JP2012254393A - Denitrification method of methane fermentation wastewater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for obtaining a BOD component, that functions as an excellent hydrogen donor, by a simple method using existing facilities without the need to increase the facilities and apparatus to liquidize by adding water or the like and crushing when utilizing solid organic waste as the BOD component.SOLUTION: The denitrification method of the methane fermentation wastewater includes: (1) a storage process of storing organic waste crushed matter, obtained by crushing the organic waste accepted in a receiving tank, to a reservoir; (2) an organic sewage recovery process of recovering organic sewage, generated during the storage of the organic waste or the organic waste crushed matter in the receiving tank or the reservoir, to a recovery tank; (3) a methane fermentation process of subjecting the organic waste crushed matter after the organic sewage is recovered to methane fermentation; and (4) a denitrification process of adding the organic sewage to the methane fermentation wastewater generated in the methane fermentation process for denitrification.

Description

  The present invention relates to a denitrification method for methane fermentation wastewater. More specifically, the present invention relates to a method for denitrification of methane fermentation wastewater that uses organic wastewater obtained from organic waste to reduce the amount of methanol generally used as a hydrogen donor in denitrification.

  2. Description of the Related Art In recent years, methane fermentation technology that generates biogas from waste (organic waste) containing organic matter at a high concentration such as garbage is attracting attention. The resulting biogas can be used not only for gas engine power generation, but also for a wide variety of applications including fuel cells and automobile fuels.

  Here, when organic waste is subjected to methane fermentation treatment, the wastewater after fermentation must be treated, and nitrogen is mainly present in the form of ammonia in the wastewater after methane fermentation. Therefore, it is necessary to remove nitrogen in order to discharge or reuse waste water.

  As a method for removing nitrogen in wastewater, a biological nitrification denitrification method is common. The biological nitrification denitrification method typically involves performing a nitrification reaction and a denitrification reaction using biological reactions performed by living organisms. The nitrification reaction and denitrification reaction are represented by the following equations. It is known to be summarized in the reactions represented.

^{_{(Nitrification) ··· NH 4 + → NO 3}} -
(Denitrification) ··· NO ₃ ^- → N ₂

The nitrification reaction is a reaction that oxidizes ammonia-form nitrogen contained in water using oxygen, and is performed by autotrophic bacteria (for example, ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, and the like). The nitrification reaction is performed using dissolved oxygen under aerobic conditions (a state where dissolved oxygen is present). A denitrification reaction is a biological reaction that uses oxygen combined with nitrogen for the respiration of bacteria. Under anaerobic conditions, bacteria that have such ability among heterotrophic bacteria (such as denitrification bacteria) ). The denitrification reaction is performed using bound oxygen (O in NO ₃ ) under anaerobic conditions (in the absence of dissolved oxygen), but is ultimately a reduction reaction using hydrogen. In order for the reaction to proceed, an organic substance as a hydrogen donor is required.

  BOD components (biochemical oxygen demand) remaining in wastewater are effective as hydrogen donors, but it is common that a sufficient amount of BOD components remain in methane fermentation wastewater that has undergone methane fermentation. There are few. Therefore, when the BOD component is smaller than the concentration necessary for denitrification, a shortage of hydrogen donor is compensated by adding a chemical such as methanol. FIG. 6 shows a conventional denitrification process of methane fermentation wastewater. Reference numeral 9 indicates a flow rate adjustment tank, reference numeral 10 indicates a denitrification tank, reference numeral 11 indicates a nitrification tank, reference numeral 12 indicates a secondary denitrification tank, reference numeral 13 indicates a re-aeration tank, and reference Reference numeral 14 denotes a settling tank. As shown in FIG. 6, conventionally, methane fermentation wastewater is denitrified by adding methanol to the denitrification tank 10 and the secondary denitrification tank 12.

  However, there is a problem that methanol added as a hydrogen donor is expensive and expensive. Therefore, a method of using organic waste as a hydrogen donor instead of methanol has been proposed (Patent Document 1).

  According to Patent Document 1, the organic waste is crushed by a crusher, and the organic waste is crushed by the crushing and sorting machine while receiving and mixing the crushed organic waste and water, A heavy organic slurry is obtained by removing unsuitable and lightweight unsuitables, and a light organic slurry is obtained by partially removing solids from the obtained heavy organic slurry by a solid-liquid separator. A wastewater treatment method using an organic slurry as a hydrogen donor has been proposed. According to the wastewater treatment method, methanol is not required as a hydrogen donor.

