JP4148286B2 - Method and apparatus for anaerobic digestion treatment of organic waste liquid - Google Patents

Description

  The present invention relates to a method and apparatus for anaerobic digestion of organic waste liquid, and in particular, an anaerobic digestion treatment method and apparatus for organic waste liquid capable of increasing the digestion efficiency of organic waste liquid and increasing the amount of methane gas recovered. About.

  A method for reducing the amount of sludge-like organic sludge such as organic sludge, human waste, and food factory wastewater by digestion in the presence of anaerobic microorganisms has been practiced for a long time.

  In such anaerobic digestion treatment, sludge (digested sludge) mainly composed of undegraded substances and anaerobic microorganisms is generated. This digested sludge is conventionally treated by incineration, landfill, etc. after mechanical dehydration.

  Japanese Patent Laid-Open No. 9-206785 describes a device that reduces the amount of sludge produced by anaerobic digestion and recovers more methane gas from organic waste liquid. An anaerobic digestion processing apparatus is described for returning quality sludge to an anaerobic digestion tank. In this equipment, digested sludge is treated with ozone to improve biodegradability, then returned to the anaerobic digester and further decomposed as a substrate for anaerobic microorganisms. The sludge is reduced and methane gas is discharged from organic waste liquid. It is an effective device to collect more.

  However, when this device is used for medium temperature anaerobic digestion, which is performed by heating the anaerobic digestion tank widely used for anaerobic digestion treatment of sewage sludge to 30-38 ° C, it is modified by ozone treatment. Since the digestion rate of the sludge was low, it was necessary to increase the amount of sludge to be modified in order to further reduce the sludge and increase the recovery rate of methane gas from the organic effluent, leading to an increase in the amount of ozone used .

  In addition, when this device is used for high-temperature anaerobic digestion, which is performed at a temperature of 45-60 ° C in an anaerobic digestion tank, which has a higher digestion rate than medium-temperature digestion, the amount of ozone used is higher than that of medium-temperature digestion. Although some of the proteins and sugars derived from the modified sludge are not degraded by enzymes produced by high-temperature microorganisms, soluble organic components that are not biodegradable in the tank are released at a significantly higher concentration than in the middle-temperature digestion. As a result, the solid organic component is reduced, but the methane gas recovery rate cannot be increased. In addition, these colloidal soluble organic components deteriorate the solid-liquid separability of digested sludge, significantly increase the amount of flocculant used, and significantly increase the load on the subsequent water treatment where the separated liquid is discharged. There was a problem to do.

In JP-A-2001-205289, after treating an organic waste liquid in a biological treatment tank, the treatment liquid is separated into solid and liquid, and the separated water is discharged as treated water, and the separated sludge is returned to the biological treatment tank. In a method for treating organic waste liquid that is partly or entirely solubilized and then returned, centrifugal force is used to convert sludge with a low percentage of organic suspended solids and sludge with a high percentage of organic suspended solids. Describes a method for treating organic waste liquid, which fractionates and discharges sludge with a low percentage of organic suspended solids out of the system and returns sludge with a high percentage of organic suspended solids to the biological treatment tank. Has been. In this method, since inorganic substances accumulated in the sludge in the biological treatment tank can be discharged out of the system preferentially, the waste liquid can be reduced without substantially reducing the proportion of organic substances in the sludge in the biological treatment tank. The amount of excess sludge generated can be stably reduced while maintaining the processing capacity.
JP-A-9-206785 JP 2001-205289 A

In the present invention, an organic waste liquid is subjected to an anaerobic digestion treatment in an anaerobic digestion tank, then the digested sludge is separated into solid and liquid, the separated liquid is discharged as treated water, and the separated sludge (concentrated sludge) is returned to the anaerobic digestion tank. In addition, in the anaerobic digestion method of organic waste liquid that reforms part of the digested sludge and returns it to the anaerobic digester, the inorganic substances accumulated in the anaerobic digester are more efficiently discharged out of the system. Accordingly, an object of the present invention is to provide an anaerobic treatment apparatus for organic waste liquid that can sufficiently reduce the amount of organic components and increase the amount of methane gas recovered even under high organic load.

