Experimental study demonstrates balanced biogas upgrading and astaxanthin production using microalgae in diluted digestate, indicating a viable integrated biorefinery pathway.
Key Points
Evaluate the effects of hydrogen sulfide levels in biogas and digestate dilution on Coelastrella sp. growth, nutrient removal, and astaxanthin biosynthesis.
Tested Coelastrella sp. under varying biogas H2S levels (0, 600, and 5000 ppmv) across untreated, pH-adjusted, and activated sludge-bioaugmented digestate.
Investigated digestate dilutions (10%, 50%, and 100%) under 600 ppmv H2S, followed by a two-stage cultivation strategy with high-light stress to stimulate carotenoid production.
Moderate H2S (600 ppmv) supported a maximum biomass concentration of 6.5 ± 0.1 g TSS L−1 with efficient CO2 and nutrient removal, whereas 5000 ppmv H2S inhibited growth unless mitigated by activated sludge bioaugmentation.
Diluted digestate (10–50%) improved growth, CO2 capture, and nitrogen assimilation, with a 10-fold dilution providing the best overall nitrogen and phosphate removal.
High-light stress induced astaxanthin accumulation up to 0.39 ± 0.07 mg g−1 at higher digestate concentrations, despite declines in lutein and β-carotene.