JP4009069B2 - Anaerobic treatment method and treatment system for oil-containing contaminants - Google Patents

Description

【００５８】
本発明による系（実施例１）では、細菌由来のリパーゼを適量（５００U/L）添加することによってバイアル瓶中の遊離高級脂肪酸濃度を約４００mg/Lに制御した条件でメタン発酵を行った。この場合、高級脂肪酸／ＭＬＶＳＳの比は約０．１であった。
【００５９】
これに対して、比較例１−１は、リパーゼの添加量(１，０００U/L)を増やし、バイアル瓶中の遊離高級脂肪酸濃度を約１１００mg/Lとして、高級脂肪酸が蓄積した条件でのメタン発酵実験を行った。高級脂肪酸／ＭＬＶＳＳの比は約０．４以上であった。
【００６０】
比較例１−２は、リパーゼの添加量をさらに増やし、バイアル瓶中の遊離高級脂肪酸濃度を約１４００mg/Lとして、高級脂肪酸がさらに蓄積した条件下でのメタン発酵実験を行った。高級脂肪酸／ＭＬＶＳＳの比は約０．５以上であった。
【００６１】
比較例１−３では、リパーゼに添加による中性脂肪の分解を行わず、遊離高級脂肪酸濃度を制御しない条件下でのメタン発酵実験を行った。
これら４種類の回分培養実験を１４日間行い、そのメタン生成特性と発酵終了後の脂質除去特性および有機物除去特性を調べた。それらの結果を図１〜図３に示す。
【００６２】
図１は、高級脂肪酸濃度を調節した回分実験系でのメタン発酵特性を示す。本発明による系（実施例１）では、高級脂肪酸濃度を適量に制御することによって、メタン発酵反応が６日間でほぼ完了していることがわかる。これに対して、比較例１−１は、高級脂肪酸の蓄積によって、メタン発酵反応が阻害された結果となり、メタン発酵反応は実験開始後６日目以降に始まり、発酵が完了するまでに１４日間を要した。さらに比較例１−２は、高級脂肪酸のさらなる蓄積によって、メタン発酵反応が阻害された結果となり、メタン発酵反応は実験開始後１４日目以降に始まった。従って、これらの結果により、嫌気反応系内の高級脂肪酸濃度を制御することによって、発酵完了までの期間を制御できることがわかった。
【００６３】
尚、比較例１−３は、中性脂肪をリパーゼにより分解処理しない場合の結果であり、メタン生成反応が極めて悪く、１４日を経てもほとんどメタン発酵が進行しなかった。従って、油脂含有排水を嫌気性処理する場合には、予めリパーゼなどにより中性脂肪を分解し、次いでメタン発酵処理することが好適であることがわかった。
【００６４】
図２は、１４日間のメタン発酵を終了した後の脂質除去特性を示す。リパーゼで中性脂肪を分解処理してメタン発酵処理した本発明による系（実施例１）は、脂質成分を９０％除去できた。これに対して、高級脂肪酸が高濃度で蓄積した比較例１−１及び比較例１−２は、脂質成分の除去は７０％と５５％であった。中性脂肪をリパーゼで分解処理しなかった比較例１−３の場合は、脂質成分の除去は５８％にとどまった。
【００６５】
図３は、１４日間のメタン発酵処理した後の有機物除去特性を示す。リパーゼで中性脂肪を分解処理してメタン発酵処理した本発明（実施例１）では、ＣＯＤ_Cr除去率が７０％弱となった。これに対して、高級脂肪酸が高濃度で蓄積した比較例１−１及び比較例１−２は、ＣＯＤ_Crの除去は５０％と３０％であった。一方、中性脂肪をリパーゼにより分解処理しなかった比較例１−３は、ＣＯＤ_Cr除去率は４０％弱にとどまった。リパーゼの添加によって、不溶性ＣＯＤ_Cr成分の減少が大きかった。
【００６６】
実施例２、比較例２
実施例1で使用した生ゴミ高温メタン発酵汚泥と豚糞尿中温メタン発酵汚泥とを種汚泥としてメタン発酵反応槽に投入し、食品工場の油脂含有排水を原水として用い、表2の条件で連続処理法でのメタン発酵実験を3ヶ月間行った。
【００６７】
【表２】

【００６８】
本発明では、メタン発酵槽内の中性脂肪と高級脂肪酸をモニターしながら、高級脂肪酸濃度を３００mg/L以下になるように、リパーゼを１００〜１０００U/L・日添加し、５５℃の高温域でメタン発酵連続実験を行った（実施例２−１）。また、実施例２−１と同じように発酵槽内の高級脂肪酸濃度を制御しながら、３５℃の中温域でメタン発酵を行い、これを実施例２−２とした。比較例として、リパーゼを１０００〜２０００U/L・日の濃度で大量添加して、メタン発酵反応槽内の高級脂肪酸濃度を１５００mg/Lに蓄積した条件下で、５５℃の高温域でメタン発酵連続実験を行った（比較例２−１）。また、反応槽内の中性脂肪を分解せずに、高級脂肪酸濃度も調節せずに、５５℃でメタン発酵連続実験を行い、これを比較例２−２とした。反応槽を３ヶ月間連続運転し、食品工場の油脂含有排水に対するメタン発酵の処理性能について調べた結果を表３に示す。
【００６９】
【表３】

【００７０】
メタン発酵槽内の高級脂肪酸濃度を適量に制御しながら、油脂含有排水を連続処理した場合は、高温(５５℃)で運転した場合(実施例２−１)及び中温(３５℃)で運転した場合(実施例２−２)共に、COD_Cr除去率は約８０％、ＢＯＤ除去率は約８５％、ｎ−ヘキサン抽出物の除去率は約９４％となり、非常に効果的な浄化が進行したことがわかった。また、高温で運転した場合(実施例２−１)のガス生成速度は中温で運転した場合(実施例２−２)より約2倍速いということがわかった。これに対して、リパーゼを大量に添加し、メタン発酵槽内の高級脂肪酸が蓄積した場合(比較例2-1)は、ＣＯＤ_Cr除去率は約３０％、ＢＯＤ除去率は約４０％、ｎ−ヘキサン抽出物の除去率は約２５％であって、ガスもほとんど生成しなかった。また、リパーゼを添加せずに高級脂肪酸濃度も調節しない比較例２−２の場合では、ＣＯＤ_Cr除去率は４０％、ＢＯＤ除去率は約４５％、ｎ−ヘキサン抽出物の除去率は３８％であった。メタンガスの生成速度は、実施例２−１＞実施例２−２＞比較例２−２＞比較例２−１の順で大きかった。
【００７１】
実施例３
本実施例においては、油脂含有排水として、豆腐製造排水（中性脂肪０．５g/L）を用いた。メタン発酵実験には、３系列の完全混合型のメタン発酵装置（有効容積３．５L)を発酵槽Ａ〜Ｃとして用い、発酵槽Ａ及びＢには生ゴミの高温メタン発酵汚泥を、発酵槽Ｃには豚糞尿の中温メタン発酵汚泥を種汚泥として用い、連続処理法でのメタン発酵実験を行った。各発酵槽での運転状態と、ガス生成速度とを図４に示す。また、各発酵槽での汚泥濃度の変動を図５に示す。更に、各発酵槽での脂肪（中性脂肪、高級脂肪酸、ＴＧ＋ＬＦＡ）とＶＳＳの比率の変動を図６に示す。なお、ここでＴＧはtriglyceride(トリグリセライド)である。発酵槽Ｂ及びＣで処理する油脂含有排水については、酵素前処理として、油脂分解酵素（リパーゼ、４KU/L)を用いて５０℃で１日処理し、酵素処理の後５℃に冷却保存した。発酵槽Ａで処理する油脂含有排水については、リパーゼ前処理を行わなかった。表４に、各槽で処理する排水原水の性状を示す。また、表５に各槽でのメタン発酵の運転条件を示す。
【００７２】
【表４】

