JP3378700B2 - Granular phosphorus adsorbent using tap water sludge and its production method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a granular phosphorus adsorbent (also referred to as a dephosphorization agent) suitable for removing phosphorus, which is a eutrophication substance, from a natural environment body such as a river. The present invention relates to a new technology for producing chemicals from tap water sludge generated as waste from tap water plants nationwide.

[0002]

2. Description of the Related Art In order to prevent eutrophication of rivers and lakes, dam lakes, seas, etc. into which rivers flow, it is increasingly necessary to remove phosphorus contained in river water. For example, a typical example of a phenomenon associated with eutrophication is the occurrence of blue-green algae and red tide, and it is said that such a phenomenon is very likely to occur at a phosphorus concentration of 0.05 mg / liter or more. Therefore, attempts to remove phosphorus contained in rivers have recently been started. Conventionally, the method of removing phosphorus from river water is to install a flocculation-precipitation device on land, pump up the river water, add a flocculant such as aluminum sulfate to flocculate phosphorus, and then precipitate the generated flocs. Methods of separating are known.
However, this method requires a coagulation-sedimentation device such as a chemical plant, a pump, piping, large pump power, etc.
In addition to the high power cost, there is a drawback that a large space for installing the device is required on land. There is also a drawback that it is necessary to dispose of the hardly dehydratable sludge generated by the coagulation sedimentation treatment.

As other methods, substances having a large phosphorus adsorption force such as Kanuma soil, allophane, aluminum hydroxide, activated alumina, and iron hydroxide have been conventionally known. Among them, activated alumina, Kanuma soil and allophane are known. Attempts have also been made to remove phosphorus in river water using a granular granular phosphorus adsorbent that is obtained by firing the above into a granular form having a particle size of several centimeters. However, these granular phosphorus adsorbents have the following drawbacks, and the reality is that the phosphorus removal technology using these adsorbents has not been put into practical use. Is desired. In other words, activated alumina has a higher price because it is made by firing activated alumina powder, which is expensive in itself, into granules and molding it.
Often impractical for water treatment, which requires low running costs. When the amount of adsorbed phosphorus reaches saturation, activated alumina is complicated to regenerate and the treatment cost is high. When filling a river with a granular phosphorus adsorbent, both activated alumina and Kanuma soil must have a large particle size of several centimeters in order to prevent blockage due to turbidity. Therefore, the diffusion of phosphate ions into the grain is poor, and the inside of the grain cannot be used for phosphorus adsorption. Granules of Kanuma soil have low phosphorus adsorption capacity and lose phosphorus adsorption power in a short period of time. The manufacturing equipment used for granulating and firing Kanuma soil is inefficient in terms of both process and productivity, and the granulating and firing cost is considerably high. Granules of activated alumina and Kanuma soil are extremely hard, and when used waste is sprinkled on forest land to be used as a fertilizer, its natural disintegration is slow and its suitability is poor. Etc.

[0004]

SUMMARY OF THE INVENTION The present invention is intended to solve the drawbacks of the above-mentioned conventional granular phosphorus adsorbents. Specifically, the following matters are intended to be solved. Is. That is, (i) establishment of a new technology for producing granular phosphorus adsorbents by effectively utilizing waste. (ii) The production of the granular phosphorus adsorbent is very simple. (iii) The firing process of the granulated product is unnecessary and the process is short. (iv) The granular phosphorus adsorbent has a high phosphorus adsorption rate and a large phosphorus adsorption amount. (v) The granular phosphorus adsorbent is porous and has good water permeability, and even large particles with a particle size of 1 cm or more can be used for adsorption up to the inside, and the phosphorus adsorption capacity is large. (vi) The waste phosphorus adsorbent is not too hard and has good natural disintegration property,
Easy to dispose. (vii) The phosphorus adsorbent is inexpensive and suitable for water treatment. It is desired to develop a granular phosphorus adsorbent having advantages such as the following. An object of the present invention is to provide an ideal granular phosphorus adsorbent having the above characteristics (advantages).

[0005]

The above object of the present invention can be achieved by the following phosphorus adsorbent of the present invention and a method for producing the same. That is, (1) Kneading water sludge, cement and super absorbent polymer
A granular phosphorus adsorbent characterized by being granulated. (2) A method for producing a granular phosphorus adsorbent, which comprises adding cement and superabsorbent polymer powder to high water content sludge and kneading and molding.

