JP2004148210A

JP2004148210A - Filtration type water treatment method, and filtration type water treatment equipment

Info

Publication number: JP2004148210A
Application number: JP2002316469A
Authority: JP
Inventors: Daichi Sakashita; 大地坂下; Takayuki Saito; 孝行斎藤; Takuhisa Handa; 拓久半田
Original assignee: Ebara Corp
Current assignee: Ebara Corp
Priority date: 2002-10-30
Filing date: 2002-10-30
Publication date: 2004-05-27
Anticipated expiration: 2022-10-30
Also published as: JP4142401B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide an operation management index which permits an appropriate operation adaptive to a characteristic change of a material to be separated in a solid-liquid separation using a dynamic filtration method. <P>SOLUTION: The filtration type water treatment method performs control of an operation cycle with the average grain size of the suspended material in the water to be treated and water temperature as part or the whole of the indices. Further, it is preferred that a suspended material density index is employed as the index, that a filtration coefficient is calculated with the average grain size of the suspended material, the suspended material density index and the water temperature as the indices, that the filterable time per cycle is determined based on these indices, that a filtration surface is renewed when the determined filterable time is attained and that the filtration system is dynamic filtration. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、固液分離における運転管理に用いる方法及び装置であって、余剰汚泥濃縮、上水膜処理における前処理、上水汚泥分離（濃縮）、無機物含有排水処理、凝集フロック分離、粗ろ過（下排水前処理）等における、有機性あるいは無機性工業廃水、及び生活排水処理、特に活性汚泥の固液分離に好ましく用いる技術に関する。
【０００２】
【従来の技術】
従来、水処理の分野では、活性汚泥や凝集フロックの固液分離は、沈殿池においてこれら対象物を重力沈降させて分離を行い、その上澄み液を処理水として流出させる方法が一般的である。しかし、こうした沈殿池は設置面積が大きいこと、滞留時間が長いこと、さらに、除去できる粒子径に限界があることなどから、処理装置の大型化と設置容積増大の要因となっている。
【０００３】
近年、こうした沈殿池の代替として、精密ろ過膜（ＭＦ膜）、限外ろ過膜（ＵＦ膜）等による膜分離も用いられるようになり、良好な処理水質が得られている。しかしながら、膜分離に用いられる膜の孔径は１μｍ以下と非常に小さいため、膜の使用時には、通常、数十〜数百ｋＰａ程度のポンプ等による加圧、または吸引を行う必要があり、ポンプ動力等のランニングコストが大きい割に、得られる透過流束が小さいため、大容量処理にはあまり適当でない。さらに、これら分離膜は、阻止した有機物、微生物の代謝産物等により膜が汚染され、膜孔の閉塞が生じてろ過性能が低下するため、定期的な薬品洗浄が不可欠であるという欠点もある。
【０００４】
以上のような沈殿分離法の代替技術、あるいは、膜分離処理における問題を解決する方策として、織布、不織布等を用いたダイナミックろ過法（特許文献１）が提案されている。ここで言う「ダイナミックろ過法」とは、分離対象よりも大きな孔径を有する織布、不織布等をろ過基盤（基材）として用いて、これを曝気槽（生物反応槽）に浸漬し、その表面に分離対象物質を付着、いわゆる“ダイナミック膜”を形成させ、「取りたいものを取りたいものでろ過する」方法である。より分かり易くいうと、前記ろ過体のろ過基材の上に分離対象物質の薄いダイナミックろ過層を形成し、被処理液をこのろ過基材の上に平行にかつ比較的早く流すことによりダイナミックろ過層の厚さを成長させないようにしてろ過を進行させる方法である。
【０００５】
