JP2005199258A - Anaerobic digestion treatment apparatus of organic waste solution - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To raise a sludge volume reducing ratio by performing efficient digestion by concentrating digested sludge of an organic waste solution, solubilizing the digested sludge while returning the concentrated sludge to an anaerobic digestion tank and returning the solubilized sludge to the anaerobic digestion tank. <P>SOLUTION: The concentrated sludge is mixed with the solubilized sludge at a suction side of a transfer pump 4 for transferring the concentrated sludge and is adjusted with respect to its concentration and then is returned to the anaerobic digestion tank 1. While performing efficient concentration by raising a concentration ratio of the digested sludge, the concentrated sludge is smoothly returned and further the returned concentrated sludge can be sufficiently dispersed in the anaerobic digestion tank to perform efficient digestion. Thus, the sludge volume reducing ratio can be raised. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an apparatus for anaerobically digesting organic waste liquid, and more particularly to an anaerobic digestion apparatus for organic waste liquid for increasing the digestion efficiency of organic waste liquid and greatly reducing sludge.

  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. However, although the conventional anaerobic digestion method requires a long residence time of 10 days or more, the digestibility (removal rate of organic components) remains at 35 to 50%, and sludge is reduced. There is a problem that the rate is low.

  In order to solve these problems, JP-A-9-206785 discloses an organic anaerobic digestion treatment in an anaerobic digestion tank, then the digested sludge is solid-liquid separated and the separated solution is discharged as treated water. There is an anaerobic digestion method for organic waste liquid that returns the separated sludge (concentrated sludge) to the anaerobic digester, and modifies the digested sludge by ozone treatment and returns it to the anaerobic digester. Has been described. In this method, digested sludge is separated into solid and liquid, and the separated sludge is returned to the anaerobic digestion tank 1 to secure the residence time of the anaerobic microorganisms, and the other part of the digested sludge is treated with ozone to facilitate easy living. After being modified to be degradable and returned to the anaerobic digestion tank, it can be decomposed again as a substrate for anaerobic microorganisms to increase the digestibility (sludge reduction rate).

  In this method, in order to increase the amount of digested sludge (digested sludge containing anaerobic microorganisms) modified by ozone treatment while maintaining the residence time of anaerobic microorganisms, the sludge concentration in the anaerobic digester is It is necessary to increase the operation to 4 to 8% compared to 1 to 2% in the conventional transient anaerobic digestion method.

  By the way, in this method, a centrifugal concentrator is usually used for solid-liquid separation of the digested sludge. However, in order to efficiently perform the centrifugal concentration of the digested sludge, the concentration rate of the digested sludge is high, for example, 2 times. It is preferable to operate as described above. In other words, if the concentration ratio is low, the throughput of the centrifugal concentrator required to obtain a certain amount of separation liquid increases remarkably, so a larger concentrator is required or the operation time of the concentrator is lengthened. There is a need or more coagulant is needed. In addition, in order to adjust the concentration by the concentrator to a desired concentration ratio, a high degree of operation technology is required, and there is a problem that it cannot be stably concentrated to a desired concentration if there is a change in conditions. Therefore, the concentration by the concentrator is preferably performed at a high concentration factor that matches the performance of the concentrator. On the other hand, since digested sludge is relatively easy to concentrate, high-concentration sludge having a TS concentration of 10% or more can be obtained by concentration.

  However, when the concentration factor is increased to increase the concentration of the concentrated sludge, the viscosity of the sludge increases exponentially with respect to the sludge concentration, and thus the viscosity of the concentrated sludge increases remarkably. As a result, it becomes difficult to return the concentrated sludge to the anaerobic digestion tank, or a pump with high power (discharge pressure) is required to transfer the concentrated sludge, or the returned concentrated sludge is anaerobically digested. There was a problem that it could not be sufficiently dispersed in the tank and the efficiency of the digestion process was lowered.

  In particular, in the method using the digested sludge solubilization treatment in combination, as described above, the sludge concentration in the anaerobic digestion tank needs to be increased to 4 to 8%, which is higher than in the case of the normal anaerobic digestion method. In this way, when the concentration of sludge in the anaerobic digester is increased to 4-8%, the concentration of concentrated sludge is very high at 8-16% when the concentration factor is increased to 2 times or more, for example. As a result, the viscosity of the concentrated sludge becomes remarkably high, and it becomes even more difficult to return the concentrated sludge to the anaerobic digester and to disperse the returned concentrated sludge in the anaerobic digester.

  In addition, the digested sludge in an anaerobic digester contains reducing inorganic substances such as sulfides, divalent iron, and manganese. Therefore, when modifying digested sludge by ozone treatment, it is difficult to decompose organic components. There is also a problem that ozone to be used for reforming is consumed for the oxidation of these reducing inorganic substances.

