JPS59105886A - Apparatus for phosphate-contg. water disposal - Google Patents

Abstract

PURPOSE:To stably remove phosphates from phosphate-contg. water, by providing a crystallizer tank for bringing phosphate-contg. water into contact with crystal seeds containing calcium phosphate at a pH above 6 in the presence of Ca ion, a feeder for supplying a crystallized effluent to a biofiltration tank, etc. CONSTITUTION:A calcium agent is injected into raw water after being pretreated by a pump 10 extending from a reservoir tank 8 for a calcium agent, and an alkali agent is injected from a reservoir tank 9 for an alkali agent into said raw water by a pump 11. Hence, Ca ion is made existent in the raw water, and a pH is adjusted above 6. After small amounts of precipitates such as calcium phosphate are removed in a filtration tank 5 at need, a reacted liquid is introduced into a crystallizer tank 6 equipped with crystal seeds containing calcium phosphate and brought as an upward or downward stream into contact with the crystal seeds to perform crystallization. By this crystallization, phosphates in the raw water are removed, and outflow water having a low concentration of phosphorus is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for treating water containing phosphates to remove phosphates.

In recent years, the progress of eutrophication in closed water areas such as lakes, marshes, and inner bays has become remarkable and is being viewed as a problem. Phosphate present in water has been highlighted as a cause of eutrophication, and its removal has been raised as an urgent issue.

Phosphates, which cause eutrophication, are found in tap water, sewage, industrial water, factory wastewater, boiler water, etc., and include inorganic phosphates such as orthophosphates and condensed phosphates. It exists in the form of organic phosphates.

How to remove such phosphates and L2.

A method has been proposed in which water containing phosphate is brought into contact with a crystalline species containing calcium phosphate, such as phosphate rock, in the presence of calcium ions. This method removes phosphate ions contained in water by converting them into calcium phosphate such as hydroxyapatite and crystallizing them into crystal seeds. The processing efficiency is also significantly improved.

By the way, in such a treatment method, the influence of pH on the crystallization and dephosphorization effect is large.

To avoid this problem, conventional processing equipment employs a method in which an alkali agent is added at the inlet of the crystallization tank and the pH at the inlet of the crystallization tank is controlled [7]. did it.

However, in such a treatment device, the phosphorus concentration of the treated water fluctuates due to fluctuations in water quality, making it impossible to perform stable treatment. In addition, the pH of the treated water fluctuates, and in some cases exceeds the regulatory value, which poses the problem of not being able to be discharged.

This invention is intended to improve the problems with the conventional equipment as described above.By installing a biological filtration tank after the crystallization tank, even when the raw water quality fluctuates, phosphorus can be stably produced under optimal conditions. The purpose of the present invention is to provide a treatment device for water containing phosphates that can remove acid salts, keep the pH of the treated water within regulated values, and obtain treated water that can be discharged as is. .

This invention comprises: a crystallization tank in which water containing phosphate is brought into contact with crystal seeds containing calcium phosphate at a pH of 6 or higher and in the presence of calcium ions; an apparatus for supplying raw water to the crystallization tank; A treatment device for water containing phosphates, comprising a device for adding an alkaline agent and a calcium agent to the raw water, a biological filtration tank, and a device for supplying the crystallization tank effluent to the biological filtration tank. It is.

The reaction that occurs when water containing phosphate is brought into contact with crystal seeds containing calcium phosphate in the presence of calcium ions varies depending on the reaction conditions, but is usually expressed by the following formula.

5Ca2++3HPOj +40H, -+0a5(G
-I)(P('%)3+3H,0・-(i) As shown from formula (1), in order to increase the phosphate removal rate,
It is necessary for the reaction to proceed to the right, and an alkaline agent and a calcium agent are added to this sump raw water.

When we investigated the cause of the change in the phosphorus removal rate depending on the raw water quality, we found that (as hydroxide ions are consumed with the reaction of equation 11, the pH decreases; , especially M alkalinity ((depending on
Even if the pH value at the inlet of the crystallization tank is controlled to the optimum pH value suitable for crystallization, the pH decreases during crystallization and the inside of the tank cannot be maintained at the optimum pH, making the process unstable. However, when the pH is increased at the inlet of the crystallization tank, the pH of the water flowing out from the crystallization tank often exceeds the discharge standard.

Therefore, in the present invention, a biological filtration tank is provided after the crystallization tank so that the pH value of the treated water can be maintained within a predetermined range. Hereinafter, the present invention will be explained with reference to embodiments of the drawings. FIG. 1 is a system diagram showing an apparatus for treating water containing phosphate according to one embodiment of the present invention.