The anaerobic digestion treatment apparatus for organic waste liquid of the present invention (Claim 1) is a treatment in which a high-temperature digestion tank having a treatment temperature of 45 to 95 ° C. and an effluent of the high-temperature digestion tank are introduced as the anaerobic digestion tank. Medium temperature digestion tank having a temperature of 25 to 40 ° C., reforming means for reforming a part of the digested sludge from the medium temperature digestion tank, and reforming for returning the reformed sludge from the reforming means to the high temperature digestion tank From the sludge return means, the solid-liquid separation means for concentrating the digested sludge from the intermediate temperature digester, the flocculant addition means for adding a flocculant to the liquid introduced into the solid-liquid separation means, and the solid-liquid separation means Concentrated sludge return means for returning the concentrated sludge to the intermediate-temperature digestion tank, a portion of the digested sludge from the intermediate-temperature digestion tank, sludge having a low ratio of organic suspended solids, and sludge having a high ratio of organic suspended solids And sludge fractionation means to discharge sludge with a low proportion of organic suspended solids out of the system An organic anaerobic wastewater having a high organic suspended solids sludge fractionated by the sludge fractionating means and returning a high organic suspended solids sludge having a high proportion of the organic suspended solids to the intermediate temperature digester It is an oxidative digestion processing apparatus, and an organic waste liquid is introduced only into the solid-liquid separation means.

  In the present invention, “sludge reforming” refers to modifying and destroying substances and sludge cells in sludge that are not easily assimilated by microorganisms to form them that are easily assimilated by microorganisms.

The organic waste liquid anaerobic digestion treatment apparatus of the present invention (Claim 2) is a treatment in which a high temperature digestion tank having a treatment temperature of 45 to 95 ° C. and an effluent of the high temperature digestion tank are introduced as the anaerobic digestion tank. Medium temperature digestion tank having a temperature of 25 to 40 ° C., reforming means for reforming a part of the digested sludge from the medium temperature digestion tank, and reforming for returning the reformed sludge from the reforming means to the high temperature digestion tank From the sludge return means, the solid-liquid separation means for concentrating the digested sludge from the intermediate temperature digester, the flocculant addition means for adding a flocculant to the liquid introduced into the solid-liquid separation means, and the solid-liquid separation means Concentrated sludge return means for returning the concentrated sludge to the intermediate-temperature digestion tank, a portion of the digested sludge from the intermediate-temperature digestion tank, sludge having a low ratio of organic suspended solids, and sludge having a high ratio of organic suspended solids And sludge fractionation means to discharge sludge with a low proportion of organic suspended solids out of the system An organic anaerobic wastewater anaerobic solution having high organic suspended solids sludge fractionated by the sludge fractionating means and returning high organic suspended solids sludge having a high proportion of organic suspended solids to the intermediate temperature digester It is a sexual digestion processing apparatus, Comprising: An organic waste liquid is introduce | transduced only into both the said intermediate temperature digestion tank and a solid-liquid separation means.

Anaerobic digestion apparatus of the organic wastewater according to claim 3, in claim 1 or 2, reforming treatment by the reforming means is characterized in that an ozone treatment.

The anaerobic digestion treatment apparatus for organic waste liquid according to claim 4 is characterized in that, in any one of claims 1 to 3 , a part of sludge from the intermediate-temperature digestion tank is introduced into the sludge fractionation apparatus. It is what.

The organic anaerobic digestion treatment method of the present invention (Claim 5 ) uses the anaerobic digestion apparatus of any one of Claims 1 to 4 .

  In an anaerobic digester, organic waste liquid is subjected to methane fermentation in the presence of sludge containing anaerobic microorganisms. In the present invention, the anaerobic digester is composed of at least two tanks, a high-temperature digester with a treatment temperature of 45 to 95 ° C. and a medium-temperature digester with a treatment temperature of 25 to 40 ° C. into which the effluent of the high-temperature digester is introduced. ing. Organic components in the waste liquid are liquefied by high-temperature anaerobic microorganisms having an optimum temperature around 55 ° C. and medium-temperature anaerobic microorganisms having an optimum temperature around 35 ° C. It is converted to methane gas through the steps of organic acid production → methane production.

  In the high-temperature digestion tank, as described above, although the decomposition of the solid organic component proceeds more rapidly than the intermediate-temperature digestion, much remains as a colloidal soluble organic component. Since these colloidal organic components can be decomposed by mesophilic microorganisms, the remaining soluble organic components are also converted into methane gas by introducing the effluent of the high-temperature digester into the intermediate-temperature digester. Therefore, according to the present invention, the solid organic component can be decomposed at a high digestion rate in the high-temperature digester, and the conversion to methane gas can be promoted in the intermediate-temperature digester.

In the present invention, a part of the sludge from the intermediate temperature digester, gravity settling, such as by centrifugation, fractionated and low proportion of organic suspended solids sludge, with high organic suspended solids sludge min, organic suspended Return sludge with a high proportion of material to an anaerobic digester and discharge sludge with a low proportion of organic suspended solids outside the system.

