JP3575312B2 - Organic wastewater treatment method - Google Patents
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- JP3575312B2 JP3575312B2 JP3310099A JP3310099A JP3575312B2 JP 3575312 B2 JP3575312 B2 JP 3575312B2 JP 3310099 A JP3310099 A JP 3310099A JP 3310099 A JP3310099 A JP 3310099A JP 3575312 B2 JP3575312 B2 JP 3575312B2
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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、有機性固形物を含む排水（ビール、デンプン、ポテト加工排水など）の処理方法に係り、特に、この有機性排水を嫌気性生物処理した後好気性生物処理する処理方法において、好気性生物処理での処理水質を高め、その後の固液分離工程におけるスカム発生、バルキングなどの機能障害を防止する方法に関する。
【０００２】
【従来の技術】
ビール、デンプン、ポテト加工排水などの有機性固形物を含む排水の処理方法として、図４に示す如く、該排水を固液分離手段１で沈殿や汚泥浮上法などによって固液分離した後、分離水（以下「前沈上澄み」と称す場合がある。）をＵＡＳＢ（Upflow Anaerobic Sludge Blanket：上向流嫌気性汚泥床）などの高負荷嫌気性生物処理工程２で嫌気性生物処理してメタンに分解し、分離汚泥（以下「前沈排泥」と称す場合がある。）をこの嫌気性処理水と混合して曝気槽３で活性汚泥による好気性生物処理し、得られた好気性処理水を、沈殿槽４で固液分離する方法がある。この方法では、嫌気性生物処理工程２、特に高速型のＵＡＳＢ反応槽に固形物が流入して蓄積すると、反応槽の有効容量が減少したり、汚泥の活性が低下し、処理能力が低下するため、予め固液分離手段１において固形物の除去が行われている。
【０００３】
【発明が解決しようとする課題】
図４に示す如く、従来の有機性排水の処理方法では、嫌気性生物処理工程２の前段で分離した固形物を嫌気性処理水と共に曝気槽３に送給して活性汚泥処理するが、この活性汚泥処理工程において、固形性有機物の流入量が多くなり、溶解性有機物の割合が減少すると、多くの場合、
(1) フロックの形成が不安定となり、フロックが分散傾向となって処理水中に微細なＳＳが流出して透視度が著しく低下する。
(2) 負荷変動によっては、後段の沈殿槽４でスカムや汚泥が浮上したり、曝気槽３での発泡が著しくなる。
など、活性汚泥処理の運転が非常に不安定となる。特に、嫌気処理水は易分解性の有機物の割合が少なく、ＣＯＤＣｒ／ＢＯＤ５の値が４〜５程度と大きくなるため、こうした現象が起こり易い。
【０００４】
このような現象を防ぐために、実際には嫌気性生物処理工程に通水する水量を制限し、原水（有機性排水）の一部（全体水量の３０％程度）を直接後段の曝気槽３に送給することが行われているが、このように原水の一部を曝気槽３に送給することは、嫌気性生物処理を採用することによる汚泥発生量の低減、曝気槽の曝気動力の削減といった効果が損われることとなり、好ましくない。
【０００５】
また、この活性汚泥処理工程での問題は、前沈排泥に起因していることから、この前沈排泥を曝気槽３に導入して処理することなく、直接脱水処理することも試みられているが、腐敗し易い有機性汚泥をそのまま脱水することは、臭気発生の問題があり、実用上不可能である。
【０００６】
本発明は上記従来の問題点を解決し、有機性固形物を含む排水を嫌気性生物処理した後好気性生物処理する処理法において、好気性生物処理での処理水質を高め、その後の固液分離工程におけるスカム発生、バルキングなどの機能障害を防止する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】
本発明の有機性排水の処理方法は、有機性排水を固液分離して、排水中の有機性固形物を分離する固液分離工程と、該固液分離工程で分離された液分を嫌気的に生物処理する嫌気性生物処理工程と、該嫌気性生物処理工程から排出される嫌気性生物処理水及び前記固液分離工程で分離した有機性固形分を好気的に生物処理する好気性生物処理工程とを有する有機性排水の処理方法に関する。
【０００８】
請求項１の発明では、該好気性生物処理工程に、脱窒処理過程が設けられているとともに、前記固液分離工程で分離された有機性固形分を、前記好気性生物処理工程から分離された汚泥の一部と混合されて好気性処理される好気処理過程を経た後、前記好気性生物処理工程に供給する。
【０００９】
請求項２の発明では、前記固液分離工程で分離された有機性固形分を、好気処理過程と脱窒処理過程とを経た後、前記好気性生物処理工程に供給する。
【００１０】
