## 3 Research Results and Their Analysis
Depending on the impurities in the water, the addition of the coagulant can lead to the formation of flocs even during the rapid mixing phase. The precipitated Al(OH)\({}_{3}\), with its highly developed adsorptive surface, serves as the initial bridging element, neutralizing the colloidal particles. The size distribution of aggregates formed with Flokor 1.2A (initial algae concentration \(C_{a,0}=0.960\) g/L) is shown in Figure 4, with floc sizes ranging from 20 to 160 \(\upmu\)m (Figure 4b). A detailed analysis of the collected experimental data revealed that the largest flocs, in terms of size, were formed at Flokor 1.2A concentrations of 0.12 and 0.2 g/L. At these concentrations, the measured minimum, average, and maximum floc sizes were 50 (100)  
Figure 4: Microscopic image of the algae sample analyzed using Motic Images Plus 3.0 (**a**); cell and floc size distribution with the Flokor 1.2A, \(C_{a,0}=0.960\) g/L and \(C_{F}=0.2\) g/L (**b**). 410 \(\upmu\)m and 100 (200) 690 \(\upmu\)m, respectively. For all algae concentrations analyzed in this study, the algal suspension was found to be polydisperse. The data presented in Figures 3 and 4 show that the average size of the aggregates in the algal suspension was 39.4 \(\upmu\)m for autofloculation and 76.4 \(\upmu\)m for flocculation with the addition of Flokor 1.2A. Given that the average size of a single algal cell is 4.6 \(\pm\) 0.2 \(\upmu\)m, the aggregates that settled in both cases were significantly larger. These differences in the size of individual cells and the formed aggregates had a substantial impact on the sedimentation rate, and consequently, on the efficiency of algal harvesting. The studies also revealed that flocs exceeding 160 \(\upmu\)m in size formed in algal suspensions with concentrations of 0.615 g/L and 0.960 g/L, when flocculant concentrations were 0.12 g/L and 0.17 g/L, respectively. Figure 5a shows the experimental setup for real-time observation of the sedimentation of the algal suspension. During the experiments, distinct zones with varying concentrations of microalgae, typical of the sedimentation process, were observed, including the clear water zone, the suspension zone, and the sludge zone. The particle size distribution of the flocs in the suspension was determined using the Dino-Lite AM7515 MT8A digital microscope, mounted on a stand near the transparent wall of the container where sedimentation occurred. This setup allowed for the observation and real-time recording of the entire suspension, rather than just a small sample taken from the beaker, as shown in Figure 5b. Observations during the sedimentation process revealed that the degree of polydispersity of aggregates and flocs in the suspension was heterogeneous and changed throughout the process. In most cases, it was challenging to clearly define the boundaries between the clear liquid, concentrated suspension, and sediment. To determine these boundaries, an analysis of numerous images and videos recorded during the experiment was conducted. Example sedimentation curves of microalgae obtained under different process conditions are shown in Figure 6.  
The curves represent the changes in the position of the boundary between the clarified liquid and the suspension. The slope of these curves reflects the sedimentation rate, and consequently, the volume of the forming supernatant. The data analysis presented in Figure 6a shows that the rate of formation of the clarified liquid zone varies over time and is influenced by the initial algal concentration in the suspension. The sedimentation curves exhibit a linear pattern throughout the entire analyzed time period, suggesting that the process rate is constant and depends solely on the algal concentration in the suspension. These results indicate that the rate of supernatant formation remains relatively low. For initial algal suspension concentrations ranging from 0.375 to 2.380 g/L, the sedimentation rate varied between 0.11 and 1.86 mm/min.