JP2007098271A - Method and system for producing organic acid - Google Patents

Method and system for producing organic acid Download PDF

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JP2007098271A
JP2007098271A JP2005291203A JP2005291203A JP2007098271A JP 2007098271 A JP2007098271 A JP 2007098271A JP 2005291203 A JP2005291203 A JP 2005291203A JP 2005291203 A JP2005291203 A JP 2005291203A JP 2007098271 A JP2007098271 A JP 2007098271A
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organic acid
sludge
tank
raw sludge
concentrated
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Hitoshi Kato
仁 加藤
Keiichi Sone
啓一 曽根
Minoru Ishii
実 石井
Masami Ebisawa
雅美 海老澤
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Sumitomo Heavy Industries Ltd
Tokyo Metropolitan Government
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Tokyo Metropolitan Government
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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
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a system for producing an organic acid, in each of which the organic acid can be produced in high efficiency. <P>SOLUTION: The organic acid is obtained by introducing raw sludge to be obtained in a first precipitation basin 5 into a pressure flotation concentration apparatus 13 to obtain concentrated sludge by a pressure flotation concentration method and fermenting the concentrated sludge anaerobically in an acid fermentation tank 40. Since the raw sludge is concentrated in an oxygen atmosphere by the pressure flotation concentration method, the activity of a methane bacterium in the raw sludge can be repressed and the organic acid can be produced in high efficiency in the acid fermentation tank 4. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

本発明は、下水から得られる汚泥を嫌気性発酵させて有機酸を生成する有機酸生成方法及び有機酸生成システムに関するものである。   The present invention relates to an organic acid production method and an organic acid production system for producing an organic acid by anaerobic fermentation of sludge obtained from sewage.

従来、このような分野の技術として、下記特許文献１に記載された有機酸生成方法がある。この有機酸生成方法においては、下水を最初沈殿池に導入して下水中の生汚泥を沈殿させ、この生汚泥を酸発酵槽に導入している。そして、酸発酵槽内の酸生成菌の働きによって生汚泥を嫌気性発酵させ、有機酸を生成している。この有機酸は、上記最初沈殿池の上澄み液を脱リン・脱窒素処理するための有機源として生物処理槽に供給され、生物処理槽内での上澄み液の生物処理に寄与する。
特開２００２−３０１５００号公報 Conventionally, as a technique in such a field, there is an organic acid generation method described in Patent Document 1 below. In this organic acid production method, sewage is first introduced into a settling basin to precipitate raw sludge in the sewage, and this raw sludge is introduced into an acid fermentation tank. And the raw sludge is anaerobically fermented by the action of acid-producing bacteria in the acid fermenter to produce organic acids. This organic acid is supplied to the biological treatment tank as an organic source for dephosphorizing / denitrogenating the supernatant of the first sedimentation basin, and contributes to biological treatment of the supernatant in the biological treatment tank.
JP 2002-301500 A

しかしながら、下水管渠を経由して最初沈殿池に集められた下水には、通常、有機酸をメタンに分解するメタン菌が多く含まれており、このメタン菌は生汚泥と一緒に最初沈殿池から酸発酵槽に導入される。このため、上記方法では、酸発酵槽内で嫌気性発酵によって生成した有機酸が、メタン菌によって一部メタンに分解されてしまうので、有機酸の生成効率が低下してしまうという問題があった。   However, the sewage collected in the first sedimentation basin via the sewer pipe usually contains many methane bacteria that decompose organic acids into methane. Is introduced into the acid fermenter. For this reason, in the said method, since the organic acid produced | generated by the anaerobic fermentation in an acid fermenter will be decomposed | disassembled partially to methane by a methane bacterium, there existed a problem that the production | generation efficiency of an organic acid will fall. .

そこで、本発明は、高い生成効率で有機酸が得られる有機酸生成方法及び有機酸生成システムを提供することを目的とする。   Then, an object of this invention is to provide the organic acid production | generation method and organic acid production | generation system which can obtain an organic acid with high production | generation efficiency.

本発明に係る有機酸生成方法は、下水から得られる汚泥を嫌気性発酵させて有機酸を生成する有機酸生成方法において、下水の沈殿物である生汚泥を濃縮し濃縮汚泥を得る濃縮ステップと、濃縮ステップで得られた濃縮汚泥を嫌気性発酵させて有機酸を得る発酵ステップと、を備え、濃縮ステップでは、加圧浮上濃縮法によって生汚泥の濃縮が行われることを特徴とする。   The organic acid production method according to the present invention is an organic acid production method for producing an organic acid by anaerobic fermentation of sludge obtained from sewage, a concentration step for concentrating raw sludge that is sediment of sewage to obtain concentrated sludge; And a fermentation step in which the concentrated sludge obtained in the concentration step is subjected to anaerobic fermentation to obtain an organic acid. In the concentration step, the raw sludge is concentrated by a pressurized flotation concentration method.

