JP2009148686A - Wastewater treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide hydrogen sulfide by treating wastewater containing organic matter. <P>SOLUTION: A water treatment facility has a treatment tank 10. Wastewater containing a large amount of organic matter is introduced into the treatment tank 10 from a first introducing pipe, and sea water containing sulfate ions is introduced thereto from a second introducing pipe 30. By keeping the environment in the treatment tank 10 at an environment with sulfuric acid reducing bacteria respiring sulfuric acid being a dominant species, the organic matter is decomposed, and hydrogen sulfide is generated. The generated hydrogen sulfide is desulfurized by a desulfurization apparatus 60, and recovered as hydrogen. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a water treatment technique, and more particularly to a technique for treating waste water containing organic matter.

Wastewater containing abundant organic matter, such as sewage, livestock wastewater, slaughterhouse wastewater, and food processing wastewater, cannot be discharged into an external system such as a river because of environmental considerations. In fact, these wastewaters are discharged into external systems after being treated by water treatment facilities under strict legal regulations.
The aeration tank plays a leading role in the treatment of wastewater by water treatment facilities. The aeration tank is maintained in an aerobic atmosphere, and an aerobic bacterium is a dominant species inside. The aerobic bacteria that became the dominant species decompose organic matter in the wastewater and change it to one that can discharge the wastewater to the outside system. In conventional water treatment facilities, the aeration tank is designed to play a leading role because when anaerobic atmosphere is used for wastewater treatment, anaerobic bacteria become dominant species. It is. Anaerobic bacteria often do not allow the wastewater treatment to proceed sufficiently, and may produce hydrogen sulfide that causes malodors.
For these reasons, it is now common knowledge when treating wastewater to avoid treating wastewater in an anaerobic atmosphere as much as possible and to treat wastewater in an aerobic atmosphere.

By the way, when waste water is treated in an anaerobic atmosphere in which anaerobic bacteria become dominant species, hydrogen sulfide may be generated as described above. Conventionally, hydrogen sulfide has been disliked because of its bad odor, and its generation should be suppressed as much as possible.
However, in the applicant's view, hydrogen sulfide may have value. Although it is possible to extract hydrogen from hydrogen sulfide by a simple process, this hydrogen has value as a material for fuel and fuel cells, for example.
The wastewater treatment is preferably performed at a low cost. On the other hand, the availability of valuable materials with wastewater treatment has the same meaning as reducing the cost of wastewater treatment.
Therefore, the applicant of the present application has come to the conclusion that it is meaningful if hydrogen sulfide can be taken out when treating the waste water.

However, although it is true that hydrogen sulfide may be generated when the environment is inclined to an anaerobic atmosphere when treating wastewater, hydrogen sulfide is not always generated.
At present, the generation of hydrogen sulfide has been disliked in the past, and there is no technology for allowing the generation of hydrogen sulfide and stably taking out the hydrogen sulfide.

  The present invention is intended to solve the above-described problems, and an object of the present invention is to provide wastewater treatment technology that can stably extract hydrogen sulfide when treating wastewater containing organic matter.

The present invention for solving the above-described problems is as follows.
The present invention introduces wastewater to be treated containing organic matter into a treatment tank, and makes the treatment tank into an environment in which sulfate-reducing bacteria that perform sulfuric acid respiration are dominant species. This is a wastewater treatment method that introduces treatment water containing ions and keeps the inside of the treatment tank in an anaerobic atmosphere to cause the sulfate-reducing bacteria to produce hydrogen sulfide from organic substances contained in the wastewater.
In the wastewater treatment method of the present invention, an aerobic bacterium is prevented from becoming a dominant species by keeping the inside of the treatment tank in an anaerobic atmosphere. In addition, in order to stably generate hydrogen sulfide as wastewater is treated, treatment water containing sulfate ions is introduced into the treatment tank. By doing so, the inside of the treatment tank becomes an environment in which sulfate-reducing bacteria that perform sulfuric acid respiration become the dominant species, and the sulfate-reducing bacteria respire using oxygen contained in sulfate ions (ie, bound oxygen). Thus, hydrogen sulfide is stably produced from organic matter.
That is, the wastewater treatment method of the present invention is intended to stably generate hydrogen sulfide in sulfate-reducing bacteria by supplying organic substances consumed by sulfate-reducing bacteria and sulfate ions into the treatment tank. is there.
Note that sulfate respiration is respiration performed by microorganisms using oxygen atoms contained in sulfate ions instead of molecular oxygen, and bacteria that perform such respiration are referred to as sulfate-reducing bacteria. In addition, the sulfate-reducing bacteria in the present invention can be actively put into the treatment tank by an administrator, but since sulfate-reducing bacteria are usually present in wastewater containing organic matter, If the environment in the treatment tank is maintained in an environment where bacteria are likely to inhabit, the sulfate-reducing bacteria contained in the wastewater will grow without the need to actively introduce sulfate-reducing bacteria, and the treatment tank will It becomes the dominant species.

