JP2002301495A - Apparatus and method for anaerobic digestion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve volume reduction efficiency of sludge in anaerobic digestion treatment, where a part of digestive sludge is subjected to solid-liquid separation and the separated sludge is returned to an anaerobic digestion tank, and another part of the sludge is modified and the modified liquid is returned to the anaerobic digestion tank. SOLUTION: A flocculant is added to a part of the digestive sludge from the anaerobic digestion tank 1 and then the sludge is subjected to solid-liquid separation. The separated sludge is returned to the anaerobic digestion tank 1. Another part of the digestive sludge from the anaerobic digestion tank 1 is modified in an ozone treatment tank 4 to be returned to the anaerobic digestion tank 1. Efficient solid-liquid separation of the digestive sludge reduces solid content discharged into a separated liquid to increase the sludge concentration in the anaerobic digestion tank 1, and increases the amount of sludge to be modified without lowering the efficiency of the anaerobic digestion treatment, thereby the volume of the sludge can be reduced drastically.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anaerobic digester and an anaerobic digestion method, and more particularly, to a method for converting raw water containing organic wastewater such as organic sludge and human waste in the presence of sludge containing anaerobic microorganisms. The present invention relates to an anaerobic digestion apparatus and an anaerobic digestion method capable of effectively reducing the volume of anaerobic digestion sludge generated during methane fermentation.

[0002]

2. Description of the Related Art An anaerobic treatment method for treating a slurry-like high-concentration organic effluent such as organic sludge, night soil and food wastewater by methane fermentation in the presence of anaerobic microorganisms is known as an anaerobic digestion method. This is a method that has been called for a long time.

[0003] In such an anaerobic digestion treatment, sludge (digested sludge) mainly composed of undegraded substances and anaerobic microorganisms is generated. Conventionally, this digested sludge is treated by incineration, landfill, etc. after mechanical dehydration.

As an apparatus for reducing the volume of sludge generated by anaerobic digestion, Japanese Patent Application Laid-Open No. 9-206785 discloses a method in which digested sludge is reformed by ozone treatment, and this reformed liquid is supplied to an anaerobic digestion tank. An anaerobic treatment device to be returned is described. This equipment is used to convert digested sludge to ozone and convert it to biodegradable, and then return it to the anaerobic digestion tank to further decompose it as a substrate for anaerobic microorganisms. It is. In order to increase the volume reduction effect of this apparatus, it is necessary to increase the amount of sludge to be reformed while maintaining the residence time of the sludge in the anaerobic digestion tank so as not to lower the efficiency of the anaerobic digestion treatment. For that purpose, it is necessary to return the high-concentration sludge separated by solid-liquid separation of the digested sludge to the anaerobic digester to increase the sludge concentration in the anaerobic digester.

[0005] However, digested sludge has poor solid-liquid separation properties, and usually a large amount of solid components flow out into the separated liquid during solid-liquid separation. As a result, there is a problem that the concentration of sludge in the anaerobic digestion tank cannot be sufficiently increased, and thus the volume reduction effect cannot be significantly increased. In addition, when the separated solution of the anaerobic digestion treatment is subjected to an aerobic biological treatment in a subsequent stage, there is also a problem that the load is significantly increased if a large amount of solids flows into the separated solution.

[0006] In the anaerobic digestion treatment, most of the organic components in the organic effluent introduced into the anaerobic digestion tank are converted into methane gas and removed outside the system. Since only the part is removed as a separated liquid, when the digested sludge is separated into solid and liquid and the separated sludge is returned to the anaerobic digestion tank, the inorganic components accumulate and increase in the anaerobic digestion tank. Therefore, in the anaerobic digestion tank, the concentration of the organic component remains almost constant, but since the concentration of the inorganic component increases with time, the sludge concentration which is the sum of the organic and inorganic components increases. And, as the concentration of inorganic components in the anaerobic digester increases, the viscosity of the digested sludge increases, resulting in insufficient stirring in the anaerobic digester, reducing the efficiency of the anaerobic digestion process and decomposing organic components. Will not be performed sufficiently. Therefore, it is necessary to extract a part of the digested sludge as surplus sludge, and there is also a problem that even organic components that would normally be decomposed in the anaerobic digestion tank are discharged as surplus sludge.

