JP2013202472A - Operation method of membrane separator, and membrane separator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an operation method of a membrane separator, capable of effectively reducing the operation cost of the membrane separator, and the membrane separator.SOLUTION: A membrane separator 6 includes a separation membrane 60 which is immersed in water to be treated, and an air diffuser 7 arranged below the separation membrane 60, and obtains treated water penetrating the separation membrane 60 while performing air diffusion from the air diffuser 7 to the separation membrane 60. The membrane separator includes a target value setting means (computation unit) 10a for setting the target value of the air diffusion from the air diffuser 7 based on the inter-membrane differential pressure, and an air diffusion quantity control means (PID control unit) 10b for controlling the air diffuser 6 so that the air diffusion reaches the target value. The target value setting means 10a sets the change or the absolute value of the rate of change of the target value when the air diffusion quantity is increased to be the value larger than the change or the absolute value of the rate of change of the target value when the air diffusion quantity is decreased.

Description

  The present invention comprises a separation membrane immersed in the water to be treated and an air diffuser disposed below the separation membrane, and permeates the separation membrane while being diffused from the air diffuser toward the separation membrane. The present invention relates to a method for operating a membrane separation apparatus for obtaining treated water and a membrane separation apparatus.

  Conventionally, as a method for treating organic wastewater (hereinafter referred to as “treated water”), along with purification treatment for decomposing organic matter using microorganisms in activated sludge, activated sludge is separated into solid and liquid by a separation membrane and separated water. Membrane separation activated sludge method is widely adopted. As a method for solid-liquid separation, various methods for solid-liquid separation of water to be treated have been studied using a membrane separation apparatus equipped with a separation membrane such as a microfiltration membrane and an ultrafiltration membrane.

  Such a membrane separation device is placed in a state of being immersed in the water to be treated, and the activated sludge itself in the treatment tank itself, solids such as contaminants in the water to be treated flowing into the treatment tank, and further, it is derived from the water to be treated or microorganisms. It is equipped with a diffuser installed at the bottom of the separation membrane to prevent so-called fouling substances such as polymer solutes, colloids, and micro solids from adhering to the surface of the separation membrane, thereby reducing the filtration efficiency. Air or the like is diffused to the surface, and the adhering solid content or the like to the surface of the separation membrane is suppressed or the adhering solid content or the like is peeled off by the upward flow of bubbles and water to be treated.

  Conventionally, the amount of diffused air supplied from the diffuser is a cleaning of the membrane surface so that the separation membrane surface is not easily clogged even if the separation membrane surface is likely to be clogged due to sludge properties, etc. Therefore, there is a problem that the power cost for air diffusion increases.

  Currently, about half of the operating cost required for treatment facilities using the membrane separation activated sludge method is spent for aeration, reducing the amount of aeration while avoiding clogging of the separation membrane is an important issue It has become.

  In Patent Document 1, for the purpose of suppressing the energy cost required for the amount of aeration air, the transmembrane pressure difference of the membrane separation apparatus is monitored, and the transmembrane pressure difference is within a normal level excluding the unsteady state. The aeration air volume is controlled to increase the aeration air volume supplied from the aeration apparatus at a non-steady time in which the transmembrane pressure difference rapidly rises above a predetermined value. Has been proposed.

  In this publication, as the aeration air volume when the behavior of the transmembrane pressure difference is at a steady level, the lower aeration air volume (allowable) The lower limit value is determined in advance by a preliminary test and set to the allowable lower limit value, and whether or not the transmembrane pressure difference has rapidly increased to a predetermined value or more is expressed by a transmembrane pressure increase rate (for example, kPa / day). ) Is evaluated.

JP 2005-144291 A

  However, there is a characteristic that the transmembrane pressure difference of the separation membrane increases with time, and the properties of the water to be treated flowing into the sludge treatment equipment change according to the season and time, and the state of the separation membrane clogging accordingly. Therefore, it is practically difficult to operate for a long time at the allowable lower limit value, and conversely, there is a possibility that early separation of the separation membrane may be caused.

  Further, when evaluating whether or not the transmembrane pressure difference has rapidly increased to a predetermined value or more with the rate of increase in transmembrane pressure difference expressed in kPa / day, the evaluation takes at least one day. There is a risk of clogging.

  Various attempts have been made in addition to the method disclosed in Patent Document 1, but it is difficult to effectively reduce the power cost.

  In view of the above-described problems, an object of the present invention is to provide a method for operating a membrane separator and a membrane separator that can effectively reduce the operating cost of the membrane separator.

