JP5742254B2 - Organic wastewater treatment method - Google Patents

Description

  The present invention relates to a method for efficiently treating organic wastewater containing a large amount of solid organic matter by organic acid fermentation and methane fermentation.

Conventionally, organic wastewater has generally been treated by an aerobic biological treatment method such as an activated sludge method.
However, the aerobic biological treatment method requires oxygen for biodegradation of organic matter, and aeration is performed for this purpose, so it cannot be said that it is an energy-saving treatment method. Moreover, since aerobic bacteria have a high sludge conversion rate, there is also a problem that a large amount of excess sludge is generated.

As a method of solving this problem, there is an anaerobic biological treatment method. The anaerobic biological treatment method is an energy-saving method that does not require aeration power because it can recover energy from methane gas as an organic substance and does not require oxygen for decomposition of the organic substance, and has the advantage that the amount of excess sludge generated is small. .
However, since the growth rate of methane bacteria is very slow, the load per bacterium cannot be higher than that of aerobic bacteria, and it is important to secure the amount of microbial cells. In addition, since methane bacteria are susceptible to inhibition by ammonia or the like, sufficient adjustment of operating conditions is required.

Currently, the following methods are mainly employed as anaerobic biological treatment methods.
(1) UASB method (Upflow Anaerobic Sludge Blanket): This treatment method is used in a sludge bed where self-granulated anaerobic microbial pellets (called granules) are developed. Organic wastewater is passed through to convert organic matter into methane gas. In this method, anaerobic microorganisms such as methane bacteria are immobilized on granules, and the granules have very good sedimentation, so no solid-liquid separation device is required, and the microorganism concentration is kept very high. Therefore, there is an advantage that high load operation is possible.

  However, the UASB method is mainly intended for the treatment of soluble organic matter, and it is difficult to decompose the solid organic matter by the UASB method, and the solid organic matter may inhibit the sedimentation property of the granules. Therefore, conventionally, when organic wastewater containing a large amount of solid organic matter is treated by the UASB method, the organic wastewater is separated into solid and liquid before the UASB reaction tank, and only the separated liquid is introduced into the UASB reaction tank. Processing has been done.

In addition to the UASB method in which cells are immobilized, the following floating anaerobic treatment methods have been proposed and put into practical use.
(2) Transient methane fermentation method: This method has been used in the treatment of excess sewage sludge and human waste, and can also treat solid organic matter. Since it is a transient type, solid-liquid separation is unnecessary and energy saving is required. On the other hand, since the bacterial cell concentration cannot be kept high, there is a disadvantage that a large-capacity methane fermenter is required.
(3) Methane fermentation method for returning sludge: In order to solve the problem of requiring a large-capacity fermenter in the above-mentioned transient type, the sludge in the methane fermenter is extracted, concentrated by centrifugation, etc., and returned. This is a method for increasing the sludge concentration in the fermenter. In this method, since a flocculant (cationic polymer) is required for the recovery of methane bacteria and the use of a centrifugal concentrator, etc., a large amount of chemical costs, power costs and construction costs are required. The reality is that it is not so popular.

  When organic wastewater containing a large amount of solid organic matter is subjected to solid-liquid separation and only the separated solution is subjected to anaerobic treatment by the UASB method, organic concentrated sludge is generated by solid-liquid separation of the organic wastewater. The activated sludge method is usually used for this sludge treatment. However, the activated sludge method cannot be said to be an energy-saving treatment method as described above, and in operation such as foaming in an aeration tank and sludge floating in a sedimentation tank. There are many troubles.

On the other hand, when the concentrated sludge obtained by solid-liquid separation of organic waste water containing a large amount of solid organic matter is subjected to anaerobic biological treatment, there are the following problems. That is, for example, organic wastewater such as food production wastewater contains a large amount of solid organic matter and contains a lot of organic nitrogen in the solid matter. Therefore, when an anaerobic biological treatment is performed on the concentrated solid organic matter, ammonia nitrogen (NH ₄ -N) is generated at a high concentration as the solid organic matter is decomposed. The inhibitory concentration of NH ₄ -N in methane bacteria (medium temperature; 35 ° C.) is about 1,000 mg / L (500 to 2,000 mg / L), and it is necessary to dilute to this inhibitory concentration or less during operation. By this dilution, the amount of water flowing into the methane fermenter is greatly increased (several times to 10 times), and a huge capacity is required in the case of the transient methane fermenter.
In addition, even in the methane fermentation method in which sludge is returned, the amount of water provided for solid-liquid separation increases, the solid-liquid separation device becomes large-scale, and the operating costs such as the flocculant and electricity cost also rise.

