JP5371510B2 - Combined treatment of wastewater and organic residue - Google Patents

Description

  The present invention relates to a combined wastewater and organic residue treatment method that can efficiently treat wastewater and organic residues.

  One treatment method of food waste includes biological treatment such as methane fermentation treatment. In the methane fermentation treatment, the decomposition reaction proceeds by being held in the methane fermentation tank for a certain period of time, but when the processing object is continuously added, the processed product (methane fermentation residue) is discharged from the methane fermentation tank. In this case, a part of the unprocessed processing object may be discharged, resulting in a problem that the processing efficiency is lowered.

  In order to improve processing efficiency, the method of extending the sludge residence time (SRT) in a methane fermentation tank is mentioned. In order to extend SRT in a methane fermenter, many methods have been proposed for solid-liquid separation of the methane fermentation residue discharged from the methane fermenter and returning the recovered sludge (see, for example, Patent Document 1). However, in practice, this method is difficult to separate because of the low sedimentation of the methane fermentation residue.

  On the other hand, in order to improve the sedimentation property of the methane fermentation residue, for example, a method of adding a flocculant to sludge stored in a methane fermentation tank is considered. However, in this method, the contact between the methane-fermenting bacterium and the object to be processed may be hindered, and the processing efficiency may be reduced (for example, see Non-Patent Documents 1 and 2). Therefore, it was considered in the art that a flocculant should not be added during methane fermentation.

  In addition, biological treatment methods such as methane fermentation are also used for the treatment of wastewater from food factories. However, no method has been proposed for treating wastewater in a complex manner in the same system as the organic residue that is solid.

JP 2006-95377 A

“Effect of flocculant treatment on anaerobic digestion of surplus activated sludge” Water Pollution Society of Japan, Vol.19, Page17-18, 1985 "Effect of ferric chloride flocculant on anaerobic digestion" Environmental Sanitary Engineering Research Vol. 16, No. 13 (2002), pp. 90-95

  The main object of the present invention is to provide a combined treatment method capable of efficiently treating waste water and organic residues.

  The inventors of the present invention pay attention to wastewater treatment originally performed separately from methane fermentation treatment of organic residues, and by performing these in combination, efficient biogas generation and waste treatment becomes possible. I found out. That is, the inventors added a flocculant to waste water from a factory, etc., and separated into solid and liquid. When the obtained solid content was subjected to methane fermentation treatment together with organic residues, contact between the methane fermentation bacteria and the treatment object Was found to be unimpeded and not adversely affect methane fermentation efficiency. The present invention has been completed as a result of further research based on these findings.

The present invention mainly provides a combined treatment method of the following waste water and organic residues.
Item 1. A combined treatment method of wastewater and organic residue,
(i) a solid-liquid separation step of separating the wastewater added with the flocculant into a solid content and a liquid content,
(ii) including a methane fermentation treatment step in which the solid content obtained in the step (i) is subjected to methane fermentation together with an organic residue;
A method, wherein a methane fermentation residue generated in the methane fermentation treatment step of the step (ii) is extracted and subjected to solid-liquid separation, and then at least a part of the obtained solid content is reintroduced into the methane fermentation treatment step.
Item 2. Item 2. The method according to Item 1, wherein in the step (i), the solid-liquid separation is carried out by pressurized flotation.
Item 3. Item 3. The method according to Item 1 or 2, wherein the methane fermentation residue obtained by methane fermentation treatment is solubilized, followed by solid-liquid separation, and the obtained solid content is introduced into the methane fermentation treatment step.
Item 4. The liquid component obtained in step (i) and the liquid component obtained by solid-liquid separation of the methane fermentation residue are converted into an upflow anaerobic sludge bed method (UASB method: Up-flow Anaerobic Sludge Blanket). Item 4. The method according to any one of Items 1 to 3, which is subjected to a methane fermentation treatment.

