JP4320386B2

JP4320386B2 - Biological filtration device backwashing method

Info

Publication number: JP4320386B2
Application number: JP2000086722A
Authority: JP
Inventors: 昭司原田; 陽三内野; 賢一松本; 優小林; 洋一鷹野; 清仁近沢; 茂樹武田; 雄司山田
Original assignee: SAITAMA PREFECTURE; Kurita Water Industries Ltd; Hitachi Plant Technologies Ltd; Metawater Co Ltd
Current assignee: SAITAMA PREFECTURE; Kurita Water Industries Ltd; Hitachi Plant Technologies Ltd; Metawater Co Ltd
Priority date: 2000-03-27
Filing date: 2000-03-27
Publication date: 2009-08-26
Anticipated expiration: 2020-03-27
Also published as: JP2001269683A

Description

【０００１】
【発明の属する技術分野】
本発明は生物濾過装置の逆洗方法に係り、特に、タイマー設定による第１の逆洗と、濾過圧損(圧力損失)に基く第２の逆洗とを組み合せて行う生物濾過装置の逆洗方法において、最適な逆洗間隔を実現する自動制御方法に関する。
【０００２】
【従来の技術】
従来、産業排水や下水等の生物濾過装置として、槽内に浮上性濾材よりなる生物濾過層を形成し、この生物濾過層の高さ方向の途中部分に散気管を設け、散気管の下部を嫌気性の脱窒部、散気管の上部を好気性の硝化部とし、処理水の一部を循環処理することで硝化脱窒を行う循環式硝化脱窒法を基本原理とした一槽式生物濾過装置が知られている。この方法は、従来の浮遊方式の硝化脱窒装置に比べて、
▲１▼ 高負荷処理が可能であるため装置のコンパクト化が図れる。即ち、浮上性濾材は小粒径で表面積が大きいため、濾材に付着する生物膜の保持量は極めて大きく、その結果、高負荷運転で高水質の処理水を得ることができる。
▲２▼ 嫌気槽や沈殿池の汚泥管理が不要なため運転管理が容易である。即ち、一槽式であるため別途曝気槽を必要とせず、また、濾材表面に微生物を付着させているため、処理水の固液分離に沈殿池を必要としない。しかして、この点からも、装置の小型化、設置スペースの省スペース化が図れる。
といった優れた効果を奏する。
【０００３】
図３（ａ）は、従来の一槽式生物濾過装置の概略的な構成図であり、濾過槽１の上部に透水性支持部材２が水平に設置され、その下側に浮上性濾材層３が設けられている。透水性支持部材２の上側に逆洗水の貯留槽４が形成されている。浮上性濾材層３の高さ方向の途中には散気管５が設けられ、それよりも上側が好気的な硝化部、下側が嫌気的な脱窒部とされている。貯留槽４内の生物処理水の一部は循環水として濾過槽１の下部に循環される。濾過槽１の下部には逆洗排水管（図示せず）が接続され、底部には空気逆洗のための散気管（図示せず）が設けられている。浮上性濾材としては、例えば、ポリスチレン、ポリプロピレンやウレタン樹脂等を直径１〜１０ｍｍの球体や不定形状に発泡成形した、比重が水より小さい濾材が用いられる。このような浮上性濾材を生物反応槽に充填し、適当な位置に配置される透水性の濾材支持部材２によって、上向流通水された際に、支持部材２の下方に浮上性濾材層３よりなる生物濾過層が形成される。
【０００４】
この生物濾過装置では、濾過槽１の下部に導入された原水及び循環水は、浮上性濾材層３を上向流で流れる間に、散気管５よりも下側の浮上性濾材層３で脱窒処理され、散気管５よりも上側の浮上性濾材層３で硝化処理される。また、原水中の有機物が酸化されて、二酸化炭素や水に分解される。
【０００５】
なお、図３（ａ）では、浮上性濾材層３の高さ方向の途中に散気管５を設けて硝化部と脱窒部を形成しているが、散気管を設けずに浮上性濾材層３全体を嫌気層とした生物濾過装置もある。
【０００６】
このような生物濾過装置では、濾材層に捕捉した濁質もしくは生物反応の結果生じた余剰汚泥のために、経時により濾過抵抗が増大し、通水が困難になるため、これを除去するために逆洗が必要である。
