JP5882653B2 - Method for methane fermentation of organic substances - Google Patents
Method for methane fermentation of organic substances Download PDFInfo
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- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 title claims description 116
- 238000000855 fermentation Methods 0.000 title claims description 46
- 230000004151 fermentation Effects 0.000 title claims description 45
- 239000000126 substance Substances 0.000 title claims description 45
- 238000000034 method Methods 0.000 title claims description 18
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- 239000010802 sludge Substances 0.000 claims description 37
- 241000894006 Bacteria Species 0.000 claims description 20
- 244000005700 microbiome Species 0.000 claims description 16
- 239000010813 municipal solid waste Substances 0.000 claims description 16
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 12
- 239000001301 oxygen Substances 0.000 claims description 12
- 229910052760 oxygen Inorganic materials 0.000 claims description 12
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- 238000006243 chemical reaction Methods 0.000 description 10
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- XBDQKXXYIPTUBI-UHFFFAOYSA-N dimethylselenoniopropionate Natural products CCC(O)=O XBDQKXXYIPTUBI-UHFFFAOYSA-N 0.000 description 6
- 230000001580 bacterial effect Effects 0.000 description 5
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 4
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- KMUONIBRACKNSN-UHFFFAOYSA-N potassium dichromate Chemical compound [K+].[K+].[O-][Cr](=O)(=O)O[Cr]([O-])(=O)=O KMUONIBRACKNSN-UHFFFAOYSA-N 0.000 description 4
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 3
- 229910018540 Si C Inorganic materials 0.000 description 3
- 239000002253 acid Substances 0.000 description 3
- 238000000354 decomposition reaction Methods 0.000 description 3
- 235000014113 dietary fatty acids Nutrition 0.000 description 3
- 238000000605 extraction Methods 0.000 description 3
- 229930195729 fatty acid Natural products 0.000 description 3
- 239000000194 fatty acid Substances 0.000 description 3
- 150000004665 fatty acids Chemical class 0.000 description 3
- 239000001257 hydrogen Substances 0.000 description 3
- 229910052739 hydrogen Inorganic materials 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
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- 235000019260 propionic acid Nutrition 0.000 description 3
- IUVKMZGDUIUOCP-BTNSXGMBSA-N quinbolone Chemical compound O([C@H]1CC[C@H]2[C@H]3[C@@H]([C@]4(C=CC(=O)C=C4CC3)C)CC[C@@]21C)C1=CCCC1 IUVKMZGDUIUOCP-BTNSXGMBSA-N 0.000 description 3
- 230000003381 solubilizing effect Effects 0.000 description 3
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- 208000035404 Autolysis Diseases 0.000 description 2
- FERIUCNNQQJTOY-UHFFFAOYSA-N Butyric acid Chemical compound CCCC(O)=O FERIUCNNQQJTOY-UHFFFAOYSA-N 0.000 description 2
- 206010057248 Cell death Diseases 0.000 description 2
- 239000001569 carbon dioxide Substances 0.000 description 2
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- 238000009826 distribution Methods 0.000 description 2
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- -1 for example Substances 0.000 description 2
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E50/00—Technologies for the production of fuel of non-fossil origin
- Y02E50/30—Fuel from waste, e.g. synthetic alcohol or diesel
Description
本発明は、基質として、たとえば、生ゴミなど食品系廃棄物に含まれる有機性物質からメタンを発酵させる技術に関する。
本発明は特に、高負荷で運転している状態で安定にメタン発酵処理を可能とする技術に関する。
The present invention relates to a technique for fermenting methane from an organic substance contained in food waste such as raw garbage as a substrate.
In particular, the present invention relates to a technology that enables methane fermentation treatment stably in a state of operating at a high load.
メタン発酵処理は、たとえば、生ごみからメタンガスとしてエネルギーを回収可能であり、有機性廃棄物の創エネルギー・省エネルギー処理として期待されている。 For example, methane fermentation treatment can recover energy from trash as methane gas, and is expected as an energy-saving / energy-saving treatment of organic waste.
メタン発酵プロセスは、たとえば、図１に図解したように、（１）高分子有機物を各種バクテリアにより単分子化、加水分解反応などにより可溶化する過程、（２）酸生成過程、（３）酢酸生成過程、および、（４）揮発性脂肪酸（Volatile Fatty Acid ：ＶＦＡ）中の酢酸やメタンからメタン生成菌によりメタン（ＣＨ4 ）と二酸化炭素（ＣＯ2 ）に分解するメタン生成過程からなる（たとえば、非特許文献１、図２．３）。
For example, as illustrated in FIG. 1, the methane fermentation process includes (1) a process of solubilizing macromolecular organic matter by various bacteria, such as unimolecularization, hydrolysis reaction, (2) acid generation process, (3) acetic acid And (4) a methane production process in which acetic acid or methane in volatile fatty acid (VFA) is decomposed into methane (CH 4 ) and carbon dioxide (CO 2 ) by methanogenic bacteria (for example, Non-Patent
有機性の溶解性（Soluble ) 物質（Total Suspended Solid ：ＴＳＳ）が酢酸や水素を経て最終的なガス物質であるメタンや二酸化炭素に変化する速度は、有機性固形物質（ＴＳＳ）が可溶化する速度より速い。 The organic solid material (TSS) is solubilized at the rate at which the organic soluble material (Total Suspended Solid: TSS) changes to methane and carbon dioxide, which are the final gas materials via acetic acid and hydrogen. Faster than speed.
