JPS6193892A - Fluidized bed type dephosphorization method - Google Patents

Abstract

PURPOSE:To efficiently remove phosphates, by applying solid-liquid separation treatment to a part of treated water before recirculate and return the same to inflow water or a fluidized bed. CONSTITUTION:Water to be treated, of which the pH was adjusted to a predetermined value, supplied to a dephosphorization tower from the lower part thereof by a raw water pump 2' through a raw water inflow pipe 2. a part of treated water used as recirculation water is guided to the solid-liquid separation process arranged on the way of a recirculation line to remove SS and the treated water is returned to the dephosphorization tower as recirculation water through a recirculation water introducing pipe 3. By this method, the action for obstructing the precipitation reaction of SS in a bed main body is suppressed and dephosphorization reaction can be performed efficiently.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for mobilizing phosphates present at relatively high concentrations in sewage, silver-based sewage, and industrial wastewater. The present invention relates to an efficient removal method using a solid particle layer.

[Conventional technology]

Generally, in the various liquids mentioned above that are discharged into natural water systems, inorganic phosphates such as orthophosphates, various condensed phosphates, and organic phosphates exist in various states. 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, and also in equipment and piping when using water for various purposes. Biological slime and chemical scale are formed, which is a major cause of accidents.

Therefore, various methods for removing phosphorus are being considered in order to remove the phosphates present in these liquids. A cylindrical or cone-shaped dephosphorization tower is filled with solid particles having a certain diameter, the pH of the liquid to be treated is adjusted to a range of 6 to 11, and the soluble sulfates contained in the liquid to be treated are further removed. By adding a calcium agent such as calcium chloride according to the concentration of calcium chloride and bringing it into contact with the fluid at a constant flow rate, calcium phosphate crystals are crystallized, fixed, and dissolved on the surface of the filled solid particles. We proposed a method to remove these phosphates.

A typical chemical reaction on the surface of a solid particle in this method example is as follows.

50a"-1-70H-+5 horse PO,-shiOa,(OH
) (POs) a+6111ao... (1) If such a dephosphorization method is applied, it is extremely easy to separate and dehydrate the solid particles to which calcium phosphate is fixed, and compared to the conventional chemical coagulation-precipitation method, the precipitation This is an excellent dephosphorization technology that not only does not require conventional sludge treatment facilities such as sludge thickeners, dehydrators, and dryers, but also can recover phosphorus as a resource.

, (RBIE[l!5.!-f, B1%'li!
i! , a) By the way, the conventional fluidized bed dephosphorization method has the following drawbacks. In the conventional method, a part of the treated water is circulated in order to achieve an optimal bed fluidization state and to efficiently remove phosphorus, but if the recycled water contains a large amount of KBs, This often had a negative effect on the crystallization reaction within the layer. In other words, as the daily amount brought into the layer by circulating water increases, compared to the amount of phosphorus that crystallizes from the liquid on the surface of the solid particles forming the layer, The ratio of crystallized phosphorus increases, and the crystallized pieces formed with 8B as the nucleus are extremely fine particles, so they are not retained in the layer and are selected out of the system, resulting in a phenomenon in which the quality of treated water deteriorates significantly. happened. This phenomenon becomes more pronounced when the raw water has a high phosphorus concentration or when the S8 in the circulating water contains a large amount of components particularly involved in crystallization reactions, such as calcium phosphate and calcium carbonate. This could be fatal to the formula dephosphorization method.

[Structure of the invention]

The present invention provides a method for removing phosphorus from the liquid while circulating a part of the treated water in the presence of calcium by passing phosphorus-containing wastewater through a bed in which solid particles are fluidized. This method is characterized by separating the solid-liquid portion into solid-liquid and then circulating it back into the inflow water or into the fluidized bed. The purpose of this invention is to provide an efficient and stable method for removing phosphoric acid by eliminating the drawback of reduced dephosphorization ability.

EMBODIMENT OF THE INVENTION Hereinafter, embodiments of the present invention will be described based on FIG.

Fig. 1 9 Reference numeral 1 is a pH adjustment tank, 2 is a raw water inflow pipe, 2' is a raw water pump, 3 is a circulating water introduction pipe, 3' is a circulating water pump,
4 is a dephosphorization tower, 5 is a treated water outflow pipe, 6 is an alkali agent storage tank, 7 is an alkali agent injection pipe, 7' is an alkali agent injection pump, 8 is a calcium agent injection pipe, 8' is a calcium agent injection pump, 9 is a calcium agent storage tank, 10 is a solid-liquid separator, 1
1 is a stirrer, A is solid particles forming a fluidized bed, and B is 5S1C remaining in the tank, indicating a fluidized bed.

The water to be treated (raw water) introduced into the pH adjustment tank 1 is agitated by the stirrer 11, and the alkali supplied from the alkali agent storage tank 6 through the alkali agent injection pipe 7 by the alkali agent injection pump 7' adjusts the water to a predetermined level. After adjusting the value 1cpH,
The raw water is supplied to the dephosphorization tower from the lower part of the raw water pump 2' through the raw water inlet pipe 2. A part of the treated water flowing out from the upper part of the dephosphorization tower 4 through the treated water outflow pipe 5 is circulated to the dephosphorization tower through the circulating water introduction pipe 3, but BE? When the circulating water containing a large amount of At the same time, a reaction occurs in which calcium phosphate is precipitated using the SS particles B as nuclei, and the crystallized substances containing floating FIB as nuclei are so fine that they are not retained in the layer and directly flow into the treated water flow pipe 5. Since the quality of the treated water will deteriorate, firstly, a part of the treated water to be used as circulating water is introduced into the solid-liquid separation process 1o installed in the middle of the circulation line, and after removing SS, the circulating water is introduced into the circulating water inlet pipe 6 as circulating liquid. By returning the SS0 layer to the dephosphorization tower, the effect of interfering with the crystallization reaction of the main body of the SS0 layer can be suppressed, and the dephosphorization reaction can be carried out efficiently. In this example, depending on the concentration of phosphorus in the raw water, a necessary amount of calcium is supplied from the calcium agent storage tank to the pump 8' and into the circulating water through the calcium agent injection pipe.

