| Summary: | 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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