.

It should be noted that the location configuration shown in FIG.
(b) As shown in FIG.
To create an inland water area that is cut off from the outer water area, and if the inner water area is the sedimentation basin 1, the length of the seawater pipe for transferring seawater and the length of the discharge pipe for discharging the supernatant water can be reduced. In addition, the running cost for transferring the supernatant water or seawater can be saved.

[0041]

As described above, according to the method for coagulating and sedimenting turbid water according to the first aspect of the present invention, suspended substances such as clay having a small particle size can be efficiently used without using a conventional coagulant. Coagulation and sedimentation can be performed well, and turbid water treatment can be performed without worrying about the effect on the environment even in areas where environmental protection regulations are strict.

According to the method for coagulating and sedimenting turbid water according to the second aspect of the present invention, as in the first aspect, a suspended substance such as clay having a small particle size can be used without using a conventional coagulant. Can be efficiently coagulated and settled, and the size of the sedimentation basin can be reduced even if the area of the turbid water generation area increases.

According to the method for coagulating and sedimenting turbid water of the present invention according to the third aspect, in addition to the effect of the second aspect, the scale of equipment required for transporting seawater and discharging supernatant water is reduced. In addition, there is an effect that their running costs can be saved.

[0044]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a state in which a method of coagulating and sedimenting turbid water according to an embodiment is performed.

FIG. 2 is a graph showing the results of a verification test of the method of coagulating and sedimenting turbid water according to the embodiment.

FIG. 3 is a cross-sectional view showing the location of the method for coagulating and sedimenting turbid water according to the embodiment.

[Explanation of symbols]

 1 sedimentation basin 11 creation area (turbid water generation area) 13 embankment (partition body)

Claims (3)

[Claims] 1. A method for coagulating and sedimenting turbid water, comprising mixing suspended water contained in the turbid water by mixing seawater with the turbid water. 2. A sedimentation basin is formed in or near a turbid water generation area, and when turbid water is generated in the area, the turbid water is stored in the sedimentation basin in a state of being mixed with seawater and contained in the turbid water. A method for coagulating and sedimenting turbid water, comprising coagulating sedimentation of a suspended substance in the sedimentation tank. 3. The method for coagulating and sedimenting turbid water according to claim 2, wherein an internal water area isolated from an external water area is created by installing a predetermined partition body in a coastal area, and the internal water area is used as the sedimentation basin.