本発明者らは、上述の従来法における問題について鋭意解析した結果、この問題の要因は前沈排泥の固形物の分解とその代謝産物による影響が大きいことが明らかになった。即ち、多くの食品排水では前沈排泥中の有機性ＳＳには、主としてタンパクに由来する固形性の窒素含有有機物が含まれており、曝気槽の滞留時間（ＳＲＴ）を５日程度或いはそれ以上に長くとると、この窒素含有有機物が、活性汚泥による分解の過程で、可溶性窒素含有有機物→アンモニア→亜硝酸→硝酸の順で分解され、活性汚泥処理水が流入する沈殿槽４において、主として硝酸、亜硝酸による脱窒現象により汚泥が浮上したり、スカムが発生するなどの問題が発生する。一般的に、汚泥を安定化させて、できるだけ余剰汚泥の発生量を低下させることが経済的であるため、曝気槽のＳＲＴを長くとって運転を行う場合が多いが、このように曝気槽のＳＲＴを長くする運転条件では、上述の硝化に起因する障害を避けることはできない。逆に、曝気槽のＳＲＴを短くして有機性ＳＳの分解を抑制しようとすると、汚泥濃度を下げざるを得ず、汚泥中に存在する菌体の割合が低いなかで、従って菌体よりも固形有機物が相対的に多い状況で運転を行うこととなり、過負荷のためバルキングが起こったり、著しい発泡現象が起こることとなる。また、曝気槽の前段で嫌気性生物処理を行うために、曝気槽の運転温度は通常３０℃程度となるが、このような温度条件では、たとえＳＲＴを短く維持したとしても、硝化反応が起こり易く、生成した亜硝酸や硝酸と汚泥中に残留する固形性有機物が沈殿槽内で反応して、脱窒が起こり、汚泥の浮上やスカムの生成といった問題を引き起こすこととなる。
【００１１】
従って、従来法における問題を根本的に解決するためには、曝気槽のＳＲＴを比較的長くとって前沈排泥中の有機性ＳＳの分解を促進した上で、活性汚泥処理水が流入する沈殿槽において、上述のような脱窒反応による汚泥の浮上やスカムの生成といった問題が起こらないようにする必要がある。
【００１２】
請求項１の有機性排水の処理方法では、好気性生物処理工程に脱窒処理過程が設けられているため、好気性生物処理工程での分解で生成した硝酸や亜硝酸が、この脱窒処理過程で除去される。このため、後段の沈殿槽に流入する活性汚泥処理水中の硝酸、亜硝酸は著しく低減され、これらに起因する汚泥の浮上やスカムの生成の問題は解消される。
【００１３】
しかも、前沈排泥だけを予め好気処理過程で分解して可溶化、低分子化した後好気性生物処理工程に送給することにより、固形物の分解を促進して余剰汚泥の発生量を低減することができる。
【００１４】
請求項２の有機性排水の処理方法では、前沈排泥を好気処理過程と脱窒処理過程とで処理することにより前沈排泥中の窒素含有有機物を直接硝化脱窒処理して除去する。このため、沈殿槽に流入する活性汚泥処理水中の硝酸、亜硝酸残留量は著しく低減され、これらに起因する汚泥の浮上やスカムの生成の問題は解消される。
【００１５】
【発明の実施の形態】
以下に本発明の実施の形態を詳細に説明する。
【００１６】
図１は参考例に係る有機性排水の処理方法を示す系統図であり、図２は本発明の有機性排水の処理方法の実施の形態を示す系統図である。
【００１７】
図１に示す方法では、原水はまず、沈殿槽、浮上分離槽又はデカンター等の固液分離手段１で固液分離され、固液分離された液分（前沈上澄み）が嫌気性生物処理工程（メタン発酵工程）２で嫌気性生物処理され、含有される有機物の８０〜９０％がメタンに分解される。
【００１８】
この嫌気性生物処理工程２は、一相式であっても良く、酸生成とメタン生成との二相式であっても良い。また、汚泥の保持方式もＵＡＳＢ方式、浮遊方式等のいずれでも良い。
【００１９】
嫌気性処理水は、固液分離手段１で分離された固形分（前沈排泥）と共に好気性生物処理工程５で好気性生物処理され、残留有機物が分解されるが、図１では、この好気性生物処理工程５が仕切壁により３つの領域に分割されており、流入液は、順次、第１番目の領域（第１曝気部）５Ａで好気性生物処理が行われた後、第２番目の領域（脱窒部）５Ｂで嫌気条件下に脱窒処理が行われ、その後、第３番目の領域（第２曝気部）５Ｃで好気性生物処理が行われるように構成されている。
【００２０】
即ち、第１曝気部５Ａでは、前沈排泥及び嫌気処理水中の有機物の分解と、有機性窒素のアンモニア化及び硝化が行われ、脱窒部５Ｂで脱窒が行われ、第２曝気部５Ｃで残留有機物を分解し、溶存酸素を高めて処理水を沈殿槽４に送給する。
【００２１】
この好気性生物処理工程５の汚泥の保持方式は、浮遊方式、固定床式、流動床式、生物膜式のいずれでも良い。
【００２２】
好気性生物処理工程５における脱窒部５Ｂの容積割合が、過度に大きいと好気性生物処理工程としての機能が損われ、過度に小さいと脱窒部を設けることによる本発明の効果が得られない。従って、脱窒部５Ｂは、好気性生物処理工程５の容積（第１曝気部５Ａ，脱窒部５Ｂ及び第２曝気部５Ｃの合計の容積）の１０〜５０％、特に２０〜３０％程度とするのが好ましい。
【００２３】
また、好気性生物処理工程５における脱窒部５Ｂは、図１に示す如く、第１曝気部５Ａと第２曝気部５Ｂとの間に設ける他、好気性生物処理工程を脱窒部とその後段の曝気部とで構成し、曝気部の流出液の一部を脱窒部に返送して循環させるようにしても良い。
【００２４】
この脱窒部５Ｂは、嫌気性条件下、即ち曝気を全く行わないか、曝気を行っても供給酸素量を制限とすることで脱窒細菌により硝酸イオン、亜硝酸イオンを窒素ガスに分解する工程であり、この脱窒部５Ｂにおける脱窒反応は、汚泥中に含まれる有機物を水素供与体とする内生脱窒であっても、脱窒効率を上げるために原水又は前沈上澄みの一部（好ましくは３〜２０％、より好ましくは５〜１０％程度）を図１の破線で示す如く、脱窒部５Ｂに直接導入するものであっても良い。原水又は前沈上澄みの一部を水素供与体として直接脱窒部５Ｂに導入した場合には、一般的には脱窒速度、脱窒効率が高められ、より一層良好な水質の処理水を得ることができる。
