Tangential streaming potential, transmembrane flux, and chemical cleaning of ultrafiltration membranes

Transmembrane flux measurements are the only practical tools used to evaluate the degree of organic fouling and the efficiency of chemical cleaning of ultrafiltration membranes in situ. Tangential pH-streaming potential profiles may become a comprehensive in situ method to analyse cleaning efficiency versus potential membrane damage. A parallel implementation of the two methods was used to assist in tuning an efficient cleaning protocol for 300 kDa polyethersulfone membranes. The membranes were fouled with a mixture of organics and cleaned with nitric acid, acetic acid, caustic soda or liquid bleach, each at concentrations of 1, 5, or 10 mg/L. A modified Kolmogorov-Smirnov test for divergence in datasets clearly indicated cleaning with 5 mg/L NaOH or NaOCl. These findings were confirmed by atomic force microscopy surface contouring and infrared spectra recording. Tangential pH-streaming potential profiling is easy in terms of operation and maintenance, inexpensive, and may be conducted in situ. Implementation of two independent tests is instrumental in the validation of the cleaning agent efficiency, optimisation of the cleaning dose and pH, and assessment of membrane fouling potential by complex organic mixtures. A combination of transmembrane flux and tangential streaming potential tests may reduce the cost of chemical cleaning and suspend membrane ageing.