Centro Internacional de Arte Parietal Lascaux IV, Francia. 34

Olive mill wastewaters are the main pollutant from two-phase extraction systems. They are constituted by the water used in different stages of oil extraction. Wastewater from olive washing (OW) and olive oil washing (OOW) was collected in a local industry operating the two-phase olive oil extraction method. The OW and OOW have a black-brownish colour with an unpleasant smell of fermented organic matter, being the colour and smell more intense in the case of OOW waste. The composition of olive oil wastewater depends on several factors: as the process used while extracting oil; operation conditions, olive variety and olive maturation grade [41]. The main physic-chemical features of the used washing wastewater (OW) and olive oil washing wastewater (OOW) are presented in Table 1. The OW and OOW are characterized by a high content of organic pollution (COD/BOD ratio between 7 and 11), pH slightly acid OOW and pH slightly basic near neutral OW. Presence of polyphenols and organic substances make the treatment of these wastewaters problematic [42].

Concerning the dry residue of the olive washing wastewater (OW) and olive oil washing wastewater (OOW), 4.4 and 7.2 % respectively, large amounts of carbon and hydrogen were determined (Table 2). However, the organic matter content of the clay was low. The incorporation of these wastes with high carbonaceous content might provide a sensible energetic contribution to the ceramic process. The HHW of dry residue was 1535 kcal/Kg for OW and 3425 kcal/kg for OOW (Table 2). Brick manufacturing usually includes some materials with variable organic matter content like olive pomace or coke [33]. Therefore, the use of waste to replace fresh water could be a saving in water consumption but also in energy requirements for the firing process in brick manufacturing.

Table 1. Physico-chemical characterization of the used olive oil wastewater Dry Residue Waste PH Density (Kg/m3₎ Conductivity (mScm-1₎ Humidity (%) COD (mg dm-3₎ BOD5 (mg dm-3₎ Organíc Matter (%) Ashes (%) OW 7.7 1006 2.27 95.5 4383 393 78.6 21.4 OOW 4.5 1012 6.54 93.8 37450 5175 88.1 11.9

Table 2. CNHS analysis and Higher Heating Value (HHV) of raw materials: clay and dry wastes Sample %C %H %N %S HHV (kcal/kg) Clay 2.30 ± 0.004 0.50 ± 0.004 0.05 ± 0.0 0.03 ±0.008 - OW 15.29±0.03 1.32±0.01 0.49±0.00 1.78±0.02 1535 OWW 35.33±0.21 5.63±0.05 0.78±0.,03 0.56±0.01 3425

In this work three types of clays were used. The chemical composition of the raw yellow, red and black clay after firing at 950 ºC was determined by XRF (Table 3). Yellow and black clays are rich in carbonates, still very high in the black clay. The decrease of calcium contents is correlated to an increase of SiO2 contents, reaching values of 54% SiO2 in yellow clay. Red

clay is characterized by a low carbonate content with higher ferrite and alumina content. Red clay does not have sufficient plasticity for the shaping of resistant unfired pieces. Regarding traditional mixture described in Table 3, and used as reference raw material in the present work, the addition of red clays allows modifying the technological behaviour of yellow and black clays. Due to the proportions of clays used, the mixture of clays has appropriate plasticity (plasticity index: 9.6%) for shaping. The mixed clay had high amounts of SiO2

(55.82 %) as the predominant oxide and of Al2O3 (12.13 %) due mainly to the silicate in the

clay. The significant content of CaO (13.52 %) is related to the abundance of carbonates, which explain the loss of ignition observed. The clay is considered calcareous if CaO>6 [43]. This information is very important for manufacturers as they can adapt the drying and firing process to avoid cracking. Carbonates acts as a pore-forming agents and generate crystalline phases during firing that enhance mechanical strength [44].XRD data show that de mixed clay materials used to the elaboration of the ceramic pieces is rich in quartz with significant amounts of clay minerals as phyllosilicates such as muscovite, orthoclase, faujasite, albite and chlorite. Carbonates as calcite and dolomite (Figure 2) are also presents in small quantities and traces of hematite can be observed. The comparison of the mineralogical composition of the used mixture with the overall composition of common raw materials for ceramics products [45] reveals that this material contains the appropriated phyllosilicates, carbonate and quartz contents to be considered inside the range of mineralogical compositions potentially suitable for structural ceramics products.

Figure 2. XRD patterns of clay.

