3.3. Results of first pass of reverse osmosis (exp1 and exp2)
Figs. 5 and 6 show the final results of the first pass of reverse osmosis,
in which permeate of previous UF was treated.
Volume reduction factor obtained in this stage (without considering
the dead volume) was 58 in experiment 1, and 55 in experiment
2. In both cases, the volume of the initial waste was reduced to 1 L.
The treatment lasted an estimated time of 3 h in both experiments.
Although some analytical parameters were not possible to be measured,
it can be expected that this reverse osmosis stage removes all
the remaining organic content of the feed as well as a significant part
of salts. In fact, conductivity was reduced from a value of 12.67 mS/cm
to a value of 3.11 mS/cm (average removal of 75.5%) in the first experiment.
In the second one, conductivity was reduced from a value of
14.5 mS/cm to a value of 5.76 mS/cm (average removal of 59.3%).
With regard to activity, in the first pass of reverse osmosis in the experiment
1, decontamination factor was 3.70 (average activity removal
of 73%), with an average activity in the permeate of 0.413 kBq/L. In the
experiment 2, the decontamination factor was 6.1, with an average
activity in the permeate of 18.163 kBq/L (average activity removal of
83.6%). The excellent performance of this RO pass in the experiment 2
(shorter storage time) must be highlighted, since activity removal was
higher than that in the experiment 1 (longer storage wastes) in spite
of having initial activity nearly 100 times higher. However, in both experiments permeate activity values were still 20 and 1000 times
higher than discharge limit, respectively. For this reason, it was decided
to apply another pass of RO to the permeate in order to decrease more
the activity values.