  The combined treatment method of the present invention adds a flocculant to the wastewater of a food factory, etc., and separates it into a solid and liquid, and uses the resulting solid content and the production residue (organic residue) of the factory together for methane fermentation treatment. The sedimentation property of the methane fermentation residue can be enhanced without impairing the methane fermentation efficiency. Since the methane fermentation residue contains a flocculant, the sedimentation property of the methane fermentation residue is improved, and the solid content in the methane fermentation residue can be easily and efficiently concentrated. Furthermore, in this invention, this concentrated solid content is returned to a methane fermentation tank, and it uses for a methane fermentation process again. As a result, the SRT (sludge retention time) in the methane fermentation tank can be substantially increased, so that the processing efficiency of the entire system can be improved, and further reduction of industrial waste can be realized. is there.

  In addition, the liquid component separated by solid-liquid separation by pressurized flotation or the like can be reduced in BOD or the like by subjecting it to biological treatment such as an upward flow type anaerobic sludge bed method (UASB method). Here, BOD (Biochemical oxygen demand) is an index representing the amount of organic matter in water by the amount of oxygen required by microorganisms for its oxidative degradation. If the BOD etc. of the liquid can be reduced below the discharge standard value by biological treatment, it can be discharged into sewage and rivers.

It is a flowchart which shows the outline of the composite processing method of this invention.

1. Combined treatment method of waste water and organic residue The combined treatment method of waste water and organic residue of the present invention (hereinafter sometimes simply referred to as “composite treatment method”) includes the following steps.

A combined treatment method of wastewater and organic residue,
(i) a solid-liquid separation step of separating the wastewater added with the flocculant into a solid content and a liquid content,
(ii) including a methane fermentation treatment step in which the solid content obtained in the step (i) is subjected to methane fermentation together with an organic residue;
After extracting the methane fermentation residue generated in the methane fermentation treatment step of the step (ii) and performing solid-liquid separation, at least a part of the obtained solid content is introduced again into the methane fermentation treatment step.

  Hereinafter, each process is explained in full detail.

(1) Step (i): In the solid-liquid separation step (i), a flocculant is added to the waste water, and the solid and liquid components are separated by a conventionally known solid-liquid separation method. The solid content obtained here may be referred to as “solid content of step (i)” and the liquid content may be referred to as “liquid content of step (i)”.

  The solid-liquid separation method that can be employed in step (i) is not particularly limited, and examples thereof include pressurized flotation, precipitation separation, and centrifugal separation.

  Solid-liquid separation by pressure flotation (hereinafter sometimes referred to simply as “pressure flotation separation”) occurs when pressure water is decompressed at once by injecting pressurized water in which air is excessively dissolved by pressure. In this method, the fine bubbles to be brought into contact with the waste water are separated into solid and liquid. This method is a method in which fine bubbles adhere to the solid content in the waste water, the solid content floats on the liquid surface, and the solid content and the liquid content are separated. Conventionally known conditions and the like can be employed. In the pressure levitation separation, a conventionally known apparatus and conditions can be employed. Specific examples of the pressurizing condition include 100 to 500 kPa.

  Precipitation separation, centrifugation, etc. can also be carried out according to a conventionally known method.

  In the present invention, a flocculant is added to the waste water to be subjected to solid-liquid separation. A conventionally well-known thing can be used as a flocculant, for example, a polymer flocculant and an inorganic flocculant are mentioned.

  Specific examples of the polymer flocculant include sodium polyacrylate, polyacrylamide partial hydrolyzate, acrylamide and sodium acrylate copolymer, acrylamide and sodium vinyl sulfonate copolymer, acrylamide and 2-acrylamide. Anionic polymer flocculants such as copolymer of sodium 2-methylpropanesulfonate, ternary copolymer of acrylamide, sodium acrylate and sodium 2-acrylamido-2-methylpropanesulfonate; dimethylaminoethyl Polymers of (meth) acrylate quaternized products or salts thereof, dimethylaminoethyl (meth) acrylate quaternized products or copolymers thereof with acrylamide, polyacrylamide Mannich modified products or quaternized products thereof, etc. Cationic polymer flocculant; Nonionic polymer flocculants such as acrylamide and polyethylene oxide; Amphoteric polymer flocculants such as quaternized products of dimethylaminoethyl (meth) acrylate or salts thereof, acrylic acid or copolymers thereof with acrylamide (anionic cations) A polymer flocculant).

