JP2004351280A

JP2004351280A - Contaminated water purification method

Info

Publication number: JP2004351280A
Application number: JP2003150053A
Authority: JP
Inventors: Miki Masuda; 幹増田; Masao Wakabayashi; 正男若林; Ryozo Ushio; 亮三牛尾
Original assignee: Sumitomo Metal Mining Co Ltd
Current assignee: Sumitomo Metal Mining Co Ltd
Priority date: 2003-05-28
Filing date: 2003-05-28
Publication date: 2004-12-16
Anticipated expiration: 2023-05-28
Also published as: JP3997949B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a contaminated water purification method which enables a suppression of the formation of by-products while keeping the rate of pollutants removed in decomposing and removing harmful pollutants from contaminated water by using ozone and ultraviolet rays. <P>SOLUTION: The contaminated water purification method is provided with gas/liquid mixers 5a and 5b mixing ozone with the contaminated water, ultraviolet irradiators 6a and 6b that irradiate polluted water mixed with ozone with ultraviolet rays to decompose contaminants, and gas/liquid separation steps 7a and 7b that separate remaining gas from the contaminated water subjected to the ultraviolet irradiation. A unit comprising each gas/liquid mixer 5a or 5b and each ultraviolet irradiator 6a or 6b is repeated in a plurality of stages, and the dose of ultraviolet irradiation in relation to the ozone injection rate in each stage is increased stepwise according to the progress of treatment. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、有害な汚染物質で汚染された地下水などの汚染水から汚染物質を分解除去して浄化する方法に関する。
【０００２】
【従来の技術】
近年、地下水などの汚染が問題になっているが、その原因となる主な汚染物質としては、トリクロロエチレン、テトラクロロエチレン、１，２−ジクロロエタン、１，１−ジクロロエチレン、１，２−ジクロロエチレン、１，１，１−トリクロロエタン、１，１，２−トリクロロエタン、ジクロロメタン、パラジクロロベンゼン、１，２−ジクロロプロパン、クロロホルム、ベンゼン、トルエン、キシレン、四塩化炭素、ホルムアルデヒドなどの揮発性有機化合物が挙げられる。
【０００３】
上記した有機塩素化合物などの揮発性の汚染物質を含む土壌を修復する方法として、いわゆる揚水曝気法が一般に広く行われている。この揚水曝気法は、揮発性汚染物質を含んだ地下水をポンプで揚水し、これに空気を効率よく接触させて揮発性汚染物質を気相に移行させることにより、汚染された地下水を浄化して土壌に戻す方法である。
【０００４】
しかし、このような揚水曝気法では、揮発性の汚染物質しか処理することができない。また、揚水曝気法は、汚染物質を分解して無害化する技術ではないため、揮発性汚染物質を含む気相の後処理が必要である。この気相の後処理としては、一般的に気相中の汚染物質を活性炭に吸着させて除去する方法がとられているが、活性炭は破過する前に新品と交換する必要があるため、交換する活性炭の費用に加え、その作業のための労務コストがかかり、交換頻度が高くなるほど費用が増大するという問題がある。
【０００５】
なお、曝気装置を出た気体中に含まれる揮発性汚染物質を化学的に分解処理する場合もあるが、有毒な副生物や酸性ガスが発生するため、その処理装置などが更に必要になるという問題がある。しかも、このような化学的分解処理では全体として装置が大型化し、設備費を含めた浄化コストが高くなることが多いため、上記した活性炭で吸着除去する方式を採用する場合が多い。
【０００６】
一方、汚染水中の汚染物質を水相中にて除去する方法として、促進酸化処理法がある。この促進酸化処理方法は、オゾン、過酸化水素、紫外線などを併用し、酸化力が強いヒドロキシルラジカルを生成させて、汚染水中の有害な汚染物質を分解除去する方法であり、特にオゾンと紫外線を組み合わせた方法はよく知られている。
