Effect of Acid Hydrolysis for Volatile Fatty Acids Production from Alginate

Abstract

Recently brown algae has received considerable attention as a feedstock for biofuel production due to its fast growth rate and high carbon fixation ability. Alginate is the major component of polysaccharide in brown algae, however, it has low solubility in water and low biodegradability due to its chemical structure. Application of various pretreatments for marine macroalgae can make more simple type carbohydrates and enhance the biofuel productivity. Therefore, the objectives of this study are to evaluate the effects of acid pretreatment on volatile fatty acids (VFAs) production from alginate in anaerobic fermentation. The dilute sulfuric acid and Amberlyst-15 were catalysts for the pretreatment of alginate, and different variables (catalyst concentration and reaction temperature) were investigated in order to enhance VFAs production. Sodium alginate of 10 g/L was pretreated in an autoclave reactor with a working volume of 100 mL. The influence of different catalyst concentrations were varied ranging from 0.5% to 10 % (w/w) at 120°C for 2 h in dilute sulfuric acid, and from 1% to 10% (w/w) at 120°C for 4 h in Amberlyst-15. The effect of the reaction temperatures were conducted from 80 to 160°C at 3% (w/w) for 2 h in dilute sulfuric acid, and from 60 to 140°C at 5% (w/w) for 4 h in Amberlyst-15. A series of anaerobic fermentation tests were carried out in a glass bottle of 250 mL with working a volume of 200 mL and placed in a shaking incubator of 120 rpm at 35°C. The molecular weight of alginate for all conditions was significantly reduced by acid pretreatment, and increases of catalyst concentrations and reaction temperatures. The maximum VFAs production yield of 45.4% was obtained with 3%(w/w) at 120°C for 2 h in dilute sulfuric acid and the yield of 18.1% was obtained with 5%(w/w) at 80°C for 4 h in Amberlyst-15. These results indicate that acid pretreatment of alginate could be affected by the reduction of molecular weight, and could enhance the VFAs production compared with raw alginate.