The solid-liquid separation step may be simple gravity sedimentation separation, coagulation sedimentation, or a filtration method in which liquid is passed through a bed filled with solid particles.

As described above, according to the present invention, the aS in the treated water discharged from the fluidized bed is separated into solid and liquid and is circulated back to the fluidized bed, thereby making it possible to carry out the dephosphorization process extremely effectively and stably. It became.

Furthermore, in the solid-liquid separation step, not only 88 but also a part of the soluble phosphorus in the liquid can be removed, so the inflow phosphorus load of the fluidized bed can be reduced, which also has the effect of further increasing the processing efficiency. Can be done.

Example 1 A crushed and sieved phosphate rock (
Effective diameter α4fi, uniformity factor 1. Riwo 1000111II
The thickness of the magazine was filled. The liquid to be treated is secondary treated water obtained by treating factory wastewater with coarse solids largely separated using the activated sludge method.After removing carbon dioxide by the acid strip method, caustic soda is added to adjust the pH of the liquid to be treated from a5 to a5. 1 [The raw water adjusted to 10 was used, calcium chloride was used as the calcium agent, and the weight ratio of aa/po was 1.0 to 1.0, corresponding to the concentration of soluble phosphates in the liquid to be treated. It was added to the circulating water in a range of 15%. As for the circulating water, the treated water was once filtered through a sand filter bed and then returned to the fluidized bed. The sand filter layer is a cylindrical column with an inner diameter of 200 mm and an effective depth of 15 m, and 1000+ g of sand (effective diameter 0.6, uniformity coefficient 1.4).
The tank was filled to a thickness of 200 m, and water was passed through it for 1 day for 'LV = 200 m. The experiment was conducted for about 2 months while flowing raw water and circulating water in the same amount as the raw water upward from the lower part of the dephosphorization tower at a flow rate of LV = 50 to 40 inertia/day. The results are shown in Table-1.

Table 1 As is clear from Table 1, as a result of circulating the filtrate of fluidized bed treated water, the phosphorus removal rate was 80% or more, and the phosphorus concentration was 3.
Treated water of ~/l (as p) or less was stably obtained.

On the other hand, as a comparative example, fluidized bed treated water was circulated without filtration.
The results obtained when water was passed for two months under all other conditions were the same, as shown in the comparative example in Table 1, but the SS concentration in the treated water was as high as 34 ■/l, and the phosphorus removal rate was 60. %, treated water phosphorus concentration & Om9/t (as P).

Example 2 In Example 1, in addition to the sand filter layer installed in the middle of the circulation line, in order to study the solid-liquid separation process, a sedimentation separation tank, a coagulation sedimentation tank, and a fixed dephosphorization tank were used, and the performance was evaluated. compared. In the experiment, the same equipment and liquid to be treated as in Example 1 were used, and the liquid to be treated was pretreated in the same manner as in Example 1, and raw water was used. Caustic soda was injected so that the intralayer plHL was 5 to 1110, and calcium chloride was added to the circulation line after solid-liquid separation to the same concentration range as in Example 1, and the ratio of raw water to circulating water was adjusted. L730~40 from the bottom of the fluidized bed dephosphorization tower upward so that the
Water was passed through at a flow rate of ML/hr.

Continuous experiments were conducted using each solid-liquid separator under the above conditions for about one month. The results are shown in Table 2.

As is clear from Table 2, no matter which of the four types of solid-liquid separators mentioned above are installed in the middle of the circulation line, the phosphorus concentration in the fluidized bed treated water is 4.0 ■/l or less, which is 70% of the raw water. It was found that the above amount of phosphorus was removed, and it was confirmed that this method can be applied.

Example 5 Table 5 shows the treatment results when sand ([L2 to [L 4 sw )] was used instead of phosphate rock as the solid particles in the fluidized bed in Example 1.゛Table-3 Processing results
゛As shown in Table 3, when sand was used, good results were not obtained initially, but as time passed, the water quality improved, and after one week, the results were comparable to those using phosphate rock. performance was obtained.

Therefore, it was found that sand can be used as solid particles in a fluidized bed.

[Brief explanation of drawings]

FIG. 1 is a schematic flow diagram for explaining one embodiment of the present invention.

Claims (1)

[Claims] 1. A method for removing phosphorus from the waste water while circulating a portion of the treated water in the presence of calcium by passing phosphorus-containing waste water through a layer in which solid particles are fluidized, A method for removing phosphates from wastewater, which comprises separating a portion of the treated water into solid-liquid and then circulating it back into the inflow water or into a fluidized bed. 2. The method for removing phosphates according to claim 1, which comprises passing liquid through a bed filled with solid particles to separate solid and liquid. 3. Claim 1 or 2 in which the solid particles are phosphate rock
Phosphate removal method described in section.