【０００７】
この逆洗方法としては、濾過槽１の上部の逆洗水貯留槽４の水を下方へ逆流させて濾過槽１下部の逆洗排水管から排出する水逆洗と、濾過槽１の底部に設けられた散気管から空気を吹き出して濾材層３を攪拌する空気逆洗とがある。即ち、生物濾過装置では、その原水通水時にあっては、図３（ｂ）に示す如く、濾材が水流により濾材層３上部の支持部材２側へ押し寄せられ濾材同士が密に充填された生物濾過層を形成しているが、逆洗水を上方から下方に流下させる水逆洗を行うことにより、図３（ｃ）に示す如く、濾材層３の濾材が下方に展開し、濾材間に捕捉されていたＳＳが放出され、また、余剰の生物膜が剥離除去されて逆洗排水と共に排出される。また、空気逆洗では、空気により濾材層３が攪拌されることで、濾材間の隙間に捕捉されているＳＳが放出される。
【０００８】
また、このような逆洗を行う時期を自動的に制御する方法として、次のような方法がある。
▲１▼ タイマーにより適当な時間間隔で自動的に逆洗を行う方法
▲２▼ 設定濾過抵抗（圧損）まで濾過抵抗が上昇したのをセンサー等により検知して自動的に逆洗を起動させる方法
▲３▼ 上記▲１▼，▲２▼を組み合わせて行う方法
【０００９】
【発明が解決しようとする課題】
しかしながら、上記従来の逆洗制御方法では、次のような問題があった。
【００１０】
▲１▼のタイマーにより適当な時間間隔で自動的に逆洗を行う方法では、濾材層の詰まり具合にかかわらず逆洗を行うので、逆洗不足で濾材層が閉塞したり、逆に洗浄しすぎる状態になることがある。逆洗不足の場合、原水中のＳＳの蓄積や生物膜の肥大などにより濾材層が閉塞して複数の濾材粒子が互いに付着して固まりをつくることがある。このような濾材の固まりが一旦生じると、通常の逆洗操作では、十分に固まりがほぐれず、更に、濾材が固まりを作ると、正常な濾材よりも比重が大きくなるため、最悪の場合、逆洗時に排水と一緒に固まった濾材が排出されてしまうという不具合が生じる。逆に、頻繁に逆洗を行うと、脱窒に必要な栄養源を濾材層に保持できず、脱窒性能が低下するなどの不具合が生じる。
【００１１】
▲２▼の設定濾過抵抗で逆洗を起動する方法では、十分な水量で逆洗を行えば、逆洗の過不足の問題はないものの、いつ逆洗が起こるかわかりにくく、運転管理しにくいという不具合がある。
【００１２】
▲３▼の方法では、具体的には、▲１▼のタイマー制御による逆洗で使用する逆洗水量に対して、▲２▼の濾過抵抗に基く逆洗で使用する逆洗の逆洗水量が半分となるように設定して逆洗に要する総水量を極力減らすように実施されている。この方法では、▲１▼の場合に比べて逆洗不足による濾材層の閉塞の可能性は低くなるが、濾過抵抗に基く逆洗水量が少ないため、濾材層閉塞の防止効果は十分であるとは言えず、また、過剰逆洗による脱窒性能低下の問題は解消されない。即ち、▲１▼，▲２▼の逆洗を併用する場合においても、逆洗水量の多い▲１▼の逆洗間隔を最適に制御することが最も重要であり、この間隔が不適当であると、濾材層の閉塞又は処理性能の低下の問題が生起する。
【００１３】
本発明は上記従来の問題点を解決し、タイマー設定による第１の逆洗と、濾過圧損に基く第２の逆洗とを組み合せて行う生物濾過装置の逆洗方法において、最適な逆洗間隔で逆洗を行うことにより、逆洗不足による濾材層の閉塞、過剰逆洗による処理性能の低下を確実に防止する自動制御方法を提供することを目的とする。
【００１４】
【課題を解決するための手段】
本発明の生物濾過装置の逆洗方法は、タイマー設定による第１の逆洗と、濾過圧損に基く第２の逆洗とを組み合せて行う生物濾過装置の逆洗方法において、第１の逆洗と次回の第１の逆洗との間の第２の逆洗の頻度を検知して、その頻度が所定回数を超える場合には、第１の逆洗のタイマー設定値を増し、処理水のＮＯ_ｘ濃度が所定値を超える場合には、第１の逆洗のタイマー設定値を減じることを特徴とする。
【００１５】
なお、本発明において「第１の逆洗のタイマー設定値を増やす」とは、第１の逆洗頻度が高くなるように、第１の逆洗間隔の設定時間を短くすることを指し、「第１の逆洗のタイマー設定値を減じる」とは、第１の逆洗頻度が低くなるように、第１の逆洗間隔の設定時間を長くすることを指す。
【００１６】