この有機酸生成方法では、下水の沈殿物である生汚泥を濃縮ステップで濃縮して濃縮汚泥を得、この濃縮汚泥を発酵ステップにおいて嫌気性発酵させる。そして、この生成方法では、濃縮ステップにおける生汚泥の濃縮が、加圧浮上濃縮法によって行われる。すなわち、まず、生汚泥が空気と一緒に加圧されることで空気が生汚泥に溶解する。或いは、空気と一緒に水を加圧し、この水を生汚泥に混合させることで、生汚泥に空気が溶解した状態となる。その後、これらの生汚泥が大気圧下に解放されることで、溶解していた空気が生汚泥中で気泡となって固体成分に付着し、浮力により固体成分を上昇させる。そして、液面に浮上した固体成分を回収することにより、生汚泥の濃縮が達成される。   In this organic acid production method, raw sludge which is a sediment of sewage is concentrated in a concentration step to obtain concentrated sludge, and this concentrated sludge is subjected to anaerobic fermentation in a fermentation step. And in this production | generation method, concentration of the raw sludge in a concentration step is performed by the pressure levitation concentration method. That is, first, raw sludge is pressurized together with air, so that air dissolves in the raw sludge. Alternatively, water is pressurized together with air, and the water is mixed with the raw sludge so that the air is dissolved in the raw sludge. Thereafter, the raw sludge is released under atmospheric pressure, so that the dissolved air becomes bubbles in the raw sludge and adheres to the solid component, and the solid component is raised by buoyancy. And concentration of raw sludge is achieved by collect | recovering the solid component which floated on the liquid level.

上記濃縮ステップにおいて、生汚泥が一旦加圧状態となった時に、大気圧下の場合よりも生汚泥に多くの酸素が溶解することになる。ここで、生汚泥に含まれるメタン菌は嫌気性の菌であるので、生汚泥に溶解した空気中の酸素によって増殖が抑制され、メタン菌は活性が低い状態となる。このように、発酵ステップに移行される前の濃縮ステップにおいて、汚泥中のメタン菌の活性が低い状態にされるので、発酵ステップにおいて生成する有機酸がメタンへ分解されてしまうことが抑えられ、有機酸の高い生成効率が得られる。   In the concentration step, when the raw sludge is once pressurized, more oxygen is dissolved in the raw sludge than when it is under atmospheric pressure. Here, since the methane bacterium contained in the raw sludge is an anaerobic bacterium, the growth is suppressed by oxygen in the air dissolved in the raw sludge, and the methane bacterium is in a low activity state. Thus, in the concentration step before being transferred to the fermentation step, the activity of methane bacteria in the sludge is brought into a low state, so that the organic acid produced in the fermentation step is prevented from being decomposed into methane, High production efficiency of organic acid can be obtained.

また、本発明に係る有機酸生成方法は、生汚泥を、濃縮ステップの前に曝気する前曝気ステップを更に備えることが好ましい。   Moreover, it is preferable that the organic acid production | generation method concerning this invention is further equipped with the pre-aeration step which aerates raw sludge before a concentration step.

この場合、前曝気ステップにおいて生汚泥が曝気される時に、酸素が生汚泥に溶解し、溶解した酸素によってメタン菌の増殖が抑制される。よって、この有機酸生成方法によれば、発酵ステップに移行される前における汚泥中のメタン菌の活性がさらに低い状態とされ、さらに高い生成効率で有機酸が得られる。   In this case, when raw sludge is aerated in the pre-aeration step, oxygen is dissolved in the raw sludge, and the growth of methane bacteria is suppressed by the dissolved oxygen. Therefore, according to this organic acid production | generation method, the activity of the methane microbe in sludge before transfering to a fermentation step is made into the state still lower, and an organic acid is obtained with still higher production efficiency.

また、本発明に係る有機酸生成方法は、濃縮ステップで得られた濃縮汚泥を、発酵ステップの前に曝気する後曝気ステップを更に備えることが好ましい。   Moreover, it is preferable that the organic acid production method according to the present invention further includes a post-aeration step in which the concentrated sludge obtained in the concentration step is aerated before the fermentation step.

この場合、後曝気ステップにおいて濃縮汚泥が曝気される時に、酸素が濃縮汚泥に溶解し、溶解した酸素によってメタン菌の増殖が抑制される。よって、この有機酸生成方法によれば、発酵ステップに移行される前における汚泥中のメタン菌の活性がさらに低い状態とされ、さらに高い生成効率で有機酸が得られる。   In this case, when the concentrated sludge is aerated in the post-aeration step, oxygen is dissolved in the concentrated sludge, and the growth of methane bacteria is suppressed by the dissolved oxygen. Therefore, according to this organic acid production | generation method, the activity of the methane microbe in sludge before transfering to a fermentation step is made into the state still lower, and an organic acid is obtained with still higher production efficiency.