In Figure 1, 1.4.10.11 is a pump, 2,5
is a filtration tank, 3 is an adjustment tank, 6 is a crystallization tank, 7 is a biological filtration tank,
8 is a calcium agent storage tank, 9 is an alkali agent storage tank, 12.1
3.14.15.16.17.18.19.20 are piping, and 21 is a stirring device.

The filtration tank 2 is filled with a P material such as anthracite so that impurities such as suspended matter in the raw water can be filtered out, and a flocculant injection means may be provided to perform coagulation filtration. The 5-filter tank is capable of removing the precipitate generated by the injection of the calcium agent and the alkaline agent, and may be small in size.

Any of these filtration tanks can be installed as needed.

The crystallization tank 6 is for crystallizing and removing phosphate ions as calcium phosphate, and is filled with crystal seeds containing calcium phosphate so that the reaction solution can be brought into contact with water by flowing upward or downward. ing.

Crystal species containing calcium phosphate include hydroxyapatite COa, (OH) (to P), fluoroapatite [Ca, (F) (PO,)3:] and tricalcium phosphate C0a3 (PO,)2). Crystal seeds containing calcium phosphate, such as, can be used, and natural phosphate rock or bone char contains these calcium phosphates as a main component, and is suitable as a crystal seed. However, it is also possible to precipitate calcium phosphate on the surface of a material such as sand and use crystal seeds.

It is desirable that the crystal seed be one whose main component is calcium phosphate of the same type as the calcium phosphate produced by the reaction.For example, in a system that produces hydroxyapatite, the use of hydroxyapatite facilitates the precipitation of new crystals, and Acid salts are removed efficiently and the removal rate increases.

The method of contacting the water containing phosphate with the crystal seeds containing calcium phosphate may be a fixed bed method or a fluidized bed method. The smaller the size of the crystal seeds, the larger the surface area, which makes it easier for new crystals to precipitate. ! However, if the crystal seeds are small and come into contact with water, separation is difficult. If the particle size is too large, the specific surface area per unit filling amount will be small, so it is usually 9 to 30.
Use something of about 0 mesosh. Among these, the larger ones are suitable for fixed beds.1. Small ones are suitable for fluidized beds. In the case of a fixed bed, fill with crystal seeds with a particle size of 9 to 35 meshes l-1
Although it is desirable that water be passed in an upward flow at a flow rate of SVI to 5 hr' to precipitate calcium phosphate crystals, water may be passed in a downward flow depending on the case.

In the apparatus configured as described above, raw water containing phosphate is brought into contact with crystal seeds containing calcium phosphate to perform crystallization. The crystallization conditions are the same as those of the conventional method, and when brought into contact with crystal seeds containing calcium phosphate in the presence of calcium ions and at a pH of 6 or more, the above (
Calcium phosphate produced by the lj formula is precipitated on the surface of the crystal seed, the crystal grows, and the phosphate in the water is removed.

In operation of the apparatus, raw water can be pretreated prior to crystallization, and in this case, the raw water is supplied to the first filtration tank 2 by the pump 1 and filtered to remove impurities. The filtration in the filtration tank 2 may be coagulation filtration as described above, or it may be replaced with other pretreatment operations such as coagulation sedimentation. Inject the alkaline agent from the alkaline agent storage tank 9 to the pump 11 to make calcium ions exist in the raw water, adjust the pH to 6 or higher, and proceed with one reaction of the above formula (1). let

Examples of calcium agents include calcium chloride and calcium hydroxide, while alkaline agents include sodium hydroxide, potassium hydroxide, ammonium hydroxide, calcium hydroxide, and the like. In particular, calcium hydroxide has both properties, which simplifies the operation and is preferred when calcium ions are present in the water from the beginning (although 〆ζ does not need to be added externally,
If it does not exist in the raw water or is insufficient, add it from outside. The amount of calcium agent and alkaline agent added should be greater than the reaction equivalent, but if too much ψ is added, fine precipitates may form in areas other than the crystal seeds, and impurities such as calcium carbonate may be formed. Therefore, it should be set within a range where these do not occur. That is, the amounts of calcium ions and hydroxide ions are (1)
The conditions are such that hydroxyapatite is produced at a concentration higher than the solubility of hydroxyapatite produced in the formula and lower than supersolubility, that is, a concentration in the metastable range. Here, supersolubility is the concentration at which crystals begin to precipitate when no crystal seeds are present in the reaction system. In other words, at a concentration higher than the supersolubility, new crystals precipitate where there are no crystal seeds, forming fine precipitates and clogging the P bed, but in a metastable region lower than the supersolubility, new crystals precipitate where the crystal seeds do not exist. A precipitate is formed simply by the precipitation of new crystals and the growth of the crystals, resulting in two layers.

