JP4027136B2

JP4027136B2 - Method for suppressing hydrogen sulfide generation in sewage pump

Info

Publication number: JP4027136B2
Application number: JP2002085987A
Authority: JP
Inventors: 光洋曽田; 太三原; 康利河村
Original assignee: Chugai Ro Co Ltd
Current assignee: Chugai Ro Co Ltd
Priority date: 2002-03-26
Filing date: 2002-03-26
Publication date: 2007-12-26
Anticipated expiration: 2022-03-26
Also published as: JP2003278261A

Description

【０００１】
【発明の属する技術分野】
本発明は下水圧送管中の硫化水素発生抑制方法、特に、下水を圧送ポンプで圧送する下水圧送システムにおいて、圧送ポンプの停止により圧送管中に下水が長時間滞留した場合に、季節的、時間的および天候等の条件の変動に関わらず、それらの条件変動に対応して所望するタイミングで所望する濃度の酸素ガスを注入して圧送管内で硫化水素が発生するのを抑制する方法に関するものである。
【０００２】
【従来の技術】
下水処理場への下水の送水方式としては、水勾配を設けた下水路で自然流下させる自然流下方式と、下水処理場までの間に複数の中継所を設け、各中継所に設けた圧送ポンプで下流側の中継所に順次圧送するポンプ圧送方式が知られているが、人口密度の低い地域では効率的な下水処理のためにポンプ圧送方式が採用されている。
【０００３】
前記ポンプ圧送方式は、自然流下方式と比較して掘削深度を浅くすることができ、また、下水圧送管の管径が小さくても良いため、工事規模を大幅に軽減できる利点があるが、下水圧送管が道路の起伏に沿って埋設されるため下水自体が空気中の酸素と接触せず、しかも、中継所での下水の貯留量が変動するため圧送ポンプが間欠運転となり、圧送ポンプが停止している間は下水が圧送管中に滞留することになり、その結果、下水圧送管内の下水が嫌気状態となって下水中に含まれる硫黄や硫黄化合物が生物学的に還元されて硫化水素が生成し、この硫化水素が気相中に拡散して雰囲気中の硫化水素濃度が十数ppm以上になると、悪臭の原因となるだけでなく、人的被害を及ぼしたり施設が腐食するという問題がある。
【０００４】
前記硫化水素の生成は、下水中に含まれる有機物、硫化塩濃度及び溶存酸素、並びに下水圧送管内の下水のｐＨ、温度及び滞留時間等の環境条件によって左右されるが、その生成には下水中に浮遊する同化細菌、蛋白質分解細菌、硫黄塩還元細菌などの細菌類及び下水圧送管内壁に付着した生物膜が関与することが知られている。
【０００５】
他方、この硫化水素の生成を抑制する方法として、薬品添加法、空気注入法及び酸素注入法が知られている。これらの方法のうち、薬品添加法は維持費が高くなるという問題があり、空気注入法は注入媒体が空気であるため全注入量の約７９％（窒素）が下水圧送管内に残留し、この残留窒素が下水圧送管中で圧力損失を増大させたり、下水圧送管の閉塞の原因となるという問題がある。これに対して、酸素注入法は、高純度酸素ガスを下水圧送管中に注入して嫌気性菌の繁殖を抑制する方法であるため、薬品添加法に比べて安価であり、また、前記空気注入法の課題であった圧力損失の増大や閉塞の問題を解決できるという利点はあるが、下水圧送管の全長が長いことに起因して下水圧送管の出口で硫化水素濃度を検出して酸素ガス供給量をフィードバック制御することはコスト面において現実的でないという問題がある。このため、定常運転時（即ち、圧送ポンプの定格量）に合わせて常に一定量の酸素ガスを注入することが行われている。
【０００６】
なお、前記従来の酸素注入法では、硫化水素抑制に必要な基準酸素消費量（Ｗ１）を公知のブーン（Boon）の式：
Ｗ１＝｛Ｒr＋(４Ｒe/Ｄ)｝×(πＤ^２Ｌ/４)
Ｒr＝６.０×１.０７^(T-15)
Ｒe＝０.７×１.０７^(T-15)
（式中、Ｗ１は基準酸素消費量（g/h）、Ｒrは浮遊バイオマスによる酸素消費速度(g/m³・h)、Ｒeはバイオフィルムによる酸素消費速度(g/m²・h)、Ｄは管内径(m)、Ｌは管路長(m)、Tは汚水温度(℃)である。）を用いて算出している。
【０００７】
【発明が解決しようとする課題】
しかしながら、中継所の貯留槽に流入する下水量は経時的に変化するため、前記従来の酸素注入法では、貯留槽内の水位の変動に応じて圧送ポンプは絶えず運転と停止とを繰り返し、酸素発生装置も前記圧送ポンプの起動に連動して運転を開始する。そのため、貯留槽への流入量が少ない時間帯には圧送ポンプの運転停止時間が長くなり、酸素注入法であっても定常運転時を想定した酸素ガス供給量では下水の再嫌気化を回避することができず、硫化水素が発生するという問題がある。
【０００８】
これらの問題を解決するため、本出願人は、特開２００１−１１９２６号公報にて、圧送ポンプの稼動に連動して圧送下の下水中に酸素ガスを注入し下水圧送管内での硫化水素の発生を抑制する方法において、１日を１サイクルとする圧送ポンプの稼働率変動パターンに基づいて基準稼働率及び圧送ポンプの稼働率が前記基準稼働率よりも上昇し始める稼働率上昇時刻と前記基準稼働率よりも低下し始める稼働率低下時刻を設定する一方、前記稼働率低下時刻よりも所定時間前の時刻を過剰酸素供給開始時刻として設定し、時刻が過剰酸素供給開始時刻に達してから稼働率上昇時刻に達するまでの時間帯は圧送下水量に対応する一定量の酸素ガスよりも過剰に酸素ガスを下水中に注入することを特徴とする下水圧送管中の硫化水素発生抑制方法を提案した。
