JP4635666B2 - Water treatment method - Google Patents

Description

  The present invention relates to a water treatment method using submerged membrane separation means. More specifically, at least the operation step is a filtration step in which the liquid to be treated is sucked through the separation membrane module to obtain membrane filtered water, and the surface of the separation membrane module is supplied with air from an air diffuser installed below the separation membrane module It is related with the water treatment method comprised from the empty washing process which wash | cleans, and the mud discharge process which discharges the suspended solid settled in the bottom part of the immersion tank as sludge to the exterior of an immersion tank.

  Membrane separation technology using separation membranes includes drinking water production in the waterworks, industrial water, industrial ultrapure water, industrial water production such as food and medicine, sewage treatment such as municipal sewage purification and industrial wastewater treatment. It is used in a wide range of fields. Moreover, the separation membrane module used for membrane separation is classified into a pressure type and an immersion type regardless of the processing field. The immersion type separation membrane module is immersed in the immersion tank and is used as an immersion type membrane separation means for obtaining membrane filtrate from the liquid to be treated in the immersion tank through the separation membrane using suction or water head difference as a driving force. .

  In this submerged membrane separation means, moisture in the liquid to be treated in the immersion tank is taken out as membrane filtrate through the separation membrane, and suspended substances remain in the liquid to be treated or on the surface of the separation membrane. The concentration of suspended solids in the treatment liquid is higher than that at the time of inflow into the immersion tank. If the concentration of suspended substances in the liquid to be treated increases or the amount of suspended substances accumulated on the surface of the separation membrane increases, the load of suspended substances on the separation membrane module increases, causing clogging or separation of the separation membrane module. The blockage of the flow path between the membranes proceeds and a predetermined amount of membrane filtration water cannot be obtained, and chemical cleaning of the separation membrane module is required.

  In order to prevent or suppress the progress of such clogging of the separation membrane module and the blockage of the flow path, generally, air is continuously or intermittently supplied from a diffuser installed at the bottom of the submerged separation membrane module. By diffusing, the suspended matter accumulated on the separation membrane surface and the flow path between the separation membranes is peeled off or removed by the shearing force of the bubbles or the separation membrane (air washing), and the separation membrane is periodically removed. Physical washing is performed to peel and remove (backwash) the suspended material layer accumulated on the surface of the separation membrane by flowing back the membrane filtrate from the membrane filtrate side to the liquid to be treated. However, the flat membrane module generally cannot be back-washed due to structural problems, and physical washing of the flat membrane module largely depends on continuous or intermittent empty washing.

  In addition, if the concentration of suspended solids in the liquid to be treated becomes too high, clogging of the separation membrane module and blockage of the flow path are likely to proceed, and a predetermined amount of membrane filtration water cannot be obtained. In order to maintain the concentration below a certain value, a part or all of the liquid to be treated is discharged out of the immersion bath continuously or intermittently. The concentration of suspended solids in the liquid to be treated is continuously obtained, and the membrane separation treatment conditions are changed so that the suspended solids concentration can be maintained below a predetermined reference value (Patent Document 1), or the sedimentation is separated from the liquid to be treated. The suspended sludge concentration in the liquid to be treated is maintained below a predetermined reference value by adjusting the amount of the settled sludge (Patent Document 2) or continuously from the air diffuser installed at the lower part of the separation membrane module The separation membrane module is continuously rinsed with a gas-liquid mixed phase flow generated by aeration, and some suspended matter is settled in a sedimentation zone that is not affected by the gas-liquid mixed phase flow formed at the bottom of the immersion tank. By doing so, an increase in the suspended substance concentration in the liquid to be treated in the vicinity of the separation membrane is suppressed (Patent Document 3).

