Algal–Bacterial Symbiotic Systems for Resource Recovery and High-Value Product Generation from Ammonia-Rich Food Wastewater: A Review

The global food processing industry generates substantial volumes of wastewater characterized by elevated ammonia nitrogen concentrations, presenting both significant environmental challenges and opportunities for nutrient recovery. Conventional biological treatment consumes substantial energy for aeration and sludge handling. Algal–bacterial symbiosis represents a promising circular-economy strategy that combines wastewater purification with biomass production. This review synthesizes current knowledge on the application of algal–bacterial consortia for treating ammonia-rich food wastewater, with emphasis on the synergistic mechanisms underpinning nitrogen removal, biomass production, and the generation of high-value products. It examines microalgae–bacteria interactions—mediated by oxygen–carbon dioxide exchange, nutrient conversion, extracellular polymeric substance dynamics, and quorum sensing signaling. Among these mechanisms, quorum sensing acts as one of several key regulatory pathways, modulating microbial community succession, biofilm formation, metabolic pathway expression, and stress tolerance, thereby contributing to pollutant removal efficiency and biomass resource quality, together with gas exchange, nutrient assimilation, and microbial metabolism. The review also evaluates recent advances in reactor configurations that facilitate scalable implementation. Furthermore, it discusses the valorization of harvested biomass into aquafeed, biofertilizers, biofuels, and bioactive compounds, alongside the principal barriers to commercialization. Finally, it highlights emerging research directions involving synthetic biology, artificial intelligence-assisted process control, and a biorefinery that may accelerate the transition of algal–bacterial symbiosis systems from laboratory research toward practical food wastewater treatment and resource recovery applications.