Effect of different physical conditions on fouling control in in-situ chemical cleaning in place (CIP) for flat sheet membranes fouled by secondary effluents

Although microfiltration (MF) system has been employed as pretreatment for reclamation, the MF process is prone to irreversible fouling by secondary effluents as feed. In particular, flat sheet (FS) membrane has trouble in controlling fouling due to restriction of backwashing. In this study, in-situ CIP (NaOCl 300, 600, 1200 mg/L) was applied to fouled membranes by secondary effluents with different physical conditions (idle, aeration, microbubble) and evaluated via examination of detached foulants (or fouled membrane) and continuous membrane process. The in-situ CIP with microbubble, the most effective method, showed cleaning efficiencies from 32.6% to 81.9% depending on operating conditions. Although microbubble could not induce hydraulic shear stress, it removed particulates and colloids on the membrane surface effectively. In addition, it influenced the structure of fouling layers. Moreover, in-situ CIP with microbubble retarded the increase of fouling resistances and controlled irreversible fouling compared to in-situ CIP with aeration.