  In order to achieve the above-mentioned object, the first characteristic configuration of the operation method of the membrane separation device according to the present invention includes a separation membrane immersed in the water to be treated and an air diffuser arranged below the separation membrane. An operation method of a membrane separation device for obtaining treated water that has permeated through the separation membrane while being diffused from the diffusion device toward the separation membrane, the diffusion device based on a transmembrane pressure difference A target value setting step for setting a target value of the amount of air diffused from, and an air amount control step for controlling the air diffuser so that the amount of air diffused becomes the target value. In the target value setting step, The absolute value of the change or rate of change in the target value when increasing the amount of air diffused is set to a value that is greater than the absolute value of the change or rate of change in the target value when decreasing the amount of air diffused. is there.

  According to the above configuration, in the target value setting step, the target value of the amount of air diffused from the air diffuser is set to increase when the transmembrane pressure difference is large, and the air diffused from the air diffuser device when the transmembrane pressure difference is low. The target value of quantity is set to decrease. At this time, the absolute value of the change amount or rate of change of the target value when increasing the amount of aeration is set to a value larger than the absolute value of the change amount or rate of change of the target value when decreasing the amount of aeration. The Then, the air diffuser is controlled so that the air diffused amount becomes the target value in the air diffused amount control step. The transmembrane pressure difference is a pressure necessary for obtaining permeate by filtration, and is also referred to as a filtration pressure difference and TMP (Trans Membrane Pressure).

  When the transmembrane pressure is high, solid substances etc. are already attached to the surface of the separation membrane, so in order to cancel the state, the change amount is larger than the change amount when reducing the amount of air diffused. By increasing, the cleaning effect of the separation membrane by the rising flow of bubbles and water to be treated can be enhanced, and the deposits on the separation membrane surface can be effectively peeled off. And when the transmembrane pressure is low, in order to reduce the risk of clogging of the separation membrane surface when the amount of air diffused is reduced, the amount of change is smaller than the amount of change when the amount of air diffused is increased. By decreasing, the rapid fluctuation of the upward flow of bubbles and the water to be treated is suppressed, the rapid decrease of the cleaning effect on the separation membrane surface is avoided, and new adhesion is suppressed.

  In the second feature configuration, in addition to the first feature configuration described above, in the air diffusion amount control step, the target value when the air diffusion amount is set to be increased regardless of the transmembrane pressure difference. The holding time is set to a time longer than the holding time of the target value when it is set so as to reduce the amount of air diffusion.

  When it is set to increase the amount of diffused air, the state is maintained for a longer time than when it is set to decrease the amount of diffused air regardless of the transmembrane pressure difference at that time, The cleaning effect on the separation membrane surface can be further enhanced. In the case of reducing the amount of diffused air, it is possible to secure a further opportunity for reducing the amount of diffused air relatively quickly by shortening the time for maintaining the state.

  In the third feature configuration, in addition to the first or second feature configuration described above, in the target value setting step, the duration of the transmembrane pressure difference indicating a value lower than the threshold value for lowering the target value, The duration is set to be longer than the duration of the transmembrane pressure difference, which is higher than the threshold for raising the target value, and the duration of the relationship between the transmembrane pressure difference and the threshold is set for each threshold value. The target value is changed when it is maintained beyond.

  When increasing the target value of the air diffusion amount, make a judgment in a shorter time than when lowering the target value, set the target value so that the adhesion / deposits on the separation membrane surface are peeled off quickly, and When lowering the target value of the volume, it is determined over a relatively long time to determine the certainty of the situation. In other words, when there is a possibility that the transmembrane pressure rises and the membrane may become clogged, priority is given to adhesion of the separation membrane surface and separation of deposits over confirmation of the certainty of the situation, and transmembrane pressure differential When the clogging is decreasing and the clogging of the membrane is being resolved, the state of the separation membrane can be adjusted well by prioritizing the confirmation of the certainty over the reduction of the amount of air diffused.

  A characteristic configuration of a membrane separation device according to the present invention includes a separation membrane that is disposed soaked in water to be treated, and an air diffuser disposed below the separation membrane, from the air diffuser to the separation membrane. A membrane separation device for obtaining treated water that has permeated through the separation membrane while diffusing toward the target, and a target value setting means for setting a target value of the amount of air diffused from the air diffusion device based on a transmembrane differential pressure; A diffused amount control means for controlling the diffuser so that the diffused amount becomes the target value, and the target value setting means changes or changes the target value when increasing the diffused amount. The absolute value of the rate is set to a value greater than the absolute value of the change amount of the target value or the change rate when the amount of air diffusion is reduced.

  As described above, according to the present invention, it is possible to provide a method for operating a membrane separator and a membrane separator that can effectively reduce the operating cost of the membrane separator.