本発明に係る有機酸生成システムは、下水から得られる汚泥を嫌気性発酵させて有機酸を生成する有機酸生成システムにおいて、下水の沈殿物である生汚泥を濃縮し濃縮汚泥を得る濃縮装置と、濃縮装置で得られた濃縮汚泥を嫌気性発酵させて有機酸を得る酸発酵槽と、を備え、濃縮装置は、加圧浮上濃縮装置であることを特徴とする。   An organic acid generation system according to the present invention is an organic acid generation system that generates an organic acid by anaerobic fermentation of sludge obtained from sewage, and a concentrating device that concentrates raw sludge that is a sediment of sewage to obtain concentrated sludge; And an acid fermentation tank for obtaining an organic acid by anaerobic fermentation of the concentrated sludge obtained by the concentrating device, wherein the concentrating device is a pressurized flotation concentrating device.

この有機酸生成システムでは、下水の沈殿物である生汚泥を濃縮装置で濃縮して濃縮汚泥を得、この濃縮汚泥を酸発酵槽において嫌気性発酵させる。そして、このシステムにおいて、濃縮装置は、加圧浮上濃縮装置である。すなわち、加圧浮上濃縮装置では、まず、生汚泥が空気と一緒に加圧されることで空気が生汚泥に溶解する。或いは、空気と一緒に水を加圧し、この水を生汚泥に混合させることで、生汚泥に空気が溶解した状態となる。その後、これらの生汚泥が大気圧下に解放されることで、溶解していた空気が生汚泥中で気泡となって固体成分に付着し、浮力により固体成分を上昇させる。そして、液面に浮上した固体成分を回収することにより、生汚泥の濃縮が達成される。   In this organic acid generation system, raw sludge, which is a sediment of sewage, is concentrated by a concentrator to obtain concentrated sludge, and this concentrated sludge is subjected to anaerobic fermentation in an acid fermentation tank. In this system, the concentration device is a pressure levitation concentration device. That is, in the pressurized flotation concentration apparatus, first, the raw sludge is pressurized together with the air, so that the air is dissolved in the raw sludge. Alternatively, water is pressurized together with air, and the water is mixed with the raw sludge so that the air is dissolved in the raw sludge. Thereafter, the raw sludge is released under atmospheric pressure, so that the dissolved air becomes bubbles in the raw sludge and adheres to the solid component, and the solid component is raised by buoyancy. And concentration of raw sludge is achieved by collect | recovering the solid component which floated on the liquid level.

この加圧浮上濃縮装置において、生汚泥が一旦加圧状態となった時に、大気圧下の場合よりも生汚泥に多くの酸素が溶解することになる。ここで、生汚泥に含まれるメタン菌は嫌気性の菌であるので、生汚泥に溶解した空気中の酸素によって増殖が抑制され、メタン菌は活性が低い状態となる。このように、汚泥が酸発酵槽に導入される前の濃縮装置において、汚泥中のメタン菌の活性が低い状態にされるので、酸発酵槽において生成する有機酸がメタンへ分解されてしまうことが抑えられ、有機酸の高い生成効率が得られる。   In this pressurized levitation concentration apparatus, when the raw sludge is once pressurized, more oxygen is dissolved in the raw sludge than when it is under atmospheric pressure. Here, since the methane bacterium contained in the raw sludge is an anaerobic bacterium, the growth is suppressed by oxygen in the air dissolved in the raw sludge, and the methane bacterium is in a low activity state. Thus, in the concentrating device before the sludge is introduced into the acid fermentation tank, the activity of the methane bacteria in the sludge is lowered, so that the organic acid produced in the acid fermentation tank is decomposed into methane. Is suppressed, and high production efficiency of the organic acid is obtained.

本発明に係る有機酸生成システムは、生汚泥を、濃縮装置に導入する前に曝気する前曝気槽を更に備えることが好ましい。   The organic acid generation system according to the present invention preferably further includes a pre-aeration tank for aeration of raw sludge before introduction into the concentrator.

この場合、前曝気槽において生汚泥が曝気される時に、酸素が生汚泥に溶解し、溶解した酸素によってメタン菌の増殖が抑制される。よって、この有機酸生成システムによれば、酸発酵槽に導入される前における汚泥中のメタン菌の活性がさらに低い状態とされ、さらに高い生成効率で有機酸が得られる。   In this case, when raw sludge is aerated in the pre-aeration tank, oxygen is dissolved in the raw sludge, and the growth of methane bacteria is suppressed by the dissolved oxygen. Therefore, according to this organic acid production | generation system, the activity of the methane microbe in sludge before being introduce | transduced into an acid fermenter is made into the state still lower, and an organic acid is obtained with still higher production efficiency.