[0007]

SUMMARY OF THE INVENTION According to the present invention, a part of digested sludge is separated into solid and liquid, and the separated sludge is returned to an anaerobic digestion tank.
In the anaerobic digestion process in which the other part is reformed and the reformed liquid is returned to the anaerobic digestion tank, the solid content flowing into the separated liquid is reduced by efficiently performing solid-liquid separation of the digested sludge. An anaerobic digester and an anaerobic digester that reduce sludge and increase sludge concentration in an anaerobic digestion tank, increase the amount of sludge to be reformed without lowering the efficiency of anaerobic digestion, and significantly reduce sludge volume It is intended to provide a sexual digestion method.

In the anaerobic digestion treatment of the present invention, the inorganic component in the returned separated sludge is transferred by preferentially transferring the inorganic component in the separated liquid in the solid-liquid separation of the digested sludge. An anaerobic digester capable of reducing the amount of inorganic components in the anaerobic digestion tank, reducing organic components in the anaerobic digestion tank, and significantly reducing the volume of sludge generated. And an anaerobic digestion method.

[0009]

An anaerobic digester according to the present invention comprises: an anaerobic digester; raw water supply means for supplying raw water containing organic wastewater to the anaerobic digester; A means for adding a flocculant to a part of the effluent of the digestion tank, a solid-liquid separating means for solid-liquid separating the effluent to which the flocculant has been added, and the anaerobic treatment of the sludge separated by the solid-liquid separating means. Sludge return means for returning to the anaerobic digestion tank, reforming means for reforming another part of the effluent of the anaerobic digestion tank to be easily biodegradable, and reforming liquid reformed by the reforming means And a means for returning the reformed liquid to the anaerobic digestion tank.

The anaerobic digestion method of the present invention comprises an anaerobic digestion step of anaerobically treating raw water containing an organic effluent, and adding a flocculant to a part of the effluent of the anaerobic digestion step to form a solid-liquid mixture. A coagulation separation step for separation, a sludge return step of returning the sludge separated in the coagulation separation step to the anaerobic digestion step, and another part of the effluent of the anaerobic digestion step to be easily biodegradable. And a reforming step of returning the reformed liquid to the anaerobic digestion step.

[0011] In the present invention, a coagulant is added when the effluent of the anaerobic digestion tank (hereinafter referred to as "digested sludge") is subjected to solid-liquid separation. It is possible to perform good solid-liquid separation, obtain a clear separated liquid with less solid outflow, and suppress the outflow of solids out of the system to maintain a high sludge concentration in the anaerobic digester. it can. Therefore, while maintaining the sludge residence time in the anaerobic digestion tank so as not to reduce the efficiency of the anaerobic digestion treatment, the volume of the sludge to be reformed is increased by increasing the amount of the sludge to be reformed, thereby increasing the volume reduction effect of the sludge by the reforming. Can be.

In the anaerobic digestion method of the present invention, a cationic polymer flocculant (hereinafter referred to as "cationic polymer") is used as the flocculant. In this case, the accumulation of the inorganic components in the anaerobic digestion tank described above can be prevented.
That is, in the anaerobic digestion tank, the organic component has a negative charge, while the inorganic component has a positive charge. For this reason, by adding a cationic polymer as a flocculant, it is possible to preferentially flocculate the negatively charged organic component and to transfer the organic component to the separated sludge which is returned to the anaerobic digestion tank. On the other hand, the positively charged inorganic component can be transferred to the separation liquid side, and the inorganic component can be preferentially discharged out of the system. As a result, the accumulation of inorganic components in the anaerobic digestion tank can be suppressed, thereby preventing the sludge concentration from increasing more than necessary in the anaerobic digestion tank, and sufficiently decomposing the organic components to greatly reduce the sludge. It is possible to reduce the volume.

