The
growth of mineral crystals on surfaces is a challenge across
multiple industrial processes. Membrane-based desalination processes,
in particular, are plagued by crystal growth (known as scaling), which
restricts the flow of water through the membrane, can cause membrane
wetting in membrane distillation, and can lead to the physical destruction
of the membrane material. Scaling occurs when supersaturated conditions
develop along the membrane surface due to the passage of water through
the membrane, a process known as concentration polarization. To reduce
scaling, concentration polarization is minimized by encouraging turbulent
conditions and by reducing the amount of water recovered from the
saline feed. In addition, antiscaling chemicals can be used to reduce
the availability of cations. Here, we report on an energy-efficient
electrophoretic mixing method capable of nearly eliminating CaSO4 and silicate scaling on electrically conducting membrane
distillation (ECMD) membranes. The ECMD membrane material is composed
of a percolating layer of carbon nanotubes deposited on porous polypropylene
support and cross-linked by poly(vinyl alcohol). The application of
low alternating potentials (2 Vpp,1Hz) had a dramatic impact
on scale formation, with the impact highly dependent on the frequency
of the applied signal, and in the case of silicate, on the pH of the
solution.
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