JP3988477B2 - Waste water treatment method and apparatus - Google Patents

Waste water treatment method and apparatus Download PDF

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JP3988477B2
JP3988477B2 JP2002033730A JP2002033730A JP3988477B2 JP 3988477 B2 JP3988477 B2 JP 3988477B2 JP 2002033730 A JP2002033730 A JP 2002033730A JP 2002033730 A JP2002033730 A JP 2002033730A JP 3988477 B2 JP3988477 B2 JP 3988477B2
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勲 上甲
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Kurita Water Industries Ltd
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Description

【０００１】
【発明が属する技術分野】
本発明は、各種有機物、アンモニア、ヒドラジン等の被酸化性物質を含む排水の処理方法と、この方法を実施するのに適した処理装置とに関し、特に、当該排水の化学的酸素要求量（ＣＯＤ）や全有機炭素（ＴＯＣ）、あるいは全窒素濃度を低減することができる処理方法とその装置に関する。
【０００２】
【従来の技術】
従来、各種有機物、アンモニア、ヒドラジン等の被酸化性物質を含む排水を処理する方法として、酸化イリジウムを表面に担持させた白金系電極を用いて電解処理し、続いて過酸化ニッケル系触媒あるいは過酸化コバルト系触媒と接触させて処理する方法が実用化されている（火力原子力発電５１（１２），１７１１（２０００）、特開平１０−１７４９７６号公報、特願平１０−２１８６７号公報等参照）。
【０００３】
【発明が解決しようとする課題】
しかし、上記の酸化イリジウムを表面に担持させた白金系電極を用いて電解処理する方法では、電解時の電流効率を高めるために、処理対象排水中の塩化物イオン濃度を６，０００ｍｇ／リットル（以下、リットルは「Ｌ」、ミリリットルは「ｍＬ」と記す）以上の条件とする方法が採られている。
塩化物イオン濃度が６，０００ｍｇ／Ｌ以下になると、電流効率の低下傾向が大きくなるため、塩化物イオン濃度を６，０００ｍｇ／Ｌ以上に維持させる必要がある。
従って、この塩化物イオン濃度（塩素系化合物）に要するコストが高く、経済的な観点から適用に限界があるばかりか、塩素系化合物に起因する装置構成材料の腐食によるトラブルの問題もある。
【０００４】
本発明は、以上の従来の処理方法よりも、被酸化性物質の除去効率に優れ、ＣＯＤやＴＯＣ、全窒素濃度の低減効率が高いばかりでなく、処理性能の安定性にも優れ、かつ適用範囲を広くすることができる被酸化性物質含有排水の処理方法と、この方法を実施するのに適した装置とを提供することを目的とする。
【０００５】
【課題を解決するための手段】
本発明者は、上記目的を達成するために検討を重ねた結果、
（１）電極として導電性ダイヤモンド電極を用いると、従来の白金電極や酸化イリジウム表面担持白金系電極を用いる場合に比して、電極面での電流密度を高めて処理することができること、
（２）従って、装置腐食の要因となる電解質物質の使用量を低減できるばかりでなく、大容量の排水をコンパクトな装置（必要電極面積が少なくて済む）で処理できること、
（３）但し、電解反応槽で、被酸化性物質の酸化分解反応で生成する炭酸ガスや窒素ガス等のガス成分が、電極表面と排水との接触を阻害し、電極間抵抗を増大させること、
（４）このため、導電性ダイヤモンド電極による上記（１），（２）の作用効果を最大限に発現させるには、上記（３）のガス成分の除去が重要であること、
の知見を得た。
【０００６】
本発明は、以上の知見に基づいてなされたものであって、本発明に係る排水の処理方法は、被酸化性物質と電解質物質を含む排水を、導電性ダイヤモンド電極を用いた複数の電解反応槽で電解処理し、少なくとも１の電解反応槽の処理済水を気液分離した後、後段の電解反応槽に通液処理することを特徴とする。この気液分離は、最終段の電解反応槽を除く各電解反応槽処理済水について行うことが好ましい。
また、本発明に係る排水の処理装置は、導電性ダイヤモンド電極を用いた電解反応槽の複数を直列に配置し、これら複数の電解反応槽間の任意の少なくとも１箇所、または少なくとも１の電解反応槽に、気液分離手段を設けてなることを特徴とする。この気液分離手段は、各電解反応槽間または最終段の電解反応槽を除く各電解反応槽に設けることが好ましい。
【０００７】
本発明の処理対象水である排水は、被酸化性物質と電解質物質を含み、各種の工場から排出される産業排水はもとより、生活排水、その他の排水であってよい。
排水中の被酸化性物質は、各種の有機物、あるいはアンモニアやヒドラジン等が挙げられ、本発明では、これら有機物、アンモニア、ヒドラジンのうちの少なくとも１つを含む排水に適用して好ましい効果を得ることができる。排水中のこれら被酸化性物質の濃度は、特に制限されず、被酸化性物質を種々の濃度で含む排水に好ましく適用することができる。
【０００８】
一方、電解質物質は、どのようなものであってもよいが、一般には無機化合物であって、例えば、ＮａＣｌ、Ｈ２ＳＯ４、Ｎａ２ＳＯ４等が好ましく、これらは単独であってもよいし、適宜の組み合わせによる２種以上であってもよい。
排水中のこれら電解質物質の濃度は、特に制限せず、従来の電解処理に必要な５０〜５０，０００ｍｇ／Ｌ程度であってもよいし、従来の電解処理では効率が極めて悪くなる６，０００ｍｇ／Ｌ未満であっても効率よく処理することができる。
すなわち、電気分解処理の際に電流効率を高める作用をなす電解質物質は、酸化イリジウム表面担持の白金系電極を用いる従来の方法では、６，０００ｍｇ／Ｌ以上の濃度を必要としていたのに対し、電流効率の改善効果を得ることができる導電性ダイヤモンド電極を用いる本発明では、６，０００ｍｇ／Ｌ未満の低濃度領域でも、十分な処理効果を得ることができる。