本法によれば、ろ過基盤（基材）の孔径が大きいため、付着したダイナミック膜が抵抗とならない範囲であれば、わずかな圧力差、例えば、数ｃｍ程度の水頭差で十分な透過流束が得られ、大容量処理が可能となる。但し、付着させたダイナミック膜は、ある厚さを越えると抵抗となって透過流束を減少させるため、定期的に空洗等により剥離して新しいダイナミック膜を形成させる、という繰り返しサイクルで運転する必要がある。この時、剥離のタイミングが適当でないと、付着したダイナミック膜が圧密化してろ過基盤（基材）から剥がれず、透過流束の低下を招くこととなる。このため、適切な運転サイクルを設定することが重要となる。
【０００６】
そこで、通水性ろ過体の表面に対して水洗を行い、初期値とほぼ同様なろ過Ｆｌｕｘを、長期にわたって安定して得られ、しかも、安定した処理水量、水質を得ることができる生物処理汚水の固液分離装置の洗浄方法及び装置を得ることを目的として、ろ過体洗浄時に、ろ過分離槽内の活性汚泥混合物を生物反応槽に完全に返送した時点で、ろ過体より上に設置された水洗ユニットをろ過体に面する液の流路に降下させて、ろ過体表面に対して水洗するろ過体の洗浄方法及び洗浄装置（特許文献２）が提案されている。
【０００７】
また、最近提案された膜分離手段を用いる分離装置では、分離膜による透水速度と上澄み液中の懸濁粒子濃度とが密接に関係しており、被処理液の上澄み液中の懸濁粒子濃度を指標にすると、適正な透水速度で円滑かつ効率よく固液分離できると説明されている。
【０００８】
【特許文献１】
特開平５−１８５０７８号公報
【特許文献２】
特開２００２−１３６８４５号公報
【０００９】
【発明が解決しようとする課題】
しかし、この方法では、上澄み液の懸濁粒子濃度を指標としているため、その試料調製に時間がかかり、生物処理液のように水質が刻々と変化する被処理液の水質を適切に把握できるとは限らない。しかも、静置の操作が入るため、上澄み濁度の測定を自動化することは難しく、連続的に安定した処理を行うことができない。さらに、被処理液の性状によっては、懸濁粒子がまったく沈殿しない、すなわち、上澄み液が得られない場合があるため、このような方法を用いて運転制御することは実質的に不可能である。
【００１０】
本発明は、このような実情に鑑みてなされたものであり、ダイナミックろ過法を用いた固液分離において、分離対象物の性状変化に対応した適切な運転を可能にする運転管理指標を提供することを目的とする。
【００１１】
【課題を解決するための手段】
本発明者らは、前記課題を達成するために鋭意研究を重ねた結果、被処理水中の懸濁物の平均粒径及び水温、さらには懸濁物密度指標との関係から、ろ過開始から空洗を行うまでの１サイクルあたりのろ過時間が設定できることを見いだし、本発明を完成させた。
【００１２】
すなわち、本発明は、下記の手段により上記の課題を解決することができた。
（１）被処理水の懸濁物平均粒径及び水温を指標の一部、又は全部として運転サイクルの制御を行うことを特徴とするろ過式水処理方法。
（２）さらに、懸濁物密度指標を指標とすることを特徴とする前記（１）記載のろ過式水処理方法。
（３）懸濁物平均粒径、懸濁物密度指標、及び水温を指標としてろ過係数を算出し、これに基づき１サイクルあたりのろ過可能時間を決定することを特徴とする前記（２）記載のろ過式水処理方法。
【００１３】
（４）懸濁物の粒径分布測定装置、ＳＳ測定装置、懸濁物容量測定装置、及び水温計を備え、懸濁物の粒径分布測定装置のデータから算出された懸濁物平均粒径、ＳＳ測定装置と懸濁物容量測定装置とから算出された懸濁物密度指標、及び水温計の測定水温からろ過係数を算出する演算装置、並びにこれに基づき１サイクルあたりのろ過可能時間を決定する制御機構を有することを特徴とするろ過式水処理装置。
（５）運転開始後に算出されたろ過係数をフィードバックし、これに基づき１サイクルあたりのろ過可能時間を再設定する制御機構を有することを特徴とする請求項４記載のろ過式水処理装置。
【００１４】
以下に、本発明の構成について個別に説明する。
本発明は、懸濁物平均粒径、及び水温の一部、又は全部、さらに、懸濁物密度指標を指標として運転サイクルの制御を行うことを特徴とするろ過式水処理方法であるが、運転サイクルの制御として、ろ過水を循環、または放出することの切り替えを含むことも特徴の一つとしている。
【００１５】
本発明は、懸濁物平均粒径及び水温、さらには懸濁物密度指標を指標としてろ過体のろ過係数を算出し、これに基づき１サイクルあたりのろ過可能時間を決定することを特徴としているが、ろ過係数を算出する際、例えば、次のような２次式（式１）が利用できる。
（式１）ｙ＝αｘ^２＋βｘ＋ｃ
ただし、ｙ：ろ過係数
ｘ：懸濁物平均粒径
α、β、ｃ：定数
なお、α、β、ｃは実験により求める。その値の例は以下に示す。さらに、ろ過係数ｙは、以下の関係式より求める。
（式２）ｙ＝μ・Ｕ^２・ｔ／ｄ
ただし、μ：水温により変動する水の粘性係数
Ｕ：膜透過速度
ｔ：ろ過速度が立ち上がり始めるまでのろ過時間
ｄ：懸濁物密度指標
【００１６】
また、上記のろ過の方法は、ダイナミックろ過であっても良く、この場合、上記式１から決定したろ過係数は、付着したダイナミック膜を更新するまでの時間、すなわち、ダイナミック膜が容易に剥離できるまでの時間、すなわち、ダイナミック膜が容易に剥離できるまでの最大時間を決定するために用いられる。
【００１７】
ダイナミックろ過において、ろ過対象とする懸濁物を含む被処理水は、例えば、平均粒径が５０〜２００μｍ程度の活性汚泥を含む生物処理液などでも良く、ろ過に用いるろ過基盤（基材）は、孔径１００〜２００μｍ程度の織布、不織布、金属網等を用いることができる。これらのろ過体を用いた場合、ろ過基盤（基材）の上に層状に形成させた懸濁物（ろ過層）で、分離対象の懸濁物をろ過するダイナミックろ過法による分離が行えるため、下水処理等、大流量の処理に用いることができる。上記式１から決定したろ過可能時間に達したら、ろ過面を更新し、新たなろ過面を形成させるという繰り返しによって、長期に渡り良好な運転が可能となる。