On the other hand, a two-phase treatment method in which organic acid fermentation is performed is also proposed as a pretreatment for methane fermentation. The two-phase processing method has the following advantages.
That is, in the anaerobic biological treatment of solid organic matter, the solid organic matter is hydrolyzed and reduced in molecular weight to sugar, amino acid, etc., then converted to an organic acid (lower fatty acid) by acid-producing bacteria, and further to acetic acid by acetic acid-producing bacteria. Become. In methane fermentation, acetic acid is further converted into methane and carbon dioxide by methanogenic bacteria.

In this microbial reaction, the growth of methanogenic bacteria is remarkably slow, so they are susceptible to various inhibitions and are slow to recover and difficult to maintain, but in the two-phase treatment method that separates organic acid fermentation and methane fermentation, Since organic acid production or acetic acid production is carried out by various bacteria in the preceding organic acid fermentation, it is less susceptible to inhibition and easier to recover than methane bacteria.
For example, the concentration of NH ₄ -N that is inhibited by ammoniacal nitrogen (NH ₄ -N) is about 1,000 mg / L for mesophilic methane bacteria as described above, whereas that for acid producing bacteria is 5,000 mg. / L or more. Furthermore, NH ₄ -N inhibition is said to be due to gasification of NH ₃ rather than NH ₄ ⁺ ions, but it is inhibited by making the acid fermenter weakly acidic at pH 5-6 to prevent the formation of NH _3. It can be made difficult to receive.

The production of excess sludge accompanying acid fermentation is 2-3 times larger than that of methane bacteria, but is about 1 / 2-1 / 3 less than that of aerobic treatment. Therefore, the amount of surplus sludge produced as a whole treatment system by the two-phase treatment method is much smaller than that of the aerobic biological treatment.
In addition, since the activity of methane bacteria is inhibited by setting the acid fermentation treatment pH to weak acidity, for example, pH 5 to 6 (preferably pH 5.0 to 5.5), generation of methane gas in the acid fermentation tank is suppressed. You can also.

  Thus, the solid organic matter is methane-fermented through a process of polymer → low molecule → acid generation, but the solid organic matter is separated into an acid fermentation step and a methane fermentation step, so that the solid organic matter is solidified. Organic substances can be decomposed more energy-saving, and more energy can be recovered.

Conventionally, in the treatment of organic wastewater by such a two-phase treatment method, the whole amount of acid fermentation broth obtained by organic acid fermentation is usually subjected to methane fermentation treatment (normally transient treatment without dilution or solid-liquid separation). However, Patent Document 1 describes that the acid fermentation liquid is subjected to solid-liquid separation and the separation liquid is subjected to methane fermentation.
In this patent document 1, when solid content (SS) much contained in an acid fermentation liquid flows into a methane fermentation tank, SS accumulates in the tank. For example, in the UASB method, the granule sludge is caused to flow into the system, Moreover, in the fixed bed method, the filter medium is blocked, and in any case, the processing efficiency is lowered. In order to solve this problem, the acid fermentation broth is subjected to solid-liquid separation, and the separated liquid is subjected to methane fermentation. .

Japanese Patent No. 2587301

  However, as in the method of Patent Document 1, the method of simply subjecting the acid fermentation broth to solid-liquid separation and subjecting the separated liquid to methane fermentation has the following problems.

(1) The solid organic matter contains a large amount of nitrogen such as protein. When this solid organic matter is subjected to organic acid fermentation, it becomes ammoniacal nitrogen (NH ₄ -N). This NH ₄ -N is as described above. Has an inhibitory effect on methane bacteria. If the acid fermentation broth is simply subjected to solid-liquid separation and the separated liquid is subjected to methane fermentation, a liquid containing NH ₄ -N produced by organic acid fermentation at an inhibitory concentration of methane bacteria will flow into the methane fermentation tank. Methane fermentation efficiency decreases.

(2) The acid fermentation broth contains a solid inorganic substance derived from organic wastewater that is raw water, and thus becomes a high-concentration SS-containing liquid having a solid matter concentration (SS) of 10,000 mg / L or more. When such an acid fermentation broth is solid-liquid separated as it is, soluble organic matter adheres to the SS contained in a large amount in the solution and is separated together with sludge, so that the soluble organic matter produced by organic acid fermentation is efficiently used. In other words, the amount of soluble organic substances that cannot be recovered in the separation liquid and contained on the concentrated sludge side and discharged out of the system increases. In this case, the recovery efficiency of methane gas falls by the reduction of the amount of soluble organic matter provided for methane fermentation.

  In Patent Document 1, a part of the methane fermentation treated water is circulated to the acid fermenter, but this is merely a circulated treatment of the treated water and does not correspond to dilution of the acid fermentation broth from the acid fermentation process. .

  An object of the present invention is to solve the above-mentioned conventional problems and to provide a method for efficiently treating organic waste water containing a large amount of solid organic matter by a two-phase treatment method.