したがって、１日１回、メタン発酵槽（反応器）へ供給される生ごみなどの基質中に含有される溶解性（Soluble ）物質に起因する化学的酸素要求量（Chemical Oxygen Demand：ＣＯＤ）Ｓ−ＣＯＤ1 と、固形物が可溶化することに起因する化学的酸素要求量Ｓ−ＣＯＤ2 との総和Ｓ−ＣＯＤT は、メタン発酵反応が良好に行われている間は、たとえば、図２に図解した特性となる。
図２は、毎日１回、反応器から汚泥を引き抜き、その後、メタン発酵槽（反応器）へ基質（廃棄物）を投入する運転を連続した場合、生成されるガスの変化を図解した図である。
図２において、最大値を示す反応器への基質の供給点から次の基質の供給点までの間は下に凸状の「ノコギリ波」状に変化する。なお、反応器からの抜液は基質供給前に１日１回実施し、メタン発酵槽のオーバーフローは起きない。
Therefore, once a day, chemical oxygen demand (COD) S caused by soluble substances contained in a substrate such as garbage that is supplied to the methane fermenter (reactor) and -COD 1, while solids are the sum S-COD T and chemical oxygen demand S-COD 2 due to be solubilized, methane fermentation reaction has been carried out satisfactorily, for example, FIG. 2 It becomes the characteristic illustrated in.
Fig. 2 is a diagram illustrating the change in the gas produced when the operation of continuously extracting the sludge from the reactor once a day and then introducing the substrate (waste) into the methane fermentation tank (reactor) is continued. is there.
In FIG. 2, a downwardly convex “sawtooth wave” shape changes from the supply point of the substrate to the reactor showing the maximum value to the supply point of the next substrate. In addition, the drainage from the reactor is carried out once a day before supplying the substrate, and the methane fermentation tank does not overflow.
汚泥を濾過してメタン発酵槽（反応器）へ返送する汚泥循環返送方式の場合、固形物可溶化がガス化反応によって消費される溶解性・化学的酸素要求量Ｓ−ＣＯＤに間に合わないと、固形物（ＴＳＳ）が徐々に反応器内に蓄積し、徐々に固形物の濃度が上昇する。
その結果、（１）可溶化速度の低下、（２）各種中間反応速度の低下、（３）酢酸経由および水素経由のメタン生成反応の低下、（４）各種反応に寄与する細菌への基質同化反応の低下により、これらのバランスが崩れ、各種揮発性脂肪酸（ＶＦＡ）、たとえば、プロピオン酸の蓄積による、いわゆる、”酸敗”や、水素分圧の上昇による、メタン発酵の系が破綻することになる。
上述した理由により、湿式メタン発酵の固形物濃度の限界は、経験的に１０％程度である。
In the case of the sludge circulation return system that filters sludge and returns it to the methane fermentation tank (reactor), if the solid solubilization is not in time for the solubility / chemical oxygen demand S-COD consumed by the gasification reaction, Solids (TSS) gradually accumulate in the reactor and the solids concentration gradually increases.
As a result, (1) decrease in solubilization rate, (2) decrease in various intermediate reaction rates, (3) decrease in methanation via acetic acid and hydrogen, (4) substrate assimilation to bacteria contributing to various reactions Due to the lowering of the reaction, these balances are lost, so that the methane fermentation system breaks down due to the accumulation of various volatile fatty acids (VFA), for example, propionic acid, so-called "acid loss" or the increase of hydrogen partial pressure. Become.
For the reasons described above, the solid concentration limit of wet methane fermentation is empirically about 10%.
通常、生ごみの連続メタン発酵処理には、嫌気性条件下で運転される完全混合型発酵槽（Continous Stirred Tank Reactor：ＣＳＴＲ）が用いられている。
嫌気性処理は、好気性処理に比較して、固形物の濃度が２〜３％程度以上の高濃度廃液や、有機性固形廃棄物がメタン発酵の処理対象とされており、一般に、汚泥返送を行わない、一過性のＣＳＴＲが用いられてきた。
嫌気性処理において、寄与する主な細菌群のうち、最も増殖速度が遅いのは、一連のメタン生成菌であり、基質の、たとえば、３％程度しか菌体に転換しない。
そのことが、これまで、ＣＳＴＲ方式における基質滞留時間（Hydrauric Retention Time：ＨＲＴ）を約３０日（３３日）にしている理由である。
Usually, a continuous mixed fermenter (Continous Stirred Tank Reactor: CSTR) operated under anaerobic conditions is used for continuous methane fermentation treatment of garbage.
In anaerobic treatment, compared to aerobic treatment, high-concentration waste liquid with a solid concentration of about 2 to 3% or more and organic solid waste are targeted for methane fermentation. Transient CSTRs have been used that do not.
In the anaerobic treatment, among the main bacterial groups that contribute, the slowest growth rate is a series of methanogens, and only about 3% of the substrate, for example, is converted into cells.
That is the reason why the substrate retention time (HRT) in the CSTR system is about 30 days (33 days).
