title: Countercurrent extraction of soluble sugars from almond hulls and assessment of the bioenergy potential.
abstract: Almond hulls contain considerable proportions (37% by dry weight) of water-soluble, fermentable sugars (sucrose, glucose, and fructose), which can be extracted for industrial purposes. The maximum optimal solids loading was determined to be 20% for sugar extraction, and the addition of 0.5% (w/v) pectinase aided in maintaining a sufficient free water volume for sugar recovery. A laboratory countercurrent extraction experiment utilizing a 1 h steep followed by three extraction (wash) stages produced a high-concentration (131 g/L fermentable sugar) syrup. Overall, sugar recovery efficiency was 88%. The inner stage washing efficiencies were compatible with solution equilibrium calculations, indicating that efficiency was high. The concentrated sugar syrup was fermented to ethanol at high efficiency (86% conversion), and ethanol concentrations in the broth were 7.4% (v/v). Thin stillage contained 233 g SCOD/L, which was converted to biomethane at an efficiency of 90% with a biomethane potential of 297 mL/g SCODdestroyed. Overall, results suggested that a minima of 49 gal (185 L) ethanol and 75 m(3) methane/t hulls (dry whole hull basis) are achievable.
authors.affiliation: PWA, WRRC, BCE, Agricultural Research Service, U.S. Department of Agriculture , 800 Buchanan Street, Albany, California 94710, United States.
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Holtman
authors.forename: Richard D
authors.initials: RD
authors.lastname: Offeman
authors.forename: Diana
authors.initials: D
authors.lastname: Franqui-Villanueva
authors.forename: Andre K
authors.initials: AK
authors.lastname: Bayati
authors.forename: William J
authors.initials: WJ
authors.lastname: Orts
mesh_terms: D056804:Biofuels; D050260:Carbohydrate Metabolism; D002241:Carbohydrates / Q000737:chemistry / Q000302:isolation & purification*; D003377:Countercurrent Distribution; D000431:Ethanol / Q000032:analysis / Q000378:metabolism*; D005285:Fermentation; D008697:Methane / Q000032:analysis / Q000378:metabolism*; D000068181:Prunus dulcis / Q000737:chemistry*; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D014866:Waste Products / Q000032:analysis
chemical_list: D056804:Biofuels; D002241:Carbohydrates; D014866:Waste Products; D000431:Ethanol; D008697:Methane
keywords: almond hulls; biogas; carbohydrates; countercurrent extraction; ethanol; fermentable sugars; fermentation