Illustration of membrane separator Illustration of separation membrane Explanatory diagram of evaluation procedure for transmembrane pressure difference (A), (b) is explanatory drawing of the update setting of the reference value of transmembrane differential pressure, (c), (d) is the fluctuation | variation of the transmembrane differential pressure of a separation membrane, and the reference value of transmembrane differential pressure Illustration of relationship Explanatory diagram showing changes in air diffused volume Flow chart showing filtration operation control Flow chart showing the procedure for evaluating the transmembrane pressure difference within one cycle Flow chart showing the target value setting procedure Flow chart showing the procedure for setting the reference value for transmembrane pressure (A) is a graph showing the transition of the reference transmembrane pressure difference, (b) is a graph showing the transition of the reference transmembrane pressure difference and the air amount with respect to ΔTMP.

Hereinafter, a method for operating a membrane separator and a membrane separator according to the present invention will be described.
FIG. 1 shows an example of a sewage treatment facility 1 in which a membrane separation device 6 is incorporated. The sewage treatment facility 1 is immersed in a pretreatment facility 2, a flow rate adjustment tank 3, an activated sludge treatment tank 4 comprising an anaerobic tank 4a and a membrane separation tank 4b filled with activated sludge, and a membrane separation tank 4b. A membrane separation device 6 that obtains permeate from the treated water in the tank and a treated water tank 5 that receives the treated water filtered by the membrane separation device 6 are provided.

  The pretreatment facility 2 is provided with a bar screen 2a for removing contaminants mixed in the raw water, and the treated water from which the contaminants have been removed by the bar screen 2a or the like is temporarily stored in the flow rate adjusting tank 3. Even when the inflow amount of raw water fluctuates, the flow rate adjusting mechanism 3a such as a pump or a valve is configured to stably supply the water to be treated at a constant flow rate from the flow rate adjusting tank 3 to the activated sludge treatment tank 4. Has been.

  A part of the water to be treated in the membrane separation tank 4b is pulled out by the return pump and returned to the anaerobic tank 4a through the return path 4c. In addition, excess sludge is withdrawn and discarded.

  The membrane separation device 6 includes a plurality of membrane elements 60 and an air diffuser 7 installed below the membrane elements 60. The plurality of membrane elements 60 are accommodated in the casing at regular intervals so that each membrane surface is in a vertical posture.

  As shown in FIG. 2, the membrane element 60 is configured by disposing separation membranes 60b on both the front and back surfaces of a resin membrane support 60a provided with a water collecting pipe 60c at the top. In the present embodiment, the separation membrane 60b is composed of a microfiltration membrane having a nominal pore diameter of about 0.4 μm bonded and impregnated with a porous resin on the surface of the nonwoven fabric. The treated water that has passed through the separation membrane 60b flows into the water collecting pipe 60c along the groove formed in the membrane support 60a.

  The type of the separation membrane 60b and the form of the membrane element 60 used in the present invention are not limited to such a configuration, and any type of separation membrane and any form of membrane element (hollow fiber membrane element) , Tubular membrane element, monolith membrane element, etc.).

  A filtration pump 8 that performs suction filtration from each membrane element 60 through a water collecting pipe 60c is connected to the header pipe, and the water to be treated in the membrane separation tank 4b permeates the separation membrane 60b with a differential pressure generated by the filtration pump 8.

  The air diffuser 7 includes an air supply source including an air diffuser 7b in which a plurality of air diffusers 7c are formed and a blower 7a that supplies air and the like to the air diffuser 7b. In addition, the structure filtered by the natural water head between the separation membrane 60b and the treated water tank 5 without using the filtration pump 8 may be sufficient.

Returning to FIG. 1, the membrane separation device 6 further controls the operation of the filtration pump 8 by a flow rate adjustment valve (not shown) or an inverter circuit of the filtration pump 8 (not shown) so that the amount of treated water that permeates the separation membrane 60 b becomes constant. A control device 10 using a computer for controlling the amount of air diffused from the air diffuser 7 is provided.
The control device 10 includes blocks such as a calculation unit 10a, a PID control unit 10b, an inverter circuit 10c, a filtration operation control unit 10d, and an operation input unit 10e.

  The filtration operation control unit 10d is a block that intermittently drives the filtration pump 8 in a constant control cycle based on a control command from the calculation unit 10a. The inverter circuit 10c is a block that increases / decreases the amount of air diffused by driving the motor of the blower 7a by increasing / decreasing the rotational speed based on a control command from the PID control unit 10b.

  The PID control unit 10b inputs the air amount PV from the air flow sensor Fm provided in the diffuser pipe 7b, and performs PID calculation so that the air amount PV becomes the aeration amount target value SV input from the calculation unit 10a. In this block, the drive frequency for the motor of the blower 7a, which is the calculation result, is output to the inverter circuit 10c.