ＣＳＴＲ方式においては、図２に図解のごとく、１日１回、基質、たとえば、生ごみを反応器に投入した容量分だけ、反応器から反応混合液（消化液（汚泥も均一に混合されている）を引き抜くので、ＳＲＴ＝ＨＲＴとなる。
なお、ＨＲＴは基質滞留時間を示し、ＳＲＴはメタン発酵槽（反応器）内の汚泥の反応器内（平均）滞留時間を示す。
したがって、反応器内で菌体変換率の低い細菌群を一定以上に増殖させることは難しく、基質分解率、メタンのガス化率には限界がある。
特に、ＣＳＴＲ方式においては、高負荷で運転した場合、安定性に問題がある。
以下、その理由を述べる。
In the CSTR system, as illustrated in FIG. 2, once a day, the reaction mixture (digested liquid (sludge is also mixed uniformly) from the reactor by the volume of the substrate, for example, garbage, put into the reactor. SRT = HRT.
HRT represents the substrate residence time, and SRT represents the sludge in the reactor (average) residence time in the methane fermentation tank (reactor).
Therefore, it is difficult to grow a bacterial group having a low cell conversion rate in the reactor to a certain level, and there are limits to the substrate decomposition rate and the gasification rate of methane.
In particular, in the CSTR system, there is a problem in stability when operating at a high load.
The reason will be described below.
メタン発酵槽（反応器）は、運転を誤ると、”酸敗”によってメタンの生成が中断し、処理系として破綻する。
酸敗は、基質の種類によって、中間生成物である酪酸や、プロピオン酸、場合によっては、酢酸やその他の揮発性脂肪酸（ＶＦＡ）、あるいは、その複合化したＶＦＡ群の蓄積によって起こる。
ＶＦＡが蓄積すると、（１）ｐＨが低下する、（２）ｐＨ低下に伴う非解離のＶＦＡ、たとえば、プロピオン酸の濃度が増すことにより、可溶化もメタン発酵も同時に阻害される。
If the methane fermenter (reactor) is operated incorrectly, the production of methane is interrupted by "acid loss" and fails as a processing system.
Depending on the type of substrate, the rancidity is caused by the accumulation of butyric acid, which is an intermediate product, propionic acid, and in some cases, acetic acid and other volatile fatty acids (VFA), or their complexed VFA groups.
As VFA accumulates, (1) the pH decreases, (2) the concentration of non-dissociated VFA, eg, propionic acid, accompanying the pH decrease increases solubilization and methane fermentation at the same time.
上記課題を解決するため、本発明は下記の構想に基づく。
（１）汚泥循環返送型のメタン発酵処理法で行う。
（２）汚泥の増殖が十分な高い容積負荷、たとえば、基質が生ごみの場合、５ｋｇＣＯＤ／ｍ3 ／日以上の容積負荷で運転する。
（３）細菌と基質との接触速度を保持し、反応器内の固形物濃度を一定量以下にした運転状態で、汚泥中の菌体濃度（生菌濃度）を極大（最大）にする。
（４）反応器への基質を連続供給する期間と、基質の供給を停止する期間との合計を１単位とし、たとえば、１単位を基質滞留時間（ＨＲＴ）とする。
（５）微生物および未分解起因固形物質の和に基づく反応器（反応槽またはメタン発酵槽）内の汚泥滞留時間（ＳＲＴ）を基質滞留時間（ＨＲＴ）より長い状態で反応器を運転する。
In order to solve the above problems, the present invention is based on the following concept.
(1) The sludge circulation return type methane fermentation treatment method is used.
(2) A high volume load sufficient for sludge growth, for example, when the substrate is garbage, it is operated at a volume load of 5 kg COD / m 3 / day or more.
(3) Maintaining the contact speed between the bacteria and the substrate and setting the solid concentration in the reactor to a certain level or less, the bacterial cell concentration (viable bacterial concentration) in the sludge is maximized (maximum).
(4) The total of the period for continuously supplying the substrate to the reactor and the period for stopping the supply of the substrate is 1 unit, for example, 1 unit is the substrate residence time (HRT).
(5) The reactor is operated with the sludge residence time (SRT) in the reactor (reaction tank or methane fermentation tank) based on the sum of microorganisms and undecomposed solid substances longer than the substrate residence time (HRT).
なお、有機性物質をメタン発酵には、固形物に起因する化学的酸素要求量（ｐ−ＣＯＤ）の割合が全ＣＯＤに対して所定の割合、たとえば、７０％以下の有機性物質をメタン発酵する場合を想定している。
固形物に起因する化学的酸素要求量の割合は、基質（廃棄物）の性状によっても異なるが、固形物基質のＣＯＤが狭すぎると速くＴＳＳ（固形物）の濃度が上がり、基質供給期間に比べて必要とする休止期間の割合が１：１程度となり、好ましくない。基質の性状としては、たとえば、（１）固形物の可溶化速度と可溶化物質（Ｓ−ＣＯＤ）の分解性、（２）固形物の粒径分布、（３）有機性物質の組成などが対象となる。
以上から、有機性物質をメタン発酵の場合、固形物に起因する化学的酸素要求量の割合が全ＣＯＤに対して所定の割合として、経験的事項をも考慮して、上記のように、たとえば、７０％以下の有機性物質をメタン発酵する場合を想定している。
In addition, for methane fermentation of an organic substance, an organic substance having a chemical oxygen demand (p-COD) ratio due to solids of a predetermined ratio with respect to the total COD, for example, 70% or less, is methane fermentation. Assume that you want to.
