JPH0720596B2 - Contaminated water treatment method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for treating a polluted water area for efficiently purifying a polluted estuary area, a river, a lake, a pond, a moat, or the like.

[Conventional technology]

In polluted waters such as estuaries, rivers, lakes, ponds, and moats, water pollution progresses due to pollutants flowing in from the outside and pollutants eluted from mud accumulated on the bottom of the water. In particular, when the mud deposited on the bottom of the water is decomposed, nutrient salts such as nitrogen and phosphorus are eluted, and a large amount of algae is likely to be generated. As a result, the visibility is remarkably reduced, and further, these algae precipitate and accumulate on the bottom of the water, and when they decompose, the algae grow again due to the nutrient salts that elute, which repeats a vicious cycle.

Oxygen in water is consumed in large quantities when aerobic bacteria decompose pollutants. Oxygen is supplied to the water during the daytime by photosynthesis of algae, but during rainy weather or at night, photosynthesis stops and only breathing occurs, and oxygen is consumed on the contrary,
Mud accumulated on the bottom of the water becomes anaerobic and pollution progresses.

Moreover, in order to aerobically decompose the organic substances in the water in this water area, the method of aerating and stirring the water in the water area is shown in "Study on river purification by aeration" (The 26th Sewer Research Conference Lecture) It has been demonstrated that it is effective in improving the self-cleaning coefficient of rivers and preventing odors.

[Problems to be Solved by the Invention]

According to the above method, oxygen can be supplied to the water and the mud accumulated on the bottom by simultaneously performing aeration and stirring in the water and the water area. The decomposition can be accelerated.

However, even by the above method, the particles and the algae floating in water have the same electric charge (usually negative) on the surface, so that the particles do not repel each other and precipitate. Therefore, there is a problem that the transparency is not improved.

The present invention flocculates particles suspended in the water of a polluted water area such as pollutants and algae that are extremely difficult to settle and reduces the transparency of water to precipitate them, and aerobically decomposes the precipitated precipitates. It is an object of the present invention to provide a method for treating a polluted water area, which makes it possible to obtain transparent water quality.

[Means for Solving the Problems]

In order to achieve the above object, the method for treating a polluted water area of the present invention is a method for causing a horizontal water flow by an aeration stirring device installed in the water of a polluted water area to simultaneously perform aeration and stirring to dissolve pollutants such as soluble organic substances. For particles that decompose and are less likely to sediment such as pollutants and algae that are suspended in water and reduce the transparency of water, add a coagulant to the rapid stirring area of the aeration stirrer to reduce the The gist of the present invention is to flocculate the particles in a rapid stirring region to cause precipitation, and aerobically decompose the precipitated precipitate to obtain transparent water quality.

〔Example〕

 The present invention will be described below based on the illustrated embodiments.

In the figure, 1 is a pond having a width of 28 m and a length of 30 m,
As shown in FIG. 1, water in the pond is stirred in the pond 1 and two aeration stirring devices 2, 2 are installed on the diagonal of the pond so that a horizontal water flow is generated and a circulating water flow is generated.

This aeration and agitation device 2 also aerates the water in the water area, and various types can be adopted. This aeration stirring device 2
If the motor capacity of 2 is set to 2.2 KW, the flow velocity in the agitating part of the aeration agitating device or the region immediately after agitation becomes 1 m / sec, and rapid agitation is performed. In addition, the flow velocity in other water areas is a slow stirring area of 15 cm / sec. Then, the motor of the aeration and agitation device 2 is controlled by an inverter or the like to control the number of revolutions thereof so that the flow velocity in each region can be adjusted.

As described above, when the aeration and agitation device 2 is provided in the water area and the water in the water area is agitated and aerated, oxygen is supplied into the water, whereby suspended substances such as soluble organic substances undergo aerobic decomposition.

By the way, since particles such as pollutants and algae floating in water have the same electric charge (usually negative) on their surfaces, they repel each other and float, and do not easily settle.
In order to accelerate this precipitation, the flocculant 4 is added in the rapid stirring region 3 of the aeration stirring device 2, that is, to the aeration part of the aeration stirring device 2, and the aeration is performed simultaneously with the rapid stirring, so that the particles and the aggregating agent are efficiently treated. Contact well to neutralize the charge on the particle surface. After that, the particles are flocculated in the slow-speed stirring region, and the particles are precipitated by stopping the aeration and stirring device 2. The precipitate decomposes if left to stand, pollutants elute and the vicious cycle of water pollution repeats. However, the oxygen supplied from the aeration and agitation device 2 decomposes the precipitate aerobically. It is possible to suppress the elution of pollutants and nutrient salts such as nitrogen and phosphorus to suppress the growth of algae.