【００１８】
この時、例えば、ろ過基盤（基材）の孔径が１７０μｍ近傍において、活性汚泥を含む生物処理液のろ過では、活性汚泥の平均粒径が５０〜２００μｍ、特に、５０〜１５０μｍの場合、上記式１のα、β、ｃはそれぞれ、
α＝０．２〜０．４、β＝−４０〜−６０、ｃ＝２０００〜５０００
とすることで、１サイクルあたりのろ過可能時間が決定できることを確認した。また、本発明は、ろ過水の懸濁物濃度を測定することで、ろ過水の循環、または放出の切り替えを行うことができ、この点も特徴としている。
【００１９】
本法で用いる装置は、懸濁物の粒径分布測定装置、ＳＳ測定装置、懸濁物容量測定装置、及び水温計を備え、懸濁物の粒径分布測定装置のデータから算出された懸濁物平均粒径、ＳＳ測定装置と懸濁物容量測定装置から算出された懸濁物密度指標、及び水温計の測定水温から、上記２次式（式１）に基づきろ過係数（ｙ）を算出する演算装置、並びに、ｙに基づき１サイクルあたりのろ過可能時間を決定する制御機構を有することを特徴とするろ過式水処理装置である。
本装置は、前記記載の制御装置により、ろ過水ライン切り替え弁を操作する弁操作機構を有することを特徴としており、さらに、この制御装置により制御される洗浄装置を備えたことを特徴とするろ過式水処理装置である。
【００２０】
また、本発明のろ過装置は、被処理水である懸濁水の撹拌装置を備えるものであり、水槽内に置かれたこれら懸濁水の撹拌装置とろ過装置のろ過体との間に仕切板を備えたことを特徴としている。懸濁水が活性汚泥のような生物処理液の場合、撹拌装置は、生物処理水槽内に設置されている曝気装置を兼用できるため、この場合、新たに撹拌装置を設置する必要はない。この時、ろ過体の設置位置、曝気強度の制御等により、ダイナミックろ過形成に最適な撹拌速度を設定することができる。
あるいは、ろ過水槽を生物処理槽と別置きにした場合は、生物処理槽から上向流、または下向流でろ過水槽に生物処理水を循環させることにより、ろ過を行う。循環速度を変化させることで、ろ過基盤（基材）の表面流速を、良好なダイナミックろ過が行える最適値に容易に制御することができる。
【００２１】
【発明の実施の形態】
本発明の実施の態様を、図面を参照して、さらに詳細に説明する。
まず、図１に、本発明による運転サイクル制御に好適な装置の一例を示す。図１は、下水処理に適用される活性汚泥法において、従来、沈殿槽を用いて行っていた活性汚泥分離を、タイナミックろ過法によるろ過分離に置換した場合の一例を示している。
【００２２】
ここで、ダイナミックろ過に用いられるろ過基盤（基材）は、その表面に活性汚泥を付着、あるいは保持できるものであれば特に限定されないが、織布、ネット、不織布、金属製網などが好んで用いられる。特に、平織の織布は、金属製網に比べて安価で、不織布のように孔径のばらつきがなく、強度にも優れていることから、本法に適用するには好ましいと考えられる。
また、その孔径は１００μｍ以上、好ましくは、１００〜２００μｍ、さらに好ましくは、１５０〜２００μｍのものが、良好なろ過性能を維持しながら、ろ過基盤（基材）の目詰まり防止も可能であるとの観点から適当である。
【００２３】
織布の材質としては、繊維が単繊維のものであれば、ポリエステル、ポリエチレン、ポリイミド、ポリテトラフロオロエチレン等いずれでも良いが、繊維表面が滑らかで、水中でも膨潤などによる構造変化がほとんどなく、種々の化学物質に対しても安定なポリエステルが特に好ましい。
【００２４】
織布を取り付ける支持材としては、集水構造を備えた枠、あるいは平板状で中央部に凹部を有するプラスチック、または金属製のもので、各支持材が相互に脱着できる構造のものが、ろ過水量に応じて基材のろ過面積を容易に増減できることから好ましい。また、織布は支持材両面に取り付ける構造とすることが、集水面積を効率的に増やすことができるため有利である。織布と支持材の間には、織布が平面を保持できるように、目開きが大きな金網、厚手のプラスチック製網をスペーサーとして介在させるか、支持材空隙に縦横に何本かの支持棒を渡しても良い。このように織布と支持材、スペーサーを組み合わせた構造体をろ過体と称する。
【００２５】
さて、このような織布を用いたダイナミックろ過においては、大きな透過圧力を必要としないため、ポンプによる吸引ろ過はもちろん、ろ過水を得るための駆動力として水頭差を利用することができる。この時、織布表面にダイナミック層（活性汚泥層）が形成していない透過初期には活性汚泥がそのまま透過し、ろ過水質が安定しないため、ろ過水は曝気槽へ返送する必要がある。このため、ろ過水ラインには、ろ過水中の懸濁物濁度により制御される電磁弁等を設置して循環／放出の切り替えを行うことが望ましい。
【００２６】
ろ過水水質の安定後、ダイナミックろ過層は徐々に成長し、ある厚さを越えるとろ過抵抗が大となってろ過水量を減少させる。このため、ある段階で、ろ過体下部に設置した散気管から空気を供給し、空洗により余剰なダイナミックろ過層を剥離してろ過抵抗を低減、ろ過水量を回復させる必要がある。しかし、ろ過開始から空洗が必要となるまでの１サイクルあたりの時間は、活性汚泥性状（水質）によって異なるため、水質に応じてその時間を設定しなければならない。
さらに、ろ過基盤（基材）の孔径が大きいため、透過初期、あるいは空洗時、ろ過体内部に懸濁物が入り込み、これがろ過開始後に流出することで、ろ過水の水質（濁度）を悪化させる可能性がある。このため、ろ過体下部に、蓄積した懸濁物の引き抜きラインを備えていることが望ましい。
【００２７】