  In the water treatment methods as described in Patent Document 1 and Patent Document 2 above, suspended solid (SS) concentration meter or sedimentation sludge and covered substance that can continuously measure the suspended substance concentration in the liquid to be treated in the immersion tank. Install a sludge interface meter that can continuously measure the interface with the treatment liquid, and use the data obtained from these instruments to determine the suspended solid concentration, sludge interface position, sludge extraction flow rate, and treatment liquid supply flow rate. It is indispensable to construct an arithmetic processing function for maintaining and controlling and a control system for opening / closing valves and changing processes, and a great amount of labor is required for construction, construction and maintenance of the water treatment apparatus. In addition, in the operation process in which the air washing process is performed continuously or intermittently during the filtration process, the suspended material in the liquid to be treated does not settle during the air washing process, but the suspended material that has settled or settled once. This is used for problems such as the problem that the suspended substance settles, the problem that the suspended substance settles only between the washing process and the washing process, and the suspension time of the suspended substance cannot be secured. There is a problem that a large amount of air is required. Furthermore, since there is no backwashing process, there is a problem that the effect of physical washing is limited. In addition, in the method of intermittently stopping the filtration operation, even if the suspended solids in the immersion tank can be settled during the filtration operation stop, the filtration operation is restarted and a new liquid to be treated flows. There is a problem that there is no means for precipitating suspended substances in the liquid to be treated.

In the water treatment apparatus as shown in Patent Document 3 above, there is an advantage that the separation membrane module can be continuously washed by gas-liquid mixed phase flow, but the suspended matter in the liquid to be treated that has flowed into the immersion tank While some settle to the sedimentation zone, the remaining suspended matter is suspended in the liquid to be treated as it continues to circulate in the vicinity of the separation membrane by the gas-liquid multiphase flow generated by continuous aeration. The suspended matter concentration increases, and the suspended matter load on the submerged separation membrane module increases. Moreover, in order to perform continuous aeration, there exists a problem that many air quantities are required.
JP-A-10-286563 (Claims) JP-A-10-286567 (Claims) JP 2002-191946 A (paragraphs [0008] to [0011])

  The object of the present invention is to perform membrane separation of the liquid to be treated by the separation membrane module installed in the immersion tank, and at the same time, to efficiently settle and separate suspended substances in the liquid to be treated, An object of the present invention is to provide a water treatment method capable of increasing the filtration operation rate by reducing the turbid substance load and efficiently ensuring a predetermined amount of membrane filtration water over a long period of time.

  The present invention for solving the above-mentioned problems is characterized by the following (1) to (6).

(1) A water treatment method for obtaining membrane filtrate using a separation membrane module immersed in a dipping tank storing a solution to be treated, wherein at least an operation process is performed with the solution to be treated via the separation membrane module. Filtration process to obtain membrane filtrate by suction, an air washing process in which air is supplied from an air diffuser installed at the bottom of the separation membrane module to wash the surface of the separation membrane module, and a suspension that has settled at the bottom of the immersion tank It consists of a mud draining process that discharges the substance as sludge to the outside of the immersion tank, and at least once in the operation process 1) after performing the filtration process alone for a predetermined time,
2) Perform the waste mud process alone, or simultaneously perform the filtration process and the waste mud process,
3) A water treatment method characterized by having an operation method in which the air washing step is performed in this order.

  (2) The water treatment method according to (1), wherein a backwashing step of intermittently backwashing the separation membrane module is performed in combination with the air washing step after completion of the mud draining step.

  (3) The water treatment method according to (1) or (2), wherein the separation membrane module is a hollow fiber membrane module.

  (4) The water treatment according to any one of (1) to (3), wherein the inflow water supplied to the immersion tank is supplied to the immersion tank via a rectification facility in the immersion tank. Method.

  (5) The water treatment method according to any one of (1) to (4), wherein the inflow water includes a flocculant.

  (6) The inflow water is a flocculation treatment of wastewater containing flocculated sludge generated when the raw water is treated with a flocculant, or membrane filtration washing effluent generated when the raw water is treated with a separation membrane module. It is water, The water treatment method in any one of (1)-(4) characterized by the above-mentioned.

  According to the present invention, as described below, the membrane to be treated is separated by the separation membrane module immersed in the immersion tank, and at the same time, the suspended substances in the liquid to be treated are efficiently settled and separated. By reducing the load of suspended solids on the separation membrane module, the filtration operation rate can be increased, and a predetermined amount of membrane filtration water can be secured stably over a long period of time. Furthermore, a high recovery rate can be obtained by discharging the sludge in which the suspended matter that has settled at the bottom of the immersion tank has been concentrated.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. However, the scope of the present invention is not limited to these.

