To provide a membrane separation device which can precisely decide the functional deterioration due to a blocking or oxidation of the membrane of a membrane module by increasing the setting precision of an initial value of water permeation constant in the membrane module.
A membrane separation device includes: a membrane module 5; a pressure pump 2 which forces supply water W1 flowing through a supply water line L1 to the membrane module 5; a pressure detector 24 which detects the discharge pressure of the pressure pump 2; a flow detector 25 which detects the flow of permeating water W2; a temperature detector 23 which detects the temperature of the supply water W1, permeating water W2 or concentrated water W3; and a control part 10 which calculates the rate of change between the first arithmetic value by the water permeation constant of the membrane module 5 and the second arithmetic value calculated after operating the first arithmetic value, based on the detected pressure value by the pressure detector 24, the detected flow value by the flow detector 25 and the detected temperature value by the temperature detector 23 and when the rate of change falls within the predetermined range, and sets the second arithmetic value as the initial value of the water permeation constant of the membrane module 5.
NOGUCHI YUKIO
WATANABE HAYATO
ROKKAKU TAKUJI
Ryota Kato