NAMS 2002 Workshop - ICOM 2008

1.5 times the nominal one for the last element in the second stage. The water
permeability was 30 percent below nominal for the first element in the first stage,
to increase with increasing position in the downstream direction, to reach the
nominal water permeability for the first element in the second stage. During
normal operation in the first stage housing, the feed flow superficial velocity
decreased from about 0.2 m/s for the first element to about 0.1 m/s for the last
element. The fouling rate was much higher for the first element than for the last
element, despite double as high feed flow rate to the first one. Most likely, the
high fouling rate for the first element was not caused by the initially higher
permeate flux for this one, because later in operation, the permeate flux would be
as high for the last element in the housing as for the first one. It is possible that
the RO elements were very good at trapping the microbes, and the that formed
biofilm was very good at catching the nutrients in the feed solutions, so it took a
long time for the downstream elements to build up a thick biofilm.