Superstructure optimization of an integrated algae biorefinery

A superstructure framework for the techno-economic optimization of an integrated algae biorefinery is presented in this work. The superstructure is developed and implemented in the Advanced Interactive Multidimensional Modeling (AIMMS) software as a mixed integer non-linear model with the objective to minimize the total biodiesel production costs. The integration concept is defined by the use of the wastewater and CO₂ emissions from a wheat straw biorefinery as feed to the algae biorefinery and the resulting algae wastes are recycled back to the wheat straw biorefinery to produce value-added chemicals. Seven stages are considered as processing sections in this superstructure, namely cultivation, harvesting and dewatering of algae, algae pretreatment, lipid extraction and remnant treatment. Even though the algae biorefinery is fed with the waste streams of a wheat straw biorefinery, the cultivation stage proved to be still the most expensive stage. The results show that the integrated concept leads to economic advantages over a stand-alone algae biorefinery since there can be up to 80% reduction in the biodiesel production costs.