The organic wastewater treatment method of the present invention (Claim 1) includes an acid fermentation step of subjecting an organic wastewater containing solid organic matter to an organic acid fermentation, and diluting the acid fermentation broth flowing out of the acid fermentation step with dilution water. It has a dilution process, the solid-liquid separation process which carries out solid-liquid separation of the dilution liquid of this dilution process, and the methane fermentation process which carries out the methane fermentation of the separated liquid of this solid-liquid separation process.

The organic wastewater treatment method of the present invention (Claim 2) includes an acid fermentation step of subjecting an organic wastewater containing solid organic matter to an organic acid fermentation, and diluting the acid fermentation broth flowing out from the acid fermentation step with dilution water. Dilution step, agglomeration step for aggregating the dilution liquid of the dilution step, a solid-liquid separation step for solid-liquid separation of the agglomeration treatment liquid of the aggregation step, and methane fermentation for methane fermentation of the separated liquid of the solid-liquid separation step And a process.

  The organic wastewater treatment method according to claim 3 has a solid-liquid separation step for solid-liquid separation of the organic wastewater containing the solid organic matter in claim 1 or 2, and the separation sludge of the solid-liquid separation step is Organic acid fermentation is performed in the acid fermentation process.

  The organic wastewater treatment method according to claim 4 has a biological treatment step of biologically treating the separated liquid of the solid-liquid separation step according to claim 3, and uses the treated water of the biological treatment step as the dilution water. It is characterized by that.

The organic wastewater treatment method according to claim 5 is the method according to any one of claims 1 to 4 , wherein in the dilution step, the acid fermentation liquor from the acid fermentation step is supplied to a dilution tank and diluted with dilution water. Or, it is a step of diluting by injecting dilution water into the acid fermentation broth transfer pipe, wherein the dilution rate in the dilution step is 5 to 20 times.

In the present invention, by diluting the acid fermentation broth and then performing solid-liquid separation, the ammonia nitrogen (NH ₄ -N) concentration in the separated liquid is lowered, and NH ₄ -N inhibition of methane bacteria in the methane fermentation process is prevented. Stable and efficient methane fermentation treatment.
In addition, by diluting the acid fermentation broth, by reducing the SS concentration of the acid fermentation broth, when the acid fermentation broth is subjected to solid-liquid separation, the soluble organic matter in the acid fermentation broth can be efficiently recovered on the separation liquid side. As a result, the amount of soluble organic matter provided to the methane fermentation process is increased, and the recovery efficiency of methane gas is improved.

  In the present invention, the dilute solution of the acid fermentation broth may be subjected to an agglomeration treatment, followed by solid-liquid separation, whereby more efficient solid-liquid separation can be performed (claim 2).

  In addition, organic wastewater containing solid organic matter may be subjected to solid-liquid separation before organic acid fermentation, and the separated sludge may be subjected to organic acid fermentation, thereby reducing the capacity of the acid fermenter, An efficient organic acid fermentation can be performed while maintaining a stable body (Claim 3).

  Further, when the organic waste water is separated into solid and liquid in this way, the solid / liquid separated liquid may be biologically treated, and the biologically treated water may be used as dilution water for the acid fermentation liquid.

  In the present invention, the acid fermentation broth is preferably diluted at a dilution factor of 5 to 20 in order to sufficiently obtain the above-described effects after dilution while suppressing an excessive increase in the amount of the liquid (claim). Item 5).

It is a systematic diagram which shows embodiment of the processing method of the organic waste_water | drain of this invention. It is a systematic diagram which shows other embodiment of the processing method of the organic waste_water | drain of this invention. It is a systematic diagram which shows the example of application at the time of applying this invention to the treatment of the rich organic waste_water | drain with a high solid organic substance density | concentration. It is a systematic diagram which shows the example of application at the time of applying this invention to the treatment of the rich organic waste_water | drain with a high solid organic substance density | concentration. It is a graph which shows the result of Experimental example 1 (relation between HRT of an acid fermenter, solubilization rate, etc.). It is a graph which shows the result (Experiment 2) (relation between HRT of an acid fermentation tank and SS recovery rate in solid-liquid separation). It is a graph which shows the result (The relationship between the PAC addition rate in the solid-liquid separation of an acid fermentation liquid, and supernatant SS) of Experimental example 3. It is a graph which shows the result of Experimental example 4 (relationship between the centrifugal force in SS of a dilution liquid, SS recovery rate, etc.).

