Wastewater-to-biofuels and bioproducts through integrated anaerobic digestion, bioelectrochemical systems, and algal biorefineries: a systematic review of techno-economic and life-cycle evidence

Wastewater management is increasingly shifting from conventional pollution control toward resource recovery systems that support clean water access, renewable energy production, and circular bioeconomy development. This systematic review synthesizes the literature on wastewater-to-biofuels and bioproducts through the integration of anaerobic digestion, bioelectrochemical systems, and algal biorefineries, with particular attention to techno-economic analysis and life-cycle assessment evidence. A systematic literature review was conducted on peer-reviewed studies published between 2005 and 2025, resulting in 90 selected articles that were analyzed through thematic and comparative synthesis. The findings show a clear transition from single-technology optimization toward integrated systems based on the water-energy-nutrient nexus. Anaerobic digestion remains the most mature pathway for organic load reduction and biogas production, while bioelectrochemical systems provide additional opportunities for electricity and hydrogen recovery. Algal biorefineries strengthen nutrient recovery and expand the production of biomass-based bioproducts. Comparative synthesis indicates that integrated systems can outperform single technologies when organic load, nutrient availability, process compatibility, operational scale, and product valorization are aligned. Integration may become counterproductive when additional capital cost, operational complexity, energy demand, or downstream processing burdens exceed the value of recovered resources. The TEA-LCA synthesis demonstrates that technology selection should be guided by trade-offs between economic feasibility and environmental performance rather than by technical efficiency alone. This review contributes a decision-oriented synthesis for selecting single or integrated wastewater-to-biofuels configurations that are technically feasible, economically viable, and environmentally sustainable.