JP2003039045A - Method for treating woody solid waste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for treating woody solid waste, whereby in wet oxidation in a treating method comprising solubilizing woody solid wastes by wet oxidation and microbially decomposing the solubilized wastes, the wastes can be microbially decomposed at good efficiency by effectively decomposing lignin, inhibiting the formation of substances being harmful to microbes and resulting from cellulose decomposition, and leaving microbially decomposable cellulose as much as possible. SOLUTION: In wet-oxidizing a slurry of woody solid wastes and water, the slurry before the wet oxidation is adjusted so that the pH of the treated product after the wet oxidation may be 6.0-8.0 and the slurry is partially decomposed under conditions in which the treatment temperature of the slurry is 170-190 deg.C, the pressure is one at which the slurry is kept in a liquid phase, and the treatment time is 30-60 min by feeding an oxygenous gas in an amount equivalent to an oxygen supply, per unit volume of the slurry, equivalent to 10-20% of the CODcr value of the slurry.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for solubilizing wood-based solid waste such as recovered waste paper such as newspaper and cardboard, and bark and wood waste discharged from the wood processing industry by wet oxidation for microbial decomposition treatment. In detail, in wet oxidation, it improves the decomposition rate of lignin that cannot be decomposed by microorganisms,
In addition, the present invention relates to a method for suppressing the production of a decomposition product unfavorable to microorganisms resulting from the decomposition of cellulose while allowing cellulose that is biodegradable to remain as much as possible so that the woody solid waste can be efficiently decomposed by microorganisms.

[0002]

2. Description of the Related Art Paper, which is contained in large amounts in household waste and business waste, is being recycled, and although the recovery rate of used paper varies depending on the type, newspaper paper and cardboard are already 95% and 80%, respectively. Reached 50% and 90%, respectively, and approached the theoretical limit value simulated from product quality. Therefore, the amount of surplus waste paper will increase in the future, and new means for utilizing waste paper is required.

Under these circumstances, attempts have been made to anaerobically digest municipal solid wastes containing a large amount of papers. However, anaerobic bacteria such as hydrolyzing bacteria and acid-producing bacteria are solid woody materials such as newspapers and toilet paper. It is difficult to decompose waste,
Energy is not efficiently recovered as methane gas.

The reason why anaerobic bacteria are difficult to decompose woody solid wastes such as papers is that natural cellulose is highly crystallized and contains lignin which is very difficult to biodegrade. It should be noted that cellulose itself can be finally decomposed into glucose by cellulase or the like which is originally produced by microorganisms, but cellulose constituted as fiber cannot be effectively decomposed because it is coated with lignin, which is difficult to biodegrade. .

In order to solve this problem, the bond between lignin and cellulose contained in papers such as newspapers and toilet papers is changed, and these carbohydrates are easily decomposed by anaerobic microorganisms, so that carbs are removed from papers during anaerobic digestion. Studies have been done to increase methane yield.

[0006] One of them is that the pH of the waste is adjusted to 13 prior to the anaerobic digestion of the waste, and then the alkali heat treatment is performed under the conditions of a reaction temperature of 200 ° C and a reaction time of 1 hour. It is reported that the increase will be possible. However, the thermochemically treated lignin concentration was 1
It has also been reported that a significant digestive inhibition is observed when it exceeds g / L (James M. Gossett, David C. Stuckey,
"Heat treatment and anaerobic digestion of refuse
：： Journal of the environmental engineering divi
sion, Vol.108, No.EE3, June 1982).

On the other hand, Japanese Patent Laid-Open No. 59-26195 discloses a method of treating cellulose-containing waste having a delignification step as shown in FIG. That is, the cellulose-containing waste 1 is anaerobically digested in the anaerobic digestion tank 8, the digestion slurry is subjected to solid-liquid separation in the solid-liquid separator 9, and the separated digestion residue is put into the alkali pretreatment tank 3. In this alkaline pretreatment tank 3, an alkali agent of 1 to 10% by weight is added to the cellulose-containing waste, and an alkali heat treatment is performed at a treatment temperature of 60 to 100 ° C. for a treatment time of 0.5 to 5 hours to lignin. Is eluted. Next, solid-liquid separation is performed by the solid-liquid separation device 5, the solid matter is washed in the washing tank 6, and then solid-liquid separation is performed again by the solid-liquid separation apparatus 7, and then the solid matter is put into the anaerobic digestion tank 8. On the other hand, the filtrate separated by the solid-liquid separation device 5 is sent to the gas-liquid contact device 10, is contacted with the digestive gas generated from the anaerobic digestion tank 8 to be neutralized, and is further ozone-treated by the gas-liquid contact device 14. Thus, the lignin dissolved in the filtrate is decomposed into organic acids such as oxalic acid and formic acid, and then returned to the anaerobic digestion tank 8, where methane gas is recovered by anaerobic digestion.

