Bioethanol production from thermochemically pre-treated olive mill solid residues using the yeast Pachysolen tannophylus

Olive oil mill solid residue (OMSR) is the solid waste generated during olive oil production process in
three-phase olive mills. It consists of the remaining pulp of olive processing after the extraction of oil,
as well as the cracked seeds of the olive fruits, containing thus mainly lignocellulose and residual oil.
The commonly used practice for OMSR management is combustion, after having extracted the
residual oil by secondary extraction using organic solvents. Other proposed ways of OMSR
management are their exploitation as substrate for edible fungi production and compost, and as
feedstock for biofuels generation such as methane and bioethanol. In the latter case, the complex
carbohydrates (cellulose and hemicellulose) of the lignocellulose of OMSR have to be degraded
towards their simple sugars and further fermented via microorganisms.
The purpose of the present study was to investigate the effect of thermochemical pre-treatment of
OMSR, on the final ethanol yield from the yeast Pachysolen tannophilus. Nine different types of
OMSR-based substrates were tested i.e. raw OMSR, hydrolysates generated from pretreated OMSR
with NaOH (0.5 %, 1.5 % w/v) and H2SO4 (0.5 %, 1.5 % v/v), and pretreated OMSR with NaOH (0.5 %,
1.5 % w/v) and H2SO4 (0.5 %, 1.5 % v/v) whole biomass. It was shown that in all cases pretreatment
enhanced the consumption of carbohydrates as well as ethanol final yields.