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Commercial- and laboratory modified- cationic cassava starches and their composites with magnetic particles were examined for characteristics and separation efficiency. Scanning electron micrographs showed that cationic starch with an increasing degree of substitution (DS) value (0.0180 to 0.91) showed greater clumped polyhedral granules and became markedly enlarged with disintegrated boundaries. Zeta potential analysis revealed that the increase in the DS value in cationic starches resulted in an increase in positive charge. The maximum harvesting efficiency of 92.86 ± 0.46% was achieved when commercial cationic starch with DS 0.040 at 1.0 g L−1 was added to the Chlorella sp. solution. The maximum recovery capacity (10.20 ± 0.16 g DCW g starch−1) was recorded by using commercial cationic starch with DS 0.040 at a lower dosage of 0.1 g L−1. Their composites showed lower separation efficiency than the commercial cationic starches. The results suggest that the commercial cationic cassava starch with 0.040 DS shows great potential as a flocculant for algal separation. This first report of using commercial cationic cassava starch as a flocculant provides a low cost and convenient process to separate algal cells from the culture medium. Moreover, uncontaminated magnetic particle biomass allows for wide range of algal utilization in food and pharmaceutical biotechnologies.

Microalgae are cultured for their useful chemicals, but their development is restricted by the costs and difficulties of harvesting them. New composites, magnetic-cationic cassava starch, were successfully developed to facilitate harvesting. Compared to naked magnetic particles, the composites exhibited higher potential for algal cell recovery. In addition, harvest capacity through the composites was positively related to the degree of cationic substitution (DS) in modified cassava starch. The application of 500 mg L−1 composites with DS value ≥ 0.76 to recover 1 g L−1 Chlorella sp. TISTR8236 (1.67 ± 0.01 g-dry cell weight g-composites−1) from medium broth at pH 9.5 was significantly (p ≤ 0.005) >98% effective. The separation efficiency of this composite for 1 g L−1 algal biomass was evaluated under different composite doses (200 to 800 mg L−1) and pH levels (4 to 10). Ninety-five percent of the algal cell separation efficiency of the magnetic and 0.76 DS cationic starch composite was recorded, when applied to the 300 mg L−1 composite to harvest 1 g L−1 Chlorella sp. TISTR8236 at pH 10 within 2 min. The adsorption isotherm fit the Langmuir model. In addition, desorption of algal cells was conducted by adjustment of the pH of the culture medium. The highest desorption (9.69%) was recorded at pH 12. These composite magnetic-cationic cassava starch particles were shown to be a new adsorption material for algal cell harvesting. This alternative composite for magnetic separation may represent an effective method for saving time and energy in algal industrial processing.

Algae has long been used as a food and a potential source of valuable and bioactive compounds due to residues left after the extraction process. Discovery of an alternative approach to the residues contributes to commercial feasibility in algae biorefinery. This study aimed to examine the cellulose composition in macroalgae. The physiochemical characteristics of cellulose and its potential use as a reinforcement to polyurethane (PU) foam were investigated. A green filamentous freshwater algal biomass composed of Cladophora sp. and Microspora sp. was treated via alkalization. The treated algae was use as a filler agent to synthesize PU-composite foams. Morphological, chemical, mechanical, physiochemical and viscoelastic properties of cellulose and PU-composite foam were investigated through field emission scanning electron microscopy (FESEM), Fourier-transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), X-ray diffraction (XRD) compressive tests, and dynamic mechanical analysis (DMA). A cellulose yield of 37.2% was obtained from Kai algae via alkalization and the crystallinity index was 63.6%. The use of algae and algal cellulose to synthesize PU-composites resulted in foam density increase, while the compressive modulus decreased. The addition of algal cellulose as filler in PU foam significantly reduced the cell size of foam. Using algae at 0.5% (w/v) and algal cellulose at 1.0% (w/v) as filler in PU-composites increased stiffness at 25–50 °C and transition temperature and decreased loss modulus. These results indicated that algae and algal cellulose added during PU-composite foam production may be integrated into the foam structure and result in more open cells and softer foam. The PU-composite showed greater shock absorbent capacity than PU foam. The results provided a new alternative approach in algal cell residue utilization in terms of material, which could be useful for the packaging industry.