JP4257961B2 - Anaerobic digestion of organic waste - Google Patents

Description

  The present invention relates to a method for treating organic waste such as manure and excess sludge.

  Organic waste such as livestock and human excreta, food residues, and excess sludge from sewage treatment plants is generally anaerobically digested, thereby reducing the volume and simultaneously recovering valuable methane gas. Yes. However, when the organic waste to be treated has a low water content and VS [organic concentration (% by weight) in the organic waste] exceeds 2% by weight, the methane production is reduced or stopped. For this reason, anaerobic digestion is usually performed by pulverizing organic waste in advance, diluting with water, and reducing the VS to 1 to 0.5% by weight. Therefore, a treatment tank having a volume of at least 50 to 200 times its weight in terms of dry weight of the organic waste is required.

  By increasing VS, anaerobic digestion in a smaller processing tank becomes possible. However, the inhibition of methane production by ammonia produced in parallel causes a problem that effective or no methane recovery can be performed.

  As a technique for avoiding the inhibition of methane production by ammonia, for example, livestock manure which originally had a high free ammonia concentration was previously deammonized under alkali, then separated into a solid component and a liquid component, and the resulting solid component was converted into a solid component. A method of performing methane fermentation has been proposed (see Patent Document 1). However, this method only removes free ammonia and not nitrogen-containing organic substances in the solid component, so it cannot suppress the inhibition of methane production by ammonia to an extent that does not cause any problems throughout the process. .

  In addition, a part of the contents of the acid fermenter, which is the pretreatment tank, is transferred to an alkali tank and deammoniaed, and then transferred to methane fermentation. Again, it is returned to the acid fermenter, and the ammonia is inhibited while circulating the treatment. Has been proposed (see Patent Document 2). However, since it is necessary to always circulate a part of the treated product in a cycle of alkalinity → neutralization → alkaline → neutralization, it is usually necessary to circulate a part of the treated product. Therefore, not only the circulation becomes difficult, but also the steady pH adjustment becomes difficult, and the feasibility is lacking.

  Anaerobic digestion by removing the ammonia in nitrogen-containing waste by treating the treated material with alkali at high temperature, or removing the released ammonia in the form of gas to remove the inhibition of methane production by ammonia. A method has been proposed. For example, a method in which organic waste is solubilized by hot alkali treatment to release ammonia, and the liquid component obtained by solid-liquid separation is used to remove free ammonia through a product gas during methane fermentation (see Patent Document 3), organic The pH of the organic waste is adjusted to 8 to 10 to make it alkaline and solubilized at a high temperature of 150 to 350 ° C. to release ammonia and remove it (see Patent Documents 4 and 5), For example, a method of solubilizing organic waste at a temperature of 35 to 100 ° C. and removing ammonia by liberation and gasification of ammonia (see Patent Document 6) and the like can be used.

  In each of the series of preceding examples listed above, alkali treatment or thermal alkali treatment is commonly performed to liberate ammonia from the nitrogen-containing organic matter in the organic waste.

  By the way, it is well known that the composition of proteins, which are representative of nitrogen-containing organic substances, consists of peptide bonds of amino acids, and the main origin of ammonia that causes inhibition of methane formation in anaerobic digestion is derived from amines in amino acids. .

  Therefore, from the viewpoint of avoiding the inhibition of methane production by ammonia, it is considered to be important how to efficiently remove ammonia derived from amines of amino acids in proteins. The ammonia that is separated from the protein by the protein is not the amine derived from the peptide bond, but is derived from the amine bound to the free carboxyl group of the acidic amino acid in the protein molecule, so the ammonia released by such treatment is the total nitrogen in the protein. Most of the nitrogen remains as peptide bonds (see Non-Patent Document 1).

  As a method of avoiding the inhibition of methane production by ammonia focusing on this point, biological treatment at 30 to 45 ° C. is performed before anaerobic digestion of organic waste, and ammonia is produced from nitrogen-containing organic matter. Although there is a method of removing the generated ammonia, it has not been studied when the TS concentration [solid content concentration (% by weight) in organic waste] exceeds 5% (see Patent Document 7).

Therefore, both of these prior arts are sufficient as a method for removing nitrogen from nitrogen-containing organic matter as ammonia and removing it as an ammonia, and anaerobic digestion of organic waste by avoiding the inhibition of methane production by ammonia. I can't say that.
Japanese Patent Application No. 11-71137 Japanese Patent Application No. 2002-25332 Japanese Patent Application No. 2001-204921 Japanese Patent Application No. 2001-266346 Japanese Patent Application No. 2001-227359 Japanese Patent Application No. 2000-375722 Japanese Patent Application No. 2002-180944 Saburo Akahori “Protein Chemistry I”, published in April 1954

  An object of the present invention is to provide a method for treating organic waste, in which inhibition of methane production by ammonia is suppressed to a substantially non-problematic level, and particularly organic waste having a low water content can be efficiently treated. Objective.

