JP4558681B2 - Waste water treatment apparatus and waste water treatment method - Google Patents

Description

  The present invention relates to a wastewater treatment apparatus and a wastewater treatment method.

  Conventionally, organic waste such as garbage is treated by methane fermentation, and the generated digested sludge is dehydrated by a dehydrator and supplied to a sludge treatment device. Supplied.

The treated water supplied to the wastewater treatment device is subjected to biological denitrification treatment, and after sludge is separated, it is discharged out of the system as treated water. As a method for separating sludge, for example, as in Patent Document 1, agglomeration separation in which sludge is agglomerated and separated by adding an inorganic aggregating agent such as aluminum or iron is used.
Japanese Patent Laid-Open No. 11-277096

  However, the treated water that has been subjected to activated sludge treatment such as biological denitrification treatment contains a large amount of carbon dioxide gas, and even if an inorganic flocculant is added for coagulation separation, it will be consumed for decarboxylation. Therefore, a larger amount of inorganic flocculant than the theoretical value must be added. Excessive addition of this inorganic flocculant leads to an increase in the amount of aggregated sludge generated.

  This invention is made | formed in view of the said subject, and it aims at providing the waste water treatment apparatus and waste water treatment method which can fully reduce the addition amount of the inorganic flocculant for agglomeration separation.

  As a result of intensive studies to achieve the above object, the present inventors have found that the above problem can be solved by bringing the hydrogen sulfide-containing gas into contact with the wastewater prior to the addition of the inorganic flocculant to the wastewater. The present invention has been completed.

  That is, the wastewater treatment apparatus of the present invention is a wastewater treatment apparatus that agglomerates and separates wastewater, and includes a gas contact means for bringing a hydrogen sulfide-containing gas into contact with wastewater, and an inorganic flocculant added to the wastewater from the gas contact means. It comprises a flocculant addition means and a solid-liquid separation means for solid-liquid separation of the agglomerated sludge generated in the waste water by the addition of the inorganic flocculant.

  The waste water before the inorganic flocculant is added and the hydrogen sulfide-containing gas are brought into contact with each other by the gas contact means provided in the waste water treatment apparatus of the present invention. When the waste water and the hydrogen sulfide-containing gas come into contact with each other, the hydrogen sulfide is absorbed into the waste water and the sulfur oxidation reaction proceeds. By this sulfur oxidation reaction, the wastewater moves to the acidic side, and decarboxylation of the wastewater is promoted. For this reason, if an inorganic flocculant is added to the wastewater that has been contacted with the hydrogen sulfide-containing gas, consumption of the inorganic flocculant during decarboxylation can be suppressed. Efficient coagulation sludge can be formed. Therefore, the amount of the inorganic flocculant added to the waste water can be sufficiently reduced, and as a result, the increase in the amount of the generated sludge is sufficiently suppressed.

  In the present invention, it is preferable to further include hydrogen ion concentration adjusting means for adjusting the hydrogen ion concentration of the wastewater to which the inorganic flocculant is added. By adjusting the hydrogen ion concentration (pH) of the wastewater in which the inorganic flocculant is dissolved, floating substances and colloidal substances contained in the wastewater can be more efficiently aggregated.

  In the present invention, the hydrogen sulfide-containing gas supplied to the gas contact means is preferably a biogas generated by subjecting organic matter to methane fermentation. Biogas obtained by subjecting organic matter to methane fermentation contains hydrogen sulfide of several hundred to several thousand volume ppm, and is suitable as a hydrogen sulfide-containing gas supplied to the gas contact means. Moreover, it is preferable that the waste_water | drain supplied to a gas contact means is obtained through the activated sludge process of the digested sludge generated by methane fermentation.

  In the present invention, in the gas contact means, the biogas generated by methane fermentation and the digested sludge generated by the methane fermentation are obtained through dehydration treatment and the activated sludge treatment of the dehydrated separation liquid separated by the dehydration treatment. It is preferable to contact the waste water. Thereby, for example, in treating waste water generated from a waste treatment apparatus that performs methane fermentation treatment of organic matter, it is possible to sufficiently effectively use biogas.

