JP3555631B2 - Wastewater treatment method - Google Patents
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- JP3555631B2 JP3555631B2 JP15166495A JP15166495A JP3555631B2 JP 3555631 B2 JP3555631 B2 JP 3555631B2 JP 15166495 A JP15166495 A JP 15166495A JP 15166495 A JP15166495 A JP 15166495A JP 3555631 B2 JP3555631 B2 JP 3555631B2
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- dithionite
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Description
【０００１】
【産業上の利用分野】
本発明は、亜二チオン酸塩を含有する廃水を処理する方法に関するものである。更に詳しくは、漂白廃液等の廃水中に残存する亜二チオン酸塩の処理方法における改良に関する方法である。
【０００２】
【従来の技術】
亜二チオン酸塩は製紙工業分野では主に機械パルプの漂白に単段漂白または過酸化水素漂白との組み合わせによる２段漂白に用いられる他、繊維工業分野ではメリヤス、タオル、綿布、綿糸の過酸化水素漂白と組み合わせて繊維の高白色度化、風合い改善等の効果を得るために用いられる。また、染料を溶解したり、繊維を染色後余分な染料を除去するために用いられる。
【０００３】
廃水中に残存する亜二チオン酸塩はそれ自身が廃水のＣＯＤ値を上昇させて環境汚染の原因となるので、これらの漂白廃液は、通常、無機もしくは有機の凝集剤による凝集沈澱処理、好気性菌による活性汚泥処理またはこれ等の組み合わせによって処理した後、放流する。
【０００４】
しかし、活性汚泥処理の場合、廃水中に残存亜二チオン酸塩が存在すると、亜二チオン酸塩が還元剤として働くために、活性汚泥処理槽中の溶存酸素が亜二チオン酸塩と反応して失われて活性汚泥処理槽の雰囲気が嫌気性となってしまう。その結果、活性汚泥中の好気性菌は活性を失うか死滅してしまい、活性汚泥処理装置の能力が大幅に低下してしまうかまたは全く処理できないというトラブルが発生する。
【０００５】
このトラブルの解決策として、廃水を中間貯槽に貯めて空気（酸素）を曝気し残存亜二チオン酸塩を処理する方法が一般的に実施されている。しかし、空気（酸素）と亜二チオン酸塩の反応が遅い事から、大きな中間貯槽が必要であるとの問題点がある。また、空気（酸素）を曝気する方法では、残存亜二チオン酸塩を完全に処理するのは困難で、どうしても亜二チオン酸塩が残存する傾向があり、また、硫黄を含む沈殿物が副生して残存亜二チオン酸塩の濃度の測定が困難になることがある。
【０００６】
【発明が解決しようとする課題】
従来の空気曝気により残存亜二チオン酸塩を処理していた方法は、処理するために長時間が必要であること、従って大きな貯槽が必要であること、微量の残存亜二チオン酸塩の処理が完全にできないこと等の問題点があった。
本発明の目的は、廃水中の残存亜二チオン酸塩を短時間で完全に処理する事である。
【０００７】
【課題を解決するための手段】
本発明者等は、残存亜二チオン酸塩を短時間で完全に処理する方法について検討した結果、廃水のｐＨをアルカリ性とし、次いで過酸化物を添加する事により、完全に残存亜二チオン酸塩を処理できる事を見い出し本発明を完成した。