In this invention, as above-mentioned, the inside of a processing tank is made into the environment where a sulfate reduction bacterium becomes a dominant species. Therefore, it is necessary to maintain an anaerobic atmosphere in the treatment tank. That is, if the inside of the treatment tank is in an aerobic atmosphere, aerobic bacteria that use molecular oxygen for respiration become the dominant species, and sulfate-reducing bacteria are reduced or the activity of sulfate-reducing bacteria is reduced. Because.
Since sulfate-reducing bacteria are obligate anaerobic bacteria whose number or activity is significantly reduced when molecular oxygen is present, reducing molecular oxygen in the treatment tank makes sulfate-reducing bacteria the dominant species. Therefore, in order to make the sulfate-reducing bacteria dominant species, it is better to keep the inside of the treatment tank in a reducing atmosphere. For example, in order to make sulfate-reducing bacteria a dominant species, the inside of the treatment tank is preferably maintained in a reducing atmosphere having an OPR (oxidation-reduction potential) of −100 mV or less. An environment maintained in a reducing atmosphere within this range is convenient for the presence of sulfate-reducing bacteria for the reasons described above. If ORP is set to an environment of −100 mV or less, sulfate-reducing bacteria are almost certainly the dominant species in the treatment tank, but if ORP is −200 mV or less, the sulfate-reducing bacteria are the dominant species in the treatment tank. And its activity can be expected to be higher.

As described above, the waste water contains organic matter. As long as it is satisfied, the drainage may be any, for example, sewage, livestock drainage, slaughterhouse drainage, food processing wastewater.
The waste water can have a BOD concentration of 500 mg / l or more. If the waste water containing organic matter is used at such a concentration, hydrogen sulfide can be generated more stably.

The treatment water contains sulfate ions as described above. As long as it is satisfied, the treatment water may be any, for example, seawater, gypsum drainage, paper mill wastewater, hot spring drainage (for example, sulfur spring hot spring drainage) can be used as the treatment water.
In particular, seawater contains a large amount of sulfate ions (seawater generally contains about 2700 mg / l of sulfate ions), is present inexhaustible and can be kept low in procurement costs. Therefore, it is convenient for use in the present invention. Other treatment waters listed above may be selected as appropriate when procurement is easy and procurement costs can be kept low.
The sulfate ion in the treatment tank is preferably supplied in such an amount that the sulfate ion does not become deficient in consideration of the consumption of bound oxygen in the sulfate ion when the sulfate-reducing bacteria decompose organic substances. For example, in the present invention, the weight ratio of the organic matter and sulfate ions in the treatment tank can be maintained such that the amount of the sulfate ions is 10% or more of the BOD amount of the waste water. Sulfate ion is sufficient if it is about 10% to 200% of the amount of BOD in the waste water.