That is, the present invention
[1] An organic waste treatment method for anaerobically digesting organic waste,
(1) Organic waste having a moisture content of 70 to 95 wt% and a VS concentration of 4.5 to 15 wt% using part of the organic waste after the decomposition and acid generation treatment as seed sludge A step of anaerobically decomposing and acid-generating the product under a temperature condition of 45 to 65 ° C. and removing the generated ammonia; and (2) organic waste that has undergone step (1) is converted into step (1) and Is a method of treating organic waste, including a process of producing methane in different fermenters ,
[2] First fermenter that decomposes and generates acid from organic waste using seed sludge, ammonia removal means for removing ammonia generated by the treatment, and methane generation from organic waste after removal of ammonia The processing apparatus of the organic waste for using for the processing method of said [1] which has a 2nd fermenter to process and a means to transfer organic waste from a 1st fermenter to a 2nd fermenter .

  According to the present invention, (1) methane can be recovered more efficiently than organic waste having a low water content, and (2) the waste has a low water content, so that its treatment volume is dramatically higher than that of the conventional method. Therefore, the installation area of the processing apparatus and the running cost can be greatly reduced. (3) Not only organic waste containing non-free nitrogen but also livestock and human excreta with high free ammonia concentration Organic wastes such as can be treated efficiently as well.

  The present invention has been made on the basis of finding a novel fact that has not been known so far with regard to ammonia consumption during anaerobic digestion of organic waste.

  In general, the reason why methane fermentation is possible at a low VS can be interpreted as the ammonia produced does not reach the inhibitory concentration because it is diluted with water. Conventionally, methane fermentation at a relatively high VS has been realized by adding large sawdust or raw garbage to the object to be treated, although it is empirical. The inventors thought that these additives substantially played the role of diluting ammonia, which is an inhibitor, as well as water at low VS.

  In the reference examples described below, the dehydrated sludge that was anaerobically digested at low VS used by the inventors as a source of bacteria involved in anaerobic digestion already produced enough ammonia during the digestion process. Do not generate. From this background, the anaerobic digestion sludge used in the reference example should be regarded as having the role of diluting the inhibitor in anaerobic digestion as equivalent to water, and treat only the target sludge as the actual condition of VS. Thus, new knowledge described in this specification was obtained.

  In general, the level of water content of organic waste correlates with the level of VS of the waste, and therefore, in this specification, the level of water content and the level of VS are treated as having the same meaning. Thus, for example, low moisture content has the same meaning as high VS.

  In general, in an anaerobic digestion process, acetic acid-producing bacteria, butyric acid-producing bacteria, etc., produce acid and release ammonia from nitrogen-containing organic substances (decomposition and acid production), and the methanogenic bacteria produce organic acids into methane. Conversion takes place (methane production). However, in fact, since these series of decomposition reactions proceed congestively, it was considered difficult to separate the processes of acid / ammonia production and methane production.

However, when surplus sludge was used as organic waste, and the ammonia consumption during the anaerobic digestion process was examined in detail, it was surprising that the acid / ammonia production process and the methane production process can be separated from each other. It was newly found that when a part of sludge is used as seed sludge, ammonia can be produced with high efficiency. Details of the examination are shown in Reference Examples and Examples below.
Here, “separable” means that the process in which decomposition / acid generation is preferentially performed in the anaerobic digestion process of organic waste can be separated from the process in which methane generation is preferentially performed. Both processes may overlap when viewed as the entire digestion process.

  That is, as shown in FIG. 1, the ammonia conversion rate of nitrogen in nitrogen-containing organic substances such as protein in excess sludge is within the first 3 to 5 days of anaerobic digestion, regardless of the VS of excess sludge. Surprisingly, it reached 65 to 70 mol% of the total nitrogen. Considering the coexistence of proteins derived from living bacteria such as acetic acid producing bacteria and methanogenic bacteria, 80 to 90 mol% of nitrogen that can be converted to ammonia is liberated, and this ratio is obtained under hot alkali treatment. Compared with the general ammonia conversion rate of 15 to 20 mol%, the value is surprisingly high.

  On the other hand, the production of organic acids such as acetic acid and methane progresses more slowly as the VS becomes higher. In particular, as shown in FIG. 2, the methane production proceeds substantially completely when the VS of excess sludge is 10% by weight or more. I didn't. As a result of examining the degree of inhibition of the methane production rate by ammonia by changing the ammonia concentration, 50% production inhibition was observed at 2,000 ppm as shown in FIG. Further, when the concentration exceeded 5,000 ppm, methane production was 10% or less.

