Membrane Fouling and Cleaning

Over long periods of operation, membrane fouling is generally not totally reversible by the hydraulic backwash procedure. As the number of filtration cycles increases, the irreversible fraction of membrane fouling also increases (see Fig. 6.13). In order to obtain the desired production flow rates (or flux), an increase in TMP is required. When this pressure reaches a maximum allowable mechanical resistance of the membrane, chemical cleaning is required for the membrane to regain most of its permeability. Regardless of the membrane system 

Scaling is a major concern for reverse osmosis (RO) and nanofiltration (NF) since these membranes reject inorganic species. Those species form a concentrated layer in the vicinity of membrane-liquid interface—a phenomenon referred to as concentration polarization. 

Although several researches have tried to identify the components of NOM that cause fouling of UF membranes, the results are confusing and conflicting. Weisner et al. (1992) identified four NOM categories that are strong foulants proteins, amino sugars. 

In other studies, Nilson and DiGiano (1996) reported most fouling was caused by hydro-phobic NOM components. However, Carroll et al. (2000) found neutral hydrophilic NOM components were the major foulants, while Cho et al. (2000) and Fan et al. (2001) reported NOM components as the major foulants on the order neutral hydrophUics hydrophobic acids transphilic acids charged hydrophilics. Due to conflicting opinions, further research on NOM in UF/MF is required. 

1 Silt Density Index The SDI is a commonly used test to predict a feed water s potential to foul a membrane by colloidal particles smaller than 0.45 xm. It is only a guide for pretreatment and is not an indication of adequate pretreatment. The SDI is a static measurement of resistance, which is determined by samples taken at the beginning and at the end of the test (EPA, 2002). 

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Nuengjamnong, C., Cho, J., Polprasert, C. and Ahn, K.H. (2006) Extracellular polymeric substances s influence on membrane fouling and cleaning during microfiltration process. Water Science and Technology Water Supply, 6, 141-148. 

Zhang, G.J. Liu Z.Z. 2003. Membrane fouling and cleaning in ultrafiltration of wastewater from banknote printing works. Journal of Membrane Science 211 235-249. 

Direct Visual Observation of Microfiltration Membrane Fouling and Cleaning... 

In Situ Characterization of Membrane Fouling and Cleaning Using a Multiphoton Microscope... 

Yangali-Quintanilla, V. A. Y. (2005). Colloidal and non-colloidal NOM fouling of ultrafiltration membranes Analysis of membrane fouling and cleaning. M.Sc. Thesis, UNESCO-IHE, Delft, The Netherlands. 

Li, J. X., Hallbauer, D. K., and Sanderson, R. D. (2003). Direct monitoring of membrane fouling and cleaning during ultrafiltration using a non-invasive ultrasoruc technique. J. Membr. Sci. 215, 33. 

Mairal, A. P., Greenberg, A. R., and Rrantz, W. B. (2000). Investigation of membrane fouling and cleaning using ultrasonic time-domain reflectometry. Desalination 130, 45. 

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