Hollow-fiber-supported liquid membranes with improved stability for nitrate removal

This paper describes the development of a hollow-fiber-supported liquid membrane (HFSLM) for the removal of nitrate ions from water. Two different membrane modules were designed which differed in length of the fibers. In order to test the HFSLMs on nitrate flux and stability, two set-ups were used: one in which feed and strip were recirculated, and one for the continuous removal of nitrate. Furthermore, part of the experiments were carried out using fibers with a toplayer of piperazine and trimesoyl chloride at the lumen side to increase the stability of the HFSLM. Nitrate fluxes of the HFSLMs were only slightly lower than those of flat-sheet SLMS despite the much larger thickness of the fiber wall. In both set-ups, the nitrate flux decreased in time. By applying a toplayer on the lumen side of the fibers, the lifetime of the liquid membrane was raised. SEM observations showed the toplayer, although defect-free, to be nonuniform in morphology, which resulted in difficulties in the reproducibility of the results.