The aim of this study was to investigate the effect of low temperature pretreatment on the anaerobic digestion of microalgal biomass grown in wastewater. To this end, microalgae were pretreated at low temperatures (55, 75 and 95 degrees C) for 5, 10 and 15 h. Biomass solubilisation was enhanced with the pretreatment temperature and exposure time up to 10 h. The methane yield was improved by 14%, 53% and 62% at 55, 75 and 95 degrees C, respectively; and was correlated with the solubilisation increase. The pretreatment at 95 degrees C for 10 h increased VS solubilisation by 1188%, the initial methane production rate by 90% and final methane yield by 60% compared to untreated microalgae. With diluted biomass (similar to 1% VS) positive energy balance was not likely to be attained. However, with concentrated biomass (>2% VS) energy requirements may be covered and even surplus energy generated. (C) 2013 Elsevier Ltd. All rights reserved.