JPS6044999B2 - Treatment method for phosphoric acid-containing wastewater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating phosphoric acid-containing wastewater, and relates to a method for sufficiently increasing the phosphorus removal efficiency when treating phosphoric acid-containing wastewater with crushed slag generated from a converter. This is an attempt to provide a possible method.

Conventionally, the coagulation-sedimentation method has been mainly used to remove phosphates from wastewater.

That is, a coagulation sedimentation tank is connected to the rapid stirring tank and the slow stirring tank, a treated water tank is connected to this settling tank, and raw water and a flocculant are introduced into the rapid stirring tank, rapidly stirred, and then slowly stirred. The precipitated water is sent to a sedimentation tank via an agitation tank, and then treated in a treated water tank.From the treated water tank, it is sent to a filtration mechanism by a pump, and then it is sterilized appropriately and then discharged, and it is used as a coagulating precipitant. The conventional method generates a large amount of sludge, and the above Coagulants are expensive and running costs are high, and it is difficult to adjust the amount of chemicals injected according to temporal fluctuations in the phosphate concentration of waste water and other maintenance management, and of course, the equipment requires a large area. However, there are disadvantages such as the necessity of installing a filtration mechanism to prevent flocs from overflowing from the coagulation and sedimentation tank. The present inventors conducted research to eliminate the disadvantages and shortcomings of the conventional method as described above, and created a layer filled with appropriately crushed slag generated from a converter.
proposed that they be effectively removed by passing through and contacting the wastewater containing these substances (Patent Application No. 169085, filed in 1982).

That is, the present inventors have repeatedly studied a method for treating phosphoric acid-containing wastewater that does not require the expensive flocculant used in the conventional general method described above, and have found that converter slag generated from steel mill converters has an excellent removal effect. Although it is not possible to clearly elucidate the details of the function of converter slag to remove phosphoric acid from wastewater, it is mainly due to the coagulation filtration mechanism. An example of the device is as shown in FIG. A gravel layer 4 is formed, a converter slag layer 5 is crushed to 1 hour or less, and a lead-out pipe 6 from the space is led to a PH adjustment tank 9.
After adjusting the pH by appropriately adding Cl or H2SO4, the water is sterilized if necessary and then released. In addition, a drain port 7 for backwash water and a rotary surface washer 8 are provided in the upper part of the tank 1, so that when the converter slag layer 5 is clogged with SS etc., it can be used for backwashing in the same way as backwashing of a gravity sand filtration mechanism. It is designed to discharge clogged SS etc. out of the system. However, an example of the composition of converter slag used in such equipment is typically shown in Table 1 below; however, when phosphoric acid-containing wastewater comes into contact with such converter slag, the converter slag The free calcium inside is eluted and reacts with phosphorus in the wastewater to form poorly soluble phosphate hydroxyapatite [Ca
5(0H)(PO4)3], and this apatite is trapped in the filter bed by the filtration action of the converter slag particles I'7, so that phosphorus is completely removed. However, in this case, there is a limit to the amount of free calcium in the converter slag, and as the amount of water flowing increases, the amount of free calcium eluted decreases, and the phosphorus removal efficiency eventually decreases.
As shown in the figure, it is difficult to maintain a desirable removal effect.

The present invention was devised after further study in view of the above-mentioned actual situation, and appropriately addresses the problem that the phosphorus removal efficiency decreases as the water flow rate increases, as described above. This method is designed to maintain excellent phosphorus removal efficiency over a long period of time, and as mentioned above, the amount of free calcium in the converter slag decreases and the pH of the treated water increases, for example, from 8.5 to 8.5. It is proposed to add a predetermined amount of alkaline agent and calcium salt at the stage when the temperature drops to 9.0.

That is, in the initial stage of water flow, free calcium in the converter slag is used to react with phosphorus in the wastewater to generate phosphoric hydroxyapatite, which is captured in the converter slag filter layer to remove phosphorus. None, the amount of water flowing increases and the pH of the treated water is 8 as above.

When the value has decreased to 5 to 9.0, an alkali agent and a calcium salt are added, and phosphorus is removed by a crystallization reaction using apatite or converter slag in the filter layer as a seed crystal.

Note that this crystallization reaction is performed at pH 8.5 to 9.0 (using Ca(0H)2, Na0H, etc. as an alkali agent), Ca2+5
0-70 Da/' (Ca as a calcium agent) (0H)2
, CaCI2, etc.).

The outline of the apparatus for carrying out the method of the present invention as described above is as shown in FIG. 8 etc. have the same configuration, but a PH and calcium adjustment tank 10 is provided in front of the tank 1, and the P
H 8.5-9.0, calcium concentration 50-70mg
/e, then the pump 11 sends the liquid to the tank 1.

