JP2004160406A - Ammonia concentration automatic control method in biogas conversion and treatment apparatus for organic waste using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow ammonia generated in a biodegradation process of organic waste by anaerobic microorganisms not to inhibit the stable generation of biogas. <P>SOLUTION: In a reaction, organic substances are biodegraded inside a fermenter 1 stirred in an airtight state by the anaerobic microorganisms, and converted into the biogas 11 containing methane and carbon dioxide gas. In the reaction, an anaerobic digestive inside the fermenter 1 is extracted and filtered by a precision membrane 3 for passing through ammonia molecules. When ammonia concentration in the filtrate is a prescribed threshold value or higher, the filtrate is fed to an ammonia emission tank 8 and ammonia is removed. When the ammonia concentration therein is the threshold value or lower, an anaerobic digestive not passing through the precision membrane 3 is also returned to the fermenter 1. <P>COPYRIGHT: (C)2004,JPO

Description

濾液をアルカリ性にすると、既知の如く、化学平衡によりアンモニウムイオンＮＨ_４ ^＋がアンモニア分子ＮＨ_３となり、飽和濃度以上になるとアンモニアガスとなって濾液より発散する。
上記アンモニア発散槽で気化されたアンモニアガスは、上記アンモニア分解槽に送風され、触媒により窒素ガスまで還元されて安全に大気に放出できる。
【００１９】
上記濾過槽内の上記精密膜の孔径は０．１〜０．５μｍとし、アンモニア分子を通すが、嫌気性微生物は通さない大きさとしている。
即ち、上記精密膜で濾過されなかった嫌気性微生物の濃縮された消化液を発酵槽へ戻すことで、発酵槽の嫌気性微生物濃度を維持し、安定、且つ、迅速な微生物反応を可能にする。
【００２０】
また、上記嫌気性微生物により有機系廃棄物を生分解する発酵槽は、中温嫌気性微生物に適した３５〜３７℃または高温嫌気性微生物に適した５３〜５６℃の加熱雰囲気とし、嫌気性微生物の活性化を図り生分解作用を促進させている。
【００２１】
【発明の実施の形態】
本発明の実施形態を図面を参照して説明する。
図１は、有機系廃薬物を安定してバイオガスに変換するためのアンモニア濃度自動管理装置の概略図を示す。
【００２２】
上記装置は有機系廃棄物が排出される工場等に設置されるもので、該有機系廃棄物が供給される供給路１２と、供給路１２に接続され有機系廃棄物を空気を遮断した状態で嫌気性微生物と撹拌する発酵槽１と、発酵槽１の嫌気性消化液がポンプ１４を介して抽出・送液されると共に内部に精密膜濾過筒３を収納している濾過槽２と、精密膜濾過筒３を通過しなかった消化液を発酵槽１へ戻す第一返送管１６と、精密膜濾過筒３を通過した濾液がポンプ１５を介して抽出・送液されるアンモニア濃度自動計測器４と、アンモニア濃度自動計測器４より流出された濾液を二方向に振り分ける弁別部１８と、アンモニア濃度自動計測器４によりアンモニア濃度が一定の閾値を超えたかどうかを弁別部１８に知らせる開閉信号５と、弁別部１８によりアンモニア濃度が閾値以上の場合に送液されるアンモニア発散槽８と、弁別部１８によりアンモニア濃度が閾値より低い場合に濾液を発酵槽１へ戻す第二返送管１７と、アンモニア発散槽８で発散されたアンモニアガスを触媒により窒素ガス１０まで分解して大気に放出するアンモニア分解槽９とを備えている。
【００２３】
発酵槽１は、雰囲気温度を３５℃〜３７℃として中温嫌気性微生物と撹拌して有機系廃棄物をメタン発酵させているか、或いは、雰囲気温度を５３℃〜６６℃として高温嫌気性微生物と撹拌して有機系廃棄物をメタン発酵させている。
メタン発酵は、第一段階の「酸生成相」で、有機系廃棄物が嫌気性微生物により分解され、種々な有機酸、水素、アルコール、アミノ酸、種々な窒素化合物に変化され、第二段階の「メタン生成相」で、多種類の酵素や微生物により更に分解されて酢酸、水素とメタン菌とによりメタンガスを含むバイオガス１１が生成される。この際、有機系廃棄物を構成する窒素化合物の一部はアンモニアとなり、嫌気性消化液の中にアンモニア分子とアンモニウムイオンになって溶解している。
【００２４】
濾過槽２は、槽内に円筒形状の精密膜濾過筒３を配置した所謂クロスフロー濾過方式であり、精密膜濾過筒３は、濾液を容易に通過できる高分子系基材の表面にポリスルフォンのような有機物を塗布して形成されており、その有孔径は０．３〜０．６μｍの細孔としてアンモニア分子を通し、かつ、嫌気性微生物を通さない大きさとしている。本実施形態では０．４５μｍの細孔を設けている。
【００２５】
