Tran, Thuy, Gray, Stephen R, Naughton, Rebecca and Bolto, Brian (2005) Improved NOM removal and membrane performance via coagulation with polysilicato-iron. Journal of Harbin Institute of Techology - English ed., 12 (supp.). pp. 56-61. ISSN 1005-9113

Abstract

The NOM removal efficiency of polysilicato-iron (PSI) coagulants and the membrane fouling potential of PSI pretreated waters have been studied using two microfiltration membrane types: polyvinylidene fluoride (PVDF2) and polypropylene (PP). The results have shown that PSI coagulant with a Si/Fe ratio of 1 is the most effective compared to conventional coagulants in removing dissolved organic carbon (DOC) and in improving the fouling potential. A relative flux of unity through the PVDF2 membrane was achieved for both water sources pretreated with PSI, compared to 0.8 for pretreatment with aluminum-based coagulants. For the PP membrane, the PSI pretreatment of one water resulted in a relative flux of 0.7, compared to 0.20.3 for aluminium-based coagulants. However, for the other water there was no difference between the different pretreatment methods. The advantage of PSI is suggested to arise from a number of factors, i.e.: (i) better removal of the hydrophobic fractions; (ii) larger floc size and higher floc density leading to less unsettleable flocs and less pore plugging; and (iii) possible formation of an iron oxide protective layer that may be effectively removed by backwashing. This oxide layer is more likely to be present on the hydrophilic PVDF2 membrane than on the hydrophobic PP membrane. It may also minimise or eliminate the adverse effect of the recalcitrant NEU fraction.

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