In addition, organic components in digested sludge are decomposed and reduced by cyclic treatment of reforming and digestion, while inorganic components in sludge are not reduced, so they accumulate in an anaerobic digester and increase sludge concentration. There was also a problem of making it happen. As the sludge concentration increases, the viscosity of the sludge increases, which hinders stirring of the anaerobic digester, reforming of the digested sludge, solid-liquid separation, and the like. Therefore, in order to maintain the sludge concentration in the anaerobic digestion tank within a certain range, the sludge in the anaerobic digestion tank is extracted and discharged, but at that time, not only the inorganic components that are not decomposed but also can be decomposed originally. Organic components are discharged out of the system, and this is a cause of hindering further improvement in digestibility (sludge reduction rate).
JP-A-9-206785

  The present invention solves the above-mentioned conventional problems, and when digesting sludge is solubilized and solubilized sludge is returned, concentrated digested sludge is concentrated and concentrated sludge is returned, and anaerobic digestion treatment is performed. The concentrated sludge can be returned smoothly while efficiently concentrating at a high magnification, and the returned sludge is fully dispersed in an anaerobic digester to efficiently digest the sludge. It aims at providing the anaerobic digestion processing apparatus of the organic waste liquid which makes a weight loss rate high.

  Another object of the present invention is to provide an anaerobic digestion treatment apparatus for organic waste liquid that can increase the ozone utilization rate in ozone treatment as a solubilization means for digested sludge and can efficiently reform sludge. To do.

  The present invention also prevents the accumulation of inorganic components in the system to increase the digestion efficiency, further increase the sludge weight loss rate, and discharges the extracted sludge having excellent dewatering properties, thereby improving its treatment efficiency and handleability. An object of the present invention is to provide an anaerobic digestion treatment apparatus for organic waste liquid.

  The apparatus for anaerobic digestion of an organic waste liquid according to claim 1 comprises an anaerobic digester for anaerobically digesting the organic waste liquid, a solubilizing means for solubilizing digested sludge extracted from the anaerobic digester, and Returning means for returning the solubilized sludge from the solubilizing means to the anaerobic digester, and solid-liquid separation means for concentrating the digested sludge discharged from the anaerobic digester (hereinafter referred to as “concentrator”). ), A pipe having a transfer pump for returning the concentrated sludge from the solid-liquid separation means to the anaerobic digester, and a liquid supply means for adding liquid to the concentrated sludge on the suction side of the transfer pump or the transfer pump It is characterized by having.

  In the present invention, “sludge solubilization” refers to denatured and destroyed sludge substances and sludge cells that are not easily assimilated by microorganisms to form a form that is easily assimilated by microorganisms.

  The organic waste liquid anaerobic digestion treatment apparatus according to claim 2 is characterized in that, in claim 1, the liquid added to the concentrated sludge is the solubilized sludge.

  The organic waste liquid anaerobic digestion treatment apparatus according to claim 3 is characterized in that, in claim 1 or 2, the solubilizing means is an oxidation treatment means.

  The anaerobic digestion treatment apparatus for organic waste liquid according to claim 4 is characterized in that, in claim 3, the anaerobic digestion sludge extracted from the anaerobic digestion tank is provided upstream of the oxidation treatment means. .

  The organic waste liquid anaerobic digestion treatment apparatus according to claim 5 is characterized in that, in claim 3 or 4, the oxidation treatment means is an ozone treatment means.

  The anaerobic digestion treatment apparatus for organic waste liquid according to claim 6 is the centrifugal separator according to any one of claims 1 to 5, wherein the digested sludge discharged from the anaerobic digestion tank is concentrated without adding a flocculant. It has a concentration means and a sludge discharge means for discharging at least a part of the concentrated sludge of the centrifugal concentration means to the outside of the system.

  According to the anaerobic digestion treatment apparatus of the organic waste liquid of the present invention, when performing anaerobic digestion treatment by solubilizing digested sludge and returning solubilized sludge, concentrating digested sludge and returning concentrated sludge, Concentrated sludge with extremely high concentration is adjusted with solubilized sludge, etc., and then returned to the anaerobic digester to efficiently return the concentrated sludge while efficiently concentrating, and within the anaerobic digester Sufficiently dispersed to perform efficient digestion and highly reduce sludge.

  That is, in the present invention, the digested sludge is concentrated, and the concentrated sludge is returned to the anaerobic digester, so that the SRT (solids residence time) of the anaerobic digester is maintained without changing the HRT (hydraulic residence time). High digestion efficiency and weight loss rate can be obtained by securing a long time. Moreover, the weight loss rate of sludge can be further increased by solubilizing digested sludge to be easily biodegradable and returning the solubilized sludge to the anaerobic digester.

