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Pilot scale membrane filtration and development of a photocatalytic membrane reactor for treatment of olive mill wastewaters
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The work developed in this thesis focused on optimizing membrane processes and in the
development of a novel hybrid photocatalytic membrane reactor to treat olive mil wastewaters.
The traditional Mediterranean diet, known for being a rich and healthy diet, uses olive oil as its
main source of fats. Therefore, in the Mediterranean region, there is an annual discharge of 30
million m3 of the wastewaters produced by this industry into the environment. Olive mill
wastewaters are a highly polluted effluent produced in olive oil industries, representing an
environmental hazard if not treated properly. These effluents present low pH and a high
concentration of solids, oil and organic compounds such as organic acids, lipids and alcohols.
The presence of phenolic compounds hinders the biological treatment of these wastewaters.
Membrane separation processes stand out as promising treatment approaches and their
application has expanded during recent decades for the treatment of wastewaters, as a result of
increasingly stringent regulations in wastewater discharge and continuing improvements in
membrane technology. However, wide acceptance of membrane processes by industries is
limited by membrane fouling. Fouling is caused by the accumulation of rejected oil, suspended
solids and other components of the wastewaters on the membrane surface and intrapore
structure. Fouling results in flux decline and low membrane lifetime due to the need to perform
frequent cleanings.
When compared with polymeric membranes, ceramic membranes present several advantages
such as higher thermal stability, mechanical resistance and chemical resistance, and thus can be
applied in extreme aggressive environmental conditions. These properties allow for a better
control of membrane fouling since higher pressures can be employed during backpulse and
backwash procedures, and cleanings can be performed with stronger chemicals, without
compromising the membrane lifetime. In the present work, the treatment of the olive mill
wastewaters was mostly performed with ultrafiltration ceramic membranes made of silicon
carbide.
Different strategies to overcome the problem of fouling were studied: (a) the optimization of
operating conditions, conducted under controlled pressure / controlled permeate flux, allowing for
a sustainable performance, and the use of backpulse and backwash strategies at pilot scale and
(b) the modification of the surface of the silicon carbide membranes to obtain a photocatalytic
membrane with a lower molecular weight cut off and higher hydrophilicity.
The new photocatalytic membranes developed were obtained using a sol-gel process combining
titanium dioxide, silicon dioxide and silicon carbide. These membranes proved to have
photocatalytic activity and were thus tested in a new hybrid reactor. The extremely efficient
removals of the compounds analyzed and the lower fouling potential observed, showed that the
developed photocatalytic membranes and the novel hybrid reactor are highly promising solutions to be used in the treatment of olive mill wastewaters, as well as in a variety of other wastewaters
and water matrices.
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Palavras-chave
Olive mill wastewater silicon carbide membranes ultrafiltration nanofiltration titanium dioxide photocatalysis submerged photocatalytic membrane reactor