Characterization and hydrolysis optimization of Sargassum cinereum for the fermentative production of 3G bioethanol

Abstract

Third-generation biofuels are gaining commercial interest because of the rapid growth rate, high productivity of nutrients, and the carbon dioxide sequestration ability of the feedstock, algae. But the selection of algae, cultivation method, and pretreatment techniques remain challenging. The present work describes the high suitability of brown seaweed as a promising feedstock for the production of bioethanol. Sargassum cinereum is a carbohydrate-rich and fast-growing brown seaweed in all marine environments and abundantly available in Gulf of Mannar, India. Proximate, ultimate, and biochemical analysis has demonstrated the potential carbohydrates in the brown seaweed composition. Preliminary studies on S. cinereum revealed that the H2SO4-assisted hydrolysis had produced more fermentable sugars than the tested. A statistical optimization method with 16 runs was employed to optimize the H2SO4 loading concentration (% w/v), residence time (min), and incubation temperature (°C) for the enhancement of fermentable sugars from the biomass. Optimization results have shown a 133% increase in reducing sugars yield. Furthermore, the obtained sugars were fermented to ethanol at a yield of 0.465 ± 0.024 g ethanol/reducing sugars using Saccharomyces cerevisiae MTCC170. The observed high ethanol yield from seaweed sugars was closer to the theoretical yield based on glucose as a substrate.