  The sludge concentration in the anaerobic digester for solubilizing such digested sludge is set high. Therefore, the concentrated sludge obtained by concentrating this relatively high-concentration digested sludge is a paste-like or very viscous liquid, and the pump discharge pressure becomes extremely large to transfer with a pump, which is difficult to realize. . Moreover, such highly viscous concentrated sludge is difficult to disperse in the anaerobic digester, which leads to a decrease in digestion efficiency. On the other hand, as described above, it is difficult to perform concentration to such an extent that it can be transferred by a pump, and the efficiency of the concentrator also deteriorates.

  In the present invention, the digested sludge is concentrated without considering the transferability by the pump, and the liquid is mixed with the obtained highly viscous concentrated sludge to dilute the concentration so that the pump can be easily transferred to adjust the concentration.

  In the present invention, it is extremely important that the concentration adjustment position of the concentrated sludge is the transfer pump or the suction side of the transfer pump, and thus the concentration is adjusted to a predetermined concentration on the suction side of the transfer pump or the transfer pump. The transfer pump can be easily transferred.

  On the other hand, for example, even if the concentrated sludge is mixed with raw sludge at the inlet side of the anaerobic digestion tank and diluted, it is difficult to transfer the concentrated sludge to the introduction side of the raw sludge. It cannot be improved.

  In the present invention, the concentrated sludge is adjusted to a concentration suitable for pump transfer on the transfer pump or the suction side of the transfer pump and efficiently returned to the anaerobic digester, and the returned sludge is uniformly distributed in the anaerobic digester. It can be dispersed for efficient anaerobic digestion.

  In addition, when the organic waste liquid subject to anaerobic digestion has a high nitrogen content, the anaerobic digestion reaction is inhibited by the ammonia that moves to the liquid side during the anaerobic digestion process, resulting in a reduction in processing efficiency. Therefore, it is necessary to dilute the organic waste liquid in advance to reduce the organic load in the anaerobic digester. However, as in the present invention, the digested sludge is concentrated and the ammonia-containing separation liquid is drawn out of the system. The anaerobic digestion treatment can be performed without lowering the organic load by diluting the concentrated sludge with another waste liquid containing less ammonia and returning it to the anaerobic digester.

  According to the anaerobic digestion treatment apparatus for organic waste liquid according to claim 2, even more efficient treatment can be performed by using solubilized sludge as a dilution liquid for adjusting the concentration of concentrated sludge. That is, since the viscosity of the sludge is reduced by the solubilization treatment, the solubilized sludge is effective for diluting the concentrated sludge. In this case, since the dilution liquid itself is a processing target, digestion efficiency is improved. On the other hand, for example, when water is added as a dilution liquid, it is necessary to concentrate again to increase digestion efficiency. However, if solubilized sludge is used, there is no need for concentration. Moreover, the solubilized sludge and the concentrated sludge are mixed in advance and then returned to the anaerobic digestion tank, so that the solubilized sludge and the concentrated sludge are more uniformly mixed and dispersed to promote digestion.

  According to the organic waste liquid anaerobic digestion treatment apparatus of claim 3, digested sludge can be efficiently solubilized by oxidation treatment.

  According to the anaerobic digestion treatment apparatus for organic waste liquid according to claim 4, by oxidizing the digested sludge to be introduced into the oxidation treatment means in advance by the aeration means, the reducing inorganic substance contained in the digested sludge is oxidized, for example, In the ozone treatment means as the subsequent oxidation treatment means, it is possible to prevent ozone from being consumed for the oxidation of the reducing inorganic substance, increase the utilization rate of ozone, and improve the solubilization efficiency.

  According to the organic waste liquid anaerobic digestion treatment apparatus of the fifth aspect, by adopting the ozone treatment means as the solubilization means, the following effects are exhibited. That is, since the solubilized sludge after ozone treatment has a low viscosity, it can be returned to the anaerobic digester in a uniform state while ensuring fluidity. And since it returns to an anaerobic digester in a uniform state, the digestive efficiency in an anaerobic digester goes up. In addition, when adding chemicals such as potassium permanganate for solubilization, manganese dioxide, etc. remains in the system, and chemical injection equipment is required, but after ozone is consumed, Since it becomes oxygen, it does not remain in the system and no chemical injection equipment is required.

  According to the anaerobic digestion treatment apparatus for organic waste liquid according to claim 6, the concentrated sludge obtained by centrifugal concentration without adding a flocculant to the digested sludge is discharged out of the system as compared with the organic components. An inorganic component having a large specific gravity can be discharged out of the system preferentially, and accumulation of inorganic components in the system can be prevented to increase digestion efficiency. In addition, since sludge containing a large amount of inorganic components is excellent in dewaterability, a dehydrated cake with a low water content can be obtained, and handling capacity for transportation, disposal, etc. is improved by reducing its capacity.