【００２５】
図１に示す如く、好気性生物処理工程５に脱窒部５Ｂを設けることにより、好気性生物処理で生成した亜硝酸や硝酸が脱窒部５Ｂで脱窒されるため、後段の沈殿槽４では脱窒現象が生起することはなく、このため沈殿槽４における汚泥の浮上やスカムの生成は防止される。
【００２６】
第２の曝気部５Ｃから沈殿槽４に送給された好気性処理水は、沈殿槽４で固液分離され、上澄水が処理水として系外へ排出される。一方、分離汚泥は返送汚泥として好気性生物処理工程５へ返送される。なお、好気性生物処理工程５の汚泥又はこの分離汚泥の一部は、必要に応じて余剰汚泥として系外へ排出される。
【００２７】
前述の如く、沈殿槽５では脱窒現象が防止され、それによる汚泥の浮上やスカムの発生が防止されるため、浮上汚泥や微細フロックの流出等による処理水水質の悪化が防止され、沈殿槽５からは高水質の処理水を得ることができる。
【００２８】
なお、好気性処理水の固液分離手段としては、沈殿槽５の代りに膜分離装置を用いても良い。
【００２９】
図２に示す方法は、汚泥安定化槽６を設け、この汚泥安定化槽６で前沈排泥を好気性生物処理した後好気性生物処理工程５に送給する点が図１に示す方法と異なり、その他は同様の構成とされている。
【００３０】
この方法では、前沈排泥だけを汚泥安定化槽６で好気性生物処理することにより滞留時間を長くでき、十分に可溶化、低分子化した後好気性生物処理工程５に送給することにより、固形物の分解を促進して余剰汚泥の発生量を低減することができる。なお、返送汚泥の一部は汚泥安定化槽６における菌体濃度の維持のために汚泥安定化槽６に送給される。この方法では、汚泥安定化槽６においても有機性窒素の硝化反応で硝酸、亜硝酸が生成するが、生成した硝酸、亜硝酸は図１の方法と同様に好気性生物処理工程５の脱窒部５Ｂで脱窒される。
【００３１】
図３に示す方法は、汚泥安定化槽６が仕切壁により２つの領域に分割されており、流入汚泥は、第１番目の領域（脱窒部）６Ａで嫌気性生物処理が行われた後、第２番目の領域（曝気部）６Ｂで好気性生物処理が行われ、この曝気部６Ｂの処理水の一部が脱窒部６Ａに循環されるように構成されている点が図２に示す方法と異なり、その他は同様の構成とされている。
【００３２】
この脱窒部６Ａも前述の脱窒部５Ｂと同様、嫌気性条件下、即ち曝気を全く行わないか、曝気を行っても供給酸素量を制限とすることで脱窒細菌により硝酸イオン、亜硝酸イオンを窒素ガスに分解するものであり、従って、この方法では、図２に示す方法と同様に、汚泥安定化槽６において、前沈排泥の可溶化、低分子化が促進されると共に、前沈排泥中の固形物由来の有機性窒素が汚泥安定化槽６の脱窒部６Ａ及び曝気部６Ｂで硝化、脱窒されて除去される。
【００３３】
なお、図３に示す方法において、前沈排泥中の有機性窒素は汚泥安定化槽６で硝化、脱窒されるため、好気性生物処理工程５の脱窒部５Ｂは必ずしも必要とされず、好気性生物処理工程５は曝気部のみで構成されていても良い。
【００３４】
図３に示す方法でも、汚泥安定化槽６、更には好気性生物処理工程５における硝化、脱窒で有機性窒素が除去されることにより、沈殿槽４に導入される好気性生物処理水中の硝酸、亜硝酸量が低減され、これらによる脱窒現象に起因する沈殿槽４での汚泥の浮上、スカムの発生、それによる処理水水質の悪化は防止される。
【００３５】
このように汚泥安定化槽６に脱窒部６Ａを設ける場合、脱窒部６Ａの容積割合は、好気性生物処理工程５の脱窒部の有無によっても異なるが、好気性生物処理工程５に脱窒部がない場合には、脱窒部６Ａは汚泥安定化槽６の全容積の２０〜５０％程度とし、好気性生物処理工程５に脱窒部を設けた場合には脱窒部６Ａは汚泥安定化槽６の全容積の１０〜３０％程度とするのが好ましい。
【００３６】
この汚泥安定化槽６についても、好気性生物処理工程５と同様、循環を行わずに曝気部、脱窒部及び曝気部の三相式とすることもできる。
【００３７】
なお、図２，３に示す方法は本発明の実施例であって、本発明はその要旨を超えない限り何ら図示の方法に限定されるものではない。
【００３８】
例えば、前述の如く、原水又は前沈上澄みは、好気性生物処理工程の脱窒部への水素供与体供給源としてその一部を直接好気性生物処理工程の脱窒部へ送給しても良い。
【００３９】
【実施例】
以下に、参考例、実施例及び比較例を挙げて本発明をより具体的に説明する。
【００４０】
なお、以下の参考例、実施例及び比較例においては、ビール工場総合排水を固液分離し、前沈上澄みをＵＡＳＢによる嫌気性生物処理した後、前沈排泥と共に好気性生物処理し、好気性処理水を固液分離する処理系に、各々の方法を適用して行った。
【００４１】
この処理系における前沈上澄み、前沈排泥、ＵＡＳＢ処理水の水質は表１に示す通りである。
【００４２】
【表１】
比較例１（図４に示す従来例）
ＰＶＣ製の曝気槽を直列に配置し、第１曝気槽（容量５．０Ｌ）、第２曝気槽（容量２．５Ｌ）、第３曝気槽（容量２．５Ｌ）で各々好気性生物処理を行った。なお、第１曝気槽へのＵＡＳＢ処理水の流入量は２１Ｌ／ｄａｙ、前沈排泥の流入量は１．２Ｌ／ｄａｙとし、各曝気槽のＭＬＳＳは約６０００〜７０００ｍｇ／Ｌとなるように汚泥の引抜き量を調整した。処理温度は約２５〜３０℃とした。第１曝気槽の負荷は表２に示す通りであった。また、汚泥返送量は原水の２倍量とした。
