Journal of Research in Peace, Gender and Development (ISSN: 2251-0036) Vol. 2(1) pp. 006-009 January 2012
Available online@ http://www.interesjournals.org/JRPGD
Copyright ©2012 International Research Journals
Full Length Research Paper
Development of Digester for Central Sewage System of
Bayero University, Kano, Nigeria
D.B. Yahaya* and B.M. Yahaya
Department of Mechanical Engineering Bayero University, Kano
Accepted 09 January, 2012
This paper looks at the possibility of producing biogas from sewage obtained from the sewage plant of
Bayero University, Kano. A digester was designed and constructed using locally available materials to
3
a capacity of 4500 cm . The dimension of which was 15x15x20 cm. The material used was galvanized
iron sheet metal, copper pipe and rubber hose. Four digesters were constructed of the same size. Two
set of experiments were set up comprising of groups 1 and 2. Group 1 consists of digester A and B
while group 2 consists of digester C and D. Sewage samples were processed by drying it for ten days,
grounded, then weighed into a mass of 1400 g. The sample collected was divided into four, i.e. 350 g
each. Digesters A, C, and D were fed with 350 g of sewage and 1400 cm3 of water making a
concentration 0.25 g/cm3, While digester B contains 350 g of the sewage and 1750 cm3 of water making
a concentration of 0.2 g/cm3. Readings were taken at 6.00 pm every day. Digesters A, B and C were
stirred after taking readings and digester D was not stirred at all throughout the experiments. The
research was conducted for over a period of 49 days this is because sewage collected has already
started decomposing when it was collected. From the experiment conducted it was discovered that
sewage from BUK produces biogas which can be use for cooking purposes. Digester C produces the
highest biogas of 4390 cm3, followed by A with 4375cm3, digester B with 3135 cm3 and finally digester
D with 3110 cm3. The PH of 7.1 was obtained for the samples which are almost neutral, there by giving
excellent anaerobic condition for complete decomposition. Concentration and Stirring are other
important factors in the production of biogas. In this experiment concentration of 0.25g/cm3 is found to
be the best and also stirring once after taking readings is important. Digesters A, B, and C that were
stirred have more biogas yield than digester D which is not stirred.
Keywords: Digester, sewage, energy and biogas.
INTRODUCTION
The basis for life is energy. The most fascinating feature
of any civilized society is the availability of energy for
domestic, agricultural and industrial purposes. The
available energy sources in Africa are wood, fossil fuels
(coal, petroleum, and natural gas), hydro etc (NAS 1977). A
more serious problem is our increasing population
culminating into high energy demand and limited and fast
depleting energy resources, which can result in severe
energy crisis. This call for serious measures and adequate
policies to be taken in perfecting utilization, exploration
and exploitation of our energy sources and pursuit of new
*Corresponding Author E-mail: dbyahaya2008@yahoo.com
alternative energy sources and its conservation. This
alternative energy should be adequate and within reach
of the rural people because 70 % of the total population
in the Africa depend almost 100 % on fuel wood for their
energy need which could lead to crisis as cutting of trees
is not balanced by proper afforestation (Eze et al., 1997).
With the development of an efficient chemical fertilizer
industry supplying plant nutrients from synthetic fertilizer
industry, become economical than from animal wastes,
because the cost of collecting, handling and spreading
the wastes. With the rising demands for fossil fuels and
reduced supplies due to a number of limiting factors
coupled with the increase cost of fuel in manufacturing
fertilizer in recent years, research shows the potential use
of the wastes as substrate for microbial biogas
concentrations (Zuru et al., 1998).
