JPH0985263A - Treatment of phosphorus in activated alumina desorbed solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively recover phosphate ions as solid particles of magnesium ammonium phosphate by mixing an activated alumina desorbed soln. with sludge treatment return flow water in a method for treating phosphorus in activated alumina desorbed soln. generated at a time of the purification of sewage secondary treated water and adjusting the pH of the mixed soln. to a specific value to add a magnesium compd. SOLUTION: When sewage secondary treated water 1 is supplied to an activated alumina packed bed 3, phosphate ions in treated water 1 are adsorbed by the activated alumina packed bed 3 to obtain activated alumina adsorbed treated water 2. After this treatment, an acidic soln. or alkaline soln. 4 is supplied in order to desorb phosphoric acid and a desorbed soln. 5 is subsequently mixed with sludge treated return flow water 7 so that [NH4 <+> ]/[PO4 <3-> ] becomes 1 or more. Subsequently, a magnesium compd. 9 is added to a granulated dephosphorizing tower 8 so that [Mg<2+> ]/[PO4 <3-> ] becomes 1 or more and pH is adjusted to 7.5-10. Formed solid particles 13 of magnesium ammonium phosphate are utilized as a compd. fertilizer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the activity produced when phosphate ions in secondary treated sewage water are adsorbed and removed by activated alumina, and the phosphoric acid adsorbed on activated alumina is desorbed by an acidic solution or an alkaline solution. The present invention relates to a phosphorus treatment method in an alumina desorption liquid, and more particularly to a phosphorus treatment method in an activated alumina desorption liquid for recovering phosphate ions in the desorption liquid as solid particles of magnesium ammonium phosphate.

[0002]

2. Description of the Related Art In recent years, phosphorus removal technology, which is one of the factors causing eutrophication, which has been a particular problem in closed water areas, has been developed by a coagulation separation method in which metal salts such as aluminum salts and iron salts are reacted with phosphorus. Crystallization method to deposit phosphorus in the form of hydroxyapatite on seed crystals such as ore and bone charcoal (catalytic dephosphorization method), biological dephosphorization method utilizing the excessive phosphorus intake of microorganisms, and adsorbents such as activated alumina There are methods such as adsorption removal.

Among these, there is an adsorption removal method using activated alumina as a method capable of reducing the phosphorus concentration in the treated water to a low concentration and further reducing waste generation. In this method, the adsorption capacity of activated alumina is reduced. To maintain
Periodic desorption operation of phosphorus is required. The phosphorus adsorption capacity of the activated alumina shows the maximum around pH 4 to 7, and is extremely reduced outside the range. Therefore, desorption of phosphoric acid from activated alumina is performed using an acidic solution or an alkaline solution, but at that time, a desorption solution containing a high concentration of phosphate ions is generated, and its disposal method becomes a problem. There is.

[0004]

Conventionally, calcium compounds such as calcium chloride and calcium hydroxide are added to the desorbed liquid of activated alumina to separate and collect them as precipitates of calcium phosphate, lime superphosphate and the like. However, there is a problem that an excessive amount of calcium is required for the precipitation reaction, the formed precipitate is in a slurry state, and handling is difficult. Therefore, even when this large amount of slurry sludge is reused as a fertilizer, it is difficult to handle and the value as a fertilizer is low. INDUSTRIAL APPLICABILITY The present invention is capable of efficiently removing phosphate ions in the activated alumina desorption solution, and further, the phosphate ions can be effectively utilized as high-quality chemical fertilizers by collecting the phosphate ions as solid particles that can be easily handled. It is an object of the present invention to provide a method for treating phosphorus in a desorbed liquid.

[0005]

Means for Solving the Problems As a result of earnest studies for solving the above problems, the present inventors have found that activated alumina desorption solution is mixed with sludge-treated return water to add a magnesium compound. By adjusting the pH to 7.5 or more and 10 or less and stirring and mixing, the phosphate ions in the desorbed liquid can be recovered and removed as solid particles of magnesium ammonium phosphate, and further recovered. The inventors have found the fact that solid particles can be effectively used as high-quality chemical fertilizers, and arrived at the present invention. That is, according to the present invention, the secondary treated water of sewage is supplied to the packed bed of activated alumina to obtain sewage 2
In the phosphorus treatment method in the activated alumina desorption liquid, which is generated when the phosphate ions in the subsequent treated water are adsorbed and removed, and then the phosphoric acid adsorbed on the activated alumina is desorbed by the acidic solution or the alkaline solution, Mix the liquid with the sludge treatment return water so that [NH ₄ ⁺ ] / [PO ₄ ^3- ] becomes 1 or more, and [Mg ²⁺ ] / [PO ₄ ^3- ] becomes 1 or more. Add magnesium compound to pH
Is adjusted to 7.5 or more and 10 or less and mixed by stirring to recover and remove the phosphate ions in the desorbed liquid as solid particles of magnesium ammonium phosphate, the activated alumina desorbed liquid. The phosphorus processing method is the main point.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below with reference to the drawings. FIG. 1 is a schematic view showing an example of a phosphorus treatment method in the activated alumina desorption liquid of the present invention. FIG.
In the sewage treatment, the secondary treated water 1 has a space velocity (flow rate / adsorbent filling volume) in the activated alumina packed bed 3 in an upward flow or a downward flow.
Is supplied at 1 to 20 (1 / h). Then, the phosphate ions in the secondary treated water 1 of the sewage are adsorbed by the activated alumina packed layer 3 to obtain the activated alumina adsorption treated water 2 from which the phosphate ions are removed. As the adsorbent used for the activated alumina filling layer 3, a commercially available product having an Al ₂ O ₃ content of 60 to 90% and a particle diameter of about 0.5 to 5 mm can be used. Examples of commercially available adsorbents include Neobead D and Neobead DS-5 (manufactured by Mizusawa Chemical Co., Ltd.).

