Algae–Aerobic Granular Sludge (AAGS) for Wastewater Treatment: Granule Stability, Pollutant Removal Performance, and Biodiesel Potential

This study investigated the granule development and pollutant removal performance of algae–aerobic granular sludge (AAGS) and aerobic granular sludge (AGS) for wastewater treatment, as well as the characterization of the fatty acid methyl ester (FAME) composition for biodiesel production. The results demonstrated that AAGS had overall better pollutant removal performance than AGS. The average removal of total nitrogen (TN), total phosphate (TP), and chemical oxygen demand (COD) of AAGS were 96.16 ± 6.8%, 58.22 ± 5.44%, and 79.5 ± 5.48%, respectively, while AGS removed 70.95 ± 31.63%, 29.53 ± 12.54, and 74.8 ± 12.13% of TN, TP, and COD, respectively. AAGS required less time (16 days) than AGS (44 days) to achieve complete TN removal. AAGS produced more bound EPS than AGS, which makes it more stable. Scanning electron microscopy (SEM) surface images showed that AGS has dense surface morphology with mineral precipitate layers, while AAGS has a porous surface with filamentous algae intertwined. The biodiesel potential (fatty acid yield) of AAGS was 45% higher than that of AGS. The fatty acid methyl ester (FAME) yields obtained in AAGS and AGS were 64.4 ± 2.61 mg/g suspended solids (SSs) and 44.4 ± 0.9 mg/g SSs, respectively. AAGS has higher proportions of monounsaturated fatty acids (MUFAs/oleate) and polyunsaturated fatty acids (PUFAs/linoleate) than AGS. Thus, AAGS generates a more prospective biodiesel potential.