Maximizing biofuel production from algal biomass: A study on biohydrogen and bioethanol production using Mg Zn ferrite nanoparticles

Algal biomass is a promising renewable feedstock for biofuel production that does not compete with food crops or require complex pretreatment like lignocellulosic biomass. This study examined biofuel production from two algae: Alkalinema pantanalense (cyanobacteria) and Chlorella vulgaris (green alga). Although there was no significant difference in their biomass, A. pantanalense showed a higher carbohydrate content (204.96 mg L⁻¹) than C. vulgaris (156.07 mg L⁻¹). To maximize reducing sugar release, three pretreatments were tested: thermotacidic, biological using the new fungal isolate Trichoderma longibrachiatum, and biological with nanoparticles. Biological pretreatment with MgZn ferrite nanoparticles (MZF-nps) at 60 mg L⁻¹ concentration gave the best results, significantly enhancing cellulase, β-glucosidase and filter paper cellulase activities by 20.94 % (A. pantanalense) and 18.63 % (C. vulgaris). For biohydrogen production, the co-culture of Klebsiella pneumoniae and Enterobacter cloacae resulted in faster fermentation and improved hydrogen evolution compared to individual cultures. A. pantanalense and C. vulgaris yields were 35.1 mL g⁻¹ and 26.6 mL g⁻¹ dry weight, with maximal cumulative production of 2478 mL L⁻¹ and 1845 mL L⁻¹, respectively. Optimized Saccharomyces cerevisiae bioethanol fermentation conditions included 72 h incubation, 5 % inoculum, 30 °C, pH 5 under shaking condition, yielded 11.2 g L⁻¹ (A. pantanalense) and 7.2 g L⁻¹ (C. vulgaris). Furthermore, MZF-nps hydrolysate significantly increased bioethanol production, by 4.2-fold (A. pantanalense) to 32.45 g L⁻¹ and 3.48-fold (C. vulgaris) to 28.6 g L⁻¹, compared to thermoacidic pretreatment. In summary, biological pretreatment demonstrates the potential of algal biomass as a renewable feedstock for sustainable biofuel production.