  The operation input unit 10e includes a touch panel for input operation, and various control information necessary for arithmetic processing for control executed by the arithmetic unit 10a, for example, a control cycle of the filtration pump 8, a set range of the air diffusion target value SV. This is a block for inputting a stop pressure and an operating pressure input timing required for obtaining the transmembrane pressure difference, a threshold value for evaluating the differential value of the transmembrane pressure difference, and the like.

  The calculation unit 10a is a block that outputs a control command for intermittently operating the filtration pump 8 to the filtration operation control unit 10d in a control cycle input via the operation input unit 10e. Furthermore, the calculation part 10a inputs the pressure from the pressure sensor Pm installed in the upstream pipe line of the filtration pump 8, calculates the air diffusion amount target value SV based on the value, and outputs it to the PID control part 10b. It is a block to do.

Hereinafter, an operation method of the membrane separation device 6 executed by the control device 10 will be described.
FIG. 6 shows a control procedure executed by the filtration operation control unit 10d. The filtration operation control unit 10d operates the filtration pump 8 (SA1), sets a filtration operation timer TMon for 9 minutes (SA2), and waits for the timer TMon to elapse (SA3).

  When the timer TMon counts up (SA3, Y), the filtration pump 8 is stopped (SA4), a 1-minute filtration operation timer TMoff is set (SA5), and the passage of the timer TMoff is awaited (SA6).

  When the timer TMoff counts up (SA6, Y), the process returns to step SA1, and thereafter the same operation is repeated. That is, the filtration operation control unit 10d controls the filtration pump 8 so as to repeat the stop for 1 minute and the filtration operation for 9 minutes in a cycle of 10 minutes. In addition, while the filtration pump 8 is stopped, the air diffusion from the air diffuser is continued, so that the surface of the separation membrane is actively washed.

  FIG. 3A illustrates the behavior of the pressure detected by the pressure sensor Pm. The operating pressure detected when the filtration pump 8 is activated gradually decreases from the stop pressure at the beginning of the operation period Tfon (9 minutes in the present embodiment) of the filtration pump 8 and changes so as to show a substantially constant value at the end. . The stop pressure detected when the filtration pump 8 is stopped rises quickly at the beginning of the stop period Tfoff (1 minute in the present embodiment) of the filtration pump 8 and is maintained at a substantially constant pressure. Such behavior is repeated at Tfcycle (10 minutes in this embodiment).

  Maximum operating pressure Pon / max. Varies depending on the surface state of the separation membrane 60b, and when the degree of membrane clogging increases, the maximum operating pressure Pon / max. Decreases (rises to the negative side). Therefore, the degree of clogging of the separation membrane 60b can be grasped by monitoring the operating pressure.

When the value of the pressure sensor Pm is input, the calculation unit 10a calculates the transmembrane pressure difference TMP based on the following equation.
TMP = stop pressure (Poff) -operating pressure (Pon)
Next, the calculation unit 10a calculates a difference value ΔTMP between the transmembrane pressure difference TMP and the reference transmembrane pressure difference based on the following equation.
ΔTMP = TMP (cur.value) −TMP (ref.value)
In the above formula, TMP (cur. Value) indicates a current value, and TMP (ref. Value) indicates a reference transmembrane pressure difference (hereinafter, also simply referred to as “reference value”).

  3 (b) shows the transmembrane pressure difference corresponding to the pressure shown in FIG. 3 (a), and FIG. 3 (c) shows the relationship between the current value of the transmembrane pressure difference TMP and the reference value, In addition, differential values ΔTMP1, ΔTMP2, ΔTMP3, ΔTMP4,.

  The value calculated in the effective determination period (see FIG. 3C) set after the second half of the operation period Tfon of the filtration pump 8 where the transmembrane pressure is stabilized at a substantially constant value is used for controlling the amount of air diffused. Adopted for transmembrane pressure difference. In the present embodiment, 3 minutes after the elapse of 6 minutes is set as the validity determination period in the 9-minute operation period Tfon. The validity determination period is not limited to this range, but needs to be set to a relatively stable period.

  FIG. 3D shows the difference values ΔTMP1, ΔTMP2, ΔTMP3, and ΔTMP4 of the transmembrane pressure difference calculated during the validity determination period. In FIG. 3D, the difference value is shown in a straight line as a substantially constant value, but actually fluctuates up and down. If the value is the same as the reference value, the value is 0. If the value is lower than the reference value, a negative value is indicated. If the value is higher than the reference value, a positive value is indicated.