【０００７】
オゾンは水への溶解度が高くなく、またオゾン発生器によって生成させるオゾン濃度にも上限があるため、オゾンの溶解効率を高める目的や必要なオゾン注入率を確保する目的で、オゾン注入を数段に分けて多段で溶解・混合することが行われている。例えば、特開平９−３８６７２号公報及び特開平１０−９９８７７号公報には、加圧型下方注入式多段オゾン接触槽を用いることで、処理水（汚染水）に対するオゾンガスの吸収効率を高め、その後処理水に紫外線を照射して有機物を分解する方法が提案されている。
【０００８】
しかしながら、このようにオゾン注入を数段に分けて多段で溶解・混合する場合、最後に行う紫外線照射において、処理水中に高濃度で存在するオゾンを反応させるだけの紫外線量を照射する必要があるが、一度に照射される紫外線量が多いと紫外線による光分解が進行し、副生物であるジクロロ酢酸などのハロ酢酸が増加してしまうという問題があった。
【０００９】
【特許文献１】
特開平９−３８６７２号公報
【特許文献２】
特開平１０−９９８７７号公報
【００１０】
【発明が解決しようとする課題】
本発明は、このような従来の問題点に鑑みてなされたものであり、汚染水中の有害な汚染物質濃度や溶存オゾン濃度に応じた最適な紫外線照射を行うことで、汚染物質の除去率を維持しながら、同時に副生物の生成を抑えることができる汚染水の浄化方法を提供することを目的とする。
【００１１】
【課題を解決するための手段】
上記目的を達成するため、本発明が提供する汚染水の浄化方法は、汚染水にオゾンを混合する気液混合工程と、オゾンを混合した汚染水に紫外線を照射して汚染物質を分解する紫外線照射工程と、紫外線照射を受けた汚染水中に残存する気体を分離する気液分離工程とを備える汚染水の浄化方法であって、前記気液混合工程と紫外線照射工程のユニットを複数段に繰り返すと共に、各段でのオゾン注入率に対する紫外線照射量を処理の進行に合わせて段階的に増加させることを特徴とする。
【００１２】
【発明の実施の形態】
本発明の汚染水の浄化方法では、汚染水にオゾンを混合する気液混合工程と、オゾンを混合した汚染水に紫外線を照射して汚染物質を分解する紫外線照射工程とを一つのユニットとして、２段以上の複数段に分けて繰り返す。例えば、２段の処理の場合には、最初の第１段の気液混合工程と紫外線照射工程の後に、最終の第２段の気液混合工程と紫外線照射工程を直列に組み合わせて処理を行う。
【００１３】
このような多段処理は、例えば有害な汚染物質が高濃度に含まれる汚染水を処理する場合において、十分に汚染物質を分解除去するために有効な手段である。即ち、オゾン発生装置で生成するオゾンガス濃度には制限があり、且つ汚染水とオゾンガスの混合比率にも上限が存在する一方、単段処理では汚染水１リットル当たりのオゾン注入量に限界があるため、有害な汚染物質が高濃度に存在する場合には、１段のみでのオゾン注入では必要なオゾン注入量を確保することができないためである。
【００１４】
このような多段処理では、従来から一般的に、各段でのオゾン注入率と紫外線照射量を全て同じにしている。しかしながら、その場合には、汚染水中の汚染物質の濃度が高い前段ほどジクロロ酢酸などの副生物が生成しやすく、全体としても副生物の生成量が多くなるため、後工程でこの副生物を処理することが大きな負担となる。
【００１５】
そこで、本発明方法においては、各段でのオゾン注入率に対する紫外線照射量を処理の進行に合わせて段階的に増加させることにより、全体として副生物の生成を抑えながら、同時に高い除去率で汚染物質の分解除去を行うことができる。例えば、気液混合工程と紫外線照射工程のユニットを２段としたとき、最初の第１段でのオゾン注入率に対する紫外線照射量を、最終の第２段でのオゾン注入率に対する紫外線照射量の０．４〜０．６倍とするが好ましい。これにより、各段でのオゾン注入率と紫外線照射量が全て同じ場合に比較して、汚染物質の除去率を維持しながら、同時に副生物の生成を大幅に抑えることができる。
【００１６】
次に、本発明方法を図面に基づいて説明する。図１は、本発明の汚染水の浄化方法に用いる浄化装置の一具体例を示す概略の工程図である。この浄化装置は、土壌中の汚染された地下水、即ち汚染水を揚水するために、地盤中に固定された多孔管１の底部近くまで設けられた揚水管２と、この揚水管２に接続され、汚染水を地表面上に汲み上げる揚水ポンプ３と、揚水ポンプ３で汲み上げられた汚染水を一旦貯留する原水槽４とを備えている。
【００１７】
尚、多孔管１は土壌中に掘削された井戸穴に挿入固定されるものであって、例えば直径１００〜１５０ｍｍ程度のポリ塩化ビニル管からなり、地下水面の上方から下端にかけて多数の開孔が設けられている。そして、揚水管２は多孔管１の上端付近から貫入され、多孔管１の下端付近に至るまで挿入されており、この揚水管２の下流側には揚水ポンプ３が取り付けられ、地下水を地表面上に汲み上げることが可能になっている。
【００１８】
この図１の浄化装置では、気液混合装置５ａ、５ｂ、紫外線照射装置６ａ、６ｂ、及び気液分離槽７ａ、７ｂを１ユニットとし、このユニットが２つ直列に接続してある。原水槽４の汚染水は、送水管を通して２段に構成した気液混合装置５ａ、５ｂ及び紫外線照射装置６ａ、６ｂに順次導入され、気液混合装置５ａ、５ｂではオゾンガス発生装置８で生成させたオゾンガスが汚染水に溶解され、紫外線照射装置６ａ、６ｂではオゾンが溶解した汚染水に紫外線が照射される。
【００１９】
気液混合装置５ａ、５ｂでのオゾン混合方式としては、例えば、散気管方式、ノズルから噴出させるエジェクター方式、渦流ポンプを用いて水中にオゾンを混合させるターボミキシング方式などが考えられるが、混合効率の高いエジェクター方式やターボミキシング方式が望ましい。
【００２０】
