JP3954688B2 - Sewage treatment equipment - Google Patents

Description

【０００９】
上記第１の手段乃至第３の手段において、前記電極に直流定電流を印加することが好ましい。
【００１０】
上記第１の手段乃至第３の手段において、前記電極に所定時間毎に極性を転換する直流定電流を印加することが好ましい。
【００１１】
上記第１の手段乃至第３の手段において、前記電極に所定時間毎にパルス状に印加電流が増大する直流電流を印加することが好ましい。
【００１２】
上記第１の手段乃至第３の手段において、前記電極に所定時間毎に極性を転換すると共にパルス状に印加電流が増大する直流電流を印加することが好ましい。
【００１３】
【発明の実施の形態】
本発明の一実施の形態を図１乃至図４に示す汚水処理装置に基づいて以下に詳述する。
【００１４】
１は地中に埋設された処理槽である。該処理槽１内部は第１仕切壁２、第２仕切壁３及び第３仕切壁４により、後述する第１嫌気部５、第２嫌気部18、好気部22、沈殿部28及び消毒部30に区画されている。
【００１５】
５は生活雑排水が流入する流入口６を有する第１嫌気部、７は前記第１嫌気部５内に配設された第１嫌気濾床で、第１嫌気部５内に流入した生活雑排水中に混入している難分解性の夾雑物を沈殿分離し、第１嫌気濾床７に付着した嫌気性微生物により有機物を嫌気分解すると共に、有機性の窒素をアンモニア性窒素に嫌気分解する。
【００１６】
８は前記第１嫌気部５の汚水より上方で且つ後述する第１点検用開口49に臨む位置に配設された矩形箱状の溶出槽で、側面に後述する第３返送管45を介して分水計量装置39から供給された処理水を第１嫌気部５に返送する排出管９を備えている。10は前記溶出槽８上部に設けられ溶出槽８内の空気を排出する排気口である。
【００１７】
11は前記溶出槽８内に配設される鉄材からなる電極12を有し、溶出槽８を閉塞する絶縁体にて形成された電極カバ−である。13は後述する制御回路57により制御され、電極12間に直流定電流を印加する電源装置で、前記電極12間に電源装置13から供給される直流定電流を印加することにより、電極12から溶出した鉄イオンを溶出槽８内に供給する。前記溶出槽８、電極12及び電源装置13により溶出装置を構成している。
【００１８】
14は前記溶出槽８底部の前記電極12間に配設された第１散気管で、多数の空気吹出口を形成すると共に、第１ブロアー15と接続され、該第１ブロアー15から供給される空気を空気吹出口から放出することにより電極12を洗浄し汚泥の付着を防止すると共に、電極12から溶出する２価の鉄イオンをオルトリン酸と反応する３価の鉄イオンに酸化する。
【００１９】
16は前記第１嫌気部５内に配設された第１移流管で、前記第１嫌気部５で嫌気分解された処理水を、第１仕切壁２上部を貫通する第１給水口17を介して後述する第２嫌気部18に供給する。
【００２０】
18は前記第１仕切壁２により第１嫌気部５と区画された第２嫌気部、19は前記第２嫌気部18内に配設された第２嫌気濾床で、該第２嫌気濾床19により、浮遊物質を捕捉し嫌気性微生物により有機物を嫌気分解すると共に、有機性の窒素をアンモニア性窒素に嫌気分解する。
【００２１】
20は前記第２嫌気部18内に配設された第２移流管で、前記第２嫌気部18で嫌気分解された処理水を、第２仕切壁３上部を貫通する第２給水口21を介して後述する好気部22に給水する。22は前記第２仕切壁３により第２嫌気部18と区画された好気部で、第２嫌気部18で嫌気処理された処理水が第２移流管20を介して流入する。23は前記好気部22内に配設された接触材で、好気性微生物の培養を促進する。
【００２２】
24は前記好気部22底部に配設された第２散気管で、多数の空気吹出口を形成すると共に、第２ブロアー25と接続され、第２ブロアー25から供給される空気を空気吹出口から放出して好気部22内を好気状態に維持し、処理水を好気性微生物により好気分解すると共に、硝酸菌や亜硝酸菌の働きによりアンモニア性窒素を硝酸性や亜硝酸性の窒素に分解する。
【００２３】
26は前記接触材23下部に配設され、多数の空気吹出口を有する第３散気管で、前記第２ブロアー25と接続されている。前記第２ブロアー25からの空気供給は第２散気管24あるいは第３散気管26のいずれか一方に後述する制御回路57により制御された第１電磁弁27によって切り換えできるようになっている。
【００２４】
前記第１電磁弁27は通常、第２散気管24に切り換えて第２ブロアー25から供給される空気を第２散気管24の空気吹出口から放出して好気部22内を好気状態に維持し、接触材23を洗浄する際には第２ブロアー25からの空気供給を第３散気管26に切り換え、第３散気管26の空気吹出口から空気を放出させて、接触材23に付着し増殖して徐々に厚くなった生物膜を剥離する。
【００２５】
28は前記第３仕切壁４により好気部22と区画された沈殿部で、第３仕切壁４底部に設けられ、好気部22と沈殿部28を連通する連通口29から流入する、好気部22で好気分解された処理水を沈殿物と上澄み液とに分離する。また、前記沈殿部28底部に堆積した沈殿物を連通口29から好気部22に戻すため、沈殿部28底部を好気部22側に傾斜させている。
【００２６】
30は前記沈殿部28上部に設けた消毒部で、沈殿部28で分離された上澄み液が流入するようになっている。31は前記消毒部30内に設けられた殺菌装置で、該殺菌装置31内に備えた塩素系等の薬品により、消毒部30に流入した処理水を消毒する。32は前記消毒部30に連通する排水口で、消毒部30において消毒された処理水を処理槽１外に排水するようになっている。
【００２７】
33は前記好気部22底部と第１嫌気部５上部を連通する第１返送管である。34は前記好気部22底部の第１返送管33内に配設された第４散気管で、多数の空気吹出口を形成すると共に、第３ブロアー35と接続され、第３ブロアー35から供給される空気を空気吹出口から放出することにより、前記好気部22底部に堆積した汚泥及び沈殿部28から好気部22に返送された沈殿物を、第１返送管33内に吸い込み第１嫌気部５に返送するようになっている。
【００２８】
36は前記沈殿部28上部と後述する分水計量装置39の流入室40を連通する第２返送管である。37は前記第２返送管36内に配設された第５散気管で、多数の空気吹出口を形成すると共に、前記第３ブロアー35と接続している。前記第３ブロアー35からの空気供給は第４散気管34あるいは第５散気管37のいずれか一方に後述する制御回路57により制御された第２電磁弁38によって切り換えできるようになっている。
【００２９】
前記第２電磁弁38は通常、第５散気管36に切り換えて第３ブロアー35から供給される空気を第５散気管36の空気吹出口から放出することにより、沈殿部28内の上澄み液を第２返送管36内に吸い込み、後述する分水計量装置39の流入室40に移送するようになっている。
【００３０】
前記接触材23を洗浄した後には第３ブロアー35からの空気供給を第４散気管34に切り換え、第４散気管34の空気吹出口から空気を放出することにより、好気部22内の処理水が第１返送管33内を通り第１嫌気床槽５に流入する。この流れに伴って好気部22底部に堆積した汚泥及び沈殿部28から好気部22に戻った沈殿物を第１返送管33内に吸い込み第１嫌気部５に返送する。
【００３１】
39は前記沈殿部28上部に配設された矩形箱状の分水計量装置で、第２返送管36により移送された上澄み液を溶出槽８へ供給する量を所定量に調整できるようになっている。前記分水計量装置39は第２返送管36と接続された流入室40と、該流入室40と下部側を連通する開口を形成した隔壁41により仕切られた中間室42と、該中間室42内の処理水が流入する第１分水室43及び第２分水室44とに区画している。