【００７３】
【表５】

【００７４】
メタン発酵運転は、発酵槽Ａ及びＢについては高温メタン発酵として５５℃で発酵を行い、発酵槽Ｃについては中温メタン発酵として３５℃で発酵を行った。発酵槽Ａ及びＢについては運転８４日目より、発酵槽Ｃについては運転１１８日目より、発酵槽の原水に豆腐揚げ廃油を１ml/L添加し、中性脂肪を１．５g/Lとして高油脂負荷条件にした。原水流量については、発酵槽Ａ及びＣはＨＲＴ＝１６日、発酵槽ＢはＨＲＴ＝１５日で運転を開始した。油脂排水原水中の有機物濃度は、リパーゼ前処理したもの及びリパーゼ前処理しないものについて、それぞれ、ＣＯＤ_Crが２．０％及び２．３％；ＢＯＤが１．１％及び１．２％；と比較的低い一方で、ｎ−ヘキサン抽出物／ＣＯＤ_Cr比はそれぞれ０．１２及び０．１１；ｎ−ヘキサン抽出物／ＢＯＤ比はそれぞれ０．１９及び０．２４；と油脂分が高いため、メタン発酵槽内に十分な微生物量を保持することが難しい上に、油脂分の分解性能も悪い。そこで、発酵槽Ａについては、原水にメタン発酵し易いＢＯＤ成分（０．５％澱粉）を添加してメタン発酵運転を開始した。また、反応槽Ｂについては、運転４３日目よりメタン発酵槽から流出する汚泥を定期的に遠心分離（３０００rpm、５分間）してその沈殿汚泥を発酵槽に返送することによって、槽内の菌体濃度を高め、ＬＦＡ／ＶＳＳ比を低く維持することを試みた。
【００７５】
リパーゼ前処理していない油脂排水（発酵槽Ａ）では、澱粉添加によって、油脂負荷の低い条件では安定なメタン発酵処理を行うことができたが、８４日目以降の豆腐揚げ廃油を添加して油脂負荷を増加させた条件下では、１０４日目にＬＦＡ／ＶＳＳ比が０．１３に上昇した（図６のＡ）。その後、中性脂肪の分解が停止すると共にガス生成速度が減少し、１３６日目にはＶＦＡが２５００mg/Lにまで蓄積したため、原水投入を停止した。発酵槽内の汚泥濃度は、メタン発酵が停止した時点で著しく低下しており（図５のＡ）、ＬＦＡ／ＶＳＳ比は０．０４と低かったものの、中性脂肪／ＶＳＳ比は０．７にまで上昇していた（図６のＡ）。その後、１４３日目より汚泥の返送を開始してＬＦＡ／ＶＳＳ比を０．２以下、中性脂肪／ＶＳＳ比を０．３以下に保持しながら運転を再開したところ（図６のＡ）、高い油脂負荷条件でも安定な連続運転が可能であることが分かった（図４のＡ）。
【００７６】
リパーゼ前処理を行った発酵槽Ｂにおいては、運転４３日目から汚泥の返送を開始したことにより、ＬＦＡ／ＶＳＳ比は０．１以下に保たれ（図６のＢ）、高い油脂負荷条件でも極めて安定な連続運転が可能であった（図４のＢ）。
【００７７】
また、リパーゼ前処理を行ったが、メタン発酵を３５℃の中温で行った発酵槽Ｃにおいては、豆腐揚げ廃油を添加しない低油脂負荷条件でも、リパーゼ前処理した油脂排水をＨＲＴ１６日の負荷条件でメタン発酵処理を十分に行うことができなかった。ガス生成速度が低下した時点の８７日目において、発酵槽内にはＶＦＡが３１１１mg/Lに蓄積しており、原水の投入を停止した。この時点でのＬＦＡ／ＶＳＳ比は０．１であった（図６のＣ）。このことから、油脂排水の中温メタン発酵の場合には、ＨＲＴは２０日以上が必要であると考えられた。そして、１１８日目にＨＲＴ＝２５日として、廃油１mL/Lを添加しながら原水投入を再開したところ、１３４日目にはＬＦＡ／ＶＳＳ比は０．１６に上昇し（図６のＣ）、ＶＦＡは運転再開時の１０mg/Lから３４６mg/Lにまで増加した。その後、運転を継続し、１４３日目より汚泥の返送を開始してＬＦＡ／ＶＳＳを０．１以下に保持しながら発酵槽の運転を開始したところ、ＣＯＤ_Cr負荷が発酵槽Ａ及びＢよりも低いためにガス生成速度は低いながらも、ＬＦＡを蓄積することなく、嫌気性処理による有機物分解、油脂分解の安定な連続運転が可能であった（図４のＣ）。
【００７８】
各槽での運転１５０日目から２７０日目までの連続運転期間中の平均メタン発生量は、発酵槽Ａが０．３L/L・日、発酵槽Ｂが０．５L/L・日、発酵槽Ｃが０．１L/L・日であった。また、分解したＣＯＤ_Cr当たりのメタンガス発生量は、発酵槽Ａが０．２７L/g-分解COD_Cr、発酵槽Ｂが０．３２L/g-分解COD_Cr、発酵槽Ｃが０．１６L/g-分解COD_Crであった。これより、リパーゼ前処理を行って５５℃で高温メタン発酵を行った発酵槽Ｂが最もメタン発生量が大きく、以下、メタン発生量は、リパーゼ前処理を行わずに５５℃で高温メタン発酵を行った発酵槽Ａ、リパーゼ前処理を行って３５℃で中温メタン発酵を行った発酵槽Ｃの順であることが分かった。
【００７９】
発酵槽Ｂ（高温メタン発酵）及び発酵槽Ｃ（中温メタン発酵）の運転１５０日目からの連続運転期間における有機物負荷は、発酵槽Ｂでは１．５g/L・日、発酵槽Ｃでは０．８g/L・日であった。また脂質負荷（ｎ−ヘキサン抽出物負荷）は、発酵槽Ｂでは１５０mg/L・日、発酵槽Ｃでは９１mg/L・日であった。これらの結果から、高温メタン発酵の方が中温メタン発酵よりも、有機物負荷及び脂質負荷を高く運転することができ、メタンガス発生量も多いことが分かった。
【００８０】
また、運転１４６日目より定期的にそれぞれのメタン発酵槽内の残留物をサンプリングし、ｎ−ヘキサンで抽出して、抽出物の組成を定量分析した。結果を図７に示す。これより、リパーゼ前処理していない発酵槽Ａでは、発酵槽内に中性脂肪が多く残留していることが分かった。これに対して、リパーゼ前処理した発酵槽Ｂ及び発酵槽Ｃにおいては、中性脂肪は８０％以上除去されており、高級脂肪酸も蓄積されていなかった。油脂排水メタン発酵においては、リパーゼによる前処理が有効であることが分かった。
【００８１】
上記の結果より、メタン発酵槽の安定な運転には、汚泥の返送によって微生物体を導入することで高級脂肪酸濃度／微生物体濃度を一定値以下に制御することが極めて有効な手段であり、また、リパーゼによる前処理の後に、汚泥返送によってＬＦＡ／ＶＳＳ比を制御しながら高温メタン発酵を行うことによって、メタン発生及び油脂分解のいずれにおいても極めて優れた結果が得られることが分かった。また、中温メタン発酵では、メタン発生についてはあまり良好な値は得られなかったものの、汚泥返送と共にメタン発酵を行うことにより、安定な運転が可能で、油脂を極めて良好に分解できることが分かった。
【００８２】
実施例４〜７、比較例３
本実施例では、メタン発酵における微生物保持担体の効果、乳化剤及びｐＨ調節剤の添加効果を調べた。実施例３と同じ油脂含有排水を、リパーゼで５０℃、１日間前処理し、１３０〜１８０日間、連続処理法での高温メタン発酵実験を行った。連続高温メタン発酵実験の運転条件及び結果を表６に示す。排水処理実験装置としては図１０に示すシステムを用いた。但し、メタン発酵槽５への汚泥の返送ラインは、好気処理槽７からのみではなく、汚泥処理槽６からの返送ラインも設置した。乳化剤として、アルギン酸ナトリウム（３００〜４００ｃＰ）、ベントナイトを用い、ｐＨ調節剤として水酸化カルシウムを用い、それぞれ乳化剤貯留槽及びｐＨ調節剤貯留槽４より系に投入した。なお、乳化剤及びｐＨ調節剤の添加量は、排水の体積比で０．０１％、排水中のｎ−ヘキサン抽出物当たりでは０．０４g/gであった。用いた試薬はいずれも、和光純薬製の特級試薬であった。実施例４及び５では、メタン発酵槽５内に微生物保持担体１３としてポリプロピレン樹脂製の充填材を詰めた上向流式の嫌気性処理槽を用いた。充填材の形状は、３０mmφ×６０mmＨ、空隙率は９０％であった。メタン発酵槽５からの流出液は、汚泥貯留槽６を経て好気処理槽７で好気処理を行った。好気処理槽７では、製菓工場排水の回分式活性汚泥プラントから採取した活性汚泥（運転時の有機物負荷０．２g-BOD/g-MLSS/日、活性汚泥浮遊物質：ＭＬＳＳ＝３５００mg/L、活性汚泥沈殿率：ＳＶ₃₀＝４２％）を種汚泥とした活性汚泥を用いて、曝気を行いながら排液の好気処理を行った。実施例６及び７においては、それぞれ、汚泥貯留槽６から流出したメタン発酵汚泥、及び好気処理槽７から流出した余剰活性汚泥を、遠心分離（３０００rpm、５分間）してその沈殿汚泥を発酵槽５に返送した。メタン発酵槽５の残留物を周期的にサンプリングして、分析装置２０によって分析することにより、ＢＯＤ除去率、ＣＯＤ_Cr除去率、ＶＴＳ（volatile total solids:揮発性全固形分）除去率、及び高級脂肪酸除去率を算出した。表６には、各除去率の平均値を示す。汚泥処理槽６及び好気処理槽７から排出された余剰汚泥は、凝集剤として高分子凝集剤（エバグロースLDC-300)を凝集剤貯留槽８から加えて、汚泥凝集槽９において汚泥を凝集させた後、スクリュープレス式汚泥脱水機１０で脱水した。脱水濾液及び脱水汚泥の性状を分析した。
【００８３】
メタン発酵槽からの発生ガス量を、シナガワ製の湿式ガスメーターWE Da-0.5B型で計測すると共に、ガス試料の一部を採取してガスクロマトグラフィーTCDでその組成を分析した。そして、分析試料以外の発生ガスについては、ペレット状の水酸化鉄(Fe(OH)₃)を充填した脱硫塔１１によってガス中の硫化水素を除去した。
【００８４】
【表６】

