JP3801004B2

JP3801004B2 - Method and apparatus for treating organic wastewater

Info

Publication number: JP3801004B2
Application number: JP2001283366A
Authority: JP
Inventors: 琢也小林; 清美荒川; 克之片岡; 俊博田中
Original assignee: Ebara Corp
Current assignee: Ebara Corp
Priority date: 2001-09-18
Filing date: 2001-09-18
Publication date: 2006-07-26
Anticipated expiration: 2021-09-18
Also published as: JP2003088885A

Description

【０００１】
【発明の属する技術分野】
本発明は、有機性廃水の処理に係り、特に、有機性廃水を生物処理し、膜分離により固液分離を行う生物処理方法と装置に関する。
【０００２】
【従来の技術】
有機性廃水の処理において、活性汚泥による生物処理方法は、多様な排水へ対応でき排水処理方法の主流となっている。生物処理法の一つに、排水中の有機物除去に加えて窒素を除去するための方法として、硝化脱窒法が知られている。これは、排水中の窒素の除去のために提案されたもので、生物処理槽を、攪拌のみを行う脱窒槽と、硝化を行う硝化槽に分け、排水を脱窒槽に流入させ、脱窒槽流出液は硝化槽に供給、硝化槽流出液は固液分離装置に流出させ、同時に一部の硝化槽流出液を脱窒槽へ循環する処理となっている。硝化槽では、ＢＯＤ酸化菌による廃水中の有機物の酸化分解の他に、活性汚泥中の硝化菌により、アンモニア性窒素が硝酸性窒素に酸化される。硝化槽から流出した活性汚泥混合液は、脱窒槽で、活性汚泥混合液中の硝酸性窒素を、活性汚泥中の脱窒菌が原水に含まれる有機物を用い、窒素に還元する。以上の工程により、廃水中のアンモニア性窒素は、気体窒素に還元され廃水中から除去される。
【０００３】
上述のように、活性汚泥による生物処理は優れた方法であるが、その一方で、生物処理槽内で増殖した微生物や流入した懸濁物質などにより、余剰汚泥が発生する問題がある。近年、余剰汚泥の処理コストが増加しているため、その抑制技術が注目されており、汚泥を微細化、可溶化し、再び生物処理槽に供給することで、液化した汚泥を生物処理槽中の活性汚泥により、無機化を行うことが提案されている。微細化や液化工程については、物理的に活性汚泥を微細化する方法や、加温し高熱細菌を利用し汚泥を可溶化する方法、オゾンを作用させて汚泥を可溶化する技術が知られている。しかし、これらの方法で汚泥の微細化、液化を行ったとき、余剰汚泥の発生量は減少するものの、微細化した汚泥の一部が処理水に流出し、処理水水質が悪化する問題点があった。また、これらの微細化、液化方法は、従来の生物処理系にさらに微細化工程や液化工程を付け加えるため、装置全体が複雑になる問題がある。
汚泥の微細化や液化による減容化において、膜分離法を用い固液分離を行えば、処理水への汚泥の流出を抑えることが可能である。しかし、同時に微細化した汚泥が系内に蓄積し、減容化効率が低下することや、膜の閉塞が起こりやすくなる問題点があった。
【０００４】
【発明が解決しようとする課題】
本発明は、上記のような従来技術に鑑みてなされたものであり、処理水水質の悪化を防ぎつつ、生物処理の過程で発生する余剰汚泥の発生量を削減し、また、生物処理槽内に蓄積する難生物分解性物質の除去が可能な、簡便な有機性廃水の生物処理方法と装置を提供することを課題とする。
【０００５】
【課題を解決するための手段】
上記課題を解決するために、本発明では、有機性廃水を生物処理槽で処理し、得られる活性汚泥を膜分離により固液分離して処理水を得る生物処理方法において、前記生物処理槽内の活性汚泥の一部を抜き出して液化処理し、該液化処理した汚泥を生物処理槽に循環させると共に、さらに、別に生物処理槽から活性汚泥原水水量の１〜１０％を抜き出して前記膜分離による固液分離とは別の固液分離を行い、該固液分離により得られた汚泥を生物処理槽に循環させ、一方、得られた分離液から０．１μｍ〜１μｍの粒径の微細汚泥を有する難生物分解性物質を除去して処理水として系外に流出することとしたものである。
前記処理方法において、液化処理は、オゾン処理又は超音波処理により行うことができ、また、前記難生物分解性物質の除去は、凝集剤の添加による凝集沈殿によるか、又は、オゾン及び／又は過酸化水素による酸化分解によることができる。
【０００６】
また、本発明では、有機性廃水を生物処理する生物処理槽と、得られる活性汚泥を固液分離して処理水を得る膜分離装置を有する生物処理装置において、前記生物処理槽の活性汚泥の一部を抜き出す経路と、該経路に接続した液化処理装置と、該液化処理した汚泥を生物処理槽に循環させる経路とを有すると共に、前記生物処理槽の活性汚泥を原水水量の１〜１０％抜き出す別の経路と、該経路に接続した前記膜分離による固液分離とは別の固液分離装置と、該固液分離した汚泥を前記生物処理槽に循環させる経路と、前記固液分離して得られた分離液から０．１μｍ〜１μｍの粒径の微細汚泥を有する難生物分解性物質を除去する除去手段と、除去した流出水を処理水として系外に流出する経路とを有することとしたものである。
【０００７】
【発明の実施の形態】
本発明では、生物処理槽に脱窒槽と硝化槽を設けることで、有機物の除去と同時に硝化脱窒を生物処理槽内で行うことができる。また、硝化脱窒反応を進行させるためには、硝化槽から活性汚泥の一部を脱窒槽に循環させることが必要であるが、この循環の途中に汚泥を液化処理する装置を設けることで、汚泥の液化処理を行いつつ、硝化槽で生成した硝酸性窒素を脱窒槽に戻すことが可能となる。また、脱窒槽における脱窒反応に必要な有機物は、排水中の有機物の他に、液化した汚泥由来の有機物を利用することが可能となる。
本発明者らは、汚泥減容化処理を行ったときに、生物処理槽内に蓄積する微細化した汚泥が０．１〜１μｍの粒径を持ち、難生物分解性であることを見いだした。そこで、膜分離法を適用することで、余剰汚泥の発生量を抑制しつつ、処理水水質の悪化を防止することできた。さらに、生物処理槽内に蓄積した難生物分解性物質を除去することで、膜汚染を防ぎ、長期間にわたり安定した運転を行うことができた。
なお、本発明における難生物分解性物質は、フミン物質、セルロースなどの繊維質、金属酸化物などに由来する強熱残留物質、内分泌かく乱性物質、ダイオキシン類が含まれる。
【０００８】
次に、本発明を図面を用いて詳細に説明する。図１は、下水を本発明の処理方法により処理する一例のフロー構成図である。
図１に示すように、下水１は脱窒槽８に供給され、脱窒槽８の活性汚泥と混合され、さらに硝化槽９に送られる。脱窒槽８と硝化槽９の活性汚泥濃度は流入下水の性状により変わるが、２０００〜１５０００ｍｇ／Ｌであることが望ましい。硝化槽９には膜分離装置１０が設けられており、硝化液３からろ過により膜ろ過処理水２を得る。膜分離装置１０の膜は、孔径が１〜０．０４μｍであることが望ましい。
硝化液３は硝化槽９から流出させ、生成した硝酸性窒素を脱窒槽８に送る。硝化液３の流量は、窒素除去量に応じて決められるが、通常は流入下水量の１〜４倍である。この循環の途中には、液化処理装置１１が設けられており、硝化液３に含まれる活性汚泥の液化処理を行う。液化手段としては、オゾンなどの酸化剤の添加や超音波による微細化が望ましい。
【０００９】
液化処理にオゾンを用いる場合は、オゾン供給量は、液化処理槽に流入する汚泥量に対し、１０〜６０ｍｇ−Ｏ₃／ｇ−ＳＳであるが、特に１０〜２０ｍｇ−Ｏ₃／ｇ−ＳＳであることが望ましい。また、超音波処理による液化処理では、液化処理槽に流入する汚泥に対し１０００〜５００００ｋＪ／ｋｇ−ＳＳで照射することが望ましい。
液化処理装置１１から流出した液化処理汚泥４は、脱窒槽８に供給される。
生物処理構内に蓄積する難生物分解性物質除去のため、硝化槽９から硝化液３の一部を抜き出し、固液分離槽１２に供給する。固液分離槽１２には、ダイナミックろ過法（不織布や織布などの通水性シートからなるろ過体を生物処理槽などに浸漬させ、ろ過体表面に形成される汚泥のダイナミックろ過層により、低い水頭圧でろ過水を得る方法）、沈殿池法、遠心分離法、加圧浮上法、膜ろ過法（膜の孔径が１μｍ以上）を用いて行うことが望ましい。また、固液分離槽１２に供給する生物処理槽の活性汚泥混合液量は、原水水量に関わらず任意に設定できるが、合理的な処理にするためには原水水量の１〜１０％が好ましい。
【００１０】
固液分離槽１２では、硝化液３から活性汚泥が分離され濃縮汚泥６として、硝化槽９に返送される。この濃縮汚泥６は、脱窒槽８に返送することも可能である。固液分離槽１２で分離した硝化液上澄５は、ＣＯＤ除去装置１３に送られ、生物処理槽内に蓄積した難生物分解性物質がＣＯＤ除去装置１３により除去され、ＣＯＤ除去処理水７が分離される。ＣＯＤ除去処理水７は、処理水として系外に流出させることが可能である。また、ＣＯＤ除去処理水７を脱窒槽８又は硝化槽９に供給し、膜分離装置１０によりろ過後、放流することも可能である。ＣＯＤ除去装置１３には、凝集剤を添加し難生物分解性物質を凝集沈殿することにより除去する方法、オゾンを注入し酸化分解により難生物分解性物質を分解除去する方法、オゾンや過酸化水素を添加し促進酸化法により難生物分解性物質を分解する方法、活性炭により吸着除去する方法、膜分離により濃縮分離する方法が望ましい。
【００１１】
【実施例】
以下において、本発明を実施例によりさらに具体的に説明する。
実施例１
この実施例１においては、図１に示すフローにより、団地下水の処理を行った。硝化液の液化処理は、オゾン含有酸素ガスにより行った。
団地下水１は、脱窒槽８と硝化槽９からなる生物処理槽に供給され、硝化槽９からの硝化液３は、液化処理装置であるオゾン反応槽１１に供給し、液化処理を行った。膜分離装置１０として、硝化槽に中空糸膜モジュールを設置し、ろ過を行った。表１に生物処理槽の運転条件を示す。
【００１２】
【表１】

