Direct contact membrane distillation applied to saline wastewater: parameters optimization Sana Abdelkader, Ali Boubakri, Sven Uwe Geissen and Latifa Bousselmi ABSTRACT Freshwater availability is suffering from an increasing pressure created by the growing demand, depleting resources and the environmental pollution. Desalination of saline wastewater is a possibility to supply households, industry and agriculture with water. However, technologies applied such as reverse osmosis, evaporation or electro dialysis are energy intensive. Membrane Distillation (MD) is a competitive technology for water desalination. In our study, Response Surface Methodology is applied to optimize the Direct Contact Membrane Distillation (DCMD) treatment of synthetic saline wastewater. The aim was to enhance the process performance and the permeate flux Jp (L/m 2 ·h) by optimizing the operating parameters: temperature difference ΔT, feed velocity Vf, salt concentration [NaCl], and glucose concentration [Gluc]. DCMD process has led to a remarkable high permeate quality with 99.9% electrical conductivity reduction and more than 99.9% COD removal rate. The predicted optimum permeate flux Jp is 34.1 L/m 2 ·h that was reached at ΔT ¼ 55.2  C and with a feed velocity Vf ¼ 0.086 m/s as the two most influencing parameters. The created model has shown a high degree of correlation between the experimental and the predicted responses with high statistical significance. Sana Abdelkader Ali Boubakri Latifa Bousselmi (corresponding author) Centre for Water Research and Technologies (CERTE), Technopark of Borj Cedria, P.B. 273, 8020 Soliman, Tunisia E-mail: latifa.bousselmi@certe.rnrt.tn Sana Abdelkader Sven Uwe Geissen Technische Universitaet Berlin (TU Berlin), Sekr. KF 2, Straße des 17. Juni 135, 10623 Berlin, Germany Key words | Desalination, direct contact membrane distillation, feed velocity, response surface methodology, temperature difference, wastewater INTRODUCTION The increasing domestic and industrial demand for clean and fresh water is creating an ever-growing pressure on the global security since water has numerous interlinkages with all the aspects in our life in terms of economic develop- ment, energetic demand, environmental security and industrial growth which is getting even more critical with the actual witnessed climate change (U.N. report ). Water desalination and more precisely wastewater treat- ment and desalination could provide an interesting alternative to partially overcome the need for more water resources by reusing the treated discharged effluents and integrate them in the industrial or domestic water cycles via multiple desalination technologies such as Membrane Distillation (MD). MD is offering the possibility to produce high quality permeates with important water recovery rates through lower energy consumption in comparison to the conventional and well established desalination pro- cesses such as reverse osmosis, multiple effect distillation, etc. (Miller ; Samblebe ). Based on its high separation performance, MD is being investigated and applied for water, and in some cases, nutrients recovery from various types of effluents, taking into consideration the effect of the experimental par- ameters (Izquierdo-Gil et al. ; Jia et al. ). Additionally to high salt rejection rates, MD is character- ized by good rejection rates of non-volatile and low adsorptive organic compounds (Carnevale et al. ; Plattner et al. ). The enhancement of MD process has drawn attention to the improvement of the membrane hydrophobicity using multiple techniques such as the utiliz- ation of hydrophobic surface modifying macromolecules on poly(vinylidene fluoride) hydrophobic composite mem- branes which has led to promising results in sea water MD treatment (Prince et al. a). Moreover, multiple studies have focused on the enhancement of the driving force for the water vapor transport in MD process through the development of hydrophobic membranes that have high resistance to pore wetting which did lead to 1 © IWA Publishing 2018 Water Science & Technology | in press | 2018 doi: 10.2166/wst.2018.274 Uncorrected Proof