Hydrogen (gas) can be easily taken out from hydrogen sulfide generated from the treatment tank. Currently, hydrogen is often produced by reacting coal and water vapor under high temperature conditions, but the energy required for this is enormous and the cost is considerable. In the present invention, hydrogen can be extracted from the hydrogen sulfide extracted from the wastewater to be treated using the power of sulfate-reducing bacteria, so the cost for obtaining hydrogen can be reduced.
That is, this invention is good also as what takes out hydrogen by desulfurizing with respect to the hydrogen sulfide produced from the said processing tank. In this case, the desulfurization may be performed as it is with respect to the hydrogen sulfide generated from the treatment tank, or may be performed after carrying the hydrogen sulfide to another facility.
When hydrogen is not taken out from hydrogen sulfide, for example, hydrogen sulfide generated from the treatment tank can be oxidized to obtain water and sulfate ions from the hydrogen sulfide. In this case, the sulfate ions extracted from the hydrogen sulfide may be mixed with the treatment water and returned to the treatment tank.

  Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings.

  In this embodiment, the waste water treatment method of the present invention is executed by the water treatment facility shown in FIG.

The water treatment facility includes a treatment tank 10.
The processing tank 10 is configured to be airtight, and can be maintained in an anaerobic atmosphere as will be described later.
The treatment tank 10 is connected to a first introduction pipe 20 for introducing waste water into the treatment tank 10 and a second introduction pipe 30 for introducing treatment water into the treatment tank 10.
Although not necessarily required, a concentrate introduction tube 22 having a concentration tank 21 upstream is connected to the first introduction tube 20 of this embodiment. The concentration tank 21 concentrates dilute wastewater having a low organic contamination ratio in the wastewater. Inside the concentration tank 21, for example, a lean wastewater introduced into the concentration tank 21 in a batch manner is left standing and precipitated by precipitation or aggregating material, so that a sludge-like concentrate 23 is generated. The produced concentrate 23 is sent to the first introduction pipe 20 through the concentrate introduction pipe 22, mixed in the waste water, and introduced into the treatment tank 10. By appropriately operating the concentration tank 22, it is possible to appropriately maintain the degree of organic matter contamination in the wastewater. Such a concentration tank 22 is useful when the amount of organic matter contained in the wastewater is small or when the amount of organic matter contained in the wastewater tends to fluctuate.
Although not necessarily required, in this embodiment, a deaeration tank 31 is provided in the second introduction pipe 30 for introducing treatment water. The deaeration tank 31 is useful for deaerating oxygen dissolved in the treatment water and keeping the inside of the treatment tank 10 anaerobic after introducing the treatment water. When the treatment water is seawater, oxygen is often melted in the treatment water. In such a case, it is better to provide the deaeration tank 31.

  A drain pipe 40 is also connected to the treatment tank 10. The drain pipe 40 is for discharging the waste water treated in the treatment tank 10 to the outside. The treated wastewater treated in the treatment tank 10 is discharged from here to an external system. It should be noted that a known mechanism for further processing the treated waste water before being discharged to the external system may be provided in the subsequent stage of the processing tank 10.

A gas discharge pipe 50 is also connected to the processing tank 10. The gas discharge pipe 50 is for drawing the gas generated in the processing tank 10 to the outside from the processing tank 10. The gas discharge pipe 50 is connected to the gas holder 80 through the first gas meter G1, the desulfurization device 60, the separation device 70, and the second gas meter G2 arranged from the upstream side.
The first gas meter G1 measures the amount of gas passing therethrough.
The desulfurization device 60 desulfurizes hydrogen sulfide contained in the gas generated in the treatment tank 10 to remove sulfur. Accordingly, when the hydrogen sulfide passes through the desulfurization device 60, it becomes hydrogen. As the desulfurization apparatus 60, any known apparatus can be used as long as it can remove sulfur from the hydrogen sulfide 60. For example, the hydrogen sulfide is heated while being in contact with iron to generate iron sulfide and hydrogen. It can be set as the apparatus which makes it. In this embodiment, the desulfurization apparatus 60 using such iron is employ | adopted.
The separation device 70 separates hydrogen generated by the desulfurization device 60 from other gases. In the treatment tank 10, carbon dioxide or water vapor is generated in addition to hydrogen sulfide. In the separation device 70, hydrogen is separated from gases other than hydrogen. As the separation device 70, any known device capable of performing such separation can be used. For example, hydrogen can be separated from other gases by utilizing the difference in gas density or by utilizing the difference in solubility in water.
The second gas meter G2 measures the amount of gas passing therethrough.
The gas holder 80 is for storing hydrogen. For example, the gas holder 80 compresses and stores hydrogen.
Of course, a valve for preventing a backflow of gas, a pump for drawing gas from the processing tank 10 to the gas holder 80, and the like can be appropriately provided between the processing tank 10 and the gas holder 80. .