【００４４】
このようにして処理を継続したときの、処理水（沈殿槽の上澄水）の透視度、処理水ＳＳ及び処理水中の硝酸性及び亜硝酸性窒素濃度の経時変化はそれぞれ、図５、図６、図７に示す通りであった。
【００４５】
参考例１（図１に示す方法）
比較例１において、第２曝気槽で曝気を行わずに嫌気性生物処理を行った（即ち、第２曝気槽を脱窒槽とする。）こと以外は比較例１と同様にして処理を行った。このときの第１曝気槽の負荷は表２に示す通り、比較例１の場合と同等である。
【００４６】
このようにして処理を継続したときの、処理水（沈殿槽の上澄水）の透視度、処理水ＳＳ及び処理水中の硝酸性及び亜硝酸性窒素濃度の経時変化はそれぞれ、図５、図６、図７に示す通りであった。
【００４７】
実施例１（図２に示す本発明法）
参考例１において、更に、第１汚泥安定化槽（容量１．５Ｌ）と第２汚泥安定化槽（容量１．５Ｌ）とを直列に配置し、前沈排泥をこれら第１，第２汚泥安定化槽で好気性生物処理した後第１曝気槽に供給すると共に、前沈上澄みのうちの一部２．２Ｌ／ｄａｙを第２槽の脱窒槽に直接送給したこと以外は参考例１と同様にして処理を行った。なお、第１汚泥安定化槽には沈殿槽で分離された汚泥の１０％を返送し、残部を第１曝気槽に返送した。
【００４８】
このときの第１曝気槽の負荷は表２に示す通りである。
【００４９】
このようにして処理を継続したときの、処理水（沈殿槽の上澄水）の透視度、処理水ＳＳ及び処理水中の硝酸性及び亜硝酸性窒素濃度の経時変化はそれぞれ、図５、図６、図７に示す通りであった。
【００５０】
実施例２（図３に示す本発明法）
実施例１において、第１汚泥安定化槽で曝気を行わず嫌気性生物処理を行い、第２汚泥安定化槽の流出液の３００％を第１汚泥安定化槽に循環し、また、前沈上澄みはその全量を嫌気性生物処理工程へ送給したこと以外は実施例１と同様にして処理を行った。このときの第１曝気槽の負荷は表２に示す通りである。
【００５１】
このようにして処理を継続したときの、処理水（沈殿槽の上澄水）の透視度、処理水ＳＳ及び処理水中の硝酸性及び亜硝酸性窒素濃度の経時変化はそれぞれ、図５、図６、図７に示す通りであった。
【００５２】
【表２】
上記比較例１、参考例１及び実施例１，２の結果から次のことが明らかである。
【００５４】
即ち、従来法による比較例１では、沈殿槽にスカムが頻繁に発生し、処理水の透視度が低かった。参考例１及び実施例２では内生脱窒のみでの脱窒であり、好気性生物処理工程に設けた脱窒槽で完全に窒素除去できていないため、やや透視度が低く、処理水に流出するＳＳも、実施例１よりも高かった。実施例１では、前沈上澄みの一部を水素供与体として直接導入することで、好気性生物処理工程に設けた脱窒槽でのＮＯｘ−Ｎ除去がほぼ完全に行われ、残留ＮＯｘ−Ｎが少ないため、処理水ＳＳ、透視度が最も良好であった。
【００５５】
【発明の効果】
以上詳述した通り、本発明の有機性排水の処理方法によれば、有機性固形物を含む排水を嫌気性生物処理した後、好気性生物処理する処理法において、好気性生物処理工程の滞留時間を十分に長くとって処理水水質を高めると共に、その後の固液分離工程におけるスカム発生やバルキング等の機能障害を防止して、安定かつ効率的な処理を行える。
【図面の簡単な説明】
【図１】参考例に係る有機性排水の処理方法の実施の形態を示す系統図である。
【図２】請求項１の有機性排水の処理方法の実施の形態を示す系統図である。
【図３】請求項２の有機性排水の処理方法の実施の形態を示す系統図である。
【図４】従来法を示す系統図である。
【図５】実施例１，２、参考例１及び比較例１における処理水透視度の推移を示すグラフである。
【図６】実施例１，２、参考例１及び比較例１における処理水ＳＳの推移を示すグラフである。
【図７】実施例１，２、参考例１及び比較例１における処理水ＮＯｘ−Ｎの推移を示すグラフである。
【符号の説明】
１ 固液分離手段
２ 嫌気性生物処理工程
３ 曝気槽
４ 沈殿槽
５ 好気性生物処理工程
６ 汚泥安定化槽[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for treating wastewater containing organic solids (beer, starch, potato-processed wastewater, etc.), and particularly to a method for treating this organic wastewater with an anaerobic biological treatment and then with an aerobic biological treatment. The present invention relates to a method for enhancing the quality of treated water in aerobic biological treatment and preventing scum generation, bulking, and other functional disorders in a subsequent solid-liquid separation step.
