Comparative Life Cycle Assessment of a microalgae-based oil metal working fluid with its petroleum-based and vegetable-based counterparts

Abstract

Microalgae recently emerged as an alternative resource to terrestrial plant-based biomass for the bio-economy, limiting the competition with food production. Whereas its main field of application is into biofuels and bioenergy products, recent developments have shown the potential of microalgae biomass for product manufacturing, including Metal Working Fluids (MWF). The environmental impact of such products, as compared to fossil-based alternatives, remains however questionable as there is a knowledge gap in published literature on the topic. This paper presents a comprehensive Life Cycle Assessment (LCA) of microalgae-based MWF, the first of its kind to our best knowledge. Primary life cycle inventories data were collected related to the production of microalgae oil from two distinct algae species, Nannochloropsis gaditana and Acutodesmus obliquus. The inventory considered the cultivation over four seasons into open raceway photobioreactor and into close vertical photobioreactor. The LCA results were then compared with the LCA of rapeseed oil-based MWF and conventional mineral oil-based MWF, to identify optimization levers.The study demonstrates that major improvements are needed to make the microalgae-based MWF process better from an environmental standpoint than its vegetable and mineral alternatives. Depending on algae species impacts from vegetable and mineral alternatives are 55–95% lower on Climate Change, 20–95% lower on Water use, and 85–95% lower on Fossil resource use. Electricity consumption during the cultivation and harvest stages, fertiliser and nutrient consumptions are the most significant contributors to environmental impacts. LCA results were found to be highly sensitive to the scenarios assessed, the background electricity mix and the allocation choices on co-products from the production of microalgae oil.