  The wastewater treatment method of the present invention is a wastewater treatment method for aggregating and separating wastewater, a gas contact step for bringing hydrogen sulfide-containing gas into contact with the wastewater, and an inorganic flocculant for adding an inorganic flocculant to the wastewater from the gas contact step An addition step; and a solid-liquid separation step for solid-liquid separation of the aggregated sludge generated in the waste water after the inorganic flocculant addition step.

  According to the waste water treatment method of the present invention, the waste water and the hydrogen sulfide-containing gas can be brought into contact with each other by performing a gas contact step. When the waste water and the hydrogen sulfide-containing gas come into contact with each other, the hydrogen sulfide is absorbed into the waste water and the sulfur oxidation reaction proceeds. This sulfur oxidation reaction promotes decarboxylation of the wastewater because the wastewater moves to the acidic side. For this reason, the quantity of the inorganic flocculant added to waste water can fully be reduced, and the increase in the generation amount of agglomerated sludge is fully suppressed by extension.

  ADVANTAGE OF THE INVENTION According to this invention, the waste water treatment apparatus and waste water treatment method which can fully reduce the addition amount of the inorganic flocculant for agglomeration separation are provided.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram of a waste treatment facility including a preferred embodiment of a waste water treatment apparatus according to the present invention. The waste treatment facility shown in FIG. 1 includes a waste treatment device 10 and a waste water treatment device 20.

  The waste treatment apparatus 10 includes a methane fermentation tank 1 for treating methane fermentation of organic waste such as garbage, a digested sludge storage tank 2 for storing digested sludge generated by methane fermentation, and dewatered sludge by dewatering the digested sludge. And a dehydrator 3 for separating into a dehydrated separation liquid (drainage).

  The waste water treatment apparatus 20 includes a dehydration / separation liquid storage tank 11 that stores the dehydration / separation liquid from the waste treatment apparatus 10, and a denitrification tank 12 and a nitrification tank that perform denitrification treatment and nitrification treatment (activated sludge treatment), respectively. 13, a precipitation tank 14 for solid-liquid separation of the activated sludge mixed liquid after nitrification denitrification treatment, and a gas for bringing the biogas (hydrogen sulfide-containing gas) from the methane fermentation tank 1 into contact with the precipitation separation liquid from the precipitation tank 14 A contact tank (gas contact means) 15 and a mixing and aggregating device 16 for mixing the gas contact liquid from the gas contact tank 15 with an inorganic flocculant and aggregating and removing floating substances and colloidal substances are provided. In addition, about the structure of the gas contact tank 15 and the mixing aggregation apparatus 16, the outline is shown in FIG.

  The methane fermentation tank 1 is for decomposing organic waste into methane gas, carbon dioxide gas, or the like by anaerobic microorganisms. As the methane fermenter 1, any methane fermenter can be applied, and the type thereof may be either a vertical type or a horizontal type, and may be either a continuous type or a batch type. Moreover, you may employ | adopt either a dry type or a wet type according to process conditions.

  A line L1 for introducing organic waste is connected to the methane fermentation tank 1. The methane fermentation tank 1 is connected to a line L2 for transferring digested sludge generated by methane fermentation to the digested sludge storage tank 2 and a line L10 for transferring biogas to the gas contact tank 15.

  The digested sludge storage tank 2 is a tank for temporarily storing the digested sludge before being transferred to the dehydrator 3. A line L3 for introducing the digested sludge into the dehydrator 3 is connected to the digested sludge storage tank 2. The line L3 has a configuration in which a dehydrating aid such as a flocculant can be added to the digested sludge.

  The dehydrator 3 is a device for dehydrating the digested sludge to separate it into a dehydrated separation liquid and a dehydrated sludge. Any dehydrator can be used as the dehydrator 3, for example, a screw press dehydrator, a centrifugal dehydrator, a multi-disc dehydrator, a belt press dehydrator, a filter press dehydrator, a rotary press dehydrator, or the like. It is done. These dehydrators may be used alone or in combination of two or more. The dehydrator 3 is connected to a line L4 for transferring the dehydrated separated liquid to the dehydrated separated liquid storage tank 11 and a line L11 for transferring the dehydrated sludge to the sludge treatment facility.

