Abstract:
The rising population, depletion of petroleum-based
fossil fuel and atmospheric contaminations by combustion of
fossil fuel have opened avenues for alternative, eco-friendly
and renewable energy sources. Bioethanol is an alternative and
renewable source that has drawn attention due environmental
concerns and energy security with non-renewable sources.
This study was aimed at determining the potential bioethanol
producing freshwater flora that are abundantly available in the
Northern Province of Sri Lanka using Saccharomyces cerevisiae
and to optimize the fermentation conditions to enhance the
ethanol yield from Chara globularis. Freshwater flora such as C.
globularis, Cabomba caroliniana, Spirodela polyrhiza, Salvinia
minima, Salvinia natans, Wolffia arrhiza and Wolffia globosa
were hydrolysed with 1M sulfuric acid solution to determine the
reducing sugar and bioethanol yields. C. globularis produced a
higher amount of reducing sugar and bioethanol than other species
tested. When C. globularis was pre-treated with 1 M acid solutions
(sulfuric acid, nitric acid, and hydrochloric acid) and alkaline
solutions (sodium hydroxide and potassium hydroxide), a higher
reducing sugar and bioethanol yields were obtained with sulfuric
acid. When bioethanol was produced from C. globularis using S.
cerevisiae following three different hydrolysis methods viz., acid
hydrolysis (1 M sulfuric acid), enzymatic hydrolysis (1% alphaamylase)
and combination of chemical and enzymatic hydrolysis
(1 M sulfuric acid and 1% alpha-amylase), the combination of
chemical and enzymatic hydrolysis gave a higher yield, thus
was selected. The conditions for fermentation of C. globularis
substrate using S. cerevisiae were optimized sequentially by
changing one factor at a time while keeping the other variables
constant. After the optimization of fermentation time (24 hours),
operating temperature (35 oC), rotation speed (200 rpm) and
sulfuric acid concentration for combined pre-treatment (0.75 M)
with an inoculum size of 100 g l-1, bioethanol yield was increased
by 2 times compared with the non-optimized condition.
