Silane-grafted sand membrane for the treatment of oily wastewater via air gap membrane distillation: Study of the efficiency in comparison with microfiltration and ultrafiltration ceramic membranes

The surface of the sand microfiltration membrane, with average pore diameter of 0.9 mu m, was chemically modified to change its hydrophilic character into hydrophobic by grafting with 1H,1H,2H,2H-perfluorodecyltriethoxysilane molecule (C-8). Various characterization methods and techniques, including infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), nitrogen adsorption/desorption isotherm (BET) and contact angle were used to check the properties of the membranes before and after grafting. Results obtained with FTIR and TGA analysis show the presence of grafted silane groups. Observation from SEM images and BET isotherms reveals a decrease in the pore size of the grafted membrane. The contact angle of the modified membrane surface indicates the enhancement of the hydrophobicity since it shows an increase from 0 degrees before grafting to 117 degrees after grafting. Furthermore, water permeability decreased from 1256 to 434 L h(-1)m(-2).bar(-1) after surface modification. The hydrophobic membrane was applied in air-gap membrane distillation processes (AGMD) for the treatment of oily wastewater at transmembrane pressure of 1 bar and a temperature of 85 degrees C. The results were compared to that obtained with microfiltration (MF) and ultrafiltration (UF) processes at a temperature of 60 degrees C and a transmembrane pressure of 1 and 3 bar using two hydrophilic ceramic membranes: zeolite microfiltration membrane (MFZ) and titania-smectite nanocomposites ultrafiltration membrane (UFTiSm). Almost total oil retention and a stabilized permeate flux maintained at interesting values between 100 and 150 L/h.m(2) were observed.

Automated summary

Chemical modification of the sand microfiltration membrane resulted in a decrease in pore size, an increase in contact angle, enhanced hydrophobicity, and reduced water permeability. In experiments treating oily wastewater, the hydrophobic membrane outperformed hydrophilic ceramic membranes, showing stable and efficient performance.