The influence of sludge drying methods on the fatty acid composi-
tion was also studied and the results are collected in Table 3. The
same fatty acids were found for all methods showing a significant
amount of palmitic (31.1 to 49.4%), oleic (18.3 to 32.6%) and stearic
(8.3 to 15.8%) acids in the sludge biodiesel. The most important differ-
ences in the composition were observed for palmitic, palmitoleic,
stearic, oleic and linoleic acids. In detail, oven at 105 °C for two days
gave the fatty acid composition almost identical with respect to
MgSO4·H2O method. The other methods showed an increase in the
fraction of oleic, linoleic and palmitoleic acids, counterbalanced by a
decrease of palmitic and stearic acids. This trend, where the fraction of
saturated fatty acids decreased while the fraction of unsaturated fatty
acids increased, is particular for the sludge. Usually, unsaturated fatty
acids are more unstable and readily oxidized than saturated ones