Effect of pretreatments and catalytic route in the quality and productivity of biodiesel obtained from secondary sludge
Yolanda Patiño, Laura Faba, Eva Dı́az, Salvador Ordóñez
Abstract
The production of biodiesel from waste activated sludge by the in-situ transesterification of its lipid content is studied in this work, comparing both basic and acidic catalytic routes. The acid mechanism is chosen as the optimum one, considering that the high percentage of free fatty acids strongly limits the yields obtained by the basic route, due to the saponification competence. Different pre-treatments are proposed (sonication, microwaves, sieving) to enhance the extraction rate, identified as the limiting step of the process. Sludge drying requirements are also analysed, concluding that water contents below 20% (weight base) does not lead to significant decreases in the transesterification activity. The acidic reaction is also chosen once the quality of the final mixture as alternative biofuel is analysed. Almost all the biodiesel properties (higher heat value, iodine number, kinematic viscosity, density, and long-chain saturated factor and cetane number) are in the optimum ranges proposed by the international normative, concluding that pretreatments do not damage the final product. Optimum results were obtained applying microwaves, with a final yield of 46.7% of FAMEs, which is a clear improvement on the previous literature of biodiesel obtaining from sewage sludge.