2011 International Conference on Alternative Energy in Developing Countries and Emerging Economies
- 86 -
Abstract
--Response surface methodology employed to
optimize the effects of nitrogen source ((NH
4
)
2
SO
4
),
phosphorus source (KH
2
PO
4
), yeast extract and inoculums
size on ethanol production from food waste hydrolysates by
co-culture of
Zymomonas mobilis
and
Candida shehatae
under non-sterile fermentation. The optimum condition for
ethanol production under non-sterile condition was 1.44 g/l
(NH
4
)
2
SO
4
, 0.93 g/l KH
2
PO
4
, 0.9 g/l yeast extract and 15
%v/v inoculums size. Ethanol production of 77.6 g/l in
optimized condition was in good agreement with the value
predicted by quadratic model (79.5 g/l), thereby confirming
its validity. The ethanol production increased by 56% as
compared with the use of raw food waste hydrolysates (34
g/l). Ethanol yield in batch fermentation using co-culture
was 0.15 g-ethanol/g-food waste (77.6 g/l), which was 94.6%
of the theoretical yield. Ethanol yield by
Z. mobilis
alone was
0.11 g-ethanol/g-food waste (54.2 g/l), which is 65% of the
theoretical yield and
C. shehatae
alone yielded 0.09 g-
ethanol/g-food waste (48 g/l) which was 58.6% of theoretical
yield in 72 h. 1 l fermentor using co-culture, the ethanol
yield was 0.16 g-ethanol/g-food waste (78.8 g/l) which was
96% of the theoretical yield. Despite being a waste, an
ethanol yield of 0.16 g-ethanol/g-food waste demonstrated
the potential of food waste as a promising biomass resource
for the production of ethanol.
Index Terms
- Co-culture, Food waste hydrolysates, Non-
sterile ethanol fermentation, Response surface methodology.
I.
I
NTRODUCTION
Food waste is a kind of organic solid waste with higher
percentage of moisture, and it is usually discharged from
restaurants, kitchens and cafeterias
[1]
. Generally,
municipal solid waste includes approximately 35
–
40%
organic waste, of which the dominating fraction is
kitchen waste
[2]
. Whereas, the amount of food waste
generated in Thailand is approximately 600,000 kg/day,
accounting for 80-90 % of total municipal solid waste
[3]
.
The disposal of food waste became a major concern in
Thailand when the direct animal feeding of food wastes
was banned completely by the Thailand government in
2005. Due to the uncertainty with regard to the safety of
its utilization as animal feed
[4]
. Currently, these food
wastes are disposed of by various methods such as
landfilling, incineration, and recovery or recycle. Most of
the food wastes are landfilled, causing ground water
contamination. In addition, landfill space is limited and
uncontrolled fermentation of organic wastes in landfill
causes emission of greenhouse gases, such as methane
and carbon dioxide
[5]
, moreover, it is difficult to find
new sites and the leachate generated by these materials
requires secondary wastewater treatments
[6]
. Hence,
food waste management has been important issue for
protecting the environment as well as for conservation of
resources. Starch and cellulose materials are the major
components of the food waste. It also contains some
protein materials. The starch and cellulosic components
of the food waste can be hydrolyzed to monomeric
sugars. The sugars then can be used as substrates in the
ethanol fermentative production
[7]
. But little information
showed the research on the utilization of food wastes for
ethanol production.
The bioethanol industry has developed rapidly in
recent years to cope with the depletion of fossil fuel.
Because of its environmental benefits, bioethanol is
regarded as a promising biofuel substitute for gasoline in
the transportation sector. It can be produced from a
variety of raw materials containing fermentable sugars.
The utilizations of edible starch material, such as corn
and cassava for bioethanol production have caused undue
pressure on the global food supply
[8,9]
. Therefore, it is
essential to research alternative and inexpensive substrate
for ethanol production at a reduced cost
[10]
. Materials
unsuitable for human consumption are considered ideal
substrates for bioethanol production such as food wastes.
For instance, bread residues can be fermented to get the
ethanol yield around 0.35 g/g substrate
[11]
.
Wilkins
et
al.
[12]
reported that the citrus peel waste can undergo
steam explosion process to remove the D-limonene and
subsequently can be consumed by the
Saccharomyces
cerevisiae
to get ethanol yield of around 0.33 % (v/v).
Reports also exist on the production of ethanol by
fermentation of fresh kitchen garbage using
S. cerevisiae
as inoculum
[13,14]
. Open fermentation of ethanol
production has various merits compared with
conventional sterile and closed-system fermentation. The
non-sterile open fermentation of food waste could be
carried out on-site at localized storage sites before
collection to centralized processing plants. Furthermore,
autoclave process could cause bad effect on desired
product, such as degradation of substrate sugars and other
nutritional elements. Some negative reactions would also
take place, such as the Maillard reaction; it could cause
decreases in the amounts of functionally useful sugars
Optimization of Ethanol Production from Food
Waste Hydrolysates by Co-culture of
Zymomonas
mobilis
and
Candida shehatae
under Non-sterile
Condition
P. Thongdumyu, N. Intrasungkha and S. O-Thong
Division of Biology, Faculty of Science, Thaksin University, (
Thailand
)
