Valorization of Shrimp Shell Waste into Chitosan for Efficient Green Harvesting of Chlorella vulgaris through Physicochemical and Performance Evaluation

Microalgae harvesting remains a major bottleneck in biomass production due to its high energy and operational costs, driving interest in sustainable and low-cost bio-based coagulants. This study aims to evaluate chitosan derived from Litopenaeus vannamei shell waste as a green coagulant for harvesting Chlorella vulgaris, with emphasis on its physicochemical characteristics and harvesting performance. Chitosan was synthesized through chitin deacetylation and characterized using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) to assess crystallinity and functional groups. The effects of chitosan dosage, medium pH, and contact time on harvesting efficiency and harvesting kinetics were systematically investigated. The synthesized chitosan exhibited a crystallinity index of 73.76% and a degree of deacetylation of 78.97%, indicating coagulation-relevant protonable amino groups. Harvesting efficiencies exceeding 95% were achieved under optimum conditions of 10 mg L^-1 dosage, pH 6, and contact time of 10 min. The rapid decrease in optical density at 680 nm was consistent with rapid algal-cell destabilization and aggregation, likely driven by charge neutralization and polymer bridging mechanisms. Kinetic analysis showed that the first-order model best described the harvesting behavior. The FTIR spectra of the harvested biomass showed no significant peak shifts compared with the control, indicating no major alteration of detectable functional groups. These findings demonstrate the feasibility of converting shrimp shell waste into chitosan as a green coagulant for efficient microalgae harvesting and support its potential application in sustainable biomass recovery.

Chitosan; Chlorella vulgaris; Kinetics; Microalgae harvesting; Shrimp shell waste

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