## 3 Results and Discussion
### Effect of Different Carbon Sources on Microalgal Growth, Pigments, and Nutrient Removal
Notably, glucose is usually preferred in _Chlorella_ species due to dedicated glucose transporters that facilitate cellular uptake, followed by mitochondrial oxidative phosphorylation to produce ATP [26]. Photosynthetic pigment profiles correlate with microalgal physiology and are modulated by strain-specific responses to carbon sources. Therefore, assessing the effect of different carbon sources on pigment profiles is essential. Chlorophyll \(a\), the dominant photosynthetic pigment in microalgae, is widely recognized as a reliable estimator for quantifying phytoplankton biomass. Generally speaking, higher chlorophyll \(a\) concentrations typically reflect a more active photosynthesis and increased uptake of nutrients, such as nitrate (NO\({}_{3}\)-), ammonium (NH\({}_{4}\)+), and phosphate (PO\({}_{4}\)3-). Thus, chlorophyll \(a\) is often positively correlated with nutrient removal efficiency and biomass accumulation [45]. As shown in Figure 3a, the chlorophyll \(a\) concentrations increased moderately in all groups after 14 days of cultivation. However, the sodium carbonate and sodium bicarbonate groups exhibited a lower chlorophyll \(a\) content compared to the control (CK). Notably, these two groups showed no significant difference in the dry cell weight relative to CK (Figure 2), indicating their inability to enhance the chlorophyll \(a\) accumulation or biomass productivity in ADSW. In contrast, glycerol-supplemented cultures achieved higher chlorophyll \(a\) levels by day 14 despite slower initial accumulation rates (Figure 3a). The glucose and sodium acetate groups displayed the most rapid chlorophyll \(a\) synthesis between days 2 and 4, followed by stabilization and a secondary increase after days 12-14 (Figure 3a). This two-phase trend corresponds to their growth dynamics, as both groups initiated the exponential phase between days 2 and 4 and subsequently entered the stationary phase (Figure 2). The late-phase increase in chlorophyll \(a\) could be attributed to the algal adaptation to ADSW and the continuous biomass accumulation supported by the exogenous carbon supplementation. Carotenoids, which function as photoprotectants and antioxidants to mitigate oxidative stress [46], exhibited concentration trends similar to chlorophyll \(a\) across various groups (Figure 3b). The levels of carotenoids often increase under high light or environmental stress conditions, helping to maintain a stable metabolism and cell function [46]. As a result, carotenoids are related to the adaptability and long-term productivity of microalgae. Collectively, these results demonstrate that glucose and sodium acetate were the most effective carbon sources for enhancing FACHB-8 growth and pigment synthesis in ADSW. Nitrogen is a key component of microalgal biomass (~10% of dry weight) [47]. Microalgae efficiently absorb nitrogen under varying substrate concentrations [48]. In terms of nutrient removal, the efficiency of FACHB-8 in ADSW supplemented with different carbon sources is summarized in Table 3. The control group (CK, wastewater only) showed a TN removal of 88.58% and a TP removal of 44.16%. However, the sodium acetate group only achieved a comparative TN removal of 87.65% and a TP removal of 48.32%. The highest TN removal of 90.62% and TP removal of 76.14% were observed in the glucose-supplemented group. As a readily assimilable carbon source, glucose supported an optimal algal growth in ADSW, thereby maximizing the nutrient removal efficiency. Consistent with these findings, the glucose group also exhibited the highest dry cell weight, chlorophyll a, and carotenoid concentrations, demonstrating its superior capacity to enhance both biomass production and wastewater remediation. This trend aligns with prior studies [49]. Consequently, glucose was identified as the optimal supplemented carbon source and served as the foundation for subsequent investigations.