  However, in the method disclosed in Patent Document 1, when the organic waste is a solid waste such as garbage, it is necessary to use it in a liquefied state. There is a problem that an additional device is required and the system becomes complicated.

JP 2001-29993 A

  The present invention has been made in view of such conventional problems, and when using solid organic waste as a BOD component, facilities and apparatuses are added to liquefy by adding water and crushing. The object is to provide a method for obtaining a BOD component that functions as an excellent hydrogen donor by a simple method using existing equipment.

The denitrification method of methane fermentation wastewater of the present invention is
A denitrification method of methane fermentation wastewater that removes nitrogen components from the wastewater after methane fermentation treatment,
(1) A storage step of storing, in a storage tank, organic waste crushed material obtained by crushing organic waste received in a receiving tank;
(2) Organic sewage recovery process for recovering organic sewage generated at the time of storage of organic waste or crushed organic waste in a receiving tank or storage tank to a recovery tank;
(3) a methane fermentation process for methane fermentation of crushed organic waste after organic wastewater has been collected;
(4) A denitrification step of adding and denitrifying the organic sewage to the methane fermentation wastewater generated by the methane fermentation step.

  By having such a configuration, the present invention eliminates the need to add facilities and equipment to liquefy by adding water and crushing when using solid organic waste as a BOD component. It is possible to provide a method for obtaining a BOD component that functions as an excellent hydrogen donor by a simple method using equipment.

    It is preferable that the storage period in the storage step is at least one day.

  By having such a configuration, the present invention can recover a sufficient amount of organic wastewater in the recovery tank.

The denitrification step is
(4-1) A wastewater receiving process for receiving methane fermentation wastewater in a flow rate adjustment tank;
(4-2) An organic sewage addition step of adding the organic sewage to the flow rate adjustment tank;
(4-3) It is preferable to include a nitrification denitrification step of denitrifying and nitrifying the methane fermentation wastewater after the addition of organic sewage.

  The flow rate adjusting tank is a tank for adjusting the flow rate so as to quantitatively input the wastewater into the wastewater treatment facility, and has a capacity for storing about 1 to 3 days worth of wastewater. Therefore, the present invention has such a configuration, so that when organic sewage is added and mixed, for example, in a flow rate adjusting tank in a batch, the concentration of the organic sewage is made uniform in the flow rate adjusting tank, and the subsequent nitrification denitrification step is performed. An appropriate amount of organic wastewater with a stable concentration can be sent.

  It is preferable that the organic sewage is added to the denitrification tank.

  By having such a configuration, the present invention can additionally add organic sewage according to the denitrification situation of the methane fermentation wastewater in the nitrification denitrification step. The amount of organic wastewater added can be adjusted so that the nitrogen content can be reduced to a desired value.

  It is preferable that methanol is added to the denitrification tank.

  By having such a configuration, the present invention is effective when denitrification is not sufficient by adding only organic sewage or when it is necessary to denitrify to a level that cannot be achieved by adding only organic sewage.

The organic waste crushed material is
Shatter organic waste,
It is preferably obtained by crushing and sorting organic waste-containing materials including organic waste.

  By having such a configuration, the present invention can be effectively used even for organic waste containing solids such as plastics and paper.

  It is preferable to add the organic sewage recovered in the organic sewage recovery step to the methane fermentation waste water in the denitrification step after separating the solid matter.

  By having such a configuration, the present invention can be used after removing impurities such as solid matter in the organic waste water. Further, as a result of removing impurities, problems such as clogging, accumulation, and floating in the wastewater treatment facility can be avoided.

  It is preferable that the biochemical oxygen demand of the organic wastewater is 20000 to 100,000 (mg / L).

  By having such a configuration, the present invention can be judged as organic sewage that can be used for denitrification, and is suitable as the amount and concentration of organic sewage obtained from crushed organic waste used for methane fermentation. It becomes.

  According to the present invention, when solid organic waste is used as a BOD component, there is no need to add equipment or equipment to liquefy by adding water or crushing, and it is easy to use existing equipment. Thus, it is possible to provide a method for denitrification of methane fermentation wastewater to obtain a BOD component that functions as an excellent hydrogen donor.

