JPS5879589A - Removing method for phosphate ion - Google Patents

Abstract

PURPOSE:To remove phosphate ions stably without carry-over of fine flocs despite the fluctuation in the flow rate of water, by passing the treated water which is subjected to a contact treatment with apatite phosphate layers through solid-liquid separating layers. CONSTITUTION:A Ca agent is added at >=7.0pH in excess sufficiently of theoretical equiv. to water to be treated and in the stage of contact between apatite phosphate layers and the water to be treated, the Ca agent is added to said water generally in such a way that the molar weight ratio of Ca/PO4 attains a 1.0-5.0 range. Thus apatite phosphate layers 5 of the compsn. consisting essentially of Ca5(OH)(PO4)3 are beforehand formed and the water contg. phosphate ions is admitted into the layers 5 from the lower or upper part thereof and is allowed to contact with the layers 5 at >=7.0pH. The water treated in such a way is passed through solid-liquid separating layers 9 packed with sand and phosphorus ore, whereby phosphate ions are removed. Since the SS components captured by the layers 5 are mainly Ca phosphate, said components are stripped by backwashing, are mixed with the water to be treated and are adsorbed in the layers 5.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for removing phosphate ions present in liquids such as tap water, municipal sewage, and industrial wastewater.

In recent years, as eutrophication phenomena have become more common in closed water bodies such as rivers, lakes, and inland seas, there is an urgent need to remove phosphate ions.

Conventionally, ion exchange resin methods, chemical coagulation methods, crystallization methods, and the like are known as methods for removing phosphates.

In Japanese Patent Application No. 56-88171, a calcium agent is added to water containing phosphate ions, mainly Ca5(OH).
Phosphate ion-containing water is introduced from the bottom or top of the phosphate apatite layer with a composition of (PO4)3, and the pH is 7.0.
It is described above that phosphate ions in water can be removed efficiently and at low cost by contacting with a phosphate apatite layer.

Although this method is certainly an excellent method, fluctuations in the amount of water that sometimes occur during water treatment can lead to carryover of fine flocs and deteriorate water quality.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for treating phosphate ion-containing water that can consistently produce good water quality without causing fine flocs to carry over even when the amount of water fluctuates.

According to the present invention, this object is achieved by passing treated water that has been subjected to contact treatment with a phosphoapatite layer through a solid-liquid separation layer filled with sand, phosphate rock, or the like.

Specifically, the method of the present invention adds a calcium agent to phosphate ion-containing water, and mainly produces Cα5 (OHXPO4).
7) A phosphate apatite layer with a composition of
The method is characterized in that the treated water is brought into contact with a tight layer and the treated water is passed through a fixed bed type solid-liquid separation layer.

Since the solubility of phosphoapatite decreases as the calcium concentration and pH increase, the water to be treated and the phosphate apatite layer are brought into contact at a pH of 7.0 or higher.

As the calcium agent, slaked lime, calcium chloride, calcium carbonate, etc. are used.

Since water such as industrial wastewater generally contains serious ions, the amount of calcium agent added cannot necessarily be determined by the reaction equivalent, but when forming a phosphoric acid azotite layer, At a pH of 7.0 or higher, a calcium agent is added in sufficient excess over the theoretical equivalent, and when the phosphoric acid a. Add calcium agent so that it is in the range of .0.

When the phosphate apatite layer thus formed is brought into contact with water containing phosphate ions, the phosphate ions in the water are added during the formation of the phosphate apatite layer and are combined with excess calcium ions or calcium ions added before the reaction. It reacts and is adsorbed and removed by phosphoapatite.

In the case of treatment according to the method of the present invention, not only phosphoapatite of the above formula but also fluoroapatite, chlorapatite, carbonate apatite, and further calcium fluoride CcLF2 may be used, depending on the nature of the wastewater and the type of calcium agent. Insoluble calcium compounds, such as calcium phosphate Ca5(PO4)s, also appear to be formed.