但し、導電性ダイヤモンド電極を使用する本発明においても、電解質物質の濃度があまり低すぎると、排水中の被酸化性物質を電気分解処理するのに十分な電流効率を得ることができない場合もあるため、本発明における好ましい電解質物質の濃度は、上記排水に対して５００〜６，０００ｍｇ／Ｌ程度である。
【０００９】
上記の電解質物質は、上記の被酸化性物質含有排水中に含まれている場合もあり、この含有電解質物質のみで上記の電解質物質濃度を確保できる場合は、別途電解質物質を投入する必要はない。
含有電解質物質のみで上記の電解質物質濃度を確保できない場合は、本発明の処理に先立って、上記の電解質物質を確保できる量の電解質物質を投入する。
【００１０】
本発明で使用する導電性ダイヤモンド電極は、Ｎｉ，Ｔａ，Ｔｉ，Ｍｏ，Ｗ，Ｚｒ等の導電性金属材料を基板とし、これら基板の表面に導電性ダイヤモンド薄膜を析出させたものや、シリコンウエハ等の半導体材料を基板とし、このウエハ表面に導電性ダイヤモンド薄膜を合成させたもの、あるいは基板を用いない条件で板状に析出合成した導電性多結晶ダイヤモンド素材を挙げることができる。
なお、導電性（多結晶）ダイヤモンド薄膜は、ダイヤモンド薄膜の調製の際にボロン又は窒素の所定量をドープして導電性を付与したものであり、ボロンをドープしたものが一般的である。
これらのドープ量は、少なすぎればドープする技術的意義が発現せず、多すぎてもドープ効果は飽和するため、ダイヤモンド薄膜素材の炭素量に対し５０〜１０，０００ｐｐｍの範囲内のものが適している。
【００１１】
本発明において、導電性ダイヤモンド電極は、一般には板状のものを使用するが、網目構造を板状にしたもの等をも使用することができる。
【００１２】
この導電性ダイヤモンド電極を使用する電気分解処理は、導電性ダイヤモンド電極表面の電流密度を１０〜１００，０００Ａ／ｍ２とし、前記の被酸化性物質と電解質物質を含む排水を、導電性ダイヤモンド電極面と平行に、通液線速度（ＬＶ）１０〜１，０００ｍ／ｈｒで、通液し、電極面と接触させることで行うことが好ましい。
【００１３】
電流密度が上記未満であると、電流効率の良い導電性ダイヤモンド電極を使用しても、排水中の被酸化性物質の十分な電気分解処理を行うための必要電極面積を大きくする必要が生じ、本発明の目的の１つであるコンパクトな装置での大容量の排水処理が達成できなくなる。
逆に、上記を超えると、極間抵抗が増大し、熱エネルギーに消費されてしまうため、不経済となる。
【００１４】
また、排水の通液方向を電極面と平行にするのは、排水と電極表面との接触効率を高めるためであり、この方向であれば、電解反応槽内に炭酸ガス等のガス成分が存在していても、このガスによる排水と電極面との接触阻害をある程度緩和することができるからである。
このときの排水の通液速度を、線速度（ＬＶ）で１０〜１，０００ｍ／ｈｒとするのは、これより遅すぎると、排水の通液方向を電極面と平行にしても、ガス成分による排水と電極表面との接触阻害を緩和する効果が得られず、これより速すぎると、排水と電極表面との接触時間を十分に取ることができず、被酸化性物質の電気分解を十分に進行させることができなくなる。
【００１５】
なお、電解反応槽内の温度は、特に限定しないが、低温すぎると、排水の電気分解が良好に進行せず、逆に高温すぎると、気化が加わってガス成分の生成が多くなり、排水と電極表面との接触阻害が増大するのみならず、上記のような低濃度領域であっても、電解質物質による装置構成材料の腐食の懸念があるため、本発明では、１０〜９５℃程度とすることが望ましい。
【００１６】
本発明の処理方法では、上記のような条件での電気分解処理を、直列に配置した複数の電解反応槽で行うが、この電気分解処理で生成する炭酸ガスや窒素ガス等のガス成分を除去するために、最終段の電解反応槽を除く各電解反応槽の処理済水に対して気液分離を行う。
この気液分離は、通常の気液分離装置をそのまま使用して行ってもよいし、あるいは上方に気相部（空間部）を備え頂部にガス抜き部（ガス抜き管、ガス抜き口等）を備えた受液槽や、電解反応槽自体の上方に気相部を備え頂部にガス抜き部を備えたもので行ってもよい。
すなわち、水中の気泡は、容易に浮上して気相に移行するため、電気分解処理で生成する炭酸ガスや窒素ガス等のガス成分は、上方に気相部を形成して下方の液層部と容易に分離する。従って、上記のようなガス抜き部や気相部を備えた受液槽や電解反応槽を用いることでも、電気分解処理で生成するガス成分は、処理済水と容易に分離することができる。
【００１７】
上記のようにして気液分離した後の処理済水は、後段の電解反応槽に送液されて、次の電気分解処理に付される。
【００１８】
気液分離でのガス成分の除去の程度は、特に制限しないが、後段の電解反応槽での電気分解処理が所望の電解効率を得ることができる程度、一般には、前段の電解反応槽での処理済水中に存在するガス成分の３０〜９０％程度、好ましくは５０〜９０％程度であればよい。
すなわち、導電性ダイヤモンド電極を使用する場合、電気分解対象液（排水）中のガス成分濃度は０〜１０％程度であれば、ガス成分による電極表面と排水との接触阻害、ひいては電極間抵抗の増大を抑えることができ、所望の電解効率に近い電解効率を得ることができる。
このガス成分濃度を確保するために、上記程度のガス成分の除去率とすることが望ましい。
【００１９】
気液分離は、各電解反応槽間または最終段を除く各電解反応槽で行うことが望ましいが、これに限定されず、電気分解対象排水（すなわち、前段の電解反応槽の処理済水）中のガス成分が上記濃度の範囲内にあれば気液分離を行う必要はないため、ガス成分濃度が上記の上限値を超える電解反応槽流出液に対して行えばよい。
この電解反応槽処理済水は、被酸化性物質が大量に存在し、従って酸化分解によるガス成分の生成量が多い第１段目の電解反応槽、あるいは被酸化性物質の酸化分解が進みガス成分の生成量が多くなる第２段目や第３段目の電解反応槽の処理済水が主となる。
このようなことから、本発明では、少なくとも１の電解反応槽の処理済水、具体的にはガス成分濃度が排水と電極の接触を阻害する上記濃度の処理済水について気液分離を行えばよい。
【００２０】
