JP2002159977A - Method and equipment for removing and recovering phosphoric acid ion from phosphorus-containing water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To establish a novel technology capable of removing phosphoric acid ions at a high degree from water containing the phosphoric acid ions of a dilute concentration and recovering phosphorus as a high-value resource. SOLUTION: The method for removing and recovering the phosphoric acid ions from the phosphorus-containing water comprises adding iron hydroxide particles to the phosphorus-containing water (raw water) to remove the phosphoric acid ions in the raw water, adding an acid to an iron hydroxide particle slurry capturing the phosphoric acid ions to regulate the slurry to acidity below pH 3, then subjecting the slurry to a solid-liquid separation, returning the separated iron hydroxide particles separated therein and adding ammonium and Mg2+ to the separated liquid obtained by the solid-liquid separation to deposit NH4 MgPO4 precipitate under alkaline pH conditions, and the equipment for the same is also provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for removing phosphate ions from water containing phosphate ions such as sewage, sewage treated water, night soil, biologically treated human waste water, and various industrial wastewaters, and using phosphorus as a resource. New technologies that can be collected.

[0002]

2. Description of the Related Art Conventionally, a technique for removing phosphate ions is as follows.
Coagulation sedimentation, adsorption, crystallization dephosphorization, etc. are known.
Was. However, about several mg / liter usually contained in sewage, etc.
Phosphate ions with a low concentration can be used for fertilizers, etc.
There was no ideal technology to recover as valuable resources. Therefore
The inventor first made the hydrated iron oxide particles and zeolite particles
Contact with water to remove ammoniacal nitrogen and phosphoric acid in raw water
Removes ions and removes ammoniacal nitrogen and phosphate ions
After bringing the captured particles into contact with a NaOH solution,
Mg in liquid ²⁺To add NH_FourMgPO_FourPrecipitate the precipitate
And removal of ammonia nitrogen and phosphate ions
(Japanese Patent Application Laid-Open No. 7-284762).

[0003]

Although this method has an excellent effect in recovering nitrogen and phosphorus as resources, it is possible to mix powdered zeolite and hydrated iron oxide particles or use polyacrylamide gel alone. There is a problem that it takes a lot of time to prepare a gel because of inclusion in the inside.
In addition, in the fluidized contact method using powdered hydrated iron oxide and zeolite without using a gel, the removal rate decreases as the removal time of ammonium nitrogen and phosphate ions of activated sludge treated sewage becomes longer. Therefore, at this time, the supply of the raw water is stopped, and the apparatus has to be temporarily stopped in order to take out the entire amount of the settling slurry at the bottom of the settling tank out of the system.

The present invention has been made in view of such conventional problems, and does not require the trouble of gel preparation and does not need to stop the apparatus. An object of the present invention is to establish an ideal new technology capable of removing a phosphorus having a low concentration and recovering the removed phosphorus as a valuable resource. Most of the phosphorus contained in sewage such as sewage in Japan is said to originate from phosphorus from imported foreign phosphate ores. In addition, since it is pointed out that phosphate ore resources will be depleted in the near future, it is extremely significant to establish a technology capable of recovering phosphorus from wastewater as in the present invention.

[0005]

The present invention has solved the above-mentioned problems by the following means. (1) Hydrated iron oxide particles were added to phosphorus-containing water to remove phosphate ions from the phosphorus-containing water, and an acid was added to the iron hydroxide particle slurry incorporating the phosphate ions to adjust the pH to an acidity of 3 or less. Thereafter, solid-liquid separation is performed, the separated iron hydroxide particles separated therefrom are returned to the phosphorus-containing water, and ammonium and Mg ²⁺ are added to the separated liquid obtained by the solid-liquid separation, and NH ₄ MgPO ₄ is added under alkaline pH conditions. _{(4) A} method for removing and recovering phosphate ions from phosphorus-containing water, which comprises causing a precipitate to precipitate.

(2) A device for contacting hydrated iron oxide particles by adding hydrated iron oxide particles and a polymer flocculant to phosphorus-containing water and bringing the particles into contact with the phosphorus-containing water. Hydraulic iron oxide particles are drawn from the apparatus, and the hydrated iron oxide particles are pulled out from the drawing tube to store the hydrated iron oxide particles. A phosphorus desorption tank for desorbing phosphorus from iron oxide particles,
A treatment slurry from a phosphorus desorption tank is introduced to precipitate hydrated iron oxide particles, and a precipitation tank for separating a slurry of desorbed hydrated iron oxide particles and a separated solution containing desorbed phosphorus, magnesium ions are added to the separated solution. MAP to be added to precipitate MAP
An apparatus for removing and recovering phosphate ions from phosphorus-containing water, comprising a precipitation tank and a circulation pipe for circulating a slurry of hydrated iron oxide particles from the precipitation tank to the supplied phosphorus-containing water.

