JP2001079590A - Method and apparatus for treating sulfate-containing organic wastewater - Google Patents

Abstract

(57) [Abstract] [Problem] To treat anaerobic organisms with methane fermentation
An object of the present invention is to provide a method for treating sulfate-containing organic wastewater, which can prevent the production of hydrogen sulfide, which is an obstacle to methane fermentation. SOLUTION: An acid generation tank 2 for generating hydrogen sulfide in a sulfate-containing organic wastewater by a sulfuric acid reduction reaction treatment in a stage preceding a methane fermentation tank 8, and hydrogen sulfide generation inhibition in a sulfate-containing organic wastewater in which hydrogen sulfide is generated. A pH adjusting tank 5 for forming a sulfide by adding an agent and precipitating and removing the formed sulfide. Therefore, in the preceding stage of the methane fermentation tank 8, sulfate ions in the sulfate-containing organic wastewater are removed. The generated hydrogen sulfide can be precipitated and removed as sulfide. Therefore, the methane fermentation tank 8
Can produce no hydrogen sulfide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for treating sulfate-containing organic wastewater in which anaerobic biological treatment involving methane fermentation is performed on sulfate-containing organic wastewater. The present invention relates to a method and an apparatus for treating sulfate-containing organic wastewater, which can prevent the generation of hydrogen sulfide, which is an obstacle to methane fermentation, during biological treatment.

[0002]

2. Description of the Related Art Japanese Patent Application Laid-Open No. 10-249383 discloses a treatment method for reducing organic substances contained in sewage sludge of industrial wastewater and domestic wastewater to methane and carbon dioxide by the action of anaerobic bacteria. Known methane fermentation methods are known. This methane fermentation method has the advantage of requiring less effort and has the feature of being able to use the recovered gas, and is attracting attention from the viewpoint of energy reuse.

[0003] In this methane fermentation, various microorganisms decompose various organic substances in wastewater, and finally various organic substances in wastewater are decomposed into methane and carbon dioxide by methanogens.

In the wastewater, sulfate ions (SO ₄ ²⁻ ),
It contains sulfite ions (SO ₃ ²⁻ ), which are reduced in the process of anaerobic biological treatment to produce sulfides (sulfur compounds). Sulfides are also generated by the decomposition of sulfur-containing amino acids.

[0005] Sulfides have a greater inhibitory effect on methane-producing bacteria (acetic acid-decomposing bacteria) in the order of sulfate <thiosulfate <sulfite <sulfide. In the treatment of wastewaters such as molasses fermentation, tanning, petroleum refining, and paper pulp, this sulfide is the biggest obstacle.

As shown in the following equation, SO ₄ ²⁻ , SO ₃
^2- is reduced to sulfides, mainly hydrogen sulfide (H ₂ S) by sulfate reducing bacteria.

[0007]

Embedded image 4H ₂ + SO ₄ ^2- + H ⁺ → HS ⁻ + 4H ₂ O CH ₃ COO ⁻ + SO ₄ ²⁻ → HS ⁻ + 2HCO _3- Sulfate-reducing bacteria have the same substrate (H ₂ , H ₂
There are species that utilize Ac) and are more energetically more advantageous than methanogens. In addition, since it is more resistant to pH and temperature changes, it exhibits higher activity than methane-producing bacteria, produces sulfides, and reduces methane production. The concentration at which sulfide inhibition appears is about 100 to 300 mg / L as the solubilized sulfide concentration. In addition,
Since H ₂ S dissociates in water as in the following formula, its inhibitory action depends on pH.

[0008]

## STR2 ## _{^{H 2 S → HS - + H}} + HS → S 2- + H + H 2 S is difficult to dissociate in acidic side, to ^{S 2-} in pH8 following areas are generally keep anaerobic biological treatment Does not dissociate. The presence ratio as H ₂ S is 20% at pH 7.5.
, But increases to 50% at pH 7.0. Undissociated H ₂ S shows a strong inhibitory effect, and even at 50 mg / l, 4
There are examples showing 0% or more methane production disturbances. this is,
This is because uncharged molecules are more likely to pass through cell membranes by molecular diffusion. In addition, H for granules
Looking effect of _{2 S} at maximum methanogenic activity, although less toxic to 100 mg / l at neutral and alkaline,
The toxicity increases in the acidic region where the non-dissociation rate is large.

Although soluble sulfides show inhibition, iron (Fe) having a small solubility product and hydrogen sulfide (FeS) precipitated by heavy metal ions are detoxified. H
_As a method of removing 2S, a method of adding Fe and precipitating it as FeS can be considered. However, the method of adding Fe is expensive and has a problem that it is accumulated in the reaction system as FeS.