【０００８】
即ち、本発明は、廃水中の亜二チオン酸塩を処理する方法において、廃水液性をアルカリ性にし、次いで過酸化物を添加する事を特徴とする残存亜二チオン酸塩の処理方法である。
【０００９】
次に、本発明を具体的に説明する。残存亜二チオン酸塩を含んだ廃水には、亜二チオン酸塩漂白を実施している製紙工業の排水、繊維の染色・漂白排水、食品排水などが含まれる。本発明においては、残存亜二チオン酸塩を含んだ廃水中には亜硫酸もしくはその塩、チオ硫酸もしくはその塩または硫化水素などの亜二チオン酸塩以外の還元性硫黄化合物が含まれていても処理可能である。
【００１０】
本発明では、まず、亜二チオン酸塩を含んだ廃水にアルカリ剤を添加し、ｐＨを９〜１３、好ましく１０〜１１に調整する。添加するアルカリ剤としては、ナトリウム、カリウム等のアルカリ金属の水酸化物、炭酸塩またはケイ酸塩、カルシウム、マグネシウム、バリウム等のアルカリ土類金属の水酸化物または炭酸塩またはケイ酸塩等であり、単独またはそれらの組み合わせが使用される。アルカリ剤としては、水酸化ナトリウム、炭酸ナトリウムが好適に使用される。アルカリ剤と廃水との混合のためには、攪拌混合槽の他、スタティックミキサー、インラインミキサー等の混合装置が使用される。
【００１１】
次に、ｐＨが調整された廃水に過酸化物が添加される。過酸化物としては、過酸化水素、過炭酸ナトリウムなどの過酸化水素と無機塩類との付加物、過ほう酸ナトリウム、過酸化ナトリウムなどの無機の過酸化物、過蟻酸、過酢酸などの有機の過酸化物が挙げられるが、好ましくは過酸化水素が使用される。残存亜二チオン酸塩の濃度は酸化還元電位計（ＯＲＰ計と略する）によって測定され、亜二チオン酸塩の濃度が １０ｐｐｍ以下、好ましくは ５ｐｐｍ 以下になった点を以て過酸化物の添加を終了する。亜二チオン酸塩の濃度を測定する方法としては、ＯＲＰ計以外に比色による方法、溶液の電動度による方法等でもよい。過酸化物と廃水との混合のためには、攪拌混合槽の他、スタティックミキサー、インラインミキサー等の混合装置が使用される。
【００１２】
ここで、亜二チオン酸塩含んだ廃水のｐＨが９未満の場合は、過酸化物との反応が遅く処理に時間がかかり、また空気中の酸素との反応により硫黄を含む沈殿物が副生し、亜二チオン酸塩の濃度の測定が困難になり、過酸化物の添加量が多量になるおそれがあり、処理後の廃液中に過酸化物が残存し、本処理後に活性汚泥処理を行う場合に多量の残存過酸化物により菌が死滅したり、分解酵素により汚泥が浮いたりして好ましくない。
【００１３】
本発明により残存亜二チオン酸塩が処理された廃水は、好ましくは中和した後、活性汚泥処理槽に送られる。中和には、塩酸、硫酸、硝酸、リン酸等の無機酸、ギ酸、酢酸、シュウ酸等の有機の酸が使用される。使用する酸としては、無機酸の水溶液が好ましく、特に硫酸が好適に使用される。ｐＨの測定には一般的にはｐＨ計が使用されるが、ｐＨが測定できる装置であればいずれの方法でもよい。中和剤と廃水との混合のためには、攪拌混合槽の他、スタティックミキサー、インラインミキサー等の混合装置が使用される。
本発明は、回分式でも実施できるが連続式で実施することが好ましい。
【００１４】
本発明によれば、亜二チオン酸塩は過酸化物により速やかに処理され、かつ、沈殿物を副生することなく、亜二チオン酸塩の濃度の測定も容易で過酸化物の添加量の制御を正確に行なう事ができる。
【００１５】
【実施例】
次に実施例により本発明を具体的に説明する。ｐＨの測定には電気化学計器（株）製ＰＨＬ−２０型ｐＨ計を使用した。酸化還元電位の測定には、ＹＯＫＯＧＡＷＡ製ＰＨ８２型ＯＲＰ計及び電極として９２２０ＹＬを使用した。亜二チオン酸塩量の分析はＪＩＳ Ｋ１４４３ 法によった。