【０００９】
前記方法は、圧送ポンプの運転停止時間が長くなっても下水の再嫌気化を防止することができ、圧送ポンプの運転停止時間の変動に拘わらず常に下水中の硫化水素濃度を一定水準以下に抑制できる利点があるが、圧送ポンプが短時間に運転と停止とを繰り返すような状態下では、酸素発生装置の酸素供給能力が追従できず、所望するタイミングで所望する濃度の酸素ガスを注入することができなくなり、必然的に下水の嫌気化を回避することができず、硫化水素等のガスが発生することが明らかとなった。
【００１０】
本発明は、前記従来技術の問題点を鑑みてなされたものであり、所望するタイミングで所望する濃度の酸素ガスを注入するとともに、季節的、時間的および天候等の条件変動があっても、それらの条件変動に対応して所要酸素ガス注入量を変更できる下水圧送中の硫化水素発生抑制方法を提供するものである。
【００１１】
【課題を解決するための手段】
本発明は、前記課題を解決する手段として、下水圧送システムで使用する酸素発生装置（例えば、PSA方式やVSA方式）では、通常、濃度が９０％以上の高純度酸素ガスを取り出せるまでに運転開始から約10分間程度のアイドリング時間が必要であることに鑑み、基本的には、圧送ポンプの運転開始に先だって酸素発生装置の起動を開始し、圧送ポンプの運転開始と同時に所定濃度の酸素ガスを下水中に注入するようにしたものである。
【００１２】
従って、本発明に係る下水圧送管内の硫化水素発生抑制方法は、圧送ポンプの稼動に連動して圧送下の下水中に酸素ガスを注入して下水圧送管内での硫化水素の発生を抑制する方法において、汚水貯留槽内の液面レベルを測定するとともに、前記汚水貯留槽内の液面レベルの経時的測定結果から予測される圧送ポンプの運転開始時刻に基づいて、前記圧送ポンプの運転開始時刻よりも所定時間前の時刻を酸素発生装置の起動開始時刻として設定する動作を繰り返しつつ、時刻が前記設定された酸素発生装置の起動開始時刻に達したとき当該起動開始時刻の液面レベルを前記圧送ポンプの運転開始時の液面レベルから減じた値に基づいて演算される、前記起動開始時刻の液面レベルから運転開始時の液面レベルまでの所要時間と前記所定時間とを比較し、当該所要時間が前記所定時間未満であるとき前記酸素発生装置の起動を開始し、前記圧送ポンプの運転開始時に所定濃度の酸素ガスを下水中に注入することを特徴とするものである。
【００１３】
好ましい実施態様においては、汚水貯留槽又は下水圧送管内における下水の温度を測定する一方、圧送ポンプの稼働時間から下水圧送管内における下水の滞留時間を演算し、前記下水の温度測定結果と下水圧送管内における下水の滞留時間とから下水中に注入するに必要な所要酸素量を演算して所定量の酸素ガスを下水中に注入することが行われる。
【００１４】
さらに、他の好ましい実施態様においては、過去に蓄積した汚水貯留槽又は下水圧送管内における下水の温度データと圧送ポンプの稼働時間から算出した下水圧送管内における下水の滞留時間データとを用いて下水中に注入するに必要な所要酸素量を演算して所定量の酸素ガスを下水中に注入することが行われる。
【００１５】
【発明の実施の形態】
以下、本発明の第１の実施形態を添付の図面を参照して説明する。
【００１６】
下水発生源から下水処理場までの間に複数の中継所を設け、各中継所に配設された下水圧送システムにより下水圧送管６を介して順次圧送されるが、各中継所における下水圧送システムは、図１に示すように、大略、汚水貯留槽１と、汚水貯留槽１の内部若しくは汚水貯留槽１の近傍に備えられた圧送ポンプ２と、酸素ガス供給源３と、前記汚水貯留槽１内の液面レベルを測定する液面レベル測定手段４と、前記貯留槽内の液面レベル測定結果から予測される前記圧送ポンプ２の運転開始時刻に基づいて酸素ガス供給源３の起動開始時刻を設定するとともに、前記汚水貯留槽１の貯水状態に応じて前記酸素ガス供給源３の動作を制御する外部監視装置５を備え、中継所の貯留槽内の下水は圧送ポンプ２により下水圧送管６を介して下流側中継所（図示せず）に圧送される。
【００１７】
前記下水圧送管６は、その上流側に酸素ガス注入孔を形成され、当該酸素ガス注入孔には酸素ガス供給ライン７を介して酸素ガス供給源３が接続されている。前記酸素ガス供給源３は、例えば、空気圧縮機、除湿機、複数の吸着槽ユニット及び酸素ガス貯留タンクで構成され、空気圧縮機で圧縮された圧縮空気を除湿機で水分除去し、これを前記複数の吸着槽ユニットに分配供給して、各吸着層内の吸着材（例えば合成ゼオライト）で窒素分を吸着させて９０％以上の濃度の高純度酸素ガスのみを取出し、前記貯留タンクで圧力調整して注入する公知の吸着分離方式（PSA方式）が用いられている。
【００１８】
前記構成のシステムにおいて、本発明方法を実施する場合、次のようにして行われる：
１）汚水貯留槽内が空に近い状態にあるとすると、季節的、時間的および天候等によって変化するが、下水の流入によって汚水貯留槽１内の液面レベルは、図２に示すように徐々に上昇して行く。
【００１９】
２）この過程で液面レベル測定手段４により現在の汚水貯留槽１内の液面レベルが連続的又は定期的に測定され、その測定結果が液面レベル信号として外部監視装置５に入力される。
