Microalgae-mediated removal and biodegradation of indoor volatile organic compounds: mechanisms, performance metrics, and engineering constraints.

Indoor volatile organic compounds (VOCs) require treatment technologies that remain effective at low concentrations and high airflow rates without generating persistent secondary waste. This structured narrative review evaluates VOC removal by microalgae and algal-bacterial consortia using an evidence hierarchy that distinguishes direct gas-phase studies, gas-liquid reactor studies, and aqueous mechanistic studies. Formaldehyde and benzene, toluene, ethylbenzene, and xylenes (BTEX) are identified as the principal indoor VOC targets, whereas studies on phenols, polycyclic aromatic hydrocarbons, and other aqueous organic contaminants are considered mainly as mechanistic evidence. Direct evidence at indoor-relevant gas-phase concentrations remains scarce, and removal efficiencies obtained from liquid batch cultures cannot be extrapolated to indoor air without considering gas-liquid partitioning, biomass loading, reactor configuration, airflow, and abiotic losses. Quantitative comparison is further limited by inconsistent units, inadequate controls, incomplete carbon balances, and insufficient data on energy demand, byproducts, long-term stability, and bioaerosol containment. Future studies should therefore report standardized performance indicators and verify mineralization through mass-balance or isotope-based approaches. Current evidence supports microalgal systems primarily as application-specific biological polishing processes rather than established replacements for conventional air-cleaning technologies.