JP6662424B2 - Anaerobic digestion method and apparatus for sewage sludge - Google Patents
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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
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Description
本発明は下水処理汚泥を嫌気性消化処理する方法及び装置に係り、特にメタンガス等の資源ガスの発生量を多くすることができる下水処理汚泥の嫌気性消化方法及び装置に関する。 The present invention relates to a method and an apparatus for anaerobic digestion of sewage sludge, and more particularly to a method and an apparatus for anaerobic digestion of sewage sludge that can increase the generation of resource gas such as methane gas.
下水処理場には、流入する汚水に含まれる固形物を沈殿させる最初沈澱池、好気性微生物の活動によって水中の有機物を浄化するエアタンク（曝気槽）、エアタンクで浄化が終わった汚泥混合水を沈殿処理して好気性微生物を含んだ汚泥フロックを回収すると共に清澄水を得るための最終沈澱池が設けられるのが一般的である。 The sewage treatment plant has an initial sedimentation basin that sediments solids contained in incoming sewage, an air tank (aeration tank) that purifies organic matter in the water by the activity of aerobic microorganisms, and sedimentation of sludge mixed water that has been purified by the air tank. In general, a sludge floc containing aerobic microorganisms is recovered by treatment, and a final sedimentation basin for obtaining clear water is provided.
最初沈澱池で沈殿した汚泥を初沈汚泥（または生汚泥）と呼ぶ。この初沈汚泥は、水処理系において再利用されることがなく、適宜、系外に排出される。 Sludge initially settled in the sedimentation basin is called initial settled sludge (or raw sludge). This initial settled sludge is not reused in the water treatment system, but is appropriately discharged outside the system.
最終沈澱池で沈殿した汚泥の一部は、エアタンクに返送され再度利用されるが、余剰の汚泥は適宜、系外に排出される。この排出する汚泥を、余剰汚泥と呼ぶ。 Part of the sludge settled in the final sedimentation basin is returned to the air tank and reused, but excess sludge is discharged to the outside of the system as appropriate. This discharged sludge is called excess sludge.
初沈汚泥や余剰汚泥は、重力濃縮槽や機械濃縮装置によってその濃度を高めた後、脱水機に送られ、脱水処理によって水分量を低減せしめたあと、焼却されたり、埋め立てされたり、また農地還元に用いられたりする。 Primary sludge and surplus sludge are sent to a dehydrator after their concentration is increased by gravity concentration tanks and mechanical concentrators, and after being reduced in water content by dehydration treatment, they are incinerated, landfilled, or farmland. It is used for reduction.
初沈汚泥や余剰汚泥を減容させるために、嫌気性消化槽を設置し、嫌気性微生物の活動によって汚泥の分解を行ない、減容させることも行われている。この嫌気性消化槽では、有機物の分解によって消化ガス（炭酸ガスやメタンガス）が発生する。このメタンガスは可燃性であり、かつカロリーが高いことから、ボイラーの燃料に用いられたり、発電機に供給して発電用の燃料として利用されたり、ガスを精製して販売されることもある。 In order to reduce the volume of primary sludge and excess sludge, an anaerobic digestion tank is installed, and sludge is decomposed by the activity of anaerobic microorganisms to reduce the volume. In this anaerobic digestion tank, digestion gas (carbon dioxide gas or methane gas) is generated by decomposition of organic matter. Since methane gas is flammable and has high calories, it is sometimes used as fuel for boilers, used as a fuel for power generation by supplying it to a generator, or sold after purifying gas.
嫌気性消化槽は、その環境を整えることで大量の有機物を処理することが可能であるが、その活動は緩やかであり、有機物消費には時間を要する。これは、嫌気性微生物は、好気性微生物のように取り込んだ有機物を自身で水と炭酸にまで分解するのではなく、嫌気性消化槽内の嫌気性消化工程には複数の段階（嫌気プロセス）があり、それぞれの工程を担う微生物群が混在し、消化工程は、分解副生成物をリレーしながら分解する連鎖系で成り立っているためである。 An anaerobic digester can treat a large amount of organic matter by adjusting its environment, but its activity is slow and organic matter consumption takes time. This is because anaerobic microorganisms do not decompose organic substances taken up like aerobic microorganisms themselves into water and carbonic acid, but instead use anaerobic digestion process in anaerobic digestion tank in multiple stages (anaerobic process) This is because a group of microorganisms that carry out each step is mixed, and the digestion step is made up of a chain system that decomposes while relaying decomposition by-products.
この連鎖系では、酸生成菌による酸生成反応で、酢酸が生成する。この酢酸から、メタン生成菌によってメタンガスが生成する。 In this chain system, acetic acid is produced by an acid producing reaction by an acid producing bacterium. From this acetic acid, methane gas is generated by methane-producing bacteria.
この連鎖系の反応を速めるために、消化槽内を高温に保ち、消化速度を高めると共に、設備の小型を図ることがある。即ち、メタン生成菌（種）は、３７℃付近の中温帯又は５５℃付近の高温帯において効率よく生育する。そのため、嫌気性槽の温度を３７℃付近の中温又は５５℃付近の高温に保つことが行われている。 In order to speed up the reaction of this chain system, the inside of the digestion tank is kept at a high temperature to increase the digestion speed and the size of the equipment may be reduced. That is, methanogens (species) grow efficiently in a medium temperature zone around 37 ° C. or a high temperature zone around 55 ° C. Therefore, the temperature of the anaerobic tank is maintained at a medium temperature around 37 ° C. or a high temperature around 55 ° C.
従来は、発生したメタンガスを、この昇温のために燃焼していたが、近年では、上記のようにガスを有効利用するようになってきている。そのため、単にメタンガスを多く発生させるだけでなく、その質も求められるようになってきている。例えば、発電用のガスエンジン向けには、メタン濃度を高めたり、濃度を安定化させることが求められるようになってきている。 Conventionally, generated methane gas is burned to raise the temperature. In recent years, however, gas has been effectively used as described above. For this reason, not only methane gas is generated in a large amount, but also its quality is required. For example, for a gas engine for power generation, it has been required to increase the methane concentration or stabilize the concentration.
このようなことから、下水処理場に設置される嫌気性消化槽には、メタン生成菌の活性を安定的に高く維持することが求められる。また、嫌気性消化槽に供給する有機物の、酸生成能を高めることが求められる。メタン生成菌が高い活性を持っていたとしても、嫌気プロセスにおける前段階の酸生成工程が上手くいかないと、メタンガス発生量が期待したように得られないばかりか、リレーが滞ると嫌気プロセスが次第に悪化し、処理の長期的な不調へと繋がることがある。 For this reason, the anaerobic digestion tank installed in the sewage treatment plant is required to maintain the activity of the methanogen stably high. Further, it is required to increase the acid generating ability of the organic substance supplied to the anaerobic digestion tank. Even if the methanogen has high activity, if the previous acid generation step in the anaerobic process is not successful, not only will methane gas generation not be obtained as expected, but if the relay is delayed, the anaerobic process will gradually It may worsen and lead to a long-term processing malfunction.
嫌気性細菌の増殖はゆっくりしており、例えば汚水処理においていちど能力低下すると、菌自身の自己回復に頼った方法では、性能回復までに長い時間を要することが知られている。 It is known that the growth of anaerobic bacteria is slow. For example, once the performance is reduced in sewage treatment, it takes a long time to recover the performance by a method relying on the self-recovery of the bacteria themselves.
そのため、メタン生成菌の活性維持と共に、酸生成に関わる菌の活性を高め、嫌気プロセスを滞りなく行なわせるような管理方法が求められるようになってきている。 For this reason, a management method has been required to maintain the activity of the methane-producing bacterium, increase the activity of the bacterium involved in acid production, and perform the anaerobic process without delay.
しかしながら、従来の方法は、嫌気性消化槽のメタン生成菌の活性を良好に保つことを目的としており、これだけでは酸生成工程の安定化には繋がらず、結果として、期待したメタン発生量を得られず、発生したガス中のメタン濃度（分圧）も低い場合が多い。 However, the conventional method aims at keeping the activity of the methanogen in the anaerobic digestion tank good, and this alone does not lead to the stabilization of the acid production step, and as a result, the expected amount of methane generation is obtained. However, the methane concentration (partial pressure) in the generated gas is often low.