[0006] Tap water sludge is used for raw water such as river water and lake water.
It is a settling sludge obtained by adding aluminum salts such as PAC (polyaluminum chloride) and a sulfuric acid band as a coagulant, and separating and separating the produced flocs. The clean water sludge contains a relatively large amount of aluminum hydroxide. It is known that the use of tap water sludge in horticultural soil causes phosphorus deficiency in plants. The present inventor has focused on this phenomenon, and has reached the recognition that if the phosphorus adsorbent can be produced by effectively utilizing the tap water sludge that has been disposed of as waste, the conventional problems can be effectively solved. .

According to the practice of the inventor of the present invention, when the tap water sludge and the cement are kneaded, a non-porous granule that is hard like stone is produced, and the phosphorus adsorption property is remarkably poor and the natural disintegration property is caused. Only bad things are formed. However, when cement and superabsorbent polymer powder are added to the water sludge and kneaded, surprisingly, the granules become remarkably porous granular agglomerates and elastic granules with appropriate strength are formed. I found a thing. The structure of the porous granular nodule with its elasticity is that countless small particles like the "okoshi" of confectionery,
Assembled through a super absorbent polymer gel that absorbed water,
It formed porous granular nodules. The external view is shown in FIG.

According to the observation of the inventor of the present invention, when the superabsorbent polymer powder is not added when kneading the tap water sludge and the cement, the tap water sludge is dehydrated and dried to obtain a dry powder. If it is not in the shape, the hardening reaction of cement does not occur. Therefore, if it is attempted to form a granular agglomerate similar to that of the present invention by using the tap water sludge and cement without using the super absorbent polymer powder, at least a drying step of the tap water sludge is required, and the cost therefor is high. It becomes something. In the case of the present invention using a super absorbent polymer powder,
It was found that the water sludge can be easily granulated and solidified even when it is a slurry with a high water content, and an important advantage is that drying is unnecessary.

As the super absorbent polymer used in the present invention,
Various super absorbent polymers that are often used in disposable diapers (polyacrylate, starch-acrylate graft polymer, vinyl acetate copolymer, polyvinyl alcohol, etc.)
Although it is possible to use the above, it is particularly preferable that the water absorption is large.
In the present invention, the superabsorbent polymer is convenient to add as a powder, but in short, the fine particles contained in the phosphorus adsorbent of the present invention (fine particles or cement particles constituting the following water sludge) The binder is not particularly limited as long as it works suitably for coupling. Further, as the cement, general cement for producing concrete such as Portland cement and alumina cement can be used, but particularly early-strength cement such as alumina cement and ultra-early-strength cement are preferable.

A typical production example of the granular dephosphorization agent (phosphorus adsorbent) of the present invention will be described with reference to FIG. When cement is added to and mixed with tap water sludge (water content of about 94 to 95%) obtained by concentrating the sludge from the coagulation sedimentation basin of a tap water field with a thickener, a super absorbent polymer powder is added. The powder quickly absorbs the water contained in the drinking water sludge and swells.
When the mixture is kneaded for a few minutes in this state, the superabsorbent polymer powder that has swollen by absorbing water has an adhesive force and acts as a binder to connect the fine particles and cement particles that constitute the water sludge to form a granular agglomerate. To form. A porous granular dephosphorizing agent can be obtained by molding this into an appropriate particle size and shape by, for example, an extrusion granulation method. If this is left in the air for several hours or more, the strength of the superabsorbent polymer particle gel increases due to the hardening phenomenon, and a dephosphorizing agent that does not collapse even when immersed in water is produced. It is possible to produce a porous and elastic granular dephosphorizing agent in a short time by an extremely simple process without providing a drying process and a firing process which have been conventionally required.

Since cement is a kind of alkaline agent, when the granular dephosphorizing agent produced by the above method is brought into contact with phosphorus-containing water, the alkaline component (CaO etc.) is initially eluted from the dephosphorizing agent and dephosphorized. The pH of treated water may rise to 9 or higher, which may adversely affect the ecosystem when phosphorus is removed from rivers and lakes. To prevent such problems, add acid to iron hydroxide slurry or aluminum hydroxide slurry to adjust the pH of the slurry to acidic (pH 4-5).
Then, by adding cement to the acidic slurry and neutralizing the alkali content of the cement with the acidic slurry, adding and mixing the superabsorbent polymer powder to the neutral slurry cement mixture. The alkaline component does not elute from the dephosphorizing agent thus produced, and the solution is solved.

