ANALYSIS OF ULPRO MEMBRANE FOULING USED FOR GROUNDWATER DEFLUORIDATION
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An ultra low pressure reverse osmosis (ULPRO) membrane process was applied to defluoridate groundwaters obtained in the Chiang Mai Basin, Thailand. The permeate water contained less than the Thai standard of 0.7 mg/L for drinking water. Although the fluoride rejection rates were high between 94.4-98.4% with all the groundwater samples, the rates went up or down during the course of filtration depending on the groundwater quality. ART-FTIR, in conjunction with saturation index, identified the foulants as Si0<SUB>2</SUB> and CaCO<SUB>3</SUB>. The fluoride transport models were presented and verified using NaF solutions. The mass-transfer coefficient of fluoride (k) in water was estimated as 3.20 × 10<SUB>-5</SUB> m/s, and the solute mass-transfer coefficient (k<SUB>i</SUB>) of fluoride through UTC-70U membrane as 1.06× 10-7m/s. Subsequently, the fluoride transport models and the mass-transfer coefficients were used to estimate fluoride concentrations at the gel-layer surface (C<SUB>G</SUB>) and at the membrane surface (C<SUB>M</SUB>). Using these values and the fluoride concentration in the bulk solution (C<SUB>B</SUB>), the changes of the ratios of CA, i/CG and C<SUB>M</SUB>/C<SUB>B</SUB> were calculated to estimate the causes of increase and decrease of fluoride rejection rates during the course of filtration experiments.
- ENVIRONMENTAL ENGINEERING RESEARCH
ENVIRONMENTAL ENGINEERING RESEARCH (45), 613-620, 2008
Japan Society of Civil Engineers