JPS6242677B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for removing phosphates present in tap water, sewage, human waste water, industrial water, factory wastewater, boiler water, and all other aqueous solutions. In general, inorganic phosphates such as orthophosphates, various condensed phosphates, and organic phosphates exist in various states in the above-mentioned wastewater discharged into natural water systems. The presence of phosphates is a factor that induces the occurrence of "blue water" and "red tide" in closed or stagnant waters such as lakes, inland seas, and inner bays. Furthermore, when using water for various purposes, it may cause Biological slime is generated and chemical scale is formed, which is a major cause of accidents. Therefore, in order to remove the phosphates present in these liquids, various phosphorus removal methods are being considered, and representative ones include biological treatment, ion exchange resin method, and chemical coagulation. Among these methods, the chemical coagulation-sedimentation method is evaluated as a treatment technology that has been completed to date.
Processing equipment of actual processing scale is already in operation in many places. The removal of phosphates by this chemical flocculation treatment is a method of removing phosphates present in the liquid as insoluble phosphates by adding a specific flocculant. Usually, slaked lime [Ca(OH) ₂ ], aluminum sulfate [Al ₂
(SO ₄ ) ₃ ], ferric chloride [FeCl ₃ ], etc. are used. However, the biggest drawback of chemical coagulation and precipitation is that it generally requires a large amount of flocculant, which is expensive, regardless of the type of flocculant used. A large amount of sludge is generated in proportion to the large amount of chemical injection, and the settling and thickening properties of this sludge are extremely poor (lime sludge is an exception).Furthermore, this sludge has poor dewatering properties (lime sludge is an exception). However, because it requires a large sludge treatment facility and treatment costs, it has many problems in practical use, even though it is a current technology. For this reason, the present inventors have previously developed a novel treatment method in which phosphate minerals containing calcium phosphate with a certain particle size are packed into a cylindrical or cone-shaped dephosphorization tower. PH of liquid 6-11
By adjusting the concentration within the range of A catalytic dephosphorization method has been proposed in which soluble phosphates are removed by crystallizing and fixing calcium hydroxyapatite crystals on the surface of phosphate minerals. In this case, typical chemical reactions on the phosphate mineral surface are as follows. 5Ca ²⁺ +70H ^- +3H ₂ PO ₄ = Ca(OH) (PO ₄ ) + 6H ₂ O ...(1) If this new dephosphorization method is applied, phosphate minerals with fixed calcium hydroxyapatite can be removed. Separation and dewatering are extremely easy, and compared to so-called flocculated sludge made using conventional chemical flocculation and sedimentation methods, it does not require preconceived sludge treatment facilities such as thickeners, dehydrators, dryers, and drying equipment. It has also been revealed that this is an excellent dephosphorization technology that can efficiently recover phosphorus as a resource. However, on the other hand, there were the following operational problems. That is, when a column is filled with phosphate minerals and raw water is passed through it in a fixed bed or fluidized bed state and the operation is continued, Ca ₅ (OH) is newly precipitated by the reaction of the previous formula (1). As a result of (PO ₄ ) ₃ depositing on the surface of the phosphate mineral one after another, the phosphate mineral gradually enlarges and grows to a particle size larger than the particle size when initially filled. In such a situation,
Because the head loss increases and fluidization becomes difficult, the operation is stopped, all of the swollen phosphate minerals in the column are taken out, and freshly prepared phosphate minerals are added to the column. It was necessary to take steps to fill the column with salt minerals, which was extremely troublesome in terms of operational management. Naturally, this operation for extracting enlarged phosphate minerals must be carried out more frequently as the concentration of phosphoric acid in the raw water increases. For example, if the concentration of phosphate ions in the raw water is about 10 mg/ It has become clear from the operational experience of pilot plants that removal operations are required once a month. In addition, the removal rate of phosphate ions increases as the surface area of phosphate minerals increases, but in the method of filling a column with phosphate minerals and operating in a fixed bed state or fluidized bed state, it is difficult to remove phosphate ions from small particles. The use of phosphate minerals is undesirable in the case of fixed bed operation because the head loss increases, and in the case of fluidized bed operation, the expansion rate of the fluidized bed tends to be excessive, which is also undesirable. The particle size of salt minerals was limited to about 0.5 mm. For this reason, the ideal state for the purpose of making the device more compact has not been achieved. The present invention aims to provide an effective method that makes it possible to solve these problems. In other words, it is necessary to take out and replenish phosphate minerals, and even if phosphate minerals with a fine particle size of 0.5 mm or less are used, operations cannot be performed stably without causing problems like in conventional methods. , and provides a method that allows the device to be made more compact. Furthermore, another object of the present invention is to provide a method that eliminates the amount of phosphate minerals required for treatment and that allows a large amount of treated water of good quality to be obtained at a significantly economical cost. In the present invention, phosphate mineral granules containing calcium phosphate and inert granules not containing calcium phosphate are forcibly separated in a tank 1 in which a calcium agent is added to a liquid to be treated containing phosphate ions and the mixture is stirred. Supplying raw water containing phosphate ions into the tank 1 while maintaining it in a suspended state by a mixing and stirring mechanism, and adding a calcium agent to the raw water or the tank 1,