Explanatory drawing for demonstrating the collection | recovery location of the organic waste water concerning one Embodiment (Embodiment 1) of this invention Explanatory drawing explaining the collection | recovery of the organic wastewater concerning one Embodiment (Embodiment 1) of this invention, and the flow to a wastewater treatment facility Explanatory drawing for demonstrating the addition location of the organic waste water concerning one Embodiment (Embodiment 1) of this invention. Explanatory drawing for demonstrating the collection | recovery location of the organic waste water concerning one Embodiment (Embodiment 2) of this invention Explanatory drawing for demonstrating the addition location of the organic waste water concerning one Embodiment (Embodiment 3) of this invention. Explanatory drawing for demonstrating the conventional denitrification process

(Embodiment 1)
Hereinafter, the denitrification method of methane fermentation wastewater according to the present embodiment will be described with reference to the drawings. FIG. 1 is an explanatory diagram for explaining the collection point of organic sewage in the present embodiment, and is an explanatory diagram for explaining the flow of methane fermentation. FIG. 2 is an explanatory diagram for explaining the flow of organic sewage recovery and wastewater treatment equipment according to the present embodiment. FIG. 3 is an explanatory diagram for explaining the location where organic sewage is added in the present embodiment, and shows an example of a wastewater treatment facility.

The denitrification method of methane fermentation wastewater according to the present embodiment is as follows:
A denitrification method of methane fermentation wastewater that removes nitrogen components from the wastewater after methane fermentation treatment,
(1) A storage step of storing, in a storage tank, organic waste crushed material obtained by crushing organic waste received in a receiving tank;
(2) Organic sewage recovery process for recovering organic sewage generated at the time of storage of organic waste or crushed organic waste in a receiving tank or storage tank to a recovery tank;
(3) a methane fermentation process for methane fermentation of crushed organic waste after organic wastewater has been collected;
(4) A denitrification step of adding and denitrifying the organic sewage to the methane fermentation wastewater generated by the methane fermentation step. Referring to FIG. 1, organic waste pulverized organic matter such as garbage discharged from kitchens of homes and restaurants, food waste discharged from supermarkets, wastes of food factories and brewing industries, etc. The case of waste crushed material will be described.

(About storage process)
The storage process will be described. The storage step is a step of storing the organic waste crushed material in the storage tank 3 based on the flow shown in FIG. As shown in FIG. 1, the organic waste is first received in the receiving tank 1. The receiving tank 1 is a tank for temporarily receiving organic waste. It does not specifically limit as a capacity | capacitance of the receiving tank 1, What is necessary is just the capacity | capacitance which can receive the quantity for 1 to 5 days of the scale of a methane fermentation processing equipment, and the organic waste carried in to the said equipment. In the present embodiment, a receiving tank 1 capable of receiving 3 tons per day as an organic waste will be described as an example.

  The organic waste received in the receiving tank 1 is immediately or after being stored for about 1 to 7 days, and then carried into the crushing device 2a. As the crushing device 2a, for example, one having two rotary blades and a type of shearing organic waste which is a crushing treatment product can be adopted. In addition, when organic waste is garbage, etc., it may be packed in garbage bags. In this case, the garbage bags are broken by a crusher and large-sized organic waste is crushed. . About 20-100 mm is illustrated as a magnitude | size of the organic waste crushed material after crushing.

  The organic waste crushed material produced by crushing by the crushing device 2a is carried into the storage tank 3 by a conveyor or chute provided integrally or separately in the vicinity of the outlet of the crushing device 2a.

  The storage tank 3 is installed for the purpose of temporarily storing (retaining) the crushed organic waste into the methane fermentation tank 5, but acid fermentation of the organic waste proceeds during the storage period. To do. That is, in the present invention, although organic waste is crushed, it is stored in the storage tank 3 as it is in a solid form without adding a solvent such as water to form a deposit. . Organic wastewater is generated by storing organic waste crushed material.

(About organic wastewater recovery process)
The organic wastewater recovery process will be described. The organic sewage recovery step is a step of recovering the organic sewage generated at the time of storing the organic waste crushed material in the recovery tank 4. As shown in FIG. 2, the organic waste crushed material that has undergone acid fermentation in the storage tank 3 produces organic sewage containing organic acids such as acetic acid, propionic acid, and lactic acid from the vicinity of the bottom of the deposit. In addition, since the kind and ratio of these acids are fluctuate | varied with a composition of organic waste, they cannot be determined unconditionally. The period of storage in the storage tank 3 for promoting acid fermentation is preferably 1 day or longer, and more preferably 2 days or longer. The limit of the storage period is not particularly limited, and the storage period can be appropriately adjusted even if it is within 3 days as long as the methane fermentation facility can be operated efficiently.

