Biocrude oil production from a self-settling marine cyanobacterium, Chroococcidiopsis sp., using a biorefinery approach

Although the whole microalgal biomass is typically used as a feedstock for hydrothermal liquefaction (HTL), the conversion of a primary metabolite (i.e., carbohydrate) to biocrude is very low. In this study, a self-settling cyanobacterium (i.e., Chroococcidiopsis sp.) was used to understand the effect of carbohydrate removal, as a pretreatment, on the net energy recovery from the residual biomass. The optimum biocrude yields from pretreated and control biomass were 50.2% (350 °C) and 41.3% (300 °C), respectively. For the temperature range studied, the biocrude yield from the pretreated biomass was higher compared to that obtained from the control feedstock. Further, maximum alkane formation of 42.7 and 23.3% occurred for pretreated and control biomass, respectively, at 325 °C. Total organic carbon and total nitrogen values in the aqueous phase liquid obtained from pretreated biomass were at least 1.31 and 1.23 times lower when compared to the corresponding values obtained from control biomass. When APL was recycled as a source of nutrients, it reduced the biomass yield (24.1%) and pigment content (68.4%) in Chroococcidiopsis sp. Further, a model was developed to understand how the cellular carbohydrate content would affect the net energy recovery for the proposed biorefinery route.