発酵槽１より濾過槽２に送られる嫌気性消化液は精密膜濾過筒３の外部に流入し、精密膜濾過筒３で濾過されて円筒内部に入った濾液はポンプ１５でアンモ二ア濃度自動計測器４に送液される。また、精密膜濾過筒３を通過しなかった円筒外部の嫌気性消化液は第一返送管１６で発酵槽１に戻される。
【００２６】
アンモニア濃度自動計測器４は、濾液を少量採取計量し、そのｐＨを１０〜１４に調節し発生するアンモニアガスをガス透過膜を透過させて０．１モルの塩化アンモニウムに吸収させ、この吸収液のｐＨを、複合型ガラス電極と変換器でｐＨを測定し、学術的に既知であるｐＨとアンモニア濃度との間の関係式からアンモニア濃度を計測している。
【００２７】
上記計測した濾液を発酵槽１へ戻すか、アンモニア発散槽８に送液するかを判断するアンモニア濃度の閾値は２０００〜５５００ｍｇ／ｌの範囲内の値とし、本実施形態では３０００ｍｇ／ｌとしている。
【００２８】
弁別部１８の構成は、アンモニア濃度自動計測器４より濾液を導出する管２０を二股に分岐して、一方の分岐管をアンモニア発散槽８に接続する送液管２１とすると共に、分岐管の他方を発酵槽１に接続する第二返送管１７としている。
上記送液管２１に第１開閉弁７を介設すると共に、第二返送管１７に第２開閉弁６を介設し、アンモニア濃度自動計測器４からの計測に基づく開閉信号５により第１、第２開閉弁７、６を開閉作動させている。
上記第１、第２開閉弁７、６は電磁弁とし、第２開閉弁６はノーマルオープンとし、第１開閉弁７はノーマルクローズとしている。
【００２９】
アンモニア発散槽８では、空気送風部１３と小型円筒型充填材（図示せず）と、ｐＨ調節部（図示せず）とを備え、ｐＨ調節部より濾液に水酸化ナトリウム１０％水溶液が添加されてｐＨを１０〜１４に調整している。本実施形態では、ｐＨを１２に自動調整している。
そして、ｐＨを１２とすることにより濾液中のアンモニアがアンモニアガスに気化される。詳しくは、アンモニア分子は、濾液中では溶解して次のような化学式（１）でアンモニウムイオンとなっている。
（式１）

この濾液をｐＨを１２としてアルカリ性にすることで、化学平衡によりアンモニウムイオンＮＨ_４ ^＋がアンモニア分子ＮＨ_３となり、飽和濃度以上になるとアンモニア分子ＮＨ_３が気化され、上記小型円筒型充填材を乱流通液することで益々アンモニア分子ＮＨ_３が気化されアンモニアガスが発散する。そのアンモニアガスは空気送風１３と共にアンモニア分解槽９へと運ばれる構成としている。
【００３０】
アンモニア分解槽９では、アンモニア発散槽８から送られたアンモニアガスを加熱し、第一段階として３００〜４５０℃で触媒により窒素酸化物にして、第二段階として６００〜７００℃でチタン系触媒により窒素ガス１０まで還元させて大気に放出している。
なお、本実施形態では、上記第一段階の温度は約３８０℃とし、上記第二段階の温度は約６５０℃としている。
【００３１】
次に、上記装置の作用を説明する。
有機系廃棄物１２を発酵槽１へ供給し、嫌気性微生物と共に空気を遮断した状態で撹拌してメタン発酵によりメタンと二酸化炭素を含むバイオガス１１へと変換する。
この有機系廃棄物の嫌気性微生物による生分解過程で発生しバイオガス生成を阻害するアンモニアは嫌気性消化液の中に溶解しており、該嫌気性消化液を発酵槽１の底部からポンプ１４により抽出して濾過槽２へと送液する。
【００３２】
濾過槽２内に流入した嫌気性消化液は精密膜濾過筒３の外表面を流動し、該精密膜濾過筒３内が低減圧状態となることで、外表面から垂直方向に精密膜濾過筒３の内部へと嫌気性消化液が通過して濾液が得られる。この際、嫌気性消化液に存在する嫌気性微生物は既に凝集しており、精密膜濾過筒３の細孔より大きいので通過できなく、嫌気性微生物が除かれアンモニアを含む嫌気性消化液が通過して濾液となる。
なお、このクロスフロー濾過法は、嫌気性消化液の主流は精密膜濾過筒３の外表面を滑るように下から上へ流れるので、精密膜濾過筒３の目詰まりを起こし難い利点がある。
【００３３】
上記精密膜濾過筒３を通過しなかった嫌気性微生物を含む嫌気性消化液は第一返送管１６を通して発酵槽１へと戻される。一方、濾過された精密膜濾過筒３内部の濾液はポンプ１５でアンモニア濃度自動計測器４へ送液され、アンモニア濃度が計測される。
【００３４】
アンモニア濃度自動計測器４では、アンモニア濃度が閾値３０００ｍｇ／ｌより低い時は、通常状態である第２開閉弁６が開状態で、第１開閉弁７が閉状態のままで、第二返送管１７により発酵槽１へと濾液が戻される。一方、閾値３０００ｍｇ／ｌ以上の場合は、アンモニア濃度計からの開閉信号５が弁別部１８に送信され、第２開閉弁６が閉状態とされると同時に第１開閉弁７が開状態とされ、アンモニア発散槽８へ濾液が送液される。
【００３５】
アンモニア発散槽８では、濾液に水酸化ナトリウム１０％水溶液が添加されてｐＨを１２に自動的調節し、小型円筒型充填材を乱流通水するときに自然にアンモニアガスに気化される。アンモニア発散槽８で気化されたアンモニアガスは外部からの空気送風１３に伴なってアンモニア分解槽９に導入される。
このアンモニアガスを含む混合ガスは約３８０℃に加熱され触媒により窒素酸化物に酸化され、次にチタン系触媒により約６５０℃の条件下で窒素ガス１０にまで還元して安全な状態として大気に放出している。
【００３６】
上記装置によると、従来法では発酵槽内からアンモニアを系外に取り出さないままの方法でバイオガスの生成が不安定であったが、本発明によれば発酵槽１内からアンモニアを取り出して適正なアンモニア濃度に自動管理することができるので、メタン発酵反応を安定化させて、バイオガスを安定的に生産することができる。
【００３７】
【発明の効果】
以上の説明より明らかなように、本発明によれば、有機系廃棄物を嫌気性微生物により生分解してバイオガスに変換する際に、その変換反応を阻害するアンモニア濃度が一定以上にならないように自動管理することができる。
また、嫌気性消化液を濾過槽の精密膜で濾過した濾液のアンモニア濃度が、バイオガス発生率を低下させない閾値以下である場合には発酵槽へ戻し、かつ、精密膜を通過しなかった嫌気性微生物を含む嫌気性消化液も発酵槽へ戻しているので、発酵槽における嫌気性微生物の活動に必要な窒素成分および嫌気性微生物の濃度低下も防止することができる。
