JP2003275789A - Method for anaerobic digestion of organic waste liquid and anaerobic digestion device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively reduce the volume of anaerobic digestion sludge generating when an organic waste liquid is treated by methane fermentation in the presence of sludge containing anaerobic microorganisms. <P>SOLUTION: After the digestion sludge from an anaerobic digestion tank 1 is drawn and heated to ≥60°C in a sludge solubilizing tank 3 to preferentially solubilize the organic component, the sludge is subjected to solid liquid separation to obtain separated sludge with an increased proportion of the inorganic component, which is then discharged as an excess sludge to the outside of the system. The separated liquid is returned to the anaerobic digestion tank 1. Or, the organic waste water to be introduced into the anaerobic digestion tank 1 is preliminarily heated to ≥60°C in a raw water solubilizing tank. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art An anaerobic digestion method for treating high-concentration organic waste liquid in the form of slurry such as organic sludge, human waste, food wastewater by methane fermentation in the presence of anaerobic microorganisms is known as an anaerobic digestion method. It is called and has been used for a long time.

In such an anaerobic digestion process, sludge (anaerobic digested sludge; hereinafter sometimes simply referred to as "digested sludge") mainly composed of undegraded substances and anaerobic microorganisms is produced. Conventionally, this digested sludge is processed by incineration, landfilling, etc. after mechanical dewatering.

As a device for reducing the volume of sludge produced by anaerobic digestion treatment, Japanese Unexamined Patent Publication No. 9-206785 discloses that the digested sludge is reformed by ozone treatment and then this reformed solution is converted into an anaerobic digestion tank. An anaerobic treatment device for returning is described. This equipment is an equipment that is effective for reducing the volume of sludge, after digesting sludge to be easily biodegradable and reforming it into an anaerobic digestion tank for further decomposition as a substrate for anaerobic microorganisms. Is.

In this device, in order to enhance the effect of reducing the volume of sludge produced by anaerobic digestion from organic waste liquid, the retention time of sludge in the anaerobic digestion tank is maintained and the efficiency of anaerobic digestion treatment is not reduced. Therefore, it is necessary to increase the amount of sludge to be modified. To this end, a part of the digested sludge is subjected to solid-liquid separation, the separated liquid is discharged as treated water, and the separated high-concentration sludge (concentrated sludge) is sent back to the anaerobic digestion tank. It is necessary to suppress outflow from the system and maintain a high sludge retention amount and sludge concentration in the anaerobic digestion tank.

[0006]

However, while the organic components in sludge are significantly reduced in volume with this device, the inorganic components are not reduced, so that the solid-liquid separated concentrated sludge is stored in the anaerobic digestion tank. By returning, the inorganic components accumulate in the anaerobic digester. When the sludge concentration in the anaerobic digestion tank increases due to the accumulation of inorganic components, the viscosity of the liquid in the tank rapidly increases, so the inside of the anaerobic digestion tank cannot be sufficiently stirred and mixed,
The efficiency of anaerobic digestion decreases. Therefore, it is necessary to appropriately extract the digested sludge as excess sludge so as to maintain the sludge concentration in the anaerobic digestion tank within a certain range (generally 5 to 6%). Then, with the removal of the sludge to prevent the accumulation of this inorganic component, the organic component that would otherwise be reduced is contained in the extracted sludge and discharged to the outside of the system.
There is a problem that the weight loss of the organic component is limited.

The present invention solves the above-mentioned conventional problems, and preferentially withdraws the inorganic components in the sludge accumulated in the anaerobic digestion treatment system, thereby significantly reducing the organic components in the sludge. It is an object of the present invention to provide an anaerobic digestion method and an anaerobic digester for an organic drainage capable of performing the above.

The present invention also reduces the sludge generated by the anaerobic digestion treatment of organic effluents and improves the anaerobic digestion sludge by ozone treatment or the like without excessively increasing the sludge concentration in the anaerobic digestion tank. It is an object of the present invention to provide an anaerobic digestion method and an anaerobic digester for an organic effluent capable of significantly reducing the volume of sludge by performing a quality treatment and then circulating the sludge.

[0009]

The method for anaerobic digestion of organic waste liquid according to claim 1 comprises an anaerobic digestion step of subjecting the organic waste liquid to methane fermentation in the presence of sludge containing anaerobic microorganisms, Organic waste including a solid-liquid separation step of solid-liquid separating the effluent of the anaerobic digestion step into a sludge and a treatment liquid, and a sludge returning step of returning the separated sludge of the solid-liquid separation step to the anaerobic digestion step In the method for anaerobic digestion of liquid, a sludge heat treatment step in which sludge produced in the anaerobic digestion step is extracted and heat-treated at a temperature of 60 ° C. or higher, and a heat-treated sludge in the sludge heat treatment step is subjected to solid-liquid separation to separate sludge And a separated liquid returning step of returning the separated liquid separated in the sludge discharging step to the anaerobic digestion step.