In general, the density of microorganisms, which are the main components of organic matter constituting sludge, is slightly higher than 1.0 g / m ³ , whereas the earth and sand components, SiO ₂ and Al, which are the main components of inorganic components, are used. The density of ₂ O ₃ is about _{2 to 4} g / m ³ . Therefore, digested sludge is introduced into a centrifuge and the centrifugal force generated by high-speed rotation is used to make sludge with a high proportion of sediment and other organic suspended solids to microorganisms and vice versa. It can be fractionated into sludge with a high ratio.

By discharging the sludge having a low proportion of organic suspended solids thus obtained out of the system, accumulation of inorganic substances in the anaerobic digester is prevented. Also, sludge with a high proportion of organic suspended solids is returned to the anaerobic digester. As a result, digested sludge having a high proportion of organic suspended solids is efficiently digested in the anaerobic digester, so that excess sludge is sufficiently reduced and a large amount of methane gas is recovered.

  Thus, according to the method and apparatus for anaerobic digestion of the organic waste liquid of the present invention, the efficiency of the anaerobic digestion is increased, and even when the organic load is higher than conventional, the heating energy and the amount of the flocculant used are reduced. Without increasing the amount, the organic components can be greatly reduced and a large amount of methane gas can be recovered.

Digested sludge is introduced into the sludge fraction apparatus, Ru der those withdrawn or Atsushi Naka digester al. In medium-temperature digester, the solubility organic components remaining in the high temperature digester is converted removed methane gas, the required amount of flocculant in the subsequent dehydration treatment, compared with the case of fractionation hot digested sludge Can be reduced.

High proportion of organic suspended solids fractionated by sludge fractionator sludge is returned to the medium-temperature digester.

In the present invention may be an organic wastewater introduced into the mesophilic digester and solid-liquid separation means.

In the present invention, at least a part of the organic waste liquid is introduced into the solid-liquid separation means, so that the digestive sludge from the intermediate temperature digester is diluted with the organic waste liquid, so that the flocculant becomes effective. Moreover, the amount of treated sludge in the solid-liquid separation means can be reduced. The solid-liquid separation by this solid-liquid separation means is performed in order to keep the liquid level in the digestion tank constant (so as not to overflow) when introducing the organic waste liquid into the treatment system. It is necessary to discharge separation water (solid-liquid separation treated water) having the same volume as the effluent from the solid-liquid separation means. Generally, the SS concentration of organic waste liquid is lower than the SS concentration of digested sludge. Therefore, when separating the mixed liquid of organic waste liquid and digested sludge by solid-liquid separation and taking out the separated water in the same volume as the amount of organic waste liquid introduced, the separated water is separated into the organic waste liquid by solid-liquid separation of only the digested sludge. The amount of sludge to be treated by the solid-liquid separation means is smaller than in the case where the same volume as the amount introduced is taken out. This makes it possible to employ a smaller apparatus as the solid-liquid separation means. Moreover, since the amount of sludge to be processed is small, it contributes to energy saving.

  Further, the solid-liquid separation device may be used as the sludge fractionation device, and the operation may be divided into when solid-liquid separation is performed and when sludge fractionation is performed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

First, a reference example and the flow of the present invention will be described with reference to FIGS. 1 to 6 show reference examples, and FIGS. 7 and 8 are system diagrams showing embodiments of an organic anaerobic digestion treatment method and apparatus of the present invention, respectively. In FIGS. The same symbols are attached to the members to be played.

[Anaerobic digestion treatment equipment for organic waste liquid in Fig. 1]
In FIG. 1, organic sludge (organic waste liquid) is introduced into the high-temperature digestion tank 1 and subjected to anaerobic digestion at 45 to 95 ° C. A part of the digested sludge in the high-temperature digester 1 is introduced into the intermediate-temperature digester 2 and subjected to anaerobic digestion at 25 to 40 ° C. A part of the digested sludge in the intermediate temperature digester 2 is extracted and concentrated by the solid-liquid separator 3. The liquid component from the solid-liquid separator 3 is taken out of the system. The concentrated sludge is returned to the intermediate temperature digester 2 through the return pipe 4.

  Further, a part of the digested sludge from the intermediate temperature digester 2 is pulled out by the pipe 5 and reformed by the reformer 6. The modified sludge is returned to the high temperature anaerobic digester 1 through the return pipe 7.

In this reference example , the remainder of the digested sludge from the high-temperature digester 1 is introduced into the sludge fractionator 10 via the pipe 9, and the sludge having a low ratio of organic suspended solids and organic matter are separated by gravity sedimentation, centrifugation, etc. It is fractionated into sludge with a high concentration of volatile suspended solids. Then, sludge having a high ratio of organic suspended solids is returned to the high-temperature digestion tank 1 through the pipes 11 and 7, and sludge having a low ratio of organic floating substances is discharged out of the system. The sludge may be returned to the high temperature digester 1 only through the pipe 11. As the sludge fractionating device 10, a centrifugal separator is preferable in terms of fractionation effect.