本発明に係る有機酸生成システムは、濃縮装置で得られた濃縮汚泥を、酸発酵槽に導入する前に曝気する後曝気槽を更に備えることが好ましい。   It is preferable that the organic acid production system according to the present invention further includes a post-aeration tank in which the concentrated sludge obtained by the concentrator is aerated before being introduced into the acid fermentation tank.

この場合、後曝気槽において濃縮汚泥が曝気される時に、酸素が濃縮汚泥に溶解し、溶解した酸素によってメタン菌の増殖が抑制される。よって、この有機酸生成システムによれば、酸発酵槽に導入される前における汚泥中のメタン菌の活性がさらに低い状態とされ、さらに高い生成効率で有機酸が得られる。   In this case, when the concentrated sludge is aerated in the post-aeration tank, oxygen is dissolved in the concentrated sludge, and the growth of methane bacteria is suppressed by the dissolved oxygen. Therefore, according to this organic acid production | generation system, the activity of the methane microbe in sludge before being introduce | transduced into an acid fermenter is made into the state still lower, and an organic acid is obtained with still higher production efficiency.

本発明の有機酸生成方法及び有機酸生成システムによれば、高い生成効率で有機酸が得られる。   According to the organic acid production method and the organic acid production system of the present invention, an organic acid can be obtained with high production efficiency.

以下、図面を参照しつつ本発明に係る有機酸生成方法及び有機酸生成システムの好適な実施形態について詳細に説明する。   Hereinafter, preferred embodiments of an organic acid generation method and an organic acid generation system according to the present invention will be described in detail with reference to the drawings.

図１に示す下水処理設備１は、ラインＬ１から導入される下水を、嫌気槽３ａ、無酸素槽３ｂ及び好気槽３ｃを有する生物処理槽３で生物的に処理する設備である。下水処理場に流入する下水は、まず沈砂池（図示せず）において、浮遊するゴミや沈降する固形物が除去された後、ラインＬ１を通じてこの下水処理設備１に導入される。ラインＬ１からの下水は、まず、最初沈殿池５に導入され、沈降分離によって固液分離される。分離された上澄み液は、生物処理槽３に導入され、嫌気槽３ａ、無酸素槽３ｂ及び好気槽３ｃを通過し、生物的処理による脱リン・脱窒素がされた後、最終沈殿池７に導入される。最終沈殿池７で沈降分離された活性汚泥は一部が生物処理槽３に返送され、残りは余剰汚泥として排出される。また、最終沈殿池７の上澄みは、後工程（図示せず）の処理を経て、処理水として河川等に放流される。   A sewage treatment facility 1 shown in FIG. 1 is a facility that biologically treats sewage introduced from a line L1 in a biological treatment tank 3 having an anaerobic tank 3a, an anaerobic tank 3b, and an aerobic tank 3c. First, sewage flowing into the sewage treatment plant is introduced into the sewage treatment facility 1 through the line L1 after removing floating dust and sedimenting solids in a sand basin (not shown). The sewage from the line L1 is first introduced into the settling basin 5 and solid-liquid separated by sedimentation separation. The separated supernatant is introduced into the biological treatment tank 3 and passes through the anaerobic tank 3a, the oxygen-free tank 3b, and the aerobic tank 3c, and after dephosphorization / denitrogenation by biological treatment, the final sedimentation tank 7 To be introduced. Part of the activated sludge settled and separated in the final sedimentation tank 7 is returned to the biological treatment tank 3 and the rest is discharged as surplus sludge. The supernatant of the final sedimentation basin 7 is discharged into a river or the like as treated water through a post-process (not shown).

このような下水処理設備１においては、脱リン・脱窒素といった生物的処理に必要な有機源を生物処理槽３に導入することが必要である。そこで、下水処理設備１は、最初沈殿池５で得られる生汚泥を原料として有機酸を生成し、この有機酸を生物処理槽３に有機源として供給する有機酸生成システム１０を備えている。この有機酸生成システム１０は、後述する生汚泥曝気撹拌槽（前曝気槽）１１、加圧浮上濃縮装置１３、濃縮汚泥槽（後曝気槽）２７、酸発酵槽４０、沈殿槽４３、及び有機酸貯留槽４５を備えている。なお、この有機酸生成システム１０で得られる有機酸には、主として酢酸、プロピオン酸等が含まれる。   In such a sewage treatment facility 1, it is necessary to introduce an organic source necessary for biological treatment such as dephosphorization / denitrogenation into the biological treatment tank 3. Therefore, the sewage treatment facility 1 includes an organic acid generation system 10 that generates an organic acid using raw sludge obtained in the first sedimentation basin 5 as a raw material and supplies the organic acid to the biological treatment tank 3 as an organic source. This organic acid generation system 10 includes a raw sludge aeration and agitation tank (pre-aeration tank) 11, a pressurized flotation concentration device 13, a concentrated sludge tank (post-aeration tank) 27, an acid fermentation tank 40, a precipitation tank 43, and an organic An acid storage tank 45 is provided. The organic acid obtained by the organic acid generation system 10 mainly includes acetic acid, propionic acid, and the like.

