In the present study, feasibility of biodiesel production from freeze dried sewage sludge was studied and its yield was enhanced by optimization of the in situ transesterification conditions (temperature, catalyst and concentration of sludge solids). Optimized conditions (45 degrees C, 5% catalyst and 0.16 g/mL sludge solids) resulted in a 20.76 +/- 0.04% biodiesel yield. The purity of biodiesel was ascertained by GC-MS, FT-IR and NMR (H-1 and C-13) spectroscopy. The biodiesel profile obtained revealed the predominance of methyl esters of fatty acids such as oleic, palmitic, myristic, stearic, lauric, palmitoleic and linoleic acids indicating potential use of sludge as a biodiesel feedstock. (C) 2016 Elsevier Ltd. All rights reserved.