JP3601015B2

JP3601015B2 - Filtration method using membrane

Info

Publication number: JP3601015B2
Application number: JP31496496A
Authority: JP
Inventors: 純一荒海; 幸夫小林
Original assignee: Maezawa Industries Inc
Current assignee: Maezawa Industries Inc
Priority date: 1996-11-26
Filing date: 1996-11-26
Publication date: 2004-12-15
Anticipated expiration: 2016-11-26
Also published as: JPH10151328A

Description

【０００１】
【産業上の利用分野】
この発明は、水処理設備、特に浄水処理設備における膜を用いた濾過方法に関するものである。
【０００２】
【従来の技術】
膜を用いた濾過方法、特に、中空糸膜を用い、原水から濁質物またはマンガンを除去する濾過技術が、近時注目され、広く採用されつつあるが、中でも、吐出ポンプを作動させて、膜表面の接線方向に原水を流し、膜を通過させる通液法により処理水を得、処理水槽に貯留する、いわゆるクロスフロー（十字流）濾過（ＣｒｏｓｓＦｌｏｗＦｉｌｔｒａｔｉｏｎ：ＣＦＦ）が有効であるとされている。これは、膜分離で膜面に形成されるゲル層（ケーキ層）を、膜面に平行に流れる液の速度を大きくすることにより剥ぎ取り、濾過抵抗を低く保ち得るためである。
【０００３】
しかし、膜表面の液流速を大きくしても、運転時間の経過とともに膜表面で濁質物が濃縮されて高濃度となり、徐々に膜が閉塞し、ゲル層が生成して、やはり、濾過抵抗を増大させる。これは、中空糸膜の内側に膜に平行に原水を流し、膜の外側に透過させ、固液分離を行う内圧式のクロスフロー濾過の場合に、顕著である。そこで、この中空糸膜の膜面に付着した濁質物を除去するために、所定時間濾過を行った後、逆洗ポンプを作動させて短時間の逆洗浄を行っている。
【０００４】
【発明が解決しようとする課題】
上記したクロスフロー濾過の場合、膜の閉塞は、膜モジュールの流入水側の圧力（または、流入水側の圧力と濾過水出口側の圧力との差より求められる有効圧力）で検知し、その圧力が設定値を超えた場合に、吐出ポンプを停止し、膜モジュールの薬品洗浄を行う時期の到来の基準としている。しかし、この従来の濾過方法では、降雨その他に起因する急激な原水濁度の上昇といった原水水質の変化によって、一時的に膜が閉塞し、膜モジュールの流入水側の圧力が急激に上昇した場合にも、装置が停止することとなり、処理水を生産することができなくなるという問題点があった。そして、前記した膜の閉塞による膜モジュールの薬品洗浄を行う時期が到来していないにもかかわらず、薬品洗浄を行ってしまう事態が生じ、状況判断を誤らせる原因となっていた。
【０００５】
この発明は、このような従来技術の問題点を解決し、原水水質の変化による膜モジュールの流入水側の圧力の上昇に対して、装置を停止することなく、濾過運転を継続できるようにした膜を用いた濾過方法を提供することを目的とする。
【０００６】
【課題を解決するための手段】
上記の目的を達成するための手段として、この発明は、吐出ポンプにより膜モジュールに原水を供給し、膜を透過させて固液分離を行い処理水を得る膜を用いた濾過方法であって、常時は膜モジュールの濾過水出口側の流量を一定として、所定時間濾過を行った後、逆洗ポンプを作動させて短時間の定流量逆洗浄を行う濾過運転を繰り返す定流量濾過を行い、膜モジュールの流入水側の圧力が所定の圧力よりも上昇したときにのみ、定流量濾過から、吐出ポンプの一定の吐出圧力で濾過を行う定圧濾過に切り換え、前記膜モジュールの膜層の内側に濁質物が付着しゲル層となることで、膜の目詰まりによる閉塞を生じて薬品洗浄の時期が到来している場合と、急激な原水濁度の上昇に伴い原水水質の変化により一時的に膜が閉塞している場合とを、前記定流量逆洗浄における逆洗水を圧送したときの逆洗圧力の変動幅の大きさにより判断するように構成したことを特徴とする膜を用いた濾過方法を構成した。
【０００７】
この場合、濾過方法が、中空糸膜の内側に膜に平行に原水を流し、膜の外側に透過させ、固液分離を行う内圧式のクロスフロー濾過方法であると有効であり、また、定流量濾過と定圧濾過の切換えを膜モジュールの流入水側の圧力によりインバータ制御すると、より有効である。
【０００８】
【発明の実施の形態】
以下に、この発明の実施の形態を図面に基づいて説明する。この実施の形態では、内圧式のクロスフロー濾過装置を用いた濾過方法について示す。図１は、クロスフロー濾過により処理水を得るフロー図である。
【０００９】
図１において、膜モジュール１は、例えばセルロースアセテートを良溶媒に溶解したあとこれに金属塩と添加溶媒を加えたポリマー溶液を紡糸した多孔膜中空糸であって、膜層と中空部とから構成される。原水槽５内の原水２は、膜モジュール１の膜層の内側である中空部に、膜層に平行に流され、膜層を透過させるクロスフロー濾過により、膜層の外側に処理水３が濾液として取り出され、処理水槽４に貯留されるものである。