【００２０】
３）外部監視装置は、その演算処理装置で、順次入力される前記液面レベル信号に基づいて下水の単位時間当たりの流入量を演算し、その演算値と運転開始時の液面レベルまでの貯留槽の容積から所要時間を演算し、これを現在時刻に加えて圧送ポンプ２の運転開始時刻（すなわち、貯留槽内の液面レベルが所定水位になる時刻）を認識する。
【００２１】
４）次いで、前記圧送ポンプ２の運転開始時刻に基づき、当該圧送ポンプ２の運転開始時刻よりも所定時間前の時刻、例えば、10分前の時刻を酸素発生装置の起動開始時刻として設定する。この酸素発生装置の起動開始時刻は任意に設定できるが、通常、圧送ポンプ２の運転開始時刻の数分前〜数十分前の時間に設定される（図２参照）。
【００２２】
５）外部監視装置は、前記汚水貯留槽内の液面レベルの経時的測定結果から予測される圧送ポンプの運転開始時刻に基づいて、前記圧送ポンプの運転開始時刻よりも所定時間前の時刻を酸素発生装置の起動開始時刻として設定する動作を繰り返し、時刻が前記設定された酸素発生装置の起動開始時刻に達したとき前記任意に設定された酸素発生装置の起動開始時刻から圧送ポンプ２の運転開始時刻までの所定時間、即ち、酸素発生装置の準備運転時間（D00）と、圧送ポンプ２の運転開始時の液面レベル（D01）から前記酸素発生装置の起動開始時刻の液面レベル（D10）を減じた値に基づいて演算される、汚水貯留槽１内の液面レベルが前記起動開始時刻の液面レベルから運転開始時の液面レベルに達するまでの所要時間とを比較し、（D01−D10）×係数＜Ｄ00の条件が整わない場合には前記動作を繰り返し、前記条件が整ったときに、即ち、前記所要時間が前記所定時間未満のときに酸素発生装置の起動信号を出力し、これを受けて酸素発生装置が起動される。この過程では、酸素発生装置の運転初期に発生する酸素ガスの濃度が低いため、所定濃度の酸素濃度になるまで取り出した酸素を大気中に排気する（図３参照）。
【００２３】
６）10分経過後、圧送ポンプ２の運転が開始され、下水圧送管６を介して下流側の汚水貯留槽（図示せず）へ下水の圧送が開始される。この時点になると、前記酸素発生装置は所定濃度、例えば、９０％以上の濃度の酸素を発生しているため、外部監視装置５は、圧送ポンプ２の運転開始信号を受けて酸素ガス供給ライン７に配設された酸素注入弁８ａを開状態にし、所望の濃度の酸素ガスが下水圧送管６内に注入されて下水圧送管６内の硫化水素の発生を安定して抑制する。圧送ポンプ２の運転に伴い、汚水貯留槽１内の液面レベルは徐々に低下し、所定のレベルまで低下すると、圧送ポンプ２および酸素発生装置が停止する。以後は、前記１）から６）の動作を繰り返す。
【００２４】
本実施例では、吸着分離方式（PSA方式）の酸素発生装置を用いた例を述べたが、前記実施態様に限定されるものではなく、真空圧再生方式（ＶＳＡ方式）の酸素発生装置を用いることができることは言うまでもない。
【００２５】
図４は本発明の第２実施形態を示し、この下水圧送システムは、前記第１の実施形態の構成に加えて、汚水貯留槽１内又は下水圧送管６内における下水の温度を測定する温度センサーを備え、外部監視装置５は圧送ポンプ２の稼働時間を計測して下水圧送管６内における下水の滞留時間を演算すると共に、前記各測定結果に基づいてBoonの式と経験値とを用いて所要酸素量を演算する演算手段と、酸素ガスの注入量を制御する制御部とを備えている。
【００２６】
前記構成の下水圧送システムにおいて、本発明方法は次のようにして実施される：
１）前記システムの基本的動作は、前記第１の実施態様と同じである。即ち、汚水貯留槽内が空に近い状態にあるとすると、季節的、時間的および天候等によって変化するが、下水の流入によって汚水貯留槽１内の液面レベルは徐々に上昇し、所定液面レベルになると、圧送ポンプ２の運転を開始すると同時に酸素発生装置から所定濃度の酸素を下水圧送管６に注入する。
【００２７】
２）前記汚水貯留槽１内又は下水圧送管６内における下水温度を温度センサーにより連続的あるいは定期的に測定され、その測定データ信号は外部監視装置５に入力される。
【００２８】
３）外部監視装置は、その演算処理装置で圧送ポンプ２の稼働時間から下水圧送管６内における下水の滞留時間を算出し、この算出データ信号を記憶手段に記憶する。
【００２９】
４）前記外部監視装置５は、その演算処理装置により、前記２）および３）のデータに基づいて前記ブーン（Boon）の式と経験値とを用いて所要酸素量を演算する。即ち、
この基準酸素消費量（Ｗ１）を算出するには、下記ブーンの式：
Ｗ１＝｛Ｒr＋(４Ｒe/Ｄ)｝×(πＤ^２Ｌ/４)
Ｒr＝６.０×１.０７^(T-15)
Ｒe＝０.７×１.０７^(T-15)
（式中、Ｗ１は基準酸素消費量（g/h）、Ｒrは浮遊バイオマスによる酸素消費速度(g/m³・h)、Ｒeはバイオフィルムによる酸素消費速度(g/m²・h)、Ｄは管内径(m)、Ｌは管路長(m)、Tは汚水温度(℃)である。）から明らかなように、管内径（Ｄ）と、管路長（Ｌ）と、汚水温度（T）との変数が必要である。このうち、管内径（Ｄ）および管路長（Ｌ）については圧送管設備の固定値と考えて問題はない。従って、汚水温度（T）のみが変数となり、圧送ポンプ運転中に必要な所要酸素量（Ｗ２）は以下の手順で算出することができる。
【００３０】
イ）汚水温度（T）を下式に代入することにより、基準酸素消費量（Ｗ１）の値を算出する。
ロ）圧送ポンプの運転時間より過剰注入係数（Ｐ）を求める。