[0010]

As described above, hydrogen sulfide is produced by the sulfate-reducing bacteria present in the methane fermentation tank containing sulfate in wastewater, and the produced hydrogen sulfide is produced by methane production. Has a strong inhibitory effect on Also,
Hydrogen sulfide caused an offensive odor, and a desulfurization tank was required downstream of the methane fermentation tank.

In view of the above circumstances, the present invention provides a method for treating a sulfate-containing organic wastewater which can prevent the production of hydrogen sulfide, which is an obstacle to methane fermentation, during anaerobic biological treatment involving methane fermentation. It is intended to provide a device.

[0012]

In order to achieve the above object, the present invention provides a method for treating a sulfate-containing organic wastewater, which comprises treating an anaerobic biological treatment involving methane fermentation with a sulfate-containing organic wastewater. An anaerobic biological treatment process for organic wastewater;
A sulfide is formed by adding a hydrogen sulfide generation inhibitor to the sulfate-containing organic wastewater, which is provided before the anaerobic biological treatment step, and forms a sulfide by a sulfate reduction reaction during methane fermentation in the anaerobic biological treatment step. And a step of suppressing generation of hydrogen.

According to a second aspect of the present invention, the sulfate-containing organic wastewater is supplied to a wastewater treatment tank including a methane fermentation tank, and an anaerobic biological treatment involving methane fermentation is performed on the sulfate-containing organic wastewater in the wastewater treatment tank. In the treatment equipment for sulfate-containing organic wastewater to be performed, an acid generation tank that generates hydrogen sulfide in the sulfate-containing organic wastewater by the sulfuric acid reduction reaction treatment, and a hydrogen sulfide generation inhibitor is added to the sulfate-containing organic wastewater that generates hydrogen sulfide. It is characterized by being provided with a pH adjusting tank for adding and forming sulfides and removing the formed sulfides by precipitation.

According to a third aspect of the present invention, in the apparatus for treating a sulfate-containing organic wastewater according to the second aspect, the pH adjustment tank adds a hydrogen sulfide generation inhibitor to the sulfate-containing organic wastewater in which hydrogen sulfide has been generated. Tank that forms a sulfide by precipitation and removes the formed sulfide by precipitation, and a second tank that receives the supernatant liquid from the first tank and supplies it to the methane fermentation tank. It is characterized by.

According to a fourth aspect of the present invention, in the apparatus for treating a sulfate-containing organic wastewater according to any of the second or third aspects, the hydrogen sulfide generation inhibitor contains sludge containing heavy metals discharged from a sewage treatment plant. It is characterized by being dried to a rate of about 45%.

It is characterized in that the sludge contained is dried to a water content of about 45%.

According to the first aspect of the present invention, a first step is provided in the step of performing the anaerobic biological treatment, and in this first step, a sulfide is formed by adding a hydrogen sulfide generation inhibitor, and the sulfide is precipitated. Since it can be removed, it is possible to prevent hydrogen sulfide from being generated by the sulfate reduction reaction in the sulfate-containing organic wastewater in the step of performing the anaerobic biological treatment.

In addition, since hydrogen sulfide causes an offensive odor, a desulfurization tower conventionally required in the latter stage of the methane fermentation tank is not required, and the initial cost and the running cost of the desulfurizing agent are reduced to zero.

According to the second aspect of the present invention, hydrogen sulfide is produced from the sulfate-containing organic wastewater supplied to the acid producing tank along with the sulfuric acid reduction reaction. In other words, in the sulfuric acid reduction reaction, as in the methane fermentation tank, the sulfuric acid reducing bacteria exist in the acid production tank,
The sulfuric acid reduction reaction always proceeds, and hydrogen sulfide is generated. Next, in a pH adjusting tank, a hydrogen sulfide generation inhibitor is added to the sulfate-containing organic wastewater in which hydrogen sulfide has been generated to form an eluted sulfide, and the formed sulfide is precipitated and removed.

For this reason, hydrogen sulfide generated from sulfate ions in the sulfate-containing organic wastewater can be precipitated and removed as sulfide at a stage prior to the methane fermentation tank. Therefore, it is possible not to generate hydrogen sulfide in the methane fermentation tank.

According to the invention of claim 3, after the sulfide is precipitated and removed in the first tank of the pH adjusting tank, the supernatant liquid from the first tank is received in the second tank and supplied to the methane fermentation tank. Therefore, the accuracy of removing sulfate ions is improved,
The methane fermentation tank can be supplied with sulfate-containing organic wastewater in which sulfate ions have been eliminated as much as possible.