  The calculation unit 10a sets two threshold values Th (a) and Th (b) (Th (b) <Th (a)) as the difference value ΔTMP of the transmembrane pressure difference in the validity determination period, and the difference value ΔTMP is If the threshold Th (b) (0.05 kPa in the present embodiment) is less than or less than the threshold Th (b), it is determined that the film clogging state is reduced and the state is relatively good, and the difference value ΔTMP is the threshold Th (a) (this implementation) If the form is 0.2 kPa) or greater, or greater than that, it is determined that the state of film clogging has progressed and purification by air diffusion needs to be promoted, and the difference value ΔTMP is determined as the threshold value Th (b) and Th (a ), It is determined that the film clogging state is not so severe and can be maintained in the current aeration state.

  As shown in FIG. 4 (b), the calculation unit 10a has updated the reference transmembrane pressure difference TMP (ref.value) most recently, and has passed at least 3 hours and at a predetermined time interval not exceeding 12 hours. The reference transmembrane pressure difference TMP (ref. Value) is updated. An appropriate value can be adopted as the time interval for updating depending on the characteristics of the water to be treated. For example, when the water to be treated is sewage, it can be arbitrarily set such that it is updated every 3 hours during daytime when the fluctuation is large, and is updated every 6 hours during nighttime when the fluctuation is small. In this embodiment, the reference transmembrane pressure difference is updated and set every 6 hours.

  More specifically, as shown in the timing charts of FIGS. 4A and 4B and the flowchart of FIG. 9, the calculation unit 10a ends the operation period Tfon of the filtration pump 8 every time 6 hours pass (SD1). The representative operating pressure is specified in the operating pressure detection area (for example, the time from 6 minutes to 9 minutes) set at a predetermined time (SD2), and is set to the predetermined time at the end of the stop period Tfoff of the filtration pump 8 The representative stop pressure is specified in the stop pressure detection region (for example, the time from 40 seconds to 60 seconds) (SD2), and the process of calculating the transmembrane pressure difference from these values is continuously performed for several cycles (SD3 , SD4), and the average value is updated to a new reference transmembrane pressure difference TMP (ref. Value) (SD5).

  In this embodiment, the operation pressure at 8 minutes 50 seconds after the start of the operation period Tfon is set as the representative operation pressure, the stop pressure at 59 seconds after the start of the stop period Tfoff is specified as the representative stop pressure, The average value of the differential pressure is updated and set to a new reference transmembrane pressure difference TMP (ref. Value).

  These conditions are merely examples, and may be set as appropriate. For example, the representative operating pressure is specified by an average value for every fixed time in the operating pressure detection region, and the representative value is expressed by an average value for every fixed time in the stop pressure detection region. The stop pressure may be specified, or the number of cycles for obtaining the average value of the transmembrane pressure difference may be increased.

  As shown in FIG. 4C, the reference transmembrane pressure difference TMP (ref. Value) calculated at predetermined time intervals is set to a new reference transmembrane pressure difference TMP (ref. Value) indicated by a solid line. However, when the calculated reference transmembrane pressure difference TMP (ref. Value) is lower than the previous value, as shown by the broken line, it is difficult to maintain the current value without newly updating. This is preferable in that the amount of air diffused can be adjusted on the safe side so as not to cause an excessive increase in air volume.

  4 (d), the membrane separation apparatus used in the present embodiment is, for example, 7 L / (min. When the filtration pump 8 is continuously operated with a sufficient amount of air diffused, the operating pressure rises by about 0.1 kPa per day, and cleaning performance is required only once every six months. I have.

  The characteristic indicated by the step-like line segment in FIG. 4D illustrates the reference transmembrane pressure difference TMP (ref. Value) calculated at intervals of 6 hours for such a separation membrane 60b. Yes. That is, the reference transmembrane pressure difference TMP (ref. Value) is a value substantially following the transmembrane pressure difference of the separation membrane 60b that changes with time, and the current transmembrane pressure difference with respect to the reference transmembrane pressure difference. By determining whether the pressure is low or high and adjusting the amount of aeration, the filtration performance can be maintained without excessive aeration.

Hereinafter, the control of the amount of air diffusion will be described in detail.
FIG. 7 shows a comparison process between the difference value of the transmembrane pressure difference and the threshold value, which is performed by the calculation unit 10a, for each cycle of the filtration pump 8 that is intermittently operated.

  When the stop pressure detection timing is reached (SB1), the stop pressure is input (SB2), and when the operation pressure detection timing is reached (SB3), the operation pressure is input (SB4). Subsequently, the transmembrane pressure difference TMP is calculated (SB5), and a difference value ΔTMP between the transmembrane pressure difference TMP and the reference transmembrane pressure difference is calculated (SB6).

  The stop pressure detection timing is a section corresponding to the stop pressure detection region in FIG. 4A, and the operation pressure detection timing is a section corresponding to the operation pressure detection region in FIG. ) And (d) are valid determination periods.

