Most of these studies focussed on chemical treatments of
the wastewaters that aimed at destructive processes like
chemical oxidation of the organic matter using ozone, fenton
oxidation, photochemical processes involving UV radiation
and hydrogen peroxide, and chemical precipitation [6-
13]. Two studies also focussed on biological treatments [8,
14].
Instead of focusing on end-of-pipe treatment, it is more
attractive to find efficient uses for these materials in terms
of both protecting the environment and preventing loss of
resources. In this particular case vegetable tannins, with
molecular weights that range from 300 to 20,000 Da, are
valuable products that can be found in the cork processing
wastewaters and can be used in the leather industry as tanning
agents, following a much more sustainable approach
to the cork wastewater treatment. The use of cork tannins in
the leather industry can lead to the production of high-quality
chrome-free leather, as suggested by Ciesla [15].
According to this author, the fine quality of Moroccan
leather of the XIX century can be related to the practice of
using tannin extracted from the inner bark of the cork oak.
The demand for this tree as a tannin source was so high that
a large area of Morocco’s cork oak forests suffered irreversible
damage toward the end of the 19th century and the
beginning of the 20th.
The concentration of polyphenolic compounds from
cork-processing wastewater using ultrafiltration has been
investigated already [16-20]. This process suffers, however,
from strong fouling of the membrane, caused by colloidal
matter and polyphenolic compounds. Furthermore, with
this process the low molecular weight tannins that are valuable
for leather tanning are lost in permeate. In the present
work, nanofiltration is used instead of ultrafiltration for
concentrating the tannins from the cork processing wastewater.
A nanofiltration membrane with a molecular weight
cut-off of 200 Da was used, which did not exhibit strong
fouling.