Electrical impedance spectroscopy for non-destructive detection of wetting, fouling and scaling in membrane distillation

Wetting, fouling, and scaling of hydrophobic membranes are significant constraints in membrane distillation (MD) technology. In recent research trends, novel membrane fabrication has been given utmost priority to address these constraints, majorly induced by the low surface tension chemicals like surfactants and dissolved organic matters present in the feed water. In this research, we fabricated a hydrophobic membrane using phase inversion technique with polyvinylidene fluoride (PVDF) polymer under an alcohol coagulation bath (ethanol). The wetting, fouling, and scaling of the membrane were monitored using electrochemical impedance spectros-copy (EIS) incorporated with direct contact membrane distillation (DCMD). The surface tension (52.14-27.5 mN m(-1)) of the synthetic brine water was reduced by adding surfactant, whereas model algal organic matters were dissolved to study the organic fouling. In the fabricated PVDF membrane, an asymmetric interconnected pore structure was obtained with a high hydrophobicity (water contact angle 146 degrees). A narrow pore size distribution (similar to 0.43 mu m), raised liquid entry pressure (similar to 1.3 bar), porosity (similar to 75 %), high surface roughness (1.06 mu m), and low surface energy (similar to 28 mN m(-1)) were noticed with the same membrane. Hence, it qualified for DCMD application under different feed compositions. Different stages of pore wetting and their progress were assessed instantaneously by adopting EIS approach. Further, the permeate side conductivity was correlated with impedance measured during EIS. Advanced proficiency in distinguishing intrusion and different stages of wetting was illustrated.