本発明は、懸濁物平均粒径、水温、懸濁物密度指標といった項目を指標として、運転サイクルの制御を行うことを特徴とするろ過式水処理方法に関するものであって、前記懸濁物平均粒径、水温、懸濁物密度を自動計測する手段を備えている、または、別途計測したそれらデータを入力する手段を備えているものである。また、入力されたデータから、１サイクルあたりの運転時間を計算するデータ解析機能を備え、さらに、ろ過水中の懸濁物容量から、ろ過水ラインのバルブ切り替えを自動的に行うバルブ切り替え機構を備えたものである。本発明によれば、被処理水水質の変動に応じて、煩わしい操作をすることなく、ダイナミックろ過における運転サイクルの設定を行うことが可能となり、専門の技術者が常駐しない場所においても、高度なろ過式水処理が適用できるようになる。本発明の適用先は、活性汚泥の固液分離に限らず、余剰汚泥濃縮、上水膜処理における前処理、上水汚泥分離（濃縮）、無機物含有排水処理、凝集フロック分離、粗ろ過（下排水前処理）等、有機性、無機性工業廃水および生活排水処理と幅広い。
【００２８】
【実施例】
以下、本発明を実施例により具体的に説明するが、本発明はこれらの実施例に何等限定されるものではない。
【００２９】
（実施例１）
基材としてポリエステル製平織織布（１００ｍｅｓｈ≒公称孔径１７０μｍ）を図１に示した装置に取り付け、実験を行った（有効膜面積＝０．０８４ｍ^２）。被処理水として、下水処理場より採取した活性汚泥を含む生物処理水を用いた。被処理水は、ろ過体を設置した水槽下部より上向流で流入させ、ろ過体表面に対して水平に０．０５ｍ／ｓの流速で流動させ、オーバーフローにより曝気槽へ返送した。単位面積当たりの設定ろ過水量を５ｍ^３／ｍ^２・ｄとして、ローラーポンプによる吸引ろ過を行った。処理水の水温、活性汚泥平均粒径、並びに懸濁物密度指標（汚泥密度指標＝ＳＤＩ）をあらかじめ測定し、式１にしたがって、１サイクル当たりのろ過可能時間を算出した。なお、本実施例においては、ポンプ吸引圧が５０ｍｍＡｑ（０．４９ｋＰａ）になったところで空洗を行うこととした。これは、良好なダイナミックろ過が行える吸引圧は、約７０ｍｍＡｑ（０．６９ｋＰａ）であることをあらかじめ確認しているため、若干の安全率を掛けて決定した値である。
【００３０】
図２に、計算式より求めた１サイクル当たりのろ過可能時間、及び実際に５０ｍｍＡｑ（０．４９ｋＰａ）に達するまでのろ過時間をそれぞれ示した。なお、試験例ごとに処理水の水温が異なるため、いずれの試験例も、水の粘性係数から水温を２０℃に換算し、その計算値により比較を行った。５回に渡る試験の結果、そのいずれの計算値も実測値にほぼ一致、または実測値より短く算出されていた。実測値よりも計算値が若干短めに算出されることは、運転条件を安全サイドに設定できることから、実用上は何ら支障がない。
【００３１】
（実施例２）
本発明におけるろ過式水処理装置の一例として、活性汚泥の粒径分布、活性汚泥浮遊物質（ＭＬＳＳ）濃度、汚泥容量及び水温を自動的に計測する測定装置を備え、これらのデータを処理、保存するための演算装置を有する装置のフロー図を図３に示す。また、本装置による活性汚泥分離における運転サイクルの一例と各機器の動作状態を図４に示す。さらに本装置は、懸濁物の粒径分布測定装置のデータから算出された活性汚泥の平均粒径、ＭＬＳＳ測定装置、および懸濁物容量測定装置から算出された懸濁物密度指標、及び水温計の測定水温を、演算装置を用いてろ過係数を算出し、並びに、これに基づき１サイクルあたりのろ過可能時間を決定する制御機構を有するろ過式水処理装置である。
【００３２】
【発明の効果】
以上詳述したとおり、本発明によれば、ダイナミックろ過法を用いた固液分離において、懸濁物平均粒径及び水温、さらには懸濁物密度指標を指標として運転制御を行うことで、ろ過開始から空洗が必要となるまでの１サイクルあたりのろ過時間を適切に設定できる。これより、分離対象物の性状が変化しても、長期に渡り安定したろ過が行える運転条件を設定することができる。
【図面の簡単な説明】
【図１】本発明のダイナミックろ過による活性汚泥分離に用いられる装置の一例を示す図である。
【図２】本発明の実施例１のろ過可能時間に関する結果を示すグラフである。
【図３】本発明の活性汚泥分離における各機器の制御フローの一例を示すフロー図である。
【図４】本発明の活性汚泥分離における運転サイクルの一例と各機器の動作状態を示す図である。
【符号の説明】
１原水流入ライン
２散気用ブロワ
２ａ空洗用ブロワ
３循環ポンプ
４生物反応槽
５散気管
６分離水槽
７ろ過モジュール
８ろ過水貯槽
９ろ過水ライン
１０電磁バルブ
１１透過水返送ライン
１２原水循環ライン
１３ドレインバルブ
１４水頭差
１５汚泥排出ライン
１６汚泥排出ポンプ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and an apparatus used for operation management in solid-liquid separation, which comprises excess sludge concentration, pretreatment in water treatment, separation of water sludge (concentration), wastewater treatment containing inorganic matter, flocculation separation, coarse filtration. The present invention relates to a technique preferably used for treating organic or inorganic industrial wastewater and domestic wastewater, particularly solid-liquid separation of activated sludge, in (pretreatment of sewage).
