JPS63264192A - Method and device for purifying sewage - Google Patents

Abstract

PURPOSE:To efficiently remove the phosphorus component in sewage by supplying sewage into a filter medium mixed with metallic iron to elute the iron component, then combining the iron component with the phosphorus component in the sewage to form insoluble iron phosphate, and holding the iron phosphate in the filter medium. CONSTITUTION:The filter medium 1 is formed by preferably using soil as a base material 2 and uniformly mixing powdery or granular metallic iron 3 into the material 2. When sewage A is supplied to the filter medium 1, the metallic iron 3 is eluted as an iron ion by the oxygen, etc., in the sewage and quickly combines with the phosphoric ion in the sewage to form the precipitate 4 of insoluble iron phosphate, and the unreacted iron ion is oxidized to form the precipitate 5 of iron hydroxide. The precipitates 4 and 5 are held in the gap between the base material 2 and the metallic iron 3, and the dephosphorized treated water B flows out to the outside of the device. This sewage purification method is appropriately used especially for the treatment of domestic waste water. In this case, the amt. of the metallic iron 3 to be added is necessarily controlled to about 2-20wt.%, based on the base material 2. In addition, the base material 2 having high water permeability is preferably used, and the granular metallic iron 3 is preferable.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method and apparatus for effectively removing phosphorus from wastewater, and particularly to a method for depositing and separating phosphorus using metal iron.

[Technical background and drawbacks of conventional technology]

In recent years, gray water and sewage treatment wastewater have attracted attention as a cause of environmental pollution, and many studies have been conducted to remove phosphorus, especially since phosphorus causes eutrophication problems in lakes, rivers, oceans, etc. .

Currently, the conventional precipitation method is the most widely used method for removing phosphorus from wastewater, and salts of calcium, aluminum, and iron are mainly used as flocculants. In addition, crystallization methods have recently been developed and put into practical use. However, the former method generates a large amount of sludge, which increases running costs such as processing costs and chemical costs, while the latter method has drawbacks such as difficulty in operation management.

On the other hand, soil purification methods that utilize the purifying power of nature have been developed and are attracting attention, but the phosphorus removal capacity is not always sufficient, and the water permeability is particularly poor when the soil is clayey. The water content decreases rapidly over the years, and together with the deterioration of water permeability, this leads to soil clogging.

[Means for solving problems]

As a result of various studies to solve the above problems, the inventors of the present invention have developed a technique for effectively removing phosphorus using metal iron.

That is, when metallic iron such as reduced iron comes into contact with air-containing water, a small amount of iron (iron ions) is eluted in the neutral region due to the oxidation effect of oxygen in the air.

When this eluted iron comes into contact with wastewater containing scales, it becomes a precipitate of insoluble iron phosphate.

Therefore, if this precipitate is separated from the treated water by some method, the dephosphorization effect will appear.

The greatest feature of the present invention is that soil is used as a support for this separation and metal iron. Further, the filter medium (mixture of soil and metal iron) of the present invention can be incorporated into a soil-type sewage treatment device or other treatment device, or used as a part thereof, to provide a comprehensive sewage removal device.

[Structure of the Present Invention] FIG. 1 is a schematic diagram for explaining the treatment principle of the present invention, and FIG. 2 shows an example of a soil-type sewage treatment apparatus using the filter medium of the present invention. Further, FIG. 3 shows an example of a test capillary trench apparatus for measuring the dephosphorization rate.

The filter medium (1) illustrated in Fig. 1 uses soil (2) as a base material, and powdered or granular metallic iron (3) (hereinafter referred to as "iron particles") is added to the soil (2) as a base material.
) are uniformly mixed.

When sewage (domestic wastewater) (A) is applied to this filter medium (1), iron particles (3) are melted in the form of iron ions by the oxygen in the sewage, and if scale acid ions are present in the sewage, they are immediately dissolved. They combine to form an insoluble iron phosphate precipitate (4).

In addition, unreacted iron ions are oxidized and precipitate iron hydroxide (
5). These precipitates are deposited on soil (2) and iron grains (3).
The treated water (
B) flows out of the device.

However, the important points in this method are a high dephosphorization rate and good water permeability.

First, the amount of iron ions eluted is approximately proportional to the amount of iron particles in the filter medium, so if it is too small, phosphorus removal will be insufficient, and if it is too large, it will flow into the treated water in the form of iron ions, causing red water. . By the way, the present invention is particularly suitable for small-scale domestic gray water treatment facilities that are characterized by general sewage, and wastewater from such facilities is usually neutral and has a phosphorus content of total phosphorus (T-
P) is approximately constant at about 4 to 5 ppm. With this in mind, the amount of iron particles added should be 2 to 20% by weight based on the base material.
degree is necessary. More preferably it is 3 to 10%.

On the other hand, water permeability is important from the viewpoint of the processing capacity of the device.

