Abstract:
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[EN] Tanneries produce large amounts of wastewater with high concentrations of suspended
solids, organic matter, and salts. Treatment and reuse of these effluents are of great importance
to preserve water resources and ...[+]
[EN] Tanneries produce large amounts of wastewater with high concentrations of suspended
solids, organic matter, and salts. Treatment and reuse of these effluents are of great importance
to preserve water resources and save costs. Although suspended solids and high percentages of
organic matter can be eliminated by physico-chemical and biological processes, refractory chemical
oxygen demand (COD) and salts will remain in the wastewater after these processes. In particular,
chloride and sulphate ion concentrations may hinder the treated wastewater from being reused or
even discharged according to legal standards. In this work, two nanofiltration membranes and two
reverse osmosis membranes are tested to assess these technologies as regeneration processes for
biologically treated tannery wastewater. Permeate flux and rejection of organic matter and ions were
measured at different operating conditions (transmembrane pressure and cross-flow velocities) at
both total recycle and concentration modes. Results showed that the difference between permeate
fluxes of nanofiltration (NF) membranes and reverse osmosis (RO) membranes was very high. Thus,
at 20 bar and 1.77 m s¿1, the permeate flux of the two tested NF membranes in the total recycle
mode experiments were 106 and 67 L m¿2 h¿1, while the obtained permeate fluxes for the RO
membranes were 25 and 18 L m¿2 h¿1. Concerning rejections, RO membranes rejected almost 100%
of the salts, whereas NF membranes reduced their rejection when faced with increasing concentration
factors (salt rejection between 50¿60% at the highest concentration factor). In addition, the fouling
of RO membranes was lower than that of NF membranes, recovering more than 90% of initial
permeability by only water rinsing. In contrast, chemical cleaning was necessary to increase the
permeability recovery of the NF membranes above 90%. The considerably lower rejections and the
higher membrane fouling of the NF membranes lead us to conclude that reverse osmosis could be
the most feasible technique for water reuse in the tannery industry, though the permeate fluxes are
lower than those achieved with NF membranes.
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