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Biogas production from blends of cassava (Manihot utilissima) peels with some animal wastes

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Cassava peels (CP) obtained after peeling cassava roots were anaerobically digested using 50L capacity fermentor and in blends with some animal wastes. The peels were blended with cow dung (CD), poultry droppings (PD) and swine dung (SD), in the ratio of 1:1. The mean flammable biogas yield of the cassava peels alone was 2.29 ± 0.97L /total mass of slurry. When blended with CD, PD and SD, mean flammable biogas yield was increased to 4.88 ± 1.73, 5.55 ± 2.17 and 5.65 ± 2.62 L /total mass of slurry respectively. Flammable biogas was produced by CP alone from the 59th day of the digestion period. The CP: CD and CP: PD produced flammable gas from the 9th day whereas CP: SD started flammable gas production from the 11th day. While the CP: SD had the highest cumulative gas yield of 169.60L/total mass of slurry, the CP: CD experienced fastest onset of flammable gas production. Overall results indicate that the relatively low flammable biogas production and slow onset of gas flammability of cassava peels can be significantly enhanced when combined with the animal wastes in definite proportions.
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International Journal of Physical Sciences Vol. 4 (7), pp. 398-402, July, 2009
Available online at http://www.academicjournals.org/IJPS
ISSN 1992 - 1950 © 2009 Academic Journals



Ful Length Research Paper

Biogas production from blends of cassava (Manihot
utilissima) peels with some animal wastes

A. U. Ofoefule* and E. O. Uzodinma

National Centre for Energy Research and Development, University of Nigeria, Nsukka, Enugu State. Nigeria.

Accepted 23 June, 2009

Cassava peels (CP) obtained after peeling cassava roots were anaerobically digested using 50L
capacity fermentor and in blends with some animal wastes. The peels were blended with cow dung
(CD), poultry droppings (PD) and swine dung (SD), in the ratio of 1:1. The mean flammable biogas yield
of the cassava peels alone was 2.29 ± 0.97L /total mass of slurry. When blended with CD, PD and SD,
mean flammable biogas yield was increased to 4.88 ± 1.73, 5.55 ± 2.17 and 5.65 ± 2.62 L /total mass of
slurry respectively. Flammable biogas was produced by CP alone from the 59th day of the digestion
period. The CP: CD and CP: PD produced flammable gas from the 9th day whereas CP: SD started
flammable gas production from the 11th day. While the CP: SD had the highest cumulative gas yield of
169.60L/total mass of slurry, the CP: CD experienced fastest onset of flammable gas production. Overall
results indicate that the relatively low flammable biogas production and slow onset of gas flammability
of cassava peels can be significantly enhanced when combined with the animal wastes in definite
proportions.

Key words:
Cassava peels, biogas production, flammable gas production, waste blends, biogas yield.


INTRODUCTION

The rising cost of petroleum products is a serious pro-
3nCH3COOH
CH4 + CO2 (3)
blem facing most developing countries of the world in-

cluding Nigeria. Again, excessive energy demands from
CO2 + 4H2
CH4 + 2H2O
(4)

both rural and urban dwel ers imply that other natural
Biogas technology has been in use in Kenya since 1957
sources of energy have to be explored. Hence, conver-
whereas in areas such as USA and in Asian countries
sion of agricultural wastes into biogas could be a leeway
like India, China and Parkistan, the gas has been ful y uti-
to solving some of these energy problems. Biogas pro-
lized (Carl and John, 2002). The raw materials used in
duction is a complex biochemical process that takes
many places for the gas production are agricultural was-
place in the absence of oxygen and in the presence of
tes ranging from animal manures to adverse selection of
highly sensitive micro-organisms that are mainly bacteria
crop residues. Cassava solid wastes, amongst other
(Hashimoto et al., 1980). The predominant component of
plant wastes have been used. In a research finding of Ko-
flammable biogas is methane (CH4) and CO2 with traces
zo et al. (1996), cassava solid waste (peels +pulp) was
of other gases like, H2S, NH3, CO, H2, N2 and water va-
utilized in anaerobic digestion process to produce biogas
pour etc. It has a heating value of 22 MJ/m3 (15.6 MJ/kg)
with methane content of 51 - 56%. Also Okafor (1998),
(FAO, 1979). Consequently, biogas can be utilized in al
utilized cassava peels and waste water to produce animal
energy consuming applications designed for natural gas
feed that was used to feed pigs. The feaces from the pigs
(Ross, 1966).
were then converted to biogas. Cassava peels are ob-