表１に示すように、本実施例の生物処理槽の容積は、硝化槽２ｍ³、脱窒槽１ｍ³であり、ＭＬＳＳは約３０００ｍｇ／Ｌであった。生物処理槽への原水流入量は１５ｍ³／ｄ、生物処理槽全体に対するＢＯＤ負荷は約０．１３ｋｇ／ｋｇ・ｄとなった。硝化槽からオゾン反応槽を経て脱窒槽に循環する循環流量は３０ｍ³／ｄに設定した。
【００１３】
オゾン反応槽１１には、硝化液を３０ｍ³／ｄで供給した。また、オゾンガスは３００ｇ／ｄの割合で供給した。表２にオゾン反応槽１１での処理結果を示す。表２に示したように、溶解性ＣＯＤ、ＢＯＤ、Ｔ−Ｎがオゾン処理後に増加しているが、これらは汚泥の液化により溶解性の各成分が増加したことによる。
【表２】

【００１４】
本実施例では系内に蓄積する難生物分解性物質の除去のため、硝化槽９より硝化液の一部を抜き出し固液分離装置１２に供給、ここで固液分離を行い汚泥６を硝化槽９に返送した。硝化液上澄５は、ＣＯＤ除去装置である凝集沈殿装置１３に供給し、凝集剤として塩化鉄（ＦｅＣｌ₃）を添加し、難生物分解性物質を凝集沈殿させた。塩化鉄は、硝化液上澄５に対し５０ｍｇ／Ｌとなるように添加し、ｐＨを６．０に調整した。分離液は、ＣＯＤ除去処理水である凝集沈殿処理水７として膜ろ過処理水２と共に放流した。表３に、硝化液上澄５と凝集沈殿処理水７の水質を示す。硝化液上澄５では、ＣＯＤとして検出された難生物分解性物質が、凝集沈殿処理により除去された。
【００１５】
【表３】

本実施例では、硝化槽９における膜分離に孔径０．４μｍの中空糸膜モジュールを用い、１３分吸引ろ過、２分停止を１サイクルとしてろ過運転を行った。この時、膜透過流束は約０．４ｍ／ｄであった。団地下水１と膜ろ過処理水２の平均水質を表４にまとめる。表４より、膜ろ過処理水２の水質は、ＢＯＤは５ｍｇ／Ｌ以下、ＳＳは検出されず、ＣＯＤも６．５ｍｇ／Ｌと良好な水質を得ることができた。また、全窒素（Ｔ−Ｎ）も７．２ｍｇ／Ｌであり、流入した全窒素の約７０％を除去することができた。
【００１６】
【表４】

本実施例における系内汚泥量の経過を図３に示す。硝化槽汚泥の一部を液化処理したことにより、系内汚泥量は約９ｋｇで安定しており、約２ヶ月間排泥を行わずに運転が行えた。また、膜分離装置における膜間差圧は４〜６ｋＰａで安定しており、薬品洗浄などを行わずに連続運転が可能であった。
【００１７】
比較例１
この比較例においては、図２に示すようなフローにより団地下水の処理を行った。実施例１とは異なり、凝集沈殿を行う部分は設けていない。硝化液の液化処理は、オゾン含有酸素ガスにより行った。
団地下水１は、脱窒槽８と硝化槽９からなる生物処理槽に供給され、硝化槽９からの硝化液３は液化処理装置であるオゾン反応槽１１に供給し、液化処理を行った。膜分離装置１０として、硝化槽に中空糸膜モジュール設置し、ろ過を行った。表５に生物処理槽の運転条件を示す。
【００１８】
【表５】

表５に示すように、本比較例の生物処理槽の容積は、硝化槽２ｍ³、脱窒槽１ｍ³であり、ＭＬＳＳは約３０００ｍｇ／Ｌであった。生物処理槽への原水流入量は１５ｍ³／ｄ、生物処理槽全体に対するＢＯＤ負荷は約０．１３ｋｇ／ｋｇ・ｄとなった。硝化槽からオゾン反応槽を経て脱窒槽に循環する循環流量は３０ｍ³／ｄに設定した。
【００１９】
オゾン反応槽１１には、硝化液を３０ｍ³／ｄで供給した。また、オゾンガスは３００ｇ／ｄの割合で供給した。表６にオゾン反応槽１１での処理結果を示す。表６に示したように、溶解性ＣＯＤ、ＢＯＤ、Ｔ−Ｎがオゾン処理後に増加しているが、これらは汚泥の液化により溶解性の各成分が増加したことによる。
【表６】

【００２０】
本比較例では、硝化槽９における膜分離に孔径０．４μｍの中空糸膜モジュールを用い、１３分吸引ろ過、２分停止を１サイクルとしてろ過運転を行った。この時、膜透過流束は約０．４ｍ／ｄであった。団地下水１と膜ろ過処理水２の平均水質を表７にまとめる。表７より、膜ろ過処理水２の水質は、ＢＯＤは５ｍｇ／Ｌ以下でＳＳは検出されなかったものの、ＣＯＤは１０ｍｇ／Ｌと実施例1よりも水質が悪化した。また、全窒素(Ｔ−Ｎ)は１０．６ｍｇ／Ｌであり、こちらも実施例１よりも水質が悪化した。
【００２１】
【表７】

本比較例における系内汚泥量の経過を図４に示す。液化処理を行ったものの系内汚泥量が増加した。さらに、膜分離装置は１ヶ月で膜間差圧が３０ｋＰａに達し、薬品洗浄を行った。以上、実施例１と比較例の運転結果から、膜分離法と硝化槽汚泥の一部を凝集沈殿により分離除去することで、良好な処理水を得つつ余剰汚泥の発生量を抑制することが可能であった。
【００２２】
実施倒２
この実施例２においては、図１に示すようなフローにより団地下水の処理を行った。硝化液の液化処理は超音波照射装置により行った。
団地下水１は、脱窒槽８と硝化槽９からなる生物処理槽に供給され、硝化槽９からの硝化液３は、液化処理装置である超音波処理槽１１に供給し、液化処理を行った。膜分離装置１０として、硝化槽に中空糸膜モジュールを設置し、ろ過を行った。表８に生物処理槽の運転条件を示す。
【表８】

【００２３】
表８に示すように、本実施例の生物処理槽の容積は、硝化槽２ｍ³、脱窒槽１ｍ³であり、ＭＬＳＳは約３０００ｍｇ／Ｌであった。生物処理槽への原水流入量は１５ｍ³／ｄ、生物処理槽全体に対するＢＯＤ負荷は約０．１３ｋｇ／ｋｇ・ｄとなった。硝化槽から超音波処理槽を経て脱窒槽に循環する循環流量は３０ｍ³／ｄに設定した。
超音波処理槽１１には、硝化液を３０ｍ³／ｄで供給した。また、超音波は汚泥量に対し６５００ｋＪ／ｋｇ−ＳＳの割合で照射した。表９に超音波処理槽１１での処理結果を示す。表９に示したように、溶解性ＣＯＤ、ＢＯＤ、Ｔ−Ｎが超音波処理後に増加しているが、これらは汚泥の液化により溶解性の各成分が増加したことによる。
【００２４】
【表９】

