JPH10323677A - Waste water treatment device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a waste water treatment device in which phosphorus is recovered efficiently and economically as ammonium magnesium phosphate hexahydrate (MAP) from waste water containing phosphorus at high concentration. SOLUTION: The waste water treatment device is equipped with a solid-liquid separation means (settling tank 1) for separating and removing solid content in waste water containing ammonium ions and phosphate ions, a seed crystal production tank 2 in which fine crystal of MAP is produced by adding magnesium compound and a pH adjustor to waste water after solid-liquid separation and a dephosphorization tank 3 in which fine crystal taken out of the seed crystal production tank 2 is grown and ammonium ions and phosphate ions are removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wastewater treatment apparatus, and more particularly, to a wastewater containing ammonium ions and phosphate ions such as a sludge treatment separation liquid generated by a biological phosphorus removal method in sewage treatment. Compound and pH
The reaction is carried out by adding an adjusting agent, and magnesium ammonium phosphate hexahydrate in crystalline state (stravit or MAP)
The present invention relates to a wastewater treatment apparatus for generating and recovering wastewater.

[0002]

2. Description of the Related Art Conventionally, as a method for removing phosphorus and nitrogen in wastewater, for example, Japanese Patent Application Laid-Open Nos.
As described in JP-A-99091, a magnesium compound is added to wastewater containing ammonium ions and phosphate ions, and a pH adjuster made of alkali is added to adjust the pH to 8 or more. These are reacted by stirring to produce and grow fine crystals of magnesium ammonium phosphate (MAP), and the suspended solids in the wastewater and the generated crystals of magnesium ammonium phosphate are separated to form ammonium ions and phosphate ions. A method of removing and collecting magnesium ammonium phosphate as solid particles is described.

An apparatus (reactor) for performing the above method
Various types have been proposed. Among these apparatuses, a draft tube type reactor which performs aeration and agitation has a feature that crystals having a relatively uniform particle size can be continuously obtained. In order to proceed efficiently, it was necessary to continuously or intermittently supply seed crystals into the reactor. For this reason, MAP recovered from the reactor is classified to take out fine crystals, or coarse particles are crushed into fine crystals, which are returned to the reactor as seed crystals.

[0004] However, the operation of classifying the recovered MAP to take out fine particles or crushing coarse particles is advantageous in a large-scale treatment plant where a relatively large amount of MAP can be recovered, but is small. In some treatment plants, there were problems in terms of economy.

[0005] Therefore, an object of the present invention is to provide a wastewater treatment apparatus that can efficiently recover MAP even in a relatively small-scale treatment plant.

[0006]

In order to achieve the above object, a wastewater treatment apparatus according to the present invention comprises a wastewater containing ammonium ions and phosphate ions containing a magnesium compound and a pH value.
In a wastewater treatment apparatus that generates a crystal of magnesium ammonium phosphate hexahydrate by adding a regulator, a solid-liquid separation unit that separates and removes a solid content in the wastewater, and the magnesium compound is added to the wastewater after the solid-liquid separation. And a pH adjusting agent to form a fine crystal of magnesium ammonium phosphate hexahydrate, and a fine crystal derived from the seed crystal generating tank is used as a wastewater to which a magnesium compound and a pH adjusting agent are added. And a dephosphorization tank for growing the medium in order to remove the ammonium ions and the phosphate ions.

Further, the wastewater treatment apparatus of the present invention is provided with a dilution water supply unit for diluting the treated water at an outlet of the treated water in the seed crystal production tank and the dephosphorization tank.
The seed crystal production tank and the dephosphorization tank are provided with a washing water jetting part for washing the tank wall.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a system diagram showing one embodiment of a wastewater treatment apparatus according to the present invention. This wastewater treatment apparatus includes a sedimentation tank 1 serving as a solid-liquid separation means, and a seed crystal for generating a magnesium ammonium phosphate hexahydrate crystal by adding a magnesium compound and a pH adjuster to the wastewater after the solid-liquid separation. A tank 2 and a dephosphorization tank 3, a magnesium compound storage tank 4 for storing the magnesium compound, for example, a magnesium chloride aqueous solution having a predetermined concentration, and a pH adjusting agent storage tank for storing a pH adjuster, for example, an aqueous sodium hydroxide solution having a predetermined concentration. 5 and an acid storage tank 6 for storing an acid for cleaning.