In order to maintain the adsorptive capacity of activated alumina, it is necessary to desorb phosphoric acid by passing water about 100 to 3000 times the packed volume. In order to desorb the phosphoric acid adsorbed on the activated alumina, it is necessary to supply an acidic solution having a pH of 1 or less or an alkaline solution 4 having a pH of 9 or more, but considering the amount used and the influence on the adsorbent, the alkaline solution is used. It is preferable to use solution 4. Alkaline solution 4 of 0.01 normal or more and 1 to 500 times the volume of the packed bed
Is supplied in an upward flow or a downward flow, most of the phosphoric acid adsorbed on the activated alumina packed layer 3 is desorbed, and the pH of the desorbed liquid 5 from which the phosphoric acid is desorbed is 11 to 13, The phosphorus concentration is as high as 100 to 5000 mg / liter.

The desorbed liquid 5 from which the phosphoric acid is desorbed is mixed with the sludge treatment return water 7 through the desorbed liquid storage tank 6. At this time,
[NH ₄ ⁺ ] / [PO ₄ ³⁻ ] needs to be mixed so as to be 1 or more, and [NH ₄ ⁺ ] / [PO ₄ ³⁻ ]
Are preferably mixed so that the ratio is 1 or more and 10 or less. Here, the sludge treatment return water 7 refers to the return water returned from the sludge treatment system that performs anaerobic digestion treatment to the water treatment system. By mixing the desorbed liquid 5 with the sludge treatment return water 7 and supplying it to the granulation dephosphorization tower 8 in the subsequent stage, it is not necessary to separately add only the NH ₄ source, and the sludge treatment return water 7
The phosphorus load inside can also be reduced at the same time.

The residence time in the granulation dephosphorization tower 8 is 1
The desorption liquid 5 mixed with the sludge treatment return water 7 is constantly supplied to the granulation dephosphorization tower 8 so as to be 0 minutes or more, and the magnesium compound 9 is added. Here, the magnesium compound 9 needs to be added so that [Mg ²⁺ ] / [PO ₄ ³⁻ ] becomes 1 or more, and [Mg ²⁺ ] / [P
O ₄ ³⁻ ] is preferably added so as to be 1 or more and 2 or less. As the magnesium compound 9 used,
Although not particularly limited, it is preferable to use a magnesium hydroxide solution or a magnesium chloride solution.

Further, it is necessary to adjust the pH inside the granulation dephosphorization tower 8 to 7.5 or more and 10 or less, and more preferably pH 8 or more and 9.5 or less. pH is 10
In the case of showing the above, the acidic solution 10 is added to adjust the pH to 10
Adjust as follows. The acidic solution 10 is not particularly limited, but hydrochloric acid is preferably used.

The inside of the granulation dephosphorization tower 8 needs to be constantly stirred and mixed. The stirring method may be mechanical stirring with a stirring blade, but from the viewpoint of required power and maintenance, stirring air 12 is preferably supplied from the bottom of the granulation dephosphorization tower 8 and stirred. . The produced magnesium ammonium phosphate solid particles 13 are withdrawn from the bottom of the granulation dephosphorization tower 8 at intervals of 1 to 2 weeks, and are effectively used as a chemical fertilizer. The treated water 11 from which phosphate ions in the desorbed liquid 5 have been removed overflows from the upper part of the granulation dephosphorization tower 8. In this way, 80% or more of phosphate ions in the activated alumina desorption solution 5 can be removed.

FIG. 2 is a schematic view showing an example of a sewage treatment process incorporating the method for treating phosphorus in the desorbed liquid of activated alumina of the present invention. The inflow sewage 14 is the first settling tank 1
After flowing into No. 5 for solid-liquid separation, activated sludge treatment is carried out in the activated sludge treatment tank 16 to flow into the final settling tank 17. Then, the sewage secondary treated water 1 which is the supernatant water is supplied to the activated alumina packed bed 3, and the phosphate ions in the sewage secondary treated water 1 are adsorbed and removed by the activated alumina. The activated alumina adsorption-treated water 2 from which the phosphate ions have been removed is discharged from the activated alumina packed layer 3, and an alkaline solution 4 is supplied to the activated alumina packed layer 3 in order to desorb the phosphoric acid adsorbed on the activated alumina.

