Modification of bi-composite membrane support layer by macro puncture for membrane distillation application

• Modifications of support layer were conducted using a commercial PTFE/PP bi-composite membrane. • Macro punctures of support layer were designed based on the porosity of the support layer. • Porosity of support layer and sizes of macro punctures affected the fluxes of the modified membranes. • The orientation, type and porosity of support layer should be considered to guarantee its tensile strength. • The flux of the modified membrane was affected by the enhanced turbulence produced by the support layer.

The effects of support layer modifications were investigated by creating patterns of macro punctures in the support layer of commercial flat sheet type bi-composite membranes, using a cut-off method. The membrane flux increased when the porosity and the size of the macro punctures were higher than 60% and 25 mm2, respectively. Feasible ranges for the sizes and locations of macro punctures and the porosity 4.6. Integrity and longevity test For the membrane integrity test, the 0.75 M NaCl solution was used for the feed solution. The I60 membrane was installed in the DCMD module and DCMD test was conducted for 130 min under the given experimental conditions (Tf & Tp = 62 °C and 20 °C, Ff & Fp = 0.7 L/min (0.15 m/s) and 0.5 L/min (0.1 m/s)). As shown in Fig. 10(a), the flux was about 49 LMH and maintained constantly during the experiment. The electronic conductivities of the feed and permeate were continuously increasing and decreasing due to the concentration of the feed solution and dilution of the permeate solution, respectively (Fig. 10(b)). According to this result, we could assume that the detached active layer was not significantly damaged during the detachment work. To evaluate the potential application of the modified membranes to wastewater reuse, the secondary effluent of a wastewater treatment plant (WWTP) was applied as the feed water of the MD system. The Table 7 Flux variations according to the velocities of the feed and the permeate and the support layer. Flux (LMH, L/m2h) Q (L/min) Feed/Permeate Pristine I60 K60 Maximum Minimum Average Standard deviation 1.6/1.2 1.6/1.5 1.6/1.2 1.6/1.0 1.2/1.2 1.2/0.8 1.2/0.8 68.4 82.6 102.0 96.5 76.6 70.6 82.1 67.6 – 78.7 75.5 72.5 – 76.3 68.0 82.6 86.8 88.1 74.5 70.6 79.2 0.6 – 13.2 9.6 2.9 – 4.1 Fig. 10. Variations of flux and permeate conductivity (Feed: 0.75 M NaCl solution, temperatures of the feed and the permeate: 62 °C and 20 °C, cross-flow velocities of the feed and permeate: 0.15 m/s and 0.1 m/s).