Table 3. Chemical composition of the fired clay

Oxide content (%) Red clay Yellow clay Black clay Mixture of Clays SiO2, 53.94 53.54 45.50 47.17 Al2O3 15.93 11.78 11.55 12.51 Fe2O3 14.22 7.02 5.82 6.49 CaO 3.84 13.67 21.45 13.52 MgO 1.81 2.20 2.10 2.11 MnO 0.032 0.063 0.10 0.05 Na2O 0.22 1.72 1.40 0.31 K2O 7.95 4.17 3.43 3.61 TiO2 1.54 1.56 1.21 0.78 P2O5 0.21 0.10 0.10 0.14 SO3 - - 2.91 1.58 NiO - - - 0.0086 CuO - - - 0.0017 ZnO - - - 0.0082 Ga2O3 - - - 0.0027 Rb2O - - - 0.017 SrO 0.035 0.096 0.22 0.043 ZrO2 - 0.059 0.141 0.035 Nb2O5 - - - 0.0021 BaO - - - 0.047 LOI - - - 10.6

Figure 3. DTA-TGA analysis of (a) raw clay; (b) wastewater from olive-washing stage (wet OW); (c) wastewater from oil olive-washing (wet OOW); (d) dry OW and (e) dry OOW.

Thermal behavior of clay and waste was studied by TGA-DTA with maximum temperature of 1000 ºC. The most significant weight loss processes associated to brick manufacturing from typical clays were physically-adsorbed or free water, water elimination by dehydroxilation of clay minerals and carbonate decomposition. Weight loss of free water mainly occurred at temperatures below 100 ºC, although the process is extended up to 200 ºC in the clay sample (Figure 3 a). An endothermic DTA effect is observed in the range from room temperature up to 200 ºC, and the weight loss associated to this process is 1.4 wt %. There are other thermal events within the range 200-600 ºC, with weight loss of 2.3 wt %, associated to the combustion of organic matter and dehydroxilation of the silicate layer identified in this sample. However, a broad exothermic effect is observed by DTA with a shoulder. A small endothermic DTA peak is detected at ca. 565 ºC, being associated to the transformation α to β quartz. Calcium carbonate (calcite) decomposition took place in the

range 600-800 ºC with the release of CO2, associated with an endothermic DTA effect,

centered at 750 ºC in the clay sample, with weight loss of 7.8 wt %. Since bricks were fired at 950 ºC, decomposition of carbonates is expected and a development in porosity of the fired samples.

TGA-DTA curves of wet OW and OWW showed a strong endothermic peak centered at 150 ºC, corresponding to evaporation of the absorbed water in 95.5 and 94.0 wt%, respectively (Figure 3 b and c), major constituent of the waste. TGA-DTA curves of the dry wastes are typical for a solid fuel (Figure 3d y f). A total weight loss of about 45.4% and 77.1% was observed at 1000 ºC for OW and OWW, respectively. The first decrease in mass observed between 25 and 180 ºC is caused by the evaporation of physical water, indicating a small endothermic reaction. The second mass loss was observed within the 200–700 ºC range, which may possibly be due to the burning of volatile organic compound (VOCs) and, at the upper temperature, it may be due to the burning of fixed carbon, as indicated two for OW and three for OOW exothermic reactions, with maxima at 363 ºC and 474 ºC for OW and 440 ºC, 525ºC and 590 ºC for OOW. Thermal degradability is affected by the composition of any biomass because different components of lignocellulosic materials have different thermal behaviour. The three major constituents of lignocellulosic materials (hemicellulose, cellulose and lignin) are chemically reactive and decompose thermochemically in the temperature range of 150-500 ºC. Some studies on the thermal decomposition of the individual components indicated that decomposition of hemicellulose starts first, followed by cellulose and, finally, the lignin [46, 47]. Organic matter started to leave the material and burns very rapidly as the strong exothermic peaks centered at 363 ºC and 474 ºC in OW, and 440 ºC and 525 ºC in OOW. Volatile compounds burn first, followed by non-volatile components. The higher thermal degradation of OWW might be due to larger percentages of volatile matter and lower ash contents than OW (Table 2). The exothermic peak at 750 ºC could correspond to the combination of residual carbon with atmospheric oxygen and CO formation. Also the lightly endothermic reaction between 700-850 ºC represented the thermal decomposition of carbonates, phosphates and potassium salts [46].