[0002]
[Prior art]
As a method for treating wastewater containing organic solids such as beer, starch, potato wastewater, etc., as shown in FIG. 4, the wastewater is subjected to solid-liquid separation by a solid-liquid separation means 1 by sedimentation or sludge flotation, and then separated. Water (hereinafter sometimes referred to as "pre-sedimentation supernatant") is subjected to anaerobic biological treatment in a high-load anaerobic biological treatment process 2 such as UASB (Upflow Anaerobic Sludge Blanket: Upflow Anaerobic Sludge Bed) to produce methane. Decomposed, separated sludge (hereinafter sometimes referred to as “pre-sedimentation sludge”) is mixed with this anaerobic treated water, subjected to aerobic biological treatment with activated sludge in the aeration tank 3, and obtained aerobic treated water. In the sedimentation tank 4 for solid-liquid separation. In this method, when solids flow into and accumulate in the anaerobic biological treatment step 2, particularly the high-speed UASB reaction tank, the effective capacity of the reaction tank decreases, the activity of sludge decreases, and the treatment capacity decreases. Therefore, solids are removed in the solid-liquid separation means 1 in advance.
[0003]
[Problems to be solved by the invention]
As shown in FIG. 4, in the conventional method for treating organic wastewater, the solid separated in the previous stage of the anaerobic biological treatment step 2 is sent to the aeration tank 3 together with the anaerobic treated water to perform the activated sludge treatment. In the activated sludge treatment step, when the inflow of solid organic matter increases and the proportion of soluble organic matter decreases, in many cases,
(1) The formation of flocs becomes unstable, the flocs tend to disperse, and fine SS flows out into the treated water, and the visibility decreases significantly.
(2) Depending on the load fluctuation, scum or sludge floats in the sedimentation tank 4 at the subsequent stage, and foaming in the aeration tank 3 becomes remarkable.
For example, the operation of the activated sludge treatment becomes very unstable. In particular, the anaerobic treated water has a low ratio of easily decomposable organic substances, and the value of COD Cr / BOD 5 is as large as about 4 to 5 , so that such a phenomenon is likely to occur.
[0004]
In order to prevent such a phenomenon, the amount of water passing through the anaerobic biological treatment process is actually limited, and a part of the raw water (organic wastewater) (about 30% of the total water amount) is directly sent to the aeration tank 3 at the subsequent stage. Although a part of the raw water is supplied to the aeration tank 3 as described above, the amount of sludge generated by adopting the anaerobic biological treatment is reduced, and the aeration power of the aeration tank is reduced. The effect of reduction is impaired, which is not preferable.
[0005]
Further, since the problem in the activated sludge treatment step is caused by the pre-sedimentation sludge, direct dehydration treatment is also attempted without introducing the pre-sedimentation sludge into the aeration tank 3 for treatment. However, it is practically impossible to dewater organic sludge which is easily rotted as it is because of the problem of odor generation.
[0006]
The present invention solves the above-mentioned conventional problems, and in a treatment method of subjecting wastewater containing organic solids to anaerobic biological treatment and then aerobic biological treatment, the quality of the treated water in the aerobic biological treatment is enhanced, It is an object of the present invention to provide a method for preventing scum generation and bulking and other functional disorders in a separation step.
[0007]
[Means for Solving the Problems]
The method for treating organic wastewater according to the present invention includes a solid-liquid separation step of solid-liquid separation of the organic wastewater to separate organic solids in the wastewater, and an anaerobic liquid separated in the solid-liquid separation step. An anaerobic biological treatment step for biological treatment, and an aerobic biological treatment for aerobic biological treatment of the anaerobic biological treatment water discharged from the anaerobic biological treatment step and the organic solids separated in the solid-liquid separation step And a biological treatment step.
[0008]
In the invention of claim 1, in該好temper biological treatment step, the denitrification process is provided, the organic solids separated in the previous SL solid-liquid separation step, separating from the aerobic biological treatment process After passing through an aerobic treatment process in which the sludge is mixed with a part of the sludge and subjected to aerobic treatment, the sludge is supplied to the aerobic biological treatment process.
[0009]
In the invention of claim 2 , the organic solid separated in the solid-liquid separation step is supplied to the aerobic biological treatment step after passing through an aerobic treatment step and a denitrification treatment step.