酸生成を効率的に行なわせるためには、処理環境を整え、連鎖に寄与する菌を十分に確保し、かつ、活性を保つ必要がある。酸生成に影響を及ぼす環境因子は、温度、時間、ｐＨなどがある。温度が適正な範囲にないと、酸生成に時間を要したり、有機物の分解が途中で停止したり、リレーが適切に行われなかったりする。また、生成した有機酸によりｐＨが下がるので、有機物量が多量に流入し、いちどに分解反応が進んだ場合にｐＨが下がり過ぎ、反応が停止することがある。 In order to efficiently generate acid, it is necessary to prepare a treatment environment, sufficiently secure bacteria contributing to linkage, and maintain the activity. Environmental factors that affect acid production include temperature, time, pH, and the like. If the temperature is not in an appropriate range, it takes time to generate an acid, decomposition of organic substances is stopped halfway, or relaying is not performed properly. In addition, since the pH is lowered by the generated organic acid, a large amount of organic matter flows in, and when the decomposition reaction proceeds at once, the pH may be too low and the reaction may be stopped.
下水処理場の嫌気性消化槽は、水処理ではなく、汚泥処理の要素が強い。水処理の場合は、水中に溶解している有機物の分解が主であるのに対し、汚泥処理の場合は水中に懸濁している有機物を分解するものであり、時間的な要素が重要である。また、水処理の場合には、酸生成とメタン発酵のプロセスを分けて、別個の反応槽を設けて行なうことが多く、また一過性で処理を行なっていることが多いのに対し、汚泥処理の場合には、１つの反応槽で連鎖反応を行なわせることが多いだけでなく、汚泥を断続的に供給する場合でも、酸生成もメタン発酵も同時並行で行なわれる混合処理であることが多い。このため、消化槽に供給する汚泥の状態が嫌気プロセスに影響を及ぼしていることが多い。 Anaerobic digestion tanks in sewage treatment plants have a strong element of sludge treatment rather than water treatment. In the case of water treatment, organic matter dissolved in water is mainly decomposed, whereas in the case of sludge treatment, organic matter suspended in water is decomposed, and the time factor is important. . In addition, in the case of water treatment, the acid production and methane fermentation processes are separated and often performed in separate reaction tanks. In the case of treatment, a chain reaction is often performed in one reaction tank, and even when sludge is intermittently supplied, a mixed treatment in which both acid generation and methane fermentation are performed simultaneously and in parallel. Many. For this reason, the state of the sludge supplied to the digester often affects the anaerobic process.
例えば、消化槽内は３５℃付近や５５℃付近の温度に制御されていることが多い。これに対して、供給する汚泥の温度は、夏場では３０℃近くまでなることもあるが、冬場には１５℃を切ってしまうこともある。１５℃では、汚泥消化に関わる嫌気性細菌群の活動は、著しく低下する。特に、槽内を５５℃で管理する高温消化槽では、その活性を活かして汚泥の槽内滞留時間はより短く、５日間から長くても１０日間で管理されることが多いが、これはすなわち、槽内にある汚泥量に対して１／５〜１／１０量を供給していることになる。実際には、消化槽で汚泥が減容していくため、仮に１／５量を供給した場合でも実は１／３量を供給したのと同じことになる。そうすると、５５℃の汚泥２重量部に対し、１５℃の汚泥１重量部を供給することになるので、供給した汚泥の周辺は供給した直後に急激な温度低下が起こることになる。 For example, the inside of the digestion tank is often controlled to a temperature around 35 ° C. or around 55 ° C. On the other hand, the temperature of the supplied sludge may be close to 30 ° C. in summer, but may be lower than 15 ° C. in winter. At 15 ° C., the activity of anaerobic bacteria involved in sludge digestion is significantly reduced. In particular, in a high-temperature digestion tank in which the inside of the tank is controlled at 55 ° C., the residence time of the sludge in the tank is shorter, taking advantage of its activity, and is often controlled in 5 days to as long as 10 days. In other words, 1/5 to 1/10 of the amount of sludge in the tank is supplied. Actually, since the sludge volume is reduced in the digestion tank, even if a 1/5 volume is supplied, it is actually the same as supplying a 1/3 volume. Then, 1 part by weight of the sludge at 15 ° C. is supplied for 2 parts by weight of the sludge at 55 ° C., so that the temperature around the supplied sludge drops rapidly immediately after the supply.
このため、消化槽内に存在する菌が十分な活性をもっていないと、有機物の分解能が不安定になり、あるいは低下し、嫌気プロセスが壊れる可能性もある。したがって、供給する汚泥の温度が低い場合には、消化槽内に存在する菌の活性をより高める必要がある。 For this reason, if the bacteria present in the digestion tank do not have sufficient activity, the resolution of the organic matter may be unstable or reduced, and the anaerobic process may be broken. Therefore, when the temperature of the supplied sludge is low, it is necessary to further increase the activity of the bacteria present in the digestion tank.
また、嫌気性消化槽へ供給する汚泥は、下水管→最初沈澱池→汚泥濃縮槽（装置）の経路を通って流入する。この間、酸素の少ない環境に長時間晒され、流入までに接した、あるいは、下水中に入り込んだ嫌気性細菌により分解を受けていることもある。このような場合には、消化槽での有機物分解反応及びメタン発生反応はスムーズに進行する。しかしながら、この分解は、いわば成り行きで起きたことであり、人的な関与によって制御されたものではないため、様々な因子により変化する。前述のように、嫌気性消化槽内での汚泥の滞留時間は、数日〜長くても十数日でしかない。このため、予め有機酸分解を受けた汚泥が供給されているときに形成された菌相に、突然、有機酸分解を受けていない汚泥が供給されると、嫌気プロセスに支障が起き、メタン生成能が低下する。したがって、供給する汚泥の有機酸分解が進んでいない場合には、消化槽内に存在する菌の活性をより高める必要がある。 Sludge to be supplied to the anaerobic digestion tank flows through a route of a sewer pipe → first sedimentation tank → sludge concentration tank (equipment). During this time, it may be exposed to an oxygen-poor environment for a long time and be degraded by anaerobic bacteria that have come into contact with the inflow or have entered the sewage. In such a case, the organic matter decomposition reaction and the methane generation reaction in the digestion tank proceed smoothly. However, since this decomposition occurs as it were, and is not controlled by human involvement, it varies depending on various factors. As described above, the residence time of sludge in the anaerobic digestion tank is only several days to at most ten and several days. For this reason, if sludge that has not been subjected to organic acid decomposition is suddenly supplied to the flora formed when sludge that has been subjected to organic acid decomposition is supplied in advance, the anaerobic process will be hindered, and methane generation will occur. Performance is reduced. Therefore, when the organic acid decomposition of the supplied sludge has not progressed, it is necessary to further increase the activity of the bacteria existing in the digestion tank.
以上のように、下水処理場の嫌気性消化槽での処理プロセスには特有の性質がある。そのため、メタン発生までのプロセスを安定して行わせるためには、（１）嫌気性消化槽に供給する汚泥スラリーの温度変化を測定し、それが低いときには対策を講じて菌の活性を維持させること、（２）嫌気性消化槽に供給する汚泥スラリーの分解進行状況を把握し、それが低いときには対策を講じて菌の活性を維持させることが、メタンガス生成量を高め、かつ濃度（分圧）を高めるために必要となるが、これまでこうした点に着目して管理を試みた例はなかった。さらに、メタン生成菌の菌種を、より能力の高い菌種＝Ｍｅｔｈａｎｏｓａｒｃｉｎａに移行させることが求められている。 As described above, the treatment process in the anaerobic digestion tank of the sewage treatment plant has unique properties. Therefore, in order to stably perform the process up to the generation of methane, (1) the temperature change of the sludge slurry supplied to the anaerobic digestion tank is measured, and when it is low, measures are taken to maintain the activity of the bacteria. (2) It is necessary to grasp the progress of decomposition of the sludge slurry supplied to the anaerobic digestion tank, and take measures to maintain the activity of the bacterium when it is low, thereby increasing the amount of methane gas generated and increasing the concentration (partial pressure). ), But no management has ever attempted to focus on these points. Further, there is a demand for transferring the species of methanogens to a more capable species = Methanosarcina.
特開平４−３００６９８及び特開平３−１５４６９２（特許文献１，２）には、下水、産業廃水、汚泥等の有機性廃水を嫌気性処理する方法において、嫌気性リアクタに導入される廃水に栄養塩類溶液として窒素化合物、リン酸化合物、ニッケル化合物又はコバルト化合物の溶液を廃水中の有機物濃度と処理水中の有機物濃度とに応じて添加することが記載されている。 JP-A-4-300698 and JP-A-3-154692 (Patent Literatures 1 and 2) disclose, in a method for anaerobically treating organic wastewater such as sewage, industrial wastewater, and sludge, nutrients added to wastewater introduced into an anaerobic reactor. It is described that a solution of a nitrogen compound, a phosphoric acid compound, a nickel compound or a cobalt compound is added as a salt solution according to the organic matter concentration in the wastewater and the organic matter concentration in the treated water.
