Trichosporon oleaginosus was grown in wastewater sludge to produce lipid. The obtained biomass was employed to study ultrasonication effect on lipid extraction and in-situ transesterification. Besides the most utilized solvents (the mixture of chloroform and methanol, 1:1 v/v), other solvents including water, hexane, and methanol were also studied to explore their capacities in lipid extraction with ultrasonication. The maximum lipid recovery was 11.8, 35.3, 62.0, and 95.3% (w/w) with water, hexane, methanol, and the mixture of chloroform and methanol (1:1 v/v), respectively within 20 min. Chloroform and methanol gave the best performance. However, due to the adverse environmental concern related to the utilization of chloroform, in-situ transesterification (single step lipid extraction and transesterification to obtain biodiesel) was investigated. In case of in-situ transesterification, biodiesel yield of 95% (w/w) was obtained in 60 min with the assistance of ultrasonication; whereas, 24 h was required to achieve similar yield without ultrasonication. (C) 2015 Elsevier Ltd. All rights reserved.