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in the field of water treatment, solid-liquid separation of activated sludge and flocculated floc is generally performed by gravity sedimentation of these objects in a sedimentation basin, separation, and the supernatant liquid flowing out as treated water. However, such a sedimentation basin has a large installation area, a long residence time, and a limitation on the particle size that can be removed, and thus causes an increase in the size of the treatment apparatus and an increase in the installation volume.
[0003]
In recent years, as an alternative to such a sedimentation basin, membrane separation using a microfiltration membrane (MF membrane), an ultrafiltration membrane (UF membrane), or the like has come to be used, and good treated water quality has been obtained. However, since the pore size of the membrane used for membrane separation is very small, 1 μm or less, it is usually necessary to perform pressurization or suction with a pump of about several tens to several hundreds kPa when using the membrane, and the pump power However, the obtained permeation flux is small in spite of the large running cost such as that described above, so that it is not very suitable for large-capacity processing. Further, these separation membranes have a drawback that periodic chemical cleaning is indispensable because the membrane is contaminated by the blocked organic substances, metabolites of microorganisms, and the like, and membrane pores are blocked and filtration performance is reduced.
[0004]
A dynamic filtration method using a woven fabric, a nonwoven fabric, or the like (Patent Document 1) has been proposed as an alternative technique to the above-described precipitation separation method or as a measure for solving the problem in the membrane separation treatment. The term "dynamic filtration method" used here means that a woven fabric or a nonwoven fabric having a pore size larger than the separation target is used as a filtration base (substrate), immersed in an aeration tank (biological reaction tank), and the surface thereof This is a method in which a substance to be separated is attached to a so-called "dynamic membrane", and "what is to be taken is filtered with what is to be taken". More simply, a dynamic filtration layer is formed by forming a thin dynamic filtration layer of a substance to be separated on the filtration substrate of the filtration body and flowing the liquid to be treated in parallel and relatively quickly over the filtration substrate. This is a method in which the filtration proceeds without increasing the thickness of the layer.
[0005]
According to this method, since the pore size of the filtration base (substrate) is large, if the attached dynamic membrane does not cause resistance, a small pressure difference, for example, a head difference of about several cm, sufficient permeation flux. And large-capacity processing becomes possible. However, the deposited dynamic film is operated in a repetitive cycle of forming a new dynamic film by periodically peeling it off by empty washing or the like in order to reduce the permeation flux when it exceeds a certain thickness because it becomes a resistance. There is a need. At this time, if the timing of peeling is not appropriate, the attached dynamic membrane is compacted and does not peel off from the filtration substrate (substrate), resulting in a decrease in permeation flux. Therefore, it is important to set an appropriate operation cycle.
[0006]
Therefore, the surface of the water-permeable filtration body is washed with water, and a filtration flux substantially similar to the initial value can be obtained stably over a long period of time. For the purpose of obtaining a method and a device for washing the solid-liquid separator, at the time when the activated sludge mixture in the filtration separation tank is completely returned to the biological reaction tank at the time of washing the filtration body, the water washing placed above the filtration body A washing method and a washing apparatus for a filter, in which a unit is lowered to a liquid flow path facing the filter and the surface of the filter is washed with water, have been proposed (Patent Document 2).
[0007]
Further, in a separation device using a recently proposed membrane separation means, the water permeation speed by the separation membrane and the concentration of suspended particles in the supernatant are closely related, and the concentration of suspended particles in the supernatant of the liquid to be treated is It is described that solid-liquid separation can be carried out smoothly and efficiently at an appropriate water permeation rate when is used as an index.
[0008]
[Patent Document 1]
JP-A-5-185078 [Patent Document 2]
JP 2002-136845 A
[Problems to be solved by the invention]
However, in this method, since the concentration of suspended particles in the supernatant is used as an index, it takes time to prepare the sample, and if the water quality of the liquid to be treated can be appropriately grasped, such as a biological treatment liquid, the water quality of which changes every moment. Not necessarily. In addition, since the operation of standing is included, it is difficult to automate the measurement of the supernatant turbidity, and it is not possible to perform a stable process continuously. Furthermore, depending on the properties of the liquid to be treated, suspended particles may not precipitate at all, that is, a supernatant may not be obtained. Therefore, it is practically impossible to control the operation using such a method. .
