Life cycle assessment with parameterised inventory to derive target values for process parameters of microalgae biorefineries

This paper presents a parameterised life cycle assessment approach to determine threshold values for input streams and target process yields to lower the resource consumption and ensure environmental competitiveness of a microalgal biorefinery producing substitutes for surfactants, palm oil, bioplastic feedstock and animal feed from Chlorella vulgaris. The biorefinery concept in this work investigated four different extraction pathways. 38 input parameters were defined and used to calculate the inventory of the biorefinery. Experimental and literature data were used to determine the lower and upper limits of the input parameters. A quasi-random Saltelli sample with a size of 4000 different combinations of input parameters was generated for a global sensitivity analysis. Different sources of heat, carbon dioxide and nutrients were considered as background system as well as a renewable electricity mix and on-site energy generation. The global sensitivity analysis was followed by a reverse analysis to identify threshold values for the key parameters. Membrane technologies for extracting proteins and polysaccharides show improved results compared to chemical extractions, while for lipid recovery, supercritical carbon extraction is more promising than conventional extraction. Needs for improvement were identified for the energy demand of drying processes, the efficiency of disruption methods, which should dissolve at least 50% of the proteins with less than 5kWh electricity per kg microalgae, as well as for the protein recovery yields of membrane technologies, which should exceed 70%. The outcomes suggest that microalgal production facilities should be integrated into existing industries to foster the use of waste streams of these industries and thereby reduce resource depletion and environmental impacts.