  The dehydrated separation liquid storage tank 11 is a tank for temporarily storing the dehydrated separation liquid before being transferred to the denitrification tank 12. The dehydrated separation liquid storage tank 11 is connected to a line L5 for introducing the dehydrated separation liquid into the denitrification tank 12.

  The denitrification tank 12 is a tank for reducing and removing nitrate or nitrite in the dehydrated separation liquid to nitrogen gas in the absence of dissolved oxygen. The nitrification tank 13 is a tank for oxidizing ammonia nitrogen to nitrite or nitrate in an aerobic state. In these tanks, the dehydrated separation liquid and activated sludge are mixed (activated sludge mixed liquid). Although not shown, the nitrification tank 13 is provided with an aeration device for aeration of air or oxygen. The nitrification tank 13 is connected to a line L12 for returning a part of the activated sludge mixed liquid in the tank to the denitrification tank 12, and a line L6 for transferring the activated sludge mixed liquid after the denitrification treatment to the precipitation tank 14.

  The sedimentation tank 14 is a tank for precipitating and removing suspended solids contained in the activated sludge mixed liquid after the denitrification treatment. Although not shown, the sedimentation tank 14 is provided with a sludge scraping machine for scraping the sludge deposited on the bottom. The sedimentation tank 14 is connected to a line L13 for extracting the sewed sludge, and the extracted sludge can be returned to the denitrification tank 12 through the line L13a or to the methane fermentation tank 1 through the line L13b. It has become. The precipitation tank 14 is connected to a line L7 for transferring the precipitate separation liquid from which suspended substances have been removed to the gas contact tank 15. In addition, if it can isolate | separate the suspended | floating substance contained in an activated sludge liquid mixture, it will not specifically limit to a sedimentation tank, You may use a pressurized flotation tank, a membrane separation apparatus, etc.

  The gas contact tank 15 is a tank for bringing the biogas introduced through the line L10 into contact with the precipitate separation liquid from the settling tank 14. Connected to the gas contact tank 15 are a line L8 for transferring the precipitate separation liquid after contact with biogas (hereinafter referred to as “gas contact liquid”) to the mixing and aggregating apparatus 16, and a line L14 for transferring biogas after the contact treatment. ing.

  As shown in FIG. 2, the gas contact tank 15 includes a device 15a for blowing biogas into the liquid. Moreover, it is preferable that the gas phase part in the gas contact tank 15 containing the biogas is blocked from the outside from the viewpoint of preventing the biogas from leaking. In order to block the gas phase portion from the outside, it is only necessary to block between the precipitation tank 14 and the gas contact tank 15 and between the gas contact tank 15 and the mixing and aggregating device 16 by water sealing. For example, a U-shaped portion may be provided in the line L7 and the line L8, and the water-sealed structure may be formed by retaining the dehydrated separation liquid therein.

The water depth of the gas contact tank 15 is preferably shallow, and the effective water depth is preferably about 1 m. Since the amount of carbon dioxide dissolved in water is proportional to the water depth, carbon dioxide contained in biogas may be dissolved in addition to the tendency for decarbonation to be difficult when the water depth of the gas contact tank 15 is deep. . Moreover, when the water depth of the gas contact tank 15 is deep, in order to blow biogas from the bottom part of the gas contact tank 15, it is necessary to raise the pressure of biogas, and the inside of the methane fermentation tank 1 will also be pressurized. The capacity of the gas contact tank 15 is preferably designed so that the space velocity of the biogas is 200 h ⁻¹ or less.

  The mixing and aggregating device 16 is a device for aggregating suspended substances and colloidal substances contained in the gas contact liquid from the gas contact tank 15 and removing them to a high degree. The mixing and aggregating apparatus 16 includes a mixing tank (mixing means) 17 for adding and dissolving an inorganic flocculant and a pH adjuster to the gas contact liquid, and a coagulating tank (solid-liquid separation means) 18 for separating the agglomerated sludge. I have. A coagulation tank 18 is disposed at the subsequent stage of the mixing tank 17 and these are connected by a line L16.