よって、有機系物質の嫌気性微生物による分解反応が安定化され、変動の少ないバイオガス生産を確保することが可能となる。
【図面の簡単な説明】
【図１】バイオガス変換におけるアンモニア濃度自動管理方法を用いた有機系廃棄物の処理装置の概略図である。
【図２】嫌気性発酵日数の経過におけるアンモニア濃度の変動およびバイオガス発生率の変動を示すグラフである。
【符号の説明】
１ 嫌気性発酵槽
２ 濾過槽
３ 精密膜濾過筒
４ アンモニア濃度自動計測器
５ 開閉信号
６ 第２開閉弁
７ 第１開閉弁
８ アンモニア発散槽
９ アンモニア分解槽
１０ 窒素ガス
１１ バイオガス
１２ 有機系廃棄物
１３ 空気送風
１４、１５ ポンプ
１６ 第一返送管
１７ 第二返送管
１８ 弁別部[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for automatically controlling the concentration of ammonia in biogas conversion and an apparatus for treating organic waste using the method. More specifically, the present invention relates to a method for biodegrading organic waste with anaerobic microorganisms to convert it into biogas. This automatically controls the concentration of ammonia that inhibits the reaction.
[0002]
[Prior art]
In recent years, in the field of organic waste recycling technology, in particular, biogas (gas containing methane and carbon dioxide) produced by methane fermentation of organic waste using anaerobic microorganisms has been used in petroleum and the like. Is attracting attention as a renewable resource to replace fossil fuels.
BACKGROUND ART Conventionally, medium-temperature anaerobic digestion treatment of night soil and high-temperature anaerobic digestion treatment of high-concentration waste liquid such as hair wash waste liquid and pharmaceutical waste liquid have been put to practical use.
[0003]
The organic waste treatment method is based on biogas by fermenting organic waste with anaerobic microorganisms about three years ago, following the enforcement of laws such as the disposal of livestock manure and human waste and the Food Recycling Law. It is developing in the direction of recycling.
In particular, the establishment of a method for converting organic wastes such as pig manure, dairy cattle manure, poultry manure, poultry manure, food production waste, household garbage, etc. into biogas by anaerobic microorganisms is strongly demanded for the use of biogas energy. Have been.
[0004]
Recent academic paper, "Anaerobic Digestion of Organic Wastes"-Reaction Factors and Equilibrium in Practice (Co-author: M. Kranert, K. Hillrecht. Source: United Nations, Advanced Research Institute (Japan): http: //www.ias. According to the method described in U.S. Nuu.edu/procedings/icibs/ic to mfa / hillrecht / paper.html, various types of biogas can be converted in a short time by high-concentration microorganisms, and various types of microbial reactions for producing high-component biogas can be performed. Various factors and the equilibrium state of various reactants are described in detail.