本発明では、タイマー設定により適当な時間間隔で自動的に行う逆洗（以下、この逆洗を「精密逆洗」と称す。）と、設定濾過圧損まで濾過圧損が上昇したのを圧力センサーにより検知して自動的に行う逆洗（以下、この逆洗を「簡易逆洗」と称す。）との組み合わせにより逆洗を行うに当り、精密逆洗と次回の精密逆洗との間に、簡易逆洗が所定回数を超えて頻繁に行われる場合（例えば、簡易逆洗が２回以上起動する場合）は、精密逆洗の頻度が少ないと判断し、濾材層の閉塞を防止するために、精密逆洗のタイマー設定値を増やし、精密逆洗の頻度を高める。逆に、精密逆洗と次回の精密逆洗との間の簡易逆洗頻度が高くなく（例えば、簡易逆洗が全く起動しない場合）、しかも処理水のＮＯ_ｘ濃度が所定値を超える場合には、逆洗頻度が高過ぎ、脱窒部での栄養源が不足していると判断し、処理性能を維持するために精密逆洗のタイマー設定値を減じて精密逆洗の頻度を低減する。
【００１７】
このような自動制御を行うことにより、精密逆洗の逆洗間隔を最適に維持することができ、濾材層の閉塞を確実に防止した上で、良好な処理性能を維持できるようになる。
【００１８】
なお、本発明において、簡易逆洗は、精密逆洗の逆洗水量の半分の逆洗水量で行うことが好ましく、例えば、各逆洗における工程例としては、下記表１，２に示すようなものが好ましい。
【００１９】
【表１】

【００２０】
【表２】

【００２１】
【発明の実施の形態】
以下に本発明の実施の形態を詳細に説明する。
【００２２】
本発明においては、タイマー設定による精密逆洗と、濾過圧損（即ち、濾過抵抗）に基く簡易逆洗とを併用して生物濾過装置の逆洗を行うに当り、次の▲１▼，▲２▼に基いて精密逆洗間隔を制御する。
▲１▼ 精密逆洗と次回の精密逆洗の間の簡易逆洗の頻度を検知して、その頻度が所定回数を超える場合には、精密逆洗のタイマー設定値を増やし、精密逆洗の頻度を高める。
▲２▼ 処理水のＮＯ_ｘ濃度が所定値を超える場合には、精密逆洗のタイマー設定値を減じ、精密逆洗の頻度を低減する。
【００２３】
上記▲１▼の制御において、精密逆洗のタイマー設定値を変更する簡易逆洗の頻度には特に制限はないが、一般的には、精密逆洗と次回の精密逆洗との間で２回以上簡易逆洗が起動する場合には、タイマー設定値を変更するようにするのが濾材層の閉塞防止の上で好ましい。
【００２４】
また、▲２▼の制御において、精密逆洗のタイマー設定値を変更するＮＯ_ｘ濃度の所定値には特に制限はなく、所望の処理水水質に応じて適宜決定されるが、例えば、処理水全窒素濃度の目標値を１０ｍｇ／Ｌ以下としたときは、ＮＯ_３−Ｎ濃度が４ｍｇ／Ｌ以上となった場合に、精密逆洗のタイマー設定値を変更するのが、処理水水質の維持の上で好ましい。
【００２５】
このタイマー設定値の変更範囲としても特に制限はなく、生物濾過装置の仕様やその他の運転条件によって適宜決定されるが、例えば、初期の精密逆洗間隔の設定時間がＴ時間であった場合、上記▲１▼の場合には、現状の設定時間の０．５〜０．９倍程度間隔を短かくし、上記▲２▼の場合には、現状の設定時間の１．１〜２．０倍程度間隔を長くするようなタイマー設定値を採用することができる。
【００２６】
なお、本発明の逆洗方法は、精密逆洗と簡易逆洗とを併用し、前述の▲１▼，▲２▼に基いて精密逆洗間隔を制御すること以外は、常法に従って実施することができる。
【００２７】
また、上記説明では、第１の逆洗として精密逆洗を行い、第２の逆洗として簡易逆洗を行う場合について説明したが、第１，第２の逆洗工程には特に制限はなく、必ずしも、第１の逆洗として逆洗水量の多い逆洗を行う必要はない。しかし、逆洗効果及びその安定性の面からは第１の逆洗として逆洗水量の多い精密逆洗を行い、第２の逆洗として逆洗水量の少ない、好ましくは、第１の逆洗の逆洗水量の０．３〜０．９倍程度の逆洗水量の簡易逆洗を行うのが好ましい。
【００２８】
本発明の方法は、図３（ａ）に示す硝化脱窒生物濾過装置や、散気管を設けない脱窒生物濾過装置等の逆洗に有効に適用可能である。
【００２９】
【実施例】
以下に実施例及び比較例を挙げて本発明をより具体的に説明する。
【００３０】
実施例１
流域下水（一部雨水合流式）の沈殿上澄水を生物濾過装置の原水として処理を行った。原水の主な水質は、ｐＨ７．０〜７．２、ＳＳ濃度９１〜１４４ｍｇ／Ｌ、ＢＯＤ濃度７１〜１１６ｍｇ／Ｌ、全窒素濃度２１．２〜３２．１ｍｇ／Ｌであった。
【００３１】
生物濾過装置としては、図３（ａ）に示す一槽式生物濾過装置を用いた。この生物濾過装置は濾過面積２ｍ^２，濾材層高さ３ｍであり、原水は濾材層容積当たりの滞留時間が３時間となるように通水した。
