Biogas Production by Anaerobic Co-Digestion of Food Wastes with Goat Manure
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Date
2017-12
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Addis Ababa University
Abstract
Due to the rapid population growth and unmanageable urbanization, one of the burning issues
faced by the world today is management of all types of wastes. This study has been conducted on
the production of biogas by anaerobic co-digestion of food wastes with goat manure. Food waste
(FW), goat manure (GM) and their mixtures were anaerobically digested for 40 working days. The
proximate composition analysis of the FW and GM had shown that, whereas the GM was higher
in TKN value (2.1%), the MFW was higher in C/N ratio (34.0). During this study FW and GM
were combined into five MFW to GM mixing ratios of 1:0, 1:1, 2:1, 1:2, and 0:1; and a total of 45
MRs (nine for each mixing system) were prepared in 1-liter plastic bottles. The pH of these MRs
was adjusted to 6, 7, and 8 by adding 10 N NaOH. Three water baths were set to three temperature
values of 30o C, 35o C and 40o C in which the 45 plastic bottles of 1-liter capacity (15 plastic
bottles in each water bath) as main digesters were immersed. The experimental AD of this study
took 120 days (40 working days for each experimental setup) to produce biogas. The combination
systems of the MFW and GM for co-digestion overcomes the imbalanced C/N ratio of the MFW.
The efficiency of the mono-digestion of MFW only, GM only and co-digestion of the MFW with
GM were studied and compared. Statistical design of the experiments and data analysis was
investigated using the general factorial design. Statistical test had shown that the model "F values"
for both the responses, the biogas volume and methane content in the biogas were statistically
significant (P<0.05). The optimum MRs between the MFW and GM were found to be the 1:1 and
1:2 MRs at process parameters of 35o C and initial pH of 7.0. The cumulative biogas generated at
these conditions were found to be 11.4 and 17.3 liters respectively from the MRs of 1:1 and 1:2.
Averagely, higher methane yield of 61.1% and 63.5% respectively was obtained by the codigestion
of MFW with GM at 35o C and initial pH value of 7.0 from the MRs of 1:1 and 1:2. The
results noted from this study showed that the anaerobic co-digestions of MFW with GM was better
than mono-digestion of the single waste alone for biogas generation.
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Keywords
Anaerobic co-digestion, biogas volume, goat manure, methane yield, Mixed food waste