[0005]
The process of decomposing organic substances by anaerobic microorganisms is the first stage of the `` acid generation phase '' in which organic substances are decomposed by spoilage bacteria and converted into various organic acids, hydrogen, alcohols, amino acids, and various nitrogen compounds. There is a second stage "methane production phase" that is further decomposed by various enzymes and microorganisms and finally produces biogas containing methane gas by acetic acid, hydrogen and methane bacteria, For waste such as chicken manure), a two-phase mesophilic anaerobic digestion method (or a two-tank mesophilic anaerobic digestion method) in which an "acid-producing phase" and a "methane-producing phase" are separated is employed.
[0006]
In addition, as a division of the conversion technology of various organic wastes into biogas by anaerobic microorganisms, the hardly decomposable substance is a two-phase medium-temperature anaerobic digestion composed of an “acid generation phase” and a “methane generation phase”. The high temperature anaerobic digestion method is adopted for easily decomposable substances. The former has a long digestive digestion time of 20 to 30 days, and the latter has a short period of 5 to 10 days. Furthermore, the biogas emission rate is 1.5 times faster in the latter than in the former, and the decomposition rate of waste is higher in the latter than in the former.
[0007]
[Non-patent document 1]
"Anaerobic digestion of organic wastes"-Reaction factors and equilibrium in practice (co-author: M. Kranert, K. Hillbrecht. Source: United Nations, Advanced Research Institute (Japan); http://www.ias.unu.edu/ (procedings / icibs / ic-mfa / hillblecht / paper.html)
[0008]
[Problems to be solved by the invention]
However, in order to stably produce high-component biogas, when the acetic acid concentration in the fermenter is below a certain level, it is judged that the microbial reaction between acetic acid molecules and methane bacteria is stable, When the nitrogen compounds constituting the organic waste become ammonia molecules in the putrefaction process or the methane production process and the ammonia concentration in the digestion tank increases to 5000 ppm or more, the ammonia molecules are combined with the acetic acid molecules, and the pH of the digestive juice is increased. As a result, an essential problem has arisen, which is about 9 and hinders biogas generation.
Countermeasures such as dilution with water and neutralization with an alkaline solution have been taken to cope with this phenomenon, but none of these measures has led to any essential countermeasures. That is the current situation.
[0009]
In particular, pig manure, cow manure, and poultry manure contain many nitrogen compounds, which generate high concentrations of ammonia in the anaerobic digestion reaction of anaerobic microorganisms and suppress the generation of biogas. It becomes.
FIG. 2 is a graph showing the relationship between the ammonia concentration and the biogas generation rate among the results obtained in a laboratory-scale mesophilic anaerobic digestion study of chicken dung. As is clear from the graph, FIG. It is confirmed that the ammonia concentration gradually increases over time and the biogas generation rate decreases.
[0010]
The present invention has been made in view of the above problems, and has as its object to prevent ammonia generated in the process of biodegrading organic waste by anaerobic microorganisms from inhibiting the stable production of biogas.
[0011]
[Means for Solving the Problems]
In order to solve the above problems, the present invention is biodegraded by anaerobic microorganisms in a fermenter in which organic waste is stirred in a state where air is shut off, and in the conversion of biogas containing methane and carbon dioxide gas, A method for automatically managing the concentration of ammonia generated by the decomposition of the organic waste,
The anaerobic digestion solution in the fermenter is extracted and filtered through a precision membrane that allows the passage of ammonia molecules. When the ammonia concentration in the filtrate is above a certain threshold value in the range of 2000 to 5500 mg / l, it is sent to the ammonia diffusion tank. While removing the ammonia by liquor, if it is lower than the threshold value, the filtrate is returned to the fermenter, and the anaerobic digestion liquid that has not passed through the precision membrane is returned to the fermenter, and the ammonia in the fermenter is removed. An automatic ammonia concentration management method in biogas conversion, characterized in that the concentration is controlled to a predetermined value or less.
[0012]
According to the above method, when the organic substance is biodegraded by anaerobic microorganisms and converted into biogas, the ammonia contained in the anaerobic digestion fluid that inhibits the conversion reaction is appropriately removed when the concentration becomes high. Then, the ammonia concentration in the fermenter can be controlled so as not to exceed a certain level.
Moreover, when the ammonia concentration of the filtrate obtained by filtering the anaerobic digestion solution through the precision membrane of the filtration tank is lower than the threshold value at which the biogas generation rate is not reduced, the ammonia is returned to the fermentation tank as it is. A necessary ammonia nitrogen component can be secured. In addition, since the digested solution containing the anaerobic microorganisms that have not passed through the precision membrane is also returned to the fermenter, a decrease in the concentration of the anaerobic microorganisms in the fermenter can also be prevented.
Therefore, it is possible to stably maintain the reaction between the organic substance and the anaerobic microorganism, and to ensure the production of biogas with little fluctuation.
[0013]
The threshold value of the ammonia concentration for determining whether to return the filtrate to the fermentation tank or to send the filtrate to the ammonia diffusion tank is a value in the range of 2000 to 5500 mg / l as described above.
