JP3699367B2

JP3699367B2 - Waste liquid treatment method

Info

Publication number: JP3699367B2
Application number: JP2001178279A
Authority: JP
Inventors: 恒夫川崎; 詔雄川島
Original assignee: Kansai Electric Power Co Inc
Current assignee: Kansai Electric Power Co Inc
Priority date: 2001-06-13
Filing date: 2001-06-13
Publication date: 2005-09-28
Anticipated expiration: 2021-06-13
Also published as: JP2001276845A

Description

【０００１】
【発明の属する技術分野】
本発明は、発電用ボイラを有機酸系洗浄液で洗浄した際に排出される洗浄廃液であって、有機化合物および重金属類を含有する廃液を処理する際に副生する汚泥量を低減し、簡易、且つ低コストで洗浄廃液を高度浄化処理する技術に関するものである。
【０００２】
【従来の技術】
従来から発電プラントなどで使用されている大型ボイラには、貫流型ボイラなど多管式ボイラが多用されている。この様な多管式ボイラでは、蒸発管管外を流通する高温ガスと、管内を流通する液体との間で熱交換を行なっているため、高いボイラ効率を維持するには伝熱量を損なわないことが重要である。しかしながらボイラの運転に伴っての蒸発管内表面にはＦｅ₃Ｏ₄などの固体微粒子が付着，堆積して硬質の金属酸化皮膜（以下、「スケール」という）が形成されるため、該スケールが管内の流れを阻害したり、伝熱面の熱伝達を阻害してボイラの熱効率を低下させるなど様々な問題を生じさせたりする原因となっていた。そのため定期的にボイラの洗浄を行なってスケールなどの不純物を除去している。ボイラの洗浄方法としては酸液などによる化学洗浄が行なわれている。また蒸発管の腐食を防止する観点から酸液としてはクエン酸やグリコール酸などの有機酸系洗浄液が用いられている。有機酸系洗浄液によって蒸発管内に堆積したスケールなどの不純物は除去されるが、洗浄後の洗浄廃液はＣＯＤ（化学的酸素要求量）が高く、強酸性であり、しかも重金属類が含まれているため、該洗浄廃液にはＣＯＤ成分の除去，重金属類の除去，ｐＨの調整などの浄化処理が施されている。特に洗浄廃液の浄化処理方法としてはフェントン法が採用されている。例えば有機酸系洗浄廃液の処理方法としては該廃液に硫酸第一鉄などを添加した後、過酸化水素水を供給して廃液中の有機物を酸化分解（ＣＯＤ低下）し、更に該処理後の廃液に消石灰などを添加して廃液のｐＨを上昇させてから凝集剤を添加することによって該廃液に含まれる重金属類を凝集沈殿させ、残存する上澄み液を濾過などの処理工程に付すと共に、凝集沈殿した沈殿物（汚泥）を別途処理工程に付す方法が知られている。しかしながらフェントン法を用いた処理方法では、廃液のＣＯＤに対して数倍の過酸化水素水と硫酸第一鉄などを必要とするためコストが高くなる。また廃液に含まれている鉄に加えて硫酸第一鉄などや消石灰などの添加物が沈殿物として副生するため、大量の汚泥が生じるという問題があった。特に発電用ボイラの洗浄廃液量は数千トン単位であるので、この様に大量の洗浄廃液の処理にフェントン法を用いると、数十トン単位の汚泥が発生するため、該汚泥処理にかかるコストも高くなっていた。特に該汚泥は鉄などを大量に含有しているため高粘度で取扱い性が悪いため汚泥処理設備の洗浄，補修など２次的な処理に要するコストが高くなり、結果として洗浄廃液処理に係るコストが全体として高くなっていた。
【０００３】
【発明が解決しようとする課題】
本発明は上記事情に鑑みてなされたものであって、その目的は洗浄廃液の処理時に生じる汚泥量を減少させ、また簡易、且つ低コストで洗浄廃液を浄化処理する技術を提供することである。
【０００４】
【課題を解決するための手段】
本発明にかかる廃液の処理方法は、発電用ボイラを有機酸系洗浄液で洗浄した際に排出される洗浄廃液であって、有機化合物および重金属類を含有する廃液に過酸化水素水を接触させる工程と、前記過酸化水素水と接触させた廃液を、発電設備の運転に伴って生成される廃水であって、化学的酸素要求量が低く重金属類を実質的に含有しない廃水を希釈用の廃水として用いて希釈する工程と、希釈された廃液に凝集剤を添加して該希釈廃液中に存在する重金属類を凝集沈殿させる工程と、前記凝集沈殿工程の後、残存する廃液の一部または全部を、活性炭に接触させて吸着処理する工程とを含むことを特徴とする。
【０００５】
上記方法において、前記希釈用の廃水として、発電用ボイラから排出されたボイラブロー水、或いは前記凝集沈殿工程で生成される上澄み廃液を用いることができる。また、本発明の方法を実施するにあたっては、高分子凝集剤を用いて前記希釈廃液中の重金属類を凝集沈殿せしめることが推奨され、更に前記廃液処理工程の前または後に廃液のｐＨを廃水基準値に調整するｐＨ調整工程を設けることも望ましい実施態様である。
【０００６】
本発明では、前記廃液に過酸化水素水を供給する装置として、過酸化水素水供給ホース、及び長手方向の側面に複数の孔を形成したノズルを有し、更に該ノズルには過酸化水素水供給時に該ノズルが接地状態を維持できる重しを付設した装置が推奨される。
【０００７】
【発明の実施の形態】
本発明者らは発電用ボイラを有機酸系洗浄液で洗浄した際に排出される洗浄廃液であって、有機化合物および重金属類を含有する廃液の処理方法について鋭意研究を重ねた結果、該廃液に過酸化水素水を接触させた後、該廃液を発電設備の運転に伴って生成される廃水であって、化学的酸素要求量（ＣＯＤ）が低く重金属類を実質的に含有しない廃水を希釈用の廃水として用いて希釈し、該希釈廃液に凝集剤を添加して該希釈廃液中に存在する重金属類を凝集沈殿せしめれば、浄化処理時に副生する汚泥量を低減できることを見出した。更に該凝集沈殿後残存する廃液（上澄み液）を廃液処理工程に付すことによって効率的、且つ低コストで高度浄化し得ることを見出し本発明に至った。
【０００８】