  Further, in the process of anaerobic digestion of surplus sludge (cultivation days: 25 days), the ammonia concentration in the sludge was examined. As a result, when the VS was 20% by weight, the ammonia concentration was 8,500 ppm. When VS was 10% by weight, the concentration was 4,000 ppm, when VS was 5% by weight, 2,500 ppm, and when VS was 4% by weight, the concentration was 2,000 ppm or less throughout. When comparing FIG. 2 with FIG. 4, it can be seen that the ammonia concentration reaches 3,000 ppm or more in the high VS region where methane formation did not occur.

  Furthermore, in the results of the 9-day anaerobic digestion experiment using acetic acid added to the low-ammonia conditioned sludge and changing the VS (reducing the water content) model sludge, as shown in FIG. Even in the case of%, methanation was observed.

  As a result of comprehensive evaluation of the above results, organic waste was decomposed and acid-generated preferentially in the initial stage of anaerobic digestion, and the generated ammonia was removed. In the next stage, methane production was processed by methane fermentation. As a result, it was predicted that even if the organic waste to be treated is in a high VS state, it can be treated efficiently. Thus, when such a two-stage anaerobic digestion was performed on organic waste with high VS, surprisingly, it was very efficient to treat the waste, which was conventionally impossible. It became clear that it can be implemented.

  In the present specification, “high VS” means that VS exceeds 2% by weight, and “low water content” means that the water content is less than 98% by weight.

  Although it does not specifically limit as an organic waste as a process target in the processing method of this invention, The processing method of this invention is used suitably for the process of the organic waste of a low moisture content. From the viewpoint of enhancing the treatment efficiency, the water content of the organic waste is preferably 70% by weight or more and less than 98% by weight, more preferably 70 to 95% by weight, and still more preferably 80 to 95% by weight. The VS of the waste is preferably more than 2% by weight and 30% by weight or less, more preferably 4.5 to 27% by weight, still more preferably 5 to 20% by weight, and even more, from the viewpoint of improving the processing efficiency. Preferably it is 5 to 15 weight%.

  When the organic waste to be treated does not have a low moisture content, it is preferable to dehydrate it by a known dehydration method such as a centrifugal concentrator or a sludge dehydrator to obtain a low moisture content before the treatment. The water content is determined by measuring the initial weight of organic waste and the weight of the residue after water evaporation, dividing the weight difference (initial weight-residue weight) by the initial weight and multiplying by 100. Can be sought. As evaporation conditions, 105-110 degreeC and 2 hours are mentioned. Moreover, when VS of organic waste is not high VS, it is preferable to set it as high VS beforehand. Since the VS is increased by reducing the water content of the waste, the water content of the organic waste may be reduced and adjusted to a desired value as described above. The VS concentration is defined as TS, which is the weight of the heat-treated sample remaining when the sample is heat-dried at 105-110 ° C. for 2 hours. Further, the heat-treated ash is heated at 600 ° C. ± 25 ° C. for 1 hour. It is possible to obtain the value by expressing “TS-IR” as “%” with respect to the weight of the sample before the treatment, where IR is the weight of the strongly heat-ashed sample remaining at the time of conversion.

  In addition, the treatment method of the present invention is very suitable particularly for the treatment of organic waste containing a high amount of nitrogen-containing organic matter. Although it does not specifically limit as content of the nitrogen-containing organic substance in organic waste, For example, it is about 3 to 10 weight%.

  Specific examples of organic wastes to be treated include excess sludge, sewage sludge, slaughterhouse waste, etc. that contain a lot of non-free nitrogen, livestock and human excreta with high free ammonia concentration, etc. Can be mentioned.

The treatment method of the present invention is an organic waste treatment method for anaerobically digesting organic waste,
(1) It includes a step of decomposing / acid-generating organic waste using seed sludge and removing the generated ammonia, and (2) a step of methane-generating organic waste that has undergone step (1). This is a method for treating organic waste. In the step (1), the decomposition / acid generation process in the anaerobic digestion process is preferentially performed, and in the next step (2), the methane generation process by methane fermentation is preferentially performed. Steps (1) and (2) may be performed in the same system (for example, in one fermenter) or in different systems (for example, in two separate fermenters) From the viewpoint of increasing the processing efficiency, it is preferable to carry out in a different system. Hereinafter, the aspect which processes organic waste in a different system | strain from a viewpoint which simplifies description is demonstrated.

  The decomposition / acid generation treatment of the organic waste in the step (a) is performed using a decomposition / acid-producing bacterium. The treatment can be carried out by optimizing conditions such as temperature, pH, treatment time and the like according to the decomposition / acid producing bacteria to be used, and allowing the decomposition / acid producing bacteria to act on the organic waste. By this treatment, the organic waste is converted into an organic acid such as acetic acid, and nitrogen of the nitrogen-containing organic substance contained therein is converted into ammonia. In addition, in the case of this process, it is preferable to stir this waste suitably from a viewpoint of improving processing efficiency. The treatment is usually completed when 50 to 70 mol% of nitrogen derived from the nitrogen-containing organic matter in the organic waste is converted to free ammonia. The nitrogen content in the organic waste can be measured by a known method.