In the anaerobic digestion method of the present invention, an amphoteric polymer flocculant (hereinafter referred to as "amphoteric polymer") is used as a flocculant. In this case, the sludge containing a large amount of inorganic components can be effectively aggregated to improve the solid-liquid separation property. That is, as described above, in the anaerobic digestion tank, the organic component has a negative charge, whereas the inorganic component has a positive charge. However, in order to perform good solid-liquid separation, it is necessary to increase the amount of addition. On the other hand, in the amphoteric polymer, the cation part and the anion part coexist, the cation part neutralizes the charge of the sludge mucus, and the anion part reacts with the cation part to enlarge the apparent polymer chain. In order to enhance the function of binding sludge particles, it works particularly effectively on sludge containing a large amount of inorganic components, and efficient and good solid-liquid separation is performed.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of an anaerobic digestion apparatus and an anaerobic digestion method of the present invention.

In FIG. 1, reference numeral 1 denotes an anaerobic digestion tank provided with a stirrer 1A. Reference numeral 2 denotes a polymer dissolution tank provided with a stirrer 2A. Reference numeral 3 denotes a solid-liquid separation device, and in FIG. 1, a sedimentation tank is used. Reference numeral 4 denotes an ozone treatment tank provided with a stirrer 4A. 5 is an ozone generator.

In this anaerobic digester, the anaerobic digester 1
Raw water containing organic effluent is introduced from the raw water passage 11 to the return sludge returned from the settling tank 3 through the return sludge passage 12;
A configuration in which the anaerobic digestion treatment is performed while mixing the reformed liquid returned from the ozone treatment tank 4 through the reformed liquid return path 20 and the sludge containing the anaerobic microorganisms in the anaerobic digestion tank 1 with gentle stirring. Have been. By the anaerobic digestion treatment performed here, organic matter is decomposed by acid-producing bacteria and methane-producing bacteria. The digestion gas containing the generated methane gas is discharged from the exhaust gas passage 13.

The digested sludge in the anaerobic digestion tank 1 is transferred to a transfer path 14.
From the polymer dissolving tank 2 through the polymer injection pipe 15 and a coagulation treatment.

In the sedimentation tank 3, the coagulated digested sludge introduced from the transfer path 14 is separated into a solid and a liquid by solid-liquid separation, and the separated liquid is discharged out of the system from the treatment water path 16 as treated water.
Part of the solid content (separated sludge) is discharged from the excess sludge removal passage 17 to the outside of the system as necessary, and the remainder is returned to the anaerobic digestion tank 1 from the return sludge passage 12 as return sludge.

The ozone treatment tank 4 is configured to ozone-treat the digested sludge taken out of the anaerobic digestion tank 1 through the sludge take-out passage 18 by blowing the ozone of the ozone generator 5 from the ozone injection pipe 19 into contact therewith. ing. By the ozone treatment performed here, the organic matter in the digested sludge is reformed to be easily biodegradable. The reforming liquid is sent from the reforming liquid return path 20 to the anaerobic digestion tank 1. Since this reformed liquid contains a readily biodegradable solid content reformed in the ozone treatment tank 4, the solid content is digested in the anaerobic digestion tank 1 and the amount of excess sludge generated from the treatment system Is reduced in volume.

The organic effluent to be treated in the present invention is an effluent (including sludge) containing an organic substance to be treated by anaerobic treatment. It may be a liquid that does not contain. Also,
Organic, inorganic, cellulose, paper, cotton,
Solid matter in wool, cloth, human waste, and the like may be contained. Such organic effluents include sewage, primary sewage sludge, night soil, septic tank sludge, livestock manure, food factory effluent, beer waste yeast, other industrial effluents, and excess sludge generated when these effluents are treated. And the like.

The anaerobic digestion tank 1 is a tank for methane fermenting such organic effluent in the presence of sludge containing anaerobic microorganisms. The sludge containing anaerobic microorganisms contains acid-producing bacteria and methane-producing bacteria, and in the anaerobic digestion tank 1, the organic components are converted to methane gas by the steps of liquefaction → low molecular weight → organic acid generation → methane generation by anaerobic microorganisms. You.

