Evaluating fermentability of hydrolyzates of pretreated pine sawdust

JULIA KRUYENISKI; ESTER CHAMORRO; ANA MARÍA ARISMENDY; FERNANDO ESTEBAN FELISSIA; MARÍA CRISTINA AREA

Workshop; Workshop on Insights and Strategies Towards a Bio-Based Economy; 2016

Pine sawdust, the most abundant and underutilized forest-industrial waste, can be used as raw material in a biorefinery. The process to obtain ethanol from cellulose in lignocellulosic waste consists of pretreatment, hydrolysis and fermentation. The aim of this work was to evaluate the ethanol production from a separate hydrolysis and fermentation process of a mixture of Pinus elliottii and Pinus taeda sawdust (forest-industrial residue) subjected to different pretreatments. Five pretreated materials of various chemical compositions were selected to evaluate fermentability. The analyzed samples included the following treatments: (1) alkaline desresination followed by steam explosion, (2) steam explosion and subsequent alkaline washing, (3) soda - anthraquinone- oxygen treatment, (4) kraft- anthraquinone and (5) soda ? anthraquinone delignification. Pretreatment conditions: (1) 90ºC, 60 min, 5% over dry wood NaOH + 200ºC, 5 min, 3% over dry material H2SO4; (2) 190ºC, 7.5 min, 0.75% over dry material H2SO4 + 60ºC, 60 min, 0.4% over dry material NaOH; (3) 170ºC, 170min, 25g/L NaOH, LSR: 10/1 + 120ºC, 60 min, 10% consistency, 6 kg/cm2; (4) 170ºC, 170min, 25g/L NaOH, LSR: 10/1 and (5) 170ºC, 140min, 55.17 g/L NaOH, LSR: 5/1. National Renewable Energy Laboratory standards were used for the characterization of the fibrous material and as guide to evaluate enzymatic activity and hydrolysis. The enzymatic hydrolysis was performed at 2% consistency, pH 4.8 and 50ºC, with an enzymatic charge of 20 FPU/ g glucan and 40 IU/ g glucan. The reaction was monitored at 24, 48 and 72 h. Fermentation was carried out using Saccharomyces cerevisiae, inoculating 10% (wt/wt) of growth culture. This process was conducted at 30ºC and monitored until 48 hours. Ethanol and residual glucose content were measured by HPLC.Solid material composition depends on the fractionation applied and its objective; glucan content varied between 52.5-78.2% over dry, hemicellullose between 2.3-18.4% over dry and lignin between 3.64 to 42.5% over dry.Enzymatic hydrolysis yield (at 72 h) of treatments 1 and 2 (both steam explosion) were lower than 25%, while treatments 3, 4 and 5 (with lignin content < 8% over dry) showed yields higher than 70%.In the fermentation stage inhibitors (such as acids or HMF) were not detected in any of the hydrolyzates. Ethanol yield at the end of the fermentation varied between 88 and 93 %. In most cases these values were reached in 30 hours, showing that hydrolyzates obtained from these pretreated materials are suitable for fermentation.