JP2008030008A - Methane fermentation method of organic waste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a methane fermentation method of organic waste which can increase the amount of generated methane gas and reduce the amount of generated sludge, hardly causes coloring reaction, and can dramatically increase the amount of recovered phosphorus from the organic waste when treating the organic waste. <P>SOLUTION: The organic waste A is sent into a methane fermentation tank 1, and microbiologically decomposed under an anaerobic condition to generate methane gas. A fermented liquid B is sent from the methane fermentation tank 1 to an acid-heat treatment device 2, and an inorganic acid is added to the fermented liquid B to heat the mixture. Acid-heat treated liquid C generated in the acid-heat treatment device 2 is returned again to the methane fermentation tank 1. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is an improvement of a method for treating organic waste, more specifically, when treating organic waste, the amount of methane gas generated can be increased, and the amount of sludge generated can be reduced. Further, the present invention relates to a method for methane fermentation treatment of organic waste, which is less likely to cause a coloring reaction and can dramatically increase the amount of phosphorus recovered from waste.

As is well known, methane fermentation treatment of organic waste can produce methane gas (CH ₄ ) as a final product while decomposing organic matter, and the residue that has not been decomposed can be reused as organic fertilizer or cement raw material. Since it is a microbiological treatment method that can be used, it can be said that this technology is suitable for the 21st century, which combines environmental conservation and biomass energy conversion.

  By the way, this organic waste has greatly different decomposability in methane fermentation treatment depending on the type. For example, organic waste that is easy to decompose such as garbage can obtain more than 80% degradability, but most organic waste such as sludge, human waste and livestock manure is less degradable, For example, in the case of sewage sludge, the average is about 50%.

  Therefore, even after methane fermentation treatment, a large amount of fermentation residue remains, and although it is being reused, final disposal such as incineration and landfilling is inevitable as industrial waste.

  Thus, since there is a limit in the decomposition | disassembly by only anaerobic microorganisms, in addition to this, combined use of physical, chemical, or biological treatment has been examined. Typical examples include heat treatment, acid or alkali treatment, mechanical treatment such as ball mill and homogenizer, chemical oxidation treatment using ozone or hydrogen peroxide, biological using high temperature aerobic bacteria or enzymes, etc. There are methods such as processing and combining two or more types of processing. However, most of these methods are unsatisfactory because they require large amounts of energy and are not cost effective.

  In addition, among the above-mentioned additional treatments, it is known from past research that solid heat decomposability is improved when pH adjustment is combined with heat treatment, and the pH in that case is overwhelmingly better on the alkali side. It was considered (see Patent Document 1).

However, the inventors' research has revealed that subsequent sludge dehydration and coloring reaction (Maillard reaction) accompanying heat treatment are remarkable on the alkali side. Therefore, the heat treatment under alkalinity is not necessarily excellent as a whole methane fermentation treatment system.
Japanese Patent Laying-Open No. 2005-186022 (page 5-10, FIG. 3-5)

  The present invention has been made in view of the above-mentioned problems in the conventional treatment method, and the object of the present invention is to reduce the amount of methane gas generated when treating organic waste. An organic material that can increase the amount of sludge, reduce the generation of sludge, hardly cause a color reaction, and can dramatically increase the amount of phosphorus recovered from waste. The object is to provide a method for methane fermentation treatment of waste.

  Means employed by the present inventor for solving the above-described problems will be described with reference to the accompanying drawings.

That is, the present invention sends the organic waste A to the methane fermentation tank 1, and microbiologically decomposes it in an anaerobic state to generate methane gas,
While sending the fermented liquor B from this methane fermenter 1 to the acid heat processing apparatus 2, adding an inorganic acid to the said fermented broth B, and heat-processing,
The technical means of returning the acid heat treatment liquid C generated in the acid heat treatment apparatus 2 back to the methane fermentation tank 1 was adopted.

  Moreover, in order to solve the said subject, in addition to the said means, this invention comprises the methane fermenter 1 in the two-stage type of the 1st methane fermenter 1A and the 2nd methane fermenter 1B, The technical means of decomposing the incompletely fermented portion of the organic waste A in the first methane fermentation tank 1A in the second methane fermentation tank 1B to generate methane gas was adopted.