Next, the water treatment method performed with the above water treatment equipment is demonstrated.
First, waste water from the first introduction pipe 20 and treatment water from the second introduction pipe 30 are introduced into the treatment tank 10, respectively. Both the timing of introduction of the waste water and the treatment water into the treatment tank 10 can be determined as appropriate, and both the batch type and the continuous type may be used.
In the waste water introduced from the first introduction pipe 20, the concentrate 23 from the concentration tank 21 is mixed through the concentrate introduction pipe 22. In this embodiment, the wastewater introduced into the treatment tank 10 from the first introduction pipe 20 is set to have a BOD concentration of 500 mg / l or more. The BOD value should just be 500 mg / l or more, for example, may be about several tens of thousands mg / l.
The water for treatment contains sulfate ions. In this embodiment, the processing water introduced from the second introduction pipe 30 is seawater. The processing water which is seawater is introduced into the processing tank 10 after oxygen is removed in the deaeration tank 31. The treatment water is not necessarily seawater, and may be, for example, gypsum drainage, paper mill drainage, and hot spring drainage. The amount of sulfate ions contained in the treatment water is adjusted so that the weight ratio of the organic matter and sulfate ions in the treatment tank 10 is in the range of about 1: 0.1-2.

In this way, waste water and water for treatment are introduced into the treatment tank 10 to keep the environment in the treatment tank 10 in an environment in which sulfate-reducing bacteria that perform sulfuric acid respiration are dominant species.
Specifically, first, the inside of the treatment tank 10 is maintained in an anaerobic atmosphere. Since the processing tank 10 is airtight, this is automatically realized unless a special operation such as aeration is performed in the processing tank 10.
Although not necessarily required, in this embodiment, the inside of the treatment tank 10 is maintained in a reducing atmosphere, and more specifically, the OPR is maintained at −100 mV or less. The OPR in the treatment tank 10 may be maintained in a reducing atmosphere of −200 mV or less. Since wastewater with a high concentration of organic substances usually contains a large amount of sulfate-reducing bacteria, the inside of the treatment tank 10 is normally maintained in a reducing atmosphere unless aeration is performed in the treatment tank 10. However, since the treatment water may contain oxygen, in order to keep the ORP in the treatment tank 10 within the above range, for example, while appropriately measuring the value of OPR in the treatment tank 10, the treatment tank Care is taken that the amount of processing water supplied to 10 is less than or equal to a predetermined amount. In addition, since the deaeration tank 31 mentioned above removes oxygen from the water for processing, it contributes to maintaining the inside of the processing tank 10 in a reducing atmosphere.
Moreover, although not necessarily required, in this embodiment, the temperature of the liquid in which the waste water in the treatment tank 10 and the treatment water are mixed is maintained at 20 ° C. or higher. This is because the activity of sulfate-reducing bacteria becomes active at a temperature of 20 ° C. or higher. However, when the temperature cannot be raised to about 20 ° C., it is sufficient if the residence time in the treatment tank 10 for waste water and treatment water is increased.
If the above conditions are maintained, the sulfate-reducing bacteria originally contained in the wastewater will become the dominant species in the treatment tank 10, and the organic matter in the wastewater will be consumed while consuming oxygen contained in sulfate ions. Decomposes to produce hydrogen sulfide. The reaction occurring at that time is represented by the following chemical formula.
C _X H _Y O _Z + SO ₄ ²⁻ → CO ₂ + H ₂ O + H ₂ S

  The waste water after the organic matter is decomposed by the reaction as described above is discharged from the drain pipe 40 to an external system.