The conditions of the methane fermentation in the anaerobic digester 1 include any temperature conditions under which medium-temperature methanogens having an optimum temperature around 35 ° C. and high-temperature methanogens having an optimum temperature near 55 ° C. grow. Can be adopted. Since the medium-temperature methanogens grow slowly, the residence time (SRT) of the anaerobic digestion tank 1 needs to be increased, that is, the capacity of the anaerobic digestion tank 1 needs to be increased, but processing at a relatively low temperature is possible. Therefore, the equipment for warming and keeping warm is simplified. On the other hand, in the case of high-temperature methanogens, heating and warming facilities are required. However, since the growth is fast, the residence time may be short and the capacity of the anaerobic digestion tank 1 can be reduced. .

When the medium temperature methanogen is mainly used, the residence time of the sludge in the anaerobic digestion tank is 10 days or more, preferably 1 day.
About 5 to 30 days are required. On the other hand, when high-temperature methanogens are mainly used, the residence time can be shorter than the above range (for example, 2 days or more).

The organic matter load of the anaerobic digester 1 is 0.5 to
2.0kg-VSS / ^{m 3} · day, M anaerobic digestion tank 1
The LSS concentration is preferably 5,000 to 100,000 mg / L, and more preferably 30,000 to 60,000 mg / L, and the temperature is preferably 30 to 38 ° C or 45 to 60 ° C.

In the present invention, a coagulant is added to the digested sludge in the anaerobic digestion tank 1 and mixed, then solid-liquid separation is performed, the separated liquid is discharged as treated water, and the separated sludge is transferred to the anaerobic digestion tank 1. I will send it back. Good solid-liquid separation is performed by solid-liquid separation after the coagulation of the digested sludge by adding the coagulant in this way, and clear separated water is obtained, and the solid content is suppressed from flowing out of the system, and anaerobic. By maintaining the sludge concentration in the anaerobic digester 1 at a high level, the sludge volume reduction effect can be enhanced.

As the flocculant, any of an organic flocculant and an inorganic flocculant can be used, but an organic flocculant is preferable because the amount of addition may be small. As shown in FIG. 1, the flocculant may be supplied to the transfer path 14 for transferring the sludge from the anaerobic digestion tank 1 to the sedimentation tank 3 and mixed therewith, or supplied to the sedimentation tank 3 and other solid-liquid separation devices. You may mix inside an apparatus. A mixing tank for mixing and coagulating digested sludge and a flocculant may be provided between the anaerobic digestion tank 1 and a solid-liquid separation device such as the sedimentation tank 3.

As the solid-liquid separator, a centrifugal separator, a flotation separator, a membrane separator or the like can be used in addition to the sedimentation tank 3.

In order to prevent the accumulation of inorganic components and hardly biodegradable organic components in the anaerobic digestion tank 1, as shown in FIG. Disposal such as incineration and landfill may be performed.

The separated liquid obtained by solid-liquid separation can be directly discharged to sewage or the like as treated water.
You may discharge after performing other post-processing.

The ozone treatment tank 4 is a tank for reforming digested sludge extracted from the anaerobic digestion tank 1 by ozone treatment. Ozone treatment is performed by bringing digested sludge into contact with ozone. By performing the ozone treatment of the digested sludge on the sludge drawn directly from the anaerobic digestion tank 1, the sludge can be efficiently reformed. That is, since the separated sludge separated in the sedimentation tank 3 forms a coarse floc by the addition of the flocculant, the contact efficiency with the sludge is extremely low, and the sludge cannot be efficiently reformed. Since the flocculant added during a long residence time in the tank is biodegraded and the flocculant is lost, the floc is fine and the sludge in the tank 1 is efficiently contacted with ozone and reformed. can do. Digested sludge may be extracted directly from the anaerobic digestion tank 1 or may be extracted from the digestion sludge transfer path 14 from the polymer injection point on the upstream side.

