JP2008000664A - Method for treating phosphorus-containing waste water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for treating phosphorus-containing waste water, in which a phosphate ion is adsorbed/removed effectively from the waste water. <P>SOLUTION: The method for removing the phosphate ion from the waste water, in which the phosphate ion coexists with a carbonate ion, comprises the steps of: converting the carbonate ion in the waste water into free carbon dioxide and removing it; and then adsorbing/removing the phosphate ion. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for recovering phosphorus from wastewater containing phosphorus. More specifically, the present invention relates to a method for adsorbing and removing ionic acid ions from wastewater containing phosphorus.

  In recent years, organic substances, nitrogen, phosphorus, etc. contained in large quantities in rivers, various industrial wastewater or domestic wastewater, are cited as factors of eutrophication that leads to water pollution of lakes and marshes that promote the generation of algae and red tide in the nearby sea. It has been. Establishing advanced water treatment technology capable of removing nitrogen and phosphorus from high to low concentrations, which are said to be 0.15ppm and 0.02ppm of phosphorus as the limiting concentrations of nitrogen and phosphorus that cause eutrophication. Is strongly desired.

  Methods for removing phosphorus in waste water are roughly classified into two methods, biological treatment methods and physicochemical treatment methods. Among the physicochemical treatment methods, a coagulation precipitation method is generally used in which a phosphorus component is removed as a poorly soluble phosphate using a flocculant from the viewpoint of economy, treatment efficiency, and the like. However, in recent years, other than the coagulation precipitation method, from the viewpoint of the outflow of salts derived from the coagulant accompanying the addition of the coagulant, the problem of sludge treatment and phosphorus recovery / reuse, and insufficient phosphorus removal in the low concentration range. As a method, an adsorption treatment method of a phosphorus component using a phosphorus adsorbent has been tried.

In the adsorption method, aluminum hydroxide gel, magnesium oxide, titanium oxide-activated carbon composite agent, zirconium oxide-activated carbon composite agent, volcanic ash soil or the like, or modified soils thereof is used as the phosphorus adsorbent. Among them, the adsorption capacity is large, and the adsorbed phosphorus can be desorbed to recover the phosphorus, and at the same time, the regeneration of the phosphorus adsorbent can be facilitated. Patent Document 1) has been developed. Phosphorus adsorbents using these phosphate ion adsorption principles usually show a high adsorption capacity due to the phosphate ion adsorption selectivity, but there are contaminant ions from the adsorption principle. Since it is close to phosphate ions, the influence may be greatly generated in wastewater in which carbonate ions coexist.
Japanese Patent No. 3131183

  An object of this invention is to provide the waste water treatment method which removes the influence of the carbonate ion contained in waste water, and fully exhibits the phosphorus removal performance in the waste water which is a target substance by the phosphorus adsorption method.

  The present inventors removed the influence of carbonate ions contained in the waste water, and intensively studied a method for sufficiently exhibiting the phosphorus adsorption performance in the phosphorus adsorption method. The carbonate ions were removed after free carbonation. Later, a method for adsorbing and removing phosphate ions was found and the present invention was completed.

That is, the object of the present invention is a method for removing phosphate ions from wastewater in which phosphate ions and carbonate ions coexist, and after removing carbonates in the wastewater after free carbonation, the phosphate ions are then removed by adsorption. This can be achieved by a method for treating phosphorus-containing wastewater.

  According to the present invention, in the method of adsorbing and removing phosphate ions contained in waste water, carbonate ions coexisting in waste water can be effectively removed before phosphorus adsorption, so the influence of carbonate ions can be eliminated. Therefore, the adsorption performance of phosphorus as the target substance can be sufficiently exhibited.

Hereinafter, the present invention will be described in detail.
The method of the present invention is a wastewater treatment method related to so-called phosphorus adsorption recovery, in which phosphate ions are adsorbed and removed from wastewater.
The phosphate ion in the present invention refers to dissociated and ionized hydrogen phosphate ions and phosphate ions, and carbonate ions and dissociated carbonate ions and hydrogen carbonate ions.

  Wastewater is recycled and reused from human waste, domestic wastewater, livestock waste, agricultural land, forestry fields, wastewater from various other industries, factory processes and landscape water. In addition, the wastewater generated when the wastewater is dehydrated from the treated water in which the wastewater is subjected to primary, secondary, and tertiary treatment, and surplus sludge generated in biological treatment is also included.