【００１０】
原水槽５内の原水２は、吐出ポンプ６により膜モジュール１に供給され、循環系１０を循環する。膜モジュール１への流入水の入口と出口には、それぞれ流入水入口圧力計ＰＴ_１と流入水出口圧力計ＰＴ_２を設けている。膜モジュール１により濾過された濾過水は、膜モジュール１の濾過水上部取出口１ａと濾過水下部取出口１ｂから取り出され、共に処理水３として処理水槽４に送給される。濾過水上部取出口１ａおよび濾過水下部取出口１ｂには、それぞれ電磁弁Ｂ_１，Ｂ_２と、これに対応する濾過水出口圧力計ＰＴ_３，ＰＴ_４とが設けられる。また、処理水３の取出径路７には、電磁弁Ｂ_３と流量計ＦＴとを設けている。さらに、処理水３が貯留されている処理水槽４からは処理水３の取出径路７に向けて逆洗水圧送路８を設け、逆洗ポンプ９と定流量弁Ｂ_４が設置される。
【００１１】
さて、この濾過方法の基本的形態は、膜モジュール１の濾過水出口側に設けている流量計ＦＴの流量を一定として、処理水槽４に常時一定の処理水３が得られる定流量濾過を行うことである。この濾過運転を続けると、膜モジュール１の膜層の内側に濁質物が付着し徐々にゲル層となって堆積する。そこで、所定時間（例えば３０分間）濾過運転を行った時点で、短時間（例えば１分間）逆洗ポンプ９を作動させ、逆洗水圧送路８から逆洗水を定流量で圧送して、濁質物を強制的に剥離除去する作業を行う。このように、所定時間の定流量濾過の後、短時間の逆洗浄を交互に繰り返す濾過運転は、膜モジュール１の流入水側の圧力、つまり流入水入口圧力計ＰＴ_１の圧力が設定値を超える事態が発生するまで継続される。
【００１２】
ところで、本発明者らは、この発明の実施に際し、１９日間に亘り、河川より原水を導入し、濾過実験を行った。図２〜図６は実験結果を示すグラフである。横軸は、それぞれ実験初日からの経過日数を示している。縦軸については、図２に原水濁度、図３に有効圧力、図４に実流束、図５に濾過運転時の各圧力計の数値、図６に逆洗圧力を示す。なお、
有効圧力（ｋＰａ）＝〔（流入水入口圧力＋流入水出口圧力）÷２−（濾過水上部取出口圧力＋濾過水下部取出口圧力）÷２〕×９８．０６６５
実流束（ｍ／日）＝濾過流量（ｍ^３／日） ÷膜面積（ｍ）
を表す。
【００１３】
濾過運転の条件を表１に示す。なお、膜モジュールの圧力の設定値を２．０ｋｇｆ／ｃｍ^２とした。
【表１】

【００１４】
図２において、実験１０日目（６／１３）に降雨による急激な濁度の上昇があり、これに伴って図３に示すように、有効圧力も実験１１〜１２日目（６／１４〜６／１５）に５３ｋＰａから１３５ｋＰａまで急激に上昇している。また、図４に示すように同期間における実流束も低下している。このとき、もし定流量濾過を継続すると、図５の▲１▼で示す流入水入口圧力（ＰＴ_１の数値）は上昇を続け、図中の二点鎖線で示すように膜モジュールの耐圧である２．０ｋｇｆ／ｃｍ^２にまで達すべきところ、この発明では、所定の圧力である１．７ｋｇｆ／ｃｍ^２よりも上昇したときに、定流量濾過から、吐出ポンプの一定の吐出圧力で濾過を行う定圧濾過に切り換わることが特徴である。
【００１５】
図５の▲１▼で示す流入水入口圧力は、実験１１〜１２日目（６／１４〜６／１５）にのみ定圧濾過となり定圧状態である１．７ｋｇｆ／ｃｍ^２に押さえられた状態で推移しているが、この定圧濾過の間も所定時間毎の短時間の逆洗浄が行われることと、原水水質が安定するに従って、図３の有効圧力も低下しはじめ、図４の実流束も１．５ｍ／日に戻り、流入水入口圧力が設定値（１．７ｋｇｆ／ｃｍ^２）以下となると、再び定流量濾過に切り換わる。
【００１６】
このように膜モジュールの流入水側の圧力が所定の圧力よりも上昇した期間中は、定流量濾過から、吐出ポンプの吐出圧力で維持される定圧濾過となり、生産処理水の量は減少するが、従来の装置のように吐出ポンプを停止する必要がなく運転を継続できる。なお、図１の吐出ポンプ６は、膜モジュールの耐圧以下の圧力で必要な処理水の量が確保できる高出力のポンプが使用される。また、定流量濾過と定圧濾過の切換えは、膜モジュール１の流入水側の圧力を制御盤２０によりインバータ制御して行われる。
【００１７】
図６は、逆洗圧力のグラフである。すなわち、図１の逆洗ポンプ９を作動させ定流量で逆洗水圧送路８から逆洗水を圧送し、膜モジュール１の濾過水出口圧力計ＰＴ_３，ＰＴ_４の圧力（平均値）を測定したものである。前述の流入水入口圧力が上昇した実験１１〜１２日目（６／１４〜６／１５）の期間における逆洗圧力は、１４０ｋＰａから１６０ｋＰａまで僅かに上昇（約１．１倍）しただけである。急激な原水濁度の上昇といった原水水質の変化によって、一時的に膜が閉塞した場合には、このように逆洗圧力は大きく変動しないが、膜モジュール１の膜層の内側に濁質物が付着しゲル層となって、いわゆる膜の目詰まりによる完全な閉塞を起こしている場合には、逆洗圧力の変動幅は大きく顕著に現れる。したがって、この発明では、膜の閉塞による膜モジュールの薬品洗浄を行う時期の到来を膜モジュールに逆洗水を圧送したときの逆洗圧力により判断することができる。