以下、本発明の廃液処理方法を図１に例示される処理手順にしたがって説明するが、本発明の廃液処理方法は以下の例示に限定する趣旨ではなく、本発明の処理効果を達成し得るのでれば、適宜変更を加えることもできる。
【０００９】
本発明において処理対象となる廃液は、発電用ボイラを有機酸系洗浄液で洗浄した際に排出される洗浄廃液であって、有機化合物および重金属類を含有する廃液である。なお、有機化合物および重金属類以外に他の物質を含有していてもよい。ここで、有機酸系洗浄液とは酸性を示す有機化合物を含有する公知の有機酸系洗浄液であり、クエン酸やグリコール酸などを含有する洗浄液が例示される。この様な有機酸系洗浄液を用いてボイラを洗浄することによって蒸発管内表面に付着しているスケールなどを効率的に除去できるが、該洗浄により排出される洗浄廃液には、鉄（重金属類として「鉄」を例示表記する。）が含有されており、しかも強酸性であり、ＣＯＤも高い。尚、本発明の方法によれば発電用ボイラの洗浄廃液が、ＣＯＤが２，０００ｍｇ／Ｌ以上，鉄５００ｍｇ／Ｌ以上，ｐＨ２〜４程度であっても優れた汚泥発生量低減効果、及び高い廃液処理効率を発揮する。
【００１０】
洗浄廃液を過酸化水素水と接触させることによって該廃液の有機物を酸化分解せしめて低ＣＯＤ化を図ることができる。本発明では洗浄廃液を過酸化水素水と接触させる手段として、発電用ボイラから排出された廃液を処理槽に移送し、該処理槽中の廃液に過酸化水素水を供給する方法を用いて説明するが、該接触手段としては例えば廃液の移送中に過酸化水素水を供給してもよく、要するに廃液と過酸化水素水を接触させることができるのであれば、方法，手段については特に限定されない。
【００１１】
発電用ボイラから排出された洗浄廃液は移送ラインを介して処理槽に供給される。処理槽には過酸化水素水と廃液との接触効率を高めるために攪拌手段、例えばバブリング装置を付設することが望ましく、間欠曝気，連続曝気など任意の方法で攪拌すればよい。
【００１２】
過酸化水素水の添加方法については特に限定されないが、過酸化水素水供給ホース、及び長手方向の側面に複数の孔を形成したノズルを有し、更に該ノズルに過酸化水素水供給時に該ノズルが接地状態を維持できる重しを付設した供給装置を用いれば、高効率且つ高分散率で過酸化水素水を供給できる。この様な供給装置を用いた供給方法としては例えば図２に示されている様に、過酸化水素水供給源（図中、タンクローリー１）に過酸化水素水供給ホース２を接続し、該接続ホース２の他の先端に、長手方向の側面に複数の孔を形成したノズル部３、更に該ノズル部３に過酸化水素水供給時に該ノズルが接地状態を維持できる程度の重し４を付設した供給装置を介して過酸化水素水を供給すればよい。ノズル長手方向の側面に複数の孔６を形成することによって、過酸化水素水を拡散供給が可能となり、洗浄廃液との接触効率を高めることができる。ノズルに形成する孔の数，サイズ，配列は特に限定されず、適宜決定すればよいが、該孔を介した拡散供給効率を上げるためには、図３に示す様にノズル先端径面７が閉塞していることが望ましいが側面に設けた孔６と同様に小径の孔を設けてもよい。尚、供給装置には、過酸化水素水と反応性を有しない材料で構成することが望ましく、ノズル部３や重し４にはステンレス系の材料を用いて構成することが推奨される。また過酸化水素水供給ホースには塩化ビニル製，ポリエチレン製，テフロン製，フッ素樹脂製など耐薬品性に優れた材料を用いることが推奨される。
【００１３】
また短時間で効率よく過酸化水素水を供給するためには、過酸化水素水をコンプレッサーなどの加圧手段（図示せず）で加圧（０．１〜０．２ＭＰａ程度）して供給すればよいが、加圧するとノズル部３が不安定になるので、過酸化水素水供給時に該ノズルが処理槽底部との接地状態を維持できる様に重し４を該ノズル部３に付設することが望ましい。この際、安定した接地状態を維持するためには、重し４としては図３に示す様に複数の接地支持部材をノズルに付設すると共に、ノズル部３が加圧によって移動したり、浮遊しない十分な重さを付与することが望ましい。
【００１４】
尚、廃水に過酸化水素水を供給すると酸化分解による反応熱によって廃液の温度が上昇するため、温度上昇による沸騰を防止するために適宜廃液の温度調節をすることが望ましい。廃液の上限温度としては廃液の組成や過酸化水素水の添加量など種々の要因を考慮して沸騰を生じない温度を選定すればよいが、発電用ボイラ洗浄廃液の場合、具体的な廃液の温度上限の目安としては４０℃程度とすることが望ましい。したがって廃液の温度が４０℃近傍まで上昇した時点で流量調節弁５などによって過酸化水素水の供給量を調節して該洗浄廃液の温度を降下させた後、過酸化水素水の供給を再開すればよい。この際の降下温度については特に限定されず、２〜４℃程度降下させればよい。また過酸化水素水の供給量については特に限定されないが、過酸化水素水の添加量の増加にともなって、酸化分解量が増加して廃液のＣＯＤも低下し、反応効率が低下するので、後記する希釈量や吸着処理効率にもよるが、供給時の廃液のＣＯＤが好ましくは５０％以上分解された時点、より好ましくは７０％以上、より好ましくは９０％以上分解された時点で過酸化水素水の供給を停止すればよい。過酸化水素水の濃度，供給量は特に限定されず、廃液のＣＯＤ等に応じて濃度を適宜決定すればよく、３５〜６０％過酸化水素水が例示される。また供給量についも上記温度，ＣＯＤとの関係で適宜決定すればよい。廃液中のＣＯＤ測定はＪＩＳＫ０１０２に規定する方法によって測定すればよい。
【００１５】
本発明の方法によれば、過酸化水素水に加えて洗浄廃液に硫酸第一鉄などを添加する必要がないので、後記する凝集沈殿した沈殿物（汚泥）は実質的に該廃液に含まれる鉄などの重金属類に由来する沈殿物（汚泥）であり、したがってフェントン法に比べて汚泥発生量を大幅に低減することができる。
【００１６】
過酸化水素水と接触させた廃液は、発電設備の運転に伴って生成される廃水であって、ＣＯＤが低く重金属類を実質的に含有しない希釈用の廃水によって希釈される。廃液を希釈して該廃液に含まれる鉄等の重金属類濃度を下げれば、後記する凝集沈殿による沈殿物の粘度を低減できる。また希釈によって後記する廃液（上澄み液）処理工程での該希釈廃液処理効率を向上できるので望ましい。
【００１７】