【００３２】
前記第１分水室43は溶出槽８に第３返送管45を介して連通すると共に、中間室42とは壁の上部をＶ字状に開放した切欠部46により連通している。前記第２分水室44は前記好気部22上部に管47により連通すると共に、中間室42とは高さ調整可能な溢流堰板48の上部に形成される開口により連通している。
【００３３】
前記溢流堰板48の高さを調整し溢流堰板48の上部に形成される開口の大きさを変え、第２分水室44から好気部22に返送する処理水量を設定することにより、第１分水室43から溶出槽８に流入する処理水量が調節できるようになっている。
【００３４】
49は前記第１仕切壁２上部の第１嫌気部５、第２嫌気部18及び溶出槽８に対向する位置に設けられた第１点検用開口、50は前記第１点検用開口49に設けられたリードスイッチで、後述する第１蓋体51の開閉状態を検知するようになっている。51は前記第１点検用開口49を開閉自在に閉塞する第１蓋体、52は前記第１蓋体51に設けられ前記リードスイッチ50をオンオフ操作する磁石である。前記第１蓋体51に設けられた磁石52がリードスイッチ50に対向するように、第１蓋体51は図示しない位置決め手段により位置決めされている。
【００３５】
前記第１蓋体51は第１嫌気部５及び第２嫌気部18底部に堆積した汚泥の吸引排除、溶出槽８の電極12のメンテナンス時等に開閉するようになっている。また、第１蓋体51開放時にはリードスイッチ50がオフとなり、この信号に基づいて制御回路57は電源装置13だけを停止させ、第１蓋体51を装着すると電源装置13を作動させる。
【００３６】
53は前記好気部22に対向する位置に設けられた第２点検用開口、54は前記第２点検用開口53を開閉自在に閉塞する第２蓋体である。55は前記殺菌装置31に対向する位置に設けられた第３点検用開口、56は前記第３点検用開口55を開閉自在に閉塞する第３蓋体で、殺菌装置31への塩素系の薬品補給の際等に開閉するようになっている。
【００３７】
57は前記第１ブロアー15、第２ブロアー25、第３ブロアー35、電源装置13、第１電磁弁27及び第２電磁弁38等を制御する制御回路である。
【００３８】
而して、家庭から排出された生活雑排水は流入口６から第１嫌気部５に流入する。第１嫌気部５内に配設された第１嫌気濾床７により、生活雑排水中のトイレットペーパ−等の比較的粗大な固形物や夾雑物を除去し、後に流入する各処理槽での処理を円滑に行うための予備的処理を行うと共に、除去した固形物、夾雑物及び第１嫌気濾床７を通過する汚水を嫌気性微生物の働きにより嫌気分解し、ＢＯＤを低減化すると共に、汚水の分解により発生した汚泥は第１嫌気部５底部に堆積する。また、有機性の窒素をアンモニア性の窒素に嫌気分解する。
【００３９】
第１嫌気部５に流入する新たな生活雑排水により、前記第１嫌気部５で嫌気分解した処理水は第１移流管16の第１給水口17から第２嫌気部18に流入する。第２嫌気部18に流入した処理水は、第２嫌気濾床19で嫌気性微生物の働きにより有機物を嫌気分解し、ＢＯＤを低減化すると共に、汚水の分解により発生した汚泥は第２嫌気部18底部に堆積する。また、有機性の窒素をアンモニア性の窒素に嫌気分解する。
【００４０】
第２嫌気部18に流入する新たな処理水により、第２嫌気濾床19で嫌気分解した処理水は第２移流管20の第２給水口21から好気部22に流入する。好気部22に流入した処理水は、第２ブロアー25から供給される空気が第２散気管24の空気吹出口から放出されることにより撹拌される。
【００４１】
さらに、処理水中に酸素が溶存され、接触材23の表面に多数付着した好気性微生物の働きにより処理水を好気分解すると共に、有機リン酸塩等をオルトリン酸に分解し、アンモニア性窒素を硝酸性や亜硝酸性窒素に分解する。また、汚水の分解により発生した汚泥は好気部22底部に堆積する。
【００４２】
好気部22に流入する新たな処理水によって、接触材23に付着した好気性微生物の働きにより好気分解した処理水が、好気部22底部の連通口29から沈殿部28に流入する。沈殿部28に流入した処理水は、沈殿部28内を上昇する間に沈降性物質が沈降して連通口29から好気部22に返送され、上澄み液は消毒部30に流入する。消毒部30に流入した上澄み液は、塩素系の薬品を備えた消毒装置31により消毒され病原菌等の細菌を死滅させて、排水口32より処理槽１外に排水される。
【００４３】
第３ブロアー35から供給される空気を第５散気管37の空気吹出口から放出することにより、沈殿部28内の上澄み液は分水計量装置39の流入室40に流入し、中間室42で整流されて第１分水室43と第２分水室44に流入する。
【００４４】
溢流堰板48の高さを調整し、第２分水室44と中間室42を連通する溢流堰板48の上方に形成される開口の大きさを変えることにより、第２分水室44から好気部22に返送される水量は決まるため、第１分水室43から溶出槽８に流入する処理水を所定量に調節することができる。
【００４５】
第１分水室43から第３返送管45を介して溶出槽８に流入した処理水には、鉄材からなる電極12間に直流定電流を印加することにより電極12から溶出する鉄イオンが供給される。溶出した鉄イオンは溶出槽８内に存在するオルトリン酸と反応し、水不溶性のリン化合物として凝集、沈殿すると共に、排出管９により第１嫌気部５に返送される。第１嫌気部５に返送された処理水中の鉄イオンは、第１嫌気部５内に存在するオルトリン酸と反応し、水不溶性のリン化合物として凝集、沈殿する。
【００４６】
また、第１嫌気部５に返送された処理水中の硝酸性や亜硝酸性の窒素は、第１嫌気部５に多く存在する脱窒菌により還元され、窒素ガスとして空気中に放散して除去される。
【００４７】
溶出槽８から第１嫌気部５に返送される処理水は、溶存酸素濃度が極端に高い好気部22からではなく、沈殿部28から供給したものであり、溶出槽８内の処理水を第１嫌気部５に返送しても嫌気性微生物に対する影響も少なく嫌気処理がおこなえる。
【００４８】
接触材23に付着した好気性微生物により形成された生物膜は増殖して徐々に厚くなるので、目詰まり防止のため、制御回路57が定期的に第１電磁弁27を制御して第２ブロアー25からの空気供給を第３散気管26に切り換え、第３散気管26の空気吹出口から空気を放出させて生物膜を剥離させる。
【００４９】
第３散気管26からの空気供給が終了すると、剥離された生物膜は好気部22底部に堆積するが、制御回路57が第２電磁弁38を制御して第３ブロアー35からの空気供給を第４散気管34に切り換え、第４散気管34の空気吹出口から空気を放出することにより、好気部22内の処理水は第１返送管33を介して第１嫌気部５に流入する。この流れに伴って好気部22底部に堆積した汚泥及び沈殿部28から好気部22に戻った沈殿物を第１返送管33を介して第１嫌気部５に返送する。
【００５０】
溶出槽８は第１点検用開口49に臨ませて配設しており、第１蓋体51を開けて第１嫌気部５及び第２嫌気部18に堆積した汚泥を吸引排除する際等に溶出槽８を点検することができる。さらに、第１蓋体51を開放すると、制御回路57は電源装置13だけを停止させ、電源装置13以外の装置は継続して動作させているため、汚水処理装置の動作及び汚水処理状況を確認することができると共に、溶出槽８メンテナンス時の感電を防止することができる。
【００５１】
溶出槽８内の電極12の電解により電極12から発生する水素ガス量はファラデーの法則により電極12に印加される電流値によって決まるものであり、例えば、電極12に印加する電流値をＢアンペアとすると、１分間に発生する水素ガス量Ａ（リットル）は、標準状態（摂氏２０度、１気圧）において次の数式で示される。
