Floating residue (FR), a surplus by-product from the alginate extraction process, contains 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 degrees C. 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 degrees C. 1.0 h) followed by enzymatic hydrolysis (50 degrees C, pH 4.8, 48 h). After fermentation by Saccharomyces cerevisiae at 30 degrees C 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 excellent prospects as a potential feedstock for the production of bioethanol. (c) 2010 Elsevier Ltd. All rights reserved.