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

1 and 2 are system diagrams showing an embodiment of the organic wastewater treatment method of the present invention.
In the method of FIG. 1, organic wastewater containing solid organic matter that is raw water is introduced into the first sedimentation tank 1 through the pipe 11 and separated into solid and liquid, and the separated liquid is supplied from the pipe 12 to another biological treatment apparatus 10. And processed by an aerobic biological treatment method such as an activated sludge method or an anaerobic biological treatment method such as a UASB method. A part of the treated water of the biological treatment apparatus 10 is supplied to the dilution tank 3 as dilution water described later from the pipe 13, and the remaining part is discharged out of the system through the pipe 14. On the other hand, the separated sludge in the first sedimentation tank 1 is fed to the acid fermentation tank 2 through the pipe 15.

  The first sedimentation tank reduces the water tank capacity of the acid fermentation tank 2 by concentrating the solid content (SS) in the raw water to a higher concentration, and also stabilizes the bacterial cell maintenance and improves the processing efficiency. It is provided to plan. That is, since the required capacity of the acid fermenter 2 is determined not by the load of organic matter but by the residence time, it is preferable that the raw water is separated into solid and liquid to increase the SS concentration prior to organic acid fermentation.

The organic wastewater to which the organic wastewater treatment method of the present invention is applied is generally factory wastewater having an SS concentration of about 500 to 5000 mg / L. In the present invention, preconcentration is performed in this way. Therefore, it is preferable to concentrate the SS concentration to 10 g / L or more, particularly to the SS concentration of 30 g / L or more, for example, about 30 to 40 g / L, and introduce it into the acid fermenter 2.
If the SS concentration of the raw water is equal to or higher than the above concentration, the pre-concentration by the first sedimentation tank 1 is unnecessary.

  The solid-liquid separation means for pre-concentration of the raw water is not particularly limited, and other means such as centrifugal concentration and pressurized levitation can be adopted in addition to gravity concentration using a precipitation tank. A method by concentration is preferred.

  In the solid-liquid separation of raw water, a flocculant may be used to improve solid-liquid separation. As the flocculant, inorganic flocculants such as PAC (polyaluminum chloride), sulfuric acid band, ferric chloride, polyiron sulfate, cationic polymer flocculants (cationic polymers), anionic polymer flocculants (anionic polymers) ) And the like can be used. These may be used alone or in combination of two or more.

  The separated sludge of the first sedimentation tank 1 introduced into the acid fermentation tank 2 is subjected to organic acid fermentation in the acid fermentation tank 2 and becomes soluble organic matter. Specifically, after solid organic substances are reduced in molecular weight by hydrolysis, they are converted into organic acids (lower fatty acids) by acid-producing bacteria and further converted into acetic acid by acetic acid-producing bacteria.

  This acid fermenter 2 is normally operated in a transient manner from the viewpoint of simplification of the apparatus.

  Acid fermentation 2 comprises a stirrer 2A, a pH meter 2B, a neutralizing agent injection means 2C, a thermometer 2D, and a heating means (steam injection means in FIG. 1) 2E. The temperature means 2E may not be necessary.

In the acid fermentation tank 2, it stirs gently with the stirrer 2A so that SS in a tank may not settle. The stirrer type may be a stirring blade or an underwater stirrer.
In addition, since an organic acid is generated by acid fermentation of solid organic matter and the pH is lowered, an alkali such as NaOH is added as a neutralizing agent from the neutralizing agent injection means 2C when the pH is lower than the pH at which acid fermentation is possible. Then, the pH meter 2B is controlled so that the pH in the tank is maintained at about 5-6.
Further, the temperature condition of the organic acid fermentation is desirably a water temperature of 20 to 55 ° C. Therefore, when the water temperature is low, monitoring and controlling with the thermometer 2D, blowing steam from the heating means 2E as necessary, The water temperature in the tank is kept at a predetermined water temperature by other indirect heating means.

  In order to obtain a sufficiently high decomposition efficiency of the solid organic matter, the residence time (HRT) of the acid fermentation tank 2 is preferably 3 days or more, particularly 5 days or more, for example, 5 to 10 days.

  In addition, when there exists an aerobic biological treatment process as a post process in a back | latter stage, it is also possible to return the surplus sludge to this acid fermentation tank 2, and to process it. Moreover, you may return the separation sludge of the 2nd settling tank 4 of a back | latter stage. Furthermore, you may introduce the surplus sludge of the above-mentioned biological treatment apparatus 10. By appropriately adjusting the residence time of the acid fermentation tank 2, about 30 to 60% of the solid organic matter in the excess sludge can be decomposed into soluble organic matter by acid fermentation.

  In the treatment in the acid fermenter 2, since methane fermentation is not performed as described above, the generation of gas is very small. However, since hydrogen sulfide, carbon dioxide, and the like are slightly generated by the activity of acid-producing bacteria and sulfate-reducing bacteria, it is preferable to perform odor collection and exhaust gas treatment in the acid fermentation tank 2. The exhaust gas treatment method may be any method such as blowing into an aeration tank for aerobic treatment or chemical deodorization.

