In this work, we formulate a nonlinear programming model for the design of an integrated microalgae- based biorefinery for the production of biodiesel and value added co-products which depend on the particular microalgae species considered. The production of biogas by anaerobic digestion of the oil cake together with waste streams is included.
The process scheme includes the possibility to use glycerol, the main by-product in biodiesel production, as substrate for the production of poly(ß-hydroxybutyrates), PHBs, which are polymers belonging to the polyesters class, bio-derived and biodegradable. In this case, we consider a three stage process: glycerol purification, fermentation and PHB extraction by cellular lysis.
The resulting model is a nonlinear programming problem and has been implemented in GAMS (Brooke et al., 2011). Numerical results provide useful insights on the design of integrated biorefineries that use carbon dioxide as carbon source.