  The organic sewage will be described. Organic sewage is a liquid composition that is generated during storage of crushed organic waste and is also called waste juice. The organic waste crushed material is obtained by crushing garbage and food waste as described above, and contains about 50 to 95% by weight of water in its components. Moreover, at the time of storage, acid fermentation advances mainly by microbial reaction, and produces | generates organic acids, such as an acetic acid, propionic acid, and lactic acid. The water in the component flows out as organic sewage containing BOD component (organic acid or the like) due to its own weight or pressure when deposited. The amount of the organic acid in the components and the amount of these BOD components varies depending on the composition of the stored organic waste crushed material. For example, when 2 tons of organic waste crushed material is stored for 2 days, acetic acid is used. 300 to 15000 mg / L, propionic acid 50 to 200 mg / L, lactic acid 500 to 30000 mg / L, BOD component 10000 to 60000 mg / L, total nitrogen (TN) 100 to 1500 mg / L, pH Organic sewage having a pH of about 4.0 to 5.0 is obtained about 20 to 100 kg. Thus, organic wastewater contains a large amount of BOD component and can be replaced with methanol as a hydrogen donor. In addition, as shown in the broken line in FIG. 2, the obtained organic wastewater may be used as a raw material to be fed into the methane fermentation tank 5 in the methane fermentation process described later, and in the case where an incineration facility is additionally provided. You may incinerate in an incinerator.

  Organic sewage produced from the crushed organic waste in the storage tank 3 is recovered in a recovery tank 4 provided at a subsequent stage of the storage tank 3. As shown in FIG. 2, the organic sewage is recovered into the recovery tank 4 by causing the organic sewage to flow out from the organic sewage discharge port provided near the bottom of the storage tank 3. This is performed by flowing into the organic wastewater temporary storage tank 6 provided in the vicinity and then sending the organic wastewater to the strainer 7 and the recovery tank 4 using the pump P.

  The configuration of the organic sewage discharge port in the storage tank 3 is not particularly limited. For example, an opening may be provided in the lower side wall of the storage tank 3 so that the generated organic sewage flows in due to its own weight. It is good. That is, a mechanism in which only liquid organic sewage flows out without flowing solid organic waste crushed material may be employed.

  The organic sewage temporary storage tank 6 is a tank provided for temporarily storing organic sewage in order to send the organic sewage to the strainer 7 and the recovery tank 4 arranged in the subsequent stage via the pump P. . That is, organic sewage is produced over time from the crushed organic waste and contains solid matter as impurities. Therefore, instead of collecting directly in the collection tank 4, a configuration is adopted in which the organic sewage temporary storage tank 6 is temporarily stored, and solids are removed through the strainer 7 using the pump P and then collected into the collection tank 4. is doing. Depending on the composition of the organic waste crushed material, it may be recovered without using the strainer 7. In that case, the strainer 7 described above may be omitted. In this way, by separating the solid matter of organic sewage through the strainer 7, problems such as clogging, sedimentation, and floating in the wastewater treatment facility can be avoided.

  In the present embodiment, the case where the collection tank 4 is provided at the subsequent stage of the storage tank 3 has been described. However, the present invention is not limited to such a configuration, and a separate collection tank is provided at the subsequent stage of the receiving tank 1 to receive it. You may collect | recover the organic waste water produced at the time of the storage in the tank 1. FIG. Further, without providing a separate recovery tank 4 in the subsequent stage of the receiving tank 1, as shown by a broken line in FIG. 1, an organic waste water recovery path leading to the recovery tank 4 is provided and mixed with the organic waste water generated in the storage tank 3 You may comprise.

(About methane fermentation process)
The methane fermentation process will be described. A methane fermentation process is a process of methane-fermenting the organic waste crushed material after organic wastewater was collect | recovered, and taking out biogas.

  As shown in FIG. 1, the organic waste crushed material after the organic sewage is collected in the storage tank 3 is water (if wastewater (drainage) that has already undergone methane fermentation is used). And the mixture is diluted with the methane fermentation tank 5 by the input device 8. It does not specifically limit as an input method, The method etc. which mix the diluted organic waste crushed material with a mixer etc., pressurize with a piston etc., and carry in to the methane fermenter 5 etc. are employable.

