JP4200601B2 - Anaerobic digestion treatment method of organic sludge - Google Patents
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- JP4200601B2 JP4200601B2 JP20066799A JP20066799A JP4200601B2 JP 4200601 B2 JP4200601 B2 JP 4200601B2 JP 20066799 A JP20066799 A JP 20066799A JP 20066799 A JP20066799 A JP 20066799A JP 4200601 B2 JP4200601 B2 JP 4200601B2
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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
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Description
【０００１】
【発明の属する技術分野】
本発明は有機性汚泥の嫌気性消化処理方法に係り、特に、有機性汚泥をオゾン処理した後嫌気性消化処理する方法において、オゾン処理に先立ち特定の条件下で曝気を行うことにより、オゾン処理におけるオゾン使用量の低減、処理効率の向上を図り、有機性汚泥を効率的に分解する方法に関する。
【０００２】
【従来の技術】
従来、有機性汚泥の嫌気性消化処理方法として、メタン醗酵等の嫌気性消化処理を行う方法が知られており、このような処理方法において、汚泥分解効率を向上させる目的で嫌気性消化処理の前処理として、ボールミルや超音波による粉砕ないし破砕、或いはオゾン処理による酸化分解又は熱処理による加熱分解等を行うことが検討されている。
【０００３】
例えば、特公昭５９−１０５８９７号公報には、廃水の生物処理で発生する余剰汚泥をオゾン処理した後嫌気性消化処理する方法が提案されている。このように、前処理としてオゾン処理を行うことにより、有機性汚泥中の難生物分解性物質が酸化分解されて生物分解可能な物質に変換されるため、後段の嫌気性消化処理における汚泥の分解効率が向上する。
【０００４】
【発明が解決しようとする課題】
しかしながら、上記従来の方法では、前処理のためのコストが高いわりには嫌気性消化処理での汚泥の分解率の向上効果が低く、一般的には前処理を行わない場合の嫌気性消化処理による汚泥の分解率は４０％程度であるのに対し、オゾン処理等の前処理を行っても、汚泥の分解率は高々５０〜６０％程度にしかならなかった。
【０００５】
また、前処理を行うほか、嫌気性消化槽内の汚泥濃度を増加させるために、嫌気性消化処理汚泥を固液分離し、分離汚泥を消化槽へ返送する方法が知られているが、この方法においても、汚泥の分解率は６０％程度が限界であった。
【０００６】
本発明は上記従来の問題点を解決し、有機性汚泥を低コストで効率的に分解処理する有機性汚泥の嫌気性消化処理方法を提供することを目的とする。
【０００７】
【課題を解決するための手段】
本発明の有機性汚泥の嫌気性消化処理方法は、有機性汚泥をオゾン処理した後嫌気性消化処理する方法において、オゾン処理に先立ち、有機性汚泥を曝気する工程を有する有機性汚泥の嫌気性消化処理方法であって、嫌気性消化処理汚泥を固液分離し、分離汚泥の一 部を嫌気性消化処理工程に返送することを特徴とする。
【０００８】
本発明においては、特に嫌気性消化処理汚泥を固液分離し、分離汚泥の一部を曝気工程及び嫌気性消化処理工程に返送するのが望ましい。
【０００９】
有機性汚泥は、通常、運搬、貯留等により腐敗していることが多いため、硫化水素が含まれている。また、嫌気性消化処理後の汚泥にも多量の硫化水素が含まれている。このため、このような硫化水素を含む有機性汚泥や嫌気性消化処理汚泥を直接オゾン処理に供すると、硫化水素の分解のために多量のオゾンを消費することとなるため、オゾン処理効率が悪い。
