## 3 Results and Discussion
### Lipid Production, Biomass, and FAME Composition in ADSW with Optimized Glucose Supplementation  
Microalgae can thrive in wastewater containing various pollutants and produce bioactive compounds, such as lipids, proteins, and carbohydrates. This approach is eco-friendly and cost-effective for wastewater treatment. This study evaluated the biomass composition and lipid productivity of the oleaginous strain FACHB-8 under an optimal carbon supplementation to assess its potential for a simultaneous lipid production. After 14 days of cultivation in ADSW, cellular components included 45.59% lipids, 29.72% proteins, and 13.05% carbohydrates (Figure 8). Lipids were the most abundant component, followed by proteins and then carbohydrates. The lipid production reached 1.73 g/L with a productivity of 123.86 mg/L/day, highlighting its good potential for lipid production. The lipid content obtained in our studies (45.59%) surpasses that reported in previous studies, in which a 19-27% lipid content was observed in _Chlorella_ species using different carbon supplement strategies [18; 41]. Our results position _C. vulgaris_ FACHB-8 as a promising oleaginous microalgal feedstock for renewable biodiesel production. Furthermore, the biomass exhibited a protein content of 29.72%, suggesting its viability as a feedstock for animal feed production. In contrast, the biomass of the control group contained 33.86% lipids, 10.63% proteins, and 8.30% carbohydrates (Figure 8). Lipid accumulation is influenced by multiple factors, including the growth conditions (autotrophic, heterotrophic, or mixotrophic cultivation), culture age, algal strain, light intensity, pH, and nutrient supply [63]. The carbon source in the culture medium contributes to 17-65% of the dried cell weight of microalgae [64]. Microalgae utilize glucose to generate ATP, with glucose metabolism relying on cellular energy sources, enzymes, metabolites, and flux requirements. Glucose is converted into pyruvate and Acetyl-CoA, which is transported to the plastid for triacylglycered synthesis; the resulting triacylglycerol and fatty acids are then returned to the cytosol for lipid assembly. Therefore, carbon supplementation significantly enhances lipid accumulation, as shown in this study. Nitrogen accounts for  
Figure 8: Cellular components of FACHB-8 before and after carbon source optimization. 1-14% of the microalgae dried cell weight [64]. While nitrogen significantly enhances the biomass growth, it has a limited impact on lipid accumulation, and a high biomass productivity does not correlate with a high lipid content [65]. Lipid accumulation typically initiates after nutrient depletion for biomass growth. Strategies such as nitrogen starvation have been demonstrated to improve the lipid and carbohydrate production [66]. Notably, lipid accumulation may also be driven by excess carbon availability during nutrient depletion, rather than solely by nutrient starvation [29]. In this study, an enhanced lipid accumulation was observed under nutrient deficient conditions after day 8 (Figure 7), while the residual carbon in the medium might therefore be utilized for lipid synthesis rather than biomass growth. In addition, as aforementioned, although wastewater sources generally contain abundant dissolved organic matter, most of these compounds are not readily available as carbon sources for microalgae-driven nutrient removal. Previous studies indicate that ADSW contains significant amounts of refractory organic matter, which is challenging for microalgae to degrade and utilize [67]. Therefore, the presence of more carbon substances is desirable to improve both the biomass and lipid accumulation. In addition, the optimal performance of strain FACHB-8 was achieved with the 20 g/L glucose supplementation, resulting in a maximum biomass productivity of 271.31 mg/L/d, alongside a maximum lipid content (45.59%) and lipid productivity (123.86 mg/L/d). The improvement was notably significant when additional carbon sources (e.g., glucose) were supplemented.