The proportion of chemical oxygen demand due to solids varies depending on the nature of the substrate (waste), but if the solid substrate COD is too narrow, the concentration of TSS (solids) will rise quickly and during the substrate supply period The ratio of the required rest period is about 1: 1, which is not preferable. The properties of the substrate include, for example, (1) solid solubilization rate and solubilizing substance (S-COD) decomposability, (2) solid particle size distribution, and (3) organic substance composition. It becomes a target.
From the above, when the organic substance is methane fermentation, the ratio of the chemical oxygen demand caused by the solid matter is a predetermined ratio with respect to the total COD, taking into account empirical matters, for example, The case where 70% or less of an organic substance is methane-fermented is assumed.
反応器内の汚泥の反応器内（平均）滞留時間（ＳＲＴ）は毎日行う反応液引き抜きと、反応液から汚泥分を分離して循環するに際して、全量を循環返送するのではなく、一部抜去処分する量を調整することにより、容易に制御可能である。ただし、一定以上の高負荷、適正な負荷をかけて運転する必要がある。 Sludge in the reactor (average) residence time (SRT) is a part of the reaction liquid withdrawn every day, and when the sludge is separated from the reaction liquid and circulated, a part of the sludge is not recirculated but returned. It can be easily controlled by adjusting the amount to be disposed. However, it is necessary to operate with a high load above a certain level and an appropriate load.
反応器内の固形物濃度を一定以上に保持しながら、汚泥中の基質の連続供給と基質供給休止期間の合体した期間を１つの単位期間として、その期間中の平均総菌体濃度を、なるべく、活性の高い状態で極大（または最大）に保つ運転を行う。 While maintaining the solid matter concentration in the reactor above a certain level, the combined total of the substrate supply in the sludge and the substrate supply suspension period is taken as one unit period, and the average total cell concentration during that period is preferably as much as possible. , Keep the maximum (or maximum) in a highly active state.
より特定的には、基質を、たとえば、生ごみとした場合、本発明のメタン発酵処理法は、固形物に起因する化学的酸素要求量（ｐ−ＣＯＤ）の割合が全ＣＯＤに対して、たとえば、７０％以下の有機性物質を基質としてメタン発酵するに際して、たとえば、５ｋｇＣＯＤ／ｍ3 ／日以上の容積負荷で、５日以上３０日以下（１日１回ないしは複数回を含めて）の連続供給と、４日以上２０日以下の基質供給停止期間を設け、（消化）汚泥（循環）返送を伴い、微生物、未分解のいずれかを含む固形物の反応槽内の滞留時間（ＳＲＴ）を基質滞留時間（ＨＲＴ）より長い３０日以上で運転する、ことを特徴とする。
なお、上述した数値は、基質としての有機性廃棄物の種類、性状によって変化する。たとえば、上述した、容積負荷が５ｋｇＣＯＤ／ｍ3 ／日以上という意味は、基質として生ごみを用いた場合、汚泥の増殖が、５ｋｇＣＯＤ／ｍ3 ／日未満では不十分となることから設定しているが、基質が異なれば、容積負荷も変化する。
More specifically, when the substrate is, for example, garbage, in the methane fermentation treatment method of the present invention, the ratio of chemical oxygen demand (p-COD) due to solids is based on the total COD. For example, when performing methane fermentation using 70% or less of an organic substance as a substrate, for example, 5 to 30 days (including one or more times a day) with a volume load of 5 kg COD / m 3 / day or more A continuous supply and a substrate supply stop period of 4 days or more and 20 days or less are provided. With (digestion) sludge (circulation) return, residence time (SRT) in the reaction vessel of solid matter containing either microorganisms or undegraded Is operated over 30 days longer than the substrate residence time (HRT).
In addition, the numerical value mentioned above changes with the kind and property of the organic waste as a substrate. For example, the above-mentioned meaning that the volume load is 5 kg COD / m 3 / day or more is set when sludge growth is insufficient when less than 5 kg COD / m 3 / day is used when garbage is used as a substrate. However, if the substrate is different, the volumetric load also changes.
本発明によれば、効率的かつ安定的に処理する、汚泥循環返送型のメタン発酵処理法を提供することができる。 ADVANTAGE OF THE INVENTION According to this invention, the sludge circulation return type methane fermentation processing method processed efficiently and stably can be provided.
本発明の実施の形態を述べる。
図３は、本発明のメタン発酵処理法を実施するメタン発酵システムの概要を示す図である。
本発明の実施の形態のメタン発酵システムは、メタン発酵槽（反応器）１０と、攪拌器１１と、反応器１０に基質を投入する投入口１２と、反応器１０から消化汚泥を抜き取る抜取口１３と、抜き取った汚泥の一部を遠心分離して細菌を分離するための遠心分離器１４と、遠心分離した細菌を含む汚泥を反応器１０に戻す返送系１５と、メタン発酵されて生成したメタンガスを排出するガス排出部１６とを有する。
本実施の形態のメタン発酵システムは、完全混合型発酵槽（ＣＳＴＲ）方式ではなく、汚泥の一部を反応器１０に返送する、「汚泥循環返送型のメタン発酵処理システム」である。
An embodiment of the present invention will be described.
FIG. 3 is a diagram showing an outline of a methane fermentation system that implements the methane fermentation treatment method of the present invention.
