New green biorefineries from cyanobacterial-microalgal consortia: Production of chlorophyll-rich extracts for the cosmetic industry and sustainable biogas

Microalgae are promising and sustainable candidates for developing biorefineries to obtain valuable bioproducts and bioenergy. However, key challenges, such as low biomass production, high-cost harvesting, and non-efficient extractions, are restricting its large-scale production. Symbiotic relationships between microalgae and cyanobacteria can simultaneously mitigate these technical and economic restrictions. This research aims to develop sustainable and cost-effective biorefineries from two microalgae-cyanobacteria consortia to produce valuable ingredients for the cosmetic field (chlorophylls) and bioenergy (biogas). Solvent screening and cell disruption experiments were carried out to optimise the chlorophyll extraction protocols. Green solvents were chosen for both consortia. The mildness method (vortexing) was enough to achieve the maximum extraction level of chlorophylls (4.8 +/- 0.2 mg/g) using 96% ethanol from a consortium composed of Chlorella vulgaris, Tetraselmis sp., and Kamptonema sp. The use of bead-beating was even more effective using water in the case of the consortium of C. vulgaris and Arthrospira platensis (13.5 +/- 1.1 mg/g). High-potential antioxidant chlorophyll extracts were obtained for the cosmetic sector. As ethanol traces were found in the residual biomass of the C. vulgaris, Tetraselmis sp., and Kamptonema sp. consortium, the highest cumulative biomethane production (472 +/- 32 mLCH4/gVS) was achieved with this residual biomass, the corresponding value for the initial consortium being significantly lower (239 +/- 32 mLCH4/gVS). The study concludes through the overall mass balances of the best biorefineries that it is possible to recover up to 100% of both consortia weight as cosmetic ingredients, biogas, and fertilisers or cultivation media.