The anaerobic digester for organic waste liquid according to claim 2 comprises an anaerobic digester for methane fermenting the organic waste liquid in the presence of sludge containing anaerobic microorganisms, and an outflow of the anaerobic digester. Anaerobic digester for organic waste liquid, including solid-liquid separation means for separating liquid into sludge and treated liquid, and sludge returning means for returning the separated sludge of the solid-liquid separation means to the anaerobic digestion means. In, sludge heat treatment means for extracting sludge from the anaerobic digestion means and / or the solid-liquid separation means and heat-treating it at a temperature of 60 ° C. or higher, and solid-liquid separation of the heat-treated sludge of the sludge heat-treatment means to separate sludge Sludge discharging means for discharging the sludge to the outside of the system, and separated liquid returning means for returning the separated liquid separated by the sludge discharging means to the anaerobic digesting means.

By heating the digested sludge, the organic components in the sludge are preferentially solubilized, and the separated sludge obtained by solid-liquid separation of the heat-treated sludge is drawn out of the system to preferentially extract the inorganic components, As a result, the amount of sludge can be significantly reduced and the amount of digestive gas generated can be increased while preventing the accumulation of inorganic components in the system.

An anaerobic digestion method of organic waste liquid according to claim 3 is an anaerobic digestion step of methane fermenting the organic waste fluid in the presence of sludge containing anaerobic microorganisms, and the outflow of the anaerobic digestion step. Anaerobic digestion method for organic waste liquid, comprising a solid-liquid separation step of separating a liquid into a sludge and a treatment liquid, and a sludge returning step of returning the separated sludge of the solid-liquid separation step to the anaerobic digestion step. In the above, there is a raw water heat treatment step in which at least a part of the organic waste liquid sent to the anaerobic digestion step is heat-treated in advance at a temperature of 60 ° C. or higher.

An anaerobic digester for organic waste liquid according to a fifth aspect of the present invention comprises an anaerobic digester for methane fermenting the organic waste liquid in the presence of sludge containing anaerobic microorganisms, and the anaerobic digester. Of organic sludge including reforming means for extracting the sludge to be reformed to be easily biodegradable, and reformed sludge returning means for returning the reformed sludge modified by the reforming means to the anaerobic digestion means. In the liquid anaerobic digester, at least a part of the organic waste liquid to be fed to the anaerobic digester is preliminarily 60
It is characterized by having a raw water heat treatment means for performing heat treatment at a temperature of ℃ or more.

By preliminarily heating and solubilizing the organic waste liquid to be subjected to the anaerobic digestion treatment, the efficiency of the anaerobic digestion treatment is improved, and the amount of sludge generated in the anaerobic digestion treatment can be reduced. With this, without excessively increasing the sludge concentration in the anaerobic digestion tank, by circulating the anaerobic digestion sludge after performing a reforming treatment such as ozone treatment, it is possible to significantly reduce the volume of the sludge, The amount of digestive gas generated can be increased.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

First, referring to FIG. 1, an embodiment of the anaerobic digestion method and apparatus for anaerobic digestion of organic effluent according to claims 1 and 2 will be described.

FIG. 1 is a system diagram showing an embodiment of an anaerobic digestion method and an anaerobic digestion apparatus for organic drainage according to claims 1 and 2.

This anaerobic digester comprises an anaerobic digester 1
And a centrifuge 2 as a treated water extraction means, a sludge solubilization tank 3 as a sludge heat treatment means, and a sedimentation tank 4 as a sludge discharge means. 1A is a stirrer.

In this anaerobic digester, the anaerobic digester 1
The organic drainage liquid is introduced from the raw water channel 11. Then, the returned sludge returned from the centrifugal separator 2 through the returned sludge passage 12, the separated liquid in the settling tank 4 returned through the separated liquid returning passage 14, and the sludge containing the anaerobic microorganisms in the anaerobic digestion tank 1 and the raw water. The anaerobic digestion treatment is performed while gently stirring and mixing and with the stirrer 1A. Due to the anaerobic digestion process performed here, most of the organic substances in the raw water are decomposed by acid-producing bacteria and methanogenic bacteria. The digestion gas containing the produced methane gas is discharged from the exhaust gas passage 15.

The effluent (digested sludge) of the anaerobic digestion tank 1 is introduced into the centrifugal separator 2 from the transfer passage 16. In the centrifugal separator 2, the digested sludge introduced from the transfer passage 16 is subjected to solid-liquid separation into a solid content (concentrated sludge) and a separated liquid, and the separated liquid is discharged as treated water from the treated water passage 17 to the outside of the system. The solid content (concentrated sludge) is returned to the anaerobic digestion tank 1 through the return sludge passage 12. A part of the solid content may be sent to the sludge solubilization tank 3 from the transfer path 19.

From the anaerobic digestion tank 1, digested sludge is extracted from the extraction sludge passage 18 and sent to the sludge solubilization tank 3.