  The degradation / acid-producing bacterium is not particularly limited, and for example, Clostridium genus, Bacteroides genus, Butyrivibrio genus, Fusobacterium genus, Enterobacter genus, Streptococcus genus, Peptococcus genus bacteria and the like are preferably used. From the viewpoint of enabling highly efficient treatment with a smaller treatment area, these bacteria are preferably supported on an arbitrary carrier in the system in which the decomposition / acid generation treatment is performed. The decomposition / acid generation treatment may be performed aerobically or anaerobically, but is preferably performed anaerobically.

  Seed sludge is used from the viewpoint of improving the processing efficiency when the organic waste is decomposed and acid-generated. As a method for using seed sludge, organic waste and seed sludge may be mixed and subjected to decomposition and acid generation treatment. As the amount of seed sludge used, any amount can be used. From the viewpoint of efficient decomposition and acid generation treatment, for example, 10 to 50 parts by weight of seed sludge per 100 parts by weight of organic waste It is preferable to mix to a certain extent. By using seed sludge, the processing time of the decomposition / acid generation treatment can be shortened. The seed sludge is usually about 30 to 65 ° C., preferably 45 to 65 ° C., more preferably 50 to 60 ° C., more preferably about 55 ° C. for about 15 to 50 days, and surplus according to the high temperature anaerobic digestion method. Sludge obtained by subjecting organic waste such as sludge to anaerobic culture or dehydrated sludge after sufficient anaerobic digestion with bacteria involved in anaerobic digestion can be used, but is not limited thereto. For the high temperature anaerobic digestion method, see, for example, biological treatment of wastewater (WW.ECKENFELDER. Jr, D.J. O'CONNOR co-authored by Shigehisa Iwai, Corona, 1965).

  In addition, when continuously decomposing / acid-generating organic waste by the batch method, an arbitrary amount of organic waste treated in the previous batch is left in the system where the treatment has been performed. By introducing new organic waste as seed sludge and treating it, more stable decomposition and acid generation treatment becomes possible. As the amount of seed sludge to be left from the previous batch, any amount can be left, but from the viewpoint of efficient decomposition and acid generation treatment, for example, 1 to 50%, preferably about 1 to 30% may be left. preferable.

  In addition, from the viewpoint of improving the treatment efficiency, nutrients such as vitamins are added to the organic waste during the decomposition and acid generation treatment of the organic waste, or the C / N (carbon content / nitrogen of the waste is added. The content ratio may be adjusted.

  Furthermore, from the viewpoint of promoting the decomposition / acid generation treatment, it is also preferable to solubilize the organic waste in advance under dry anaerobic or aerobic conditions. Such solubilization can be performed by a known method, for example, high temperature heating, ozone treatment, ultrasonic treatment, mechanical method and the like.

  The temperature for performing the decomposition / acid generation treatment is usually about 30 to about 65 ° C., but is preferably 45 to 65 ° C. or less, more preferably 50 to 60 ° C. from the viewpoint of improving the treatment efficiency, 55 A temperature around about 0 ° C. is more preferable. The pH of the mixture of organic waste and seed sludge is usually about 5-9. Further, the decomposition / acid generation treatment time of the organic waste is usually about 2 to 7 days.

  The method for removing ammonia generated by the decomposition and acid generation treatment of organic waste is not particularly limited as long as ammonia can be removed, but by adjusting the pH of the organic waste to the alkali side and heating it. A hot alkali treatment method in which ammonia is taken out of the system is preferred. In such a method, for example, the pH is adjusted to about 8.5 to 10, preferably around 9.5, and the organic waste in the system is heated with an electric heater or a hot water jacket, or low-pressure steam is used as the organic waste. The organic waste is heated to about 60 to 100 ° C. by blowing it into the inside, and ammonia is released from the waste and taken out of the system.

  The ammonia taken out of the system is absorbed into the acid solution, for example, by passing it through dilute hydrochloric acid or dilute sulfuric acid solution with an external device or introducing it into a gas chamber and spraying the acid solution. Can be removed. Moreover, the ammonia removal effect can be enhanced by recovering the ammonia from the acid solution that has absorbed ammonia and returning the regenerated acid solution to the organic waste.

  In addition, ammonia can be removed rapidly by methods such as making the pH of organic waste alkaline to 10.5 or higher, or setting the operation temperature to 120 ° C. or higher with high-pressure steam. In addition to the increased energy consumption and the need for more acid for neutralization after treatment, the large amount of chloride that is generated inhibits methane fermentation in the next step. The processing method has higher overall processing efficiency.

  As described above, the step (1) in the treatment method of the present invention removes nitrogen that can be converted into ammonia, which originates from nitrogen-containing organic matter in the organic waste having a low water content. This greatly increases the efficiency of the methane generation process in the next step, and has a unique meaning as a pretreatment when anaerobically digesting the waste. Therefore, as another aspect of the present invention, there is provided a method for removing nitrogen in organic waste, which includes a step of decomposing / acid-generating organic waste using seed sludge and removing generated ammonia. .

