## 1 Introduction
The unique properties of algae necessitate addressing the high costs associated with their harvesting and separation from the cultivation medium. The colloidal nature of microalgae, combined with the negative charge on their cell surface due to carboxylate ions and other negatively charged functional groups (ranging from \(-\)7.5 to \(-\)40 mV), promotes their buoyancy in the liquid, leading to the formation of stable suspensions that are difficult to separate [32]. The negative surface charge of the cells induces electrostatic repulsion, effectively preventing coagulation or flocculation [8]. Additionally, the low sedimentation velocity of microalgae (0.008 mm/s) further complicates the harvesting process [31]. In fact, microalgae biomass dewatering typically accounts for 20 to 60% of the total cultivation cost, presenting a major barrier to large-scale commercial production [20; 33]. To reduce the costs of algae harvesting and ensure high purity of wastewater discharge, numerous research efforts are currently underway to explore economically viable techniques for separating microalgae biomass from the cultivation medium [34]. These efforts are focused on adapting the separation methods based on the scale of cultivation, microalgae species, and the intended practical applications, such as for energy, chemicals, or food purposes. Microalgae harvesting and dewatering can be carried out via single-stage or multi-stage processes, depending on the desired quality and concentration of the end product [29]. Various conventional techniques are employed for microalgae dewatering, including mechanical methods (gravity sedimentation, filtration, centrifugation) [11; 35], chemical methods (coagulation, flocculation) [8; 36; 37], electrical methods (electrophoresis) [33; 38], and biological methods (biofloculation) [34]. Among other researchers, [PERSON] et al. [17] emphasize biofloculation as a cost-effective, environmentally friendly, and industrially feasible method for microalgal harvesting. Meanwhile, [PERSON] and [PERSON] [39] demonstrated that the electrocoagulation-flotation (ECF) method is an efficient approach for recovering _Chlorella vulgaris_ biomass, achieving up to 98.7% efficiency. Additionally, [PERSON] et al. [40] investigated electro-osmotic and electro-dewatering processes and found that excessively high ionic strength can decrease the effectiveness of algae electro-dewatering. [PERSON] et al. [38] optimized electro-coagulation with iron electrodes for harvesting _Chlorella vulgaris_, achieving \(>\)95% efficiency with low iron residues meeting food standards. Using electrocoagulation before centrifugation reduced energy costs to 0.136 kWh/kg, less than 14% of the energy cost of centrifugation alone. Multistep methods for algae separation, such as flocculation-sedimentation followed by centrifugation, are being explored for improved efficiency. [PERSON] et al. [37] compared gravity sedimentation and dissolved air flotation (DAF) for floc separation, achieving 87% and 98% harvesting efficiency, respectively. They concluded that combining these methods can significantly reduce capital and operational costs for large-scale production. Each of the methods listed has its own advantages and drawbacks, necessitating effective operational optimization and management to enhance dewatering efficiency. Extensive research is also being conducted on the use of various membrane filtration methods for microalgal dewatering [29]. In these methods, fouling--which reduces permeate flux, increases cleaning frequency, and overall energy consumption--represents a major bottleneck in microalgal dewatering. The choice of a specific algae biomass concentration method is also influenced by its level of technical maturity for industrial-scale application. Therefore, methods that have proven effective in water treatment technology for organic pollution removal are currently the most commonly used [41]. Gravitational sedimentation is one of the simplest and most cost-effective dewatering methods.