【００２５】
実施例２は系内に蓄積する難生物分解性物質の除去のため、硝化槽９より硝化液の一部を抜き出し固液分離装置１２に供給、ここで固液分離を行い汚泥を硝化槽９に返送した。硝化液上澄５は、ＣＯＤ除去装置である凝集沈殿装置１３に供給し、凝集剤として塩化鉄（ＦｅＣｌ₃）を添加し、難生物分解性物質を凝集沈殿させた。塩化鉄は、硝化液上澄５に対し５０ｍｇ／Ｌとなるように添加し、ｐＨは６．０に調整した。分離液は、ＣＯＤ除去処理水である凝集沈殿処理水７として膜ろ過処理水２と共に放流した。表１０に硝化液上澄５と凝集沈殿処理水７の水質を示す。硝化液上澄５には、ＣＯＤとして検出された難生物分解性物質が、凝集沈殿処理により除去された。
【表１０】

【００２６】
本実施例では、硝化槽９における膜分離に孔径０．４μｍの中空糸膜モジュールを用い、１３分吸引ろ過、２分停止を１サイクルとしてろ過運転を行った。この時、膜透過流束は約０．４ｍ／ｄであった。団地下水１と膜ろ過処理水２の平均水質を表１１にまとめる。表１１より、膜ろ過処理水２の水質は、ＢＯＤは５ｍｇ／Ｌ以下、ＳＳは検出されず、ＣＯＤも５．９ｍｇ／Ｌと良好な水質を得ることができた。また、全窒素（Ｔ−Ｎ）も７．１ｍｇ／Ｌであり、流入した全窒素の約７０％を除去することができた。
【００２７】
【表１１】

本実施例における系内汚泥量の経過を図５に示す。硝化槽汚泥の一部を液化処理したことにより、系内汚泥量は約９ｋｇで安定しており、約２ヶ月間排泥を行わずに運転が行えた。また、膜分離装置における膜間差圧は４〜６ｋＰａで安定しており、薬品洗浄などを行わずに連続運転が可能であった。
【００２８】
実施例３
この実施例３においては、図１に示すようなフローにより団地下水の処理を行った。硝化液の液化処理は、オゾン含有酸素ガスにより行った。また、硝化液の一部を固液分離槽１２により固液分離し、硝化液上澄５をＣＯＤ除去装置である第２オゾン反応槽１３に供給した。第２オゾン反応槽１３にはオゾンガスを注入し、硝化液上澄５に残留したフミン物質などの難生物分解性物質を酸化分解した。
表１２に硝化液上澄５とＣＯＤ除去処理水である第２オゾン反応槽処理水７の水質を示す。硝化液上澄５には、ＣＯＤとして検出されたフミン物質などの難生物分解性物質が、酸化分解により除去された。
【００２９】
【表１２】

団地下水１と膜ろ過処理水２の平均水質を表１３にまとめる。表１３より、膜ろ過処理水２の水質は、ＢＯＤは５ｍｇ／Ｌ以下、ＳＳは検出されず、ＣＯＤも５．９ｍｇ／Ｌと良好な水質を得ることができた。また、全窒素（Ｔ−Ｎ）も７．２ｍｇ／Ｌであり、流入した全窒素の約７０％を除去することができた。
【００３０】
【表１３】