上述の最初沈殿池５の底部に沈殿した沈殿物は、引き抜きポンプｐ１によって底部から引き抜かれ、ラインＬ２を通じ、有機酸の原料の生汚泥として生汚泥曝気撹拌槽（前曝気槽）１１に導入される。通常、下水は嫌気性状態で下水処理場に導入されるので、ここで導入される生汚泥には、下水が導入される間に増殖したメタン菌が多く含まれている。   The sediment deposited on the bottom of the first sedimentation basin 5 is drawn from the bottom by a drawing pump p1, and is introduced into a raw sludge aeration and agitation tank (pre-aeration tank) 11 as raw sludge of an organic acid raw material through a line L2. The Usually, since sewage is introduced into a sewage treatment plant in an anaerobic state, the raw sludge introduced here contains a lot of methane bacteria grown during the introduction of sewage.

生汚泥曝気撹拌槽１１には、散気装置１１ａが設けられており、この散気装置１１ａは、送風機１１ｂから送られる空気によって槽内の生汚泥を曝気し撹拌する（前曝気ステップ）。このとき、生汚泥には散気装置１１ａからの空気に含まれる酸素が溶解することになるので、生汚泥中の溶存酸素量が増加する。ここで、メタン菌は嫌気性菌であるので、溶存酸素量が増加した生汚泥中においては、酸素雰囲気に曝されることでメタン菌が減少し、メタン菌の活性が低く抑えられる。   The raw sludge aeration and agitation tank 11 is provided with an air diffuser 11a. The air diffuser 11a aerates and stirs the raw sludge in the tank with air sent from the blower 11b (pre-aeration step). At this time, since oxygen contained in the air from the air diffuser 11a is dissolved in the raw sludge, the amount of dissolved oxygen in the raw sludge increases. Here, since the methane bacterium is an anaerobic bacterium, in the raw sludge in which the amount of dissolved oxygen is increased, the methane bacterium is reduced by exposure to an oxygen atmosphere, and the activity of the methane bacterium is kept low.

生汚泥曝気撹拌槽１１で曝気された生汚泥は、加圧ポンプｐ２によって加圧されながら、全量が加圧浮上濃縮装置１３に送られる。この加圧浮上濃縮装置１３は、加圧浮上濃縮法により生汚泥を濃縮する装置であって、加圧槽１３ａと加圧浮上槽１３ｂとを備えている。加圧槽１３ａは、加圧ポンプｐ２によって加圧された生汚泥と空気圧縮機１３ｃから送り出される圧縮空気とを、３〜４気圧の加圧状態で一緒に貯留する。この加圧槽１３ａにおいて、空気と一緒に加圧された生汚泥中には、大気圧下よりも３〜４倍の酸素が溶解することになるので、生汚泥中の溶存酸素量が更に増加する。従って、濃度が高い酸素雰囲気に曝されることで生汚泥中のメタン菌が更に減少し、メタン菌の活性が更に低く抑えられることになる。   The raw sludge aerated in the raw sludge aeration and agitation tank 11 is sent to the pressurized levitation concentrator 13 while being pressurized by the pressure pump p2. The pressure levitation concentration apparatus 13 is an apparatus that concentrates raw sludge by a pressure levitation concentration method, and includes a pressure tank 13a and a pressure levitation tank 13b. The pressurizing tank 13a stores the raw sludge pressurized by the pressurizing pump p2 and the compressed air sent out from the air compressor 13c together in a pressurized state of 3 to 4 atm. In the pressurized tank 13a, oxygen is dissolved in the raw sludge pressurized together with air, so that the amount of dissolved oxygen in the raw sludge is further increased. To do. Therefore, exposure to an oxygen atmosphere with a high concentration further reduces the methane bacteria in the raw sludge, and the activity of the methane bacteria can be further suppressed.