As a method of contacting with ozone, a method of introducing digested sludge into the ozone treatment tank 4 and blowing ozone, a method of mechanical stirring, a method of using a packed bed, and the like can be adopted.

As the ozone, ozone-containing water can be used in addition to the ozone-containing gas.
_{1~0.08g-O 3 / g-VSS} , preferably 0.0
It is a _{2~0.05g-O 3 / g-VSS} .

By performing such ozone treatment,
The cells in the digested sludge are killed and are reformed to be easily biodegradable together with other organic substances.

The amount of digested sludge that is pulled out from the anaerobic digestion tank 1 and subjected to ozone treatment is determined as the amount of solid matter (VSS) contained in the digested sludge in order to sufficiently secure the sludge volume reduction effect. It is preferable that the amount is 1/3 to 5 times, preferably 1/2 to 3 times the amount of the solid (VSS) introduced into the tank 1. The amount of digested sludge to be treated with ozone per day is 1/5 of the total amount of sludge held in the anaerobic digestion tank 1.
It is preferable to set the amount to 1/50. By setting the amount of ozone treatment per day to the above amount, the amount of microorganisms required for anaerobic digestion can be held in the anaerobic digestion tank 1, and the efficiency of anaerobic digestion can be kept high. .

As means for reforming digested sludge, in addition to an ozone treatment tank, an oxidizing agent having a strong oxidizing power such as hydrogen peroxide,
Any of a chemical treatment with an acid, an alkali, or the like, a physical treatment such as grinding with a mill, and a thermal treatment may be used.

In the present invention, a cationic polymer or an amphoteric polymer is preferably used as a flocculant to be added to digested sludge to be separated into solid and liquid, and the following effects are exhibited.

As described above, in the anaerobic digestion tank 1, the organic component has a negative charge, while the inorganic component has a positive charge.
Organic components can be preferentially flocculated. Therefore, the organic components in the digested sludge preferentially move to the separated sludge side after solid-liquid separation and are returned to the anaerobic digestion tank 1, while
The inorganic component moves to the separation liquid side and is discharged out of the system. In this way, the accumulation of the inorganic component in the anaerobic digestion tank 1 can be suppressed by preferentially discharging the inorganic component out of the system.

The cationic polymer used can be produced by homopolymerization of a cationic monomer or copolymerization of a cationic monomer and a nonionic monomer.

Here, as the cationic monomer, for example, dimethylaminomethyl acrylate or methacrylate, dimethylaminoethyl acrylate or methacrylate, dimethylaminopropyl acrylate or methacrylate, dimethylamino-2-hydroxypropyl acrylate or methacrylate, diethylaminomethyl acrylate or methacrylate , Diethylaminoethyl acrylate or methacrylate, diethylaminopropyl acrylate or methacrylate, diethylamino-2-hydroxyacrylate or methacrylate, dimethylaminomethylacrylamide or methacrylamide, dimethylaminoethylacrylamide or methacrylamide, dimethylaminopropylacrylamide or methacrylia Tertiary such as dimethylamino-2-hydroxypropylacrylamide or methacrylamide, diethylaminomethylacrylamide or methacrylamide, diethylaminoethylacrylamide or methacrylamide, diethylaminopropylacrylamide or methacrylamide, diethylamino-2-hydroxypropylacrylamide or methacrylamide. Salts and quaternary compounds are exemplified. Acids used for the tertiary salt include, for example, hydrochloric acid, sulfuric acid, nitric acid, formic acid, acetic acid and the like, while quaternizing agents include, for example, methyl chloride, methyl iodide, benzyl chloride, dimethyl sulfate, diethyl sulfate Sulfuric acid, ethyl chloride, ethyl iodide and the like. One of these cationic monomers may be used, or two or more thereof may be used in combination.