オゾンガス発生装置８に要求されるオゾン発生能力は、汚染水中の汚染物質の濃度や処理の構成によって異なるが、汚染物質濃度が数十ｍｇ／リットル以上の場合は８０ｇ／Ｎｍ^３以上のオゾンガスを生成する装置を用いることが好ましい。尚、オゾンガス発生装置８は、原料として酸素ガスを用いるのが好ましい。しかし、酸素ボンベを使用すると交換などの保守に関わる手間が加わるため、圧力スイッチング吸着法（ＰＳＡ）などにより酸素を生成させる装置のような原料ガス発生装置９を備えるものが望ましい。
【００２１】
紫外線照射装置６ａ、６ｂの紫外線照射方法には、内部照射型と外部照射型の２種類がある。内部照射型は２重構造をとり、外壁の内部に透過性保護管に収納された紫外線ランプが配置され、外壁と透過性保護管の間に処理すべき汚染水が流れる構造となっている。一方、外部照射型では、汚染水が流れる透過性保護管の外周に紫外線ランプが配置されている。透過性保護管は紫外線透過性の高い材料からなり、例えば、石英、透明フッ素樹脂などが用いられる。また、紫外線ランプは、ピーク波長が１８５±１０ｎｍ、２５４±１０ｎｍの紫外線を照射するものが利用できるが、オゾンのラジカル化に有効に作用すると共に、設置コストが低くて消費電力の少ない、２５４±１０ｎｍのピーク波長を持つ低圧水銀ランプを用いることが望ましい。
【００２２】
この紫外線照射により、汚染水中に溶解したオゾンからヒドロキシルラジカル等の活性なラジカルが生成され、汚染水中の汚染物質が分解される。このとき、オゾン注入率に対する紫外線照射量を、処理の進行に合わせて段階的に増加させる。その理由は、汚染水中の汚染物質濃度が高いほど、紫外線との反応によりジクロロ酢酸などの副生物が生成しやすくなるため、汚染物質濃度の高い前段ほど紫外線照射量を少なくすることで、副生物の生成を抑えることができるからである。
【００２３】
また、照射した紫外線は汚染物質にも吸収されるため、同じ紫外線照射量では、処理水中の汚染物質濃度が高いほど未反応の残存オゾン量が増加することが分った。例えば、図１に示す浄化装置の第１段（気液混合装置５ａと紫外線照射装置６ａ）だけを用い、テトラクロロエチレン（ＰＣＥ）の初期濃度の異なる汚染水の処理を行い、処理後の液中に溶存して残った残存オゾン濃度を測定した結果を図２に示す。この図２から分るように、汚染水中のテトラクロロエチレン濃度が高いほど、処理後の残存オゾン濃度が増加している。
【００２４】
従って、図２から分るように、気液混合装置と紫外線照射装置のユニットを複数段に配置した場合、各段での紫外線照射後における残存オゾンが次第に蓄積され、後段にいくほど紫外線照射装置導入前の汚染水中に溶存しているオゾン量が増加する傾向にある。このため、処理の進行に伴って増加する溶存オゾン量に合わせて、後段ほど紫外線照射量を増やすことによって、十分な量の活性ラジカルが生成され、汚染物質の分解効率を高めることができる。
【００２５】
照射する紫外線照射量は、分解対象汚染物質の分解特性、汚染水のｐＨ、オゾン注入率などに依存する。また、各段での紫外線照射量は、上記のごとく処理の進行に従って（段数が増えるに伴って）増加するように設定する。具体的には、汚染水中の汚染物質の種類と濃度などに応じて、最終的に汚染物質を所望の濃度まで分解除去できる最終段での紫外線照射量を定め、この最終段に対して前の段ほど紫外線照射量を少なくすればよい。
【００２６】
例えば、汚染物質がオゾンによる分解特性が低いテトラクロロエチレン単独で、汚染水のｐＨが８、各段でのオゾン注入率が２０ｍｇ／ｌの場合、多段処理の最終段での汚染水１リットル当たりの紫外線照射量を０．０２〜０．０３Ｗｈ／ｌとし、前の段に行くほど照射量を低下させ、最初の段では最終段の半分程度の照射量にすることが望ましい。また、オゾンによる分解特性が高いトリクロロエチレン単独で上記と同じオゾン注入率の場合には、最終段での汚染水１リットル当たりの紫外線照射量を０．０１〜０．０２Ｗｈ／ｌとし、前の段に行くほど低下させ、最初の段では最終段の半分程度の照射量にすることが望ましい。
【００２７】
紫外線照射後の汚染水は、紫外線照射装置６ａ、６ｂから送水管を介して気液分離装置７ａ、７ｂに導入される。この気液分離装置７ａ、７ｂにおいて、処理後の汚染水中に混入している未溶解の気体や残存しているオゾンなどが気相に移行する。なお、気液分離装置としては大気下に開放する方式が最も簡単であるが、この場合には処理した汚染水を一定時間滞留させることが好ましい。
【００２８】
このようにして処理された汚染水は、気液分離装置７ａ、７ｂからそのまま系外に排水するか、吸着剤などで２次処理した後に系外に排水される。また、気液分離装置７ａ、７ｂからの排ガスは、排オゾン処理装置１０ａ、１０ｂなどで処理した後、大気に放出される。
【００２９】
【実施例】
図１に示す気液混合装置５ａ、５ｂと紫外線照射装置６ａ、６ｂを直列に２段に配置した浄化装置を使用して、汚染物質としてテトラクロロエチレン２０ｍｇ／ｌを含有する汚染水（ＰＣＥ排水）、及びテトラクロロエチレン２０ｍｇ／ｌとトリクロロエチレン１０ｍｇ／ｌを含有する汚染水（ＶＯＣ排水）を、それぞれ処理する試験を行った。
【００３０】
その際、第１段（気液混合装置５ａと紫外線照射装置６ａ）及び第２段（気液混合装置５ｂと紫外線照射装置６ｂ）における紫外線照射量を、それぞれ下記表１に示すように設定した。その他の試験条件として、処理水量は１．２ｍ^３／ｈ、オゾンガス発生濃度は１００ｇ／Ｎｍ^３、及び全体のオゾン注入率は２０ｍｇ／ｌ（１段当たり１０ｍｇ／ｌ）とした。
【００３１】
この処理試験における汚染物質の除去率を下記表１に合わせて示すと共に、処理後の汚染水中に生成した副生物であるハロ酢酸（ジクロロ酢酸、トリクロロ酢酸）の濃度と生成率を下記表２に示した。
【００３２】
【表１】