The flocculating agent 4 is added in the rapid stirring region 3 for about 1 to 2 hours, and after the addition is completed, the aeration stirring device 2 is operated for about 1 hour to perform slow stirring, and then the aeration stirring device 3 is stopped. To do.

The time T1 [H] for adding the flocculant 4 in the rapid stirring area 3 and rapid stirring and the slow stirring time T2 [H] for stopping the aeration stirring device after the addition is appropriate according to the nature of water. Shall be adjusted.

The rapid stirring time T1 [H] can be considered as the time during which all the water in the water area contacts the stirring section.

Assuming that the flow velocity v [m / sec] in the stirring section and the flow passage cross section is φD [m], the stirring flow rate Q [m ³ H] is If the water capacity of the water area is V [m ₃ ], then T 1 [H] According to the experiment on a laboratory scale, the slow stirring time T2 [H] almost completes the flocculation in about 10 minutes, and if it is set to 20 minutes or more, the flocculation is sufficiently performed.

As the aggregating agent 4 added in the rapid stirring region 3, a cationic synthetic polymer, an anionic synthetic polymer,
Nonionic synthetic polymers, chitosan and the like are used, and the relationship between the added concentration of the condensing agent and the transparency is shown in FIG. Based on this determination result, the concentration of the flocculant is set to a value of around 2 mg / l, which gives the best clarity of the supernatant water, but this varies depending on the type of flocculant used and the concentration of sewage.

As shown in FIG. 3, the cationic synthetic polymer and chitosan are effective for the water in the above-mentioned water area, but the cationic synthetic polymer needs to be twice as much as the chitosan at the addition rate that gives the best transparency, and the economical efficiency is improved. Chitosan is excellent in.

This chitosan is made by treating the biopolymer chitin contained in the shells of shrimp and crab with alkali, has no toxicity to living organisms such as fish, is easily decomposed in the ecosystem, and has a higher safety than other synthetic polymers. Is.

Although the synthetic polymer as described above is used as the flocculant, it is preferable to use the natural polymer flocculant chitosan, which is produced by being extracted from the shell of a crab or the like, in consideration of the safety and the economical efficiency for water bodies.

Furthermore, by using aeration together with rapid stirring, the fifth
As shown in the figure, the cohesiveness can be improved.

It is also possible to adjust the direction of the water flow caused by the aeration and agitation device 2 so that the particles settled at the bottom of the water area gather in the center of the water area, and this sediment (sludge) can be absorbed and discharged by an underwater pump or the like. is there.

[Effect of the Invention] According to the present invention, since the flocculant is added to the rapid stirring region of the aeration stirrer, the particles floating in water and the flocculant can be efficiently brought into contact with each other. Flocculates and precipitates in the slow stirring area inside, and the precipitated precipitate can be aerobically decomposed by the oxygen supplied from the aeration stirring device, which enables aeration treatment of soluble organic substances, etc. The transparency of polluted water can be improved by a simple method.

[Brief description of drawings]

FIG. 1 is a plan view showing a state where an aeration and agitation device is installed in a closed water area, FIG. 2 is a longitudinal sectional view thereof, and FIG. 3 is a graph showing the relationship between the coagulant addition rate and transparency, and FIG. Is a flow chart for explaining water pollution in a closed water area, and FIG. 5 is a graph showing the relationship between the presence or absence of aeration and cohesiveness. 1 is a pond, 2 is an aeration stirring device, 3 is a rapid stirring region, 4 is a flocculant.

 ─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-61-136496 (JP, A) JP-A-63-171699 (JP, A)

Claims (1)

[Claims] 1. An aeration and agitation device installed in the water of a polluted water area causes a horizontal water flow to aerate and agitate simultaneously to decompose pollutants such as soluble organic substances, and
For particles such as contaminants and algae that are suspended in water that are extremely unlikely to settle and reduce the visibility of water, add a coagulant to the rapid stirring area of the aeration stirring device, and in the slow stirring area within the water area. A method for treating a polluted water area, characterized in that the particles are flocculated and precipitated, and the precipitated precipitate is aerobically decomposed to obtain transparent water quality.