  Specific examples of inorganic flocculants include aluminum compounds such as aluminum sulfate, sodium aluminate and polyaluminum chloride (PAC), iron compounds such as ferric chloride and polyferric sulfate, calcium compounds such as lime, and magnesium compounds. Etc. are exemplified.

  The aggregating agent can be appropriately selected according to the type of waste water supplied to the solid-liquid separation step. Moreover, the said flocculant may be used individually by 1 type, and may be used in combination of 2 or more type. The flocculant is preferably added to the waste water and mixed before being subjected to the solid-liquid separation treatment.

  The amount of the flocculant added is not particularly limited as long as it does not interfere with solid-liquid separation, and can be appropriately set depending on the type of flocculant used. 300 to 2000 ppm per unit, preferably 300 to 1800 ppm; in the case of polyaluminum chloride, 10 to 100% by weight, preferably 30 to 60% by weight, per SS of the object to be treated.

  The liquid obtained by solid-liquid separation is subjected to methane fermentation by subjecting it to biological treatment such as an upflow anaerobic sludge bed method (hereinafter sometimes referred to as the UASB method). It can also be used to generate This will be described in detail in item (4) below.

  Moreover, about solid content, it uses for a methane fermentation process in the following process (ii). Since the solid content obtained in this step contains a flocculant, the sedimentation property of the solid content (sludge) obtained from the residue after methane fermentation treatment (ie, methane fermentation residue) can be enhanced.

(2) Step (ii): In the methane fermentation treatment step (ii), the solid content obtained in step (i) (that is, the solid content in step (i)) is subjected to methane fermentation treatment together with the organic residue. Provide. The solid content and the organic residue in step (i) may be mixed in a methane fermentation tank, or may be previously mixed in a mixing tank or the like and subjected to a methane fermentation treatment.

  Here, the organic residue is a production residue discarded from a food factory or the like, and is not particularly limited as long as it contains an organic substance. Specific examples include a beer bowl at a beer factory, a coffee bowl and a tea bowl at a beverage factory.

  In this step, the mixing ratio when the solid content and the organic residue in step (i) are both subjected to the methane fermentation treatment is not particularly limited as long as methane fermentation is possible. When the amount of the flocculant added to the wastewater satisfies the above blending ratio, the sedimentation property of the subsequent methane fermentation residue is improved, and the solid-liquid separation process can be easily performed.

  In this step, the form of methane fermentation is not particularly limited, and may be any known form utilized in methane fermentation, such as a batch type or a fixed bed type. The methane fermentation may be dry or wet. The solid content and organic residue in step (i) are decomposed into methane gas and carbon dioxide by the methane fermentation treatment.

  The temperature conditions during methane fermentation can be appropriately set from a wide temperature range depending on the type of methane fermentation bacteria used, and are not particularly limited, but are generally about 30 to 60 ° C, for example, about 35 ° C. Or a so-called high temperature of about 55 ° C.

  Sludge residence time (SRT) in this process varies depending on the amount of solids and organic residues in process (i), the type of methane fermentation bacteria used, fermentation temperature, fermentation mode, etc., but cannot be defined uniformly. Usually, 10 to 30 days, preferably 10 to 20 days, and more preferably 10 to 14 days can be mentioned. According to the method of the present invention, the sludge residence time can be substantially extended as compared with the prior art, so that the methane fermentation efficiency can be increased.

  Moreover, you may implement by supplying the mixture of the solid content of process (i), and an organic residue, and extracting the methane fermentation residue in a methane fermentation tank by performing continuously or intermittently. When the supply of the mixture and the extraction of the methane fermentation residue are performed continuously or intermittently, the supply rate of the mixture and the extraction rate of the methane fermentation residue are determined by the solid content residence time (sludge residence time) in the methane fermentation tank. It can set suitably so that it may become time required for methane fermentation.

