The 5th Maghreb Conference on Desalination and Water Treatment 2015 Optimization of process parameters for the removal of fluoride by membrane distillation using response surface methodology approach Ali Boubakri a,*, Raja Bouchrit a, Amor Hafiane a , Salah Al Tahar Bouguecha b a Laboratory of Water and Membrane Technologies, Center of Researches and Water Technologies, P.B 273, 8020 Soliman, Tunisia. b Department of Mechanical Engineering, Faculty of Engineer, King Abdul-Aziz University, P.B: 80204 Jeddah 21589, Kingdom of Saudi Arabia. Abstract Regression model for flux The obtained model equation, in terms of uncoded variables, which determine the relation between permeate flux and all independent variables and their interactions. The removal of fluoride using membrane distillation process was investigated. The effect of various operating parameters such as temperature, feed and permeate flow rate and fluoride concentration was optimized by response surface methodology. The second-order regression models have been tested by the analysis of variance (ANOVA). ΔT was considered to be the most important parameters. The optimum conditions included a ΔT of 46.82°C, Qf of 30 L/h, Qp of 4.9 L/h and an [F-] of 75.2 mg/L. All experimental results proved that MD is able to produce water with very low fluoride content (removal rate more than 99.8%).   R2 = 97.90% Good agreement between Experimental and predicted data Contour plot for flux Materials and methods The permeate flux Jp (L.m-2.h-1) was calculated by :   Fluoride removal Fig. 1: DCMD setup - (1) Permeate tank; (2) Cooling element (3) peristaltic pumps; (4) thermocouples; (5) conductimeter; (6) flat sheet module; (7) Feed tank; (8) Heating element. The fluoride rejection rate (%) was calculated by : Using membrane distillation process, PVDF membrane can achieved a very high fluoride rejection above 99.42% else at high initial concentration with 147 mg/L. The fluoride removal cannot be modelled as function of studied operating parameters.   Table 1: Operating parameters used for experimental design Factors Symbol Actual value of coded levels -α -1 +1 +α ΔT (°C) X1 13.18 20 30 40 46.82 Qf (L/h) X2 4.88 10 17.5 25 30.11 Qp (L/h) [F-] (mg/L) X3 12.72 80 120 147.28 Conclusion Membrane characterization revealed that PVDF membrane can be suitable for used for membrane distillation process. Temperature difference has the highest influence on DCMD flux. At high ΔT of 46.82°C, a maximum permeate flux of 15.25 L.m-2.h-1 was obtained. In the studied range of feed fluoride concentration, the obtained permeate concentration was largely below 1.5 mg/L Based on desirability function in RSM, and under optimum condition, the maximum permeate flux of 17.23 L.m-2.h-1 was obtained. For all experimental runs, it was obtained that fluoride removal exceed 99.42% even at high feed fluoride concentration. Results and discussion PVDF membrane characterization * Corresponding authors: Ali Boubakri Phone number: +216 99 155 999 E-mail: ali.boubakri@certe.rnrt.tn Fig. 2: AFM, CA, and DSC membrane characterization