Integrated Microalgae-Based Biorefinery for Astaxanthin Production

In this work, we address the optimization of an integrated microalgae-based biorefinery through the formulation of a nonlinear programming (NLP) model for the production of the natural ketocaroteinoid astaxanthin, a powerful antioxidant with application in nutraceuticals, pharmaceuticals, cosmetics and food industries andco-products. Biodiesel from microalgae and biogas from waste streams are considered to reduce the dependency of external energy sources. Biodiesel is produced from oil transesterification, producing glycerol as a by-product. Glycerol is mostly used for pharmaceutical products, food and cosmetics but be also used as raw material for higher added value products as polyhydroxibutirates (PHB). PHB is a biopolymer produced by microorganisms and it constitutes an alternative to fossil fuel based polymers as it has similar properties. In this work, PHBis used for packaging proposes. A combined heat and power cycle to transform biogas generated by the anaerobic digestion of waste streams(algal cake, waste paper, glycerol, sludge and cell residual material from PHB extraction) is also included. Anaerobic digestion model accounts for detailed composition of the different feed streams. Detailed cost models are formulated for process equipment. The proposed model is implemented in GAMS to maximize net present value and minimize energy consumption. Numerical results provide useful insights on integrated biorefineries that use carbon dioxide as carbon source, as well as quantitative information on green processes.