As described above, the density of microorganisms, which are the main components of the organic matter constituting the sludge, is slightly higher than 1.0 g / m ³ , whereas the earth and sand components, SiO ₂ and Al, which are the main components of the inorganic content. The density of ₂ O ₃ is about _{2 to 4} g / m ³ , and the sludge fractionator 10 makes sludge having a high ratio of sediment components and low organic suspended solids to microorganisms, and vice versa. It can be fractionated into sludge with a high proportion of suspended solids.

  When a centrifugal separator is used as the sludge fractionator 10, the processing flow rate, processing time, and centrifugal force applied in the centrifugal separator are appropriately set according to the concentration of sludge to be introduced, the ratio of inorganic substances, etc., and are not particularly limited. . Moreover, a batch type or a continuous type may be sufficient.

Since the sludge of the modified intermediate temperature digester is processed in the high temperature digester 1, the ratio of organic suspended solids in the sludge is generally lower than that of the intermediate temperature digester 2. Therefore, when the sludge in the high-temperature digestion tank 1 is fractionated as in this reference example , sludge with a lower ratio of organic suspended solids is easily obtained, and the moisture content of the cake in the subsequent dehydration treatment is reduced. The amount of cake to be disposed of can be reduced.

  In addition, it is preferable to return the sludge fractionated by the sludge fractionation apparatus 10 to the high-temperature digestion tank 1 from which the sludge has been extracted, but both the high-temperature digestion tank 1 and the intermediate-temperature digestion tank 2 are used. You may return it to

  The sludge fractionated by the sludge fractionator 10 and having a low ratio of organic suspended solids is drawn out of the system as excess digested sludge via the pipe 12. The excess digested sludge is preferably extracted so as to maintain the sludge (TS) concentration in the digesters 1 and 2 at 2 to 12%, particularly 4 to 8%.

[Anaerobic digestion treatment equipment of organic waste liquid of FIGS. 2-4]
In FIG. 2, the organic waste liquid is supplied to the intermediate temperature digester 2, and only the reformed sludge from the reformer 6 and the highly organic suspended solids sludge from the sludge fractionator 10 are introduced into the high temperature digester 1. Yes. The other structure is the same as that of FIG. 1, and the same code | symbol has shown the same part.

  In FIG. 3, the organic waste liquid is supplied to both the intermediate temperature digester 2 and the solid-liquid separator 3, and in FIG. 4, the organic waste liquid is supplied to the solid-liquid separator 3. The other structure is the same as that of FIG. 1, and the same code | symbol has shown the same part.

[Anaerobic digestion treatment equipment of organic waste liquid of FIGS. 5-8]
5 to 8, a part of the intermediate temperature digested sludge sent from the intermediate temperature digester 2 to the reformer 6 is introduced into the sludge fractionator 10. The high organic soluble suspended solids sludge fractionated in the sludge fraction 10 is returned to the mesophilic digester 4 via a pipe 11, 4.

  FIGS. 5 to 8 correspond to FIGS. 1 to 4, respectively. In FIG. 5, the organic waste liquid is introduced into the high temperature digestion tank 1, in FIG. 6, the organic waste liquid is introduced into the intermediate temperature digestion tank 2, and in FIG. The organic waste liquid is introduced into both the intermediate-temperature digestion tank 2 and the solid-liquid separator 3, and the organic waste liquid is introduced into the solid-liquid separator 3 in FIG.

  Other configurations are the same as those in FIGS.

Generally, in the intermediate temperature digestion tank 2, soluble organic components remaining in the high temperature digestion tank 1 are converted to methane gas and removed. Thus, the sludge by sending a portion of the digested sludge from the mesophilic digester 2 into sludge fraction 10, the required amount of flocculant in the dewatering process in the solid-liquid separator 3, the sludge from the hot digestion tank 1 This can be reduced compared to the case where the image is sent to the fractionation device 10 for fractionation processing.

The sludge having a high organic suspended solid fraction fractionated by the sludge fractionator is returned to the intermediate temperature digestion tank 2 from which the sludge has been extracted .

[Treatment waste liquid]
The organic waste liquid to be treated in the present invention is a waste liquid containing an organic substance that is reduced by anaerobic digestion treatment, and may be a slurry containing a solid or a liquid containing no solid. . In addition, non-biodegradable organic substances, inorganic substances, cellulose, paper, cotton, wool, cloth, solid matter in human waste may be contained. Examples of such organic waste liquid include sewage, sewage initial sedimentation sludge, human waste, septic tank sludge, wastewater and residue from food factories, beer waste yeast, other industrial waste liquids, and surplus sludge generated when these waste liquids are treated. Natural sludge.