本発明では廃液の希釈方法として該廃液を廃水槽に移送し、任意の廃水と希釈する方法について説明するが、該希釈手段としてはこれに限定されず、例えば廃水槽を設けずに、洗浄廃液をパイプなどを介して凝集沈殿槽へ移送する過程で任意の位置から廃水を供給して該廃液を希釈することもでき、適宜変更できる。
【００１８】
また上記処理槽と同様にバブリング装置などの攪拌手段を廃水槽に設けると混合希釈効率が向上するので望ましい。
【００１９】
希釈倍率としては特に限定されないが、洗浄廃液に含まれる重金属類濃度を好ましくは５倍以上、より好ましくは７倍以上、最も好ましくは１０倍以上希釈すると凝集沈殿による沈殿物の粘度を低減できる。また同様に洗浄廃液のＣＯＤを低減すれば廃液（上澄み液）処理効率、特に吸着処理効率が向上するので望ましく、具体的な希釈後のＣＯＤとしては処理効率の観点から好ましくは１００ｍｇ／Ｌ，より好ましくは５０ｍｇ／Ｌ，最も好ましくは３０ｍｇ／Ｌである。したがって廃水の供給量は汚泥量低減を目的とするのであれば上記重金属類濃度を達成し得る程度の供給量とすることが望ましい。また凝集沈殿後の廃液（上澄み液）の高度浄化処理を達成するには、上記希釈後ＣＯＤを達成し得る程度の供給量とすることが望ましい。
【００２０】
本発明において希釈用の廃水とは、廃液の重金属類濃度、或いは更にＣＯＤを低減できる廃水である。この様な廃水として、本発明では発電設備の運転に伴って生成される廃水（例えばボイラブロー水，純水装置再生廃水，デミ再生廃水など）が用いられる。また、かかる廃水には、後記する凝集沈殿処理した後の廃液（上澄み廃液）が含まれる。この様な発電設備の運転に伴って生成する廃水を用いて廃液を希釈すれば、簡易且つ低コストで廃液の重金属類濃度、或いは更にＣＯＤを低減でき、しかも少ない廃水量で上記希釈目的が達成できるので、希釈後の廃液（以下、「希釈廃液」という。）の処理量を低減できる。即ち、希釈用廃水のＣＯＤが低く（例えば上記例示した発電設備の運転に伴って生成する廃水であれば２〜５ｍｇ／Ｌ程度）、鉄をほとんど含有していなければ、単純に該廃水を洗浄廃液に供給して所望の倍率に希釈すれば、ＣＯＤ及び鉄濃度を同時に所望の倍率に希釈することが容易である。また該希釈によって廃液中に残存している過酸化水素はほぼ完全に消費されるので、凝集沈殿処理後の希釈廃液を後記する廃液処理工程（活性炭を用いた吸着処理工程）に付しても、過酸化水素による処理効率低下（活性炭劣化）が生じない。
【００２１】
廃液の希釈後、該希釈廃液に凝集剤を添加して該希釈廃液中に存在する重金属類を凝集沈殿させる。本発明では該凝集沈殿方法として、該希釈廃液を凝集沈殿槽に移送して凝集沈殿させるが、該凝集沈殿方法としてはこれに限定されず、例えば希釈廃液を移送せずに廃水槽にて凝集沈殿処理をおこなうこともでき、適宜変更できる。
【００２２】
本発明において凝集剤とは希釈廃液中に存在する重金属類を凝集沈殿できるものであれば特に限定されず、公知の凝集剤を用いればよく、また凝集効率を向上させるために必要に応じて適宜希釈廃液のｐＨを調節すればよい。上記した様に希釈廃液に重金属類として鉄が含有されていれば塩化第２鉄などの鉄塩系の無機凝集剤を用いなくても有機高分子凝集剤を用いれば高い凝集沈殿効率を発揮でき、しかも該無機凝集剤に由来する沈殿物が生じない。高分子凝集剤としては特に限定されないが、アニオン系高分子凝集剤（例えばポリアクリル酸ナトリウム，ポリアクリル酸アンモニウム，ポリスチレンスルホン酸ナトリウムなど）を用いると優れた凝集沈殿効果（凝集・沈殿速度，凝集物の結合強度など）が得られるので推奨される。尚、アニオン系高分子凝集剤の添加に先立って希釈廃液に水酸化ナトリウムなどのアルカリ性物質を添加して該廃液のｐＨを好ましくは８〜１０，より好ましくはｐＨ８〜９としておけば、該凝集剤の凝集沈殿効果を高めることができ、しかも該凝集剤の添加量も低減できるので望ましい。凝集剤の添加量としては特に限定されず、希釈廃液中の重金属類を十分凝集沈殿できる量を添加すればよい。尚、十分な凝集沈殿とは、該凝集沈殿処理後の上澄み液（廃液処理工程に付す場合は該供給廃液）の重金属類含有量が０ｍｇ／Ｌ，少なくとも１ｍｇ／Ｌ未満であることを意味する。したがってこの様な重金属含有量を達成する様に適宜凝集剤添加量を調整すればよいが、例えばアニオン系凝集剤を用いる場合、希釈廃液中の重金属類（鉄）含有量が１００ｍｇ／Ｌであれば、該凝集剤を１〜２ｍｇ／Ｌ程度添加すれば十分に凝集沈殿させることができる。尚、重金属類含有量の測定方法としてはＪＩＳＫ０１０２に規定されている方法を用いればよい。
【００２３】
尚、凝集沈殿せしめた沈殿物（汚泥）は凝集槽から取り出され任意の処理工程に付せばよい。本発明の方法によって得られる沈殿物量はフェントン法による処理よって副生する沈殿物量の１／１０程度であるので処理コストが低減できる。また本発明の沈殿物の粘度は上記の如くフェントン法による沈殿物の粘度よりも低いため、該沈殿物をフィルタープレスなどによって水分除去した後の沈殿物（ケーキ）は粘着性が低く、取扱いが容易である。
【００２４】
また凝集沈殿せしめた後、残存する廃液（上澄み液）の一部または全部を廃液処理工程に付して処理することで、洗浄廃液を高度浄化処理できる。ここで廃液の一部または全部とは、廃液の一部を前記の如く廃液の希釈に用いてもよく、あるいは他の工程で処理してもよいという意味である。
【００２５】
上記廃液処理工程とは、該残存廃液のＣＯＤなど該廃液中の不純物を酸化・分解などによって取り除いて浄化処理する工程であるが、本発明においては吸着処理工程をいう。この吸着処理工程とは、上澄み液中の有機化合物などの不純物を吸着除去する工程であって、具体的には、廃液を活性炭に接触させて吸着処理を行うものである。この吸着処理工程において、活性炭を用いることで、有機化合物などの不純物に対する高い吸着率が発揮され、しかも浄化処理効率を高くすることができる。この様な活性炭としては、例えば木炭を水蒸気で活性化したものや、ヤシガラ活性炭が例示され、粒状の炭素質が望ましいが特に限定されない。また処理工程には公知の処理装置を用いればよく、具体的な処理装置は限定されない。
【００２６】
活性炭を用いた吸着処理工程によって処理すれば、得られる被処理液は有機化合物などの不純物をほとんど含まず（ＣＯＤ：０〜２ｍｇ程度）、高度な浄化処理を達成できる。尚、凝集沈殿処理時にｐＨを調整した場合、例えば上記の如くｐＨを８〜９に調整した場合、必要に応じて該廃液処理工程の前または後に廃液のｐＨを廃水基準値に調整するｐＨ調整工程を設けることが推奨される。この際のｐＨ調整方法については特に限定されないが、該廃液のｐＨに応じて廃水基準値、即ちｐＨ６〜８，より好ましくはｐＨ６．６〜７．７となる様に適宜アルカリ性物質或いは酸性物質を添加すればよい。