【００５２】
【数３】

【００５３】
水素ガスの爆発濃度は４〜７５％であるため、第１散気管14を介して第１ブロア−15から供給される空気により、溶出槽８内の水素ガス濃度を４％未満にするために１分間に最低限必要な空気供給量Ｖ（リットル）は次の数式で示される。
【００５４】
【数４】

【００５５】
従って、第１ブロアー15の空気供給量を制御して、制御回路57が上記関係式Ｖ＝０．１７９Ｂ（リットル／分）から算出される空気供給量より多くの空気を第１ブロアー15から第１散気管14を介して溶出槽８に供給することにより、溶出槽８内の水素ガスを爆発濃度より低い濃度に低下させることができ、爆発を防止することができる。
【００５６】
また、家に住んでいる人数により、汚水処理装置に流入するリンの量は略決まり、流入したリンに対応する鉄イオンを溶出させるために電極12に印加する電流値が決定されるため、施工御者が電極12に印加する電流値に応じて最適な空気供給量の第１ブロアー15を選択して設置する構成、あるいは、電極12に印加した電流値に応じて第１ブロアー15の空気供給量を調節して水素による爆発を防止する構成としてもよい。
【００５７】
さらに、溶出槽８内に電極を複数組配設した場合は、各々の電極に印加する電流値を合計した総電流値に対して算出した水素ガス発生量に基づいて、必要量の空気供給を行えばよい。
【００５８】
空気より軽い水素ガスは溶出槽８上部に溜まりやすくなるが、排気口10を溶出槽８上部に設けているため、溶出槽８内の水素ガスは空気と共に効率よく溶出槽８外に排出され、溶出槽８内に水素ガスが残留することによる水素ガス濃度の上昇を防止している。
【００５９】
本発明の実施の形態において、鉄材からなる電極12を長期にわたって溶出槽８内の処理水中に浸漬していると、電極表面に酸化被膜が発生し、不動態化状態となって鉄イオンの溶出が徐々に減少し、脱リン性能が低下する。
【００６０】
従って、鉄材からなる一対の電極間に直流定電流を印加し、その電流を所定時間毎に極性転換する構成とすることが好ましい。陽極側の鉄材表面には、長期にわたって使用していると酸化被膜が発生するが、陰極側の鉄材表面は、陰極側鉄材から発生する水素ガスにより洗浄され、酸化被膜は生じない。よって、陽極側の鉄材表面に酸化被膜が発生して鉄イオンの溶出が減少するまでの時間間隔で極性を転換することにより、鉄イオンの溶出を略一定に維持することができ、脱リン性能を一定に維持することができる。
【００６１】
また、この構成では、両電極を鉄材とすることにより、常時陽極側電極となる鉄材から鉄イオンが溶出して処理水に供給されるため、脱リン性能を常時一定の状態に維持することができる。
【００６２】
また、電極の少なくとも陽極側に鉄材を用い、両電極間に直流定電流を印加し、所定時間毎にパルス状に印加電流を増大させる構成としてもよい。この構成においては、パルス状に印加電流を増大させることにより、陽極側鉄材表面に発生した酸化被膜を剥離させることができ、鉄イオンの溶出を略一定に維持して、脱リン性能を一定に維持することができる。印加電流の増大に伴って水素ガス発生量は増大するが、印加電流の増大に伴って第１ブロア−15の空気供給量を増大させれはよい。
【００６３】
さらに、鉄材からなる一対の電極間に直流定電流を印加し、その電流を所定時間毎に極性転換すると共に、パルス状に印加電流を増大させる構成としてもよい。極性転換するまでの時間が長い場合には、陽極側の鉄材表面に酸化被膜が生じており、極性を転換することによって水素ガスにより洗浄して酸化被膜を剥離することができるが、酸化被膜が剥離されるまでに若干の時間を必要とし、酸化被膜が剥離されるまでの間の電気的抵抗が大きいため、消費電力が増大するおそれがある。
【００６４】
従って、上記構成としてパルス状に印加電流を増大させることにより陽極から陰極に転換した鉄材表面の酸化被膜を短時間に除去することができ、消費電力の増大を防止することができる。
【００６５】
尚、本発明の実施の形態では、直流定電流を印加して鉄イオンを溶出する電極として両極に鉄材を用いたが、陽極側の電極に鉄材を用い、陰極側の電極をチタンや白金等の不溶性材料とした構成にしてもよい。
【００６６】
また、本発明の実施の形態では、直流定電流を印加して鉄イオンを溶出する電極として両極に鉄材を用いたが、アルミニウムを用いた構成としてもよい。
【００６７】
【発明の効果】
本発明の請求項１の構成によると、電極の電解により発生した水素ガスを希釈することができ、メンテナンス時等の爆発を防止し、信頼性を向上することができる等の効果を奏する。
【００６８】
本発明の請求項２の構成によると、電極の電解により発生した水素ガスを希釈することができ、メンテナンス時等の爆発を防止し、信頼性を向上することができる等の効果を奏する。
【００６９】
本発明の請求項３の構成によると、電極の電解により発生した水素ガスを送風手段により希釈することができ、メンテナンス時等の爆発を防止し、信頼性を向上することができる等の効果を奏する。
【００７０】
本発明の請求項４の構成によると、イオン溶出量を略一定に保つことができる等の効果を奏する。
【００７１】
本発明の請求項５の構成によると、両電極を略均一に減少させて、両電極を同時交換することができ、メンテナンスを容易にすることができる等の効果を奏する。
【００７２】
本発明の請求項６の構成によると、陽極側鉄材表面に発生した酸化被膜を剥離することができ、イオン溶出量低下を防止すると共に、消費電力を減少させることができる等の効果を奏する。
【００７３】
本発明の請求項７の構成によると、陽極側鉄材表面に発生した酸化被膜を剥離することができ、イオン溶出量低下を防止すると共に、両電極を略均一に減少させて、両電極を同時交換することができ、メンテナンスを容易にすることができる等の効果を奏する。
【図面の簡単な説明】
【図１】本発明一実施の形態の汚水処理装置の断面図である。
【図２】同他の方向から見た断面図である。
【図３】同溶出装置の拡大断面図である。
【図４】同分水計量装置の斜視図である。
【符号の説明】
１ 処理槽
５ 第１嫌気部（嫌気部）
８ 溶出槽
12 電極
14 第１散気管（散気管）
15 第１ブロア−（送風手段）
22 好気部
28 沈殿部
57 制御回路（制御手段）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sewage treatment apparatus that purifies sewage, and more particularly to a sewage treatment apparatus that removes phosphorus from sewage.
[0002]
[Prior art]
As this type of sewage treatment device, the sewage in the aerobic tank is returned to the anaerobic tank through an elution device that elutes iron ions, and the iron ions are reacted with orthophosphoric acid in the sewage to aggregate as a water-insoluble phosphorus compound. One that precipitates and removes phosphorus from sewage is known.