A methane fermentation system according to an embodiment of the present invention includes a methane fermentation tank (reactor) 10, a
The methane fermentation system of the present embodiment is not a fully mixed fermenter (CSTR) system but a “sludge circulation return type methane fermentation treatment system” that returns a part of sludge to the
図４は、化学的酸素要求量（ＣＯＤ）容積負荷（ｋｇ−ＣＯＤ／ｍ3 ／ｄａｙ）と、反応器内の汚泥生成量、たとえば、固形物ＴＳＳの蓄積速度（ｍｇ−ｓｓ／ｌ（リットル）／ｄａｙ）との関係を示した図である。横軸は有機物負荷比率（ＯＬＲ）を示し、縦軸は固形物（ＴＳＳ）蓄積比率を示す。
図４の図解から、高い容積負荷をかけるほど汚泥の生成量が増加することが理解できる。
FIG. 4 shows the chemical oxygen demand (COD) volumetric load (kg-COD / m 3 / day) and sludge production in the reactor, for example, the accumulation rate of solid TSS (mg-ss / l (liters). ) / Day). The horizontal axis represents the organic substance load ratio (OLR), and the vertical axis represents the solid matter (TSS) accumulation ratio.
From the illustration of FIG. 4, it can be understood that the amount of sludge generated increases as the volume load increases.
汚泥の増加速度について述べる。
総菌体Ｓの増殖速度ｄＳ／ｄｔは、ｄＳ／ｄｔ＝Σ（ｄＳi ／ｄｔ）として表すことができる。下記式１、２は、嫌気発酵に寄与する菌体ｉの増加速度を示す。
The increase rate of sludge is described.
The growth rate dS / dt of the total cell S can be expressed as dS / dt = Σ (dS i / dt). The following
ｄＳi ／ｄｔ＝ｋSiＣi Ｓi −ｋdiＳi
…（１）
ただし、ｉは細菌ｉであり、
Ｓi は細菌ｉの濃度であり、
ｋSiは細菌ｉの基質との接触速度に起因する係数であり、
Ｃi は細菌ｉが作用する対象とする基質の濃度であり、
ｋdiは細菌ｉの自己消化係数である。
dS i / dt = k Si C i S i −k di S i
... (1)
Where i is a bacterium i and
S i is the concentration of bacteria i,
k Si is a coefficient resulting from the contact speed of bacteria i with the substrate,
C i is the concentration of the target substrate on which bacteria i act,
k di is the autolysis coefficient of bacteria i.
細菌ｉは、たとえば、図１に図解した過程における、加水分解細菌、酢酸形成細菌などである。
細菌ｉの自己消化係数ｋdiは、基質の種類、特性状態（性状）、反応器の形式、攪拌方法と反応器とのマッチングに依存する。
式１において、右辺第１項：ｋSiＣi Ｓi は増殖項であり、第２辺：ｋdiＳi は分解項である。
The bacterium i is, for example, a hydrolyzing bacterium or an acetic acid-forming bacterium in the process illustrated in FIG.
The autodigestion coefficient k di of the bacterium i depends on the type of the substrate, the characteristic state (property), the type of the reactor, and the matching between the stirring method and the reactor.
In
ｄＣi ／ｄｔ＝−ｋci（ｋmax Ｃi ／（ｋhi＋Ｃi ）×Ｓi
…（２）
ただし、ｋciは細菌ｉと基質との接触速度に起因する係数であり（ｋci≦１）、
ｋmax は最大比基質利用速度（ｇＣＯＤ／ｇｖｓｓ／月）であり、
Ｃi は細菌ｉが作用する対象とする基質の濃度であり、
ｋhiは半飽和定数（ｍｇ／ｌ）である。
dC i / dt = −k ci (k max C i / (k hi + C i ) × S i
... (2)
Where k ci is a coefficient resulting from the contact speed between bacteria i and the substrate (k ci ≦ 1),
k max is the maximum specific substrate utilization rate (gCOD / gvss / month),
C i is the concentration of the target substrate on which bacteria i act,
k hi is a half-saturation constant (mg / l).
一般に、反応器内において、溶解性の基質成分Ｓ−ＣＯＤは比較的速やかに分解するため、固体物質の可溶化が可溶化した物質の消費に間に合わない。したがって、消化汚泥循環（返送）運転（以下、汚泥循環法）を続けた場合、ある程度の容積負荷以上では反応器内の固体成分は徐々に増加していく。 In general, the soluble substrate component S-COD decomposes relatively quickly in the reactor, so that the solubilization of the solid substance is not in time for the consumption of the solubilized substance. Therefore, when the digested sludge circulation (return) operation (hereinafter referred to as the sludge circulation method) is continued, the solid components in the reactor gradually increase above a certain volume load.
式１を参照すると、反応器内の固形物濃度（ＴＳＳ濃度）が増加すると、細菌と基質との接触速度に起因する係数ｋsiは低下するが、細菌ｉの自己消化係数ｋdiは余り変化しないため、左辺の菌体増殖速度ｄＳi ／ｄｔは減少する。
Referring to
図５は、容積負荷を、６．０、９．０、１２．０、１２．０、１５．０（ｋｇ−ＣＯＤ／ｍ3 ／ｄａｙ）の６フェーズについて段階的に変化させたときの、運転日数と、単位ＴＳＳに含まれる微生物の数の経時変化を示した図である。
図５において、各々の黒丸は、反応器への基質を連続供給する期間と、基質の供給を停止する期間との合計を１単位とし、たとえば、１単位を基質滞留時間（ＨＲＴ）としたことを示している。
各フェーズの間に休止期間が設けられている。
FIG. 5 shows a case where the volumetric load is changed stepwise for 6 phases of 6.0, 9.0, 12.0, 12.0, 15.0 (kg-COD / m 3 / day). It is the figure which showed the time-dependent change of the number of operation days and the number of the microorganisms contained in unit TSS.
