## 2 Scope and Methodology of the Research
\begin{table}
\begin{tabular}{l c} \hline
**Parameter** & **Value** \\ \hline Density (20 \({}^{\circ}\)C) kg/m\({}^{3}\) & 1280 \\ \hline Viscosity, mPas & 115 \\ \hline [Al\({}_{2}\)O\({}_{3}\)], wt.\% & 20.79 \\ \hline [Al\({}^{3+}\)], \% & 11.0 \\ \hline [Cl\({}^{-}\)], wt.\% & 7.0 \\ \hline Basicity, \% & 80.0 \\ \hline pH & 4.2 \\ \hline \end{tabular}
\end{table} 
Table 1: Characteristics of coagulant Flokor 1.2A. 60 \(\times\) 60 cm and 60 \(\times\) 120 cm. The photobioreactor was equipped with a narrow, rectangular glass partition mounted inside the tank, in which a LED panel (60 \(\times\) 60 cm) was placed to provide the necessary light for algal growth. Additionally, an LED panel (60 \(\times\) 120 cm), positioned above the tank, illuminated the culture from above, supporting the photosynthesis process. The cultivation was conducted continuously, with regular harvesting of the biomass produced, and simultaneous replenishment of fresh water and nutrients. The studies on the sedimentation efficiency of algae were conducted in two setups: specifically, in individual cylinders with a volume of 100 mL and using a four-position flocculation tester JT-40E from EnviSense (Lublin, Poland). The tester was equipped with four paddle stirrers, allowing for precise adjustment of both their suspension height and rotational speed. This design enabled the optimal adjustment of the mixing parameters to meet the specific requirements of each stage of the experiment, facilitating a detailed analysis of the sedimentation process. Additionally, the flocculation tester was equipped with an illuminated panel with adjustable positioning (vertical or horizontal), enabling observation and photographic documentation of the sedimentation process under transmitted light. Each 1 L beaker was filled with a microalgae suspension obtained from the photobioreactor tank. The stirrers were positioned 15 mm above the bottom of the beakers, ensuring efficient homogenization of the algal suspension. A precisely measured dose of coagulant was added to each beaker using a Sartorius pipette, followed by a two-stage mixing process. In the first stage, the suspension was vigorously mixed for 1 min at a speed of 150 rpm to ensure uniform distribution of the coagulant throughout the solution. In the second stage, gentle mixing was applied at a speed of 45 rpm for 9 min, facilitating the  
Figure 1: Photobioreactor for _Chlorella vulgaris_ BA-167 cultivation: (**a**) schematic diagram, (**b**) real view at the initial stage of cultivation—low cell concentration, (**c**) view of pH (left) and mixing (right) controller, and (**d**) real view at the highest cell concentration during algae cultivation. 1—glass tank (200 L); 2—pH sensor and controller; 3—propeller pump; 4—pH sensor; 5—peristaltic pump (nutrients dosing); 6—temperature controller; 7— heater; 8—CO\({}_{2}\) supply; 9—CO\({}_{2}\) ceramic sparger; 10—lighting (LED panel). initiation of the floc formation process. In each series of experiments, one beaker was filled with a suspension without the addition of a coagulant to serve as a control for comparing sedimentation efficiency. The study tested nine doses of the coagulant Flokor 1.2A, ranging from 0.01 to 0.36 g/L, selected based on preliminary studies of _Chlorella vulgaris_ BA-167 harvesting efficiency. The coagulant doses were determined with an accuracy of \(\pm\)0.001 g, and all flocculation experiments were performed in triplicate. During the observation of the microalgal sedimentation process, recorded with a Canon EOS 300D digital camera (Canon, Tokyo, Japan) and a Dino-Lite AM7515 MT8A digital microscope (Torrance, CA, USA), measurements were taken of the increase in the clarified liquid layer and the sediment layer. Sedimentation tests were conducted for suspensions with varying initial concentrations (\(C_{a,0}\)), ranging from 0.375 to 2.38 g/L. The concentrations of the algal suspension sampled from the photobioreactor were determined based on the spectrophotometer's calibration, as defined by Equation (1).