【００１０】
本発明では、曝気により、汚泥中に含まれる硫化水素が生物反応により硫酸に酸化されると共に、有機性汚泥及び嫌気性消化を経て処理された残留汚泥の一部が好気的に消化され、微生物細胞内の蓄積有機物や汚泥粘質物が生物的に分解され、汚泥の可溶化、減量化が促進される。
【００１１】
また、嫌気性消化処理工程に汚泥を返送することにより、嫌気性消化処理工程の汚泥濃度を高めて嫌気性消化処理効率を高めることができる。
【００１２】
本発明では、曝気によるこのような硫化水素の除去効果により、後段のオゾン処理における、汚泥分解へのオゾンの利用効率を高めると共に、汚泥の好気的消化による分解効果でオゾン処理効率及び消化処理効率を向上させることができる。
【００１３】
本発明では、曝気処理した後、オゾン処理し、次いで嫌気性消化処理し、嫌気性消化処理汚泥を固液分離し、分離汚泥を曝気工程及び嫌気性消化処理工程に返送することにより、汚泥の分解率を８０％以上に向上させることができ、特に曝気工程へ返送する汚泥量と嫌気性消化処理工程へ返送する汚泥量を調整することにより、長期に亘り、系外への汚泥の引き抜きを行うことなく処理を継続することが可能である。
【００１４】
【発明の実施の形態】
以下、図面を参照して本発明の有機性汚泥の嫌気性消化処理方法の実施の形態を詳細に説明する。
【００１５】
図１（ａ）及び図２（ａ）は参考例に係る有機性汚泥の嫌気性消化処理方法を示す系統図であり、図１（ｂ）及び図２（ｂ）は本発明の有機性汚泥の嫌気性消化処理方法の実施の形態を示す系統図である。図１，２において、同一機能を奏する部材には同一符号を付してある。
【００１６】
本発明において、処理対象となる有機性汚泥は、好気性処理、嫌気性処理又はこれらを組み合わせて各種の有機性排液を処理する際に固液分離により生じる分離汚泥（余剰汚泥）が挙げられるが、これに限らず、固液分離する前の混合液の状態の生物汚泥、或いはこれらの混合汚泥であっても良い。
【００１７】
図１（ａ），（ｂ）の方法では、まず、このような有機性汚泥を曝気槽１に導入して曝気処理する。曝気処理により、有機性汚泥中の硫化水素が生物反応により硫酸に酸化されて除去されると共に、汚泥の一部が好気的に消化される。
【００１８】
曝気槽１における硫化水素の酸化のためには、通常、曝気槽滞留時間は１時間程度以上で良いが、好気性消化反応には、曝気槽１内の滞留時間は長い程効果的であり、１時間以上好ましくは１２〜７２時間の曝気時間が確保されるように汚泥の曝気槽１内の滞留時間を調整する。なお、この曝気処理において、４０〜９０℃程度に加温することにより高温細菌の作用で反応が著しく促進されるため、より汚泥の分解効率を高めることができる。
【００１９】
曝気槽１で曝気処理することにより、汚泥の一部を生物分解すると共に硫化水素を除去した汚泥は、次いでオゾン処理槽２に導入してオゾン処理する。このオゾン処理は汚泥をオゾンと接触させることにより行う。接触方法としては、図示の如く、オゾン処理槽２に汚泥を導入してオゾンを吹込む方法、機械撹拌による方法、充填層を利用する方法などが採用できる。オゾンとしては、オゾンガスの他、オゾン含有空気、オゾン化空気などが使用できる。
【００２０】
このオゾン処理は、ｐＨ５以下の酸性下のオゾン処理であっても、オゾン単独処理であっても良い。
【００２１】
酸性下でのオゾン処理では、オゾンの反応効率が高められ、オゾン使用量の低減を図ることができる。この場合のオゾン使用量は、１０〜１００ｇ−Ｏ3／ｋｇ−汚泥、特に１５〜５０ｇ−Ｏ3／ｋｇ−汚泥とするのが好ましい。オゾン吹込みの場合は、ＳＶを０．２５〜４ｈｒ-1、特に０．５〜２ｈｒ-1とするのが好ましい。
【００２２】
一方、オゾン単独処理の場合のオゾン使用量は２０〜２５０ｇ−Ｏ3／ｋｇ−汚泥、特に３０〜１００ｇ−Ｏ3／ｋｇ−汚泥とするのが好ましい。オゾン吹込みの場合は、ＳＶを０．２５〜４ｈｒ-1、特に０．５〜２ｈｒ-1とするのが好ましい。