なお、本発明は以下の実施例によって限定されるものではない。
【００１６】
実施例１
脱イオン水に１０重量％水酸化ナトリウム１．５ｍｌ を添加した溶液に亜二チオン酸ナトリウム ０．３０６ｇｒを溶解した。得られた溶液のｐＨは１２．１であった。この溶液にＯＲＰ計を差し込み、１重量％のＨ２Ｏ２溶液を滴下して亜二チオン酸塩の処理を行った。Ｈ２Ｏ２溶液の滴下は、酸化還元電位勾配の急になるところを以て終点とした。この終点までに滴下した１重量％ Ｈ２Ｏ２ は１８．１ｍｌ（１００％Ｈ２Ｏ２ 換算１８１ｍｇ）であり、終点のｐＨは１０．２であり、残存亜二チオン酸塩は測定されなかった。
【００１７】
比較例１
脱イオン水に亜二チオン酸ナトリウム ０．３０６ｇｒを溶解した。得られた溶液のｐＨは７．８ であった。この溶液にＯＲＰ計を差し込み、空気を６０Ｌ／ｈｒの速度で吹き込んで亜二チオン酸塩の処理を行った。
その結果、酸化還元電位勾配の急になるところは明確には分からなかった。空気を３ｈｒ 吹き込んだ時点で残存亜二チオン酸塩の残存量を分析した結果、０．０２５１ｇｒ（残存率８．２％） であった。この時の溶液のｐＨは２．８ であり、また、溶液は白濁していた。
【００１８】
比較例２
脱イオン水に亜二チオン酸ナトリウム ０．３０６ｇｒを溶解した。得られた溶液のｐＨは７．８ であった。この溶液にＯＲＰ計を差し込み、１重量％のＨ２Ｏ２溶液を滴下して亜二チオン酸塩の酸化を行った。
その結果、酸化還元電位勾配の急になるところは明確には分からなかった。この時の溶液のｐＨは２．６ であり、また、溶液は白濁していた。
【００１９】
比較例１のように、従来の空気曝気による方法では、残存亜二チオン酸塩の処理に長時間を要し、また残存亜二チオン酸塩又は亜二チオン酸塩の分解によって生じた還元物質を完全に酸化する事が困難である。
比較例２のアルカリ剤を添加していない系での過酸化水素による方法では、過酸化水素を滴下する終点を求める事が難しい。
【００２０】
実施例２
脱イオン水に亜二チオン酸ナトリウム ０．１５３ｇｒを溶解した溶液を３つ作り、それぞれの溶液に１重量％水酸化ナトリウム１．５ｍｌ 、３ｍｌ 、１０ｍｌを添加した。得られた溶液のｐＨはそれぞれ９．１ 、１０．１、１１．６であった。それぞれの溶液にＯＲＰ計を差し込み、０．５ 重量％のＨ２Ｏ２溶液を滴下して亜二チオン酸塩の処理を行った。Ｈ２Ｏ２溶液の滴下は、酸化還元電位勾配の急になるところを以て終点とした。この終点までに滴下した１重量％ Ｈ２Ｏ２ は、それぞれ１７．９ｍｌ（１００％Ｈ２Ｏ２ 換算８９．５ｍｇ） 、１８．０ｍｌ（１００％Ｈ２Ｏ２ 換算９０．０ｍｇ） 、１８．１ｍｌ（１００％Ｈ２Ｏ２ 換算９０．５ｍｇ） であり、残存亜二チオン酸塩は測定されなかった。
【００２１】
比較例３
脱イオン水に１重量％水酸化ナトリウムを０．５ｍｌ を添加した溶液に亜二チオン酸ナトリウム ０．１５３ｇｒを溶解した。得られた溶液のｐＨは８．５ であった。この溶液にＯＲＰ計を差し込み、０．５ 重量％のＨ２Ｏ２溶液を滴下して亜二チオン酸塩の処理を行った。
その結果、酸化還元電位勾配の急になるところは明確には分からなかった。この時の溶液は白濁していた。
【００２２】
実施例２に示すように、本発明においては、残存亜二チオン酸塩を処理する前の溶液のｐＨは９以上が必要であり、比較例３に示すように、残存亜二チオン酸塩を処理する前の溶液のｐＨが９未満では、過酸化水素を滴下する終点を求める事が難しい。
【００２３】
実施例３
