## 3 Results and Discussion
### Nutrient Removal Efficiency  
The effectiveness of a microalgal wastewater treatment system is primarily determined by its nutrient removal efficiency. The concept of using microalgae to remove nutrients from wastewater is receiving significant global attention [10]. This study investigated the phycoremediation of unfiltered and sterilized whey wastewater by assessing the removal of TN (total nitrogen), NO\({}_{3}\)-N (nitrate), NH\({}_{4}\)-N (ammonia), PO\({}_{4}\)-P (phosphate), COD (chemical oxygen demand), TC (total carbon), TOC (total organic carbon), lactose, lactate, and acetate using _Chromochloris zofingiensis_ (Figures 3 and 4, and Table 2). Figure 3: Nutrient uptake from whey wastewater diluted in BBM medium by _Chromochloris zofingiensis:_ (**a**) Nitrate removal efficiency; (**b**) Phosphate removal efficiency; (**c**) Ammonia removal efficiency; (**d**) TN removal efficiency; (**e**) TC removal efficiency; (**f**) TOC removal efficiency. \(-\blacklozenge\)- BBM medium; \(-\square\)- 10% WW; \(-\triangle\)- 20% WW; \(-\times-50\%\) WW. Figure 4: Lactose, lactate, and acetate uptake from whey wastewater diluted in BBM medium by _Chromochlors zofingiensis_: **(a)** Lactose removal efficiency; **(b)** Lactate removal efficiency; **(c)** Acetate removal efficiency. –\(\square\)–\(10\%\) WW; \(-\triangle\)–\(20\%\) WW; \(-\times-50\%\) WW. Microalgal cells absorb nutrients such as carbon, nitrogen, and phosphorus from wastewater to synthesize essential compounds like proteins, phospholipids, and nucleic acids [55]. The whey wastewater used in this study exhibited elevated levels of these nutrients, requiring their removal before environmental discharge. The changes in nutrient concentrations (NO\({}_{3}\)-N, NH\({}_{4}\)-N, TN, PO\({}_{4}\)-P, COD, TC, TOC, lactose, lactate, and acetate) in sterilized whey wastewater compared to BBM medium during the cultivation period are shown in Figures 3 and 4. Figure 3a illustrates that nitrate (NO\({}_{3}\)-N) concentrations decreased daily in all experiments, with the degree of reduction varying among them. Cultivation of _C. zofingiensis_ in 10% whey wastewater diluted in BBM medium (90%) achieved the highest removal efficiency of 98.19% \(\pm\) 0.06%, followed by 20% WW (92.98% \(\pm\) 2.08%), 50% (34.58% \(\pm\) 1.69%), and BBM alone (31.34% \(\pm\) 4.02%). Remarkably, _C. zofingiensis_ removed over 80% of NO\({}_{3}\)-N within 3 days compared to BBM medium (3.66%), demonstrating that the addition of whey wastewater enhanced the nitrate removal efficiency. For ammonia (NH\({}_{4}\)-N), the removal efficiencies were similarly high, with 97.11% \(\pm\) 1.44% and 91.92% \(\pm\) 1.50% achieved for 10% and 20% whey wastewater, respectively. However, for 50% whey wastewater, the reduction was significantly lower at 38.47% \(\pm\) 7.94%. Total nitrogen (TN), total carbon (TC), and total organic carbon (TOC) were measured using a TOC-V CSN analyzer coupled with a Shimadzu TNM-1 instrument on days 0, 2, 4, and 7. These measurements provided insights into nutrient utilization by _C. zofingiensis_ and its potential for effective wastewater treatment. The amounts of these parameters in all variants of whey wastewater steadily declined until the final stage of culture, as seen in Figure 3d-f. The final total nitrogen (TN) contents in 10%, 20%, and 50% whey wastewater were reduced to 24.07 mg L\({}^{-1}\)\(\pm\) 1.09 mg L\({}^{-1}\), 48.59 mg L\({}^{-1}\)\(\pm\) 2.17 mg L\({}^{-1}\), and 196.40 mg L\({}^{-1}\)\(\pm\) 3.15 mg L\({}^{-1}\), respectively. The highest total nitrogen removal efficiency of about 92.69% \(\pm\) 0.29% was achieved in 10% whey wastewater. This finding was followed by 88.00% \(\pm\) 0.50% and 44.78% \(\pm\) 0.50% in 20% and 50% effluent, respectively.