【００２７】
以下、本発明の方法を実施例に基づいて詳述するが、本発明の方法は以下の実施例に限定される趣旨ではない。
【００２８】
【実施例】
発電用ボイラ（貫流型ボイラ）を有機酸系洗浄液（クエン酸１．５％，グリコール酸１．５％，腐食抑制剤０．３％，還元剤０．１％）で洗浄した。洗浄後排出された洗浄廃液（８３０ｍ3）をバブリング装置を備えた処理槽（容量１０００ｍ3）に移送して以下の処理を行なった。尚、洗浄廃液はＣＯＤ：２３００ｍｇ／Ｌ，ｐＨ：３．４，鉄：９８０ｍｇ／Ｌであった。
【００２９】
過酸化水素水供給源（タンクローリー）から過酸化水素水（３５％過酸化水素水）をコンプレッサーで加圧（０．１２ＭＰａ）しながら処理槽の洗浄廃液に供給（過酸化水素水の供給量０．９ｍ3／ｈ）した。この際、図４に示す様な供給装置を用いて過酸化水素水を処理槽に供給し、バブリング装置で攪拌した。洗浄廃液と過酸化水素水との反応により、洗浄廃液の温度が上昇したが、４０℃付近まで上昇した時点で、過酸化水素水の供給を休止し、洗浄廃液の温度が２〜４℃低下した後、過酸化水素水の供給を再開し、洗浄廃液のＣＯＤが３００ｍｇ／Ｌになるまで過酸化水素水の供給を繰り返した。その後、該洗浄廃液を廃水槽（容量２０００ｍ3）に移送すると共に、発電用ボイラから排出されたボイラブロー水（ＣＯＤ２ｍｇ／Ｌ，鉄０ｍｇ／Ｌ）を供給ラインを介して供給（５０ｍ3／ｈ）し、廃水槽でバブリング装置を用いて混合した。尚、希釈後廃液のＣＯＤは３０ｍｇ／Ｌ，鉄濃度１００ｍｇ／Ｌであった。混合後、希釈廃液を移送ラインを介して凝集沈殿槽に移送し、該廃液に含まれる鉄の凝集沈殿処理を行なった。この際、該廃液のｐＨが８〜９を維持する様に適宜水酸化ナトリウム（４４０ｍｇ／Ｌ）を添加するとともに、高分子凝集剤（栗田工業株式会社：ＥＤＰフロック３５１）を２ｍｇ／Ｌとなる様に該廃液に添加して３時間滞留させた。滞留後、沈殿槽内では鉄が凝集沈殿して沈殿物層を形成していた。このときの廃液（上澄み液）のＣＯＤは２０ｍｇ／Ｌ，鉄含有量は１ｍｇ／Ｌであった。該廃液のみをｐＨ調整槽に移送して硫酸を添加して洗浄廃液のｐＨが７前後となる様に調整した後、活性炭吸着塔（ヤシガラ活性炭を２５ｍ3充填，下向流型）に通水量４５ｍ3／ｈとなる様に供給して吸着処理を行なった。該吸着処理後の洗浄廃液（処理水）はＣＯＤ：０〜２ｍｇ／Ｌ，ｐＨ：６〜８，鉄１ｍｇ／Ｌ未満であり、不純物をほとんど含まない高度に浄化された処理水が得られた。尚、沈殿槽内に凝集沈殿している沈殿物は廃液１ｍ3中１．２ｋｇ（総沈殿物量１０００ｋｇ）であり、粘性を有していなかった。該沈殿物をフィルタープレス脱水処理したが詰まりなどの問題は生じなかった。また得られた沈殿物ケーキは他の処理工程で別途処理したが粘性がほとんどないため、取扱いが容易であった。
【００３０】
比較例
発電用ボイラ（貫流型ボイラ）を有機酸系洗浄液（クエン酸２．３％，グリコール酸２．３％，腐食抑制剤０．３％，還元剤０．１％）で洗浄した。洗浄後排出された洗浄廃液（８４０ｍ3）を処理槽（容量１０００ｍ3）に移送して以下の処理を行なった。尚、洗浄廃液はＣＯＤ：３８００ｍｇ／Ｌ，ｐＨ：３．１，鉄：８５０ｍｇ／Ｌであった。
【００３１】
処理槽の洗浄廃液にＣＯＤ処理準備剤を３３０ｋｇを添加して脱臭，消泡し、その後該洗浄廃液に６２．５％硫酸（２６４０ｋｇ）と硫酸鉄塩（５５００ｋｇ）とを添加してｐＨを１．５〜２．０に調整した。ｐＨ調整後、更に該廃液に３５％過酸化水素水を供給し、該廃液のＣＯＤが８ｍｇ／Ｌになるまで廃液の温度を調整しながら供給した。その後、消石灰を添加（４０００ｋｇ）してｐＨを８．８に調整し、高分子凝集剤（栗田工業株式会社：クリマイティ２０２）を供給（２ｍｇ／Ｌ）して４８時間沈殿させた。沈殿後、沈殿槽内では鉄が凝集沈殿して沈殿物層を形成していた。このときの廃液（上澄み液）のＣＯＤは５．２ｍｇ／Ｌ，鉄含有量は１ｍｇ／Ｌであった。沈殿槽内に凝集沈殿している沈殿物は廃液１ｍ3中１５．８ｋｇ（総沈殿物量１３３００ｋｇ）であり、高粘性であるため手動で搬出した。また該沈殿物をフィルタープレス脱水処理したが粘性が高いため詰まりなどの問題が生じ、随時メンテナンスを要した。尚、脱水後得られた沈殿物は他の処理工程で別途処理したが高粘性であるため、取扱いが困難であった。また廃液（上澄み液）はｐＨを６〜８に調整し、活性炭吸着処理した。得られた処理水のＣＯＤ：０〜２ｍｇ／Ｌ，ｐＨ：６〜８，鉄１ｍｇ／Ｌ未満であった。
【００３２】
【発明の効果】
本発明の方法によれば、廃液の処理時に生じる汚泥量を減少させることができる。本発明の廃液処理方法によれば、高効率でしかも廃液の高度浄化を低コストで達成することができる。
【図面の簡単な説明】
【図１】本発明の廃液処理方法の概略を例示する工程図である。
【図２】本発明の過酸化水素水の供給方法を例示する概略説明図である。
【図３】本発明の過酸化水素供給装置を例示する概略見取り図（（ａ）は側面図，（ｂ）は斜視図）である。
【符号の説明】
１過酸化水素水供給源
２接続ホース
３ノズル部
４重し
５流量調節弁
６孔
７ノズル先端径面[0001]
BACKGROUND OF THE INVENTION
The present invention is a cleaning waste liquid discharged when a power generation boiler is cleaned with an organic acid cleaning liquid, and reduces the amount of sludge produced as a by-product when processing a waste liquid containing organic compounds and heavy metals. In addition, the present invention relates to a technology for highly purifying cleaning waste liquid at low cost.