【００８５】
上記の表６に示す結果から、メタン発酵槽において微生物保持担体を充填した実施例４と担体を充填せずにメタン発酵汚泥を返送した実施例６とを比較すると、消化ガス発生速度と有機物処理性能が両者でほぼ同等の試験結果であったことから、メタン発酵槽内に微生物保持担体を用いることの効果が示された。また、汚泥の高濃度化の効果は、実施例６及び７と比較例３とを比較して、消化ガス発生速度、有機物処理性能、汚泥脱水性能のいずれの点でも、高濃度に汚泥を保持した場合（実施例６及び７）に良好な処理成績が得られたことから、その効果が示された。更に、乳化剤及びｐＨ調節剤の添加効果は、返送汚泥の種類は異なるものの、実施例６と実施例７とを比較して、特に、消化ガス発生速度と有機物処理性能の点で、乳化剤及びｐＨ調節剤を添加した場合に有効な成績が得られたことから、それらの添加効果が示された。
【００８６】
汚泥凝集剤添加率と脱水汚泥含水率は汚泥性状を示す指標でもある。油脂分が殆ど存在しない有機性排水を正常に生物処理した場合、通常、汚泥凝集剤添加率は０．５〜０．７％（対ＳＳ比）であり、脱水汚泥含水率は、脱水機にもよるが７８〜８０％程度であるとされている。一方、汚泥中に油脂分が分解されずに残留していると、汚泥凝集剤による汚泥凝集能が低下するために、汚泥凝集剤添加率は高くなると共に、汚泥凝集能が悪いために脱水汚泥含水率も増加する。
【００８７】
同様に、脱水濾液性状も汚泥性状を示す指標であり、油脂分による汚泥凝集能の低下によって凝集できなかった微細な汚泥（ＳＳ）が脱水濾液側に流出するためにＳＳ値が増加すると共に、それに伴ってＢＯＤ値も増大する。
【００８８】
消化ガス組成は、メタン発酵性能を示すものである。メタン発酵で有機物分解率が低下すると、微生物の消化不良が生じるために消化ガス発生速度及びメタンガス含有率が低下する。消化ガス発生速度は、対象排水や運転方法によって異なるものであるが、メタンガス含有率は、１槽式タイプでの正常なメタン発酵処理の場合、６０〜６８％程度である。
【００８９】
【発明の効果】
本発明によれば、嫌気反応槽内の油脂を酵素または酵素生成微生物体により分解し、分解生成物である高級脂肪酸の濃度を所定以下に調節しながら、45〜70℃の高温域で油脂含有排水あるいは廃棄物を浄化することにより、排水を高効率で浄化することが可能となった。さらに、嫌気性生物により有機物を分解するので、バイオガス（特にメタン）として回収することができ、これよりエネルギー回収効率を著しく向上させることが可能となった。
【図面の簡単な説明】
【図１】図１は、高級脂肪酸濃度の調節によるメタン発酵の特性を示すグラフである。
【図２】図２は、高級脂肪酸濃度の調節によるメタン発酵の脂質除去特性を示すグラフである。
【図３】図３は、高級脂肪酸濃度の調節によるメタン発酵の有機物除去特性を示すグラフである。
【図４】図４は、実施例３において行ったメタン発酵連続運転によるガス生成速度を示すグラフである。
【図５】図５は、実施例３において行ったメタン発酵連続運転における発酵槽内の汚泥濃度を示すグラフである。
【図６】図６は、実施例３において行ったメタン発酵連続運転における発酵槽内の脂肪（中性脂肪、高級脂肪酸、ＴＧ＋ＬＦＡ）とＶＳＳの比率の変動を示すグラフである。
【図７】図７は、実施例３において行ったメタン発酵連続運転における発酵槽内の残留物の分析結果を示す図である。
【図８】図８は、本発明の一態様に係る方法を用いた油脂含有排水の嫌気性処理プロセスの概要を示すフロー図である。
【図９】図９は、本発明の他の態様に係る方法を用いた油脂含有排水の嫌気性処理プロセスの概要を示すフロー図である。
【図１０】図１０は、本発明の更に他の態様に係る方法を用いた油脂含有排水の嫌気性処理プロセスの概要を示すフロー図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an anaerobic treatment method (methane fermentation method) and apparatus for fat-containing wastewater or fat-containing waste, and in particular, by suppressing the accumulation of higher fatty acids in an anaerobic reaction tank, stable operation is achieved. It provides an anaerobic treatment method that enables it. According to the present invention, by providing a treatment device and a treatment process for promoting higher fatty acid decomposition in an anaerobic environment, oil-containing wastewater or oil-containing waste is purified with high efficiency, and energy recovery efficiency by biogas Can be improved.
[0002]
[Prior art]
Biological treatment methods are used for the treatment of wastewater containing organic pollutants, and in particular, aerobic treatment methods centered on the activated sludge method have been frequently used. However, the aerobic treatment method consumes a lot of energy, and in particular, disposal of excess sludge has become a big problem recently. On the other hand, anaerobic treatment methods have been conventionally applied in various forms in the treatment of wastewater and organic sludge containing high-concentration organic pollutants. This method is known to be advantageous in that it can save energy consumption because aeration is unnecessary, and the amount of surplus sludge generated is small, so that the treatment cost is low and methane gas useful as energy can be recovered. (See, for example, Shu Shuung-ho, Lee Yuyu, Takashi Miyahara, Tatsuya Noike, JSCE, No. 559 / VII-2, pp. 31-38, 1997, etc.).
[0003]
On the other hand, typical fats and oils as organic pollutants are hardly decomposable substances in both aerobic treatment and anaerobic treatment. This is because the dispersibility of fats and oils is poor, and it floats in the treatment tank and forms scum. Therefore, in order to purify wastewater containing fats and oils using such biological treatment methods (aerobic treatment and anaerobic treatment), in many cases, conventional methods physically separate and remove fats and oils by flotation separation. A process was required. However, it is difficult to separate fats and oils to a level applicable to general biological treatment, and the work load is also large, and the separated and removed fats and oils are difficult to handle, and the drainage channels are blocked and treated. There were many problems such as equipment malfunction, generation of odors and pests. As described above, since the disposal cost is high for oil-containing wastewater and waste, a technical and economical countermeasure has been required.
[0004]
As a method for purifying oils and fats without separating and removing them from wastewater or waste, a method for decomposing oils and fats in oily and fat-containing wastewater with an enzyme using an immobilized lipase has been proposed. However, in this method, fatty acids and glycerol which are decomposition products of fats and oils remain in water. That is, decomposition products, particularly fatty acids are temporarily converted into insoluble salts and trapped in the packed bed of immobilized lipase, the packed bed is clogged, and the processing efficiency is lowered. Accordingly, there is a need to further biologically treat such degradation products and in addition to purify wastewater by controlling biological reactions that degrade fatty acids.
[0005]
As another method of biologically treating fat-containing wastewater or waste without separating and removing fats and oils, non-immobilized lipase is added to treat the wastewater, and the fats and oils in the wastewater (especially neutral fats) ) Is hydrolyzed to make it susceptible to assimilation by microorganisms, and then introduced into an aerobic treatment reactor. However, the aerobic treatment is problematic in that it consumes a large amount of energy as described above, and that it is necessary to dispose of excess sludge later, and that it is necessary to take measures against the original odor and scum of fats and oils.
[0006]
Further, a method has been proposed in which lipase is added to fat-and-oil containing waste water to decompose the fat and oil, and then the waste water is subjected to anaerobic treatment. However, it is known that the following problems exist in the method of anaerobic treatment (particularly treatment with methanogenic bacteria) after lipase treatment in this way. In other words, when higher fatty acids produced by the decomposition of neutral fat are present in the treated wastewater, methanogens that act on methane fermentation in anaerobic treatment, especially acetate-utilizing methanogens and hydrogen-utilizing methanogens In addition, the growth of such microorganisms is also inhibited (the above-mentioned Chu Shuung-ho, Lee Yuyu, Takashi Miyahara, Tatsuya Noike, et al., Japan Society of Civil Engineers, No. 559 / VII-2, No. 31- 38, 1997; Shuzo Tanaka, Kazuo Taku et al., Abstracts of the 42nd Annual Scientific Lecture Meeting of Japan Society of Civil Engineers, pages 868-869, September 1987; Naomi Tsue, Hideki Harada, Kiyoshi Momoi, Satoshi Takizawa, Masatoshi Kamei et al., 44th Annual Scientific Lecture, Japan Society of Civil Engineers, pages 1014-1015, September 1989;
[0007]
Furthermore, using fat and oil-based food waste whose components were adjusted to a fat and oil content of 8 to 40% (TS (total solids: evaporation residue) base, fat and oil concentration 9 to 44 g / L), HRT = 7.5 In the laboratory experiment of methane fermentation at high temperature (55 ° C) in the day, COD_CrIt has been reported that the decomposition rate was 73-80% and the VS decomposition rate was 76-80% (Koji Yamashita, Hiroshi Sasaki, Yu Yu Li, Junji Seki, 11th Annual Conference of Japan Society for Waste Management) Conference Proceedings I, 283-285, November 8, 2000). However, when calculating the gas generation rate based on the data reported here, when the oil content is 40%, 0.176 L-CH_Four/ g-input COD_Cr, 0.220 L-CH_Four/ g-decomposition COD_CrWhen the oil content is 23%, 0.167 L-CH_Four/ g-input COD_Cr, 0.214 L-CH_Four/ g-decomposition COD_CrIt is. Here, decomposed organic matter (COD_CrThe theoretical methane gas generation rate is 0.35 L-CH_Four/ g-decomposition COD_Cr(In the above, HRT is a hydraulic retention time), COD_CrIs chemical oxygen demand (oxygen consumption by potassium dichromate), and VS is volatile solids). Therefore, it can be said that the decomposition rate of organic matter is high in high-temperature methane fermentation of fat-based waste from the case of methane fermentation of fat-based food waste, but methane gas recovery corresponding to the amount of organic matter decomposition cannot be obtained. It is inferred that intermediate metabolites such as higher fatty acids accumulate in the tank, and oil components float and separate in the fermenter. From a long-term viewpoint, this lacks the performance, stability, and certainty of methane fermentation treatment, and needs to be improved.
[0008]
Once the higher fatty acid starts to accumulate, it inhibits the activity of microorganisms useful for anaerobic treatment as described above, and as a result, higher fatty acids that are no longer decomposed are further accumulated. Stop. That is, if the higher fatty acid produced by the hydrolysis of the neutral fat is large, the inhibition of methane fermentation becomes large, and as a result, the methane production reaction itself does not proceed. In this context, in medium and high temperature methane fermentation, C_{10: 0}, C_{12: 0}, C_{14: 0}, C_{16 : 0}, C_{18: 0}, C_{18: 1}(trans), C_{18: 1}(cis), C_{18: 2}, C_{18: 3}Have also been reported on the inhibitory properties of individual higher fatty acids on microorganisms (as mentioned above, Shu Shuung-ho, Lee Yuyu, Takashi Miyahara, Tatsuya Noike, et al., Japan Society of Civil Engineers, No. 559 / VII-2, No. 31- 38, 1997). Therefore, in the prior art, it has been technically difficult to purify wastewater containing high-concentration fat or waste or waste using a methane fermentation treatment method after pretreatment with lipase.
[0009]
On the other hand, most of the fats and oils are composed of carbon and hydrogen, and if the fat and oil decomposition rate is improved in anaerobic biodegradation, the amount of conversion to methane gas is also improved. For example, the amount of methane gas generated when anaerobically treating 1 g of degradable organic substances is compared for fat, carbohydrate, and protein, and they are 850 mL / g, 395 mL / g, and 500 mL / g, respectively (sewage / wastewater) Treatment of sludge, Shigehisa Iwai, Tohru Shinoka, Makoto Natori, 1968, see Corona, pages 42-42). That is, from the viewpoint of energy recovery, the advantage of anaerobic treatment (particularly methane fermentation treatment) of fats and oils is great.
[0010]
The technical problems of the purification method in which fat-containing wastewater or fat-containing waste is pretreated by lipase and then treated by anaerobic treatment mainly consisting of methane fermentation are summarized as follows.
[0011]
(1) Unsaturated fatty acids are converted to saturated fatty acids and then β-oxidatively decomposed. However, since the rate of degradation of saturated fatty acids is slow, it is the rate-limiting reaction for oil degradation.
(2) Accumulation of higher fatty acids tends to inhibit decomposition of higher fatty acids and acetic acid-assimilating methane formation. This inhibitory action is stronger with unsaturated higher fatty acids than with saturated fatty acids (Chu Shun-ho, Lee Yuyu, Takashi Miyahara, Tatsuya Noike et al., Journal of Japan Society of Civil Engineers, No. 559 / VII-2, pp. 31-38) 1997; and Shuzo Tanaka, Kazuo Taku, et al., Abstracts of the 42nd Annual Scientific Lecture Meeting of Japan Society of Civil Engineers, pages 868-869, September 1987, etc.).
[0012]
The above problem (1) is an anaerobic treatment tank for salts (for example, metal salts such as sulfate, sulfite, phosphate, iron salt, etc.) or nutrients (for example, citric acid, lactic acid, methanol, peptones, etc.) In the past, a method for activating the anaerobic microorganisms and promoting β-oxidative degradation of fatty acids has been used. However, since the solution to the above problem (2) has not been shown so far, it has been difficult to stably and efficiently anaerobically treat oil-containing wastewater or oil-containing waste.
[0013]
[Problems to be solved by the invention]
Therefore, the objective of this invention is providing the purification method and purification apparatus which can perform the anaerobic process of fats and oils containing waste water or fats and oils containing waste stably and efficiently. Furthermore, according to this invention, it aims at the improvement and stabilization of energy recovery efficiency as biogas, and the improvement of treated water quality.
[0014]
[Means for Solving the Problems]
As a result of earnest examination of the above-mentioned problems, the present inventor has found that methane fermentation in an anaerobic tank can be stably performed by suppressing the accumulation of higher fatty acids in the anaerobic reaction tank, and suppresses the accumulation of higher fatty acids. The above problem has been solved by providing specific means to do this. In the present invention, the means for suppressing the accumulation of higher fatty acids is, first of all, the concentration of higher fatty acids in an anaerobic reaction system is monitored, and the fat-degrading enzyme added in the oil-and-oil decomposing step by the former oil-degrading enzyme accordingly. By controlling the amount and limiting the amount of higher fatty acids introduced into the anaerobic reaction system, the concentration of higher fatty acids in the anaerobic reaction system is controlled. Second, microorganisms are added to the anaerobic reaction system. By actively introducing it, the decomposition of higher fatty acids in an anaerobic reaction system is promoted.
[0015]
That is, one embodiment of the present invention is a method for purifying fat-containing wastewater or fat-containing waste by an anaerobic treatment method, and decomposes fats by acting with fat-degrading enzymes or microorganisms that produce the enzymes. A pretreatment; and an anaerobic treatment of the pretreated waste water or waste; and during the anaerobic treatment, the higher fatty acid concentration in the anaerobic reaction system is monitored to control the concentration. The purification method is provided. Furthermore, the second aspect of the present invention is a method for purifying fat-containing wastewater or fat-containing waste by an anaerobic treatment method, wherein the fat is allowed to act on an oil-degrading enzyme or a microorganism that produces the enzyme. A pretreatment for decomposing and an anaerobic treatment of the pretreated wastewater or waste, and promoting the decomposition of higher fatty acids by introducing anaerobic or aerobic microorganisms into the anaerobic treatment step. The purification method is provided.
[0016]
In the present invention, “oil and fat” is a glycerol ester of saturated fatty acid and unsaturated fatty acid as a main component, and includes unsaponifiable substances such as free fatty acid, long chain alcohol, sterol, hydrocarbon, fat-soluble vitamin, and pigment. Ingredients that are widely present in natural animals and plants. Oils and fats include both liquid and solid cases at room temperature. Examples of fats and oils include dry oils such as oil, linseed oil, persimmon oil, soybean oil, semi-dry oils such as cottonseed oil, sesame oil, rapeseed oil, rice oil, and non-drying oils such as peanut oil, olive oil, and camellia oil. Besides, vegetable oils and fats including vegetable oils such as palm oil and palm oil, animal fats such as head and lard, animal oils such as sheep oil, whale oil, fish oil and liver oil, and mixtures thereof can be mentioned.
[0017]
“Neutral fat” is a glycerol ester of a fatty acid and refers to a lipid that, when hydrolyzed, produces one molecule of glycerin and one to three molecules of fatty acid. Examples of the neutral fat include monoacylglycerol in which one molecule of glycerin and one molecule of fatty acid are ester-bonded, diacylglycerol in which one molecule of glycerol and two molecules of fatty acid are ester-bonded, and triacyl in which one molecule of glycerin and three molecules of fatty acid are ester-bonded Glycerol and mixtures thereof are mentioned.
[0018]
A fatty acid obtained as a hydrolyzed product of an O-acyl lipid having an ester bond (neutral fat, wax, etc.) or an N-acyl lipid having an acid-acid bond (sphingolipid, etc.) is referred to as “free fatty acid”. Free fatty acids include “lower (short-chain) fatty acids” with fewer carbon atoms, typically less than 11 carbons (eg, butyric acid, valeric acid, caproic acid, pelargonic acid, capric acid, undecyl acid, etc.); There are “higher (long chain) fatty acids” with a large number of carbon atoms, typically 11 or more carbon atoms. Examples of the higher fatty acid include lauric acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicin Examples thereof include saturated fatty acids such as acid and laccelic acid, unsaturated fatty acids such as oleic acid, elaidic acid, celetic acid, erucic acid, brassic acid, linoleic acid, linolenic acid, arachidonic acid and stearolic acid, and mixtures thereof. The definition of carbon number of “higher fatty acid” itself is not clear. For example, there is a document in which “higher fatty acid” is one having 8 or more carbon atoms (for example, Naomi Tsue, Hideki Harada, Kiyoji Momoi, (See Satoshi Takizawa, Masatoshi Kamei et al., 44th Annual Scientific Lecture, Japan Society of Civil Engineers, pages 1014-1015, September 1989, etc.). Therefore, the “higher fatty acid” in the present invention should be interpreted widely.
[0019]
In the present invention, as an enzyme used for decomposing neutral fat contained in fats and oils in the pretreatment step, for example, glycerol represented by triacylglycerol lipase, monoacylglycerol lipase, lipoprotein lipase and the like An enzyme having an activity of hydrolyzing an ester to release a fatty acid can be mentioned. These may be used alone or in a mixed form of several kinds of glycerol esterase. In addition, normal wastewater or waste contains not only fats and oils but also sugars, proteins, etc., in addition to these glycerol ester-degrading enzymes, α-glucosidase, amylase, cellulase, β-glucosidase, avicerase, xylanase Alternatively, a carbohydrate degrading enzyme such as mannosidase or β-galactosidase, or a proteolytic enzyme typified by exopeptidase, endopeptidase, pepsin, trypsin, chymotrypsin or the like may be used.
[0020]
In the present invention, not only the enzyme itself but also a microbial cell that produces the above-mentioned enzyme (in the present invention, referred to as “enzyme-producing microbial cell” or “microorganism that produces the enzyme”) is included. Good. If the process of purifying the enzyme from the enzyme-producing microorganism is simplified and the present invention is carried out using a product in which the enzyme and the microorganism are mixed, the fats and oils can be decomposed at a lower cost. Examples of such enzyme-producing microorganisms include aerobic microorganisms such as Candida, Rhizopus, and Pseudomonas, and anaerobic microorganisms such as Anaerovibrio, Butyrivibrio, Desulfovibrio, Clostridium, Ruminococcus, and Enterobacterium. . Furthermore, since the anaerobic treatment, which is a subsequent treatment step of the method of the present invention, is preferably performed at 45 to 70 ° C. as described later, the enzyme or the enzyme-producing microorganism is subjected to such a temperature condition of 45 to 70 ° C. It is desirable that the enzyme or the enzyme-producing microorganism be in a temperature range in which the activity can be maintained or the optimum reaction temperature is applied.
[0021]
In the method of the present invention, the waste water or waste, in which fats and oils, particularly neutral fats therein are hydrolyzed by the pretreatment, is then subjected to an anaerobic treatment. “Anaerobic treatment” refers to treatment performed by an anaerobic microorganism that is generally a microorganism that grows in the absence of molecular oxygen, especially anaerobic fermentation in which anaerobic microorganisms decompose organic matter under anaerobic conditions. It is used for processing.
[0022]