過酸化水素による漂白を受けた綿繊維を、亜二チオン酸ナトリウムによる漂白を行った。亜二チオン酸ナトリウムによる漂白廃水中には残存亜二チオン酸塩が０．１３ｇｒ／ｌおよび還元性硫黄化合物が含まれていた。この漂白廃水３００ｍｌ に１０重量％水酸化ナトリウム１．５ｍｌ を添加してｐＨを１２．１とした。この溶液にＯＲＰ計を差し込み、１重量％のＨ２Ｏ２溶液を滴下して亜二チオン酸塩の処理を行った。Ｈ２Ｏ２溶液の滴下は、酸化還元電位勾配の急になるところを以て終点とした。この終点までに滴下した１重量％ Ｈ２Ｏ２ は２．４ｍｌ（１００％Ｈ２Ｏ２換算２４ｍｇ） であった。また終点のｐＨは１１．５であり、残存亜二チオン酸塩は測定されなかった。
【００２４】
比較例４
実施例３で用いた漂白廃水３００ｍｌ にＯＲＰ計を差し込み、空気を６０Ｌ／ｈｒ吹き込んで亜二チオン酸塩の処理を行った。
その結果、酸化還元電位勾配の急になるところは明確には分からなかった。空気を３ｈｒ吹き込んだ時点で残存亜二チオン酸塩の残存量を分析した結果、０．０１７７ｇｒ（残存率１３．６％ ）であった。この時の溶液ｐＨは４．３ であった。
【００２５】
比較例５
比較例４の残存亜二チオン酸塩を除去した廃水（ＣＯＤ ４１７ｐｐｍ）を希硫酸でｐＨ７．４ に中和後、活性汚泥処理を実施したところＣＯＤ １８７ｐｐｍまで低下し、ＣＯＤ低減率は５５．２％ であった。
【００２６】
実施例４
実施例３の残存亜二チオン酸塩を除去した廃水（ＣＯＤ ３８２ｐｐｍ）を希硫酸でｐＨ７．４ に中和後、活性汚泥処理を実施したところＣＯＤ ６８ｐｐｍ まで低下し、ＣＯＤ低減率は８２．２％ であった。
以上のように、残存亜二チオン酸塩を除去する事により、活性汚泥におけるＣＯＤ低減率が大幅に改善された。
【００２７】
【発明の効果】
本発明によれば、処理時間が短く、処理を連続にでき、微量の亜二チオン酸塩でも完全に処理する事ができる等の効果が得られる。
本発明を活性汚泥処理の前段に組み合わせれば、残存亜二チオン酸塩に起因する活性汚泥処理トラブルが全く無くなり、活性汚泥処理が安定する事から、安定した水質の廃水を放流できる。[0001]
[Industrial applications]
The present invention relates to a method for treating wastewater containing dithionite. More specifically, it relates to an improvement in a method for treating dithionite remaining in wastewater such as bleaching wastewater.
[0002]
[Prior art]
In the paper industry, dithionite is mainly used for single-stage bleaching or two-stage bleaching in combination with hydrogen peroxide bleaching for mechanical pulp. Used in combination with hydrogen oxide bleaching to obtain effects such as higher fiber whiteness and improved texture. It is also used for dissolving the dye or removing excess dye after dyeing the fiber.
