Filtration of perchlorate from water using hexadecyltrimethylammonium (HDTMA)-modified montmorillonite
Cary, Mary Elizabeth
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Perchlorate (ClO4-) has been detected in the drinking water supplies of millions of people and is potentially hazardous to humans due to its passive interference with iodide uptake by the thyroid gland. Surfactant-modified montmorillonite (SMM) was evaluated as a cost-effective filtration media to treat perchlorate-contaminated waters. SMM has a high perchlorate sorption capacity and remains selective for perchlorate, even when applied to filter perchlorate from brines produced during the regeneration of ion-exchange resin. In parallel tests performed with surfactant-modified zeolite (SMZ), the SMM had a relatively higher perchlorate sorption capacity. The physical characteristics of SMM and SMZ determine their effectiveness as filtration media for perchlorate. The low hydraulic conductivity of SMM makes it best suited for use as a landfill liner or as filtration media in fluidized-bed reactors. SMZ is suitable for use in packed-bed reactors and permeable sorption barriers. Perchlorate transport was modeled through a 100cm long column with an inner diameter of 50cm. In a packed column filled with SMZ, with an average solution velocity of 10cm/hr and with a dispersion of 500cm2/hr, breakthrough would occur after 2.5yrs, and 4,388 pore volumes (431m3) of perchlorate-contaminated water would be treated. Meanwhile, in a column filled with SMM, with an average solution velocity of 1.008cm/d, and with a dispersion of 84cm2/d, perchlorate breakthrough would occur after 712yrs. Prior to breakthrough, 5,697 pore volumes (514m3) of solution would be treated. While filtration is widely accepted as a means to remove contaminants from water, this process merely transfers the contaminant from the solution to the solid phase. Unless treated, spent filtration media requires disposal as a hazardous waste. Biodegradation was successful at degrading perchlorate bound to the spent SMM. When water was added to the spent SMM containing 21,500mg ClO4-/kg, the resulting solution contained 12mg ClO4-/L. Throughout the treatment, SMM provided a constant source of perchlorate, due to continuous desorption. After 120 days of treatment, the solution concentration was <1.1mg ClO4-/L, a 94% reduction. The results of this study provide a cost-effective process for filtration of perchlorate from water and treatment of the spent SMM using biodegradation. Enhancement of the process is needed for pilot scale testing.