JPS6213053B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the removal of phosphate ions, which have become a social problem as a main cause of eutrophication of lakes and inland seas, and particularly relates to a method for regenerating phosphate ion adsorbents.

Conventional methods for removing phosphate ions from wastewater include:
Generally, a method is known in which calcium hydroxide is added to wastewater and separated by precipitation as phosphate apatite.
However, in this method, the total amount of wastewater to be treated must be adjusted to a pH close to 11, and therefore a large amount of calcium hydroxide is required even if the wastewater contains a low concentration of phosphate ions. In addition, large equipment is required for the precipitation and separation of phosphoapatite, and there are many problems such as equipment for neutralizing the treated water and a large amount of cost required for this operation.

On the other hand, as an alternative to these methods, adsorption of phosphate ions using, for example, an adsorbent containing activated alumina or titanic acid has been proposed. However, these methods do not necessarily have good adsorbent regeneration efficiency, and because the adsorbent is a fine powder, it is difficult to prevent the adsorbent from flowing out and handle it in the separation and recovery process before it can be used for wastewater treatment. This has become a serious obstacle in the process of development.

The present inventors have conducted intensive studies on how to put these adsorbents having excellent properties against dilute phosphate ions into practical use, and as a result, have arrived at the present invention described below.

That is, in the present invention, after bringing wastewater containing phosphate ions into contact with an adsorbent made of a fibrous material carrying an oxide of a group element and/or an oxide of a group element, the adsorbent is first treated with an aqueous alkali hydroxide solution in regenerating the adsorbent. The method for regenerating the adsorbent is characterized in that after washing, the adsorbent is treated with an aqueous solution containing sulfate ions.

The adsorbent used in the present invention is a fibrous material carrying an oxide of a group and/or group element of the periodic table.

The oxide supported on the adsorbent is, for example, an oxide of aluminum, titanium, zirconium, etc., and is a metal oxide powder that is reactive with phosphate ions.

These metal oxide powders are mixed with organic polymers (e.g., polyacrylonitrile polymers, polyamide polymers, polyimide polymers, etc.), then formed into fibers or small pieces, and then subjected to metal oxidation. It becomes an adsorbent that supports substances.

Among these, it is a fibrous or small piece molded product that is manufactured by a wet coagulation method or the like and supports powder of the metal oxide mentioned above.
% to 93% (weight ratio), and the water retention capacity of the molded product after immersion in water and centrifugation at 1600G is 0.4 to 4 times that of the powder. It has excellent properties as an adsorbent material, such as fast absorption, high abrasion resistance, and strong chemical resistance. A preferred method for producing the adsorbent of the present invention is described in, for example, Japanese Patent Application Laid-Open No. 54-27018.

The above-mentioned adsorbent is used by being packed into a normal adsorption device, for example, an adsorption tower, in the same way as normal granular activated carbon and granular ion exchange resin. In order to prevent the flow and outflow of the adsorbent, it is preferable that the adsorption tower has a presser made of, for example, a net or a porous member at the upper and lower parts of the adsorption tower.

Such adsorption devices treat wastewater containing low concentrations of phosphate ions.

The adsorbent material is broken through by passing a large amount of waste water through it.
For its regeneration, the breakthrough adsorbent is first washed with an aqueous alkali hydroxide solution containing hydroxides of group elements such as sodium and potassium, thereby desorbing almost 100% of the adsorbed phosphate ions. Note that it is also possible to use other alkaline aqueous solutions such as sodium bicarbonate aqueous solution in place of the alkali hydroxide aqueous solution.

The aqueous alkali hydroxide solution preferably has a molar concentration of 0.1 to 3.0.

In addition, the amount of aqueous alkali hydroxide solution required for this operation is a small amount, about twice the volume of the adsorption tower, and therefore, this operation can remove the phosphoric acid contained in the wastewater at a low concentration. Ions are highly concentrated.

The alkaline hydroxide aqueous solution used for cleaning contains about the same amount of desorbed phosphate ions, such as Ca ^+2.
Group element ions such as (alkaline earth metal ions) or Al ⁺³ are added to separate the phosphate ions by precipitation, and after removing the precipitate, the separation water (alkaline hydroxide aqueous solution) is added to the adsorbent again. It can also be used for attaching and detaching.

The adsorbent from which phosphate ions have been desorbed with an alkaline aqueous solution is then washed and activated with an aqueous solution containing sulfate ions.

Here, the aqueous solution containing sulfate ions refers to a solution containing 0.1 to 2 moles of sulfuric acid or sulfate. Also, the amount used is, for example,
When using an adsorption tower, the amount may be about twice the volume of the adsorption tower. This operation allows the adsorbent to completely regain its original adsorption performance.

In the adsorbent regeneration method consisting of the above-mentioned steps, simply desorbing with an alkaline aqueous solution will not reach the original adsorption performance. Furthermore, even if an attempt is made to activate using an acid other than the sulfuric acid ion solution, the adsorption performance is less than half of the original adsorption performance, and the most effective method for restoring adsorption performance is to satisfy all of the requirements of the present invention. In the case of adsorption treatment, treatment of the desorption liquid is always a problem. Simply converting phosphate ion contamination in wastewater to phosphate ion contamination in the desorption solution does not mean that the wastewater has been treated.
As mentioned above, the alkaline desorption solution contains group elements such as
It was found that the addition of Ca ⁺² can be used many times by separating Ca ₃ (PO ₄ ) ₂ by sedimentation. It was also found that the activity did not decrease even if an aqueous solution containing sulfate ions was used continuously as an activating solution. In addition, the adsorbent used is not only easier to handle by forming it into a fibrous form compared to a simple powder, but also has significantly improved durability against acids and alkalis compared to a powder, and is not damaged after about 20 uses. This was not recognized at all from the appearance or performance standpoint. Furthermore, molded products containing a large amount of fixed water have a fast adsorption/desorption rate and can be treated in a short time.

