JP2003320382A - Method for removing dissolved sulfide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for efficiently removing dissolved sulfide contained in wastewater as sulfur alone by oxidation to obtain treated water with a small amount of a suspended substance. <P>SOLUTION: An oxidizing agent is added to wastwater containing dissolved sulfide under a pH condition of 6.45 or more and dissolved sulfide is oxidized to form sulfur. This sulfur is removed by flocculation treatment or membrane treatment. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for removing dissolved sulfide. More specifically, the present invention relates to a method for removing dissolved sulfide, which is capable of efficiently removing dissolved sulfide contained in wastewater as sulfur simple substance by oxidation to obtain treated water with less suspended substances.

[0002]

2. Description of the Related Art When sewage, human waste and the like are digested by anaerobic microorganisms, digestive gas containing methane, hydrogen sulfide, carbon dioxide and the like is generated. Prior to the effective use of methane as a fuel, digestive gas is contacted with an absorbing liquid in a gas-liquid contact tower to remove hydrogen sulfide and the like, and at this time, sulfide-dissolved waste water is generated. Dissolved sulfides are often contained in wastewater generated from petroleum refining processes and paper pulp processes. Dissolved sulfides generate hydrogen sulfide in the neutral region, causing not only bad odor, but high concentration may endanger human life. For this reason, it is necessary to remove the dissolved sulfides in the wastewater by appropriate treatment.
The conventional methods for removing dissolved sulfides in wastewater are roughly classified into oxidation by microorganisms and oxidation using chemicals. For example, JP-A-5-68849 discloses a method for detoxifying hydrogen sulfide in digestive gas generated by anaerobic digestion, in which the digestive gas is brought into gas-liquid contact with a treatment liquid to absorb hydrogen sulfide, A method has been proposed in which ox is oxidized by an aerobic microorganism. In addition, JP-A-8-168785
Japanese Patent Application Laid-Open No. 11-253971 proposes a method of treating wastewater containing hydrogen sulfide in the presence of a transition metal compound and hydrogen peroxide, and Japanese Patent Application Laid-Open No. 11-253971 comprises a carrier coated with an amorphous alloy on its surface. Sulfide oxidizing agents have been proposed. However, the method using microorganisms has a problem that a large-scale apparatus and a long time are required to oxidize sulfide. On the other hand, the method using a chemical has a problem that it is not easy to control the degree of oxidation, and the sulfate ion is oxidized beyond the simple substance of sulfur, and the treatment is required. For this reason, there has been a demand for a method of effectively and economically removing dissolved sulfides contained in wastewater.

[0003]

DISCLOSURE OF THE INVENTION According to the present invention, dissolved sulfide contained in wastewater can be efficiently removed as a simple substance of sulfur by oxidation, and a treated water with less suspended matter can be obtained. The purpose is to provide a method.

[0004]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventor has found that by adding an oxidizer at a pH of 6.45 or higher to wastewater containing dissolved sulfides,
It has been found that sulfide ions are oxidized to sulfur simple substance, and this sulfur simple substance can be easily removed by aggregation treatment or membrane treatment, and based on this finding, the present invention has been completed. That is, according to the present invention, (1) an oxidant is added to a wastewater containing a dissolved sulfide at a pH of 6.45 or higher to oxidize the dissolved sulfide into sulfur, and then the sulfur is removed by a coagulation treatment or a membrane treatment. The present invention provides a method for removing dissolved sulfides, and (2) a method for removing dissolved sulfides according to item 1, wherein the oxidizing agent is chlorite.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for removing dissolved sulfides of the present invention, an oxidizer is added to a wastewater containing dissolved sulfides at a pH of 6.45 or higher to oxidize the dissolved sulfides to form sulfur. Sulfur is removed by coagulation or membrane treatment. In the method of the present invention, chlorite can be preferably used as the oxidizing agent. As the wastewater containing dissolved sulfide to which the method of the present invention is applied, for example, wastewater generated when removing hydrogen sulfide contained in gas by gas-liquid contact treatment, oil refining process wastewater, paper pulp process wastewater, fish bone Examples include wastewater from treatment plants, wastewater from sewage treatment plants, and wastewater from waste treatment plants. The oxidizing agent used in the present invention is not particularly limited,
For example, chlorine, bromine, iodine, hypochlorite, chlorite, bromate, periodate and other halogen compounds, potassium permanganate, manganese dioxide and other manganese compounds, ferric chloride, sulfuric acid Examples thereof include iron compounds such as ferric iron, nitrogen compounds such as nitrous acid, nitric acid and nitrogen dioxide, oxygen compounds such as ozone, oxygen gas and hydrogen peroxide. Among these, sodium chlorite is commercially available as an aqueous solution, is relatively easy to handle, has a weak oxidizing power in the alkaline region, and is easy to stop the oxidation of sulfide ions at the stage of sulfur alone, and thus is particularly preferable. Can be used.

