The study addressed the need for sustainable greywater treatment, aiming to mitigate water scarcity and pollution. The potential of using microalgae cultivated in greywater with zinc oxide nanoparticles (ZnO/GAC-nanocomposite) was investigated for these purposes. A batch photobioreactor was employed for 15 d. The nanocomposite system significantly improved nutrient removal, with optimal removal efficiency of 80 % for TOC, 94.2 % for PO43−, and 99.6 % for NH4+. The presence of nanocomposites improved microalgae growth, achieving a density of 1.8 g/L compared to 0.83 g/L without nanocomposites. The microalgal biomass obtained had a high volatile matter content of 74.4 %, low ash content of 5.1 %, and fixed carbon of 20.4 %. The biomass includes 46.74 % carbon, 5.72 % hydrogen, and 38.75 % oxygen, with a high heating value of 18.32 MJ/kg. The reusability of ZnO/GAC-nanocomposite was also assessed, which maintained effective nutrient removal after four cycles, with NH4+, PO43−, and TOC removal rates of 86.1 %, 83.2 %, and 69.8 %, respectively. Comparison of treated greywater with a pH of 8.5, turbidity <4 NTU, COD, NH4+, PO43− of 34, 0.032, and 0.48 mg/L, respectively, with various reuse standards, indicated its potential reuse for toilet flushing.