  Embodiments of an anaerobic digestion apparatus for organic waste liquid according to the present invention will be described below in detail with reference to the drawings.

  1 and 2 are system diagrams showing an embodiment of the organic waste liquid anaerobic digestion treatment apparatus of the present invention. 1 and 2, members having the same function are denoted by the same reference numerals.

[Anaerobic digestion treatment equipment for organic waste liquid in Fig. 1]
In FIG. 1, organic sludge (organic waste liquid) is introduced into an anaerobic digester 1 and subjected to anaerobic digestion. A part of the digested sludge in the anaerobic digester 1 is extracted and concentrated by the concentrator 2. Moreover, the other part of the anaerobic digester 1 is extracted and solubilized by the ozone treatment apparatus 5 as a solubilizing means. At least a part of the solubilized sludge is fed to the mixing tank 3 and the remainder is returned to the anaerobic digester 1. The concentrated sludge concentrated in the concentrator 2 is fed to the mixing tank 3 and mixed with the solubilized sludge from the ozone treatment device 5 to adjust the concentration, and the sludge diluted to a concentration suitable for pump transfer is transferred by the transfer pump 4. Return to anaerobic digester 1.

  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.

  In the anaerobic digester 1, 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.

  As the conditions for anaerobic digestion, any temperature condition in which a medium temperature methanogen having an optimum temperature near 35 ° C. and a high temperature methanogen having an optimum temperature around 55 ° C. can be used. 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.

  When mainly mesophilic methanogens are used, the SRT of sludge in the anaerobic digester is required to be 10 days or longer, preferably about 15 to 50 days. On the other hand, when a high temperature methanogen is mainly used, it is possible to set SRT (2 days or more) shorter than the above range.

The organic load is 0.2 to 3.0 kg-TVS / m ³ · day, preferably 0.4 to 0.8 kg-TVS / m ³ · day, and the TS concentration in the anaerobic digester is 1 to 10%, preferably Can be performed under conditions of 3 to 6% and a temperature of 30 to 38 ° C or 45 to 60 ° C.

  The concentrator 2 for concentrating the digested sludge is not particularly limited as long as it can separate and concentrate the digested sludge by solid-liquid separation. However, the centrifugal concentrator, the flotation concentrator, and the screw press concentrator. A filter cloth type concentrator can be used. Moreover, solid-liquid separators, such as a precipitation tank, a membrane separator, and a filtration apparatus, can also be used.

  In the concentration of the digested sludge, a flocculant, preferably a polymer flocculant, is added to the digested sludge to agglomerate the SS content in the digested sludge, thereby increasing the concentration factor and obtaining a clear separation liquid. Can do. As the flocculant, known ones generally used for concentration and dehydration of digested sludge can be applied, but a cationic polymer flocculant is preferable because the addition amount is small. The polymer flocculant is added to tap water, industrial water, sewage secondary treated water or the like preferably dissolved at a concentration of about 0.2 to 0.4% by weight, and the addition rate is 0 per SS of digested sludge. It is preferable to set it as 0.05 to 1.5 weight%. When a flocculant is added to the digested sludge, the flocculant may be injected into the digested sludge transfer line, may be added to the concentrator, or may be agglomerated by separately providing a coagulation tank.

  The degree of concentration of digested sludge in the concentrator 2 depends on the performance of the concentrator used, but usually digested sludge with a TS (solid matter) concentration of about 3 to 6% is pasty or highly viscous about 8 to 20%. It is preferable to concentrate in the liquid form.

  A part of the concentrated sludge from the concentrator 2 may be discharged out of the system as extracted sludge (excess sludge) as necessary, and may be subjected to disposal such as dehydration, incineration, landfill, composting, and the like. If the extracted sludge to be discharged has a high viscosity, the power of the discharge pump can be reduced by diluting and discharging with the dilution liquid. As the liquid for dilution, treated water (separated liquid of the concentrator 2), biologically treated water of other organic waste liquids, or the like can be used.

  The sludge extraction is preferably performed so as to maintain the sludge (TS) concentration in the anaerobic digester 1 at 3 to 10%.

  The drawn sludge may be discharged directly from the anaerobic digester 1.

  In addition, the concentrated separation liquid of the concentrator 2 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.

  In addition, since this concentrated separation liquid contains ammonia, phosphorus, and the like in high concentrations, magnesium ammonium phosphate (MAP) crystals may precipitate in the transfer pipe, which may block the pipe. In this case, by introducing tap water, industrial water, sewage secondary treated water or the like into the concentrated separation liquid, the concentration can be lowered and precipitation can be prevented.

