Fungal–Algal Co-Pellets from Coffee Effluent: A Sustainable Biorefinery Approach for Bioproducts and Waste Treatment

This study looked at a fungal–cyanobacterial co-pellet system for cleaning up coffee waste and producing high-value polymers. Optimization focused on the pelletization process, waste removal efficiency, and biomass yield. Optimal conditions, including pH (6.5), glucose concentration (6 g/L), and shaking speed (130 rpm), achieved a maximum cyanobacterial immobilization efficiency of up to 97% on the fungal mycelium. Scanning electron microscopy (SEM) confirmed the formation of an integrated co-pellet structure, with fungal hyphae acting as a physical scaffold and extracellular polymeric substances (EPSs) enhancing cell–cell adhesion. The co-culture system exhibited superior performance compared to fungal (20.56 g/L) and algal (1.09 g/L) monocultures. It effectively removed major coffee effluent pollutants, achieving a significant reduction in total phenolic compounds (74.5%). Furthermore, the co-pellets displayed a remarkable final biomass yield (24.33 g/L) and high production of extracellular polymeric substances (EPSs) (5.28 g/L) and intracellular polymeric substances (IPSs) (3.84 g/L). The synergistic relationship was further confirmed by high nitrogen contents in the co-pellets (15.24%), which significantly surpassed that of the individual fungal biomass, suggesting interspecies nutrient transfer. Valuable glycerol-lipids were detected and identified in the fermentative broth of the co-culture confirming a highly efficient bioconversion process. Analyses revealed a targeted metabolic flow toward the accumulation of monoglycerides, notably monooleoylglycerol and monopalmitin, highlighting a powerful cooperative compatibility for producing high-value emulsifiers. Overall, these findings firmly establish the cyano-fungal co-pellet system as a robust and sustainable biorefinery approach for treating complex industrial wastewater while producing a high-quality, value-added biomass suitable for utilization as a biofertilizer or animal feed.