  The treatment liquid (acid fermentation liquid) in the acid fermentation tank 2 is then fed from the pipe 16 to the dilution tank 3 and diluted with dilution water from the pipe 13.

  In the present invention, the acid fermentation liquid is thus diluted with dilution water prior to solid-liquid separation and methane fermentation treatment.

  The purpose of dilution in the present invention is as follows.

(1) The solid organic matter contains much nitrogen content of protein, and when this solid organic matter is solubilized, NH ₄ —N is obtained. This NH ₄ -N has an inhibitory action on methane bacteria as described above. For this reason, in the present invention, prior to solid-liquid separation of the acid fermentation broth, the acid fermentation broth is diluted so that the NH ₄ -N concentration is less than or equal to the inhibitory concentration of methane bacteria (for example, about 1000 mg / L or less in the case of food wastewater). ).
(2) Since the solid inorganic substance derived from raw water remains in the acid fermentation broth, the solid matter concentration (SS) is 10000 mg / L or more. For this reason, even if an acid fermentation liquid is solid-liquid separated as it is, the soluble organic substance solubilized in the acid fermentation tank 2 cannot be effectively obtained in the separation liquid. By diluting the acid fermentation broth, many soluble organic substances can be obtained in the separated liquid.

If the degree of dilution of the acid fermentation liquor (dilution ratio) is too low, the above-mentioned effect due to dilution cannot be obtained sufficiently. If it is too high, the water load on the solid-liquid separation means at the subsequent stage increases, If it exists, a water area load will become large and is not preferable.
Accordingly, the dilution rate is usually 5 to 20 times, particularly preferably 10 to 15 times, although it depends on the solid-liquid separation means in the latter stage and the SS concentration of the acid fermentation liquid. However, when the solid-liquid separation means in the subsequent stage is based on centrifugation or membrane separation, the dilution ratio can be 5 times or less, for example, about 2 to 5 times.

  As dilution water used for dilution of an acid fermentation liquid, what is necessary is just water with little SS, and there is no restriction | limiting in particular. In FIG. 1, the treated water of the biological treatment apparatus 10 is diluted water, but it may be treated water of other systems such as treated water of the methane fermentation tank 5 in the subsequent stage. Moreover, if SS density | concentration is low, the diluted waste water of another system | strain may be sufficient.

  In FIG. 1, a dilution tank 3 is provided, and the acid fermentation liquid and dilution water are mixed and diluted in the dilution tank 3 by the stirrer 3 </ b> A, but the dilution tank 3 is omitted and the acid fermentation liquid transfer pipe 16 is provided. You may dilute by injecting dilution water directly.

  The dilution liquid in the dilution tank 3 is then fed from the pipe 17 to the second sedimentation tank 4 for solid-liquid separation, and the separation liquid containing soluble organic substances is fed from the pipe 18 to the methane fermentation tank 5 to separate the sludge ( The solubilized residue) is discharged out of the system through the pipe 19.

  The solid-liquid separation means for the diluted liquid is not particularly limited, and in addition to gravity-type sedimentation separation by a sedimentation tank, means such as centrifugal separation, pressurized flotation, and membrane separation can also be adopted, but from the aspect of energy saving, A method by gravity type sedimentation is preferred.

  In addition, if it is centrifugation and membrane separation, the below-mentioned aggregation process will become unnecessary and the amount of dilution water will be small and sufficient effect can be acquired.

  In the solid-liquid separation of the diluted solution, no flocculant may be added. However, when it is desired to lower the SS concentration of the separated solution or because the residence time of the acid fermentation tank 2 is relatively short, it is difficult to form flocs. When the liquid separation property is poor, or when the inflow of SS into the UASB tank as the subsequent methane fermentation tank is not preferable, an aggregating agent may be added to perform the aggregation treatment. As the flocculant, a combination of the above-mentioned inorganic flocculant such as PAC and an anionic polymer, a cationic polymer alone, or a combination of an anionic polymer and a cationic polymer is preferable.

  In FIG. 1, the second settling tank 4 is provided with a stirrer 4A. However, the installation of the stirrer 4A is not an essential condition because it can be handled by setting the bottom of the tank to an angle of repose or more.

A suitable water area load in the second sedimentation tank 4 varies depending on whether or not a flocculant is added, 0.5 to ² m ³ / m ² / hr when no flocculant is added, and 1 to ² when a flocculant is added. It is about 4 m ³ / m ² / hr.

  In addition, when using a centrifuge as a solid-liquid separation means of a dilution liquid, it is preferable not to add a flocculant in principle and to carry out with the centrifugal force about 1000-2100G.

