Effect of swine wastewater on Jatropha curcas L. oil acidity

The experiment included a jatropha plantation area of 900 m2, of which 216 m2 were divided into eighteen plots that received six treatments with different amounts of swine wastewater. Applications were performed in triplicate with intervals of three months. Seed harvest was performed manually during the entire plant production period. Oil was extracted with the use of ethanol as a solvent, which is cheaper, less toxic and less damaging to the environment than other organic solvents such as hexane. Acidity was determined by titration with sodium hydroxide (NaOH), in which there was a reduction inversely proportional to the acid number expressed in mg KOH g−1 of oil with the increase of wastewater applied. This result is extremely important for the energy sector, once that in order to enable the production of biodiesel, the acidity of crude oils is usually reduced by oil refining, which is a costly process. In this study we were able to reduce this cost to zero, besides using swine wastewater, which avoids many environmental problems. Analyses by gas chromatography showed that the treatments with higher amounts of wastewater favored an increase in the production of oleic acid (C18:1) that was proportional to the sum of the decreases in the production of linoleic acid (C18:2) and stearic acid (C18). The reduction in the percentage of linoleic acid can be responsible for reducing acidity, giving oil increased stability to oxidation and therefore fewer amounts of free fatty acids.