However, in the treatment method of FIG. 4, the step of eluting and decomposing lignin, which is difficult to biodegrade, is a delignification step of eluting lignin by alkali heat treatment, and an ozone treatment step of decomposing the eluted lignin with ozone. Is a two-step treatment, and requires the installation of solid-liquid separators 5 and 7 after the alkali pretreatment tank 3 and the cleaning tank 6, and further gas-liquid contact for neutralizing the filtrate from the solid-liquid separator 5. Since the device 10 is also required, the device is complicated, and labor is required for operation and maintenance.

On the other hand, in JP-A-2000-84520, an aqueous medium and an oxidizing agent are added to a wood-based solid waste,
A method for treating a wood-based waste in which the waste is solubilized and gasified by a wet oxidation treatment under heating and pressure is described. The wet oxidation treatment in this method has a reaction temperature of 100 to 2
The reaction temperature is maintained at 50 ° C., preferably 120 to 200 ° C. for 0 to 1 hour, preferably 20 to 30 minutes, and the reaction pressure is determined by using an inert medium or self-generated pressure by an aqueous medium. keeping. As the aqueous medium, water or a mixture of water and an organic solvent is used; to this aqueous medium, an alkaline substance such as sodium hydroxide is added in an amount of about 0.5 to 1.5% by weight based on the raw material waste. What can be done; hydrogen peroxide can be used as an oxidant; this oxidant is used in a proportion of 1 to 15% by weight, preferably 5 to 15% by weight, in terms of oxygen atoms, relative to the absolutely dried waste. As a result, the solubilization reaction of waste mainly occurs when the reaction temperature is maintained at 100 to 130 ° C, and the gasification reaction of waste mainly occurs when the reaction temperature is maintained at 140 ° C or higher. .

However, when the treatment method described in JP-A-2000-84520 was reproduced using waste paper as a target waste, sodium hydroxide as an alkaline substance in an aqueous medium was added to the raw waste at 1.5% by weight. %, The obtained solubilized product shows an acidity of 5 or less, and when the solubilized product is anaerobically digested, the amount of methane gas generated is reduced, and finally the methane gas is not generated. I stopped. From this, it was confirmed that an inhibitor against anaerobic digestion was produced in this treatment method.

Further, conventionally, as a method for treating human waste or organic sludge, a liquid phase oxidation method called Zimmerman method is used to remove organic matter in water from an oxygen-containing gas such as air under a pressure at which water maintains a liquid phase at a specific temperature. There is known a wet oxidation method in which oxygen is used for oxidative decomposition. This wet oxidation method for treating night soil and organic sludge can supply a large amount of oxygen in order to complete the self-combustion by satisfying the amount of heat required to heat the wet oxidation target with the oxidation heat generated by the oxidation reaction. Only oxidative decomposition is done.

[0012]

However, when the wood-based solid waste is subjected to the wet oxidation treatment as described above, a substance harmful to microorganisms is produced,
Significant digestive inhibition was observed in microbial decomposition treatment such as anaerobic digestion, and there was a demand for elucidation of the harmful substances and countermeasures.

Therefore, the present invention provides a method for solubilizing woody solid waste by wet oxidation to decompose microorganisms. In the wet oxidation, lignin is effectively decomposed, and microorganisms resulting from cellulose decomposition are decomposed. It is an object of the present invention to provide a treatment method capable of efficiently microbially degrading a wood-based solid waste by suppressing the production of harmful substances and leaving a microbially degradable cellulose as much as possible.

[0014]

[Means for Solving the Problems] The present inventors have found that substances harmful to microorganisms produced by the wet oxidation treatment of wood-based solid waste are dissolved in the liquid phase by the decomposition of cellulose and hemicellulose. We discovered that they are furans and phenolic compounds such as certain furfurals and hydroxymethylfurfurals. Furthermore, by wet-oxidizing woody solid waste under specific conditions, the inhibitory action of these harmful substances becomes apparent. It has been found that while it can be suppressed to a low concentration that does not occur, it decomposes lignin, which is difficult to biodegrade as much as possible, and that cellulose and hemicellulose, which are originally biodegradable, can remain as much as possible. It is a thing.

That is, the method for treating a wood-based solid waste according to claim 1 of the present invention for achieving the above object comprises a wet oxidation step of wet-oxidizing a wood-based solid waste formed into a slurry with water. A method for treating a wood-based solid waste, comprising a microbial decomposition step of microbially decomposing at least a part of a treated product that has undergone the wet oxidation process, wherein in the wet oxidation process, the pH of the treated product after the wet oxidation is Is 6.0 to 8.
The pH of the slurry before wet oxidation is adjusted so as to be 0, and the treatment temperature of the slurry is 170 to 190 ° C.
And the pressure for holding the liquid phase of the slurry and the treatment time of 30 to 60 minutes, the oxygen supply amount per unit volume of the slurry is 10 to 2 of the CODcr value of the slurry.
It is characterized in that an oxygen-containing gas corresponding to 0% is supplied for partial decomposition.

