Comparison of ethanol production from Gracilaria fisheri and Gracilaria tenuistipitata cultivated in aquaculture system in Thailand

Abstract

Several species of seaweeds contain higher amounts of polysaccharides and low lignin. These species can be sources for bioethanol production and can be utilized for other biochemical production. In Thailand, large amounts of the red seaweeds Gracilaria fisheri and G. tenuistipitata can easily grow in effluents from aquaculture ponds and are used for wastewater treatment. This study was done to assess the potential substrates from these two Gracilaria species to produce ethanol. Different concentrations of substrate from each species (20–200 mg) were pretreated with 1 M H2SO4 at 95 °C for 150 min. The optimal pretreatment was 60 mg of substrate treated with 1 M H2SO4 at 95 °C for 150 min. This condition gave the highest amount of fermentable sugars in both Gracilaria species. Under these conditions, G. fisheri showed a higher catalytic efficiency (E = 5.2) than G. tenuistipitata (E = 4.1). Ethanol fermentation was performed by using the yeast strain Saccharomyces cerevisiae TISTR 5339. The ethanol produced from the G. tenuistipitata fermentation had the highest yield, producing 0.19 g ethanol g−1 glucose, whereas that of G. fisheri yielded 0.16 g ethanol g−1 glucose. This study suggests that the biomass of G. fisheri and G. tenuistipitata from a marine aquaculture system is a potential source for ethanol production.