[0010]
The present invention has been made in view of such circumstances, and provides an operation management index that enables an appropriate operation corresponding to a change in properties of an object to be separated in solid-liquid separation using a dynamic filtration method. The purpose is to:
[0011]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to achieve the above object, and as a result, from the relationship with the average particle size and water temperature of the suspended matter in the water to be treated and the suspended matter density index, the present inventors have found that the filtration from the start of filtration to The inventor has found that the filtration time per cycle before washing can be set, and completed the present invention.
[0012]
That is, the present invention has solved the above-mentioned problems by the following means.
(1) A filtration type water treatment method characterized in that the operation cycle is controlled by using the average particle diameter and the water temperature of the suspension of the water to be treated as part or all of the indices.
(2) The filtration type water treatment method according to the above (1), further using a suspended matter density index as an index.
(3) The above-mentioned (2), wherein the filtration coefficient is calculated using the average particle diameter of the suspension, the suspension density index, and the water temperature as the indexes, and the filterable time per cycle is determined based on the calculated filtration coefficient. Filtration type water treatment method.
[0013]
(4) The average particle size of the suspension calculated from the data of the particle size distribution measuring device of the suspension, which is provided with a device for measuring the particle size distribution of the suspension, the SS measuring device, the device for measuring the volume of the suspended material, and the water thermometer The arithmetic unit that calculates the filtration coefficient from the diameter, the SS density index calculated from the SS measurement device and the suspension volume measurement device, and the measured water temperature of the water thermometer, and the filterable time per cycle based on the calculation device. A filtration type water treatment apparatus having a control mechanism for determining.
(5) The filtration type water treatment apparatus according to (4), further comprising a control mechanism that feeds back a filtration coefficient calculated after the operation is started and resets a filterable time per cycle based on the feedback.
[0014]
Hereinafter, the configuration of the present invention will be individually described.
The present invention is a filtration-type water treatment method characterized by performing a control of an operation cycle using an average suspension particle diameter, and a part or all of the water temperature as an index of the suspension density index, One of the features is that the control of the operation cycle includes switching of circulating or discharging the filtered water.
[0015]
The present invention is characterized by calculating a filtration coefficient of a filter using a suspended matter average particle diameter and a water temperature, and further, a suspended matter density index as an index, and determining a filterable time per cycle based on the calculated coefficient. However, when calculating the filtration coefficient, for example, the following quadratic equation (Equation 1) can be used.
(Equation 1) y = αx ² + βx + c
Here, y: filtration coefficient x: average particle diameter of suspension α, β, c: constants α, β, c are determined by experiments. Examples of the values are shown below. Further, the filtration coefficient y is obtained from the following relational expression.
(Equation 2) y = μ · U ² · t / d
Here, μ: viscosity coefficient of water fluctuating with water temperature U: membrane permeation rate t: filtration time t until the filtration rate starts to rise d: suspension density index
In addition, the above-mentioned filtration method may be dynamic filtration. In this case, the filtration coefficient determined from the above equation 1 is the time required for renewing the attached dynamic membrane, that is, the dynamic membrane can be easily peeled off. Is used to determine the maximum time until the dynamic film can be easily peeled off.
[0017]
In the dynamic filtration, the water to be treated containing the suspension to be filtered may be, for example, a biological treatment liquid containing activated sludge having an average particle size of about 50 to 200 μm. , A woven fabric, a nonwoven fabric, a metal net or the like having a hole diameter of about 100 to 200 μm can be used. When these filters are used, the suspension (filtration layer) formed in layers on the filtration base (substrate) can be separated by a dynamic filtration method in which the suspension to be separated is filtered. It can be used for large flow rate treatment such as sewage treatment. When the filterable time determined from the above equation 1 is reached, the filter surface is renewed and a new filter surface is formed, so that good operation can be performed over a long period of time.
[0018]
At this time, for example, when the pore size of the filtration base (substrate) is around 170 μm, in the filtration of the biological treatment liquid containing activated sludge, when the average particle size of the activated sludge is 50 to 200 μm, particularly 50 to 150 μm, the above formula is used. Α, β, c of 1 are
α = 0.2 to 0.4, β = −40 to −60, c = 2000 to 5000
As a result, it was confirmed that the filterable time per cycle can be determined. In addition, the present invention can switch the circulation or discharge of the filtered water by measuring the concentration of the suspended matter in the filtered water, and this is also characterized.
[0019]
The apparatus used in this method includes a suspension particle size distribution measuring device, an SS measuring device, a suspension volume measuring device, and a water thermometer, and the suspension calculated from the data of the suspension particle size distribution measuring device. The filtration coefficient (y) is calculated based on the above quadratic equation (Equation 1) from the suspended matter average particle diameter, the suspended matter density index calculated from the SS measuring apparatus and the suspended matter volume measuring apparatus, and the measured water temperature of the water thermometer. A filtration type water treatment apparatus comprising: a calculation device for calculating; and a control mechanism for determining a filterable time per cycle based on y.
This device is characterized by having a valve operating mechanism for operating the filtered water line switching valve by the control device described above, and further comprising a washing device controlled by this control device. It is a type water treatment device.
