## 4 Discussion
\begin{table}
\begin{tabular}{l l l l l l l l l l} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{2}{c}{**Day**} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} \\ \cline{2-10}  & **1** & **5** & **10** & **15** & **20** & **25** & **30** & **35** & **40** \\ \hline
**10 CvA** & 2.3 & 6.7 & 16.7 & 25.3 & 34.5 & 42.4 & 51.5 & 53.2 & 57.8 \\ \hline
**10 CvB** & 3.8 & 14.1 & 40.3 & 80.1 & 104.3 & 117.1 & 156.5 & 160.3 & 173.7 \\ \hline
**5 CvA** & 1.2 & 3.9 & 10.2 & 15.8 & 21.6 & 26.7 & 32.2 & 34.5 & 36.0 \\ \hline
**5 CvB** & 2.2 & 9.5 & 29.5 & 48.5 & 64.9 & 80.0 & 97.3 & 99.3 & 107.8 \\ \hline
**10 ScA** & 2.2 & 6.7 & 15.9 & 25.2 & 35.6 & 44.1 & 53.2 & 58.1 & 60.2 \\ \hline
**10 ScB** & 4.0 & 14.5 & 40.3 & 73.1 & 99.4 & 127.9 & 184.6 & 191.7 & 195.7 \\ \hline
**5 ScA** & 1.3 & 3.8 & 9.2 & 15.4 & 21.3 & 26.6 & 32.4 & 35.6 & 36.8 \\ \hline
**5 ScB** & 2.4 & 10.1 & 30.5 & 50.6 & 67.8 & 78.8 & 92.9 & 97.7 & 102.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Growth rate of microalgal biomass: \(\mu\) (d\({}^{-1}\)). was 0.01625 mg/L [19]. In the present study, the concentration values of photosynthetic pigments obtained were higher, which proves the stimulating effect of coke wastewater on chlorophyll-a concentration in microalgae species. This could be due to the high turbidity of the wastewater, which limited the access of solar radiation and microalgae were forced to increase the production of photosynthetic pigments to meet the energy demand. The pH values obtained during the tests (6.7-7.8) were close to the optimal range for the growth of _C. vulgaris_, which ranges from pH 6.0 to 9.0 [20]. During the experiment, the gradual decrease in the pH value was consistent with the results obtained by [PERSON] and [PERSON] [21], who found lower pH values during the logarithmic growth phase, when photosynthesis takes place most intensively, and higher pH values in the lag and stationary phases. It should be emphasized that too high pH values may have unfavourable influence on algal cells at the biochemical level. [PERSON] [22] showed that at pH\(>9\), the sugar metabolism in _C. vulgaris_ microalgae can be disturbed. Algae can be cultured using phototrophic, mixotrophic or heterotrophic nutrition. _C. vulgaris_ can be grown using both auto- and heterotrophic nutrition. It has been shown that this species can grow in the presence of light and CO\({}_{2}\), or in the dark when an external source of organic carbon is supplied [23]. This particular property allows the growth of this species of algae in wastewater with significant turbidity and limited access to light [24]. The assimilation of organic compounds will take place in both mixed conditions, in light and in heterotrophic conditions, in the dark [21]. The volatile fatty acids contained in wastewater could be a source of carbon for microalgae. _C. vulgaris_ is a species extremely resistant to toxic substances present in the environment (e.g., phenols). Therefore, it can be used for treatment of wastewater with the content of toxic compounds. _S. armatus_ is more sensitive than _C. vulgaris_ to toxic substances present in the environment. This illustrates the observed changes in the growth phases of the microalgae population for both cultures. The results are consistent with [PERSON] and [PERSON] [21], who studied the effect of NH\({}_{3}\)-N on the growth of microalgae _C. vulgaris_ in the range of concentrations from 10 to 1000 mg/L. The researchers observed that the higher the initial concentration of NH\({}_{3}\)-N, the faster decrease in pH [21]. Nitrogen transformation in wastewater influenced the growth of microalgae biomass. According to [PERSON] et al. [25] the dynamics of growth of _Scenedensmus_ spp.