According to the fourth aspect of the present invention, excess sludge generated in a sewage treatment plant, which has been mainly used as a fertilizer in the past, is dried to a water content of about 45% (hereinafter referred to as dry sludge). Since it is reused for ion removal, it is suitable for the current situation where excess supply and incineration are more than demand, and it is possible to contribute to reduction of incineration cost.

Here, the hydrogen sulfide generation inhibitor is generally a heavy metal such as copper, zinc, or lead used in a precipitation reaction.
This heavy metal is ionized by elution, and can contribute to the formation of sulfide. As the hydrogen sulfide generation inhibitor, for example, since excess sludge generated in a sewage treatment plant contains heavy metals, dried excess sludge can be used.

[0024]

FIG. 1 is a configuration diagram showing an embodiment of a methane fermentation apparatus to which the present invention is applied.

In the figure, the methane fermentation apparatus 1 includes an acid generating tank 2, a pH adjusting tank 5 connected to the acid generating tank 2 via a pipe 3 and a pump 4, a pH adjusting tank 5 and a pipe 6 And a methane fermentation tank 8 connected via a pump 7 and a treated water tank 10 connected to the methane fermentation tank 8 via a pipe 9.

In the acid generating tank 2, hydrogen sulfide is generated from the supplied sulfate-containing organic wastewater by a sulfuric acid reduction reaction. In other words, in the sulfuric acid reduction reaction, as in the methane fermentation tank 8 described later, a sulfuric acid reducing bacterium exists in the acid production tank 2, so that the sulfuric acid reduction reaction always proceeds to generate hydrogen sulfide.

The pH adjusting tank 5 includes a first tank 5a and a second tank 5b.
And divided into two tanks. In a first tank 5a of the pH adjusting tank 5, a dry sludge hopper 12 for supplying dry sludge as a hydrogen sulfide inhibitor via a pump 11 and a NaOH tank 1 for supplying NaOH via a NaOH injection pump 13
4 and a stirrer 16 that stirs wastewater in the tank by a motor 15.

Then, in the first tank 5a of the pH adjusting tank 5,
Dry sludge is added as a hydrogen sulfide generation inhibitor used for a precipitation reaction from a dry sludge hopper 12 to a sulfuric acid group-containing organic wastewater containing hydrogen sulfide supplied from an acid generation tank 2 by a pump 3 via a pump 11. At the same time, the wastewater to which the dried sludge has been added is stirred by a stirrer 16 driven by a motor 15.

Here, the dried sludge is obtained by drying the sludge discharged from the sewage treatment plant. The dried sludge of the T municipal sewage treatment plant used this time is shown in Table 1 below. Thus, it was dried to a water content of about 45%. Further, the hydrogen sulfide generation inhibitor is generally a heavy metal such as copper, zinc, or lead used in a precipitation reaction, and is ionized by elution of the heavy metal and can contribute to the formation of sulfide. As the hydrogen sulfide generation inhibitor, for example, it is possible to use a dried excess sludge by paying attention to the fact that excess sludge generated in a sewage treatment plant contains heavy metals.

[0030]

[Table 1] In the first tank 5a of the pH adjusting tank 5, in the process of mixing hydrogen sulfide and dry sludge by stirring by the stirrer 16,
When the NaOH stored in the NaOH tank 14 is injected by the NaOH injection pump 13 to adjust the pH to a weak alkali optimal for methane fermentation, the dried sludge is dissolved into the sulfate-containing organic wastewater with the dissolution of the dried sludge. Heavy ions such as copper ions (Cu ²⁺ ), zinc ions (Zn ²⁺ ), and lead ions (Pb ²⁺ ) included in the components are mixed.

As a result, the heavy metal ions react with sulfur (S) in the wastewater to form sulfides, and the formed sulfides precipitate. Further, the supernatant liquid generated by precipitation of the sulfide becomes sulfate-containing organic wastewater from which hydrogen sulfide has been removed.

[0032] ^{Incidentally,} Cu 2+, although ^{Pb 2+} is waste water results in precipitation of sulfides in acid, ^{Zn 2 +} results in precipitation of sulfides when slightly alkaline. Therefore, it is effective to adjust the pH to a weak alkali optimal for methane fermentation in the first tank 5a of the pH adjusting tank 5 for mixing the dry sludge.

The precipitated sulfide is drawn together with the sludge by the sludge drawing pump 17 and discharged to the outside of, for example, a dehydrator. On the other hand, the supernatant from which hydrogen sulfide has been removed is
It is discharged to the second tank 5b of the pH adjusting tank 5 by overflow.

Thus, the supernatant of the first tank 5a of the pH adjusting tank 5 flows into the second tank 5b, and after the pH is adjusted again, is supplied to the methane fermentation tank 8 by the liquid supply pump 7.