The seed crystal production tank 2 and the dephosphorization tank 3 have the same basic structure, and two large-diameter and small-diameter cylinders are placed inside a bottomed cylindrical reaction vessel 11 having a bottom surface formed in a funnel shape. Body 1
2 and 13 are arranged, and a stirring blade 14 is provided inside the small-diameter cylindrical body 13. At the bottom of the reaction tank 11, there is provided a crystal discharge unit 15 for extracting the generated MAP crystals. On the inner peripheral side of the large-diameter cylinder 12 at the top of the tank, a wastewater inflow path 16, a magnesium compound Supply route 1
7. A pH adjusting agent supply path 18 is provided, and a treated water discharge unit 19 and a dilution water supply path 20 are provided on the outer peripheral side of the large-diameter cylindrical body 12. Further, at an appropriate position in each tank, a washing water jetting section 21 for washing the inside of the tank and an acid supply section 22 are provided, and the dephosphorization tank 3 is withdrawn from the seed crystal generation tank 2. There is provided a seed crystal supply path 23 for supplying the fine crystal of the MAP.

The large-diameter cylinder 12 is provided in a ring shape from the upper portion of the small-diameter cylinder 13 to above the water surface. The small-diameter cylinder 13 installed inside the large-diameter cylinder 12 is This acts as a draft tube for forming a circulating flow in the treated water, and the internal agitating blade 14 causes a downward flow, for example, toward the inner peripheral side of the small-diameter cylindrical body 13 and rises to an outer peripheral side where a large water area can be obtained. Each stream is formed into a circulating stream.

The outer peripheral portion of the large-diameter cylindrical body 12, the reaction tank 1
The water substantially corresponding to the amount of wastewater flowing from the wastewater inflow path 16 rises between the inner peripheral surface of the MAP 1 and the MAP crystal, and acts as a product separation part that sediments and separates the generated MAP crystals during the rising process. This portion has a sufficient water area so that small crystals of MAP and small pieces generated by collision can be reliably settled.

The wastewater inflow path 16, magnesium compound supply path 17, and pH adjusting agent supply path 18 are provided with appropriate flow rate control means, respectively. The magnesium compound is sent to the reaction tank 11 at a constant flow rate, and the magnesium compound is sent to the reaction tank 11 at a predetermined flow rate according to the amount of phosphorus to be treated. Seawater can also be used as the magnesium compound-containing liquid.

The flow rate of the pH adjusting agent supplied from the pH adjusting agent supply path 18 is adjusted so that the inside of the reaction tank 11 has a predetermined pH, for example, pH 8.5 to 8.7. It is sent to the tank 11.

In the wastewater treatment apparatus having such a configuration,
In the sedimentation tank 1, of the suspended solids in the water to be treated, those having relatively good sedimentation are separated by sedimentation. Thereby, the amount of solids that settles together with the MAP crystals generated in the seed crystal generation tank 2 and the dephosphorization tank 3 can be reduced, and the purity of the MAP to be recovered can be increased. It is more effective that the water area load of the sedimentation tank 1 is smaller than the water area load of the product separation section (the outer peripheral portion of the large-diameter cylindrical body 12) in the dephosphorization tank 3.

The treated water subjected to solid-liquid separation in the settling tank 1 is
It is distributed to the seed crystal production tank 2 and the dephosphorization tank 3 at a predetermined ratio. The water to be treated flowing into the seed crystal production tank 2 is adjusted to a predetermined pH value by the pH adjuster supplied from the pH adjuster supply path 18 together with the magnesium ion-containing water supplied from the magnesium compound supply path 17. And circulates inside and outside the small-diameter cylindrical body 13.
Thereby, ammonium ions and phosphate ions in the water to be treated react with magnesium ions to generate MAP crystals.