【００３２】
精密逆洗及び簡易逆洗は、それぞれ前述の表１，２に示す工程で実施し、次のような条件で自動制御した。
【００３３】
簡易逆洗の制御方法：
濾過抵抗が１．５ｍＨ_２Ｏとなったときに起動する。
【００３４】
精密逆洗の制御方法：
初期は精密逆洗の起動設定時間（逆洗間隔）を４８時間とし、次のようにして±１２時間で制御する。
【００３５】
精密逆洗と次回の精密逆洗との間に簡易逆洗が２回起動される場合には、精密逆洗間隔が長過ぎるとして、精密逆洗の起動設定時間を現状よりも１２時間減じる。例えば、現状が４８時間であれば、３６時間とする。即ち、図１（ａ）に示す如く、精密逆洗と次回の精密逆洗との間に２回目の簡易逆洗が起動することを検知した場合には、この２回目の簡易逆洗を行わずに精密逆洗を開始し、以降３６時間間隔で精密逆洗を行う。
【００３６】
また、処理水のＮＯ_３−Ｎ濃度が６ｍｇ／Ｌ以上となった場合は精密逆洗間隔が短か過ぎるとして、精密逆洗の起動設定時間を現状よりも１２時間増やす。例えば、現状が４８時間であれば、６０時間とする。即ち、図１（ｂ）に示す如く、処理水のＮＯ_３−Ｎ濃度が６ｍｇ／Ｌ以上を検知したら、その時点で最も近い精密逆洗から６０時間後に次回の精密逆洗を行い、以降６０時間間隔で精密逆洗を行う。
【００３７】
この逆洗条件で一ヶ月半実験を行った。このときの原水のＳＳ濃度、ＢＯＤ濃度及び全窒素濃度を図２（ａ）に、また、処理水のＮＯ_３−Ｎ濃度の経時変化及び濾材の固まりの有無（逆洗時にのぞき窓より目視にて確認した。）と、精密逆洗及び簡易逆洗の起動状況とタイマー設定変更の状況をそれぞれ図２（ｂ），（ｃ）に示す。
【００３８】
比較例１
実施例１において、精密逆洗の間隔を４８時間で一定としたこと以外は同様にして実験を行った。このときの処理水のＮＯ_３−Ｎ濃度の経時変化及び濾材の固まりの有無と、精密逆洗及び簡易逆洗の起動状況をそれぞれ図２（ｄ），（ｅ）に示す。
【００３９】
図２の結果から次のことが明らかである。即ち、濾材層の閉塞の危険性を示す濾材の固まりの有無は、比較例１で原水ＳＳ濃度の高くなる１４日目以降に確認されたが、実施例１では、濾材の固まりが確認されなかった。また、脱窒性能の低下を示す、処理水硝酸性窒素（ＮＯ_３−Ｎ）濃度の上昇については、比較例１では、原水のＢＯＤ濃度が低下した４２日目付近で、処理水ＮＯ_３−Ｎ濃度が最大９．４ｍｇ／Ｌまで増加し、脱窒性能の低下を確認したが、実施例１では、処理水ＮＯ_３−Ｎ濃度が７.５ｍｇ／Ｌを超えることはなく、脱窒性能を良好に維持できた。
【００４０】
【発明の効果】
以上詳述した通り、本発明の生物濾過装置の逆洗方法によれば、タイマー設定による第１の逆洗と、濾過圧損に基く第２の逆洗とを組み合せて行う生物濾過装置の逆洗方法において、最適な逆洗間隔を自動制御することにより、逆洗不足による濾材層の閉塞、過剰逆洗による処理性能の低下を確実に防止して安定かつ効率的な処理を行うことができる。
【図面の簡単な説明】
【図１】実施例１における精密逆洗の制御方法を説明するグラフである。
【図２】実施例１及び比較例１の結果を示すグラフである。
【図３】図３（ａ）は従来の一般的な生物濾過装置の概略的な構成図であり、図３（ｂ）は通水時の濾材層を説明する模式図であり、図３（ｃ）は逆洗時の濾材層を説明する模式図である。
【符号の説明】
１濾過槽
２支持部材
３濾材層
４逆洗水貯留槽
５散気管[0001]
BACKGROUND OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biological filtration device backwashing method, and more particularly, a biological filtration device backwashing method in which a first backwashing by timer setting and a second backwashing based on filtration pressure loss (pressure loss) are combined. The present invention relates to an automatic control method for realizing an optimal backwash interval.
