Abstract: Provided is a method for cleaning a filtration membrane provided in a membrane filtration device that is immersed in a liquid to be treated and performs solid-liquid separation on the liquid to be treated. When a transmembrane pressure difference exceeds a first predetermined pressure difference P1, a first cleaning step W1 for cleaning a filtration membrane is performed using a first chemical solution; when the transmembrane pressure difference immediately after performing the first cleaning step W1 exceeds a second predetermined pressure difference P2 that is lower than the first predetermined pressure difference, a second cleaning step W2 for cleaning the filtration membrane is performed using a second chemical solution having a concentration higher than the first chemical solution; and when the second cleaning step W2 is performed, the concentration of the second chemical solution and/or the cleaning time is changed according to the temperature of the liquid to be treated.

Abstract: Provided is a method for cleaning a filtration membrane provided in a membrane filtration device that is immersed in a liquid to be treated and performs solid-liquid separation on the liquid to be treated. When a transmembrane pressure difference exceeds a first predetermined pressure difference P1, a first cleaning step W1 for cleaning a filtration membrane is performed using a first chemical solution; when the transmembrane pressure difference immediately after performing the first cleaning step W1 exceeds a second predetermined pressure difference P2 that is lower than the first predetermined pressure difference, a second cleaning step W2 for cleaning the filtration membrane is performed using a second chemical solution having a concentration higher than the first chemical solution; and when the second cleaning step W2 is performed, the concentration of the second chemical solution and/or the cleaning time is changed according to the temperature of the liquid to be treated.

Abstract: An organic wastewater treatment apparatus includes (a) a treatment tank, (b) a plurality of membrane separation devices immersed in the treatment tank, where each membrane separation device is provided with a diffuser device and a permeated liquid extracting device, (c) a plurality of sludge characteristics measuring devices dispersedly disposed in the treatment tank, and (d) a controller. An operating method divides the treatment tank into a plurality of regions, and sets at least one of an amount of air diffusion and a flow rate of permeated liquid for each membrane separation device based on a measured value of the sludge characteristics measuring device disposed in the corresponding region. The controller sets at least one of the amount of air diffusion and the flow rate of permeated liquid based on the measured value of the sludge characteristics measuring device in a vicinity of which the membrane separation device is disposed.