【００１８】
なお、上記の実施形態では、濾過方法として中空糸膜を用い原水を膜モジュール１に供給して循環系を循環させるクロスフロー濾過による方法を用いる場合について説明したが、もちろん全量濾過による膜濾過方法に適用してもよい。
【００１９】
【発明の効果】
上記の構成からなるこの発明の膜を用いた濾過方法によれば、常時は膜モジュールの濾過水出口側の流量を一定として、所定時間濾過を行った後、逆洗ポンプを作動させて短時間の逆洗浄を行う濾過運転を繰り返す定流量濾過を行い、膜モジュールの流入水側の圧力が所定の圧力よりも上昇したときにのみ、定流量濾過から、吐出ポンプの一定の吐出圧力で濾過を行う定圧濾過に切り換える方法を採用したので、降雨その他に起因する急激な原水濁度の上昇といった原水水質の変化による一時的な膜の閉塞に対して、装置を停止することなく、膜モジュールの耐圧以下の圧力で運転を継続することができる。したがって、従来の装置のように処理水の生産が中断されることがない。そして、装置を停止する必要がないので、膜モジュールに接触する原水の腐敗を防ぐことができ、膜に与えるダメージが少ない。
【００２０】
また、原水水質の変化による一時的な膜の閉塞と、薬品洗浄を必要とする膜モジュールの膜の目詰まりによる完全な閉塞とは、膜モジュールに逆洗水を圧送したときの逆洗圧力が大きく異なることから、これにより膜モジュールの薬品洗浄を行う時期を明確に判断することができ、従来のように、薬品洗浄を行う時期が到来していないにもかかわらず、薬品洗浄を行ってしまうといった判断の誤りを未然に防止することができる。
【図面の簡単な説明】
【図１】この発明に係る膜を用いた濾過方法を説明するための濾過装置の一例を示すフロー図である。
【図２】この発明に係る膜を用いた濾過方法を実施した実験結果を示す原水濁度のグラフである。
【図３】この発明に係る膜を用いた濾過方法を実施した実験結果を示す有効圧力のグラフである。
【図４】この発明に係る膜を用いた濾過方法を実施した実験結果を示す実流束のグラフである。
【図５】この発明に係る膜を用いた濾過方法を実施した実験結果を示す濾過運転時の各圧力計の数値のグラフである。
【図６】この発明に係る膜を用いた濾過方法を実施した実験結果を示す逆洗圧力のグラフである。
【符号の説明】
１ …膜モジュール
２ …原水
３ …処理水
４ …処理水槽
５ …原水槽
６ …吐出ポンプ
８ …逆洗水圧送路
９ …逆洗ポンプ
１０ …循環系
２０ …インバータ
Ｂ_１，Ｂ_２，Ｂ_３…電磁弁
Ｂ_４ …定流量弁
ＰＴ_１…流入水入口圧力計
ＰＴ_２…流入水出口圧力計
ＰＴ_３，ＰＴ_４…濾過水出口圧力計
ＦＴ …流量計[0001]
[Industrial applications]
The present invention relates to a filtration method using a membrane in a water treatment facility, particularly, a water purification treatment facility.
[0002]
[Prior art]
Filtration methods using membranes, in particular, filtration techniques for removing turbid matter or manganese from raw water using hollow fiber membranes have recently attracted attention and are being widely adopted. It is said that so-called Cross Flow Filtration (CFF), in which raw water is flowed in a tangential direction of the surface and treated water is passed through a membrane to obtain treated water and stored in a treated water tank, that is, Cross Flow Filtration (CFF) is effective. I have. This is because the gel layer (cake layer) formed on the membrane surface by membrane separation can be peeled off by increasing the velocity of the liquid flowing parallel to the membrane surface to keep the filtration resistance low.
[0003]
