## 3 Results  
### Batch Culture Cultivation Techniques of microalgae  
The oxygen concentration is an important factor for the indication of cell activity. Oxygen in water and wastewater comes mainly from the atmosphere and from the process of photosynthesis by aquatic plants. Figure 1 presents the oxygen concentration changes with time during the cultivation of _C. vulgaris_ and _S. armatus_ in wastewater. The oxygen concentration was rather low because the wastewater was heavily contaminated with several contaminants. In the initial period of research, the concentration of dissolved oxygen decreased in the control samples (C). These phenomena can be influenced by other reactions (e.g., nitrification) besides algal growth that took place in wastewater. From thirty days until eightty days dissolved oxygen concentration remained relatively constant, and on day one hundred the maximum value of 4.1 mg/L was reached. Oxygen concentrations varied in the samples of wastewater with algae. In the wastewater with the addition of _C. vulgaris_ microalgae, the oxygen concentrations reached the maximum values ranging from 4.2 to 4.4 mg/L. In the samples containing _S. armatus_, oxygen concentrations reached the maximum values ranging from 4.4 to 4.8 mg/L. Figure 2 presents the chlorophyll-a concentration changes with time during the cultivation of _C. vulgaris_ and _S. armatus_ in wastewater. The contaminants contained in the wastewater affected the duration of individual growth phases of the microalgae population. The analysis of the individual growth phases of microalgae (based on changes in chlorophyll-a) revealed that for the concentration of microalgae of 100 g/L, the logarithmic growth phase began after ten days and lasted for the next thirty days. The following phases of microalgae population growth were observed: lag, exponential (logarithmic) growth, stationary and death phase. However, in the samples containing _S. armatus_ microalgae, the death phase began by the fiftieth day, which can be explained by the lower resistance of this species of algae, compared to _C. vulgaris_, and to the contaminants contained in the wastewater. Furthermore, in the case of microalgae _C. vulgaris_, after completion of the stationary phase (from 40 to 50 days) the phase of a very slow logarithmic growth started and lasted until the end of the research. Figure 1: Oxygen concentration observed during the batch culture cultivation of microalgae. It can be concluded that industrial wastewater with high ammonium concentrations can be used to cultivate microalgal biomass of _C. vulgaris_ and _S. armatus_ species. Figure 3 presents changes in pH values with time during cultivation of _C. vulgaris_. and _S. armatus_ in wastewater. Initially, a high pH above 9 was unfavourable for the growth of the population of microalgae and the assimilation of ammonium nitrogen. At high pH values, the form of NH\({}_{3}\) has a higher proportion, which is less preferred by microalgae, and at a pH of \(\sim\)7 the content of nitrogen in the form of N-NH\({}_{4}^{+}\), which is more easily assimilated by algae, is \(>\)95%. Regardless of the type of sorbents and their concentration, there was a gradual decrease in the pH value during the tests, from the initial values in the range of pH = 9.1-9.3 to the final pH values of 7.3-8.0. In the control sample (C), pH was in the range of 8.1-9.2. The analysis of the obtained test results shows that the use of algal biomass as a sorbent had a significant effect on the reduction in con N-NH\({}_{4}^{+}\) concentration in wastewater. Figure 3: pH values observed during the batch culture cultivation of microalgae. Figure 2: Chlorophyll-a concentration observed during the batch culture cultivation of microalgae. When microalgae were used at a dose of 100 g/L, the concentration of ammonium nitrogen in the wastewater decreased to 110 mgN-NH4\({}^{+}\)/L after sixty days, and to 20 mgN-NH4\({}^{+}\)/L after eighty days.