[1] A membrane separation device comprising:
a separation membrane which filters treatment target water in a membrane separation tank;
a membrane surface aeration device which supplies air for performing membrane surface aeration for the separation membrane;
organic substance concentration measurement means which measures an organic substance concentration in the treatment target water;
a pressure measurement unit which measures a transmembrane pressure of the separation membrane;
transmembrane pressure increase speed comparing means which compares a transmembrane pressure increase speed RT selected on the basis of a value of the organic substance concentration measured by the organic substance concentration measurement means, with a transmembrane pressure increase speed RM calculated from the transmembrane pressure measured by the pressure measurement unit; and
a control unit which controls a membrane surface aeration flow amount of the membrane surface aeration device, wherein
the control unit changes the membrane surface aeration flow amount on the basis of the difference, obtained by the transmembrane pressure increase speed comparing means,

between the transmembrane pressure increase speed RT selected on the basis of the value of the organic substance concentration measured by the organic substance concentration measurement means and the transmembrane pressure increase speed RM calculated from the transmembrane pressure measured by the pressure measurement unit.
[2] The membrane separation device according to claim 1, wherein
in selection of the transmembrane pressure increase speed RT on the basis of the value of the organic substance concentration measured by the organic substance concentration measurement means, the transmembrane pressure increase speed RT is selected from data in which a relationship between an organic substance concentration in treatment target water and a transmembrane pressure increase speed, acquired in advance, is stored.
[3] The membrane separation device according to claim 1 or 2, wherein
in calculation of the transmembrane pressure increase speed RM from the transmembrane pressure measured by the pressure measurement unit, the transmembrane pressure increase speed RM is calculated from temporal change in the transmembrane pressure of the separation membrane.

[4] A membrane separation device comprising:
a separation membrane which filters treatment barget water in a membrane separation tank;
a membrane surface aeration device which supplies air for performing membrane surface aeration for the separation membrane;
organic substance concentration measurement means which measures an organic substance concentration in the treatment target water;
a pressure measurement unit which measures a transmembrane pressure of the separation membrane;
target transmembrane pressure increase speed setting means which sets a target transmembrane pressure increase speed RT on the basis of a value of the organic substance concentration in the treatment target water;
transmembrane pressure increase speed measurement neans which calculates a transmembrane pressure increase speed RM from the transmembrane pressure of the separation nembrane;
transmembrane pressure increase speed comparing neans which compares the target transmembrane pressure increase speed RT from the target transmembrane pressure increase speed setting means, with the transmembrane pressure increase speed RM from the transmembrane pressure increase

speed measurement means; and
a control unit which controls a membrane surface aeration flow amount of the membrane surface aeration device, wherein
the control unit changes the membrane surface aeration flow amount on the basis of the difference, obtained oy the transmembrane pressure increase speed comparing means, oetween the transmembrane pressure increase speed RT selected on the basis of the value of the organic substance concentration measured in the treatment target water and the bransmembrane pressure increase speed RM calculated from the bransmembrane pressure measured by the pressure measurement jnit.
[5] The membrane separation device according to claim 4, wherein
the target transmembrane pressure increase speed setting means includes: a database in which a relationship oetween an organic substance concentration in treatment barget water and a transmembrane pressure increase speed, acquired in advance, is stored; and a target transmembrane pressure increase speed selecting unit which selects the barget transmembrane pressure increase speed RT on the basis of the value of the organic substance concentration measured oy the organic substance concentration measurement means and

data in the database.
[6] The membrane separation device according to claim 4 or 5, wherein
the transmembrane pressure increase speed measurement means includes a transmembrane pressure increase speed calculation unit which calculates the transmembrane pressure increase speed RM from the transmembrane pressure measured by the pressure measurement unit.
[7] The membrane separation device according to any one of claims 1 to 6, wherein
when the transmembrane pressure increase speed RT selected on the basis of the value of the organic substance concentration measured by the organic substance concentration measurement means is greater than the transmembrane pressure increase speed RM calculated from the transmembrane pressure measured by the pressure measurement unit, the control unit decreases the membrane surface aeration flow amount, and when the transmembrane pressure increase speed RT selected on the basis of the value of the organic substance concentration measured by the organic substance concentration measurement means is smaller than the transmembrane pressure increase speed RM calculated from the transmembrane pressure measured by the pressure measurement unit, the control unit increases

the membrane surface aeration flow amount.
[8] The membrane separation device according to claim 5, further comprising database update means which calculates a new target transmembrane pressure increase speed RT' for the organic substance concentration measured by the organic substance concentration measurement means, and updates the relationship between the organic substance concentration in the treatment target water and the transmembrane pressure increase speed, stored in the database.
[9] The membrane separation device according to claim 8, wherein
the database update means includes:
membrane surface aeration flow amount comparing means which compares a membrane surface aeration flow amount QM when the transmembrane pressure increase speed RT selected on the basis of the value of the organic substance concentration measured by the organic substance concentration measurement means and the transmembrane pressure increase speed RM calculated from the transmembrane pressure measured by the pressure measurement unit have become equal to each other through control, with a membrane surface aeration flow amount QT corresponding to the target transmembrane pressure increase speed RT, stored in the database;

