Integrating Microalgae-Based Technologies for Wastewater Purification and Resource Recovery: Emerging Opportunities

Abstract Microalgae-based systems can couple wastewater purification, nutrient recovery, carbon capture, and biomass valorization, but their deployment is limited by scale-up losses and uncertain economics. This review integrates bibliometric analysis of 426 publications (Web of Science and Scopus, 2014–2024), patent analysis of 418 families (Espacenet, 2009–2024), and a critical techno-economic synthesis. The evidence shows that Chlorella, Scenedesmus, and microalgae-bacteria consortia dominate research, with high nutrient removal reported mainly under optimized conditions. However, performance depends strongly on wastewater composition, reactor design, hydraulic retention time, climatic exposure, and harvesting route. Open ponds remain attractive for low-cost treatment, photobioreactors provide greater control but higher capital and energy demand, and biofilm systems may reduce dewatering costs. Techno-economic studies indicate that fuel-only pathways are fragile because cultivation, harvesting, drying, and conversion dominate costs. Feasibility improves when wastewater treatment services, nutrient recovery, carbon credits, and high-value coproducts are integrated in multiproduct biorefineries. Future work should prioritize primary-source-verified numerical reporting, long-term outdoor validation with real wastewater, and models that separate measured performance from assumptions.