[0010]
The present inventors have conducted intensive analysis on the problem in the above-mentioned conventional method, and as a result, it has been found that the cause of this problem is largely affected by decomposition of solids in the pre-set sludge and its metabolites. That is, in many food wastewaters, the organic SS in the pre-sedimentation sludge contains solid nitrogen-containing organic matter mainly derived from proteins, and the residence time (SRT) in the aeration tank is about 5 days or less. If it takes longer, this nitrogen-containing organic matter is decomposed in the order of soluble nitrogen-containing organic matter → ammonia → nitrous acid → nitric acid in the course of decomposition by activated sludge, and mainly in the sedimentation tank 4 into which the activated sludge treated water flows. Problems such as sludge floating and scum are generated due to the denitrification by nitric acid and nitrous acid. In general, it is economical to stabilize the sludge and reduce the amount of excess sludge generated as much as possible. Therefore, it is often the case that the operation is performed with a long SRT of the aeration tank. Under the operating conditions that lengthen the SRT, the above-mentioned obstacles caused by nitrification cannot be avoided. Conversely, if the SRT in the aeration tank is shortened to suppress the decomposition of organic SS, the sludge concentration must be reduced, and the ratio of bacterial cells present in the sludge is low. The operation is performed in a state where the amount of solid organic matter is relatively large, and bulking occurs due to overload, and a remarkable foaming phenomenon occurs. In addition, since the anaerobic biological treatment is performed before the aeration tank, the operation temperature of the aeration tank is usually about 30 ° C. Under such temperature conditions, even if the SRT is kept short, the nitrification reaction occurs. Easily, the generated nitrous acid or nitric acid reacts with the solid organic matter remaining in the sludge in the sedimentation tank, causing denitrification and causing problems such as sludge floating and scum formation.
[0011]
Therefore, in order to fundamentally solve the problem in the conventional method, the SRT of the aeration tank is set relatively long to promote the decomposition of the organic SS in the pre-sedimentation sludge, and then the activated sludge treated water flows in. In the settling tank, it is necessary to prevent problems such as sludge floating and scum formation due to the denitrification reaction as described above.
[0012]
In the method for treating organic waste water according to claim 1, since the aerobic biological treatment step is provided with a denitrification treatment step, nitric acid or nitrous acid generated by decomposition in the aerobic biological treatment step is subjected to the denitrification treatment. Removed in the process. For this reason, the amount of nitric acid and nitrous acid in the activated sludge treatment water flowing into the subsequent settling tank is remarkably reduced, and the problems of sludge floating and scum generation due to these are eliminated.
[0013]
In addition, only the pre-sedimentation sludge is decomposed and solubilized in advance in the aerobic treatment process to reduce the molecular weight, and then sent to the aerobic biological treatment process to promote the decomposition of solids and generate excess sludge. Can be reduced.
[0014]
In the method for treating organic wastewater according to the second aspect, the pre-settled sludge is subjected to an aerobic treatment process and a denitrification treatment process, whereby nitrogen-containing organic matter in the pre-settled sludge is directly removed by nitrification and denitrification treatment. I do. For this reason, the residual amounts of nitric acid and nitrous acid in the activated sludge treatment water flowing into the settling tank are significantly reduced, and the problems of sludge floating and scum generation due to these are eliminated.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
[0016]
FIG. 1 is a system diagram showing a method for treating organic wastewater according to a reference example, and FIG. 2 is a system diagram showing an embodiment of a method for treating organic wastewater of the present invention.
[0017]
In the method shown in FIG. 1, raw water is first subjected to solid-liquid separation by a solid-liquid separation means 1 such as a sedimentation tank, a flotation tank or a decanter, and the separated liquid (pre-sedimentation supernatant) is subjected to an anaerobic biological treatment step. (Methane fermentation step) The anaerobic biological treatment is carried out in 2, and 80 to 90% of the contained organic matter is decomposed into methane.
[0018]
The anaerobic biological treatment step 2 may be a single-phase system or a two-phase system of acid generation and methane generation. Further, the sludge holding method may be any of the UASB method, the floating method, and the like.
[0019]
The anaerobic treated water is subjected to aerobic biological treatment in the aerobic
[0020]
That is, in the first aeration unit 5A, decomposition of organic matter in the pre-sedimentation sludge and anaerobic treated water, ammoniaation and nitrification of organic nitrogen are performed, denitrification is performed in the denitrification unit 5B, and the second aeration unit is performed. The residual organic matter is decomposed at 5C, the dissolved oxygen is increased, and the treated water is fed to the sedimentation tank 4.
[0021]
The method of holding sludge in the aerobic
[0022]
If the volume ratio of the denitrification part 5B in the aerobic
[0023]
As shown in FIG. 1, the denitrification unit 5B in the aerobic
[0024]
The denitrification section 5B decomposes nitrate ions and nitrite ions into nitrogen gas by denitrifying bacteria under anaerobic conditions, that is, by not performing aeration at all or limiting the amount of supplied oxygen even if aeration is performed. In the denitrification reaction in the denitrification section 5B, even in the case of endogenous denitrification in which the organic matter contained in the sludge is a hydrogen donor, one of the raw water or the pre-sedimentation supernatant is used to increase the denitrification efficiency. 1 (preferably about 3 to 20%, more preferably about 5 to 10%) may be directly introduced into the denitrification section 5B as shown by the broken line in FIG. When a part of the raw water or the pre-sedimentation supernatant is directly introduced into the denitrification section 5B as a hydrogen donor, the denitrification rate and the denitrification efficiency are generally increased, and the treated water with better water quality is obtained. be able to.