Yahaya and Yahaya 007
Table 1. PH values
Samples
Digester A
Digester B
Digester C
Digester D
PH Before Digestion
7.10
7.10
7.10
7.10
Biogas is a flammable gas produced during anaerobic
digestion of biologically degradable organic matters such
as straws, weeds, human or animal excrements,
garbage, sludge, domestic sewage, organic liquid wastes
from factories, etc. Generally biogas is a flammable gas
which contains 50 -70 % methane (CH4), 30 – 40 %
carbon dioxide (CO2) with small quantity of other gases
such as hydrogen (H2), hydrogen sulphide (H2S), nitrogen
(N2) and other hydrocarbons
Design
A simple box shape digester was designed and
constructed with a capacity of 4500 cm3 called “micro
digester”. Galvanised iron sheet metal was used for the
construction of four digesters of the same size and
capacity. The digester has an inlet/outlet and the gas
outlet. It is arc welded and body filled to be airtight. The
inlet and outlet are made of the same galvanized iron
sheet metal while the gas outlet is made from copper
pipe, conducting the gas from the digester into the
collecting measuring cylinder through a rubber pipe. The
measuring cylinder is placed upside down to collect the
produced gas, thereby making readings easy as it is
graduated.
Processing of the slurry
Partially dried slurry was collected from the sewage plant
in BUK. The slurry was then dried and grounded to a
powder form. Mass of 1.40 kg was used in this research.
It was divided into four equal parts i.e. 350 g each and
was fed into the four digesters.
Experimental Setup
Four digesters are grouped into two groups, group 1
consist of digesters A and B while group 2 consist of
digesters C and D. Digester A contain 350 g of the dried
sewage and 1400 cm3 of water. Digester B contain same
amount of slurry but 1750 cm3 of water, thereby having
different production. Digester C contains 350 g of slurry
with 1400 cm3 of water. Digester D also contains the
same 350 g of slurry and 1400 cm3 of water.
PH After Digestion
7.78
7.67
7.78
7.78
In group 2, however digester C contains same amount
of sewage and water with digester D but the stirring
H
conditions varies. The P and temperature are same for
all the digesters and no additional chemicals or inhibitors
are added.
Therefore group 1 will have different concentrations
but same temperature, stirring rate and PH and no
chemical inhibitors added. Group 2 will have same
concentration, temperature, PH and no chemical inhibitors
added but will have different rate of stirring.
It is important to note why variations on concentrations
and stirring were considered this is because they are the
most common factors that will affect the gas production,
should BUK decide to produce this gas from its sewage
plant. Temperature and PH will certainly be the same, as it
will be in an open environment
RESULTS AND DISCUSSIONS
The PH of the samples are presented in table 1 above, 2,
3 and 4 below
DISCUSSIONS
The PH obtained before the digestion is lower than after
digestion in all the digesters this may be due to presence
of large amount of organic acid in the slurry produced by
the acid forming bacteria and accumulation of carbon
H
dioxide. The P of 7.1 was obtained from the sewage of
the four digesters tested. This is more or less a neutral,
thereby giving an excellent anaerobic condition for
complete decomposition.
Digesters:- The gas production in all the digesters
started after 3 days and continued through out the
retention period. The highest peaks in digesters A and C
3
are obtained on the 5th day with gas yield of 265 cm and
3
270 cm respectively. For digester B the highest peak is
th
th
th
on the 6 , 10 , and 20 days with the gas yield of 160
3
th
cm . In digester D the highest peak is obtained on the 6
3
st
nd
th
th
day with gas yield of 185 cm . On 21 , 22 , 38 and 40
the gas production were 0 because it was rainy days the
temperature falls below 30oC these affects all the
digesters (A,B,C, and D). Virtually production of biogas in
all the digesters ceases by the 46th day, three days were
given to confirm there is no more gas production in the
008 J. Res. Peace Gend. Dev.
Table 2. Readings obtained from Digesters during the Experiments
3
S/No
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
Date
Days
Approx.