  Further, as a method for adjusting the wastewater to be acidic in order to liberate carbonic acid, a method in which an acid is directly added to the wastewater is generally used. As the acid to be added, inorganic salts such as sulfuric acid, hydrochloric acid, nitric acid and acetic acid, organic acids such as citric acid, benzoic acid and citric acid, polyphosphoric acid and carboxylic acid can also be used. Further, the waste water may be acidified by a method in which acidic gas such as hydrogen chloride other than carbon dioxide gas is dissolved in the waste water to make it acidic. Furthermore, when ammonia nitrogen is oxidized to nitrous acid or nitric acid by nitrifying action of nitrifying bacteria, a method is also included in which the wastewater is acidified by biological reaction so that hydrogen ions are generated in the wastewater and become acidic. . Further, when the drainage pH is inclined toward the acidic side, the ionization equilibrium of carbonic acid shifts from bicarbonate ion or carbonate ion to free carbonic acid (carbon dioxide dissolved in the wastewater). At pH 6.0, the proportion of free carbonic acid is 69%, most of which is free carbon, so the pH of the waste water before carbonation removal is preferably 6.0 or lower, and more preferably 5.0 or lower. It is preferable.

  In addition, when free carbonic acid is removed in the process of removing carbonic acid, and when ionized hydrogen carbonate ions are transferred to free carbonic acid, the pH of the wastewater becomes higher than the pH before carbonic acid removal, but the pH of the wastewater before carbonic acid removal If it can be adjusted to 6.0 or less, carbonate ion removal performance can be sufficiently exhibited.

  In this wastewater treatment process, first, in order to make the wastewater acidic as a pretreatment, the pH is measured on the exit side of the acidification step, and acid is added to adjust the pH to the target value or below the target pH. Or acidify by other acidification methods.

  In addition, after the pH of the drainage reaches 6.0 or less, as a method of removing free carbonic acid, carbonation can be removed only by standing the drainage or by diffusion from the surface of the drainage. Carbon dioxide can be effectively removed by blowing and aeration. As the gas used for aeration, free carbon dioxide can be effectively removed by blowing pure nitrogen, helium, or water vapor that does not contain carbon dioxide. The amount of carbonic acid that can be dissolved in the waste water follows Henry's law, so a very small amount of carbonic acid, for example, the amount of carbonic acid contained in standard air, is very small. The phosphorus adsorption performance can be improved.

  The amount of aeration gas blown is preferably adjusted so that the ratio G / Q is 1 to 100, more preferably 5 to 100, where G is the aeration amount and Q is the amount of treated wastewater. It is preferable. The aeration time is preferably 2 minutes to 120 minutes, more preferably 6 minutes to 120 minutes. The blowing position where the aeration nozzle for aeration is installed is preferably 0.05 m to 10 m deep from the water surface, more preferably 0.2 m to 5 m.

  As aeration methods, a nozzle for gas ejection is installed at the bottom of the tank or aeration tank, and a method of directly blowing gas, a method of turbulent mixing of waste water and gas with an inline mixer, etc., tower tanks, equipment Among them, baffle plates and Raschig rings can be installed to improve the contact efficiency between gas and drainage. For the bubbles ejected from the nozzle, it is preferable to reduce the bubble diameter for the purpose of improving the interface of the bubbles for gas exchange and extending the residence time in the drainage. In order to be dissolved in the waste water and disappear, the bubble diameter is 50 mm to 0.0001 mm, more preferably 10 mm to 0.001 mm.

  As a method for removing carbonic acid, carbon dioxide can be effectively removed by continuously sucking a system containing wastewater under reduced pressure in addition to blowing gas. The decompression condition is preferably 10 kPa or less, more preferably 5 kPa or less.

The series of steps for removing the carbonic acid after acidifying the waste water can be performed intermittently or continuously.
After the carbonic acid removal, the pH of the waste water can be adjusted again according to the characteristics of the subsequent phosphate ion adsorbent.

  Adsorbents that adsorb and remove phosphoric acid after removing free carbonic acid from wastewater include ion exchange resins, hydrotalcite compounds, hydrated metal oxides, pyrolite compounds, calcium salts, etc. It is not particularly limited as long as it can adsorb and remove ions.

  Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto.