図１（Ａ）は、本発明に係る排水処理装置の一実施態様例を説明するためのフロー図であって、同図では、２つの電解反応槽３，６を直列に配置し、これら２つの電解反応槽３，６間に通常の気液分離装置４を設けている。
これらの電解反応槽３，６は、図１（Ｂ）にその模式図を示すように、直方体の槽であって、相対する両側壁面に導電性ダイヤモンド電極１１，１１を備え、下部に排水導入管１２、上部に処理済水導出管１３を備えている。
【００２１】
このように構成される排水処理装置において、本発明の処理対象排水は、原排水貯槽１に一旦貯留され、これがポンプ２で送液され、第１段目の電解反応槽３に、排水導入管１２から導入される。
この第１の電解反応槽３に導入された排水は、該槽３を、図１（Ｂ）の二重矢印で示すように、下部から上部に移送され、この間に導電性ダイヤモンド電極１１，１１の表面と平行に接触して電気分解処理される。
【００２２】
このようにして電気分解処理された第１の電解反応槽３での処理済水は、電気分解処理途上で発生した炭酸ガス等のガス成分を伴って、該槽３内を上昇し、処理済水導出管１３からオーバーフローして、気液分離装置４に導入される。
この装置４で分離されたガス成分は、ガス抜き部４′から系外に抜き出され、分離された水が、本例では、図１（Ａ）に示すように、気液分離装置４の下部に開口する導出管から、ポンプ５により、抜き出される。
【００２３】
この抜き出し水は、上記の第１の電解反応槽３と同一に構成される第２段目の電解反応槽６に、排水導入管１２から導入され、第１の電解反応槽３と同様にして電気分解処理される。
この第２の電解反応槽６において、排水導入管１２から導入される排水中には、ガス成分が殆ど含まれていないため、該排水とダイヤモンド電極表面との接触が良好に行われ、高効率での電気分解処理が行われる。
【００２４】
このようにして、第２の電解反応槽６で電気分解処理された処理済水は、第１の電解反応槽３の場合と同様に、第２の電解反応槽６内を上昇し、該槽６の上部に設けられている処理済水導出管１３からオーバーフローして、処理済水貯槽７に貯留される。
【００２５】
また、図１（Ａ）の気液分離装置４に代えて、図２に示すような、単なる処理済水の受け槽４１を使用してもよい。
この受け槽４１は、その内部の下方を液相部４１Ｌとし、上方を気相部４１Ｇとし、頂部にガス抜き部４１′を設けてあり、また頂部に第１の電解反応槽３での処理済水導出管１３の出口側端を開口させ、液相部４１Ｌの下部近傍に開口させて、分離水の導出管４２を設けてある。
【００２６】
このように構成される受け槽４１の場合、第１の電解反応槽３での処理済水が導出管１３の開口から導入されて、液相部４１Ｌに貯留される。
液相部４１Ｌでの貯留中にガス成分が浮上し、気相部４１Ｇに溜まり、ガス抜き部４１′から系外に抜き出される。
このガス成分の液相部４１Ｌから気相部４１Ｇまでへの浮上は、数分から数１０分程度の短時間で行われるため、受け相４１は、この程度の滞留時間が取れる程度の容積があれば十分である。
なお、第１の電解反応槽３での処理済水を、導出管１３の開口から液相部４１Ｌに落（滴）下するようにすれば、この落（滴）下中にも該水中のガス成分が分離されることとなるため、気液分離時間をより一層短縮することができる。
【００２７】
このようにして受け槽４１で気液分離された分離水は、導出管４２から、図１（Ａ）に示すポンプ５により抜き出され、第２の電解反応槽６に送られて、後段の電気分解処理に付される。
【００２８】
図３は、第１の電解反応槽３自体に、気液分離手段（機能）を設けたものであって、本例では、図示するように、電解反応槽３の下方を液相部３１Ｌとし、上方を気相部３１Ｇとし、頂部にガス抜き部３１′を設けている。
この液相部３１Ｌにおいて、相対する両側壁面に導電性ダイヤモンド電極１１，１１を備え、下部に排水導入管１２、上部に処理済水導出管１３を備えている。
【００２９】
本例では、電気分解処理で発生するガス成分が、電気分解処理途上で液相部３１Ｌを浮上して、気相部３１Ｇに溜まり、ガス抜き部３１′から系外に抜き出される。
このガス成分の液相部３１Ｌから気相部３１Ｇまでへの浮上は、数分から数１０分程度の短時間で行われるため、排水の電気分解処理途上で十分な気液分離が行われることとなる。
【００３０】
このようにして第１の電解反応槽３１で、液相部３１Ｌを上昇中に電気分解処理と同時に気液分離された分離水は、導出管１３から、ポンプ５により抜き出され、第２の電解反応槽６に送られて、ガス成分のない状態で高効率での電気分解処理に付される。
【００３１】
【実施例】
実施例１
ボロンドープ法を用いて気相析出合成した積層状の多結晶ダイヤモンド電極板（２ｃｍ×２ｃｍ×０．０５ｃｍ）２枚を、極間距離３ｍｍとなるように、内寸２ｃｍ×２ｃｍ×０．４ｃｍのガラス製容器に設置して電解反応槽とした。
この構成の電解反応槽を２つ用い、図１（Ａ）に示すフローと類似のフローによる処理装置を設定した。
すなわち、上記構成の第１の電解反応槽３と第２の電解反応槽６を直列に配置し、これら各槽３，６間に、図２に示す構成の処理済水受け槽４１（容量５００ｍＬ）を設置した。
【００３２】
この処理装置に、フェノール５０ｍｇ／ＬとＮａ２ＳＯ４１４ｇ／Ｌを含む合成排水（ＣＯＤ濃度１２０ｍｇ／Ｌ）を、２Ｌ／ｈｒの通液速度で通液し、第１の電解反応槽３→処理済水受け槽４１→第２の電解反応槽６の順で処理した。
なお、第１，第２の電解反応槽３，６への投入電気量は、両槽３，６とも、電流密度が０．０５Ａ／ｃｍ２となるように設定した。
【００３３】
通液開始後、３時間経過した後の第２の電解反応槽６からの流出水は、ＣＯＤ濃度が１．９ｍｇ／Ｌであった。
また、上記と同じ条件で２週間連続処理した結果、安定した処理効果が持続できることが確認された。
この電解処理結果をまとめると、表１の通りとなる。
【００３４】
【表１】

Figure 0003988477
【００３５】
実施例２
実施例１の第１の電解反応槽３を、図３に示す構成の第１の電解反応槽３に置き換え、処理済水受け槽４１を使用しないで、図３に示す態様の処理装置を設定した。
すなわち、実施例１と同じ多結晶ダイヤモンド電極板（２ｃｍ×２ｃｍ×０．０５ｃｍ）２枚を、極間距離３ｍｍとなるように、内寸２ｃｍ×３ｃｍ×０．４ｃｍのガラス製容器に設置し、該容器の下方を液相部３１Ｌとし、上方を気相部３１Ｇとして、第１の電解反応槽３１とした。なお、第２の電解反応槽６は、実施例１と同じ構成のものを使用した。
