Pre-treatment optimization of Scenedesmus obliquus microalga for bioethanol production

Virus infection of Chlorella variabilis and enzymatic saccharification of algal biomass for bioethanol production

Experiments were conducted to investigate the application of virus infection and amylolytic enzyme treatment on sugar release from Chlorella variabilis NC64A and bioethanol production from released sugars via Escherichia coli KO11 fermentation. Chlorella variabilis NC64A accumulated starch when it was cultured in a nitrogen-limited medium. The accumulated starch was not consumed during viral infection based on analysis of sugars released during infection. Both amylolytic enzyme addition and virus infection increased the hydrolysis of carbohydrates. Addition of amylolytic enzymes increased the release of glucose from algal biomass while virus addition increased the release of non-glucose neutral sugars. The combination of enzyme addition and virus infection also resulted in the highest ethanol production after fermentation. Acetic acid was generated as a co-product during fermentation in all sets of experiments. This study demonstrated that infection of microalgae with an algal virus resulted in disruption and hydrolysis of algal biomass to generate fermentable sugars.

Chemo-enzymatic saccharification and bioethanol fermentation of lipid-extracted residual biomass of the microalga, Dunaliella tertiolecta

Chemo-enzymatic saccharification and bioethanol fermentation of the residual biomass of Dunaliella tertiolecta after lipid extraction for biodiesel production were investigated. HCl-catalyzed saccharification of the residual biomass at 121 °C for 15 min produced reducing sugars with a yield of 29.5% (w/w) based on the residual biomass dry weight. Various enzymes were evaluated for their ability to saccharify the residual biomass. Enzymatic saccharification using AMG 300 L produced 21.0 mg/mL of reducing sugar with a yield of 42.0% (w/w) based on the residual biomass at pH 5.5 and 55 °C. Bioethanol was produced from the enzymatic saccharification products without additional pretreatment by Saccharomyces cerevisiae with yields of 0.14 g ethanol/g residual biomass and 0.44 g ethanol/g glucose produced from the residual biomass. The waste residual biomass generated during microalgal biodiesel production could be used for the production of bioethanol to improve the economic feasibility of microalgal biorefinery.

Hydrolysis of macroalgae using heterogeneous catalyst for bioethanol production

Utilization of macroalgae biomass for bioethanol production appears as an alternative source to lignocellulosic materials. In this study, for the first time, Amberlyst (TM)-15 was explored as a potential catalyst to hydrolyze carbohydrates from Eucheuma cottonii extract to simple reducing sugar prior to fermentation process. Several important hydrolysis parameters were studied for process optimization including catalyst loading (2-5%, w/v), reaction temperature (110-130°C), reaction time (0-2.5 h) and biomass loading (5.5-15.5%, w/v). Optimum sugar yield of 39.7% was attained based on the following optimum conditions: reaction temperature at 120°C, catalyst loading of 4% (w/v), 12.5% (w/v) of biomass concentration and reaction time of 1.5h. Fermentation of the hydrolysate using Saccharomyces cerevisiae produced 0.33 g/g of bioethanol yield with an efficiency of 65%. The strategy of combining heterogeneous-catalyzed hydrolysis and fermentation with S. cerevisiae could be a feasible strategy to produce bioethanol from macroalgae biomass.