【００３３】
【表２】

【００３４】
上記表１及び表２における試料１〜３と試料５の比較、及び試料７と試料８の比較から分るように、第１段の紫外線照射量を第２段（最終段）の０．４〜０．６倍の範囲とすることで、汚染物質である有機塩素化合物の除去率を維持しながら、ハロ酢酸の生成率を低下させることができる。また、試料１〜３と試料４の比較から、第１段の紫外線照射量を第２段（最終段）の０．４倍よりも更に低くすると、汚染物質である有機塩素化合物の除去率が大きく低下してしまうことが分る。
【００３５】
更に、試料６と試料１〜３との比較から、第２段の紫外線照射量を第１段よりも低下させた試料６の条件では、副生物であるハロ酢酸の生成率低下の割合が小さくなるだけでなく、汚染物質である有機塩素化合物の除去率も低下することが分る。
【００３６】
【発明の効果】
本発明によれば、高濃度の汚染物質を含む汚染水であっても、少ない紫外線照射量で、汚染物質の除去率を低下させずに、副生物の生成量を抑制しながら、汚染物質を分解除去して汚染水を浄化することができる。
【図面の簡単な説明】
【図１】本発明の汚染水の浄化方法に用いる浄化装置の一具体例を示す概略の工程図である。
【図２】汚染水中のポリクロロエチレン初期濃度と処理後の汚染水中の残存Ｏ_３濃度との関係を示すグラフである。
【符号の説明】
１多孔管
２揚水管
３揚水ポンプ
４原水槽
５ａ、５ｂ気液混合ポンプ
６ａ、６ｂ紫外線照射装置
７ａ、７ｂ気液分離装置
８オゾンガス発生装置
９原料ガス発生装置[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method of purifying decomposed substances by removing pollutants from contaminated water such as groundwater contaminated with harmful pollutants.
[0002]
[Prior art]
In recent years, pollution of groundwater and the like has become a problem, and as main pollutants causing the pollution, trichloroethylene, tetrachloroethylene, 1,2-dichloroethane, 1,1-dichloroethylene, 1,2-dichloroethylene, 1,1 , 1-trichloroethane, 1,1,2-trichloroethane, dichloromethane, paradichlorobenzene, 1,2-dichloropropane, chloroform, benzene, toluene, xylene, carbon tetrachloride, and volatile organic compounds such as formaldehyde.
[0003]
As a method for repairing soil containing volatile pollutants such as the above-mentioned organic chlorine compounds, a so-called pumping aeration method is generally widely used. This pumping and aeration method purifies contaminated groundwater by pumping groundwater containing volatile pollutants and bringing air into efficient contact with this to transfer the volatile pollutants to the gas phase. It is a method of returning to the soil.
[0004]
However, such a pumping aeration method can only treat volatile pollutants. Moreover, since the pumping aeration method is not a technique for decomposing pollutants to make them harmless, post-treatment of a gas phase containing volatile pollutants is necessary. As the post-treatment of the gas phase, a method is generally adopted in which contaminants in the gas phase are adsorbed and removed by activated carbon, but since activated carbon needs to be replaced with a new one before breakthrough, In addition to the cost of the activated carbon to be replaced, labor costs for the operation are required, and the higher the replacement frequency, the higher the cost.
[0005]
In some cases, volatile contaminants contained in the gas discharged from the aeration apparatus may be chemically decomposed, but toxic by-products and acid gases are generated, so that an additional processing apparatus is required. There's a problem. Moreover, in such a chemical decomposition treatment, the size of the apparatus becomes large as a whole, and the purification cost including the equipment cost is often high. Therefore, the above-mentioned method of adsorption and removal with activated carbon is often used.
[0006]
On the other hand, as a method for removing contaminants in contaminated water in an aqueous phase, there is an accelerated oxidation treatment method. This accelerated oxidation treatment method is a method in which ozone, hydrogen peroxide, ultraviolet rays, etc. are used in combination to generate hydroxyl radicals having strong oxidizing power and decompose and remove harmful pollutants in contaminated water. Combined methods are well known.
[0007]
Ozone is not highly soluble in water, and there is an upper limit to the concentration of ozone generated by the ozone generator. Therefore, several steps of ozone injection are required to increase the ozone dissolution efficiency and to secure the required ozone injection rate. And dissolving and mixing in multiple stages. For example, in Japanese Patent Application Laid-Open Nos. 9-38672 and 10-99877, the absorption efficiency of ozone gas with respect to treated water (contaminated water) is increased by using a pressurized downward injection type multi-stage ozone contact tank, and the subsequent treatment is performed. A method has been proposed in which water is irradiated with ultraviolet rays to decompose organic substances.
[0008]
However, when the ozone injection is divided into several stages and dissolved and mixed in multiple stages as described above, it is necessary to irradiate the amount of ultraviolet light sufficient to react the ozone present at a high concentration in the treated water in the last ultraviolet irradiation. However, there is a problem that if the amount of ultraviolet light irradiated at a time is large, photodecomposition by ultraviolet light proceeds, and haloacetic acid such as dichloroacetic acid as a by-product increases.
[0009]
[Patent Document 1]
JP-A-9-38672 [Patent Document 2]
JP-A-10-99877
[Problems to be solved by the invention]