そして、加圧槽１３ａで加圧状態となった生汚泥は、加圧浮上槽１３ｂに送られる。この加圧浮上槽１３ｂは、断面円形をなしており、駆動装置１５によって回転する駆動軸１７を有している。この駆動軸１７には、槽内に滞留する生汚泥を撹拌するレーキ１９と、生汚泥液面に沿って水平に回転するスキンマー２１が取り付けられている。   And the raw sludge which became the pressurization state in the pressurization tank 13a is sent to the pressurization floating tank 13b. The pressurized levitation tank 13 b has a circular cross section and has a drive shaft 17 that is rotated by the drive device 15. A rake 19 that stirs the raw sludge staying in the tank and a skinmer 21 that rotates horizontally along the raw sludge liquid surface are attached to the drive shaft 17.

加圧槽１３ａからの生汚泥が加圧浮上槽１３ｂ内のフィールドウェル２３に供給されると、大気圧下の槽内に滞留する生汚泥に混入される。このとき、加圧下で生汚泥に溶解していた空気が、大気圧まで減圧されたことで気泡化するので、槽内で滞留する生汚泥中に、大量の気泡が発生することになる。この気泡が生汚泥中の固体成分に付着するので、その気泡の浮力によって、固体成分が生汚泥液面まで浮上する。そして、液面に浮上した固体成分は、スキンマー２１によって掻き寄せられフロートボックス２５に落下した後、濃縮汚泥として濃縮汚泥槽２７に集められる（濃縮ステップ）。一方、生汚泥の液体成分は、槽内上部に設けられた越流渠２９に集められ、処理水槽３１に貯留された後、沈砂池（図示せず）等に返水される。なお、濃縮汚泥槽２７は、加圧浮上濃縮装置１３と一体に設けられているが、濃縮汚泥槽２７は、加圧浮上濃縮装置１３から独立した別体の槽として設けられてもよい。   When the raw sludge from the pressurized tank 13a is supplied to the field well 23 in the pressurized floating tank 13b, it is mixed into the raw sludge that stays in the tank under atmospheric pressure. At this time, since air dissolved in the raw sludge under pressure is reduced to atmospheric pressure, the air bubbles are formed, so that a large amount of bubbles are generated in the raw sludge staying in the tank. Since the bubbles adhere to the solid component in the raw sludge, the solid component rises to the raw sludge liquid surface by the buoyancy of the bubbles. The solid components floating on the liquid surface are scraped by the skinmer 21 and dropped into the float box 25, and then collected in the concentrated sludge tank 27 as concentrated sludge (concentration step). On the other hand, the liquid component of raw sludge is collected in the overflow basin 29 provided in the upper part of the tank, stored in the treated water tank 31, and then returned to a sand basin (not shown). Although the concentrated sludge tank 27 is provided integrally with the pressurized levitation concentrating device 13, the concentrated sludge tank 27 may be provided as a separate tank independent of the pressurized levitation concentrating device 13.

濃縮汚泥槽２７に集められた濃縮汚泥は、撹拌送風機３３によって空気が送り込まれて曝気撹拌される（後曝気ステップ）。このとき、濃縮汚泥には、送り込まれた空気中の酸素が溶解することで、溶存酸素量が増加することになる。従って、濃縮汚泥に含まれるメタン菌は、酸素雰囲気に曝されることで減少し、メタン菌の活性が更に低く抑えられることになる。   The concentrated sludge collected in the concentrated sludge tank 27 is aerated and agitated by sending air by the agitating blower 33 (post-aeration step). At this time, the oxygen concentration in the sent air is dissolved in the concentrated sludge, so that the amount of dissolved oxygen increases. Therefore, the methane bacteria contained in the concentrated sludge are reduced by exposure to an oxygen atmosphere, and the activity of the methane bacteria is further suppressed.

その後、濃縮汚泥槽２７の濃縮汚泥は、ポンプｐ３によって酸発酵槽４０へ送られる。酸発酵槽４０に導入された濃縮汚泥は、槽内に設けられた攪拌機４０ａによって効率よく撹拌される。そして、濃縮汚泥中の有機物は、槽内を滞留しながら酸生成菌による嫌気性発酵によって有機酸に変化する。なお、このとき、槽内で滞留する濃縮汚泥の酸化還元電位は、−５０ｍＶ〜−２３ｍＶであることが好ましい。そして、生成した有機酸を含む上澄みは、酸発酵槽４０の上部から、発酵汚泥として沈殿槽４３に送られる。   Thereafter, the concentrated sludge in the concentrated sludge tank 27 is sent to the acid fermentation tank 40 by the pump p3. The concentrated sludge introduced into the acid fermentation tank 40 is efficiently stirred by a stirrer 40a provided in the tank. And the organic substance in concentrated sludge changes to an organic acid by the anaerobic fermentation by an acid producing microbe, staying in the tank. At this time, the redox potential of the concentrated sludge staying in the tank is preferably -50 mV to -23 mV. And the produced | generated supernatant containing the organic acid is sent to the sedimentation tank 43 from the upper part of the acid fermentation tank 40 as fermentation sludge.