[0003]
Since the dithionite remaining in the wastewater itself raises the COD value of the wastewater and causes environmental pollution, these bleaching effluents are usually subjected to coagulation sedimentation treatment with an inorganic or organic coagulant. After being treated by activated sludge treatment with aerial bacteria or a combination thereof, it is discharged.
[0004]
However, in the case of activated sludge treatment, if residual dithionite is present in the wastewater, the dissolved oxygen in the activated sludge treatment tank reacts with the dithionite because the dithionite acts as a reducing agent. Then, the atmosphere of the activated sludge treatment tank becomes anaerobic. As a result, the aerobic bacteria in the activated sludge lose their activity or die, causing a problem that the capacity of the activated sludge treatment apparatus is greatly reduced or the activated sludge cannot be treated at all.
[0005]
As a solution to this trouble, a method of storing wastewater in an intermediate storage tank and aerating air (oxygen) to treat residual dithionite is generally practiced. However, since the reaction between air (oxygen) and dithionite is slow, there is a problem that a large intermediate storage tank is required. Further, in the method of aerating air (oxygen), it is difficult to completely treat the remaining dithionite, and the dithionite tends to remain inevitably. It may be difficult to measure the concentration of residual dithionite.
[0006]
[Problems to be solved by the invention]
The conventional method of treating residual dithionite by air aeration requires a long time for treatment, and therefore requires a large storage tank, and treatment of a trace amount of residual dithionite. However, there was a problem that it could not be performed completely.
An object of the present invention is to completely treat residual dithionite in wastewater in a short time.
[0007]
[Means for Solving the Problems]
The present inventors have studied a method for completely treating residual dithionite in a short period of time. As a result, the pH of the wastewater is made alkaline, and then peroxide is added to completely remove residual dithionite. They found that they could treat salt and completed the present invention.
[0008]
That is, the present invention relates to a method for treating dithionite in wastewater, in which the liquidity of the wastewater is made alkaline, and then a peroxide is added. .
[0009]
Next, the present invention will be described specifically. Wastewater containing residual dithionite includes wastewater from the paper industry where dithionite bleaching is performed, textile dyeing / bleaching wastewater, food wastewater, and the like. In the present invention, even if the wastewater containing residual dithionite contains a reducing sulfur compound other than dithionite such as sulfurous acid or a salt thereof, thiosulfuric acid or a salt thereof, or hydrogen sulfide. Can be processed.
[0010]
In the present invention, first, an alkaline agent is added to wastewater containing dithionite to adjust the pH to 9 to 13, preferably 10 to 11. Examples of the alkali agent to be added include hydroxides, carbonates or silicates of alkali metals such as sodium and potassium, and hydroxides or carbonates or silicates of alkaline earth metals such as calcium, magnesium and barium. Yes, alone or in combination. Sodium hydroxide and sodium carbonate are preferably used as the alkaline agent. For mixing the alkaline agent and the wastewater, a mixing device such as a static mixer or an in-line mixer is used in addition to the stirring and mixing tank.
[0011]
Next, peroxide is added to the pH adjusted wastewater. Examples of peroxides include hydrogen peroxide, adducts of hydrogen peroxide and inorganic salts such as sodium percarbonate, inorganic peroxides such as sodium borate and sodium peroxide, and organic peroxides such as formic acid and peracetic acid. Peroxides are mentioned, but preferably hydrogen peroxide is used. The concentration of residual dithionite is measured by an oxidation-reduction potentiometer (abbreviated as ORP meter), and when the concentration of dithionite becomes 10 ppm or less, preferably 5 ppm or less, the addition of peroxide is performed. finish. As a method for measuring the concentration of the dithionite, a method using colorimetry, a method using the degree of electric power of the solution, and the like may be used in addition to the ORP meter. In order to mix the peroxide and the wastewater, a mixing device such as a static mixer or an in-line mixer is used in addition to a stirring and mixing tank.