[Configuration of digesters 1 and 2]
In the high-temperature digestion tank 1 and the intermediate-temperature digestion tank 2, such organic waste liquid is treated by methane fermentation in the presence of sludge containing anaerobic microorganisms. Sludge containing anaerobic microorganisms contains acid-producing bacteria and methanogens. In the anaerobic digestion process, organic substances are converted to methane gas and processed by anaerobic microorganisms through the steps of liquefaction → low molecular weight → organic acid production → methane production.

  In the high-temperature digestion tank 1, high-temperature methane-producing bacteria having an optimum temperature around 55 ° C. are mainly held, and in the intermediate-temperature digestion tank 2, medium-temperature methane-producing bacteria having an optimum temperature around 35 ° C. are mainly held. Since mesophilic methanogens grow slowly, it is necessary to lengthen the SRT, that is, to increase the size of the anaerobic digester. However, since treatment at a relatively low temperature is possible, facilities for warming and heat insulation are simplified. be able to. On the other hand, in the case of a high-temperature methanogen, heating and heat insulation facilities are required, but since the growth is fast, the SRT may be short, and the anaerobic digester can be made small.

  The high-temperature digestion tank 1 is heated so that the inside of the tank reaches the above temperature by blowing steam, introducing hot water, circulating sludge to the heat exchanger, and the like. The intermediate temperature digestion tank can maintain the temperature in the tank at the above-mentioned value by introducing the effluent of the high temperature digestion tank and the organic waste liquid, but may be heated or cooled.

  The sludge residence time (SRT) in the anaerobic digester is 5 days or more, preferably 10-30 days in the high-temperature digester 1, and is 10 days or more, preferably 15-50 days in the medium-temperature digester 2. The SS concentration in each anaerobic digester 1 and 2 is 20,000 to 120,000 mg / L (2 to 12%), preferably 40,000 to 80,000 mg / L (4 to 8%).

  Note that the longer the SRT, the higher the sludge decomposition rate, but the larger the tank capacity. As the SS concentration in the digestion tank is increased, the amount of sludge to be reformed increases even in the same residence time and the decomposition rate increases, but stirring and mixing in the tank and solid-liquid separation of sludge become difficult.

[Configuration of Solid-Liquid Separator 3]
The solid-liquid separation device 3 for concentrating the digested sludge may be any device capable of concentrating the digested sludge by solid-liquid separation, such as a centrifugal separator, a flotation separator, a sedimentation tank, a membrane separator, and filtration. Although an apparatus etc. can be used, a centrifuge is preferable.

  The daily withdrawal amount of the digested sludge extracted from the intermediate temperature digester 2 to the solid-liquid separator 3 is preferably about 1/60 to 1/10 of the retained sludge in the intermediate temperature digester 2.

  In addition, it is preferable to operate the solid-liquid separation device 3 in a state cut off from the atmosphere. For example, when the contact between the sludge and oxygen is restricted by concentrating the concentrator in a sealed state, the anaerobic bacteria are utilized. It can be returned to the anaerobic digestion tank as it is, and it becomes easy to maintain and increase the number of viable bacteria in the anaerobic digestion tank, thereby improving the digestion efficiency.

In the present invention, a flocculant, preferably a polymer flocculant, is added to the digested sludge from the intermediate temperature digester 2 and then introduced into the solid-liquid separator 3. Thus, by adding the flocculant and aggregating the SS component in the digested sludge, the concentration factor in the solid-liquid separator 3 can be increased, and a clear separation liquid can be obtained. Moreover, the outflow of the solid content from the solid-liquid separator 3 can be suppressed, and the reduction of sludge organic components and the conversion to methane gas can be promoted.

  The soluble organic components remaining in the high-temperature digester increase the amount of flocculant added necessary for solid-liquid separation, but these soluble organic components are converted to methane gas and removed in the intermediate-temperature digester. Therefore, the digested sludge from the intermediate temperature digester 2 can be satisfactorily coagulated without increasing the amount of the flocculant added so much.

  In order to enhance the effect of this flocculation treatment, a mixing tank is provided in the front stage of the solid-liquid separator 3, and a flocculant is added to this mixing tank or to the digested sludge flowing into this mixing tank. Good.

  As the flocculant, either organic or inorganic, or both of them may be used. However, since the addition amount may be small and it is difficult to decompose and accumulate in the digester, organic polymer aggregation Agents, particularly cationic or amphoteric polymer flocculants are preferred.

