Annual Research & Review in Biology

The global agro-industrial sector generates billions of cubic metres of nutrient-rich effluents annually, constituting both a significant environmental liability and an underexploited resource for biological valorisation. Microalgal cultivation in agro-industrial wastewaters offers a dual-benefit platform: simultaneous tertiary-level wastewater treatment and production of high-value biomass for biofuels, biofertilisers, and speciality biochemicals. This comprehensive review critically examines (i) the physicochemical characteristics of dominant agro-industrial effluents, including dairy wastewater, swine effluent, palm oil mill effluent (POME), sugarcane vinasse, abattoir wastewater, and aquaculture discharge as substrates for algal cultivation; (ii) the nutrient dynamics governing nitrogen and phosphorus assimilation, with removal efficiencies reaching >95% under optimised conditions; (iii) strain-specific selection criteria encompassing tolerance to ammonia toxicity, turbidity, organic loading, and pathogen presence; (iv) comparative performance of cultivation systems from open raceway ponds to closed photobioreactors (PBRs) and hybrid configurations; and (v) techno-economic analysis (TEA) and life cycle assessment (LCA) findings that expose the current cost barriers, particularly harvesting (accounting for 20–30% of total production cost) and upstream pre-treatment. Emerging strategies including bioflocculation, microalgal–bacterial consortia, genetic strain engineering, and biorefinery integration are evaluated for their potential to reduce production costs below $2.00/kg biomass. This review synthesises evidence from peer-reviewed Q1-indexed studies (2018–2025) and identifies critical knowledge gaps that must be addressed to transition algal wastewater biorefinery from laboratory proof-of-concept towards commercially viable, potentially climate-positive technology.