[0003]
However, hydrogen gas generated from the electrode accompanies the electrolysis of the electrode and accumulates in the elution tank, and there is a risk of explosion if fire is brought close by mistake during maintenance.
[0004]
[Problems to be solved by the invention]
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a sewage treatment apparatus that can prevent explosion during maintenance and improve reliability.
[0005]
[Means for Solving the Problems]
A first means for solving the above-described problems includes a treatment tank having an anaerobic part, an aerobic part and a precipitation part, an electrode made of iron material or aluminum and eluting iron ions or aluminum ions by applying an electric current, iron A sewage treatment apparatus for supplying air to the sewage in the treatment tank, wherein the sewage is supplied from the diffusion pipe to the sewage. The air supply amount is set according to the total current value applied to the electrodes.
[0006]
The second means for solving the above problems includes a treatment tank having an anaerobic part, an aerobic part and a precipitation part, an electrode made of iron material or aluminum and eluting iron ions or aluminum ions by applying an electric current, iron A sewage treatment apparatus comprising a diffuser for supplying air into sewage from which ions or aluminum ions are eluted, and supplying the eluted iron ions or aluminum ions to sewage in the treatment tank, which is applied to the electrodes Control means for detecting the total current value and controlling the amount of air supplied from the diffuser to the sewage based on the detected total current value is provided.
[0007]
A third means for solving the above-mentioned problems includes a treatment tank having an anaerobic part, an aerobic part and a precipitation part, an electrode made of iron material or aluminum and applying an electric current to elute iron ions or aluminum ions, and an electrode A diffusing pipe disposed at a lower position of the diffusing pipe, and a blowing means connected to the diffusing pipe for supplying air into the sewage through the diffusing pipe, and eluting iron ions or aluminum ions into the treatment tank A sewage treatment apparatus that supplies a total current value applied to the electrodes, and based on the detected total current value, air represented by the following formula A is supplied to the sewage from an air diffuser. Control means for controlling is provided.
[0008]
[Expression 2]

[0009]
In the first to third means, it is preferable to apply a constant DC current to the electrode.
[0010]
In the first to third means, it is preferable that a constant DC current that changes polarity every predetermined time is applied to the electrode.
[0011]
In the first to third means, it is preferable to apply a direct current that increases the applied current in a pulse shape every predetermined time to the electrode.
[0012]
In the first to third means, it is preferable to apply a direct current that changes the polarity at predetermined intervals and increases the applied current in a pulsed manner to the electrodes.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
One embodiment of the present invention will be described in detail below based on the sewage treatment apparatus shown in FIGS.