However, even if the liquid flow velocity on the membrane surface is increased, the turbid matter is concentrated on the membrane surface to a high concentration with the elapse of the operation time, the membrane is gradually closed, a gel layer is formed, and the filtration resistance is also reduced. Increase. This is remarkable in the case of internal pressure type cross-flow filtration in which raw water flows in parallel with the membrane inside the hollow fiber membrane, permeates outside the membrane, and performs solid-liquid separation. Therefore, in order to remove the suspended matter adhering to the membrane surface of the hollow fiber membrane, after performing filtration for a predetermined time, the backwashing pump is operated to perform the backwashing for a short time.
[0004]
[Problems to be solved by the invention]
In the case of the cross-flow filtration described above, the blockage of the membrane is detected by the pressure on the inflow side of the membrane module (or the effective pressure obtained from the difference between the pressure on the inflow side and the pressure on the outlet side of the filtrate), and the When the pressure exceeds the set value, the discharge pump is stopped, and the time for chemical cleaning of the membrane module is reached. However, in this conventional filtration method, when the raw water quality changes such as a sudden increase in raw water turbidity caused by rainfall or the like, the membrane is temporarily blocked, and the pressure on the inflow water side of the membrane module rises sharply. In addition, there is a problem that the apparatus stops, and it becomes impossible to produce treated water. In addition, although the time for performing the chemical cleaning of the membrane module due to the blockage of the film has not arrived, a situation in which the chemical cleaning is performed has occurred, causing a situation determination error.
[0005]
The present invention solves such a problem of the prior art, and makes it possible to continue the filtration operation without stopping the apparatus in response to a rise in the pressure on the inflow side of the membrane module due to a change in the quality of the raw water. It is an object to provide a filtration method using a membrane.