[0020]
Further, the filtration device of the present invention is provided with a stirring device for the suspension water as the water to be treated, and a partition plate is provided between the stirring device for the suspension water placed in the water tank and the filter of the filtration device. It is characterized by having. In the case where the suspension water is a biological treatment liquid such as activated sludge, the stirring device can also serve as the aeration device installed in the biological treatment water tank. In this case, it is not necessary to newly install a stirring device. At this time, the optimal stirring speed for dynamic filtration can be set by controlling the installation position of the filter, the aeration intensity, and the like.
Alternatively, when the filtration water tank is provided separately from the biological treatment tank, the filtration is performed by circulating the biological treatment water from the biological treatment tank to the filtration water tank in an upward flow or a downward flow. By changing the circulation speed, the surface flow velocity of the filtration substrate (substrate) can be easily controlled to an optimum value at which good dynamic filtration can be performed.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described in more detail with reference to the drawings.
First, FIG. 1 shows an example of an apparatus suitable for operation cycle control according to the present invention. FIG. 1 shows an example of the activated sludge method applied to sewage treatment, in which the activated sludge separation conventionally performed using a sedimentation tank is replaced by filtration separation by a dynamic filtration method.
[0022]
Here, the filtration base (substrate) used for the dynamic filtration is not particularly limited as long as the activated sludge can be attached to or retained on the surface thereof, but a woven fabric, a net, a nonwoven fabric, a metal net, and the like are preferred. Used. In particular, plain woven fabric is considered to be preferable for application to the present method because it is inexpensive as compared with a metal net, has no variation in pore diameter, and has excellent strength unlike a nonwoven fabric.
Moreover, the pore diameter is 100 μm or more, preferably 100 to 200 μm, and more preferably 150 to 200 μm, which can prevent clogging of the filtration base (substrate) while maintaining good filtration performance. It is appropriate from the viewpoint of.
[0023]
As the material of the woven fabric, if the fiber is a single fiber, any of polyester, polyethylene, polyimide, polytetrafluoroethylene, etc. may be used, but the fiber surface is smooth, and there is almost no structural change due to swelling in water. Polyesters that are stable to various chemical substances are particularly preferred.
[0024]
The supporting material to which the woven fabric is attached is a frame with a water collecting structure, or a flat plate-shaped plastic with a concave portion at the center, or a metal-made material that can be detached from each other by filtration. It is preferable because the filtration area of the substrate can be easily increased or decreased according to the amount of water. In addition, it is advantageous to use a structure in which the woven fabric is attached to both sides of the support member because the water collecting area can be efficiently increased. Between the woven fabric and the support material, a wire mesh with a large opening or a thick plastic mesh is used as a spacer so that the woven fabric can maintain a flat surface, or several support rods are provided in the support material space vertically and horizontally. May be passed. Such a structure in which the woven fabric, the support material, and the spacer are combined is referred to as a filter.
[0025]
By the way, in dynamic filtration using such a woven fabric, a large permeation pressure is not required. Therefore, not only suction filtration by a pump but also a head difference can be used as a driving force for obtaining filtered water. At this time, in the initial stage of permeation when a dynamic layer (activated sludge layer) is not formed on the surface of the woven fabric, the activated sludge permeates as it is, and the quality of the filtered water is not stable. Therefore, the filtered water needs to be returned to the aeration tank. For this reason, it is desirable to install a solenoid valve or the like controlled by the turbidity of the suspension in the filtered water in the filtered water line to switch between circulation and discharge.
[0026]
After the quality of the filtered water is stabilized, the dynamic filtration layer gradually grows, and when the thickness exceeds a certain thickness, the filtration resistance increases and the amount of the filtered water decreases. For this reason, at a certain stage, it is necessary to supply air from the air diffuser provided below the filter, to remove the excess dynamic filtration layer by washing with air, reduce the filtration resistance, and recover the amount of filtered water. However, the time per cycle from the start of filtration to the necessity of empty washing varies depending on the activated sludge property (water quality), and therefore, the time must be set according to the water quality.
Furthermore, since the pore size of the filtration base (substrate) is large, suspended matter enters the inside of the filter at the initial stage of permeation or at the time of empty washing, and flows out after the start of filtration, thereby reducing the quality (turbidity) of the filtered water. May worsen. For this reason, it is desirable to provide a line for extracting the accumulated suspension below the filter.
[0027]
The present invention relates to a filtration-type water treatment method, characterized in that an operation cycle is controlled by using items such as an average particle diameter of a suspension, a water temperature, and an index of a suspension density as indexes. Either a means for automatically measuring the average particle diameter, the water temperature, and the density of the suspended matter is provided, or a means for inputting the separately measured data is provided. It also has a data analysis function that calculates the operating time per cycle from the input data, and a valve switching mechanism that automatically switches the valve of the filtered water line based on the volume of suspended solids in the filtered water. It is a thing. According to the present invention, it is possible to set the operation cycle in the dynamic filtration according to the fluctuation of the quality of the water to be treated without performing a troublesome operation. Filtration type water treatment can be applied. The application of the present invention is not limited to solid-liquid separation of activated sludge, but also includes excess sludge concentration, pretreatment in water treatment, separation of water sludge (concentration), treatment of wastewater containing inorganic matter, coagulation floc separation, coarse filtration (lower Wastewater treatment), organic and inorganic industrial wastewater and domestic wastewater treatment.