  The organic waste crushed material is solubilized mainly by the action of microorganisms present in the waste, organic acids used as raw materials for methane fermentation and higher fatty acids, amino acids, saccharides, etc. used as precursors of organic acids, etc. Produced in organic matter. In the methane fermenter 5, a gas (biogas) of about 60% methane and about 40% carbon dioxide is generated from the organic acid by the action of the methanogen. The generated gas is stored in the gas holder via the generated gas line and then used mainly as fuel.

  Of the waste water after fermentation (methane fermentation waste water), the dehydrated filtrate that has been dehydrated by the dehydrator is partially reused as the water for adjusting the moisture as necessary, and the remainder is the denitrification step described later. Sent to. In addition, dewatered sludge other than dehydrated filtrate is discharged and usually composted and used as fertilizer, or simply incinerated.

(About denitrification process)
A denitrification process is demonstrated. A denitrification process is a process of adding and denitrifying organic wastewater to the methane fermentation waste water generated by a methane fermentation process. As described in the background art, etc., methane fermentation wastewater contains a large amount of nitrogen, so it is necessary to dewater it through denitrification. As shown in FIG. 3, the methane fermentation wastewater is
(4-1) A wastewater receiving process for receiving methane fermentation wastewater in the flow rate adjusting tank 9,
(4-2) Organic sewage addition step of adding the organic sewage to the flow rate adjusting tank 9,
(4-3) including a nitrification denitrification step of denitrifying and nitrifying the methane fermentation wastewater after the addition of organic sewage. Hereinafter, each process will be described.

(About wastewater receiving process)
The waste water receiving step is a step of receiving the methane fermentation waste water into the flow rate adjusting tank 9. The flow rate adjusting tank 9 is provided to adjust the flow rate of the methane fermentation wastewater sent to the nitrification denitrification step so that the denitrification is efficiently performed when the methane fermentation wastewater is denitrified. Moreover, it is provided in order to equalize the components of methane fermentation wastewater by temporarily storing it in the flow rate adjusting tank 9, for example, for a period of about one day.

  As shown in FIG. 3, the methane fermentation wastewater flows into the flow rate adjustment tank 9. It does not specifically limit as a capacity | capacitance of the flow control tank 9, It determines with the scale etc. of a methane fermentation processing equipment. In this Embodiment, the flow volume adjustment tank 9 whose capacity | capacitance is 2 days worth of methane fermentation wastewater amount is employ | adopted. The flow rate is adjusted to be constant by monitoring the flow rate with a flow meter.

(About organic wastewater addition process)
The organic contamination addition step is a step of adding organic waste water in the flow rate adjusting tank 9. Thus, organic sewage is uniformly mixed in the flow rate adjusting tank 9 by adding the organic sewage to the flow rate adjusting tank 9. It does not specifically limit as an addition method of organic wastewater, For example, you may add the predetermined amount of organic wastewater (for example, about 20 kg) for every batch by a batch method. In addition, although total nitrogen is also contained in organic sewage as mentioned above, since the total nitrogen of organic sewage is about 100-1500 mg / L, even if it mixes with the methane fermentation wastewater with the said capacity | capacitance, the increase in total nitrogen amount Has almost no effect. Methane fermentation wastewater to which organic wastewater is added is subjected to a subsequent nitrification denitrification step.

(About nitrification denitrification process)
The nitrification denitrification step is a step of denitrifying and nitrifying the methane fermentation wastewater after the addition of organic sewage. Nitrogen existing mainly as ammonia in the methane fermentation wastewater is converted to N ₂ and removed by the nitrification denitrification method circulating in the denitrification tank 10 and the nitrification tank 11 shown in FIG. The chemical reaction in denitrification and nitrification is as described above. The total nitrogen in the methane fermentation wastewater is reduced to about 100 mg / L through the nitrification denitrification step. Confirmation of the status of the denitrification process in the nitrification denitrification step can be confirmed by a conventionally known management method, for example, by a method of managing nitrate nitrogen (NO ₃ -N) concentration or pH as an index. it can. At that time, for example, if it is determined that the BOD component necessary for denitrification is insufficient, organic sewage may be additionally added to the denitrification tank 10 as indicated by a broken line in FIG. Also good. By additionally adding organic wastewater, the amount of organic wastewater added can be adjusted so that the nitrogen content in the methane fermentation wastewater can be reduced to a desired value. In addition, if it is necessary to denitrify to the extent that the influence of total nitrogen contained in organic sewage cannot be ignored, methanol can be added to denitrify to a level that cannot be reached by adding only organic sewage. Is possible. The methane fermentation wastewater that has undergone the denitrification treatment is discharged after being subjected to treatments such as SS (floating matter) separation and phosphorus removal as necessary. It is also reused as raw material adjustment water in the facility.