target transmembrane pressure increase speed calculation means which, when the membrane surface aeration flow amount QM and the membrane surface aeration flow amount QT are different from each other in the membrane surface aeration flow amount comparing means, causes the control unit to change the membrane surface aeration flow amount, and calculates a new target transmembrane pressure increase speed RT '; and
a database update unit which stores, in the database, the new target transmembrane pressure increase speed RT' calculated by the target transmembrane pressure increase speed calculation means, a membrane surface aeration flow amount QT' corresponding thereto, and the value of the organic substance concentration measured by the organic substance concentration measurement means.
[10] The membrane separation device according to claim 9, wherein
the target transmembrane pressure increase speed calculation means includes: a membrane surface aeration flow amount change command unit which sends a signal to the control unit so as to change the membrane surface aeration flow amount; and a target transmembrane pressure increase speed calculation unit which calculates the new target transmembrane pressure increase speed RT' on the basis of a

relationship between the membrane surface aeration flow amount when the membrane surface aeration flow amount has been changed by the control unit in accordance with a command sent from the membrane surface aeration flow amount change command unit, and the transmembrane pressure increase speed at that time.
[11] The membrane separation device according to claim 10, wherein
the membrane surface aeration flow amount change command unit sends a command to the control unit so as to decrease the membrane surface aeration flow amount when the membrane surface aeration flow amount QM is greater than the membrane surface aeration flow amount QT and so as to increase the membrane surface aeration flow amount when the membrane surface aeration flow amount QM is smaller than the membrane surface aeration flow amount QT, and
the target transmembrane pressure increase speed calculation unit calculates the new target transmembrane pressure increase speed RT' on the basis of a relationship between the membrane surface aeration flow amount and the transmembrane pressure increase speed corresponding thereto when the membrane surface aeration flow amount has been changed from QM to QT.

[12] A membrane separation device comprising:
a separation membrane which filters treatment target water in a membrane separation tank;
a membrane surface aeration device which supplies air for performing membrane surface aeration for the separation membrane;
first organic substance concentration measurement means which measures an organic substance concentration in the treatment target water;
second organic substance concentration measurement means which measures an organic substance concentration in filtered water filtered by the separation membrane;
a pressure measurement unit which measures a transmembrane pressure of the separation membrane;
transmembrane pressure increase speed comparing means which compares a transmembrane pressure increase speed RT selected on the basis of an organic substance concentration difference obtained by subtracting a value of the organic substance concentration measured by the second organic substance concentration measurement means from a value of the organic substance concentration measured by the first organic substance concentration measurement means, with a transmembrane pressure increase speed RM calculated from the transmembrane pressure measured by the pressure measurement unit; and

a control unit which controls a membrane surface aeration flow amount of the membrane surface aeration device, wherein
the control unit changes the membrane surface aeration flow amount on the basis of the difference, obtained by the transmembrane pressure increase speed comparing means, between the transmembrane pressure increase speed RT selected on the basis of the value of the organic substance concentration measured by the organic substance concentration measurement means and the transmembrane pressure increase speed RM calculated from the transmembrane pressure measured by the pressure measurement unit.
[13] The membrane separation device according to any one of claims 1 to 12, wherein
in measurement for the organic substance concentration, the treatment target water in the membrane separation tank is subjected to solid-liquid separation by any of filtration separation, centrifugal separation, and precipitation separation, and an organic substance concentration in liquid obtained by the solid-liquid separation is measured.
[14] The membrane separation device according to any one of claims 1 to 13, wherein

for the organic substance concentration, at least one of an ultraviolet absorbance, a total organic carbon concentration, a biochemical oxygen demand, a chemical oxygen demand, a humic acid concentration, a sugar concentration, and a protein concentration, is measured.
[15] The membrane separation device according to any one of claims 1 to 14, wherein
in selection of the transmembrane pressure increase speed RT on the basis of the organic substance concentration, the transmembrane pressure increase speed RT is selected by using at least one of a water temperature of the treatment target water, a suspended solid concentration in the treatment target water, and a filtration flux of the separation membrane.
[16] A membrane separation method comprising:
filtering a treatment target water in a membrane
separation tank by a separation membrane;
measuring an organic substance concentration in the
treatment target water when performing membrane surface
aeration for supplying bubbles by a diffuser pipe from below
the separation membrane;
selecting a transmembrane pressure increase speed
RT as a target on the basis of a measured value of the

organic substance concentration;
comparing the transmembrane pressure increase speed
RT with an increase speed RM of a transmembrane pressure of
the separation membrane; and
i setting a flow amount of the membrane surface
aeration so that a difference between the transmembrane pressure increase speed RT and the increase speed RM becomes small.