【００３６】
この処理装置に実施例１と同じ合成排水（ＣＯＤ濃度１２０ｍｇ／Ｌ）を、実施例１と同じ通液速度、投入電気量で通液し、第１の電解反応槽３１→第２の電解反応槽６の順で処理した。
通液開始後、３時間経過した後の第２の電解反応槽６からの流出水は、ＣＯＤ濃度が１．９ｍｇ／Ｌであった。
また、上記と同じ条件で２週間連続処理した結果、安定した処理効果が持続できることが確認された。
この電解処理結果をまとめると、表２の通りとなる。
【００３７】
【表２】
Figure 0003988477
【００３８】
比較例１
実施例１と同様にボロンドープ法を用いて気相析出合成した積層状の多結晶ダイヤモンド電極板（２ｃｍ×４ｃｍ×０．０５ｃｍ）２枚を、極間距離３ｍｍとなるように、内寸２ｃｍ×４ｃｍ×０．４ｃｍのガラス製容器に設置して電解反応槽とした。
この１つの電解反応槽の通液断面積と全電極面積は、実施例１の第１と第２の電解反応槽の合計通液断面積と合計全電極面積と同じとなる。
また、電解反応槽への投入電気量も実施例１と同じ電流密度０．０５Ａ／ｃｍ２に設定した。
【００３９】
この処理装置に実施例１と同じ合成排水（ＣＯＤ濃度１２０ｍｇ／Ｌ）を、実施例１と同じ通液速度で通液して処理した。
通液開始後、３時間経過した後の電解反応槽からの流出水は、ＣＯＤ濃度が１７．８ｍｇ／Ｌであった。
この電解処理結果をまとめると、表３の通りとなる。
【００４０】
【表３】
Figure 0003988477
【００４１】
【発明の効果】
以上のように、本発明によれば、電気分解処理の際に、被酸化性物質の酸化分解反応で発生する炭酸ガス等のガス成分を、次段の電解反応槽での排水処理前に除去するため、該ガス成分による排水と上記電極表面との接触阻害が解消され、電極間抵抗の増大や、電気分解効率の低下等はなくなり、極めて高効率での電気分解処理を行うことができる。
【００４２】
また、本発明によれば、電気分解処理の際の電極として電流効率の高い導電性ダイヤモンド電極を用いるため、処理対象排水中に存在させる電解質物質の濃度を、従来の電解質物質（塩化物イオン）の濃度より大幅に低減することができる。
このため、処理コストが低減するばかりでなく、電解質物質による装置構成材料の腐食によるトラブルの問題を解消することができる。
【図面の簡単な説明】
【図１】本発明に係る処理装置の一実施態様例を説明するための図で、（Ａ）が排水のフローを示す図、（Ｂ）が第１，第２の電解反応槽の態様を模式的に示す図である。
【図２】本発明に係る処理装置の他の実施態様例を説明するための図である。
【図３】本発明に係る処理装置の更に他の実施態様例を説明するための図である。
【符号の説明】
１ 原水貯槽
２，５ ポンプ
３，３１ 第１の電解反応槽
４，４１ 気液分離手段
６ 第２の電解反応槽
７ 処理済水貯槽
１１ 導電性ダイヤモンド電極[0001]
[Technical field to which the invention belongs]
The present invention relates to a method for treating wastewater containing oxidizable substances such as various organic substances, ammonia and hydrazine, and a treatment apparatus suitable for carrying out this method, and more particularly to chemical oxygen demand (COD) of the wastewater. ), Total organic carbon (TOC), or a processing method and apparatus capable of reducing the total nitrogen concentration.
[0002]
[Prior art]
Conventionally, as a method for treating wastewater containing oxidizable substances such as various organic substances, ammonia, hydrazine, etc., electrolytic treatment is performed using a platinum-based electrode having iridium oxide supported on the surface, followed by a nickel peroxide-based catalyst or a catalyst. A method of treatment by contacting with a cobalt oxide catalyst has been put into practical use (see thermal nuclear power generation 51 (12), 1711 (2000), Japanese Patent Application Laid-Open No. 10-174976, Japanese Patent Application No. 10-21867, etc.) .
[0003]
[Problems to be solved by the invention]
However, in the method of electrolytic treatment using the platinum-based electrode having iridium oxide supported on the surface, the chloride ion concentration in the waste water to be treated is set to 6,000 mg / liter ( Hereinafter, a method is adopted in which the liter is referred to as “L” and the milliliter is referred to as “mL”.
