JPS646833B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a method for removing phosphates present in tap water, sewage, human waste water, industrial water, factory wastewater, boiler water, and all other liquids. The present invention relates to a method for improving the ability of a catalytic dephosphorizing material used to remove salts. Generally, in the various liquids mentioned above that are discharged into natural water systems, inorganic phosphates such as orthophosphates, various condensed phosphates, and organic phosphates exist in various states. The presence of phosphates is a factor that induces the formation of "blue water" and "red lake" in closed or stagnant waters such as lakes, inland seas, and inner bays, and when water is used for various purposes, living organisms may be present in equipment and piping. Chemical slime is generated and chemical scale is formed, which is a major cause of accidents. Therefore, various phosphorus removal methods are being considered in order to remove the phosphates present in these liquids. A cylindrical or conical dephosphorization tower is filled with a catalytic dephosphorization material containing calcium phosphate having a particle size, and the pH of the liquid to be treated is set to 6.
-11, and then add a calcium agent such as calcium chloride depending on the concentration of soluble phosphates contained in the liquid to be treated, and let it pass through and come into contact with it at a constant flow rate. Therefore, we proposed a method to remove soluble phosphates by crystallizing and fixing calcium hydroxyapatite crystals on the surface of the catalytic dephosphorization material.
A typical chemical reaction on the surface of the catalytic dephosphorizing material in this method is as follows. _5Ca ^{2 +} _{_} ^_ _{_ _ _ _} Separation and dewatering of phosphorus materials is extremely easy, and compared to so-called flocculated sludge produced by conventional chemical coagulation and sedimentation methods, there is no need for preconceived sludge treatment facilities such as thickeners, dehydrators, and dryers. It is also an excellent dephosphorization technology that can recover phosphorus as a resource. However, in this new catalytic dephosphorization method,
The soluble phosphates contained in the liquid are called calcium hydroxyapatite [Ca ₅ (OH) (PO ₄ ) ₃ ].
In order to fix it as a crystal, calcium agents such as CaCl ₂ , Ca(OH) ₂ , CaSO ₄ etc. are added under appropriate pH conditions. Calcium carbonate is produced according to the reaction formula shown below. Ca ²⁺ +HCO ₃ ^- +OH ^- →CaCO ₃ +H ₂ O...(2) This calcium carbonate can be used if the pH of the liquid is in the pH range suitable for producing calcium hydroxyapatite or if it has been adjusted. Apatite is not produced because the production rate is higher than that of calcium carbonate, but complete PH control is difficult in actual processing equipment.
Furthermore, if the alkalinity component is concentrated, it is inevitable that the reaction of formula (2) will proceed to some extent the moment the calcium agent is added. Although the amount of calcium carbonate crystals produced under such conditions is extremely small, the calcium carbonate crystals gradually grow fixedly on the surface of the catalytic dephosphorization material over a long period of time. As a result, the surface activity of the catalytic dephosphorization material deteriorates, the dephosphorization function decreases, and the dephosphorization effect cannot be expected to be as high as initially. An object of the present invention is to provide a method that can efficiently remove phosphorus by improving the dephosphorizing ability of a catalytic dephosphorizing material whose dephosphorizing function has deteriorated in the catalytic dephosphorizing method. That is, in the present invention, by passing a liquid to be treated through a catalytic dephosphorization material containing calcium phosphate,
In a method for removing phosphates present in a liquid, the catalytic dephosphorizing material is contacted with an acid aqueous solution and then further contacted with an alkaline aqueous solution to improve the dephosphorizing ability of the catalytic dephosphorizing material. It is characterized by: An embodiment of the present invention will be described below with reference to the drawings, targeting so-called secondary treated sewage water. First, if there is a large amount of suspended solids in this secondary treated water, the suspended solids will be removed. Remove in advance through a sedimentation tank or overtank. Raw water from which suspended solids have been removed in advance through such pre-treatment operations is treated with acidic acid or alkali pH adjustment after a calcium agent is added according to the concentration of soluble phosphate in the raw water as necessary. PH to 6.0 with agent
11.0, and introduce it into the upper part of the dephosphorization tower 2 from the raw water inlet pipe 1. This dephosphorization tower 2 is filled with a catalytic dephosphorization agent containing crushed and sieved phosphate minerals containing calcium phosphate to a certain particle size (0.42 to 1.0 mm). It descends while contacting this contact dephosphorizing material 3, and the treated water flows out from the pipe 4.
and lead it out of the tower. As the catalytic dephosphorizing material 3, instead of phosphate minerals, bone char, coral sand, sand, etc., which have calcium phosphate supported on their surfaces, can also be used. In such a dephosphorization operation, the surface activity of the catalytic dephosphorizing material 3 deteriorates due to the formation of calcium carbonate and the adhesion of impurities in the raw water on the catalytic dephosphorizing material 3, and the dephosphorizing function decreases. Therefore, at the same time as the raw water is passed through the dephosphorization tower 2, or after a certain period of time has elapsed, the catalytic dephosphorization material 3 in the tower is continuously or intermittently fed into the reaction tank 6 from the take-out pipe 5,