[Example 1]
Adjusting the pH of the wastewater to 4.7 by adding 0.1 mol / L hydrochloric acid to ² L of wastewater having a phosphorus concentration of 2.6 mg-P / L, carbonate ion concentration of 49 mg-CO ₃ ²⁻ / L, pH 7.3 did.
After pH adjustment, air was blown into the waste water at a flow rate of 6 L / min from an aeration nozzle made of a sintered metal having a filtration accuracy of 0.5 μm, an outer diameter of 25 mm, and a length of 100 mm to perform aeration. The installation position of the diffuser nozzle was 200 mm from the water surface, and the bubbles formed were bubbles having a diameter of 1 to 10 mm. In this state, aeration was performed for 15 minutes.

  Next, the pH of the waste water was neutralized with a 0.1 mol / L sodium hydroxide aqueous solution so that the pH was 6.8 to 7.3. After neutralization treatment, powder of hydrotalcite (Tonda Pharmaceutical Co., Ltd. TPEX (registered trademark)), a phosphorus adsorbent, was used to make polymetaphenylene terephthalamide (Teijin Techno Products Co., Ltd., Conex (registered trademark). Phosphorus adsorption was performed using a fibrous phosphorus-adsorbed molded body (diameter: 100 μm, fiber length: 2 mm) molded using)) as a binder. Phosphorus adsorption is performed by adding 0.5 g of a phosphorus-adsorbed molded body into 2 L of waste water, stirring slowly so that the phosphorus adsorbent does not settle, sampling the waste water periodically during stirring, and determining the phosphate ion concentration in the sample. Quantification was performed by the molybdenum blue method to evaluate the adsorption rate of phosphorus. The result is shown in FIG.

[Example 2]
In Example 1, after adjusting the pH to 4.7 without performing aeration treatment, drain water is put into a sealed container and sucked continuously for 60 minutes using a diaphragm pump so that the pressure in the container becomes 5 kPa. The same operation was performed except that the pH of the waste water was neutralized with a 0.1 mol / L sodium hydroxide aqueous solution so that the pH was 6.8 to 7.3. The results are shown in FIG.

[Example 3]
Phosphorus concentration is 4.3 mg-P / L, carbonate ion concentration is 52 mg-CO ₃ ²⁻ / L, pH is 7.4, 1 L of waste water is added with 0.1 mol / L hydrochloric acid to adjust pH of waste water to 5 Adjusted to .1.
After adjusting the pH, the waste water was poured into the flask, and steam generated by heating pure water to 107 ° C. in another flask was blown into the waste water for 15 minutes. Next, the water vapor that passed through the waste water was aspirated in a flask containing another barium hydroxide aqueous solution, and the gas coming out of the flask containing the waste water was completely collected. The collected barium hydroxide aqueous solution formed a barium carbonate salt and became cloudy. Next, the phenolphthalene solution was added dropwise to the cloudy solution for titration, and the amount of collected carbonic acid was calculated. The amount collected was 41 mg-CO ₃ ^2- , which was 78.8% of the carbonate ions in the initial waste water.

[Example 4]
In Example 1, the same operation was performed except that 0.8 L of waste water subjected to pH adjustment and stripping treatment with water vapor in Example 5 was used as waste water, and 0.2 g of a phosphorus adsorption molded body was used. The results are shown in FIG.

[Example 5]
In the continuous waste water treatment system shown in FIG. 4, the average phosphorus concentration is 6.1 mg-P / L and the average carbonate ion concentration is 52 mg-CO ₃ ²⁻ / L. The raw water was taken up at 3.6 ml per minute, and 0.1 mol / L hydrochloric acid 2 was added with the titration pump 3 so that the pH of the pH adjusting tank 4 was adjusted to 4.6 to 5.3. .
Next, the raw water after pH adjustment was introduced into the aeration tank 5 having a capacity of 900 ml, and an aeration nozzle 6 installed at a position 0.2 m from the water surface was installed. The flow meter 7 was adjusted so that 500 ml of air per minute was blown into the waste water from the diffuser nozzle 6. Bubbles 8 exiting from the diffuser nozzle 6 had a diameter of 1 to 5 mm.