Furthermore, in order to solve the above-mentioned problems, the present invention sends the fermentation liquid B discharged from the methane fermentation tank 1 to the precipitation separation tank 3 and contains it in the fermentation liquid B in addition to the above means as necessary. While precipitating solids and sending this precipitate D to the acid heat treatment device 2,
The technical means of discharging the remaining effluent E was adopted.

  Furthermore, in order to solve the above-described problems, the present invention sends the fermentation broth B from the methane fermentation tank 1 to the solid-liquid separator 4 in addition to the above means as necessary, and the fermentation broth B is divided into a liquid component F. And a technical means of separating the concentrate G into the acid heat treatment apparatus 2 was adopted.

  Furthermore, in order to solve the above-mentioned problems, the present invention comprises a methane fermenter 1 in a two-stage system including a first methane fermenter 1A and a second methane fermenter 1B in addition to the above means as necessary. The fermented liquor B ′ from the second methane fermenter 1B is sent to the solid-liquid separator 4 to separate the fermented liquor B into a liquid F and a concentrate G. Adopted technical means to send to.

  Furthermore, in order to solve the above problems, the present invention employs technical means for discharging solid residue from the acid heat treatment liquid C generated from the acid heat treatment apparatus 2 in addition to the above means as necessary. .

  Furthermore, in order to solve the above-described problems, the present invention employs technical means of adding hydrochloric acid or sulfuric acid in the acid heat treatment apparatus 2 in addition to the above means as necessary.

  Furthermore, in order to solve the above-described problems, the present invention provides, in addition to the above means as necessary, the contents in the organic waste A or the sulfide generated by the sulfate reduction reaction in the methane fermentation tank 1. Was removed using a desulfurization apparatus.

  Furthermore, in order to solve the above-mentioned problems, the present invention employs technical means for setting the heating temperature in the acid heat treatment apparatus 2 to 40 ° C. or higher in addition to the above means as necessary.

  Furthermore, in order to solve the above-mentioned problems, the present invention employs technical means for performing an acid treatment in the acid heat treatment apparatus 2 with an inorganic acid having a pH of 6 or less in addition to the above-described means as necessary.

  In the present invention, organic waste is fed into a methane fermentation tank, and anaerobic conditions are microbiologically decomposed to generate methane gas. From this methane fermentation tank, the fermentation liquor is sent to an acid heat treatment apparatus. In addition, an inorganic acid is added to the fermentation broth and the heat treatment is performed, and the acid heat treatment liquid generated in the acid heat treatment apparatus is returned again to the methane fermentation tank, so that organic waste is highly efficient. Can be processed automatically.

  In this way, when acid heat treatment with an inorganic acid is incorporated following methane fermentation, the microbiologically difficult-to-decompose solid matter is decomposed and solubilized with the help of acid heat treatment and returned to the methane fermentation tank. By this, solid matter decomposability and methane generation can be increased. Moreover, under pH acidity, the sludge dewaterability can be improved and the coloring reaction can be suppressed, and the performance of the entire system is improved. Therefore, the practical utility value is very high.

  BEST MODE FOR CARRYING OUT THE INVENTION The best mode for carrying out the present invention will be described in more detail with reference to the drawings specifically shown as follows.

“First Embodiment”
A first embodiment of the present invention will be described with reference to FIGS. In the figure, what is indicated by reference numeral 1 is a methane fermentation tank, and this methane fermentation tank 1 is capable of digesting organic waste in an anaerobic state by microorganisms. As this microorganism, Methanosarcina genus, Methanococcus genus, Methanobacteria genus and the like can be selected.

  Also, what is indicated by reference numeral 2 is an acid heat treatment apparatus, and this acid heat treatment apparatus 2 can add strong acid into the apparatus by means of, for example, a pump, and is also equipped with an electric heater, heat exchanger, high temperature A heating mechanism such as water vapor injection is provided.