Examples of the nonionic monomer include vinyl group-containing amides such as acrylamide, methacrylamide, dimethylacrylamide and dimethylmethacrylamide; vinyl cyanide compounds such as acrylonitrile and methacrylonitrile; methyl acrylate; (Meth) acrylic acid alkyl esters such as ethyl acrylate, methyl methacrylate and ethyl methacrylate;
Examples thereof include vinyl esters of carboxylic acids such as vinyl acetate, and aromatic vinyl compounds such as styrene, α-methylstyrene and p-methylstyrene. One type of these nonionic monomers may be used, or two or more types may be used in combination.

The cationic polymer is preferably dissolved and added to a concentration of about 0.05 to 0.3% by weight, particularly about 0.2% by weight. 0.2 to 2% by weight, particularly preferably 0.4 to 1.2% by weight.

On the other hand, in the case of an amphoteric polymer, the cation portion and the anion portion coexist, and the cation portion neutralizes the charge of the sludge mucus, and the anion portion reacts with the cation portion to form an apparent polymer chain. In order to enhance the function of binding the sludge particles by making it larger, it works particularly effectively on sludge containing a large amount of inorganic components, and good solid-liquid separation is performed.

The amphoteric polymer used can be produced by copolymerization of the above-mentioned cationic monomer and the following anionic monomer, or, if necessary, by further copolymerizing the above-mentioned nonionic monomer. .

Examples of the anionic monomer include unsaturated carboxylic acids such as acrylic acid, methacrylic acid and ethacrylic acid (α-ethylacrylic acid) and their sodium, potassium and ammonium salts, and vinyl sulfone. Acid, 2-acrylamido-2-methylpropanesulfonic acid and its sodium and potassium salts,
Ammonium salts and the like. These anionic monomers may be used alone or in combination of two or more.

0.05 to 0.3% by weight of the amphoteric polymer,
In particular, it is preferable to add it after dissolving it to a concentration of about 0.1% by weight.
It is preferably from 2 to 1.5% by weight, especially from 0.4 to 1.0% by weight.

[0047]

The present invention will be described more specifically below with reference to examples and comparative examples.

Examples 1 and 2 Mixed raw sludge collected from a sewage treatment plant (VSS concentration 11,
500 mg / L) as raw water and the anaerobic digester of FIG.
The processing was performed with a processing amount of 50 L / day. Anaerobic
The digestion tank treatment conditions were as follows. [Treatment conditions of anaerobic digester] Anaerobic digester capacity: 1m³  Organic substance load: 0.6 kg-VSS / m³MLSS concentration: 60,000 mg / L MLVSS concentration: 36,000 mg / L Hydraulic residence time: 20 days Temperature: 35 ° C

From the anaerobic digestion tank, the amount of solids (VSS) introduced into the anaerobic digestion tank is 1.5 times, which is equivalent to 1/40 of the total amount of sludge held in the anaerobic digestion tank per day. Amount of digested sludge is extracted, and 0.04 g-
After ozone treatment with the ozone used amount of O ₃ / g-VSS, it was returned to the anaerobic digestion tank.

Further, for 100 L / day of digested sludge withdrawn from the anaerobic digestion tank, 0.1% aqueous solution of the polymer shown in Table 1 was added, and the amount shown in Table 1 was added. Then, 65 L / day of the separated liquid was discharged out of the system. On the other hand, a part of the separated sludge was drawn out of the system as surplus sludge, and the remainder was returned to the anaerobic digestion tank so that the MLSS concentration did not exceed 60,000 mg / L.

In this treatment, the properties of the separated liquid and the separated sludge obtained by the solid-liquid separation and the amount of excess sludge discharged (including the amount discharged as the separated liquid) were examined, and the results are shown in Table 1. .

Comparative Example 1 An anaerobic digestion treatment was performed in the same manner as in Example 1 except that no coagulant was added, and the properties of the obtained separated liquid and separated sludge and the amount of excess sludge discharged were examined. The results are shown in Table 1.

[0053]

[Table 1]

From Table 1, it can be seen that by adding a flocculant to digested sludge and performing solid-liquid separation, solid-liquid separation is enhanced, SS is prevented from flowing into the separated liquid, and the concentration of separated sludge is increased. It can be seen that the sludge volume reduction rate can be improved and the excess sludge amount can be reduced.