In the ozone treatment apparatus 5, the digested sludge from the anaerobic digester 1 is solubilized by contacting with ozone. As a contact method with ozone in the ozone treatment apparatus 5, a method of introducing digested sludge into an ozone treatment tank and blowing ozone, a method of mechanical stirring, a method of using a packed bed, or the like can be employed. As ozone, in addition to ozone-containing gas such as ozonated oxygen and ozonized air, ozone-containing water can be used. The amount of ozone used is 0.01 to 0.08 g-O per VSS of digested sludge that is usually treated with ozone. ₃ / g-VSS, preferably 0.02 to 0.05 g-O ₃ / g-VSS.

  By performing such ozone treatment, the bacterial cells in the digested sludge are killed and modified to be readily biodegradable together with other organic substances. Moreover, the viscosity of sludge falls remarkably in that case. Part or all of the solubilized sludge solubilized by the ozone treatment device 5 is fed to the mixing tank 3, and the remainder (when part of the solubilized sludge is fed to the mixing tank 3) is an anaerobic digester 1. Will be returned.

  In the mixing tank 3, the concentration is adjusted by adding the solubilized sludge from the ozone treatment device 5 to the concentrated sludge from the concentrator 2. Dilution liquids used to adjust the concentration of this concentrated sludge include solubilized sludge, digested sludge, organic sludge of the original sludge (organic waste liquid), treated water (separator of the concentrator 2), industrial water, Water, sewage secondary treated water, and other waste liquids or biological treated water may be used, but solubilized sludge is preferably used. The TS concentration of the concentrated sludge is usually 8 to 20% and extremely high viscosity, but the TS concentration of the solubilized sludge is usually 3 to 6% and the viscosity is further lowered by the solubilization treatment. Such solubilized sludge can efficiently dilute the concentrated sludge.

  In order to adjust the concentration of the concentrated sludge, it is not always necessary to provide a mixing tank. In the concentrated sludge transfer pipe, the dilution liquid may be simply injected into the suction side of the transfer pump or the transfer pump. However, when the viscosity of the concentrated sludge is high, it is preferable to provide a mixing tank 3 and mechanically mix as shown in FIG. As the mixing means, a stirrer, gas blowing, a static mixer, or the like can be used.

  Since the residence time of the mixing tank 3 for adjusting the concentration of the concentrated sludge may be about 1 minute to 6 hours, the volume of the mixing tank 3 may be small. Further, compared with the case where the concentrated sludge is directly fed into the anaerobic digestion tank and mixed with the digested sludge and the raw sludge, the power required for mixing in the mixing tank 3 can be remarkably small.

  The degree of concentration adjustment of the concentrated sludge may be such that it can be smoothly transferred with, for example, a single monopump. Generally, the TS concentration is 6 to 12% so that the discharge pressure of the transfer pump 4 is 0.4 MPa or less. For example, it is preferable to concentrate to about 8%.

  In the apparatus of FIG. 1, the concentrated sludge concentrated by the concentrator 2 is dropped into the mixing tank 3, and the concentration of this concentrated sludge is adjusted by the solubilized sludge. The sludge whose concentration has been adjusted in this way can be efficiently returned to the anaerobic digester 1 by the transfer pump 4, and can be easily dispersed in the anaerobic digester 1, thereby efficiently anaerobically. Digested.

  Although there is no restriction | limiting in particular as the transfer pump 4 for transfer of the sludge after density | concentration adjustment, A monopump, a hose pump, etc. can be used.

  In the present invention, a part of the digested sludge in the anaerobic digester 1 is extracted in this way and concentrated by the concentrator 2, and the concentration of the concentrated sludge is adjusted and returned to the anaerobic digester 1, thereby changing the HRT. The SRT can be lengthened without causing a sludge reduction rate to be reduced.

  The amount of digested sludge withdrawn from the anaerobic digester 1 for concentration is not particularly limited, but about 1/30 to 1/10 of the retained sludge in the anaerobic digester 1 is withdrawn to concentrate and adjust the concentration. By post-circulating, the SRT can be extended at least about three times that of the case where such sludge circulation is not performed, and even if it is a non-biodegradable organic waste liquid, the reduction of sludge is promoted. Can be made.

  The amount of digested sludge extracted from the anaerobic digester 1 for solubilization is anaerobic digestion as the amount of organic solids (VSS) contained in the digested sludge in order to ensure a sufficient weight reduction effect due to solubilization. It is preferable that the amount corresponds to 1/3 to 5 times, preferably 1/2 to 2 times the amount of organic solid (VSS) introduced into the tank 1. The amount of digested sludge to be solubilized per day is 1/10 or less, preferably 1/100 to 1/15, more preferably 1/50 of the total amount of organic solids (VSS) in the anaerobic digester 1. An amount corresponding to ˜1 / 30 is preferable. By setting the amount of solubilization treatment per day to such an 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. it can.