Example 1 Activated sludge treated water containing 1 (mg/) of PO ₄ ^-3 -P was used as raw water, and activated alumina powder was added at 70% of the raw water.
Water was passed through the adsorption tower (5 cmφ x 100 cm, 2) filled with adsorbent (260 g) containing 2% by weight of polyacrylonitrile and formed into short fibers by wet coagulation method, at a linear flow rate of 10 m/Hr in a downward flow. did. PO ₄ ^-3 -P in the treated water is less than 0.1 (mg/), and after passing through the water
The breakthrough occurred in 133 hours, so after draining the drain from the bottom of the column, a desorption solution of about 1M NaOH was passed upward in an amount of twice the column volume in about two and a half minutes at a linear speed of 50 m/h, and the drain was drained. The desorption solution was collected from. Approximately 0.5M more
An activation liquid containing H ₂ SO ₄ was passed in an upward flow at a linear velocity of 50 m/h in an amount twice the column volume in about 2 and a half minutes, and the activation liquid was recovered from the drain. After washing the packing material in the column with water, raw water was passed through it again, but the treatment performance was the same as before.
Although the desorption liquid (4) contains a high concentration of PO ₄ ^-3 -P, Ca ₃ (PO ₄ ) ₂ generated by adding approximately equivalent amount of Ca(OH) ₂ is separated by sedimentation. Even when it was used again for the next desorption operation, there was no deterioration in desorption performance. 20 minutes of adsorption and regeneration operations
Although the test was repeated several times, no difference was observed in adsorption/desorption performance. In other words, according to this example, dilute PO ₄ ^-3 in the raw water could be separated and recovered as approximately equivalent amount of solid phosphoapatite. In addition, a 0.5M aqueous solution of ammonium sulfate was used as the activation liquid instead of sulfuric acid, but almost the same results as in the case of sulfuric acid were obtained.

Example 2 Using the same raw water as in Example 1, an adsorbent (300%
Water was passed through the adsorption tower (same as in Example 1) packed with g) in a downward flow at a linear flow rate of 10 m/Hr. PO ₄ ^-3 -P in the treated water was 0.1 (mg/) or less and broke through about 107 hours after water flow, so desorption and activation were carried out in the same manner as in Example 1. Desorption solution is approximately 1M NaOH
Two times the column volume was passed through the column at a linear velocity of 50 m/h in about 2 and a half minutes. Activation liquid is approximately 0.25M H ₂ SO ₄
It is water that contains The activation liquid was passed in an upward flow at a linear velocity of 50 m/Hr in an amount approximately twice the column volume in 2 and a half minutes. Al(OH) ₃ was used to precipitate and separate PO ₄ ^-3 in the desorption solution, and it was separated as aluminum phosphate. The adsorption/desorption operation was repeated 20 times, but no difference in adsorption/desorption performance was observed.

Example 3 Using secondary treated human waste water (containing PO ₄ ^-3 -P = 12.8 mg/) as raw water, the aim was to remove pigments (yellow to orange) and COD components at the same time as PO ₄ ^-3 in this raw water. Water was passed through the same adsorption tower as in Example 2, which was filled with adsorbent containing 70% by weight of titanic acid and formed into short fibers by wet coagulation with polyacrylonitrile. PO ₄ ^-3 −P in treated water is 0.2
(mg/) or less, at the same time more than 80% of the color was removed, and at the same time 20% of COD was removed. Since PO ₄ ^-6 -P broke through about 6 hours after water flow, desorption and activation were carried out in the same manner as in Example 1. Desorption liquid is 1M
It is water containing NaOH, and the activation liquid is a 0.25MH ₂ SO ₄ aqueous solution. Ca is used for sedimentation separation of PO ₄ ^-3 in the desorption solution.
(OH) ₂ was used. The desorption solution from which this phosphoapatite has been removed has an orange color, and the pigment and COD components are still desorbed.The solution is then led to another adsorption tower filled with activated carbon (granular) to remove the pigment and COD components. Even when used again for desorption operation, there was no deterioration in desorption performance. The adsorption and regeneration operations were repeated 20 times, but no difference in adsorption/desorption performance was observed.

In the embodiments of the present invention, the powder supported on the fibrous adsorbent does not fall off or the adsorbent is worn out during all of the adsorption/desorption and activation steps, and the linear velocity ranges from 10 m/h to 50 m/h or more (contact Sufficient adsorption and desorption was achieved in a short treatment time of 6 minutes to 2 and a half minutes). Of course, it is completely impossible to pass water at such a high linear velocity if the metal oxide powder remains.

Claims (1)

[Claims] When regenerating a phosphate ion adsorbent made of a fibrous material supporting group 1 and/or group element oxides, the adsorbent is washed with an aqueous alkali hydroxide solution and then treated with an aqueous solution containing sulfate ions. A method for regenerating the phosphate ion adsorbent.