Here, the hydrated iron oxide referred to in the present invention is a solution of iron salt containing NaOH, Mg (OH) ₂ , MgO,
In addition to ferric hydroxide or the like, which is formed by adding an alkali such as Ca (OH) ₂ , CaO, or CaCO ₃ to increase the pH of the solution, Fe ₂ O ₃ .nH ₂ O or FeOOH.nH ₂ O It means hydrate of iron oxide. In addition, the hydrated iron oxide particles refer to the hydrated iron oxide particles that are formed in the form of fine particles when the hydrated iron oxide particles are formed. At this time, as a configuration of the contact device, it is preferable to form a fluidized bed or, after the adsorption of phosphorus, consider a solid-liquid separation, and the particle size is such that those operations are easily performed. Is preferred.

[0008]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of a treatment system for carrying out the present invention, in which an iron hydroxide particle fluidized bed device is used as an iron hydroxide particle contact device. This treatment system mainly comprises a cylindrical column 1 containing an iron hydroxide particle fluidized bed 12, a drawing slurry storage tank 2, a phosphorus desorption tank 3, a precipitation tank 4, and a MAP crystallization tank 5. In the cylindrical column 1, a treated water supply pipe 6 for supplying the phosphorus-containing water 11 to the treatment system is connected to a lower portion of the cylindrical column 1. Before the supply pipes of the fine particles 14 and the polymer flocculant 15 are connected to the lower part of the cylindrical column 1, they are connected to mix each of the chemicals with the phosphorus-containing water 11. Further, the cylindrical column 1 is provided with a treated water discharge pipe 7 at a large diameter portion 8 at the top thereof, and is provided with a valve 9 at an intermediate position for discharging the iron hydroxide particles adsorbing phosphorus. An iron particle extraction tube 10 is provided, which defines the height of the blanket of the iron hydroxide particle fluidized bed 12. Note that the phosphorus-containing water may be referred to as “raw water”.

The raw water supplied from the treated water supply pipe 6 is
The iron hydroxide fine particles 14 and the polymer flocculant 15 are supplied from a supply pipe of the iron hydroxide fine particles 14 and the polymer flocculant 15, and the circulating iron hydroxide slurry 18 is supplied thereto. 1 and contact with the iron hydroxide fine particles 14 and the like in the iron hydroxide particle fluidized bed 12 so that phosphorus in the raw water is adsorbed to the iron hydroxide fine particles 14 and removed. The iron hydroxide particles having adsorbed phosphorus are drawn out from the iron hydroxide particle drawing pipe 10 at an intermediate position of the cylindrical column 1 and enter the drawing slurry storage tank 2. The mounting position of the iron hydroxide particle extraction tube 10 in the cylindrical column 1 determines the position of the surface of the iron hydroxide particle fluidized bed 12. An overflow portion is formed at the large diameter portion 8 at the top of the cylindrical column 1, from which treated water 13 is discharged by a treated water discharge pipe 7.

The iron hydroxide particles having adsorbed phosphorus once stored in the drawing slurry storage tank 2 are sent to a phosphorus desorption tank 3, where sulfuric acid 16 is added and adjusted to pH 3 or less, preferably pH 2-3. Next, it is sent to the precipitation tank 4 and separated into a separated liquid 17 containing phosphorus and a slurry of iron hydroxide particles from which phosphorus has been desorbed. The separated liquid 17 is sent from the upper part of the sedimentation tank 4 to the MAP crystallization tank 5, and the latter iron hydroxide particles are circulated from the bottom part of the sedimentation tank 4 as a circulating iron hydroxide slurry 18 in the water supply pipe 6 for the treated water supply pipe 6. It is configured to be returned to the vicinity of the supply pipe of the iron fine particles 14. Separation liquid 17 is mixed with Mg (O 2) in the middle of the pipe to MAP crystallization tank 5.
H) is added ₂ 19, NH ₄ in MAP crystalliser 5 ⁺
20 is added to precipitate a MAP 21 precipitate, which is separated and recovered from the tank bottom.

FIG. 1 is a schematic diagram showing the operation of the present invention.
It is an outline to explain the theory. FIG.
As shown in the figure, the present invention takes the following reaction process.
It is. a) Phosphate ions in wastewater (hereinafter PO_Four ^3-Also called)
It is removed by the phosphorus adsorption action of the hydrated iron oxide particles. b) Desorbed PO_Four ^3-Hydrated iron oxide particles
By contact with an acidic solution (preferably pH 2-3)_Four ^3-To
After desorption, solid-liquid separation is performed. PO isolated _Four ^3-Desorption
The particles are added to the raw water again and_Four ^3-Is removed. c) Desorbed PO_Four ^3-Ammonium in acidic aqueous solution containing
And Mg²⁺Is added and the alkaline pH (pH 8.5 to 8.5)
9.5 is preferred) and NH_FourMgPO_Four(Abbreviated as MAP)
Let it settle. The present invention is based on a technology that combines the above-described reaction processes.
And PO from waste water_Four ^{Three -}High speed and high
Phosphorus is added to fertilizer value MAP while preventing soil pollution.
Collecting it as a resource is the key to its technical philosophy
I have.