The whole amount of raw water aerated in the aeration tank 5 was fed to a column 10 filled with a phosphorus adsorption molded body by a water feed pump 9. The phosphorus adsorption molded body 11 filled in the column 10 is made of polymetaphenylene terephthalamide (Teijin Techno Products Co., Ltd.) using a powder of hydrotalcite (Tonda Pharmaceutical Co., Ltd. TPEX (registered trademark)) which is a phosphorus adsorbent. ) Conex (registered trademark)) is used as a binder, and the phosphorous-adsorbed molded body 11 has a mean particle size of 900 μm and hydrotalcite 90 wt%.
The column 10 was packed with the molded body at a packing density of 0.33 g / cm ³ . The waste water after passing through the column 10 is periodically sampled, and the pH of the waste water is neutralized with a 0.1 mol / L sodium hydroxide aqueous solution so that the pH becomes 6.8 to 7.3, and then in the sample. As a result of quantifying the phosphoric acid ion concentration by the molybdenum blue method, the time for the phosphorus concentration after adsorption to reach 1 mg-P / L or more was 174 hours after the start of water flow through the column 10. The result is shown in FIG.

[Comparative Example 1]
In Example 1, the same operation was performed except that the pH adjustment operation was not performed. After the aeration treatment, it was confirmed again that the pH was 6.8 to 7.3, and the phosphorus adsorption rate was evaluated. The result is shown in FIG.

[Comparative Example 2]
In Example 1, the same operation was performed except that neutralization was performed so that the pH was immediately adjusted to 6.8 to 7.3 without aeration. After neutralization, the same phosphorus adsorption rate as in Example 1 was evaluated. The result is shown in FIG.

[Comparative Example 3]
In Example 1, the same operation was performed except that the aeration time was 2 minutes. After the aeration treatment, the same phosphorus adsorption rate as in Example 1 was evaluated. The result is shown in FIG.

[Comparative Example 4]
In Example 3, when steam was blown in the same manner except that the pH was not adjusted, the amount of carbonate collected in the barium hydroxide aqueous solution was 5 mg-CO ₃ ^2- , and carbonate ions in the initial waste water Of 9.6%.

[Comparative Example 5]
In Example 4, the same operation was performed except that 0.8 L of the waste water obtained in Comparative Example 4 was used. The phosphorus adsorption rate was evaluated. The result is shown in FIG.

[Comparative Example 6]
In Example 5, the same column liquid feeding was performed except that pH adjustment and aeration treatment were not performed, and the phosphate ion concentration after passing through the column was quantified by the molybdenum blue method.
As a result, the time for the phosphorus concentration after adsorption to reach 1 mg-P / L or more was 93 hours after the start of column flow. The result is shown in FIG.

  The present invention is expected to be applied to the wastewater treatment field in which phosphorus is recovered by a method for recovering phosphorus of eutrophication substances contained in various wastewaters, in particular, dephosphorization by an adsorption method. For example, an efficient and economical wastewater treatment can be performed by treating the wastewater that flows into a closed water area and has a problem of eutrophication of the water area by the method of the present invention.

It is the result of the phosphorus adsorption test in Examples 1, 2 and Comparative Examples 1, 2, 3. It is a result of the phosphorus adsorption test in Example 4 and Comparative Example 5. It is a result of the phosphorus adsorption test in Example 5 and Comparative Example 6. FIG. 6 is a flowchart schematically showing a step of wastewater treatment performed in Example 5.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid feed pump 2 Hydrochloric acid 3 Titration pump 4 pH adjustment tank 5 Aeration tank 6 Aeration nozzle 7 Flowmeter 8 Bubble 9 Liquid feed pump 10 Column 11 Phosphorus adsorption molding

Claims (7)

  A method for removing phosphate ions from wastewater in which phosphate ions and carbonate ions coexist, wherein the carbonate ions in the wastewater are removed after being converted to free carbonic acid, and then phosphate ions are adsorbed and removed. Treatment method for phosphorus-containing wastewater.   The treatment method according to claim 1, wherein free carbonation of carbonate ions is performed by making the pH of the wastewater acidic.   The processing method of Claim 2 which makes pH of waste water 6.0 or less.   The processing method according to claim 1, wherein the removal of free carbonic acid is carried out by deaeration treatment of waste water.   The treatment method according to claim 4, wherein the deaeration treatment is performed by blowing and aeration of at least one gas selected from the group consisting of air, nitrogen, water vapor, and helium into the waste water.   The ratio G / Q is 1 to 100 when the amount of aeration / aeration in aeration is Q and the amount of treated water is Q, the aeration time is 2 minutes to 120 minutes, and the aeration position is 0.05 m to 10 m from the drainage liquid surface. The processing method according to claim 5, wherein the depth is set.   The processing method of Claim 4 which performs a deaeration process under the reduced pressure of 10 kPa or less.

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