特開平３−１６５８９５（特許文献３）には、有機性廃液にニッケル、鉄、コバルトを添加してメタン発酵処理することが記載されている。 JP-A-3-165895 (Patent Document 3) discloses that methane fermentation treatment is performed by adding nickel, iron, and cobalt to an organic waste liquid.
特開平１１−２８４４５（特許文献４）には、生ゴミ、厨芥や、農水産廃棄物などの事業系ゴミを解破砕した後、塩化第一鉄などの鉄化合物、塩化ニッケルなどのニッケル化合物、塩化コバルトなどのコバルト化合物の少なくとも１種よりなる栄養塩類を添加し、５５〜６０℃で撹拌してメタン発酵処理することが記載されている。 Japanese Patent Application Laid-Open No. 11-28445 (Patent Document 4) discloses that, after crushing business-related garbage such as garbage, kitchen garbage, and agricultural and marine waste, an iron compound such as ferrous chloride, a nickel compound such as nickel chloride, It describes that a methane fermentation treatment is carried out by adding a nutrient consisting of at least one cobalt compound such as cobalt chloride and stirring at 55 to 60 ° C.
なお、嫌気性処理装置に対して、カルシウム化合物又は鉄塩を添加する方法が、特許第３３８７２４１（特許文献５）、及び特許第３８１４８５１（特許文献６）に記載されている。 In addition, the method of adding a calcium compound or an iron salt to an anaerobic treatment apparatus is described in Japanese Patent No. 387241 (Patent Document 5) and Japanese Patent No. 3814851 (Patent Document 6).
しかしながら、特許文献５，６は、いずれもグラニュール汚泥で形成されたスラッジブランケットに有機性排水を上向流通水する方法に関するものであり、本発明とはカルシウム化合物又は鉄塩の添加対象が異なる。また、特許文献３，４は、グラニュール内部の空隙にＣａＣＯ３又はＦｅＳを生成させて充填することでグラニュールの沈降性を高め、グラニュールの浮上流出を防止することを目的とするものであって、本発明方法とはカルシウム化合物又は鉄塩の作用が異なる。
However,
前述のように、嫌気性消化槽において発生したメタンガスが有効利用されるようになり、メタンガス発生量を効率的に増やすことに加えて、メタン濃度を高めること、及びメタンの濃度を安定化させることが求められるようになってきた。 As described above, the methane gas generated in the anaerobic digestion tank will be used effectively, and in addition to increasing the amount of methane gas generated efficiently, increasing the methane concentration and stabilizing the methane concentration Has been required.
ところが、従来より採用されている、嫌気性消化槽の温度をメタン生成菌の温度帯（３５℃付近又は５５℃付近）に合わせる方法は、消化を促進して汚泥減容率を高めることを主目的としていることから、トータルでのメタンガス発生量を高めることはできても、メタンガスの濃度（分圧）を高めることはできなかった。 However, the conventional method of adjusting the temperature of the anaerobic digestion tank to the temperature zone of methanogens (around 35 ° C. or 55 ° C.) mainly promotes digestion and increases the sludge volume reduction rate. Because of the purpose, although the total amount of methane gas generated could be increased, the concentration (partial pressure) of methane gas could not be increased.
この理由としては、以下の２つがある。
（１）メタン生成菌は、前述の連鎖系の最後に活動する菌である。メタン生成菌は、適性温度帯が限られていることに見られるように、生物学的に劣勢の菌であり、増殖速度も他の細菌に比較すると小さい。嫌気性消化槽を高温にすることで嫌気性細菌の活動が活発になり、消化速度が高められる。しかしながら、消化タンク（嫌気性消化槽）への汚泥の供給量を増加させると、嫌気性消化槽内での汚泥の滞留時間が短くなるためメタン生成菌の増殖が間に合わず、結果として期待したよりもメタンガスが生成しないことがある。例えば、消化タンクへの汚泥投入量が増えたとき、メタン生成菌の酢酸摂取量が低下すると、連鎖系における有機酸の受け渡しが滞り、系内に有機酸が残存することで有機酸生成に関わる菌の活性が低下することがある。また、有機酸生成に伴うｐＨ低下で菌の活性が低下して、結果としてメタン濃度もメタン生成量も低下することがある。このように、温度による制御だけでは、投入汚泥量が変化し消化タンクの負荷変動があるときにメタンガスの発生量が安定しない。
（２）下水汚泥処理系におけるメタン生成菌には、主に次の２種がいる。
（ｉ） Ｍｅｔｈａｎｏｓａｅｔａ（糸状菌）
（ii） Ｍｅｔｈａｎｏｓａｒｃｉｎａ（分散菌）
これらは形状（形態）が異なるだけでなく、次のような性質が報告されている。
There are two reasons for this.
(1) Methanogenic bacteria are the last active bacteria in the above-mentioned chain system. Methanogens are biologically inferior bacteria, as evidenced by their limited aptitude temperature zone, and have a slower growth rate than other bacteria. By raising the temperature of the anaerobic digestion tank, the activity of anaerobic bacteria is increased, and the digestion speed is increased. However, when the amount of sludge supplied to the digestion tank (anaerobic digestion tank) is increased, the residence time of the sludge in the anaerobic digestion tank is shortened, so that the growth of methanogens cannot be made in time, and as a result, May not produce methane gas. For example, when the sludge input to the digestion tank increases, if the acetic acid intake of the methanogen decreases, the delivery of the organic acid in the chain system is delayed, and the organic acid remains in the system and is involved in organic acid generation. Bacterial activity may decrease. In addition, the activity of the bacterium may be reduced due to a decrease in pH accompanying the production of the organic acid, and as a result, both the methane concentration and the methane production may be reduced. As described above, only by the control based on the temperature, the amount of methane gas generated becomes unstable when the amount of input sludge changes and the load of the digestion tank fluctuates.
(2) There are mainly two types of methanogens in the sewage sludge treatment system.
(I) Methanosaeta (filamentous fungus)
(Ii) Methanosarcina (dispersed bacteria)
These not only differ in shape (form), but also the following properties are reported.
糸状菌：酢酸利用速度８ｋｇ／ｍ３−日、 消化必要日数２０日程度
分散菌：酢酸利用速度３０ｋｇ／ｍ３−日、 消化必要日数５日程度
したがって、分散菌を優占種として繁殖させることができれば、前記（１）のような環境変化・変動に対しても対応できるが、下水汚泥を「餌」とした処理環境では、糸状菌が多数であることが、数々の現場調査、研究によって判っている。
Filamentous fungi: acetic acid utilization rate of 8 kg / m 3 -day, required digestion time about 20 days Dispersed bacteria: acetic acid utilization rate of 30 kg / m 3 -day, required digestion time of about 5 days If it is possible, it can respond to environmental changes and fluctuations as described in (1) above. However, in a treatment environment where sewage sludge is used as “feed”, it has been confirmed by numerous field surveys and studies that there are a large number of filamentous fungi. I know.
なお、有機性排水を嫌気性反応槽に上向流通水して処理する、ＵＡＳＢ法（Ｕｐｆｌｏｗ Ａｎａｅｒｏｂｉｃ Ｓｌｕｄｇｅ Ｂｌａｎｋｅｔ：上向流式嫌気性汚泥床）や、ＥＧＳＢ法（Ｅｘｐａｎｄｅｄ Ｇｒａｎｕｌａｒ Ｓｌｕｄｇｅ Ｂｅｄ：グラニュール汚泥膨張床）では、嫌気性細菌がグラニュールを形成して菌の充填密度を高め、かつ、上向流速よりも大きい沈降速度を持って流出しないようにするために、糸状菌を優占種として繁殖させることが試みられているが、本発明で対象としている嫌気性消化槽ではむしろ分散菌が優占種である方が好ましい。 The UASB method (Upflow Anaerobic Sludge Blanket: Upflow type anaerobic sludge bed) and the EGSB method (Expanded Granular Sludge: Granular sludge) in which organic wastewater is treated by flowing upward water to an anaerobic reactor. In the case of an expanded bed, anaerobic bacteria form granules to increase the packing density of the bacteria and prevent them from flowing out with a sedimentation velocity greater than the upward flow velocity. Although breeding has been attempted, it is preferable that the disperse bacteria be the dominant species in the anaerobic digester targeted by the present invention.
ＵＡＳＢ法やＥＧＳＢ法においても実際は、生成したグラニュールの中心部は糸状菌が優占種となって“粒子”を形成しているが、表面に近い層には分散菌が多く存在することが、数多くの実機調査や学術的研究及び実験で判っている。 In the UASB method and the EGSB method, filamentous fungi are dominant in the center of the generated granules to form “particles”. However, there are many disperse bacteria in the layer near the surface. Has been found in a number of actual equipment surveys, academic studies and experiments.