[0002]
[Prior art]
Conventionally, multi-tube boilers such as once-through boilers are widely used for large boilers used in power plants. In such a multi-tube boiler, heat exchange is performed between the high-temperature gas that flows outside the evaporation tube and the liquid that flows in the tube, so that the amount of heat transfer is not impaired in order to maintain high boiler efficiency. This is very important. However, since solid fine particles such as Fe ₃ O ₄ adhere to and deposit on the inner surface of the evaporation tube as the boiler operates, a hard metal oxide film (hereinafter referred to as “scale”) is formed. This has caused various problems such as obstructing the flow of heat and reducing the heat efficiency of the boiler by inhibiting the heat transfer of the heat transfer surface. Therefore, boilers are periodically cleaned to remove impurities such as scale. As a boiler cleaning method, chemical cleaning with an acid solution or the like is performed. From the viewpoint of preventing the corrosion of the evaporation tube, an organic acid cleaning solution such as citric acid or glycolic acid is used as the acid solution. Impurities such as scale accumulated in the evaporation tube are removed by the organic acid cleaning liquid, but the cleaning waste liquid after cleaning has high COD (chemical oxygen demand), is strongly acidic, and contains heavy metals. Therefore, the cleaning waste liquid is subjected to purification treatment such as removal of COD components, removal of heavy metals, and adjustment of pH. In particular, the Fenton method is adopted as a cleaning treatment method for cleaning waste liquid. For example, as a method for treating an organic acid cleaning waste liquid, ferrous sulfate or the like is added to the waste liquid, and then hydrogen peroxide is supplied to oxidatively decompose (degrade COD) organic substances in the waste liquid. Adding slaked lime to the waste liquid to raise the pH of the waste liquid and then adding a flocculant to agglomerate and precipitate heavy metals contained in the waste liquid, subject the remaining supernatant to a treatment step such as filtration, and agglomeration There is known a method in which a deposited precipitate (sludge) is separately subjected to a treatment process. However, the treatment method using the Fenton method requires a hydrogen peroxide solution and ferrous sulfate that are several times as large as the waste liquid COD, resulting in high costs. In addition to iron contained in the waste liquid, ferrous sulfate and other additives such as slaked lime are by-produced as precipitates, resulting in a problem that a large amount of sludge is generated. In particular, since the amount of washing waste liquid for power generation boilers is in the thousands of tons, if the Fenton method is used for the treatment of such a large amount of washing waste liquid, sludge in the order of several tens of tons is generated. It was also expensive. In particular, the sludge contains a large amount of iron and the like, and has a high viscosity and poor handling. Therefore, the cost required for secondary treatment such as cleaning and repairing of the sludge treatment equipment is increased, and as a result, the cost associated with the treatment of the washing waste liquid. Was higher overall.
[0003]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and an object thereof is to provide a technique for reducing the amount of sludge generated during the treatment of cleaning waste liquid and purifying the cleaning waste liquid at a simple and low cost. .
[0004]
[Means for Solving the Problems]
The waste liquid treatment method according to the present invention is a cleaning waste liquid discharged when a power generation boiler is cleaned with an organic acid cleaning liquid, and a step of bringing hydrogen peroxide water into contact with a waste liquid containing an organic compound and heavy metals And waste water that has been brought into contact with the hydrogen peroxide solution as a result of operation of the power generation equipment, and waste water that has a low chemical oxygen demand and does not substantially contain heavy metals is diluted. And a step of diluting the diluted waste liquid, adding a flocculant to the diluted waste liquid and aggregating and precipitating heavy metals present in the diluted waste liquid, and part or all of the waste liquid remaining after the agglomeration and precipitation process And a step of carrying out an adsorption treatment by contacting with activated carbon.
[0005]
In the above method, boiler blow water discharged from a power generation boiler or supernatant waste liquid generated in the coagulation sedimentation step can be used as the waste water for dilution. In carrying out the method of the present invention, it is recommended to coagulate and precipitate heavy metals in the diluted waste liquid using a polymer flocculant, and the pH of the waste liquid is adjusted to the waste water standard before or after the waste liquid treatment step. It is also a desirable embodiment to provide a pH adjusting step for adjusting the value.
[0006]
In the present invention, as a device for supplying the hydrogen peroxide solution to the waste liquid, a hydrogen peroxide solution supply hose and a nozzle having a plurality of holes formed in the side surface in the longitudinal direction are provided. A device provided with a weight capable of maintaining the grounded state of the nozzle during supply is recommended.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The inventors of the present invention have been extensively researched on a method for treating a waste liquid containing organic compounds and heavy metals, which is a cleaning waste liquid discharged when a power generation boiler is cleaned with an organic acid cleaning liquid. After contacting the hydrogen peroxide solution, the waste liquid is generated as a result of the operation of the power generation facility. The waste water is low in chemical oxygen demand (COD) and does not substantially contain heavy metals. It was found that the amount of sludge produced as a by-product during the purification treatment can be reduced by diluting it as waste water and adding a flocculant to the diluted waste liquid to coagulate and precipitate heavy metals present in the diluted waste liquid. Furthermore, the present inventors have found that the waste liquid (supernatant liquid) remaining after the coagulation sedimentation can be highly purified efficiently and at low cost by subjecting it to a waste liquid treatment step.
[0008]
Hereinafter, the waste liquid treatment method of the present invention will be described in accordance with the treatment procedure illustrated in FIG. 1, but the waste liquid treatment method of the present invention is not intended to be limited to the following examples, and can achieve the treatment effect of the present invention. If necessary, changes can be made as appropriate.
[0009]
The waste liquid to be treated in the present invention is a cleaning waste liquid that is discharged when a power generation boiler is cleaned with an organic acid cleaning liquid, and is a waste liquid containing an organic compound and heavy metals. In addition to organic compounds and heavy metals, other substances may be contained. Here, the organic acid cleaning liquid is a known organic acid cleaning liquid containing an acidic organic compound, and examples thereof include a cleaning liquid containing citric acid or glycolic acid. By cleaning the boiler using such an organic acid cleaning liquid, scales attached to the inner surface of the evaporation pipe can be removed efficiently. However, the cleaning waste liquid discharged by the cleaning contains iron (as heavy metals). "Iron" is shown as an example.), And it is strongly acidic and has a high COD. According to the method of the present invention, the cleaning waste liquid of the power generation boiler has an excellent sludge generation amount reducing effect even when the COD is 2,000 mg / L or more, iron 500 mg / L or more, and pH of about 2 to 4, and high. Demonstrate the efficiency of waste liquid treatment.
[0010]
By bringing the cleaning waste liquid into contact with the hydrogen peroxide solution, the organic matter in the waste liquid can be oxidatively decomposed to reduce COD. In the present invention, as a means for bringing the cleaning waste liquid into contact with the hydrogen peroxide solution, a method of transferring the waste liquid discharged from the power generation boiler to the treatment tank and supplying the hydrogen peroxide solution to the waste liquid in the treatment tank will be described. However, as the contact means, for example, hydrogen peroxide water may be supplied during the transfer of the waste liquid. In short, the method and means are not particularly limited as long as the waste liquid and the hydrogen peroxide water can be contacted. .