The generated MAP crystal is a large-diameter cylinder 12
By appropriately setting the upward flow rate at the outer periphery of the tank, it is possible to separate from the SS component and by-product calcium phosphate in the water to be treated and settle it at the bottom of the tank. In other words, M having a crystal length of 0.046 to 0.074 mm
The upward flow velocity at which the AP crystal particles start to rise with the upward flow is about 10 cm / min, and the calcium phosphate is a few c / min.
m starts rising at the upward flow velocity, so that the large-diameter cylindrical body 12
The upward flow rate at the product separation section on the outer periphery of
cm or less, for example, about 5 cm, it is possible to create a state in which calcium phosphate and the like flow out of the treated water discharge unit 19 together with the treated water, but MAP hardly flows out.

By appropriately setting the upward flow rate at the outer peripheral portion of the small-diameter cylindrical body 13, it is possible to settle a MAP crystal in a desired range suitable as a seed crystal. By setting the size to about 50 cm, crystals of about 0.1 to 0.2 mm
Can be allowed to settle to the bottom.

On the other hand, in the reaction tank 11 of the dephosphorization tank 3, similarly to the above, the treated water after solid-liquid separation from the wastewater inflow path 16, the magnesium ion-containing water from the magnesium compound supply path 17, p from the pH regulator supply path 18
H regulator and the seed crystal supply path 23
From the MAP, fine crystals of MAP extracted together with a part of the treatment water from the crystal discharge part 15 of the seed crystal production tank 2 are supplied as seed crystals.

Therefore, the ammonium ions and phosphate ions in the water to be treated, which flow into the reaction tank 11, and the magnesium ions in the water containing magnesium ions have a small diameter while being sufficiently mixed with the crystals of MAP circulating in the circulation flow. By circulating inside and outside the cylindrical body 13, the MAP generation reaction mainly occurs on the crystal surface of the MAP, whereby the MAP gradually grows and becomes large crystal particles.

The large MAP crystal particles settle at the bottom of the reaction tank 11 due to the difference in specific gravity with water, and the SS component and by-product calcium phosphate in the wastewater are removed from the large-diameter cylindrical body 12.
Rises along with the treated water and is discharged from the treated water discharge unit 19.

As described above, in the normal operation state, a predetermined amount of the water to be treated, the magnesium compound and the predetermined amount are supplied from the wastewater inflow path 16, the magnesium compound supply path 17 and the pH adjusting agent supply path 18 in the seed crystal production tank 2. pH
Fine MAP crystals are generated by the flow of the adjusting agent. In the dephosphorization tank 3, in addition to a predetermined amount of water to be treated, a magnesium compound, and a pH adjusting agent, fine MAP crystals generated in the seed crystal generating tank 2 are formed. The MAP crystal is grown by flowing a suitable MAP crystal as a seed crystal from the seed crystal supply path 23. A predetermined size, for example, 0.5 to 1.0 m
The MAP crystals that have grown to about m and settled at the bottom of the tank are withdrawn from the crystal discharge unit 15 and subjected to dehydration and drying operations, and then used as a slow-release fertilizer as a product. Can be effectively used as a fertilizer containing the three major nutrients of plants by subjecting them to processing such as granulation.

By supplying the fine crystals generated in the seed crystal forming tank 2 as seed crystals to the dephosphorizing tank 3,
Since the concentration of the reaction product (MAP) in the dephosphorization tank 3 can always be maintained at a predetermined value or more, the reaction for generating a new crystal nucleus can be suppressed, and the crystal growth reaction on the crystal surface can be promoted. Can be increased, the residence time in the apparatus can be reduced, and the size of the entire apparatus can be reduced. Since the seed crystal having a size of about 0.1 to 0.2 mm has a sedimentation speed of about 50 cm per minute, the surface area load on the product separation part of the dephosphorization tank 3 and the sedimentation tank 1 is reduced. Can be set high, so that the equipment scale can also be reduced in size.

