JPH0331120B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for treating COD-containing wastewater, particularly persistent COD-containing wastewater. (Prior Art) In recent years, with the increasing social demand for preventing water sludge in public water bodies, various wastewater treatment methods and devices have been proposed. This persistent COD
"Water Treatment Technology" Volume 23 regarding the treatment of wastewater containing
No. 12, pp. 13-22 (Japan Water Treatment Technology Research Society, published December 15, 1981) and "Environmental Technology" No. 11
Volume, No. 4, pp. 63-65 (Environmental Technology Research Group, Showa
(Published on April 30, 1957) describes a technology for treating persistent organic compound wastewater by Fuenton treatment and a combination treatment of the Fuenton method and activated sludge method. Generally, Fuenton treatment is performed using hydrogen peroxide (H ₂ O ₂ ).
This method uses the oxidizing power of COD to treat persistent COD. In the conventional Fuenton method, as shown in Figure 3, ferrous sulfate and hydrogen peroxide are added to wastewater containing persistent COD (raw water), the pH is adjusted to 3.5 or less with acid, and the mixture is heated for 1 to 3 hours. This is done by stirring the liquid. During this time, hydrogen peroxide acts on the recalcitrant COD using ferrous sulfate as a catalyst.
Process. Next, the treated liquid is neutralized to a pH of 7 to 7.5, forming a floc (sludge) of iron, etc.
Leave to stand for 1 hour to separate treated water and floc. (Problems to be Solved by the Invention) In the conventional method for treating wastewater containing persistent COD using the Fuenton method, after the Fuenton treatment, the pH after treatment is adjusted to 7 to 7.5, and the treated water is mixed with the treated water. Therefore, in the case of excessive addition of hydrogen peroxide or when the required amount of hydrogen peroxide changes over time, hydrogen peroxide may remain and, on the contrary,
There is a problem that COD and BOD may be increased and the wastewater treatment is not always satisfactory. (Means for Solving the Problems) The present invention involves the treatment of COD-containing wastewater, particularly persistent COD-containing wastewater, by Fuenton oxidation treatment, adding alkali to the treated solution to adjust the pH to 10 or higher, further aeration, and then sedimentation separation. This is based on the finding that COD and BOD can be significantly reduced by separating flocs and supernatant water. In the method of the present invention, as shown in Figure 1, in the same way as the conventional Fuenton treatment, persistent COD
The pH of the water contained was adjusted to 3.5 or less with hydrochloric acid or sulfuric acid, then hydrogen peroxide and ferrous sulfate (FeSO ₄ 7H ₂ O) were added thereto, and the mixture was heated for 1 to 3 hours, e.g.
Stir at 60 rpm for 3 hours and perform Fuenton treatment, adjust the pH after treatment to 10 or more, preferably 10.5 to 12,
After adjustment, the treatment liquid is preferably transferred to tank 1 in an aeration tank.
Aerate for 1 to 2 hours at an aeration rate of 0.3 to 1.5 m ³ per m ³ /Hr. At this time, the smaller the amount of aeration, the longer the aeration time. The supernatant water is separated by aeration, and the supernatant water is neutralized with hydrochloric acid or sulfuric acid to be used as treated water.The polluted sludge is further left to stand, and the supernatant water is returned to raw water. In the above treatment, (a) the amount of hydrogen peroxide added varies depending on the water quality, but it is initially added in three stages in the range of 0 to 2000 mg/distance, and formal data is obtained by increasing or decreasing it based on the water quality results. (b) The amount of ferrous sulfate (FeSO ₄ 7H ₂ O) to be added is generally 80 to 100% of the amount of hydrogen peroxide, but it is important to avoid hydrogen peroxide decomposition (COD reduction) reaction during Fuenton treatment and aeration. It increases if the flocculation during sedimentation treatment is poor. (c) The pH during Fuenton treatment is
As mentioned above, it is generally said that 3.5 or less is good.
(d) A strong alkali with a pH of around 11 is best for decomposing residual hydrogen peroxide, while a weak alkali has a slow decomposition rate.
Figure 2 shows the relationship between aeration time and residual H ₂ O ₂ amount.
As shown in the figure, hydrogen peroxide decomposition during aeration (COD
(decreased) reaction, the decomposition rate slows down in the absence of Fe. In the method of the present invention, the liquid after Fenton treatment is
The pH is set to 10 or more, but if it is less than 10, the decomposition rate of hydrogen peroxide decreases to 1/10, which is not preferable. In addition, precipitation of metals that are neutral and difficult to precipitate, such as Fe
Precipitation of (OH) ₂ , CaCO ₃ , etc. occurs when the pH is approximately 10.5 or higher, and setting the pH to 10.5 to 12 reduces the formation of flocs such as iron, and the formation of CaCO ₃ flocs that are difficult to precipitate in neutral conditions. ₂ +CO ^-- ₃ +2NaOH→ CaCO ₃ ↓+2NaCl+OH Ca (HCO ₃ ) ₂ +NaOH→ CaCO ₃ ↓+Na ₂ CO ₃ +2H ₃ O Promotion of decomposition of residual hydrogen peroxide and stripping of ammonia nitrogen NH ₄ Cl+NaOH→ NH ₃ ↑ +NaCl+H ₂ O (NH ₄ ) ₂ SO ₄ +2NaOH→ 2NH ₃ ↑ +Na ₂ SO ₄ +2H ₂ O is promoted, so it is preferably 10.5 to 12. Next, the liquid whose pH has been adjusted to 10 or higher is aerated,
This aeration decomposes residual hydrogen peroxide and causes stripping of ammonia nitrogen and growth of metal flocs. The amount of aeration in this aeration is preferably 0.3 to 1.5 m ² /Hr・m ³ tank as described above, but the reason for this is that if it is less than 0.3, the decomposition of residual hydrogen peroxide is insufficient and the flocs will settle.
On the other hand, if it exceeds 1.5, the metal flocs will become fragmented and the settling properties will deteriorate. The preferred range of aeration time is 1 to 2 hours; however, if the aeration time is less than 1 hour, the residual hydrogen peroxide will not be sufficiently decomposed, while if it exceeds 2 hours, the grown metal flocs will become fragmented, which is not preferred. (Examples) The present invention will be explained by the following examples and comparative examples. Example: Landfill wastewater (raw water) is shown in Table 1.
No.．． Tests 1 to 3 were conducted. Raw water for each test
200 into a 200-dose stainless steel drum. A stirrer was set in this drum and stirred at 60 rpm. Then add 1000mg/sulfuric acid (10
%), adjust the pH to 3, and add the first
_H2O2 (30%), _FeSO4.7H2O (100 _% ) in the amounts shown in the table _.
%) and continued stirring at 60 rpm for 3 hours. After 3 hours of treatment, the amount shown in Table 1 was
The pH was adjusted to 11 by adding NaOH (10%). this
The pH-adjusted water was transferred to an aeration tank (0.3 m x 0.3 m x 2.5 m height: with a diffuser plate) and aerated at 160/Hr (0.8 m ³ /Hr·m ³ aeration tank) for 1.5 hours. After completing the aeration, let it stand for 30 minutes, separate the supernatant water using the decanting method, and transfer it to the 200-capacity stainless steel drum.
The remaining amount of sulfuric acid (10%) after subtracting 1000 mg from the amount shown in Table 1 was added to adjust the pH to 7.5 to 8 to obtain treated water. Analyze raw water and treated water,
The obtained results are also listed in Table 1.

