Value-added chemicals from microalgae: Greener, more economical, or both?

This paper addresses the sustainable design and synthesis of manufacturing processes for making algal bioproducts. We propose by far the most comprehensive superstructure capable of producing biodiesel, hydrogen, propylene glycol, glycerol-tert-butyl ether, and poly-3-hydroxybutyrate from microalgae. The major processing sections include cultivation, harvesting, lipid extraction, remnant treatment, biogas utilization, biofuel proneduction, and bioproduct manufacturing. On the basis of the superstructure, we integrate a cradle-to-gate life cycle analysis and techno-economic analysis with multiobjective optimization to simultaneously optimize the environmental and economic performance. We also apply a tailored global optimization algorithm to efficiently solve the problem in reasonable computation times. Results show that the most environmentally sustainable processes reduce life cycle greenhouse gas emissions per kilogram of the algal bioproducts by 5% to 63%, compared with petrochemical counterparts. In addition, the coproduction of value-added bioproducts in the algal glycerol process helps reduce the biodiesel production cost to as low as 2.79 per gasoline-gallon-equivalent.