where J is the permeate flux (m/s), TMP is the transmembrane pressure (Pa) measured using a vacuum meter, η is the dynamic viscosity of permeate (Pa s) assumed as the viscosity of water at the given temperature, and Rt is the total filtration resistance (1/m). When normalized TMP increased to 40 kPa, membranes were removed from the reactor and then physically cleaned by carefully removing the thick sludge cake layer deposited on the membrane with spraying pressurized water. If the membrane flux was not restored after this cleaning procedure, chemical cleaning was needed. In chemical cleaning, the membrane was soaked in 0.5% NaClO solution overnight, followed by thorough flushing with deionized water. Regarding the UF-RO dual membrane device, physical membrane cleaning was carried out by rinsing with deionized water after operation every day.