Novel geopolymeric support for microfiltration membranes applied in wastewater treatment

Microfiltration membranes are widely used in wastewater treatment and are typically made of ceramic or polymer materials. Despite the great durability of ceramic membranes, polymeric membranes are very often preferred due to production costs. By using geopolymers, however, it is possible to obtain microfiltration membranes with durability characteristics similar to those of ceramic materials, but with considerably reduced production costs since geopolymers do not require a sintering treatment. In this study, a geopolymer support for asymmetric microfiltration membranes is characterized in terms of porosity and hydraulic permeability. The support was obtained by uniaxially pressing a dry mixed powder consisting of metakaolin and anhydrous sodium silicate, sprayed with 12 wt% of water. Curing was carried out at 70 °C for 24 hours and 6 more days at room temperature. The porosity of samples pressed using 2 MPa (total open porosity of 39 % and a modal pore size of 23 μm) are comparable to those of ceramic membranes for microfiltration [1]. The support permeability was measured in a dead-end apparatus at a trans-membrane pressure varying from 0.2 to 0.5 bar, with pure water and ethanol-water solutions. Hydraulic permeability of 30500 ± 3090 L/(h·m2·bar) was obtained with 4 samples, whereas the use of 100 and 200 g/L ethanol-water solutions showed a reduction in permeability to 26140 ± 2640 and 20820 ± 1430 L/(h·m2·bar) respectively. Further tests performed on less porous samples obtained by pressing the powder at 5 MPa (total open porosity and modal pore size of 27% and 15 μm, respectively) led to similar results. These initial characterizations highlight the potential of this new material in the treatment of wastewater by membrane separation. Future studies are ongoing to develop geopolymer selectives layer by dip coating to be applied on geopolymer supports.