When the chloride ion concentration is 6,000 mg / L or less, the current efficiency tends to decrease, so the chloride ion concentration must be maintained at 6,000 mg / L or more.
Therefore, the cost required for the chloride ion concentration (chlorine compound) is high, and there is a problem of troubles due to corrosion of equipment constituent materials caused by the chlorine compound, as well as application from the economical viewpoint.
[0004]
The present invention is superior in the removal efficiency of oxidizable substances and has high efficiency in reducing COD, TOC, and total nitrogen concentration as compared with the above conventional processing methods, and is excellent in stability of processing performance and application. It is an object of the present invention to provide a method for treating wastewater containing oxidizable substances capable of widening the range and an apparatus suitable for carrying out this method.
[0005]
[Means for Solving the Problems]
As a result of repeated studies to achieve the above object, the present inventor,
(1) When a conductive diamond electrode is used as an electrode, the current density on the electrode surface can be increased and processed compared to the case of using a conventional platinum electrode or a platinum-based electrode supported with iridium oxide,
(2) Therefore, it is possible not only to reduce the amount of electrolyte substance used to cause corrosion of the device, but also to treat a large volume of wastewater with a compact device (requires a small electrode area).
(3) However, in the electrolytic reaction tank, gas components such as carbon dioxide gas and nitrogen gas generated by the oxidative decomposition reaction of the oxidizable substance inhibit the contact between the electrode surface and the waste water, and increase the resistance between the electrodes. ,
(4) Therefore, in order to maximize the effects (1) and (2) of the conductive diamond electrode, it is important to remove the gas component (3).
I got the knowledge.
[0006]
The present invention has been made on the basis of the above knowledge, and the wastewater treatment method according to the present invention comprises a plurality of electrolytic reactions using a conductive diamond electrode for wastewater containing an oxidizable substance and an electrolyte substance. It is characterized by performing electrolytic treatment in a tank and subjecting treated water in at least one electrolytic reaction tank to gas-liquid separation and then passing through a subsequent electrolytic reaction tank. This gas-liquid separation is preferably performed on the water treated in each electrolytic reaction tank excluding the final stage electrolytic reaction tank.
Moreover, the wastewater treatment apparatus according to the present invention includes a plurality of electrolytic reaction tanks using conductive diamond electrodes arranged in series, and at least one place between the plurality of electrolytic reaction tanks, or at least one electrolytic reaction. The tank is provided with gas-liquid separation means. This gas-liquid separation means is preferably provided between each electrolytic reaction tank or in each electrolytic reaction tank excluding the final stage electrolytic reaction tank.
[0007]
The wastewater that is the water to be treated of the present invention includes an oxidizable substance and an electrolyte substance, and may be domestic wastewater or other wastewater as well as industrial wastewater discharged from various factories.
Examples of oxidizable substances in wastewater include various organic substances, ammonia, hydrazine, and the like. In the present invention, the present invention can be applied to wastewater containing at least one of these organic substances, ammonia, and hydrazine to obtain a preferable effect. Can do. The concentration of these oxidizable substances in the wastewater is not particularly limited, and can be preferably applied to wastewater containing oxidizable substances in various concentrations.
[0008]
On the other hand, the electrolyte substance may be any kind, but is generally an inorganic compound, and for example, NaCl, H 2 SO 4 , Na 2 SO 4 and the like are preferable, and these may be used alone. And it may be two or more by an appropriate combination.
The concentration of these electrolyte substances in the waste water is not particularly limited, and may be about 50 to 50,000 mg / L required for conventional electrolytic treatment, or 6,000 mg, which is extremely inefficient in conventional electrolytic treatment. Even if it is less than / L, it can be processed efficiently.
That is, the electrolyte material that has the effect of increasing the current efficiency during the electrolysis treatment requires a concentration of 6,000 mg / L or more in the conventional method using a platinum-based electrode supported on an iridium oxide surface. In the present invention using the conductive diamond electrode capable of obtaining the effect of improving current efficiency, a sufficient treatment effect can be obtained even in a low concentration region of less than 6,000 mg / L.
However, even in the present invention using a conductive diamond electrode, if the concentration of the electrolyte substance is too low, it may not be possible to obtain sufficient current efficiency to electrolyze the oxidizable substance in the waste water. Therefore, the preferable concentration of the electrolyte substance in the present invention is about 500 to 6,000 mg / L with respect to the waste water.
[0009]
The electrolyte substance may be contained in the oxidizable substance-containing waste water, and when the electrolyte substance concentration can be secured only by the contained electrolyte substance, it is not necessary to add an electrolyte substance separately. .
If the above electrolyte substance concentration cannot be ensured only by the contained electrolyte substance, an amount of the electrolyte substance that can ensure the above electrolyte substance is introduced prior to the treatment of the present invention.
[0010]
The conductive diamond electrode used in the present invention has a conductive metal material such as Ni, Ta, Ti, Mo, W, Zr or the like as a substrate, and a conductive diamond thin film is deposited on the surface of the substrate, or a silicon wafer. Examples thereof include a semiconductor material such as a substrate and a conductive diamond thin film synthesized on the wafer surface, or a conductive polycrystalline diamond material deposited and synthesized in the form of a plate under the condition that the substrate is not used.
In addition, the conductive (polycrystalline) diamond thin film is obtained by doping a predetermined amount of boron or nitrogen during the preparation of the diamond thin film and imparting conductivity, and generally doped with boron.
If the doping amount is too small, the technical significance of doping will not be manifested. If the doping amount is too large, the doping effect will be saturated, so that the doping within the range of 50 to 10,000 ppm with respect to the carbon content of the diamond thin film material is suitable. ing.
[0011]
In the present invention, the conductive diamond electrode is generally a plate-like one, but it is also possible to use a plate having a network structure.