  In FIG. 1, an ozone treatment device is used as the solubilization means. However, in the present invention, the solubilization treatment is not limited to the ozone treatment device, and the sludge cells are denatured and destroyed to be assimilated by microorganisms. Any method can be used as long as it can be solubilized in an easy form, and any method known as a sludge solubilization method can be adopted. Adopt various methods such as chemical treatment with strong oxidizer, acid, alkali, etc., ultrasonic treatment, physical treatment such as milling, thermal treatment, etc. alone or in combination of two or more. Can do.

  Further, the solubilization treatment may be performed on the digested sludge extracted from the anaerobic digestion tank, or may be performed on a part or all of the concentrated sludge obtained by concentrating the digested sludge.

  In addition, it is preferable to operate the concentrator and the mixing tank in a state cut off from the atmosphere. For example, by concentrating the concentrator in a sealed state to limit the contact between sludge and oxygen, the anaerobic bacteria are utilized. It can be returned to the anaerobic digestion tank as it is, and the number of viable bacteria in the anaerobic digestion tank can be easily maintained and increased, and the digestion efficiency can be improved.

  It is also preferable to effectively use the digestion gas (methane gas) generated in the anaerobic digestion tank to cover part or all of the power necessary for the digestion tank heating, solubilization means, concentrator and the like.

[Organic waste liquid anaerobic digestion treatment equipment in Fig. 2]
The organic waste liquid anaerobic digestion treatment apparatus of FIG. 2 omits the mixing tank 3 and injects the solubilized sludge from the ozone treatment apparatus 5 into the suction side of the transfer pump 4 and mixes it with the concentrated sludge from the concentrator 2. The point which was made to perform, the pre-aeration tank 6 was provided in the front | former stage of the ozone treatment apparatus 5, the point which was made to carry out ozone treatment after digesting sludge in the pre-aeration tank 6 beforehand, Anaerobic digestion treatment of the organic waste liquid in FIG. 1 is concentrated in the drawing centrifugal concentrator 7, the concentrated sludge is discharged out of the system as the drawn sludge, and the separated liquid is injected into the suction side of the transfer pump 4. Unlike the device, the rest of the configuration is the same.

The treatment conditions for pre-aeration tank 6 is not particularly limited, but the air oxidation of the reducing inorganic digested sludge from the viewpoint of efficiently carried out, the aeration air 0.2~1.0m ³ / ^{m 3} · min It is preferable that the aeration is performed under the above conditions and the residence time is about 5 minutes to 8 hours. By providing such a pre-aeration tank 6 in the preceding stage of the ozone treatment device 5, the reducing inorganic substance in the digested sludge is oxidized in advance, and the sludge solubilization efficiency by the ozone treatment in the ozone treatment device 5 can be increased. it can.

  If exhausted ozone gas from the ozone treatment device 5 is used as the aerated air in the pre-aeration tank 6, it is possible to more efficiently oxidize the reducing inorganic substance in the digested sludge by effectively using the exhaust gas. In particular, the use of ozonated oxygen as ozone is effective because the oxygen concentration of the exhaust gas is high.

By providing such a pre-aeration tank 6, the amount of ozone used in the ozone treatment device 5 can be reduced. For example, 0.01 to 0.04 kg− with respect to digested sludge introduced into the ozone treatment device 5. As O ₃ / kg-VSS, sludge can be efficiently solubilized.

  To the centrifugal concentrator 7, a necessary amount of digested sludge for maintaining the sludge concentration in the anaerobic digester 1 in the above-described preferred range is introduced without adding a flocculant and concentrated by centrifugation. By centrifugally concentrating the digested sludge to which no flocculant is added, the inorganic components in the digested sludge are preferentially concentrated. By drawing this concentrated sludge out of the system, the inorganic components are preferentially discharged out of the system, and accumulation of the inorganic components in the system can be prevented to increase digestion efficiency.

  This extracted sludge is disposed of by dehydration, incineration, landfill, composting, and the like. This drawn sludge has a high inorganic component content, is excellent in dewaterability, and becomes a dehydrated cake with a low moisture content, which is advantageous for handling.

  In the organic waste liquid anaerobic digestion treatment apparatus of FIG. 2, other processing conditions and means that can be replaced are the same as those described above for the organic waste liquid anaerobic digestion treatment apparatus of FIG.