[0006]
[Means for Solving the Problems]
As a means for achieving the above object, the present invention is a filtration method using a membrane to supply raw water to a membrane module by a discharge pump, to permeate the membrane and perform solid-liquid separation to obtain treated water, Normally, the flow rate at the filtrate water outlet side of the membrane module is kept constant, and after performing the filtration for a predetermined time, the backwashing pump is operated to perform a short-time constant-flow reverse-washing, which is a constant-flow filtration that repeats a filtration operation. Only when the pressure on the inflow water side of the module rises above a predetermined pressure, switching from constant flow filtration to constant pressure filtration in which filtration is performed at a constant discharge pressure of the discharge pump, and turbidity is formed inside the membrane layer of the membrane module. The substance adheres and forms a gel layer, causing clogging due to clogging of the membrane, and the time for chemical cleaning has arrived, and temporary changes in the quality of the raw water due to a sudden increase in raw water turbidity. Is blocked Was constructed filtration method using a membrane which is characterized by being configured to determine the magnitude of the fluctuation width of the backwash pressure when the pumping backwash water in the constant flow backwashing.
[0007]
In this case, it is effective that the filtration method is an internal pressure type cross-flow filtration method in which raw water flows in parallel with the membrane inside the hollow fiber membrane, permeates outside the membrane, and performs solid-liquid separation. It is more effective if the switching between flow rate filtration and constant pressure filtration is controlled by an inverter using the pressure on the inflow side of the membrane module.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this embodiment, a filtration method using an internal pressure type cross flow filtration device will be described. FIG. 1 is a flow chart for obtaining treated water by cross-flow filtration.
[0009]
In FIG. 1, a membrane module 1 is a porous membrane hollow fiber obtained by, for example, dissolving cellulose acetate in a good solvent and then spinning a polymer solution obtained by adding a metal salt and an additive solvent, and comprises a membrane layer and a hollow portion. Is done. The raw water 2 in the raw water tank 5 is flowed in parallel to the membrane layer into the hollow portion inside the membrane layer of the membrane module 1, and the treated water 3 is discharged to the outside of the membrane layer by cross-flow filtration through the membrane layer. It is taken out as a filtrate and stored in the treated water tank 4.
[0010]
The raw water 2 in the raw water tank 5 is supplied to the membrane module 1 by the discharge pump 6, and circulates in the circulation system 10. The inlet and outlet of the influent water to the membrane module 1, respectively provided influent inlet pressure gauge PT ₁ and influent water outlet pressure gauge PT _2. The filtered water filtered by the membrane module 1 is taken out from the filtered water upper outlet 1a and the filtered water lower outlet 1b of the membrane module 1, and both are fed to the treated water tank 4 as the treated water 3. Solenoid valves B ₁ and B ₂ and corresponding filtered water outlet pressure gauges PT ₃ and PT ₄ are provided in the filtered water upper outlet 1a and the filtered water lower outlet 1b, respectively. Further, the extraction channel 7 of treated water 3 is provided with an electromagnetic valve B ₃ and flowmeter FT. Further, from the process water tank 4 that treated water 3 is stored backwash water pressure sending passage 8 toward the extraction channel 7 of treated water 3 is provided backwash pump 9 and constant flow valve B ₄ is installed.
[0011]
The basic form of this filtration method is to perform a constant flow rate filtration in which a constant treatment water 3 is always obtained in a treatment water tank 4 with a constant flow rate of a flow meter FT provided on a filtrate water outlet side of the membrane module 1. That is. When this filtration operation is continued, the suspended matter adheres to the inside of the membrane layer of the membrane module 1 and gradually becomes a gel layer and deposits. Therefore, when the filtration operation is performed for a predetermined time (for example, 30 minutes), the backwash pump 9 is operated for a short time (for example, 1 minute), and the backwash water is pumped at a constant flow rate from the backwash water pressure feed line 8. Work to forcibly remove and remove suspended matter. Thus, after a constant flow filtration of a predetermined time, a filtration operation to repeat the backwashing momentary alternating pressure of the incoming water side of the membrane module 1, i.e. the pressure of the influent inlet pressure gauge PT ₁ is a set value It is continued until an overrun occurs.