[0002]
[Prior art]
Conventionally, as a biological filtration device for industrial wastewater, sewage, etc., a biological filtration layer made of levitating filter material is formed in the tank, and a diffuser pipe is provided in the middle of the height direction of this biological filtration layer, and the lower part of the diffuser pipe An anaerobic denitrification unit and an aerobic nitrification unit at the upper part of the air diffuser, and a one-tank biofiltration based on the basic principle of the circulation nitrification denitrification method, which performs nitrification denitrification by circulating part of the treated water The device is known. Compared to the conventional floating nitrification denitrification equipment, this method
(1) Since the high load processing is possible, the apparatus can be made compact. That is, since the floatable filter medium has a small particle size and a large surface area, the amount of biological film adhering to the filter medium is extremely large, and as a result, high-quality treated water can be obtained at high load operation.
(2) Operation management is easy because sludge management in anaerobic tanks and sedimentation basins is unnecessary. That is, since it is a single tank type, a separate aeration tank is not required, and since microorganisms are attached to the surface of the filter medium, no sedimentation basin is required for solid-liquid separation of treated water. From this point, the apparatus can be downsized and the installation space can be saved.
There are excellent effects.
[0003]
FIG. 3A is a schematic configuration diagram of a conventional one-tank biological filtration apparatus, in which a water-permeable support member 2 is horizontally installed at the upper part of the filtration tank 1, and a levitating filter medium layer 3 is disposed below the water-permeable support member 2. Is provided. A backwash water storage tank 4 is formed above the water permeable support member 2. A diffuser pipe 5 is provided in the middle of the floating filter medium layer 3 in the height direction, and the upper side is an aerobic nitrification part and the lower part is an anaerobic denitrification part. A part of the biologically treated water in the storage tank 4 is circulated in the lower part of the filtration tank 1 as circulating water. A backwash drain pipe (not shown) is connected to the lower part of the filtration tank 1, and an air diffuser pipe (not shown) for air backwashing is provided at the bottom. As the levitation filter medium, for example, a filter medium having a specific gravity smaller than that of water, which is formed by foaming polystyrene, polypropylene, urethane resin or the like into a sphere having a diameter of 1 to 10 mm or an indefinite shape, is used. When such a floatable filter medium is filled in a biological reaction tank and is circulated upward by the water-permeable filter medium support member 2 disposed at an appropriate position, the floatable filter medium layer 3 is placed below the support member 2. A biofiltration layer is formed.
[0004]
In this biological filtration apparatus, the raw water and the circulating water introduced into the lower part of the filtration tank 1 are desorbed by the floating filter medium layer 3 below the diffuser pipe 5 while flowing upward in the floatable filter medium layer 3. Nitrogen treatment is performed, and nitrification treatment is performed on the floatable filter medium layer 3 above the diffuser tube 5. In addition, organic matter in the raw water is oxidized and decomposed into carbon dioxide and water.
[0005]
In FIG. 3A, a diffusing tube 5 is provided in the height direction of the levitation filter medium layer 3 to form a nitrification part and a denitrification part. There is also a biological filtration device in which the whole 3 is an anaerobic layer.
[0006]
In such a biological filtration device, turbidity trapped in the filter medium layer or surplus sludge generated as a result of biological reaction increases filtration resistance with time, making it difficult to pass water. Backwashing is necessary.