In order to remove phosphorus from the phosphorus-containing water using the granular dephosphorizing agent of the present invention, the granular dephosphorizing agent may be packed in a column and the phosphorus-containing water may be passed through at an appropriate space velocity (SV). . Also, in order to remove phosphorus from a river, a method of packing a dephosphorizing agent granulated into a few centimeters of granularity in a water-permeable container such as a bag made of a net and submerging this in a river causes less clogging due to turbidity in the river, It can be recommended as the simplest phosphorus removal technology.

The prior application of the present inventor (Japanese Patent Laid-Open No. 6-154)
597), "Composite Granules of Metal Hydroxide and Super Absorbent Polymer" utilizes a superabsorbent polymer, but the action of the superabsorbent polymer is essential to the present invention. Are different. That is, the technology of the invention of the prior application is that "a metal hydroxide is held inside each of the hydrogel particles which are made of a superabsorbent polymer and swell in water and exhibit elasticity."
On the other hand, in the present invention, the phosphorus-adsorptive fine particles are present outside the superabsorbent polymer gel particles. In addition, the technique of the invention of the prior application utilizes each hydrogel as a phosphorus adsorbent having a small particle size in a dispersed state, and cannot produce a dephosphorizing agent having a large particle size. In other words, the “composite granular material of metal hydroxide and superabsorbent polymer” of the present inventor's prior application does not have the structure of aggregated particles as in the present invention.

[0014]

EXAMPLES The present invention will be specifically described below with reference to examples. However, the present invention is not limited to this embodiment. Example 1 Sulfuric acid was added to tap water sludge slurry (pH 6.8, water content 95%, aluminum content 120 g / kg dry solid),
After adjusting to pH 5, 60 g of early-strength alumina cement was added to and mixed with 500 cc of slurry, 70 g of superabsorbent polymer powder was added, and the mixture was kneaded for 3 minutes. The superabsorbent polymer powder, which had been absorbed by the powder and whose water content had been reduced, absorbed the water, was used as a binder to assemble into a porous granular agglomerate. When this was molded into a particle size of 8 to 12 mm and air-dried for 6 hours, the strength increased due to the hardening effect of cement, and it was moderately elastic (it can be broken by grasping it strongly with the hands).
Porous dephosphorizing agent was produced.

Example 2 Using the porous dephosphorizing agent produced in Example 1, a phosphorus-removing phosphorus-removing column test was conducted on the assumption of phosphorus removal in a dam inflowing river. Table 1 shows the test conditions and the test results.

[0016]

[Table 1]

It can be seen from Table 1 that the phosphorus adsorbent of the present invention, which uses the raw water sludge as a raw material, exhibits good dephosphorization performance. The pH of the raw water was 7.2, whereas the pH of the treated water was in the range of 7.4 to 8.3, which satisfied the water quality regulation.

[0018]

EFFECTS OF THE INVENTION According to the present invention, (1) the tap water sludge that has been conventionally disposed of is not dried and fired (that is, dehydration of the tap water sludge, drying, and drying and firing of the granulated product are performed. That is, it is unnecessary), and it is possible to manufacture a granular phosphorus adsorbent having a proper strength and being porous in a very simple and short time. Therefore, it is suitable for mass production, and both the manufacturing equipment cost and the running cost can be significantly reduced as compared with the conventional one. (2) The amount of wastewater sludge to be disposed of is reduced according to the amount of phosphorus adsorbent that is effectively used. (3) Since it is porous, it has a large surface area and excellent phosphorus adsorption performance even with a large particle size. (4) Since the strength is appropriate and the disintegration is excellent, it is easy to dispose of the waste adsorbent on the forest.

[Brief description of drawings]

FIG. 1 shows a schematic diagram of a granular phosphorus adsorbent having an aggregate structure according to the present invention.

FIG. 2 is a flow explanatory view showing a production process of the phosphorus adsorbent of the present invention.

[Explanation of symbols]

1 Granular phosphorus adsorbent of the present invention 2 porous granular nodules 3 Phosphorus adsorptive fine particles

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Claims (2)

(57) [Claims] 1. A granular phosphorus adsorbent characterized by kneading and granulating clean water sludge, cement and super absorbent polymer. 2. A method for producing a granular phosphorus adsorbent, which comprises adding cement and superabsorbent polymer powder to high water content sludge and kneading and molding.