Chitosan-Driven Bioflocculation for Low-Energy Microalgae Harvesting: Optimization Using Response Surface Methodology

Abstract

Micro-algae are recognised as a promising renewable resource for biofuels, nutraceuticals, and wastewater treatment. However, large-scale commercialisation is hindered by the difficulty and cost of biomass harvesting due to the small size and negative charge of algal cells. This study explores chitosan - a natural, biodegradable, and non-toxic biopolymer derived from chitin - as an eco-friendly bioflocculant for efficient micro-algae recovery. The flocculation process of Chlorella vulgaris was optimised using a three-factor, three-level Box–Behnken design under response surface methodology (RSM). The independent variables examined were chitosan dosage (0.10-0.20 mg/L), pH (5-9), and settling time (1–5 min). Statistical analysis (ANOVA) revealed that settling time (p = 0.002) and the quadratic effect of chitosan dosage (p = 0.001) significantly influenced flocculation efficiency, while pH had minimal impact. The developed quadratic regression model showed good agreement with experimental data (F = 11.79, p < 0.05), confirming its adequacy for predicting biomass recovery. Results demonstrate that chitosan effectively promotes cell aggregation at low concentrations, minimises sludge formation, and preserves biomass integrity. Hence, chitosan-based bioflocculation presents a sustainable and energy-efficient alternative for large-scale microalgal harvesting.

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