Cleaning method of membrane housing, membrane housing cleaned by the cleaning method, and ultrapure water manufacturing apparatus including the membrane housing

A method for cleaning a membrane housing having an inlet for introducing a liquid to be treated and an outlet for discharging the treated liquid, wherein the liquid to be treated introduced from the inlet is treated and the treated liquid is discharged from the outlet,

• the method comprising:
• a first cleaning introducing a cleaning solution having a metal concentration (concentration of each element) of 100 ng/L or less into the membrane housing, thereby bringing the interior of the membrane housing into contact with the cleaning solution;
• a second cleaning, performed after completion of the first cleaning, of passing ultrapure water through the membrane housing, thereby bringing the interior of the membrane housing into contact with the ultrapure water;
• an analysis, performed during or after completion of the second cleaning, of
• analyzing the metal concentration in the ultrapure water that has come into contact with the interior of the membrane housing and has been discharged from the membrane housing during the second cleaning, or
• analyzing the metal concentration in the ultrapure water that has come into contact with the interior of the membrane housing and has been discharged from the membrane housing after completion of the second cleaning, by passing ultrapure water through the membrane housing again;
• and
• determining, based on the results obtained during the analysis,
• whether it is necessary to perform the second cleaning again, or to perform both the first cleaning and the second cleaning again.