As described above, the sulfate-containing organic wastewater containing hydrogen sulfide is removed from the first tank 5a in the second tank 5b after the sulfide is precipitated and removed in the first tank 5a of the pH adjusting tank 5. Is supplied to the methane fermentation tank 8 after receiving the supernatant liquid, so that the accuracy of removing sulfate ions is improved.
The methane fermentation tank 8 can be supplied with sulfate-containing organic wastewater from which sulfate ions have been eliminated as much as possible.

The methane fermentation tank 8 includes a gas holder 18 for storing gas generated by methane fermentation, and a hot water boiler 19 for circulating and supplying heated hot water to the methane fermentation tank 8 using the gas stored in the gas holder 18 as fuel. Is provided.

The methane fermentation tank 8 is subjected to a treatment for decomposing wastewater containing no hydrogen sulfide by various bacteria required for methane fermentation.
Is overflowed. Also, the gas generated by methane fermentation to obtain this treated water does not contain hydrogen sulfide,
It is sent as it is to the gas holder 18 and can be reused as fuel for the hot water boiler 19.

In addition, excess sludge generated in a sewage treatment plant, which has been mainly used as a fertilizer in the past, has a water content of 45%.
Since the dried sludge that has been dried to a certain extent is reused for removing sulfate ions, it is suitable for the current situation in which excess incineration and excess incineration are required more than demand, and can contribute to reduction of incineration disposal costs.

In addition, since hydrogen sulfide causes an offensive odor, a desulfurization tower conventionally required in the latter stage of the methane fermentation tank becomes unnecessary, and the initial cost and the running cost of the desulfurizing agent are eliminated.

[0040]

As described above, according to the present invention, hydrogen sulfide generated from sulfate ions in wastewater is precipitated and removed as sulfide at the preceding stage of the methane fermentation tank. Generation can be prevented.

[0041] Fertilizers are mainly used for the reuse of dried sludge, but can be reused for removing sulfate ions.

Further, since hydrogen sulfide causes an offensive odor, a desulfurization tower conventionally required in the latter stage of the methane fermentation tank is not required, so that the initial cost is greatly reduced and the running cost of the desulfurizing agent is eliminated. It becomes possible.

[Brief description of the drawings]

FIG. 1 is a schematic process diagram of an embodiment of a methane fermentation apparatus to which a method for treating a sulfate-containing organic wastewater according to the present invention is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Methane fermentation apparatus 2 Acid production tank 3, 6, 9 Piping 4 Pump 5 pH adjustment tank 5a First tank of pH adjustment tank 5b Second tank of pH adjustment tank 7 Feeding pump 8 Methane fermentation tank 10 Treated water tank 11 Pump 12 Dry Sludge Hopper 13 NaOH Injection Pump 14 NaOH Tank 15 Motor 16 Stirrer 17 Sludge Extraction Pump 18 Gas Holder 19 Hot Water Boiler

Claims (4)

[Claims] 1. An anaerobic biological treatment step for performing anaerobic biological treatment involving methane fermentation on a sulfate-containing organic wastewater, and provided in a preceding stage of the anaerobic biological treatment step; Adding a hydrogen production inhibitor to form a sulfide, and suppressing the production of hydrogen sulfide by a sulfuric acid reduction reaction during methane fermentation in the anaerobic biological treatment step. Organic wastewater treatment method. 2. Sulfate-containing organic wastewater is supplied to a wastewater treatment tank including a methane fermentation tank, and anaerobic biological treatment involving methane fermentation is performed on the sulfate-containing organic wastewater in the wastewater treatment tank. An acid generation tank that generates hydrogen sulfide in sulfate-containing organic wastewater by a sulfuric acid reduction reaction treatment, and a hydrogen sulfide generation inhibitor is added to the sulfate-containing organic wastewater that generates hydrogen sulfide. An apparatus for treating sulfate-containing organic wastewater, comprising: a pH adjusting tank for forming sulfides and removing precipitates formed by the sulfides. 3. The apparatus for treating a sulfate-containing organic wastewater according to claim 2, wherein the pH adjusting tank is configured to add a hydrogen sulfide generation inhibitor to the sulfate-containing organic wastewater in which hydrogen sulfide has been generated, and to form a sulfide. And a second tank for receiving the supernatant from the first tank and supplying the supernatant to the methane fermentation tank. Sulfur-containing organic wastewater treatment equipment. 4. The apparatus for treating a sulfate-containing organic wastewater according to claim 2, wherein the hydrogen sulfide generation inhibitor contains sludge containing heavy metals discharged from a sewage treatment plant at a water content of 45%. An apparatus for treating sulfate-containing organic wastewater, which is dried to a degree.