Examples of the anaerobic microorganism that can be used in the anaerobic treatment of the method of the present invention include methanogenic bacteria (for example, Methanosarcina, Methanothrix, Methanobacterium, and Methanobrevibacter), sulfate-reducing bacteria (for example, Desulfovibrio and Desulfotomaculum , Desulfobacterium genus, Desulfobacter genus, Desulfococcus genus), acid producing bacteria (eg Clostridium genus, Acetivibrio genus, Bacteroides genus, Ruminococcus genus), facultative anaerobes (eg Bacillus genus, Lactobacillus genus, Aeromonas genus, Streptococcus genus, Micrococcus Genus) and the like. From the viewpoint of energy recovery, it is preferable to use methanogenic bacteria.
[0023]
In addition, higher fatty acids are decomposed mainly by the joint work of sulfate-reducing bacteria, hydrogen-producing acetic acid-producing bacteria, hydrogen-utilizing methane-producing bacteria, and acetic acid-assimilating methane-producing bacteria. That is, the decomposition reaction from higher fatty acid to acetic acid is so-called β-oxidation, and acetic acid generated by such β-oxidation reaction is utilized by acetic acid-assimilating methanogens and converted into methane gas. Therefore, it is preferable to use a mixture of these microorganisms from the viewpoint of efficient degradation of higher fatty acids. These anaerobic microorganisms are, for example, microorganisms that exist universally in nature, such as sludge obtained by subjecting raw garbage to high-temperature methane fermentation and sludge obtained by subjecting livestock manure such as pigs to medium-temperature methane fermentation. An anaerobic reaction tank in the present invention can be formed by arranging sludge obtained by acclimatizing these sludges as seed sludge with oil-containing wastewater or the like in the tank.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail, but the present invention is not limited thereto. Hereinafter, the purification method by methane fermentation treatment will be described for convenience, but the present invention is not limited to this.
[0025]
The method for purifying fat-containing wastewater or fat-containing waste according to the first aspect of the present invention by an anaerobic treatment method is a microorganism that produces fat-degrading enzyme or fat-degrading enzyme such as neutral fat in fat. A pretreatment for decomposing by acting on the body; a treatment for anaerobically treating the pretreated waste water or waste; and monitoring the higher fatty acid concentration in the anaerobic reaction system during the anaerobic treatment. The density is controlled.
[0026]
In order to promote the methane fermentation treatment of fat and oil-containing wastewater or fat and oil-containing waste, it is important and indispensable that the fat and oil and anaerobic sludge (anaerobic microorganisms) are in homogeneous contact. However, when the fat content is high, fat and oil containing neutral fat is not easily floated and dispersed in the reaction tank, and fermentation by anaerobic microorganisms is difficult to proceed. Therefore, in the present invention, as a pretreatment step, a hydrolase (preferably lipase) of fats and oils such as neutral fat or a microbial body (preferably Candida cylindracea [yeast fungus], Rhizopus arrhizus [fungus], Pseudomonas cepacia [bacteria] etc.) act on neutral fat, which is hydrolyzed into easily dispersible fatty acid and glycerol. As a result, the free higher fatty acid is uniformly dispersed and does not come into contact with the anaerobic microorganisms without the lipid floating in the reaction tank. Pre-treatment that decomposes fats and oils such as neutral fat by adding lipase to fat-containing wastewater or fat-containing waste directly in an anaerobic treatment tank (simply called methane fermentation tank) mainly consisting of methane fermentation Alternatively, the pretreatment may be performed in a pretreatment tank different from the methane fermentation tank, and the treated waste water or waste may be charged into the methane fermentation tank. In addition, the pretreatment reaction for decomposing the fats and oils such as neutral fats with the enzyme or its enzyme-producing microorganism is performed with stirring from the viewpoint of maintaining uniform dispersion of the fats and oils such as neutral fats. preferable.
[0027]
The pretreatment reaction that decomposes fats and oils such as neutral fat with lipase is carried out by maintaining the inside of the methane fermentation tank under neutral to weakly alkaline conditions (pH 6 to 8.5, preferably pH 7 to 8). desirable. This is because the optimum pH of the lipase is usually in this range. By carrying out the pretreatment step while maintaining neutrality to weak alkalinity, hydrolysis by lipase of fats and oils such as neutral fat proceeds easily and quickly.
[0028]
The pretreatment reaction for decomposing oil and fat such as neutral fat with lipase is preferably performed in a so-called intermediate temperature range (30 to 45 ° C) or a so-called high temperature range (45 to 70 ° C). This is because the optimum temperature for lipase is within this range. In addition, when the pretreatment reaction is performed directly in the methane fermenter, it is effective to maintain the inside of the methane fermenter at 45 to 70 ° C. as described later, so the pretreatment is also maintained within this temperature range. It is desirable to do this. In that case, it is preferable to use a heat-resistant lipase that can withstand such a high temperature range. When pretreatment is performed while maintaining such a high temperature state, the fluidity of lipid is increased, and oil and fats such as neutral fat are more easily dispersed.
[0029]
Furthermore, since the reaction rate of an enzyme reaction is generally proportional to the temperature, the pretreatment in such a high temperature region is more effective because the decomposition efficiency of fats and oils such as neutral fat is greatly improved.
[0030]
The treatment with an enzyme such as lipase or an enzyme-producing microorganism is generally performed independently prior to the anaerobic treatment, but can also be performed simultaneously with the anaerobic methane fermentation treatment. However, in the latter case, it is necessary to pay attention to the processing conditions.
[0031]
The wastewater or waste that has been pretreated with the enzyme or enzyme-producing microorganism as described above is decomposed by methane fermentation in the next step. As a result, in addition to glycerol obtained as a hydrolysis product of neutral fat, carbohydrates, proteins, and other various components contained in waste water or waste are used as a substrate for methane fermentation and decomposed.
[0032]
Of the free fatty acids obtained as neutral fat hydrolysis products, lower fatty acids are susceptible to degradation by methanogenic bacteria as precursors in the methane fermentation process and are therefore readily converted to methane. However, higher free fatty acids are not only difficult to ferment methane originally, but when they become high in concentration, they accumulate in an anaerobic treatment tank and inhibit the action of methane fermenting enzymes and the growth of enzyme-producing bacteria. That is, higher fatty acids are first converted to acetic acid by β-oxidation, and the acetic acid produced is converted to methane by the action of acetic acid-assimilating methanogenic bacteria, but a high concentration of higher fatty acids not only inhibits this β-oxidation itself. It also inhibits the activity of acetic acid-utilizing methanogens.
[0033]
Based on such knowledge, in the first aspect of the present invention, it has been found that methane fermentation can be efficiently advanced by maintaining the concentration of free higher fatty acids in the methane fermentation tank at a value equal to or lower than a predetermined concentration. The object was achieved by monitoring and controlling the higher fatty acid concentration in the anaerobic treatment step.
[0034]
In order to confirm the higher fatty acid concentration, the higher fatty acid concentration in the methane fermenter is sequentially sampled and monitored. The method for monitoring the higher fatty acid concentration needs to adopt a technique that can cope with a high-speed decomposition reaction by enzymes or microorganisms because the purification apparatus is a system containing enzymes, enzyme-producing microorganisms, anaerobic microorganisms, and the like. For example, the neutral acid and fatty acid concentrations in the methane fermenter can be quickly monitored by a chemical acid value and saponification value measuring method using ethanolic caustic potash. In addition, a higher fatty acid labeling reagent such as Adam reagent (9-anthryldiazomethane, ADAM) is added to the sample to label the higher fatty acid, and a high-speed detector equipped with an ultraviolet absorption (UV) detector or a fluorescence (FL) detector. It is also possible to separate and quantify higher fatty acids using liquid chromatography (HPLC). This method is preferable from the viewpoint of rapid quantitative analysis because the higher fatty acid concentration can be easily analyzed in 1 to 2 hours per sample. Furthermore, extraction with an organic solvent capable of extracting lipids such as normal hexane / isopropanol, chloroform / methanol, acetone, ethers, etc., and neutral fat with a TLC (thin layer chromatography) / FID (flame ionization detector) analyzer. And higher fatty acids can be accurately quantitatively analyzed with a gas chromatograph analyzer. When this method is used, it takes about 1 day until the determination, but this is preferable in that the higher fatty acid concentration can be accurately grasped. Therefore, in the present invention, it is desirable to monitor the higher fatty acid concentration in the fermenter by appropriately combining the simple and rapid quantitative analysis method described above, the TLC / FID analysis method, and the gas chromatographic analysis method. . Furthermore, for example, in a reaction system in which it is known in advance that a specific higher fatty acid such as palmitic acid or stearic acid is prominently produced, it can be quickly obtained by using a chemical sensor or a microbial sensor that can specifically detect them. And easy monitoring is possible.
[0035]
In the method of the present invention, the preferred higher fatty acid concentration in the methane fermentation tank varies depending on the quality of raw water, the composition of higher fatty acid, the sludge concentration in the reaction tank, the type of anaerobic microorganisms, the methane fermentation treatment system, and the like. In the case of adopting a method in which pretreatment of reacting fat-containing wastewater or fat-containing waste with lipase is simultaneously performed in a methane fermentation tank, typically, the higher fatty acid concentration is 1000 mg / L or less, preferably 700 mg / L or less. Further, it is necessary to control the amount of the enzyme or the enzyme-producing microorganism so that it is maintained at 500 mg / L or less, most preferably 300 mg / L or less, and most preferably 250 mg / L or less. In addition, when the pretreatment is performed in a pretreatment tank separate from the methane fermentation tank and then treated wastewater or waste is introduced into the methane fermentation tank, the concentration of higher fatty acids in the fermentation tank after introduction into the methane fermentation tank Is maintained at 2000 mg / L or less, preferably 1000 mg / L or less, more preferably 500 mg / L or less, most preferably 300 mg / L or less, and most preferably 250 mg / L or less. The amount of addition is controlled. The higher fatty acids listed above are mainly those derived from vegetable oils such as soybean oil, sesame oil, coconut oil, and palm oil, and animal fats such as head and lard. On the other hand, in animal oils such as sheep oil, whale oil, fish oil and liver oil, higher fatty acids (C₂₀The above is likely to be the main higher fatty acid, and these long-chain higher fatty acids are more likely to inhibit the methane fermentation reaction. Therefore, it is desirable to maintain the concentration of the higher fatty acid at a value of about 1/10 or less. .
[0036]
In order to maintain the higher fatty acid concentration within the above range, the amount of lipase added to decompose fats and oils such as neutral fat may be adjusted in the first embodiment of the present invention. That is, the higher fatty acid concentration in the methane fermenter is sequentially monitored by the above-mentioned method. If the higher fatty acid concentration is lower than the appropriate value, the amount of lipase added is increased to hydrolyze fats and oils such as neutral fat. When the higher fatty acid concentration is higher than an appropriate value, the higher fatty acid concentration is decreased by decreasing the amount of lipase added or by temporarily suspending the higher fatty acid concentration. Therefore, the purification apparatus for carrying out the method according to the first aspect of the present invention further includes means for feeding back the measured higher fatty acid concentration value, determining the amount of lipase added, and adjusting this. More preferably.
[0037]
In order to maintain the higher fatty acid concentration, in addition to controlling the amount of lipase added as described above, treatment with various organisms including well water, tap water or activated sludge treatment is performed in the pretreatment step with lipase. It is also effective to adjust the higher fatty acid concentration by mixing and diluting with water.
[0038]
The methane fermentation of the present invention may be carried out in either a so-called intermediate temperature range of 30 to 45 ° C, preferably 30 to 40 ° C, or a so-called high temperature range of 45 to 70 ° C. However, if the methane fermenter is maintained in a high temperature range, the neutral fatty acid and the higher fatty acid decomposed and produced by the oil-degrading enzyme or the enzyme-producing microorganism are likely to disperse in the liquid and are susceptible to reaction by anaerobic microorganisms. It is also known that the inhibitory effect of higher fatty acids on methane fermentation is remarkably mitigated under high temperature conditions (Chuu Shun Hou, Lee Yuyu, Takashi Miyahara, Tatsuya Noike, et al., Japan Society of Civil Engineers, No.559 / VII- (See 2, 31-38, 1997; and Shuzo Tanaka, Kazuo Taku et al., Abstracts of the 42nd Annual Conference of the Japan Society of Civil Engineers, pages 868-869, September 1987)) . Therefore, from the viewpoint of performing anaerobic treatment efficiently while avoiding activity inhibition by higher fatty acids, a temperature range of 45 to 70 ° C, preferably 50 to 65 ° C, more preferably 50 to 60 ° C. It is preferable to perform an anaerobic treatment.
[0039]
Moreover, although the inside of the anaerobic reaction tank of this invention changes with kinds of the waste_water | drain to purify | clean and the kind of sludge to be used, it is preferable to maintain in pH 6-9 neutral-weakly alkaline range. This is because anaerobic microorganisms effectively decompose organic substances within such a range. That is, if the pH in the anaerobic reaction tank is too high (that is, if it is strongly alkaline), the fatty acid becomes soapy and decomposition by anaerobic microorganisms is difficult to proceed rapidly. Moreover, it is preferable to stir the anaerobic reaction tank so that the organic substance and the anaerobic microorganisms are uniformly and effectively in contact with each other. Therefore, it is more preferable that the purification system or the purification device for carrying out the method according to the present invention has a stirring means.
[0040]
The anaerobic treatment tank used in the method of the present invention can be filled with a microorganism holding carrier. As a method for binding a microorganism to a carrier, a binding method or a comprehensive method can be applied. In the microbial reaction in the anaerobic treatment of an oil-containing contaminant in the present invention, sand, quartz sand, activated carbon, ceramics, synthetic resin, plastic It is advantageous to form a biofilm by attaching microorganisms to the surface of particles such as beads, glass beads, polyethylene glycol, polyvinyl alcohol, polyurethane, polypropylene, sludge incineration ash, charcoal powder, coal ash fly ash. These holding carriers are roughly classified into a fixed bed and a fluidized bed depending on the form of existence in the anaerobic treatment tank and the flow state, but both types can be applied in the present invention. However, in the fixed bed type, clogging of the immobilized carrier and sludge floating due to excessive adhesion of oil and fat tends to be a problem, and in the fluid type, sludge peeling due to collision between carriers tends to be a problem. It is necessary to pay attention to raw water conditions such as concentration, raw water supply method during fermenter operation, organic load, sludge concentration and sludge properties. In determining these operating conditions, the operating conditions are determined in consideration of the raw water condition, the amount of water fluctuation, and the target treated water quality.
[0041]
The technical idea according to the first aspect of the present invention described above is to control the amount of higher fatty acid introduced into the anaerobic reaction system while suppressing the amount of enzyme added in the pretreatment system. In place of the method, by actively introducing anaerobic or aerobic microorganisms into the anaerobic reaction system, the decomposition of higher fatty acids in the anaerobic treatment process is also promoted, preventing the accumulation of higher fatty acids and stable. Anaerobic treatment can be achieved. That is, the second aspect of the present invention is a method for purifying oil-containing wastewater or oil-containing waste by an anaerobic treatment method, and produces a fat-degrading enzyme or its enzyme for neutral fats in the fat. A pretreatment that causes the microorganisms to act and decompose; and a treatment that anaerobically treats the pretreated waste water or waste, by introducing anaerobic or aerobic microorganisms into the anaerobic treatment step. The purification method is characterized by promoting the decomposition of higher fatty acids.
[0042]
As a method of introducing anaerobic or aerobic microorganisms into the anaerobic treatment process, acid sludge and methane fermentation sludge that flowed out from the anaerobic treatment process are returned to the anaerobic treatment tank, A method of returning concentrated sludge obtained by concentration by gravity sedimentation or mechanical concentration to an anaerobic treatment tank can be applied. In this sludge concentration step, sludge concentration / aggregation is achieved by adding 0.1 to 1.0% sludge coagulant such as polymer coagulant per SS (suspended solids) to the spilled sludge. Promoting techniques are also effective. In addition, as a mechanical concentration method, those used as a sludge dehydrator such as a centrifugal dehydrator or a screw press dehydrator can be applied. Further, when returning the dewatered sludge to a normal anaerobic treatment tank, there is no problem even if the sludge dehydrated by these dehydrators is charged. Furthermore, sludge can be kept at a high concentration in the methane fermentation tank by applying a process using a separation membrane such as a submerged membrane. For example, a separation membrane composite type methane fermentation system using a submerged membrane using a microfiltration membrane made of a polyethylene material is effective. In particular, high-temperature methane fermentation is advantageous for application of a separation membrane because the dispersibility of sludge is improved as compared with medium temperature.
[0043]
In addition, when adjusting the amount of microorganisms introduced into the anaerobic treatment system, it is also effective to use aerobic sludge such as surplus activated sludge at the same time. When the aerobic treatment tank is arranged, the aerobic microorganisms can be introduced into the anaerobic treatment system by returning the surplus activated sludge of the aerobic treatment tank to the anaerobic tank. This is because the unsaturated higher fatty acid is adsorbed on the sludge and effectively acts on the saturation reaction of the higher fatty acid. Furthermore, sludge mainly composed of surplus activated sludge acts as a nutrient source for microorganisms in anaerobic treatment, and is effective in improving the efficiency of digestion of fats and oils and promoting digestion. . In addition, in order to increase the effect as a nutrient source over the saturation reaction of higher fatty acids in the introduction of microorganisms, sludge such as surplus activated sludge is subjected to ultrasonic crushing, wet mill crushing, ball mill crushing, homogenizing crushing, heat treatment, high temperature It is also effective to introduce it into the anaerobic treatment step after performing physical and chemical crushing treatments typified by high-pressure treatment, acid or alkali treatment, ozone oxidation and the like.