  The specific procedure of the methane fermentation treatment method of the present invention will be described below. First, the organic waste A is sent into the methane fermenter 1 and microbiologically decomposed in an anaerobic state to generate methane gas. This organic waste A is, for example, sewage treatment sludge, garbage, human waste, livestock manure, and other general and industrial wastes. Further, at this time, the inside of the methane fermentation tank 1 can be appropriately decomposed by stirring appropriately.

  Subsequently, this fermentation broth B is sent to the acid heat treatment apparatus 2, and hydrochloric acid or sulfuric acid is added to the fermentation broth B as an inorganic acid. In the present embodiment, the reason why hydrochloric acid or sulfuric acid is used as the strong acid will be described below.

  First, when hydrochloric acid (HCl) is used, it has a property of easily corroding stainless steel, but since it does not involve a microbial reaction, it may be considered to be merely an action of lowering pH. At this time, regarding the recovery of phosphorus from the waste, it is interpreted that the elution of phosphorus into the liquid phase increases in proportion to the decomposition of the solid matter. Therefore, since the solid matter of the fermentation residue still contains a lot of phosphorus, it is suitable for reuse as an organic fertilizer as it is, final disposal such as landfill and incineration.

On the other hand, when sulfuric acid (H ₂ SO ₄ ) is used, a sulfate reduction reaction occurs microbiologically in the methane fermentation tank, and sulfuric acid is converted to sulfide. Since the amount of methane fermentation is consumed and the amount of methane generated is slightly reduced, care should be taken when adding too much sulfuric acid. In addition, since the decomposition | disassembly effect | action with respect to fiber parts, such as a cellulose, is strong, the possibility of the methane fermentation for woody waste is anticipated.

  In addition, sulfide ions generated by sulfate reduction substitute for phosphate ions in the solid matter, and promote elution of phosphorus into the liquid phase. Thereafter, if a phosphorus recovery step is provided, phosphorus as a depleted resource can be recovered with high efficiency and high purity. Therefore, sulfuric acid is suitable for removing phosphorus from solids or for elution and recovery of phosphorus. For example, when sewage sludge is reused as an increasing cement raw material in recent years, it is known that phosphorus has an adverse effect, so sulfuric acid that can obtain sludge with a low phosphorus content is suitable.

Nitric acid (HNO ₃ ) is known as a representative strong acid, but when nitric acid is used, a denitrification reaction occurs microbiologically in the methane fermentation tank, and nitric acid is converted to nitrogen gas. Is done. Accordingly, the amount of methane fermentation is reduced, and the amount of methane generated decreases. At the same time, the generated nitrogen gas lowers the methane concentration in the gas, which is not preferable.

  Furthermore, since nitric acid does not remain in the fermentation broth, there is no action to elute phosphorus like sulfuric acid. From the above, it is considered that there is not much merit in using nitric acid as long as the purpose is not only the decomposition of solids but also the generation and recovery of methane.

  Therefore, in this embodiment, hydrochloric acid or sulfuric acid is used as the strong acid. And about the heating in the acid heat processing apparatus 2, it can heat-process at heating temperature 40 degreeC or more, More preferably, 170-180 degreeC, and can accelerate | stimulate reaction more.

  Furthermore, in the present embodiment, the acid treatment in the acid heat treatment apparatus 2 can be inorganic acid treatment at pH 6 or less. At this time, the lower the pH in the acid heat treatment, the higher the effect. However, in addition to increasing the amount of strong acid to be administered, methane fermentation has an appropriate operating pH near neutrality. When the pH of the solution is low, it is necessary to add an alkaline agent to the treatment liquid. If the pH at the time of the acid heat treatment is up to about 5, the pH of the methane fermenter is economical because the neutrality is maintained without the administration of the alkaline agent.

  And processing efficiency can be improved by returning the acid heat processing liquid C remaining in this acid heat processing apparatus 2 to the said methane fermentation tank 1 again. In addition, since the acid heat processing liquid C is excellent in sedimentation property and dehydration property, a solid substance (residue: c) can be discharged | emitted from the acid heat processing liquid C suitably. Although this solid residue needs to be discarded, only a small amount is generated as compared with the conventional case by adopting the method of the present embodiment.

