Abstract
Environmental contextPerchlorate from rocket fuel plants or firework manufacturing units can seriously contaminate drinking water. We developed a separation skin on a microfiltration membrane and on sand that can remove perchlorate from water in the presence of competing ions. This method is suitable for a domestic water purification unit selective for perchlorate removal. AbstractThis study reports an interactive separation of perchlorate (ClO4−) by polyethyleneimine (PEI) and poly (styrene sulfonate) (PSS) deposited on a microfiltration membrane and on sand surfaces. The variation of the interaction with respect to deposition and feed variables was assessed. The 9 bilayered ((PEI/PSS) 0.15M NaCl, pH 6)) membranes showed a ClO4− rejection of ~80%. An increase in the feed concentration to 25mgL−1 reduced the rejection to 58%. With a feed pH from 4 to 10, the rejection varied between almost 100% and 16%. The presence of ions reduced the rejection percentage of ClO4− with the interference by the ions in the order of SO42−>HCO3−>NO3−>Cl−. The interference is attributed to the characteristics of the competing ions and the nature of the multilayers. A positive impact of post-treatment (98%) and capping layers on rejection percentage (80% to nearly complete) for synthetic and ClO4− contaminated field water samples is clearly established. The presence of competing ions is also accounted for by a capped membrane system. The selectivity of the competing ions increases with capping layers of 1M NaCl in the order of HCO3−>NO3−>SO42−. In the field water samples up to a SO42− concentration of 3.0mgL−1, the capping layers with 0.4M NaCl result in a near complete rejection of ClO4−, whereas further enhancement requires a capping layer of 1M NaCl. A sand filtration system was developed by incorporating the pre-optimised polyelectrolyte multilayer on sand. Deposition of a single bilayered PEI/PSS multilayer on sand effectively (nearly completely) removes ClO4−.
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