[Table] In this treatment, BOD also shows almost the same removability as COD. Regarding nitrogen removal, most of the nitrogen (N) in waste water is ammoniacal N and organic N. The organic N in this is converted to ammoniacal N by the Fuenton treatment, and by aeration at PH11, it is removed by ammonia stripping along with the ammoniacal N that originally existed, showing a decrease in TN and a reduction in _CaCO3 . Regarding removal, wastewater contains Ca.
exists as highly soluble CaCl ₂ and Ca(HCO ₃ ) ₂ . By adjusting this pH to 11 and aerating it, CaCl ₂ is converted to CO ^-2 ₃ originally present in the wastewater.
Ca(HCO ₃ ) ₂ is also removed by combining with CO ^-2 ₃ supplied by aeration and becoming CaCO ₃ with low solubility.
This shows a significant decrease as it reacts with NaOH to form _CaCO3 . Comparative Example Regarding the same garbage landfill wastewater (raw water) as in the example, No. 1 shown in Table 2 was used. Tests 1 to 3 were conducted. In each test, 200ml of raw water was placed in the same stainless steel drum as in the example and stirred. Next, the second per raw water
Add the amount of sulfuric acid (10%) shown in the table to adjust the pH to 3, and add H ₂ O ₂ (30%), FeSO ₄ 7H ₂ O to this solution.
(100%) and continued stirring at 60 rpm for 3 hours. After treatment for 3 hours, NaOH (10%) in the amount shown in Table 2 was added to adjust the pH to 7.5, and treated water was obtained. Raw water and treated water were analyzed, and the results are listed in Table 2.

【table】

[Table] From the results in Tables 1 and 2, it is clear that the method of the example provided a treatment effect that was significantly superior to the method of the comparative example using the conventional Fenton method. (Effects of the Invention) As explained above, in the method for treating COD-containing wastewater of the present invention, after performing Fuenton treatment, the pH of the treated liquid is adjusted to 10 or more, aeration is performed, precipitation is performed, and then the supernatant liquid is Because the configuration is such that it is neutralized and discharged as treated water, residual hydrogen peroxide in the Fuenton treatment, which could not be handled with conventional technology, is removed (residual
This process also removes CaCO ₃ , which causes pipe scale, total nitrogen (T-N), and Fe, which cannot be removed in the neutral pH range.
The effect is that metals such as (OH) ₂ can also be removed. Therefore, the method of the present invention can be used to treat organic wastewater, especially wastewater containing persistent COD, and is therefore effective in rubber landfill wastewater treatment, which also requires hardness treatment and nitrogen removal.

[Brief explanation of drawings]

FIG. 1 is a process diagram of the method of the present invention, FIG. 2 is a diagram showing the relationship between aeration time and residual H ₂ O ₂ amount, and FIG. 3 is a process diagram of the conventional wastewater treatment method.

Claims (1)

[Scope of Claims] 1. Add acid, hydrogen peroxide and ferrous sulfate to COD-containing wastewater and stir to bring the pH to 3.5 or less. After the Fuenton treatment, add alkali to bring the pH to 10 or more. A method for treating COD-containing wastewater, which is characterized by transferring adjusted water to an aeration tank, aerating it, and then separating it into sludge and supernatant water by sedimentation. 2. The method for treating COD-containing wastewater according to claim 1, wherein the aeration amount is 0.3 to 1.5 m ³ /Hr, the aeration time is 1 to 2 hours in a m ³ aeration tank. 3. According to claim 1 or 2, the pH of wastewater after Fuenton treatment is 10.5 to 12.
Treatment method for COD-containing wastewater.