A comparative study on pre-treatment methods for enhanced saccharification from tropical seaweeds to aid in bioethanol production

The selection of suitable pretreatment strategy that facilitates saccharification is the most critical step in the valorisation of seaweed biomass into bioethanol. Considering the scarcity of data on the comparative efficacy of different pretreatments particularly in tropical seaweed species, 50 pretreatment strategies were analysed on three major species representing all the three broad seaweed categories, viz. Ulva fasciata (green algae), Sargassum wightii (brown algae), and Gracilaria corticata (red algae). An improved release of reducing sugars was observed in all the tested pretreatments, with different conversion ratios for different species in each pretreatment. Ultrasonication and magnetic stirring showed maximum yield among physical pretreatments. In thermal methods, microwave oven incubation resulted in maximum yield from both U. fasciata and S. wightii, while it was autoclaving for G. corticata. Sulphuric acid was the best chemical for U. fasciata and G. corticata, while it was orthophosphoric acid for S. wightii. Hydrochloric acid was the best chemical for physicothermochemical pretreatment in all species. Maximum conversion ratios of 2.58, 2.11, and 2.0 were recorded in U. fasciata, G. corticata, and S. wightii respectively. In short, the paper sketches the best pretreatment method for three major tropical seaweeds along with their proximate composition. The results can be applied for aiding the valorisation of biomass of these seaweeds through a cost-effective manner. [Display omitted] •Seaweeds were compared for sugar yield after physical and chemical hydrolysis.•Chemical treatments resulted highest yield.•Ulva fasciata had the highest carbohydrate content and fermentable sugar yield.•HCl was adjudged as the most appropriate hydrolysing agent for seaweeds.•Sargassum wightii showed most efficient conversion of polysaccharides to sugars.