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

Sewage primary sedimentation sludge and excess sludge were anaerobically digested at 35 ° C in a transient manner. The volume of the anaerobic digester is 1,100 m ³ , the TVS load is 0.65 kg / m ³ · day, and the HRT is 45 days (the amount of sludge input per day is 24.4 m ³ ). Digested sludge concentration is 1.6% (TVS / TS ratio 73%), compared to the input sludge concentration (TS concentration, the same applies below) 3.5% (TVS / TS ratio 83%), and digestibility (reduction of TVS) Rate) was 60%. In the anaerobic digestion treatment by the anaerobic digestion tank, the sludge retention time is increased by solid-liquid separation of the sludge in the anaerobic digestion tank and returning the concentrated sludge, and the sludge in the tank is solubilized and returned. Thus, an attempt was made to increase the weight loss rate, and a centrifugal concentrator was used as a solid-liquid separation means. Moreover, an ozone treatment apparatus was used as a solubilizing means.

The tank sludge was sent to the ozone treatment apparatus at 1.0 m ³ / hr and reacted with ozone so that the amount of ozone used was 0.03 kg-O ₃ / kg-VSS. Further, 3.7 m ³ of the sludge in the tank corresponding to 15% of the input sludge amount was drawn out, and the remaining 85% was discharged out of the system as a separation liquid when the sludge in the tank was centrifugally concentrated. Centrifugal concentration is performed by supplying sludge in the tank to a centrifugal concentrator at 2.0 m ³ / hr and dissolving at 0.2 wt% under a centrifugal strength of 2,100 G and a differential speed of 15 min ^−1. The aggregating agent was added while adding 0.6% by weight per SS. At this time, the concentrated sludge concentration was 12%, and the SS recovery rate was 95% or more. When the concentrated sludge discharged from the centrifugal concentrator to the concentrated sludge receiving tank (mixing tank) was returned to the anaerobic digester with a monopump, the pressure of the monopump reached 0.8 MPa, and the pump tripped. I was unable to return it.

  Therefore, the following examples and comparative examples were processed.

Example 1
Concentrated sludge was introduced into the mixing tank, and a part of the sludge solubilized by ozone treatment was introduced into the mixing tank and mixed while gently stirring with a stirrer. The sludge concentration in the mixing tank was 3.6. Since the pressure of the monopump decreased to 0.12 MPa, it could be promptly returned to the anaerobic digester.

  FIG. 3 shows the transition of the digestibility obtained from the sludge concentration in the anaerobic digester when such operation is continued for one year, the balance of solids, and the amount of digestion gas generated. As shown in FIG. 3, after the fifth month from the start of operation, the TVS concentration in the tank began to change around 2.3%, and a digestibility of 80% or higher was continuously obtained. As the sludge concentration in the tank increased to 4.6%, the concentrated sludge concentration after mixing with ozone-treated sludge increased to 7.2%, but the pressure of the monopump was 0.3 MPa or less, and returned without difficulty. We were able to.

Comparative Example 1
The centrifugal concentration conditions were changed to reduce the pressure to such an extent that it could be pumped with a monopump. When the centrifugal strength was lowered to 1,000G and the flocculant addition rate was lowered to 0.2% by weight, the concentration of concentrated sludge became about 7%, the pressure of the monopump decreased to 0.3 MPa, and it was returned to the anaerobic digester. I was able to do that. However, the SS recovery rate at this time was 70%, and sludge flowed out to the separation liquid side.

  FIG. 4 shows the transition of the sludge concentration in the anaerobic digester and the digestibility when such operation is continued for one year. As shown in FIG. 4, since the SS recovery rate was low, the sludge concentration in the tank could not be increased even if the operation was continued, and the digestibility could not be increased to 70% or more.

Example 2
Except that the digested sludge from the anaerobic digestion tank is centrifugally concentrated at 4.0 m ³ / hr, the secondary treated water of sewage is introduced into the mixing tank at 1.0 m ³ / hr, and gently stirred with a stirrer and mixed. When the treatment was performed in the same manner as in Example 1, the pressure of the monopump for returning the concentrated sludge decreased to 0.2 MPa and could be returned quickly to the anaerobic digester.

FIG. 5 shows the transition of the sludge concentration in the anaerobic digester and the digestibility when such operation is continued. As shown in FIG. 5, when the TS concentration in the tank exceeded 3.7% after 5 months from the start of operation, the centrifugal solidifier became too solid to be operated. Therefore, when the extraction amount of sludge in the tank was increased to 6 m ³ / day corresponding to 25% of the input sludge amount, the TS concentration in the tank changed around 3.7%, and the operation could be continued. Digestibility improved to 78%.

  Below, the experimental example which shows the preferential discharge effect of the inorganic component by the solubilization effect by ozone treatment and the centrifugal concentration without flocculant addition is given.

Experimental example 1
The properties of the sludge before and after the ozone treatment when the digested sludge was ozone treated with an ozone reaction rate of 0.03 kg-O ₃ / kg-VSS are shown in Table 1.

