Microalgae-fungi co-cultivation for swine wastewater treatment: Insights into EPS-mediated aggregation mechanism

Although microalgae-fungi consortia (MFCS) have emerged as a sustainable strategy for swine effluent remediation, the mechanistic link between extracellular polymeric substances (EPS) evolution and aggregate stability is not fully understood. In this study, efficient MFCS were developed using Scenedesmus obliquus, Chlorella pyrenoidosa, and Chlorella vulgaris co-cultivated with Aspergillus niger. The S. obliquus–A. niger consortium achieved the best performance, achieving superior removal efficiencies for total phosphorus (TP, 89.93%), chemical oxygen demand (COD, 79.36%), and total nitrogen (TN, 73.85%). Physiological analyses revealed that high ammonia nitrogen stress in monocultures triggered severe oxidative damage, evidenced by 55–62% higher SOD/CAT activities and 56% higher MDA content compared to co-cultivation systems. Fungal co-cultivation increased EPS production by approximately 40% compared with the monoculture system and induced the formation of protein-rich, humic-like macromolecules enriched with carboxyl and carbonyl groups. These compositional changes enhanced EPS viscoelasticity and cohesion, resulting in compact algal–fungal granules with high structural stability. Techno-economic assessment revealed a total treatment cost of 0.304 USD/m³, which is comparable to conventional activated sludge treatment (∼0.30 USD/m³). However, the system distinguishes itself by eliminating sludge disposal costs, highlighting its cost-effectiveness for swine wastewater management. Overall, this study elucidates the EPS-mediated aggregation mechanism and demonstrates the feasibility of MFCS as an energy-efficient and economically sustainable strategy for swine wastewater management.