  Methane gas generated by the methane fermentation is recovered. Methane gas can be separated and recovered by a known methane gas recovery means, and can be used as an energy source.

(3) Solid-liquid separation of methane fermentation residue After the methane fermentation treatment in the step (ii), the methane fermentation residue generated by the methane fermentation treatment is drawn out from the methane fermentation tank, and solid-liquid separation is performed. Here, the amount of methane fermentation residue to be extracted may be appropriately set in consideration of the solid content residence time (sludge residence time) in the methane fermentation tank.

  The solid-liquid separation is preferably performed by precipitation, and for example, a known method such as sedimentation separation or centrifugation can be employed. Sedimentation separation is a method of precipitating particles heavier than water by retaining an object in a water tank. Centrifugation is a method in which a centrifugal force is applied to an object and separated into different phases according to the difference in density. The methane fermentation residue produced by the methane fermentation treatment contains a flocculant and has improved sedimentation, so that solid-liquid separation can be easily performed. By returning to the fermenter, the substantial sludge residence time is extended and the methane fermentation efficiency is increased. The solid content separated from the methane fermentation residue in this step may be referred to as “solid content in step (ii)”.

  In addition, the methane fermentation residue may be subjected to a solubilization treatment prior to solid-liquid separation. The solubilization treatment reduces the molecular weight of organic substances remaining in the methane fermentation residue (that is, organic substances not decomposed by methane fermentation). The solubilization treatment is not particularly limited as long as the organic matter remaining in the methane fermentation residue can be reduced in molecular weight, and a solubilization treatment conventionally employed in waste treatment can be used. Specific examples of the solubilization treatment include heat treatment, alkali treatment, acid treatment, decomposition treatment with microorganisms other than methane fermentation bacteria, ultrasonic treatment, pressure treatment, ozone treatment, and the like. For these solubilization treatments, treatment conditions that are usually used in waste treatment may be adopted, and examples of specific conditions thereof will be exemplified below.

  Specific conditions for the heat treatment are, for example, 50 ° C. or more, preferably about 60 to 90 ° C., more preferably about 65 to 80 ° C., and particularly preferably about 70 to 80 ° C. with respect to the methane fermentation residue. Below, for example, the method of processing for 1 to 96 hours, Preferably it is 12 to 72 hours, More preferably, it is 24 to 48 hours is mentioned. In this heat treatment, heavy oil, city gas, electric power, etc. may be used as an energy source for maintaining the heating temperature. However, the methane gas obtained in the combined treatment method of the present invention is used to obtain heat and electric power. It is desirable to use exhaust heat obtained by a generation means (gas engine, fuel cell, etc.).

  Specific conditions for the alkali treatment include, for example, a method of treating the methane fermentation residue under conditions of pH 9 to 14, preferably 10 to 12 days or less, preferably about 1 hour.

  Examples of the acid treatment include a method of treating the methane fermentation residue under conditions of pH 1 to 5, preferably 2 to 4 days or less, preferably about 1 hour.

  Among these solubilization treatments, heat treatment is preferable from the viewpoint of simplicity and increasing the solubilization rate (low molecularization rate) of the remaining organic matter.

  The solubilized product obtained by the solubilization treatment can be subjected to solid-liquid separation by the above-described sedimentation separation, centrifugation, or the like to obtain the solid content of step (ii).

  In the present invention, at least a part of the solid content obtained by solid-liquid separation (that is, the solid content in the step (ii)) is again introduced into the methane fermentation treatment step. By this operation, the solid content in step (ii) is further thoroughly decomposed, so that the amount of waste solid content can be further reduced and the methane gas generation amount can be increased. However, if the return ratio is large, the sludge residence time in the methane fermenter will be extended, but the solid content concentration in the methane fermenter will increase, which is disadvantageous in terms of stirring and pumping in the methane fermenter. Therefore, it is recommended to decide the return amount after comprehensively judging these aspects.

