Trisynergy of photosynthetic biogas upgrading, anaerobic digestate bioremediation, and pigment biosynthesis

Integrating environmental biotechnologies with valuable product biosynthesis can enhance the economic feasibility of environmental protection while reducing the costs of bioactive compound production. This study presents the first proof of concept for photosynthetic biogas upgrading and nutrient removal from anaerobic digestate, coupled with pigment biosynthesis in algae and cyanobacteria cultures. Pre-cultivation with aerobic activated sludge mitigated the toxicity of NH 4 + from the liquid fraction of anaerobic digestate and H 2 S from biogas, protecting pigment-producing strains. Partial pre-nitrification of NH 4 + followed by complete H 2 S pre-oxidation with aerobic activated sludge supported the growth of Chlorella sp. and Coelastrella sp., while Arthrospira platensis required complete pre-nitrification to grow with both clean and H 2 S-laden biogases. In the liquid fraction of anaerobic digestate, sulfur supplementation via H 2 S-laden biogas stimulated the propagation of all cultures. Under these conditions, the complete removal of H 2 S by aerobic activated sludge was recorded, while final CO 2 levels of 6.0%, 2.4%, and 0.07% were observed in Chlorella sp., Coelastrella sp., and A. platensis tests, correspondingly. Chlorella sp. and Coelastrella sp., respectively, removed 79 and 70% nitrogen and 64 and 65% of phosphorus under clean biogas, while A. platensis achieved 82% nitrogen and 73% phosphorus removals under pre-desulfurized H 2 S-laden biogas. These findings support the development of efficient cultivation strategies for biogas upgrading and the remediation of the liquid fraction of anaerobic digestate using pigment-producing strains. • Simultaneous biogas upgrading, digestate treatment and pigment synthesis validated • Biogas served as CO 2 source for culturing pigment-producing algae and cyanobacteria • Anaerobic digestate served as a culture medium for pigment biosynthesis • Activated sludge mitigated H 2 S and NH 4 + toxicities for algae and cyanobacteria • H 2 S containing biogas as headspace mitigated S deficiency of anaerobic digestate