[0014]
Reference numeral 1 denotes a treatment tank buried in the ground. The inside of the treatment tank 1 is divided into a first anaerobic part 5, a second anaerobic part 18, an aerobic part 22, a sedimentation part 28, and a disinfecting part by a first partition wall 2, a second partition wall 3 and a third partition wall 4. There are 30 sections.
[0015]
Reference numeral 5 denotes a first anaerobic part having an inlet 6 through which miscellaneous wastewater flows. Reference numeral 7 denotes a first anaerobic filter bed disposed in the first anaerobic part 5. The hard-to-decompose contaminants mixed in the wastewater are separated by precipitation, the organic matter is anaerobically decomposed by anaerobic microorganisms attached to the first anaerobic filter bed 7, and the organic nitrogen is anaerobically decomposed into ammonia nitrogen. .
[0016]
Reference numeral 8 denotes a rectangular box-shaped elution tank disposed above the sewage of the first anaerobic part 5 and facing a first inspection opening 49 which will be described later, and a side surface via a third return pipe 45 which will be described later. A discharge pipe 9 is provided for returning the treated water supplied from the diversion device 39 to the first anaerobic part 5. An exhaust port 10 is provided at the upper part of the elution tank 8 and discharges air in the elution tank 8.
[0017]
Reference numeral 11 denotes an electrode cover having an electrode 12 made of iron material disposed in the elution tank 8 and formed of an insulator that closes the elution tank 8. 13 is a power supply device that is controlled by a control circuit 57 to be described later and applies a DC constant current between the electrodes 12. By applying a DC constant current supplied from the power supply device 13 between the electrodes 12, elution from the electrode 12 The iron ions are supplied into the elution tank 8. The elution tank 8, the electrode 12 and the power supply device 13 constitute an elution apparatus.
[0018]
Reference numeral 14 denotes a first air diffuser disposed between the electrodes 12 at the bottom of the elution tank 8, which forms a large number of air outlets, is connected to the first blower 15, and is supplied from the first blower 15. By discharging air from the air outlet, the electrode 12 is washed to prevent sludge from adhering, and the divalent iron ions eluted from the electrode 12 are oxidized to trivalent iron ions that react with orthophosphoric acid.
[0019]
Reference numeral 16 denotes a first advection pipe disposed in the first anaerobic part 5. The treated water decomposed anaerobically in the first anaerobic part 5 is passed through a first water supply port 17 penetrating the upper part of the first partition wall 2. To the second anaerobic section 18 to be described later.
[0020]
Reference numeral 18 denotes a second anaerobic part partitioned from the first anaerobic part 5 by the first partition wall 2, and 19 denotes a second anaerobic filter bed disposed in the second anaerobic part 18, the second anaerobic filter bed. 19 traps suspended solids and anaerobically decomposes organic matter by anaerobic microorganisms, and anaerobically decomposes organic nitrogen to ammonia nitrogen.
[0021]
Reference numeral 20 denotes a second advection pipe disposed in the second anaerobic part 18. The treated water decomposed anaerobically in the second anaerobic part 18 is passed through a second water supply port 21 penetrating the upper part of the second partition wall 3. Then, water is supplied to the aerobic part 22 described later. Reference numeral 22 denotes an aerobic part partitioned from the second anaerobic part 18 by the second partition wall 3, and treated water that has been anaerobically treated by the second anaerobic part 18 flows through the second advection pipe 20. Reference numeral 23 denotes a contact material disposed in the aerobic part 22 and promotes culture of aerobic microorganisms.
[0022]
Reference numeral 24 denotes a second air diffuser disposed at the bottom of the aerobic part 22, which forms a large number of air outlets and is connected to the second blower 25, and the air supplied from the second blower 25 is used as an air outlet. The aerobic part 22 is released from the aerobic state and the treated water is aerobically decomposed by aerobic microorganisms, and ammonia nitrogen is converted to nitrate or nitrite by the action of nitrate bacteria and nitrite bacteria. Decomposes into nitrogen.
[0023]
Reference numeral 26 denotes a third air diffuser disposed below the contact material 23 and having a number of air outlets, and is connected to the second blower 25. The air supply from the second blower 25 can be switched to either the second air diffuser 24 or the third air diffuser 26 by a first electromagnetic valve 27 controlled by a control circuit 57 described later.
[0024]
The first electromagnetic valve 27 normally switches to the second air diffuser 24 and discharges air supplied from the second blower 25 from the air outlet of the second air diffuser 24 to bring the aerobic portion 22 into an aerobic state. When maintaining and cleaning the contact material 23, the air supply from the second blower 25 is switched to the third air diffuser 26, and air is discharged from the air outlet of the third air diffuser 26 to adhere to the contact material 23. The biofilm that has grown and gradually thickened is peeled off.
[0025]
Reference numeral 28 denotes a sedimentation portion partitioned from the aerobic portion 22 by the third partition wall 4 and is provided at the bottom of the third partition wall 4 and flows in from a communication port 29 that communicates the aerobic portion 22 and the sedimentation portion 28. The treated water that has been aerobically decomposed in the gas part 22 is separated into a precipitate and a supernatant. Further, in order to return the sediment deposited on the bottom of the sedimentation portion 28 from the communication port 29 to the aerobic portion 22, the bottom of the sedimentation portion 28 is inclined toward the aerobic portion 22 side.
[0026]
Reference numeral 30 denotes a disinfecting unit provided at the upper part of the settling unit 28, and the supernatant liquid separated in the settling unit 28 flows in. 31 is a sterilization device provided in the sterilization unit 30, and sterilizes the treated water flowing into the sterilization unit 30 with a chemical such as chlorine based in the sterilization device 31. A drain port 32 communicates with the sterilization unit 30 and drains the treated water sterilized in the sterilization unit 30 to the outside of the treatment tank 1.
[0027]
A first return pipe 33 communicates the bottom of the aerobic part 22 and the upper part of the first anaerobic part 5. Reference numeral 34 denotes a fourth air diffuser disposed in the first return pipe 33 at the bottom of the aerobic part 22, which forms a large number of air outlets and is connected to the third blower 35 and supplied from the third blower 35. By discharging the air to be discharged from the air outlet, the sludge accumulated at the bottom of the aerobic part 22 and the sediment returned to the aerobic part 22 from the settling part 28 are sucked into the first return pipe 33 and the first Returned to the anaerobic part 5.
