3.2. Results of ultrafiltration stage (exp1 and exp2)
Figs. 3 and 4 show the final results of pretreatment UF stage applied
to wastes with the longest storage time (exp1) and wastes with the
shortest storage time (exp2), respectively.
As it can be seen, volume reduction in this stage is quite important in
both cases. Values of volume reduction factor have been calculated
deducting the dead volume of the plant (4 L) because this volume is independent
of the amount of liquid treated. In fact, the volume of the initial
waste was reduced to 1 L of final concentrate, in both experiments.
Thus, VRF is 63 in the first experiment and 60 in the second experiment.
The UF treatment lasted around 30 min in both experiments.
Although some analytical parameters were not possible to be measured,
it can be expected that this ultrafiltration stage removes most of
organic and microbiological contents of the wastes. As it was expected,
conductivity values were hardly modified from the initial feed values.
With regard to activity removal, decontamination factors are quite
similar in both experiments (around 2). These values are higher than
the ones found in the literature for UF applications without complexing
agents [27]. UF activity removal in the experiment 1 was 45.4%, and
53.9% in the experiment 2. This fact confirms that part of 125I is labeled
to high molecular weight compounds (proteins) which are retained
by UF membrane. In order to remove the remaining activity associated
to less size compounds or ionic ones it is necessary to apply reverse
osmosis.