Bioprospecting marine microalgae and cyanobacteria as alternative feedstocks for bioethanol production

Abstract

In view of fossil fuel depletion at an alarming rate, bioethanol is considered a sustainable alternative fuel to meet the global insatiable energy needs. In this regard, the present study focused on bioprospecting eight marine cyanobacteria and four marine green microalgae to select suitable feedstock for bioethanol production based on their biomass yield and carbohydrate accumulation. Before fermentation, hydrolysis is enhanced by the standardization of sulphuric acid and Lewis acid concentrations at a specific biomass-to-liquid ratio. Based on comprehensive carbohydrate component analysis, Leptolyngbya valderiana BDU 41001 with maximum fermentable sugar content (27% dry cell weight) was selected as a potential third-generation feedstock from eight cyanobacteria with high carbohydrate content (>25% dcw) for bioethanol production. The synergistic impact of 2% sulphuric acid (v/v) and 2% magnesium sulfate (w/v) at a biomass-liquid ratio of 1:15 yielded the highest hydrolysis yield of 88%. Scanning Electron Microscopy examination also evidently demonstrated the morphological changes that occurred during the hydrolyzation of cyanobacterial filaments. Separate Hydrolysis and Fermentation (SHF) were then used to produce bioethanol from the acquired hydrolysate by the conventional yeast Saccharomyces cerevisiae at an ideal pH of 5.5, yielding 0.16 g g-1 bioethanol yield with 45% bioethanol conversion. This study demonstrated the selection criteria of bioethanol feedstock and establishes an effective method for manufacturing bioethanol from marine cyanobacterium L. valderiana. Furthermore, this research contributes to the potential of Lewis acid as a cost-effective and environment-friendly source in the biomass conversion process.