According to the invention of claim 1, in the wet oxidation step as a pretreatment of the microbial decomposition step for microbially decomposing the woody solid waste, the wet oxidation is performed under predetermined optimum conditions. It can suppress the generation of substances harmful to microorganisms generated by wet oxidation of cellulose and hemicellulose to a low concentration that does not reveal an inhibitory effect, efficiently decomposes lignin that is difficult to biodegrade, and, in addition, originally Biodegradable cellulose and hemicellulose can be left behind, and effective microbial decomposition of wood-based solid waste is carried out in the microbial decomposition process.

According to a second aspect of the present invention, there is provided a method for treating a wood-based solid waste according to the first aspect, wherein in the wet oxidation step, the pH of the treated material after the wet oxidation is the same.
Is adjusted to 6.5 to 7.5, the pH of the slurry before wet oxidation is adjusted. According to the invention of claim 2, it is possible to further suppress the generation of substances harmful to microorganisms in the wet oxidation step, and as a result, microbial decomposition of the wood-based solid waste in the microbial decomposition step. Can be done more efficiently.

According to a third aspect of the present invention, there is provided a method for treating a wood-based solid waste according to the first or second aspect of the present invention.
The processed product which has undergone the wet oxidation step of carrying out the microbial decomposition step in the microbial decomposition step is one in which at least a part of the oxidation separated liquid which is a liquid phase is removed by solid-liquid separation of the oxidized slurry from the wet oxidation step. It is characterized by According to the invention of claim 3 as described above, a substance harmful to the solubilized microorganism can be removed together with the oxidative separation liquid.
In the microbial decomposition step, the wood-based solid waste can be microbially decomposed more efficiently.

According to a fourth aspect of the present invention, there is provided a method for treating wood-based solid waste according to the first or second aspect of the present invention.
The treated product that has undergone the microbial decomposition process in the microbial decomposition process is an oxidized slurry from the wet oxidation process, and is directly supplied to the microbial decomposition process without solid-liquid separation. According to the invention of claim 4 as described above, since the liquid phase to be the oxidation separated liquid in the invention of claim 3 is also subjected to the microbial decomposition treatment, the organic matter load in the biological treatment process by the activated sludge in the latter stage can be reduced.

According to a fifth aspect of the present invention, there is provided a method for treating a woody solid waste according to any one of the first to fourth aspects, wherein the microbial decomposition step is anaerobic digestion. It is characterized by being a process. According to the invention of claim 5, methane gas having high energy conversion efficiency can be produced from the woody solid waste by anaerobic digestion.

According to a sixth aspect of the present invention, in the method for treating woody solid waste, in the treatment method according to any one of the first to fourth aspects, the microbial decomposition step is hydrogen fermentation with an anaerobic hydrogen-producing bacterium. It is characterized by being a process. According to the invention of claim 6, hydrogen gas, which is clean energy, can be produced from the wood-based solid waste by the anaerobic hydrogen-producing bacterium.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION In the embodiment of the present invention shown in FIG. 1, a wood-based solid waste 1 is put into a wet crushing device 2 by a conveyor, a power shovel, or the like, and water is added to make a slurry. The wood-based solid wastes include recovered waste paper such as newspapers and dunholes, and wood chips and bark discharged from the wood processing industry. In addition, liquid organic waste such as human waste and septic tank sludge can be used as a foreign matter removing device with openings 2 to 2.
Since a large amount of toilet paper, dust paper, and the like, which are contaminants removed by the treatment with a 5 mm drum screen, are included as wood-based solid waste. It should be noted that woody solid waste such as wood chips and bark which is not easily slurried by adding water and stirring, 10 mm by a dry crushing device (not shown) such as a cutter or crusher before being put into the wet crushing device 2.
It is necessary to cut below the corner.

The water added to the wet crushing apparatus 2 is for slurrying the woody solid waste, and tap water, industrial water or the like may be used at the start of operation, but after-treatment at steady operation. The biologically treated water produced by the biological treatment device 24 in the process can be used. The amount of water may be such that fluidity is maintained in the slurried wood-based solid waste and there is no hindrance to the transfer. Generally, the TS concentration of the wood-based solid waste slurry is 1.5 to 3. It is preferably 0% by mass. This TS concentration refers to JIS K0102 (199
8) Total evaporation residue specified in the Industrial Wastewater Test Method.

In the wet crushing device 2, it is roughly crushed,
The slurried woody solid waste is sent to the fine crusher 5, crushed to a width of 5 mm or less and a length of 10 mm or less, and then transferred to the alkali slurry adjusting tank 6. In the alkaline slurry adjusting tank 6, the alkaline aqueous solution is supplied from the alkaline storage tank 3 by the alkaline supply pump 4. The alkaline aqueous solution is supplied from the alkaline storage tank 3 to the alkaline slurry adjusting tank 6 by measuring the pH of the oxidizing slurry with a pH meter installed in the oxidizing slurry storage tank 19 in the subsequent wet oxidation step, and the value is 6. It is carried out by operating the alkali supply pump 4 via the pH controller 7 so as to be in the range of 0 to 8.0, preferably 6.5 to 7.5. Further, the alkaline aqueous solution may be supplied from the alkali storage tank 3 to the wet crushing device 2 by operating the valve. Note that the wet crushing device 2 is usually operated by a batch operation (batch operation), and the alkali slurry adjusting tank 6 and the subsequent operations are performed continuously.