In the reaction tank 6, the catalytic dephosphorizing material is first subjected to a contact treatment with an aqueous acid solution introduced from a tank 16 by a pump 7 and occasionally stirred by a stirrer 8. After the reaction is completed, the acid aqueous solution is discharged through the drain pipe 9. Next, tap water is introduced into the reaction tank 6 as washing water through the tap water introduction pipe 10, and the catalytic dephosphorizing material 3 is washed until the pH of the washing wastewater no longer decreases, and the washing wastewater is discharged from the drain pipe 9. Ru. Next, the catalytic dephosphorization material 3 that has been washed is further stirred from time to time by the stirrer 8 and subjected to a contact treatment with an alkaline aqueous solution introduced from the tank 17 by the pump 11 in the reaction tank 6. It is best to adjust the pH to 8 to 9.5. However, since the pH of the liquid in the reaction tank 6 decreases over time, it is desirable to adjust the pH to 8 to 9.5 with an alkaline aqueous solution while reacting with the dephosphorizing material 3. After the reaction has finished, the catalytic dephosphorization material 3 is separated from the reaction liquid and then pumped to the pump 1.
3, it is returned to the dephosphorization tower 2 and used repeatedly. The acid used in the contact treatment may be either a mineral acid or an organic acid, with an appropriate acid concentration of 0.2 to 20% and a contact time of 30 to 60 minutes.On the other hand, caustic soda or slaked lime can be used as the alkali. Activation can be achieved with a minimum contact time of 1 hour and a maximum of 3 days. When the catalytic dephosphorizing material 3 is subjected to contact treatment with an alkaline aqueous solution, calcium ions are added to the alkaline aqueous solution from the tank 18 by the pump 12 while maintaining the pH at 8 to 9.5. It is also possible to enhance the activation effect. In this case, the source of calcium ions is
Any of CaCl ₂ , Ca(OH) ₂ and CaSO ₄ can be used. Note that the amount of alkali used can be reduced by washing the catalytic dephosphorizing material 3 with clean water prior to the contact treatment with the aqueous alkali solution. In addition, the dephosphorization capacity of the catalytic dephosphorizing material 3 can be increased by performing the same operation as in the reaction tank 6 in the contact treatment outside the cylinder in the dephosphorizing tower 2 without leading the catalytic dephosphorizing material 3 out of the tower. can be increased.
In this case, the acid aqueous solution and/or alkaline aqueous solution used for the contact treatment is passed through the dephosphorization tower 2 in an upward flow from the inflow pipe 14 to the outflow pipe 15, and the catalytic dephosphorization material 3
It is more effective if the contact is carried out under conditions such that the particles expand and become fluidized. The contact treatment of the catalytic dephosphorizing material with an acid aqueous solution and an alkaline aqueous solution is carried out not only when the dephosphorizing effect of the catalytic dephosphorizing material decreases due to the passage of the liquid to be treated, but also before the passage of the liquid to be treated. This is also possible when adjusting the catalytic dephosphorization material. That is, as mentioned above, there are various types of catalytic dephosphorization materials, and depending on the type, some have calcium carbonate deposited on the surface or organic matter attached to the surface. By performing a contact treatment in advance before passing the liquid to be treated through the dephosphorization tower, the dephosphorization ability can be maintained in a good state from the beginning. As described above, according to the method of the present invention, the catalytic dephosphorizing material is subjected to a contact treatment with an acid aqueous solution and then an alkaline aqueous solution as necessary during the dephosphorization operation, thereby dephosphorizing the catalytic dephosphorizing material. The phosphorus effect could be maintained in good condition for a long period of time, making it possible to perform stable dephosphorization treatment. Next, examples of the method of the present invention will be shown. Example 1 A cylindrical dephosphorization tower with a diameter of 0.5 m and an effective depth of 2.5 m was filled with crushed and sieved phosphate rock having a particle size of 0.42 to 0.54 mm. Sewage from which coarse solids have been roughly separated is treated using the conventional activated sludge method, and secondary treatment water is used as the liquid to be treated, and the pH of the liquid to be treated is brought to around 9.0 with caustic soda (the same effect was obtained with slaked lime). In addition, calcium chloride was used as the calcium agent, and the molar weight ratio of Ca/PO ₄ was adjusted to be in the range of 1.0 to 1.5, depending on the concentration of soluble phosphates in the liquid to be treated. Added. This liquid to be treated was introduced into the dephosphorization tower and passed from above to below on the flow side at LV=2.5 m/H. Once a month, the entire amount of catalytic dephosphorization material is taken out from the dephosphorization tower and immersed in 1 ^m3 of 0.2% hydrochloric acid aqueous solution for about 1 hour, and then the catalytic dephosphorization material is washed with tap water to reduce the pH.
The contact treatment was completed by immersing it in a caustic soda aqueous solution maintained at a pH of 8.5 to 9.0 for about 1 hour, and then immersing it in 1 m ³ of a 2% calcium chloride solution maintained at a pH of about 9 for about 24 hours. and sent it back to the dephosphorization tower. While performing the above operations periodically, a water flow experiment was conducted for approximately 12 months at LV = 2.55 (m/H) using secondary treated water with pH adjusted to around 9 and calcium added as the liquid to be treated. The results are shown in Table-1. As is clear from Table 1, the phosphorus concentration of the treated water was 0.27mg/d after 12 months when the filled catalytic dephosphorization material was taken out once a month and treated with acid. Therefore, no reduction in the dephosphorization effect was observed at all. On the other hand, as a comparative example, when treatment was continued for 12 months under the same conditions without catalytic dephosphorization, the results are shown in Table 1, and the dephosphorization effect at the beginning of water flow was significant. 12 days after starting water flow
The phosphorus concentration in Kezuki's treated water was approximately 1.2mg/, and the dephosphorization effect deteriorated significantly.

