Monday, April 30, 2007

Biological conversion of pretreated olive tree pruning biomass to fuel ethanol

Paloma Manzanares1, Maria J. Negro1, Jose M. Oliva1, Felicia Saez1, Mercedes Ballesteros1, Cristobal Cara2, Encarnación Ruiz2, and Ignacio Ballesteros1. (1) Renewable Energies Department, CIEMAT, Avda. Complutense 22, MADRID, Spain, (2) Chemical, Environmental and Materials Engineering Department, University of Jaen, Campus Las Lagunillas, Jaen, Spain

Over 8 million ha of olive trees are cultivated world wide, especially in Mediterranean countries. Olive tree pruning generates a huge amount of a lignocellulosic, renewable, inexpensive residue, whose disposal may cause an economic and environmental problem. As an alternative use, this residue could provide a promising feedstock for bioethanol industry, due to its carbohydrate content (37% on dry matter basis). However, research is needed to determine the feasibility to produce ethanol from this raw material by technologies developed so far. Among biomass to ethanol existing technologies, enzymatic hydrolysis-based processes are advantageous because they catalyze only specific reactions and consequently there are no side reactions or byproducts, and the hydrolysis can potentially be run at very high yields.

In the present study olive tree pruning biomass pretreated by both liquid hot water (LHW) and diluted sulfuric acid was tested as substrate for ethanol production by the Simultaneous Saccharification and Fermentation (SSF) bioconversion process. The effect of catalyst addition and pre-treatment temperature on SSF yield was evaluated. The highest SSF yield (70% of theoretical) in experiments at 10% substrate loading was obtained using olive tree pruning biomass pretreated by LHW at 210ºC. No significant effect of acid impregnation was observed.

In order to increase final ethanol concentration in the SSF media, further experiments at higher substrate loading and fed-batch process configuration were performed. The results from this study will be presented.