  At the operating pressure detection timing, if the state in which the difference value ΔTMP is equal to or greater than the threshold value Th (a) continues for 10 seconds (SB7), the flag Fa is set on the condition that the flag Fb is not set (SB9). When the state where ΔTMP is equal to or less than the threshold Th (b) continues for 30 seconds (SB10), the flag Fb is set on the condition that the flag Fa is not set (SB12).

  That is, if no flag is finally set, the difference value ΔTMP exists between the threshold values Th (a) and Th (b). In this example, both flags are not set at the same time in one cycle of the filtration pump 8, and the previously set flag is valid. However, the other flag is reset when one flag is set. Processing may be performed, in which case the latest set flag is valid.

  FIG. 8 shows a target value setting process for the amount of air diffused based on the difference value ΔTMP performed by the calculation unit 10a. The process is executed after the comparison process between the difference value ΔTMP and the threshold value described with reference to FIG. 7, and increases the amount of air diffusion based on the tendency of the difference value ΔTMP in a plurality of cycles of intermittent operation of the filtration pump 8. It is a process to set whether to decrease.

  When the flag Fa is set (SC1), the flag Fa is reset (SC2) for the next comparison process described in FIG. 7, the counter corresponding to the flag Fa is incremented by 1, and the counter corresponding to the flag Fb is added. Is reset (SC3).

  Each counter is a counter for determining whether or not the flag is set continuously in a plurality of cycles as a result of the comparison processing described with reference to FIG. The process of step SC3 is a process of resetting the counter corresponding to the flag Fb while the counter corresponding to the flag Fa is continuously counted a predetermined number.

  When the counter corresponding to the flag Fa reaches a predetermined number, 3 in this embodiment (SC4), the counter is reset (SC5), and the aeration amount target value SV is set to increase (SC6).

  If the flag Fa is not set in step SC1, the state of the flag Fb is determined (SC7). If the flag Fb is set, the flag Fb is set for the next comparison process described in FIG. It is reset (SC8), the counter corresponding to the flag Fb is incremented by 1, and the counter corresponding to the flag Fa is reset (SC9).

  The process of step SC9 is a process of resetting the counter corresponding to the flag Fa while the counter corresponding to the flag Fb is continuously counted a predetermined number.

  When the counter corresponding to the flag Fb reaches a predetermined number, 4 in this embodiment (SC10), the counter is reset (SC11) and the aeration amount target value SV is set to decrease (SC12). Although the maximum value of the counter corresponding to the flag Fa is 3 and the maximum value of the counter corresponding to the flag Fb is 4, an example is not limited to this value, and the maximum value of the counter corresponding to the flag Fa is shown. It is sufficient that the maximum value of the counter corresponding to the flag Fb is larger than the value.

  FIG. 5 shows the transition state of the air diffusion amount set in steps SC6 and SC12. The air diffusion amount of 2Q (= 7 l / (min.)) Was initially set, but in the area A1, every time the counter corresponding to the flag Fb indicates 4, that is, the difference value ΔTMP is the lower threshold value. Each time four cycles of the state below Th (b), the value is gradually lowered by a slight value of Q / 3.

  In the region A2, such a state continues and the minimum air diffusion amount is fixed to Q. In the region A3, when the counter corresponding to the flag Fa indicates 3, that is, when the state where the difference value ΔTMP is equal to or larger than the upper limit threshold Th (a) has passed three cycles, the maximum air diffusion amount 3Q is immediately set to be increased. Is continued for 60 minutes.

  After 60 minutes, the amount of air diffused is set to 2Q in the area A4, and then the air amount target value setting process described with reference to FIG. 8 is performed. Note that the air diffusion amount target value setting process may be performed in the state where the maximum air diffusion amount 3Q is set without reducing the air diffusion amount to 2Q in the region A4. Further, the maximum air diffusion amount 3Q is an example, and is not limited to this value. Moreover, it is not restricted to the aspect which increases to the maximum air diffusion amount 3Q at a stretch, and may be set to the maximum air diffusion amount 3Q by increasing in a plurality of stages over several cycles.

  That is, the absolute value of the change amount or change rate of the target value SV when increasing the air diffusion amount is set to a value larger than the absolute value of the change amount or change rate of the target value SV when decreasing the air diffusion amount. Is done.

  As a result, when the transmembrane pressure difference is high, solids etc. are already attached to the surface of the separation membrane, so in order to release the state quickly and reliably, the amount of air diffused is reduced. By increasing the amount of change larger than the amount of change, the effect of cleaning the separation membrane due to the rising flow of bubbles and water to be treated can be enhanced, and the deposits on the surface of the separation membrane can be effectively peeled off.

