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<p>Abstract</p><p>As natural resource scarcity and industrial productivity continue
to rise, membrane filtration technologies provide a compelling solution for the production
of clean water. Membranes are versatile, energy-efficient, and highly effective, yet
they suffer from the indomitable problem of fouling. Abundant research has been conducted
on this topic, but new methods for understanding and assessing fouling are still emerging,
and are nevertheless needed. The present work endeavors to study membrane fouling
from yet another perspective using a powerful electrochemical technique known as electrochemical
impedance spectroscopy (EIS). EIS is a non-destructive electrical perturbative method,
thus it can be performed during filtration. While some research groups have applied
EIS for membrane characterization, none have yet incorporated conductive polymeric
membranes into the electrochemical setup. </p><p>The primary objectives of this study
were to (1) synthesize a robust and sufficiently conductive polymeric membrane for
use as a working electrode; (2) develop a non-invasive non-Faradaic EIS method to
characterize membrane fouling in real time; (3) separate contributions to total fouling
from processes happening on the membrane surface and within the interior pore network.
Membrane fouling was studied using three model foulants, bovine serum albumin (BSA),
humic acid, and colloidal silica in a supporting electrolyte of phosphate buffered
saline (PBS) and potassium nitrate (KNO3), respectively. To better understand the
spatial position and magnitude of fouling, EIS spectra were interpreted by fitting
equivalent circuits informed by the physical structures of the membrane surface and
interior. </p><p>Data from the EIS fouling tests showed good agreement between changes
in impedance, conductance, and capacitance and reduction in permeate flow, which is
the conventional parameter used to monitor fouling severity. The conductive coating
also allowed for fouling to be differentiated between the surface and interior layers
of the membrane. Moreover, experiments with feed solutions containing separate foulants
in different solution chemistries verified that EIS is sensitive enough to differentiate
between various membrane fouling effects as well as irreversible fouling phenomena.
These results suggest that conductive membranes can be used alongside EIS to spatially
and temporally characterize membrane fouling as it happens in real time without the
need to remove or damage the membrane for analysis.</p>
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