【００３１】
ハ）圧送ポンプ運転中に圧送管に注入する所要酸素量（Ｗ２）は、工程イ）およびロ）より求めた基準酸素消費量（Ｗ１）と過剰注入係数（Ｐ）との積、
Ｗ２＝Ｗ１×Ｐ
により求めることができる。
【００３２】
５）前記４）の演算結果に基づいて、外部監視装置５内部の制御部は、酸素発生装置の下流側に設けた酸素注入制御弁８ｂを制御し、常に最適な所要酸素量を注入する。
【００３３】
したがって、本発明の第２実施形態を用いることによって図５に示すように、季節的、時間的および天候等の条件変動があっても、それらの条件変動に対応して所要酸素ガス注入量を制御するので、下水圧送中の硫化水素ガスの発生を安定して抑制できる。なお、本実施態様では現状の下水温度および下水の滞留時間を用いて所要酸素ガス注入量を制御する例を述べたが、本発明は、前記実施態様に限定されるものではなく、過去に蓄積したデータを用いても所要酸素ガス注入量を制御できることはいうまでもない。
【００３４】
【実施例】
図４に示す下水圧送システムを用い、汚水温度が２０〜２４ ℃（平均２２ ℃）の汚水を上流側中継所から２５０mmφの下水圧送管で２４２５m離れた下流側中継所（図示せず）に２.７m³/分の圧送能力を有する圧送ポンプにより、平均２５００m³/日で圧送するに当たり、圧送ポンプの運転開始時刻より１０分前の時刻を酸素発生装置の起動開始時刻として設定すると共に、圧送ポンプの運転開始時に酸素ガスを下水圧送管内に注入した後、前記条件変動に応じて酸素ガス注入量を制御して、上流側中継所での硫化水素濃度を所定時間毎にそれぞれ測定した。その結果を図５に示す。
【００３５】
また、図４の下水圧送システムを用い、前記実施例１と同様にして、表１に示す種々の条件下の下水を圧送した。その時の結果を表１に示す。
【００３６】
【比較例】
実施例で用いた下水圧送システムにおいて、酸素ガス供給量が零になるようにした以外は同じ条件で下水圧送システムを稼働させ下流側中継所での硫化水素濃度を所定時間毎に測定した。その結果を表１及び図５に示す。
【００３７】
【表１】

【００３８】
表１及び図５から明らかなように、圧送下水中に酸素ガスを供給しない状態では時間帯によって下流側中継所での硫化水素濃度が７０ppm〜０ppmと大きく変動するのに対して、本発明方法では、常に最適な所要酸素量を制御して注入するので２４時間の全時間帯に渡って硫化水素濃度を、酸素欠乏症等防止規則の基準値である１０ppm以下に抑制することができる。
【００３９】
【発明の効果】
以上説明したように、本発明は、汚水貯留槽内の液面レベル測定結果から予測される圧送ポンプの運転開始時刻に基づいて、圧送ポンプの運転開始時刻よりも所定時間前の時刻を酸素発生装置の起動開始時間として設定したのち、酸素発生装置の起動を開始するので濃度が９０％以上の酸素ガスを圧送ポンプの運転開始時に下水圧送管内へ注入することができ、下水圧送管内の硫化水素の発生を安定して抑制できる。また、圧送ポンプの稼働時間から下水圧送管内における下水の滞留時間を演算し、前記下水の温度測定結果と下水圧送管内における下水の滞留時間とから下水中に注入するに最適な所要酸素量を演算して最適な量に制御された酸素ガスを下水中に注入するので、時間的、季節的および天候等の条件変動、即ち、汚水温度変化や圧送ポンプの運転時間変動があっても作業員が現場に赴いて所要酸素量を算出したのち、所要酸素量を設定変更する必要がなく、人的負担を軽減できると共に、常に硫化水素濃度を１０ppm以下に抑制できるので、下水圧送システムの腐食を防止できる。
【図面の簡単な説明】
【図１】本発明方法に実施に使用する下水圧送システムの構成図
【図２】図１の下水圧送システムに於ける圧送ポンプの運転時間と酸素発生装置との時間的関係を示す図
【図３】図１の下水圧送システムに於ける酸素発生装置の起動時の酸素濃度の変化を示すグラフ
【図４】本発明方法の他の実施態様に実施に使用する下水圧送システムの構成図
【図５】本発明方法及び従来法による硫化水素の発生状況を示すグラフ
【符号の説明】
１…汚水貯留槽
２…圧送ポンプ
３…酸素ガス供給源
４…液面レベル測定手段
５…外部監視装置
６…下水圧送管
７…酸素ガス供給ライン[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for suppressing the generation of hydrogen sulfide in a sewage pumping pipe, in particular, in a sewage pumping system that pumps sewage with a pumping pump, when sewage stays in the pumping pipe for a long time due to the pumping pump being stopped. This relates to a method for suppressing the generation of hydrogen sulfide in a pressure-feed pipe by injecting oxygen gas of a desired concentration at a desired timing in response to the fluctuations of the conditions such as target and weather. is there.
