Verification of NOM removal in MIEX-NF system for advanced water treatment

An experimental study was conducted to verify NOM removal in a combined MIEX-NF process for advanced water treatment. A fluidized bed type magnetic ion exchange (MIEX) column was used as a pretreatment process of the Nano-filtration (NF) membranes. Instrumental analysis was conducted to identify the composition of NOM in the raw water taken from Nakdong River in Korea, MIEX treated water and the membrane permeates. Two NF membranes, hydrophilic (NE70) and hydrophobic (NE90), were used to investigate rejection of NOM compounds and filtration characteristics. The raw water contains low MW NOM with the hydrophilic compounds of hydrocarbon (carboxylic, phenolic, and aliphatic), amino sugar, and N-compounds (Protein). MIEX could significantly remove NOM compounds having low SUVA value, which were phenolic compounds, aliphatic hydrocarbon and amino sugars, while it showed low efficiency for removing carboxylic compounds. The analysis of organic fraction in the membrane permeates showed that the major NOM compounds of raw water filtration were carboxylic and phenolic compounds, while the pretreated water filtration exhibited low phenolic compounds. Protein, polysaccharide and amino sugars were completely retained by the two membranes. However polyhydroxy aromatic (PHA) and lignin were still detected in the permeate of both membranes with MIEX pretreatment. Fatty acid was also found in the permeate of the two membranes without pretreatment. Better performance in terms of removal efficiency was found from NE90 having MIEX pretreatment. However, NE70 exhibited lower flux decline than NE90 due to its high zeta potential and low roughness. Ionic compounds strongly influenced the less flux decline of NE70 due to its hydrophilicity and charge effect. Severe initial flux decline of NE90 was caused by adsorption of nonionic hydrophobic compounds on the membrane surface and the diffusion of adsorbed compounds through the membrane resulted in a slower flux decline after a 1 h operation.

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► We examine organic fraction of river water, MIEX treated water and NF permeate.
► Nakdong River water contains low MW NOM with the hydrophilic compounds, amino sugar and protein.
► MIEX could remove low SUVA NOM, which is phenolic, aliphatic hydrocarbon and amino sugar.
► Protein, polysaccharide and amino sugar were completely retained by the two membranes.
► NE90 showed better removal efficiency. NE70 showed better flux characteristic due to its properties.