The present invention has been made in view of such conventional problems, and reduces the pollutant removal rate by performing optimal ultraviolet irradiation in accordance with the concentration of harmful pollutants and dissolved ozone in the contaminated water. It is an object of the present invention to provide a method for purifying contaminated water that can maintain and simultaneously suppress generation of by-products.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, a method for purifying contaminated water provided by the present invention includes a gas-liquid mixing step of mixing ozone with the contaminated water, and an ultraviolet ray for irradiating the contaminated water mixed with ozone with ultraviolet rays to decompose the contaminants. A method for purifying contaminated water, comprising an irradiation step and a gas-liquid separation step of separating gas remaining in the contaminated water that has been subjected to ultraviolet irradiation, wherein the unit of the gas-liquid mixing step and the ultraviolet irradiation step is repeated in a plurality of stages. At the same time, the amount of ultraviolet irradiation with respect to the ozone injection rate in each stage is increased stepwise as the processing proceeds.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
In the method for purifying contaminated water of the present invention, a gas-liquid mixing step of mixing ozone with contaminated water, and an ultraviolet irradiation step of irradiating contaminated water mixed with ozone with ultraviolet rays to decompose pollutants as one unit, Repeat in two or more stages. For example, in the case of the two-stage processing, the processing is performed by combining the final second-stage gas-liquid mixing step and the ultraviolet irradiation step in series after the first first-stage gas-liquid mixing step and the ultraviolet irradiation step. .
[0013]
Such a multi-stage treatment is an effective means for sufficiently decomposing and removing contaminants when, for example, treating contaminated water containing harmful contaminants at a high concentration. That is, the concentration of ozone gas generated by the ozone generator is limited, and the mixing ratio of contaminated water and ozone gas has an upper limit. On the other hand, the amount of ozone injected per liter of contaminated water in single-stage treatment is limited. This is because, when harmful pollutants are present at a high concentration, the required ozone injection amount cannot be secured by only one stage of ozone injection.
[0014]
In such a multi-stage process, conventionally, the ozone injection rate and the amount of ultraviolet irradiation in each stage have generally been the same. However, in this case, by-products such as dichloroacetic acid are more likely to be generated in the former stage where the concentration of contaminants in the contaminated water is higher, and the amount of by-products generated as a whole increases. Doing so is a heavy burden.
[0015]
Therefore, in the method of the present invention, the amount of ultraviolet irradiation with respect to the ozone injection rate in each stage is increased stepwise in accordance with the progress of the treatment, whereby the generation of by-products is suppressed as a whole, and at the same time, the contamination is reduced at a high removal rate. Decomposition and removal of substances can be performed. For example, when the units of the gas-liquid mixing step and the ultraviolet irradiation step are two stages, the ultraviolet irradiation amount with respect to the ozone injection rate in the first stage is the ultraviolet irradiation amount with respect to the ozone injection ratio in the final second stage. It is preferably 0.4 to 0.6 times. As a result, as compared with the case where the ozone injection rate and the ultraviolet irradiation dose in each stage are all the same, the generation of by-products can be significantly suppressed at the same time while the contaminant removal rate is maintained.
[0016]
Next, the method of the present invention will be described with reference to the drawings. FIG. 1 is a schematic process diagram showing a specific example of a purification device used in the method for purifying contaminated water of the present invention. This purifying device is provided with a pumping pipe 2 provided near the bottom of a perforated pipe 1 fixed in the ground to pump contaminated groundwater in soil, that is, contaminated water, and is connected to the pumping pipe 2. A pump 3 for pumping contaminated water onto the ground surface; and a raw water tank 4 for temporarily storing the contaminated water pumped by the pump 3.
[0017]
The perforated pipe 1 is inserted and fixed in a well hole excavated in the soil, and is formed of, for example, a polyvinyl chloride pipe having a diameter of about 100 to 150 mm. Is provided. The pumping pipe 2 penetrates from the vicinity of the upper end of the perforated pipe 1 and is inserted to the vicinity of the lower end of the perforated pipe 1. A pump 3 is attached to the downstream side of the pumping pipe 2, and groundwater is supplied to the ground surface. It is possible to pump it up.
[0018]
In the purification device of FIG. 1, the gas-liquid mixing devices 5a and 5b, the