In the method of the present invention, when the pH of the wastewater containing dissolved sulfide is 6.45 or more, the oxidizing agent can be added as it is, but when the pH of the wastewater is less than 6.45, The pH is adjusted to 6.4 by adding alkali.
After adjusting to 5 or more, an oxidizing agent is added. The alkali used for adjusting the pH is not particularly limited, and examples thereof include sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, potassium carbonate and the like. Among these, sodium hydroxide can be particularly preferably used. When the pH of wastewater containing sulfide is 6.45 or more, when sodium chlorite, for example, is used as an oxidant, the sulfide ion is oxidized into sulfur as shown in the following formula. . 2S ^2- + NaClO ₂ + 2
When the pH of the waste water containing H ₂ O → 2S + NaCl + 4OH ^- sulfide is less than 6.45, the sulfide ion is represented by the following formula when, for example, sodium chlorite is used as the oxidant. Thus, it is oxidized to sulfite ion or sulfate ion. 2S ^2- + 3NaClO ₂ → 2SO ₃ ^2- + 3NaCl S ^2- + 2NaClO ₂ → SO ₄ ^2- + 2NaCl That is, when the pH is less than 6.45, the sulfide ion 1
The amount of sodium chlorite required for the molar oxidation treatment is 1.5
When the pH is 6.45 or more, the amount of sodium chlorite required for the oxidation treatment of 1 mol of sulfide ion is 0.5 mol, while the amount of sodium chlorite is 0.5 mol. Dissolved sulfides can be efficiently removed from sulfide-containing wastewater using a small amount of sodium chlorite. Further, in order to remove the sulfite ion or the sulfate ion from water, it is necessary to further remove as a water-insoluble compound such as a calcium salt. According to the method of the present invention, the sulfide ion is precipitated as a simple substance of sulfur. Therefore, it can be immediately removed by solid-liquid separation.

In the method of the present invention, the method of coagulating the precipitated sulfur is not particularly limited. For example, aluminum sulfate, polyaluminum chloride, ferric chloride, ferrous sulfate,
Inorganic flocculants such as polysulfate, polydimethyldiallylammonium chloride, alkylamine / epichlorohydrin adducts, polyethyleneimine, alkylenedichloride / polyalkylenepolyamine adducts, cationic polymer flocculants such as dicyandiamide / formalin condensate, polyacryl The flocculation treatment can be performed using sodium acid, a copolymer of sodium acrylate and acrylamide, an anionic polymer flocculant such as poly-2-acrylamido-2-methylpropanesulfonic acid, or the like.
These aggregating agents may be used alone or in combination of two or more.
The treatment liquid obtained by growing the precipitated sulfur flocs by coagulation treatment is a filtration device, centrifugal dehydrator, belt press dehydrator, screw press dehydrator, filter press dehydrator, vacuum dehydrator, sedimentation tank, pressurized flotation tank, etc. The solid-liquid separation can be performed by using to obtain clear treated water with less suspended substances. In the method of the present invention, there is no particular limitation on the membrane treatment method of the precipitated sulfur, for example, using a microfiltration membrane, ultrafiltration membrane, reverse osmosis membrane, etc., the precipitated sulfur is filtered off,
Clear treated water can be obtained. The form of the membrane used is not particularly limited, and examples thereof include a flat membrane module, a spiral module, a tubular module, and a hollow fiber module. The material of the film is not particularly limited,
Since the pH of the treatment liquid is high, it is preferable to select an alkali resistant material. Examples of the alkali resistant material include polytetrafluoroethylene, polyvinylidene fluoride, and polysulfone. According to the method for removing dissolved sulfides of the present invention, sulfides in wastewater are oxidized to sulfur simple substance and removed by coagulation treatment or membrane treatment, so that the amount of oxidizer used is small and efficient. It is possible to obtain treated water of good water quality with little contamination of turbid substances.