【００２３】
酸性下でオゾン処理を行う場合には、塩酸、硫酸等の酸を添加して曝気処理汚泥をｐＨ調整すれば良い。
【００２４】
オゾン処理により酸化分解を行ったオゾン処理汚泥は、次いで嫌気性消化槽３に導入して嫌気性消化処理する。この嫌気性消化処理においては、汚泥の有機酸醗酵、メタン醗酵で汚泥が可溶化ないし分解される。この嫌気性消化処理温度は３０〜６０℃とするのが好ましい。このうち、３０〜４０℃では中温性のメタン醗酵菌が、また４５〜６０℃では高温性のメタン醗酵菌が働いて有機酸醗酵の結果、生成した酢酸、水素をメタンに変換する。この嫌気性消化処理は、有機酸醗酵とメタン醗酵とを別の反応槽で行う２相方式であっても良く、またこれらの両反応を同じ槽内で行う１相方式であっても良い。また、この嫌気性消化槽３の滞留時間は５〜４０日、特に１０〜２０日とするのが好ましい。
【００２５】
なお、嫌気性消化処理においてはｐＨ６〜８の範囲に維持するのが好ましく、従って、オゾン処理において酸オゾン処理を行った場合のように、汚泥のｐＨが低い場合には、適宜水酸化ナトリウム、石灰、炭酸ナトリウム等のアルカリを添加することによりｐＨ調整を行う。
【００２６】
嫌気性消化槽３からの嫌気性消化処理水は、通常の場合、沈殿槽や加圧浮上槽、遠心分離機、精密濾過膜分離装置、限外濾過膜分離装置等の固液分離装置４で固液分離され、分離液が処理水として系外へ排出される。この固液分離に当り、特に、図１（ｂ）に示す如く、分離汚泥の返送を行う場合、メタン醗酵菌が酸素に弱いため加圧浮上や沈殿分離等では汚泥が空気に触れないことが好ましい。また、遠心分離では分離液中のＳＳの低減のため、高分子凝集剤を併用することが好ましい。
【００２７】
本発明においては、特に、固液分離装置４で分離した分離汚泥の一部を図１（ｂ）に示す如く、曝気槽１と嫌気性消化槽３に返送するのが好ましい。
【００２８】
このように、分離汚泥の返送を行う場合、分離汚泥のうちの一部をそれぞれ曝気槽１及び嫌気性消化槽３へ返送し、残部を系外へ引き抜いて脱水等の処理工程へ送給しても良く、また、一部を曝気槽１へ返送し、残部を嫌気性消化槽３に返送して、汚泥の引き抜きなしで処理を行っても良い。いずれの場合においても、分離汚泥の大部分を嫌気性消化槽３へ送給し、少量を曝気槽１へ返送することが好ましい。この返送割合は、嫌気性消化槽３の滞留時間や汚泥濃度によっても異なるが、この汚泥濃度が１％で滞留時間が２０日の場合、分離汚泥のうちの約１０〜３０％を曝気槽１へ、残部を嫌気性消化槽３へ返送することが好ましい。
【００２９】
なお、図１（ａ），（ｂ）に示す方法は、有機性汚泥を順次曝気処理、オゾン処理及び嫌気性消化処理するものであるが、本発明の方法は、嫌気性消化処理に供される汚泥が、曝気処理及びオゾン処理されていれば良く、例えば、図２（ａ）に示す如く、嫌気性消化槽３の汚泥の一部を抜き出し、曝気槽１にて曝気処理し、その後オゾン処理槽２でオゾン処理した後嫌気性消化槽３に戻し、この場合において、図２（ｂ）に示す如く、固液分離装置４の分離汚泥を曝気槽１及び嫌気性消化槽３に返送するようにしても良い。
【００３０】
【実施例】
以下に比較例、参考例及び実施例を挙げて本発明をより具体的に説明する。
【００３１】
比較例１
下水を処理している活性汚泥法の余剰汚泥と最初沈殿池汚泥を１：１で混合した有機性汚泥を濃度１．５％に調整した汚泥（ｐＨ６．１，温度２２℃）を原泥としてオゾン処理及び嫌気性消化処理を行った。
【００３２】
まず、原泥０．５Ｌを容積１Ｌの洗浄びんにとり、濃度２５ｇ/ｍ3のオゾン含有ガスを１０ｍＬ/ｍｉｎ通気した。流入及び排出オゾン濃度を測定し、オゾン消費量が５０ｇ/ｋｇ−原泥となった時点でオゾン処理を終了し、オゾン処理汚泥を取り出して嫌気性消化槽に投入し、同量の液を嫌気性消化槽から引き抜き、これを嫌気性消化処理水とし、その一部で汚泥濃度の分析を行った。なお、嫌気性消化槽（メタン発酵槽）としては、有効容積７．５Ｌで、種汚泥として下水嫌気性消化槽の汚泥を乾燥重量で７５ｇ投入したものを用いた。