ultraviolet irradiation devices

6a and 6b, and the gas-liquid separation tanks 7a and 7b constitute one unit, and two units are connected in series. The contaminated water in the raw water tank 4 is sequentially introduced into two-stage gas-liquid mixing devices 5a and 5b and

ultraviolet irradiation devices

6a and 6b through a water supply pipe, and is generated by the ozone gas generator 8 in the gas-liquid mixing devices 5a and 5b. The dissolved ozone gas is dissolved in the contaminated water, and the

ultraviolet irradiation devices

6a and 6b irradiate the contaminated water with the dissolved ozone with ultraviolet light.
[0019]
As the ozone mixing system in the gas-liquid mixing devices 5a and 5b, for example, a diffuser tube system, an ejector system ejecting from a nozzle, a turbo mixing system in which ozone is mixed in water using a vortex pump, and the like are considered. An ejector method and a turbo mixing method with high speed are desirable.
[0020]
The ozone generation capacity required for the ozone gas generator 8 varies depending on the concentration of the contaminants in the contaminated water and the configuration of the treatment. When the contaminant concentration is several tens mg / liter or more, ozone gas of 80 g / Nm ³ or more is generated. It is preferable to use a device that performs the above. The ozone gas generator 8 preferably uses oxygen gas as a raw material. However, when an oxygen cylinder is used, the labor involved in maintenance such as replacement is added, and therefore, it is desirable to use an oxygen cylinder provided with a source gas generator 9 such as an apparatus that generates oxygen by pressure switching adsorption (PSA) or the like.
[0021]
There are two types of ultraviolet irradiation methods for the