[0028]
【Example】
Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to these examples.
[0029]
(Example 1)
A plain woven polyester fabric (100 mesh, nominal pore diameter 170 μm) was attached to the apparatus shown in FIG. 1 as a substrate, and an experiment was conducted (effective film area = 0.084 m ² ). Biologically treated water containing activated sludge collected from a sewage treatment plant was used as the water to be treated. The water to be treated was allowed to flow in an upward flow from the lower part of the water tank in which the filter was installed, flowed at a flow rate of 0.05 m / s horizontally to the surface of the filter, and returned to the aeration tank by overflow. The set filtration water amount per unit area was set to 5 m ³ / m ² · d, and suction filtration was performed using a roller pump. The temperature of the treated water, the average particle size of the activated sludge, and the suspended matter density index (sludge density index = SDI) were measured in advance, and the filterable time per cycle was calculated according to Equation 1. In this embodiment, the empty washing is performed when the pump suction pressure becomes 50 mmAq (0.49 kPa). This is a value determined by multiplying a little safety factor because it has been previously confirmed that the suction pressure at which good dynamic filtration can be performed is about 70 mmAq (0.69 kPa).
[0030]
FIG. 2 shows the filterable time per cycle determined by the calculation formula and the filtration time until the pressure actually reaches 50 mmAq (0.49 kPa). In addition, since the water temperature of the treated water differs for each test example, the water temperature was converted to 20 ° C. from the viscosity coefficient of the water in each test example, and the comparison was performed based on the calculated value. As a result of the test over five times, any of the calculated values was almost equal to or shorter than the actually measured value. If the calculated value is calculated to be slightly shorter than the actually measured value, the operating conditions can be set on the safe side, so that there is no problem in practical use.
[0031]
(Example 2)
As an example of the filtration type water treatment apparatus of the present invention, a measurement apparatus is provided for automatically measuring the particle size distribution of activated sludge, the concentration of activated sludge suspended solids (MLSS), the sludge volume and the water temperature, and these data are processed and stored. FIG. 3 is a flow chart of an apparatus having an arithmetic unit for performing the operation. FIG. 4 shows an example of an operation cycle in activated sludge separation by the present apparatus and the operation state of each device. Further, the present apparatus can be used to measure the average particle diameter of activated sludge calculated from the data of the apparatus for measuring the particle size distribution of suspended matter, the MLSS measuring apparatus, the suspended matter density index calculated from the apparatus for measuring suspended solid volume, and the water temperature. This is a filtration type water treatment apparatus having a control mechanism that calculates a filtration coefficient of a measured water temperature of a meter using an arithmetic device and determines a filterable time per cycle based on the calculated filtration coefficient.
[0032]
【The invention's effect】
As described in detail above, according to the present invention, in solid-liquid separation using a dynamic filtration method, by performing operation control using the suspended matter average particle diameter and water temperature, and further, the suspended matter density index as an index, filtration It is possible to appropriately set the filtration time per cycle from the start until the necessity of empty washing. Accordingly, it is possible to set operating conditions under which stable filtration can be performed over a long period of time even if the properties of the separation target change.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of an apparatus used for activated sludge separation by dynamic filtration according to the present invention.
FIG. 2 is a graph showing a result regarding a filterable time in Example 1 of the present invention.
FIG. 3 is a flowchart showing an example of a control flow of each device in the activated sludge separation of the present invention.
FIG. 4 is a diagram showing an example of an operation cycle in activated sludge separation of the present invention and an operation state of each device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Raw water inflow line 2 Blower for aeration 2a Blower for air washing 3 Circulation pump 4 Biological reaction tank 5 Diffusion tube 6 Separation tank 7 Filtration module 8 Filtration water storage tank 9 Filtration water line 10 Electromagnetic valve 11 Permeated water return line 12 Raw water circulation line 13 Drain valve 14 Head difference 15 Sludge discharge line 16 Sludge discharge pump

Claims

A filtration type water treatment method, wherein an operation cycle is controlled using a part of or the entirety of an average particle diameter and a water temperature of a suspension of water to be treated.

The filtration water treatment method according to claim 1, further comprising using a suspended matter density index as an index.

The filtration water according to claim 2, wherein a filtration coefficient is calculated by using the average particle diameter of the suspended matter, the suspended matter density index, and the water temperature as indices, and a filterable time per cycle is determined based on the calculated filtration coefficient. Processing method.

Equipped with a suspension particle size distribution measuring device, an SS measuring device, a suspension volume measuring device, and a water thermometer, the average particle size of the suspension calculated from the data of the particle size distribution measuring device of the suspension, SS A computing device that calculates a filtration coefficient from a suspended matter density index calculated from a measuring device and a suspended solids volume measuring device and a measured water temperature of a water thermometer, and a control that determines a permissible filtration time per cycle based on the computing device. A filtration type water treatment apparatus having a mechanism.

The filtration type water treatment apparatus according to claim 4, further comprising a control mechanism that feeds back a filtration coefficient calculated after the operation is started and resets a filterable time per cycle based on the feedback.