Selective separation of low-molecule-weight substances from hydrothermally oxidized cyanobacterial slurry to improve cultivation of Scenedesmus obliquus

Abstract

Using waste biomass as raw material for culture medium is an important way to lower the production cost of biodiesel. In this study, Scenedesmus obliquus was used as an oil-producing microalgae and culture medium was prepared from a cyanobacterial bloom by hydrothermal oxidation. The growth of S. obliquus was strongly inhibited by organic compounds with molecular weight >3 kDa. However, nutrients <3 kDa accounted for >85% of the total nutrition in the raw medium, and medium containing only low-molecular-weight organic matter (i.e., from which material >3 kDa was removed) promoted the growth of S. obliquus: the maximum dry weight of S. obliquus reached 2.61 g L−1 and the logarithmic-phase specific growth rate 0.371 d−1, while the oil content remained >14%. These data represent a considerable improvement in the biomass and total oil yields compared with growth in BG11 medium or the unfractionated raw medium prepared from the cyanobacterial slurry.