| High demands for energy and concerns about global climate changes have led to the resurgence of bio-fuels. Bio-fuels are liquid or gaseous fuels made from plants and residues such as agricultural crops, municipal wastes and agricultural or forestry by-products. The second generation of bioethanol uses cellulosic wastes as feedstock because of its relative abundance and low cost. The materials investigated for the conversion of second generation bioethanol at present are extensive and most of them come from the land-derived resource.While marine-derived resource, Laminaria japonica is a type of brown algae which can be used for the production of alginate, iodine, and mannitol. The utilization of seaweeds as an energy resource to produce biogas has been studied. Floating residue (FR), the surplusage which is massively produced in the alginate extracting process, has large amount of cellulosic materials. The technical feasibility of FR utilization as a resource of renewable energy was investigated in this paper. The production of yeast-fermentable sugars (glucose) from FR was studied by dilute sulfuric acid pretreatment and further enzymatic hydrolysis. Dilute sulfuric acid pretreatment was conducted by using sulfuric acid at concentration of 0,0.1,0.2,0.5 and 1.0%(w/v) for 0.5,1.0 and 1.5 h respectively at 121℃. The system of enzymatic hydrolysis consisted of cellulase and cellobiase. Results showed that FR might be a perfect bioenergy resource, containing high content of cellulose (30.0±0.07%) and little hemicellulose (2.2±0.86%). The acid pretreatment improved the hydrolysis efficiency of cellulase and cellobiase by increasing the reaction surface area of FR and enhanced the final yield of glucose for fermentation. The maximum yield of glucose reached 277.5 mg/g FR under the optimal condition of dilute sulfuric acid pretreatment (0.1% w/v,121℃,1.0 h) followed by enzymatic hydrolysis (50℃, pH 4.8,48 h). After fermentation by Saccharomyces cerevisiae at 30℃for 36 h, the ethanol conversion rate of the concentrated hydrolysates reached 41.2%, which corresponds to 80.8% of the theoretical yield. It indicates that cellulose in seaweed processing wastes including FR is easily hydrolyzed to produce glucose in comparison with that in terrestrial plants. FR shows brilliant prospect as potential feedstocks for the production of bioethanol. In the present study, because of the advantage of FR in chemical composition, low sulfuric acid concentration and temperature were taken for pretreatment. The subsequent enzymatic hydrolysis of FR and the ethanol fermentation of the hydrolysate by S. cerevisiae were investigated. Under the optimal pretreatment (0.1%, 121℃,1.0 h), enzymatic hydrolysis was conducted at 50℃, pH 4.8 for 48 h. The maximum of glucose yield reached 277.5 mg/g, and the conversion of cellulose reached,92.5%. Finally 0.143 L ethanol from lkg FR was achieved. Compared with the reference, a significant increase of glucose yield under that condition was get. Although the amount of acid concentration added to FR was relatively lower (0.1%, w/v), it improved the enzymatic hydrolysis of cellulose.As shown in this research, FR, an abundant by-product of alginate processing, is a potential and novel bioresource for the conversion of bioethanol. The worldwide annual yields of alginate, carrageenan and agar reach 30,000-40,000,20,000 and 10,000 tons, respectively. Among them, the yield of alginate in China occupies 1/4-1/3 of the worldwide yield. The same amount of alginate processing waste was produced during alginate production. It caused severe environmental pollution due to low recycling capacity. The advantages of FR in chemical composition and spatial structure make it an ideal bioenergy resource. It is necessary to further develop the bioethanol conversion technique, which can facilitate a pilot scale of bioethanol production.
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