JPH08281261A - Method for removing phosphorus in river water - Google Patents

Abstract

PURPOSE: To remove only phosphorus in a river water easily and at low cost by adding magnetic iron oxide fine particles having phosphorus adsorptivity to a river water containing phosphorus and suspending particles to bring the particles into contact with the river water before performing magnetic separation and also causing the suspending particles to flow out to the downstream side of a river. CONSTITUTION: At a point A upstream to a place where a magnetic separation part 5 is installed in a river usually containing suspending particles, a suitable quantity of magnetic iron oxide fine particles 1 is thrown in a river water containing phosphorus 3. In a work region B from the point A to the magnetic separation part 5, only phosphorus in the river water containing phosphorus 3 is adsorbed and removed by the magnetic iron oxide fine particles 1. Finally, the magnetic iron oxide fine particles containing phosphorus 2 to which phosphorus has been adsorbed and which have removed phosphorus 3 from the river water containing phosphorus 3 are rapidly subjected to magnetic separation. That is, the phosphorus concentration of the river water 4 is surely reduced, but leaving the suspended particles such as silt due to earth and sand contained in the dephosphorized river water 4 passed through the magnetic separation part 5 as they are. On the other hand, the magnetic iron oxide fine particles containing phosphorus 2 subjected to magnetic separation are effectively used as a phosphorus fertilizer as they are.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a new technique capable of extremely reasonably selective removal of a trace amount of phosphate ions contained in river water containing suspended particles such as silt.

[0002]

2. Description of the Related Art Rivers and lakes, dam lakes, where rivers flow in,
In recent years, attempts have been made to remove phosphorus contained in river water in order to prevent eutrophication of the sea and the like. The conventional method for removing phosphorus in river water is to install a coagulating sedimentation device on land,
A method is known in which river water is pumped up, a flocculant such as aluminum sulfate is added to flocculate phosphorus, and then the produced flocs are separated by precipitation. However, this method requires a coagulation-sedimentation device like a chemical plant, a pump, piping, large pump power, etc., and the equipment cost and power cost are high,
There is a drawback that a large space for installing the device is required on land. In addition, when trying to remove phosphorus from a river in a tourist area, the installation of such a device has a drawback that the natural landscape is damaged. There is also a drawback that it is necessary to dispose of the hardly dehydratable sludge generated by the coagulation sedimentation treatment.

As another method, a granular dephosphorization material (such as Kanuma soil or allophane molded into a granular shape having a particle size of several cm) is filled into a river, and the river water is circulated in the filled portion to collect the river water. Attempts have also been made to remove phosphorus.
However, there was a drawback that the turbid mass of the river water increased rapidly during heavy rain, and the suspended matter quickly blocked the filling part of the dephosphorizing material. In addition, since the dephosphorization material is a granular material with a particle size of several centimeters in order to prevent it from flowing out when the river water flow rate increases during heavy rainfall, the surface area is small and therefore the phosphorus adsorption rate is also low. was there. Therefore, there is a problem that effective phosphorus removal cannot be performed unless a large amount of dephosphorization material is filled into the river. In addition to the large amount of equipment and manufacturing cost for producing dephosphorization material for that purpose, the drawback is that the construction of transporting a large amount of dephosphorization material to the site and filling it into the river is complicated, and its cost is also large. There was also. Furthermore, it is difficult to dispose of the waste dephosphorization material whose phosphorus removal capacity has reached saturation, and the construction of replacing the waste dephosphorization material with a new dephosphorization material was troublesome.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a new technique capable of fundamentally solving the above-mentioned drawbacks of the prior art, such as a coagulating sedimentation device, a pumping pump, and piping. The present invention provides a new technology that does not require all of the above and does not have the above-mentioned many drawbacks in the method of removing phosphorus in river water by using granular dephosphorization material.

[0005]

The above object of the present invention is solved by the method for removing phosphorus in river water according to the present invention. That is, magnetic iron oxide fine particles having a phosphorus adsorption property are added to river water containing phosphorus and suspended particles, and the iron oxide fine particles are brought into contact with river water, then magnetically separated and suspended particles in river water Is a method for removing phosphorus in river water, which is characterized by discharging it to the downstream side of the river as it is.