The sludge solubilization tank 3 is a tank for solubilizing the digested sludge drawn from the anaerobic digestion tank 1 by heating it at a temperature of 60 ° C. or higher, and the organic components in the digested sludge are prioritized by the heat treatment. Is solubilized. The heat-treated sludge in the sludge solubilization tank 3 is sent from the transfer path 21 to the settling tank 4 for solid-liquid separation, the separated sludge is discharged as excess sludge from the discharge sludge path 22 to the outside of the system, and the separated liquid is separated liquid. Return route 14
It is returned to the anaerobic digestion tank 1. In this separated liquid,
Since the organic component solubilized in the sludge solubilization tank 3 is contained, it is digested in the anaerobic digestion tank 1.

The sludge heat treatment step, that is, the sludge solubilization tank 3,
This is a step of solubilizing the digested sludge drawn from the anaerobic digestion tank 1 by heating it at a temperature of 60 ° C. or higher. By the heat treatment, the organic components in the digested sludge are preferentially solubilized with respect to the inorganic components. The heat treatment temperature is 60 ° C or higher, preferably 120 to 180 ° C. At the time of this heat treatment, the solubilization efficiency can be improved by applying a pressure equal to or higher than the saturated vapor pressure of the treatment temperature and then raising the temperature to the treatment temperature to cause a chemical reaction. The heat treatment time depends on the treatment temperature, but is 0.
5 to 1.0 hours.

The amount of digested sludge extracted from the anaerobic digestion tank 1 and heat-treated corresponds to 1 to 5 times, preferably 1.5 to 3 times, the amount of the solid inorganic components introduced into the anaerobic digestion tank 1. The amount is preferable. Also, the amount of digested sludge that is heat-treated per day is 1 of the total amount of sludge retained in the anaerobic digestion tank 1.
It is preferably not more than / 15 and particularly preferably an amount corresponding to 1/20 to 1/40. By setting the heat treatment amount per day to the above amount, the amount of microorganisms necessary for the anaerobic digestion treatment can be retained in the anaerobic digestion tank 1, and the efficiency of the anaerobic digestion treatment can be kept high. .

The solid-liquid separation step of the heat-treated sludge is a step of solid-liquid separating the heat-treated sludge, returning the separated liquid to the anaerobic digestion step, and discharging the separated sludge out of the system. In this step, the amount of separated sludge containing the same amount of inorganic components as the inorganic components introduced into the anaerobic digester 1 is discharged out of the system as excess sludge, thereby accumulating the inorganic components in the anaerobic digester 1. Can be prevented. Since the organic components in the digested sludge are preferentially solubilized by the heat treatment, the separated sludge has a higher ratio of inorganic components than the original digested sludge. This separated sludge with a high ratio of inorganic components is discharged to the outside of the system, and the separated liquid containing the solubilized organic components is returned to the anaerobic digestion process, so that the amount of organic components withdrawn is reduced and retained in the system. As a result, the effect of reducing the amount of organic components can be enhanced. For solid-liquid separation of the heat-treated sludge, a solid-liquid separator such as a centrifugal separator, a flotation separator, or a membrane separator can be used in addition to the settling tank shown in FIG. The separated sludge may be dehydrated as surplus sludge as it is and subjected to incineration, land reclamation or the like, or may be subjected to aerobic or anaerobic biological treatment and then dehydrated, incinerated, land reclamation or the like. This heat-treated sludge has improved dewatering properties as compared with digested sludge, and the bulk when dehydrated can be significantly reduced. Further, the separated liquid returned to the anaerobic digestion step contains a large amount of easily decomposable components produced by the heat treatment, and these are rapidly decomposed in the anaerobic digestion step to further remove excess sludge generated from the treatment system. It can be reduced.

Next, with reference to FIG. 2, an embodiment of the anaerobic digestion method and apparatus for anaerobic digestion of organic waste liquid according to claims 3 to 6 will be described.

FIG. 2 is a system diagram showing an embodiment of an anaerobic digestion method and an anaerobic digester for organic waste liquid according to claims 3 to 6. 2, members having the same functions as those shown in FIG. 1 are designated by the same reference numerals.

This anaerobic digester comprises a raw water solubilization tank 1 as a raw water heat treatment means for organic waste liquid, and an anaerobic digestion tank 1.
A centrifugal separator 2 as a treated water extracting means, an ozone treatment tank 5 as a reforming means, an ozone generator 6 for supplying ozone to the ozone treatment tank 5, and the like. 1A, 5
A is a stirrer.

In this anaerobic digester, the raw water solubilization tank 7
Into the anaerobic digestion tank 1 is introduced from the raw water channel 10 to the anaerobic digester tank 1 after being heated to a temperature of 60 ° C. or higher. In the anaerobic digestion tank 1, the return sludge returned from the centrifugal separator 2 through the return sludge passage 12, the reformed sludge returned from the ozone treatment tank 5 through the reformed sludge return passage 13, and the anaerobic gas in the anaerobic digestion tank 1. An anaerobic digestion treatment is performed while gently stirring and mixing the sludge containing the sex microorganisms and the raw water with the stirrer 1A. Due to the anaerobic digestion process performed here, most of the organic substances in the raw water are decomposed by acid-producing bacteria and methanogenic bacteria. The digestion gas containing the produced methane gas is discharged from the exhaust gas passage 15.

