Microalgae biotechnology applied to wastewater treatment and biopolymer production: A sustainable alternative for resource recovery

Cultivating microalgae in wastewater offers the dual benefit of efficiently removing pollutants while generating biomass suitable for high-value bioplastics, thus supporting the principles of a circular bioeconomy. Despite this potential, integrating microalgae cultivation for biopolymer obtention into wastewater treatment remains unresolved. Unlike existing reviews, this manuscript primarily aims to explore effective large-scale strategies for accumulating valuable compounds such as polysaccharides, proteins, and polyhydroxyalkanoates from biomass within a wastewater treatment plant context. It addresses the main routes for obtaining biopolymers through the valorization of microalgae biomass, emphasizing a comprehensive approach that blends biomass with other plastic sources, employs two-stage anaerobic digestion, and recovers organic acids for polyhydroxyalkanoate production alongside operational strategies to enhance biomass quality. High-rate algal ponds arranged in series and a two-stage cultivation process are proposed as promising operational strategies to increase the value of biomass for biopolymer production. Key challenges include scalable production processes and improved economic viability to encourage wider industry adoption. The manuscript also offers insights for enhancing the sustainability performance of bioplastics, emphasizing the need to tackle the social and environmental impacts, the last derived from low biodegradability and toxicity due to additives and solvents. Regulatory and public policies, along with transforming wastewater treatment plants into wastewater biorefineries, are also crucial factors in making the technology more commercially feasible. By consolidating current research, this review aims to promote sustainable strategies through microalgal applications that optimize environmental and economic outcomes.