[0011]
The cleaning waste liquid discharged from the power generation boiler is supplied to the treatment tank via the transfer line. In order to increase the contact efficiency between the hydrogen peroxide solution and the waste liquid, the treatment tank is desirably provided with a stirring means, for example, a bubbling device, and may be stirred by any method such as intermittent aeration or continuous aeration.
[0012]
The method for adding hydrogen peroxide solution is not particularly limited, but has a hydrogen peroxide solution supply hose and a nozzle having a plurality of holes formed in the side surfaces in the longitudinal direction. If a supply device provided with a weight capable of maintaining a ground contact state, hydrogen peroxide solution can be supplied with high efficiency and high dispersion. As a supply method using such a supply device, for example, as shown in FIG. 2, a hydrogen peroxide solution supply hose 2 is connected to a hydrogen peroxide solution supply source (tank lorry 1 in the figure), and the connection is made. The other end of the hose 2 is provided with a nozzle portion 3 having a plurality of holes formed on the side surfaces in the longitudinal direction, and a weight 4 that can maintain the grounding state of the nozzle portion 3 when hydrogen peroxide is supplied. The hydrogen peroxide solution may be supplied through the supply device. By forming the plurality of holes 6 on the side surface in the longitudinal direction of the nozzle, the hydrogen peroxide solution can be diffused and supplied, and the contact efficiency with the cleaning waste liquid can be increased. The number, size, and arrangement of the holes formed in the nozzle are not particularly limited and may be appropriately determined. In order to increase the efficiency of diffusion supply through the holes, the nozzle tip diameter surface 7 is formed as shown in FIG. Although it is desirable to close, a small-diameter hole may be provided in the same manner as the hole 6 provided on the side surface. The supply device is preferably made of a material that is not reactive with hydrogen peroxide solution, and the nozzle unit 3 and the weight 4 are preferably made of a stainless steel material. It is recommended to use a material with excellent chemical resistance such as vinyl chloride, polyethylene, Teflon, and fluororesin for the hydrogen peroxide water supply hose.
[0013]
Further, in order to efficiently supply the hydrogen peroxide solution in a short time, the hydrogen peroxide solution should be supplied under pressure (about 0.1 to 0.2 MPa) with a pressurizing means (not shown) such as a compressor. However, since the nozzle unit 3 becomes unstable when pressurized, a weight 4 is attached to the nozzle unit 3 so that the nozzle can be kept in contact with the bottom of the processing tank when hydrogen peroxide water is supplied. Is desirable. At this time, in order to maintain a stable grounding state, as the weight 4, a plurality of grounding support members are attached to the nozzle as shown in FIG. 3, and the nozzle portion 3 does not move or float due to pressure. It is desirable to give sufficient weight.
[0014]
When hydrogen peroxide is supplied to the waste water, the temperature of the waste liquid rises due to reaction heat due to oxidative decomposition. Therefore, it is desirable to appropriately adjust the temperature of the waste liquid to prevent boiling due to the temperature rise. As the upper limit temperature of the waste liquid, a temperature that does not cause boiling should be selected in consideration of various factors such as the composition of the waste liquid and the amount of hydrogen peroxide solution added. It is desirable that the upper limit of the temperature be about 40 ° C. Accordingly, when the temperature of the waste liquid rises to around 40 ° C., the supply amount of the hydrogen peroxide solution is adjusted by the flow rate control valve 5 or the like to lower the temperature of the cleaning waste solution, and then the supply of the hydrogen peroxide solution is resumed. That's fine. The temperature drop at this time is not particularly limited, and may be lowered by about 2 to 4 ° C. The supply amount of the hydrogen peroxide solution is not particularly limited. However, as the addition amount of the hydrogen peroxide solution is increased, the amount of oxidative decomposition is increased and the COD of the waste liquid is reduced, and the reaction efficiency is lowered. Depending on the amount of dilution to be performed and the adsorption treatment efficiency, the hydrogen peroxide at the time when the COD of the waste liquid at the time of supply is decomposed is preferably 50% or more, more preferably 70% or more, more preferably 90% or more. What is necessary is just to stop supply of water. The concentration and supply amount of the hydrogen peroxide solution are not particularly limited, and the concentration may be appropriately determined according to the COD or the like of the waste liquid, and 35 to 60% hydrogen peroxide solution is exemplified. Further, the supply amount may be appropriately determined in relation to the temperature and COD. What is necessary is just to measure COD in a waste liquid by the method prescribed | regulated to JISK0102.
[0015]
According to the method of the present invention, since it is not necessary to add ferrous sulfate or the like to the cleaning waste liquid in addition to the hydrogen peroxide solution, the aggregated and precipitated precipitate (sludge) described later is substantially contained in the waste liquid. It is a precipitate (sludge) derived from heavy metals such as iron, and therefore the amount of sludge generated can be greatly reduced compared to the Fenton method.
[0016]
The waste liquid brought into contact with the hydrogen peroxide solution is waste water generated when the power generation facility is operated, and is diluted with waste water for dilution that has a low COD and does not substantially contain heavy metals. If the concentration of heavy metals such as iron contained in the waste liquid is decreased by diluting the waste liquid, the viscosity of the precipitate due to the aggregation precipitation described later can be reduced. Further, it is desirable because the dilution waste liquid treatment efficiency in the waste liquid (supernatant liquid) treatment step described later can be improved by dilution.
[0017]
In the present invention, as a method of diluting the waste liquid, a method of transferring the waste liquid to a waste water tank and diluting with an arbitrary waste water will be described, but the diluting means is not limited to this, for example, without providing a waste water tank, In the process of transferring the liquid to the coagulation sedimentation tank through a pipe or the like, the waste liquid can be diluted by supplying waste water from an arbitrary position, and can be changed as appropriate.
[0018]
Further, it is desirable to provide a stirring means such as a bubbling device in the waste water tank in the same manner as the above processing tank because the mixing and dilution efficiency is improved.
[0019]
The dilution rate is not particularly limited, but the viscosity of the precipitate due to coagulation precipitation can be reduced by diluting the heavy metal concentration contained in the washing waste liquid preferably 5 times or more, more preferably 7 times or more, and most preferably 10 times or more. Similarly, if the COD of the cleaning waste liquid is reduced, the waste liquid (supernatant liquid) treatment efficiency, particularly the adsorption treatment efficiency, is improved, and the specific diluted COD is preferably 100 mg / L from the viewpoint of the treatment efficiency. Preferably it is 50 mg / L, most preferably 30 mg / L. Accordingly, if the amount of waste water supplied is intended to reduce the amount of sludge, it is desirable to set the amount of waste water to a level that can achieve the above heavy metal concentration. Further, in order to achieve advanced purification treatment of the waste liquid (supernatant liquid) after the coagulation sedimentation, it is desirable to set the supply amount to such an extent that the above-described diluted COD can be achieved.