tained through processing of cassava roots to produce
n (C6H10O5) + nH2O n (C6H12O6)
(1)
garri (a staple food eaten in the tropics especial y in Ni-

n (C
geria) and cassava foo-foo. These peels could make up
6H12O6)
3nCH3 COOH (2)

to about 10% of net weight of the roots and contain toxic
cyanogenic glycosides. As a result of their reasonable

large quantities in homes engaged in farming activities

and industrial areas where commercial quantities are pro-
*Corresponding author. E-mail: akuzuoo@yahoo.com.
duced, these peels have become a nuisance and create


Ofoefule and Uzodinma 399






Stirrer
Outlet
Inlet
f

CP
14
21 cm
CP:CD
15.5 cm
a
s
s
o

15.6 cm
8

1
8

1
3

12
CP:PD

t
a
l

m

1
4

10
CP:SD
8
r
r
y
)



(
l
i
t
e
r
s
/
t
o

6
s
l
u

4
4
0

c
m
a
s

y
i
e
l
d

2
g
i
o

0
B
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29
55.4 cm

Days



Figure 1. Schematic diagram of the biodigester.
Figure 2. Biogas production for the pure and blended CP.




waste disposal problems. Initial digestion studies carried
days under mesophilic temperature conditions of 25.3 - 29.9°C (for
out on the peels showed that the peels are poor produ-
the ambient temperature) and 27.0 - 42.0°C (for the influent tempe-
cers of biogas probably as a result of their content of to-
rature). Daily biogas production, ambient and slurry temperatures,
xic cyanogenic glycosides (Okafor, 1998). As a result,
pressure and pH at alternate days were monitored. The total viable
microbial loads of the wastes undergoing digestion were also moni-
they require treatment to enhance their yield of biogas
tored at different times (At charging, at the point of being flamma-
and onset of gas flammability. This study was then un-
ble, at the peak of gas production and towards the end of the diges-
dertaken to investigate the effect on these two para-
tion).
meters of cassava peels when blended with some animal

wastes. The peels were combined with animal wastes;

Cow dung (CD), poultry droppings (PD) and Swine dung
Analyses of wastes

(SD) in the ratio of 1:1 for each of the blends.
Ash, moisture and fiber contents were determined using AOAC

method of 1990. Fat, crude nitrogen and protein contents were de-

termined using soxhlet extraction and micro-Kjedhal methods as
MATERIALS AND METHODS
described in Pearson (1976). Carbon content was determined using

Walkey and Black (1934) method while Total and Volatile solids
The cassava peels used for this study were obtained from the local
were determined using Meynel (1976) method.
processors of garri, while poultry droppings and swine dung were

obtained from the Animal and Veterinary farms, University of Nige-

ria, Nsukka, Enugu state. The cow dung was procured from an aba-
Microbial analysis
ttoir at Nsukka town of Enugu state, Nigeria. Cassava peels were

col ected between December, 2006 and January, 2007 while the
Total viable counts (TVC) for both pure and the blended slurries
experimental studies were carried out between May and June,
were carried out to determine the microbial load of the samples
2007. Biodigesters of 50 L working volume were used for the fer-
using modified Miles and Misra method as described in Okore
mentation studies and the reactors were constructed from a galva-
(2004).
nized metal plate of gauge 16”. Other materials used were weighing

balance 50 kg capacity (“Five Goats” with model No: Z051599),

water troughs, graduated transparent plastic buckets, K- thermo-
RESULTS AND DISCUSSION
couple thermometer (Hanna Instrument - HI 8757…), digital pH me-

ter (Jenway, 3510), hose pipes, biogas burner fabricated local y for
Daily biogas production from the cassava peels and the
checking gas flammability and Manometer for taking pressure read-
blends are graphical y displayed in Figure 2. Biogas pro-
ings.