[Table] Reference Example 1 Secondary treated sewage water prepared under the same conditions as in Example was passed through the water for 12 months, and the catalytic dephosphorization material with reduced phosphorus removal performance was extracted from the dephosphorization tower and treated with hydrochloric acid with a concentration of approximately 2%. , sulfuric acid, nitric acid, and phosphoric acid for 1 hour to contact treatment with an inorganic acid aqueous solution. On the other hand, the catalytic dephosphorization material was immersed in each aqueous solution of acetic acid, citric acid, and tartaric acid at a concentration of 10% for one hour, and was subjected to contact treatment with an organic acid aqueous solution. In this case, 500 g each of the catalytic dephosphorization material and one acid aqueous solution were used. After washing the acid-treated catalytic dephosphorization material with tap water, it was packed into a dephosphorization tower with an inner diameter of 25 mm, and the phosphorus removal performance was maintained under the same conditions as in Example 1 at LV = 2.5 (m/H) for about 1 month. compared. The results are shown in Table-2. As is clear from Table 2, the acids used for acid treatment of catalytic dephosphorization materials include inorganic acids (hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid) and organic acids (acetic acid, citric acid,
Even with tartaric acid), the phosphorus removal performance remained almost unchanged, confirming that any acid could be used.

【table】

[Table] Reference Example 2 500 each of catalytic dephosphorization materials whose phosphorus removal performance decreased after being used for 12 months of dephosphorization treatment in the same manner as in Example 1.
The samples were immersed in 0.2%, 5%, and 10% aqueous hydrochloric acid solutions for 1 hour, respectively, for contact treatment. On the other hand, contact treatment was performed by immersing the catalytic dephosphorization material in aqueous acetic acid solutions having concentrations of 5%, 10%, and 20% for 1 hour. After each acid-treated catalytic dephosphorization material was washed with tap water, it was filled into a dephosphorization tower with an inner diameter of 2.5 mm, and water was passed through it at LV = 2.5 (m/H) for about 1 month under the same conditions as in Example 1. , the phosphorus removal performance was compared. The results are shown in Table-3. As is clear from Table 3, the phosphorus concentration in the treated water after 30 days for the catalytic dephosphorization materials treated with hydrochloric acid is the same, and there is no significant difference in phosphorus removal performance due to the difference in the concentration of hydrochloric acid. It was confirmed that the same contact treatment as with high concentrations is possible even at dilute concentrations. Therefore, the concentration of hydrochloric acid in acid treatment is 0.2~
It may be diluted appropriately within a range of 5%. On the other hand, in the case of acetic acid, which is an organic acid, unlike hydrochloric acid, the phosphorus concentration of treated water that has been passed for 30 days is the lowest when treated at a concentration of 10%, so the concentration conditions have a significant difference in phosphorus removal performance. It has become clear that the optimum concentration for contact treatment with acetic acid is approximately 10%, and by maintaining this condition, acid treatment can be carried out efficiently.

