Energy Analysis of Electrofiltration in a Homogeneous Macroporous α-Al2O3 Membrane

Abstract

Membrane filtration offers high-quality permeate at the cost of energy-intensive mechanical pumping. Electrofiltration, or electric field-assisted water permeation, has shown promise in reducing energy expenses, eliminating mechanical components, and providing instantaneous flow reversal for membrane defouling. However, fundamental analysis of the energy consumption, energy efficiency, defined as the specific energy consumption, SEC, and standardized nomenclature hinders development. Using a sintered random loose packing of monodisperse α-Al₂O₃ spheres to create a well-defined geometry, microstructure, and composition, we investigated electroosmotic flow through the membrane to evaluate the SEC of components within an electrofiltration membrane. At minimal transmembrane pressure and compared to no electric field, application of an electrical potential, ΔΦ, of 10 V (pressure difference of 1.2 kPa, pH 3.8, and 22 °C) increased the membrane flux 15-fold from the initial 2–31 LMH. The observed energy consumption with the well-defined physical membrane properties and net electroosmotic flow (EOF) of 29 LMH resulted in SEC_EOF = 0.31 kWh/m³. A fundamental determination of the theoretical minimum SEC, SEC_EOF^min, is estimated to be 0.006 kWh/m³. While the SEC_EOF determined is efficient for traditional membrane filtration and literature reported SEC_EOF, the SEC_EOF in this study is ascribed almost entirely to electrode losses and ionic transport resistance. These energy losses indicate significant opportunities to improve energy efficiency of electric field-assisted filtrations. This quantitative evaluation identifies electrofiltration performance and reasons for energy loss within an EOF system, which may be further studied to improve the energy efficiency of electric field-assisted filtration.