The effluent (digested sludge) of the anaerobic digestion tank 1 is introduced into the centrifugal separator 2 from the transfer passage 16. In the centrifugal separator 2, the digested sludge introduced from the transfer passage 16 is subjected to solid-liquid separation into a solid content (concentrated sludge) and a separated liquid, and the separated liquid is discharged as treated water from the treated water passage 17 to the outside of the system. If necessary, a part of the solid content (concentrated sludge) is discharged as excess sludge from the excess sludge extraction passage 22 to the outside of the system, and the rest is returned to the sludge passage 1
Return from 2 to anaerobic digester 1.

From the anaerobic digestion tank 1, digested sludge is extracted from the extraction sludge passage 18 and sent to the ozone treatment tank 5.

The ozone treatment tank 5 is constructed so that ozone of the ozone generator 6 is blown into contact with the digested sludge from the anaerobic digestion tank 1 through the ozone injection pipe 23 to bring it into contact with the digested sludge. By the ozone treatment performed here, the organic matter in the digested sludge is easily biodegradable. The modified sludge is sent from the modified sludge return path 13 to the anaerobic digestion tank 1. This modified sludge contains easily biodegradable solids that have been modified in the ozone treatment tank 5, so this solid content is digested in the anaerobic digestion tank 1 and the amount of excess sludge generated from the treatment system is increased. Is reduced in volume.

The heat treatment step of the organic waste liquid in the raw water solubilization tank 7 or the like is a step of solubilizing the organic waste liquid by heating it at a temperature of 60 ° C. or higher prior to the anaerobic digestion treatment. . By this heat treatment, the efficiency of anaerobic digestion in the latter stage is improved, and the amount of sludge generated in the anaerobic digestion treatment can be reduced. This heat treatment temperature is 60 ℃
As described above, the temperature is preferably 120 to 180 ° C. During the heat treatment, the solubilization efficiency can be improved by applying a pressure equal to or higher than the saturated vapor pressure of the treatment temperature and then raising the temperature to the treatment temperature to cause a chemical reaction. Although the heat treatment time depends on the treatment temperature, for example, when the treatment temperature is 150 ° C., 0.5
~ 1.0 hours.

The amount of the organic drainage liquid to be subjected to such heat treatment is preferably the total amount of the organic drainage liquid introduced into the anaerobic digestion tank 1, but only a part of the organic drainage liquid is subjected to the heat treatment. The rest may be directly introduced into the anaerobic digestion tank 1.

The organic waste liquid to be treated in the present invention is a waste liquid (including sludge) containing an organic substance to be treated by an anaerobic treatment. It may be a liquid that does not contain it. Also,
Biodegradable organic substances, inorganic substances, cellulose, paper, cotton,
Wool, cloth, solid matter in human waste, etc. may be contained. Such organic effluents include sewage, sewage first settled sludge, human waste, septic tank sludge, livestock excrement, food factory wastewater, beer waste yeast, other industrial effluents, and excess sludge generated when these effluents are treated. The sludge etc. are mentioned.

The anaerobic digestion step in the present invention, that is, the anaerobic digester 1 is operated in the presence of sludge containing anaerobic microorganisms.
This is a step of methane-fermenting such an organic waste liquid.
Sludge containing anaerobic microorganisms contains acid-producing bacteria and methanogenic bacteria, and in the anaerobic digestion tank 1, organic components are converted to methane gas by the steps of liquefaction → low molecular weight → organic acid generation → methanogenesis by anaerobic microorganisms. It

As the conditions for methane fermentation in the anaerobic digestion step, any temperature condition in which a mesophilic methanogen having an optimum temperature near 35 ° C. and a high temperature methanogen having an optimum temperature near 55 ° C. grow are adopted. It is possible. Since the mesophilic methanogen grows slowly, it is necessary to lengthen the residence time (SRT) of the anaerobic digester 1, that is, to increase the capacity of the anaerobic digester 1, but it is possible to treat at a relatively low temperature. Therefore, the equipment for heating and keeping warm becomes simple. On the other hand, in the case of the high temperature methanogen, a heating and heat retaining facility is required, but since the growth is fast, the residence time may be short and there is an advantage that the capacity of the anaerobic digester 1 can be reduced. .

When the mesophilic methanogens are mainly used, the retention time of sludge in the anaerobic digester is 10 days or more, preferably 1
It takes about 5 to 30 days. On the other hand, when the high temperature methanogen is mainly used, the residence time (for example, 2 days or more) shorter than the above range can be set.

The organic matter load in the anaerobic digestion process is 0.5 to
2.0 kg-TVS / m ³ · day, T in anaerobic digester 1
S concentration is 5,000 to 100,000 mg / L, preferably 20,000 to 60,000 mg / L, and temperature is 30.
It is preferable to set the conditions to 38 ° C or 45 to 60 ° C.

