3. Results and discussion
3.1. Reverse osmosis
Fig. 3 shows the evolution of the permeate flux and soluble solids
during camu–camu juice pre-concentration by reverse osmosis.
There was a decrease in the permeate flux and an increase in the
soluble solids concentration along time. This flux decrease may
be attributed to the increase in the osmotic pressure that decreases
the driving force and in the juice viscosity, which occurs due to the
increase of solids content during water removal, making the mass
transfer more difficult. The average permeate flux (calculated as
the mean value between the fluxes observed overtime) was
11.3 L h1 m2 and the volumetric reduction ratio achieved at the
end of the process was 4.2.
Concentration by reverse osmosis is also limited by the membrane
fouling and the concentration polarization layer. This last
factor has special importance due to the increase in osmotic pressure
as the concentration at the membrane surface increases.
In membrane processes governed by a pressure gradient, the
permeate flux can be expressed by a phenomenological equation
like: