Effect of backwashing process on the performance of an interlayer-free silica–pectin membrane applied to wetland saline water pervaporation

Abstract

This article describes a study that shows the effect that backwashing has on the performance of an interlayer-free silica–pectin membrane. The research described was carried out to investigate an interlayer-free silica–pectin membrane, applied to wetland saline water, under backwashing mode, using air-sparging. Wetland saline water has a high salinity – it contains 232 568 ppm of salt (measured salinity equivalent to 10% NaCl), a conductivity of 150–190 mS.cm-1 and total dissolved solids of 75–92.5 g.L-1. The work involved testing a membrane using pervaporation, which was applied to wetland saline water desalination over a period of seven months at room temperature (~25 ± 0.5°C). A common flux drop occurred due to the salt and natural organic matter contained in the water. Furthermore, the backwashing process employed air that was injected into the membrane for 20 minutes in order to reduce the formation of the cake layer of membrane fouling. In addition, the pervaporation process using wetland saline water heated to 40°C was used to “fight” internal fouling, and was also followed three times by pervaporation at room temperature (~25 ± 0.5°C). The results show that water flux and salt rejection, which fluctuated under the same conditions, reached 0.400 kg.m-2.s-1 and up to 99.99%, respectively. This indicates that the flux after backwashing was 10 times greater than before the backwashing process. Also, the salt concentration decreased to 230.18 ppm, whilst minerals dissolved in the water dropped to 10.6342 ppm and UV254 rejection increased to 31.63% – showing that the benefit of the backwashing process increases membrane performance.