[0008]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Example 1 Using sodium sulfide nonahydrate, a sulfide ion concentration of 18
0 mg / L (pH 12.0) of synthetic wastewater was prepared. 500 mL of this synthetic waste water was placed in a beaker, and 500 mg of a 25 wt% sodium chlorite aqueous solution (pH 11.5) was added to a liquid whose pH was adjusted to 6.50 with sulfuric acid, followed by stirring for 10 seconds. The pH after treatment is 9.88 and the concentration of suspended matter is 19
0 mg / L, sulfide ion concentration was less than 1 mg / L.
To this treated water, 250 mg of polyaluminum chloride was added and stirred for 1 minute, then the pH was adjusted to 6.50 and further stirred for 1 minute. Next, 1 mg of a polymer flocculant [Clifloc PA, Kurita Water Industries Ltd.] was added and stirred for 2 minutes. The concentration of suspended substances in this supernatant was less than 10 mg / L. Also,
25-wt% sodium chlorite aqueous solution 100-400
The same operation as above was repeated after adding mg. However, when sulfide ions remained, the pH was lowered by adding a flocculant and hydrogen sulfide gas was generated. Therefore, the flocculation treatment was not performed. Comparative Example 1 Using the same synthetic wastewater as in Example 1,
The same operation was performed except that the pH was adjusted to 6.40. That is, 500 mL of this waste water was placed in a beaker, and 1,000 mg of a 25 wt% sodium chlorite aqueous solution (pH 11.5) was added to a solution whose pH was adjusted to 6.40 with sulfuric acid to obtain 10
Stir for 2 seconds. After the treatment, the pH was 2.57, the concentration of suspended substances was less than 10 mg / L, and the concentration of sulfide ions was 9 mg / L. Further, 100 to 900 mg of a 25 wt% sodium chlorite aqueous solution was added for oxidation treatment. The results of Example 1 and Comparative Example 1 are shown in Table 1.

[0009]

[Table 1]