ここで、酸発酵槽４０内で生成した有機酸の一部は、槽内のメタン菌によって更にメタンに分解されてしまう。ところが、この有機酸生成システム１０においては、酸発酵槽４０に導入される前の生汚泥或いは濃縮汚泥が、生汚泥曝気撹拌槽１１、加圧浮上濃縮装置１３及び濃縮汚泥槽２７の３段階で酸素雰囲気とされている。従って、酸素雰囲気に曝された汚泥中のメタン菌が減少し、メタン菌の活性が低く抑えられた状態の濃縮汚泥が酸発酵槽４０に導入されることになる。よって、酸発酵槽４０内におけるメタン菌の活性が低く抑えられ、槽内でメタンに分解される有機酸も少なく抑えられる。その結果、酸発酵槽４０内において、高い生成効率で有機酸が得られる。   Here, a part of the organic acid generated in the acid fermentation tank 40 is further decomposed into methane by the methane bacteria in the tank. However, in this organic acid generation system 10, raw sludge or concentrated sludge before being introduced into the acid fermentation tank 40 is divided into three stages of the raw sludge aeration and agitation tank 11, the pressurized flotation concentration apparatus 13 and the concentrated sludge tank 27. The atmosphere is oxygen. Therefore, the methane bacteria in the sludge exposed to the oxygen atmosphere is reduced, and the concentrated sludge in a state where the activity of the methane bacteria is kept low is introduced into the acid fermentation tank 40. Therefore, the activity of methane bacteria in the acid fermentation tank 40 is kept low, and the organic acid decomposed into methane in the tank is also kept low. As a result, an organic acid is obtained with high production efficiency in the acid fermentation tank 40.

次に、沈殿槽４３に送られた発酵汚泥は沈降分離され、上澄みが有機酸貯留槽４５に送られ、分離された固体成分は一部が酸発酵槽４０に返送され、残りは余剰汚泥として排出される。そして、有機酸貯留槽４５に貯留された液体は、有機酸を含んでおり、ラインＬ３を通じて上述した生物処理槽３の嫌気槽３ａに有機源として供給され、生物処理槽３における下水の生物的処理に寄与する。   Next, the fermented sludge sent to the settling tank 43 is settled and separated, the supernatant is sent to the organic acid storage tank 45, a part of the separated solid component is returned to the acid fermenter 40, and the rest as surplus sludge. Discharged. The liquid stored in the organic acid storage tank 45 contains organic acid, and is supplied as an organic source to the anaerobic tank 3a of the biological treatment tank 3 described above through the line L3. Contributes to processing.

本発明は、前述した実施形態に限定されるものではない。例えば、上記実施形態における加圧浮上濃縮装置１３では、生汚泥の全量を加圧槽１３ａで加圧して加圧浮上槽１３ｂに供給する全量加圧法を採用しているが、生汚泥の一部のみを加圧する部分加圧法や、加圧していない生汚泥を加圧した水と一緒に加圧浮上槽１３ｂに供給する循環加圧法を採用してもよい。また、酸発酵槽４０への導入前に生汚泥を処理するためには、加圧浮上濃縮装置１３のみがあればよく、生汚泥曝気撹拌槽１１及び濃縮汚泥槽２７は省略してもよい。また、生汚泥曝気撹拌槽１１及び濃縮汚泥槽２７においては、汚泥中に空気を送り込んでいるが、酸素を送り込んで汚泥の曝気を行ってもよい。   The present invention is not limited to the embodiment described above. For example, the pressurized flotation concentration apparatus 13 in the above embodiment employs a full pressure method in which the entire amount of raw sludge is pressurized in the pressure tank 13a and supplied to the pressurized flotation tank 13b. Alternatively, a partial pressurizing method in which only the pressure is applied, or a circulating pressurizing method in which unstressed raw sludge is supplied to the pressurized flotation tank 13b together with pressurized water may be employed. Moreover, in order to process raw sludge before introduction into the acid fermentation tank 40, only the pressurized flotation concentration device 13 is required, and the raw sludge aeration and agitation tank 11 and the concentrated sludge tank 27 may be omitted. In the raw sludge aeration and agitation tank 11 and the concentrated sludge tank 27, air is sent into the sludge, but oxygen may be sent to aerate the sludge.

本発明に係る有機酸生成システムの実施形態を示す概要図である。1 is a schematic diagram showing an embodiment of an organic acid generation system according to the present invention.