To obtain dense hydrated iron oxide particles having a high ability to adsorb and remove PO ₄ ^3- , it is necessary to prepare an aqueous solution of ferric polysulfate, ferric chloride, ferrous sulfate, and ferric sulfate using Mg. System, C
It is obtained by a method of neutralizing with an a-based alkaline agent. What is obtained by such a method includes ferric hydroxide particles as well as hydrates of iron oxides such as Fe ₂ O ₃ .nH ₂ O and FeOOH.nH ₂ O. Further, when the aqueous solution of ferric polysulfate or the like is neutralized with an Mg-based or Ca-based alkali agent to form particles of ferric hydroxide or the like, the precipitate is easily precipitated and concentrated, not as a bulky slurry that is not easily precipitated and concentrated. Dense particles of hydrated iron oxide and the like can be obtained. In addition, aluminum hydroxide, activated alumina, allophane and Kanuma soil are also PO
₄ ^3- can be adsorbed, but when it is brought into contact with an acidic solution to desorb phosphorus (hereinafter also referred to as P), these adsorbents dissolve as aluminum ions. I can not use it.

In order to carry out the present invention, a method in which iron hydroxide particles are brought into contact with raw water while acting as a fluidized bed can be recommended. In this case, a part for regenerating (desorbing phosphorus) the iron hydroxide particles having adsorbed phosphorus is provided separately from the fluidized bed,
Iron hydroxide particles are continuously or intermittently withdrawn from the fluidized bed portion little by little into the regenerating portion, and sulfuric acid or hydrochloric acid is added thereto to adjust the pH to 2.
And stirred for about 1 hour in the ~ 3 acidic, PO ₄ ^3- is desorbed from the iron hydroxide particles incorporating the PO ₄ ^3-, PO ₄ ^3-
Is obtained at a high concentration. In addition, as a contact device for bringing iron hydroxide particles into contact with raw water, in addition to a fluidized bed device, there is a contact device for bringing into contact in a stirring state, a vortex state, or the like. Therefore, a fluidized bed apparatus is preferable in that contact and separation can be performed by one apparatus.

When the iron hydroxide fine particles from which phosphorus has been desorbed are subjected to solid-liquid separation and the separated iron hydroxide fine particles are returned to raw water again, the recycled iron hydroxide fine particles adsorb and remove phosphorus in the raw water. The amount of phosphoric acid adsorbed by the iron hydroxide from the phosphorus-containing water is most preferably weakly acidic at a pH of about 6. Therefore, when an acidic solution of the present invention having a pH of 3 or less, preferably pH 2 to 3 is added to the raw water, Has a great effect that the pH of the solution can be appropriately reduced, and it is easy to match the optimum pH for phosphorus removal. Since the the separation solution containing phosphorus desorbed at a high concentration, when this was added magnesium hydroxide or magnesium oxide and ammonium ions to a pH of about _{^{9, MH 4 + + Mg 2+}} + PO 4 3- → The precipitation reaction of NH ₄ MgPO ₄ ↓ proceeds to precipitate crystalline magnesium ammonium phosphate (MAP), which is separated and collected.

[0015]

EXAMPLES Hereinafter, with reference to PO ₄ ^3- way removal and recovery of the water present invention, raw water PO ₄ ^{3 -} shows a specific embodiment for removing and recovering. However, embodiments of the present invention are not limited by the following description.

[0016] (Example 1) PO ₄ ^3- of removing test: The complex sewage activated sludge treatment and treated water [(as P) PO ₄ ^3- including 1.2～1.8Mg / l] and the raw water, Iron hydroxide fine particles (produced by neutralizing ferric sulfate with magnesium hydroxide)
A PO ₄ ^3- removal test was carried out. That is, diameter 10
Raw water was supplied to a cylindrical column having a height of 1 m and a height of 150 cm / min. 150 mg / L of iron hydroxide fine particles were added to the raw water, and 1 mg / L of a polyacrylamide polymer flocculant was added, and then the mixture was supplied to the column. As a result, a high concentration of iron hydroxide fine particles aggregated in the column (iron hydroxide particles SS concentration 52 g
/ Liter) of a fluidized bed. The height of the fluidized bed by extracting the slurry from the fluidized bed interface is 750 mm
Was controlled.