In the alkali slurry adjusting step, the pH of the treated material after wet oxidation is 6.0 to 8.0, preferably 6.5.
By adjusting the pH of the slurry before wet oxidation to 7.5, it improves the lignin decomposition rate in the wet oxidation process and suppresses the generation of decomposition products unfavorable to anaerobic digestive microorganisms resulting from cellulose decomposition. Let
It improves the efficiency of anaerobic digestion. In addition, when the pH of the treated product after the wet oxidation is out of the range of 6.0 to 8.0, that is, the addition amount of the alkaline aqueous solution is insufficient and the pH is 6
When the amount becomes less than the above, or when the amount of the alkaline aqueous solution added becomes excessively high and the pH becomes 8 or more, it is not possible to suppress the generation of decomposition products which are unfavorable to the anaerobic digestion microorganisms in the wet oxidation step, and the solid wood-based solids are obtained in the anaerobic digestion step. The waste cannot be decomposed efficiently.

The alkaline agent used in the alkaline aqueous solution may be a general-purpose one, and sodium carbonate, sodium hydrogen carbonate, sodium hydroxide, calcium hydroxide or the like is usually used. The amount of alkali added varies depending on the slurry concentration of the woody solid waste and the treatment temperature of the wet oxidation process. The higher the slurry concentration of the woody solid waste and the higher the treatment temperature of the wet oxidation process, the larger the amount of alkali needs to be added. Becomes This is because cellulose, hemicellulose, lignin, etc. are hydrolyzed and partially oxidatively decomposed by the wet oxidation treatment, and a high concentration of organic acids such as acetic acid and butyric acid are produced, so that a large amount of alkali is consumed. Generally, the amount of alkali added is 15 to 25% by mass with respect to solid wood waste.
Is. The alkaline slurry adjusting tank 6 plays a role of a cushion tank so that the wet oxidation process in the subsequent stage can be continuously operated.

The alkali slurry in the alkali slurry adjusting tank 6 is sequentially transferred by the alkali slurry supply pump 8 to the first heat exchanger 9, the second heat exchanger 10 and the reaction tower 11, and the alkali slurry is converted into the alkali slurry in the reaction tower 11. Wet oxidation is performed, and the product is hydrolyzed or partially oxidatively decomposed to obtain a wet oxidation-treated product. In the first heat exchanger 9, heat exchange between the alkali slurry and the high temperature wet oxidation product discharged from the reaction tower 11 is carried out, and in the second heat exchanger 10, the first heat exchanger 9 heats it. Heat exchange is performed between the obtained alkaline slurry and the steam from the heating boiler 12. The alkali slurry is supplied to the reaction tower 11 while being heated to 160 to 180 ° C. The temperature of the alkali slurry in the reaction tower 11 is further increased by 5 due to the heat of oxidation of itself.
Since the temperature rises by -10 ° C, the temperature becomes 170-190 ° C.
At this temperature, the processing time is 30 to 60 minutes and the absolute pressure is 1.
The hydrolysis and partial oxidation treatment are performed under the conditions of 0 to 2.5 MPa (liquid phase holding pressure at the required treatment temperature), preferably 1.2 to 2.2 MPa.

Oxygen is supplied to the reaction tower 11 from the snapper (compressed air storage tank) of the compressor 13 for compressing air (oxygen-containing gas) to the lower part of the reaction tower 10 via the flow rate adjusting valve (FCV) 14. To be done. The oxygen supply amount per unit volume of the alkali slurry is C of the alkali slurry.
The amount of air supplied is controlled by the flow rate adjusting valve 14 so as to be 10 to 20% of the ODcr value.

This CODcr value is JIS K0102
(1998) means the oxygen consumption by potassium dichromate specified in the Industrial Waste Water Test Method, and in the present invention,
COD cr value of woody solid waste slurry is, for example, 30 g
/ L, the CODcr value is 10 to 20%, that is, 3.0 to 1 L of wood-based solid waste slurry.
It suffices to mix an oxygen-containing gas containing an oxygen amount of 6.0 g. The oxygen-containing gas is not limited to air, and may be any oxygen-containing gas that does not pose a risk of explosion or containing harmful substances, such as air, oxygen-enriched gas, pure oxygen, or exhaust gas from a prime mover or a boiler. Etc. In some cases, it is also possible to use the exhaust gas from the heating boiler 12. In that case, the residual oxygen concentration in the exhaust gas may be measured and the required exhaust gas amount according to the oxygen concentration may be supplied.