As described above, the water to be treated and the magnesium compound are separately supplied to the reaction tank 11 so that
There is almost no need to stop the equipment for scale removal because the pipes and the like are not blocked by scale, and the phosphorus contained in the digestion tank desorbed liquid etc. in the sewage treatment equipment is continuously used as MAP which is extremely effective as a fertilizer. Can be recovered. Furthermore, two cylindrical bodies 12, 13 of large diameter and small diameter
Impeller 1 in draft tube type stirring section formed by
By appropriately setting the stirring state by means of No. 4, sufficient and uniform stirring can be performed, collision of crystals can be suppressed as compared with air stirring, and the generated M
Since the AP can be sufficiently mixed, the MAP generation reaction can be performed on the crystal surface of the MAP, and the generation of scale on each wall surface of the reaction tank 11 and the cylindrical bodies 12 and 13 can be suppressed. . In addition, by applying a fluororesin coating to the inner surface of the reaction tank 11 and the liquid contact parts such as the cylindrical bodies 12 and 13, it is possible to more reliably prevent the scale from adhering to these parts.

Further, by providing a diluted water supply path 20 in the treated water discharge section 19 and appropriately diluting the treated water discharged, the reaction in the drainage path can be suppressed, and the reaction product can be reduced in the piping of the drainage path. Can be prevented from adhering to the pipe, and the clogging of the pipe by the scale can be prevented. Further, by providing the washing water jetting part 21 at an appropriate place of the apparatus and washing out the MAP in the tank prior to the acid washing, the amount of acid used in the acid washing can be reduced.

[0025]

As described above, according to the wastewater treatment apparatus of the present invention, fine MAP crystals generated in the seed crystal generation tank are supplied as seed crystals to the dephosphorization tank which is the main reactor. No mechanical equipment for obtaining seed crystals as in the prior art is required, and phosphorus contained in a digestion tank effluent in a relatively small-scale sewage treatment equipment can be used as a MAP useful as a fertilizer.
Can be efficiently collected as crystal particles.

[Brief description of the drawings]

FIG. 1 is a system diagram showing one embodiment of a wastewater treatment apparatus of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... settling tank, 2 ... seed crystal generation tank, 3 ... dephosphorization tank, 4 ... magnesium compound storage tank, 5 ... pH adjuster storage tank, 6 ...
Acid storage tank, 11: reaction tank, 12: large diameter cylinder, 13: small diameter cylinder, 14: stirring blade, 15: crystal discharge part, 16: wastewater inflow path, 17: magnesium compound supply path, 18
... pH adjuster supply path, 19 ... treated water discharge section, 20 ... dilution water supply path, 21 ... wash water jetting section, 22 ... acid supply section
23 ... Seed crystal supply route

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Tsuno 2-8-14, Kinugawa, Otsu-shi, Shiga Prefecture (72) Inventor Makoto Yao 1-3-3 Kyobashi, Chuo-ku, Tokyo Inside Maezawa Kogyo Co., Ltd. 72) Inventor Masaaki Yoshino 1-3-3 Kyobashi, Chuo-ku, Tokyo Inside Maezawa Industrial Co., Ltd.

Claims (3)

[Claims] 1. A wastewater treatment apparatus for adding a magnesium compound and a pH adjuster to wastewater containing ammonium ions and phosphate ions to generate crystals of magnesium ammonium phosphate hexahydrate, wherein solids in the wastewater are removed. A solid-liquid separating means for separating and removing, a seed crystal forming tank for adding the magnesium compound and the pH adjuster to waste water after solid-liquid separation to form fine crystals of magnesium ammonium phosphate hexahydrate, A wastewater treatment apparatus comprising: a dephosphorization tank for growing fine crystals derived from a production tank in wastewater to which a magnesium compound and a pH adjuster have been added to remove the ammonium ions and phosphate ions. . 2. The wastewater treatment according to claim 1, wherein the seed crystal production tank and the dephosphorization tank have a dilution water supply unit for diluting the treatment water at an outlet of the treatment water. apparatus. 3. The wastewater treatment apparatus according to claim 1, wherein the seed crystal generation tank and the dephosphorization tank include a washing water jet for washing a tank wall.