[0012]
By the way, the present inventors conducted a filtration experiment by introducing raw water from a river for 19 days when implementing the present invention. 2 to 6 are graphs showing experimental results. The horizontal axis represents the number of days elapsed from the first day of the experiment. With respect to the vertical axis, FIG. 2 shows the raw water turbidity, FIG. 3 shows the effective pressure, FIG. 4 shows the actual flux, FIG. 5 shows the values of the respective pressure gauges during the filtration operation, and FIG. 6 shows the backwash pressure. In addition,
Effective pressure (kPa) = [(inflow water inlet pressure + inflow water outlet pressure) ÷ 2- (filtered water upper outlet pressure + filtered water lower outlet pressure) ÷ 2] × 98.0665
Actual flux (m / day) = Filtration flow rate (m ³ / day) ÷ Membrane area (m)
Represents
[0013]
Table 1 shows the conditions for the filtration operation. The set value of the pressure of the membrane module was set to 2.0 kgf / cm ² .
[Table 1]

[0014]
In FIG. 2, on the 10th day of the experiment (6/13), there was a sharp increase in turbidity due to rainfall, and as shown in FIG. 3, the effective pressure also increased on the 11th to 12th days of the experiment (6/14 to 6/13). On June 15), it increased sharply from 53 kPa to 135 kPa. Further, as shown in FIG. 4, the actual flux during the same period is also reduced. At this time, if the constant flow rate filtration is continued, the inflow water inlet pressure (the numerical value of PT1) indicated by ( ₁ ) in FIG. 5 continues to increase, and is the pressure resistance of the membrane module as indicated by the two-dot chain line in the figure. Where the pressure should reach 2.0 kgf / cm ² , according to the present invention, when the pressure rises above a predetermined pressure of 1.7 kgf / cm ² , filtration is performed at a constant discharge pressure of the discharge pump from constant flow filtration. It is characterized by switching to constant pressure filtration.
[0015]
The inflow water inlet pressure indicated by {circle around (1)} in FIG. 5 was filtered at a constant pressure only on the 11th to 12th days of the experiment (6/14 to 6/15) and was kept at a constant pressure of 1.7 kgf / cm ^2. The effective pressure in FIG. 3 also begins to decrease as the backwashing is performed for a short period of time every predetermined time during the constant pressure filtration, and as the raw water quality becomes stable, the actual flux in FIG. Is returned to 1.5 m / day, and when the inflow water inlet pressure becomes equal to or lower than the set value (1.7 kgf / cm ² ), the flow is switched to the constant flow filtration again.
[0016]
During the period in which the pressure on the inflow water side of the membrane module rises above the predetermined pressure in this manner, from constant flow filtration to constant pressure filtration maintained at the discharge pressure of the discharge pump, the amount of the treated water to be produced decreases. The operation can be continued without having to stop the discharge pump unlike the conventional apparatus. As the discharge pump 6 in FIG. 1, a high-output pump capable of securing a required amount of treated water at a pressure lower than the pressure resistance of the membrane module is used. Switching between the constant flow filtration and the constant pressure filtration is performed by controlling the pressure on the inflow water side of the membrane module 1 by the control panel 20 using an inverter.
[0017]
FIG. 6 is a graph of the backwash pressure. That is, the backwash pump 9 of FIG. 1 is operated to pump backwash water at a constant flow rate from the backwash water pressure feed line 8, and the pressures (average values) of the filtered water outlet pressure gauges PT ₃ and PT ₄ of the membrane module 1 are measured. Measured. The backwash pressure during the period from the 11th to the 12th day (6/14 to 6/15) of the experiment in which the inflow water inlet pressure was increased only slightly increased (about 1.1 times) from 140 kPa to 160 kPa. . When the membrane is temporarily blocked due to a change in the quality of the raw water such as a sharp rise in the turbidity of the raw water, the backwash pressure does not fluctuate greatly as described above, but turbid substances adhere to the inside of the membrane layer of the membrane module 1. When the gel layer is completely blocked due to so-called clogging of the film, the fluctuation width of the backwash pressure is large and remarkable. Therefore, according to the present invention, it is possible to determine the timing of performing the chemical cleaning of the membrane module due to the blockage of the membrane based on the backwash pressure when the backwash water is pumped to the membrane module.