[0012]
In the electrolysis treatment using this conductive diamond electrode, the current density on the surface of the conductive diamond electrode is 10 to 100,000 A / m 2, and the waste water containing the oxidizable substance and the electrolyte substance is discharged into the conductive diamond electrode. In parallel with the surface, it is preferable that the liquid is passed at a liquid flow velocity (LV) of 10 to 1,000 m / hr and brought into contact with the electrode surface.
[0013]
If the current density is less than the above, even if a conductive diamond electrode with good current efficiency is used, it is necessary to increase the necessary electrode area for sufficient electrolysis treatment of the oxidizable substance in the waste water, Large-capacity wastewater treatment with a compact apparatus, which is one of the objects of the present invention, cannot be achieved.
On the other hand, if the above is exceeded, the resistance between the electrodes increases and is consumed by heat energy, which is uneconomical.
[0014]
In addition, the drainage flow direction is made parallel to the electrode surface in order to increase the contact efficiency between the drainage and the electrode surface. In this direction, there is a gas component such as carbon dioxide in the electrolytic reaction tank. Even if it does, it is because contact inhibition with the waste_water | drain by this gas and an electrode surface can be relieved to some extent.
At this time, the drainage flow rate is set to 10 to 1,000 m / hr in terms of linear velocity (LV). If the drainage flow rate is too slower than this, the gas component can be used even if the drainage flow direction is parallel to the electrode surface. The effect of alleviating the contact inhibition between the drainage and the electrode surface due to water is not obtained, and if it is too fast, the contact time between the drainage and the electrode surface cannot be taken sufficiently, and the oxidizable substance is sufficiently electrolyzed. Can no longer progress.
[0015]
The temperature in the electrolytic reaction tank is not particularly limited, but if the temperature is too low, the electrolysis of the wastewater does not proceed well.On the other hand, if the temperature is too high, vaporization occurs and the generation of gas components increases. Not only the contact inhibition with the electrode surface is increased, but also in the low concentration region as described above, there is a concern of corrosion of the device constituent material by the electrolyte substance. It is desirable.
[0016]
In the treatment method of the present invention, the electrolysis treatment under the above conditions is performed in a plurality of electrolytic reaction tanks arranged in series, but gas components such as carbon dioxide gas and nitrogen gas generated by this electrolysis treatment are removed. In order to achieve this, gas-liquid separation is performed on the treated water in each electrolytic reaction tank excluding the final stage electrolytic reaction tank.
This gas-liquid separation may be performed using a normal gas-liquid separation device as it is, or a gas phase part (space part) is provided above and a gas vent part (gas vent pipe, gas vent port, etc.) at the top. May be carried out using a liquid receiving tank provided with a gas phase part above the electrolytic reaction tank itself or a gas vent part at the top.
That is, since bubbles in water easily float and move to the gas phase, gas components such as carbon dioxide gas and nitrogen gas generated by the electrolysis process form a gas phase portion on the upper side and a lower liquid layer portion. And easily separated. Therefore, the gas component produced | generated by an electrolysis process can be easily isolate | separated from processed water also using the receiving tank and electrolytic reaction tank provided with the above gas venting parts and a gaseous-phase part.
[0017]
The treated water after the gas-liquid separation as described above is sent to the subsequent electrolytic reaction tank and subjected to the next electrolysis treatment.
[0018]
The degree of removal of the gas component in the gas-liquid separation is not particularly limited, but to the extent that the electrolysis treatment in the subsequent electrolytic reaction tank can obtain a desired electrolysis efficiency, generally in the previous electrolytic reaction tank. What is necessary is just about 30 to 90% of the gas component which exists in treated water, Preferably it is about 50 to 90%.
That is, when a conductive diamond electrode is used, if the concentration of the gas component in the electrolysis target liquid (drainage) is about 0 to 10%, contact inhibition between the electrode surface and the drainage due to the gas component, and thus the interelectrode resistance The increase can be suppressed, and an electrolysis efficiency close to a desired electrolysis efficiency can be obtained.
In order to secure this gas component concentration, it is desirable to set the gas component removal rate to the above level.
[0019]
It is desirable to perform gas-liquid separation between each electrolytic reaction tank or in each electrolytic reaction tank except the final stage, but is not limited to this, and in the waste water subject to electrolysis (that is, treated water in the previous electrolytic reaction tank) If the gas component is within the above-mentioned concentration range, it is not necessary to perform gas-liquid separation. Therefore, the gas component concentration may be performed for the electrolytic reactor effluent exceeding the upper limit.
This electrolytic reaction tank treated water has a large amount of oxidizable substances, and therefore, the first stage electrolytic reaction tank in which a large amount of gas components are generated by oxidative decomposition, or the oxidative decomposition of oxidizable substances proceeds. The treated water in the second and third stage electrolytic reaction tanks in which the amount of components generated increases is mainly used.
For this reason, in the present invention, when the gas-liquid separation is performed on the treated water in at least one electrolytic reaction tank, specifically, the treated water having the above-mentioned concentration that prevents the concentration of the gas component from contacting the drainage and the electrode, Good.
[0020]
FIG. 1A is a flowchart for explaining an embodiment of the waste water treatment apparatus according to the present invention. In the figure, two electrolytic reaction tanks 3 and 6 are arranged in series, and these 2 A normal gas-liquid separator 4 is provided between the two electrolytic reaction tanks 3 and 6.
These electrolytic reaction tanks 3 and 6 are rectangular parallelepiped tanks as shown in the schematic diagram of FIG. 1B, and are provided with conductive diamond electrodes 11 and 11 on opposite side wall surfaces, and drainage is introduced into the lower part. A treated water outlet tube 13 is provided at the upper portion of the tube 12.
[0021]
In the wastewater treatment apparatus configured as described above, the wastewater to be treated according to the present invention is temporarily stored in the raw wastewater storage tank 1, which is fed by the pump 2, and the drainage introduction pipe is supplied to the first-stage electrolytic reaction tank 3. 12 is introduced.
The waste water introduced into the first electrolytic reaction tank 3 is transferred from the lower part to the upper part as shown by a double arrow in FIG. Electrolysis is performed in parallel with the surface of the substrate.
