The potential of microalgae as an all-in-one bioremediation system of agricultural drainage water: A comprehensive review

Agricultural drainage water is an underutilized resource in water-scarce regions, but its reuse is limited by complex pollutant mixtures of nutrients, salinity, organic matter, pesticides, heavy metals, and pathogens. Conventional treatment methods are often fragmented, costly, and poorly suited to integrated removal. Microalgae offer a single-step bioremediation approach, coupling pollutant removal with biomass generation for value-added uses. This review synthesizes 1266 experimental datasets from 256 peer-reviewed studies (2010–2025) to quantify pollutant-specific removal efficiencies, identify top-performing genera, and evaluate operational factors across laboratory, pilot, and field scales. Median removal efficiencies were 84 % for total nitrogen (IQR: 66.5–95.1 %; 95 % CI: 80.8–87.1 %; n = 300), 88.8 % for total phosphorus (IQR: 76.9–98 %; 95 % CI: 85.3–92.3 %; n = 190), 70 % for pesticides (IQR: 37–90 %; 95 % CI: 53.6–78.5 %; n = 78) and 99 % for pathogens (IQR: 98.1–99.9 %; 95 % CI: 85.4–100 %; n = 16), with Chlorella excelling as a generalist, Scenedesmus achieving high COD and TDS removal, and halophiles such as Dunaliella thriving in saline environments. Performance was influenced by pollutant concentration, salinity, hydraulic retention time, and reactor configuration, with field systems showing 22 % lower efficiency than laboratory trials. Implementation analysis highlights photobioreactors for precision control and high-rate algal ponds for cost-effective scale-up. Key challenges include seasonal variability, contamination, harvesting costs, and biomass market barriers. This synthesis provides evidence-based pathways for advancing microalgae-based agricultural drainage water treatment from proof-of-concept to field deployment, supporting water reuse and circular bioeconomy goals in agriculture. • Systematic analysis of 1,266 experiments confirms microalgae as a powerful, single-step bioremediation platform for complex agricultural drainage. • Exceptional pollutant removal capabilities are quantified, with median efficiencies reaching 99% for pathogens and over 84% for key nutrients (N, P), demonstrating the technology's robust performance. • Genus-specific performance analysis identifies Chlorella as a versatile generalist, while halophiles (Dunaliella) and mixed consortia offer specialized advantages for saline and unstable field environments. • A critical performance gap of ~22% between laboratory and field conditions is identified, alongside major economic barriers to harvesting, representing the primary hurdles for practical implementation. • Future viability hinges on developing integrated biorefinery models that couple water remediation with biomass valorization, enabling a circular bioeconomy for water-stressed agricultural regions.