In addition, crystals do not precipitate in systems lower than the solubility.

The level at which hydroxyapatite is produced is controlled by the phosphate ion concentration, calcium ion concentration, and pH of the reaction system. Calcium ion il b and pH value that bring the amount of hydroxyl-patai I produced within the metastable range can be determined experimentally by changing these values for each reaction system. t・Approximate range is phosphate ion 50'
ml/l or less, calcium ions are
~100mg/e, pH is about 6 to 12, but varies depending on each condition.

A trace amount of precipitate such as calcium phosphate generated by adding a calcium agent and an alkaline agent is removed from the filter tank 5 as necessary.
Remove at. Next, the reaction liquid is introduced into the crystallization tank 6,
Water is passed upwardly or downwardly and brought into contact with crystals (gray metal) for crystallization. At this time, hydroxyapatite in the reaction solution is precipitated on the surface of the crystal glaze and removed, causing contamination on the surface of the crystal seeds during water flow. If the crystal seed bed is washed or clogged, it is desirable to perform periodic backwashing using −L countercurrent flow to develop and clean the crystal seed bed, and to peel off impurities attached to the surface.

Water flow conditions during backwashing include a flow rate of 20 to 80 m/h [
The backwashing time is about 5 to 60 minutes.

If necessary, reactivation treatment of the crystal seeds may be performed at this time.

In the reactivation process, the sample is taken out in a crystallization tank or into a reactivation tank (not shown) and brought into contact with a calcium hydroxide solution, an acid solution (an inorganic acid such as hydrochloric acid, an organic acid such as acetic acid), a chlorine agent, etc. This can be done by heating or sipping for 7y.

By performing the crystallization as described above, phosphates in the raw water are removed, and effluent water with a low phosphorus concentration is obtained.

The pH of the effluent thus obtained depends on the quality of the raw water and the conditions of the crystallization process, but in the present invention, the pH of the final treated water is within the effluent standard, for example 8.
Next, a biological filtration tank 7 is provided so that the ratio is 2 to 8.6.

Known fixed-bed biological treatment equipment can be used, such as a water-sprinkled bed or an immersed bed in which a biofilm is attached to a support such as sand, gravel, or a honeycomb tube.

The residence time is usually about several minutes to several hours, but it is preferable to provide a pH tank in the pipe 20, so that when the pH of the treated water exceeds a predetermined value, the treated water is circulated to the biological tank 1 again. do.

By the way, there is a crystallization tank filled with 300 ml of phosphate rock in an acrylic column with an inner diameter of 30 mm and a height of 5001 + lfi, and an acrylic column with an inner diameter of 30 mm and a height of -y4 oomm filled with 200 ml of gravel with a grain size of 3 to 6. A phosphorus concentration of 2 mq/
The secondary treated sewage water containing l.

After adjusting the p I-1 of the crystallization tank population to 9.0 and passing water at SV 2, water was passed at SV 4.2 to meet biological requirements.
The pH of the liquid to be treated at the bio-qualified inlet was 869, while the pH at the bio-qualified outlet was 826, indicating a sufficient pH lowering effect.

According to this invention, since the water flowing out of the crystallization tank is further passed through the biological filtration tank, the crystallization conditions can be set to favorable conditions, that is, high p)T decoy, and the phosphorus The removal rate and reaction time are improved.

Moreover, even if the 130D in the crystallization tank effluent is extremely low, by adopting biological R qualification, it is possible to achieve sufficient treatment performance and further reduce the BOD of the treated water.

[Brief explanation of drawings]

The drawing is a system diagram showing one embodiment of the present invention, and in the drawing 1.4.10.11. is the pump, and 2 and 5 are f1 tanks. 3 is an adjustment tank, 6 is a crystallization tank, 7 is a biological 1 perax, 8 calcium agent storage tank, 9 is an alkali agent storage tank, ■2゜13, 14.
15.16.17.1B, 19.201d piping, and 2nd design indicate the stirring device, respectively. Patent applicant Kurita Industries Co., Ltd.

Claims (1)

[Claims] a crystallization tank that brings water containing phosphate into contact with crystal seeds containing calcium phosphate at a pH of 6 or higher and in the presence of calcium ions; a device that supplies raw water to the crystallization tank; 1. A treatment device for water containing phosphate, comprising a device for adding a calcium agent and a calcium agent, a biological filtration tank, and a device for supplying effluent water from a crystallization tank to biological conditions.