[0028]
Reference numeral 36 denotes a second return pipe that communicates between the upper part of the settling portion 28 and an inflow chamber 40 of a water diversion meter 39 described later. Reference numeral 37 denotes a fifth air diffuser disposed in the second return pipe 36, which forms a large number of air outlets and is connected to the third blower 35. The air supply from the third blower 35 can be switched to either the fourth diffuser pipe 34 or the fifth diffuser pipe 37 by a second electromagnetic valve 38 controlled by a control circuit 57 described later.
[0029]
The second solenoid valve 38 normally switches to the fifth air diffuser 36 and discharges the air supplied from the third blower 35 from the air outlet of the fifth air diffuser 36, so that the supernatant liquid in the settling portion 28 is discharged. The air is sucked into the second return pipe 36 and transferred to an inflow chamber 40 of a water metering device 39 described later.
[0030]
After cleaning the contact material 23, the air supply from the third blower 35 is switched to the fourth air diffuser 34, and the air is discharged from the air outlet of the fourth air diffuser 34. Water flows into the first anaerobic floor tank 5 through the first return pipe 33. Along with this flow, the sludge accumulated at the bottom of the aerobic part 22 and the sediment returned from the precipitation part 28 to the aerobic part 22 are sucked into the first return pipe 33 and returned to the first anaerobic part 5.
[0031]
Reference numeral 39 denotes a rectangular box-shaped water metering device disposed on the upper part of the sedimentation section 28. The amount of the supernatant liquid transferred by the second return pipe 36 can be adjusted to a predetermined amount. ing. The diversion meter 39 includes an inflow chamber 40 connected to the second return pipe 36, an intermediate chamber 42 partitioned by a partition wall 41 having an opening communicating with the inflow chamber 40 and the lower side, and the intermediate chamber 42 It is divided into a first water diversion chamber 43 and a second water diversion chamber 44 into which the treated water flows.
[0032]
The first water diversion chamber 43 communicates with the elution tank 8 via a third return pipe 45, and communicates with the intermediate chamber 42 by a notch 46 whose upper portion of the wall is opened in a V shape. The second water diversion chamber 44 communicates with the upper portion of the aerobic portion 22 through a pipe 47 and communicates with the intermediate chamber 42 through an opening formed in the upper portion of the overflow dam plate 48 whose height can be adjusted.
[0033]
Adjust the height of the overflow dam plate 48, change the size of the opening formed in the upper part of the overflow dam plate 48, and set the amount of treated water to be returned from the second diversion chamber 44 to the aerobic part 22. Thus, the amount of treated water flowing from the first water diversion chamber 43 into the elution tank 8 can be adjusted.
[0034]
49 is a first inspection opening provided at a position facing the first anaerobic part 5, the second anaerobic part 18 and the elution tank 8 on the first partition wall 2, and 50 is provided in the first inspection opening 49. The opened / closed state of the first lid 51 to be described later is detected by the reed switch. Reference numeral 51 denotes a first lid that closes the first inspection opening 49 so that the first inspection opening 49 can be opened and closed. Reference numeral 52 denotes a magnet that is provided on the first lid 51 and that turns the reed switch 50 on and off. The first lid 51 is positioned by positioning means (not shown) so that the magnet 52 provided on the first lid 51 faces the reed switch 50.
[0035]
The first lid 51 is opened and closed during suction and removal of sludge accumulated on the bottoms of the first anaerobic part 5 and the second anaerobic part 18 and during maintenance of the electrode 12 of the elution tank 8. Further, when the first lid 51 is opened, the reed switch 50 is turned off. Based on this signal, the control circuit 57 stops only the power supply device 13 and operates the power supply device 13 when the first lid 51 is attached.
[0036]
53 is a second inspection opening provided at a position facing the aerobic part 22, and 54 is a second lid for closing the second inspection opening 53 so as to be freely opened and closed. 55 is a third inspection opening provided at a position facing the sterilizing device 31, and 56 is a third lid for closing the third inspection opening 55 so as to be openable and closable. It opens and closes when replenishing.
[0037]
A control circuit 57 controls the first blower 15, the second blower 25, the third blower 35, the power supply device 13, the first electromagnetic valve 27, the second electromagnetic valve 38, and the like.
[0038]
Thus, household wastewater discharged from the household flows into the first anaerobic part 5 from the inlet 6. The first anaerobic filter bed 7 disposed in the first anaerobic part 5 removes relatively coarse solids and contaminants such as toilet paper in domestic wastewater, and in each treatment tank that flows later. While performing a preliminary treatment for smoothly performing the treatment, anaerobic microorganisms anaerobically decompose the removed solids, contaminants and sewage passing through the first anaerobic filter bed 7 to reduce BOD, Sludge generated by the decomposition of the sewage accumulates at the bottom of the first anaerobic part 5. Organic nitrogen is anaerobically decomposed into ammonia nitrogen.
[0039]
The treated water decomposed anaerobically in the first anaerobic part 5 flows into the second anaerobic part 18 from the first water supply port 17 of the first advection pipe 16 due to the new domestic wastewater flowing into the first anaerobic part 5. The treated water flowing into the second anaerobic part 18 anaerobically decomposes organic matter by the action of anaerobic microorganisms in the second anaerobic filter bed 19 to reduce BOD, and sludge generated by the decomposition of sewage is the second anaerobic part. 18 Deposit at the bottom. Organic nitrogen is anaerobically decomposed into ammonia nitrogen.
[0040]
The treated water decomposed anaerobically in the second anaerobic filter bed 19 by the new treated water flowing into the second anaerobic part 18 flows into the aerobic part 22 from the second water supply port 21 of the second advection pipe 20. The treated water flowing into the aerobic part 22 is agitated by releasing the air supplied from the second blower 25 from the air outlet of the second air diffuser tube 24.
[0041]
Furthermore, oxygen is dissolved in the treated water, and the treated water is aerobically decomposed by the action of aerobic microorganisms adhering to the surface of the contact material 23, and the organic phosphate is decomposed into orthophosphoric acid, and ammonia nitrogen is removed. Decomposes into nitrate and nitrite nitrogen. In addition, sludge generated by the decomposition of sewage accumulates at the bottom of the aerobic part 22.