  The mixing tank 17 includes an inorganic flocculant supplier (inorganic flocculant adding means) W1 for adding an inorganic flocculant to the gas contact liquid, a pH adjuster supplier W2 for adding a pH adjuster, and a gas in the mixing tank 17. A pH measuring device X1 for measuring the pH of the contact liquid is provided. Based on the measured value of the pH measuring device X1, the supply amount of the pH adjusting agent supply device W2 can be controlled. The pH adjuster supply device W2 and the pH measuring device X1 constitute a hydrogen ion concentration adjusting means. The mixing tank 17 includes a stirrer 17a and is configured to mix and stir the gas contact liquid, the inorganic flocculant, and the pH adjuster.

  The inorganic flocculant supply device W1 may have a suitable configuration depending on whether the inorganic flocculant to be supplied is powder or liquid. When the inorganic flocculant is a powder, a quantitative feeder and a weight meter can be used, and when the inorganic flocculant is a liquid, a level meter, a weight meter and a flow meter can be used. Moreover, a level meter, a weight meter, a flow meter, etc. can be used as pH adjuster supply device W2.

  The coagulation tank 18 includes a scraper 18a for scraping the coagulated sludge precipitated on the bottom. The agglomeration tank 18 is connected to a line L9 for discharging the agglomerated treated water and a line L15 for extracting the agglomerated sludge, and the extracted agglomerated sludge is passed through the line L15 to the methane fermentation tank. 1 can be returned.

  A means for adding a polymer flocculant may be further provided between the mixing tank 17 and the coagulation tank 18. In addition, a tank for adding and mixing an inorganic flocculant and a tank for adding and mixing a pH adjuster may be separately provided for the gas contact liquid. Moreover, you may arrange | position the processing apparatus for performing processing, such as sand filtration, activated carbon adsorption | suction, and disinfection, to the treated water discharged | emitted from the line L9 in the back | latter stage of the aggregation tank 18. FIG.

  The biogas discharged from the gas contact tank 15 may still contain some hydrogen sulfide. Therefore, it is preferable to install a desulfurization device in the subsequent stage of the gas contact tank 15. Examples of the desulfurization apparatus include a dry desulfurization apparatus using iron oxide, a wet desulfurization apparatus using water or an alkaline solution, and a biological desulfurization apparatus using a living organism.

  Next, the operation of this embodiment, that is, the waste water treatment method according to the present invention will be specifically described.

In the methane fermentation tank 1, the organic component of the organic waste is decomposed into methane gas, carbon dioxide gas, etc. by the anaerobic microorganisms in the tank. At this time, the sulfur content contained in the organic waste is decomposed into hydrogen sulfide or solid sulfur content by the following sulfuric acid reduction reaction.
SO ₄ ²⁻ + 4H ₂ → S ²⁻ + 4H ₂ O
SO ₄ ²⁻ + 3H ₂ → S ⁰ + 2H ₂ O + 2OH ⁻

  The digested sludge after the methane fermentation treatment is sent to the digested sludge storage tank 2 through the line L2. On the other hand, the biogas generated in the methane fermentation tank 1 is introduced into the gas contact tank 15 through the line L10.

  In the methane fermentation tank 1, a biogas containing hydrogen sulfide (hydrogen sulfide-containing gas) is generated by methane fermentation of organic waste. Biogas contains several hundred to several thousand ppm of hydrogen sulfide, and the main components are methane (50 to 65% by volume) and carbon dioxide (35 to 50% by volume).

  The digested sludge once stored in the digested sludge storage tank 2 is transferred to the dehydrator 3 after addition of a dehydrating aid such as a flocculant in the line L3. The digested sludge is separated into a dehydrated separation liquid and a dehydrated sludge by a dehydration process by the dehydrator 3. The dehydrated separation liquid separated by the dehydration process is transferred to the dehydrated separation liquid storage tank 11 via the line L4. On the other hand, the dewatered sludge separated from the digested sludge is transferred to the sludge treatment facility via the line L11. Processing such as composting, carbonization or incineration of dewatered sludge is performed in the sludge treatment facility.