  The separation liquid containing soluble organic substances from the second sedimentation tank 4 is fed to the methane fermentation tank 5 through the pipe 18 and subjected to methane fermentation. There are no particular restrictions on the means of methane fermentation, but high-load, high-speed and efficient methane fermentation is possible, and solid-liquid separation after treatment is unnecessary, saving space and energy, and recovering energy as methane gas It is preferable to use a UASB tank because of its high efficiency.

  The treated water in the methane fermentation tank 5 is discharged out of the system through the pipe 20.

  On the other hand, the separated sludge in the second settling tank 4 is discharged out of the system and used for aerobic biological treatment, finishing methane fermentation treatment, etc., but may be dehydrated as it is. However, since this separated sludge contains a large amount of intermediate decomposition products in organic acid fermentation, a large amount of dehydrating chemicals or odor may be a problem. In that case, it is possible to reduce the amount of dehydrated chemicals and the odor of the dehydrated cake by sufficiently using the amount of diluted water in the previous dilution step and washing the residue generated in the organic acid fermentation.

  Even if the separated sludge in the second sedimentation tank 4 is treated by aerobic biological treatment, methane fermentation treatment, or the like, in the present invention, most of the solid organic matter in the raw water becomes soluble organic matter by acid fermentation, and this soluble organic matter Since most of the liquid is transferred into the separation liquid, the load in the treatment of the separated sludge in the second sedimentation tank 4 can be remarkably small, and the scale of the treatment equipment is larger than that in the case where the raw water is directly subjected to aerobic biological treatment. Is greatly reduced.

In addition, as mentioned above, the acid fermentation tank 2 is normally operated in a transient manner, and there is no need to return the separated sludge (solubilized residue) in the second sedimentation tank 4. However, in the following cases, part of the separated sludge in the second sedimentation tank 4 may be returned to the acid fermentation tank 2 for the purpose of securing the necessary amount of bacterial cells.
(1) When the solid organic matter (VSS) density | concentration of the raw | natural water introduced into the acid fermenter 2 or its solid-liquid separation sludge is thin.
(2) When it is desired to increase the acid generation degree of solid organic matter.
(3) When biodegradation of solid organic matter is slow.

  In the method shown in FIG. 2, prior to solid-liquid separation of the diluted solution, after aggregating with an inorganic flocculant from the pipe 21 in the first aggregating tank 6, anionic polymer from the pipe 22 is used in the second aggregating tank 7. Unlike the method shown in FIG. 1, the other configuration and procedure are the same in that the flocs are coarsened and the aggregating treatment liquid thus agglomerated is subjected to solid-liquid separation. In FIG. 2, members having the same functions as those shown in FIG.

  That is, as described above, when the solid-liquid separation property of the diluted solution of the acid fermentation solution is poor or when it is desired to reduce the SS concentration of the solid-liquid separated solution fed to the methane fermentation tank 5, the solid-liquid separation of the diluted solution is performed. Prior to the agglomeration treatment.

  In the method of FIG. 2, the diluting liquid from the diluting tank 3 is introduced into the first coagulating tank 6 through the pipe 17A, an inorganic flocculant is added, and rapid stirring is performed with the stirrer 6A. Here, the pH is appropriate if it is a normal addition amount of the inorganic flocculant, but if the pH is not optimal for aggregation, the pH is adjusted with an alkali agent or acid. The aggregating treatment liquid using the inorganic aggregating agent is then introduced into the second aggregating tank 7 through the pipe 17B, an anionic polymer is added, and agitation is performed with the agitator 7A to form a floc. The aggregating treatment liquid in the second aggregating tank 7 is fed from the pipe 17 to the second sedimentation tank 4 for solid-liquid separation.

When the aggregating treatment is performed as described above, as the aggregating agent,
-Combined use of inorganic flocculant and anionic polymer-Combined use of anionic polymer and cationic polymer-Use of cationic polymer alone. Usually, a combination of an inorganic flocculant and an anionic polymer is used, but only a polymer may be used to avoid the formation of SS by the inorganic flocculant.

The flocculant suitable for the flocculant treatment of the diluted solution and the preferred addition amount are as follows.
Inorganic flocculants: Ferric chloride and polyaluminum chloride (PAC) that aggregate in a weakly acidic range of about pH 5 to 6 and do not contain sulfate radicals are preferable, and a suitable addition amount is about 25 to 50 mg / L.
Anionic polymers: acrylates and the like are preferable, and the preferred addition amount is about 1 to 3 mg / L.
Cationic polymer: dimethylaminoethyl acrylate (DAA type), dimethylaminoethyl methacrylate (DAM type), diallyldimethylammonium chloride (DADMAC type), diamine type and chitosan type are preferable, and the preferred addition amount is 3-5 mg / About L.

  Next, an application example in the case where the present invention is applied to the treatment of rich organic waste water having a high solid organic matter concentration will be described with reference to FIGS.