  In such a method for removing nitrogen from organic waste, from the viewpoint of enhancing the processing efficiency, it is preferably 45 to 65 ° C., more preferably 50 to 60 ° C., and even more preferably about 55 ° C., decomposition and acid generation. It is preferable to carry out the treatment.

  In the step (2), the organic waste from which nitrogen derived from the nitrogen-containing organic matter has been removed as ammonia through the step (1) is subjected to methane fermentation to perform methane generation treatment. The conditions for methane fermentation are not particularly limited, and conditions such as temperature, pH, treatment time and the like may be optimized as appropriate according to the methane-producing bacteria used. By this treatment, the organic component of the organic waste becomes methane gas, and the waste finally becomes the gas and inorganic substances such as phosphorus and calcium. Any of these products can be effectively used as resources. In addition, in the case of this process, it is preferable to stir this waste suitably from a viewpoint of improving processing efficiency.

  In this aspect, when implementing a process (2), the organic waste which passed through the process (1) is transferred from the system which performed the decomposition | decomposition and an acid production process to another system which performs a methane production process. At that time, although not particularly limited, for example, the organic waste is cooled to about 30 to 60 ° C., and the pH is adjusted to about 7 to 8.5 (neutralization treatment). preferable.

  The methanogen is not particularly limited. For example, bacteria belonging to the genus Methanobacterium, the genus Methanococcus, the genus Methanosarcina, the genus Methanosaeta, the genus Methanogenium, and the genus Methanospirillum are preferably used. These methanogens are preferably supported on an arbitrary carrier in the system for performing the methane production treatment from the viewpoint of enabling highly efficient treatment with a smaller treatment area. The temperature for performing the methane production treatment is usually about 30 to 60 ° C, preferably about 55 ° C. As pH, it is about 6-8 normally. The treatment time for organic waste is usually about 10 to 30 days. The methane generation process is performed anaerobically under the above conditions.

  The treatment method of the present invention has at least the above-described configuration. In addition, a more efficient organic waste can be obtained by appropriately combining the waste treatment means and treatment methods known in the organic waste treatment field. Can be achieved. The same applies to the processing apparatus of the present invention described below.

  According to the treatment method of the present invention, inhibition of methane production by ammonia can be suppressed to an extent that there is substantially no problem, and organic waste having a low moisture content can be treated efficiently. Therefore, the effect as described above is exhibited. Further, when the present invention is viewed from another viewpoint, the present invention provides an efficient method for recycling organic waste, which is a very excellent method from the viewpoint of resource recovery.

  Moreover, this invention provides the processing apparatus of the organic waste which can be used suitably for implementation of the said processing method of this invention as the one aspect | mode. Such an apparatus includes a first fermenter that decomposes and acid-generates organic waste using seed sludge, an ammonia removal means that removes ammonia generated by the treatment, and methane into organic waste after removal of ammonia. It has the 2nd fermenter to produce | generate, and a means to transfer organic waste from a 1st fermenter to a 2nd fermenter.

  As a 1st fermenter, what is necessary is just to use the fermenter which consists of a housing | casing made from steel etc., for example. Further, for example, the microorganisms used in the decomposition / acid generation treatment are known methods (Young, JC et al., The anaerobic filter for waste treatment. J. Water Pollution Control Fed., 41, 161 (1969), etc.) Therefore, it may be supported on an arbitrary carrier such as a plastic filter medium and held in the fermenter. The first fermenter is equipped with a stirring mechanism capable of stirring organic waste in the fermenter, a means for heating the contents, a temperature control mechanism in the container, a temperature measurement mechanism in the container, a pH measurement mechanism in the container, etc. It may be.

  As a means for supplying seed sludge to the first fermenter, for example, when the first fermenter has a stirring function, means for introducing a certain amount of seed sludge before or after introducing organic waste, Regardless of whether or not the fermenter has a stirring function, a separate mixing tank is provided to mix the organic waste and seed sludge and then put into the first fermentor, or the organic waste is pumped or the like. In the case of charging, there is a means for joining a pipe for charging seed sludge in the middle of the transfer route and continuously mixing a certain amount of seed sludge and organic waste. It is not limited. In addition, the seed sludge is obtained by mixing a part of organic waste previously decomposed and acid-generated with the waste when the organic waste is introduced by the supply means, or in the first fermentation. You may supply by leaving in a tank.

  From the viewpoint of increasing the processing efficiency of the organic waste, it is preferable that the ammonia removing means coexist in the fermenter rather than present as a part independent of the first fermenter.

