SUMMARY 1
SUMMARY
Second generation bioethanol production technology is currently in the
area of interest of many research centers in the world. Biofuels can be
produced from non-food organic lignocellulosic materials. The composition
and huge quantities of lignocellulosic biomass available worldwide, its
renewability and non-consumer character are the main arguments for using
it for the purpose of bioethanol production. Waste lignocellulosic biomass is
mainly a by-product of the distilling, starch, and fruit and vegetable
industries. Lignocellulosic waste also comprises wood residues (e.g.
sawdust), pulp and paper industry waste, household food waste and
municipal solid waste.
The main objective of this study was to determine the optimal
conditions of pre-treatment, enzymatic hydrolysis and ethanol fermentation
of selected lignocellulosic raw materials, allowing for efficient conversion of
their biomass to ethanol.
The feedstocks used in the study included lignocellulosic waste, byproducts of the wood industry (aspen, birch and oak chips) and the distilling
(stillage) industry, as well as fiber hemp having a high potential to be
converted into bioethanol.
The first stage of the study was to evaluate the efficiency of commercial
cellulolytic preparations on lignocellulosic biomass. Their in vitro activity
and their activity in the process of hydrolysis of raw materials were
examined. It has been shown that high in vitro activity of a preparation
does not guarantee the effective hydrolysis of lignocellulosic biomass.
Therefore, an important stage was to determine the effectiveness of the
preparations in relation to the examined materials.
The next step of the study was to evaluate the impact of the biomass
pre-treatment method on the efficiency of enzymatic hydrolysis. The
influence of sulfuric acid, sodium hydroxide, Steam Explosion, sonication
and microwave treatment on the degree of porosity of the lignocellulosic
complex, which makes it possible to increase the efficiency of hydrolysis,
was evaluated. It has been shown that in the case of the hydrolysis of wood
SUMMARY 2
residues and hemp fiber, alkaline pre-treatment was the most effective
method, while in the case of stillage it caused a significant loss of reducing
sugars. It was also found that acid pre-treatment leads to the formation of
considerable amounts of inhibitory compounds that affect ethanolic
fermentation.
While assessing the suitability of the examined materials for
enzymatic hydrolysis, it has been shown that the highest hydrolysis yield
(up to 95%) was obtained by treating the biomass of fiber hemp. The
maximum efficiency obtained in the process of the hydrolysis of wood chips
ranged from 55% (birch and oak chips) to 80% (aspen chips). The hydrolysis
of stillage resulted in obtaining only about 40% of the yield of the process.
The final stage of the study was the fermentation of the obtained
hydrolysates. The highest yield (43 – 68% of theoretical efficiency) was
obtained by the treatment of fiber hemp. The fermentation yield of wood
waste hydrolysates ranged from 20% to 68%, whereas the yield of the
stillage – from 20% to 45%. Considering the pre-treatment method, the best
results were obtained by using the Steam Explosion method on oak chips
and fiber hemp.
Additionally, the effect of lignocellulose degradation products, i.e.
furans (furfural, 5-hydroxymethylfurfural), phenolic compounds (vanillin,
4-hydroxybenzaldehyde) and aliphatic acids (acetic acid) on ethanol
fermentation
determined.
by
It
Saccharomyces
has
been
cerevisiae
shown
that
(Thermosacc
the
addition
Dry)
of
was
furfural,
5-hydroxymethylfurfural and vanillin to the fermentation media at the
concentration of up to 3 g/l did not cause a significant reduction in ethanol
production. However, it led to a prolongation of the lag phase during
fermentation. 4-hydroxybenzaldehyde at the concentration of 0.5 g/l has
been shown to be profitable for the fermentation process, whereas a dose of
2 g/l caused a significant prolongation of the lag phase and a decrease in
efficiency of about 70%. The addition of acetic acid at the concentration of
10 g/l led to complete inhibition of the fermentation process.
SUMMARY 3
It has been shown that an appropriately selected pre-treatment
method makes it possible to obtain a sufficient yield of enzymatic hydrolysis
and of the subsequent fermentation.