  As described above, according to the present embodiment, when solid organic waste is used as a BOD component, it is not necessary to add facilities and equipment to liquefy by adding and crushing water and the like. It is possible to provide a method for denitrification of methane fermentation wastewater to obtain a BOD component that functions as an excellent hydrogen donor using a simple method.

(Embodiment 2)
A denitrification method for methane fermentation wastewater according to the present embodiment will be described with reference to the drawings. FIG. 4 is an explanatory diagram for explaining the collection point of organic sewage in the present embodiment, and is an explanatory diagram for explaining the flow of methane fermentation.

  In the present embodiment, the organic waste crushed material is the same as in the first embodiment except that the waste material containing solids such as plastics and paper is the same as in the first embodiment, and the description of the overlapping steps is omitted. . With reference to FIG. 4, the case where the pulverized organic waste is a crushed organic waste such as garbage including paper quality will be described.

(About storage process)
The storage process will be described. The storage step is a step of storing the organic waste crushed material in the storage tank 3 based on the flow shown in FIG. As shown in FIG. 4, the organic waste is first carried into the receiving tank 1. Since the receiving tank 1 is the same as that described in the first embodiment, the same reference numerals are assigned and description thereof is omitted.

  The organic waste received in the receiving tank 1 is immediately or after being stored for about 1 to 7 days, and then carried into the crushing and sorting apparatus 2b. The crushing and sorting device 2b is a device for removing (sorting) in advance some foreign substances that cannot contribute to methane fermentation, such as plastics, from organic waste such as garbage containing paper quality, and crushing. The crushed organic waste crushed material is carried into the storage tank 3 in the same manner as in the first embodiment, the organic sewage is recovered by the same procedure as described above, and the organic sewage is recovered. The product is subjected to a methane fermentation process. The denitrification treatment of methane fermentation wastewater is the same as that described in the first embodiment.

(Embodiment 3)
A method for denitrification of methane fermentation wastewater according to the present embodiment will be described with reference to the drawings. FIG. 5 is an explanatory diagram for explaining the location where organic sewage is added in the present embodiment, and shows an example of a wastewater treatment facility.

  In the present embodiment, as shown in FIG. 5, the nitrification denitrification step is performed except that a secondary denitrification tank 12, a re-aeration tank 13, and a precipitation tank 14 are provided after the nitrification tank 11. This is the same as Form 1, and the description of the overlapping steps is omitted.

  In the present embodiment, as described above, the secondary denitrification tank 12, the re-aeration tank 13, and the precipitation tank 14 are provided. This assumes the case where the total amount of nitrogen in the wastewater must be further reduced, for example, when draining the methane fermentation wastewater after the denitrification treatment into a river. That is, in order to drain into the river, for example, in accordance with the drainage standard of the Water Pollution Control Law, the amount of total nitrogen must be reduced to 60 mg / L (daily average) or less, so these facilities are provided. Yes.

  The secondary denitrification tank 12 is provided to denitrify the methane fermentation waste water that has been denitrified to some extent through the nitrification tank 11 to a higher degree. As the BOD component added in the secondary denitrification tank 12, organic sewage or methanol can be used. However, since the influence of total nitrogen in the organic sewage cannot be ignored, it is preferable to add methanol.

  The re-aeration tank 13 is provided for, for example, oxidizing the excess of the BOD component added in the secondary denitrification tank 12 in the previous stage to adjust it below the discharge standard.

  The sedimentation tank 14 is provided to separate SS from the nitrified and denitrified wastewater and collect the separated SS as concentrated sludge. In the sedimentation tank 14, the SS of methane fermentation wastewater re-aerated in the re-aeration tank 13 is separated by settling. The SS precipitated in the settling tank 14 is discharged as return sludge or excess sludge. On the other hand, the supernatant is drained.