  The degree of concentration of digested sludge in the solid-liquid separator 3 depends on the performance of the concentrator used, but usually digested sludge having a TS (solid matter) concentration of about 4 to 8% is paste-like about 8 to 20%. It is preferable that the liquid is concentrated to a highly viscous liquid.

  The concentrated separation liquid of the solid-liquid separation device 3 can be discharged as treated water as it is to a sewer or the like, but may be discharged after aerobic biological treatment or other post-treatment.

Concentrated sludge at the time of solid-liquid separation, return to Atsushi Naka digester 2. By returning to the intermediate-temperature digestion tank 2, the sludge residence time of the intermediate-temperature digestion tank 2 can be lengthened, and the intermediate-temperature anaerobic microorganisms with slow growth can be maintained in the tank.

Also, as in the fifth to eighth view, to concentrate digested sludge is returned to the mesophilic digester 2, it is returned to the mesophilic digester by mixing a high organic soluble suspended solids sludge from the sludge fractionator Although it is preferable, it may be separately introduced into the intermediate temperature digester 2.

The concentrated sludge may be mixed with the organic waste liquid , clean water, industrial water, biological treatment water of other organic waste liquid, etc., and then returned to the intermediate temperature digester.

  The digested sludge taken out from the intermediate temperature digester 2 and sent to the solid-liquid separator 3 is part of the organic waste liquid supplied to this device (anaerobic digester) as shown in FIGS. 4 and 8, after mixing and diluting with all of the organic waste liquid supplied to this device, solid-liquid separation is performed, and the concentrated sludge containing the solid content in the organic waste liquid is put into the anaerobic digester. You may return it. By diluting the digested sludge with the organic waste liquid, the flocculant becomes effective, and the amount of the treated sludge in the solid-liquid separator 3 can be reduced.

  In order to prevent the accumulation of inorganic components and hardly biodegradable organic components in the digestion tanks 1 and 2, the low-organic suspended solids sludge of the sludge fractionator 10 is discharged out of the system. A part of the digested sludge of the 1 or the intermediate temperature digester 2 and the concentrated sludge of the solid-liquid separator 3 may be discharged as surplus digested sludge and disposed of such as dehydration, incineration, and landfill.

[Configuration of reformer 6]
In the reformer 6, the anaerobic digested sludge extracted from the digester 2 is reformed by ozone treatment, heat treatment, milling, acid / alkali treatment, or the like. By performing such a modification treatment, the cells in the anaerobic digested sludge are killed and modified to be readily biodegradable together with other hardly decomposable organic components. By digesting these readily biodegradable components in the anaerobic digester, more organic components are reduced from the treatment system, and methane gas is recovered.

When an ozone treatment device is employed as the reforming device, the ozone treatment device is modified by bringing digested sludge from the intermediate temperature digestion tank 2 into contact with ozone. The pH of the ozone treatment is 4 to 10, and the amount of ozone used is usually 0.01 to 0.08 g-O ₃ / g-VSS, preferably 0.02 to 0.05 g-O per digested sludge treated with ozone. ₃ / g-VSS is preferable.

  The amount of digested sludge to be modified per day is 1/10 or less, preferably 1/100 to 1/15, more preferably 1 of the total amount of organic solids (VSS) in the high-temperature digester 1 and the intermediate-temperature digester 2. An amount corresponding to / 50 to 1/30 is preferable. By setting the amount of modification treatment per day to such an amount, the amount of microorganisms necessary for anaerobic digestion treatment can be maintained in the digestion tanks 1 and 2, and the efficiency of the anaerobic digestion treatment can be kept high. it can.

In addition, although the decomposability improves as the amount of ozone used is increased, it gradually reaches a peak (not doubled when doubled), so 0.02 to 0.05 g-O ₃ / g- VSS is efficient. In addition, as the amount of sludge to be modified increases, the amount of feed that undergoes biodegradation increases. At the same time, the amount of microorganisms that decompose the feed decreases, so the sludge decomposition rate as a whole has a peak within a certain range. Further, since the ozone consumption per degraded sludge amount is smaller as the reforming treatment amount is smaller, it may be more efficient to reduce the reforming treatment amount even if the decomposition rate is somewhat lowered.

In the present invention, the digested sludge to be modified is extracted from the intermediate temperature digester 2 . In the intermediate temperature digestion tank 2, the soluble organic components remaining in the high temperature digestion tank 1 are decomposed to reduce the amount of biodegradable organic components. Can be done.

Sludge after reforming, as each figure, it returns to the high temperature digester 1. By returning to the high-temperature digestion tank 1, the reformed sludge can be quickly decomposed by high-temperature digestion with a digestion rate higher than the intermediate temperature.