In addition, in the case of treatment according to the method of the present invention, excessive calcilam ions are contained in the water treated to contact the phosphoapatite layer, so it is recommended to use part or all of this treated water as circulating water to contact the apatite layer again. By circulating the J-treated water, it is possible to cope with fluctuations in the quality of the inflow water, to make the contact time with the phosphate apatite layer constant, and to effectively utilize excess calcium ions in the treated water.

After contacting the phosphate apatite layer, the treated water is further passed through a solid-liquid separation layer filled with sand, phosphate rock, etc.
is captured by the solid-liquid separation layer. Since the captured 88 min is mainly calcium phosphate, it is removed by backwashing, mixed with the water to be treated, and adsorbed onto the phosphate apatite layer.

Next, the present invention will be explained in detail based on the drawings.

The drawing is a system diagram showing one embodiment of the method of the present invention. Raw water is introduced into a mixing tank 2 through a conduit 1, where it is mixed with a calcium agent injected through an inlet 3. The raw water containing the calcium agent then flows into the contact tank 4 from its lower part. A phosphate apatite layer 5 is previously formed in the contact tank 4. Therefore, water flowing into the contact tank 4 comes into contact with the phosphoapatite layer 5 and flows out from the upper part of the contact tank 4. Part or all of the effluent is circulated as circulating water through the circulation conduit 7, and flows into the contact tank 4 together with the raw water.

Excess phosphoapatite is extracted from the extraction tube 6.

The effluent from the upper part of the contact tank 4 is then introduced into the solid-liquid separation tank 9, and passes through a packed bed IO of sand, phosphate rock, etc. The treated water from which 88 minutes have been removed by the packed bed 10 is discharged from the outflow pipe 8.

When operated for a long period of time, the packed bed IO may become clogged, so the packed bed is backwashed as necessary or periodically to remove the captured 88 minutes.
The backwash water containing water is returned to the mixing tank via conduit 11.

In this way, according to the present invention, even if the quality and quantity of the water to be treated changes, good water quality can always be obtained without causing carryover of fine flocs.

Next, the present invention will be described in detail based on Examples, but the present invention is not limited thereto.

Example 1 Sand ν peroxide of fertilizer industrial wastewater (containing 41 to 60 m9/ of orthophosphoric acid as PO4) was adjusted to 7) H8,O-,
Calcium hydroxide was added in a mixing tank so that the Cα/PO4 molar weight ratio was 20, and this was mixed into a container with an inner diameter of 2.5 cm.
A phosphoapatite layer was formed to a height of 50 crn using a column with a length of 10 crn. Raw water to which calcium ions had been added was passed in an upward flow at 5V=3, and then flowed into a solid-liquid separation tank filled with sand. Table 1 shows the results of measuring the PO4 concentration and SS of the treated water before and after solid-liquid separation.

As can be seen from this table, by performing solid-liquid separation, P
Not only does it remove O&, but it also removes water well for 88 minutes, ensuring good water quality at all times.

[Brief explanation of the drawing]

The drawing is a system diagram showing -FJ of an apparatus for carrying out the method of the present invention. Explanation of symbols 2...Mixing tank 4...Contact tank 5...Phosphate apatite layer 9...Solid-liquid separation tank 10...Filled bed.

Claims (2)

[Claims] (1) A phosphate apatite layer with a composition mainly of Cα5(OH)(PO4)3 is formed in advance, and water containing phosphate ions is flowed in from the bottom or top of the phosphate apatite layer to pH 7, A method for removing phosphate ions, which comprises bringing the treated water into contact with a phosphate apatite layer at a temperature of 0 or more, and passing the treated water through a fixed bed type solid-liquid separation layer. (2) The method according to claim 1, in which the 88 minutes trapped in the solid-liquid separation layer is peeled off by backwashing and returned to the phosphoapatite layer.