前述のように、下水処理場の嫌気性消化槽の中に存在する主なメタン生成菌には、Ｍｅｔｈａｎｏｓａｅｔａ（糸状菌）、Ｍｅｔｈａｎｏｓａｒｃｉｎａ（分散菌）の２種がある。糸状菌よりも酢酸利用速度が大きい分散菌を優先種とすることにより、嫌気性消化反応が早くなり、生成する消化ガス中のメタンガス濃度も高くなるが、従来の嫌気性消化槽では糸状菌が優先種となりがちである。この理由の一つとして、分散菌の世代寿命が短いことが挙げられる。いちど分散菌の生殖／増殖のバランスを崩してしまうと分散菌が劣勢種となってしまう。特に、嫌気性消化槽への投入汚泥量が多い場合には、分散菌が槽から押し出されてますます菌数が少なくなり、前述したようにメタン生成が律速となって有機物のリレーが滞ってしまう。 As described above, there are two main methanogens present in the anaerobic digestion tank of a sewage treatment plant: Methanosaeta (filamentous fungi) and Methanosaarcina (dispersed bacteria). Anaerobic digestion reaction is accelerated and the methane gas concentration in the generated digestion gas is increased by using the dispersed bacteria having a higher acetic acid utilization rate than the filamentous fungi as the priority species. Tends to be a preferred species. One of the reasons is that the generation life of the dispersed bacteria is short. Once the reproduction / proliferation balance of the dispersed bacteria is disrupted, the dispersed bacteria become the inferior species. In particular, when the amount of sludge fed into the anaerobic digestion tank is large, the number of dispersed bacteria is pushed out of the tank and the number of bacteria is reduced, and as described above, methane production is rate-limiting, and the relay of organic substances is delayed. I will.
糸状菌が優占種となり易いもう一つの理由として、Ｆｅ，Ｎｉ，Ｃｏ等の添加物が不足して分散菌の活性が低下することが挙げられる。このような添加物が不足して有機酸リレープロセスが停滞していたり、酢酸消費速度が低下して活性の落ちていた環境にＦｅ，Ｎｉ，Ｃｏ等の添加物を添加することにより分散菌が優占種にシフトし、メタン生成量及びメタン生成速度が増加する。前述のように、分散菌は世代寿命が短いことから、Ｆｅ，Ｎｉ，Ｃｏ等の要求量が糸状菌のそれよりも多く、したがって不足すると糸状菌が優占種となってしまう。 Another reason that filamentous fungi tend to be the dominant species is that the activity of dispersed bacteria is reduced due to the lack of additives such as Fe, Ni, and Co. By adding additives such as Fe, Ni, and Co to an environment where the organic acid relay process is stagnant due to lack of such additives or the activity of acetic acid is reduced due to a decrease in acetic acid consumption rate, disperse bacteria can be obtained. Shift to dominant species, increasing methane production and methane production rate. As described above, since the dispersed bacteria have a short generation life, the required amount of Fe, Ni, Co, etc. is larger than that of the filamentous fungi.
嫌気性細菌は、好気性細菌と異なり菌体の増殖速度がそれほど速くないため、好気性細菌で要求されるような、大量の窒素成分を要求しない。一方、前述のように嫌気性細菌は有機物の分解をリレーして行なうが、これは逆説すれば分解できる有機物の種類が限られている、すなわち、菌自身の持つ分解酵素の種類が少ない，ということになる。また、よく知られているように、酵素を効率的に働かせるためにはＦｅ，Ｃｏ，Ｎｉ等の微量金属が必要とされる。 Anaerobic bacteria, unlike aerobic bacteria, do not require a large amount of nitrogen, as required by aerobic bacteria, because the growth rate of cells is not so fast. On the other hand, as described above, anaerobic bacteria relay the decomposition of organic substances, but paradoxically, the types of organic substances that can be decomposed are limited, that is, the types of degrading enzymes that the bacteria themselves have are few. Will be. As is well known, trace metals such as Fe, Co, and Ni are required for the enzyme to work efficiently.
実際の下水施設においては、このような微量金属が不足していることが多い。前述のように下水の嫌気性消化槽での汚泥の滞留時間は、水処理系での滞留時間と比較して明らかに短いので、菌体の入れ替わりが激しい。増殖が速くない嫌気性細菌でも、系内に保持されない限りは、微量金属の蓄積が期待できないので、必要量を適宜補充する必要がある。 Actual sewage facilities often lack such trace metals. As described above, the residence time of the sludge in the anaerobic digestion tank for sewage is clearly shorter than the residence time in the water treatment system, so that the cells are rapidly replaced. Even for anaerobic bacteria that do not grow rapidly, accumulation of trace metals cannot be expected unless they are retained in the system, so it is necessary to appropriately supplement the required amount.
本発明は、下水処理汚泥を嫌気性消化処理する方法及び装置において、上向流通水式反応槽ではなく、槽内撹拌・混合型の嫌気性消化槽又はそれへの供給汚泥に対し、Ｆｅ，Ｃｕ，Ｚｎ，Ｍｇ，Ｍｎ，Ｋ，Ｃａ，Ｎｉ，Ｍｏ，Ｓｅ，Ｓ，Ｖ，Ｃｒ，Ｉ及びＣｏの少なくとも１種を含む添加物を添加することにより、分散菌が優占種となるように環境を整え、メタンガス生成量を高め、かつメタンガス濃度（分圧）を高めることができる下水処理汚泥の嫌気性消化方法及び装置を提供することを目的とする。 The present invention relates to a method and an apparatus for anaerobic digestion of sewage treatment sludge, in which an upflow circulating water type reaction tank, not a stirred / mixed type anaerobic digestion tank or sludge supplied thereto, is fed with Fe, By adding an additive containing at least one of Cu, Zn, Mg, Mn, K, Ca, Ni, Mo, Se, S, V, Cr, I and Co, the disperse bacteria become the dominant species. It is an object of the present invention to provide a method and an apparatus for anaerobic digestion of sewage sludge capable of improving the environment, increasing the amount of methane gas generated, and increasing the methane gas concentration (partial pressure).
本発明の下水処理汚泥の嫌気性消化方法は、下水処理場において、最初沈澱池で沈降した初沈汚泥及び／又は生物処理反応槽から引き抜かれた余剰汚泥よりなる下水処理汚泥を、嫌気性消化槽にて嫌気性消化処理する下水処理汚泥の嫌気性消化方法において、該嫌気性消化槽に導入される汚泥又は嫌気性消化槽に、Ｆｅ，Ｃｕ，Ｚｎ，Ｍｇ，Ｍｎ，Ｋ，Ｃａ，Ｎｉ，Ｍｏ，Ｓｅ，Ｓ，Ｖ，Ｃｒ，Ｉ及びＣｏの少なくとも１種を含む添加物を添加する方法に関する。 The anaerobic digestion method for sewage sludge of the present invention is an anaerobic digestion method for sewage sludge consisting of primary sludge initially settled in a sedimentation basin and / or excess sludge drawn out from a biological treatment reaction tank in a sewage treatment plant. In the anaerobic digestion method for sewage sludge which is subjected to anaerobic digestion in a tank, the sludge introduced into the anaerobic digestion tank or the anaerobic digestion tank contains Fe, Cu, Zn, Mg, Mn, K, Ca, Ni. , Mo, Se, S, V, Cr, I and Co.
本発明方法の一態様では、前記嫌気性消化槽に導入される汚泥の温度又は前記嫌気性消化槽内の温度を測定し、この温度が所定温度よりも低いときに前記添加物を添加する。 In one aspect of the method of the present invention, the temperature of sludge introduced into the anaerobic digestion tank or the temperature in the anaerobic digestion tank is measured, and the additive is added when the temperature is lower than a predetermined temperature.
本発明方法の一態様では、前記嫌気性消化槽に導入される汚泥のｐＨ又は前記嫌気性消化槽内のｐＨを測定し、このｐＨが所定値よりも高いときに前記添加物を添加する。 In one embodiment of the method of the present invention, the pH of sludge introduced into the anaerobic digestion tank or the pH in the anaerobic digestion tank is measured, and when the pH is higher than a predetermined value, the additive is added.
本発明方法の一態様では、前記嫌気性消化槽に導入される汚泥のＯＲＰ又は前記嫌気性消化槽内のＯＲＰを測定し、このＯＲＰが所定値よりも高いときに前記添加物を添加する。 In one embodiment of the method of the present invention, the ORP of sludge introduced into the anaerobic digestion tank or the ORP in the anaerobic digestion tank is measured, and when the ORP is higher than a predetermined value, the additive is added.