  FIG. 1 is a schematic view showing a preferred embodiment of the present invention. The inflow water is continuously or intermittently flowed into the immersion tank 1 via the inflow water pipe 3 and the rectification equipment 4 in the immersion tank, and the settled sludge consisting of suspended solids that have settled with the liquid phase 1 a in the immersion tank 1. Separated into phase 1b. A separation membrane module 2 is immersed in the immersion tank 1, and membrane filtration water is taken out from the liquid phase 1a by the suction pump 6 through the separation membrane module 2, the filtration valve 7, and the membrane filtration water pipe 5 (filtering). Process). Since the immersion tank 1 is left in the filtration step in the filtration step, the suspended substance settles out of the liquid phase 1a, and the suspended substance concentration in the liquid phase 1a is reduced and suspended in the separation membrane module 2. Material load is reduced. After performing the filtration process alone for a predetermined time, the suction pump 6 is stopped, the filtration valve 7 is closed, and the filtration process is stopped. Subsequently, the backwash valve 10 is opened, and backwash water is sent to the separation membrane module 2 through the backwash water pipe 8 by the backwash pump 9 to perform backwashing (backwashing process). At the same time, the air supplied from the blower 11 is diffused as bubbles through the air washing valve 13, the air washing air pipe 12, and the air diffuser 14 installed below the separation membrane module 2 (air washing process). The separation membrane module 2 is swung by backwashing and air washing, and suspended substances accumulated on the separation membrane surface and the flow path between the separation membranes are peeled off and removed. At this time, the suspended matter accumulated on the separation membrane surface and the flow path between the separation membranes returns to the liquid phase 1a, and the suspended matter that has settled in the liquid phase 1a or once settled returns to the liquid phase 1a. Increased suspended solids concentration. On the other hand, the time before performing the backwashing step and the air washing step is the time for performing the filtration step alone, that is, the settling time of the suspended substance in the liquid phase 1a after the inside of the immersion tank 1 is in a stationary state. This is the longest point, the amount of suspended matter in the sedimented sludge phase 1b is maximized, the concentration of the suspended matter settled is most advanced, and the suspended matter concentration is maximized. At this time, the mud valve 16 is opened, and the suspended solids settled in the settled sludge phase 1b are extracted as sludge out of the immersion tank through the mud pipe 15 (sludge process). Therefore, the mud draining process is performed as a pre-process of the back washing process and the air washing process as a process subsequent to the filtration process.

  Here, the stationary state means that, for example, there is no circulation flow in the vertical direction mainly in the immersion tank due to the gas-liquid mixed phase flow generated by the diffuser from the diffuser installed at the lower part of the submerged separation membrane module. Furthermore, it refers to a state where there is little disturbance of the water flow mainly in the vertical direction or uneven flow caused by the inflow of the inflow water into the immersion tank, and the sedimentation inhibition of suspended substances by the water flow is small. For example, the average flow velocity of the water flow in the immersion bath is 0.4 m / min or less, and the average rising flow velocity of the water flow in the immersion bath is 80 mm / min or less.

  When performing membrane filtration in a state where there is no inflow of inflow water to the immersion tank, the present inventors have a small disturbance of the water flow in the immersion tank due to the movement of the liquid to be treated accompanying the membrane filtration. Paying attention to the fact that the suspended substance is in a stationary state where the suspended substance settles, and confirming that the suspended substance in the immersion tank settles in the stationary state, In addition, in the case where the stationary state is not disturbed, the stationary state in which the suspended substance settles in the immersion tank, as in the case where the membrane filtration is performed without the inflow of the liquid to be treated into the immersion tank. The idea was obtained from the fact that it was confirmed that, and the present invention was reached.

  As a means to continuously or intermittently flow in the inflow water to the immersion tank so as not to disturb the stationary state, a means for inflowing from the side of the immersion tank through a rectifying wall or a perforated plate, troughs and overflow weirs Inflowing water by means of inflow from the upper end of the immersion tank, means of inflowing from the upper part of the immersion tank via a perforated plate or inclined tube installed between the water surface of the immersion tank and the upper end of the separation membrane module, However, any means may be used as long as it is an inflow means for inflowing water that does not disturb the stationary state. These means are used as rectification equipment in the immersion tank. Among these, when inflowing water is made to flow from the upper part of the immersion tank, the sedimentation speed of the suspended solids and the downward movement speed due to the water mass of the liquid to be treated consisting of the inflowing water newly flowing from the upper part are added, This is preferable because the efficiency of sedimentation of suspended substances is increased.