[0002]
[Prior art]
As a sewage water supply system to the sewage treatment plant, there are a natural flow method that allows natural flow in a sewage channel with a water gradient, and a plurality of relay stations between the sewage treatment plants, and a pressure pump provided at each relay station. However, a pumping system is known in which the pumping system is sequentially pumped to a relay station on the downstream side. However, in an area where the population density is low, a pumping system is used for efficient sewage treatment.
[0003]
The pump pumping method can reduce the depth of excavation compared to the natural flow method, and the pipe diameter of the sewage pumping pipe may be small, so there is an advantage that the construction scale can be greatly reduced. Since the pumping pipe is buried along the road undulations, the sewage itself does not come into contact with oxygen in the air, and the amount of sewage stored at the relay station fluctuates, causing the pumping pump to operate intermittently and the pumping pump to stop. During this period, the sewage stays in the pumping pipe. As a result, the sewage in the sewage pumping pipe becomes anaerobic and the sulfur and sulfur compounds contained in the sewage are biologically reduced to hydrogen sulfide. If this hydrogen sulfide diffuses into the gas phase and the hydrogen sulfide concentration in the atmosphere becomes more than 10 ppm, it will cause not only bad odor but also human damage and corrosion of the facility. There is.
[0004]
The generation of the hydrogen sulfide depends on the environmental conditions such as the organic matter contained in the sewage, the concentration of sulfide and dissolved oxygen, and the pH, temperature and residence time of the sewage in the sewage pressure feeding pipe. It is known that bacteria such as assimilating bacteria, proteolytic bacteria, sulfur salt-reducing bacteria, and biofilms attached to the inner wall of the sewage pressure feeding tube are involved.
[0005]
On the other hand, chemical addition methods, air injection methods, and oxygen injection methods are known as methods for suppressing the formation of hydrogen sulfide. Among these methods, the chemical addition method has a problem that the maintenance cost becomes high. In the air injection method, since the injection medium is air, about 79% (nitrogen) of the total injection amount remains in the sewage pressure feeding pipe. There is a problem that residual nitrogen increases the pressure loss in the sewage pressure feed pipe and causes the clogging of the sewage pressure feed pipe. On the other hand, the oxygen injection method is a method that suppresses the growth of anaerobic bacteria by injecting high-purity oxygen gas into the sewage pressure feeding pipe, and is therefore less expensive than the chemical addition method. Although there is an advantage that it can solve the problem of increase in pressure loss and blockage that were the problems of the injection method, the oxygen sulfide concentration is detected by detecting the hydrogen sulfide concentration at the outlet of the sewage pressure feed pipe due to the long total length of the sewage pressure feed pipe. There is a problem that feedback control of the gas supply amount is not practical in terms of cost. For this reason, a constant amount of oxygen gas is always injected in accordance with the steady operation (that is, the rated amount of the pressure feed pump).
[0006]
In the conventional oxygen injection method, the reference oxygen consumption (W1) necessary for suppressing hydrogen sulfide is calculated using the well-known Boon equation:
W1 = {Rr + (4Re / D)} × (πD ² L / 4)
Rr = 6.0 × 1.07 ^(T-15)
Re = 0.7 × 1.07 ^(T-15)
(W1 is the reference oxygen consumption (g / h), Rr is the oxygen consumption rate by floating biomass (g / m ³ · h), Re is the oxygen consumption rate by biofilm (g / m ² · h), D is the pipe inner diameter (m), L is the pipe length (m), and T is the sewage temperature (° C.).
[0007]
[Problems to be solved by the invention]
However, since the amount of sewage flowing into the storage tank of the relay station changes with time, in the conventional oxygen injection method, the pump is continuously operated and stopped according to the fluctuation of the water level in the storage tank. The generator also starts operation in conjunction with the activation of the pressure pump. For this reason, the pump pump operation stop time becomes longer when the amount of inflow into the storage tank is small, and even in the oxygen injection method, the oxygen gas supply amount assuming steady operation avoids re-anaerobic sewage treatment. There is a problem that hydrogen sulfide is generated.
[0008]
In order to solve these problems, the applicant of Japanese Patent Application Laid-Open No. 2001-11926 injects oxygen gas into the sewage under pressure in conjunction with the operation of the pressure feed pump, and forms hydrogen sulfide in the sewage pressure feed pipe. In the method of suppressing the occurrence, the reference operation rate and the operation rate rise time at which the operation rate of the pumping pump starts to rise from the reference operation rate based on the operation rate fluctuation pattern of the pumping pump with one cycle as one cycle and the reference While the operation rate lowering time at which the operation rate starts to decrease is set, the time before the operation rate lowering time is set as the excess oxygen supply start time, and the operation is started after the time reaches the excess oxygen supply start time. How to suppress the generation of hydrogen sulfide in the sewage pressure feed pipe, characterized by injecting oxygen gas into the sewage in excess of a certain amount of oxygen gas corresponding to the pressure sewage flow rate until the rate rise time is reached It was proposed.
[0009]
The method can prevent sewage re-anaerobic even if the pumping pump shutdown time is long, and the hydrogen sulfide concentration in the sewage is always kept below a certain level regardless of fluctuations in the pumping pump shutdown time. Although there is an advantage that it can be suppressed, under a state where the pumping pump repeats operation and stop in a short time, the oxygen supply capacity of the oxygen generator cannot follow, and oxygen gas of a desired concentration is injected at a desired timing. It became impossible to avoid the anaerobic sewage inevitably and gas such as hydrogen sulfide was generated.
[0010]
The present invention has been made in view of the above-described problems of the prior art, injecting oxygen gas of a desired concentration at a desired timing, and even if there is a change in conditions such as seasonal, temporal, and weather, The present invention provides a method for suppressing the generation of hydrogen sulfide during sewage pumping, which can change the required oxygen gas injection amount in response to these condition fluctuations.