In the anaerobic digestion process, as shown in FIGS. 1 and 2, a part of the anaerobic digestion sludge is solid-liquid separated, the separated liquid is discharged as treated water, and the concentrated sludge is returned to the anaerobic digestion process. It is preferable to configure it, and by doing so, it is possible to suppress the outflow of the solid matter out of the system and to maintain a high sludge retention amount in the anaerobic digestion step, thereby enhancing the sludge weight reduction effect. For the solid-liquid separation of the anaerobic digestion sludge, a solid-liquid separation device such as a flotation separation device, a membrane separation device or a precipitation tank can be used in addition to the centrifugal separation device shown in FIGS. The separated liquid obtained by solid-liquid separation can be directly discharged as sewage to sewage or the like, but may be discharged after performing aerobic biological treatment and other post-treatments.

In the solid-liquid separation of this digested sludge, a coagulant is added to coagulate the digested sludge, whereby good solid-liquid separation is performed and clear separated water is obtained.
It is possible to suppress the outflow of solids from the system and enhance the volume reduction effect of sludge.

As the aggregating agent, either an organic type or an inorganic type may be used, but an organic polymer aggregating agent, particularly an amphoteric organic polymer aggregating agent (amphoteric polymer), may be used because the addition amount may be small. preferable.

In the case of an amphoteric polymer, the cation part and the anion part coexist, the cation part performs charge neutralization of the sludge mucilage, and the anion part reacts with the cation part to enlarge the apparent polymer chain. Since it strengthens the action of binding sludge particles with each other, it works particularly effectively for sludge containing a large amount of inorganic components such as digested sludge, and good solid-liquid separation is performed.

The amphoteric polymer used may be a copolymer of a cationic monomer and an anionic monomer, or
If necessary, it can be produced by further copolymerizing 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-hydroxy acrylate or methacrylate, dimethylaminomethyl acrylamide or methacrylamide, dimethylaminoethyl acrylamide or methacrylamide, dimethylaminopropyl acrylamide or methacrylamide Tertiary such as amide, dimethylamino-2-hydroxypropylacrylamide or methacrylamide, diethylaminomethylacrylamide or methacrylamide, diethylaminoethylacrylamide or methacrylamide, diethylaminopropylacrylamide or methacrylamide, diethylamino-2-hydroxypropylacrylamide or methacrylamide. Examples include salts and quaternary compounds. Examples of the acid used for the tertiary salt include hydrochloric acid, sulfuric acid, nitric acid, formic acid, acetic acid and the like, while examples of the quaternizing agent include methyl chloride, methyl iodide, benzyl chloride, dimethylsulfate and diethyl. Examples thereof include sulfuric acid, ethyl chloride and ethyl iodide. These cationic monomers may be used alone or in combination of two or more.

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

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 and acryl. Alkyl esters of (meth) acrylic acid such as ethyl acidate, methyl methacrylate, and ethyl methacrylate,
Examples thereof include vinyl esters of carboxylic acids such as vinyl acetate, aromatic vinyl compounds such as styrene, α-methylstyrene and p-methylstyrene. These nonionic monomers may be used alone or in combination of two or more.

The organic polymer flocculant is preferably added by dissolving it in a concentration of 0.05 to 0.3% by weight, particularly about 0.1% by weight, and the amount of addition is from the anaerobic digestion tank 1. 0.2 to 1.5% by weight, especially 0.
It is preferably 4 to 1.0% by weight.

The organic polymer flocculant may be supplied to the transfer passage 16 for transferring digested sludge from the anaerobic digestion tank 1 to the centrifugal separator 2 and mixed therewith, and may be mixed in the centrifugal separator 2 and other solid-liquid separation means. It may be supplied and mixed inside the apparatus. Further, a mixing tank may be provided between the anaerobic digestion tank 1 and the solid-liquid separating means such as the centrifugal separator 2 for mixing the digested sludge and the coagulant to coagulate them.

The reforming step, that is, the ozone treatment tank 5 is a step of reforming the digested sludge drawn from the anaerobic digestion tank 1 by ozone treatment. Ozone treatment is performed by contacting this digested sludge with ozone.

As a method of contacting with ozone, a method of introducing digested sludge into the ozone treatment tank 5 and blowing in ozone, a method of mechanical stirring, a method of utilizing a packed bed and the like can be adopted.

As ozone, not only ozone-containing gas but also ozone-containing water can be used, and the amount of ozone used is usually 0.0
_{1~0.08g-O 3 / g-TVS} , preferably 0.0
Is a _{2~0.05g-O 3 / g-TVS} .

By performing such ozone treatment,
The microbial cells in the digested sludge are killed and are easily biodegradable along with other organic substances. Therefore, by returning the modified sludge modified in the ozone treatment tank 5 to the anaerobic digestion tank 1, the easily biodegradable components in the modified sludge are converted into the anaerobic digestion tank 1.
The excess sludge generated from the treatment system is reduced.