[0042]
The treated water that has been aerobically decomposed by the action of aerobic microorganisms attached to the contact material 23 by the new treated water flowing into the aerobic part 22 flows into the sedimentation part 28 from the communication port 29 at the bottom of the aerobic part 22. The treated water that has flowed into the sedimentation section 28 settles while the ascending inside the sedimentation section 28, and is returned to the aerobic section 22 through the communication port 29, and the supernatant liquid flows into the disinfection section 30. The supernatant liquid that has flowed into the sterilization unit 30 is sterilized by a sterilization apparatus 31 equipped with chlorinated chemicals, kills bacteria such as pathogenic bacteria, and is drained from the treatment tank 1 through the drain port 32.
[0043]
By discharging the air supplied from the third blower 35 from the air outlet of the fifth diffuser pipe 37, the supernatant liquid in the settling portion 28 flows into the inflow chamber 40 of the diversion device 39, and in the intermediate chamber 42. The flow is rectified and flows into the first water diversion chamber 43 and the second water diversion chamber 44.
[0044]
By adjusting the height of the overflow weir 48 and changing the size of the opening formed above the overflow weir 48 connecting the second diversion chamber 44 and the intermediate chamber 42, the second diversion chamber Since the amount of water returned from 44 to the aerobic part 22 is determined, the treated water flowing into the elution tank 8 from the first water diversion chamber 43 can be adjusted to a predetermined amount.
[0045]
The treated water flowing into the elution tank 8 from the first water diversion chamber 43 through the third return pipe 45 is supplied with iron ions eluted from the electrodes 12 by applying a DC constant current between the electrodes 12 made of iron. Is done. The eluted iron ions react with the orthophosphoric acid present in the elution tank 8 to agglomerate and precipitate as a water-insoluble phosphorus compound and are returned to the first anaerobic part 5 by the discharge pipe 9. The iron ions in the treated water returned to the first anaerobic part 5 react with orthophosphoric acid present in the first anaerobic part 5 and aggregate and precipitate as a water-insoluble phosphorus compound.
[0046]
Also, nitrate and nitrite nitrogen in the treated water returned to the first anaerobic part 5 is reduced by denitrifying bacteria present in the first anaerobic part 5 and diffused and removed as nitrogen gas in the air. The
[0047]
The treated water returned from the elution tank 8 to the first anaerobic section 5 is not supplied from the aerobic section 22 where the dissolved oxygen concentration is extremely high, but is supplied from the sedimentation section 28. Even if it returns to the 1st anaerobic part 5, there is little influence with respect to anaerobic microorganisms, and anaerobic processing can be performed.
[0048]
Since the biofilm formed by the aerobic microorganisms attached to the contact material 23 grows and gradually thickens, the control circuit 57 periodically controls the first solenoid valve 27 to prevent clogging in order to prevent clogging. The air supply from 25 is switched to the third air diffuser 26, and air is released from the air outlet of the third air diffuser 26 to peel off the biofilm.
[0049]
When the air supply from the third air diffuser 26 is completed, the peeled biofilm is deposited on the bottom of the aerobic part 22, but the control circuit 57 controls the second electromagnetic valve 38 to supply the air from the third blower 35. Is switched to the fourth air diffuser 34 and air is discharged from the air outlet of the fourth air diffuser 34 so that the treated water in the aerobic part 22 flows into the first anaerobic part 5 through the first return pipe 33. To do. Accompanying this flow, the sludge accumulated at the bottom of the aerobic part 22 and the sediment returned from the precipitation part 28 to the aerobic part 22 are returned to the first anaerobic part 5 via the first return pipe 33.
[0050]
The elution tank 8 is disposed so as to face the first inspection opening 49. When the first lid 51 is opened and the sludge accumulated in the first anaerobic part 5 and the second anaerobic part 18 is sucked out, etc. The elution tank 8 can be inspected. Further, when the first lid 51 is opened, the control circuit 57 stops only the power supply device 13 and the devices other than the power supply device 13 are continuously operated, so the operation of the sewage treatment device and the sewage treatment status are confirmed. It is possible to prevent electric shock during the elution tank 8 maintenance.
[0051]
The amount of hydrogen gas generated from the electrode 12 by electrolysis of the electrode 12 in the elution tank 8 is determined by the current value applied to the electrode 12 according to Faraday's law. For example, the current value applied to the electrode 12 is expressed as B ampere. Then, the hydrogen gas amount A (liter) generated per minute is expressed by the following formula in the standard state (20 degrees Celsius, 1 atmosphere).
[0052]
[Equation 3]

[0053]
Since the explosion concentration of hydrogen gas is 4 to 75%, in order to make the hydrogen gas concentration in the elution tank 8 less than 4% by the air supplied from the first blower-15 through the first air diffuser 14. The minimum required air supply amount V (liter) per minute is expressed by the following equation.
[0054]
[Expression 4]

[0055]
Therefore, the air supply amount of the first blower 15 is controlled, and the control circuit 57 supplies more air from the first blower 15 than the air supply amount calculated from the relational expression V = 0.179B (liters / minute). By supplying the elution tank 8 via the 1 air diffuser 14, the hydrogen gas in the elution tank 8 can be lowered to a concentration lower than the explosion concentration, and explosion can be prevented.
[0056]
In addition, the amount of phosphorus flowing into the sewage treatment device is substantially determined by the number of people living in the house, and the current value applied to the electrode 12 to elute iron ions corresponding to the flowing phosphorus is determined. A configuration in which the first blower 15 having an optimum air supply amount is selected and installed according to the current value applied to the electrode 12 by the user, or the air supply of the first blower 15 according to the current value applied to the electrode 12 It is good also as a structure which adjusts the quantity and prevents the explosion by hydrogen.
[0057]
Furthermore, when a plurality of sets of electrodes are arranged in the elution tank 8, the required amount of air is supplied based on the hydrogen gas generation amount calculated for the total current value obtained by summing the current values applied to the electrodes. Just do it.
[0058]
Hydrogen gas that is lighter than air easily collects in the upper part of the elution tank 8, but since the exhaust port 10 is provided in the upper part of the elution tank 8, the hydrogen gas in the elution tank 8 is efficiently discharged together with air to the outside of the elution tank 8, The hydrogen gas concentration is prevented from increasing due to the hydrogen gas remaining in the elution tank 8.
[0059]
In the embodiment of the present invention, when the electrode 12 made of iron is immersed in the treated water in the elution tank 8 for a long period of time, an oxide film is generated on the electrode surface, and the iron ion is eluted and becomes a passivated state. Gradually decreases, dephosphorization performance decreases.
