## 2 Scope and Methodology of the Research  
The study assessed algae harvesting efficiency at pH 6.6, which corresponds to optimal cultivation conditions, without the addition of any chemicals that could alter the suspension's pH. During cultivation in photobioreactors, pH 6.6 was continuously maintained through automated CO\({}_{2}\) dosing, providing an environment conducive to microalgae growth. Analyzing the flocculation process under these cultivation conditions provides practical insights into optimizing algae harvesting processes. This approach ensures that the results are directly related to real-world microalgae production systems, closely reflecting the conditions used during cultivation. To evaluate the effect of microalgae concentration on harvesting efficiency, sedimentation studies were conducted under conditions of autoflocculation and flocculation using the coagulant Flokor 1.2A. This coagulant belongs to the group of pre-hydrolyzed, highly alkaline, polymerized aluminum coagulants of the latest generation, produced by Dempolic Eco (Opole, Poland). FLOKOR(r) products are available in liquid form and are used in the treatment of drinking water, process water, swimming pool water, industrial and municipal wastewater, as well as in technological processes across various industrial sectors. When Flokor 1.2A is used, a slight decrease in the pH and alkalinity of the water after coagulation can be observed (pH 6.8-7.5). Due to its high polymerization level (Al/Cl up to 1.8) and basicity >75%, it operates effectively across a wide range of impurity concentrations by neutralizing the surface charge of colloidal contaminants. This reduces the required dosage compared to other aluminum- and iron-based coagulants, thereby minimizing the volume of coagulation sludge and improving the efficiency of the technological system. The basic characteristics of Flokor 1.2A are presented in Table 1.  
The material used in the research consisted of the unicellular Baltic green algae _Chlorella vulgaris_ BA-167, obtained from the Culture Collection of Baltic Algae (CCBA) at the Institute of Oceanography, University of Gdansk. The inoculum of _Chlorella vulgaris_ BA-167 was prepared in 100 mL glass Erlenmeyer flasks, each containing 50 mL of f/2 medium, which contains nitrogen, phosphorus, vitamins, and trace elements [50]. The medium was prepared with demineralized water and autoclaved for 20 min at 121 \({}^{\circ}\)C.  
The cultures were incubated for 21 days under constant light conditions (12 h light/12 h dark photoperiod, neutral white light provided by an LED panel) at room temperature (20 \({}^{\circ}\)C). The inoculum prepared in this way was used to initiate large-scale cultivation in the photobioreactors. The algae were cultivated in two rectangular glass tanks measuring 109 \(\times\) 45 \(\times\) 50 cm, with a total volume of 200 L and a working volume of 170 L, as shown in Figure 1. Each photobioreactor was equipped with a propeller pump (Jebao SINE Wave Maker SOM-16, Jebao Co., Ltd., Zhongshan, China) to maintain a constant flow of the algal suspension and ensure effective mixing. The photobioreactors were operated under controlled pH and temperature conditions. The pH was maintained at 6.6 and automatically regulated by a pH controller with an ERH-AQ1 sensor (Hydromet, Gliwice, Poland) integrated with the photobioreactor's carbon dioxide supply system. The use of a porous ceramic sparger enabled the generation of fine CO\({}_{2}\) bubbles in the algal suspension, enhancing gas-phase dissolution. Heaters installed in the photobioreactors ensured that the cultivation temperature remained constant within the range of 25-27 \({}^{\circ}\)C, with an accuracy of \(\pm\)1 \({}^{\circ}\)C. Light energy was supplied by LED panels (GREENLUX, Stare Mesto u Frydku-Mistku, Czech Republic) emitting neutral white light (4000 K), with dimensions of