[0020]
In the present invention, the waste water for dilution is waste water that can reduce the concentration of heavy metals in the waste liquid or COD. As such waste water, waste water (for example, boiler blow water, deionized water regeneration waste water, demi regeneration waste water, etc.) generated with the operation of the power generation equipment is used in the present invention. Further, such waste water includes waste liquid (supernatant waste liquid) after a coagulation sedimentation treatment described later. By diluting the waste liquid using waste water generated during operation of such power generation facilities, the concentration of heavy metals in the waste liquid or COD can be reduced easily and at low cost, and the above-mentioned dilution purpose is achieved with a small amount of waste water. Therefore, the amount of waste liquid after dilution (hereinafter referred to as “diluted waste liquid”) can be reduced. That is, the COD of the waste water for dilution is low (for example, about 2 to 5 mg / L if the waste water is generated in accordance with the operation of the power generation facility exemplified above), and if it contains almost no iron, the waste water is simply washed. If the waste liquid is supplied and diluted to a desired magnification, it is easy to simultaneously dilute the COD and iron concentrations to the desired magnification. Further, since the hydrogen peroxide remaining in the waste liquid is almost completely consumed by the dilution, it can be subjected to a waste liquid treatment process (adsorption treatment process using activated carbon) which will be described later on the diluted waste liquid after the coagulation sedimentation treatment. No reduction in processing efficiency due to hydrogen peroxide (deterioration of activated carbon) does not occur.
[0021]
After diluting the waste liquid, a flocculant is added to the diluted waste liquid to coagulate and precipitate heavy metals present in the diluted waste liquid. In the present invention, as the coagulation sedimentation method, the diluted waste liquid is transferred to a coagulation sedimentation tank for coagulation sedimentation. However, the coagulation sedimentation method is not limited to this. Precipitation treatment can also be performed and can be changed as appropriate.
[0022]
In the present invention, the aggregating agent is not particularly limited as long as it can agglomerate and precipitate heavy metals present in the diluted waste liquid, and a known aggregating agent may be used, and as necessary in order to improve the aggregating efficiency. The pH of the diluted waste liquid may be adjusted. As described above, if iron is contained as a heavy metal in the diluted waste liquid, high coagulation-precipitation efficiency can be achieved by using an organic polymer flocculant without using an iron salt-based inorganic flocculant such as ferric chloride. Moreover, no precipitate derived from the inorganic flocculant is produced. The polymer flocculant is not particularly limited, but if an anionic polymer flocculant (for example, sodium polyacrylate, ammonium polyacrylate, sodium polystyrene sulfonate, etc.) is used, excellent coagulation precipitation effect (aggregation / precipitation rate, aggregation) This is recommended because it provides the bond strength of the object. In addition, prior to the addition of the anionic polymer flocculant, if an alkaline substance such as sodium hydroxide is added to the diluted waste liquid to adjust the pH of the waste liquid to preferably 8 to 10, more preferably pH 8 to 9, the aggregation It is desirable because the coagulation precipitation effect of the agent can be enhanced and the amount of the coagulant added can be reduced. The addition amount of the flocculant is not particularly limited, and an amount capable of sufficiently coagulating and precipitating heavy metals in the diluted waste liquid may be added. In addition, sufficient coagulation sedimentation means that the heavy metal content of the supernatant liquid after the coagulation sedimentation treatment (the supply waste liquid in the case of the waste liquid treatment step) is 0 mg / L, or at least less than 1 mg / L. . Therefore, the amount of flocculant added may be adjusted as appropriate to achieve such heavy metal content. For example, when an anionic flocculant is used, the heavy metal (iron) content in the diluted waste liquid should be 100 mg / L. For example, if the flocculant is added in an amount of about 1 to 2 mg / L, sufficient aggregation and precipitation can be achieved. In addition, what is necessary is just to use the method prescribed | regulated to JISK0102 as a measuring method of heavy metal content.
[0023]
The precipitate (sludge) that has been coagulated and precipitated may be taken out of the coagulation tank and subjected to an arbitrary treatment step. Since the amount of precipitate obtained by the method of the present invention is about 1/10 of the amount of precipitate produced as a by-product by the treatment by the Fenton method, the treatment cost can be reduced. In addition, since the viscosity of the precipitate of the present invention is lower than the viscosity of the precipitate obtained by the Fenton method as described above, the precipitate (cake) after the moisture is removed by a filter press or the like has low tackiness and can be handled. Easy.
[0024]
After coagulating and precipitating, the cleaning waste liquid can be highly purified by subjecting a part or all of the remaining waste liquid (supernatant liquid) to the waste liquid treatment step. Here, the part or all of the waste liquid means that a part of the waste liquid may be used for dilution of the waste liquid as described above, or may be processed in another process.
[0025]
The waste liquid treatment process is a process of removing impurities such as COD of the residual waste liquid and purifying it by oxidation and decomposition. In the present invention, it means an adsorption treatment process. This adsorption treatment step is a step of adsorbing and removing impurities such as organic compounds in the supernatant liquid. Specifically, the adsorption treatment is performed by bringing the waste liquid into contact with activated carbon. In this adsorption treatment step, by using activated carbon, a high adsorption rate for impurities such as organic compounds can be exhibited, and the purification treatment efficiency can be increased. Examples of such activated carbon include those obtained by activating charcoal with water vapor and coconut husk activated carbon, and granular carbon is desirable, but is not particularly limited. A known processing apparatus may be used for the processing step, and a specific processing apparatus is not limited.
[0026]
If it processes by the adsorption process process using activated carbon, the to-be-processed liquid obtained will hardly contain impurities, such as an organic compound (COD: about 0-2 mg), and can achieve a high purification process. In addition, when the pH is adjusted during the coagulation sedimentation treatment, for example, when the pH is adjusted to 8 to 9 as described above, the pH adjustment for adjusting the pH of the waste liquid to the waste water reference value before or after the waste liquid treatment step as necessary. It is recommended to provide a process. The pH adjustment method in this case is not particularly limited, but an alkaline substance or an acidic substance is appropriately added so that the waste water reference value is adjusted according to the pH of the waste liquid, that is, pH 6 to 8, more preferably pH 6.6 to 7.7. What is necessary is just to add.
[0027]
Hereinafter, although the method of this invention is explained in full detail based on an Example, the method of this invention is not the meaning limited to a following example.
[0028]
【Example】
The power generation boiler (through-flow boiler) was cleaned with an organic acid cleaning solution (citric acid 1.5%, glycolic acid 1.5%, corrosion inhibitor 0.3%, reducing agent 0.1%). The washing waste liquid (830 m 3) discharged after washing was transferred to a treatment tank (capacity 1000 m 3) equipped with a bubbling device and subjected to the following treatment. The washing waste liquid was COD: 2300 mg / L, pH: 3.4, iron: 980 mg / L.