As can be seen in Table 1, sulfide ion 1
The pH of synthetic wastewater (pH 12.0) containing 80 mg / L was 6.50.
In Example 1, in which the treatment was performed by adding the aqueous solution of sodium chlorite, the pH of the treatment liquid increased and the concentration of suspended solids increased as the amount of the aqueous sodium chlorite solution added increased. This is considered to indicate that the sulfide ions in the water are oxidized to form sulfur alone and are suspended in the water. When polyaluminum chloride and a polymer flocculant are added to a treatment liquid having a sulfide ion concentration of less than 1 mg / L for coagulation treatment and filtration is performed, the flocculated suspended matter is removed. As the amount of sodium chlorite aqueous solution added increases, the sulfide ion concentration decreases, and when the amount of 25 wt% sodium chlorite aqueous solution added is 1,000 mg / L, the sulfide ion concentration is 1 mg / L or less. Become. In contrast, the pH of the same wastewater
Was adjusted to 6.40 and treated with an aqueous solution of sodium chlorite, in Comparative Example 1, the pH was lowered as the amount of the aqueous solution of sodium chlorite was increased, and the suspended substance was a constant value of 10 mg / L. no change. This is considered to indicate that sulfide ions in water are oxidized to sulfite ions or sulfate ions. The decrease in the concentration of sulfide ions was smaller than that in Example 1, and even when 2,000 mg / L of 25 wt% sodium chlorite aqueous solution was added, 9 mg / L of sulfide ions still remained. Example 2 Desalter wastewater of a petroleum process plant having a sulfide sulfur concentration of 80 mg / L and a pH of 6.17 was treated. 500 mL of the waste water was taken in a beaker and the pH was adjusted to 6.50 by adding a sodium hydroxide aqueous solution, and then 300 mg of a 25 wt% sodium chlorite aqueous solution (pH 11.5) was added and stirred for 10 seconds. The pH of the treatment liquid was 8.72, the sulfide ion concentration was less than 1 mg / L, and the suspended substance concentration was 85 mg / L. The treatment liquid was filtered using a pleated cartridge filter equipped with a polytetrafluoroethylene microfiltration membrane. The concentration of suspended matter in the filtrate was 10 mg / L or less. The waste water (500 mL) was placed in a beaker, the pH was adjusted to 6.50 by adding sodium hydroxide aqueous solution, 100 mg of 25 wt% sodium chlorite aqueous solution (pH 11.5) was added, and the mixture was stirred for 10 seconds. The treatment solution had a pH of 7.01, a sulfide ion concentration of 50 mg / L, and a suspended substance concentration of 20 mg / L. This treatment liquid was filtered using the cartridge filter described above. The concentration of suspended matter in the filtrate was 10 mg / L or less. The same operation was repeated with the addition amount of the 25 wt% sodium chlorite aqueous solution being 200 mg. The pH of the treatment liquid is 8.55, the sulfide ion concentration is 15 mg / L, and the suspended substance concentration of the filtrate is 10 mg / L.
It was below. Comparative Example 2 Desalter wastewater 500 of the same oil process plant as in Example 2
The mL was placed in a beaker, 100 mg of a 25 wt% sodium chlorite aqueous solution was added, and the mixture was stirred for 10 seconds. The treatment liquid had a pH of 5.70, a sulfide ion concentration of 60 mg / L, and a suspended substance concentration of 10 mg / L or less. The amount of 25 wt% sodium chlorite aqueous solution added was 0 mg, 200
The same operation was repeated for mg, 300 mg, 400 mg, 500 mg and 1,000 mg. When the amount of the 25 wt% sodium chlorite aqueous solution added was 300 mg, the pH of the treatment liquid was 3.50, the sulfide ion concentration was 25 mg / L, and the suspended substance concentration was 10 mg / L or less. When the amount of 25 wt% sodium chlorite aqueous solution added is 1,000 mg, the p
H is 2.84, sulfide ion concentration is 1 mg / L or less,
The suspended substance concentration was 10 mg / L or less. The results of Example 2 and Comparative Example 2 are shown in Table 2.

[0011]

[Table 2]

As can be seen in Table 2, sulfide ions 8
In Example 2 in which the pH of the desalter wastewater of a petroleum process plant containing 0 mg / L was adjusted to 6.50 and the treatment was performed by adding a sodium chlorite aqueous solution, the treatment liquid increased as the amount of the sodium chlorite aqueous solution added increased. The higher the pH, the higher the suspended solids concentration. This is considered to indicate that the sulfide ions in the water are oxidized to form sulfur alone and are suspended in the water. When this treatment liquid is filtered using a microfiltration membrane, suspended substances are removed. As the amount of sodium chlorite aqueous solution added increases, the sulfide ion concentration decreases, and
Addition amount of 5 wt% sodium chlorite aqueous solution is 600 mg
When / L, the sulfide ion concentration is 1 mg / L or less.
On the other hand, the same desalter wastewater with a pH of 6.17,
Comparative Example 2 treated by adding an aqueous solution of sodium chlorite
Then, as the amount of sodium chlorite aqueous solution added increases
The pH drops and the suspended solids do not change below a certain value of 10 mg / L. This is considered to indicate that sulfide ions in water are oxidized to sulfite ions or sulfate ions. The decrease in the concentration of the sulfide ion was less than that in Example 2, and 25% by weight aqueous sodium chlorite solution was added to 1,
Add 000mg / L, and finally sulfide ion 1mg / L
Reach

[0013]

EFFECTS OF THE INVENTION According to the method for removing dissolved sulfides of the present invention, sulfides in waste water are oxidized to sulfur simple substance and removed by coagulation treatment or membrane treatment. Therefore, it is possible to obtain treated water of good water quality with little contamination of suspended substances.

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Claims (2)

[Claims] 1. A sewage containing dissolved sulfide is added with an oxidizing agent at a pH of 6.45 or higher to oxidize the dissolved sulfide to sulfur, and then sulfur is removed by coagulation treatment or membrane treatment. Method for removing dissolved sulfide. 2. The method for removing dissolved sulfide according to claim 1, wherein the oxidizing agent is chlorite.