Versatile templates were fabricated using plant-derived nanomaterials, TEMPO-oxidized cellulose nanofibrils (TEMPO CNF) for the efficient and sustainable production of biofuels from cyanobacteria and green algae. We used three different approaches to immobilize the model filamentous cyanobacteria or green algae to the TEMPO CNF matrix. These approaches involved the fabrication of: (A) a pure TEMPO CNF hydrogel; (B) a Ca 2+ -stabilized TEMPO CNF hydrogel; and (C) a solid TEMPO CNF film, which was crosslinked with polyvinyl alcohol (PVA). The different immobilization approaches resulted in matrices with enhanced water stability performance. In all cases, the photosynthetic activity and H 2 photoproduction capacity of cyanobacteria and algae entrapped in TEMPO CNF were comparable to a conventional alginate-based matrix. Green algae entrapped in Ca 2+ -stabilized TEMPO CNF hydrogels showed even greater rates of H 2 production than control alginate-entrapped algae under the more challenging submerged cultivation condition. Importantly, cyanobacterial filaments entrapped within dried TEMPO CNF films showed full recovery once rewetted, and they continued efficient H 2 production. The immobilization mechanism was passive entrapment, which was directly evidenced using surface sensitive quartz crystal microbalance with dissipation monitoring (QCM-D). The results obtained demonstrate a high compatibility between CNF and photosynthetic microbes. This opens new possibilities for developing a novel technology platform based on CNF templates with tailored pore-size and controllable surface charges that target sustainable chemical production by oxygenic photosynthetic microorganisms.

The value and efficiency of microalgal biofuel production can be improved in an integrated system using waste streams as feed-stock, with fuel-rich biomass and treated wastewater being key end-products. We have evaluated seven native cyanobacterial isolates and one native green alga for their nutrient removal, biomass accumulation and lipid production capacities. All native isolates were successfully grown on synthetic wastewater mimicking secondary treated municipal wastewater (without organic carbon). Complete phosphate removal was achieved by the native green alga, isolated from Tvärminne (SW Finland). Optimisation of the C:N ratio available to this strain was achieved by addition of 3% CO 2 and resulted in complete ammonium removal in synthetic wastewater. The native green alga demonstrated similar nutrient removal rates and even stronger growth in screened municipal wastewater, which had double the ammonium concentration of the synthetic media and also contained organic carbon. Sequencing of the genes coding for 18S small rRNA subunit and the ITS1 spacer region of this alga placed it in the Scenedesmaceae family. The lipid content of native isolates was evaluated using BODIPY (505/515) staining combined with high-throughput flow cytometry, where the native green alga demonstrated significantly greater neutral lipid accumulation than the cyanobacteria under the conditions studied.

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