[0011]
[Means for Solving the Problems]
According to the present invention, as a means for solving the above-mentioned problems, in an oxygen generator (for example, PSA method or VSA method) used in a sewage pumping system, operation is usually started before high-purity oxygen gas having a concentration of 90% or more can be extracted. Basically, starting the operation of the oxygen pump is started prior to the start of operation of the pump, and oxygen gas of a predetermined concentration is supplied simultaneously with the start of the pump. Injected into sewage.
[0012]
Therefore, the method for suppressing the generation of hydrogen sulfide in the sewage pressure feeding pipe according to the present invention is a method for suppressing the generation of hydrogen sulfide in the sewage pressure feeding pipe by injecting oxygen gas into the sewage under pressure feeding in conjunction with the operation of the pressure feeding pump. In the above, the liquid level in the sewage storage tank is measured, and the operation start time of the pressure pump is based on the operation start time of the pressure pump predicted from the measurement result of the liquid level in the sewage storage tank over time while repeating the operation for setting the time of a predetermined time before the start-up time of the oxygen generator than time the liquid level of the activation start time when it reaches the activation start time of the set oxygen generator It is calculated on the basis of the value obtained by subtracting from the operation start time of the liquid level of the pressure pump, the required time and the predetermined time from the activation start time of the liquid level up to start of operation of the liquid level In comparison, the oxygen generator is started when the required time is less than the predetermined time, and a predetermined concentration of oxygen gas is injected into the sewage when the operation of the pressure pump is started. .
[0013]
In a preferred embodiment, while measuring the temperature of the sewage in the sewage storage tank or the sewage pressure feeding pipe, the residence time of the sewage in the sewage pressure feeding pipe is calculated from the operation time of the pressure feeding pump, and the temperature measurement result of the sewage and the inside of the sewage pressure feeding pipe are calculated. The required amount of oxygen required for injection into the sewage is calculated from the residence time of the sewage, and a predetermined amount of oxygen gas is injected into the sewage.
[0014]
Further, in another preferred embodiment, the sewage is stored using the sewage temperature data accumulated in the past or the sewage temperature data in the sewage pressure feed pipe and the residence time data in the sewage pressure feed pipe calculated from the operation time of the pressure feed pump. The required amount of oxygen required to be injected into the water is calculated and a predetermined amount of oxygen gas is injected into the sewage.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a first embodiment of the present invention will be described with reference to the accompanying drawings.
[0016]
A plurality of relay stations are provided between the sewage generation source and the sewage treatment plant, and the sewage pumping system in each relay station is sequentially pumped by the sewage pumping system disposed in each relay station through the sewage pumping pipe 6. As shown in FIG. 1, generally, the sewage storage tank 1, the pumping pump 2 provided in the sewage storage tank 1 or in the vicinity of the sewage storage tank 1, the oxygen gas supply source 3, and the sewage storage tank The start of activation of the oxygen gas supply source 3 based on the liquid level measurement means 4 for measuring the liquid level in 1 and the operation start time of the pressure pump 2 predicted from the liquid level measurement result in the storage tank An external monitoring device 5 that sets the time and controls the operation of the oxygen gas supply source 3 in accordance with the water storage state of the sewage storage tank 1 is provided. Downstream relay via pipe 6 It is pumped to the (not shown).
[0017]
The sewage pressure feed pipe 6 is formed with an oxygen gas injection hole on the upstream side, and an oxygen gas supply source 3 is connected to the oxygen gas injection hole via an oxygen gas supply line 7. The oxygen gas supply source 3 includes, for example, an air compressor, a dehumidifier, a plurality of adsorption tank units, and an oxygen gas storage tank, and removes moisture from the compressed air compressed by the air compressor using a dehumidifier. Distributing and supplying to the plurality of adsorption tank units, adsorbing nitrogen with an adsorbent (for example, synthetic zeolite) in each adsorption layer, taking out only high-purity oxygen gas having a concentration of 90% or more, and pressure in the storage tank A well-known adsorption separation method (PSA method) in which injection is adjusted is used.
[0018]
When the method of the present invention is carried out in the system having the above configuration, it is performed as follows:
1) Assuming that the inside of the sewage storage tank is close to the sky, the liquid level in the sewage storage tank 1 changes due to the inflow of sewage as shown in FIG. It goes up gradually.
[0019]
2) During this process, the liquid level in the sewage storage tank 1 is continuously or periodically measured by the liquid level measuring means 4, and the measurement result is input to the external monitoring device 5 as a liquid level signal. .
[0020]
3) The external monitoring device calculates the amount of inflow per unit time of sewage based on the liquid level signal that is sequentially input, and the calculated value and the liquid level at the start of operation. The required time is calculated from the volume of the storage tank, and this is added to the current time to recognize the operation start time of the pumping pump 2 (that is, the time when the liquid level in the storage tank reaches a predetermined water level).
[0021]
4) Next, based on the operation start time of the pressure pump 2, a time before the operation start time of the pressure pump 2, for example, a time 10 minutes before, is set as the start time of the oxygen generator. The activation start time of the oxygen generator can be arbitrarily set, but is usually set to a time several minutes to several tens of minutes before the operation start time of the pump 2 (see FIG. 2).
