Life cycle assessment of microalgae based biodiesel production to evaluate the impact of biomass productivity and energy source

Abstract

In the present study the life cycle assessment (LCA) of three scenarios for biodiesel production from Scenedesmus dimorphus, a freshwater microalgae, cultivated in open raceway ponds using primary and secondary data was investigated. The main differences in the scenarios were related to biomass productivity, mode of culture mixing and type of energy source. The process steps included algal cultivation in open raceway ponds, harvesting by chemical flocculation, dewatering by mechanical drying option (MDO)/Spray Drying (SD) followed by extraction, reaction, and purification. Supplementation of the cultivation process with electricity derived from defatted algal biomass waste was also analyzed. The scenarios were evaluated for energy demand and environmental impacts amongst the boundary conditions based on a “cradle-to-gate” inventory. The results revealed that among all the scenarios, cultivation in raceway pond was ascertained to be the most energy intensive process with the mode of culture mixing and biomass productivity being the principal determinants. The impacts were found to be directly linked to energy demand and had an inverse relationship with biomass productivity. The geographic location of the energy sources affected the environmental implications of a given process. The integration of defatted algal biomass waste derived electricity with the cultivation system showed a minor reduction in the overall energy demand.