Method for operating membrane separation device with halt process

A method for operating a membrane separation device for performing solid-liquid separation of water to be treated via a separation membrane, the method comprising:

• a membrane filtration process including:
• setting a flow amount M(t) of permeated water from the membrane separation device so as to satisfy a relationship expressed by the following equation:
• M(t)=KQ(t−1), where M(t) is the flow amount s f the permeated water during a time period t having a predetermined length, K is a gain (>1), and Q(t−1) is an amount of inflow of the water to be treated during a time period t−1 immediately prior to the time period t;
• and
• extracting the permeated water from the membrane separation device by the set flow amount M(t) of the permeated water;
• and
• a halt process including:
• temporarily stopping extracting the permeated water from the membrane separation device when a water level of a first water tank in which the membrane separation device is immersed, a water level of a second water tank which is in communication with the first water tank such that the water level thereof is the same as that of the first water tank, or a water level of a third water tank into which overflowing water from the first water tank is flowing, becomes lower than a predetermined halt water level.