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

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.