  And when the transmembrane pressure is low, the amount of change when increasing the amount of air diffused to reduce the risk of clogging the surface of the separation membrane when reducing the amount of air diffused and to carefully judge the decrease. By reducing the amount of change with a smaller amount, the rapid fluctuations in the upward flow of bubbles and water to be treated are suppressed, the sudden decrease in the peeling action of the deposits, etc. on the separation membrane surface is avoided, and new adhesion Can be suppressed.

  Further, when the air diffusion amount is set to increase, the target value is held for at least one hour regardless of the subsequent difference value ΔTMP. The holding time may be set to an appropriate value between 30 minutes and 3 hours. That is, regardless of the transmembrane pressure difference, the retention time of the target value SV when it is set to increase the amount of aeration is the retention time of the target value SV when it is set to decrease the amount of aeration. Is set to a longer time.

  The target value SV of the air diffusion amount set by the calculation unit 10a is output to the PID control unit 10b, and the PID control unit 10b performs PID calculation based on the deviation between the air amount PV from the air flow sensor Fm and the target value SV. The control value MV necessary for the air amount PV to become the target value SV is input to the inverter circuit 10c. The frequency of the motor that is the drive source of the blower B is controlled by the inverter circuit 10c, and the amount of aeration is adjusted.

  That is, the membrane separation device 6 according to the present invention includes a calculation unit 10a as target value setting means for setting a target value of the amount of air diffused from the air diffuser 7 based on the transmembrane pressure, and the amount of air diffused is a target value. And a PID calculation unit 10b as an aeration amount control means for controlling the aeration device 7 so that the target value setting means is the absolute value of the change amount or change rate of the target value when the aeration amount is increased. The value is set to a value larger than the absolute value of the amount of change or rate of change of the target value when the amount of air diffusion is reduced.

  In addition, the calculation unit 10a includes a reference transmembrane differential pressure setting unit that updates and sets a reference transmembrane differential pressure for evaluating a measured value of the transmembrane differential pressure every predetermined time, and a reference transmembrane differential pressure and a transmembrane difference. It also functions as target value setting means for setting the target value of the amount of air diffused from the air diffuser 7 based on the difference value from the measured pressure value.

  By such a control device 10, the operation method of the membrane separation device according to the present invention is realized. That is, a target value setting step for setting a target value SV for the amount of air diffused from the air diffuser 7 based on the transmembrane pressure, and a diffuser for controlling the air diffuser 7 so that the amount of air diffused becomes the target value SV. Including the air volume control step, in the target value setting step, the absolute value of the change or change rate of the target value when increasing the aeration amount is the change or change rate of the target value when decreasing the aeration amount This is a method of operating the membrane separation apparatus set to a value larger than the absolute value of.

  In the aeration amount control step, when the retention time of the target value SV is set so as to decrease the aeration amount when it is set to increase the aeration amount regardless of the transmembrane pressure difference. Is set to a time longer than the holding time of the target value SV.

  In the target value setting step, the duration of the transmembrane pressure difference that is lower than the threshold value Th (b) for lowering the target value is exemplified as 30 seconds in this embodiment, but it is not a fixed value. ) Is longer than the duration of the transmembrane pressure difference that is higher than the threshold value Th (a) for increasing the target value (in this embodiment, it is exemplified as 10 seconds but is not a fixed value). The target value is changed when the relationship between the transmembrane pressure difference and the threshold value is maintained beyond the duration set for each threshold value.

  Further, in such an operation method of the membrane separation apparatus, in the target value setting step, the amount of air diffused from the air diffuser 7 is determined based on the difference value between the reference transmembrane differential pressure and the measured value of the transmembrane differential pressure. It is preferable to set a target value, and it is preferable to execute a reference transmembrane pressure setting step for updating and setting a reference transmembrane pressure difference for evaluating a measured value of the transmembrane pressure difference at regular intervals.

  Similarly, in the target value setting step, two threshold values are set for the difference value ΔTMP between the reference transmembrane pressure difference TMP (ref. Value) and the transmembrane pressure difference measurement value TMP (cur. Value). When the first threshold Th (a) exceeds or exceeds the target value, the target value is increased, and when the difference value is less than or less than the second threshold Th (b), which is smaller than the first threshold Th (a), the target value is decreased. Then, the target value is set so that the target value is maintained when the difference value is between the first threshold value and the second threshold value.

  In the reference transmembrane pressure setting step, when the updated setting value of the reference transmembrane pressure TMP (ref. Value) is smaller than the reference transmembrane pressure that has been updated and set in the latest past, The reference transmembrane differential pressure is updated and set so that the updated reference transmembrane differential pressure is continuously adopted as the reference transmembrane differential pressure.

  Further, in the reference transmembrane pressure setting step, at least 3 hours have elapsed and the reference transmembrane pressure difference is updated and set at a time not exceeding 12 hours.