硝化槽汚泥の一部を液化処理したことにより、系内汚泥量は約９ｋｇで安定しており、約２ヶ月間排泥を行わずに運転が行えた。また、フミン物質などを第２オゾン反応槽１３で分解したことにより、硝化槽９にフミン物質などが蓄積せず、膜分離装置における膜間差圧は４〜６ｋＰａで安定しており、薬品洗浄などを行わずに連続運転が可能であった。
【００３１】
【発明の効果】
本発明によれば、生物の処理過程で発生する余剰汚泥の発生量を削減し、また生物処理槽内に蓄積する難生物分解性物質を除去でき、処理水水質の悪化を防ぎつつ余剰汚泥の発生量を抑制することが可能な、従来よりも簡便な処理フローを提供することができた。
【図面の簡単な説明】
【図１】本発明の処理方法の一例を示すフロー構成図。
【図２】比較例１に用いた処理方法のを示すフロー構成図。
【図３】実施例１の運転日数による汚泥量の経過を示すグラフ。
【図４】比較例１の運転日数による汚泥量の経過を示すグラフ。
【図５】実施例２の運転日数による汚泥量の経過を示すグラフ。
【符号の説明】
１：下水、２：膜ろ過処理水、３：硝化液、４：液化処理汚泥、５：硝化液上澄、６：濃縮汚泥、７：ＣＯＤ除去処理水、８：脱窒槽、９：硝化槽、１０：膜分離装置、１１：液化処理装置、１２：固液分離槽、１３：ＣＯＤ除去装置[0001]
BACKGROUND OF THE INVENTION
The present invention relates to treatment of organic wastewater, and more particularly to a biological treatment method and apparatus for biologically treating organic wastewater and performing solid-liquid separation by membrane separation.
[0002]
[Prior art]
In the treatment of organic wastewater, the biological treatment method using activated sludge is compatible with various wastewaters and has become the mainstream wastewater treatment method. As one of biological treatment methods, a nitrification denitrification method is known as a method for removing nitrogen in addition to removing organic substances in waste water. This was proposed to remove nitrogen in the wastewater. The biological treatment tank is divided into a denitrification tank that performs only agitation and a nitrification tank that performs nitrification, and the wastewater flows into the denitrification tank and flows out of the denitrification tank. The liquid is supplied to the nitrification tank, the nitrification tank effluent is discharged to the solid-liquid separator, and at the same time, a part of the nitrification tank effluent is circulated to the denitrification tank. In the nitrification tank, ammonia nitrogen is oxidized to nitrate nitrogen by nitrifying bacteria in activated sludge in addition to oxidative decomposition of organic matter in wastewater by BOD oxidizing bacteria. The activated sludge mixed solution flowing out of the nitrification tank is reduced to nitrogen in the denitrification tank using nitrate nitrogen in the activated sludge mixed solution and organic matter containing denitrifying bacteria in the activated sludge in the raw water. Through the above steps, ammoniacal nitrogen in the wastewater is reduced to gaseous nitrogen and removed from the wastewater.
[0003]
As described above, biological treatment with activated sludge is an excellent method, but on the other hand, there is a problem that surplus sludge is generated due to microorganisms grown in the biological treatment tank, suspended solids, and the like. In recent years, the treatment cost of surplus sludge has increased, and its suppression technology has attracted attention. Fine sludge is refined, solubilized, and supplied to the biological treatment tank again, so that the liquefied sludge is fed into the biological treatment tank. It has been proposed to mineralize with activated sludge. As for the refinement and liquefaction process, there are known methods of physically refining activated sludge, methods of heating and solubilizing sludge using high-heat bacteria, and technology of solubilizing sludge by the action of ozone. Yes. However, when sludge is refined and liquefied by these methods, the amount of excess sludge generated is reduced, but a part of the refined sludge flows into the treated water and the quality of the treated water deteriorates. there were. In addition, these refinement and liquefaction methods have a problem that the entire apparatus becomes complicated because a refinement process and a liquefaction process are added to the conventional biological treatment system.
In volume reduction by sludge refinement or liquefaction, if solid-liquid separation is performed using a membrane separation method, it is possible to suppress the outflow of sludge to the treated water. However, at the same time, the refined sludge accumulates in the system, resulting in a problem that volume reduction efficiency is lowered and membrane clogging is likely to occur.
[0004]
[Problems to be solved by the invention]
The present invention has been made in view of the prior art as described above, and reduces the amount of excess sludge generated in the course of biological treatment while preventing deterioration of the quality of treated water, and also in the biological treatment tank. It is an object of the present invention to provide a simple biological wastewater treatment method and apparatus capable of removing a hardly biodegradable substance that accumulates in water.
[0005]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, in the present invention, in the biological treatment method for treating the organic wastewater in the biological treatment tank and obtaining the treated water by solid-liquid separation of the resulting activated sludge by membrane separation, the inside of the biological treatment tank some activated sludge liquefaction process by extracting the sludge treated liquid along with the circulation to the biological treatment tank, further, by the membrane separation separately extracted 1-10% activated sludge raw water from the biological treatment tank Solid-liquid separation different from solid-liquid separation is performed, and the sludge obtained by the solid-liquid separation is circulated to the biological treatment tank, while fine sludge having a particle diameter of 0.1 μm to 1 μm is obtained from the obtained separated liquid. The difficult-to-decompose decomposable substances are removed and the treated water flows out of the system .
In the treatment method, the liquefaction treatment can be carried out by ozone treatment or ultrasonic treatment, and the removal of the hardly biodegradable substance is carried out by agglomeration and precipitation by addition of a flocculant, or ozone and / or excess. It can be by oxidative decomposition with hydrogen oxide.
[0006]
Further, in the present invention, in the biological treatment device comprising a biological treatment tank for biological treatment of organic wastewater, the resulting Ru membrane separator treated water to separate the solid and the resulting activated sludge solution, activated sludge of the biological treatment tank And a liquefaction treatment device connected to the route, and a route for circulating the liquefied sludge to the biological treatment tank, and the activated sludge of the biological treatment tank is 1 to 10 of the amount of raw water % and another route for extracting a path for circulating a separate solid-liquid separation device and solid-liquid separation by the membrane separation connected to the pathway, the sludge solid-liquid separation in the biological treatment tank, the solid-liquid separation Removal means for removing a non-biodegradable substance having fine sludge having a particle diameter of 0.1 μm to 1 μm from the obtained separation liquid, and a path for flowing the removed effluent water out of the system as treated water That's what it meant.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, by providing the biological treatment tank with a denitrification tank and a nitrification tank, nitrification and denitrification can be performed in the biological treatment tank simultaneously with the removal of organic substances. Moreover, in order to advance the nitrification denitrification reaction, it is necessary to circulate a part of the activated sludge from the nitrification tank to the denitrification tank, but by providing a device for liquefying the sludge in the middle of this circulation, While performing sludge liquefaction treatment, nitrate nitrogen produced in the nitrification tank can be returned to the denitrification tank. In addition, the organic matter necessary for the denitrification reaction in the denitrification tank can use liquefied sludge-derived organic matter in addition to the organic matter in the waste water.