In the wet oxidation step of the present invention, since the oxygen supply amount is limited and stopped by partial oxidation, the amount of heat required to heat the wet oxidation object is satisfied by the heat of oxidation generated by the oxidation reaction, that is, Unlike the conventional wet oxidation method of self-combustion, in order to maintain the treatment temperature at 170 to 190 ° C., heating must be continued from the outside. Such heating may be either indirect heating such as steam by a heat exchanger or direct heating in which steam or the like is brought into direct contact with the alkali slurry.

The supply location of oxygen to the reaction tower 11 is not limited to the lower part of the reaction tower 11, and the alkali slurry flowing out from the second heat exchanger 10 is combined with oxygen and supplied to the reaction tower 11. Alternatively, oxygen may be merged with the alkali slurry flowing out from the alkali slurry supply pump 8 and supplied to the inlet of the first heat exchanger 9.

The wet-oxidation product discharged from the reaction tower 11 passes through the first heat exchanger 9 to reach a liquid temperature of 50 to 80 ° C. and flows into the pressure control valve (PVC) 15, where the pressure in the reaction system is increased. While the pressure is kept constant, the absolute pressure is reduced from 1.0 to 2.5 MPa to the atmospheric pressure of 0.1 MPa, and then the gas-liquid separator 1
6 and is separated into oxidizing exhaust gas and oxidizing slurry.
The oxidized exhaust gas is treated by the exhaust gas treatment device 17 and released into the atmosphere, or is used as a part of aeration gas for biological treatment as a post-treatment of the anaerobic digestion process. On the other hand, the oxidized slurry is supplied to the oxidized slurry storage tank 19 by the oxidized slurry transfer pump 18.

PH of alkali slurry before wet oxidation treatment
Is usually 10 or more, but due to the wet oxidation treatment,
Cellulose, hemicellulose, lignin, etc. in the woody solid waste are hydrolyzed and partially oxidatively decomposed to produce organic acids such as acetic acid and butyric acid, and carbonic acid, and alkali is consumed. The pH of the oxidized slurry is almost neutral. Therefore, improving the decomposition rate of lignin that can not be decomposed by microorganisms, and while suppressing the generation of undesired decomposition products to microorganisms resulting from cellulose decomposition,
Biodegradable cellulose can be left as much as possible and no special neutralization device is required.

The oxidizing slurry in the oxidizing slurry storage tank 19 is supplied to the anaerobic digestion tank 21 by the oxidizing slurry supply pump 20.
Is thrown into. The treatment conditions in anaerobic digestion are medium temperature fermentation at a tank temperature of 32 to 38 ° C (or high temperature fermentation at 53 to 57 ° C) and a hydraulic retention time (HRT) of 10.
-25 days, preferably 12-20 days.

In the illustrated example, the oxidizing slurry is supplied to the anaerobic digestion step as it is without solid-liquid separation, but the oxidizing slurry is subjected to solid-liquid separation to obtain at least one of the oxidation separated liquids in the liquid phase. Anaerobic digestion tank 21 excluding parts
The oxidative separation liquid supplied and separated to the above may be treated by the biological treatment device 24 in the post-treatment step. In the first aspect of the present invention, the term "processed product after the wet oxidation step" is used as a term that includes both an oxidized slurry that is not solid-liquid separated and a solid-liquid separated product that is obtained by removing at least a part of the oxidized separated liquid. There is.

The anaerobic digestion tank 21 is generally a one-tank type in which an acid-producing phase and a methanogenic phase are combined, but one tank may be divided into two tanks, or it is conventionally used. Any structure may be used as long as it is an agitating type in a tank, such as a two-tank system in which separate tanks are used, or a multi-tank system in which temperature and the like are changed to improve digestion efficiency. However, in consideration of heat radiation from the anaerobic digestion tank and transfer of digestive fluid, the one-tank type or the two-tank type is preferable.

The digestion slurry in the anaerobic digestion tank 21 flows into the solid-liquid separation tank 22 and is separated into digestion-desorption liquid and concentrated digestion sludge. The digested-desorbed liquid thus separated is sent to the biological treatment device 24 by the digested-desorbed liquid transfer pump 23 and biologically treated with activated sludge, and then the biologically treated water is discharged to the outside of the system.
A part of the biologically treated water may be returned to the wet crushing device 2 by the biologically treated water transfer pump 25 and used as water for forming a slurry of the woody solid waste. Further, the excess sludge generated in the biological treatment device 24 is returned to the wet crushing device 2 by the excess sludge transfer pump 26 and treated together with the slurry of the wood-based solid waste.

