Lipid production for biofuels from hydrolyzate of waste activated sludge by heterotrophic Chlorella protothecoides

Microalga Chlorella protothecoides can accumulate high proportion of lipids during the heterotrophic growth with glucose as the carbon source. However, its commercial application is restricted due to the high cost of the carbon source. In this study, the wasted activated sludge (WAS) was hydrolyzed after ultrasonic pre-treatment and the hydrolyzate obtained was used as an alternative carbon source for algal biomass and biodiesel production. The results indicate that C. protothecoides can proliferate in the WAS hydrolyzate and accumulate biolipid. The final lipid content of the culture fed with the hydrolyzate was 21.5 ± 1.44% (weight percent) after 156 h cultivation in flasks and the maximum biomass obtained was 0.5 g L−1. Acetic acid and isovaleric acid were favorable carbon sources for cell growth. The soluble microbial products (SMP) presents in the hydrolyzate can also be used as a carbon source for cell growth.