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−.
The use of bottled water is increasing every day even after the reported presence of microbial and other contaminants. The present study analyzed bromate in bottled water samples collected from four major cities in Kerala, India. It was found that about 40% of the samples contain bromate with a maximum concentration of 9.68 μg/L with an average of 1.56 μg/L. The study also includes the development of a multilayer membrane for the removal of bromate from water. Bilayers of quaternary chitosan salt (QCS)/sodium polystyrene sulfonate (PSS) were deposited on polyethersulfone (PES) microfiltration membrane and which are employed for bromate removal studies. Deposition of six bilayers of QCS/PSS increased the rejection efficiency from ∼4% to ∼84%. The influence of different fabrication and feed parameters on bromate removal efficiency was also studied. Six bilayers of QCS/PSS deposited at pH 2 with 0.5 M NaCl were found to be effective in removing > 90% of bromate from marketed bottled water samples with low energy expense. This study is recommended to implement such a multilayer system as a polishing step in the final stage of water purification in bottling plants to avoid possible contamination and toxicity of bromate in bottled water users.
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