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

Abstract

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 spectroscopy (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°). A narrow pore size distribution (∼0.43 μm), raised liquid entry pressure (∼1.3 bar), porosity (∼75 %), high surface roughness (1.06 μm), and low surface energy (∼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.