  Part of the solid content in step (ii) is returned to the methane fermenter as described above, and the other is withdrawn as necessary. The extracted sludge is discarded and treated by various methods. For example, as it is, it is returned to farmland as liquid manure, composted after dehydration, returned to farmland, dehydrated and discarded, incinerated after dehydration, discarded after dehydration and drying, incinerated after dehydration and drying, etc. . In addition, low-temperature waste heat can be effectively used for drying. For example, when methane gas generated by the combined treatment method of the present invention is used in a gas engine, a micro gas turbine, a boiler, etc., the waste heat is used. It is possible to dry.

  In addition, a liquid component obtained by subjecting the methane fermentation residue to solid-liquid separation (this may be referred to as “liquid component of step (ii)”) may be subjected to wastewater treatment by biological treatment described later. .

(4) Biological treatment The liquid component generated in the solid-liquid separation step of the above step (i) (the liquid component of step (i)) and the liquid component generated by the solid-liquid separation of the methane fermentation residue (ie, “step (ii) ) The liquid portion]) can be subjected to biological treatment. At this time, the liquid component in step (i) and the liquid component in process (ii) can be separately subjected to biological treatment, or both can be subjected to treatment. As a biological treatment method, a conventionally known method can be adopted, and examples thereof include an upflow anaerobic sludge bed method (UASB method), an activated sludge treatment method, etc., which are energy saving and highly efficient. From the viewpoint, the UASB method is preferable.

  For example, by the methane fermentation treatment by the UASB method, the organic matter in the liquid part of step (i) and the organic matter in the liquid part of step (ii) are decomposed into methane gas and carbon dioxide, and finally discharged wastewater. The organic matter concentration can be reduced to such an extent that sewerage can be discharged.

  Hereinafter, a methane fermentation process by the UASB method will be described as an example.

  In the UASB method, a fluidized bed is formed with microbial particles obtained by self-granulating anaerobic methanogens, and the liquid in step (i) and step (ii) is circulated in an upward flow to produce biological organisms of methanogens. In this method, organic substances in liquid components are decomposed by chemical action to purify wastewater. By treating the liquid component using the UASB method, a part of the total organic carbon (TOC) in the liquid component is converted into biogas (methane and carbon dioxide). The generated methane gas is used as energy for various purposes.

  The liquid component to be subjected to the methane fermentation treatment by the UASB method includes the liquid component of step (i), the liquid component of step (ii), or a mixture thereof, and if necessary, other waste water or tap water. It may be mixed.

  The methane fermentation treatment by the UASB method can be performed according to a method conventionally employed in wastewater treatment. As a specific example of methane fermentation treatment by the UASB method, granule sludge containing methane fermentation bacteria is introduced, and the residence time of the liquid component in step (i) or the liquid component in step (ii), or a mixture thereof is 1 to 24 An example is a method of allowing water to pass for a time, preferably 4 to 8 hours. Here, the liquid component in step (i) and the liquid component in step (ii) can be passed simultaneously or separately.

  In addition, the temperature conditions in the methane fermentation treatment by the UASB method can be appropriately set from a wide temperature range according to the type of methane fermentation bacteria contained in the granular sludge, and are not particularly limited. What is necessary is just about 20-60 degreeC, for example, what is called medium temperature of about 30-35 degreeC, and what is called high temperature of about 50-55 degreeC may be sufficient.

  Wastewater discharged after being treated in this way has a reduced organic matter concentration (for example, an SS concentration of less than 600 mg / L and a BOD concentration of less than 600 mg / L). It has been purified to the extent that it does not have an adverse effect.

2． Wastewater and organic residue combined treatment apparatus The present invention also provides a wastewater and organic residue combined treatment apparatus (hereinafter sometimes abbreviated as "composite treatment apparatus") for carrying out the combined treatment method. . The composite processing apparatus of the present invention will be described more specifically with reference to FIG.

  The treatment apparatus of the present invention includes a solid-liquid separation tank 1 that separates waste water into a solid content and a liquid content, a methane fermentation tank 2 that performs methane fermentation on the solid content separated by the solid-liquid separation tank 1, and methane fermentation. Biological treatment is performed on the liquid component separated by the solid-liquid separation tank 3 for solid-liquid separation of the methane fermentation residue discharged from the tank 2 and the solid-liquid separation tank 1 and the solid-liquid separation tank 3. And a treatment tank 4, and a return means 5 for reintroducing at least a part of the solid content obtained in the solid-liquid separation tank 3 into the methane fermentation tank 2.