The present inventors have found that when sludge volume reduction treatment is performed, the refined sludge accumulated in the biological treatment tank has a particle diameter of 0.1 to 1 μm and is hardly biodegradable. . Therefore, by applying the membrane separation method, it was possible to prevent the quality of the treated water from deteriorating while suppressing the generation amount of excess sludge. Furthermore, by removing the non-biodegradable substances accumulated in the biological treatment tank, it was possible to prevent membrane contamination and perform stable operation over a long period of time.
The hardly biodegradable substances in the present invention include humic substances, fibrous substances such as cellulose, ignition residual substances derived from metal oxides, endocrine disrupting substances, and dioxins.
[0008]
Next, the present invention will be described in detail with reference to the drawings. FIG. 1 is a flow configuration diagram of an example in which sewage is treated by the treatment method of the present invention.
As shown in FIG. 1, sewage 1 is supplied to a denitrification tank 8, mixed with activated sludge in the denitrification tank 8, and further sent to a nitrification tank 9. The activated sludge concentration in the denitrification tank 8 and the nitrification tank 9 varies depending on the properties of the inflow sewage, but is preferably 2000 to 15000 mg / L. A membrane separation device 10 is provided in the nitrification tank 9, and membrane filtration treated water 2 is obtained from the nitrification solution 3 by filtration. The membrane of the membrane separation device 10 preferably has a pore diameter of 1 to 0.04 μm.
The nitrification liquid 3 is caused to flow out of the nitrification tank 9 and the generated nitrate nitrogen is sent to the denitrification tank 8. The flow rate of the nitrification liquid 3 is determined according to the nitrogen removal amount, but is usually 1 to 4 times the inflow sewage amount. In the middle of this circulation, a liquefaction treatment device 11 is provided, and liquefaction treatment of activated sludge contained in the nitrification solution 3 is performed. As a liquefaction means, addition of an oxidizing agent such as ozone or miniaturization by ultrasonic waves is desirable.
[0009]
When ozone is used for the liquefaction treatment, the ozone supply amount is 10 to 60 mg-O ₃ / g-SS with respect to the amount of sludge flowing into the liquefaction treatment tank, but in particular 10 to 20 mg-O ₃ / g-SS. It is desirable that Moreover, in the liquefaction process by ultrasonic treatment, it is desirable to irradiate the sludge flowing into the liquefaction tank at 1000 to 50000 kJ / kg-SS.
The liquefied sludge 4 flowing out from the liquefaction processing apparatus 11 is supplied to the denitrification tank 8.
A part of the nitrification liquid 3 is extracted from the nitrification tank 9 and supplied to the solid-liquid separation tank 12 in order to remove the hardly biodegradable substances accumulated in the biological treatment premises. In the solid-liquid separation tank 12, a dynamic filtration method (a filter made of a water-permeable sheet such as a nonwoven fabric or a woven cloth is immersed in a biological treatment tank or the like, and a sludge dynamic filtration layer formed on the surface of the filter makes a low water head. It is desirable to use a method of obtaining filtered water under pressure), a sedimentation basin method, a centrifugal separation method, a pressurized flotation method, and a membrane filtration method (a membrane pore size of 1 μm or more). The amount of the activated sludge mixed liquid in the biological treatment tank to be supplied to the solid-liquid separation tank 12 can be arbitrarily set regardless of the amount of raw water, but 1 to 10% of the amount of raw water is preferable for rational treatment. .
[0010]
In the solid-liquid separation tank 12, the activated sludge is separated from the nitrification liquid 3 and returned to the nitrification tank 9 as concentrated sludge 6. The concentrated sludge 6 can be returned to the denitrification tank 8. The nitrified liquid supernatant 5 separated in the solid-liquid separation tank 12 is sent to the COD removal apparatus 13, the inbiodegradable substances accumulated in the biological treatment tank are removed by the COD removal apparatus 13, and the COD removal treated water 7 is obtained. To be separated. The COD removal treated water 7 can be discharged out of the system as treated water. Further, it is also possible to supply the COD removal treated water 7 to the denitrification tank 8 or the nitrification tank 9, filter it with the membrane separation device 10 and discharge it. The COD removing device 13 includes a method of removing a biodegradable substance by adding a flocculant and coagulating and precipitating, a method of injecting ozone and decomposing and removing the non-biodegradable substance by oxidative decomposition, ozone and hydrogen peroxide A method of decomposing a hardly biodegradable substance by an accelerated oxidation method, a method of adsorptive removal with activated carbon, and a method of concentration separation by membrane separation are desirable.
[0011]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples.
Example 1
In Example 1, the groundwater was treated according to the flow shown in FIG. The nitrification solution was liquefied with ozone-containing oxygen gas.
The groundwater 1 was supplied to a biological treatment tank composed of a denitrification tank 8 and a nitrification tank 9, and the nitrification liquid 3 from the nitrification tank 9 was supplied to an ozone reaction tank 11 which is a liquefaction treatment apparatus, and subjected to liquefaction treatment. As the membrane separator 10, a hollow fiber membrane module was installed in a nitrification tank, and filtration was performed. Table 1 shows the operating conditions of the biological treatment tank.
[0012]
[Table 1]

