Natural organic fouling

Of particular interest in this study is the fouling of membrane processes by natural organics. Fouling depends on the characteristics of the natural organics. A detailed review of the characteristics of interest is required to highlight the factors that may influence membrane fouling. Membrane filtration... 

The type of membrane cleaning required depends on both the type and degree of fouling experienced, but typically it is either organic (bacterial slimes, natural organics, or process foulants and nutrients) or inorganic (silica, carbonate, sulfate, or phosphate deposits). 

Heijman SGJ, Verliefde ARD, Comelissen ER, Amy G, van Dijk JC (2007) Influence of natural organic matter (NOM) fouling on the removal of pharmaceuticals by nanoflltration and activated carbon filtration. Water Sci Technol Water Supply 7 17-23... 

D. Violleau, H. Essis-Tome, H. Habarou, J.P. Croue, M. Pontie, fouling studies of a polyamide nanofiltration membrane by selected natural organic matter an analytical approach, Desalination 173 (2005) 223-238. 

Schafer, A. I., A. G. Fane, and T. D. Waite, "Nanofiltration of Natural Organic Matter Removal, Fouling, and the Influence of Multivalent Ions," Desalination, 118 (1998). 

Seidel, Arza, and Menachem Elimelech, Coupling Between Chemical and Physical Interactions in Natural Organic Matter (NOM) Fouling of Nanofiltration Membranes Implications for Fouling Control," Journal of Membrane Science, 203 (2002). 

Divalent cations, particularly calcium, have been shown to enhance fouling of membranes with natural organic matter (NOM).3 Because is it s acidic nature, NOM can form complexes with dissolved metal ions. The strongest bonds occur with calcium. This is a function of the size of the metal ion, it s electronic charge, and the... 

Hong, S. and Elimelech, M., Chemical and physical aspects of natural organic matter (NOM) fouling of nanofiltration membranes, J. Membr. ScL, 132, 159, 1997. 

T. Carroll, N. A. Booker, and J. Meier-Haack, Polyelectrolyte-grafted microfiltration membranes to control fouling by natural organic matter in drinking water. Journal of Membrane Science 203, 3-13 (2002). 

In this book pressure-driven membrane processes are compared on the basis of their potential to remove natural organic matter (NOM), critical fouling conditions, and the structure of the deposit formed in and on the membranes. 

The charge of natural organics determines their interaction with membranes, cations, colloids and their solubility. Charge is therefore a very relevant characteristic for water treatment and the distinction between the charges of functional groups is of particular interest in the interpretation of pH effects on membrane rejection and fouling. 

Cations in conjunction with natural organics enhance membrane fouling. This effect, although being generally accepted, is not well understood. Therefore, the interactions of natural organics and cations are of particular importance. The effect of cations on natural organics solubility was discussed in section 2.5.9. 

After a brief description of membrane materials, membrane rejection and fouling will be addressed. Both rejection of and fouling ly natural organics and inorganic colloids, will be a major focus of this work. A further issue is the characterisation of clean andfouled membranes as well as fouling control. 

Unfouled MF does not retain natural organics unless they are associated with particulates and measured as turbidit). This means that a pretreatment step, such as coaguladon, is required. MF can remove Giardia and Cryptosporidium but the extent of removal of Cryptosporidium depends on size, adsorption and cake layer built-up. Jacangelo et at (1995a) observed that fouling of MF membranes increased rejection of various species. Consequently, Kumar et al. (1998) found a significant removal of trihalomethanes (THMs) by MF in an extended pilot study. 

While gel formation and precipitation are reported frequently as the source of fouling in all membrane processes, only a small amount of work has been done on a quantitative determination of gel layer concentration and the solubility of natural organics. Naturally, flux or transmembrane pressure are important for concentration polarisation, which seems to be the major factor in gel formation. The MTC can also describe this, as was shown above. Organic characteristics such as solubility and hydrophobicity require further investigation as do their interaction with ions. The solubilities of HS and their complexes with salts are relatively unknown, as was discussed in Chapter 2. 

From this review it appears that the application of theoretical models to natural organics separation and fouling would be premature. Model substances are required, but it appears that they do not to give similar fouling as the surface water mixture. 

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