ultraviolet irradiation devices

6a and 6b, an internal irradiation type and an external irradiation type. The internal irradiation type has a double structure, in which an ultraviolet lamp housed in a transparent protective tube is disposed inside an outer wall, and contaminated water to be treated flows between the outer wall and the transparent protective tube. On the other hand, in the external irradiation type, an ultraviolet lamp is arranged on the outer periphery of the transparent protective tube through which contaminated water flows. The transparent protective tube is made of a material having a high ultraviolet transmittance, and for example, quartz, transparent fluororesin, or the like is used. As the ultraviolet lamp, a lamp that emits ultraviolet light having a peak wavelength of 185 ± 10 nm or 254 ± 10 nm can be used. The ultraviolet lamp effectively acts on radicalization of ozone and has a low installation cost and low power consumption. It is desirable to use a low-pressure mercury lamp having a peak wavelength of 10 nm.
[0022]
By this ultraviolet irradiation, active radicals such as hydroxyl radicals are generated from ozone dissolved in the contaminated water, and contaminants in the contaminated water are decomposed. At this time, the amount of ultraviolet irradiation with respect to the ozone injection rate is increased stepwise as the processing proceeds. The reason is that the higher the concentration of contaminants in the contaminated water, the more easily by-products such as dichloroacetic acid are generated by reaction with ultraviolet light. This is because the generation of can be suppressed.
[0023]
In addition, since the irradiated ultraviolet light is also absorbed by the contaminants, it was found that, at the same irradiation amount of the ultraviolet light, the unreacted residual ozone amount increases as the contaminant concentration in the treated water increases. For example, using only the first stage of the purification device shown in FIG. 1 (gas-liquid mixing device 5a and ultraviolet irradiation device 6a), treatment of contaminated water having a different initial concentration of tetrachloroethylene (PCE) is performed, and FIG. 2 shows the result of measuring the residual ozone concentration remaining after the dissolution. As can be seen from FIG. 2, the higher the concentration of tetrachloroethylene in the contaminated water, the higher the residual ozone concentration after the treatment.
[0024]
Therefore, as can be seen from FIG. 2, when the units of the gas-liquid mixing device and the ultraviolet irradiation device are arranged in a plurality of stages, the residual ozone after the ultraviolet irradiation in each stage is gradually accumulated. The amount of ozone dissolved in contaminated water before introduction tends to increase. For this reason, a sufficient amount of active radicals is generated by increasing the amount of ultraviolet irradiation in the later stage in accordance with the amount of dissolved ozone that increases with the progress of the treatment, and the decomposition efficiency of contaminants can be increased.
[0025]
The irradiation amount of the ultraviolet rays depends on the decomposition characteristics of the pollutant to be decomposed, the pH of the contaminated water, the ozone injection rate, and the like. Further, the amount of ultraviolet irradiation in each stage is set so as to increase as the processing proceeds as described above (as the number of stages increases). Specifically, according to the type and concentration of the contaminants in the contaminated water, the amount of ultraviolet irradiation in the final stage at which the contaminants can be finally decomposed and removed to a desired concentration is determined. It is only necessary to reduce the amount of irradiation of ultraviolet rays as the level increases.
[0026]
For example, when the contaminant is tetrachloroethylene alone having low decomposition characteristics due to ozone, the pH of the contaminated water is 8, and the ozone injection rate in each stage is 20 mg / l, the ultraviolet light per liter of the contaminated water in the final stage of the multi-stage treatment is used. It is desirable to set the irradiation amount to 0.02 to 0.03 Wh / l, to decrease the irradiation amount toward the previous stage, and to set the irradiation amount to about half of the irradiation amount at the first stage as compared to the final stage. In the case of the same ozone injection rate as above using trichloroethylene alone having a high decomposition characteristic by ozone, the ultraviolet irradiation amount per liter of contaminated water in the final stage is set to 0.01 to 0.02 Wh / l, and It is desirable that the irradiation amount is decreased as the position goes to the first stage, and the irradiation amount is set to about half of the irradiation amount in the first stage.
[0027]
The contaminated water after the ultraviolet irradiation is introduced into the gas-liquid separation devices 7a and 7b from the