The amount of digested sludge extracted from the anaerobic digestion tank 1 and subjected to ozone treatment is adjusted so that the solid matter (TV) contained in the extracted digested sludge is sufficient to ensure a sufficient volume reduction effect of the sludge.
The amount of S) is preferably 1/3 to 5 times, preferably 1/2 to 3 times, the amount of solids (TVS) introduced into the anaerobic digestion tank 1. Further, the amount of digested sludge to be ozone-treated per day is preferably an amount corresponding to 1/5 to 1/50 of the total amount of sludge retained in the anaerobic digestion tank 1. By setting the ozone treatment amount per day to the above amount, the amount of microorganisms required for the anaerobic digestion treatment can be retained in the anaerobic digestion tank 1, and the efficiency of the anaerobic digestion treatment can be kept high. .

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

In the method and apparatus for anaerobic digestion of organic effluent according to claims 3 to 6 shown in FIG. 2, the digested sludge in the anaerobic digestion tank 1 is extracted as shown in FIG. By heating at a temperature of 60 ° C or higher, the organic components in the digested sludge are preferentially solubilized, the heat-treated sludge is subjected to solid-liquid separation, and the separated sludge is discharged to the outside of the system as excess sludge and the separated liquid May be returned to the anaerobic digestion tank 1. By doing so, it is possible to discharge sludge having a high ratio of inorganic components to the outside of the system, prevent accumulation of inorganic components in the system, and to achieve favorable reduction of sludge.

The heating conditions of the digested sludge and the amount of the digested sludge drawn out for the heat treatment in this case are as described above.

When the digestion sludge is subjected to the heat treatment and the solid-liquid separation in this manner, the separated sludge is discharged as an excess sludge, and the concentrated sludge of the centrifugal separator 2 is entirely anaerobic digester. It is preferable to return to 1.

The digestion gas generated in the anaerobic digestion process is used as an energy source for power generation to obtain electric power,
Steam and / or hot water generated by power generation can also be used as a heat source for heating the organic waste solution, the digestive sludge, and the anaerobic digestion step.

[0060]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples below.

Example 1 Mixed raw sludge collected from a sewage treatment plant (TS concentration 2%, T
VS concentration 1.6%) as raw water, and anaerobic digester of Fig. 1
The processing amount was 80 L / day. [Treatment conditions for anaerobic digester] Anaerobic digester capacity: 2m^Three Organic matter load: 0.64 kg-TVS / m^Three·Day Hydraulic retention time: 25 days Temperature: 35 ° C

Prior to the input of raw water, 200 L of anaerobic digested sludge was drawn out from the anaerobic digestion tank, 50 of which was extracted.
L was heat-treated in an autoclave at 121 ° C. for 30 minutes, then 10 L of the precipitate gravity-precipitated for 30 minutes was drawn out of the system as excess sludge, and the rest was returned to the anaerobic digestion tank. The amount of digested sludge subjected to this heat treatment corresponds to 1/20 of the total amount of sludge retained in the anaerobic digestion tank. In addition, the remaining 150 L of the extracted anaerobic digested sludge was centrifuged (2,100
Solid-liquid separation was performed in G), and 100 L of the separated liquid was discharged to the outside of the system as treated water, and the concentrated sludge was returned to the anaerobic digestion tank. In addition,
To the centrifugal concentrator, 0.2 L of an organic polymer coagulant dissolved in 0.2% was added per 1 L of sludge. By this operation,
The sludge concentration in the anaerobic digester could be maintained at 5%.

At this time, the total amount of excess sludge generated (total of the amount of TS discharged to the outside as excess sludge and the amount of TS contained in the solid-liquid separated liquid discharged to the outside as treated water) and the sludge reduction rate The amount of digested gas generated from the anaerobic digestion tank and the quality of treated water were examined, and the results are shown in Table 1.

Comparative Example 1 In Example 1, the digestion sludge was not heat-treated prior to the addition of the raw water, and the anaerobic digestion sludge 16 was removed from the anaerobic digestion tank.
8 L was drawn, 18 L of which was drawn out of the system as excess sludge, and the remaining 150 L was centrifugal concentrator (2,100
The anaerobic digestion treatment was performed in the same manner except that solid-liquid separation was performed in G), 100 L of the separated liquid was discharged out of the system as treated water, and the concentrated sludge was returned to the anaerobic digestion tank. By this operation, the sludge concentration in the anaerobic digestion tank could be maintained at 5%.

At this time, the total excess sludge generation amount, the sludge reduction rate, the digestion gas generation amount and the treated water quality were examined, and the results are shown in Table 1.
It was shown to.

[0066]

[Table 1]

As is clear from Table 1, in Example 1 in which the digested sludge was subjected to heat treatment, solid-liquid separation was performed, and the separated sludge was discharged out of the system as excess sludge, in comparison with Comparative Example 1, total excess sludge was generated. The amount was reduced, the sludge reduction rate was improved by 16%, and the digestion gas generation amount was increased by 1.4 times.