[0044]
In the method according to the second aspect of the present invention, the higher fatty acid concentration / microorganism concentration in the anaerobic reaction system is introduced by introducing an anaerobic or aerobic microorganism into the anaerobic reaction system as described above. The ratio is preferably maintained at 0.4 or less by weight. Here, the microbial concentration can be expressed by VSS (volatile suspended solids), and in the following, in the meaning of “higher fatty acid concentration / microorganism concentration”, “higher fatty acid concentration / The term “VSS ratio” or “LFA (long-chain fatty acid) / VSS” is used as appropriate. The range of the higher fatty acid concentration / VSS ratio preferable in the anaerobic treatment step of the present invention varies depending on the type of raw water and the operation method of the anaerobic treatment. The target higher fatty acid is C₁₈In the following cases, the anaerobic treatment is preferably carried out at 0.5 or less, preferably 0.4 or less in the batch treatment method, and 0.2 or less, preferably 0.1 or less in the continuous treatment method. C₁₈In the case where a higher fatty acid having a longer chain is mainly used, the inhibitory action on microorganisms is further strengthened. Therefore, it is necessary to perform anaerobic treatment at a lower ratio than the above-mentioned LFA / VSS ratio, and preferably To about 1/3 to 1/5 of the value of. In the case of higher fatty acids that are longer than C18, the number of carbon atoms and the degree of unsaturation greatly affect the inhibitory action on microorganisms, so the LFA / VSS ratio is controlled according to their higher fatty acid composition. In the step of adjusting these ratios, the higher fatty acid concentration in the oil-containing wastewater is appropriately monitored by, for example, the method described above, and at the same time, the VSS concentration in the anaerobic treatment tank is grasped. Furthermore, neutral fat before being decomposed into higher fatty acids can form oil balls when accumulated in the methane fermentation tank, or block the equipment, piping, equipment, etc., impairing the methane fermentation process and microbial reaction. Therefore, it is desirable to perform anaerobic treatment at a neutral fat concentration to prevent these from being 1.5 g / L or less, preferably 0.7 g / L or less. The neutral fat / VSS value is 1.0 or less, preferably 0.5 or less in the batch processing method, and is 0.3 or less, preferably 0.2 or less in the continuous processing method. preferable. In addition, when neutral fat accumulates in the methane fermenter, neutral fat is decomposed and higher fatty acid production may occur rapidly, and higher fatty acid / VSS ratio increases, leading to inhibition of microbial reaction. Caution must be taken. VSS concentration in fat and oil-containing wastewater is measured by a gravimetric method (sewage test method, first volume-1997 edition, Japan Sewerage Association), as well as by sludge concentration meters such as optical, ultrasonic and microwave methods. Measurement methods can be used. Sludge densitometers that use infrared LEDs as the light source (for example, MLSS-2A, a submersible sludge densitometer made by Toa Denpa Kogyo Co., Ltd., ML-2 portable sludge densitometer made by Central Science Co., Ltd.) 52), microwave reflective sludge concentration meter (made by Meidensha Co., Ltd.), etc. can be used. In particular, the microwave reflection sludge densitometer has a wide sludge measurement concentration range of 0 to 10%, is less affected by sludge color and contained bubbles, and has excellent linearity and repeatability (No. 12 This is an effective measurement method for methane fermentation systems with high sludge concentration, EICA Research Presentation, EICA, Vol. 5, No. 2, 89-92, 2000). At present, the measurement method using a sludge densitometer measures the sludge concentration of organic and inorganic substances. Therefore, the accurate VSS measurement requires the VSS / in the target wastewater and its biological treatment process. It is desirable that correction values such as the SS ratio or the ash content (Ash content) / SS ratio are obtained in advance by a weight method or the like, and the values measured by the sludge densitometer are corrected and applied. Furthermore, a method of determining the amount of microorganisms (VSS concentration) by measuring the amount of DNA, RNA, and ATP contained in the microorganism can also be applied. If the higher fatty acid / VSS ratio is lower than the appropriate value, the higher the fatty acid / VSS ratio can be restored to an appropriate value by reducing the sludge return operation to lower the VSS. Furthermore, along with the reduction of the sludge return operation, it is possible to increase the amount of lipase added to the oil-containing wastewater to promote the hydrolysis of neutral fat and increase the higher fatty acid concentration. On the other hand, when the higher fatty acid / VSS ratio is higher than an appropriate value, the VSS is increased by performing the sludge return operation to the anaerobic treatment tank, and the higher fatty acid / VSS ratio is lowered, and lipase is added. The amount can be reduced or suspended. Therefore, the purification system or purification apparatus for carrying out the method according to the present invention feeds back the measured values of higher fatty acid concentration and VSS concentration, and determines the sludge return amount, raw water input amount, and lipase addition amount. It is more preferable to further have a means for adjusting this.
[0045]
Further, in the present invention, in order to make the anaerobic treatment reaction proceed more stably and efficiently, salts (for example, metal salts such as sulfates and phosphates) that activate the action of anaerobic microorganisms and nutrients ( For example, by adding citric acid, lactic acid, peptones, etc.) into the anaerobic reaction tank, it is possible to adjust the higher fatty acid concentration by promoting the β-oxidative degradation of the fatty acid itself. That is, when the higher fatty acid concentration is higher than an appropriate value, such salts or nutrients can be added to the anaerobic reaction tank to activate anaerobic microorganisms and promote β-oxidative degradation of higher fatty acids.
[0046]
Furthermore, in decomposing higher fatty acids, it is important to accelerate the β-oxidation reaction by microorganisms by dispersing oils and fats and higher fatty acids in waste water and waste as much as possible. For this purpose, it is effective to use bentonite or the like as an emulsifier or dispersant for fats and oils. Conventionally, the use of an emulsifier such as bentonite is considered effective in mesophilic methane fermentation treatment (for example, M. Beccari, M. Majone, C. Riccardi, F. Savarese and L. Torrisi: Integrated treatment of olive oil mill effluents: effect of chemical and physical pretreatment on anaerobic treatability, Water Science and Technology, Vol. 40, No. 1, pp.347-355, 1999). The effect of emulsification with bentonite has also been reported in high-temperature methane fermentation treatment of fat and oil-containing wastewater (I. Angelidaki, SP Petersen, and BK Ahring, Effects of lipids on thermophilic anaerobic digestion and reduction of lipid inhibition upon addition of bentonite, Applied Microbiology and Biotechnology, Vol.33, pp.469-472, 1990). However, according to the present invention, in the anaerobic treatment tank, the dispersibility of fats and oils is improved by methane fermentation in a high temperature range as compared with the case of medium temperature, but the fats and oils are decomposed into microorganisms that produce fat-degrading enzymes or their enzymes. The pretreatment for decomposing by acting as described above tends to deteriorate the dispersion of fats and oils under the treatment conditions where the load of fats and oils and higher fatty acids is high. Once higher fatty acids begin to accumulate, higher fatty acids extremely degrade the activity of microorganisms useful for anaerobic treatment, especially acetic acid-utilizing methanogenic bacteria and hydrogen-utilizing methanogenic bacteria. The lost higher fatty acid will be further accumulated, and eventually the methane production reaction will be stopped. Therefore, for wastewater / waste having a high oil content, the use of an emulsifier has a high effect of oil decomposition and enables stable treatment. In particular, in the present invention, the number of carbon atoms that are likely to exert an inhibitory action on microorganisms (C₁₈In order to prevent the adsorption of higher fatty acids to microorganisms and to promote the dispersion of higher fatty acids, an oil is added by adding an emulsifier in the step of adjusting the ratio of higher fatty acid concentration / microorganism concentration (VSS). To promote degradation. In this case, the addition method of the emulsifier may be added directly to the anaerobic treatment tank, or added when introducing anaerobic fermentation sludge or excess aerobic sludge generated from the aerobic process into the anaerobic treatment process. Also good. Moreover, as the emulsifier to be used, bentonite which is a mineral, saponin derived from microorganisms or plants, etc. are inexpensive and effective. On the other hand, sodium salt emulsifiers such as sodium alginate are often poorly emulsified and dispersed because sodium salts are easily adsorbed by microorganisms, and biodegradable emulsifiers are biodegradable as well as fats and oils. As a result, it is considered that the emulsifying action is lowered, so that care must be taken during use. The amount of these emulsifiers added is 0.01 to 10% in the volume ratio of the waste water, 0.01 to 5 g / g per n-hexane extract in the waste water, preferably 0.01 to 1 in the volume ratio of the waste water. %, 0.01-1.5 g / g per n-hexane extract in the waste water. In addition, since these addition amount changes with properties of fat-and-oil containing wastewater, the kind and presence state of fats and oils, the addition method of an additive, etc., the addition amount suitable for a processing method should be determined. In addition, as a guideline for the fat and oil content when using an emulsifier, the drainage / disposal of the normal hexane extract / BOD ratio is 10% or more, preferably 20% or more, more preferably 25% or more, and most preferably 30% or more. It is a thing. When adding an emulsifier, Ca (OH) as a pH adjuster₂Or CaCl₂It is also effective to use a calcium agent such as The effect of this calcium agent is to aggregate and remove excess higher fatty acids as well as pH adjustment.
[0047]
In addition, the physical dispersion and crushing treatment of fats and oils is also effective in place of the chemical dispersing action with emulsifiers. Especially in high-temperature methane fermentation, the dispersibility of fats and oils is higher than that of medium-temperature methane fermentation. Therefore, physical means have an effect. As such physical means, mixing / stirring treatment, ultrasonic crushing, homogenizing crushing and the like are effective in that a general mechanical device can be applied. It is also effective to use a combination of these physical means and emulsifier addition, which leads to a reduction in the amount of emulsifier added.
[0048]
The structural example of the apparatus which processes fats and oils containing waste_water | drain using this invention method is demonstrated with reference to FIGS.
FIG. 8 is a schematic diagram of a process for performing the anaerobic treatment of the fat and oil-containing wastewater by carrying out the method according to the first aspect of the present invention. The anaerobic treatment apparatus according to the present invention includes a pretreatment tank 3 that decomposes fats and oils such as neutral fat by adding fat-degrading enzymes or enzyme-producing microorganisms to fat-containing wastewater, and wastewater treated in the pretreatment tank. On the other hand, the methane fermentation tank 5 which performs a methane fermentation process is provided as an essential component. In addition, as mentioned above, a pretreatment tank and a methane fermentation tank can also be comprised with the same tank. In the treatment process, a raw water storage tank 2 for storing raw water and a storage tank 1 for storing an oil-degrading enzyme or an enzyme-producing microorganism can be provided. The raw water to which an enzyme or an enzyme-decomposing microorganism is added as required is subjected to a fat and oil decomposition reaction such as neutral fat in the pretreatment tank 3. If necessary, an emulsifier and a pH adjuster can be introduced into the reaction system from the storage tank 4 and / or a physical crushing process such as ultrasonic crushing can be performed in the pretreatment tank 3. The wastewater treated in the pretreatment tank is then sent to the methane fermentation tank 5. The methane fermentation tank 5 holds sludge containing methanogenic bacteria and the like, and methane fermentation treatment is performed here. In the processing apparatus according to the present invention, a measuring apparatus 20 for measuring the higher fatty acid concentration in the tank can be connected to the methane fermentation tank, and depending on the value of the higher fatty acid concentration monitored here, the enzyme Alternatively, the higher fatty acid concentration in the methane fermentation tank 5 can be maintained below a predetermined preferable range by controlling the introduction amount of the enzyme-producing microorganism or the introduction amount of the emulsifier by the valve 21. The wastewater treated in the methane fermentation tank can then be sent to the aerobic treatment tank 7 through the sludge storage tank 6 as necessary. Activated sludge is held in the aerobic treatment tank 7, and aerobic treatment is performed by the action of microorganisms contained in the activated sludge. In addition, the waste liquid discharged | emitted from the methane fermentation tank 5 can also be discharged | emitted as it is, and it can also utilize as liquid fertilizer. The aerobic treated waste water can then be subjected to a dewatering process in a sludge dewatering machine 10 after adding a flocculant in the sludge aggregation tank 9. The exhaust gas discharged from the methane fermentation tank 5 is methane, CO₂And iron sulfide (Fe (OH), for example)_Three) And the like, and after the treatment in the desulfurization tower 11, the digestion gas tank 12 can be used for applications such as gas boilers, digestion gas power generation, and fuel cells.
[0049]
Next, FIG. 9 is a schematic diagram of a process for carrying out the anaerobic treatment of oil-containing wastewater by carrying out the method according to the second aspect of the present invention. 8 is different from the process shown in FIG. 8 in that it has a line for returning anaerobic fermentation sludge from the sludge storage tank 6 and surplus aerobic sludge from the aerobic treatment tank to the methane fermentation tank 5. Similar to the apparatus shown in FIG. 8, the apparatus for measuring higher fatty acid concentration and VSS concentration in the tank can be connected to the methane fermentation tank 5, and the higher fatty acid / VSS ratio monitored here. Depending on the value of the sludge, the return amount of sludge, and if necessary, the introduction amount of the enzyme or the enzyme-producing microorganism or the introduction amount of the emulsifier may be controlled by the valve 21 and / or By applying a physical crushing process such as ultrasonic crushing in the treatment tank 3, the higher fatty acid / VSS ratio in the methane fermentation tank 5 can be maintained within a predetermined preferable range.
[0050]
FIG. 10 is a schematic diagram of a process for treating oil-containing wastewater according to still another embodiment of the present invention. In the process shown in FIG. 10, the microorganism holding carrier 13 is filled in the methane fermentation tank 5, thereby enabling methane fermentation to proceed more efficiently. In the embodiment using the microorganism holding carrier 13 as shown in FIG. 10, generally, the anaerobic microorganism concentration in the methane fermentation tank can be kept high, so that sludge return from the sludge storage tank 6 is usually necessary. is not. However, it is of course possible to provide a sludge return line from the sludge storage tank 6 as necessary.
[0051]
【Example】
Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited to these examples.
[0052]
In the examples of the present invention, lipase derived from bacteria having stability at 55 ° C. (100,000 U / g) (manufactured by Novo Nordisk Bioindustry) or lipase derived from Candida cylinndracea (360,000) U / g) (manufactured by Meito Sangyo Co., Ltd.) was used. 1 unit (U) is an enzyme that liberates 1 millimole of butyric acid from tributyrin per minute under certain standard conditions (pH 7.0, 30 ° C., 4.8% m / v tributyrin, 0.094% m / v gum arabic) Is the amount.
[0053]
For the enzyme pretreatment of the fat and oil-containing wastewater (raw water), lipase (4KU / L) was used and treated at 50 ° C. for 1 day. After the enzyme pretreatment, the wastewater was cooled and stored at 5 ° C.
The quantitative analysis of lipids and higher fatty acids carried out in the examples of the present invention was carried out by the following procedure. Oily and fat-containing waste water (raw water) or methane fermentation treatment liquid (5 ml) was extracted with an organic solvent (40 ml) of n-hexane / isopropanol (5: 3 (v: v)). Using the n-hexane extract (1.5 ml), Shimadzu gas chromatograph GC-17A type, FID detector, DB-FFAP (length 30 m, inner diameter 0.25 mm, film thickness 0.25 μm) capillary column for higher fatty acid Quantitative analysis was performed. The n-hexane extract (20 ml) was dried on an 80 ° C. hot plate, and the n-hexane extract concentration of the sample was calculated using the obtained dry weight. Furthermore, the dried n-hexane extract is redissolved with chloroform to a concentration of 5 mg / ml, developed and separated with Chromarod S-III, and quantitative analysis of total lipids is performed with a TLC / FID analyzer (Iatroscan TH-10). went.
[0054]
VSS is measured by the gravimetric method described in the General Sludge Test (Chapter 4) of "Sewage Test Method, Volume 1 -1997 Edition" (Japan Sewerage Association, issued on September 12, 1997). Went in the way.
[0055]
The methane gas composition in the generated gas was analyzed using an Active carbon 30/60 column with a GL Science Gas Chromatograph-320 type TCD detector.
Volatile fatty acid (VFA) is analyzed by high performance liquid chromatograph (Alma Optics ERC-8710, detector RI, column Shodex Ionpack KC-811, column temperature 60 ° C, mobile phase 0.1% phosphoric acid). did. COD_CrThe analysis was conducted by the closed-type reflux method according to the US Standard Method (18th Edition, 1992). For pH measurement, a pH composite electrode GST-5311C manufactured by Toa Denpa Kogyo Co., Ltd. and an automatic titrator AUT-301 type were used. The analysis of TS (total solids), VS (volatile solids), and SS (suspended solids) was in accordance with the sewage test method (1984 version).
[0056]
Example 1 and Comparative Example 1
Using sludge obtained by high-temperature (55 ° C) methane fermentation of raw garbage as seed sludge, high-temperature methane-fermented sludge acclimatized for three months with oil-containing wastewater from a food factory was prepared. Using this high-temperature methane fermentation sludge, a methane fermentation batch experiment was conducted on oil-containing wastewater. Table 1 shows the experimental conditions.
[0057]
[Table 1]