The essence of the technical idea of the present invention is based on the new findings obtained from the results of the experiments conducted by the present inventors. Further, as described below, the phenomenon of the natural environment itself of rivers is used. It is to effectively remove phosphorus in river water and completely solve many drawbacks of the prior art. That is, there is a flow in the river, and where there is a flow, there are stirring, mixing, and transport functions. Focusing on this natural phenomenon, the present inventors have added a trace amount of iron oxide-based phosphorus adsorbent having magnetic properties in the form of fine particles with a particle size of the order of micron, which was created by the method described below, to coexist in a small amount of river water, After dephosphorizing material is suspended in the flow of the river and flowed down for several minutes,
By flowing into the magnetic separation device by the flow of the river itself, magnetic iron oxide is magnetically separated, and suspended particles (silt etc. derived from sediment) in the river water are not separated but flowed out as it is, so that only phosphorus is contained. It was found that it can be effectively removed by adsorption.

The above principle will be described with reference to FIG. FIG.
5 is a magnetic separation unit for magnetically separating an iron oxide-based phosphorus adsorbent that adsorbs phosphorus by installing a magnetic separation device, and is usually a magnetic separation unit for rivers containing suspended particles. An appropriate amount of magnetic iron oxide fine particles 1 is introduced into the phosphorus-containing river water 3 at the point A upstream of the position where the is installed, and phosphorus in the phosphorus-containing river water 3 is added between the action area B from the point A to the magnetic separation unit 5. Only the magnetic iron oxide fine particles 1 are adsorbed and removed. As a result of the experiment, the addition amount of the particulate phosphorus removing material (magnetic iron oxide fine particles 1) sufficient to remove phosphorus is extremely small, and the phosphorus concentration in the phosphorus-containing river water 3 is about 0.1 mg / liter. 1 to 5 mg / liter (as the dry weight of the phosphorus removing material fine particles 1) may be added in a very small amount. The particulate phosphorus removing material was added at point A, and the particulate phosphorus removing material was placed on the water flow of the river and allowed to flow down for several minutes, and then passed through the magnetic separation unit 5 equipped with a magnetic separation device (a rotary disk type permanent magnet is preferable). The phosphorus-containing magnetic iron oxide fine particles 2 from which phosphorus is adsorbed and removed from the phosphorus river water 3 are rapidly magnetically separated. Therefore, suspended particles such as silt derived from the sediment contained in the dephosphorized river water 4 that has passed through the magnetic separation unit 5 remain as they are, and the phosphorus concentration of the river water 4 is reliably reduced to 0.02 mg / liter or less. It was found that it can be removed. It was also found that the magnetically separated phosphorus-containing magnetic iron oxide fine particles 2 adsorbed phosphorus, so that the phosphorus-containing magnetic iron oxide fine particles 2 can be effectively used as a phosphorus fertilizer by spraying the phosphorus as it is on a forest or the like. Therefore, no sludge treatment equipment such as sludge dewatering was required.

As a result of various studies on the method of producing the magnetic iron oxide of the present invention in the form of fine particles and having a high phosphorus adsorption property, it was found that
A solution obtained by mixing an aqueous iron solution and ferric sulfate at a specific mixing ratio described below is neutralized with sodium hydroxide, slaked lime, etc. to a pH of about 9 to 11, and stirred while heating to adsorb phosphorus with a particle size of several tens of microns or less. It has been found that magnetic iron oxide having a remarkably large capacity is produced, which is suitable as a particulate phosphorus removing material for removing phosphorus in river water.

As shown in Table 1 below, as a result of various studies for preparing magnetic iron oxide having a large phosphorus adsorption capacity,
A known method for producing magnetic iron oxide (magnetite), that is, a method for neutralizing an equimolar mixture of ferrous sulfate and ferric sulfate to pH 10 with sodium hydroxide is a known method for producing phosphorus of magnetic iron oxide. In order to produce a magnetic iron oxide having a low adsorptivity and not a suitable condition and having a high phosphorus adsorptivity, a mixed solution containing ferric sulfate in excess (more than 1 in molar ratio) than ferrous sulfate is used. We have found that neutralization is important. That is, Table 1 shows a specific example of the method for producing magnetic iron oxide having a large phosphorus adsorption property.

[0010]

[Table 1]

From Table 1, in order to prepare a magnetic iron oxide having a large phosphorus adsorption property, it is preferable to set the molar ratio of ferrous sulfate to ferric sulfate to 1: 1.4 to 1: 2. Was confirmed. Therefore, in order to improve the balance between magnetism and phosphorus adsorptivity, and to effectively carry out the present invention, as described above, the mixture liquid in which ferric sulfate is excessively mixed in a molar ratio rather than ferrous sulfate is neutralized. It turns out that is important.

It is to be noted that the particle size of the iron oxide particles is important in order to allow the phosphorus removal material particles to flow down for several minutes without settling on the river bottom using the flow of the river. If so, the phosphorus removal material may settle to the bottom of the river before it enters the magnetic separation device unless the flow velocity of the river is fairly high. In this case, aeration may be performed to increase the flow. In a place where the flow velocity of the river is small (such as a river mouth), even fine particles having a particle size of several tens of microns may be precipitated, so it is preferable to perform aeration and stirring.