Moreover, the produced iron phosphate and iron hydroxide accumulate in the filter medium over time and reduce water permeability, so this is also important from the point of view of extending the life of the device.

Therefore, it is preferable that the soil used as the base material has high water permeability if possible. Incidentally, Table 1 shows the hydraulic permeability coefficients of several types of soil, and among these, river sand with a low clay and silt content is the most preferable. River sand is also chemically stable. The particle size is 0.02 to 2 mm, more preferably 0.02 to 2 mm.
25~0.5mm.

Similarly, granular metal iron is also preferable. The size is 2
It is about 0 to 80 meshes, more preferably about 40 to 60 meshes. Incidentally, powdered materials are chemically active and have good reactivity, but on the other hand, they are dangerous and scatter, making them difficult to handle, so powders in the size of 1.6 mm are preferable.

Table 1 Next, FIG. 2 shows an example of a trench (soil-type purification device) incorporating the filter medium (11) of the present invention.
) is a sewage sprinkler pipe (8), 8I plaster (9), Neso) (10
) is provided with a wastewater supply section (11) consisting of a treatment layer (7
) under the gravel layer (13) for drainage via a net (12).
), a covering soil layer (14) made of sandy soil is disposed on the upper side, and the whole is housed in concrete 1uff (+s). Then, the wastewater (A) moves from the wastewater supply section (11) to the surrounding treatment layer (7) by capillary action or the action of gravity, and during this time, the treated water (B) from which phosphorus has been removed through the above-mentioned reaction ) is r+'t! ! (+2) and drain pipe (16) to be discharged out of the system.

[Experiment example]

(Experimental equipment) The experiment was carried out using a test capillary trench equipment (as shown in Figure 3).
17). This device (17) is made entirely of a transparent plastic plate so that the inside can be clearly seen, and the filter media (11) are made of river sand (2) and iron particles (3) with different mixing ratios in the filter media storage section (18). A test water supply pipe (19) is filled at the top, and a treated water discharge pipe (22) covered with a net 1-(20) and a gravel layer (2I) is arranged at the bottom. Water (23) is continuously passed through the test water supply pipe (19) at a constant pressure, and the treated water discharge pipe (2
The filtered water (24) coming out of 2) is received in a beaker (25) and used for the test.

(Filter media) River sand (particle size 0.25 to 0.5On+
m) with a particle size of 0.25 to 0.35 mm (4
A mixture of iron particles (0 to 60 mesh) in the ratio (weight ratio) shown in Table 2 was used.

Table 2 (Test water) The test water (20) is considered to be the secondary treated water of domestic wastewater, and the table of KII2PO4 solution (concentration equivalent to T-P5ppn+) and C6H1206 (concentration equivalent to BOD 25ppm)
3 A mixed solution was prepared and used.

(Results) The experimental results are shown in Table 3. From these results, the amount of metallic iron added is 3 to 15% by weight, especially 5 to 10% by weight, based on the base soil.
It turns out that about % is most preferable.

If it is less than 3%, the dephosphorization rate will be low, and if it is more than 15%, the dephosphorization rate will drop somewhat and the eluted iron concentration will become high, which is not preferable.

Incidentally, the wastewater standard value for iron ions is 10 ppm.

〔effect〕

As detailed above, the undeveloped method is to elute iron by feeding wastewater into a filter medium mixed with metallic iron, and combine the iron with phosphorus contained in the wastewater to form insoluble phosphoric acid. The iron phosphate is retained in a filter medium and separated from water.

Therefore, unlike the coagulation-sedimentation method, there are no running costs such as chemicals and sludge treatment costs, and unlike the crystallization method, there are no operational management problems, and the service life is longer and the descaling capacity is larger than the soil method. Therefore, it can be said to be an optimal dephosphorization method especially for small-scale sewage purification equipment.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram for explaining the treatment principle of the present invention, Fig. 2 is a sectional view showing an example of the soil-type sewage treatment equipment according to the present invention, and Fig. 3 is a test for measuring the dephosphorization rate. This is an example of a capillary trench device for use (al is a plan view showing the piping state, (
b) is a longitudinal sectional view of the entire device. 1...Filter material 6...Trench 2...River sand 17...Test capillary 3...Iron grains Trench device 4... ...Precipitate of iron phosphate A...
・Sewage 5... Hydroxide precipitation B...
2nd batch of treated water / 3 batches of treated water (b)

Claims (1)

[Scope of Claims] 1. Feeding wastewater into a filter medium mixed with metallic iron to elute iron content, and combining the iron content with phosphorus contained in the wastewater to form insoluble iron phosphate; A method for purifying wastewater, which comprises retaining the iron phosphate in a filter medium and separating it from water. 2. The method for purifying wastewater according to claim 1, wherein soil with excellent water permeability is used as the base material of the filter medium. 3.Fill a filter medium containing metal iron around the wastewater supply source,
A sewage purification device characterized in that its upper part is covered with soil.