  The solid-liquid separation tank 1 is configured so that drainage from a food factory or the like is supplied and the solid and liquid components separated from each other can be discharged. Moreover, the processing apparatus of this invention should just be provided with the supply means 11 for enabling solid content isolate | separated from the solid-liquid separation tank 1 to the methane fermentation tank 2 to be conveyed. Furthermore, you may provide the supply means 12 which supplies a liquid component from the solid-liquid separation tank 1 to the biological treatment tank 4. FIG.

  The methane fermentation tank 2 is configured so that the solid content of wastewater from a food factory or the like is supplied by the supply means 11 so that methane fermentation of the solid content can be performed and the methane fermentation residue generated after the methane fermentation treatment can be discharged. Has been. Further, in the processing apparatus of the present invention, supply means 21 for supplying the methane fermentation residue discharged from the methane fermentation tank 2 to the solid-liquid separation tank 3 in order to make it possible to transport the methane fermentation residue to the solid-liquid separation tank 3. It only has to have.

  The methane fermentation residue can be subjected to a solubilization treatment before solid-liquid separation in the solid-liquid separation tank 3. When performing solubilization processing, although not shown in FIG. 1, a solubilization tank 6 can be provided between the methane fermentation tank 2 and the solid-liquid separation tank 3. At this time, a means for supplying the methane fermentation residue from the methane fermentation tank 2 to the solubilization tank 6 and a means for supplying the solubilized product from the solubilization tank 6 to the solid-liquid separation tank 3 may be appropriately provided.

  The solid-liquid separation tank 3 is configured so that the methane fermentation residue is supplied by the supply means 21, the solid-liquid separation of the methane fermentation residue is possible, and the processing product generated after the solid-liquid separation can be discharged. Furthermore, in the processing apparatus of this invention, the return means 5 for returning a part of solid content discharged | emitted from the solid-liquid separation tank 3 to the methane fermentation tank 2 is provided, Thereby, a part of solid content is methane again. It can be subjected to fermentation treatment, and the decomposition efficiency of organic matter can be improved.

  Further, in the processing apparatus of the present invention, in order to enable the liquid content obtained in the solid-liquid separation tank 3 to be transported to the biological treatment tank 4, the liquid content discharged from the solid-liquid separation tank 3 is biologically separated. What is necessary is just to provide the supply means 31 supplied to the processing tank 4. FIG. Examples of the treatment in the biological treatment tank 4 include biological treatment by the above-mentioned UASB method and activated sludge method, and the biological treatment tank 4 uses conventionally known means necessary for performing these treatments. It only has to be provided.

  The biological treatment tank 4 is supplied with each liquid component by the supply means 12 or 31 so that the mixture can be subjected to the methane fermentation treatment by the biological treatment method, and the waste water generated after the methane fermentation treatment can be discharged. It is configured. The waste liquid discharged from the biological treatment tank 4 can be discharged into the sewer because the organic matter concentration is sufficiently reduced.

  EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated in detail, this invention is not limited to these.

Example 1
The washing waste water and the production residue (organic residue) of the food factory were subjected to pressurized flotation separation, methane fermentation, solid-liquid separation, and methane fermentation by the UASB method, and then the residual organic matter concentration was measured. Specific conditions and results are as follows. SS, BOD, and COD were measured for about two months after the processing state of the following composite processing step was stabilized.

1. Solid-liquid separation process (pressure floatation separation)
1 to 5 mg of anionic polymer flocculant (Orfloc AP-1 manufactured by Organo Corp.) as a flocculant for 1 L / day of industrial wastewater (300 to 1700 ppm per SS (mg / L) from Table 1 below) , PAC (polyaluminum chloride) was added in an amount of 1000 to 1500 mg (30 to 50% by weight per SS (mg / L) from Table 1), and solid-liquid separation was carried out by pressurized flotation separation (300 kPa pressure) . Table 1 shows the values of industrial wastewater flow rate, SS (Suspended Solid), BOD (Biochemical oxygen demand) and COD (Chemical oxygen demand). COD represents the amount of oxygen required to oxidize oxidizable substances in water. CODcr represents an oxygen demand amount by potassium dichromate having strong oxidizing power.