[0022]
5) The external monitoring device sets a time a predetermined time before the operation start time of the pumping pump based on the operation start time of the pumping pump predicted from the measurement result of the liquid level in the sewage storage tank over time. The operation set as the start time of the oxygen generator is repeated, and when the time reaches the start time of the set oxygen generator, the operation of the pump 2 is started from the start time of the arbitrarily set oxygen generator. predetermined time until the start time, i.e., a preparation operation time of the oxygen generator (D00), the operation start time of the liquid level of the pressure pump 2 (D01) of the activation start time of the oxygen generator liquid level (D10 ) Is calculated on the basis of the value obtained by subtracting the time required for the liquid level in the sewage storage tank 1 to reach the liquid level at the start of operation from the liquid level at the start-up time. D01−D10) If the condition of the coefficients <D00 does Seiwa repeatedly the operation, when the conditions are in place, i.e., the time required to output the activation signal of the oxygen generating device when less than the predetermined time, receiving this The oxygen generator is activated. In this process, since the concentration of oxygen gas generated in the initial stage of operation of the oxygen generator is low, the extracted oxygen is exhausted to the atmosphere until the oxygen concentration reaches a predetermined concentration (see FIG. 3).
[0023]
6) After 10 minutes, the operation of the pressure pump 2 is started, and the pumping of sewage is started to the sewage storage tank (not shown) on the downstream side via the sewage pumping pipe 6. At this time, since the oxygen generator generates oxygen having a predetermined concentration, for example, 90% or more, the external monitoring device 5 receives the operation start signal of the pressure pump 2 and receives the oxygen gas supply line 7. The oxygen injection valve 8a disposed in the open state is opened, and oxygen gas of a desired concentration is injected into the sewage pressure feed pipe 6 to stably suppress the generation of hydrogen sulfide in the sewage pressure feed pipe 6. As the pressure pump 2 is operated, the liquid level in the sewage storage tank 1 gradually decreases, and when the pressure level is lowered to a predetermined level, the pressure pump 2 and the oxygen generator are stopped. Thereafter, the operations 1) to 6) are repeated.
[0024]
In this example, an example using an adsorption separation type (PSA type) oxygen generator was described. However, the present invention is not limited to the above embodiment, and a vacuum pressure regeneration type (VSA type) oxygen generator is used. It goes without saying that it can be done.
[0025]
FIG. 4 shows a second embodiment of the present invention, and this sewage pumping system is a temperature for measuring the temperature of sewage in the sewage storage tank 1 or the sewage pumping pipe 6 in addition to the configuration of the first embodiment. A sensor is provided, and the external monitoring device 5 measures the operation time of the pump 2 to calculate the residence time of the sewage in the sewage pump 6 and uses Boon's formula and experience values based on the measurement results. Calculating means for calculating the required oxygen amount and a control unit for controlling the injection amount of oxygen gas.
[0026]
In the sewage pumping system having the above configuration, the method of the present invention is carried out as follows:
1) The basic operation of the system is the same as that of the first embodiment. That is, assuming that the inside of the sewage storage tank is near the sky, the liquid level in the sewage storage tank 1 gradually increases due to the inflow of sewage, although it changes depending on the season, time, and weather. When the surface level is reached, the operation of the pressure pump 2 is started, and at the same time, a predetermined concentration of oxygen is injected into the sewage pressure feed pipe 6 from the oxygen generator.
[0027]
2) The sewage temperature in the sewage storage tank 1 or the sewage pressure feeding pipe 6 is continuously or periodically measured by a temperature sensor, and the measurement data signal is input to the external monitoring device 5.
[0028]
3) The external monitoring device calculates the residence time of the sewage in the sewage pressure feed pipe 6 from the operation time of the pressure feed pump 2 by the arithmetic processing unit, and stores this calculated data signal in the storage means.
[0029]
4) The external monitoring device 5 uses the arithmetic processing unit to calculate the required oxygen amount using the Boon equation and experience values based on the data of 2) and 3). That is,
To calculate this reference oxygen consumption (W1), Boone's formula:
W1 = {Rr + (4Re / D)} × (πD ² L / 4)
Rr = 6.0 × 1.07 ^(T-15)
Re = 0.7 × 1.07 ^(T-15)
(W1 is the reference oxygen consumption (g / h), Rr is the oxygen consumption rate by floating biomass (g / m ³ · h), Re is the oxygen consumption rate by biofilm (g / m ² · h), D is the pipe inner diameter (m), L is the pipe length (m), and T is the sewage temperature (° C).) As is clear from the pipe inner diameter (D), the pipe length (L), and the sewage A variable with temperature (T) is required. Of these, the pipe inner diameter (D) and the pipe length (L) are considered to be fixed values of the pumping pipe equipment and there is no problem. Accordingly, only the sewage temperature (T) becomes a variable, and the required oxygen amount (W2) required during the operation of the pressure pump can be calculated by the following procedure.
[0030]
B) The value of the reference oxygen consumption (W1) is calculated by substituting the sewage temperature (T) into the following equation.
B) Obtain the excess injection coefficient (P) from the operating time of the pump.
[0031]
C) The required oxygen amount (W2) to be injected into the pressure feed pipe during the operation of the pressure feed pump is the product of the reference oxygen consumption (W1) and the excess injection coefficient (P) obtained from the steps (a) and (b).
W2 = W1 × P
It can ask for.
[0032]
5) Based on the calculation result of 4), the control unit inside the external monitoring device 5 controls the oxygen injection control valve 8b provided on the downstream side of the oxygen generator, and always injects the optimum required oxygen amount.
[0033]
Therefore, by using the second embodiment of the present invention, as shown in FIG. 5, even if there are seasonal, temporal, and weather condition fluctuations, the required oxygen gas injection amount is set corresponding to those condition fluctuations. Since it controls, generation | occurrence | production of the hydrogen sulfide gas during sewage pumping can be suppressed stably. In this embodiment, an example of controlling the required oxygen gas injection amount using the current sewage temperature and sewage residence time has been described. However, the present invention is not limited to the above embodiment, and accumulated in the past. It goes without saying that the required oxygen gas injection amount can also be controlled using the obtained data.