[0025]
As shown in FIG. 1, by providing the denitrification unit 5B in the aerobic
[0026]
The aerobic treated water sent from the
[0027]
As described above, the denitrification phenomenon is prevented in the
[0028]
In addition, as the solid-liquid separation means of the aerobic treated water, a membrane separation device may be used instead of the
[0029]
The method shown in FIG. 2 is different from the method shown in FIG. 1 in that a sludge stabilization tank 6 is provided, and the pre-sedimentation sludge is subjected to aerobic biological treatment in the sludge stabilization tank 6 and then sent to the aerobic
[0030]
In this method, the residence time can be lengthened by subjecting only the pre-sedimentation sludge to the aerobic biological treatment in the sludge stabilization tank 6, and the sludge is sufficiently solubilized and depolymerized before being sent to the aerobic
[0031]
In the method shown in FIG. 3, the sludge stabilization tank 6 is divided into two regions by a partition wall, and the inflow sludge is subjected to the anaerobic biological treatment in the first region (denitrification section) 6A. The point that the aerobic biological treatment is performed in the second region (aeration unit) 6B and a part of the treatment water of the aeration unit 6B is circulated to the denitrification unit 6A is shown in FIG. Unlike the method shown, the other components have the same configuration.
[0032]
Similarly to the above-mentioned denitrification unit 5B, this denitrification unit 6A is also subjected to anaerobic conditions, that is, no aeration is performed, or even if aeration is performed, the amount of supplied oxygen is limited, so that nitric ions and nitrous ions are removed by denitrification bacteria. This method decomposes nitrate ions into nitrogen gas. Therefore, in this method, as in the method shown in FIG. In addition, organic nitrogen derived from solid matter in the pre-sedimentation sludge is removed by nitrification and denitrification in the denitrification section 6A and the aeration section 6B of the sludge stabilization tank 6.
[0033]
In the method shown in FIG. 3, since the organic nitrogen in the pre-sedimentation sludge is nitrified and denitrified in the sludge stabilization tank 6, the denitrification part 5B of the aerobic
[0034]
Also in the method shown in FIG. 3, the organic nitrogen is removed by the nitrification and denitrification in the sludge stabilization tank 6 and the aerobic
[0035]
When the denitrification section 6A is provided in the sludge stabilization tank 6 as described above, the volume ratio of the denitrification section 6A varies depending on whether or not the denitrification section is provided in the aerobic
[0036]
As with the aerobic
[0037]
The method shown in FIGS. 2 and 3 is an embodiment of the present invention, and the present invention is not limited to the illustrated method unless it exceeds the gist.
[0038]
For example, as described above, raw water or pre-sedimentation supernatant may be directly supplied to the denitrification part of the aerobic biological treatment step as a hydrogen donor supply source to the denitrification part of the aerobic biological treatment step. good.
[0039]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Reference Examples, Examples, and Comparative Examples.
[0040]
In the following Reference Examples, Examples and Comparative Examples, the beer factory general wastewater was subjected to solid-liquid separation, and the pre-sedimentation supernatant was subjected to anaerobic biological treatment with UASB, followed by aerobic biological treatment together with pre-sedimentation sludge. Each method was applied to a treatment system for solid-liquid separation of gaseous treated water.
[0041]
The quality of the pre-settling supernatant, pre-settling sludge, and UASB treated water in this treatment system is as shown in Table 1.
[0042]
[Table 1]
Comparative Example 1 (conventional example shown in FIG. 4)
Aeration tanks made of PVC are arranged in series, and the first aeration tank (capacity: 5.0 L), the second aeration tank (capacity: 2.5 L), and the third aeration tank (capacity: 2.5 L) are each used for aerobic biological treatment. went. In addition, the inflow of the UASB treated water into the first aeration tank was 21 L / day, the inflow of the pre-sedimentation sludge was 1.2 L / day, and the MLSS of each aeration tank was about 6000 to 7000 mg / L. The amount of sludge withdrawn was adjusted. The processing temperature was about 25-30 ° C. The load of the first aeration tank was as shown in Table 2. The amount of sludge returned was twice the amount of raw water.
[0044]
When the treatment was continued in this manner, the time-dependent changes in the transparency of the treated water (supernatant water in the settling tank) and the nitrate and nitrite nitrogen concentrations in the treated water SS and the treated water were respectively shown in FIGS. , As shown in FIG.
[0045]
Reference Example 1 ( method shown in FIG. 1)
In Comparative Example 1, treatment was performed in the same manner as in Comparative Example 1 except that the anaerobic biological treatment was performed without performing aeration in the second aeration tank (that is, the second aeration tank was used as a denitrification tank). . As shown in Table 2, the load of the first aeration tank at this time is equal to that of Comparative Example 1.
[0046]
When the treatment was continued in this manner, the time-dependent changes in the transparency of the treated water (supernatant water in the settling tank) and the nitrate and nitrite nitrogen concentrations in the treated water SS and the treated water were respectively shown in FIGS. , As shown in FIG.
[0047]
Example 1 (the method of the present invention shown in FIG. 2)
In Reference Example 1, a first sludge stabilization tank (capacity 1.5 L) and a second sludge stabilization tank (capacity 1.5 L) are further arranged in series, and the pre-sedimentation sludge is removed from the first and second sludges. Reference example except that after aerobic biological treatment in the sludge stabilization tank, it was supplied to the first aeration tank, and 2.2 L / day of a part of the supernatant was directly sent to the denitrification tank of the second tank. Processing was performed in the same manner as in Example 1. In addition, 10% of the sludge separated in the sedimentation tank was returned to the first sludge stabilization tank, and the remainder was returned to the first aeration tank.
[0048]
The load on the first aeration tank at this time is as shown in Table 2.