[0029]
Supply hydrogen peroxide solution (35% hydrogen peroxide solution) from the hydrogen peroxide solution supply source (tank lorry) to the cleaning waste liquid of the treatment tank while applying pressure (0.12 MPa) with a compressor (supply amount of hydrogen peroxide solution 0 0.9 m @ 3 / h). At this time, hydrogen peroxide solution was supplied to the treatment tank using a supply device as shown in FIG. 4 and stirred with a bubbling device. The temperature of the cleaning waste liquid rises due to the reaction between the cleaning waste liquid and the hydrogen peroxide solution, but when the temperature rises to around 40 ° C, the supply of the hydrogen peroxide solution is stopped and the temperature of the cleaning waste solution decreases by 2 to 4 ° C. Then, the supply of the hydrogen peroxide solution was restarted, and the supply of the hydrogen peroxide solution was repeated until the COD of the cleaning waste liquid reached 300 mg / L. Thereafter, the cleaning waste liquid is transferred to a waste water tank (capacity 2000 m 3), and boiler blow water (COD 2 mg / L, iron 0 mg / L) discharged from the power generation boiler is supplied (50 m 3 / h) through a supply line. It mixed using the bubbling apparatus in a wastewater tank. The diluted waste liquid had a COD of 30 mg / L and an iron concentration of 100 mg / L. After mixing, the diluted waste liquid was transferred to a coagulation sedimentation tank via a transfer line, and the iron contained in the waste liquid was coagulated and precipitated. At this time, sodium hydroxide (440 mg / L) is appropriately added so that the pH of the waste liquid is maintained at 8 to 9, and the polymer flocculant (Kurita Kogyo Co., Ltd .: EDP floc 351) becomes 2 mg / L. In this manner, the waste liquid was added and allowed to stay for 3 hours. After the residence, iron coagulated and precipitated in the precipitation tank to form a precipitate layer. The COD of the waste liquid (supernatant liquid) at this time was 20 mg / L, and the iron content was 1 mg / L. Only the waste liquid is transferred to a pH adjustment tank, and sulfuric acid is added to adjust the pH of the cleaning waste liquid to around 7. After that, the activated carbon adsorption tower (filled with 25 m3 of coconut shell activated carbon, downward flow type) has a water flow rate of 45 m3. The adsorbing treatment was performed by supplying at a rate of / h. The washing waste liquid (treated water) after the adsorption treatment was COD: 0 to 2 mg / L, pH: 6 to 8, less than 1 mg / L of iron, and highly purified treated water containing almost no impurities was obtained. . The precipitate coagulated in the sedimentation tank was 1.2 kg (total amount of precipitate 1000 kg) in 1 m 3 of the waste liquid and had no viscosity. The precipitate was subjected to a filter press dehydration treatment, but problems such as clogging did not occur. Moreover, although the obtained precipitate cake was processed separately by another processing process, since there was almost no viscosity, handling was easy.
[0030]
Comparative Example A power generation boiler (through-flow boiler) was cleaned with an organic acid cleaning solution (2.3% citric acid, 2.3% glycolic acid, 0.3% corrosion inhibitor, 0.1% reducing agent). The washing waste liquid (840 m 3) discharged after washing was transferred to a treatment tank (capacity 1000 m 3) and subjected to the following treatment. The washing waste liquid was COD: 3800 mg / L, pH: 3.1, iron: 850 mg / L.
[0031]
Deodorizing and defoaming by adding 330 kg of COD treatment preparatory agent to the washing waste liquid in the treatment tank, and then adding 62.5% sulfuric acid (2640 kg) and iron sulfate salt (5500 kg) to the washing waste liquid to bring the pH to 1 Adjusted to .5 to 2.0. After pH adjustment, 35% hydrogen peroxide solution was further supplied to the waste liquid, and the waste liquid was supplied while adjusting the temperature of the waste liquid until the COD of the waste liquid reached 8 mg / L. Thereafter, slaked lime was added (4000 kg) to adjust the pH to 8.8, and a polymer flocculant (Kurita Kogyo Co., Ltd .: Crimety 202) was supplied (2 mg / L) to precipitate for 48 hours. After the precipitation, iron coagulates in the precipitation tank to form a precipitate layer. The COD of the waste liquid (supernatant liquid) at this time was 5.2 mg / L, and the iron content was 1 mg / L. The precipitate coagulated in the settling tank was 15.8 kg (total amount of precipitate 13300 kg) in 1 m 3 of the waste liquid, and since it was highly viscous, it was manually carried out. Further, the precipitate was subjected to a filter press dehydration treatment, but due to its high viscosity, problems such as clogging occurred, requiring maintenance as needed. Although the precipitate obtained after dehydration was separately treated in other treatment steps, it was difficult to handle because of its high viscosity. The waste liquid (supernatant liquid) was adjusted to pH 6-8 and subjected to activated carbon adsorption treatment. The obtained treated water had a COD of 0 to 2 mg / L, a pH of 6 to 8, and an iron content of less than 1 mg / L.
[0032]
【The invention's effect】
According to the method of the present invention, it is possible to reduce the amount of sludge generated during the treatment of waste liquid. According to the waste liquid treatment method of the present invention, it is possible to achieve high efficiency and advanced purification of waste liquid at low cost.
[Brief description of the drawings]
FIG. 1 is a process diagram illustrating an outline of a waste liquid treatment method of the present invention.
FIG. 2 is a schematic explanatory view illustrating the method for supplying hydrogen peroxide solution of the present invention.
FIG. 3 is a schematic sketch illustrating a hydrogen peroxide supply apparatus of the present invention ((a) is a side view, (b) is a perspective view).
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Hydrogen peroxide water supply source 2 Connection hose 3 Nozzle part 4 Weight 5 Flow control valve 6 Hole 7 Nozzle tip diameter surface

Claims

A cleaning waste liquid discharged when the power generation boiler is cleaned with an organic acid cleaning liquid, and a step of bringing hydrogen peroxide water into contact with a waste liquid containing organic compounds and heavy metals;
The waste liquid brought into contact with the hydrogen peroxide solution is waste water generated as a result of the operation of the power generation facility, and the waste water having a low chemical oxygen demand and substantially free of heavy metals is used as the waste water for dilution. Diluting and
Adding a flocculant to the diluted waste liquid to coagulate and precipitate heavy metals present in the diluted waste liquid;
And a step of adsorbing a part or all of the remaining waste liquid with activated carbon after the coagulation sedimentation step.

The waste liquid treatment method according to claim 1, wherein boiler blow water discharged from a power generation boiler is used as the waste water for dilution.

The waste liquid treatment method according to claim 1, wherein the supernatant waste liquid produced in the coagulation sedimentation step is used as the waste water for dilution.

The method for treating a waste liquid according to claim 1, wherein a heavy metal in the diluted waste liquid is coagulated and precipitated using a polymer flocculant.

The waste liquid treatment method according to any one of claims 1 to 4, further comprising a pH adjustment step for adjusting the pH of the waste liquid to a predetermined value before or after the adsorption treatment step.

A method using an apparatus for supplying hydrogen peroxide water to the waste liquid, the apparatus having a hydrogen peroxide supply hose and a nozzle having a plurality of holes formed in a side surface in the longitudinal direction, The method for treating a waste liquid according to any one of claims 1 to 5, wherein a weight capable of maintaining the grounding state of the nozzle is provided when hydrogen peroxide water is supplied.