The dehydrated separation liquid once stored in the dehydrated separation liquid storage tank 11 is transferred to the denitrification tank 12 through the line L5. In the denitrification tank 12, nitrate nitrogen (nitrite ions, nitrate ions) is reduced to nitrogen gas by denitrifying bacteria in the absence of dissolved oxygen. On the other hand, in the nitrification tank 13, ammoniacal nitrogen is oxidized to nitrite or nitrate in an aerobic state. These reactions are as follows.
(Nitrite-type denitrification)
NH ₄ ⁺ + 3 / 2O ₂ → NO ₂ ⁻ + 2H ⁺ + H ₂ O
2NO ₂ ⁻ + 3H ₂ → N ₂ + 2OH ⁻ + 2H ₂ O
(Nitrate-type denitrification)
NH ₄ ⁺ + 2O ₂ → NO ₃ ⁻ + 2H ⁺ + H ₂ O
2NO ₃ ⁻ + 5H ₂ → N ₂ + 2OH ⁻ + 4H ₂ O

In either case the nitrite type denitrification and nitrate type denitrification as described above also, NH 4 ₊ ¹ when the molar the nitrifying 2 moles H ⁺ is generated in, NO ₂ ^- or NO 3 _- ¹ mol of the denitrification 1 mol of OH ⁻ is produced. Therefore, if the biological denitrification is performed satisfactorily, NO ₂ ^- or NO 3 _- ^per mole of denitrification, the process proceeds to H + ¹ mole fraction acidic side.

  The activated sludge mixed liquid in the nitrification tank 13 is returned to the denitrification tank 12 through the line L12 and is circulated between the denitrification tank 12 and the nitrification tank 13, thereby allowing nitrate nitrogen and ammoniacal contained in the dehydration separation liquid to be circulated. Both nitrogens are eventually decomposed and removed to nitrogen gas. The activated sludge mixed liquid from which the nitrogen content has been sufficiently removed by repeating the circulation is transferred to the settling tank 14 through the line L6.

  In the sedimentation tank 14, suspended substances and the like contained in the activated sludge mixed solution are settled and concentrated. The sediment at the bottom of the sedimentation tank 14 is returned to the denitrification tank 12 through the lines L13 and L13a, or returned to the methane fermentation tank 1 through the lines L13 and L13b. On the other hand, the precipitate separation liquid from which the precipitate is removed is transferred to the gas contact tank 15 through the line L7.

  In the gas contact tank 15, by bringing the biogas and the precipitate separation liquid into contact with each other, hydrogen sulfide contained in the biogas is absorbed by the precipitation separation liquid (gas contact step). When hydrogen sulfide is absorbed into the precipitate separation liquid, the precipitation separation liquid moves to the acidic side by the sulfur oxidation reaction, and therefore decarboxylation is performed. In the biological denitrification treatment of the dehydrated separation liquid, carbon dioxide gas may be dissolved in the dehydrated separation liquid. According to the gas contact process in the gas contact tank 15, even a precipitate separation liquid that has undergone biological denitrification treatment can be effectively decarboxylated, so that the inorganic agglomeration used when producing agglomerated sludge is produced. The amount of the agent can be sufficiently suppressed.

  The biogas in contact with the precipitate separation liquid has a reduced hydrogen sulfide content. The biogas with reduced hydrogen sulfide is sent to the desulfurization facility through the line L14. The biogas introduced into the desulfurization facility has a reduced hydrogen sulfide concentration compared to the time when it was discharged from the methane fermentation tank 1, so that the equipment in the desulfurization facility is compared to the case where this biogas is directly introduced. Can be reduced in size, and even when chemicals are used, the amount used can be reduced. For this reason, there is an advantage that the running cost required for the desulfurization process is reduced.

  It is also possible to increase the methane concentration of the biogas after desulfurization using a gas purification device such as a gas separation membrane, PSA, or high-pressure water absorption method. The biogas purified in this way passes through the gas holder, and is used as power generation by a gas engine, a gas turbine, a fuel cell, etc., automobile fuel, or the like. In addition, when it may contain low concentration hydrogen sulfide at the time of resource utilization, it can be set as the format which does not require desulfurization equipment.