As is clear from Table 1, the TS, VS, and total COD _Cr concentrations were almost unchanged before and after the ozone treatment, but the SS and VSS concentrations were decreased by less than 10% compared to those before the ozone treatment, and soluble COD _Cr , Total BOD concentration increased. From this result, it can be seen that a part of the VSS component in the sludge was solubilized and converted into a soluble component by the ozone treatment, and biodegradation was facilitated.

Experimental example 2
Decanter-type centrifugal concentration by adding 0.5% by weight of polymethacrylate polymer dissolved in 0.2% by weight of sewage secondary treatment water as a polymer flocculant to digested sludge (TS 5%) The concentration (TS) and amount of the obtained concentrated sludge and the concentrated separated liquid were as shown in Table 2 when supplied to the machine at 4 m ³ / hr and centrifugally concentrated at a centrifugal strength of 2100 G.

  In addition, when this digested sludge was centrifugally concentrated under the same conditions without adding a flocculant, the concentration (TS) and amount of the obtained concentrated sludge and the concentrated separation liquid were as shown in Table 2.

  Next, several types of digested sludges with different concentrations were subjected to centrifugal concentration in the same manner as above without adding a flocculant, and the TVS / TS ratio of the sludge supplied to the centrifugal concentrator and the discharged sludge (concentrated sludge and supernatant sludge ( The relationship between the concentrated separation liquid)) and the TVS / TS ratio was examined, and the results are shown in FIG.

  As is clear from FIG. 6, the TVS / TS ratio of the concentrated sludge is 0.02 to 0.04 lower than the TVS / TS ratio of the supplied sludge, whereas the supernatant sludge is about 0.03 higher. It was. This result shows that the inorganic component was concentrated preferentially to the concentrated sludge side.

  In addition, each concentrated sludge and supplied sludge were dehydrated under the same conditions (filtration speed, filter cloth pressure, coagulant addition rate) with a belt press dehydrator, respectively, and the water content of the obtained dehydrated cake was The concentrated sludge dehydrated cake is about 5% lower than the supplied sludge dehydrated cake. When compared with the same amount of solids, the concentrated sludge dehydrated cake has a dehydrated cake amount of 15 compared to the supplied sludge dehydrated cake. Reduced by ~ 20%. From this result, it is clear that the concentrated sludge with a high content of inorganic components obtained by centrifugal concentration without adding a flocculant is excellent in dewaterability.

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 other embodiment of the anaerobic digestion processing apparatus of the organic waste liquid of this invention. It is a graph which shows the time-dependent change of the sludge density | concentration in the anaerobic digestion tank in Example 1, and a digestibility. It is a graph which shows the time-dependent change of the sludge density | concentration and digestibility in the anaerobic digester in the comparative example 1. It is a graph which shows the time-dependent change of the sludge density | concentration in the anaerobic digester in Example 2, and a digestibility. It is a graph which shows the relationship between TVS / TS ratio of the supply sludge calculated | required in Experimental example 2, and TVS / TS ratio of discharge sludge (concentrated sludge and supernatant sludge (concentrated separation liquid)).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Anaerobic digester 2 Concentrator 3 Mixing tank 4 Transfer pump 5 Ozone treatment device 6 Pre-aeration tank 7 Centrifugal concentrator

Claims (6)

An anaerobic digester for anaerobically digesting organic waste liquid;
Solubilization means for solubilizing digested sludge extracted from the anaerobic digester;
Returning means for returning the solubilized sludge from the solubilizing means to the anaerobic digester;
Solid-liquid separation means for concentrating the digested sludge discharged from the anaerobic digester;
A pipe having a transfer pump for returning the concentrated sludge from the solid-liquid separation means to the anaerobic digester;
An apparatus for anaerobic digestion of organic waste liquid, comprising: a liquid supply means for adding a liquid to the concentrated sludge on the transfer pump or a suction side of the transfer pump.   2. The organic waste liquid anaerobic digestion apparatus according to claim 1, wherein the liquid added to the concentrated sludge is the solubilized sludge.   3. The organic waste liquid anaerobic digestion treatment apparatus according to claim 1, wherein the solubilization means is an oxidation treatment means.   The anaerobic digestion treatment apparatus for organic waste liquid according to claim 3, further comprising aeration means for aeration of the digested sludge extracted from the anaerobic digestion tank before the oxidation treatment means.   5. The organic waste liquid anaerobic digestion apparatus according to claim 3, wherein the oxidation treatment means is an ozone treatment means.   The centrifugal concentration means for concentrating the digested sludge discharged from the anaerobic digester without adding a flocculant and at least a part of the concentrated sludge of the centrifugal concentration means according to any one of claims 1 to 5. An apparatus for anaerobic digestion of organic waste liquid, comprising sludge discharge means for discharging the wastewater out of the system.

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