The lipid extraction using hexane and methanol:hexane increased the biodegradability of Nannochloropsis oculata by 36% and 24% respectively. Moreover, hexane increased the methane production from raw microalgae, from 253 +/- 11 to 313 +/- 9 mLaidgvs. Methanol:hexane did not affect the methane production, which yielded 254 +/- 10 ml.o.pilgvs, mainly due to the significant changes in the biomass composition. On the other hand, the lipid extraction failed to increase the biodegradability of Chlorella vulgaris, which resulted around 44% for raw and lipid -extracted microalgae. The methane productions were 219 +/- 6, 202 +/- 1 and 200 +/- 4 mk-H4/gys from raw and pre-treated microalgae using hexane and methanol:hexane respectively. Regarding the lipid extraction yields, using methanol:hexane the yields were 4.7 and 3.7 times higher for N. oculata and C. vulgaris than using hexane. The biodiesel yields were also higher using methanol:hexane, 2A and 1.9 times than using hexane. However, the biodiesel composition was unaffected by the solvent. The substrate to inoculum ratio influenced raw N. oculata digestion. At 1:1 VSsubstrate:VSinoculum, the methane production throughout the first days decreased but not the ultimate methane production. C vulgaris digestion was unaffected, probably due to the biomass characteristics. Finally, the co-digestion of microalgae and sewage sludge showed no synergy, nor inhibition. (C) 2015 Elsevier B.V. All rights reserved.