【００３３】
上記操作を１日１回で週に５回、３ヶ月間継続した。なお、嫌気性消化槽のｐＨは７．２、温度は３７℃、滞留時間は２０日である。
【００３４】
その結果、オゾン処理前の有機性汚泥の濃度は１．５％であったが、嫌気性消化処理水の汚泥濃度（平均値）は０．７１％に低減した。
【００３５】
参考例１
オゾン処理に先立ち、原泥を内容積１Ｌの曝気槽（２５℃）に０．５Ｌ／ｄａｙの流速で連続通水した（滞留時間４８ｈｒ）こと以外は、比較例１と同様にしてオゾン処理及び嫌気性消化処理を行った。なお、曝気槽の曝気量は２Ｌ／ｍｉｎとした。
【００３６】
この結果、３ヶ月経過後の嫌気性消化処理水の汚泥濃度（平均値）は０．４１ｇ／Ｌで、比較例１の場合に比べて約１／２となった。
【００３７】
実施例１
参考例１において、嫌気性消化槽からの流出液を１５０００ｒｐｍで１０分間遠心分離し、得られた分離汚泥のうちの１／３を曝気槽に、残り２／３を嫌気性消化槽へ戻したこと以外は、同様にして処理を行った。
【００３８】
その結果、３ヶ月経過後の嫌気性消化槽中の汚泥濃度は１６．２ｇ／Ｌとなり、３ヶ月間汚泥の引き抜きなしで運転したにもかかわらず、殆ど汚泥濃度の上昇はなかった。なお、遠心分離により得られた分離水の汚泥濃度は５７ｍｇ／Ｌと著しく低かった。
【００３９】
参考例２
実施例１において、遠心分離により得られた分離汚泥のうちの１／１０を曝気槽に返送し、残部を系外へ引き抜いたこと以外は同様にして処理を行った。
【００４０】
その結果、３ヶ月経過後の嫌気性消化槽中の汚泥濃度は１９ｇ／Ｌとなり、遠心分離により得られた分離水の汚泥濃度は８９ｍｇ／Ｌと著しく低かった。
【００４１】
実施例２
実施例１において、遠心分離により得られた分離汚泥のうちの１／２０を嫌気性消化槽に返送し、残部を系外へ引き抜いたこと以外は同様にして処理を行った。
【００４２】
その結果、３ヶ月経過後の嫌気性消化槽中の汚泥濃度は６．４ｇ／Ｌとなり、遠心分離により得られた分離水の汚泥濃度は４４ｍｇ／Ｌと著しく低かった。
【００４３】
【発明の効果】
以上詳述した通り、本発明の有機性汚泥の嫌気性消化処理方法によれば、有機性汚泥をオゾン処理した後嫌気性消化処理して分解する方法において、オゾン処理に先立ち曝気を行うことにより、オゾン処理におけるオゾン使用量の低減、処理効率の向上を図り、有機性汚泥を低コストで効率的に分解することが可能となる。
【図面の簡単な説明】
【図１】 （ａ）図は参考例に係る有機性汚泥の嫌気性消化処理方法を示す系統図であり、（ｂ）図は本発明の有機性汚泥の嫌気性消化処理方法の実施の形態を示す系統図である。
【図２】 （ａ）図は参考例に係る有機性汚泥の嫌気性消化処理方法を示す系統図であり、（ｂ）図は本発明の有機性汚泥の嫌気性消化処理方法の別の実施の形態を示す系統図である。
【符号の説明】
１ 曝気槽
２ オゾン処理槽
３ 嫌気性消化槽
４ 固液分離装置[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an anaerobic digestion treatment method for organic sludge, and in particular, in a method of anaerobic digestion treatment after treating organic sludge with ozone, by performing aeration under specific conditions prior to the ozone treatment, The present invention relates to a method for efficiently decomposing organic sludge by reducing ozone usage and improving processing efficiency.
