International audienceTangential streaming current measurements were performed to investigate the surface charge properties and the charge formation mechanism of various NF/RO membranes. Unlike what is usually done in electrokinetic studies of membranes, experiments were conducted with degassed background solutions under a controlled atmosphere by means of nitrogen gas in order to get accurate electrokinetic measurements even in the basic range of pH. It was demonstrated that the streaming current technique implemented with these rigorous experimental conditions is a reliable tool to verify the presence of an additional coating on a commercial TFC membrane. It was also shown that these electrokinetic measurements allow a more clear discrimination between coated and uncoated membranes than the ATR-FTIR technique. Moreover, experiments performed with and without a nitrogen environment revealed specific adsorption of bicarbonate and carbonate ions coming from the dissolution of carbon dioxide in the air onto the surface of RO polyamide membranes containing hexafluoroalcohol functional groups
In this study, nineteen different brands of bottled mineral waters (7 brands local and 12 brands imported) were collected from supermarkets and independent food stores throughout Djibouti. The chemical composition mentioned on the labels of the nineteen bottled mineral waters has made the subject of a first verification by Ionic Balance Error (IBE). It was found out of the nineteen brands selected, 12 brands (2 brands local and 10 brands imported) had acceptable charge balance error. Correlation Analysis (CA), Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA) were used to analyze the data collected from the labels of bottled water. The obtained results showed that the 12 brands of studied waters can be grouped in 4 distinct classes with similar chemical characteristics. Two local and one imported brands have the same chemical composition but marketed under different names. It was observed that the chemical content local water brands were within the normal range prescribed by both WHO and USEPA except five imported water brands that have concentration values Ca, HCO 3 , Mg and SO 4 beyond acceptable standards. Total hardness values classified most of the studied brands from moderate to very hard water.
International audienceIn this study, hexafluoroalcohol-containing polyamide layer (HFAPA) was prepared on top of a conventional polyamide under-layer (REFPA) via sequential interfacial polymerization (SIP) to improve RO separation behavior, and the performance of the resulting bilayer membrane was thoroughly optimized by investigating the effect of cross-contamination in the SIP process. When several coupons of the polyamide bilayer membrane were prepared by SIP of MPD(aq), TMC(hx) and hexafluoroalcohol-containing diamine (HFAMDA)(aq) in the manner of subsequent membrane dipping, unreacted MPD monomer (mostly captured in the porous PSF support) carried over from the 1st interfacial reaction dissolved and accumulated in the 2nd aqueous solution as verified by UV spectroscopic analysis. The MPD contaminant then participated in the 2nd interfacial reaction, forming copolyamide with HFAMDA monomer onto the REFPA. Depending on the amount of MPD contaminant accumulated in the 2nd aqueous solution, the composition of the resulting co-polyamide in the top-layer varied, causing a significant variation of RO performance; the flux was gradually decreased with the increase of MPD contaminants while the salt rejection slightly increased (from 1st coupon toward 4th coupon). This result indicated that a trace amount of MPD contaminant may be necessary to maximize RO separation behavior. Through in-depth performance evaluation of polyamide bilayer membranes prepared by adding various known-amount of MPD into 2nd HFAMDA solution, and also by applying a frame process (2nd amine solution was applied only top surface of membrane) to eliminate uncontrollable MPD contamination, we have successfully demonstrated consistent RO performance, and identified an optimum material composition to provide superior separation performance. The bilayer membrane prepared by adding 1.2 mol% of MPD to the total amount of HFAMDA in the 2nd aqueous solution showed 99.8% NaCl rejection with the water flux of 45 LMH under the cross-flow filtration performed with 2000 ppm NaCl solution at 400 psi, 25 °C
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