Microalgal-bacterial granular sludge: bridging the gap between laboratory discovery and engineering reality

Microalgal-bacterial granular sludge (MBGS) has been extensively studied as a promising process for energy-efficient and carbon-neutral wastewater treatment. The self-sustaining synergy of this process has been validated under laboratory conditions, and CO₂ supplementation has been shown to push the system toward carbon-negative operation. However, the technology remains largely confined to laboratory benchtops, with most studies conducted under constant conditions using synthetic wastewater. Existing reviews have mainly summarized performance or individual operational factors, but have not translated these findings into a coherent engineering framework for scalable deployment. Based on a comprehensive synthesis of past review articles and experimental studies, this Perspective proposes seven testable and, where possible, quantifiable engineering perspectives: dynamic diel carbon management for net greenhouse gas removal, active microbiome engineering for targeted pollutant degradation, multi-layer stacked photobioreactors with integrated light-guide systems, self-cleaning reactor walls to overcome biofouling, integrated design strategies for simultaneous shear delivery and light utilization in a single reactor, hydrocyclone-based physical selection for long-term stability, and tiered biorefinery with integrated life-cycle assessment. The key advance is not the individual concepts themselves, but their integration into a coordinated, hypothesis-driven framework that shifts the focus from laboratory feasibility to scalable engineering implementation. These perspectives are grounded in established knowledge and offered as testable hypotheses to guide the next generation of research and development toward full-scale deployment.