[0002]
[Prior art]
Conventionally, as an anaerobic digestion treatment method of organic sludge, a method of performing anaerobic digestion treatment such as methane fermentation is known, and in such a treatment method, anaerobic digestion treatment is performed for the purpose of improving sludge decomposition efficiency. As pretreatment, it has been studied to perform pulverization or crushing using a ball mill or ultrasonic waves, oxidative decomposition using ozone treatment, or heat decomposition using heat treatment.
[0003]
For example, Japanese Examined Patent Publication No. Sho 59-105897 proposes a method of anaerobic digestion treatment after surplus sludge generated by biological treatment of wastewater is treated with ozone. In this way, by performing ozone treatment as a pre-treatment, the difficult biodegradable substances in the organic sludge are oxidatively decomposed and converted into biodegradable substances. Therefore, the sludge decomposition in the latter-stage anaerobic digestion treatment Efficiency is improved.
[0004]
[Problems to be solved by the invention]
However, in the above conventional method, although the cost for the pretreatment is high, the improvement effect of the sludge decomposition rate in the anaerobic digestion treatment is low, and generally due to the anaerobic digestion treatment when the pretreatment is not performed. While the sludge decomposition rate is about 40%, even when pretreatment such as ozone treatment is performed, the sludge decomposition rate is only about 50 to 60%.
[0005]
In addition to pretreatment, in order to increase the sludge concentration in the anaerobic digestion tank, a method of solid-liquid separation of the anaerobic digestion sludge and returning the separated sludge to the digestion tank is known. Even in the method, the decomposition rate of sludge was limited to about 60%.
[0006]
The object of the present invention is to solve the above-mentioned conventional problems and to provide an anaerobic digestion treatment method for organic sludge that efficiently decomposes organic sludge at low cost.
[0007]
[Means for Solving the Problems]
The method of anaerobic digestion treatment of organic sludge according to the present invention is an anaerobic digestion treatment method in which an organic sludge is subjected to an anaerobic digestion treatment after ozone treatment, and the organic sludge is aerated prior to the ozone treatment . a digestion process method, the anaerobic digestion sludge solid-liquid separation, characterized by returning the part of the separation sludge anaerobic digestion process.
[0008]
In the present invention, in particular anaerobic digester sludge to the solid-liquid separation, to return a portion of the separated sludge to the aeration step and the anaerobic digestion process is desirable.
[0009]
Since organic sludge is usually spoiled by transportation, storage, etc., it contains hydrogen sulfide. A large amount of hydrogen sulfide is also contained in the sludge after the anaerobic digestion treatment. For this reason, if such organic sludge containing hydrogen sulfide or anaerobic digestion-treated sludge is directly subjected to ozone treatment, a large amount of ozone is consumed for decomposition of hydrogen sulfide, resulting in poor ozone treatment efficiency. .
[0010]
In the present invention, by aeration, hydrogen sulfide contained in the sludge is oxidized to sulfuric acid by biological reaction, and a part of the residual sludge treated through organic sludge and anaerobic digestion is aerobically digested, Accumulated organic matter and sludge mucilage in microbial cells are biologically degraded, and sludge solubilization and weight reduction are promoted.
[0011]
Moreover, by returning sludge to an anaerobic digestion process, the sludge density | concentration of an anaerobic digestion process can be raised and anaerobic digestion process efficiency can be improved.
[0012]
In the present invention, the removal effect of hydrogen sulfide by aeration improves the efficiency of ozone utilization for sludge decomposition in the subsequent ozone treatment, and the ozone treatment efficiency and digestion treatment by the decomposition effect by aerobic digestion of sludge. Efficiency can be improved.
