A comparative analysis of the environmental impacts of cultivating microalgae in different production systems and climatic zones: A systematic review and meta-analysis

Abstract Microalgae are used as alternative fuel, feed and food sources. As the production of microalgae requires energy, inorganic substances and technical equipment, life cycle assessments are necessary to evaluate the advantages of microalgae production in comparison to conventional systems. This review aims to compare different microalgae production systems that are used to produce microalgae for human nutrition in different climatic zones. A systematic literature review according to the systematic review checklist STARR-LCA was performed using ScienceDirect and Google Scholar . The studies were included that utilized primary data, used a functional unit based on dry algal biomass and were modeled cradle-to-gate. Only the studies conducted in real pilot and experimental plants were considered. The data for the life cycle inventory were recorded and harmonized, and the environmental performance of the different microalgae species and their cultivation methods were then modeled in SimaPro according to ISO 14040/44 using the ecoinvent database v3.4. Sixteen different production scenarios were examined with cultivation plants located in the Netherlands, Spain, the United States and Singapore. Open raceway ponds were compared to horizontal, vertical and bubble column photobioreactors. Five different microalgae species were investigated: Nannochloropsis sp., Scenedesmus dimorphus , Heterosigma akashiwo , Alexandrium minutum and Karlodinium veneficum . Regardless of the cultivation system design, the hotspot processes were ‘heating’, ‘aeration and CO 2 ’, ‘base energy for cultivation’, ‘cooling’ and ‘mixing’. Furthermore, the biomass productivity and corresponding environmental impacts were all confirmed to be highly dependent on the climatic conditions and the cultivation systems used. Open ponds and photobioreactors are each most suitable for a different climatic zone.