[0012]
Here, when the pH of the wastewater containing dithionite is less than 9, the reaction with peroxide is slow and it takes a long time to process, and the reaction with oxygen in the air causes the formation of a precipitate containing sulfur as a by-product. And the measurement of the concentration of dithionite becomes difficult, and the amount of peroxide added may increase.Peroxide remains in the waste liquid after the treatment, and after the treatment, activated sludge treatment is performed. However, it is not preferable that bacteria are killed by a large amount of residual peroxide or sludge floats by a decomposing enzyme.
[0013]
The wastewater treated with the residual dithionite according to the present invention is sent to an activated sludge treatment tank, preferably after neutralization. For the neutralization, inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid, and organic acids such as formic acid, acetic acid and oxalic acid are used. As the acid to be used, an aqueous solution of an inorganic acid is preferable, and particularly, sulfuric acid is suitably used. Generally, a pH meter is used for measuring pH, but any method may be used as long as it can measure pH. For mixing the neutralizing agent and the wastewater, a mixing device such as a static mixer or an in-line mixer is used in addition to the stirring and mixing tank.
The present invention can be carried out in a batch system, but is preferably carried out in a continuous system.
[0014]
According to the present invention, the dithionite is promptly treated with the peroxide, and the concentration of the dithionite can be easily measured without forming a precipitate as a by-product, and the amount of the peroxide added can be easily measured. Control can be performed accurately.
[0015]
【Example】
Next, the present invention will be specifically described with reference to examples. The pH was measured using a PHL-20 type pH meter manufactured by Electrochemical Instruments Co., Ltd. For measurement of the oxidation-reduction potential, 9220YL was used as a PH82 type ORP meter manufactured by YOKOGAWA and an electrode. The analysis of the amount of dithionite was carried out according to the JIS K1443 method.
The present invention is not limited by the following examples.
[0016]
Example 1
0.306 gr of sodium dithionite was dissolved in a solution of 1.5 ml of 10% by weight sodium hydroxide in deionized water. The pH of the resulting solution was 12.1. An ORP meter was inserted into this solution, and a 1 wt% H 2 O 2 solution was added dropwise to treat the dithionite. The end point of the dropping of the H 2 O 2 solution was determined when the oxidation-reduction potential gradient became steep. The 1 wt% H 2 O 2 dropped to this end point was 18.1 ml (181 mg in terms of 100% H 2 O 2 ), the pH at the end point was 10.2, and the residual dithionite was not measured. Was.
[0017]
Comparative Example 1
0.306 gr of sodium dithionite was dissolved in deionized water. The pH of the resulting solution was 7.8. An ORP meter was inserted into the solution, and air was blown at a rate of 60 L / hr to treat the dithionite.
As a result, it was not clearly understood where the oxidation-reduction potential gradient became steep. As a result of analyzing the residual amount of the residual dithionite when air was blown in for 3 hours, the residual amount was 0.0251 gr (residual rate: 8.2%). At this time, the pH of the solution was 2.8, and the solution was cloudy.
[0018]
Comparative Example 2
0.306 gr of sodium dithionite was dissolved in deionized water. The pH of the resulting solution was 7.8. An ORP meter was inserted into this solution, and a 1 wt% H 2 O 2 solution was added dropwise to oxidize the dithionite.
As a result, it was not clearly understood where the oxidation-reduction potential gradient became steep. At this time, the pH of the solution was 2.6, and the solution was cloudy.
[0019]
As in Comparative Example 1, in the conventional method using air aeration, it takes a long time to treat the residual dithionite, and the reducing substance generated by the decomposition of the residual dithionite or the dithionite is used. Is difficult to completely oxidize.
In the method using hydrogen peroxide in the system to which the alkali agent is not added in Comparative Example 2, it is difficult to find the end point of dropping the hydrogen peroxide.
