| Forward osmosis (FO) is an emerging water treatment technology, which possesses the advantages of low energy consumption, high water recovery and fouling resistance. These advantages bring FO a broad application prospect in the fields of wastewater treatment, desalination and so on. However, the efficiency of the filtration is seriously restricted by the phenomenon of concentration polarization (CP). As a kind of CP, external concentration polarization (ECP) usually can be mitigated by improving the hydrodynamic conditions. In this study, the corrugated wall channel was used to the design of FO module. The simple special structure could induce vortex in the channel and enhance the wall shear stress on the membrane surface, then ECP would be mitigated. In this study, experiments and computational fluid dynamics (CFD) simulation were adopt to study the performance and mechanism of the novel module in mitigating ECP.With a traditional flat membrane module (FMM) as control, this study evaluated the role of the corrugated membrane module (CMM) in mitigating ECP, by a series of experiments. The result showed that CMM could mitigate ECP and then enhance water flux. NaCl solution (2 M) was used as draw solution (DS). When deionized water was taken as feed solution (FS), based on FMM, CMM could enhance water flux by 17.45% and 18.55% in FO mode(active layer facing FS) and PRO mode(active layer facing DS), respectively. When NaCl solution (0.5 M) was taken as FS, the corresponding value were 15.97% and 17.12%. Meanwhile the selectivity of membrane was unchanged. The specific shape of CMM affected its performance in mitigating ECP. The CMM with greater wave angle and smaller wavelength, exhibited higher water flux. Reynolds number (Re) also affected the performance of CMM. When Re <800, a greater Re meant higher water flux and greater water flux enhancement. When Re>800, water flux increased while water flux enhancement decreased slightly as Re increased. CMM was evaluated with feed solutions (FS) and draw solution (DS) of various concentration. When the FS concentration was lower or the DS concentration was higher, water flux and water flux enhancement were greater. CMM couldn’t efficiently mitigate internal concentration polarization (ICP). The CMM enhanced the water flux when membrane fouling coexisted with CP. In addition, the CMM could lessen membrane fouling.The computational fluid dynamics software, Fluent, was adopted to analyze the flow pattern in the membrane channel. The results showed that the flow in FMM channel was relatively stable, and no vortex was observed. The CMM could contribute to the generation and development of the vortex, which would promote the mixing of solution in the channel and enhance the wall shear stress on membrane surface. CMM improved hydraulic conditions and then enhanced water flux. The specific shape of CMM affected the flow pattern in the channel. Smaller wavelength and larger wave angle helped to induce vortex and stronger wall shear stress. Re also affected the intensity of vortex in CMM; greater Re meant greater vortex, wall shear stress and wall shear stress enhancement. |
