This study aimed to evaluate the potential of microalgae grown in wastewater to recover carotenoids and biogas in a biorefinery approach. To this end, two pilot raceway ponds treating real wastewater were operated with a hydraulic retention time (HRT) of 8 and 6 days. The maximum total carotenoid content in harvested biomass was 4.3 mg·gDW-1 with a HRT of 8 days, while it stabilized at 1.5–2.2 mg·gDW-1 with a HRT of 6 days. Biochemical methane potential tests were then run to quantify the biogas production from carotenoid-extracted biomass (136.3 mLCH4·gVS-1), which corresponded to 86% of the methane yield achievable from raw microalgal biomass. Co-digestion with primary sludge increased the methane yield production both for raw and carotenoid-extracted biomass by 58 and 86%, respectively, when a 75:25 ratio was employed and by 28 and 44%, respectively, when a 50:50 ratio (VS basis) was used. This approach is promising for recovering resources (bio-based products and bioenergy) in the framework of a circular bioeconomy.

This research has received funding from MCIN/AEI/10.13039/501100011033 and “ERDF A way of making Europe’’ under the projects AL4BIO (RTI2018-099495-B-C21) and Cyan2Bio (PID2021-126564OB-C32). E. Ruales acknowledges her grant 2020 FISDUR 00592 funded by AGAUR (Generalitat de Catalunya). M. Bellver acknowledges her grant PRE2019-091552 funded by MCIN/AEI/ 10.13039/501100011033 and “ESF Investing in your future”.