On the other hand, a part of the sludge settled in the final settling tank 17 is returned to the activated sludge treatment tank 16 as a return sludge 20, and the remaining sludge 21 is dehydrated by a dehydrator 19 through an anaerobic digestion tank 18. It is then separated into the sludge treatment return water 7 and the dehydrated cake 22. Then, the desorbed liquid 5 from which phosphoric acid has been desorbed by the above desorption operation is mixed with the sludge treatment return water 7 and supplied to the granulation dephosphorization tower 8. Here, the magnesium compound 9 was added, the pH was adjusted, and the mixture was stirred and mixed, whereby the phosphate ions in the desorbed liquid 5 were recovered as solid particles of magnesium ammonium phosphate 13, and the phosphate ions were removed. The granulated dephosphorized water 11 is first returned to the settling tank 15.

[0014]

Next, the present invention will be described specifically with reference to examples and comparative examples. Example 1 A glass column having a diameter of 32 mm and a length of 450 mm was charged with neo-bead D (Al ₂ O ₃ 80.57) as activated alumina.
%, Particle size 4-5 mesh 91.0%, manufactured by Mizusawa Chemical Industry Co., Ltd.) so that the adsorbent layer becomes 400 mm, and the packed layer has a phosphoric acid phosphorus concentration of 1.5 mg / liter When the treated water was treated by passing it through at a space velocity of 5 (1 / h), the phosphate concentration of the treated water was maintained at 0.5 mg / liter or less until it passed 3000 times the activated alumina filling volume. Was done. As a desorption operation, by adding 1N sodium hydroxide solution in an amount three times the volume of the packed bed to the packed bed of activated alumina and circulating it, about 90% of the phosphorus adsorbed on the activated alumina was desorbed, and the phosphoric acid Concentration 90
An eluent of 0 mg / liter, pH 13 was produced.

This desorbed liquid was used as an anaerobic digestion sludge dehydrated filtrate (ammonia nitrogen concentration 400 mg / liter, pH 7.
5, phosphoric acid phosphorus concentration 100 mg / liter) and [NH
₄ ⁺ ] / [PO ₄ ^{3 −} ] = 1 and mixed and introduced into the granulation dephosphorization tower, where 35% magnesium hydroxide [Mg ²⁺ ] / [PO ₄ ^{3 −} ] = The pH was adjusted to 9.5 with 1N hydrochloric acid, while adding 1 to the above. By reacting for 20 minutes while stirring and mixing, 80% or more of the phosphate ions in the desorbed liquid were removed, and solid particles of magnesium ammonium phosphate having good sedimentation properties were generated.

Comparative Example 1 An activated alumina desorption liquid obtained in the same manner as in Example 1 was
The pH was adjusted to 10 by adding 1N hydrochloric acid, and a 2M calcium chloride solution was added so that [Ca ²⁺ ] / [PO ₄ ^3- ] = 3. As in Example 1, 80% or more of the phosphate ions in the desorbed liquid were removed, but Ca, which had a very poor sedimentation property, was used.
_A large amount of slurry sludge of ₂ (OH) PO ₄ and calcium carbonate was generated.

[0017]

INDUSTRIAL APPLICABILITY In the present invention, the phosphate ions in the activated alumina desorption solution can be efficiently removed, and the removed phosphate ions are recovered as solid particles of magnesium ammonium phosphate, which results in high quality. It can be effectively used as a chemical fertilizer. Further, in the present invention, since the activated alumina desorption liquid is mixed with the sludge-treated return water to perform the granulation dephosphorization treatment, it is not necessary to add only the NH ₄ source separately, and the phosphorus in the sludge-treated return water is not required to be added. It is possible to reduce the load at the same time.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a phosphorus treatment method in a desorbed solution of activated alumina of the present invention.

FIG. 2 is a schematic view showing an example of a sewage treatment process incorporating the method for treating phosphorus in the desorbed liquid of activated alumina of the present invention.

[Explanation of symbols]

 1 Sewage Secondary treated water 2 Activated alumina adsorption treated water 3 Activated alumina packed bed 4 Alkaline solution 5 Desorbed liquid 6 Desorbed liquid storage tank 7 Sludge treatment return water 8 Granulation dephosphorization tower 9 Magnesium compound 10 Acidic solution 11 Granulation desorption Phosphorus treated water 12 Stirring air 13 Magnesium ammonium phosphate solid particles

Claims (1)

[Claims] 1. Secondary treated sewage water is supplied to a packed bed of activated alumina to adsorb and remove phosphate ions in the secondary treated sewage water, and then phosphoric acid adsorbed on the activated alumina by an acidic solution or an alkaline solution is removed. In the phosphorus treatment method in the activated alumina desorption liquid generated when desorbing, the desorption liquid is mixed with sludge treatment return water to [NH ₄ ⁺ ] / [PO
₄ ^3- ] becomes 1 or more, and [Mg ²⁺ ]
A magnesium compound is added so that / [PO ₄ ³⁻ ] becomes 1 or more, the pH is adjusted to 7.5 or more and 10 or less, and the mixture is stirred and mixed, whereby the phosphate ion in the desorbed solution is converted into phosphoric acid. A method for treating phosphorus in a desorbed liquid of activated alumina, which comprises recovering and removing magnesium ammonium solid particles.