After converting the phosphate ions in the raw water into insoluble calcium phosphate precipitates, the phosphate mineral granules and inert granules are separated and recovered in the granule separation section 2, and returned to the tank 1. , SS containing calcium phosphate precipitates in the effluent from the granular material separation section 2 is removed in a solid-liquid separation section 3 such as a sand filter following the separation section 2. This is a removal method. Hereinafter, one embodiment of the present invention will be described with reference to the drawings. In FIG. 1, raw water A of the liquid to be treated containing phosphate ions and calcium agent B are supplied to a tank 1 serving as a mixing and stirring section, and Phosphate mineral granules containing calcium phosphate and inert granules not containing calcium phosphate (hereinafter referred to as inert granules) are brought into contact with a stirring mechanism such as a mechanical rotary stirring blade 4 under mixing and agitating conditions. the acid ions are converted into insoluble calcium phosphate precipitates, and the tank 1 is connected to the granular material separation section 2 through a pipe 5;
The phosphate mineral granules and inert granules are separated and recovered in the granule separation section 2 and recycled to the tank 1 through a pipe 6, and the water flowing out from the granule separation section 2 is transferred to the pipe 8. SS containing calcium phosphate precipitates in the effluent is removed by the solid-liquid separator 3, resulting in clear treated water.
SS is led out of the system as A', and SS is recycled to the tank 1 through a circulation path 9 as necessary. In the figure, 7 is a pump, which is provided as required. 20
is the activation device. In addition, the tank 1, the granular material separation section 2, and the solid-liquid separation section 3
Although they are installed in series, they can also be divided into multiple systems and connected in parallel. Although they are formed separately, the tank 1 of the mixing and stirring section and the granular material separation section 2 can also be formed in the same tank as shown in FIG. In this case, the stirring blades 4 are provided in the draft tube 10, and the granular material separation section 2 is defined and communicated with the inside of the tank 1 by a partition wall 12. Note that the tank 1 functions not only as a mixing and stirring tank but also as a contact reaction tank, and the tank 1 contains particles with a particle size in the range of 0.05 to 0.45 mm, preferably 0.1 to 0.45 mm.
Phosphate rock as 0.2 mm phosphate mineral granules and silica sand grain size 0.1 to 0.2 mm as inert granules are added and suspended at 20% (volume %) of the volume of tank 1.
By stirring blade 4, tank 1 or draft tube 1
It circulates through the tank 1 through the tank 1. The raw water A flows, for example, from the bottom of the tank 1, and the Ca(OH) ₂ calcium agent B is added to at least one of the raw water inlet pipe and/or the draft tube 10. Next, raw water A remains in tank 1 for a predetermined time (about 5 to 20 minutes was sufficient according to experimental results), and dissolved phosphoric acid and calcium ions in the raw water undergo a contact reaction in the coexistence of phosphate rock. causes insoluble Ca ₅
It is converted into a precipitate consisting mainly of (OH)(PO ₄ ) ₃ . Under simple fluidized bed conditions as in the conventional method, this Ca ₅ (OH) (PO ₄ ) ₃ deposits and adheres to the surface of the phosphate rock, causing the phosphate rock to enlarge, but in this tank 1,
Since a forced mixing and stirring mechanism such as the stirring blade 4 is adopted, when passing through the cooperative shear field near the stirring blade, the phosphate rock and the inert granules collide violently with each other, causing the phosphate rock to disintegrate from the surface of the phosphate rock. Since the enlarged material is peeled off, the phosphate rock can be processed without progressing to enlargement. In Figure 2, 11 is a water collection groove, 13 is an overlayer,
14 is a cleaning drain pipe, and 15 is an on-off valve. The embodiment shown in FIG. 3 is a compact example in which the mixing and agitation section, the granular material separation section 2, and the solid-liquid separation section 3 are integrated into the same tank 1, and the raw water supply pipe has a cone-shaped tank bottom. Draft tube 1 connected to the center
A cylindrical partition wall 23 interposed between the draft tube 10 and the tank wall is provided on the rotating shaft 24 of the stirring blade 4 in the tank 1, and an overlayer 13 is provided above the tank 1 as the solid-liquid separation section 3. Treated water A' is led out through a water collection groove 11 upwards. In the figure, 21 is a backwash water valve, and 22 is a backwash water pipe. The example in FIG. 4 is an example in which gas lift stirring is adopted by connecting the air supply pipe 19 to the draft tube 10 as the stirring means in the tank 1 of the mixing and stirring section.
The illustrated example employs pump circulation stirring, and the discharge pipe 17 and suction pipe 16 of the pump 18 are connected to the upper and lower parts of the tank 1 to provide a circulation flow path. Further, the specific example shown in FIG. 6 is an example in which an ejector system using raw water inflow energy is adopted, and a nozzle 26 is provided at the tip of the raw water supply pipe 25 and the draft tube 10 is
It is arranged within the tank 1 to induce an ejector action, and is made to circulate and flow within the tank 1 together with the phosphate mineral granules and the inert granules. However, in both of these embodiments, the mixture is stirred in the tank 1 to cause a contact reaction, resulting in insoluble
