abstract
Abstract: In this work, the salinity of permeate obtained with membrane distillation (MD) in pilot scale
systems was analyzed. Experiments were performed with three di erent spiral-wound commercial
modules, one from Solar Spring with 10 m2 surface membrane area and two from Aquastill with
7.2 and 24 m2. Intermittent operation meant that high permeate conductivity was measured in
the beginning of each experiment, which was gradually decreasing until reaching a constant value
(3–143 Scm1 for seawater feed). The final quality reached did not depend on operating conditions,
only the time it took to reach it. This can be because the permeate flux dilutes the minimal feed
leak taking place through pinholes in the membranes. Larger feed leak through the membrane
was observed when operating in vacuum-enhanced air-gap MD configuration (V-AGMD), which is
compatible with this explanation. However, for the increase of feed leak with salinity (up to 1.8 M),
a conclusive explanation cannot be given. Pore wetting due to crystallization is discarded because
the high permeate quality was recovered after washing with distilled water. More studies at higher
salinities and also at membrane level are required to investigate this.
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