The steady-state and periodic performances of a seawater
desalination unit based on a small-scale commercial spiral-wound membrane were
studied. For the steady-state case, operating pressures ranging from 30 bar to
50 bar and temperatures ranging from 22°C to 28°C were investigated. As
expected, increasing the pressure resulted in improvements in the water
recovery, salt rejection and energy consumed by the feed pump per
m
$^3$
of permeate produced. The improvements were larger for
operation at low to moderate pressures than at high pressures. Both the
permeation rate and salt rejection changed linearly with temperature; the
permeate flux increased by 2.8%/°C whereas the salt rejection decreased by
0.007%/°C. For the case of unsteady-state operation, the operating pressure
was varied according to a symmetric square wave function around an average
pressure of 50 bar. The production rate increased as the period of the wave
decreased. Such an improvement was obtained at the expense of a marginal
increase in the total energy consumed. For a wave period of two minutes, the
production rate increased by 8% over that obtained from steady-state operation
while the energy consumed increased by a mere 0.15%. A simple theoretical
analysis showed that a 12.3% improvement in the permeation rate would be
obtained in the absence of concentration polarization. The salt rejection was
not affected by this mode of operation.