On the other hand, the concentrated digested sludge from the solid-liquid separation tank 22 is supplied to the dehydrator 28 by the concentrated digested sludge supply pump 27, is dehydrated, and is then sent to the composting device 29 for composting. In the composting apparatus 29, digested sludge contains almost no undecomposed cellulose or lignin, so that composting is promoted and high-quality compost can be produced. The dehydrated filtrate generated by the dehydration treatment is sent to the biological treatment device 24 by the dehydrated filtrate transfer pump 30 and biologically treated together with the digested and desorbed liquid. In addition, a part of the concentrated digested sludge may be returned to the wet crushing device 2 by the concentrated digested sludge transfer pump 31, and may be treated together with the wood-based solid waste and the excess sludge. As a result, there is a large seasonal fluctuation in demand,
It requires storage for a long period of time, and it is possible to reduce the production amount of compost, which tends to be bulky in recent years.

[0039]

EXAMPLE An example in which the present invention is applied to a newspaper and a dehydrated residue generated from a human waste treatment plant will be described below.

Example 1 Newspapers were wet-oxidized under different treatment conditions, and the wet-oxidation products of furan such as hydroxymethylfurfural and furfural which exert an inhibitory effect on the decomposition efficiency of cellulose and lignin and microorganisms. We examined the generation. The newspaper used in the experiment contained 54.0% by mass of cellulose and 16.9% by mass of lignin, and 20 g was cut with a shredder, 1 L of distilled water was added, and then slurried with a homogenizer. Under alkaline conditions, the pH of the newsprint slurry after wet oxidation was 6.
Sodium carbonate was added so as to have a concentration of 5 to 7.5, and under acidic conditions, wet oxidation treatment was performed without adding sodium carbonate. For the wet oxidation treatment, use a shaking type autoclave experimental device,
A predetermined amount of the newspaper slurry adjusted to the alkaline condition and the acidic condition described above was put into a reaction vessel having an inner volume of 760 mL, and the oxygen supply amount per unit volume of the newsprint slurry was 20% of the CODcr measured value of the newsprint slurry. Filled with compressed air. The reaction container was placed in an electric furnace with a shaking function, and the temperature was raised while shaking to reach a predetermined temperature, and then wet oxidation treatment was carried out for 1 hour. Table 1 shows wet oxidation treatment conditions and final pH (pH of the treated product after wet oxidation treatment), and Table 2 shows decomposition efficiency of cellulose and lignin after wet oxidation treatment.
And Table 3 shows the formation of furan derivative in the wet oxidation treatment.

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

[Table 3]

As can be seen from Table 2, the decomposition efficiency of lignin is higher and the decomposition efficiency of cellulose is lower (190 ° C. or lower) under alkaline conditions than under acidic conditions. Therefore, it is suggested that the treated product that is subjected to the wet oxidation treatment under alkaline conditions that decomposes lignin, which is difficult to biodegrade, and leaves biodegradable cellulose, is more suitable for anaerobic digestion. In addition, from Table 3, the production of furans such as hydroxymethylfurfural and furfural, which decompose cellulose and hemicellulose and exert an inhibitory effect on microorganisms, is significantly reduced under alkaline conditions as compared with acidic conditions.
Therefore, the wet oxidation treatment product under alkaline conditions is
It can be seen that more stable anaerobic digestion treatment is possible.

Example 2 The wet oxidation treatment product of newspaper was anaerobically digested, and the optimum wet oxidation condition was examined from the amount of methane produced. Using the wet oxidation treated product obtained in Example 1, 450 mL thereof, 300 mL of digested sludge obtained by anaerobically digesting sewage sludge, and 300 mL of vitamin-inorganic salt solution were placed in a 2 L vial bottle and continuously placed with a magnetic stirrer. It was digested anaerobically at 35 ° C. with mechanical stirring. FIG. 2 shows the cumulative amount of methane produced when the wet oxidation treatment product was subjected to anaerobic digestion at each treatment temperature under alkaline conditions and acidic conditions.

As can be seen from FIG. 2, the amount of methane produced from the wet oxidation treatment product under alkaline conditions is larger than the amount of methane production from the wet oxidation treatment product under acidic conditions, and the optimum treatment temperature is 170 to 190 ° C. there were. Further, wet oxidation treatment (treatment temperature 170 to 210) under acidic conditions without pH adjustment.
The methane production amount increased by 30% or more as compared with the methane production amount from the treated product.

Example 3 20 g of newspaper was cut with a shredder, 1 L of distilled water and 5 g of sodium carbonate were added, and then slurried with a homogenizer. A predetermined amount of this alkaline slurry of newspaper was put into a reaction vessel having an internal volume of 760 mL, and when the oxygen supply amount per unit volume of the alkaline slurry was 20% of the CODcr value of the slurry, the reaction time was varied to perform wet oxidation, and When the reaction time was set to 60 minutes, the oxygen supply amount was varied to perform wet oxidation, and the decomposition efficiency of the treated cellulose and lignin was examined. Table 4 shows the decomposition efficiency of cellulose and lignin at each oxygen supply amount and each reaction time.