ultraviolet irradiation devices

6a and 6b via a water pipe. In the gas-liquid separation devices 7a and 7b, undissolved gas or remaining ozone mixed in the treated contaminated water is transferred to the gas phase. In addition, as a gas-liquid separation device, the method of opening to the atmosphere is the simplest, but in this case, it is preferable to keep the treated contaminated water for a certain period of time.
[0028]
The contaminated water treated in this manner is discharged from the gas-liquid separators 7a and 7b as it is to the outside of the system, or after being subjected to secondary treatment with an adsorbent or the like, to the outside of the system. Exhaust gas from the gas-liquid separation devices 7a and 7b is discharged to the atmosphere after being processed by the waste

ozone treatment devices

10a and 10b.
[0029]
【Example】
Contaminated water (PCE effluent) containing 20 mg / l of tetrachloroethylene as a pollutant using a purifying apparatus in which gas-liquid mixing devices 5a and 5b and

ultraviolet irradiation devices

6a and 6b shown in FIG. A test was conducted for treating contaminated water (VOC wastewater) containing 20 mg / l of tetrachloroethylene and 10 mg / l of trichlorethylene.
[0030]
At that time, the amount of ultraviolet irradiation in the first stage (gas-liquid mixing device 5a and ultraviolet irradiation device 6a) and the second stage (gas-liquid mixing device 5b and ultraviolet irradiation device 6b) were set as shown in Table 1 below. . As other test conditions, the treated water amount was 1.2 m ³ / h, the ozone gas generation concentration was 100 g / Nm ³ , and the overall ozone injection rate was 20 mg / l (10 mg / l per stage).
[0031]
The removal rate of contaminants in this treatment test is shown in Table 1 below, and the concentration and formation rate of haloacetic acids (dichloroacetic acid and trichloroacetic acid), which are by-products generated in the treated contaminated water, are shown in Table 2 below. Indicated.
[0032]
[Table 1]

[0033]
[Table 2]

[0034]
As can be seen from the comparison between Samples 1 to 3 and Sample 5 and the comparison between Samples 7 and 8 in Tables 1 and 2 above, the first-stage UV irradiation dose was set to 0.4 in the second stage (final stage). By setting the range to 0.6 times, the production rate of haloacetic acid can be reduced while maintaining the removal rate of the organic chlorine compound as a contaminant. Also, from the comparison between Samples 1 to 3 and Sample 4, when the UV irradiation amount in the first stage is lower than 0.4 times that in the second stage (final stage), the removal rate of the organic chlorine compound as a contaminant is reduced. It turns out that it falls greatly.
[0035]
Further, from the comparison between Sample 6 and Samples 1 to 3, under the conditions of Sample 6 in which the second stage ultraviolet irradiation dose was lower than that in the first stage, the rate of reduction in the production rate of by-product haloacetic acid was small. In addition, the removal rate of the organic chlorine compound as a contaminant also decreases.
[0036]
【The invention's effect】
According to the present invention, even in the case of contaminated water containing a high concentration of contaminants, the amount of contaminants is reduced while reducing the amount of by-products without reducing the contaminant removal rate with a small amount of ultraviolet irradiation. Decomposition and removal can purify contaminated water.
[Brief description of the drawings]
FIG. 1 is a schematic process diagram showing a specific example of a purification device used in a method for purifying contaminated water of the present invention.
FIG. 2 is a graph showing the relationship between the initial concentration of polychloroethylene in contaminated water and the concentration of residual O _{3 in} contaminated water after treatment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Perforated pipe 2 Pumping pipe 3 Pump 4 Raw water tank 5a, 5b Gas-

liquid mixing pump

6a, 6b Ultraviolet irradiation device 7a, 7b Gas-liquid separator 8 Ozone gas generator 9 Raw material gas generator

Claims

A gas-liquid mixing step of mixing ozone with contaminated water, an ultraviolet irradiation step of irradiating contaminated water mixed with ozone with ultraviolet light to decompose pollutants, and a gas separation step of separating gas remaining in contaminated water subjected to ultraviolet irradiation. A method of purifying contaminated water comprising a liquid separation step, wherein the unit of the gas-liquid mixing step and the ultraviolet irradiation step is repeated in a plurality of stages, and the amount of ultraviolet irradiation with respect to the ozone injection rate in each stage is adjusted according to the progress of the treatment. A method for purifying contaminated water, wherein the contaminated water is gradually increased.

The unit of the gas-liquid mixing step and the ultraviolet irradiation step is divided into two stages, and the ultraviolet irradiation amount with respect to the ozone injection ratio in the first stage is 0.4 to 0.6 of the ultraviolet irradiation amount with respect to the ozone injection ratio in the second stage. The method for purifying contaminated water according to claim 1, wherein the number is doubled.