Integrating Fungal-Assisted Microalgal Harvesting for Sustainable Treatment and Resource Recovery from Wastewater

Microalgae cultivation is often limited by the high cost and inefficiency of harvesting, making it a major barrier to large-scale resource recovery. Traditional methods such as centrifugation or chemical flocculation are expensive and environmentally unsustainable. As a biological alternative, filamentous fungi can form pellets or hyphal networks that entrap microalgae cells via bio-flocculation, facilitating easier separation from the culture medium. This study aimed to optimize culture conditions for fungal pellet formation and develop effective microalgae–fungal composites for improved harvesting. Fungal isolates including Aspergillus niger, A. fumigatus, A. flavus, and unidentified strains were screened for their pelleting capacity and nutrient removal efficiency. Through OVAT analysis, key factors such as pH, agitation speed, carbon source, and C:N ratio were found to significantly influence pellet formation. One isolate (FP) showed strong potential, forming pellets under stationary conditions and performing best at neutral to alkaline pH. Molecular analysis identified FP as a fungal consortium containing members of Ascomycota, Mucoromycota, Basidiomycota, and Rozellomycota. When applied to cocoa pulp wastewater, the microalgae–fungi composites outperformed monocultures in reducing NH₄⁺-N, COD, and PO₄³⁻-P. Interestingly, microalgae delayed fungal sporulation. These findings highlight the potential of fungal consortia in enhancing both microalgae harvesting and wastewater bioremediation.