[0048]

[Table 4]

From Table 4, as the conditions for degrading lignin, which is difficult to biodegrade, and leaving the biodegradable cellulose, the reaction time is 30 to 60 minutes and the oxygen supply is COD.
It can be seen that it is 10 to 20% of the cr value.

Example 4 Wet oxidation treatment product obtained by subjecting dehydrated residue generated from a night soil treatment plant to wet oxidation treatment under alkaline conditions, heat treatment product obtained by heat treatment under alkaline conditions, and wet oxidation treatment The untreated dehydrated residue without heat treatment and heat treatment was subjected to anaerobic digestion, respectively, and the effectiveness of pretreatment for methane production was examined.

The dehydrated residue from the urine treatment plant used for the experiment had a water content of 55.4% by mass and a VTS content of 94.6% by mass. After dehydration and addition of 1 L of tap water to 60 g of the residue, a homogenizer was used. Was slurried. In the alkaline wet oxidation treatment of the dehydrated residue, the treatment temperature was set to 170 ° C.
I went in the same way. Alkaline heat treatment has a treatment temperature of 1
The temperature was set to 70 ° C., the supply of oxygen was cut off, and the gas phase part was replaced with nitrogen gas in order to maintain the liquid phase, and then the mixture was filled to a predetermined pressure. Table 5 shows the processing conditions of these alkaline wet oxidation treatment and alkaline heat treatment and the final pH (pH of the treated product after the treatment).

For anaerobic digestion, an anaerobic digestion tank having an effective volume of 5 L is used, and after digesting sludge obtained by anaerobic digesting sewage sludge as seed sludge, digestion temperature is 36 ° C. and digestion days are 20.
250 mL / day of alkaline wet oxidation product, alkaline heat treatment product and untreated dehydrated residue slurry
The same amount of digested sludge was drawn out. FIG. 3 shows the progress of methane production.

As can be seen from FIG. 3, the daily methane production amount is about 4 in the alkaline heat treatment as compared with the untreated dehydrated residue.
1%, about 55% increased by the alkaline wet oxidation treatment, and the methane yield was highest when the pretreatment was performed by the alkaline wet oxidation treatment.

[0054]

[Table 5]

In the above description, an example in which the microbial decomposition step in the method of the present invention is carried out based on anaerobic digestion has been described, but the cellulolytic bacterium and Clostridium butyricum SC-E1 which is an anaerobic hydrogen-producing bacterium. Stocks and Clostrid
ium sp. KT-7B strain and the like, even by using a hydrogen fermentation step to coexist, by culturing these anaerobic hydrogen-producing bacteria at the predetermined culture temperature and residence time in the oxidizing slurry, the present invention A microbial degradation step in the method can be performed. For example, Clostridium sp., Which is a hydrogen-producing bacterium, is added to seed sludge that has been pretreated to heat anaerobic digested sludge at 70 to 80 ° C for about 15 minutes to suppress hydrogen-utilizing bacteria.
In a hydrogen fermentation process using a mixed microorganism group in which Clostridium sp. Is predominantly added and cultivated, hydrogen gas is oxidized from the oxidizing slurry in a culture tank at a culture temperature of 35 ° C. and a residence time of 6 to 10 hours. Obtainable. Also, since Clostridium sp. Originally exists in anaerobic digested sludge, seed sludge that has been subjected to a pretreatment to suppress hydrogen-utilizing bacteria by heat-treating the anaerobic digested sludge for 15 minutes at 70-80 ° C. The hydrogen gas can be obtained in a culture tank at a culture temperature of 35 ° C. and a residence time of 6 to 10 hours by directly culturing the above with the oxidized slurry.

Further, in the above description, an example in which the wet oxidation step in the method of the present invention is carried out based on an apparatus in which a heating boiler is added to the conventional wet oxidation apparatus has been described. Even when using a heat treatment apparatus that utilizes a contacting and heating Porches process or a hydrothermal reaction, an oxygen-containing gas whose oxygen supply amount per unit volume of the slurry corresponds to 10 to 20% of the CODcr value of the reslurry is supplied. In addition, the method of the present invention is performed by performing a predetermined pH adjustment, heat treatment at a treatment temperature of 170 to 190 ° C., and a pressure for holding the liquid phase of the slurry under the condition of a treatment time of 30 to 60 minutes. A wet oxidation step of partial decomposition in can be carried out.

[0057]

As described in detail above, according to the invention of claim 1, a wet oxidation step is provided as a pretreatment for the microbial decomposition step of microbially decomposing woody solid waste, and in this wet oxidation step, the wet oxidation step is performed. The pH of the treated product after oxidation is 6.0 to
Since the pH was adjusted before the wet oxidation to reach 8.0, the wet oxidation was performed under predetermined optimum conditions. Therefore, the formation of substances harmful to the microorganisms produced by the wet oxidation of cellulose or hemicellulose is prevented. It is possible to suppress the concentration to such a low level that the inhibitory action does not become apparent, efficiently decompose lignin, which is difficult to biodegrade, and leave cellulose and hemicellulose that are originally biodegradable. As a result, effective microbial decomposition of the wood-based solid waste is carried out in the microbial decomposition process, and high-quality compost without lignin residue can be produced when composting digested sludge after microbial decomposition. further,
Since the pH of the wet-oxidized product becomes almost neutral, the product can be directly supplied to the microbial decomposition process without pH adjustment, the equipment for pH adjustment is not required, and the labor required for operation and maintenance. Can also be reduced.

