JP3451764B2 - Method of deodorizing wastewater containing odorous substances - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for deodorizing waste water containing sulfur-containing malodorous substances generated in a kraft pulp manufacturing process or the like.

[0002]

2. Description of the Related Art Hydrogen sulfide (H ₂ S), methyl mercaptan (CH ₃ SH, hereinafter MeSH), dimethyl sulfide (CH ₃ SCH ₃ , hereinafter DMS), dimethyl disulfide are known as malodorous substances produced in the manufacturing process of kraft pulp. (CH ₃ SSCH ₃ , hereinafter DMDS) and the like are included. In the present invention, the term kraft pulp manufacturing process is a general term for a pulp manufacturing process, a chemical recovery process, and a gas / wastewater treatment process around them. In addition to the production process of kraft pulp, removal of these malodorous substances has become an important issue from the viewpoint of environmental protection.

As a method for deodorizing wastewater containing these malodorous substances, a stripping treatment method, an activated sludge treatment method, an oxidation method using activated carbon as a catalyst and the like are generally known. The stripping method includes an air stripping method and a steam stripping method. The former is lower in cost and easier to operate and maintain than the latter, but the DMDS removal rate is said to be low. The latter has less exhaust gas and is DMD
It is excellent in S removal, but the running cost due to the use of steam is high, and maintenance is troublesome. In the activated sludge treatment method, the deodorization rate varies depending on the load of malodorous substances, and DMS
There is a possibility that S may increase and that a foul-smelling substance may be volatilized into the atmosphere by aeration.

As an oxidative deodorizing method using activated carbon as a catalyst, for example, a method of contacting activated carbon with waste water containing mercaptans in the presence of an oxygen-containing gas to deodorize the waste water (Japanese Patent Publication No. 55-33956) is known. Has been. Activated carbon is inexpensive and harmless, and a reactor filled with activated carbon is said to be easy to carry out a reaction operation. As an oxidative deodorization method, a method using chlorine-based chemicals (chlorine, sodium hypochlorite, etc.) and ozone is also known, but the former is preferable from the viewpoint of environmental protection because there is concern about the formation of organic chlorine compounds. Not a method. Ozone is a strong oxidant, but when treating wastewater containing a large amount of malodorous substance alone, the amount of ozone added is large, and this is not an economical method.

[0005]

Among the above-mentioned conventional methods, the oxidative deodorizing method using activated carbon as a catalyst is inexpensive and harmless and can oxidize and deodorize mercaptans, but among the malodorous substances generated in the pulp manufacturing process. However, it has a drawback that DMDS cannot be removed. INDUSTRIAL APPLICABILITY The present invention employs the oxidative deodorizing process having the above advantages, and is effective against all sulfur-containing malodorous substances generated from the kraft pulp manufacturing process including DMDS, and is an economical deodorizing method. The challenge is to provide. The sulfur-containing malodorous substance referred to in the present invention refers to four substances, H ₂ S, MeSH, DMS and DMDS.

[0006]

The present invention adopts the following constitution in order to solve the above problems. That is, the first invention of the present invention is, "In a method of deodorizing wastewater containing sulfur-containing malodorous substances, a treatment step A in which the wastewater is brought into contact with activated carbon in the presence of an oxygen-containing gas, and the obtained treatment liquid is Further, it is a deodorizing method characterized by comprising a treatment step B of treating with an ozone-containing gas ”.

A second invention of the present invention is "In the first invention, the molar amount [O] of the ozone introduced in the treatment step B is [O].
₃ ] and the sulfur content molar amount [S] of the sulfur-containing malodorous substance remaining in the liquid to be treated, which is a ratio of [O ₃ ] / [S] of 0.2 or more. Method ".

A third aspect of the present invention is the "first or second aspect".
In the invention, the deodorizing method is characterized in that wastewater containing a sulfur-containing malodorous substance is generated from the kraft pulp manufacturing process ”.

Hereinafter, the present invention will be described in detail by taking a kraft pulp manufacturing process as an example. The wastewater containing the sulfur-containing malodorous substance generated from the kraft pulp manufacturing process is first provided to the activated carbon treatment process (treatment process A). In this step, the oxygen-containing gas is supplied together with the wastewater, and the sulfur-containing malodorous substance contained in the wastewater is oxidized at the active points on the surface of the activated carbon.
In our experiments, H ₂ S.MeSH is almost oxidized. That is, H ₂ S is added to sulfuric anhydride (SO ₃ ) to Me
It is considered that SH is oxidized to odorless methyl sulfonic acid (CH ₃ SO ₃ H).

The method of contacting the wastewater with the oxygen-containing gas may be countercurrent or co-current. The oxygen-containing gas may be not only air, but also pure oxygen gas, PSA oxygen gas, etc. Any gas containing

The quantitative relationship between the activated carbon and the liquid to be treated is influenced by the scale of the apparatus, the flow rate of the liquid, and the concentration of the malodorous substance in the liquid, and therefore cannot be unconditionally limited. But,
For example, the liquid concentration of each malodorous substance is 1 ppm to 1000 p.
In the range of about pm, the volume standard liquid space velocity y defined by the following formula is preferably in the range of 0.1 to 100, more preferably 1 to 50. Here, the volume reference space velocity is the liquid supply velocity x (liter / liter
hr. ) Divided by the volume z (liter) of the activated carbon layer,
That is, y = x / z.

The amount of the oxygen-containing gas used is not limited to the same as above, but generally, the molar amount of oxygen molecules [O ₂ ] in the oxygen-containing gas, hydrogen sulfide in the liquid, and mercaptan are approximately the same. Ratio with the total molar amount of sulfur [S]
[O ₂ ] / [S] is preferably about 1 to 100.