本発明方法の一態様では、前記嫌気性消化槽に導入される汚泥のＭアルカリ度（酸消費量）又は前記嫌気性消化槽内のＭアルカリ度を測定し、このＭアルカリ度が所定値よりも低いときに前記添加物を添加する。 In one embodiment of the method of the present invention, M alkalinity (acid consumption) of sludge introduced into the anaerobic digestion tank or M alkalinity in the anaerobic digestion tank is measured, and the M alkalinity is higher than a predetermined value. When the additive is low.
本発明方法の一態様では、前記嫌気性消化槽に導入される汚泥の揮発性脂肪酸濃度又は前記嫌気性消化槽内の揮発性脂肪酸濃度を測定し、この揮発性脂肪酸濃度が所定値よりも低いときに前記添加物を添加する。 In one embodiment of the method of the present invention, the volatile fatty acid concentration of the sludge introduced into the anaerobic digestion tank or the volatile fatty acid concentration in the anaerobic digestion tank is measured, and the volatile fatty acid concentration is lower than a predetermined value. Sometimes the above additives are added.
本発明方法では、前記下水処理汚泥を濃縮してから前記嫌気性消化槽に導入してもよい。 In the method of the present invention, the sewage sludge may be concentrated and then introduced into the anaerobic digestion tank.
本発明の下水処理汚泥の嫌気性消化装置は、下水処理場の最初沈澱池で沈降した初沈汚泥及び／又は生物処理反応槽から引き抜かれた余剰汚泥よりなる下水処理汚泥を嫌気性消化処理する嫌気性消化槽を有する下水処理汚泥の嫌気性消化装置において、該嫌気性消化槽に導入される汚泥又は嫌気性消化槽に、Ｆｅ，Ｃｕ，Ｚｎ，Ｍｇ，Ｍｎ，Ｋ，Ｃａ，Ｎｉ，Ｍｏ，Ｓｅ，Ｓ，Ｖ，Ｃｒ，Ｉ及びＣｏの少なくとも１種よりなる添加物を添加する添加手段を備えた下水処理汚泥の嫌気性消化装置であって、前記嫌気性消化槽に導入される汚泥又は前記嫌気性消化槽内液の温度、ｐＨ,ＯＲＰ,Ｍアルカリ度及び揮発性脂肪酸濃度の少なくとも１つの水質指標値を測定する測定手段と、該測定手段で測定した少なくとも１つの水質指標値が所定範囲を逸脱したときに前記添加手段を作動させる制御手段とを備えたことを特徴とするものである。 The anaerobic digester for sewage treated sludge of the present invention anaerobically digests sewage treated sludge consisting of primary sludge settled in a first settling basin of a sewage treatment plant and / or excess sludge extracted from a biological treatment reaction tank. In an anaerobic digester for sewage sludge having an anaerobic digestion tank, sludge introduced into the anaerobic digestion tank or Fe, Cu, Zn, Mg, Mn, K, Ca, Ni, Mo is added to the anaerobic digestion tank. Anaerobic digester for sewage sludge provided with an adding means for adding an additive consisting of at least one of Se, S, V, Cr, I and Co, wherein the sludge introduced into the anaerobic digestion tank Or measuring means for measuring at least one water quality index value of the temperature, pH, ORP, M alkalinity and volatile fatty acid concentration of the solution in the anaerobic digestion tank, and at least one water quality index value measured by the measuring means. Predetermined range Is characterized in that a control means for operating said adding means when departing.
本発明では、嫌気性消化槽に導入される汚泥又は嫌気性消化槽内液の温度、ｐＨ,ＯＲＰ,Ｍアルカリ度及び揮発性脂肪酸濃度の少なくとも１つの水質指標値が所定範囲を逸脱したときに添加物を添加するので、添加物を適切に添加することができる。 In the present invention, when at least one water quality index value of the temperature, pH, ORP, M alkalinity and volatile fatty acid concentration of the sludge or anaerobic digester internal liquid introduced into the anaerobic digester deviates from a predetermined range. Since the additive is added, the additive can be appropriately added.
Ｆｅ，Ｎｉ，Ｃｏが、メタン生成菌の活性維持・向上に効果のあることは、様々な研究報告がなされている。この３種の金属に、さらにＭｎを加えると、下水処理場に設置される嫌気性消化槽内に存在している主なメタン生成菌２種Ｍｅｔｈａｎｏｓａｅｔａ、Ｍｅｔｈａｎｏｓａｒｃｉｎａの内、メタン生成速度がより高く、かつ、菌体当たりのメタンの総発生量が低い後者を優占種にシフトさせることができ、消化槽のメタンの生成能を高めることができる。 Various research reports have shown that Fe, Ni, and Co are effective in maintaining and improving the activity of methanogens. When Mn is further added to these three metals, the methane production rate is higher among the two main methanogens, Methanosaeta and Methanosarcina, present in an anaerobic digestion tank installed in a sewage treatment plant. In addition, the latter, which has a low total amount of methane generated per cell, can be shifted to the dominant species, and the methane generation capacity of the digester can be increased.
Ｃｕ，Ｚｎ，Ｍｇ，Ｋ，Ｃａ，Ｍｏ，Ｓｅ，Ｓ，Ｖ，Ｃｒ，Ｉ，の中から選ばれる元素、または、その金属塩の、いずれか１つ，または、複数を、嫌気性消化槽に供給する汚泥に予め添加・混合する、乃至は、嫌気性消化槽に直接添加することで、酸生成に関わる細菌の酵素を活性化させることができ、酸生成能を高めることができる。例えば、Ｓｅは脂質の加水分解酵素を正常働かせるために必要な触媒となり、ＣｕやＺｎはＡＴＰ生成・貯蔵に必須の元素である。 An anaerobic digester containing one or more of an element selected from Cu, Zn, Mg, K, Ca, Mo, Se, S, V, Cr, and I, or a metal salt thereof; By adding and mixing in advance to the sludge to be supplied to the anaerobic digester, or by directly adding the sludge to the anaerobic digestion tank, the enzyme of bacteria involved in acid generation can be activated, and the acid generating ability can be enhanced. For example, Se serves as a catalyst necessary for the normal operation of a lipid hydrolase, and Cu and Zn are elements essential for ATP generation and storage.
図１に示すように、本発明の好適態様においては、下水処理現場の初沈汚泥及び／又は余剰汚泥よりなる下水処理汚泥を混合槽１に導入し、添加物添加手段２によって添加物を添加する。この添加物はＦｅ，Ｃｕ，Ｚｎ，Ｍｇ，Ｍｎ，Ｋ，Ｃａ，Ｎｉ，Ｍｏ，Ｓｅ，Ｓ，Ｖ，Ｃｒ，Ｉ，及びＣｏの少なくとも１種の単体又は化合物である。添加物は、嫌気性消化槽３に添加されてもよいが、Ｆｅ等が嫌気性消化汚泥に取り込まれて沈降してしまうことがあるので、嫌気性消化槽３よりも前段側において汚泥に添加されることが好ましい。混合槽２は撹拌機２ａを備えることが好ましい。
As shown in FIG. 1, in a preferred embodiment of the present invention, sewage sludge consisting of primary sludge and / or excess sludge at a sewage treatment site is introduced into a mixing tank 1, and an additive is added by an
初沈汚泥及び／又は余剰汚泥よりなる汚泥を混合槽１に導入する前に濃縮装置によって濃縮してもよい。濃縮装置は、重力式濃縮槽であってもよく、遠心分離機などの機械的濃縮装置であってもよい。 Before introducing sludge consisting of primary sludge and / or excess sludge into the mixing tank 1, the sludge may be concentrated by a concentration device. The concentrator may be a gravity concentrator or a mechanical concentrator such as a centrifuge.
添加物が添加された汚泥を嫌気性消化槽３に導入し、必要に応じ加温し、例えば５５〜６０℃で適宜撹拌し、酸生成菌、メタン生成菌などの嫌気性微生物にて有機性廃棄物中の有機性物質をメタン発酵処理する。発生した消化ガスは消化ガス取出管４を介して取り出される。嫌気性消化槽３で消化処理することにより生じた嫌気性消化液を固液分離手段５に導入し、スクリーンや膜などによる濾過分離や沈降分離処理、遠心分離処理などにて脱水ケーキと分離液とに固液分離する。
The sludge to which the additive has been added is introduced into the anaerobic digestion tank 3 and, if necessary, heated, and appropriately stirred at, for example, 55 to 60 ° C., and organically treated with anaerobic microorganisms such as acid-producing bacteria and methane-producing bacteria. Organic matter in waste is subjected to methane fermentation. The generated digestive gas is taken out through the digestive gas take-out
固液分離により分離された液分は混合槽１に返送される。固形分については、系外に取り出し、別途処理したり、燃料、肥料、建材などの製造に有効利用する。なお、固形分の一部を混合槽１又は嫌気性消化槽３に返送してもよい。 The liquid separated by the solid-liquid separation is returned to the mixing tank 1. Solids are taken out of the system and processed separately, or used effectively for the production of fuels, fertilizers and building materials. Note that a part of the solid content may be returned to the mixing tank 1 or the anaerobic digestion tank 3.