[0020]
Example 2
Three solutions of 0.153 gr of sodium dithionite in deionized water were prepared, and 1.5 ml, 3 ml and 10 ml of 1% by weight sodium hydroxide were added to each solution. The pH of the obtained solution was 9.1, 10.1, and 11.6, respectively. An ORP meter was inserted into each of the solutions, and a 0.5 wt% H 2 O 2 solution was added dropwise to treat the dithionite. The end point of the dropping of the H 2 O 2 solution was determined when the oxidation-reduction potential gradient became steep. The 1 wt% H 2 O 2 dropped to this end point was 17.9 ml (89.5 mg in terms of 100% H 2 O 2 ), 18.0 ml (90.0 mg in terms of 100% H 2 O 2 ), and 18. It was 1 ml (90.5 mg in terms of 100% H 2 O 2 ), and no residual dithionite was measured.
[0021]
Comparative Example 3
0.153 gr of sodium dithionite was dissolved in a solution of 0.5 ml of 1% by weight sodium hydroxide in deionized water. The pH of the resulting solution was 8.5. An ORP meter was inserted into this solution, and a 0.5% by weight H 2 O 2 solution was added dropwise to perform treatment with dithionite.
As a result, it was not clearly understood where the oxidation-reduction potential gradient became steep. The solution at this time was cloudy.
[0022]
As shown in Example 2, in the present invention, the pH of the solution before the treatment with the residual dithionite is required to be 9 or more. If the pH of the solution before the treatment is less than 9, it is difficult to find the end point of dropping hydrogen peroxide.
[0023]
Example 3
The cotton fibers bleached with hydrogen peroxide were bleached with sodium dithionite. The bleaching wastewater with sodium dithionite contained 0.13 gr / l of residual dithionite and a reducing sulfur compound. 1.5 ml of 10% by weight sodium hydroxide was added to 300 ml of the bleaching wastewater to adjust the pH to 12.1. An ORP meter was inserted into this solution, and a 1 wt% H 2 O 2 solution was added dropwise to treat the dithionite. The end point of the dropping of the H 2 O 2 solution was determined when the oxidation-reduction potential gradient became steep. The amount of 1 wt% H 2 O 2 dropped to this end point was 2.4 ml (24 mg in terms of 100% H 2 O 2 ). The pH at the end point was 11.5, and no residual dithionite was measured.
[0024]
Comparative Example 4
An ORP meter was inserted into 300 ml of the bleaching wastewater used in Example 3, and air was blown at 60 L / hr to treat dithionite.
As a result, it was not clearly understood where the oxidation-reduction potential gradient became steep. As a result of analyzing the residual amount of the residual dithionite at the time when air was blown in for 3 hours, the residual amount was 0.0177 gr (residual rate: 13.6%). The solution pH at this time was 4.3.
[0025]
Comparative Example 5
The wastewater (COD 417 ppm) from Comparative Example 4 from which residual dithionite had been removed was neutralized to pH 7.4 with dilute sulfuric acid, and then activated sludge treatment was carried out. % Met.
[0026]
Example 4
The wastewater (382 ppm of COD) from Example 3 from which residual dithionite had been removed was neutralized to pH 7.4 with dilute sulfuric acid, and activated sludge treatment was carried out. As a result, COD was reduced to 68 ppm, and the COD reduction rate was 82.2. % Met.
As described above, by removing the residual dithionite, the COD reduction rate in the activated sludge was greatly improved.
[0027]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, processing time is short, processing can be performed continuously, and the effect that a trace amount of dithionite can be completely processed is acquired.
If the present invention is combined with the preceding stage of the activated sludge treatment, the activated sludge treatment trouble caused by the residual dithionite is completely eliminated, and the activated sludge treatment is stabilized, so that the wastewater of stable water quality can be discharged.
Claims (2)
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| JP15166495A JP3555631B2 (en) | 1995-06-19 | 1995-06-19 | Wastewater treatment method |
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| JP15166495A JP3555631B2 (en) | 1995-06-19 | 1995-06-19 | Wastewater treatment method |
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