According to the second aspect of the present invention, by setting the pH of the treated product after the wet oxidation to a more optimal range of 6.5 to 7.5, it is possible to prevent the microorganisms from reacting in the wet oxidation step. It is possible to further suppress the generation of harmful substances, and as a result, it is possible to more efficiently perform microbial decomposition of the woody solid waste in the microbial decomposition process.

According to the third aspect of the present invention, the oxidized slurry from the wet oxidation step is subjected to solid-liquid separation to remove at least a part of the oxidized separated liquid, which is harmful to solubilized microorganisms. Since the substance can be removed together with the oxidation separated liquid, the wood-based solid waste can be more efficiently microbially decomposed in the microbial decomposition step.

Further, according to the invention of claim 4, the oxidized slurry from the wet oxidation step is directly supplied to the microbial decomposition step without solid-liquid separation, and becomes a liquid phase which becomes the oxidized separation solution in the invention of claim 3. Since the microbial decomposition treatment is also carried out, the organic matter load in the biological treatment process by the activated sludge in the latter stage can be reduced.

According to the fifth aspect of the present invention, methane gas with high energy conversion efficiency can be produced from the woody solid waste by using the anaerobic digestion step as the microbial decomposition step.

Further, according to the invention of claim 6, hydrogen gas which is clean energy can be produced from the woody solid waste by making the microbial decomposition step a hydrogen fermentation step by an anaerobic hydrogen-producing bacterium. .

[Brief description of drawings]

FIG. 1 is a flow sheet showing a basic embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the difference in wet oxidation treatment conditions and the cumulative methane production amount in the anaerobic digestion process.

FIG. 3 is a graph showing the relationship between the difference in pretreatment in the anaerobic digestion step and the amount of methane produced in the anaerobic digestion step.

FIG. 4 is a flow sheet showing a conventional method for treating cellulose-containing waste.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B09B 3/00 A (72) Inventor Shin Hoshino 953 Iwase, Kamakura-shi, Kanagawa Leopalace Camellia 2 Building Room 104 (72) ) Inventor Hisayo Onizuka 5-6-11-502 Yokokodai, Isogo-ku, Yokohama, Kanagawa F Term (reference) 4D004 AA12 AA31 BA03 CA01 CA13 CA18 CA35 CA36 CC07 DA02 DA03 DA06 DA10 4D059 AA01 AA07 BA12 BA21 BC01 BF13 EA05 EA06 EA06 EA06 EA06 EA06 EA06 EA06 EB05 EB06 EB09 EB16

Claims (6)

[Claims] 1. A wet oxidation step of wet-oxidizing a woody solid waste formed in a slurry with water, and a microbial decomposition step of microbially decomposing at least a part of a treated product after the wet oxidation step. A method for treating wood-based solid waste, comprising the step of:
The pH of the slurry before wet oxidation is adjusted so that H becomes 6.0 to 8.0, the treatment temperature of the slurry is 170 to 190 ° C., and the pressure is such that the liquid phase of the slurry is retained. Under the condition that the treatment time is 30 to 60 minutes, the oxygen supply amount per unit volume of the slurry is CO of the slurry.
A method for treating a wood-based solid waste, comprising supplying an oxygen-containing gas corresponding to 10 to 20% of a Dcr value to partially decompose it. 2. The wet oxidation step is characterized in that the pH of the slurry before wet oxidation is adjusted so that the pH of the treated product after wet oxidation becomes 6.5 to 7.5. Item 1. A method for treating a wood-based solid waste according to Item 1. 3. A treated product which has undergone the microbial decomposition process in the microbial decomposition process is a liquid-phase oxidative separation liquid obtained by solid-liquid separation of the oxidizing slurry from the wet oxidization process. The method for treating wood-based solid waste according to claim 1 or 2, characterized in that 4. The treated product which has been subjected to the wet oxidation step of performing the microorganism decomposition treatment in the microorganism decomposition step is an oxidized slurry from the wet oxidation step, and is directly supplied to the microorganism decomposition step without solid-liquid separation. The method for treating wood-based solid waste according to claim 1 or 2. 5. The microbial decomposition step is an anaerobic digestion step for performing anaerobic digestion.
4. The method for treating wood-based solid waste according to any one of 4 above. 6. The microbial decomposition process is a hydrogen fermentation process using an anaerobic hydrogen-producing bacterium.
4. The method for treating wood-based solid waste according to any one of 4 above.