As shown in Table 1, the volume of the biological treatment tank of the present embodiment, nitrification tank 2m ^3, a denitrification tank 1 m ^3, MLSS was about 3000 mg / L. The amount of raw water flowing into the biological treatment tank was 15 m ³ / d, and the BOD load on the entire biological treatment tank was about 0.13 kg / kg · d. The circulation flow rate circulating from the nitrification tank to the denitrification tank through the ozone reaction tank was set to 30 m ³ / d.
[0013]
The ozone reaction tank 11 was supplied with a nitrifying solution at 30 m ³ / d. Ozone gas was supplied at a rate of 300 g / d. Table 2 shows the processing results in the ozone reaction tank 11. As shown in Table 2, soluble COD, BOD, and TN are increased after ozone treatment, and these are due to an increase in each soluble component due to liquefaction of sludge.
[Table 2]

[0014]
In this embodiment, a part of the nitrification liquid is extracted from the nitrification tank 9 and supplied to the solid-liquid separation device 12 for removing the non-biodegradable substances accumulated in the system. Returned to 9. The nitrating liquid supernatant 5 was supplied to a coagulation sedimentation apparatus 13 which is a COD removal apparatus, and iron chloride (FeCl ₃ ) was added as a coagulant to coagulate and precipitate the hardly biodegradable substance. Iron chloride was added to the nitrating supernatant 5 at 50 mg / L, and the pH was adjusted to 6.0. The separated liquid was discharged together with the membrane filtration treated water 2 as the coagulation sedimentation treated water 7 which is COD removal treated water. Table 3 shows the water quality of the nitrating liquid supernatant 5 and the coagulated sediment treated water 7. In the nitrating liquid supernatant 5, the hardly biodegradable substance detected as COD was removed by the coagulation sedimentation treatment.
[0015]
[Table 3]