  Table 2 shows the amount of solids (pressurized flotation sludge), CODcr, SS and BOD obtained by pressure flotation separation.

2. Methane fermentation treatment
A 10-liter methane fermentation tank (anaerobic, 37 ° C) is mixed with 0.93 L of solids recovered from factory effluent and 0.07 L of factory residue (organic residue) and put into the methane fermentation tank for methane fermentation. It was. The CODcr, SS, and BOD of the factory residue were as shown in Table 3 below.

  Table 4 below shows the CODcr, SS and BOD concentrations of the mixed residue before being subjected to the methane fermentation treatment, and the average values of CODcr, SS and BOD after the methane fermentation treatment for about 2 months.

  From the above results, it was shown that even if methane fermentation was performed using a mixed residue containing a flocculant, methane fermentation treatment efficiency was not impaired.

3. The methane fermentation residue discharged from the solid-liquid separation treatment methane fermentation tank was left in the solid-liquid separation tank for 1 day, and solid-liquid separation was performed using sedimentation. The sludge (solid content) settled in the solid-liquid separation tank was returned to the methane fermentation tank, and the liquid content of the methane fermentation treatment product from which the sludge (solid content) was separated was transferred to the biological treatment tank (UASB tank). The SS of returned sludge (returned sludge) is as shown in Table 5 below.

  From the above results, it was shown that sludge having a high SS concentration can be recovered from the methane fermentation residue containing a flocculant only by standing for one day by natural sedimentation.

Reference example 1
When the methane fermentation residue was allowed to stand for 1 day, the sludge sedimentation rate (SV) was 50% or more. The SV of 50% or more means that the volume below the boundary between the supernatant and solids (sludge) when the methane fermentation residue is left for 1 day in a 1 L graduated cylinder is 500 mL or less.

  If the solid portion is extracted from the methane fermentation residue separated into the solid content and the supernatant, almost all of the solid content (sludge) originally contained in 1 L can be extracted. In other words, the SS of the extracted solid (sludge) is more than twice the SS of the original methane fermentation residue.

  Thus, according to the method of this invention, it was shown that the sludge sedimentation rate of a methane issue residue is raised. Substantial sludge residence time (SRT) can be extended by subjecting the sludge thus obtained to methane fermentation again. Furthermore, the processing efficiency of organic residues can be increased by extending the SRT.

Reference example 2
When SS in factory wastewater (drainage before combined treatment) and SS in liquid obtained by solid-liquid separation of methane fermentation residue were compared, it was treated when sludge was not returned. Later SS was 40%, and when sludge was returned, SS was 30%. That is, it was confirmed that the SS decomposition efficiency when sludge was not returned was 60%, whereas the SS decomposition efficiency when sludge was returned was increased to 70%.

Claims (2)

A combined treatment method of wastewater and organic residue,
(i) a solid-liquid separation process in which the wastewater to which the flocculant is added is pressurized and separated into a solid and a liquid;
(ii) including a methane fermentation treatment step in which the solid content obtained in the step (i) is subjected to methane fermentation together with an organic residue;
After extracting and solid-liquid separating the methane fermentation residue generated in the methane fermentation treatment step of the step (ii), reintroducing at least a part of the obtained solid content into the methane fermentation treatment step ; and
Subjecting the liquid content obtained in the step (i) and the liquid content obtained by solid-liquid separation of the methane fermentation residue to a methane fermentation treatment by an upflow anaerobic sludge bed method <br / > A method characterized by The method according to claim 1, wherein the methane fermentation residue obtained by the methane fermentation treatment is solubilized, followed by solid-liquid separation, and the obtained solid content is introduced into the methane fermentation treatment step.

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