Ca ₅ (OH) (PO ₄ ) ₃ is generated, and fine SS mainly consisting of Ca ₅ (OH) (PO ₄ ) ₃ exfoliated from the phosphate rock surface and SS in raw water are phosphate mineral granules. and the granular material separation section 2 together with the inert granular material.
However, the water area load of the granular material separation section 2 is lower than the sedimentation velocity of these granular materials, and newly generated Ca ₅ (OH) (PO ₄ ) ₃ etc. are initially introduced into the SS and raw water. Since the sedimentation rate is set to be higher than the sedimentation rate of the SS existing in the granule, fine SS other than the granule is not separated in the granule separation section 2 and flows out. For example, the water area load of the granular material separation section 2 has a particle size of 0.1 to
When using 0.2mm phosphate rock (specific gravity 2.6),
150 to 200 m ³ /m ² ·d is appropriate. In this way, the effluent from the granular material separation section 2 flows into the subsequent solid-liquid separation section 3, such as a filter tank, a sedimentation tank, or a flotation tank, and the newly generated Ca ₅ (OH)
SS containing calcium phosphate precipitates such as (PO ₄ ) ₃ is removed. In the process of this solid-liquid separation section 3, SS can be most accurately removed by adopting the filtration method as shown in Fig. 2 or 3, and requires a more compact device compared to the sludge method. This is a preferable example. Note that the newly generated calcium phosphate precipitate flowing into the solid-liquid separation section 3 is highly active, so instead of being disposed of as it is, for example, the cleaning waste water of the overlayer 13 is recycled to the tank 1 for the contact reaction. This is an extremely preferred embodiment since the phosphoric acid removal rate is improved when the phosphoric acid is used as a solid phase in the catalytic reaction together with inert granules. In this case, it is convenient to employ a continuous filter in the solid-liquid separation section 3 where the filter layer 13 is located, since the washing waste water can be continuously recycled to the tank 1 for contact reaction. In addition, as shown in Fig. 7, another way to use the concentrated SS of the solid-liquid separation section 3, such as the washing waste water of the filter tank 13, is to apply it to biologically treated water such as the activated sludge method. , solid-liquid separation section 3 with overlayer 13
When the washing wastewater is recycled to the aeration tank 27 through the pipe 30, calcium phosphate SS etc. in the washing wastewater are incorporated into the activated sludge flocs, and the settling properties of the activated sludge flocs in the final settling tank 28 can be improved. In FIG. 7, 29 is a valve, 31 is a diffuser pipe, 3
2 is a mud drain pipe, 33 is a mud drain valve, 34 is a wash water pipe,
35 is a valve. The reason for co-suspending inert granules is to reduce the amount of phosphate minerals required, and we are considering reducing costs by reducing the amount of phosphate minerals that are initially introduced. As a result, when inert granules that do not contain calcium phosphate, such as sand made of other phosphate minerals, coexist, the surface of the sand does not change much for about a month after the start of operation, but
After the moon, the surface of the sand gradually became whitish, and
During Kagetsu, they discovered that the appearance changed to something that could not be distinguished from phosphate minerals. X-ray diffraction analysis of the precipitate attached to the surface of the sand revealed that it was a calcium phosphate compound containing mainly Ca ₅ (OH) (PO ₄ ) ₃ , and that the sand that had changed to this state was equivalent to a phosphate mineral. Column tests showed that it has the ability to dephosphorize catalytically. On the other hand, when operating under the same conditions without coexisting any phosphate minerals and suspending only inert sand particles, the removal rate of phosphate ions remained low even after 6 months of continuous operation. It was only about 10-20%. Therefore, in the mixing and stirring step in the tank 1, inert granules such as sand, coke, activated carbon, anthracite, zeolite, and synthetic resin are co-suspended together with phosphate mineral granules. Even if the amount of phosphate mineral particles is small, phosphoric acid can be effectively removed. Examples of the present invention are shown below. Example 1 A circular tank with a diameter of 0.5m and a direct depth of 25m, a diameter of 0.2m
A draft tube with a length of 2 m is installed in the center of the circular tank, and an axial flow impeller with a diameter of 0.15 m is installed in the middle of the draft tube. While stirring at 150 rpm, phosphate rock from Florida (particle size 0.1 to 0.2 mm) is poured into the tank capacity. (490
) to 10% Volume and silica sand (particle size 0.1~0.2
mm) at 10% of the tank capacity, and while suspending and fluidizing it, sewage biologically treated water (PH7.4, M alkalinity 90-110ppm, orthophosphoric acid 8.0-12.4ppm as
PO ₄ SS (15-25 ppm) was flowed in at a flow rate of 120/min. In addition, slaked lime is placed inside the draft tube.
The injection rate was such that the pH was 8 to 9. The water area load of the granule separation section was set to 150 m ³ /m ² ·d. The operation continued under these conditions for about 6 months, and when a small amount of phosphate rock in the contact reaction tank 1 was taken out and the particle size was measured using a microscope, no enlargement in the particle size of the phosphate rock that was introduced at the start of operation was observed. Nakatsuta. In addition, the outflow water from the granular material separation section (SS35~
50ppm) is an anthracite/sand two-layer filtration device (anthracite grain size 1.5mm layer thickness 40cm sand grain size 0.6mm layer thickness)
60cm) at a speed of 200m/d and measured the quality of the overflow water.