[Table] Example 2 500 g of the catalytic dephosphorization material treated with 5% hydrochloric acid in Reference Example 2 was washed with tap water and then immersed in caustic soda aqueous solution 1 whose pH was maintained at 7, 9, and 11 for 1 hour. contact treatment. The catalytic dephosphorization materials treated with alkali under each PH condition were packed into a dephosphorization tower with an inner diameter of 25 mm, and water was passed through it at LV = 2.5 (m/H) for about 1 month under the same conditions as in Example 1.
The phosphorus removal performance was compared. The results are shown in Table 4. As is clear from Table 4, when acid-treated catalytic dephosphorization material is treated with an alkaline aqueous solution, the phosphorus concentration of the treated water reaches its lowest around PH9, and it can be seen that the phosphorus removal performance varies depending on the PH conditions of the alkaline aqueous solution. In other words, it was confirmed that the PH condition of the aqueous alkaline solution is 8.0 to 9.5 as the optimum PH range for activation.

[Table] Example 3 In Reference Example 2, 500 g of the catalytic dephosphorization material was acid-treated with 5% hydrochloric acid, and a calcium chloride solution was adjusted to give calcium ions of 5 g/50 g/ each, and caustic soda PH was added. The contact treatment was carried out by immersing it in Solution 1, which had a concentration of about 9%, for about 24 hours.
This catalytic dephosphorization material and the catalytic dephosphorization material treated only with an alkaline aqueous solution were each packed into a dephosphorization tower with an inner diameter of 25 mm, and under the same conditions as Example 1, LV = 2.5 (m/
H) was run for about one month and the phosphorus removal performance was compared. The results are shown in Table-5. As is clear from Table 5, the phosphorus concentration in the treated water of the catalytic dephosphorization material treated by this method is lower than that of the catalytic dephosphorization material simply treated with an alkaline aqueous solution, and the addition of calcium ions is found in the catalytic dephosphorization material. It was found that it is effective in improving the phosphorus removal performance of. Also, the amount of calcium ions added is 5g/50
It was possible to confirm that the amount of water per gram was almost the same, and that it was sufficient to add 50 g/or less.

【table】

【table】 [Brief explanation of drawings]

The drawing is a flow sheet of one embodiment of the method of the present invention. 1... Raw water inflow pipe, 2... Dephosphorization tower, 3... Catalytic dephosphorization material, 4... Treated water outflow pipe, 5... Output pipe, 6... Reaction tank, 7... Pump, 8... Stirrer, 9... Drain pipe, 10... Tap water introduction pipe, 11
~13...pump, 14...inflow pipe, 15...outflow pipe.

Claims (1)

[Scope of Claims] 1. A method for removing phosphates present in a liquid by passing a liquid to be treated through a catalytic dephosphorizing material containing calcium phosphate, wherein the catalytic dephosphorizing material is brought into contact with an acid aqueous solution. A catalytic dephosphorization method characterized in that after the treatment, the catalytic dephosphorization material is further subjected to a contact treatment with an alkaline aqueous solution to improve the dephosphorization ability of the catalytic dephosphorization material. 2. The method according to claim 1, wherein the concentration of the acid aqueous solution used is 0.5 to 20% when contacting the catalytic dephosphorizing material with the acid aqueous solution. 3. The method according to claim 1, wherein the catalytic dephosphorization material is subjected to contact treatment with an alkaline aqueous solution at a pH of 8 to 9.5. 4. The method according to claim 1, 2, or 3, wherein the alkaline aqueous solution is used with a calcium salt added thereto so that the amount of calcium ions is 50 g or less. 5. Claim 2, wherein the catalytic dephosphorizing material is subjected to contact treatment with an acid aqueous solution, washed with washing water, and then contact treatment with an alkaline aqueous solution.
3. The method described in Section 3, Section 3 or Section 4.