o
Temp ( C)
14/5/03
15/5/03
16/5/03
17/5/03
18/5/03
19/5/03
20/5/03
21/5/03
22/5/03
23/5/03
24/5/03
25/5/03
26/5/03
27/5/03
28/5/03
29/5/03
30/5/03
31/5/03
1/6/03
2/6/03
3/6/03
4/6/03
5/6/03
6/6/03
7/6/03
8/6/03
9/6/03
10/6/03
11/6.03
12/6/03
13/6/03
14/6/03
15/6/03
16/6/03
17/6/3
18/6/03
19/6/03
20/6/03
21/6/02
22/6/03
23/6/03
24/6/03
25/6/03
26/6/03
27/6/03
28/6/03
29/6/03
30/6/03
1/7/03
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
40.5
40.3
40.5
40.0
39.3
40.0
41.5
41.0
41.5
41.5
41.0
36.0
37.0
38.5
31.5
33.3
39.8
39.5
38.8
40.3
26.5
31.5
36.5
37.0
39.5
40.3
39.5
34.5
31.5
33.5
38.8
34.0
39.0
40.3
40.5
41.3
25.0
24.0
29.0
27.0
40.0
38.5
38.0
40.5
41.0
38.0
39.5
38.5
39.0
Volume of Biogas Produced (cm )
Digester
Digester
Digester
A
B
C
0
0
0
0
0
0
0
0
0
80
135
85
265
115
270
170
160
180
210
120
210
205
100
210
210
140
205
180
160
180
150
100
150
90
7
85
80
110
85
110
100
110
60
30
60
90
50
90
110
80
110
140
110
140
130
120
135
190
160
190
0
0
0
0
0
0
110
70
115
110
100
110
150
105
150
165
120
160
145
110
150
100
50
100
50
10
40
90
60
100
100
80
95
90
70
90
150
110
145
160
115
160
140
100
145
150
70
150
0
0
0
0
0
0
20
10
15
0
0
0
40.0
25
45
40.0
30
40
30.0
20
30
30.0
15
35
20.0
0
10
15.0
10
10
0
0
0
0
0
0
0
0
0
Digester
D
0
0
0
60
110
185
105
110
120
120
110
100
105
60
40
50
70
100
100
130
0
0
70
80
80
140
140
70
30
80
60
80
130
145
130
100
0
0
10
0
30
25
15
10
0
10
0
0
0
Yahaya and Yahaya 009
Table 3. Biogas Yield data for Analysis of variance Tests
Digesters
A
B
C
D
Grand Total
3
Total Biogas Yield (cm )
4375
3135
4390
3110
15,010
Mean Biogas Produced
89.29
63.98
89.59
63.47
306.33
Table 4. Result of Analysis of Variance Test
Source of
Variance
Sewage
Experimental
Error
Total
Degree of
Freedom
Sum of
Squares
Mean
Squares
Computed F
Tabular F
3
192
32,408.67
404,076.02
10,802.89
2,104.69
5.13
1%
4.238
195
436,484.69
Tabular
F
5%
2.088
Coefficient of Variance (CV) = 14.98 %
Note: 1 % Indicate highly Significant, 5 % Significant. Values of Tabular F were obtained by interpolation on 5 %
and 1 % of F distribution table. This shows that the Hypothesis is acceptable.
digesters. Digester C is rated 1st in terms of biogas
production with a total biogas production of 4390 cm3,
followed by digester A with a total biogas production of
4375 cm3, then followed by digester B with total
production of 3135 cm3 and lastly digester D with total
biogas production of 3110 cm3
Concentration is another important factor affecting the
production of biogas. In varying the concentration of the
samples in digesters A and B it was observed that a
difference of 1240 cm3 of the total biogas was obtained
between the two digesters. From this result we confirm
that concentration is an important factor in producing
biogas.
CONCLUSIONS
It can be seen from the research conducted that biogas
are produced in commercial quantities which can be
harnessed for utilization for cooking, heating, electricity
generation, etc,. With these findings Bayero University
can use the results of these findings in deciding to build a
large biogas plant for the production of biogas.
REFERENCES
Eze JI, Garba B, Atiku AT (1997). “Application of biogas slurry
(biofertilizer) in crop production”, Niger. J. Renewable Energy, vol. 6
(1 and 2), pp. 81 -83
Fernando CEC, Dangoggo SM (1980). “Investigation of parameters
which affect the performance of biogas plant”, Niger. J. Solar Energy,
vol. 5, pp. 142 -147
Raju BSN (1995). “Water supply and waste water Engineering", Tata
McGraw Hill Publishing Company, New Delhi, India.
NAS (1977). “Methane Generation from Human Animal and Agricultural
Wastes”, Wasshington D.C., pp. 44 -67
Zuru AA, Sa’idu H, Odum EA, Onuorah OA (1998). “Comparative Study
of Biogas Production from Horse, Goat and Sheep Dungs”, Niger. J.
Renewable Energy, vol.6 (1/2), pp. 43 -47.