## 1 Introduction  
Microalgae are garnering growing attention for their promising role as a sustainable resource for food, bioenergy, and a range of value-added products. Antioxidants, pigments, and vitamins derived from microalgae have found commercial applications across diverse industries, showcasing their versatility and economic potential [1]. With the growing concerns about food security, climate change, and the depletion of natural resources, microalgae have emerged as a promising solution to address these challenges. Among microalgal species, _Chlorella vulgaris_, a freshwater green alga, is extensively cultivated for its economic potential. These microscopic photosynthetic organisms exhibit a rapid growth rate, a rich nutritional profile, and the ability to thrive in diverse environments, making them attractive candidates for applications ranging from biofuel production to wastewater treatment [2]. However, the harvesting of microalgae remains a significant challenge that impedes the scalability and economic viability of these applications [3]. This process, constituting a significant portion of biomass production costs (up to 30%), poses a barrier to large-scale production. The economic challenge is particularly evident in the context of low-value products like biofuels, where cost reduction is imperative for competitiveness against fossil fuels. Moreover, the fragility of microalgal cells raises concerns about potential damage during harvesting, leading to the loss of intracellular products. Microalgal harvesting presents significant challenges due to various factors. Microalgae are typically very small (2-30 \(\upmu\)m) and are often found at low biomass concentrations, so they do not naturally sediment easily. Typical biomass concentrations are 0.2-6 g.L\({}^{-1}\), with an average of approximately 0.5 g.L\({}^{-1}\) in a standard 20 cm deep raceway pond [3; 4]. The negatively charged surface of microalgal cells, the presence of alogenic organic matter (AOM), and other impurities on microalgal cultures add complexity to the harvesting process, and impede easy aggregation, resulting in stable suspensions [3; 5]. The negative charge is attributed to deprotonated carboxylic and amine groups on the surface. The characteristics and quantity of AOM are influenced primarily by extracellular organic matter (EOM) produced and released during microalgal growth [6]. [PERSON] et al. [7] further highlight the impact of stress factors on EOM production in _Chlorella_-dominated cultures, underlining the importance of avoiding nutrient limitations and abrupt temperature changes. Currently, the methods most used to harvest microalgae can be: (i) mechanical (gravity sedimentation, filtration, centrifugation, flotation); (ii) physical (electroflocculation, magnetic separation); (iii) biological (biof flocculation); or (iv) chemical (chemical flocculation). Microalgal harvesting is typically a two-stage concentration procedure that involves a thickening and a dewatering phase, though both techniques can be used separately. Initially, 2-7% of total suspended solids (TSS) are concentrated from the dilute cell suspension. The slurry is then concentrated producing a cake that contains 15-25% TSS [5]. This reduces the overall cost of the process, as the thickening stage can be completed by an affordable method (flocculation), before the expensive dewatering step (centrifugation, filtration) [8]. Optimizing the energy and financial balance of microalgal harvesting is thought to be possible using a low-cost alternative technique of chemical flocculation followed by sedimentation [8; 9]. Flocculation involves the application of compounds, either inorganic or organic, exhibiting flocculant activity. These compounds play a crucial role in the formation of flocs, employing processes such as adsorption and charge neutralization, adsorption and interparticle bridging, and enmeshment in a precipitate--a phenomenon referred to as sweep flocculation [10].