  Next, the method for denitrification of methane fermentation wastewater of the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

Example 1
Based on the flow shown in FIG. 1, organic wastewater was recovered and methane fermentation wastewater was obtained. First, 2 tons of organic waste is carried into the receiving tank 1 (capacity 3 tons), the garbage components are immediately crushed using the crushing device 2a (biaxial shearing method), and the organic waste is crushed to about 30 mm. A crushed material was obtained. The obtained organic waste crushed material was carried out to the storage tank 3 using a conveyor. In storage tank 3 (capacity 6 tons), 2 tons of organic waste crushed material was stored for about 2 days, and organic sewage generated during storage was collected. The properties of the organic waste used and the organic wastewater obtained are as follows. The organic waste after organic sewage recovery was diluted with water and adjusted for raw materials, and then charged into the methane fermentation tank 5 for methane fermentation. The conditions for methane fermentation are as follows. After the methane fermentation treatment, solid-liquid separation was performed to obtain 2 tons of supernatant methane fermentation wastewater. The properties of the obtained methane fermentation wastewater are as follows.
<Organic waste used in Example 1 (per ton)>
Solid content 25%
Water content 75%
Organic wastewater recovery 20kg
<Organic wastewater obtained in Example 1>
Acetic acid 13000mg / L
Propionic acid 100mg / L
Lactic acid Not available pH 4.6
TN 1100mg / L
BOD component 41000mg / L
<Methane fermentation conditions in Example 1>
High temperature dry methane fermentation (fermentation temperature: 55 ° C)
<Methane fermentation wastewater obtained in Example 1 (per ton)>
TN 3000mg / L
BOD component 7000mg / L

In this example, the total nitrogen (TN) in 1 ton of methane fermentation wastewater is 3000 mg / L. Therefore, in order to denitrify the nitrogen,
3000 mg / L x 2.86 = 8580 mg / L
(Assuming that 2.86 g of BOD component per 1 g of total nitrogen is required)
Of BOD components are required. Since methane fermentation wastewater contains 7000 mg / L of BOD component,
8580mg / L-7000mg / L = 1580mg / L
Insufficient BOD component.

In this example, when 20 kg of organic waste water containing 41000 mg / L of BOD component is added to 1 ton of methane fermentation wastewater,
BOD concentration is
(7000 mg / L × 1000 kg + 41000 mg / L × 20 kg) / 1020 kg = 7670 mg / L
TN concentration is
(3000 mg / L × 1000 kg + 1100 mg / L × 20 kg) / 1020 kg = 2960 mg / L
And the BOD component (BOD shortage) necessary to denitrify TN 2960 mg / L is
2960 mg / L × 2.86-7670 mg / L = 796 mg / L
It becomes. This BOD deficiency may be supplemented with other organic waste water or methanol. If the methane fermentation wastewater generated in this example is all subjected to denitrification treatment with methanol, about 1320 g of methanol is required, but by using organic waste water together as in this example, about 680 g of methanol wastewater is used. Methanol is sufficient.

(Example 2)
Based on the flow shown in FIG. 1, organic wastewater was recovered and methane fermentation wastewater was obtained. First, 2 tons of organic waste is carried into the receiving tank 1 (capacity 3 tons), the garbage components are immediately crushed using the crushing device 2a (biaxial shearing method), and the organic waste is crushed to about 30 mm. A crushed material was obtained. The obtained organic waste crushed material was carried out to the storage tank 3 using a conveyor. In storage tank 3 (capacity 6 tons), 2 tons of organic waste crushed material was stored for about 2 days, and organic sewage generated during storage was collected. The properties of the organic waste used and the organic wastewater obtained are as follows. The organic waste after organic sewage recovery was diluted with water and adjusted for raw materials, and then charged into the methane fermentation tank 5 for methane fermentation. The conditions for methane fermentation are as follows. After the methane fermentation treatment, solid-liquid separation was performed to obtain 2 tons of supernatant methane fermentation wastewater. The properties of the obtained methane fermentation wastewater are as follows.
<Organic waste used in Example 2 (per ton)>
Solid content 9%
Water content 91%
Organic wastewater recovery amount 40kg
<Organic wastewater obtained in Example 2>
Acetic acid 5500mg / L
Propionic acid 100mg / L
Lactic acid 25000mg / L
pH 4.4
TN 400mg / L
BOD component 33000mg / L
<Methane fermentation conditions in Example 2>
High temperature dry methane fermentation (fermentation temperature: 55 ° C)
<Methane fermentation wastewater obtained in Example 2 (per ton)>
TN 1300mg / L
BOD component 2700mg / L

In this embodiment, the total nitrogen (TN) in 1 ton of methane fermentation wastewater is 1300 mg / L. Therefore, in order to denitrify the nitrogen,
1300 mg / L × 2.86 = 3720 mg / L
(Assuming that 2.86 g of BOD component per 1 g of total nitrogen is required)
Of BOD components are required. Since methane fermentation wastewater contains 2700 mg / L of BOD component,
3720 mg / L-2700 mg / L = 1020 mg / L
Insufficient BOD component.