In FIG. 5, each black circle indicates that the total of the period for continuously supplying the substrate to the reactor and the period for stopping the substrate supply is 1 unit, for example, 1 unit is the substrate residence time (HRT). Is shown.
There is a rest period between each phase.
図５において、各フェーズの容積負荷の設定条件での一定期間の運転後、基質供給休止期間後に、矢印で示したように、固形物ＴＳＳ中に占める菌体濃度が増加していることが理解される。
各フェーズ間に基質供給の休止期間を設けることにより、すなわち、ＳＲＴ＞ＨＲＴとすることにより、反応器内の固体物質の可溶化が進み、攪拌効果が改善されて、式１における可溶化した基質濃度Ｃi の増加とともに、接触速度に起因する係数ｋsiが増大する。その結果、式１の右辺第１項ｋSiＣi Ｓi は増殖項の値が増大して、菌体増殖速度ｄＳi
／ｄｔが増大する。
In FIG. 5, it is understood that after the operation for a certain period under the setting condition of the volumetric load of each phase, and after the substrate supply suspension period, as shown by the arrows, the concentration of the cells in the solid TSS increases. Is done.
By providing a substrate supply pause period between phases, that is, by setting SRT> HRT, solubilization of the solid substance in the reactor proceeds and the stirring effect is improved, solubilized substrate in
/ Dt increases.
最終的には、高い容積負荷のもとで、安定した運転を達成するということは、各素反応に寄与する菌体ｉの濃度Ｓi が高い濃度で反応器内に保持され、式２において、分解に寄与する細菌ｉと基質との接触速度に起因する係数ｋciがなるべく１に近い値に保持されることである。
Ultimately, under a high volume loading, stable that to achieve operation is held in the reactor at a concentration S i is high concentration of contributing cell i to each elementary reaction, in
たとえば、基質としての生ごみについて考察すると、種々の生ごみを収集混合するとほぼ同じになるように、基質がそれほど変化しなければ、関与する菌体ｉが反応に関与する基質Ｃi （中間生成物を含む）の組成は大きく変化しない。したがって、反応器に投入する基質（廃棄物）の性状に合わせて、反応器から引き抜く汚泥量を制御すること、および、微生物および未分解基質のいずれかを含む固形物の反応器内の滞留時間（ＳＲＴ）を適切な値に制御することができる。 For example, when considering the garbage as a substrate, if the substrate does not change so much that the various garbages are collected and mixed, if the substrate does not change so much, the substrate C i (intermediate production) in which the cell i involved participates in the reaction. The composition of the product (including the product) does not change greatly. Therefore, the amount of sludge withdrawn from the reactor is controlled in accordance with the properties of the substrate (waste) charged into the reactor, and the residence time of the solid matter containing either microorganisms or undegraded substrates in the reactor (SRT) can be controlled to an appropriate value.
実施例
有機性物質として、図３に例示した装置を用いて、破砕生ごみを対象としたメタン発酵の実施例を述べる。
また、図５〜図７の実験値を考察する。
Example An example of methane fermentation targeting crushed garbage is described using the apparatus illustrated in FIG. 3 as the organic substance.
Also consider the experimental values of FIGS.
本実施例において、固形物に起因する割合が生ＣＯＤに対して一定の割合、たとえば、、７０％以下の有機性物質をメタン発酵する場合を例にとる。
なお、上述したとおり、固形物に起因する化学的酸素要求量の割合は、基質（廃棄物）の性状によっても異なるが、固形物基質のＣＯＤが狭すぎると速くＴＳＳ（固形物）の濃度が上がり、基質供給期間に比べて必要とする休止期間の割合が１：１程度となり、好ましくない。基質の性状としては、たとえば、（１）固形物の可溶化速度と可溶化物質（Ｓ−ＣＯＤ）の分解性、（２）固形物の粒径分布、（３）有機性物質の組成などが対象となる。
以上から、有機性物質をメタン発酵の場合、固形物に起因する化学的酸素要求量の割合が全ＣＯＤに対して所定の割合として、経験的事項をも考慮して、上記のように、たとえば、７０％以下の有機性物質をメタン発酵する場合を想定している。
In the present embodiment, an example is given of a case where methane fermentation is performed on an organic substance whose ratio attributable to the solid matter is a constant ratio relative to raw COD, for example, 70% or less.
As described above, the ratio of chemical oxygen demand caused by solids varies depending on the properties of the substrate (waste). However, if the COD of the solid substrate is too narrow, the concentration of TSS (solids) increases quickly. The ratio of the required rest period is about 1: 1 compared with the substrate supply period, which is not preferable. The properties of the substrate include, for example, (1) solid solubilization rate and solubilizing substance (S-COD) decomposability, (2) solid particle size distribution, and (3) organic substance composition. It becomes a target.
From the above, when the organic substance is methane fermentation, the ratio of the chemical oxygen demand caused by the solid matter is a predetermined ratio with respect to the total COD, taking into account empirical matters, for example, The case where 70% or less of an organic substance is methane-fermented is assumed.