In particular, when a cationic polymer is used as a flocculant, it is possible to prevent the accumulation of the inorganic components in the anaerobic digestion tank by transferring the inorganic components into the separation liquid.

When an amphoteric polymer is used as the coagulant, good coagulability is obtained and the separated sludge can be highly concentrated.

[0057]

As described in detail above, according to the anaerobic digestion apparatus and the anaerobic digestion method of the present invention, a part of the digested sludge is separated into solid and liquid, and the separated sludge is returned to the anaerobic digestion tank. In the anaerobic digestion treatment in which a part of the wastewater is reformed and the reformed liquid is returned to the anaerobic digestion tank, a coagulant is added to the digested sludge for coagulation and solid-liquid separation. , A clear separated liquid with a small amount of solid content is obtained, and the solid content of the anaerobic digestion tank can be kept high by suppressing the solid content from flowing out of the system. Therefore, the amount of sludge to be reformed can be increased without lowering the efficiency of the anaerobic digestion treatment, and the sludge volume can be significantly reduced.

In particular, according to the anaerobic digestion method of the third aspect, by adding a cationic polymer as a flocculant, the organic component having a negative charge is preferentially flocculated, and the organic component is supplied to the anaerobic digestion tank. It can be transferred to the separated sludge to be returned, while the positively charged inorganic component can be transferred to the separated liquid side, and the inorganic component can be preferentially discharged out of the system. For this reason, the accumulation of inorganic components in the anaerobic digestion tank can be suppressed, whereby the organic components can be sufficiently decomposed in the anaerobic digestion tank to greatly reduce the volume of sludge.

According to the anaerobic digestion method of the present invention, the charge neutralization of the sludge mucus is carried out in the cation part using the amphoteric polymer in which the cation part and the anion part coexist, and the sludge particles are made in the anion part. By strengthening the binding function, sludge containing a large amount of inorganic components can be effectively coagulated, solid-liquid separation properties can be enhanced, and the sludge concentration in the system can be more reliably increased.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of an anaerobic digestion apparatus and an anaerobic digestion method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Anaerobic digestion tank 2 Polymer dissolution tank 3 Sedimentation tank 4 Ozone treatment tank 5 Ozone generator

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C02F 11/06 C02F 11/06 Z 11/14 11/14 DF Term (Reference) 4D015 BA19 BA23 BA25 BB05 CA02 CA12 DB02 DB03 DC06 DC07 EA03 EA32 FA24 FA26 4D040 AA25 AA27 4D059 AA01 AA04 BA11 BC10 BK12 CA24 DA43

Claims (4)

[Claims] An anaerobic digestion tank, raw water feeding means for feeding raw water containing organic wastewater to the anaerobic digestion tank, and a coagulant added to a part of the effluent of the anaerobic digestion tank Means for performing solid-liquid separation on the effluent to which the coagulant has been added; solid-liquid separation means for returning the sludge separated by the solid-liquid separation means to the anaerobic digestion tank; and A reforming means for reforming another part of the effluent of the anaerobic digestion tank to be easily biodegradable; and a reformed liquid returning the reformed liquid reformed by the reforming means to the anaerobic digestion tank. An anaerobic digester characterized by comprising means. 2. An anaerobic digestion step of anaerobically treating raw water containing an organic effluent, and a coagulation separation step of adding a coagulant to a part of the effluent of the anaerobic digestion step to perform solid-liquid separation. A sludge return step of returning the sludge separated in the coagulation separation step to the anaerobic digestion step, and reforming another part of the effluent of the anaerobic digestion step to readily biodegradable, An anaerobic digestion method, comprising: a reforming step of returning to the anaerobic digestion step. 3. The anaerobic digestion method according to claim 2, wherein the coagulant is a cationic polymer coagulant. 4. The anaerobic digestion method according to claim 2, wherein the coagulant is an amphoteric polymer coagulant.