In this example, when 40 kg of organic wastewater containing 33,000 mg / L of BOD component is added to 1 ton of methane fermentation wastewater,
BOD concentration is
(2700 mg / L × 1000 kg + 33000 mg / L × 40 kg) / 1040 kg = 3870 mg / L
TN concentration is
(1300 mg / L × 1000 kg + 400 mg / L × 40 kg) / 1040 kg = 1270 mg / L
The BOD component necessary for denitrifying T-N 1270 mg / L is
1270 mg / L × 2.86 = 3630 mg / L
It becomes. Since the BOD concentration is 3870 mg / L as described above, it is not necessary to add other organic waste water or methanol in this example.

  As described above, according to the present invention, when solid organic waste is used as a BOD component, there is no need to add equipment or equipment to liquefy by adding water or crushing, and existing equipment is used. It is possible to provide a method for denitrification of methane fermentation wastewater to obtain a BOD component that functions as an excellent hydrogen donor by a simple and simple method. Thereby, the amount of methanol used conventionally can be reduced.

  According to the denitrification method of methane fermentation wastewater of the present invention, by using organic waste water obtained from organic waste, it is possible to reduce the amount of methanol commonly used as a hydrogen donor in denitrification treatment. Therefore, for example, it can be suitably used in the field of denitrifying methane fermentation wastewater generated when trash is treated with methane fermentation.

DESCRIPTION OF SYMBOLS 1 Accepting layer 2a Crushing device 2b Crushing and sorting device 3 Storage tank 4 Recovery tank 5 Methane fermentation tank 6 Organic waste water temporary storage tank 7 Strainer 8 Input device 9 Flow control tank 10 Denitrification tank 11 Nitrification tank 12 Secondary denitrification tank 13 Reaeration tank 14 Settling tank P Pump

Claims (8)

A denitrification method of methane fermentation wastewater that removes nitrogen components from the wastewater after methane fermentation treatment,
(1) A storage step of storing, in a storage tank, organic waste crushed material obtained by crushing organic waste received in a receiving tank;
(2) Organic sewage recovery process for recovering organic sewage generated at the time of storage of organic waste or crushed organic waste in a receiving tank or storage tank to a recovery tank;
(3) a methane fermentation process for methane fermentation of crushed organic waste after organic wastewater has been collected;
(4) A denitrification method for methane fermentation wastewater, comprising a denitrification step of adding and denitrifying the organic sewage to the methane fermentation wastewater generated by the methane fermentation step.   The denitrification method of methane fermentation wastewater according to claim 1, wherein a storage period in the storage step is at least one day. The denitrification step includes
(4-1) A wastewater receiving process for receiving methane fermentation wastewater in a flow rate adjustment tank;
(4-2) An organic sewage addition step of adding the organic sewage to the flow rate adjustment tank;
(4-3) The denitrification method for methane fermentation wastewater according to claim 1 or 2, further comprising a nitrification denitrification step of denitrifying and nitrifying the methane fermentation wastewater after addition of organic sewage.   The method for denitrification of methane fermentation wastewater according to claim 3, wherein the organic waste water is added to the denitrification tank.   The method for denitrification of methane fermentation wastewater according to claim 3 or 4, wherein methanol is added to the denitrification tank. The organic waste crushed material is
Shatter organic waste,
The method for denitrification of methane fermentation wastewater according to any one of claims 1 to 5, wherein the method is obtained by crushing and sorting organic waste-containing materials including organic waste.   The organic wastewater recovered in the organic wastewater recovery step is separated into solids, and then added to the methane fermentation wastewater in a denitrification step. The methane fermentation wastewater according to any one of claims 1 to 6, Denitrification method.   The biochemical oxygen demand of the organic wastewater is 10,000 to 60000 (mg / L). The denitrification treatment method of methane fermentation wastewater according to any one of claims 1 to 7.

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