If the above threshold value is 5500 mg / l or more, the filtrate is returned to the fermenter even though the ammonia concentration is high enough to inhibit the biogas conversion reaction. On the other hand, when the threshold value is set to 2000 mg / l or less, the organic substance is sent to the ammonia diffusion tank and is not returned to the fermentation tank even though the ammonia concentration does not significantly reduce the biogas conversion reaction. This is because the nitrogen component required for biogas conversion is reduced.
Therefore, by using a value in the range of 2000 to 5500 mg / l as the threshold value, it becomes possible to perform an automatic operation in which both the prevention of the increase in the ammonia concentration in the fermenter and the securing of factors necessary for bioconversion are achieved.
[0014]
The present invention also provides an apparatus for treating organic waste, which decomposes organic waste into biogas containing methane and carbon dioxide, using the ammonia concentration management method. The processing device comprises:
A fermenter in which organic waste is stirred with anaerobic microorganisms in a state where air is shut off,
A filtration tank having a precision membrane into which the anaerobic digestion fluid extracted from the fermentation tank flows,
An ammonia concentration automatic measuring device to which the filtrate filtered in the filtration tank is sent,
A first return pipe in which the anaerobic digestion liquid that has not passed through the precision membrane in the filtration tank is returned to the fermentation tank,
An ammonia diffusion tank that is fed when the ammonia concentration of the filtrate measured by the ammonia concentration automatic measuring device is equal to or higher than a predetermined threshold,
When the ammonia concentration of the filtrate measured by the ammonia concentration automatic measuring device is lower than the threshold value, a second return pipe for refluxing the filtrate to the fermenter is provided.
[0015]
The pipe for drawing out the filtrate from the ammonia concentration automatic measuring device is branched into two branches, one of the branch pipes is used as a liquid sending pipe connected to the ammonia diffusion tank, and the other of the branch pipes is connected to a fermentation tank. The second return pipe,
A first opening / closing valve is provided in the branched liquid supply pipe, and a second opening / closing valve is provided in the second return pipe. The first and second opening / closing valves are provided by a measurement signal from the ammonia concentration automatic measuring device. The valve is opened and closed, and when the ammonia concentration is equal to or higher than a certain threshold value in the range of 2000 to 5500 mg / l, the first on-off valve is opened and the second on-off valve is closed, while the ammonia concentration is lower than the threshold value In this case, the first on-off valve is closed and the second on-off valve is open.
[0016]
With the above configuration, when the ammonia concentration of the filtrate obtained by filtering the anaerobic digestion solution in the filtration tank is determined to be lower than the threshold value by the ammonia concentration automatic measuring device, the first and second on-off valves are turned on and off according to the on-off signal. Is operated and returned to the fermenter with the second return pipe, and the anaerobic digestion solution containing the anaerobic microorganisms that did not pass through the precision membrane is also returned to the fermenter by the first return pipe. In this case, the concentration of anaerobic microorganisms can be prevented from lowering, and the nitrogen component required for the activity of anaerobic microorganisms can be prevented from lowering.
[0017]
In addition, the ammonia diffusion tank is connected to an ammonia decomposition tank. In the ammonia diffusion tank, the filtrate is adjusted to pH 10 to 14, and then ammonia is vaporized with a filler, and the ammonia supplied from the ammonia diffusion tank to the ammonia decomposition tank is supplied to the ammonia decomposition tank. The gas is decomposed into nitrogen gas by a catalyst and released to the atmosphere.
[0018]
As described above, when the ammonia concentration of the filtrate is determined to be equal to or more than the threshold value by the ammonia concentration automatic measuring device, the ammonia is sent to the ammonia dispersion tank, the pH is adjusted to 10 to 14, and the ammonia in the filtrate is passed through the filler. It has been vaporized into ammonia gas. More specifically, the ammonia molecules are dissolved in the filtrate to form ammonium ions according to the following chemical formula (1).
(Equation 1)

When the filtrate is made alkaline, as is known, ammonium ion NH ₄ ⁺ becomes ammonia molecule NH ₃ due to chemical equilibrium, and when the concentration exceeds the saturation concentration, it becomes ammonia gas and emanate from the filtrate.
The ammonia gas vaporized in the ammonia diffusion tank is sent to the ammonia decomposition tank, reduced to nitrogen gas by a catalyst, and can be safely released to the atmosphere.
[0019]
The precision membrane in the filtration tank has a pore diameter of 0.1 to 0.5 μm, and has a size that allows passage of ammonia molecules but does not allow passage of anaerobic microorganisms.
That is, by returning the digested liquid in which the anaerobic microorganisms not filtered by the precision membrane are concentrated to the fermenter, the anaerobic microorganism concentration in the fermenter is maintained, and a stable and rapid microbial reaction is enabled. .