[0058]
In the system according to the present invention (Example 1), methane fermentation was performed under the condition that the free higher fatty acid concentration in the vial was controlled to about 400 mg / L by adding an appropriate amount (500 U / L) of lipase derived from bacteria. In this case, the higher fatty acid / MLVSS ratio was about 0.1.
[0059]
On the other hand, in Comparative Example 1-1, the amount of lipase added (1,000 U / L) was increased, the free higher fatty acid concentration in the vial was about 1100 mg / L, and methane under the condition where higher fatty acids were accumulated. A fermentation experiment was conducted. The higher fatty acid / MLVSS ratio was about 0.4 or greater.
[0060]
In Comparative Example 1-2, the amount of lipase added was further increased, the free higher fatty acid concentration in the vial was about 1400 mg / L, and a methane fermentation experiment was conducted under the condition where higher fatty acids further accumulated. The higher fatty acid / MLVSS ratio was about 0.5 or greater.
[0061]
In Comparative Example 1-3, a methane fermentation experiment was performed under conditions where neutral fats were not decomposed by addition to lipase and the free higher fatty acid concentration was not controlled.
These four types of batch culture experiments were carried out for 14 days, and their methanogenesis characteristics, lipid removal characteristics after completion of fermentation, and organic substance removal characteristics were examined. The results are shown in FIGS.
[0062]
FIG. 1 shows methane fermentation characteristics in a batch experiment system in which higher fatty acid concentration is adjusted. In the system according to the present invention (Example 1), it is understood that the methane fermentation reaction is almost completed in 6 days by controlling the higher fatty acid concentration to an appropriate amount. On the other hand, Comparative Example 1-1 resulted in the inhibition of the methane fermentation reaction due to the accumulation of higher fatty acids. The methane fermentation reaction started after the 6th day after the start of the experiment, and 14 days until the fermentation was completed. Cost. Further, Comparative Example 1-2 resulted from the inhibition of the methane fermentation reaction due to further accumulation of higher fatty acids, and the methane fermentation reaction started after the 14th day after the start of the experiment. Therefore, from these results, it was found that the period until completion of fermentation can be controlled by controlling the higher fatty acid concentration in the anaerobic reaction system.
[0063]
In addition, Comparative Example 1-3 is a result when neutral fat is not decomposed by lipase, the methane production reaction is extremely poor, and methane fermentation hardly progresses even after 14 days. Therefore, it has been found that when an oil-containing wastewater is subjected to anaerobic treatment, it is preferable to decompose neutral fat in advance with lipase or the like and then to perform methane fermentation treatment.
[0064]
FIG. 2 shows the lipid removal characteristics after 14 days of methane fermentation. The system (Example 1) according to the present invention in which neutral fat was decomposed with lipase and then subjected to methane fermentation treatment was able to remove 90% of lipid components. In contrast, in Comparative Example 1-1 and Comparative Example 1-2 in which higher fatty acids were accumulated at a high concentration, the removal of lipid components was 70% and 55%. In the case of Comparative Example 1-3 in which neutral fat was not decomposed with lipase, the removal of the lipid component was only 58%.
[0065]
FIG. 3 shows the organic matter removal characteristics after 14 days of methane fermentation treatment. In the present invention (Example 1) in which neutral fat is decomposed with lipase and methane fermentation is performed, COD_CrThe removal rate became a little less than 70%. On the other hand, Comparative Example 1-1 and Comparative Example 1-2 in which higher fatty acids are accumulated at a high concentration are COD._CrRemoval was 50% and 30%. On the other hand, Comparative Example 1-3 in which neutral fat was not decomposed by lipase was_CrThe removal rate was only 40%. Insoluble COD by adding lipase_CrThe decrease of the component was large.
[0066]
Example 2 and Comparative Example 2
The raw garbage high-temperature methane fermentation sludge and swine manure medium temperature methane fermentation sludge used in Example 1 were introduced into the methane fermentation reaction tank as seed sludge, and the fat and oil-containing wastewater from the food factory was used as raw water, and was continuously treated under the conditions shown in Table 2. The methane fermentation experiment was conducted for 3 months.
[0067]
[Table 2]