符号の説明Explanation of symbols

１…下水処理設備、５…最初沈殿池、１０…有機酸生成システム、１１…生汚泥曝気撹拌槽（前曝気槽）、１３…加圧浮上濃縮装置（濃縮装置）、２７…濃縮汚泥槽（後曝気槽）、４０…酸発酵槽。   DESCRIPTION OF SYMBOLS 1 ... Sewage treatment equipment, 5 ... First sedimentation basin, 10 ... Organic acid production system, 11 ... Raw sludge aeration and stirring tank (pre-aeration tank), 13 ... Pressurized flotation concentration apparatus (concentration apparatus), 27 ... Concentration sludge tank ( Post-aeration tank), 40 ... acid fermentation tank.

Claims (6)

下水から得られる汚泥を嫌気性発酵させて有機酸を生成する有機酸生成方法において、
前記下水の沈殿物である生汚泥を濃縮し濃縮汚泥を得る濃縮ステップと、
前記濃縮ステップで得られた前記濃縮汚泥を嫌気性発酵させて前記有機酸を得る発酵ステップと、を備え、
前記濃縮ステップでは、加圧浮上濃縮法によって前記生汚泥の濃縮が行われることを特徴とする有機酸生成方法。 In an organic acid production method for producing an organic acid by anaerobic fermentation of sludge obtained from sewage,
A concentration step of concentrating raw sludge, which is a precipitate of the sewage, to obtain concentrated sludge;
Anaerobic fermentation of the concentrated sludge obtained in the concentration step to obtain the organic acid, and
In the concentration step, the raw sludge is concentrated by a pressurized flotation concentration method. 前記生汚泥を、前記濃縮ステップの前に曝気する前曝気ステップを更に備えることを特徴とする請求項１に記載の有機酸生成方法。   The organic acid generation method according to claim 1, further comprising a pre-aeration step in which the raw sludge is aerated before the concentration step. 前記濃縮ステップで得られた前記濃縮汚泥を、前記発酵ステップの前に曝気する後曝気ステップを更に備えることを特徴とする請求項１又は２に記載の有機酸生成方法。   The organic acid production method according to claim 1 or 2, further comprising a post-aeration step in which the concentrated sludge obtained in the concentration step is aerated before the fermentation step. 下水から得られる汚泥を嫌気性発酵させて有機酸を生成する有機酸生成システムにおいて、
前記下水の沈殿物である生汚泥を濃縮し濃縮汚泥を得る濃縮装置と、
前記濃縮装置で得られた前記濃縮汚泥を嫌気性発酵させて前記有機酸を得る酸発酵槽と、を備え、
前記濃縮装置は、加圧浮上濃縮装置であることを特徴とする有機酸生成システム。 In an organic acid production system that produces an organic acid by anaerobic fermentation of sludge obtained from sewage,
A concentrating device for concentrating raw sludge that is the sediment of the sewage to obtain concentrated sludge;
An acid fermentor for anaerobically fermenting the concentrated sludge obtained by the concentrator to obtain the organic acid,
The organic acid generating system, wherein the concentrating device is a pressurized flotation concentrating device. 前記生汚泥を、前記濃縮装置に導入する前に曝気する前曝気槽を更に備えることを特徴とする請求項４に記載の有機酸生成システム。   The organic acid generation system according to claim 4, further comprising a pre-aeration tank for aeration of the raw sludge before introduction into the concentrator. 前記濃縮装置で得られた前記濃縮汚泥を、前記酸発酵槽に導入する前に曝気する後曝気槽を更に備えることを特徴とする請求項４又は５に記載の有機酸生成システム。   6. The organic acid generation system according to claim 4, further comprising a post-aeration tank in which the concentrated sludge obtained by the concentration apparatus is aerated before being introduced into the acid fermentation tank.
JP2005291203A 2005-10-04 2005-10-04 Method and system for producing organic acid Pending JP2007098271A (en)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0731998A (en) * 1993-07-13 1995-02-03 Ebara Res Co Ltd Slightly anaerobic hydrogen fermentation method for organic waste
JPH0889991A (en) * 1994-09-26 1996-04-09 Mitsubishi Heavy Ind Ltd Treatment of waste water
JPH08238499A (en) * 1995-03-06 1996-09-17 Kubota Corp Treating method for excess sludge
JP2005161110A (en) * 2003-11-28 2005-06-23 Sumitomo Heavy Ind Ltd Method and apparatus for treating organic sludge

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0731998A (en) * 1993-07-13 1995-02-03 Ebara Res Co Ltd Slightly anaerobic hydrogen fermentation method for organic waste
JPH0889991A (en) * 1994-09-26 1996-04-09 Mitsubishi Heavy Ind Ltd Treatment of waste water
JPH08238499A (en) * 1995-03-06 1996-09-17 Kubota Corp Treating method for excess sludge
JP2005161110A (en) * 2003-11-28 2005-06-23 Sumitomo Heavy Ind Ltd Method and apparatus for treating organic sludge

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