  In the acid heat treatment apparatus 2, sulfuric acid can be added. As described above, when sulfuric acid is added as a strong acid, generation of harmful sulfides such as hydrogen sulfide increases due to sulfur contained in the sulfuric acid when it is returned to the methane fermentation tank 1 again. It is preferable to install a desulfurization apparatus in the tank 1 so that the sulfide can be removed. In addition, this desulfurization apparatus removes the sulfide originally contained in the organic waste A.

  In this embodiment, as shown in FIG. 2, the methane fermenter 1 is configured in a two-stage system including a first methane fermenter 1A and a second methane fermenter 1B, and the organic in the first methane fermenter 1A. The incompletely fermented portion of the organic waste A can be decomposed in the second methane fermentation tank 1B to generate methane gas.

  Moreover, in this embodiment, as shown in FIG. 3, the fermented liquid B discharged | emitted from the methane fermenter 1 is sent to the precipitation separation tank 3, and the solid content contained in the fermented liquid B is precipitated, This precipitate D can be sent to the acid heat treatment apparatus 2. It is effective when the sludge settleability of the fermentation broth B is good. In addition, solid matter (residues: c, d) can be appropriately discharged from the acid heat treatment liquid C and the precipitate D.

“Second Embodiment”
A second embodiment of the present invention will be described with reference to FIGS. In the present embodiment, a solid-liquid separation device indicated by reference numeral 4 is installed.

  And as shown in FIG. 4, the fermentation liquid B is sent to the solid-liquid separator 4 from the said methane fermenter 1, and this fermentation liquid B is isolate | separated into the liquid component F and the concentrate G. FIG. In the present embodiment, a high-speed rotary centrifugal concentrator, a pressure levitation method, a membrane separation method, or the like can be employed as the solid-liquid separation device 4.

  Moreover, as shown in FIG. 5, similarly to 1st Embodiment, also in this embodiment, the methane fermentation tank 1 is comprised in the two-stage type of the 1st methane fermentation tank 1A and the 2nd methane fermentation tank 1B, The incompletely fermented portion of the organic waste A in the first methane fermentation tank 1A can be decomposed in the second methane fermentation tank 1B to generate methane gas, and then the solid-liquid separation device 4 in this embodiment. Can be sent to.

  In addition, from the acid heat treatment liquid C and the concentrate G, solids (residues: c, g) can be appropriately discharged.

  Furthermore, in this embodiment, although not shown, the fermentation liquid B discharged from the methane fermentation tank 1 is sent to the precipitation separation tank 3 to precipitate the solid content contained in the fermentation liquid B, and this precipitate D is It can also be configured such that it can be sent to the acid heat treatment device 2 and the remaining fermentation broth B can be sent to the solid-liquid separator 4.

The experimental result by the methane fermentation treatment method of this embodiment is shown below. The conventional treatment method corresponds to treatment of only the methane fermentation tank 1.
[Experimental conditions]
Single-stage methane fermentation with a sewage sludge (TS concentration of about 25 g / L) as a treatment target, a retention time of 20 days, a fermentation temperature of 35 ° C., and an experiment period of 63 days for hydrochloric acid and sulfuric acid, respectively. , PH 5-6, using centrifugal concentrator (2000 rpm, 10 minutes) as solid-liquid separator [Experimental results]
Type of strong acid Change ratio with conventional treatment method Sludge generation amount (VTS standard) Hydrochloric acid 95% reduction
63% decrease in sulfuric acid Methane generation volume 22% increase in hydrochloric acid
Sulfuric acid 13% increase Sludge dewaterability (CST / SS standard) Hydrochloric acid 20% increase
Sulfuric acid 32% increase Phosphorus elution amount (PO ₄ -P concentration standard) Hydrochloric acid 2 times increase
Sulfuric acid 19 times increase

[Discussion]
From the above experimental results, the following advantages are recognized according to the methane fermentation treatment method of the present invention.
(1) Since the amount of sludge generated decreases, the final disposal amount and disposal cost decrease.
(2) The amount of energy that can be used increases as the amount of methane generated increases.
(3) Since the sludge dewaterability is improved, the amount of the flocculant can be reduced.
(4) The increase in phosphorus elution amount greatly increases the recoverable amount of phosphorus.