[0034]
【Example】
Using the sewage pumping system shown in FIG. 4, sewage having a sewage temperature of 20 to 24 ° C. (average 22 ° C.) is transferred from the upstream relay station to a downstream relay station (not shown) 2425 m away by a 250 mmφ sewage pump pipe. the pressure pump with .7m ³ / min pumping capacity, when pumped at average 2500 m ³ / day, and sets the 10 minutes before the time from the starting time of the pressure pump as an activation starting time of the oxygen generator, pumping After injecting oxygen gas into the sewage pressure feeding pipe at the start of the pump operation, the oxygen gas injection amount was controlled according to the change in the conditions, and the hydrogen sulfide concentration at the upstream relay station was measured every predetermined time. The result is shown in FIG.
[0035]
Moreover, the sewage under various conditions shown in Table 1 was pumped in the same manner as in Example 1 using the sewage pumping system in FIG. The results at that time are shown in Table 1.
[0036]
[Comparative example]
In the sewage pumping system used in the examples, the sewage pumping system was operated under the same conditions except that the oxygen gas supply amount was zero, and the hydrogen sulfide concentration at the downstream relay station was measured every predetermined time. The results are shown in Table 1 and FIG.
[0037]
[Table 1]

[0038]
As is apparent from Table 1 and FIG. 5, the hydrogen sulfide concentration at the downstream relay station varies greatly from 70 ppm to 0 ppm depending on the time zone when oxygen gas is not supplied into the pumped sewage. Then, since the optimal required amount of oxygen is always controlled and injected, the hydrogen sulfide concentration can be suppressed to 10 ppm or less, which is the reference value of the regulation rules for prevention of oxygen deficiency, etc. over the entire 24-hour period.
[0039]
【The invention's effect】
As described above, the present invention generates oxygen at a time that is a predetermined time before the operation start time of the pressure pump based on the operation start time of the pressure pump estimated from the liquid level measurement result in the sewage storage tank. After the start-up time of the device is set, the oxygen generator is started, so that oxygen gas having a concentration of 90% or more can be injected into the sewage pressure feed pipe at the start of the operation of the pressure feed pump, and hydrogen sulfide in the sewage pressure feed pipe Can be stably suppressed. Also, the residence time of sewage in the sewage pumping pipe is calculated from the operating time of the pumping pump, and the optimum amount of oxygen required for injection into the sewage is calculated from the temperature measurement result of the sewage and the sewage residence time in the sewage pumping pipe. Therefore, the oxygen gas controlled to the optimum amount is injected into the sewage, so that even if there is a change in conditions such as time, season and weather, that is, a change in sewage temperature or a change in the operation time of the pump, After calculating the required amount of oxygen at the site, there is no need to change the required amount of oxygen, reducing the human burden, and constantly reducing the hydrogen sulfide concentration to 10 ppm or less, preventing corrosion of the sewage pumping system. it can.
[Brief description of the drawings]
FIG. 1 is a block diagram of a sewage pumping system used in the method of the present invention. FIG. 2 is a diagram showing a temporal relationship between an operation time of a pumping pump and an oxygen generator in the sewage pumping system of FIG. 3 is a graph showing a change in oxygen concentration when the oxygen generator is started in the sewage pumping system in FIG. 1. FIG. 4 is a block diagram of a sewage pumping system used in another embodiment of the method of the present invention. 5] Graph showing the state of hydrogen sulfide generated by the method of the present invention and the conventional method.
DESCRIPTION OF SYMBOLS 1 ... Sewage storage tank 2 ... Pressure feed pump 3 ... Oxygen gas supply source 4 ... Liquid level measuring means 5 ... External monitoring device 6 ... Sewage pressure feed pipe 7 ... Oxygen gas supply line

Claims

In the method for suppressing the generation of hydrogen sulfide in the sewage pressure feeding pipe by injecting oxygen gas into the sewage under pressure feeding in conjunction with the operation of the pressure feeding pump, the liquid level in the sewage storage tank is measured, and the sewage Based on the operation start time of the pumping pump predicted from the measurement result of the liquid level in the storage tank over time, the time before the operation start time of the pumping pump is set as the start time of starting the oxygen generator. Based on the value obtained by subtracting the liquid level at the start time of the pumping pump from the liquid level at the start of the operation of the pumping pump when the time reaches the set start time of the oxygen generator while repeating the operation The calculated time from the liquid level at the start time to the liquid level at the start of operation is compared with the predetermined time, and when the required time is less than the predetermined time, the oxygen Starts the activation of the raw device, the lower pressure feed hydrogen sulfide generation suppression method in the tube, which comprises injecting a predetermined concentration of oxygen gas in the sewage at the start of operation of the pressure pump.

While measuring the temperature of the sewage in the sewage storage tank or the sewage pressure feed pipe, calculating the residence time of the sewage in the sewage pressure feed pipe from the operating time of the pressure feed pump, the sewage temperature measurement result and the residence time of the sewage in the sewage pressure feed pipe 2. A method for suppressing the generation of hydrogen sulfide in a sewage pressure feeding pipe according to claim 1, wherein a required amount of oxygen required to be injected into the sewage is calculated and a predetermined amount of oxygen gas is injected into the sewage.

The temperature data of sewage in the sewage storage tank or sewage pressure feed pipe that has accumulated the required amount of oxygen necessary to inject into the sewage in the past, and the residence time data of sewage in the sewage pressure feed pipe calculated from the operating time of the pressure pump. 2. The method according to claim 1 , wherein a predetermined amount of oxygen gas is injected into the sewage based on the calculation result.