In Situ Transesterification of Sewage Sludge for Biodiesel Production

To develop new clean energy has become an urgent task for many countries forced by the energy and environment crisis. To make biodiesel from sewage sludge is one of the solutions. In this study, biodiesel production from sewage sludge by in situ transesterification was discussed. The solvent is methanol and catalyst is sulfuric acid. In-situ transesterification, has many merits over conventional transesterification reaction such as it simply the procedure by skipping the step of lipid extraction and as a result cost can be saved. That is, the steps — sludge dissolved, lipid extraction and transesterification reactions — take place simultaneously. Methanol acts as an extraction solvent and as an esterification reagent as well. Experiments were conducted to determine the optimal parameters of in-situ transesterification for maximizing the yield of biodiesel, which are methanol to sludge mass ratio, acid concentration and temperature. The optimum synthesis condition was determined by orthogonal test L16 (43), and it was found that an optimum biodiesel yield can be obtained from sewage sludge by in-situ transesterification (16.6%) at methanol to sludge mass ratio 10:1(w/w), H2SO4 concentration 5% (v/v), and temperature 65°C. Temperature, H2SO4 concentration, and methanol to sludge mass ratio in sequence had significant influence on FAMEs yield. The FAMEs in the product were analyzed by GC-MS and the purity can be higher than 96%.