  In addition, the inflow of inflow water to the immersion tank is intermittent, and even when the rectification equipment in the immersion tank is not installed, the operation of the filtration process in the immersion tank is stopped for a predetermined time when the inflow water flows in, There is also a means of waiting for the inflow of the inflowing water and the inside of the immersion tank to be in a stationary state (stationary step), and then starting a filtration step and the like. However, it is more preferable to install the rectification equipment in the immersion tank because the filtration operation rate can be increased.

  Here, the filtration operation rate is the ratio of the time of the filtration process in the operation process composed of the filtration process, the backwash process, the air washing process, the waste mud process, and the stationary process, or the total filtration process in one day. Indicates the percentage of time.

  On the other hand, in the filtration process, suspended substances that do not settle in the liquid to be treated accumulate alone on the surface of the separation membrane and the flow path between the separation membranes when the liquid to be treated is membrane filtered. Or by periodically performing a process combining the air washing process and the back washing process. At this time, the backwash process is not necessarily a process, but it is highly effective in peeling and removing suspended substances accumulated on the separation membrane surface and the flow path between the separation membranes. Preferably it is done. At this time, as a combination of the backwashing step and the air washing step, even if the air washing step is performed after the backwashing step is completed, the backwashing step is performed after the air washing step is completed, Even if the air washing step and the air washing step are performed simultaneously, the back washing step and the air washing step are started at the same time, and either one is completed first, and after either one is performed for a predetermined time, the back washing step and It is good also as a process which transfers to the simultaneous process of an air washing process, and it does not matter as what kind of combination. In particular, a process having a combination in which a backwashing process and an air washing process are performed at the same time is preferable because the effect of peeling and removing suspended substances is further enhanced.

  It is separated or removed from the separation membrane surface and the flow path between the separation membranes by backwashing and air washing, or during sedimentation mainly by the circulating flow in the vertical direction in the immersion tank due to the gas-liquid mixed phase flow generated by air washing or Since suspended solids once settled back, the concentration of suspended solids in the liquid to be treated becomes the highest immediately after backwashing and air washing. Therefore, immediately after backwashing and air washing, a step of allowing the suspended substance to settle in a standing state (a standing step) without performing membrane filtration may be provided. In this case, it is preferable because the suspended matter load on the separation membrane module can be further reduced, and a predetermined amount of membrane filtrate can be stably secured over a longer period. In the present invention, a static treatment step may be provided to select a water treatment method that can stably secure a predetermined amount of membrane filtration water over a longer period of time, or increase the filtration operation rate without providing a static step. A water treatment method may be selected, and may be appropriately selected depending on the use of the treatment.

  Further, it is preferable to keep the distance between the air diffuser and the sludge interface at a certain level or more, since the suspended matter that has once settled is difficult to return during the washing. The distance is generally 0.3 to 0.5 m or more.

  The settled suspended solids are discharged as sludge to the outside of the immersion tank via a valve or pump, but the discharge amount is based on the amount of sludge generated based on the predicted sludge generation results. It may be determined by setting the open / close time or pump start time, and based on the amount of sludge generated from the sludge detection means such as the sludge interface meter installed in the immersion tank, the valve open / close time and pump The activation time may be controlled. Here, the discharge amount refers to the amount of water discharged as sludge outside the immersion tank. From the gist of the present invention, any method may be used as long as the amount of suspended matter discharged is equal to the amount of suspended suspended matter. For example, if sludge is discharged by controlling the valve open / close time and pump start time based on the amount of sludge generated from the sludge detection means such as a sludge interface meter, the discharge amount (water amount) will be minimized. This is preferable because the recovery rate is improved.

  When this waste mud process is carried out alone for a predetermined time and then performed simultaneously with the filtration process or after the completion of the filtration process, that is, as a pre-process of the air washing process, the stationary state in the filtration process, that is, suspended matter In addition to maximizing the sedimentation time, the amount of suspended matter settled at the bottom of the immersion tank is maximized, and the concentration of suspended suspended matter is the most advanced, resulting in the highest suspended matter concentration, thus minimizing the discharge amount. It is preferable because it can be made.

