Ultrasonic cleaning of polytetrafluoroethylene membrane fouled by natural organic matter

•NOM-containing water was pre-treated with iron coagulant and bentonite clay.•Polytetrafluoroethylene (PTFE) membrane was fouled by pretreated NOM-water.•Pretreated NOM-water enhanced filterability of PTFE microfiltration.•NOM-fouled PTFE membrane was effectively cleaned by ultrasound irradiation.

Chemical cleaning of membranes fouled by natural organic matter (NOM) generates secondary pollution. In this study, the effect of ultrasonic cleaning of polytetrafluoroethylene (PTFE) membrane fouled by pre-coagulated humic acid-bentonite mixture was investigated. Results show that chemical coagulation prior to microfiltration improved turbidity and TSS removals by 9.5% and 11.4%, respectively. Experimental data fitted to constant pressure filtration models determined the sequence of dominant fouling mechanism as follows: (i) membrane resistance-limited, (ii) pore blocking resistance-limited, and (iii) cake formation resistance-limited. Relative membrane permeability of 53 and flux recovery of 45% were achieved when continuous ultrasonic cleaning was done at a 2.0 cm probe distance, 25 min total cleaning time, 15 mg/L coagulant dose, and 15 W ultrasonic power. Ultrasonic cleaning was found to be more effective than hydraulic cleaning in terms of flux recovery. Compared to chemical cleaning, it is a competitive and safer alternative in mitigating NOM-induced fouling.