[0068]
In the present invention, while monitoring the neutral fat and higher fatty acid in the methane fermenter, lipase is added at 100 to 1000 U / L / day so that the higher fatty acid concentration is 300 mg / L or less, and the high temperature range of 55 ° C. A methane fermentation continuous experiment was conducted (Example 2-1). Moreover, methane fermentation was performed in the middle temperature range of 35 degreeC, controlling the higher fatty acid density | concentration in a fermenter like Example 2-1, and this was made into Example 2-2. As a comparative example, lipase was continuously added at a high temperature of 55 ° C. under the condition that a large amount of lipase was added at a concentration of 1000 to 2000 U / L · day and the higher fatty acid concentration in the methane fermentation reaction tank was accumulated at 1500 mg / L. An experiment was performed (Comparative Example 2-1). In addition, a methane fermentation continuous experiment was conducted at 55 ° C. without decomposing the neutral fat in the reaction tank and without adjusting the higher fatty acid concentration, and this was designated as Comparative Example 2-2. Table 3 shows the results obtained by continuously operating the reaction tank for 3 months and examining the processing performance of the methane fermentation for the fat and oil-containing wastewater of the food factory.
[0069]
[Table 3]

[0070]
When oil and fat-containing wastewater was continuously treated while controlling the higher fatty acid concentration in the methane fermentation tank to an appropriate amount, it was operated at a high temperature (55 ° C) (Example 2-1) and at a medium temperature (35 ° C). In both cases (Example 2-2), COD_CrThe removal rate was about 80%, the BOD removal rate was about 85%, and the removal rate of the n-hexane extract was about 94%, indicating that very effective purification progressed. Moreover, it turned out that the gas production | generation rate | velocity at the time of driving | running at high temperature (Example 2-1) is about twice as fast as the case of driving | running at medium temperature (Example 2-2). On the other hand, when a large amount of lipase is added and higher fatty acids in the methane fermentation tank accumulate (Comparative Example 2-1), COD_CrThe removal rate was about 30%, the BOD removal rate was about 40%, the removal rate of the n-hexane extract was about 25%, and almost no gas was produced. Further, in the case of Comparative Example 2-2 in which the higher fatty acid concentration is not adjusted without adding lipase, COD_CrThe removal rate was 40%, the BOD removal rate was about 45%, and the removal rate of the n-hexane extract was 38%. The production rate of methane gas was larger in the order of Example 2-1> Example 2-2> Comparative Example 2-2> Comparative Example 2-1.
[0071]
Example 3
In this example, tofu production wastewater (neutral fat 0.5 g / L) was used as the fat-containing wastewater. In the methane fermentation experiment, three series of fully mixed type methane fermentation apparatuses (effective volume 3.5 L) are used as fermentation tanks A to C, and high temperature methane fermentation sludge of raw garbage is used for the fermentation tanks A and B. For C, medium temperature methane fermentation sludge from pig manure was used as seed sludge, and methane fermentation experiments were conducted by a continuous treatment method. The operation state in each fermenter and the gas generation rate are shown in FIG. Moreover, the fluctuation | variation of the sludge density | concentration in each fermenter is shown in FIG. Furthermore, the fluctuation | variation of the ratio of fat (neutral fat, higher fatty acid, TG + LFA) and VSS in each fermenter is shown in FIG. Here, TG is triglyceride. About the fat and oil containing wastewater processed with fermenters B and C, as an enzyme pretreatment, it processed at 50 degreeC for 1 day using fat and oil-degrading enzyme (lipase, 4KU / L), and it cooled and preserve | saved at 5 degreeC after the enzyme treatment. . For the fat and oil-containing wastewater to be treated in the fermenter A, lipase pretreatment was not performed. Table 4 shows the properties of the raw wastewater to be treated in each tank. Table 5 shows the operating conditions for methane fermentation in each tank.
[0072]
[Table 4]