The above reaction produces carbon dioxide, water, and hydrogen sulfide. Of these, water is basically absorbed into the wastewater.
Water vapor generated from carbon dioxide and hydrogen sulfide, and waste water and water for treatment flows out of the treatment tank 10 through the gas discharge pipe 50. These are measured by the first gas meter G1 and then go to the desulfurization apparatus 60. In addition, it is appropriate in the processing tank 10 by measuring the amount of gas passing through the first gas meter G1 with the first gas meter G1 (the amount may be the amount for each composition or not) over time. It is possible to monitor whether or not a reaction is occurring.
In the desulfurization apparatus 60, as described above, desulfurization is performed on hydrogen sulfide contained in the gas that has flowed out of the processing tank 10. Thereby, hydrogen sulfide turns into hydrogen. Further, in the desulfurization apparatus 60, the iron used as described above at the time of desulfurization combines with sulfur taken from hydrogen sulfide to become iron sulfide. Since this iron sulfide is naturally oxidized in the air and converted into iron sulfate, when this is dissolved in water, an aqueous solution containing sulfate ions is formed. Since this aqueous solution contains sulfate ions, it can be used as treatment water. In FIG. 1, the arrow shown by the broken line extended from the desulfurization apparatus 60 means that the sulfate ion made based on the iron sulfide produced in the desulfurization apparatus 60 can be returned to the water for treatment. It is.
The gas that has passed through the desulfurization device 60 is guided to the separation device 70. The gas guided to the separation device 70 includes carbon dioxide, water vapor, and hydrogen. Here, hydrogen is separated from other gases. Water vapor and carbon dioxide are discharged from the separation device 70 to an external system.
The hydrogen separated by the separation device 70 passes through the second gas meter G2 to the gas holder 80 and is stored there. In the second gas meter G2, the amount of hydrogen passing therethrough is measured over time. Even if the gas for each composition is not measured by the first gas meter G1, the amount of hydrogen measured by the second gas meter G2 and the amount of gas measured by the first gas meter G1 are subtracted. The appropriateness of the reaction occurring can be monitored.

≪Modification≫
The above-described water treatment facility has been focused on removing hydrogen from hydrogen sulfide generated from the treatment tank 10, but when the amount of hydrogen that can be removed is not so large, hydrogen is removed from hydrogen sulfide. If it is made to take out, the cost concerning the desulfurization apparatus 60, the separation apparatus 70, and the gas holder 80 required for that may exceed the profit obtained by taking out hydrogen.
In such a case, the hydrogen sulfide taken out from the treatment tank 10 is oxidized with oxygen in an aerobic atmosphere to generate water and sulfate ions (sulfates) from the hydrogen sulfide, and the sulfate ions are converted into the above-described implementation. As in the case of the embodiment, it may be returned to the treatment water again.

The figure which shows schematically the structure of the water treatment facility of this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Treatment tank 20 1st introduction pipe 30 2nd introduction pipe 40 Drain pipe 50 Gas discharge pipe 60 Desulfurization apparatus 70 Separation apparatus 80 Gas holder

Claims (7)

Introduce wastewater that contains organic matter into the treatment tank,
In order to make the inside of the treatment tank an environment in which sulfate-reducing bacteria that perform sulfuric acid respiration become a dominant species, water for treatment containing sulfate ions is introduced into the treatment tank, and the inside of the treatment tank is brought into an anaerobic atmosphere. By keeping
Causing the sulfate-reducing bacteria to produce hydrogen sulfide from the organic matter contained in the waste water,
Wastewater treatment method. In order to make the inside of the treatment tank an environment in which the sulfate-reducing bacteria are the dominant species, the inside of the treatment tank is maintained in a reducing atmosphere with an OPR of −100 mV or less.
The wastewater treatment method according to claim 1. The waste water has a BOD concentration of 500 mg / l or more.
The wastewater treatment method according to claim 1. Seawater is used as the treatment water,
The wastewater treatment method according to claim 1. Maintaining the weight ratio of the organic matter and sulfate ion in the treatment tank so that the amount of the sulfate ion is 10% or more of the amount of BOD of the waste water,
The wastewater treatment method according to claim 1. Hydrogen is removed by desulfurizing the hydrogen sulfide generated from the treatment tank,
The wastewater treatment method according to claim 1. Oxidizing hydrogen sulfide generated from the treatment tank to obtain water and sulfate ions from the hydrogen sulfide;
The wastewater treatment method according to claim 1.

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