  When coexisting in the fermenter, the ammonia removing means is provided with the fermenter, for example, pH adjusting means for organic waste (for example, an inlet for an alkaline substance such as sodium hydroxide and pH measurement in the container) Mechanism), the heating means (for example, an electric heater, a hot water jacket, etc.) or a low-pressure steam introduction means (for example, a boiler and a pump for blowing steam), and an ammonia absorption and removal means (for example, passing ammonia from within the system) A dilute hydrochloric acid or dilute sulfuric acid storage container, a gas chamber for spraying the acid solution, and the like. Moreover, a means for recovering the absorbed ammonia by recovering the absorbed ammonia and a means for returning the regenerated acid solution into the first fermentor may be further provided. The ammonia removing means can be appropriately configured using known parts, containers, devices, and the like.

  In addition, as described above, since the step (1) in the treatment process of the present invention has its own significance, similarly, as another aspect of the present invention, the organic waste is decomposed and acidified using seed sludge. There is provided a device for removing nitrogen in organic waste having a fermenter for production treatment and ammonia removal means for removing ammonia produced by the treatment. As such an apparatus, for example, the apparatus having the first fermenter provided with the ammonia removing means described above can be cited. For example, the desired effect of the present invention can be obtained by treating the organic waste in advance with this apparatus and then subjecting it to conventional methane fermentation. It is included in the processing method of the invention.

  A 2nd fermenter can be comprised like the said 1st fermenter using the said microorganisms used for a methane production | generation process, for example.

  The means for transferring the organic waste from the first fermenter to the second fermenter is not particularly limited, for example, a natural gravity flow by a drain pipe, a known arbitrary pipe comprising a screw pump, and the like, It can be configured using any known pump that allows transfer of organic waste from the first fermentor to the second fermentor. In the apparatus of the present invention, the means connects the first fermenter and the second fermenter.

  Although the apparatus of the present invention has the above-described configuration, the same effects as those of the processing method of the present invention can be obtained by processing organic waste having a low water content using the apparatus.

  EXAMPLES Hereinafter, although an Example demonstrates this invention more concretely, this invention is not limited only to this Example.

Reference Examples 1, 2, and 4
Dehydrated sludge after sufficient anaerobic digestion as a source of bacteria involved in anaerobic digestion (containing bacteria: Clostridium, Bacteroides, Butyrivibrio, Methanobacterium, Methanosarcina, Methanosaeta, etc .; ammonia concentration: 1000 ppm; , The same) was used as seed sludge and mixed well with surplus sludge in a mortar (prepared to pH 7.5, water content 80% by weight). At that time, the mixing ratio of the dewatered sludge and the excess sludge was changed so that the VS of the excess sludge was 4, 5, 7, 10, 13, 15, 16% by weight. 20 g of sludge mixed in a 125 ml vial was added and the gas phase was ventilated with nitrogen gas, and then quickly sealed with a butyl rubber stopper and an aluminum fastener. Culturing was performed for 30 days in a thermostatic chamber at 55 ° C under static conditions. Methane was analyzed by gas chromatography after extracting 0.5 ml of gas phase from a vial using a gas tight syringe. The amount of methane produced was determined by the water replacement method, and was expressed as the amount of methane produced (kg / kg) per 1 kg of solid moisture content of excess sludge. The ammonia concentration (ppm) in the sludge was measured with Ammonia Test Wako (manufactured by Wako Pure Chemical Industries, Ltd.) for the supernatant obtained by extracting a sludge sample, diluting with distilled water and centrifuging. The ammonia conversion rate was determined by measuring the nitrogen content (A mmol) in the excess sludge before culturing with the Kjeldahl method and the ammonia content (B mmol) at each time point during the culturing with Ammonia Test Wako.
Ammonia conversion (mol%) = [1- (B / A)] × 100
Determined by The results are shown in FIGS.

Reference example 3
Use dehydrated sludge after sufficient anaerobic digestion as a source of bacteria involved in anaerobic digestion, and mix well with surplus sludge and mortar (pH 7.5, moisture content 80 wt%, surplus sludge VS is 5 wt% Prepared). At that time, ammonium chloride was added so that the initial ammonia concentration was 1000 to 5000 ppm. 20 g of sludge mixed in a 125 ml vial was added and the gas phase was ventilated with nitrogen gas, and then quickly sealed with a butyl rubber stopper and an aluminum fastener. Culturing was performed for 18 days in a thermostatic chamber at 55 ° C. under static conditions. Methane was analyzed by gas chromatography after extracting 0.5 ml of gas phase from a vial using a gas tight syringe. The amount of methane produced was determined by the water displacement method in the same manner as described above, and expressed as the amount of methane produced per 1 kg of solid moisture weight of excess sludge per day, that is, the methane production rate (mmol / kg / day). The ammonia concentration in the sludge was measured in the same manner as described above. The results are shown in FIG.