In this example, a hollow fiber membrane module having a pore diameter of 0.4 μm was used for membrane separation in the nitrification tank 9, and filtration operation was performed with 13 minutes suction filtration and 2 minutes stop as one cycle. At this time, the membrane permeation flux was about 0.4 m / d. Table 4 summarizes the average water quality of the groundwater 1 and the membrane-filtered water 2. From Table 4, as for the water quality of the membrane filtration treated water 2, BOD was 5 mg / L or less, SS was not detected, and COD was 6.5 mg / L. Moreover, total nitrogen (TN) was 7.2 mg / L, and about 70% of the total nitrogen that flowed in could be removed.
[0016]
[Table 4]

The progress of the amount of sludge in the system in this example is shown in FIG. By liquefying a part of the nitrification tank sludge, the amount of sludge in the system was stable at about 9 kg, and operation was possible without draining for about 2 months. Moreover, the transmembrane pressure difference in the membrane separator was stable at 4 to 6 kPa, and continuous operation was possible without chemical cleaning.
[0017]
Comparative Example 1
In this comparative example, the groundwater was treated according to the flow shown in FIG. Unlike Example 1, the part which performs aggregation precipitation is not provided. The nitrification solution was liquefied with ozone-containing oxygen gas.
The groundwater 1 was supplied to a biological treatment tank composed of a denitrification tank 8 and a nitrification tank 9, and the nitrification liquid 3 from the nitrification tank 9 was supplied to an ozone reaction tank 11 which is a liquefaction treatment apparatus to perform liquefaction treatment. As the membrane separation apparatus 10, a hollow fiber membrane module was installed in a nitrification tank and filtered. Table 5 shows the operating conditions of the biological treatment tank.
[0018]
[Table 5]

As shown in Table 5, the volume of the biological treatment tank of the present comparative example, nitrification tank 2m ^3, a denitrification tank 1 m ^3, MLSS was about 3000 mg / L. The amount of raw water flowing into the biological treatment tank was 15 m ³ / d, and the BOD load on the entire biological treatment tank was about 0.13 kg / kg · d. The circulation flow rate circulating from the nitrification tank to the denitrification tank through the ozone reaction tank was set to 30 m ³ / d.
[0019]
The ozone reaction tank 11 was supplied with a nitrifying solution at 30 m ³ / d. Ozone gas was supplied at a rate of 300 g / d. Table 6 shows the processing results in the ozone reaction tank 11. As shown in Table 6, soluble COD, BOD, and TN are increased after ozone treatment, and these are due to an increase in each soluble component due to liquefaction of sludge.
[Table 6]

[0020]
In this comparative example, a hollow fiber membrane module having a pore diameter of 0.4 μm was used for membrane separation in the nitrification tank 9, and filtration operation was performed with 13 minutes suction filtration and 2 minutes stop as one cycle. At this time, the membrane permeation flux was about 0.4 m / d. Table 7 summarizes the average water quality of the groundwater 1 and membrane-treated water 2. From Table 7, the water quality of the membrane filtration treated water 2 was 5 mg / L or less and SS was not detected, but the COD was 10 mg / L, which was worse than that of Example 1. Moreover, total nitrogen (TN) was 10.6 mg / L, and the water quality was also worse than Example 1.
[0021]
[Table 7]

The progress of the amount of sludge in the system in this comparative example is shown in FIG. Although the liquefaction treatment was performed, the amount of sludge in the system increased. Furthermore, the membrane separation apparatus reached a chemical pressure of 30 kPa in one month, and chemical cleaning was performed. As described above, from the operation results of Example 1 and the comparative example, by separating and removing part of the membrane separation method and nitrification tank sludge by coagulation sedimentation, it is possible to suppress the generation amount of excess sludge while obtaining good treated water. It was possible.
[0022]
Implementation defeat 2
In Example 2, the groundwater was treated according to the flow shown in FIG. The nitrification solution was liquefied by an ultrasonic irradiation device.
The groundwater 1 is supplied to a biological treatment tank composed of a denitrification tank 8 and a nitrification tank 9, and the nitrification liquid 3 from the nitrification tank 9 is supplied to an ultrasonic treatment tank 11 which is a liquefaction treatment apparatus, and subjected to liquefaction treatment. . As the membrane separator 10, a hollow fiber membrane module was installed in a nitrification tank, and filtration was performed. Table 8 shows the operating conditions of the biological treatment tank.
[Table 8]

[0023]
As shown in Table 8, the volume of the biological treatment tank of the present embodiment, nitrification tank 2m ^3, a denitrification tank 1 m ^3, MLSS was about 3000 mg / L. The amount of raw water flowing into the biological treatment tank was 15 m ³ / d, and the BOD load on the entire biological treatment tank was about 0.13 kg / kg · d. The circulation flow rate circulating from the nitrification tank to the denitrification tank through the ultrasonic treatment tank was set to 30 m ³ / d.
A nitrating solution was supplied to the ultrasonic treatment tank 11 at 30 m ³ / d. Moreover, the ultrasonic wave was irradiated in the ratio of 6500 kJ / kg-SS with respect to the amount of sludge. Table 9 shows the processing results in the ultrasonic processing tank 11. As shown in Table 9, soluble COD, BOD, and TN are increased after ultrasonic treatment, and these are due to an increase in each soluble component due to liquefaction of sludge.
[0024]
[Table 9]

[0025]
In Example 2, in order to remove the hardly biodegradable substances accumulated in the system, a part of the nitrification liquid is extracted from the nitrification tank 9 and supplied to the solid-liquid separation device 12, where solid-liquid separation is performed and sludge is removed from the nitrification tank 9. Returned to. The nitrating liquid supernatant 5 was supplied to a coagulation sedimentation apparatus 13 which is a COD removal apparatus, and iron chloride (FeCl ₃ ) was added as a coagulant to coagulate and precipitate the hardly biodegradable substance. Iron chloride was added at 50 mg / L to the nitrating liquid supernatant 5, and the pH was adjusted to 6.0. The separated liquid was discharged together with the membrane filtration treated water 2 as the coagulation sedimentation treated water 7 which is COD removal treated water. Table 10 shows the water quality of the nitrating liquid supernatant 5 and the coagulated sediment treated water 7. In the nitrifying liquid supernatant 5, the hardly biodegradable substance detected as COD was removed by the coagulation sedimentation treatment.
[Table 10]