In Example 1, the anaerobic digested sludge, the heat-treated sludge obtained by heat-treating the anaerobic digested sludge, and the separated sludge obtained by solid-liquid separation of the heat-treated sludge, that is, excess sludge, was discharged outside the system. When the sludge properties of the discharged sludge were examined, as shown in Table 2, the organic matter in the solid content was preferentially solubilized by the heat treatment, and TVS / TS was reduced in the excess sludge obtained by sedimentation of the heat-treated sludge. I was able to confirm that it will be done.

[0069]

[Table 2]

Example 2 Mixed raw sludge collected from a sewage treatment plant (TS concentration 2%, T
The raw water (SS concentration: 1.6%) was used to treat the anaerobic digester shown in FIG. 2 at a treatment amount of 80 L / day.

The processing conditions of the anaerobic digester are as follows:
Raw water is heat-treated at 150 ℃ for 1 hour and then anaerobic digestion
It was introduced into the tank. 50L per day from anaerobic digester
Digested sludge (subtract 1/40 of total sludge in anaerobic digester)
Perforated, 0.04g-O in ozone treatment tank_Three/ G-TV
After ozone treatment with the ozone usage amount of S, it is returned to the anaerobic digestion tank.
Sent. [Treatment conditions for anaerobic digester] Anaerobic digester capacity: 2m^Three Organic matter load: 0.64 kg-VSS / m^Three·Day Hydraulic retention time: 25 days Temperature: 35 ° C

Prior to the introduction of raw water, 100 L of anaerobic digested sludge was drawn out from the anaerobic digestion tank, solid-liquid separated by a centrifuge (2,100 G), and the separated liquid was discharged out of the system as treated water. On the other hand, a part of the separated sludge was drawn out of the system so that the TS concentration in the anaerobic digestion tank did not exceed 5%, and the rest was returned to the anaerobic digestion tank. In addition, 1 L of sludge was added to the centrifugal concentrator with the organic polymer flocculant dissolved in 0.2%.
0.2 L was added per unit.

The total amount of excess sludge generated at this time (the total amount of TS discharged to the outside as excess sludge and the amount of TS contained in the solid-liquid separated liquid discharged to the outside as treated water) and sludge volume reduction The rate and the amount of digested gas generated from the anaerobic digester and the quality of treated water were examined, and the results are shown in Table 3.

Comparative Example 2 An anaerobic digestion treatment was carried out in the same manner as in Example 2 except that the heat treatment of the raw water introduced into the anaerobic digestion tank was not performed.

At this time, the total excess sludge generation amount, the sludge volume reduction rate, the digestion gas generation amount and the treated water quality were examined, and the results are shown in Table 3.
It was shown to.

Example 3 In Example 2, the following operation was carried out prior to the addition of raw water, instead of pulling out 100 L of the anaerobic digestion sludge from the anaerobic digestion tank and performing solid-liquid separation. That is, 200 L of anaerobic digested sludge was drawn from the anaerobic digestion tank,
L was heat-treated in an autoclave at 121 ° C. for 30 minutes, and then 5 L of the precipitate gravity-precipitated for 30 minutes was drawn out of the system as excess sludge, and the separated liquid was returned to the anaerobic digestion tank. The amount of digested sludge subjected to this heat treatment corresponds to 1/40 of the total amount of sludge retained in the anaerobic digestion tank. In addition, the remaining 150 L of the extracted anaerobic digested sludge was centrifuged (2,100
Solid-liquid separation was performed in G), and 100 L of the separated liquid was discharged to the outside of the system as treated water, and the concentrated sludge was returned to the anaerobic digestion tank. In addition,
To the centrifugal concentrator, 0.2 L of an organic polymer coagulant dissolved in 0.2% was added per 1 L of sludge. By this operation,
It was possible to maintain the sludge concentration in the anaerobic digestion tank at 5% or less.

At this time, the total excess sludge generation amount, sludge volume reduction rate, digestion gas generation amount and treated water quality were examined, and the results are shown in Table 3.
It was shown to.

[0078]

[Table 3]

As is clear from Table 3, in Example 2 in which the raw water was preheated, the total excess sludge generation amount was reduced as compared with Comparative Example 2, and the sludge volume reduction rate was improved by 16%.
The amount of digestive gas generated increased 1.3 times. Furthermore, according to Example 3 in which the digested sludge was subjected to the heat treatment and then solid-liquid separated, and the separated sludge was discharged out of the system as excess sludge, the total excess sludge generation rate, sludge volume reduction rate, and digestive gas generation rate were further improved. Was observed.

[0080]

As described in detail above, according to the anaerobic digestion method and apparatus for anaerobic digestion of organic effluent according to claims 1 and 2,
When treating organic effluent such as organic sludge and human waste by methane fermentation in the presence of sludge containing anaerobic microorganisms,
By preferentially extracting the inorganic components in the sludge accumulated in the anaerobic digestion treatment system, the sludge can be significantly reduced and the digestive gas generation amount can be increased.