[0020]
The fermenter for biodegrading organic waste by the anaerobic microorganisms has a heating atmosphere of 35 to 37 ° C. suitable for medium-temperature anaerobic microorganisms or 53 to 56 ° C. suitable for high-temperature anaerobic microorganisms. To promote biodegradation.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a schematic diagram of an automatic ammonia concentration management device for stably converting an organic waste drug into biogas.
[0022]
The above device is installed in a factory or the like from which organic waste is discharged, and is provided with a supply path 12 to which the organic waste is supplied and a state in which the organic waste is connected to the supply path 12 and air is shut off. A fermenter 1 for stirring with an anaerobic microorganism in a filter tank 2 in which an anaerobic digestion solution of the fermenter 1 is extracted and sent through a pump 14 and contains a precision membrane filter tube 3 therein; A first return pipe 16 for returning the digested liquid that has not passed through the precision membrane filtration tube 3 to the fermenter 1, and an automatic measurement of the ammonia concentration at which the filtrate that has passed through the precision membrane filtration tube 3 is extracted and sent via the pump 15. Device 4, a discriminating unit 18 for distributing the filtrate discharged from the ammonia concentration automatic measuring device 4 in two directions, and an opening / closing signal for notifying the discriminating unit 18 whether the ammonia concentration has exceeded a certain threshold value by the ammonia concentration automatic measuring device 4. 5 and the discriminator 18 Ammonia diffusion tank 8 that is sent when the ammonia concentration is equal to or higher than the threshold, second return pipe 17 that returns the filtrate to fermenter 1 when ammonia concentration is lower than the threshold by discriminating section 18, and emission in ammonia diffusion tank 8 And an ammonia decomposition tank 9 for decomposing the ammonia gas into nitrogen gas 10 by a catalyst and releasing the gas to the atmosphere.
[0023]
The fermenter 1 stirs the organic waste at methane fermentation with an ambient temperature of 35 ° C. to 37 ° C. and agitates with a medium temperature anaerobic microorganism, or stirs a high temperature anaerobic microorganism with an ambient temperature of 53 ° C. to 66 ° C. The organic waste is then methane fermented.
Methane fermentation is the first stage of the `` acid-producing phase, '' in which organic waste is decomposed by anaerobic microorganisms and converted into various organic acids, hydrogen, alcohols, amino acids, and various nitrogen compounds. In the "methane production phase", biogas 11 containing methane gas is produced by acetic acid, hydrogen and methane bacteria by being further decomposed by various kinds of enzymes and microorganisms. At this time, a part of the nitrogen compound constituting the organic waste becomes ammonia, and is dissolved in the anaerobic digestive solution as ammonia molecules and ammonium ions.
[0024]
The filtration tank 2 is a so-called cross-flow filtration system in which a cylindrical precision membrane filtration tube 3 is disposed in the tank, and the precision membrane filtration tube 3 is provided with a polysulfone on the surface of a polymer base material through which a filtrate can easily pass. Is formed by applying an organic substance as described above, and has a pore diameter of 0.3 to 0.6 μm, which allows ammonia molecules to pass therethrough and does not allow anaerobic microorganisms to pass therethrough. In this embodiment, pores of 0.45 μm are provided.
[0025]
The anaerobic digestion liquid sent from the fermenter 1 to the filtration tank 2 flows into the outside of the precision membrane filtration tube 3, and is filtered by the precision membrane filtration tube 3 and enters the inside of the cylinder. The liquid is sent to the measuring device 4. Further, the anaerobic digestion solution outside the cylinder that has not passed through the precision membrane filtration tube 3 is returned to the fermenter 1 by the first return pipe 16.
[0026]
The ammonia concentration automatic measuring device 4 collects a small amount of the filtrate, weighs it, adjusts its pH to 10 to 14, allows the generated ammonia gas to permeate through the gas permeable membrane and absorbs it into 0.1 mol of ammonium chloride. Is measured with a composite glass electrode and a converter, and the ammonia concentration is measured from a scientifically known relational expression between pH and ammonia concentration.
[0027]
The threshold value of the ammonia concentration for determining whether to return the measured filtrate to the fermenter 1 or to send it to the ammonia divergence tank 8 is a value within the range of 2000 to 5500 mg / l, and is 3000 mg / l in the present embodiment. .
[0028]
The configuration of the discriminating unit 18 is such that the pipe 20 for leading out the filtrate from the ammonia concentration automatic measuring device 4 is branched into two branches, and one of the branch pipes is used as a liquid sending pipe 21 connected to the ammonia diffusion tank 8. The other is a second return pipe 17 connected to the fermenter 1.
A first opening / closing valve 7 is provided in the liquid supply pipe 21 and a second opening / closing valve 6 is provided in the second return pipe 17, and a first opening / closing signal 5 based on the measurement from the automatic ammonia concentration measuring device 4 is used. , The second on-off valves 7 and 6 are opened and closed.
The first and second on-off valves 7 and 6 are electromagnetic valves, the second on-off valve 6 is normally open, and the first on-off valve 7 is normally closed.