[Table] It was. Example 2 In Example 1, after continuous operation for two months, a mixture of phosphate rock and sand (referred to as Material A) was taken out from the tank and packed into an acrylic column with a diameter of 5 cm and a length of 1 m to a layer thickness of 60 cm. Three columns were arranged in parallel: one containing only phosphate rock, one containing only phosphate rock, and _one containing only sand.
The test was carried out by adding water so that The biologically treated sewage water described in Example 1 was used as the raw water. The results were as shown in the table below.

[Table] There was no difference in the catalytic dephosphorization ability of Material A compared to that of phosphate rock only. Example 3 The backwash wastewater from the Ansler Kaga Formation in Example 1 was stored in a backwash wastewater tank, and then returned to the contact reaction tank 1 to remove phosphate rock granules in the contact reaction tank.
The operation was carried out under the same conditions as in Example 1, except that the SS concentration was controlled to be about 200 ppm.
As a result, the phosphoric acid concentration of the treated water decreased as shown in the following table.

[Table] As described above, according to the present invention, it is easy to maintain fluidized bed operation in an ideal state, there is no need to take out and replenish phosphate minerals, and the particle size is 0.5
Even when using phosphate rock with a fine particle size of mm or less, it can be operated stably without causing the problems of conventional methods.
In addition to making the equipment more compact,
There is an advantage in that the required amount of phosphate minerals used in the treatment can be reduced and a large amount of treated water of good quality can be obtained at a significantly economical cost.

[Brief explanation of the drawing]

Fig. 1 is a conceptual flow sheet of the method of the present invention, Fig. 2 is an explanatory diagram of the system, Fig. 3 is a longitudinal cross-sectional view of another embodiment, and Figs. 4 to 6 are other embodiments of the mixing and stirring section. FIG. 7 is a diagram illustrating a system applied to the activated sludge method. 1... Tank, 2... Granular material separation section, 3... Solid-liquid separation section, 4... Rotating stirring blade, 5, 6, 8... Piping,
7...Pump, 9...Circulation path, 10...Draft tube, 11...Water collection groove, 12...Partition wall, 1
3...Superlayer, 14...Washing drain pipe, 15...Opening/closing valve, 16...Suction pipe, 17...Discharge pipe, 18...
... Pump, 19 ... Air supply pipe, 20 ... Drive device, 21 ... Backwash water valve, 22 ... Backwash water piping, 2
3... Partition wall, 24... Rotating shaft, 25... Raw water supply pipe, 26... Nozzle, 27... Aeration tank, 28...
Final sedimentation tank, 29... Valve, 30... Piping, 31...
...Diffuser pipe, 32...Sludge drain pipe, 33...Sludge drain valve, 3
4...Washing water piping, 35...Valve.

Claims (1)

[Claims] 1. A calcium agent is added to the liquid to be treated containing phosphate ions, and in a mixing and stirring section, sand, coke, activated carbon, anthracite, zeolite, synthetic resin, etc. that do not contain calcium phosphate are mixed together with phosphate mineral granules containing calcium phosphate. After the inert granules are co-suspended and brought into contact with each other under mixing and stirring to convert phosphate ions into insoluble calcium phosphate precipitates, the phosphate mineral granules and inert granules are separated in a granule separation section. The phosphates in the liquid are separated and recovered and returned to the mixing and stirring section, and the SS containing calcium phosphate precipitates in the effluent from the granule separation section is removed in the solid-liquid separation section. Removal method.