Enhanced oxidation of polyamide membranes using monochloramine and ferrous iron

Reverse osmosis testing using monochloramine (NH2Cl) and free chlorine (HOCl) in the presence of ferrous iron [Fe(II)] resulted in accelerated chlorination of polyamide membranes. Similar effects were not observed when using ferric iron. Membrane damage was detected through irreversible increases in salt passage and the presence of chloride on the membrane surface using energy-dispersive spectroscopy. A mechanistic study suggested that the formation of an amidogen radical (NH2) during NH2Cl decomposition with Fe(II) led to the reduction of the activation energy for the chlorination reaction to proceed using NH2Cl. Enhanced oxidation using HOCl and Fe(II) may have resulted from the formation of OH radicals, which also lowered the chlorination-activation energy. Both pH suppression (from 8.0 to 6.0) and dechlorination (7.0 mg/L sodium sulfite) successfully halted the chlorination reaction.