[0018]
In the above embodiment, the case where the method by cross-flow filtration in which raw water is supplied to the membrane module 1 and the circulation system is circulated by using a hollow fiber membrane as the filtration method has been described. May be applied.
[0019]
【The invention's effect】
According to the filtration method using the membrane of the present invention having the above configuration, the flow rate at the filtrate water outlet side of the membrane module is always constant, and after performing filtration for a predetermined time, the backwash pump is operated for a short time. A constant flow filtration is repeated by repeating the filtration operation of performing the back washing, and only when the pressure on the inflow water side of the membrane module rises above a predetermined pressure, the filtration is performed from the constant flow filtration at a constant discharge pressure of the discharge pump. The method adopted is to switch to constant pressure filtration, which allows the membrane module to withstand the pressure of the membrane module without stopping the equipment against temporary membrane blockage due to a change in the quality of the raw water such as a sudden rise in raw water turbidity caused by rainfall or the like. Operation can be continued at the following pressures. Therefore, the production of treated water is not interrupted unlike the conventional apparatus. And since there is no need to stop the apparatus, it is possible to prevent the raw water coming into contact with the membrane module from being spoiled, and to cause less damage to the membrane.
[0020]
In addition, temporary blockage of the membrane due to changes in the quality of raw water and complete blockage due to clogging of the membrane of the membrane module requiring chemical cleaning are caused by the backwash pressure when the backwash water is pumped to the membrane module. Since there is a great difference, this makes it possible to clearly judge when to perform chemical cleaning of the membrane module, and to perform chemical cleaning even when the time to perform chemical cleaning has not arrived as in the past. Such an erroneous determination can be prevented beforehand.
[Brief description of the drawings]
FIG. 1 is a flowchart showing an example of a filtration device for explaining a filtration method using a membrane according to the present invention.
FIG. 2 is a graph of raw water turbidity showing an experimental result of performing a filtration method using a membrane according to the present invention.
FIG. 3 is a graph of effective pressure showing experimental results obtained by performing a filtration method using a membrane according to the present invention.
FIG. 4 is a graph of actual flux showing an experimental result of performing a filtration method using a membrane according to the present invention.
FIG. 5 is a graph of numerical values of respective pressure gauges at the time of a filtration operation showing an experimental result of performing a filtration method using a membrane according to the present invention.
FIG. 6 is a graph of backwash pressure showing the results of an experiment in which a filtration method using a membrane according to the present invention was performed.
[Explanation of symbols]
1 ... membrane module 2 ... raw water 3 ... treated water 4 ... treatment water tank 5 ... raw water tank 6 ... discharge pump 8 ... backwash water pressure sending passage 9 ... backwash pump 10 ... circulation system 20 ... inverter _B _1, B 2, _{B 3} ... electromagnetic valve _{B 4} ... constant flow valve PT 1 _... influent inlet pressure gauge PT 2 _... influent outlet pressure gauge _PT 3, PT 4 _... filtered water outlet pressure gauge FT ... flowmeters

Claims

This is a filtration method using a membrane in which raw water is supplied to a membrane module by a discharge pump and solid-liquid separation is performed by permeating the membrane to obtain treated water. After performing filtration for a predetermined time, the backwashing pump is operated to perform a constant flow rate filtration in which a filtration operation for performing a short-time constant flow backwash is performed, and the pressure on the inflow water side of the membrane module rises above a predetermined pressure. Only when is it switched from constant flow filtration to constant pressure filtration that performs filtration at a constant discharge pressure of the discharge pump ,
The turbid matter adheres to the inside of the membrane layer of the membrane module to form a gel layer. The case where the membrane is temporarily blocked due to a change in the quality of the raw water is also determined based on the magnitude of the fluctuation width of the backwash pressure when the backwash water is pumped in the constant flow backwash. A filtration method using a membrane characterized by the above-mentioned.

The filtration method using a membrane according to claim 1, wherein the filtration method is an internal pressure type cross-flow filtration method in which raw water flows inside the hollow fiber membrane in parallel with the membrane, passes through the outside of the membrane, and performs solid-liquid separation. Method.

The filtration method using a membrane according to claim 1 or 2, wherein the switching between the constant flow filtration and the constant pressure filtration is inverter-controlled by the pressure on the inflow water side of the membrane module.