[0007]
As this backwashing method, water in the backwashing water storage tank 4 at the top of the filtration tank 1 is flowed back and discharged from the backwash drain pipe at the bottom of the filtration tank 1, and the bottom of the filtration tank 1 is used. There is air backwashing in which air is blown out from the provided air diffuser and the filter medium layer 3 is stirred. That is, in the biological filtration device, when the raw water is passed, as shown in FIG. 3 (b), the filter medium is pushed toward the support member 2 side above the filter medium layer 3 by the water flow, and the filter medium is packed closely with each other. Although the filtration layer is formed, the filter medium of the filter medium layer 3 expands downward as shown in FIG. 3 (c) by performing the water back-wash that causes the backwash water to flow downward from above. The captured SS is released, and the surplus biofilm is peeled off and discharged together with the backwash waste water. In the air backwashing, the filter medium layer 3 is agitated by air, so that the SS captured in the gaps between the filter media is released.
[0008]
In addition, as a method for automatically controlling the timing for performing such backwashing, there is the following method.
(1) A method of automatically performing backwashing at an appropriate time interval by a timer (2) A method of automatically starting backwashing by detecting that the filtration resistance has increased to the set filtration resistance (pressure loss) using a sensor or the like. (3) Method of combining the above (1) and (2)
[Problems to be solved by the invention]
However, the conventional backwash control method has the following problems.
[0010]
In the method of automatically backwashing at an appropriate time interval with the timer of (1), backwashing is performed regardless of the clogging condition of the filter medium layer. It may be too much. In the case of insufficient backwashing, the filter medium layer may be clogged due to accumulation of SS in the raw water or enlargement of the biofilm, and a plurality of filter medium particles may adhere to each other to form a lump. Once such a filter medium mass occurs, the normal backwash operation does not sufficiently loosen the mass, and further, if the filter medium forms a mass, the specific gravity is larger than that of a normal filter medium. A problem arises in that the filter medium solidified together with the waste water is discharged during washing. On the other hand, if backwashing is frequently performed, a nutrient source necessary for denitrification cannot be retained in the filter medium layer, resulting in problems such as a decrease in denitrification performance.
[0011]
In the method of starting backwashing with the filtration resistance set in (2), if backwashing is performed with a sufficient amount of water, there is no problem of over- and under-washing, but it is difficult to know when backwashing occurs and operation management is difficult. There is a problem that.
[0012]
In the method (3), specifically, the amount of backwash water used for backwashing based on the filtration resistance of (2) as compared to the amount of backwash water used for backwashing by the timer control of (1). Is set to be halved to reduce the total amount of water required for backwashing as much as possible. In this method, the possibility of clogging of the filter medium layer due to insufficient backwashing is lower than in the case of (1), but since the amount of backwash water based on the filtration resistance is small, the effect of preventing clogging of the filter medium layer is sufficient. In addition, the problem of denitrification degradation due to excessive backwashing cannot be solved. That is, even when backwashing of (1) and (2) is used together, it is most important to optimally control the backwashing interval of (1) with a large amount of backwashing water, and this interval is inappropriate. Then, the problem of clogging of the filter medium layer or deterioration of processing performance occurs.
[0013]
The present invention solves the above-mentioned conventional problems, and an optimal backwash interval in a backwashing method for a biological filtration device that is a combination of the first backwash by timer setting and the second backwash based on filtration pressure loss. It is an object of the present invention to provide an automatic control method that reliably prevents clogging of the filter medium layer due to insufficient backwashing and deterioration of processing performance due to excessive backwashing.
[0014]
[Means for Solving the Problems]
The backwashing method of the biological filtration device of the present invention is the first backwashing method of the biological filtration device which is a combination of the first backwashing by the timer setting and the second backwashing based on the filtration pressure loss. When the frequency of the second backwash between the first backwash and the next time is detected and the frequency exceeds a predetermined number of times, the timer setting value of the first backwash is increased and the treated water is increased. When the NO _x concentration exceeds a predetermined value, the first backwash timer set value is decreased.
[0015]
In the present invention, “increasing the first backwash timer set value” refers to shortening the set time of the first backwash interval so that the first backwash frequency increases. “Reducing the first backwash timer setting value” means increasing the set time of the first backwash interval so that the first backwash frequency is lowered.
