Microalgal biorefineries: a systematic review of technological trade-offs and innovation pathways

This review critically examines the entire value chain of microalgal biorefineries, with the central aim of elucidating the key technological, economic, and environmental enablers and barriers that govern their transition from pilot-scale demonstrations to commercially viable, circular-economy applications. A systematic literature search was conducted across five major scientific databases using predefined Boolean strings: "algal biorefineries," "microalgae biofuel," "techno-economic analysis," "life-cycle assessment," and "bioproduct recovery." Inclusion criteria encompassed peer-reviewed studies and authoritative policy documents published between January 2007 and March 2025 that provided empirical data on upstream cultivation, midstream processing, and downstream conversion, as well as techno-economic assessments (TEA) and life-cycle analyses (LCA). Exclusion criteria included non-English commentaries, purely theoretical models without experimental validation, and studies that focused exclusively on single-product streams. Unlike previous reviews that address isolated segments of the algal biorefinery pipeline, this work delivers a novel, integrative framework that synthesizes recent advances across cultivation modes, genetic and metabolic engineering, AI-enabled optimization, and IoT-driven monitoring. This review critically evaluates the trade-offs between CAPEX and OPEX, energy penalties associated with harvesting and drying, and inconsistencies in LCA to identify, where performance improvements yield the most significant economic and environmental returns. Finally, this review proposes a targeted research roadmap, spanning multivariate strain engineering, hybrid cultivation architectures, low-energy harvesting technologies, cascade-compatible fractionation platforms, standardized LCA/TEA protocols, and supportive policy mechanisms, that charts a clear path toward overcoming current bottlenecks. This comprehensive, evidence-based synthesis aims to inform both academic research and industrial strategy, thereby advancing the field of sustainable algal biorefineries.