Smart and Reusable Biopolymer Nanocomposite for Simultaneous Microalgal Biomass Harvesting and Disruption: Integrated Downstream Processing for a Sustainable Biorefinery

Abstract

One of the major technological challenges in developing a microalgal biorefinery is to minimize the fossil energy inputs, particularly in two important downstream unit operations, cell harvesting and disruption. Hence, this study involved synthesizing and applying biopolymer nanocomposite to achieve concomitant biomass harvesting, cell disruption, and nanocomposite recovery by exploiting its cationic, photocatalytic, and magnetic properties respectively, in an integrated and optimized process chain. Accordingly, dual-functionalized chitosan-TiO 2 conjugated particles (CTC) and trifunctionalized magnetic nanocomposites (MNCs) namely, chitosan coated core−shell structures of Fe 3 O 4 −TiO 2 , were prepared and characterized. The harvesting efficiency of >98% was achieved at the optimal dosages of chitosan, CTC and MNCs of 0.11, 0.09, and 0.07 g g −1 Chlorella minutissima biomass, respectively. TiO 2 driven photocatalysis could effectively disrupt harvested wet-biomass, when exposed to UV irradiation in the presence of either CTC or MNCs for 2 h, and when subjected to visible light with only MNCs for 3 h. Photocatalytic cell disruption helped recover 96−97% of the intracellular lutein and lipid, when compared to ultrasonication as control. Subsequently, the MNCs were separated from residual biomass by physicochemical treatment, resulting in over 98% detachment efficiency for reuse in the downstream process chain. To the best of our knowledge, this integrated green process is novel, in terms of meeting a contemporary technological challenge in downstream processing of microalgal biomass, and this research outcome may inspire the development of sustainable microalgal biorefinery for the production of lutein and biodiesel.

Bare Iron Oxide Nanoparticles for Magnetic Harvesting of Microalgae: From Interaction Behavior to Process Realization

“…The most important result is probably the discovery that efficiencies of 95% are achievable for both algae species. Similar results have previously been published for different, mainly coated magnetic particles and several algae species [ 31 , 32 , 36 , 37 , 41 , 48 , 49 , 50 , 51 , 52 ].…”

Flocculation Harvesting Techniques for Microalgae: A Review

“…The dosage of 0.07 g particle/g biomass from chitosan-coated Fe 3 O 4 -TiO 2 resulted in a harvesting efficiency of over 98% for C. minutissima within 2 min (due to the magnetic property of Fe 3 O 4 ). This dosage was significantly lower than that reported for chitosan only (0.11 g particle/g biomass) under the conditions of that study [113]. High percentage of lipid recovery at 96% and 97% could be obtained after exposure to UV for 2 h and visible light for 3 h, respectively, relative to lipid recovery in 10 min of ultrasonic treatment.…”

“…The dosage To couple harvesting and disruption of algal cells for biofuel production, it is essential to use flocculant composites that have dual cationic and photocatalytic properties. For instance, chitosan-coated Fe 3 O 4 -TiO 2 composites were able to electrostatically attract algal cells causing floc formation [113]. In addition, this composite showed sufficient photocatalytic activity (due to the TiO 2 shell) in disrupting the cell wall of harvested algae after exposure to UV irradiation or visible light.…”

Current advances in microalgae harvesting and lipid extraction processes for improved biodiesel production: A review

“…The zeta potential increases with the simultaneous increase in the concentration of chitosan, the charge on microalgae neutralized and the cells flocculate at 0.12g/L of chitosan. In another study [36], chitosan was conjugated with TiO2 (MNCs) for harvesting of Chlorella minutissima at optimal dosage of 0.07g/g. Further, an increase in dose above the optimal range led to a decline in harvesting efficiency due to the electrostatic repulsion of amino groups present on chitosan which destabilized the microalgae cells.…”