Targeting greens and yellows: A solar biorefinery analysis for the microalgae-based co-production of pigments, proteins, and fuel

Microalgae biorefineries can enable cost effective cascaded biomass use to produce multiple product and revenue streams (e.g., protein-rich foods & feeds, pigments, biomaterials and high-density liquid fuels). The aim of this work is to develop a multi-product microalgae biorefinery simulation that employs a green chemistry-based alkaline saponification treatment to extract proteins, chlorophyllins, and lutein from microalgal ( Chlorella sp.) biomass and subject it to techno-economic evaluation for a 50-ha facility. Optimisation of the saponification parameters revealed that the most value-generating strategy is a sequential saponification in which the biomass is first treated at mild conditions (0.4 % NaOH, 45 °C, 0.5 h) to recover a high quality protein fraction (with a calculated extraction efficiency of 42.5 %), followed by a harsher treatment (4 % NaOH, 70 °C, 8.5 h) to extract carotenoids and recover chlorophyllins for the synthesis of copper chlorophyllin. Water-insoluble chlorophylls are usually not refined, but their water-soluble and stable copper chlorophyllin derivatives offer significant utility for materials science, nutrition, and biomedicine. The obtained protein fraction has a purity of 44 %. It contains high molecular weight proteins and has a relatively unchanged amino acid composition, making it competitive with common plant-based protein meals on the market. The purities of the obtained carotenoid (mainly lutein) and the copper chlorophyllin fractions are estimated to be 5.47 % and 10.9–13.6 %, respectively. The process also produced a low-nitrogen fuel feedstock that can be converted into renewable diesel using hydrothermal liquefaction. The techno-economic analysis results show that at a 10 % internal rate of return (IRR) competitive bioproduct valuation (7 US$·kg −1 for 5 % lutein, 16 US$·kg −1 for 10 % Cu-chlorophyllin, 3.28 US$·kg −1 for 44 % protein, and US$0.67 L −1 for renewable diesel) can be achieved, which shows promise for saponification as a major biomass fractionation process. Multi-product microalgae biorefineries will help achieve a circular bioeconomy.