  In the present invention, the modification treatment is not limited to an ozone treatment apparatus, and any treatment can be used as long as it can denature and destroy sludge cells and can be modified to a form that is easily assimilated by microorganisms. In addition, various methods such as chemical treatment with strong oxidizing power such as hydrogen peroxide, chemical treatment with acid, alkali, etc., ultrasonic treatment, physical treatment such as grinding with mill, thermal treatment, etc. It can be employed alone or in combination of two or more.

[Configuration of Sludge Fractionation Device 10]
The sludge fractionation apparatus 10 fractionates the sludge extracted from the anaerobic digestion tank into sludge having a low ratio of organic suspended solids and sludge having a high organic suspended solid content by gravity sedimentation, centrifugation, etc. Is a device that returns sludge having a high proportion of volatile suspended matter to an anaerobic digester and discharges sludge having a low proportion of organic suspended matter to the outside of the system, and a centrifugal separator is preferred in terms of fractionation effect.

  The processing flow rate, processing time, and centrifugal force applied in the centrifuge are appropriately set depending on the concentration of sludge to be introduced, the ratio of inorganic substances, and the like, and are not particularly limited. The centrifuge may be a batch type or a continuous type.

  Further, the solid-liquid separation device may be used as the sludge fractionation device, and the operation may be divided into when solid-liquid separation is performed and when sludge fractionation is performed.

  In the present invention, the digestion gas (methane gas) generated in the anaerobic digester is effectively used, and part or all of the power required for heating the digester, reforming means, operation of the sludge fractionator, etc. It is also preferable to cover.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

[ Comparative Example 1]
As organic waste liquid, mixed raw sludge (average TS concentration 40 g / L, TVS / TS ratio 0.83) collected from the sewage treatment plant is used, and the volume of the high-temperature digester 1 and the intermediate-temperature digester 2 is as follows. Each was 0.9 m ^{3, and the} solid-liquid separation device 3 was a centrifuge.

  High temperature digested sludge and medium temperature digested sludge collected from the anaerobic digester of the sewage treatment plant were used as seed sludge for the digesters 1 and 2, respectively.

  After operating for about 6 months, the concentration in the tank became almost constant, and the system was considered to have reached a steady state. Table 1 shows the operation results for the subsequent six months.

High temperature digester 1 temperature: 53 ° C
Medium temperature digester 2 temperature: 37 ° C
Input sludge amount: 60 L / day (add half amount to high temperature digester 1 and medium temperature digester 2)
Reformer 6: Ozone treatment device Ozone concentration: 150mg / NL
Ozone treatment sludge amount: 36L / day
Ozone reaction rate: 0.03 g-O ₃ / g-TVS
Solid-liquid separation: Cationic polymer dissolved in 0.2% in sludge extracted from the intermediate temperature digester 2
The SS concentration of the supernatant after centrifugation is 1,000 mg / L or less.
And centrifuged about 2.5 times with a centrifugal force of 2,000 G. This separation liquid
Was discharged out of the system. The rest (concentrated sludge) was returned to the intermediate temperature digester 2.

Extraction of digested sludge: Sludge fractionator 1 so that the TS concentration in the intermediate temperature digester 2 does not exceed 6%
0 concentrated sludge (low organic suspended solids sludge) is appropriately pulled from the pipe 12
I pulled it out.

Dewatering of drawn sludge: For diluted sludge diluted 5 times with secondary sewage water
Then, a cationic polymer dissolved in 0.2% is added as appropriate to obtain a surface pressure.
Used for compression dehydration test under conditions of 9.8 kPa and pressing time 5 min.
The water content of the dehydrated cake was determined.

[Example 1]
Using the apparatus shown in FIG. 8, a portion of the digested sludge from the intermediate temperature digester 2 is fractionated with a sludge fractionator (same centrifuge as in Example 1. Same as centrifugal reduction and concentration ratio) 10 and concentrated. other sludge (high organic soluble suspended solids sludge) was then supplied to the mesophilic digester 2 was treated the same organic wastewater in Comparative example 1 under the same conditions (mixed raw sludge).

[Comparative Example 2]
The high organic soluble suspended solids sludge from centrifugal concentrator 20 of the apparatus (as sludge fractionator 9, return the concentrated sludge after solid-liquid separation in each digester 1A. The other flows and FIG. 5 Identical), both digesters 1A and 2A were maintained at 37 ° C. Other conditions were the same as those in Comparative Example 1.

[Comparative Example 3 ]
In Comparative Example 2 , both digesters 1 and 2 were maintained at 53 ° C. Other conditions were the same as those in Comparative Example 1.

  Table 1 shows the operation results for about 6 months when the system seems to have reached the steady state after operating for about 6 months using the digested sludge collected from the sewage treatment plant as the seed sludge for each digestion tank 1 and 2. Show.

