Use of crude glycerol for mixotrophic culture of Phaeodactylum tricornutum

Crude glycerol is a waste stream from biodiesel production, which has previously been shown to be useable for mixotrophic cultivation of microalgae; however, at high concentrations the presence of contaminants may limit culture growth. In this study two previously identified methods of contaminant removal from crude glycerol were trialled for use in mixotrophic culture of Phaeodactylum tricornutum. Neither crude glycerol without contaminant removal, nor crude glycerol which has had contaminants removed through calcium precipitation, lead to culture growth of P. tricornutum. However, pH adjusted crude glycerol gave comparable cell densities (6.03 ± 0.24 × 106 cells ml−1 compared to 5.66 ± 0.15 × 106 cells ml−1), growth rates (3.25 ± 0.26 days compared to 2.85 ± 0.21 days) and fatty acid profiles compared to reagent grade glycerol. There were alterations in the carbon partitioning of the microalgae, in addition to changes in cell widths. Cell widths increasing when harvested at stationary phase, compared to reagent grade glycerol (4.88 compared to 4.28 μm), while chlorophyll (11.38 compared to 6.25 %DW) and carbohydrate contents decreased (17.29 compared to 14.15 %DW respectively). As a result, it can be concluded that this method of contaminant removal meant that crude glycerol may be successfully used for culture of P. tricornutum, which may reduce the costs of microalgal culture, depending upon the end use.