## 3 Results
### The Components of the Cultivation Medium  
The results of the analysis of the cultivation medium components are presented in Table 2. About 50% of the biomass consists of carbon during the cultivation of _Arthrospira platensis_, so the main contribution to the result of cultivation is made by the amount of carbon [38]. The cultivation medium determines the biomass growth rate and the biochemical parameters that will change during cultivation [37;44;45]. The main research is currently focused on identifying the factors influencing the cultivation of microalgae. Currently, the key factors include the following: pH [16;17;37], nutrient medium [36;38;46], type of cultivation [38;45;47], geometric dimensions of the reactor [47;48], temperature [44;47;49], light [38;44;47], diffuser  
\begin{table}
\begin{tabular}{p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt}} \hline \hline
**Results/** & **COD, mgO/dm3** & **BOD, mgO2/dm3** & **Bicarbonates, mg/dm3** & **Carbonates, mg/dm3** & **Potassium, mg/dm3** & **Magnesium, mg/dm3** & **Phosphates, mg/dm3** & **Nitrates, mg/dm3** & **Sulfrates, mg/dm3** \\ \hline
0 day & 120 & 70 & 11050 & 1400 & 1800 & 20.5 & 376 & 1950 & 450 \\ \hline Absolute change & 39 & 25.1 & \(-\)160 & 97 & \(-\)69 & \(-\)2.5 & \(-\)43 & \(-\)618 & \(-\)27 \\ \hline Relative change.\% & 24.5 & 26.4 & \(-\)1.5 & 6.5 & \(-\)4.0 & \(-configuration [41; 48; 49], mixing speed of nutrient medium components [38; 48; 49], nutrient supply method (additional supply of nutrients during cultivation [40; 46; 47] and method and nature of CO2 supply [37; 38; 48]) and nitrogen and phosphorus consumption [17; 47; 48]. Variations of Zarrouk's medium are mainly used as a nutrient medium [47]. The main directions of research on its application are related to the search for a cheaper source of carbon, since the carbon source is its most expensive component in the price of Zarrouk medium [38; 47] (studies are also being conducted to find a cheaper source of nitrogen [38; 47], which is especially important for microalgae with a high concentration of proteins). Currently, the main ideas to reduce the cost of the carbon source are associated with the use of carbon dioxide in the cultivation medium, which is a by-product of many factories, for example, the use of blue gases as a source of carbon or only CO\({}_{2}\) from blue gases [46; 49]; however, its use is limited by pollutants in flue gases (heavy metals, SO\({}_{\chi}\), NOx). For example [49], at SO\({}_{2}\) concentrations of 150 ppmv, Chlorella KR-1 cell growth is inhibited (inhibition starts from 60 ppmv). At the same time, research is underway to find a cheaper culture medium. For example, the use of wastewater or any by-products of industry as components of a nutrient medium for the cultivation of microalgae [47]. Few studies have been conducted to investigate the effect of aeration on the growth pattern of _Arthospira platensis_[48]. At the same time, it was shown for _Arthospira platensis_ that growth is better with CO\({}_{2}\) aeration, and it is also easier to maintain a constant pH in a system with intermittent aeration compared with a continuous supply of carbon dioxide [16]. At the same time, critical concentrations of CO\({}_{2}\) lead to a decrease in the growth rate of microalgae [16]. It is necessary to take into account the efficiency of CO\({}_{2}\) utilization for the growth of microalgae, since only a part of carbon from carbon dioxide will be spent on photosynthesis [16]. The utilization efficiency, in turn, shows a dependence on the gas-liquid transfer of CO\({}_{2}\)[16]. The growth of _Arthospira platensis_ is accelerated at an aeration rate of 150-500 mL \(\times\) min\({}^{-1}\) and that at an aeration rate of 2000 mL \(\times\) min\({}^{-1}\) and higher, a decrease in the growth rate of microalgae is observed [38].