Optimization of thermal acid hydrolysis for bioethanol production from Ulva rigida with yeast Pachysolen tannophilus

We investigated the feasibility of bioethanol production from hydrolysate of green seaweed Ulva rigida. The pretreatment of the green macroalgae was optimized using thermal acid hydrolysis to obtain a high reducing sugars yield. The dry seaweed biomass, (5 to 15% w/v) was hydrolyzed with two different acid catalysts, H2SO4 and HCl at a concentration of 0 to 10.0% (v/v). The hydrolysis times ranging from 30 to 60 min were investigated when the mixture was autoclaved. A condition of 4% (v/v) sulfuric acid, 10% (w/v) biomass loading and 1 h of incubation time was optimum to obtain maximum total fermentable reducing sugar concentration of 34 ± 0.25 mg/ml and 0.50 ± 0.02 mg/ml of phenolic compounds. Fermentation of the hydrolysate using adapted and non-adapted Pachysolen tannophilus produced 0.12 g/g and 0.09 g/g (ethanol to dry seaweed), respectively. These preliminaries results indicate a potential use of the macroalgae U. rigida for bioethanol production.