Removal of Iron and Manganese by UF in Combination with Prechlorination in Drinking Water Treatment

摘要

Removal of iron and manganese from lake water using different UF systems in conjunction with an in-line prechlorination step was investigated at various iron and manganese levels and chlorine dosages. For feedwater containing 1.0 mg/L as Fe and/or 0.5 mg/L as Mn, substantial iron removal was achieved even without chlorine addition due to the oxidation of ferrous iron to ferric one by dissolved oxygen and consequent formation of less sparingly soluble iron hydroxide particles. Negligible manganese removal occurred in the absence of chlorine, but with a dose of chlorine manganese removal efficiency increased markedly and reached more than 80% (corresponding to less than 0.1 mg/L Mn) at a chlorine dosage of 3 mg/L as Cl_2. With a higher dosage of chlorine (e.g., 5 mg/L Cl_2), further removal of the metal ions was not that significant but more serious membrane fouling took place. This phenomenon was in close association with the kinetics of oxidation of the manganese and its oxidized particles’ deposition inside the pores during backwashing, rather than its accumulation on top of the membrane skin layer. Turbidity and natural organic matter (NOM) removal efficiencies were enhanced with chlorine addition in the presence of iron and manganese because the metal oxides created by chlorination could serve as adsorbents.