PH adjustment in the adjustment tank 10 is performed by a PH controller 12, and slaked lime is usually used as the alkaline agent and supplied from the chemical tank 13, thereby serving as pH adjustment and calcium adjustment at the same time. Of course, caustic soda or the like may be used as the alkaline agent, and calcium chloride or the like may be used as the calcium agent. In addition, the present invention can be implemented in various apparatuses since it is sufficient to simply pass the phosphoric acid-containing wastewater through a packed bed of converter slag particles.

For example, by using a pre-tank that receives phosphoric acid-containing waste water with an appropriate head difference, from the pre-tank to the bottom of the tank 1 filled with the converter slag layer 5 as described above, depending on the head difference (or a pump An upflow format may be adopted in which the wastewater is introduced (at pumping pressure) and the treated water overflows from the top of tank 1, and the converter slag particles are transferred to the flow of wastewater in the channel flowing from the top to the bottom. It is possible to adopt a method in which filled layers are installed cross-sectionally. With any of these types, the same removal effect can be obtained by ensuring the contact time as in the example described later.
Since no special stirring or precipitation is required, the equipment is simple and can operate stably. Specific examples according to the present invention will be described below.

Example 1 Converter slag pulverized to a particle size of 0.5 to 1.2 Ttm was packed in an acrylic resin cylinder with a diameter of 30 mm, and 3 m9/l of orthophosphoric acid solution was passed through it at SV=2. As shown in A, the phosphoric acid concentration of the treated water increases after 15 days of water flow.
On the 23rd day, the removal efficiency reached 2 mg/' and a significant decrease in removal efficiency was observed.

On the other hand, after 10 days of running water, the pH was 9. In the case of FIG. 3B according to the present invention in which the calcium concentration was adjusted to 70 m9/e, the phosphoric acid concentration remained 0.0 m9/e even after 60 days or more.
It was confirmed that the phosphoric acid removal efficiency was maintained at 3 mg/' or less and that the phosphoric acid removal efficiency could be maintained at a high level over a long period of time.
Example 2 Orthophosphoric acid test solution with constant concentration (PO4-P: 10-M
9/e), add 1000 ppm of 200 to 300 mesh converter slag that has been crushed and sieved in advance, and shake it for 2 hours with a shaker to add the converter slag and a small amount of the shaker to the container. The liquid was left behind and filtered, and the phosphoric acid concentration in the filtrate was measured.

This was tested again; the test solution was added, and the shaking → filtration → analysis operations were repeated. As a result, the phosphorus removal rate decreased from the third shaking experiment under conditions where the pH and calcium concentration of the converter slag were not adjusted. did. On the other hand, as in Example 1, PH9
．． In the case where the Ol calcium concentration was adjusted to 70 mg/e, the phosphoric acid concentration was 0.6 even in the sixth shaking experiment, as shown in Table 2 below along with the case without adjustment.
We were able to keep it below m9/e.

In contrast, when phosphate rock crushed and sieved to 200 to 300 mesh is used, as shown in Table 2, by adjusting as in the present invention, the converter slag is 3. I learned that the phosphorus removal rate decreases even after the first time.

According to the present invention as described above, when treating phosphoric acid-containing wastewater using crushed converter slag, an alkali agent and calcium are added at the stage when the amount of free calcium eluted from the converter slag has decreased. Add, pH 8 or higher,
By adjusting the calcium concentration to 50 m9/' or more, a preferable phosphorus removal efficiency can be ensured over a long period of time, and smooth treatment operations can be carried out.This invention is industrially highly effective.

[Brief explanation of drawings]

The drawings show the technical contents of the present invention, and FIG. 1 is an explanatory diagram of a dephosphorization treatment apparatus according to the prior art by the present inventors, and FIG. 2 is an explanation of a dephosphorization treatment apparatus according to the method of the present invention. figure,
FIG. 3 is a chart showing the relationship between the number of days of water passage and the phosphoric acid deficiency removal effect in the case of the prior art shown in FIG. 1 and the method of the present invention. However, in these drawings, 1 is a processing tank, 2 is a space, 3 is a support member, 4 is a gravel layer, 5 is a converter slag layer,
Reference numeral 6 indicates an outlet pipe, 7 indicates a drain port, 9 indicates a JPH adjustment tank, 10 indicates a calcium adjustment tank, 11 indicates a pump, 12 indicates a PH controller, and 13 indicates a drug tank.

Claims (1)

[Claims] 1. When dephosphorizing the wastewater by bringing the crushed slag generated from the converter into contact with wastewater containing phosphoric acid, an alkali agent is applied at the stage when the amount of free calcium eluted from the converter slag has decreased. and calcium added to pH 8
As described above, a method for treating phosphoric acid-containing wastewater is characterized in that the treatment is performed by adjusting the calcium concentration to 50 mg/l or more.