[0073]
[Table 5]

[0074]
In the methane fermentation operation, the fermenters A and B were fermented at 55 ° C. as high temperature methane fermentation, and the fermenters C were fermented at 35 ° C. as medium temperature methane fermentation. For fermenters A and B, from the 84th day of operation, for fermenter C from the 118th day of operation, add 1 ml / L of tofu waste oil to the raw water of the fermenter and increase the neutral fat to 1.5 g / L. The oil and fat loading conditions were set. Regarding the raw water flow rate, the fermenters A and C started operation at HRT = 16 days, and the fermenter B started at HRT = 15 days. The organic matter concentration in the oil and fat wastewater is the COD for lipase pretreated and non-lipase pretreated, respectively._CrIs relatively low with 2.0% and 2.3%; BOD 1.1% and 1.2%, while n-hexane extract / COD_CrThe ratio is 0.12 and 0.11, respectively, and the n-hexane extract / BOD ratio is 0.19 and 0.24, respectively. In addition to being difficult, the oil and fat decomposition performance is also poor. Then, about fermenter A, the BOD component (0.5% starch) which is easy to carry out methane fermentation was added to raw water, and the methane fermentation operation was started. For reaction tank B, the sludge flowing out from the methane fermentation tank from the 43rd day of operation is periodically centrifuged (3000 rpm, 5 minutes), and the precipitated sludge is returned to the fermentation tank, so that the bacteria in the tank Attempts were made to increase body concentration and keep the LFA / VSS ratio low.
[0075]
In fat and oil drainage (fermenter A) that has not been pretreated with lipase, by adding starch, stable methane fermentation treatment could be performed under conditions of low fat loading, but added tofu fried waste oil after the 84th day was added. Under the condition of increasing the oil load, the LFA / VSS ratio increased to 0.13 on day 104 (A in FIG. 6). Thereafter, the decomposition of neutral fat stopped and the gas generation rate decreased. On the 136th day, VFA accumulated to 2500 mg / L, so the raw water input was stopped. The sludge concentration in the fermenter was significantly reduced when methane fermentation was stopped (A in FIG. 5), and the LFA / VSS ratio was as low as 0.04, but the neutral fat / VSS ratio was 0.7. (A in FIG. 6). After that, when the sludge was returned from day 143 and the operation was resumed while maintaining the LFA / VSS ratio at 0.2 or less and the neutral fat / VSS ratio at 0.3 or less (A in FIG. 6), It was found that stable continuous operation was possible even under high oil load conditions (A in FIG. 4).
[0076]
In the fermenter B subjected to the lipase pretreatment, the LFA / VSS ratio was kept at 0.1 or less by starting the return of sludge from the 43rd day of operation (B in FIG. 6), even under high oil load conditions. An extremely stable continuous operation was possible (B in FIG. 4).
[0077]
Moreover, although the lipase pretreatment was performed, in the fermenter C in which the methane fermentation was performed at a medium temperature of 35 ° C., the oil effluent subjected to the lipase pretreatment was loaded on the HRT 16 days under the low fat load condition in which tofu waste oil was not added. The methane fermentation process could not be performed sufficiently. On the 87th day when the gas generation rate decreased, VFA accumulated in the fermenter at 3111 mg / L, and the input of raw water was stopped. At this time, the LFA / VSS ratio was 0.1 (C in FIG. 6). From this, it was considered that HRT requires 20 days or more in the case of medium temperature methane fermentation of fat and oil wastewater. And when HRT = 25 days on the 118th day and raw water input was resumed while adding 1 mL / L of waste oil, the LFA / VSS ratio rose to 0.16 on the 134th day (C in FIG. 6), VFA increased from 10 mg / L at the resumption of operation to 346 mg / L. Thereafter, the operation was continued, and the return of sludge was started from the 143rd day, and the operation of the fermenter was started while maintaining LFA / VSS at 0.1 or less._CrSince the load is lower than fermenters A and B, the gas generation rate is low, but stable organic organic decomposition and fat decomposition by anaerobic treatment were possible without accumulating LFA (Fig. 4). C).
[0078]
The average amount of methane generated during the continuous operation period from the 150th day to the 270th day of operation in each tank is 0.3 L / L · day for Fermenter A, 0.5 L / L · day for Fermenter B, and Fermentation The tank C was 0.1 L / L · day. Also, decomposed COD_CrThe amount of methane gas generated per fermenter is 0.27 L / g-decomposed COD in fermenter A_CrFermenter B is 0.32L / g-decomposed COD_CrFermenter C is 0.16L / g-decomposed COD_CrMet. From this, the fermenter B which performed the lipase pretreatment and performed the high temperature methane fermentation at 55 ° C. has the largest methane generation amount. Hereinafter, the methane generation amount is the high temperature methane fermentation at 55 ° C. without performing the lipase pretreatment. It turned out that it was the order of the fermenter A which performed the fermenter A and the lipase pretreatment which were performed, and the intermediate temperature methane fermentation was performed at 35 degreeC.
[0079]
The organic load in the continuous operation period from the 150th day of operation of the fermenter B (high temperature methane fermentation) and the fermenter C (medium temperature methane fermentation) is 1.5 g / L · day in the fermenter B and 0. 0 in the fermenter C. It was 8 g / L · day. The lipid load (n-hexane extract load) was 150 mg / L · day in Fermenter B and 91 mg / L · day in Fermenter C. From these results, it was found that high-temperature methane fermentation can be operated at higher organic load and lipid load than medium-temperature methane fermentation, and the amount of methane gas generated is large.
[0080]
Moreover, the residue in each methane fermenter was sampled regularly from the 146th day of operation, extracted with n-hexane, and the composition of the extract was quantitatively analyzed. The results are shown in FIG. From this, it was found that in the fermenter A that was not pretreated with lipase, a large amount of neutral fat remained in the fermenter. On the other hand, in the fermenter B and fermenter C pretreated with lipase, neutral fat was removed by 80% or more, and higher fatty acids were not accumulated. It has been found that pretreatment with lipase is effective in methane fermentation of fats and oils.
[0081]
From the above results, for stable operation of the methane fermenter, it is an extremely effective means to control the higher fatty acid concentration / microorganism concentration to a certain value or less by introducing microbial organisms by returning sludge. After the pretreatment with lipase, it was found that by performing high-temperature methane fermentation while controlling the LFA / VSS ratio by returning sludge, extremely excellent results were obtained in both methane generation and fat decomposition. Moreover, in mesophilic methane fermentation, although a very good value for methane generation was not obtained, it was found that stable operation is possible and oils and fats can be decomposed very well by performing methane fermentation together with sludge return.
[0082]
Examples 4-7, Comparative Example 3
In this example, the effect of the microorganism-retaining carrier in methane fermentation and the effect of adding an emulsifier and a pH regulator were examined. The same fat and oil-containing wastewater as in Example 3 was pretreated with lipase at 50 ° C. for 1 day, and a high-temperature methane fermentation experiment was performed by a continuous treatment method for 130 to 180 days. Table 6 shows the operating conditions and results of the continuous high-temperature methane fermentation experiment. As the wastewater treatment experiment apparatus, the system shown in FIG. 10 was used. However, the return line of the sludge to the methane fermentation tank 5 was installed not only from the aerobic treatment tank 7 but also from the sludge treatment tank 6. Sodium alginate (300 to 400 cP) and bentonite were used as the emulsifier, calcium hydroxide was used as the pH adjuster, and the system was charged into the system from the emulsifier storage tank and the pH adjuster storage tank 4, respectively. In addition, the addition amount of the emulsifier and the pH regulator was 0.01% in terms of the volume ratio of the wastewater, and 0.04 g / g per n-hexane extract in the wastewater. All the reagents used were special grade reagents manufactured by Wako Pure Chemical Industries. In Examples 4 and 5, an upward flow type anaerobic treatment tank in which a filler made of polypropylene resin was packed as the microorganism holding carrier 13 in the methane fermentation tank 5 was used. The shape of the filler was 30 mmφ × 60 mmH, and the porosity was 90%. The effluent from the methane fermentation tank 5 was subjected to an aerobic treatment in an aerobic treatment tank 7 through a sludge storage tank 6. In the aerobic treatment tank 7, the activated sludge collected from the batch activated sludge plant of the confectionery factory wastewater (organic load 0.2g-BOD / g-MLSS / day during operation, activated sludge suspended solids: MLSS = 3500mg / L, Activated sludge settling rate: SV₃₀= 42%) The activated sludge was used as seed sludge, and the aerobic treatment of the drainage was performed while aeration was performed. In Examples 6 and 7, methane fermentation sludge flowing out from the sludge storage tank 6 and surplus activated sludge flowing out from the aerobic treatment tank 7 are centrifuged (3000 rpm, 5 minutes) to ferment the precipitated sludge. Returned to tank 5. By periodically sampling the residue in the methane fermenter 5 and analyzing it with the analyzer 20, the BOD removal rate, COD_CrThe removal rate, VTS (volatile total solids) removal rate, and higher fatty acid removal rate were calculated. Table 6 shows the average value of each removal rate. The excess sludge discharged from the sludge treatment tank 6 and the aerobic treatment tank 7 is added with a polymer flocculant (Ebagulose LDC-300) as a flocculant from the flocculant storage tank 8, and the sludge is coagulated in the sludge flocculant tank 9. After that, it was dehydrated with a screw press type sludge dehydrator 10. The properties of the dehydrated filtrate and dehydrated sludge were analyzed.
[0083]
The amount of gas generated from the methane fermenter was measured with a wet gas meter WE Da-0.5B manufactured by Shinagawa, and a part of the gas sample was collected and analyzed by gas chromatography TCD. And for the generated gas other than the analytical sample, pellet-like iron hydroxide (Fe (OH)_Three) To remove hydrogen sulfide in the gas.
[0084]
[Table 6]

[0085]
From the results shown in Table 6 above, when the Example 4 in which the microorganism-retaining carrier was filled in the methane fermentation tank and the Example 6 in which the methane fermentation sludge was returned without filling the carrier were compared, the digestion gas generation rate and the organic matter treatment were compared. Since the performance was almost the same in both cases, the effect of using the microorganism-supporting carrier in the methane fermentation tank was demonstrated. In addition, the effect of increasing the concentration of sludge is that the sludge is retained at a high concentration in any of the digestion gas generation rate, organic matter treatment performance, and sludge dewatering performance as compared with Examples 6 and 7 and Comparative Example 3. In this case (Examples 6 and 7), good treatment results were obtained, indicating the effect. Further, the effect of adding the emulsifier and the pH adjuster is different from that of the return sludge, but compared with Example 6 and Example 7, particularly in terms of digestion gas generation rate and organic matter treatment performance, the emulsifier and pH. Effective results were obtained when regulators were added, indicating the effect of their addition.
[0086]
Sludge flocculant addition rate and dehydrated sludge moisture content are also indicators of sludge properties. When organic wastewater containing almost no oil or fat is normally biologically treated, the sludge flocculant addition rate is usually 0.5 to 0.7% (vs. SS ratio), and the dewatered sludge moisture content is Although it depends, it is said that it is about 78 to 80%. On the other hand, if the fats and oils remain in the sludge without being decomposed, the sludge coagulant ability by the sludge coagulant decreases, so the sludge coagulant addition rate increases and the sludge coagulant capacity is poor. Water content also increases.
[0087]
Similarly, the dehydrated filtrate property is an index indicating sludge properties, and the SS value increases because fine sludge (SS) that could not be aggregated due to a decrease in sludge coagulation ability due to oil and fat flows out to the dehydrated filtrate side, Along with this, the BOD value also increases.
[0088]
The digestion gas composition indicates methane fermentation performance. When the organic matter decomposition rate is reduced by methane fermentation, digestion gas generation rate and methane gas content rate are lowered because of indigestion of microorganisms. The digestion gas generation rate varies depending on the target waste water and the operation method, but the methane gas content is about 60 to 68% in the case of normal methane fermentation treatment in a single tank type.
[0089]
【The invention's effect】
According to the present invention, fats and oils in an anaerobic reaction tank are decomposed by enzymes or enzyme-producing microorganisms, and the fats and oils are contained in a high temperature range of 45 to 70 ° C. while adjusting the concentration of higher fatty acids as decomposition products to a predetermined level or less By purifying wastewater or waste, it became possible to purify wastewater with high efficiency. Furthermore, since organic substances are decomposed by anaerobic organisms, they can be recovered as biogas (especially methane), which makes it possible to significantly improve energy recovery efficiency.
[Brief description of the drawings]
FIG. 1 is a graph showing characteristics of methane fermentation by adjusting higher fatty acid concentration.
FIG. 2 is a graph showing the lipid removal characteristics of methane fermentation by adjusting the higher fatty acid concentration.
FIG. 3 is a graph showing the organic matter removal characteristics of methane fermentation by adjusting the higher fatty acid concentration.
FIG. 4 is a graph showing the gas production rate by the continuous operation of methane fermentation performed in Example 3.
FIG. 5 is a graph showing the sludge concentration in the fermenter in the continuous operation of methane fermentation performed in Example 3.
6 is a graph showing a change in the ratio of fat in the fermenter (neutral fat, higher fatty acid, TG + LFA) and VSS in the continuous operation of methane fermentation performed in Example 3. FIG.
FIG. 7 is a diagram showing the analysis result of residues in the fermenter in the continuous operation of methane fermentation performed in Example 3.
FIG. 8 is a flowchart showing an outline of an anaerobic treatment process for fat-and-oil-containing wastewater using the method according to one embodiment of the present invention.
FIG. 9 is a flowchart showing an outline of an anaerobic treatment process for fat-and-oil-containing wastewater using a method according to another embodiment of the present invention.
FIG. 10 is a flowchart showing an outline of an anaerobic treatment process for fat-containing wastewater using a method according to still another embodiment of the present invention.

Claims (8)

It is a method of purifying fat-containing wastewater or fat-containing waste by an anaerobic treatment method, and pretreating the fat by acting with a fat-degrading enzyme or a microorganism producing the enzyme, and performing the pretreatment Introducing wastewater or waste into the anaerobic treatment process, introducing anaerobic or aerobic microorganisms into the anaerobic treatment process, and collecting the higher fatty acid concentration / microorganism concentration of the sample collected from the anaerobic treatment process The said purification method characterized by calculating | requiring a ratio value and feeding back this ratio value and adjusting the quantity of the anaerobic or aerobic microorganisms introduce | transduced into an anaerobic treatment process. A step of adjusting the amount of higher fatty acid and the anaerobic or aerobic microorganism introduced so that the ratio of higher fatty acid concentration / microorganism concentration in the anaerobic reaction system is maintained at 0.4 or less by weight. The method of claim 1 . The method according to claim 1 , further comprising a step of subjecting the effluent discharged from the anaerobic treatment step to an aerobic treatment. By returning a part of the anaerobic fermentation sludge flowing out from the anaerobic treatment process and / or surplus aerobic sludge generated from the aerobic treatment process to the anaerobic treatment process, the anaerobic treatment process is anaerobic or favorable. The method according to any one of claims 1 to 3, wherein a temperate microorganism is introduced. The method in any one of Claims 1-4 which perform an anaerobic treatment process at the temperature of 45-75 degreeC. The method according to any one of claims 1 to 5, wherein the anaerobic treatment step is performed in an anaerobic treatment tank filled with a microorganism holding carrier. Improve fat and oil decomposition by adding emulsifiers to fat-containing wastewater or fat-containing waste and / or subjecting oil-containing wastewater or fat-containing waste to physical means such as ultrasonic treatment and crushing treatment. 7. A method according to any one of claims 1-6. An apparatus for purifying fat-containing wastewater or fat-containing waste by anaerobic treatment, wherein fat-containing wastewater or fat-containing waste is treated with an oil-degrading enzyme that decomposes fats or oils or a microorganism that produces the enzyme And a pretreatment tank for decomposing the fats and oils with an oil-degrading enzyme; and an anaerobic reaction tank for introducing the pretreated waste water or waste and anaerobically treating it. Means for adding anaerobic or aerobic microorganisms to the system; means for measuring the higher fatty acid concentration and microbial concentration of the sample collected from the anaerobic reactor; and the higher fatty acid concentration / microbe concentration of the measured sample Means for feeding back the ratio value and adjusting the amount of anaerobic or aerobic microorganisms added to the anaerobic reaction system.

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