固形物が難分解性であり、固形物の占める割合ｒP が比較的小さい場合、たとえば、ｒP ＜０．６の場合、メタン生成の関連が取り扱い易い重クロム酸カリウム（ＣＯＤcr）の指標をもって示す。
本実施例では、重クロム酸カリウム（ＣＯＤcr）の指標を持って示す。
Indices of potassium dichromate (COD cr ) that are easy to handle when the solid matter is hardly decomposable and the proportion r P of the solid matter is relatively small, for example, r P <0.6 Show with.
In this embodiment, it is shown with an index of potassium dichromate (COD cr ).
Ｔ−ＣＯＤ＝ｐ−ＣＯＤ＋Ｓ−ＣＯＤ
ただし、Ｔ−ＣＯＤは、全基質のＣＯＤであり、
ｐ−ＣＯＤは、固形物起因のＣＯＤであり、
ｓ−ＣＯＤは、溶解しているＣＯＤである。
T-COD = p-COD + S-COD
However, T-COD is the COD of all substrates,
p-COD is COD due to solid matter,
s-COD is dissolved COD.
とすると、固形物の占める割合ｒP は下記となる。 Then, the ratio r P of the solid matter is as follows.
ｒP ＝ｐ−ＣＯＤ／Ｔ−ＣＯＤ r P = p-COD / T-COD
また、溶解物の占める割合ｒS は下記になる。 Further, the ratio r S occupied by the melt is as follows.
ｒS ＝ｓ−ＣＯＤ／Ｔ−ＣＯＤ＝１−ｒP r S = s-COD / T-COD = 1-r P
図５に図解したように、微生物および未分解固形物質を含む固形物の反応器内の汚泥滞留時間（ＳＲＴ）をＨＲＴより長い６０日とし、他方、ＨＲＴ＝１６日として、容積負荷を５段階に上昇させた運転の結果、各運転中で、各段階において、終期において、固形物（ＴＳＳ）濃度はほぼ一定値となった。
このことから、常法では言われている湿式運転の限界濃度１０％値における容積負荷を、図５において、内挿すると、容積負荷が約１７ｋｇ−ＣＯＤ／ｍ3 ／ｄａｙとなった。この値は、一般の生ごみを対象としたＣＳＴＲ方式に比べると、かなり高い値であり、本実施例は、高い効率で運転できたことを示している。
As illustrated in FIG. 5, the sludge residence time (SRT) in the reactor of solid matter containing microorganisms and undegraded solid material is 60 days longer than HRT, while HRT = 16 days, and the volumetric load is 5 stages. As a result, the solids (TSS) concentration was almost constant at each stage during the operation.
From this, when the volume load at the
その理由を考察する。
図５は、上述したように、各有機物負荷速度における単位ＴＳＳに含まれる微生物数の経時変化を図解した図である。
微生物濃度は、反応器に有機物（基質）を投入していない休止期間に、上向きの矢印を示したように、増加する。
図５において、たとえば、フェーズ１〜３の休止時間は、微生物濃度を段階的に増加させたが、フェーズ相互間のＴＳＳ濃度には余り変化がない。このことは、汚泥内に存在する固形量は増減せず、微生物だけが休止期間に増加したことを意味する。
他方、フェーズ３〜６におけるフェーズ間の休止期間には固形物濃度の急激な減少が起きているにも関わらず、微生物濃度には大きな変化が認められない。このことは、フェーズ間の微生物濃度の変化に関わらず、単位ＴＳＳに含まれる微生物濃度が休止期間において増加していることを示している。
このように、本願発明者は、基質を投入しない休止期間に、単位ＴＳＳに含まれる微生物濃度が増加していることを見いだし、基質供給期間と休止期間を設けることにより、効果的な微生物量を保持することができる有機性物質のメタン発酵法を発明するに至った。
Consider the reason.
FIG. 5 is a diagram illustrating the change over time in the number of microorganisms contained in the unit TSS at each organic substance loading speed as described above.
The microbial concentration increases as indicated by the upward arrow during the rest period when the organic substance (substrate) is not charged into the reactor.
In FIG. 5, for example, during the rest periods of
On the other hand, no significant change is observed in the microbial concentration in spite of the sudden decrease in the solid concentration during the suspension period between phases 3-6. This indicates that the microbial concentration contained in the unit TSS increases during the rest period regardless of the microbial concentration change between phases.
Thus, the inventor of the present application finds that the concentration of microorganisms contained in the unit TSS is increased during the rest period in which the substrate is not added, and provides an effective amount of microorganisms by providing the substrate supply period and the rest period. It came to invent the methane fermentation method of the organic substance which can be hold | maintained.
各有機物負荷での定常状態でのＴＳＳ濃度は、反応器に投入する有機物の分解性と、固形物の滞留時間、および有機物の負荷速度によって決定されている。有機物負荷速度を上昇させ続けると、定常状態におけるＴＳＳ濃度は上昇する。
このまま有機物負荷速度を上昇させると、半乾式メタン発酵あるいは乾式メタン発酵で使用されるような高濃度ＴＳＳ濃度領域へと増加し、分解率は低下すると予想される。
The steady-state TSS concentration at each organic substance load is determined by the decomposability of the organic substance charged into the reactor, the residence time of the solid substance, and the organic substance loading rate. As the organic loading rate continues to increase, the TSS concentration in the steady state increases.