[0016]
In the present invention, backwashing that is automatically performed at appropriate time intervals by setting a timer (hereinafter, this backwashing is referred to as “precision backwashing”), and the filtration pressure loss is increased to the set filtration pressure loss by the pressure sensor. When performing backwashing in combination with backwashing that is automatically detected and detected (hereinafter referred to as “simple backwashing”), between the precision backwashing and the next precision backwashing, In order to prevent clogging of the filter media layer by determining that the frequency of precision backwashing is low when simple backwashing is frequently performed over a predetermined number of times (for example, when simple backwashing is started twice or more). Increase the precision backwash timer setting and increase the frequency of precision backwash. Conversely, not have high simple backwash frequency between the precision backwash-order precision backwashing (for example, if the simple backwashing does not start at all), yet when the concentration of NO _x in the treated water exceeds a predetermined value Judge that the frequency of backwashing is too high and the nutrient source in the denitrification section is insufficient, and reduce the frequency of precision backwashing by reducing the timer setting value of precision backwashing in order to maintain the processing performance. .
[0017]
By performing such automatic control, the backwashing interval of the precision backwashing can be maintained optimally, and good treatment performance can be maintained while reliably preventing the filter medium layer from being blocked.
[0018]
In addition, in this invention, it is preferable to perform simple backwashing with the amount of backwashing water of half of the amount of backwashing of precision backwashing, for example, as shown in the following Tables 1 and 2 as a process example in each backwashing Those are preferred.
[0019]
[Table 1]

[0020]
[Table 2]

[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
[0022]
In the present invention, the following (1) and (2) are used for the backwashing of the biological filtration device by using both the precision backwashing by the timer setting and the simple backwashing based on the filtration pressure loss (that is, the filtration resistance). Control precision backwash interval based on ▼.
(1) If the frequency of simple backwashing between the precision backwashing and the next precision backwashing is detected and the frequency exceeds the specified number of times, the timer setting value for precision backwashing is increased and Increase frequency.
▲ 2 ▼ when the concentration of NO _x treated water exceeds a predetermined value, subtracting the timer settings of the precision backwash, reduce the frequency precision backwashing.
[0023]
In the control (1) above, there is no particular limitation on the frequency of simple backwashing for changing the timer setting value for precision backwashing. When simple backwashing is started more than once, it is preferable to change the timer set value in order to prevent the filter medium layer from being blocked.
[0024]
Further, ▲ 2 in the control of ▼, not particularly limited to a predetermined value of the NO _x concentration for changing the timer settings of the precision backwash is appropriately determined depending on the desired treated water quality, for example, treated water When the target value of the total nitrogen concentration is 10 mg / L or less, it is possible to maintain the quality of treated water when the NO ₃ -N concentration is 4 mg / L or more and the timer setting value for precision backwashing is changed. Is preferable.
[0025]
There is no particular limitation on the change range of the timer set value, and it is appropriately determined depending on the specifications of the biological filtration device and other operating conditions. For example, when the initial precision backwash interval setting time is T hours, In the case of (1) above, the interval is shortened by about 0.5 to 0.9 times the current set time, and in the case of (2) above, 1.1 to 2.0 times the current set time. A timer set value that makes the interval longer can be adopted.
[0026]
In addition, the backwashing method of the present invention is carried out in accordance with a conventional method except that precision backwashing and simple backwashing are used in combination, and the precise backwashing interval is controlled based on the above-mentioned (1) and (2). be able to.
[0027]
Further, in the above description, the case where the precise backwashing is performed as the first backwashing and the simple backwashing is performed as the second backwashing is described, but there is no particular limitation on the first and second backwashing steps. It is not always necessary to perform backwashing with a large amount of backwashing as the first backwashing. However, from the aspect of backwashing effect and stability, precision backwashing with a large amount of backwashing water is performed as the first backwashing, and backwashing water amount is small as the second backwashing, preferably the first backwashing. It is preferable to perform simple backwashing with a backwashing water amount of about 0.3 to 0.9 times the backwashing water amount.
[0028]
The method of the present invention can be effectively applied to backwashing of the nitrification denitrification biological filtration apparatus shown in FIG. 3 (a), the denitrification biological filtration apparatus without a diffuser tube, or the like.
[0029]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.
[0030]
Example 1
Precipitation supernatant water of basin sewage (partial rainwater confluence) was treated as raw water for the biological filtration device. The main water quality of the raw water was pH 7.0 to 7.2, SS concentration 91 to 144 mg / L, BOD concentration 71 to 116 mg / L, and total nitrogen concentration 21.2 to 32.1 mg / L.
[0031]
As a biological filtration apparatus, the one tank type biological filtration apparatus shown to Fig.3 (a) was used. This biological filtration apparatus had a filtration area of 2 m ² and a filter medium layer height of 3 m, and the raw water was passed so that the residence time per filter medium layer volume was 3 hours.