上記の添加物のうち、金属は、可溶性の塩の顆粒、解砕物、粉末又は水溶液として添加されるのが好ましい。 Of the above additives, the metal is preferably added as a soluble salt granule, crushed product, powder or aqueous solution.
Ｓ，Ｓｅについては、単体の粉末又は顆粒として添加されてもよく、硫化物、セレン化物、硫酸塩、セレン酸塩の顆粒、粉末又は水溶液の形態で添加されてもよい。 S and Se may be added as a single powder or granules, or may be added in the form of sulfide, selenide, sulfate, or selenate granules, powder, or an aqueous solution.
Ｉについてはヨウ化物の顆粒、粉末又は水溶液の形態で添加されるのが好ましい。 I is preferably added in the form of iodide granules, powder or aqueous solution.
なお、いずれの添加物も、水溶液として添加するのが、定量添加が容易である。また、添加物が、予め水に溶かしてイオン状になっていると、該消化槽内に存在する汚泥スラリーに混合・拡散しやすいだけでなく、目的とする嫌気性細菌に取り込まれやすいので、好ましい。 In addition, it is easy to add all the additives as an aqueous solution in a quantitative manner. Further, when the additive is dissolved in water in advance and becomes ionic, not only is it easy to mix and diffuse into the sludge slurry present in the digestion tank, but it is easy to be taken up by the target anaerobic bacteria, preferable.
ＦｅやＺｎ，Ｍｇは反応性が高く、硫化物と結合して沈殿したり、リンと反応してＭＡＰなどのスケールを析出してしまうことがあるので、消化槽へ直接添加する際には注意が必要である。このようなときには、ＦｅやＺｎ，Ｍｇを消化槽に直接に添加するではなく、消化槽へ供給する汚泥に予め混合した後に消化槽へ供給することが好ましい。金属類はすべてをいちどに添加してもよいし、添加する順序を決めて順番に添加してもよいし、上記のような影響を考えて添加する場所を変えてもよい。 Fe, Zn, and Mg are highly reactive and can precipitate and combine with sulfides or react with phosphorus to precipitate scales such as MAP. is necessary. In such a case, it is preferable that Fe, Zn, and Mg are not added directly to the digestion tank, but are mixed in advance with sludge to be supplied to the digestion tank and then supplied to the digestion tank. The metals may be added all at once, may be added in a predetermined order, or may be added at different locations in consideration of the above-described effects.
どの添加物が効果的であるかは、予め消化槽内の汚泥スラリーと消化槽に投入される汚泥とを混ぜた試料に添加物を添加して適正な温度の下で数日間放置し（このとき、撹拌装置によって連続、または、間欠的に緩速撹拌すると、より好ましい）、発生したガス量、メタンガス濃度（分圧）を測定する試験を行なって決めることができる。どの添加物が不足しているかは、投入汚泥が流入するまでの履歴によって異なり、季節によっても異なるので、予め上記試験を行なって決定するのが好ましい。 Which additive is effective is determined by adding the additive to a sample in which the sludge slurry in the digestion tank and the sludge to be fed into the digestion tank are mixed in advance, and allowing the mixture to stand at an appropriate temperature for several days. At this time, it is more preferable that the stirring is performed continuously or intermittently with a stirring device at a slow speed. Which additive is in shortage depends on the history up to the inflow of the input sludge, and varies depending on the season. Therefore, it is preferable to determine the additive by performing the above test in advance.
適正添加量は、この試験において条件を種々変更することにより調べることもできる。なお、投入汚泥の全固形物質の重量当たり１％を超えない範囲であれば、仮に添加物が適正量よりも過剰添加されても、菌の活性には影響は出ない。 The appropriate addition amount can also be examined by changing the conditions in this test in various ways. In addition, as long as the amount does not exceed 1% based on the weight of the total solid substance of the input sludge, even if the additive is added in excess of an appropriate amount, the activity of the bacteria is not affected.
このように添加物は１種のみ添加されてもよく、２種以上添加されてもよい。上記添加率範囲内で複数の添加物を添加するようにしてもよい。２種以上添加する場合、各添加物を混合して添加してもよく、同時に別々に添加してもよく、添加時期を異ならせて別々に添加してもよい。 As described above, only one type of additive may be added, or two or more types may be added. A plurality of additives may be added within the above-mentioned addition rate range. When two or more kinds are added, the respective additives may be mixed and added, may be added separately at the same time, or may be added separately at different addition times.
前述のように、嫌気性消化槽に供給する汚泥スラリーの温度が下がると、消化槽に流入したときに局所的な温度低下を生み、嫌気性細菌の活性が低下する。このとき、必要な元素が供給されていれば、活性度低下は最小限に抑えることができる。また、嫌気性消化槽に供給する汚泥の温度が下がっていると、下水管→最初沈澱池→汚泥濃縮槽（装置）の経路を通ってくる際に、分解を受けていないことが予想される。一般に、２５℃を下回ると、嫌気性細菌の活性は著しく低下する。 As described above, when the temperature of the sludge slurry supplied to the anaerobic digestion tank decreases, a local temperature decrease occurs when the sludge slurry flows into the digestion tank, and the activity of the anaerobic bacteria decreases. At this time, if the necessary elements are supplied, the decrease in activity can be minimized. If the temperature of the sludge supplied to the anaerobic digestion tank is lowered, it is expected that the sludge will not be decomposed when passing through the route of sewer pipe → first settling tank → sludge thickening tank (equipment). . Generally, below 25 ° C., the activity of anaerobic bacteria is significantly reduced.
そこで、本発明では、嫌気性消化槽３に導入される汚泥の温度（例えば混合槽１内の汚泥の温度）、又は嫌気性消化槽３内の液の温度を測定し、この温度が所定値（温度）よりも低いときに添加物を添加するようにしてもよい。この場合、検出温度と該所定値との差が大きくなるほど、添加物の添加量を多くするのが好ましい。温度の閾値には制限はなく、その処理場，処理設備に合った値で、自由に設定することができるが、一般的な下水処理場の嫌気性消化槽供給汚泥の場合には、おおむね１７℃が目安となる。 Therefore, in the present invention, the temperature of the sludge introduced into the anaerobic digestion tank 3 (for example, the temperature of the sludge in the mixing tank 1) or the temperature of the liquid in the anaerobic digestion tank 3 is measured, and this temperature is set to a predetermined value. The additive may be added when the temperature is lower than (temperature). In this case, it is preferable that the larger the difference between the detected temperature and the predetermined value is, the larger the additive amount of the additive is. The temperature threshold is not limited, and can be freely set to a value suitable for the treatment plant and the treatment equipment. However, in the case of sludge supplied to the anaerobic digestion tank of a general sewage treatment plant, the temperature is generally about 17%. C is a guide.
嫌気性消化槽に供給する汚泥が分解を受けていないと、汚泥のｐＨは（有機酸生成量が少ないために）高い状態であることが多い。そこで、本発明では、嫌気性消化槽３に導入される汚泥のｐＨ（例えば混合槽１内の汚泥のｐＨ）、又は嫌気性消化槽３内の液のｐＨを測定し、このｐＨが所定値よりも高いときに添加物を添加するようにしてもよい。この場合、検出ｐＨと該所定値との差が大きくなるほど、添加物の添加量を多くするのが好ましい。この所定値は６〜７の範囲で設定されるのが好ましい。 If the sludge supplied to the anaerobic digestion tank has not undergone decomposition, the pH of the sludge is often high (because the amount of organic acid produced is small). Therefore, in the present invention, the pH of the sludge introduced into the anaerobic digestion tank 3 (for example, the pH of the sludge in the mixing tank 1) or the pH of the liquid in the anaerobic digestion tank 3 is measured, and this pH is set to a predetermined value. The additive may be added at a higher temperature. In this case, it is preferable to increase the amount of the additive as the difference between the detected pH and the predetermined value increases. This predetermined value is preferably set in the range of 6 to 7.