If the organic substance loading rate is increased as it is, it is expected that the decomposition rate will decrease while increasing to a high concentration TSS concentration region as used in semi-dry methane fermentation or dry methane fermentation.
図６は、横軸に負荷速度をとり、縦軸に定常状態のＴＳＳ濃度を示した特性図である。 図６を参照すると、本発明法（湿式メタン発酵法）における半乾式状態や乾式状態でのメタン発酵法との境界の有機物容積負荷率は、約１７（ｋｇＣＯＤ／ｍ3 ／ｄａｙ）である。
この図から、基質として生ごみを用いた場合、容積負荷は５ｋｇＣＯＤ／ｍ3 ／ｄａｙ以上が好ましい。すなわち、５ｋｇＣＯＤ／ｍ3 ／日以上であると、汚泥の増殖が十分となる。もちろん、上述した数値は、基質としての有機性廃棄物の種類、性状によって変化する。
FIG. 6 is a characteristic diagram in which the horizontal axis indicates the load speed and the vertical axis indicates the steady-state TSS concentration. Referring to FIG. 6, the organic substance volumetric load factor at the boundary with the methane fermentation method in the semi-dry state or the dry state in the method of the present invention (wet methane fermentation method) is about 17 (kgCOD / m 3 / day).
From this figure, when garbage is used as the substrate, the volume load is preferably 5 kg COD / m 3 / day or more. That is, if it is 5 kg COD / m 3 / day or more, the sludge is sufficiently propagated. Of course, the above-mentioned numerical values vary depending on the type and properties of organic waste as a substrate.
図７は、有機物負荷速度（容積負荷）を６．０（ｋｇ−ＣＯＤ／ｍ3 ／ｄａｙ）、９．０（ｋｇ−ＣＯＤ／ｍ3 ／ｄａｙ）、１２．０（ｋｇ−ＣＯＤ／ｍ3 ／ｄａｙ）と３段階に変化させた場合の、生ごみの嫌気性連続実験における修正した微生物濃度を図解した図である。
基質供給期間と休止期間を設けることにより、微生物の濃度が増加していることが理解される。
7, organic loading rate (volumetric loading) 6.0 (kg-COD /
It is understood that the concentration of microorganisms is increased by providing a substrate supply period and a rest period.
なお、基質（廃棄物）供給時の有機物容積負荷を小さくとれば、廃棄物供給期間を長くし、休止期間を短くすることができる。もちろん、その逆も言える。 In addition, if the organic substance volume load at the time of substrate (waste) supply is taken small, a waste supply period can be lengthened and a rest period can be shortened. Of course, the reverse is also true.
本発明の実施に際しては、上述した例示した数値に限らず、上述した技術思想を敷衍した変形例をとることができる。 In carrying out the present invention, the present invention is not limited to the above-described numerical values, but can be modified based on the technical idea described above.
１０…メタン発酵槽（反応器）、１１…攪拌器、１２…基質投入口、１３…抜取口、１４…遠心分離器、１５…返送系、１６…ガス排出部。
DESCRIPTION OF
Claims (2)
固形物に起因する化学的酸素要求量（ＣＯＤ）の割合が、全ＣＯＤに対して７０％以下の有機性物質を基質としてメタン発酵するに際して、
汚泥を濾過してメタン反応器に返送する汚泥循環返送型のメタン発酵処理法で、汚泥の増殖を十分にする５ｋｇＣＯＤ／ｍ3 ／ｄａｙ以上の容積負荷で運転し、
細菌と前記基質との接触速度を保持するため、反応器内の固形物濃度を１０％以下（００ｇ／ｌ以下）にした運転状態で、
５日以上３０日以下の前記反応器への前記基質を連続供給する期間と、微生物濃度の増加が促進される４日以上２０日以下の基質の供給を停止する期間とを設け、両期間の合計を周期的に連続運転するときの１単位とし、
前記反応器内の汚泥滞留時間（ＳＲＴ）を１６日の基質滞留時間（ＨＲＴ）より長い状態で、周期的に連続運転する、
ことを特徴とする、微生物の集積に基づく有機性物質のメタン発酵方法。 Using raw garbage as a substrate,
When methane fermentation is performed using an organic substance as a substrate in which the ratio of chemical oxygen demand (COD) due to solids is 70% or less of the total COD,
A sludge circulation return type methane fermentation treatment method that filters sludge and returns it to the methane reactor, and operates at a volume load of 5 kg COD / m 3 / day or more to sufficiently increase sludge growth.
In order to maintain the contact speed between the bacteria and the substrate, the solids concentration in the reactor is 10% or less (00 g / l or less) .
A period for continuously supplying the substrate to the reactor for 5 days or more and 30 days or less and a period for stopping the substrate supply for 4 days or more and 20 days or less for which an increase in microbial concentration is promoted are provided. The total is one unit for periodic continuous operation.
Periodic continuous operation with the sludge residence time (SRT) in the reactor longer than the substrate residence time (HRT) of 16 days.
Wherein the methane fermentation process based rather organic material in accumulation of microorganisms.
ことを特徴とする、
請求項１に記載の、微生物の集積に基づく有機性物質のメタン発酵方法。 The sludge residence time (SRT) in the reactor is 30 days or more,
It is characterized by
According to claim 1, methane fermentation method of organic substance rather based on accumulation of microorganisms.
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