The treatment liquid obtained from the treatment step A is then subjected to the ozone oxidation step (treatment step B). That is, the treatment liquid is sent to the ozone oxidizer, and the ozone-containing gas is supplied from the ozone generator to the ozone oxidizer. In order to improve the reaction efficiency in the ozone oxidizer,
Fill the material with a large specific surface area (Raschig ring, Lessing ring, Activated carbon, etc.). The method for contacting the liquid to be treated with ozone and the ozone-containing gas may be countercurrent or cocurrent. As a guideline for the amount of ozone used, the molar amount of ozone [O ₃ ]
It is preferable that the relationship with the sulfur molar amount [S] of the sulfur-containing malodorous substance remaining in the liquid to be treated is 0.2 or more in the ratio [O ₃ ] / [S].

It is considered that the DMS / DMDS remaining in the liquid to be ozone-treated in the treatment step B is oxidized to dimethyl sulfone (CH ₃ SOCH ₃ ) / methylsulfonic acid by ozone, respectively. The deodorized final treatment liquid is discharged. A feature of the present invention is that the ozone oxidation treatment (treatment step B) is performed subsequent to the activated carbon treatment step (treatment step A). Although it is possible to oxidize and deodorize the sulfur-containing malodorous substance in the wastewater only by the ozone oxidation step (treatment step B), it is not economical because it requires an excessive amount of ozone as shown in Comparative Examples 2-3. In the activated carbon treatment (treatment step A), H ₂ S.MeSH is oxidized by oxygen in the oxygen-containing gas using activated carbon as a catalyst, but DMS / DMDS remains poorly reactive and almost unreacted. On the other hand, ozone can efficiently oxidatively decompose DMS / DMDS in a system in which the amount of H ₂ S / MeSH present is small. Therefore, in the activated carbon treatment (treatment step A), the oxygen-containing gas oxidizes H ₂ S / MeSH / DMS to reduce the sulfur-containing malodorous substance load brought into the ozone oxidation step (treatment step B), and thereafter, the remaining DMS / DMD
The required amount of ozone can be reduced by oxidizing S with ozone.

[0015]

The present invention will be described in more detail with reference to Examples. <Examples 1 to 4> a. Treatment step A: Waste water having the malodorous substance composition shown in Table 1 was treated under the conditions shown in Table 2. However, air was introduced after the concentration of each sulfur-containing malodorous substance contained in the aqueous solution discharged from the lower part of the activated carbonation device reached almost equilibrium. The H ₂ S in the obtained treatment liquid is “For the method of determining the regulation standard of the malodorous substances contained in the discharged water, March 28, 1994,
The analysis was performed according to the measurement method (headspace method) described in "Central Environmental Council."
・ For DMS and DMDS, extract the treatment liquid with benzene,
This benzene was injected into a gas chromatograph and analyzed.

B. Treatment step B: The treatment liquid (treatment liquid to be treated with ozone) obtained from the activated carbonation device was treated under the conditions shown in Table 3. The amount of ozone added was based on the analysis of sulfur-containing malodorous substances remaining in the treatment liquid, and was added so as to be a predetermined multiple shown in Table 5 with respect to the total number of moles of sulfur atoms in the sulfur-containing malodorous substances. The analysis of the treatment liquid obtained from the ozone oxidizer was performed in the same manner as the treatment liquid. The analysis results of the treatment liquid are shown in Table 5.

<Comparative Example 1> An aqueous solution having a sulfur-containing malodorous substance composition shown in Table 1 was subjected only to the treatment step A under the treatment conditions shown in Table 2, and the obtained treatment liquid was analyzed. The results are shown in Table 4.

<Comparative Examples 2 to 3> An aqueous solution having a sulfur-containing malodorous substance composition shown in Table 1 was subjected only to the treatment step B under the treatment conditions shown in Table 3, and the obtained treatment liquid was analyzed. The results are shown in Table 4.
Described in.

<Table 4> and <Table 5> show that the malodorous substance residual rate (%)
Is the ratio of (concentration of malodorous substance after treatment) to (concentration of malodorous substance before treatment) in%. ND in the table is
Indicates that the residual rate of sulfur-containing malodorous substances is below the detection limit.
The ozone addition amount in Table 4 is shown as a relative value when the addition amount in Example 4 is 100.

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

[Table 3]

[0023]

[Table 4]

[0024]

[Table 5]

[0025]

As shown in the examples, by combining the activated carbonation treatment step A and the ozone oxidation treatment step B,
Wastewater containing malodorous substances can be effectively deodorized with a small amount of ozone added.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI C02F 1/58 ZAB C02F 1/58 ZABP 1/78 ZAB 1/78 ZAB (56) Reference JP-A-55-5742 (JP, A) JP-A-55-152527 (JP, A) JP-A-55-152526 (JP, A) JP-A-57-174191 (JP, A) JP-A-55-152590 (JP, A) JP-A-61 -257238 (JP, A) JP-A-49-115099 (JP, A) JP-A-49-76774 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C02F 1/00- 1/78

Claims (3)

(57) [Claims] 1. A method for deodorizing wastewater containing sulfur-containing malodorous substances, a treatment step A in which the wastewater is brought into contact with activated carbon in the presence of an oxygen-containing gas, and the obtained treatment liquid is further treated with an ozone-containing gas. A deodorizing method comprising a treatment step B. 2. In the treatment step B, the relationship between the molar amount of ozone introduced [O ₃ ] and the molar amount of sulfur of the sulfur-containing malodorous substance remaining in the liquid to be treated [S ₃ ] is [O ₃ ] / [S]
The deodorizing method according to claim 1, wherein the ratio is 0.2 or more. 3. The deodorizing method according to claim 1 or 2, wherein wastewater containing a sulfur-containing malodorous substance is generated in the kraft pulp manufacturing process.