  FIG. 10 (a) shows experimental data showing the transition of the reference transmembrane pressure difference for three days of the membrane separation device 6 controlled by the control device 10 described above. Here, the experimental data corresponding to FIG. 4C, which represents the change in the amount of air diffusion peculiar to the present invention, was employed instead of the experimental data in which the amount of air diffusion was kept low. Incidentally, the maximum value of the amount of air diffused in the experimental data is the value that has been diffused at a constant flow rate. The reference transmembrane pressure difference is updated at an interval of about 6 hours.

  FIG. 10B shows a difference value ΔTMP between the amount of air diffused from the air diffuser 7 of the same membrane separation device 6 and the reference transmembrane differential pressure of the transmembrane differential pressure TMP as a basis thereof, Each transition of transmembrane pressure is shown.

  Two timings A and B in which the air amount rises stepwise can be grasped. Immediately before this, it is determined that the clogging of the separation membrane has increased as the difference value ΔTMP shows a large value. Thereafter, the difference value ΔTMP is maintained at a substantially low value across 0, and the air amount is reduced stepwise.

  In this experiment, after the air amount increases at timing B, the reference transmembrane pressure difference is updated to a value lower than that immediately before at timing C. As can be understood from the fact that the difference value ΔTMP shows a large value for a while after that, when the reference transmembrane pressure difference is lower than the previous value, the current value is not updated again. It is preferable to maintain.

  Note that the values of the first threshold value Th (a) and the second threshold value Th (b) are examples, and are not limited to the above-described values, and may be set as appropriate. Further, the threshold value is configured by one value, and the target value of the air diffusion amount may be increased when the difference value ΔTMP is larger than the threshold value, and the target value of the air diffusion amount may be decreased when the difference value ΔTMP is smaller. .

  In embodiment mentioned above, although the case where the membrane separation activated sludge processing apparatus was comprised with two tanks of an anaerobic tank and a membrane separation tank, even if comprised with three tanks of an anaerobic tank, an aeration tank, and a membrane separation tank, is demonstrated. Good. The anaerobic tank is not necessarily required, and may be a sewage treatment apparatus that employs a membrane separation activated sludge method including an initial settling site, an aeration tank, and a membrane separation tank.

  The above-described embodiment is one aspect of the present invention, and the present invention is not limited by the description. Specific configurations and control aspects of each part can be appropriately changed and designed within the scope of the effects of the present invention. Needless to say.

1: Sewage treatment facility 2: Pretreatment facility 3: Flow rate adjustment tank 4: Activated sludge treatment tank 4a: Anaerobic tank 4b: Membrane separation tank 5: Treated water tank 6: Membrane separation device 60: Separation membrane 7: Aeration device 8: Filtration pump 10: Control device

Claims (4)

A separation membrane that is immersed in the water to be treated and a diffuser disposed below the separation membrane, and passes through the separation membrane while being diffused from the diffuser toward the separation membrane An operation method of a membrane separation device for obtaining treated water,
A target value setting step of setting a target value of the amount of air diffused from the air diffuser based on the transmembrane pressure difference;
An aeration amount control step of controlling the aeration device so that the aeration amount becomes the target value;
In the target value setting step, the absolute value of the change amount or change rate of the target value when increasing the amount of air diffusion is greater than the absolute value of the change amount or change rate of the target value when decreasing the air diffusion amount. A method for operating a membrane separator characterized in that the value is set to a value.   In the aeration amount control step, the target value holding time when the aeration amount is set to increase regardless of the transmembrane pressure is the target value when the aeration amount is set to decrease. 2. The method for operating a membrane separation device according to claim 1, wherein the time is set to be longer than the holding time.   In the target value setting step, the duration of the transmembrane pressure difference showing a value lower than the threshold value for lowering the target value is longer than the duration time of the transmembrane pressure difference showing a value higher than the threshold value for raising the target value. The target value is changed when a long time is set and the relationship between the transmembrane pressure difference and the threshold is maintained beyond the duration set for each threshold. The operation method of the membrane separator according to claim 2. A separation membrane that is immersed in the water to be treated and a diffuser disposed below the separation membrane, and passes through the separation membrane while being diffused from the diffuser toward the separation membrane A membrane separator for obtaining treated water,
Target value setting means for setting a target value of the amount of air diffused from the air diffuser based on the transmembrane pressure difference;
An aeration amount control means for controlling the aeration device so that the aeration amount becomes the target value,
The target value setting means has an absolute value of a change amount or a change rate of the target value when increasing the amount of air diffusion, and is larger than an absolute value of the change amount or the change rate of the target value when decreasing the air diffusion amount. A membrane separator characterized by being set to a value.

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