It is the schematic showing the procedure of the methane fermentation processing method of 1st Embodiment of this invention. It is the schematic showing the procedure of the processing method using the two-stage methane fermenter of 1st Embodiment of this invention. It is the schematic showing the procedure of the processing method using the precipitation separation tank of 1st Embodiment of this invention. It is the schematic showing the procedure of the methane fermentation processing method of 2nd Embodiment of this invention. It is the schematic showing the procedure of the processing method using the two-stage methane fermenter of 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Methane fermenter 1A 1st methane fermenter 1B 2nd methane fermenter 2 Acid heat treatment device 3 Precipitation separation tank 4 Solid-liquid separation device A Organic waste B (B ') Fermentation liquid C Acid heat treatment liquid D Precipitate E Discharged liquid F Liquid content G Concentrate c ・ d ・ g Solid

Claims (11)

Organic waste A is sent to the methane fermenter 1 and decomposed microbiologically in anaerobic condition to generate methane gas.
While sending the fermented liquor B from this methane fermenter 1 to the acid heat processing apparatus 2, adding an inorganic acid to the said fermented broth B, and heat-processing,
An organic waste methane fermentation treatment method, wherein the acid heat treatment liquid C generated in the acid heat treatment apparatus 2 is returned to the methane fermentation tank 1 again.   The methane fermenter 1 is configured in a two-stage system including a first methane fermenter 1A and a second methane fermenter 1B, and the incompletely fermented portion of the organic waste A in the first methane fermenter 1A is second methane fermented. The method for methane fermentation treatment of organic waste according to claim 1, wherein methane gas is generated by decomposition treatment in the tank 1B. While sending the fermented liquor B discharged from the methane fermenter 1 to the precipitation separation tank 3, the solid content contained in the fermented liquor B is precipitated, and this precipitate D is sent to the acid heat treatment device 2,
3. The method for methane fermentation treatment of organic waste according to claim 1, wherein the remaining effluent E is discharged.   The fermented liquid B is sent from the methane fermenter 1 to the solid-liquid separator 4, the fermented liquid B is separated into the liquid F and the concentrate G, and the concentrated G is sent to the acid heat treatment apparatus 2. The methane fermentation treatment method for organic waste according to any one of claims 1 to 3.   The methane fermenter 1 is configured in a two-stage system of a first methane fermenter 1A and a second methane fermenter 1B, and the fermented liquid B ′ from the second methane fermenter 1B is sent to the solid-liquid separator 4 and this The organic waste according to any one of claims 1 to 4, wherein the fermentation broth B is separated into a liquid F and a concentrate G, and the concentrate G is sent to the acid heat treatment apparatus 2. Methane fermentation treatment method.   6. The organic waste methane fermentation treatment method according to claim 1, wherein the solid residue is discharged from the acid heat treatment liquid C generated from the acid heat treatment apparatus 2.   In the acid heat processing apparatus 2, hydrochloric acid is added, The methane fermentation processing method of the organic waste as described in any one of Claims 1-6 characterized by the above-mentioned.   In the acid heat processing apparatus 2, a sulfuric acid is added, The methane fermentation processing method of the organic waste as described in any one of Claims 1-6 characterized by the above-mentioned.   In the methane fermentation tank 1, the content in the organic waste A or the sulfide generated by the sulfate reduction reaction is removed using a desulfurization apparatus. The methane fermentation processing method of the organic waste as described in 2.   The method for methane fermentation treatment of organic waste according to any one of claims 1 to 9, wherein the heating temperature in the acid heat treatment apparatus 2 is 40 ° C or higher.   The method for methane fermentation treatment of organic waste according to any one of claims 1 to 10, wherein the acid treatment in the acid heat treatment apparatus 2 is an inorganic acid treatment with a pH of 6 or less.

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