  In the mixing tank 17 of the mixing and aggregating apparatus 16, an inorganic flocculant is added to the gas contact liquid (inorganic flocculant adding step). Examples of the inorganic flocculant used here include ferrous or ferric chlorides, sulfates, nitrates and organic acid salts, or aluminum chlorides, sulfates, nitrates and organic acid salts. These may be used singly or in combination of two or more.

  Further, in the mixing tank 17, a pH adjusting agent is added to the gas contact liquid, and the pH of the gas contact liquid is adjusted to a value suitable for aggregation (hydrogen ion concentration adjusting step). As the pH adjuster used here, an alkali agent such as sodium hydroxide is generally used. It is preferable to adjust to near neutrality (pH is about 5 to 9) suitable for the production of iron hydroxide or aluminum hydroxide by adding a pH adjusting agent. Further, a polymer flocculant can be used in combination to strengthen the coagulated sludge containing iron hydroxide or aluminum hydroxide. In addition, when using a membrane separator instead of a precipitation tank, addition of a polymer flocculant is unnecessary.

  The agglomerated sludge scraped to the bottom of the agglomeration tank 18 is extracted by a line L15 and removed from the gas contact liquid (solid-liquid separation step). The agglomerated sludge extracted by the line L15 is transferred to the methane fermentation tank 1 and again subjected to the methane fermentation treatment.

  In the above description, the case where the denitrification tank and the nitrification tank are provided separately has been described as an example, but the present invention is not limited to such equipment. For example, a structure in which the denitrification tank and the nitrification tank are separated by a partition wall that can overflow, a membrane, etc., a facility that performs denitrification and nitrification alternately by changing aeration conditions in the same tank, and oxidation The present invention can be suitably applied to facilities such as a ditch where the treated water is flowed and the region satisfying the aerobic condition and the region satisfying the anaerobic condition coexist in the flow path.

It is a schematic block diagram of a waste disposal facility provided with suitable embodiment of the waste water treatment equipment concerning the present invention. It is the schematic which shows the suitable form of the gas contact tank 15 and the mixing aggregation apparatus 16. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Methane fermentation tank, 2 ... Digested sludge storage tank, 3 ... Dehydrator, 11 ... Dehydration separation liquid storage tank, 12 ... Denitrification tank, 13 ... Nitrification tank, 14 ... Precipitation tank, 15 ... Gas contact tank (gas contact means), DESCRIPTION OF SYMBOLS 16 ... Mixing and aggregation apparatus, 17 ... Mixing tank, 18 ... Coagulating tank (solid-liquid separation means), W1 ... Inorganic flocculant supply device (inorganic flocculant addition means), W2 ... pH adjuster supply device, X1 ... pH measuring device DESCRIPTION OF SYMBOLS 10 ... Waste-treatment apparatus, 20 ... Waste water treatment apparatus.

Claims (5)

A wastewater treatment device for aggregating and separating wastewater,
Gas contact means for bringing hydrogen sulfide-containing gas into contact with the waste water;
An inorganic flocculant addition means for adding an inorganic flocculant to the waste water from the gas contact means;
Solid-liquid separation means for solid-liquid separation of the coagulated sludge generated in the wastewater by the addition of the inorganic flocculant;
A wastewater treatment apparatus comprising:   The waste water treatment apparatus according to claim 1, further comprising hydrogen ion concentration adjusting means for adjusting a hydrogen ion concentration of the waste water to which the inorganic flocculant is added.   The wastewater treatment apparatus according to claim 1 or 2, wherein the hydrogen sulfide-containing gas supplied to the gas contact means is a biogas generated by methane fermentation of an organic substance.   The wastewater treatment apparatus according to any one of claims 1 to 3, wherein the wastewater supplied to the gas contact means is obtained through an activated sludge treatment of digested sludge generated by methane fermentation. . A wastewater treatment method for coagulating and separating wastewater,
A gas contact step of bringing hydrogen sulfide-containing gas into contact with the waste water;
An inorganic flocculant addition step of adding an inorganic flocculant to the waste water from the gas contact step;
A solid-liquid separation step for solid-liquid separation of the coagulated sludge generated in the waste water after the inorganic flocculant addition step;
A wastewater treatment method comprising:

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