[0022]
The treated water in the first electrolytic reaction tank 3 thus electrolyzed rises in the tank 3 with a gas component such as carbon dioxide generated during the electrolysis treatment, and has been treated. Overflow from the water outlet pipe 13 is introduced into the gas-liquid separator 4.
The gas component separated by this device 4 is extracted from the gas vent 4 'to the outside of the system, and the separated water is separated from the gas-liquid separation device 4 in this example as shown in FIG. The pump 5 is extracted from the outlet pipe that opens at the bottom.
[0023]
This extracted water is introduced from the drainage introduction pipe 12 into the second stage electrolytic reaction tank 6 configured in the same manner as the first electrolytic reaction tank 3 and is the same as the first electrolytic reaction tank 3. It is electrolyzed.
In the second electrolytic reaction tank 6, the wastewater introduced from the wastewater introduction pipe 12 contains almost no gas component, so that the wastewater and the surface of the diamond electrode are in good contact with each other, and high efficiency is achieved. The electrolysis process is carried out.
[0024]
Thus, the treated water electrolyzed in the second electrolytic reaction tank 6 rises in the second electrolytic reaction tank 6 as in the case of the first electrolytic reaction tank 3, and the tank 6 overflows from the treated water outlet pipe 13 provided in the upper part of 6 and is stored in the treated water storage tank 7.
[0025]
Moreover, it may replace with the gas-liquid separation apparatus 4 of FIG. 1 (A), and you may use the receiving tank 41 of simple processed water as shown in FIG.
The receiving tank 41 has a liquid phase part 41L in the lower part thereof, a gas phase part 41G in the upper part, a gas vent part 41 'provided at the top part, and a treatment in the first electrolytic reaction tank 3 at the top part. An outlet side end of the finished water outlet pipe 13 is opened and opened near the lower portion of the liquid phase portion 41L, and a separation water outlet pipe 42 is provided.
[0026]
In the case of the receiving tank 41 configured in this way, treated water in the first electrolytic reaction tank 3 is introduced from the opening of the outlet pipe 13 and stored in the liquid phase part 41L.
During the storage in the liquid phase part 41L, the gas component rises, accumulates in the gas phase part 41G, and is extracted out of the system from the gas vent part 41 ′.
Since the rising of the gas component from the liquid phase part 41L to the gas phase part 41G is performed in a short time of several minutes to several tens of minutes, the receiving phase 41 should have a volume that can take such a residence time. It is enough.
If the treated water in the first electrolytic reaction tank 3 is dropped (dropped) from the opening of the outlet pipe 13 into the liquid phase portion 41L, the water in the water is also dropped. Since the gas component is separated, the gas-liquid separation time can be further shortened.
[0027]
The separated water thus separated into gas and liquid in the receiving tank 41 is extracted from the outlet pipe 42 by the pump 5 shown in FIG. 1 (A), sent to the second electrolytic reaction tank 6, and the latter stage Subjected to electrolysis.
[0028]
FIG. 3 shows the first electrolytic reaction tank 3 itself provided with gas-liquid separation means (function). In this example, the lower part of the electrolytic reaction tank 3 is a liquid phase portion 31L as shown in the figure. The upper part is a gas phase part 31G, and a gas vent part 31 'is provided at the top.
In this liquid phase portion 31L, conductive diamond electrodes 11 and 11 are provided on opposite side wall surfaces, a drainage introduction pipe 12 is provided in the lower part, and a treated water outlet pipe 13 is provided in the upper part.
[0029]
In this example, the gas component generated in the electrolysis process floats in the liquid phase part 31L during the electrolysis process, accumulates in the gas phase part 31G, and is extracted out of the system from the gas vent part 31 '.
Since the rising of the gas component from the liquid phase part 31L to the gas phase part 31G is performed in a short time of several minutes to several tens of minutes, sufficient gas-liquid separation is performed during the electrolysis process of the waste water. Become.
[0030]
In this way, the separated water that has been gas-liquid separated simultaneously with the electrolysis while the liquid phase portion 31L is rising in the first electrolytic reaction tank 31 is extracted from the outlet pipe 13 by the pump 5, and the second It is sent to the electrolytic reaction tank 6 and subjected to electrolysis with high efficiency in the absence of gas components.
[0031]
【Example】
Example 1
Two laminated polycrystalline diamond electrode plates (2 cm × 2 cm × 0.05 cm) synthesized by vapor deposition using a boron doping method have an inner size of 2 cm × 2 cm × 0.4 cm so that the distance between the electrodes is 3 mm. It installed in the glass container and it was set as the electrolytic reaction tank.
Using two electrolytic reaction tanks of this configuration, a processing apparatus was set up with a flow similar to the flow shown in FIG.
That is, the 1st electrolytic reaction tank 3 and the 2nd electrolytic reaction tank 6 of the said structure are arrange | positioned in series, and the treated water receiving tank 41 (capacity 500 mL of a structure shown in FIG. ) Was installed.
[0032]
A synthetic wastewater (COD concentration 120 mg / L) containing 50 mg / L of phenol and 14 g / L of Na 2 SO 4 was passed through this processing apparatus at a flow rate of 2 L / hr, and the first electrolytic reaction tank 3 → It processed in order of the processed water receiving tank 41-> 2nd electrolytic reaction tank 6. FIG.
The amount of electricity charged into the first and second electrolytic reaction tanks 3 and 6 was set so that the current density was 0.05 A / cm 2 in both tanks 3 and 6.
[0033]
The effluent water from the second electrolytic reaction tank 6 after 3 hours had passed since the start of liquid passage had a COD concentration of 1.9 mg / L.
Further, as a result of continuous treatment for 2 weeks under the same conditions as described above, it was confirmed that a stable treatment effect could be sustained.
The results of the electrolytic treatment are summarized as shown in Table 1.
[0034]
[Table 1]
Figure 0003988477
[0035]
Example 2
The first electrolytic reaction tank 3 of Example 1 is replaced with the first electrolytic reaction tank 3 having the configuration shown in FIG. 3, and the treatment apparatus of the aspect shown in FIG. 3 is set without using the treated water receiving tank 41. did.