  In FIG. 3, since the concentration of solid organic matter in the raw water is high, it is introduced directly into the acid fermentation tank 21 without pre-concentration, diluted by injecting dilution water into the acid fermentation broth transfer pipe, and then the solid-liquid separation means 22 To be separated into solid and liquid. The separation liquid of the solid-liquid separation means 22 is supplied to the UASB tank 23 and subjected to methane fermentation treatment, and the UASB treated water and the separated sludge of the solid-liquid separation means 22 are further treated by the aerobic biological treatment device 24. In this example, a part of the treated water of the aerobic biological treatment device 24 is returned to the previous stage as dilution water, and the remainder is post-treated and then discharged. Moreover, a part of the excess sludge of the aerobic biological treatment apparatus 24 is returned to the acid fermentation tank 21, the remaining part is dehydrated by the dehydrator 25, and the dehydrated cake is discharged out of the system.

  Note that dilute waste water is injected into the separation liquid transfer pipe and the UASB treated water transfer pipe of the solid-liquid separation means 22 for SS concentration adjustment and merge processing, respectively.

  In many cases, food wastewater is mixed with rich wastewater and dilute wastewater to form total wastewater. FIG. 4 shows an application example in this case. In FIG. 4, the concentrated sludge of the pre-concentration means 31 is subjected to organic acid fermentation in the acid fermentation tank 32, diluted with dilution water, and solid-liquid separated by the solid-liquid separation means 33. The separation liquid of the solid-liquid separation means 33 is fed to the inlet side of the pre-concentration means 31, the inlet side of the UASB tank 34, or a separately provided UASB tank 36 and subjected to UASB treatment, and is then favored by the aerobic biological treatment apparatus 35. Tempered biological treatment.

  The separated sludge of the solid-liquid separation means 33 is subjected to aerobic biological treatment in the aerobic biological treatment device 35 subsequent to the UASB tank 34 (may be subjected to methane fermentation treatment before this aerobic biological treatment). Dehydrated.

  On the other hand, the separation liquid of the pre-concentration means 31 is processed in the UASB tank 35, a part of the UASB treated water is supplied as dilution water to the transfer pipe of the acid fermentation tank 32, and the remainder is sent to the aerobic biological treatment apparatus 35. It is supplied and treated with aerobic organism, and this treated water is discharged after being further treated. In addition, you may use the treated water of the aerobic biological treatment apparatus 35 as dilution water of an acid solution.

  In any case, compared to the case where organic wastewater containing solid organic matter is subjected to aerobic biological treatment or UASB treatment as it is, the aeration power and surplus sludge generation amount are greatly reduced, and there is a problem due to SS in the UASB tank. In this way, energy can be recovered by performing efficient processing with space saving and energy saving.

  Hereinafter, the present invention will be described in more detail with reference to experimental examples corresponding to the examples.

[Experimental Example 1]
An organic acid fermentation experiment was conducted on the following water quality separated liquid obtained by solid-liquid separation of the potato wastewater discharged from the company A factory B by gravity sedimentation.

<Separate liquid quality>
SS: about 30-40 g / L
VSS: about 25-34 g / L
VSS / SS: 75-85%
COD _Cr : about 40 to 55 g / L

As a test apparatus, a 1 L jar fermenter was used, and the water temperature was adjusted at 35 ° C. ± 1 ° C.
The operation method was a batch operation and a one-time operation method (treatment liquid extraction and raw water input were performed once / day).
As the solid organic matter (VSS) in the tank solubilizes and generates acid, the pH of the liquid in the tank decreases, so adjust the pH in the tank to pH 5.0 to 5.5 using NaOH according to the instructions of the pH meter. did.

  FIG. 5 shows the effect of VSS decomposition (solubilization) when the hydraulic residence time (HRT) is changed in this treatment. In addition, the analysis of the soluble substance was performed about the liquid which filtered the liquid in a tank with the microfiltration membrane with the hole diameter of 0.45 micrometer. Further, the solubilization rate is the decomposition (decrease) rate of VSS.

FIG. 5 shows that VSS decreases with increasing HRT, soluble organic acid (COD _Cr ) increases with the decomposition of VSS, and NH ₄ -N from the decomposition of protein also increases. .
In addition, the degradation of VSS can be effectively performed by setting the HRT to 3 days or more, preferably 5 days or more. From the VSS degradation rate, it can be seen that there is little bacterial cell proliferation accompanying solid VSS degradation.

[Experiment 2]
A solid-liquid separation experiment of the acid fermentation broth obtained in Experimental Example 1 was performed.
A diluted solution (MLSS after dilution is about 3.5 to 1.2 g / L) diluted 10 times by adding tap water to the acid fermentation broth at each HRT is placed in a 1 L graduated cylinder and allowed to stand for 30 minutes. The amount of SS that subsequently settled was measured, and the results are shown in FIG.

