Critical Assessment of the Nanofiltration for Reusing Brackish Effluent from an Anaerobic Membrane Bioreactor

摘要

In this study, a saline effluent from an anaerobic membrane bioreactor was treated by nanofiltration in order to allow its agricultural reuse. Short-term tests were conducted to investigate membrane fouling and selective rejection of ions and emerging organic contaminants (EOCs). The study has been conducted with a negatively charged commercial thin-film composite membrane (DK, GE Osmonics). The effect of operating pressure (5-20 bar) and cross-flow velocity (0.12-0.37 m/s) on membrane performance have been researched. Dimensional analysis of steady permeate flux indicated that the gel layer or the polarization layer can be completely removed at critical cross-flow velocity. At a sub-critical velocity, membrane autopsies by scanning electron microscopy (SEM) and energy dispersive X-Ray spectroscopy revealed a complex mixture of organic matter, phosphates and colloidal silica over the membranes surface. Since the rejection of monovalent cations (76-88%) was lower than that of multivalent cations (above 96%), the treated effluent was characterized by a very high levels of sodium adsorption ratio and ammonium. In addition, moderate rejection of low molecular weight EOCs (clofibric acid and caffeine) was observed. Therefore, the treated effluent did not achieve enough quality to be reused for agricultural irrigation. During the last decade, interest in the application of nanofiltration in wastewater treatment has grown in response to stringent water quality standards and increasing concern about the presence of emerging organic contaminants (EOCs). Nevertheless, information remains scarce about membrane fouling and EOCs rejection. The current research addresses these issues during its application to a brackish effluent from an anaerobic membrane bioreactor to be reused for agricultural irrigation. Dimensional analysis has allowed establishing the optimum operation conditions in terms fouling control. As regard of EOCs rejection, low molecular weight compounds were not completely retained by the membrane.