また、嫌気性消化槽に供給する汚泥が分解を受けていないと、汚泥の酸化還元電位（ＯＲＰ：Ｏｘｉｄａｔｉｏｎ Ｒｅｄｕｃｔｉｏｎ Ｐｏｔｅｎｔｉａｌ）の値が高い状態であることが多い。そこで、本発明では、嫌気性消化槽３に導入される汚泥のＯＲＰ（例えば混合槽１内の汚泥のＯＲＰ）、又は嫌気性消化槽３内の液のＯＲＰを測定し、このＯＲＰが所定値よりも高いときに添加物を添加するようにしてもよい。この場合、検出ＯＲＰと該所定値との差が大きくなるほど、添加物の添加量を多くするのが好ましい。この所定値は−１００〜０ｍＶの範囲で設定されるのが好ましい。 In addition, if the sludge supplied to the anaerobic digestion tank has not been decomposed, the sludge often has a high oxidation-reduction potential (ORP: Oxidation Reduction Potential) value. Therefore, in the present invention, the ORP of the sludge introduced into the anaerobic digestion tank 3 (for example, the ORP of the sludge in the mixing tank 1) or the ORP of the liquid in the anaerobic digestion tank 3 is measured, and this ORP is a predetermined value. The additive may be added at a higher temperature. In this case, it is preferable that the larger the difference between the detected ORP and the predetermined value is, the larger the additive amount of the additive is. This predetermined value is preferably set in the range of -100 to 0 mV.
嫌気性消化槽に供給する汚泥が分解を受けていないと、汚泥中の酸消費度（Ｍ−アルカリ度）が低い場合が多い。そこで、本発明では、嫌気性消化槽３に導入される汚泥のＭアルカリ度（例えば混合槽１内の汚泥のＭアルカリ度）、又は嫌気性消化槽３内の液のＭアルカリ度を測定し、このＭアルカリ度が所定値よりも低いときに添加物を添加するようにしてもよい。この場合、検出Ｍアルカリ度と該所定値との差が大きくなるほど、添加物の添加量を多くするのが好ましい。この所定値は５０〜２００ｍｇ／Ｌ−ａｓＣａＣＯ３特に５０〜１５０ｍｇ／Ｌ−ａｓＣａＣＯ３の範囲で設定されるのが好ましい。 If the sludge supplied to the anaerobic digestion tank has not been decomposed, the acid consumption (M-alkalinity) in the sludge is often low. Therefore, in the present invention, the M alkalinity of the sludge introduced into the anaerobic digestion tank 3 (for example, the M alkalinity of the sludge in the mixing tank 1) or the M alkalinity of the liquid in the anaerobic digestion tank 3 is measured. The additive may be added when the M alkalinity is lower than a predetermined value. In this case, it is preferable to increase the amount of the additive as the difference between the detected M alkalinity and the predetermined value increases. This predetermined value is preferably set in the range of 50 to 200 mg / L-asCaCO 3, particularly preferably 50 to 150 mg / L-asCaCO 3 .
嫌気性消化槽に供給する汚泥が分解を受けていないと、汚泥中の揮発性脂肪酸濃度（ＶＦＡ：Ｖｏｌａｔｉｌｅ Ｆａｔｔｙ Ａｃｉｄ）が低い場合が多い。ＶＦＡは通常、酢酸とプロピオン酸と酪酸の総量である。そこで、嫌気性消化槽に供給する汚泥スラリー中のＶＦＡ濃度（例えば混合槽１内の汚泥のＶＦＡ濃度）、又は嫌気性消化槽３内の液のＶＦＡ濃度を測定し、このＶＦＡ濃度が所定値よりも低いときに添加物を添加するようにしてもよい。この場合、検出ＶＦＡ濃度と該所定値との差が大きくなるほど、添加物の添加量を多くするのが好ましい。この所定値は処理場ごとによって異なり、また初沈汚泥と余剰汚泥の混合比率によっても異なるが、おおむね０〜１０００ｍｇ／Ｌ特に１０〜５００ｍｇ／Ｌの範囲で設定されるのが好ましい。 If the sludge supplied to the anaerobic digestion tank has not been decomposed, the volatile fatty acid concentration (VFA: Volatile Fatty Acid) in the sludge is often low. VFA is usually the sum of acetic acid, propionic acid and butyric acid. Then, the VFA concentration in the sludge slurry supplied to the anaerobic digestion tank (for example, the VFA concentration of the sludge in the mixing tank 1) or the VFA concentration of the liquid in the anaerobic digestion tank 3 is measured, and this VFA concentration is set to a predetermined value. The additive may be added at a lower temperature. In this case, it is preferable that the larger the difference between the detected VFA concentration and the predetermined value is, the larger the amount of the additive is. This predetermined value varies depending on the treatment plant and also depends on the mixing ratio of the initial sludge and the excess sludge, but is preferably set in a range of generally 0 to 1000 mg / L, particularly preferably 10 to 500 mg / L.
本発明では、上記の温度、ｐＨ、ＯＲＰ、Ｍアルカリ度、ＶＦＡ濃度の２以上の項目（水質指標値）について測定し、いずれか１つの項目でも前記所定値の範囲を逸脱するときに添加物を添加するようにしてもよい。 In the present invention, two or more items (water quality index values) of the above-mentioned temperature, pH, ORP, M alkalinity, and VFA concentration are measured, and when any one of the items deviates from the predetermined value range, the additive is added. May be added.
添加物の添加制御は、自動制御で行われてもよく、手動制御で行われてもよい。 The addition control of the additive may be performed by automatic control or may be performed by manual control.
以下の実施例及び比較例では、被処理汚泥（以下、原汚泥という。）として実際の都市下水処理場の初沈汚泥を用い、消化槽汚泥としてはこの下水処理場の嫌気性消化槽汚泥を用いた。原汚泥の温度は１７℃、消化槽汚泥の温度は３３℃である。 In the following Examples and Comparative Examples, the sludge to be treated (hereinafter, referred to as raw sludge) is actual primary sludge from an urban sewage treatment plant, and anaerobic digester sludge from this sewage treatment plant is used as digester sludge. Using. The temperature of the raw sludge is 17 ° C and the temperature of the digester sludge is 33 ° C.
［比較例１］
図２のように、原汚泥１００ｍＬと消化槽汚泥４００ｍＬとをそのまま三角フラスコ（容量：５００ｍＬ）に投入した。
[Comparative Example 1]
As shown in FIG. 2, 100 mL of raw sludge and 400 mL of digester sludge were directly charged into an Erlenmeyer flask (capacity: 500 mL).
図３の通り、三角フラスコの口に、発生したガスを排出できるステンレス管を備えたゴム栓を挿入した。ステンレス管はステンレスチューブに接続され、内部を水で満たして内部の空気を置換したのちに別個設けた水槽中に倒立させたメスシリンダー内に導かれ、三角フラスコで発生したガスはこのメスシリンダー内で上方採取されるようになっている。 As shown in FIG. 3, a rubber stopper provided with a stainless steel tube capable of discharging generated gas was inserted into the mouth of the Erlenmeyer flask. The stainless steel tube is connected to the stainless steel tube, the inside of which is filled with water to replace the air inside, and then led into an inverted measuring cylinder in a separately provided water tank. At the top.
この三角フラスコを、試験開始後に温度３５〜４０℃に調整された水槽で湯浴し、内部をおおよそ３７℃に保つようにした。また、撹拌子及びマグネチックスターラーでフラスコ内部を撹拌できるようにした。 This Erlenmeyer flask was heated in a water bath adjusted to a temperature of 35 to 40 ° C. after the start of the test, so that the inside was kept at approximately 37 ° C. Further, the inside of the flask was stirred by a stirrer and a magnetic stirrer.
７日間の試験期間中、発生したガス量をメスシリンダーで捕集したガスの体積から求めた。結果を図４に示す。また、試験終了後にメスシリンダー内に溜まったガス層から注射器を用いてガス分析用サンプルを採取し、ガスクロマトグラフィーでメタンガス濃度，炭酸ガス濃度、窒素ガス濃度、硫化水素濃度（ｖｏｌ％）を測定した。結果を表１に示す。 During the test period of 7 days, the amount of gas generated was determined from the volume of gas collected by the measuring cylinder. FIG. 4 shows the results. After the test is completed, a sample for gas analysis is collected from the gas layer accumulated in the measuring cylinder using a syringe, and the methane gas concentration, carbon dioxide gas concentration, nitrogen gas concentration, and hydrogen sulfide concentration (vol%) are measured by gas chromatography. did. Table 1 shows the results.
［比較例２］
原汚泥を予め湯浴によって２８℃に昇温させ、消化槽汚泥と合わせて三角フラスコに投入したこと以外は比較例１と同様にして行った。結果を図４、表１に示す。
[Comparative Example 2]
The operation was performed in the same manner as in Comparative Example 1 except that the raw sludge was heated to 28 ° C. in advance with a hot water bath and put into an Erlenmeyer flask together with the digester sludge. The results are shown in FIG.