duction for al the systems commenced within 24 h of

charging the digesters though the quantity of gas pro-
Experimental studies
duced varied as shown in the figure. The flammable gas

production of each of the system also commenced at dif-
The cassava peels used for the experiment were al owed to dry up
and degrade for about four months to reduce the toxicity of the
ferent lag periods (which is from the time of gas pro-
waste. They were then soaked in a big metal ic drum for one week
duction to onset of gas flammability) (Table 2). Biogas sy-
to al ow partial decomposition of the peels by aerobic microbes.
stems become flammable when the methane content is
The animal manures were used as col ected without further treat-
at least 45%. If it does not burn, it means the methane
ment. The moisture content of the feed stocks determined the water
content is less than 45% and contains mainly CO
to waste ratios during the charging. The blending ratio was chosen
2 (http:
as 50:50 as a starting combination from the other possibilities
file: //A:\Design-Tutor.htm. 2003). The pure cassava peels
(60:40, 70:30, 80:20 and 90: 10), Srinivasan (1997). The wastes
system produced flammable biogas 58 days post charg-
were mixed with water in the ratio of 1:2.7 (10kg of waste: 27 kg of
ing period with low cumulative gas yield of 68.70 liters/
water). The anaerobic digestion process was batch operated for 30
total mass of slurry. The pH change was mainly from aci-

400 Int. J. Phys. Sci.



Table 1. Physicochemical composition of pure and undigested wastes.

Parameters
CD
PD
SD
CP
CP:CD CP:PD CP:SD
Moisture (%)
22.62 16.20 58.05 14.25
21.35
6.70
10.05
Ash %
42.05 37.90 40.15 21.90
20.05
29.90
31.02
Fiber (%)
21.25 28.70 51.05 32.00 23..50
23.45
33.60
Crude Nitrogen (%)
1.40
2.94
1.47
1.40
1.40
2.17
1.43
Crude Protein (%)
8.75 18.38 9.19
8.74
8.75
13.56
8.96
Fat Content (%)
0.45
0.35
0.10
0.75
0.75
0.05
0.15
Total Solids (%)
77.38 13.95 51.94 68.25
71.93
69.53
70.09
Volatile Solids (%)
35.33 7.02 17.02 33.87
30.75
40.53
41.52
Carbon Content (%) 26.87 13.80 15.25 41.27
44.02
30.27
63.28
C/N Ratio
19.20 4.70 10.37 30.00
27.00
20.00
25.00
pH
8.11
7.82
7.43
5.68
7.16
7.68
7.05



9
ble 2). CP: SD had the highest cumulative gas volume.
8
From the profile of pH changes in the first two weeks of
7
CP
digestion, it was observed that blending of the cassava
6
CP:CD
peels with these animal wastes stabilized the waste for
5
H
gas production (Figure 3). This could be as a result of its
p
CP:PD
4
high fiber and carbon contents (Table 1). Swine in this
CP:SD
3
part of the country are normal y fed with spent grains oc-
2
casional y, which may contain a lot of fiber. The presence
1
of hydrocyanic acid in the cassava peels may have brou-
0
ght about the de-lignification of the fibrous plant structure
2
4
6
8
10
12
14
16
of the spent grain observed in the swine waste making
Time (days)

nutrients available for the methanogens during the diges-

tion period (Mathewson, 1980). The CP: PD combination
Figure 3. pH changes in the first two weeks of the digestion.
had a cumulative gas yield close to that of CP: SD (Table