[0032]
Precision backwashing and simple backwashing were carried out in the steps shown in Tables 1 and 2, respectively, and were automatically controlled under the following conditions.
[0033]
Simple backwash control method:
It starts when the filtration resistance reaches 1.5 mH ₂ O.
[0034]
Precision backwash control method:
Initially, the precise backwash start-up setting time (backwash interval) is set to 48 hours, and control is performed within ± 12 hours as follows.
[0035]
If the simple backwash is activated twice between the precision backwash and the next precision backwash, the precise backwash start setting time is reduced by 12 hours from the current state because the precision backwash interval is too long. For example, if the current state is 48 hours, it is 36 hours. That is, as shown in FIG. 1A, when it is detected that the second simple backwash is started between the precise backwash and the next precise backwash, the second simple backwash is performed. Start precision backwashing, and then perform precision backwashing at 36-hour intervals.
[0036]
In addition, when the NO ₃ —N concentration of the treated water is 6 mg / L or more, it is assumed that the precise backwash interval is too short, and the precise backwash start setting time is increased by 12 hours from the current state. For example, if the current state is 48 hours, it is set to 60 hours. That is, as shown in FIG. 1 (b), when the NO ₃ —N concentration of the treated water is detected to be 6 mg / L or more, the next precision backwash is performed 60 hours after the closest precision backwash at that time, and thereafter 60 Perform precision backwash at time intervals.
[0037]
The experiment was conducted for one and a half months under these backwash conditions. The SS concentration, BOD concentration, and total nitrogen concentration of the raw water at this time are shown in FIG. 2 (a). Also, the NO ₃ -N concentration of the treated water changes with time and the presence or absence of filter media clumps (from the observation window during backwashing) 2) and FIG. 2 (b) and FIG. 2 (c), respectively, show the start situation of precision backwashing and simple backwashing and the situation of timer setting change.
[0038]
Comparative Example 1
In Example 1, the experiment was performed in the same manner except that the interval of the precision backwashing was fixed at 48 hours. FIGS. 2 (d) and 2 (e) show the change over time in the NO ₃ —N concentration of the treated water at this time, the presence or absence of filter media clumps, and the startup status of precision backwashing and simple backwashing, respectively.
[0039]
The following is clear from the results of FIG. That is, the presence or absence of filter media indicating the risk of clogging of the filter media layer was confirmed after the 14th day when the raw water SS concentration increased in Comparative Example 1, but in Example 1, no filter media was confirmed. It was. Also shows the reduction in denitrification performance, the rise of the treated water nitrate nitrogen (NO 3 _-N) concentration, in Comparative Example 1, at around 42 days the BOD concentration decreased raw water, treated water NO ₃ - Although the N concentration increased to a maximum of 9.4 mg / L and a decrease in denitrification performance was confirmed, in Example 1, the concentration of treated water NO ₃ -N did not exceed 7.5 mg / L, and the denitrification performance Was maintained well.
[0040]
【The invention's effect】
As described above in detail, according to the backwashing method of the biological filtration device of the present invention, the backwashing of the biological filtration device is performed by combining the first backwashing by the timer setting and the second backwashing based on the filtration pressure loss. In the method, by automatically controlling the optimum backwashing interval, it is possible to surely prevent the clogging of the filter medium layer due to insufficient backwashing and the deterioration of the processing performance due to excessive backwashing, thereby performing stable and efficient treatment.
[Brief description of the drawings]
FIG. 1 is a graph illustrating a control method for precision backwashing in Example 1. FIG.
FIG. 2 is a graph showing the results of Example 1 and Comparative Example 1.
FIG. 3 (a) is a schematic configuration diagram of a conventional general biological filtration device, and FIG. 3 (b) is a schematic diagram for explaining a filter medium layer during water flow. c) is a schematic diagram illustrating a filter medium layer during backwashing.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Filtration tank 2 Support member 3 Filter material layer 4 Backwash water storage tank 5 Aeration pipe

Claims

In the backwashing method of the biological filtration device that combines the first backwash by the timer setting and the second backwash based on the filtration pressure loss,
When the frequency of the second backwash between the first backwash and the next first backwash is detected and the frequency exceeds a predetermined number of times, the timer setting value of the first backwash is set. increases, if the concentration of NO _x in the treated water exceeds a predetermined value, the backwash process of biological filtration device characterized by subtracting the timer set value of the first backwash.