  As shown in FIG. 6, as the HRT in the acid fermenter becomes longer, the SS of the diluted solution of the acid fermentation solution tends to settle, so that most of the SS can settle and separate in about 5 days or more of the HRT, It turns out that it can use for methane fermentation.

[Experiment 3]
As shown in Experimental Example 2, although most of the SS can be separated by sedimentation without adding a flocculant, the sedimentation speed is not sufficient and a large sedimentation tank is required. Furthermore, a large amount of SS remains in the separation liquid, which is inappropriate for direct UASB treatment.
In order to solve these problems, a coagulation treatment experiment of the diluted solution was performed.

  In Experimental Example 1, PAC as an inorganic flocculant was added to a diluted solution (water quality was pH 5.3, SS = 1.4 g / L, VSS / SS = 54%) obtained by diluting the acid fermentation broth of HRT 5 days with tap water. In various addition amounts, 0.5 to 1.0 mg / L of anionic polymer (acrylate polymer) was added, and after agglomeration treatment, solid-liquid separation by standing was performed as in Experimental Example 2. The SS concentration of the separation liquid was measured, and the results are shown in FIG.

From FIG. 7, good flocs were formed at a PAC addition rate of 25 to 50 mg / L with respect to a 10-fold diluted solution of the acid fermentation broth, and SS in the separated solution was also 200 to 300 mg / L.
Even in the flocculation treatment with a cationic polymer (DAA) alone, a good floc is formed at a polymer addition rate of 3 to 5 mg / L with respect to this 10-fold diluted solution, and the SS in the separation liquid is also 200 to 300 mg / L. It was confirmed that

[Experimental Example 4]
A solid-liquid separation experiment was performed using a centrifuge of the diluted acid fermentation broth.
An acid fermentation broth with SS = 15.38 g / L and a solubilization rate of about 72% obtained in the same manner as in Experimental Example 1 was diluted twice with tap water, and then solidified by a centrifuge without adding a flocculant. The liquid was separated.
The relationship between the centrifugal force of the centrifuge at this time and the SS concentration, water recovery rate, and SS recovery rate of the obtained filtrate is shown in FIG.

As shown in FIG. 8, it can be seen that 95% or more of the organic matter solubilized by acid fermentation is transferred to the filtrate side from the water recovery rate. The separated sludge had an SS of about 150 g / L (water content of about 85%).
In addition, in the solid-liquid separation by this centrifuge, the separation sludge having a water content of 80 to 83% can be obtained by adding about 0.3 to 0.5% by weight of cationic polymer (DAA system) per SS. This could be disposed of as a dehydrated cake.

DESCRIPTION OF SYMBOLS 1 1st precipitation tank 2 Acid fermentation tank 3 Dilution tank 4 2nd precipitation tank 5 Methane fermentation tank 6 1st coagulation tank 7 2nd coagulation tank

Claims (5)

An acid fermentation process for organic acid fermentation of organic wastewater containing solid organic matter,
A dilution step of diluting the acid fermentation liquor that has flowed out of the acid fermentation step with dilution water;
A solid-liquid separation step for solid-liquid separation of the dilution liquid of the dilution step;
A method for treating organic wastewater containing solid organic matter, comprising: a methane fermentation step of methane fermentation of a separated liquid of the solid-liquid separation step. An acid fermentation process for organic acid fermentation of organic wastewater containing solid organic matter,
A dilution step of diluting the acid fermentation liquor that has flowed out of the acid fermentation step with dilution water;
An aggregating step for aggregating the diluted solution of the diluting step;
A solid-liquid separation step of solid-liquid separation of the aggregation treatment liquid of the aggregation step;
A method for treating organic wastewater containing solid organic matter, comprising: a methane fermentation step of methane fermentation of a separated liquid of the solid-liquid separation step.   In Claim 1 or 2, it has a solid-liquid separation process which carries out solid-liquid separation of the organic waste water containing the solid organic matter, and the separation sludge of the solid-liquid separation process is subjected to organic acid fermentation in the acid fermentation process. A method for treating organic wastewater containing solid organic matter.   The organic substance containing a solid organic material according to claim 3, further comprising a biological treatment step for biologically treating the separated liquid in the solid-liquid separation step, wherein the treated water in the biological treatment step is used as the dilution water. Wastewater treatment method. In any one of claims 1 to 4, wherein the dilution step, or the acid fermentation liquid from the acid fermentation step is diluted with dilution water to feed into the dilution tank or transfer pipe of the acid fermentation liquor A method for treating organic wastewater containing solid organic matter , wherein the dilution is carried out by injecting dilution water into the diluting solution, and the dilution ratio in the diluting step is 5 to 20 times.

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