2) but faster onset of gas flammability. This may be as a
dic to slightly acidic for a long period (Figure 3). Figure 3
result of its low total solids (TS) of the undigested single
shows the pH changes for CP system and the blended
poultry waste (Table 1). Adequate physicochemical pro-
wastes within the first two weeks of the digestion period.
perties are known to favor biogas production. A higher TS
One of the major problems associated with biogas pro-
level for poultry droppings implies high ammonia content
duction from cassava roots (cassava wastewater, cassa-
of the slurry. Shivaraj and Seenayya (1994) reported that
va solid waste and cassava tuber) is acidification (low
digesters fed with 8% TS of poultry waste gave better
pH) (Barana and Cereda, 2000; Kozo et al., 1996; Wan-
biogas yield than the higher TS levels. Again, earlier work
tanee and Sureelak, 2004). The thin brownish outer
carried out by Waksman and Hutchings (1936), pointed
membrane of cassava root consists of lignified cel ulosic
out the significance of organic sources of nitrogen in the
material while the white inner portion comprises paren-
decomposition of lignin in plant materials. They asserted
chymateous material known to contain most of the toxic
that lignin-decomposing microbes prefer organic protein-
cyanogenic glycosides and linamarin, in the entire cassa-
nitrogen to inorganic forms. Tinsley and Nowkawski
va root, (Okafor, 1998). The linamarin is broken down
(1959) also submitted that, application of poultry dropp-
with the production of the hydrocyanic acid during the
ings as fluid slurry to Brewer’s spent grain brought an
processing. Consequently, effective biogas production
abundant and vigorous micro-flora immediately into con-
from the wastes would require a pH between 6.5 and 8.5
tact with feedstock substrate. They further explained that
(Anonymous, 1989). This is because the methanogens
as uric acid is decomposed, ammonia is produced which
that produce flammable gas from the waste are highly pH
diffuse rapidly so that the cel ulose-decomposing orga-
sensitive. Hence, in most of the work done on biogas pro-
nisms were wel supplied with nitrogen from an early
duction using cassava materials, inoculums and neutrali-
stage. This organic source of nitrogen as biogas produc-
zers has been applied to the slurry to bring the pH to neu-
tion catalyst was also highlighted in the report of Ezeonu
trality (Wantanee and Sureelak, (2004), Kozo et al.,
et al. (2002) in the biomethanation of Brewery spent grain
1996). Al the blends as shown in Figure 2 produced rela-
(BSG) with chicken droppings and Cow rumen liquor. The
tively higher cumulative gas yield with reduced number of
system with BSG / droppings ratio of4:1 had the highest
lag days in comparison with the cassava peels alone (Ta-
gas yield when compared with the other ratios of 5:1 and

Ofoefule and Uzodinma 401



Table 2. Lag period, cumulative and mean volume of gas production for pure and waste blends.

Parameters
CP
CP:CD CP:PD CP:SD
Lag period (days)
58
9
9
11
Cumulative gas yield (Liters/total mass of slurry)
68.70 146.50 166.50 169.60
Mean volume of gas production (Liters/total mass of slurry) 2.29
4.88
5.55
5.65
Standard Deviation (SD)
±0.97
±1.73
±2.17
±2.62



Table 3. Total viable counts for the pure and blended organic wastes during the
digestion period (cfu/ml).

Period
CP
CP:CD
CP:PD
CP:SD
At charging
1.13x106 2.73x106 4.93x107 1.53x107
At point of flammability
1.59x106 1.09x107 2.26x107 1.84x107
At the peak of production
1.45x107 4.15x107 5.55x107 7.32x107
Towards end of the digestion 2.05x106 1.07x107 1.39x107 1.59x107



3:1. This explanation might account for the faster onset of
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gas flammability of poultry blended system in the current
Treatment using a two phase anaerobic digester. Ciencia Techno.
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Carl N, John L (2002). “The Minnesota Project”. Http://www.mnproject.
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during the digestion period shows that the population of
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microbes was stil high even when the experiment was
Brewers Spent Grain (BSG) Biomethanation: 1. Optimal Conditions
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