Abstract
The objective of this study was to investigate powdered activated carbon (PAC) contribution to natural organic matter (NOM) removal by a submerged MF and UF hybrid systems. It was found that filtration of surface waters by a bare MF and UF membranes removed negligible TOC; by contrast, significant amounts of TOC were removed when daily added PAC particles were predeposited on the membrane surfaces. These results support the assumption that the membranes surface properties and PAC layer structure might have considerably influential factor on NOM removal. Moreover, it was concluded that the dominant removal mechanism of hybrid membrane system is adsorption of NOM within PAC layer rather than size exclusion of NOM by both of membrane pores. Transmembrane pressure (TMP) increases with PAC membrane systems support the view that PAC adsorption pretreatment will not prevent the development of membrane pressure; on the contrary, PAC particles themselves caused membrane fouling by blocking the entrance of pores of MF and UF membranes. Although all three source waters have similar HPI content, it appears that the PAC interaction with the entrance of membrane pores was responsible for offsetting the NOM fractional effects on membrane fouling for these source waters.
Highlights
Natural organic matter (NOM) is composed of a heterogeneous mixture of humic substances, carboxylic acids, proteins, amino acids, hydrocarbons, and polysaccharides [1,2,3]
Since the MF membrane pore diameter (0.1 μm) is too large compared to molecular size of NOM present in three source waters (Table 1), the dominant removal mechanism of powdered activated carbon (PAC)/MF hybrid system is adsorption of organic matter within PAC layer rather
These findings indicate that the PAC particles accumulated onto the MF membrane pores at short time and this resulted in more NOM related compounds removal
Summary
Natural organic matter (NOM) is composed of a heterogeneous mixture of humic substances, carboxylic acids, proteins, amino acids, hydrocarbons, and polysaccharides [1,2,3]. Because of the complex nature of NOM, surrogate parameters of total organic carbon (TOC), ultraviolet absorbance at 254 nm (UV254), and specific UV254 (SUVA254) are often used to represent its general properties. The physical and chemical nature of NOM varies according to the water source, age, and season [4]. Effective removal of NOM has been a challenge for water utilities. Previous studies regarding the membrane filtration of surface waters have identified NOM as one of the major foulants in the membrane process [6,7,8]. Effective removal of NOM by MF and UF process may not be sufficient when they are solely used. To improve the membrane performance level, various hybrid membrane systems have been developed, such as coagulation-UF/MF, powdered activated carbon-UF (PAC-UF), and iron oxide adsorption-UF [8,9,10,11,12,13,14]
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