## 3 Results and Discussion
### The Removal Rate of N-NH4+ Removal from Coke Wastewater  
Table 1 presents the values of the removal rate of N-NH4+ from coke wastewater. The obtained values of \(\eta_{\rm N}\) for the mixture of _C. vulgaris_ and clinoptiolite were at a similar level (approx. 8.8-10.3 mg/L d), regardless of the form of microalgae used (immobilized or in the form of a suspension). The addition of successive portions of wastewater affected changes in the rate of N-NH4+ removal from coke wastewater. The results showed that after the application of microalgae at a concentration of 100 g/L, higher maximum values of the N-NH4+ removal rate from coke wastewater were obtained (6.9 \(\pm\) 0.1 mg/L d for _C. vulgaris_ and 20.9 \(\pm\) 0.9 mg/L d for _S. armatus_) than when microalgae at a dose of 50 g/L (6.4 \(\pm\) 0.09 mg/L d for _C. vulgaris_ and 28.4 \(\pm\) 0.2 mg/L d for _S. armatus_) were applied. Similarly, using clinoptiolite at a concentration of 100 g/L resulted in higher maximum \(\eta_{\rm N}\) values (11.2 \(\pm\) 0.2 mg/L d) than when clinoptiolite was used at a concentration of 50 g/L, where \(\eta_{\rm N}\) was 10.3 \(\pm\) 0.1 mg/L d.  
Zeolite with immobilized _C. vulgaris_ reached \(\eta_{\rm N}\) of 10.3 \(\pm\) 0.09 mg/L d and with _S. armatus_ achieved a value for \(\eta_{\rm N}\) of 21.9 \(\pm\) 0.2 mg/L d, while zeolite with _C. vulgaris_ suspended achieved a value for \(\eta_{\rm N}\) of 10.2 \(\pm\) 0.02 mg/L d and with _S. armatus_ achieved a value for \(\eta_{\rm N}\) of 39.2 \(\pm\) 0.1 mg/L d.  
The rate of ammonium nitrogen removal from coke wastewater using microalgae immobilized on a carrier at concentrations of 100 and 50 g/L was higher than the rate of ammonium nitrogen removal from wastewater using microalgae in the form of a suspension. This result is in agreement with other authors. [PERSON] et al. (2022) utilized immobilized algae in an alginate-calcium hydrogel and discovered that the dry weight rose 4.75 times during 2-day semicontinuous cultivation. The authors indicated that immobilized microalgae achieved a high nutrient removal rate from wastewater at continuous operation. The highest removal rate for ammonia was 28.95 mg/L d [32]. The highest concentration of N-NH4+ of 72.51 mg/L used by [PERSON] et al. (2022) was lower than in the present study, and that could have resulted in the higher removal rate than they achieved. The use of natural sorbents, such as microalgae and clinoptiolite embedded in hydrogel, is an alternative way to support the treatment of industrial wastewater with high concentrations of ammonium nitrogen, reducing the consumption of chemical reagents \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & \multicolumn{4}{c}{\(\eta_{\rm N}\), mg/L d} \\ \hline \hline  & \multicolumn{4}{c}{**Days**} \\ \hline  & **10** & **20** & **30** & **40** \\ \hline
10 CvA & 3.8 \(\pm\) 0.04 & 5.3 \(\pm\) 0.01 & 5.7 \(\pm\) 0.1 & 6.9 \(\pm\) 0.1 \\
10 CvB & 3.1 \(\pm\) 0.03 & 2.1 \(\pm\) 0.03 & 4.8 \(\pm\) 0.03 & 5.9 \(\pm\) 0.03 \\
5 CvA & 2.6 \(\pm\) 0.02 & 1.8 \(\pm\) 0.01 & 4.8 \(\pm\) 0.1 & 6.4 \(\pm\) 0.09 \\
5 CvB & 2.5 \(\pm\) 0.01 & 1.3 \(\pm\) 0.01 & 4.2 \(\pm\) 0.01 & 5.6 \(\pm\) 0.03 \\
5 Cv5 ZA & 10.3 \(\pm\) 0.09 & 9.0 \(\pm\) 0.03 & 9.9 \(\pm\) 0.02 & 9.9 \(\pm\) 0.02 \\
5 Cv5 ZB & 10.2 \(\pm\) 0.02 & 8.9 \(\pm\) 0.02 & 9.6 \(\pm\) 0.1 & 9.8 \(\pm\) 0.09 \\
10Z & 11.2 \(\pm\) 0.2 & 10.3 \(\pm\) 0.03 & 10.8 \(\pm\) 0.02 & 10.6 \(\pm\) 0.02 \\
5Z & 10.3 \(\pm\) 0.1 & 8.8 \(\pm\) 0.1 & 9.5 \(\pm\) 0.1 & 9.9 \(\pm\) 0.02 \\
10 ScA & 4.2 \(\pm\) 0.2 & 4.4 \(\pm\) 0.1 & 17.0 \(\pm\) 0.2 & 20.9 \(\pm\) 0.9 \\
10 ScB & 2.0 \(\pm\) 0.03 & 2.4 \(\pm\) 0.03 & 13.8 \(\pm\) 0.7 & 17.7 \(\pm\) 0.5 \\
5 ScA & 2.4 \(\pm\) 0.04 & 7.5 \(\pm\) 0.4 & 7.7 \(\pm\) 0.3 & 28.4 \(\pm\) 0.2 \\
5 ScB & 2.7 \(\pm\) 0.05 & 0.2 \(\pm\) 0.03 & 9.0 \(\pm\) 0.2 & 10.5 \(\pm\) 0.3 \\
55 ScZA & 1.2 \(\pm\) 0.03 & 6.1 \(\pm\) 0.7 & 17.4 \(\pm\) 0.9 & 21.9 \(\pm\) 0.2 \\
5 Sc5 ZB & 10.1 \(\pm\) 0.2 & 19.1 \(\pm\) 0.2 & 32.0 \(\pm\) 1.0 & 39.2 \(\pm\) 0.1 \\ \hline \hline \end{tabular}
\end{table}