  In addition, the drainage process is not carried out as a pre-process of every air washing process, and the operation method ("operation method 2") is performed by including at least the filtration process and the air washing process without including the waste mud process. Is performed at least once, and at least includes a filtration step, a mud removal step, and an air washing step. 1) After performing the filtration step alone for a predetermined time, 2) The waste mud process is performed alone, or the filtration process and the waste mud process are simultaneously performed. 3) Next, when the operation method (hereinafter referred to as “operation method 1”) in which the air washing step is performed in this order is performed. This is preferable because the concentration of suspended solids at the bottom of the dipping bath is further advanced, and the discharge amount can be further suppressed. As a result, the recovery rate is further improved by combining the operation method with the drainage process. When the operation method 1 is performed once during the operation method 2 n times, the frequency at which the operation method 1 is performed, that is, the frequency at which the mud draining step is performed is determined by the suspended matter that settles at the bottom of the immersion tank. What is necessary is just to determine suitably according to quantity, and since the operation method 2 is performed in the range of n = 1-10, since the sludge interface by the suspended suspended substance can be suppressed low, it is preferable.

  Here, the recovery rate indicates the ratio of the amount of product water that flows out as production water out of the membrane filtrate to the amount of inflow water that flows into the immersion tank, and the amount of backwash water used for backwashing from the amount of membrane filtrate to the amount of inflow water. Is calculated as the ratio of the production water volume minus the inflow water volume, or the ratio of the production water volume minus the discharge volume from the inflow water volume. The same value can be obtained regardless of which calculation method is used to obtain the recovery rate.

  The time distribution of each process in the present invention may be various combinations depending on the quality of the influent water and the use of the treatment, but basically, the filtration process is 10 to 120 minutes, the air washing process is 10 to 120 seconds, and the back washing is performed. The range of 10 to 120 seconds is preferable because the operation is easily continued stably over a long period of time. The air washing step is preferable because a sufficient physical washing effect can be secured in the range of 10 to 120 seconds and the amount of air used for the air washing can be suppressed. In addition to ensuring the cleaning effect, the amount of backwash water used for backwashing can be suppressed, and the recovery rate can be improved.

  Here, the submerged separation membrane module refers to a single or a plurality of separation membrane elements interpolated, and the shape of the separation membrane element includes a hollow fiber membrane, a tubular membrane, a flat membrane, etc. . Here, the hollow fiber membrane means a tubular separation membrane having a diameter of less than 2 mm, and the tubular membrane means a tubular separation membrane having a diameter of 2 mm or more. In the present invention, any shape of separation membrane element may be used, but during the filtration process, the accumulation of suspended substances proceeds on the separation membrane surface and the flow path between the separation membranes, so In order to obtain a sufficient physical cleaning effect for preventing or suppressing clogging or blocking of the flow path between the separation membranes, it is preferable to perform back washing and empty washing. It is preferable to use a hollow fiber membrane or tubular membrane-shaped separation membrane element, which is a structure capable of backwashing, rather than a flat membrane-shaped separation membrane element which often has a structure that cannot be used.

  Since air washing is a washing in which the suspended matter accumulated on the separation membrane surface and the flow path between the separation membranes is peeled and removed by rocking the separation membrane or by shearing force caused by bubbles, it is generally a support. Hollow fiber membranes and tubes in which the distance between the separation membranes and the positional relationship between the separation membranes vary due to the oscillation of the separation membrane, rather than the flat membrane-shaped separation membrane element that is fixed on the surface and the distance between the separation membranes is less likely to change In addition to the physical cleaning effect due to the shearing force caused by bubbles, the separation membrane element in the shape of a large membrane has a suspended substance due to large fluctuations in the flow path between the separation membranes and contact between the separation membranes during air washing. Since the effect of peeling and removing is added, it is also preferable from the viewpoint of the physical washing effect by air washing alone. Further, a hollow fiber membrane-shaped separation membrane element having a small diameter is more preferable because the physical washing effect is enhanced because the oscillation of the separation membrane by air washing is large.