[0013]
In the present invention, after aeration treatment, ozone treatment, followed by anaerobic digestion treatment, anaerobic digestion treatment sludge is solid-liquid separated, and the separated sludge is returned to the aeration step and anaerobic digestion treatment step. Degradation rate can be improved to 80% or more, especially by adjusting the amount of sludge to be returned to the aeration process and the amount of sludge to be returned to the anaerobic digestion process, so that sludge can be extracted outside the system for a long period of time. It is possible to continue processing without doing it.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of an anaerobic digestion treatment method for organic sludge according to the present invention will be described in detail with reference to the drawings.
[0015]
Fig.1 (a) and FIG.2 (a) are systematic diagrams which show the anaerobic digestion processing method of the organic sludge which concerns on a reference example, FIG.1 (b) and FIG.2 (b) are the organic sludge of this invention. It is a systematic diagram which shows embodiment of the anaerobic digestion processing method of this. 1 and 2, members having the same function are denoted by the same reference numerals.
[0016]
In the present invention, the organic sludge to be treated includes an aerobic treatment, an anaerobic treatment, or separated sludge (excess sludge) generated by solid-liquid separation when treating various organic waste liquids in combination. However, the present invention is not limited to this, and biological sludge in a mixed solution state before solid-liquid separation or mixed sludge thereof may be used.
[0017]
In the method shown in FIGS. 1A and 1B, first, such organic sludge is introduced into the aeration tank 1 and aerated. By aeration treatment, hydrogen sulfide in the organic sludge is oxidized and removed by sulfuric acid by a biological reaction, and a part of the sludge is digested aerobically.
[0018]
In order to oxidize hydrogen sulfide in the aeration tank 1, the aeration tank residence time is usually about 1 hour or longer. However, the longer the residence time in the aeration tank 1, the more effective the aerobic digestion reaction. The residence time of the sludge in the aeration tank 1 is adjusted so as to ensure an aeration time of 1 hour or more, preferably 12 to 72 hours. In this aeration treatment, the reaction is remarkably accelerated by the action of high-temperature bacteria by heating to about 40 to 90 ° C., so that the sludge decomposition efficiency can be further increased.
[0019]
The sludge from which a part of the sludge has been biodegraded and hydrogen sulfide has been removed by aeration treatment in the aeration tank 1 is then introduced into the ozone treatment tank 2 and subjected to ozone treatment. This ozone treatment is performed by bringing sludge into contact with ozone. As a contact method, as shown in the figure, a method of introducing sludge into the ozone treatment tank 2 and blowing ozone, a method of mechanical stirring, a method of using a packed bed, and the like can be employed. As ozone, ozone-containing air, ozonized air, or the like can be used in addition to ozone gas.
[0020]
This ozone treatment may be an ozone treatment under an acidic pH of 5 or less, or an ozone alone treatment.
[0021]
In the ozone treatment under acidic conditions, the reaction efficiency of ozone is increased, and the amount of ozone used can be reduced. The amount of ozone used in this case is preferably 10 to 100 g-O 3 / kg-sludge, particularly 15 to 50 g-O 3 / kg-sludge. For inclusive ozone blowing, the SV 0.25~4hr -1, preferably Of particular 0.5~2hr -1.
[0022]
On the other hand, the amount of ozone used in the case of ozone alone treatment is preferably 20 to 250 g-O 3 / kg-sludge, particularly 30 to 100 g-O 3 / kg-sludge. For inclusive ozone blowing, the SV 0.25~4hr -1, preferably Of particular 0.5~2hr -1.
[0023]
When the ozone treatment is performed under acid conditions, an acid such as hydrochloric acid or sulfuric acid may be added to adjust the pH of the aerated sludge.
