Cell disruption can increase the extraction efficiency of total lipids from microalgae for further conversion to biodiesel. Four different pretreatment methods were tested on mixed cultures of microalgae harvested in a stabilization pond system treating sewage: ultrasonication (US), microwaving (MW), autoclave (AC) and electroflotation by alternating current (EFAC). The best results in terms of total lipid yield were: MW (33.7 +/- 5.3%), followed by EFAC (24.8 +/- 7.1%), AC (15.4 +/- 2.3%), and US (13.3 +/- 3.0%). However, when both efficiency and costs are considered, EFAC gave the best result and can be an excellent option for simultaneous microalgae harvesting and cell disruption. (C) 2013 Elsevier Ltd. All rights reserved.