  The separation membrane may be either a microfiltration membrane or an ultrafiltration membrane, and the separation performance or fractionation performance of the microfiltration membrane is preferably in the range of nominal pore diameters of 0.01 μm to 3 μm, and has excellent separation performance. The range of 0.02 μm to 0.45 μm is more preferable in terms of the surface and the surface where clogging is difficult to proceed. In the ultrafiltration membrane, the nominal molecular weight cutoff is preferably in the range of 1000 Da to 1 million Da.

  The material of the separation membrane is not particularly limited from the gist of the present invention, but when an organic material is used, polyethylene, polypropylene, polyacrylonitrile, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, Polytetrafluoroethylene, polyvinyl fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, and chlorotrifluoroethylene-ethylene copolymer, polyvinylidene fluoride, polysulfone, polyethersulfone, cellulose acetate, etc. can be used, inorganic materials When using, ceramics can be used. Among these, from the viewpoint of film strength and chemical resistance, organic materials containing fluorine and ceramics are preferable. In addition, an organic material containing polyacrylonitrile or cellulose acetate, which is generally a hydrophilic material, is preferred from the viewpoint of resistance to dirt and recoverability of washing.

  Here, the filtration flow rate control method of the separation membrane module may be a constant flow filtration method or a constant pressure filtration method, but a constant flow filtration method is generally used. Further, the filtration method is not particularly limited from the gist of the present invention, and examples thereof include a method using a suction pump as a driving force and a method using a water head difference as a driving force.

  The inflow water in the present invention is not particularly limited, and may be any raw water such as river water, lake water, groundwater, industrial water, urban sewage, industrial wastewater, etc. Water treated by any water treatment process such as flocculation, precipitation, sand filtration, membrane filtration, biological treatment, etc., or waste water generated in the water treatment process may be used, but from the gist of the present invention, it has sedimentation properties. Water containing suspended solids is preferred, and when these waters contain a flocculant, the suspended solids are more preferable because they have good sedimentation properties. In addition, wastewater containing agglomerated sludge generated when the raw water is treated with a flocculant, or membrane filtration washing wastewater produced when the raw water is treated with a separation membrane module is used as the influent water. In this case, the suspended substance is further preferred because it shows better sedimentation.

  In particular, water obtained by agglomeration treatment of membrane filtration washing wastewater generated when the raw water is treated with the separation membrane module, or membrane filtration washing wastewater produced when the raw water is agglomerated and treated with the separation membrane module. When influent water is used, suspended substances exhibit good sedimentation, so that the suspended substance load on the separation membrane module can be reduced, and suspended substances once blocked by the separation membrane module can be removed again. Since clogging of the separation membrane can be suppressed since the membrane is filtered using the above, the effect of the present invention is most highly exhibited and preferable.

  The flocculant used in the present invention is not particularly limited from the gist of the present invention. For example, inorganic flocculants such as polyaluminum chloride, sulfate band, iron chloride, iron sulfate, polyiron, polysilica iron, An organic polymer flocculant containing an acrylamide polymer can be used, and a coagulant aid such as activated silicic acid and sodium alginate for water supply, an acid, and an alkali agent can be used.

The invention is explained in more detail using the following examples. In Examples and Comparative Examples, both ends of a hollow fiber membrane bundle of 1800 polyvinylidene fluoride hollow fiber membranes having an outer diameter of 1.5 mm and a nominal pore diameter of 0.05 μm are fixed with an adhesive, and an adhesive fixing portion thereof A cylindrical hollow fiber membrane module having a length of 1 m and an effective membrane area of 7 m ² was created by cutting a part of one end of the hollow fiber membrane to open the inside of the hollow fiber membrane. Using this single hollow fiber membrane module as an immersion type separation membrane module, experiments shown in Examples and Comparative Examples were conducted. The experiment was performed according to the flow shown in FIG. As long as there is no notice, as for the rectification equipment in the immersion tank, when the inflow water flows from the upper part of the immersion tank, the liquid to be processed is caused to flow into the liquid to be processed in the immersion tank by connecting the wall surface. A means for preventing the static state of the stool from being disturbed was used. In addition, when the polyaluminum chloride was injected into the raw water for the coagulation treatment, the polyaluminum chloride injection method was a proportional injection method using the raw water turbidity as an index.