[0024]
The ozone-treated sludge that has been oxidatively decomposed by ozone treatment is then introduced into the anaerobic digestion tank 3 and subjected to anaerobic digestion. In this anaerobic digestion treatment, sludge is solubilized or decomposed by sludge organic acid fermentation and methane fermentation. The anaerobic digestion treatment temperature is preferably 30 to 60 ° C. Among these, mesophilic methane fermentation bacteria work at 30 to 40 ° C, and high temperature methane fermentation bacteria work at 45 to 60 ° C to convert acetic acid and hydrogen produced as a result of organic acid fermentation into methane. This anaerobic digestion treatment may be a two-phase system in which organic acid fermentation and methane fermentation are performed in separate reaction tanks, or may be a single-phase system in which both these reactions are performed in the same tank. The residence time of the anaerobic digester 3 is preferably 5 to 40 days, particularly 10 to 20 days.
[0025]
In the anaerobic digestion treatment, it is preferable to maintain the pH in the range of 6 to 8. Therefore, when the sludge has a low pH as in the case of the acid ozone treatment in the ozone treatment, sodium hydroxide, The pH is adjusted by adding alkali such as lime and sodium carbonate.
[0026]
The anaerobic digestion treated water from the anaerobic digestion tank 3 is usually a solid-liquid separation device 4 such as a precipitation tank, a pressurized flotation tank, a centrifuge, a microfiltration membrane separation device, an ultrafiltration membrane separation device or the like. Solid-liquid separation is performed, and the separated liquid is discharged out of the system as treated water. In this solid-liquid separation, as shown in FIG. 1 (b), particularly when the separated sludge is returned, the sludge may not come into contact with the air during pressure flotation or precipitation separation because the methane fermentation bacteria are vulnerable to oxygen. preferable. In the centrifugal separation, it is preferable to use a polymer flocculant in combination in order to reduce SS in the separation liquid.
[0027]
In the present invention, it is particularly preferable that a part of the separated sludge separated by the solid-liquid separator 4 is returned to the aeration tank 1 and the anaerobic digestion tank 3 as shown in FIG.
[0028]
As described above, when returning the separated sludge, a part of the separated sludge is returned to the aeration tank 1 and the anaerobic digestion tank 3, respectively, and the remainder is drawn out of the system and sent to a treatment process such as dehydration. Alternatively, a part may be returned to the aeration tank 1 and the remaining part may be returned to the anaerobic digestion tank 3 to perform the treatment without extracting sludge. In any case, it is preferable to feed most of the separated sludge to the anaerobic digestion tank 3 and return a small amount to the aeration tank 1. The return ratio varies depending on the residence time and sludge concentration in the anaerobic digester 3, but when the sludge concentration is 1% and the residence time is 20 days, about 10 to 30% of the separated sludge is aerated tank 1. It is preferable to return the remainder to the anaerobic digester 3.
[0029]
In addition, although the method shown to Fig.1 (a), (b) carries out an aeration process, an ozone process, and anaerobic digestion processing of organic sludge one by one, the method of this invention is used for the anaerobic digestion process. For example, as shown in FIG. 2A, a part of the sludge in the anaerobic digestion tank 3 is extracted and aerated in the aeration tank 1, and then the ozone is treated. It returned to the anaerobic digestion tank 3 after ozone treatment in the processing tank 2, returned in this case, as shown in FIG. 2 (b), the solid-liquid separator 4 separates the sludge to the aeration tank 1 and the anaerobic digestion tank 3 You may make it do.
[0030]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Comparative Examples , Reference Examples and Examples.
[0031]
Comparative Example 1
Sludge (pH 6.1, temperature 22 ° C) adjusted to 1.5% concentration of organic sludge mixed with surplus sludge from the activated sludge process treating sewage and the first sedimentation basin sludge at 1: 1 is used as the raw sludge. Ozone treatment and anaerobic digestion treatment were performed.
[0032]
First, 0.5 L of raw mud was placed in a washing bottle having a volume of 1 L, and ozone-containing gas having a concentration of 25 g / m 3 was aerated at 10 mL / min. Inflow and discharge ozone concentrations are measured, and when the ozone consumption reaches 50 g / kg-raw mud, the ozone treatment is terminated, the ozone-treated sludge is taken out and put into an anaerobic digester, and the same amount of liquid is anaerobic. It was pulled out from the digestive digestion tank and used as anaerobic digestion-treated water. As an anaerobic digester (methane fermentation tank), an effective volume of 7.5 L was used, and 75 g of sludge from a sewage anaerobic digester was added as seed sludge by dry weight.