[0029]
The ammonia diffusion tank 8 includes an air blowing unit 13, a small cylindrical filler (not shown), and a pH adjusting unit (not shown), and a 10% aqueous solution of sodium hydroxide is added to the filtrate from the pH adjusting unit. PH is adjusted to 10-14. In the present embodiment, the pH is automatically adjusted to 12.
Then, by adjusting the pH to 12, ammonia in the filtrate is vaporized into ammonia gas. More specifically, the ammonia molecules are dissolved in the filtrate to form ammonium ions according to the following chemical formula (1).
(Equation 1)

The filtrate is made alkaline at pH 12 so that ammonium ion NH ₄ ⁺ becomes ammonia molecule NH ₃ by chemical equilibrium, and when the concentration exceeds the saturation concentration, ammonia molecule NH ₃ is vaporized and turbulently flows through the small cylindrical filler. As the liquid is liquefied, ammonia molecules NH ₃ are further vaporized and ammonia gas is diverged. The ammonia gas is carried to the ammonia decomposition tank 9 together with the air blow 13.
[0030]
In the ammonia decomposition tank 9, the ammonia gas sent from the ammonia diffusion tank 8 is heated and converted into a nitrogen oxide by a catalyst at 300 to 450 ° C. as a first step, and a titanium-based catalyst at 600 to 700 ° C. as a second step. It is reduced to nitrogen gas 10 and released to the atmosphere.
In the present embodiment, the temperature of the first stage is about 380 ° C., and the temperature of the second step is about 650 ° C.
[0031]
Next, the operation of the above device will be described.
The organic waste 12 is supplied to the fermenter 1 and is stirred together with anaerobic microorganisms in a state where air is shut off, and is converted into biogas 11 containing methane and carbon dioxide by methane fermentation.
Ammonia which is generated in the process of biodegradation of the organic waste by anaerobic microorganisms and inhibits biogas generation is dissolved in the anaerobic digestion solution, and the anaerobic digestion solution is pumped from the bottom of the fermenter 1 through the pump 14. And the solution is sent to the filtration tank 2.
[0032]
The anaerobic digestion fluid that has flowed into the filtration tank 2 flows on the outer surface of the precision membrane filtration tube 3, and when the inside of the precision membrane filtration tube 3 is in a reduced pressure state, the precision membrane filtration tube is vertically moved from the outer surface. The anaerobic digestion fluid passes into the inside of 3 to obtain a filtrate. At this time, the anaerobic microorganisms present in the anaerobic digestion fluid have already been aggregated and cannot pass through because they are larger than the pores of the precision membrane filtration tube 3, and the anaerobic microorganisms are removed and the anaerobic digestion fluid containing ammonia passes. To form a filtrate.
The cross-flow filtration method has an advantage that the main flow of the anaerobic digestion fluid flows from the bottom to the top so as to slide on the outer surface of the precision membrane filtration tube 3, and thus the clogging of the precision membrane filtration tube 3 does not easily occur.
[0033]
The anaerobic digestion liquid containing the anaerobic microorganisms that has not passed through the precision membrane filtration tube 3 is returned to the fermenter 1 through the first return pipe 16. On the other hand, the filtered filtrate inside the precision membrane filtration tube 3 is sent to the ammonia concentration automatic measuring device 4 by the pump 15, and the ammonia concentration is measured.
[0034]
In the ammonia concentration automatic measuring device 4, when the ammonia concentration is lower than the threshold value of 3000 mg / l, the second return pipe is kept in the normal state, the second on-off valve 6 is open and the first on-off valve 7 is closed. The filtrate is returned to the fermenter 1 by 17. On the other hand, when the threshold value is 3000 mg / l or more, the opening / closing signal 5 from the ammonia concentration meter is transmitted to the discriminating section 18, the second opening / closing valve 6 is closed, and the first opening / closing valve 7 is opened simultaneously. Then, the filtrate is sent to the ammonia diffusion tank 8.
[0035]
In the ammonia diffusion tank 8, a 10% aqueous solution of sodium hydroxide is added to the filtrate to automatically adjust the pH to 12, and when the small cylindrical filler is turbulently circulated, it is naturally vaporized into ammonia gas. The ammonia gas vaporized in the ammonia diffusion tank 8 is introduced into the ammonia decomposition tank 9 along with an external air blow 13.
The mixed gas containing the ammonia gas is heated to about 380 ° C., oxidized to nitrogen oxides by the catalyst, and then reduced to nitrogen gas 10 by the titanium-based catalyst at about 650 ° C. to a safe state to the atmosphere. Has released.
[0036]
According to the above-described apparatus, in the conventional method, the production of biogas was unstable by a method in which ammonia was not taken out of the fermenter from the outside of the system. Since the ammonia concentration can be automatically controlled to a low level, the methane fermentation reaction can be stabilized and biogas can be stably produced.
[0037]
【The invention's effect】
As is clear from the above description, according to the present invention, when the organic waste is biodegraded by anaerobic microorganisms and converted into biogas, the ammonia concentration that inhibits the conversion reaction does not exceed a certain level. Can be automatically managed.