Example 1
The lake water is used as raw water and flows into the immersion tank as inflow water by connecting the wall from the top of the immersion tank, using a constant flow filtration method of 1.0 m ³ / m ² / day, a filtration time of 30 minutes, a backwash time of 60 seconds, empty The washing process was performed for 60 seconds, and in the mud discharge process, the discharge amount was 2.5 L, and the operation was performed in the order of the filtration process, the mud discharge process, the back washing process, and the air washing process. At two months later, the transmembrane pressure difference was approximately flat at about 20 kPa. The recovery rate at this time was 98.2%.

(Example 2)
The lake water is used as raw water, and 5 to 10 mg / L of polyaluminum chloride is injected. Then, it flows into the immersion tank as inflow water from the upper part of the immersion tank and flows into the immersion tank at a constant flow rate of 1.0 m ³ / m ² / day. Filtration time 30 minutes, backwash time 60 seconds, air washing time 60 seconds, waste mud process with 2.5L discharge, the order of filtration process, mud process, back washing process and air washing process at the same time The operation was performed in the operation process consisting of At two months later, the transmembrane pressure difference was approximately flat at about 15 kPa. The recovery rate at this time was 98.2%.

(Example 3)
The lake water is used as raw water, and 5 to 10 mg / L of polyaluminum chloride is injected. Then, it flows into the immersion tank as inflow water from the upper part of the immersion tank and flows into the immersion tank at a constant flow rate of 1.0 m ³ / m ² / day. Filtration time is 30 minutes, backwash time is 60 seconds, air washing time is 60 seconds, and the amount of discharge is 2.5L in the mud discharge process. The process and the waste mud process were performed at the same time, and then the operation was performed in the operation process configured in the order of the simultaneous back washing process and the air washing process. At two months later, the transmembrane pressure difference was approximately flat at about 15 kPa. The recovery rate at this time was 98.2%. In addition, since the time required for the mud draining process was about 5 seconds, the operation rate was 96.8%, which is slightly higher than 96.5% in Example 1 and Example 2.

Example 4
The lake water is used as raw water, and 5 to 10 mg / L of polyaluminum chloride is injected. Then, it flows into the immersion tank as inflow water from the upper part of the immersion tank and flows into the immersion tank at a constant flow rate of 1.0 m ³ / m ² / day. Filtration time 30 minutes, backwashing time 60 seconds, air washing time 60 seconds, drainage process 5D discharge amount 5L, operation process configured in the order of filtration process, backwashing process and air washing process at the same time After performing 1 twice, the driving | running | working which performed the driving | running process 2 comprised in the order made into the simultaneous process of a filtration process, a waste mud process, a backwashing process, and an air washing process was performed once. At two months later, the transmembrane pressure difference was almost flat at about 17 kPa. The recovery rate at this time was 98.8%, and the operation rate was 96.7%.

(Example 5)
A pressurized separation membrane module (Toray Industries, Inc.) having an effective membrane area of 72 m ² made of a hollow fiber membrane made of polyvinylidene fluoride having a nominal pore diameter of 0.05 μm by injecting 5 to 10 mg / L of polyaluminum chloride into raw water. Manufactured by Trefil HFS-2020), the membrane filtration washing wastewater generated when membrane filtration is used as the inflow water, and it flows in from the upper part of the immersion tank through the baffle plate and is performed at a constant flow rate filtration method of 0.7 m ³ / m ² / day. Filtration time 30 minutes, back washing time 60 seconds, air washing time 60 seconds, in the mud discharge process, the discharge amount is 3L, and the operation process 1 configured in the order of the filtration process, the back washing process and the air washing process is the same. After performing 4 times, the driving | running | working process 2 comprised in the order made into the simultaneous process of a filtration process, a waste mud process, a backwashing process, and an air washing process was performed once. At one month later, the transmembrane pressure difference was almost flat at about 10 kPa. At this time, the recovery rate of the submerged membrane filtration means was 99.4%. Moreover, when the ratio of the product water volume which added the product water obtained from a pressurization type membrane filtration means and an immersion type membrane filtration means with respect to the amount of raw water was made into the purified water recovery rate, it was 99.96%.