［実施例１］
原汚泥に対し予め
塩化第一鉄：０．１重量％
塩化ニッケル：０．００１重量％
塩化コバルト：０．００１重量％
塩化マンガン：０．０００３重量％
を水溶液の形態で加えて１時間撹拌混合したこと以外は比較例１と同様にして行った。結果を図４、表１に示す。
[Example 1]
In advance for raw sludge
Ferrous chloride: 0.1% by weight
Nickel chloride: 0.001% by weight
Cobalt chloride: 0.001% by weight
Manganese chloride: 0.0003% by weight
Was added in the form of an aqueous solution, followed by stirring and mixing for 1 hour, in the same manner as in Comparative Example 1. The results are shown in FIG.
なお、金属塩水溶液は、各金属塩を５ｍＬの水に溶解させた後、ｐＨを６に調整したものである。 The aqueous solution of the metal salt was prepared by dissolving each metal salt in 5 mL of water and then adjusting the pH to 6.
［考察］
表１の通り、原汚泥に対し金属塩を添加した実施例１は、比較例１（何の前処理もせず）及び比較例２（原汚泥を予め２８℃に昇温した）と比較して、ガス総発生量が多く、メタンガス濃度も高い。
[Discussion]
As shown in Table 1, Example 1 in which a metal salt was added to raw sludge was compared with Comparative Example 1 (no pretreatment was performed) and Comparative Example 2 (raw sludge was heated to 28 ° C. in advance). , The total amount of gas generated is large, and the methane gas concentration is high.
［比較例３〜５、実施例２］
原汚泥を予め以下の前処理を行なって調整した後に、いずれも湯浴で３５℃に昇温した。この３５℃に昇温後の原汚泥１００ｍＬと、３３℃の消化槽汚泥４００ｍＬとを三角フラスコに投入したこと以外は比較例１と同様にして実験を行った。
[Comparative Examples 3 to 5, Example 2]
The raw sludge was adjusted by performing the following pretreatment in advance and then heated to 35 ° C. in a hot water bath. An experiment was performed in the same manner as in Comparative Example 1 except that 100 mL of the raw sludge after the temperature was raised to 35 ° C and 400 mL of the digester sludge at 33 ° C were charged into an Erlenmeyer flask.
比較例３：３５℃で２４時間放置
比較例４：２５℃で２４時間放置
比較例５：４℃で冷蔵保存
実施例２：４℃で冷蔵保存、三角フラスコに入れて昇温後に、該・供給汚泥に対し予め
塩化第一鉄：０.１重量％
塩化ニッケル：０.００１重量％
塩化コバルト：０.００１重量％
塩化マンガン：０.０００３重量％
を水溶液の形態で加えて撹拌混合したのち、消化槽汚泥を加えた。
Comparative Example 3: Left at 35 ° C. for 24 hours Comparative Example 4: Left at 25 ° C. for 24 hours Comparative Example 5: Refrigerated storage at 4 ° C. Example 2: Refrigerated storage at 4 ° C. In advance for feed sludge
Ferrous chloride: 0.1% by weight
Nickel chloride: 0.001% by weight
Cobalt chloride: 0.001% by weight
Manganese chloride: 0.0003% by weight
Was added in the form of an aqueous solution, followed by stirring and mixing, and then digester sludge was added.
なお、金属塩水溶液は、各金属塩を５ｍＬの水に溶解させた後、ｐＨを７に調整したものである。 The aqueous metal salt solution was prepared by dissolving each metal salt in 5 mL of water and then adjusting the pH to 7.
ガス発生量及びガス組成分析結果を図５及び表２に示す。また、実験開始後、７日目におけるフラスコ内のｐＨ、ＯＲＰ、Ｍ−アルカリ度及びＶＦＡ濃度を表３に示す。 FIG. 5 and Table 2 show the gas generation amount and the gas composition analysis results. Table 3 shows the pH, ORP, M-alkalinity, and VFA concentration in the flask on day 7 after the start of the experiment.
［考察］
表２，３の通り、比較例５は比較例３，４よりもガス総発生量が少なく、発生ガス中のメタンガス濃度が低い。これは、嫌気プロセスが進んでいないためであり、ｐＨやＯＲＰが高く、Ｍ−アルカリ度やＶＦＡ濃度が低い。
[Discussion]
As shown in Tables 2 and 3, Comparative Example 5 has a smaller total gas generation amount than Comparative Examples 3 and 4, and the methane gas concentration in the generated gas is lower. This is because the anaerobic process has not progressed, and the pH and ORP are high, and the M-alkalinity and the VFA concentration are low.
比較例５にＦｅ，Ｎｉ，Ｃｏ，Ｍｎの各塩を添加したものが実施例２である。この実施例２では、初期のガス発生量は比較例３，４よりも少ないが、３日後頃からの上昇率が他を引き離して、最終的なガス発生量もメタンガス濃度も高くすることができた。 Example 2 is obtained by adding each salt of Fe, Ni, Co, and Mn to Comparative Example 5. In Example 2, the initial gas generation amount was smaller than that of Comparative Examples 3 and 4, but the rate of increase from around 3 days later was higher than that of Comparative Examples 3 and 4, and both the final gas generation amount and the methane gas concentration could be increased. Was.
フラスコ内の汚泥の状態は、ｐＨで把握することもできるし、ＯＲＰやＭ−アルカリ度、ＶＦＡ濃度で把握することもできる。 The state of the sludge in the flask can be grasped by pH, or can be grasped by ORP, M-alkaliness, and VFA concentration.
例えばこの汚泥処理系においては、閾値を
ｐＨ：７（−）
ＯＲＰ：−１００（ｍＶ）
Ｍ−アルカリ度：９０（ｍｇ／Ｌ ａｓ ＣａＣＯ３）
ＶＦＡ：１０（ｍｇ／Ｌ）
と定め、これらを逸脱したとき（ｐＨ、ＯＲＰの場合は上回ったとき、Ｍ−アルカリ度、ＶＦＡ濃度の場合は下回ったとき）にＦｅ，Ｎｉ，Ｃｏ，Ｍｎの各塩を添加すれば、メタンガス発生効果を高め、ガス発生量を多くし，かつ、メタン濃度を高くすることができる。
For example, in this sludge treatment system, the threshold is pH: 7 (-)
ORP: -100 (mV)
M-alkalinity: 90 (mg / L as CaCO 3 )
VFA: 10 (mg / L)
When these values deviate from each other (when the pH exceeds ORP, when the M-alkalinity decreases, and when the VFA concentration decreases, the respective salts of Fe, Ni, Co, and Mn are added), methane gas can be obtained. The generation effect can be enhanced, the amount of gas generated can be increased, and the methane concentration can be increased.
１ 混合槽
３ 嫌気性消化槽
５ 固液分離手段
1 mixing tank 3 anaerobic digestion tank 5 solid-liquid separation means
Claims (1)
該嫌気性消化槽に導入される汚泥又は嫌気性消化槽に、Ｆｅ，Ｃｕ，Ｚｎ，Ｍｇ，Ｍｎ，Ｋ，Ｃａ，Ｎｉ，Ｍｏ，Ｓｅ，Ｓ，Ｖ，Ｃｒ，Ｉ及びＣｏの少なくとも１種よりなる添加物を添加する添加手段を備えた下水処理汚泥の嫌気性消化装置であって、
前記嫌気性消化槽に導入される汚泥又は前記嫌気性消化槽内液の温度、ｐＨ，ＯＲＰ，及びＭアルカリ度の少なくとも１つの水質指標値を測定する測定手段と、
該測定手段で測定した少なくとも１つの水質指標値が所定範囲を逸脱したときに前記添加手段を作動させる制御手段と
を備えたことを特徴とする下水処理汚泥の嫌気性消化装置。 Anaerobic keeping the primary sludge and / or biological treatment reactor sewage sludge consisting of excess sludge is withdrawn from the settled in the first sedimentation tank sewage treatment plant predetermined temperature, pH, in the range of ORP, and M alkalinity In an anaerobic digester for sewage sludge having an anaerobic digester for anaerobic digestion,
Sludge introduced into the anaerobic digestion tank or at least one of Fe, Cu, Zn, Mg, Mn, K, Ca, Ni, Mo, Se, S, V, Cr, I and Co is introduced into the anaerobic digestion tank. An anaerobic digester for sewage sludge provided with an addition means for adding an additive comprising:
The anaerobic introduced into the digester are sludge or the temperature of the anaerobic digestion tank liquid, measuring means for measuring pH, ORP, and at least one quality index value of the M alkalinity,
An anaerobic digester for sewage sludge, comprising: control means for operating the addition means when at least one water quality index value measured by the measurement means deviates from a predetermined range.
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