[0033]
The above operation was continued once a day, 5 times a week for 3 months. The pH of the anaerobic digester is 7.2, the temperature is 37 ° C., and the residence time is 20 days.
[0034]
As a result, the concentration of organic sludge before ozone treatment was 1.5%, but the sludge concentration (average value) of anaerobic digestion treated water was reduced to 0.71%.
[0035]
Reference example 1
Prior to the ozone treatment, the raw mud was subjected to the ozone treatment and the same treatment as in Comparative Example 1 except that the raw mud was continuously passed through the aeration tank (25 ° C.) with a flow rate of 0.5 L / day (residence time 48 hours). Anaerobic digestion treatment was performed. The aeration amount in the aeration tank was 2 L / min.
[0036]
As a result, the sludge concentration (average value) of the anaerobic digested water after 3 months was 0.41 g / L, which was about ½ that of Comparative Example 1.
[0037]
Example 1
In Reference Example 1, the effluent from the anaerobic digester was centrifuged at 15000 rpm for 10 minutes, and 1/3 of the obtained separated sludge was returned to the aeration tank and the remaining 2/3 was returned to the anaerobic digester. The process was performed in the same manner except that.
[0038]
As a result, the sludge concentration in the anaerobic digester after 3 months was 16.2 g / L, and the sludge concentration was hardly increased even though the operation was performed without removing the sludge for 3 months. In addition, the sludge density | concentration of the separation water obtained by centrifugation was remarkably as low as 57 mg / L.
[0039]
Reference example 2
In Example 1 , 1/10 of the separated sludge obtained by centrifugation was returned to the aeration tank, and the treatment was performed in the same manner except that the remainder was drawn out of the system.
[0040]
As a result, the sludge concentration in the anaerobic digester after 3 months was 19 g / L, and the sludge concentration in the separated water obtained by centrifugation was remarkably low at 89 mg / L.
[0041]
Example 2
In Example 1 , 1/20 of the separated sludge obtained by centrifugation was returned to the anaerobic digester and the same treatment was performed except that the remainder was drawn out of the system.
[0042]
As a result, the sludge concentration in the anaerobic digester after 3 months was 6.4 g / L, and the sludge concentration of the separated water obtained by centrifugation was as extremely low as 44 mg / L.
[0043]
【The invention's effect】
As described above in detail, according to the method of anaerobic digestion treatment of organic sludge of the present invention, by aeration prior to ozone treatment in a method of decomposing by digestion treatment of organic sludge after ozone treatment. It is possible to reduce the amount of ozone used in the ozone treatment and improve the treatment efficiency, and to efficiently decompose the organic sludge at a low cost.
[Brief description of the drawings]
FIG. 1A is a system diagram showing an anaerobic digestion treatment method for organic sludge according to a reference example, and FIG. 1B is an embodiment of an organic sludge anaerobic digestion treatment method according to the present invention . FIG.
2A is a system diagram showing an anaerobic digestion treatment method of organic sludge according to a reference example, and FIG. 2B is another implementation of the anaerobic digestion treatment method of organic sludge according to the present invention . It is a systematic diagram which shows the form.
[Explanation of symbols]
1 Aeration tank 2 Ozone treatment tank 3 Anaerobic digestion tank 4 Solid-liquid separator
Claims (3)
オゾン処理に先立ち、有機性汚泥を曝気する工程を有する有機性汚泥の嫌気性消化処理方法であって、
嫌気性消化処理汚泥を固液分離し、分離汚泥の一部を嫌気性消化処理工程に返送することを特徴とする有機性汚泥の嫌気性消化処理方法。In the method of anaerobic digestion after ozone treatment of organic sludge,
Prior to the ozone treatment, an anaerobic digestion method of organic sludge having a process of aeration of organic sludge,
An anaerobic digestion treatment method of organic sludge characterized by solid-liquid separation of anaerobic digestion treatment sludge and returning a part of the separated sludge to the anaerobic digestion treatment step .
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