(Example 6)
The operation was performed under exactly the same conditions as in Example 2 except that the method of inflowing water into the immersion tank was introduced from the bottom of the immersion tank via an inflow water pipe installed by branching the mud drainage pipe. It was. At this time, it is observed that the liquid to be treated in the dip tank is moving upward from the bottom of the dip tank, and suspended substances in the liquid to be treated are coarsely suspended while being subjected to sedimentation inhibition by the upward flow. The material was observed to settle. At two months later, the transmembrane pressure difference was about 38 kPa under a gentle upward trend. The recovery rate at this time was 98.2%.

(Comparative Example 1)
While the lake water is used as raw water and flows into the immersion tank as inflow water by connecting the wall from the upper part of the immersion tank and continuously diffused in the immersion tank, a constant value of 1.0 m ³ / m ² / day is set. The flow filtration method was 30 minutes, the backwash time was 60 seconds, and the drainage process was 2.5L, and the operation was performed in the operation process consisting of the filtration process, the wastewater process, and the backwash process. . At two months later, the transmembrane pressure difference was about 45 kPa under a gentle upward trend. The recovery rate at this time was 98.2%.

(Comparative Example 2)
The lake water is used as raw water, 5 to 10 mg / L of polyaluminum chloride is injected, and then the inflowing water is made to flow from the upper part of the immersion tank to the immersion tank and is continuously diffused in the immersion tank. Among them, a constant flow rate filtration system of 1.0 m ³ / m ² / day, filtration time 30 minutes, backwash time 60 seconds, filtration process with a frequency of one sludge process for six filtration processes, filtration 50L The driving | operation comprised in order of a process, a mud discharge process, and a backwashing process was performed. The discharge amount 50L is the total volume of the liquid to be processed in the immersion tank. At two months later, the transmembrane pressure difference was almost flat at about 21 kPa. The recovery rate at this time was 94.2%.

  The present invention relates to a water treatment method using an immersion type separation membrane module. More specifically, submerged separation used in the field of drinking water production in waterworks, industrial water, industrial ultrapure water, industrial water production such as food and medicine, and sewage treatment such as municipal sewage purification and industrial wastewater treatment. The present invention relates to a water treatment method using a membrane module, but the present invention is not limited to these.

It is a schematic diagram which shows one preferable embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1: Soaking tank 1a: Liquid phase 1b: Settling sludge phase 2: Separation membrane module 3: Inflow water piping 4: Rectification equipment in immersion tank 5: Membrane filtration water piping 6: Suction pump 7: Filtration valve 8: Backwash water Pipe 9: Backwash pump 10: Backwash valve 11: Blower 12: Air washing air pipe 13: Air washing valve 14: Air diffuser 15: Mud pipe 16: Waste mud valve

Claims (6)

A water treatment method for obtaining membrane filtered water by using a separation membrane module immersed in a dipping tank in which the treatment liquid is stored, wherein at least an operation step sucks the treatment liquid through the separation membrane module A filtration step for obtaining membrane filtrate, an air washing step for cleaning the surface of the separation membrane module by supplying air from a diffuser installed at the lower part of the separation membrane module, and sludge for suspended matter settled at the bottom of the immersion tank As a drainage process for discharging out of the immersion tank and at least once in the operation process 1) After the filtration process alone for a predetermined time,
2) Perform the waste mud process alone, or simultaneously perform the filtration process and the waste mud process,
3) A water treatment method characterized by having an operation method in which the air washing step is performed in this order. The water treatment method according to claim 1, wherein a backwashing step of intermittently backwashing the separation membrane module is performed in combination with the air washing step after the completion of the mud draining step. The water treatment method according to claim 1 or 2, wherein the separation membrane module is a hollow fiber membrane module. The water treatment method according to any one of claims 1 to 3, wherein the inflow water supplied to the immersion tank is supplied to the immersion tank via a rectification facility in the immersion tank. The water treatment method according to claim 1, wherein the inflow water includes a flocculant. The inflow water is wastewater containing agglomerated sludge generated when the raw water is treated with a flocculant, or water obtained by agglomerating the membrane filtration washing wastewater produced when the raw water is treated with the separation membrane module. The water treatment method according to any one of claims 1 to 4.

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