Reference Example 5
In the above Reference Examples 1 to 4, since the dehydrated sludge used contained organic matter but did not produce ammonia, it was treated as equivalent to water from the viewpoint of ammonia generation, and its VS was not considered. On the other hand, in this reference example, from the viewpoint of clarifying the relationship between VS and anaerobic digestion when there is no inhibition of methane fermentation due to the generation of ammonia, the VS of dehydrated sludge was changed and the methane production of the sludge was examined. .

  Dehydrated sludge after sufficient anaerobic digestion was used as seed sludge as a source of bacteria involved in anaerobic digestion. The seed sludge was washed with degassed water, centrifuged, and dried at 55 ° C. to make the VS about 50% by weight. Distilled water was added to the sludge to adjust VS to 5 to 20% by weight, and sodium acetate as a substrate was added at 750 mmol per kg of sludge dry weight. 20 g of sludge mixed in a 125 ml vial was added and the gas phase was ventilated with nitrogen gas, and then quickly sealed with a butyl rubber stopper and an aluminum fastener. Culturing was carried out for 9 days at 55 ° C. at a pH of 8 under static conditions. Methane was analyzed by gas chromatography after extracting 0.5 ml of gas phase from a vial using a gas tight syringe. The amount of methane produced was determined by the water displacement method as described above. The results are shown in FIG.

Example 1
Dehydrated sludge after sufficient anaerobic digestion was used as seed sludge as a source of bacteria involved in anaerobic digestion. 1 kg of seed sludge and 4 kg of surplus sludge were mixed (water content 80 wt%, surplus sludge VS 18 wt%), adjusted to pH 7 and cultured at 55 ° C. for 6 days to produce ammonia. The resulting ammonia was recovered by being diffused as a gas at 80 ° C. and pH 9 to prepare deammoniated sludge (water content 80 wt%, ammonia concentration: 300 ppm). Seed sludge (15 g) and deammonia sludge (5 g) were mixed, put in a vial, and cultured at pH 8 at 55 ° C. For methane and carbon dioxide, 0.5 ml of gas phase was extracted using a gas tight syringe and analyzed by gas chromatography. The amount of each gas produced was determined by the water displacement method in the same manner as described above. Further, the ammonia concentration in the sludge was measured in the same manner as described above. The results are shown in FIG.

Comparative Example 1
Dehydrated sludge after sufficient anaerobic digestion was used as seed sludge as a source of bacteria involved in anaerobic digestion. Seed sludge (15 g) and surplus sludge (5 g) were mixed (pH 8, water content 80 wt%, surplus sludge VS was 18 wt%), placed in a vial, and cultured at 55 ° C. Methane and carbon dioxide were extracted from a gas phase of 0.5 ml using a gas tight syringe and analyzed by gas chromatography. The amount of each gas produced was determined by the water displacement method in the same manner as described above. Further, the ammonia concentration in the sludge was measured in the same manner as described above. The results are shown in FIG.

  In Example 1, in the experiment using deammonia sludge, methane production was almost completed in 10 days. At this time, the removal rate of TOC (Total Organic Carbon) was 60%, and no increase in ammonia concentration was observed. In the case of Comparative Example 1 using surplus sludge not subjected to deammonia treatment, the ammonia concentration reached 2000 to 3000 ppm, the appearance of methane took 7 to 10 days, and about 20 days or more to reach TOC removal rate of 60% Cost. Comparing the result of Example 1 with the result of Comparative Example 1, it can be said that the processing efficiency was amazing.

  Of course, methane is not produced in a system with an ammonia concentration of 5000 ppm. However, when continuous methane fermentation is performed, ammonia accumulates during the fermentation as shown in FIG. Stopping the fermentation is inevitable unless it is removed. On the other hand, in the method of the present invention, as can be seen from FIG. 6, ammonia does not accumulate and methane fermentation is also promoted, so that continuous treatment is possible.

Example 2
Addition of seed sludge by mixing seed sludge and surplus sludge so that the dewatered sludge after sufficient anaerobic digestion is used as seed sludge, and the VS concentration of surplus sludge is about 5 wt%, 10 wt%, and 15 wt% A sample and 10 g of seed sludge non-added sample in which water was added to excess sludge so that the VS concentration would be 5% by weight were put in a vial and sealed tightly, and then purged with nitrogen to obtain a plurality of temperature conditions (35 ° C., (45 ° C., 55 ° C., 65 ° C.) for 5 days. In the same manner as described above, the conversion rate of nitrogen derived from nitrogen-containing organic substances in the sample to ammonia was determined and plotted against the culture temperature. The results are shown in FIG. In FIG. 8, “without seed” means a sample without seed sludge, and “with seed” means a sample with seed sludge added.