[0013]

EXAMPLES Examples of the method for producing the phosphorus-adsorptive magnetic iron oxide fine particles of the present invention and the water treatment using the same will be shown below. However, the embodiment of the present invention is not limited to this description. (Example 1) An artificial waterway (water depth: 30) simulating a natural river
cm, length 4 m, width 10 cm) 5 mg of magnetic iron oxide fine particles (average particle size 10 micron) prepared by the method described later while flowing tap water containing 0.05 mg / liter of phosphorus added at a flow rate of 50 cm / min. / Liter,
The water channel was allowed to flow down for 7 minutes. 5mm cross section at the end of the channel
Nine 5 mm rod-shaped permanent magnets were installed at 5 mm intervals. The phosphorus-containing magnetic iron oxide fine particles were easily attached to the magnetic separation portion and removed. Water flowing out from the magnetic separation part was collected and analyzed for phosphorus. As a result, it was 0.012 mg / liter. The preparation of magnetic iron oxide fine particles having a large phosphorus adsorption capacity was carried out by adding sodium hydroxide to a mixture of 10% aqueous solution of ferrous sulfate and 20% aqueous solution of ferric sulfate to neutralize the pH to 10, It was prepared by heating to 80 ° C. and stirring for 2 hours.

(Embodiment 2) As yet another embodiment,
An example of removing phosphorus from a river flowing into a dam lake will be described. As shown in FIG. 2, a weir 6 is provided in the river, and a rotating disk type magnetic separator 7 is installed in the overflow portion of the weir. On the upstream side of the weir 6, the magnetic iron oxide fine particles 1 were added to the phosphorus-containing river water 3 (containing suspended particles such as silt),
Put on the flow of a river and let it flow down and contact for several minutes to adsorb and remove phosphorus. The magnetic iron oxide fine particles 1 having adsorbed phosphorus are separated by the magnetic separation device 7 and river water from which phosphorus has been removed (the dephosphorized river water 4 contains suspended particles such as silt) is a weir 6. To the downstream.

As a result, no pumping pump or piping is required, and phosphorus can be selectively removed from the river simply by providing a simple magnetic separator.

[0016]

The phosphate ion adsorbent of the present invention has the following effects. A simple method of adding a minute amount of the magnetic phosphorus removing material fine particles of the present invention to a river and using the flow of the river itself to pass through a magnetic separation device. Therefore, all of the coagulation-sedimentation device, pumping pump, piping, sludge treatment facility and huge pump power cost for pumping a large amount of river water as in the prior art becomes unnecessary.

Granular dephosphorizing material having a particle size of several centimeters is filled in a river to remove phosphorus, which is required in the conventional technology for producing granular dephosphorizing material, manufacturing equipment, transportation to the site, and filling in a river. Since it is not necessary to replace all the waste dephosphorization material, it is possible to significantly rationalize. Since the suspended particles in the river water are not removed, the trouble of blocking the phosphorus removal part due to the suspended particles does not occur. When the amount of rainfall is large, the suspended mass in river water increases considerably, but even in such a case, the technique of the present invention causes no problem.

No sludge treatment is required, and the iron oxide fine particles adsorbing the magnetically separated phosphorus are sprayed in the form of slurry on the forest land for easy disposal. Phosphorus adsorbed on iron oxide is used as a fertilizer for plants.

[Brief description of drawings]

FIG. 1 is a flow diagram showing the principle of an example of a method for removing phosphorus in river water according to the present invention.

FIG. 2 is a side view showing an example in which the phosphorus removal method in river water of the present invention is applied to a river flowing into a dam lake.

[Explanation of symbols]

 1 Magnetic Iron Oxide Fine Particles 2 Phosphorus-containing Magnetic Iron Oxide Fine Particles 3 Phosphorus-containing River Water 4 Dephosphorized River Water 5 Magnetic Separation Part 6 Weir 7 Magnetic Separation Device A Particle Input Point B Action Area

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahide Takada 11-1 Haneda Asahicho, Ota-ku, Tokyo Ebara Corporation (72) Inventor Yoshinori Asai 11-11 Haneda-Asahicho, Ota-ku, Tokyo Inside the EBARA CORPORATION

Claims (1)

[Claims] 1. A river water containing phosphorus and suspended particles is added with magnetic iron oxide fine particles having a phosphorus adsorbing property, and the iron oxide fine particles are brought into contact with river water, and then magnetic separation is carried out, and A method for removing phosphorus in river water, characterized in that suspended particles are directly discharged to the downstream side of the river.