## 3 Results and Discussion
### Biomass Production of C. zofingiensis in Whey Wastewater  
The high nutrient content in most wastewater necessitates expensive chemical treatments to eliminate it. Table 1 confirms that the raw and autoclaved whey wastewaters (WW) required treatment due to their significant pollutant potential caused by high levels of organic matter, nitrogen, and phosphorus. In this study, whey wastewater was diluted without any chemical treatment to reduce the effects of solids and high nutrient content on the growth of _Chromochloris zofingiensis_. Figures 1 and 2 show the growth curves and pH of _Chromochloris zofingiensis_ cultivated separately in different concentrations of whey wastewater (10%, 20%, and 50% \(\
u/\
u\)) diluted in BBM medium (control). Figure 1: Biomass production of _C. zofingiensis_ cultivated in various concentrations of whey wastewater (WW) compared to BBM medium. \(-\blacklozenge\) BBM medium; \(-\square\)–10% WW; \(-\square\)–20% WW; \(-\times\)–50% WW. As seen in the figures, biomass production decreased as the proportion of whey wastewater increased from 0% to 50%, and throughout the observation period, the pH in all treatments increased daily. A similar finding was observed by [PERSON] et al. [6] using mozzarella cheese whey. By contrast, [PERSON] et al. [51] and [PERSON] et al. [4] reported that increasing the proportion of whey wastewater led to a significant increase in cell number, demonstrating the varying effects of different wastewater compositions on microalgae. The maximum biomass production of 3.86 \(\pm\) 0.17 g L\({}^{-1}\) and productivity of 0.53 \(\pm\) 0.02 g L\({}^{-1}\) d\({}^{-1}\) were achieved in cultures containing 10% WW, followed by 20% WW (0.63 \(\pm\) 0.11 g L\({}^{-1}\); 0.25 \(\pm\) 0.03 g L\({}^{-1}\) d\({}^{-1}\)) and 50% WW (0.26 \(\pm\) 0.00 g L\({}^{-1}\); 0.02 \(\pm\) 0.00 g L\({}^{-1}\) d\({}^{-1}\)). Non-diluted raw whey wastewater resulted in total inhibition of cell growth. Biomass obtained with 10% WW was approximately double that of the BBM medium control (1.88 \(\pm\) 0.24 g L\({}^{-1}\)), indicating that the addition of this concentration of whey wastewater could enhance the growth of _C. zofingiensis_. The use of mixotrophic cultivation, which combines light and both organic and inorganic carbon sources, is regarded as the most effective method for producing microalgal biomass [52; 53]. The increase in biomass production of _C. zofingiensis_ using 10% whey wastewater was likely due to the utilization of lactose as an organic carbon source and the availability of other nutrients (Table 1). This fraction of whey wastewater produced a biomass comparable to that found by [PERSON] et al. [54] when using 30% whey wastewater to cultivate _C. prototheoides_. [PERSON] et al. [6] used 20% mozzarella cheese whey as a substrate for _Dunialella salina_ and reported a maximum biomass of 0.41 g L\({}^{-1}\), which was higher than that obtained using 50% and 75% whey wastewater. The use of 50% whey wastewater for _C. zofingiensis_ resulted in a biomass similar to that produced by _D. salina_. The production of biomass by _Chromochloris zofingiensis_ varies depending on the type of wastewater used [15; 16; 21]. Ref. [15] reported that the microalgae _C. zofingiensis_ could produce 2.21 g L\({}^{-1}\) biomass using 80% municipal wastewater as a culture medium. In another experiment, this species achieved 0.48 g L\({}^{-1}\) biomass when grown in 2.5% palm oil mill effluent [21]. In the present study, using 10% whey wastewater, _C. zofingiensis_ produced 3.86 g L\({}^{-1}\) biomass, consistent with the findings of [PERSON] et al. [16], who used dairy wastewater. Differences in wastewater composition, pretreatment techniques, and culture conditions could account for variations in biomass production. [PERSON] et al. [16] cultivated _C.