Abstract
In this study, the performance of a forward osmosis system was assessed over a 30-h period during desalination of a local oil refinery effluent using NaCl as the draw solute. The study was conducted with the active layer of the membrane facing the draw solution. Assessment was done based on the water flux, salt rejection (SO42− and CO32−), membrane fouling and fouling reversal after membrane cleaning. Critical to this study was the performance of manual scrubbing of the membrane after each run and the application of chemically enhanced osmotic backwash. Scanning electron microscope (SEM) analysis of the cellulose triacetate (CTA) membrane was conducted before and after cleaning to ascertain the degree of fouling and fouling reversal after membrane cleaning. The results showed an average water flux of 3.78 ± 0.13 L/m2 h, reverse solute flux (RSF) of 1.56 ± 0.11 g/m2·h, SO42− rejection of 100%, CO32− rejection of 95.66 ± 0.32% and flux recovery of 95% after membrane cleaning. This study identifies that intermittent manual scrubbing of the membrane plays a major role in overall membrane performance. It also provides a practical basis for further research and decision making in the use of FO and CTA membranes for oil refinery effluent desalination.
Highlights
In a study conducted by Honda, et al [30], using a cellulose triacetate (CTA) membrane, it was established that the PRO mode of forward osmosis (FO) operation is characterised by high initial water fluxes and rapid flux declines
The study was conducted with the active layer of the membrane facing the draw solution (PRO mode) using a CTA membrane sourced from Fluid Technology Solutions, OR, USA
Water Flux and Water Flux Decline driven by the DS concentration
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The authors observed that while nearly 70% of the membrane surface was covered by the latex particles during the PRO mode, coverage in the FO mode was nearly zero This was attributed to the smooth nature of the active layer and the low flux levels. In a study conducted by Honda, et al [30], using a CTA membrane, it was established that the PRO mode of FO operation is characterised by high initial water fluxes and rapid flux declines. This was attributed to the surface characteristics of the support layer, in terms of surface roughness and loose pores. The possibility of obtaining high fluxes in the PRO mode and maintaining the fluxes while achieving excellent salt rejection efficiencies is high and gives room for exploration
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