[0026]
In this example, a hollow fiber membrane module having a pore diameter of 0.4 μm was used for membrane separation in the nitrification tank 9, and filtration operation was performed with 13 minutes suction filtration and 2 minutes stop as one cycle. At this time, the membrane permeation flux was about 0.4 m / d. Table 11 summarizes the average water quality of the groundwater 1 and the membrane filtered water 2. From Table 11, as for the water quality of the membrane filtration treated water 2, BOD was 5 mg / L or less, SS was not detected, and COD was 5.9 mg / L, and a good water quality could be obtained. Moreover, total nitrogen (TN) was also 7.1 mg / L, and about 70% of the inflowing total nitrogen could be removed.
[0027]
[Table 11]

The progress of the amount of sludge in the system in this example is shown in FIG. By liquefying a part of the nitrification tank sludge, the amount of sludge in the system was stable at about 9 kg, and operation was possible without draining for about 2 months. Moreover, the transmembrane pressure difference in the membrane separator was stable at 4 to 6 kPa, and continuous operation was possible without chemical cleaning.
[0028]
Example 3
In Example 3, the groundwater was treated according to the flow shown in FIG. The nitrification solution was liquefied with ozone-containing oxygen gas. Further, a part of the nitrification liquid was subjected to solid-liquid separation by the solid-liquid separation tank 12, and the nitrification liquid supernatant 5 was supplied to the second ozone reaction tank 13 which is a COD removing device. Ozone gas was injected into the second ozone reaction tank 13 to oxidize and decompose hardly biodegradable substances such as humic substances remaining in the nitrating liquid supernatant 5.
Table 12 shows the water quality of the nitrification supernatant 5 and the second ozone reaction tank treated water 7 which is COD removal treated water. In the nitrating liquid supernatant 5, the hardly biodegradable substances such as humic substances detected as COD were removed by oxidative decomposition.
[0029]
[Table 12]

Table 13 summarizes the average water quality of the groundwater 1 and the membrane filtered water 2. From Table 13, as for the water quality of the membrane filtration treated water 2, BOD was 5 mg / L or less, SS was not detected, and COD was 5.9 mg / L, and a good water quality could be obtained. Moreover, total nitrogen (TN) was 7.2 mg / L, and about 70% of the total nitrogen that flowed in could be removed.
[0030]
[Table 13]

By liquefying a part of the nitrification tank sludge, the amount of sludge in the system was stable at about 9 kg, and operation was possible without draining for about 2 months. Further, since the humic substances are decomposed in the second ozone reaction tank 13, the humic substances are not accumulated in the nitrification tank 9, and the transmembrane pressure difference in the membrane separator is stable at 4 to 6 kPa. It was possible to operate continuously without performing such operations.
[0031]
【The invention's effect】
According to the present invention, it is possible to reduce the amount of surplus sludge generated in the biological treatment process and to remove the hardly biodegradable substances accumulated in the biological treatment tank, while preventing the deterioration of the quality of the treated water. It was possible to provide a simpler processing flow that can suppress the generation amount than before.
[Brief description of the drawings]
FIG. 1 is a flow configuration diagram showing an example of a processing method of the present invention.
FIG. 2 is a flow configuration diagram showing a processing method used in Comparative Example 1;
FIG. 3 is a graph showing the progress of the sludge amount according to the operation days of Example 1.
4 is a graph showing the progress of the amount of sludge according to the operation days of Comparative Example 1. FIG.
FIG. 5 is a graph showing the progress of the amount of sludge according to the operation days of Example 2.
[Explanation of symbols]
1: Sewage, 2: Membrane filtration treated water, 3: Nitrification liquid, 4: Liquefaction sludge, 5: Nitrification liquid supernatant, 6: Concentrated sludge, 7: COD removal treated water, 8: Denitrification tank, 9: Nitrification tank DESCRIPTION OF SYMBOLS 10: Membrane separation apparatus, 11: Liquefaction processing apparatus, 12: Solid-liquid separation tank, 13: COD removal apparatus

Claims

In the biological treatment method of treating organic wastewater in a biological treatment tank and separating the obtained activated sludge by solid-liquid separation by membrane separation to obtain treated water, a part of the activated sludge in the biological treatment tank is extracted and liquefied. the sludge was treated liquid along with the circulation to the biological treatment tank, further, make another solid-liquid separation and solid-liquid separation by the membrane separation separately extracting 1-10% of the raw water water activated sludge from biological treatment tank The sludge obtained by the solid-liquid separation is circulated through the biological treatment tank, while the biodegradable substance having fine sludge having a particle diameter of 0.1 μm to 1 μm is removed from the obtained separated liquid to treat the treated water. A method for treating organic wastewater, characterized in that it flows out of the system .

The method for treating organic wastewater according to claim 1, wherein the liquefaction treatment is performed by ozone treatment or ultrasonic treatment.

The organic wastewater treatment according to claim 1 or 2, wherein the removal of the hardly biodegradable substance is by coagulation precipitation by addition of a coagulant or by oxidative decomposition with ozone and / or hydrogen peroxide. Method.

Route extracting a biological treatment tank for biological treatment of organic wastewater, the biological treatment device having a resulting Ru membrane separation device activated sludge to solid-liquid separation and the process water obtained, a portion of the activated sludge of the biological treatment tank And a liquefaction treatment device connected to the route, and a route for circulating the liquefied sludge to the biological treatment tank, and another route for extracting 1 to 10% of the raw sludge from the biological treatment tank. , 0 with another solid-liquid separator and the membrane separation device connected to said path, a path for circulating the sludge solid-liquid separation in the biological treatment tank, from the separation liquid obtained above by solid-liquid separation Organic wastewater characterized by having removal means for removing a non-biodegradable substance having fine sludge having a particle diameter of 1 μm to 1 μm, and a path for flowing the removed effluent out of the system as treated water Processing equipment.