## 3 Results and Discussion  
### N-Nh\({}_{4}\)\({}^{*}\) Removal from Coke Wastewater  
The concentrations of ammonium nitrogen in coke wastewater with the use of the sorbents _C. vulgaris_, _S. armatus_, and zeolite, and their mixtures, in dynamic conditions are shown in Figure 1.  
Figure 1: \(Cont.\)  
The results show that for the first 10 days, the presence of all sorption materials had an impact on the lowering of the N-NH\({}_{4}\)+ concentration. A high efficiency of N-NH\({}_{4}\)+ removal was found from the fourth to the twelfth day in wastewater to which a mixture of microalgae and clinoptilolite had been added (Figure 1C), regardless of whether the microalgae were in suspension (samples marked \"B\"--samples 5 Cv5 ZB and 5 Sc5 ZB) or immobilized on hydrogel beads (samples marked \"A\"--samples 5 Cv5 ZA and 5 Sc5 ZA). At that time, the concentration of ammonium nitrogen in these samples did not exceed 20 mg  
Figure 1: Concentration of nitrogen ammonium observed in wastewater: (**A**)—C. _ vulgaris_, (**B**)—S. _arnatus_, (**C**)—microalgae and zeolite. N-NH4\({}^{+}\)/L. A high efficiency was also obtained in the sample to which only clinoptilolite had been added at a dose of 100 g/L (sample 10Z); the content of ammonium nitrogen did not exceed 11 mg N-NH4\({}^{+}\)/L. When clinoptilolite was used to remove ammonium nitrogen at a dose of 50 g/L (sample 5Z), the content of ammonium nitrogen did not exceed 22 mg N-NH4\({}^{+}\)/L. This result is in agreement with some previous studies. It was reported that zeolite is a good material for the adsorption of ammonium from wastewater. [PERSON] et al. (2019) indicated that zeolite used as a pretreatment can mitigate ammonium toxicity for algae.The addition of zeolite can improve the recovery efficiency of ammonium in wastewater. After the adsorption of ammonium by zeolite, the process of slowly releasing ammonium back to the wastewater starts [18,19]. [PERSON] et al. (2019) indicated that such ammonium released by zeolite could be utilized by _Spirulina_. It is worth mentioning that _Spirulina_ is a bacterium and not a plant like _Chlorella_ sp., and therefore, there are different mechanisms for the growth and assimilation of ammonium by these two strains. Moreover, the innovative approach in the present study is that zeolite and microalgae were both utilized simultaneously at the same time for industrial wastewater treatment. [PERSON] et al. (2016) [20] also found that the tolerance level of ammonium for _Spirulina_ was very low, approximately 127.5 mg NH4\({}^{+}\)-N/L. However, some researchers found that the maximum tolerance level for NH4\({}^{+}\)-N for _Spirulina_ is 100 mg/L, while others stated that _Spirulina_ can grow in wastewater with a level of NH4\({}^{+}\)-N above 100 mg/L. Otherwise, _Chlorella_ sp. could grow in wastewater with 600 mg N-NH4\({}^{+}\)/L [19]. The low level of NH4\({}^{+}\)-N is insufficient for _Chlorella_ sp. growth. [PERSON] et al. (2016) indicated that the limiting factor for algae growth on dairy wastewater was the ammonia nitrogen deficiency. Nitrogen is needed for the synthesis of proteins, which is essential to algae replication. The researchers found that the initial concentrations of NH4\({}^{-}\)-N (4.96-21.45 mg/L) in diluted dairy wastewaters were extremely low, and there was a need to add nitrogen to increase the microalgal growth [20]. [PERSON] et al. (2019) also reported that high concentrations of ammonia could be toxic for microalgae in high-strength ammonium wastewaters like manure-free piggery. The researchers found that the removal efficiency of NH4\({}^{+}\)-N, as consumed by _C. vulgaris_, for 27.5, 55, and 110 mg N-NH4\({}^{+}\)/L was 100%. When the initial concentration of NH4\({}^{+}\)-N reached 220 mg/L, the removal efficiency was then only 50%. The researchers indicated that such an ammonium concentration inhibited _C. vulgaris_ growth, and as a result, limited removal efficiency from piggery wastewater was observed [21].