[0060]
Therefore, it is preferable to apply a constant DC current between a pair of electrodes made of iron and to change the polarity of the current every predetermined time. When used for a long period of time, an oxide film is generated on the surface of the iron material on the anode side, but the surface of the iron material on the cathode side is washed with hydrogen gas generated from the iron material on the cathode side, and no oxide film is formed. Therefore, the elution of iron ions can be maintained substantially constant by changing the polarity at a time interval until an oxide film is generated on the surface of the iron material on the anode side and the elution of iron ions is reduced. Can be kept constant.
[0061]
Moreover, in this structure, since both electrodes are made of iron material, iron ions are always eluted from the iron material serving as the anode side electrode and supplied to the treated water, so that the dephosphorization performance can be constantly maintained in a constant state. it can.
[0062]
Alternatively, an iron material may be used at least on the anode side of the electrode, a constant DC current may be applied between both electrodes, and the applied current may be increased in a pulsed manner every predetermined time. In this configuration, by increasing the applied current in a pulsed manner, the oxide film generated on the surface of the anode-side iron material can be peeled off, the elution of iron ions is maintained substantially constant, and the dephosphorization performance is kept constant. Can be maintained. Although the amount of hydrogen gas generated increases as the applied current increases, the amount of air supplied to the first blower-15 may increase as the applied current increases.
[0063]
Furthermore, it is good also as a structure which applies a direct-current constant current between a pair of electrodes which consist of iron materials, changes the polarity of the electric current for every predetermined time, and increases an applied electric current in a pulse form. When the time until the polarity change is long, an oxide film is formed on the surface of the iron material on the anode side. By changing the polarity, the oxide film can be removed by washing with hydrogen gas. Some time is required until peeling, and since the electric resistance until the oxide film is peeled off is large, power consumption may increase.
[0064]
Therefore, by increasing the applied current in a pulsed manner as described above, the oxide film on the iron material surface converted from the anode to the cathode can be removed in a short time, and an increase in power consumption can be prevented.
[0065]
In the embodiment of the present invention, an iron material is used as an electrode for eluting iron ions by applying a DC constant current. However, an iron material is used for the anode side electrode, and the cathode side electrode is made of titanium, platinum, or the like. Alternatively, the insoluble material may be used.
[0066]
Further, in the embodiment of the present invention, the iron material is used for both electrodes as an electrode for eluting iron ions by applying a DC constant current, but a configuration using aluminum may be used.
[0067]
【The invention's effect】
According to the configuration of the first aspect of the present invention, it is possible to dilute the hydrogen gas generated by the electrolysis of the electrode, to prevent the explosion at the time of maintenance and to improve the reliability.
[0068]
According to the configuration of the second aspect of the present invention, the hydrogen gas generated by electrolysis of the electrode can be diluted, and there is an effect that the explosion during maintenance or the like can be prevented and the reliability can be improved.
[0069]
According to the configuration of the third aspect of the present invention, the hydrogen gas generated by the electrolysis of the electrode can be diluted by the blowing means, and the explosion can be prevented during maintenance and the reliability can be improved. Play.
[0070]
According to the configuration of the fourth aspect of the present invention, there is an effect that the ion elution amount can be kept substantially constant.
[0071]
According to the configuration of the fifth aspect of the present invention, it is possible to reduce both the electrodes substantially uniformly and to replace both the electrodes at the same time.
[0072]
According to the structure of Claim 6 of this invention, there exists an effect that the oxide film which generate | occur | produced on the anode side iron material surface can be peeled, an ion elution amount fall can be prevented, and power consumption can be reduced.
[0073]
According to the configuration of the seventh aspect of the present invention, the oxide film generated on the surface of the anode side iron material can be peeled off, the decrease in the amount of ion elution is prevented, and both electrodes are reduced substantially uniformly, so that both electrodes can be simultaneously used. It can be exchanged, and there are effects such as easy maintenance.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a sewage treatment apparatus according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view seen from the other direction.
FIG. 3 is an enlarged sectional view of the elution apparatus.
FIG. 4 is a perspective view of the water splitting device.
[Explanation of symbols]
1 treatment tank 5 1st anaerobic part (anaerobic part)
8 Elution tank
12 electrodes
14 First air diffuser (air diffuser)
15 First blower (air blowing means)
22 Aerobic part
28 Settling part
57 Control circuit (control means)

Claims (7)

Air is supplied to a treatment tank having an anaerobic part, an aerobic part and a precipitation part, an electrode made of iron or aluminum and eluting iron ions or aluminum ions by applying an electric current, and sewage water from which iron ions or aluminum ions are eluted. A sewage treatment apparatus for supplying the eluted iron ions or aluminum ions to the sewage in the treatment tank, wherein an air supply amount from the diffusion pipe to the sewage is applied to the electrode A sewage treatment apparatus, which is set according to a total current value. Air is supplied to a treatment tank having an anaerobic part, an aerobic part and a precipitation part, an electrode made of iron or aluminum and eluting iron ions or aluminum ions by applying an electric current, and sewage water from which iron ions or aluminum ions are eluted. A sewage treatment apparatus that supplies the eluted iron ions or aluminum ions to the sewage in the treatment tank, and detects a total current value applied to the electrode, to the detected total current value A sewage treatment apparatus provided with a control means for controlling the amount of air supplied from the air diffusing pipe to the sewage on the basis thereof. A treatment tank having an anaerobic part, an aerobic part and a precipitation part, an electrode made of iron or aluminum and applying an electric current to elute iron ions or aluminum ions, an air diffuser disposed below the electrode, A sewage treatment apparatus that is connected to the diffuser pipe and has a blowing means for supplying air into the sewage through the diffuser pipe, and supplies the eluted iron ions or aluminum ions into the treatment tank, which is applied to the electrodes And a control means for controlling the amount of air supplied from the air diffuser to the sewage based on the detected total current value. Processing equipment.

  The sewage treatment apparatus according to claim 1, wherein a direct current constant is applied to the electrode.   The sewage treatment apparatus according to claim 1, wherein a direct current constant current that changes polarity every predetermined time is applied to the electrode.   The sewage treatment apparatus according to claim 1, wherein a direct current that increases the applied current in a pulse shape every predetermined time is applied to the electrode.   4. The sewage treatment apparatus according to claim 1, wherein a direct current that increases the applied current in a pulsed manner is applied to the electrode at a predetermined time.

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