Cleaning of micro- and ultrafiltration membranes with infrasonic backpulsing.

[摘要] ENGLISH ABSTRACT: Membrane fouling is universally considered to be one of the most critical problems in thewider application of membranes in filtration separation. Fouling is caused by the deposition ofparticles not only on the surface of the membrane, but also inside the membrane pores, whichreduces permeate flux and leads to a reduction of the efficiency and the longevity of themembrane. The backpulsing cleaning method can be used to remove deposited foulants fromthe surface of the membrane, without having to shut down the plant. Ultrasonic time-domainreflectometry (UTDR) is a nondestructive technique, used to detect and measure the growthof fouling layer on the membrane surface during microfiltration and ultrafiltration processes.In this study flat-sheet microfiltration (MF) and ultrafiltration (UF) membranes were fouledduring a cross-flow filtration processes using dextrin, yeast or alumina (feed pressure 100 kPaand feed flow rate 0.45 liter/minute), in a flat cell. Infrasound frequency backpulsing, in thepermeate space, was used to clean the membranes. Backpulsing was carried out using thepermeate water or soap solutions. The peak pressure amplitude of the pulses used to clean themembranes was 140 kPa, the pulsing was applied at a frequency of 6.7 Hz.The main objectives of this research were: (1) to obtain a fundamental understandimg of howfoulants deposit on membrane surfaces and how the foulant deposits can be removed usingthe backpulsing cleaning technique during MF and UF, (2) to use the ultrasonic measurementtechnique for monitoring the growth and removal of the fouling layer on the membranesurface and (3) Use scanning electron microscopy (SEM) as a direct measurement techniqueto analyze the structure the foulant deposits on membrane surfaces before and after cleaning.Results showed that a flux value of between 55% and 98% of the clean water flux value canbe achieved by backpulsing cleaning. UTDR was successfully applied to monitor membranecleaning and provide information about the growth and removal of fouling layers on themembrane surface.

[发布机构] Stellenbosch University