Example 3
20g of sludge mixed with seed sludge and surplus sludge is anaerobically digested so that the VS concentration of surplus sludge becomes 10% by weight, and half of the amount is used as seed sludge so that the VS concentration of surplus sludge becomes 10% by weight again. The process of anaerobic digestion by mixing with excess excess sludge was repeated at various intervals until ammonia production reached a steady state (treatment temperature: 37 ° C. or 55 ° C.). The ammonia conversion rate of nitrogen derived from nitrogen-containing organic substances in the sludge at that time was determined in the same manner as described above, and plotted against the sludge replacement frequency (times / day). The results are shown in FIG.

  As shown in FIG. 8, the temperature suitable for anaerobic digestion in the seed sludge non-added sample having a VS concentration of 5% by weight is 35 ° C. or more and less than 45 ° C., and the ammonia conversion rate within the temperature range is 41% on average. there were. On the other hand, the anaerobic digestion in the seed sludge added sample having a VS concentration of 5% by weight was suitably performed at 45 to 65 ° C., and the ammonia conversion rate within the temperature range was as high as 54% on average. Further, under the temperature condition of 45 to 55 ° C., even in a high VS sample having a VS concentration of 10 or 15% by weight, high ammonia conversion rates of 51 and 57% on average were shown, respectively. That is, it was shown that high VS organic waste can be decomposed and acid-generated with high efficiency by using seed sludge. It was also found that anaerobic digestion using seed sludge is more suitably performed at about 45 to about 65 ° C.

  As shown in FIG. 9, when the treatment temperature was 55 ° C., the ammonia conversion rate higher than 50% was maintained even when sludge was drawn out at about 1.5 times / day, whereas it was 37 ° C. In this case, the ammonia conversion rate decreased to 50% or less when the sludge was drawn out more frequently than about 0.25 times / day. That is, it was shown that the anaerobic digestion treatment at 55 ° C. can be performed at a high efficiency six times or more than the anaerobic digestion treatment at 37 ° C.

FIG. 1 is a graph showing the change over time in the ammonia conversion rate of nitrogen derived from nitrogen-containing organic matter in the sludge when the VS of excess sludge is changed. FIG. 2 is a graph showing the change over time in the amount of methane produced (per 1 kg of solid moisture weight) when the VS of excess sludge is changed. FIG. 3 is a graph showing the influence of the ammonia concentration on the methane production rate by methane fermentation of excess sludge. FIG. 4 is a graph showing the change over time in the ammonia concentration in the sludge when the VS of the excess sludge is changed. FIG. 5 is a graph showing changes over time in the amount of methane produced by methane fermentation (per kg of solid moisture) when the VS of dehydrated sludge with an ammonia concentration of 1000 ppm is changed. In the figure, white circles are data with 20% by weight of VS, black squares with 15% by weight, black triangles with 10% by weight, and black circles with 5% by weight. FIG. 6 shows the amount of methane and carbon dioxide produced per methane fermentation of 80% by weight deammonia sludge having a water content of 1 wt. It is a graph which shows a time-dependent change. In the figure, black circles represent methane production, white circles represent carbon dioxide production, and white squares represent ammonia concentration data. FIG. 7 is a graph showing changes over time in methane and carbon dioxide production (per kg of solid moisture weight) and ammonia concentration in methane fermentation of excess sludge having a water content of 80% by weight. In the figure, black circles represent methane production, white circles represent carbon dioxide production, and white squares represent ammonia concentration data. FIG. 8 is a graph showing the conversion rate of nitrogen derived from nitrogen-containing organic matter in a sample to ammonia with respect to the culture temperature. The black triangle is a sample with a VS concentration of 5% by weight added with seed sludge, the black circle is a sample with a VS concentration of 10% by weight added with seed sludge, the black square is a sample with a VS concentration of 15% by weight added with seed sludge, and the white circle is water. It is the data of the ammonia conversion rate of the sample of VS concentration 5 weight% which added only. FIG. 9 is a graph showing the ammonia conversion rate relative to the sludge replacement frequency (times / day) when ammonia production reaches a steady state under a temperature condition of 37 ° C. or 55 ° C. In the figure, the black square indicates the ammonia conversion rate with respect to the replacement frequency at 37 ° C. and the black circle indicates 55 ° C.

Claims (2)

An organic waste processing method for anaerobically digesting organic waste,
(1) Organic waste having a moisture content of 70 to 95 wt% and a VS concentration of 4.5 to 15 wt% using part of the organic waste after the decomposition and acid generation treatment as seed sludge A step of anaerobically decomposing and acid-generating the product under a temperature condition of 45 to 65 ° C. and removing the generated ammonia; and (2) organic waste that has undergone step (1) is converted into step (1) and Is a method for treating organic waste, which includes a process of producing methane in different fermenters . A first fermenter for decomposing / acid-generating organic waste using seed sludge, an ammonia removing means for removing ammonia generated by the treatment, and a methane-producing treatment for organic waste after removing ammonia. The processing apparatus of the organic waste for using for the processing method of Claim 1 which has a 2 fermenter and a means to transfer organic waste from a 1st fermenter to a 2nd fermenter.

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