[0049]
When the treatment was continued in this manner, the time-dependent changes in the transparency of the treated water (supernatant water in the settling tank) and the nitrate and nitrite nitrogen concentrations in the treated water SS and the treated water were respectively shown in FIGS. , As shown in FIG.
[0050]
Example 2 (the method of the present invention shown in FIG. 3)
In Example 1 , an anaerobic biological treatment was performed without performing aeration in the first sludge stabilization tank, and 300% of the effluent from the second sludge stabilization tank was circulated to the first sludge stabilization tank. The supernatant was treated in the same manner as in Example 1 except that the entire amount was sent to the anaerobic biological treatment step. The load on the first aeration tank at this time is as shown in Table 2.
[0051]
When the treatment was continued in this manner, the time-dependent changes in the transparency of the treated water (supernatant water in the sedimentation tank) and the nitrate and nitrite nitrogen concentrations in the treated water SS and the treated water were respectively shown in FIGS. , As shown in FIG.
[0052]
[Table 2]
The following is apparent from the results of Comparative Example 1 , Reference Example 1, and Examples 1 and 2 .
[0054]
That is, in Comparative Example 1 according to the conventional method, scum was frequently generated in the settling tank, and the visibility of the treated water was low. In Reference Example 1 and Example 2 , denitrification was carried out only by endogenous denitrification, and nitrogen was not completely removed by the denitrification tank provided in the aerobic biological treatment process. SS to be performed was also higher than that of Example 1 . In Example 1, before a portion of the precipitated supernatant by introducing directly as hydrogen donor, NO x -N removal in denitrification tank provided in the aerobic biological treatment step is carried out almost completely, remaining NO x - Since N was small, the treated water SS and the visibility were the best.
[0055]
【The invention's effect】
As described in detail above, according to the method for treating organic wastewater of the present invention, the wastewater containing organic solids is subjected to anaerobic biological treatment, and then aerobic biological treatment is performed. A sufficiently long time is taken to improve the quality of the treated water, and it is possible to prevent scum and bulking and other functional disorders in the subsequent solid-liquid separation step, thereby performing stable and efficient treatment.
[Brief description of the drawings]
FIG. 1 is a system diagram showing an embodiment of a method for treating organic wastewater according to a reference example .
FIG. 2 is a system diagram showing an embodiment of the method for treating organic wastewater according to claim 1 ;
FIG. 3 is a system diagram showing an embodiment of an organic wastewater treatment method according to claim 2 ;
FIG. 4 is a system diagram showing a conventional method.
FIG. 5 is a graph showing changes in treated water transparency in Examples 1 and 2, Reference Example 1, and Comparative Example 1.
FIG. 6 is a graph showing changes in treated water SS in Examples 1 and 2, Reference Example 1, and Comparative Example 1.
FIG. 7 is a graph showing changes in treated water NO x -N in Examples 1 and 2, Reference Example 1, and Comparative Example 1.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Solid-liquid separation means 2 Anaerobic biological treatment process 3 Aeration tank 4
Claims (2)
該固液分離工程で分離された液分を嫌気的に生物処理する嫌気性生物処理工程と、
該嫌気性生物処理工程から排出される嫌気性生物処理水及び前記固液分離工程で分離した有機性固形分を好気的に生物処理する好気性生物処理工程と、
を有する有機性排水の処理方法において、
該好気性生物処理工程に、脱窒処理過程が設けられているとともに、
前記固液分離工程で分離された有機性固形分が、前記好気性生物処理工程から分離された汚泥の一部と混合されて好気性処理される好気処理過程を経た後、前記好気性生物処理工程に供給されることを特徴とする有機性排水の処理方法。A solid-liquid separation step of solid-liquid separation of the organic wastewater and separation of organic solids in the wastewater,
Anaerobic biological treatment step of anaerobically biologically treating the liquid component separated in the solid-liquid separation step,
An aerobic biological treatment step of aerobically biologically treating the anaerobic biological treatment water discharged from the anaerobic biological treatment step and the organic solids separated in the solid-liquid separation step,
In a method for treating organic waste water having
The aerobic biological treatment step is provided with a denitrification treatment step ,
The organic solids separated in the solid-liquid separation step are subjected to an aerobic treatment process in which the organic solids are mixed with a part of the sludge separated from the aerobic biological treatment step and aerobic treated, and then the aerobic A method for treating organic wastewater, which is supplied to a treatment step .
該固液分離工程で分離された液分を嫌気的に生物処理する嫌気性生物処理工程と、
該嫌気性生物処理工程から排出される嫌気性生物処理水及び前記固液分離工程で分離した有機性固形分を好気的に生物処理する好気性生物処理工程と、
を有する有機性排水の処理方法において、
前記固液分離工程で分離された有機性固形分が、好気処理過程と脱窒処理過程とを経た後、前記好気性生物処理工程に供給されることを特徴とする有機性排水の処理方法。A solid-liquid separation step of solid-liquid separation of the organic wastewater and separation of organic solids in the wastewater,
Anaerobic biological treatment step of anaerobically biologically treating the liquid component separated in the solid-liquid separation step,
An aerobic biological treatment step of aerobically biologically treating the anaerobic biological treatment water discharged from the anaerobic biological treatment step and the organic solids separated in the solid-liquid separation step,
In a method for treating organic waste water having
Organic wastewater separated in the solid-liquid separation step is subjected to an aerobic treatment step and a denitrification treatment step, and then supplied to the aerobic biological treatment step, a method for treating organic wastewater. .
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