In addition, when the ammonia concentration of the filtrate obtained by filtering the anaerobic digestion solution with the precision membrane in the filtration tank is equal to or lower than a threshold value that does not reduce the biogas generation rate, the anaerobic digestion liquid is returned to the fermentation tank, and the anaerobic reaction that has not passed through the precision membrane Since the anaerobic digestion solution containing the anaerobic microorganisms is also returned to the fermenter, it is possible to prevent a decrease in the concentration of nitrogen components and anaerobic microorganisms required for the activity of the anaerobic microorganisms in the fermenter.
Therefore, the decomposition reaction of the organic substance by the anaerobic microorganism is stabilized, and it is possible to secure biogas production with little fluctuation.
[Brief description of the drawings]
FIG. 1 is a schematic view of an organic waste treatment apparatus using an automatic ammonia concentration management method in biogas conversion.
FIG. 2 is a graph showing changes in ammonia concentration and changes in biogas generation rate over the course of anaerobic fermentation days.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Anaerobic fermentation tank 2 Filtration tank 3 Precision membrane filtration cylinder 4 Ammonia concentration automatic measuring instrument 5 Open / close signal 6 Second open / close valve 7 First open / close valve 8 Ammonia emission tank 9 Ammonia decomposition tank 10 Nitrogen gas 11 Biogas 12 Organic waste Object 13 Air blow 14, 15 Pump 16 First return pipe 17 Second return pipe 18 Discriminator

Claims (6)

Ammonia generated by the decomposition of the organic waste in the conversion of biogas containing methane and carbon dioxide gas in the fermenter where the organic waste is stirred with the air shut off A method for automatically controlling the concentration,
The anaerobic digestion solution in the fermenter is extracted and filtered through a precision membrane that allows the passage of ammonia molecules. When the ammonia concentration in the filtrate is above a certain threshold value in the range of 2000 to 5500 mg / l, it is sent to the ammonia diffusion tank. While removing the ammonia by liquor, if it is lower than the threshold value, the filtrate is returned to the fermenter, and the anaerobic digestion liquid that has not passed through the precision membrane is returned to the fermenter, and the ammonia in the fermenter is removed. An automatic ammonia concentration management method in biogas conversion, wherein the concentration is controlled to a predetermined value or less. An organic waste treatment device in which organic waste is decomposed and converted into biogas containing methane and carbon dioxide,
A fermenter in which organic waste is stirred with anaerobic microorganisms in a state where air is shut off,
A filtration tank having a precision membrane into which the anaerobic digestion fluid extracted from the fermentation tank flows,
An ammonia concentration automatic measuring device to which the filtrate filtered in the filtration tank is sent,
Anaerobic digestion fluid that did not pass through the precision membrane in the filtration tank, the first return pipe returned to the fermentation tank,
An ammonia diffusion tank that is fed when the ammonia concentration of the filtrate measured by the ammonia concentration automatic measuring device is equal to or higher than a predetermined threshold,
An organic waste treatment apparatus, comprising: a second return pipe for refluxing the filtrate to the fermenter when the ammonia concentration of the filtrate measured by the ammonia concentration automatic measuring device is lower than the threshold. The pipe for drawing out the filtrate from the ammonia concentration automatic measuring device is branched into two branches, one of the branch pipes is used as a liquid sending pipe connected to the ammonia diffusion tank, and the other of the branch pipes is connected to a fermentation tank. The second return pipe,
A first on-off valve is interposed in the branched liquid supply pipe, and a second on-off valve is interposed in the second return pipe, and the first and second valves are operated according to a measurement signal from the ammonia concentration automatic measuring instrument. The on-off valve is opened and closed, and when the ammonia concentration is equal to or more than a certain threshold value in the range of 2000 to 5500 mg / l, the first on-off valve is opened and the second on-off valve is closed, while the ammonia concentration is higher than the threshold value. The organic waste treatment apparatus according to claim 2, wherein the first on-off valve is closed and the second on-off valve is open when the temperature is low. The ammonia diffusion tank is connected to an ammonia decomposition tank,
In the above ammonia diffusion tank, the filtrate is adjusted to pH 10 to 14 and then ammonia is vaporized by the filler. The ammonia gas sent from the ammonia diffusion tank to the ammonia decomposition tank is decomposed into nitrogen gas by the catalyst and released to the atmosphere. The organic waste treatment apparatus according to claim 2 or 3, wherein the apparatus is configured. The pore size of the precision membrane in the filtration tank is 0.1 to 0.5 μm, and has a size that allows passage of ammonia molecules but does not allow anaerobic microorganisms to pass therethrough. Organic waste treatment equipment. The organic waste according to any one of claims 2 to 5, wherein the fermenter for biodegrading the organic waste by the anaerobic microorganism has a heating atmosphere of 35 to 37 ° C or 53 to 56 ° C. Processing equipment.

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