Osmotic Membrane Distillation
OMD experiments were performed using a laboratory setup,
schematically depicted in Fig.
1
. The OMD module consists
of two compartments. The volume of each compartment is
150 cm
3
. The stripping solutions (NaCl or CaCl
2
) and the feed
juice solution (apple or beet juice) are separated by the hydro-
phobic flat membranes (Table
1
). The raw juices were used
without any additives or preservatives. Apple juice was pur-
chased from
B
Marwit Sp. z o.o.
^
(Poland) company, and beet
juice from by
B
Piotr i Pawe
ł
^
(Poland) company. NaCl and
CaCl
2
were purchased from Avantor Performance Materials
Poland S.A. The stripping compartment was hermetically
sealed, so the volume measured by the pipette is equal to the
volume of water transported across the membrane from the
juice solution to the stripping solution (Fig.
1
). Both solutions
were constantly stirred. All experiments were done at a con-
stant temperature of 20 °C. The choice of room temperature
aimed to show the efficiency of dewatering juices without
requiring an elevated temperature. However, the following
experimental conditions were varied: the duration of the ex-
periment (from 3 to 11 h), different stripping solutions (satu-
rated NaCl
—
25 %
w
/
w
—
and CaCl
2
—
50 %
w
/
w
), and differ-
ent feed solutions (apple and beet juices). Moreover, the ex-
periments were done for all purchased membranes (Table
1
).
Deionized water (0 °Brix) and fresh juices (apple and beet) of
initial concentration (
∼
11 °Brix) were used as feed solutions.
Juices were pre-filtrated to remove the fruit pulp before the
OMD process. This procedure was required, because raw
juices, containing a lot of pulp that could clog the pores of
membranes, were utilized. The pre-filtration process was con-
ducted under low pressure with application of 2-
μ
m filter
papers. It was found that the pre-treatment step had no impact
on the quality of the juices subsequently processed by the
OMD process.
Each OMD experiment was run in batch mode using a new
membrane sample, fresh feed, and stripping solution. Every
single experiment was repeated three times