Further, according to the anaerobic digestion method and the anaerobic digester of the organic effluent according to claims 3 to 6, the organic effluent such as organic sludge and human excrement is converted into the presence of sludge containing anaerobic microorganisms. When treating by methane fermentation under the conditions below, without excessively increasing the sludge concentration in the anaerobic digestion tank, the anaerobic digestion sludge can be ozone-treated and circulated, and the volume of the sludge can be greatly reduced, The amount of digestive gas generated can be increased.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of an anaerobic digestion method and an anaerobic digester for organic waste liquid according to claim 1.

FIG. 2 is a system diagram showing an embodiment of an anaerobic digestion method and an anaerobic digester for organic drainage according to claims 3 to 6.

[Explanation of symbols]

1 Anaerobic digester 2 Centrifuge 3 Sludge solubilization tank 4 settling tank 5 Ozone treatment tank 6 Ozone generator 7 Raw water solubilization tank

Continued front page    F-term (reference) 4D040 AA12 AA23 AA27 AA55                 4D059 AA01 AA02 AA04 AA05 AA08                       AA23 BA12 BA21 BA56 BB03                       BE31 BE38 BE49 BE56 BE58                       BF02 BF20 BJ01 BK12 CA22                       DA43 DB08 DB24 DB25 DB26                       DB28

Claims (6)

[Claims] 1. An anaerobic digestion step of subjecting an organic waste liquid to methane fermentation in the presence of sludge containing anaerobic microorganisms, and a solid-liquid separation of the effluent of the anaerobic digestion step into sludge and treated liquid. In an anaerobic digestion method of organic waste liquid, which comprises a liquid separation step and a sludge return step of returning the separated sludge of the solid-liquid separation step to the anaerobic digestion step, the sludge produced in the anaerobic digestion step is extracted. 6
A sludge heat treatment step of heat treatment at a temperature of 0 ° C. or higher, a sludge discharge step of solid-liquid separating the heat-treated sludge of the sludge heat treatment step and discharging the separated sludge to the outside of the system, and a separation separated in the sludge discharge step An anaerobic digestion method for organic waste liquid, comprising a separated liquid return step for returning a liquid to the anaerobic digestion step. 2. An anaerobic digestion means for methane-fermenting an organic effluent in the presence of sludge containing anaerobic microorganisms, and a solid for separating the effluent of the anaerobic digestion means into sludge and treatment liquid. In an anaerobic digester for organic waste liquid, which comprises a liquid separating means and a sludge returning means for returning the separated sludge of the solid-liquid separating means to the anaerobic digesting means, the anaerobic digesting means and / or the solid liquid Sludge heat treatment means for extracting sludge from the separation means and heat-treating it at a temperature of 60 ° C. or higher; sludge discharge means for solid-liquid separating the heat-treated sludge of the sludge heat treatment means and discharging the separated sludge out of the system; and the sludge. An anaerobic digester for organic waste liquid, comprising a separated liquid returning means for returning the separated liquid separated by the discharging means to the anaerobic digesting means. 3. An anaerobic digestion step in which organic effluent is subjected to methane fermentation in the presence of sludge containing anaerobic microorganisms, and a solid phase for separating the effluent of the anaerobic digestion step into sludge and treatment solution. In the method for anaerobic digestion of organic effluent, which comprises a liquid separation step and a sludge return step of returning the separated sludge of the solid-liquid separation step to the anaerobic digestion step, an organic substance fed to the anaerobic digestion step An anaerobic digestion method comprising a raw water heat treatment step of preliminarily heat-treating at least a part of the effluent at a temperature of 60 ° C. or higher. 4. The sludge heat treatment step according to claim 3, wherein sludge generated in the anaerobic digestion step is extracted and heat-treated at a temperature of 60 ° C. or higher, and the heat-treated sludge in the sludge heat treatment step is subjected to solid-liquid separation. Anaerobic organic wastewater characterized by having a sludge discharging step of discharging the separated sludge to the outside of the system, and a separated liquid returning step of returning the separated liquid separated in the sludge discharging step to the anaerobic digestion step. Digestion method. 5. An organic effluent is anaerobically digested by methane fermentation in the presence of sludge containing anaerobic microorganisms, and sludge produced in the anaerobic digester is extracted to be easily biodegradable. An anaerobic digester for an organic waste liquid, comprising: a reformer and a reformed sludge return unit for returning the reformed sludge modified by the reformer to the anaerobic digester. An anaerobic digestion apparatus comprising a raw water heat treatment means for preliminarily heat-treating at least a part of the organic waste liquid to be fed to the above. 6. The sludge heat treatment means for extracting sludge generated in the anaerobic digestion means and heat-treating it at a temperature of 60 ° C. or higher, and solid-liquid separation of the heat-treated sludge of the sludge heat treatment means according to claim 5. An anaerobic digester for organic waste liquid, comprising sludge discharge means for discharging the separated sludge to the outside of the system, and return means for returning the separated liquid separated by the sludge discharge means to the anaerobic digester means. .