Sulfuric acid was added to the slurry containing iron hydroxide particles extracted from the interface of the fluidized bed to adjust the pH to 2.5. After stirring for 1 hour, the iron hydroxide was precipitated and separated. One liter was detected, and it was confirmed that phosphorus was desorbed from the phosphorus-adsorbed iron hydroxide by this operation. Thereafter, the liquid was allowed to stand, iron hydroxide was settled and separated, and the separated particles were added to raw water. After 48 hours from the start of this circulation operation, the phosphorus concentration of the treated water at the time when it is considered to reach a steady state is 0.07 to 0.09.
mg / l and phosphorus were highly removed.

Next, magnesium hydroxide and ammonium chloride were added to the acidic separation solution in a molar ratio of [NH ₄ ⁺ ]: [M
g ²⁺ ]: [PO ₄ ^3- ] = 1: 2: 1 and stirred for 30 minutes at pH 9 to produce a precipitate of NH ₄ MgPO ₄ , which has a large fertilizer value, and P inside
Was reduced to 3 mg / liter and phosphorus was effectively recovered as MAP.

[0019]

According to the method and apparatus for removing and recovering phosphate ions of the present invention, the following remarkable effects can be obtained. (1) A small amount of PO ₄ ^3- contained in various types of water such as sewage
Can be highly removed. (2) MAP with high value of removed phosphorus as fertilizer
And contribute to prevention of depletion of phosphorus resources. (3) When desorbing phosphoric acid from iron hydroxide particles that have taken in phosphate ions, it is performed by adding an acid to the iron hydroxide particle slurry and adjusting the pH to an acidity of 3 or less.
It is easy to recover the iron hydroxide particles, and when the recovered and circulated iron hydroxide particle slurry is added to the raw water, the pH can be easily adjusted to a range suitable for phosphorus adsorption. And p
When H2 to H3 is used, the required amount of acid can be reduced.

[Brief description of the drawings]

FIG. 1 shows a schematic diagram of an example of an apparatus for removing and recovering phosphate ions of the present invention.

[Explanation of symbols]

Reference Signs List 1 cylindrical column 2 drawing slurry storage tank 3 phosphorus desorption tank 4 sedimentation tank 5 MAP crystallization tank 6 treated water supply pipe 7 treated water discharge pipe 8 large diameter section 9 valve 10 iron hydroxide extraction pipe 11 phosphorus-containing water 12 iron hydroxide particle fluidized bed 13 treated water 14 iron hydroxide particle 15 polymer flocculant 16 sulfate 17 separated liquid 18 circulating iron hydroxide slurry _{19 Mg (OH) 2 20 NH} 4 + 21 MAP

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D015 BA19 BB05 CA18 DB02 EA32 FA01 FA02 FA22 FA28 4D024 AA04 AB12 BA14 BB01 BC05 DA08 DB20 DB21 4D038 AA08 AB48 AB54 BA04 BB18 4D062 BA19 BB05 CA18 DB02 EA32 FA01 FA02 FA22 FA28

Claims (2)

[Claims] 1. The method of claim 1, wherein the hydrated iron oxide particles are added to the phosphorus-containing water to remove phosphate ions from the phosphorus-containing water, and an acid is added to the iron hydroxide particle slurry containing the phosphate ions to obtain an acidity of pH 3 or less. After the adjustment, solid-liquid separation was performed, the separated iron hydroxide particles separated therefrom were returned to the phosphorus-containing water, and ammonium and Mg ²⁺ were added to the separated liquid obtained by the solid-liquid separation to obtain NH 4 under alkaline pH conditions. ₍₄ ) A method for removing and recovering phosphate ions from phosphorus-containing water, comprising causing precipitation of ₄ MgPO ₄ precipitates. 2. A hydrated iron oxide particle contact device for adding hydrated iron oxide particles and a polymer coagulant to phosphorus-containing water and bringing the hydrated iron oxide particles into contact with the phosphorus-containing water, and the contact device. A drawing slurry storage tank for withdrawing hydrated iron oxide particles from a hydrated iron oxide particle withdrawal tube and storing the hydrated iron oxide particles, introducing hydrated iron oxide particles from the storage tank and adding a mineral acid to hydrated oxidation. A phosphorus desorption tank for desorbing phosphorus from iron particles, a treatment slurry from the phosphorus desorption tank is introduced to precipitate hydrated iron oxide particles, and into a slurry of desorbed hydrated iron oxide particles and a separated solution containing desorbed phosphorus. Having a sedimentation tank for separating, a MAP precipitation tank for adding magnesium ions to the separated liquid to precipitate MAP, and a circulation pipe for circulating slurry of hydrated iron oxide particles from the precipitation tank to the supplied phosphorus-containing water. Characterized by phosphorus-containing water Equipment for removing and recovering phosphate ions.