In addition, the digestibility in Table 1 is (1−drawn sludge amount / input sludge amount) × 100%.

[Discussion]
As shown in Table 1, in Comparative Example 1 and Example 1 , a high digestibility and methane gasification rate can be obtained with a smaller amount of ozone used than in Comparative Example 2, and compared with Comparative Example 3 , A high methane gasification rate was obtained with a low coagulant addition rate during dehydration.

Reference Example anaerobic digestion apparatus organic wastewater is a system diagram showing a. Reference Example anaerobic digestion apparatus organic wastewater is a system diagram showing a. Reference Example anaerobic digestion apparatus organic wastewater is a system diagram showing a. Reference Example anaerobic digestion apparatus organic wastewater is a system diagram showing a. Reference Example anaerobic digestion apparatus organic wastewater is a system diagram showing a. Reference Example anaerobic digestion apparatus organic wastewater is a system diagram showing a. It is a systematic diagram which shows embodiment of the anaerobic digestion processing apparatus of the organic waste liquid of this invention. It is a systematic diagram which shows embodiment of the anaerobic digestion processing apparatus of the organic waste liquid of this invention. It is a systematic diagram which shows the anaerobic digestion processing apparatus of the organic waste liquid of the comparative examples 2 and 3. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 High temperature digestion tank 2 Medium temperature digestion tank 3 Solid-liquid separation device 6 Reformers, such as an ozone treatment device 10 Sludge fractionation device

Claims (5)

As the anaerobic digester, a high-temperature digester with a treatment temperature of 45 to 95 ° C and a medium-temperature digester with a treatment temperature of 25 to 40 ° C into which the effluent of the high-temperature digester is introduced,
Reforming means for reforming a part of the digested sludge from the intermediate temperature digester,
Modified sludge return means for returning the modified sludge from the reforming means to the high-temperature digestion tank;
Solid-liquid separation means for concentrating the digested sludge from the intermediate temperature digester,
A flocculant addition means for adding a flocculant to the liquid introduced into the solid-liquid separation means;
Concentrated sludge return means for returning the concentrated sludge from the solid-liquid separation means to the intermediate temperature digestion tank;
A portion of the digested sludge from the medium temperature digestion tank is divided into sludge having a low ratio of organic suspended solids and sludge having a high ratio of organic suspended solids, and sludge having a low ratio of organic suspended solids is excluded from the system. Sludge fractionation means to be discharged into
High organic suspended solids sludge return means for returning high organic suspended solids sludge having a high proportion of organic suspended solids fractionated by the sludge fractionating means to the intermediate temperature digester,
An anaerobic digestion treatment apparatus for organic waste liquid having
An organic waste liquid anaerobic digestion treatment apparatus, wherein the organic waste liquid is introduced only into the solid-liquid separation means. As the anaerobic digester, a high-temperature digester with a treatment temperature of 45 to 95 ° C and a medium-temperature digester with a treatment temperature of 25 to 40 ° C into which the effluent of the high-temperature digester is introduced,
Reforming means for reforming a part of the digested sludge from the intermediate temperature digester,
Modified sludge return means for returning the modified sludge from the reforming means to the high-temperature digestion tank;
Solid-liquid separation means for concentrating the digested sludge from the intermediate temperature digester,
A flocculant manual addition stage for adding the flocculant to the liquid introduced into the solid-liquid separation means;
Concentrated sludge return means for returning the concentrated sludge from the solid-liquid separation means to the intermediate temperature digestion tank;
A portion of the digested sludge from the medium temperature digestion tank is divided into sludge having a low ratio of organic suspended solids and sludge having a high ratio of organic suspended solids, and sludge having a low ratio of organic suspended solids is excluded from the system. Sludge fractionation means to be discharged into
High organic suspended solids sludge return means for returning high organic suspended solids sludge having a high proportion of organic suspended solids fractionated by the sludge fractionating means to the intermediate temperature digester,
An anaerobic digestion treatment apparatus for organic waste liquid having
An apparatus for anaerobic digestion of organic waste liquid, wherein the organic waste liquid is introduced only into both the intermediate temperature digestion tank and the solid-liquid separation means.   3. The organic waste liquid anaerobic digestion apparatus according to claim 1, wherein the reforming process by the reforming means is an ozone process.   The sludge fractionation device according to any one of claims 1 to 3, wherein the sludge fractionation device is a device for fractionating into sludge having a low ratio of organic suspended solids and sludge having a high ratio of organic suspended solids using centrifugal force. An apparatus for anaerobic digestion of organic liquid waste, characterized by being.   An anaerobic digestion treatment method for organic waste liquid using the anaerobic digestion treatment apparatus according to any one of claims 1 to 4.

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