That is, two polycrystalline diamond electrode plates (2 cm × 2 cm × 0.05 cm) identical to those in Example 1 were placed in a glass container having an inner dimension of 2 cm × 3 cm × 0.4 cm so that the distance between the electrodes was 3 mm. The lower part of the container was the liquid phase part 31L, and the upper part was the gas phase part 31G. In addition, the 2nd electrolytic reaction tank 6 used the thing of the same structure as Example 1. FIG.
[0036]
The same synthetic wastewater (COD concentration 120 mg / L) as in Example 1 is passed through this treatment apparatus at the same liquid flow rate and charged electricity as in Example 1, and the first electrolytic reaction tank 31 → second electrolytic reaction. It processed in the order of the tank 6. FIG.
The effluent water from the second electrolytic reaction tank 6 after 3 hours had passed since the start of liquid passage had a COD concentration of 1.9 mg / L.
Further, as a result of continuous treatment for 2 weeks under the same conditions as described above, it was confirmed that a stable treatment effect could be sustained.
The results of the electrolytic treatment are summarized as shown in Table 2.
[0037]
[Table 2]
Figure 0003988477
[0038]
Comparative Example 1
In the same manner as in Example 1, two laminated polycrystalline diamond electrode plates (2 cm × 4 cm × 0.05 cm) synthesized by vapor deposition using the boron dope method were used, and the inner dimension was 2 cm × 2 so that the distance between the electrodes was 3 mm. It installed in the glass container of 4 cm x 0.4 cm, and was set as the electrolytic reaction tank.
The cross-sectional area and total electrode area of this one electrolytic reaction tank are the same as the total cross-sectional area and total electrode area of the first and second electrolytic reaction tanks of Example 1.
The amount of electricity input to the electrolytic reaction tank was also set to the same current density of 0.05 A / cm 2 as in Example 1.
[0039]
The same synthetic wastewater (COD concentration 120 mg / L) as in Example 1 was passed through this processing apparatus at the same liquid passing speed as in Example 1 for processing.
The COD concentration of the effluent from the electrolytic reaction tank after 3 hours had elapsed after the start of liquid passage was 17.8 mg / L.
The results of the electrolytic treatment are summarized as shown in Table 3.
[0040]
[Table 3]
Figure 0003988477
[0041]
【The invention's effect】
As described above, according to the present invention, during the electrolysis treatment, gas components such as carbon dioxide generated by the oxidative decomposition reaction of the oxidizable substance are removed before the waste water treatment in the subsequent electrolytic reaction tank. Therefore, the contact inhibition between the drainage due to the gas component and the electrode surface is eliminated, and there is no increase in interelectrode resistance, decrease in electrolysis efficiency, etc., and an extremely high efficiency electrolysis process can be performed.
[0042]
In addition, according to the present invention, since a conductive diamond electrode with high current efficiency is used as an electrode in the electrolysis process, the concentration of the electrolyte substance present in the waste water to be treated is set to a conventional electrolyte substance (chloride ion). The concentration can be significantly reduced.
For this reason, not only the processing cost is reduced, but also the problem of trouble due to corrosion of the device constituent material by the electrolyte substance can be solved.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram for explaining an embodiment of a treatment apparatus according to the present invention, in which (A) shows a flow of drainage, and (B) shows aspects of first and second electrolytic reaction tanks. It is a figure shown typically.
FIG. 2 is a diagram for explaining another embodiment of the processing apparatus according to the present invention.
FIG. 3 is a diagram for explaining still another embodiment of the processing apparatus according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Raw water storage tank 2, 5 Pump 3,31 1st electrolytic reaction tank 4,41 Gas-liquid separation means 6 2nd electrolytic reaction tank 7 Treated water storage tank 11 Conductive diamond electrode

Claims (4)

被酸化性物質と電解質物質を含む排水を、導電性ダイヤモンド電極を用いた複数の電解反応槽で電解処理し、少なくとも１の電解反応槽の処理済水を気液分離した後、後段の電解反応槽に通液処理することを特徴とする排水の処理方法。The waste water containing the oxidizable substance and the electrolyte substance is subjected to electrolytic treatment in a plurality of electrolytic reaction tanks using conductive diamond electrodes, and the treated water in at least one electrolytic reaction tank is gas-liquid separated, and then the subsequent electrolytic reaction A method for treating waste water, wherein the treatment is conducted through a tank. 導電性ダイヤモンド電極を用いて行う電気分解は、導電性ダイヤモンド電極表面の電流密度を１０〜１００，０００Ａ／ｍ２とし、排水の通液方向を導電性ダイヤモンド電極面と平行とし、その通液線速度を１０〜１，０００ｍ／ｈｒとすることを特徴とする請求項１記載の排水の処理方法。The electrolysis performed using the conductive diamond electrode is such that the current density on the surface of the conductive diamond electrode is 10 to 100,000 A / m 2 , the direction of drainage is parallel to the surface of the conductive diamond electrode, The wastewater treatment method according to claim 1, wherein the speed is set to 10 to 1,000 m / hr. 導電性ダイヤモンド電極を用いた電解反応槽の複数を直列に配置し、
これら複数の電解反応槽間の少なくとも１箇所、または少なくとも１の電解反応槽に、気液分離手段を設けてなることを特徴とする排水の処理装置。A plurality of electrolytic reaction tanks using conductive diamond electrodes are arranged in series,
A wastewater treatment apparatus comprising gas-liquid separation means in at least one place between the plurality of electrolytic reaction tanks or at least one electrolytic reaction tank. 気液分離手段を、各電解反応槽間または最終段の電解反応槽を除く各電解反応槽に設けることを特徴とする請求項３記載の排水の処理装置。4. The wastewater treatment apparatus according to claim 3, wherein the gas-liquid separation means is provided between the electrolytic reaction tanks or in each electrolytic reaction tank excluding the final stage electrolytic reaction tank.
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