Abstract:
Production of biogas through anaerobic digestion of organic waste materials provides an
alternative environmentally friendly renewable energy. In this study, biogas production from
co-digestion of cladodes of Opuntia ficus-indica with cow dung and goat manure in the
same mix ratios was evaluated under mesophilic conditions (38ºC) using batch digester in
bioenergy laboratory of Addis Ababa institute of technology . In all substrates, TS and VS,
organic carbon, percent moisture and pH were measured before and after digestion. The daily
biogas production was subsequently measured by using 100ml calibrated gas syringe and
methane content of the gas was measured by using gas analyzer for 14 days. All measured
physico-chemical parameters of each substrate were significantly varied between before and
after AD, and also the rate of variation of these parameters between before and after AD was
varied between substrates. Gas production was noticed in all of the substrates types from the
first day of digestion experiment and went to minimum at about 14 days in all substrates.
Assessment of cumulative biogas production revealed that substrate in a mix ratio of 66.4%
GM and 33.6% CC showed the highest production, suggesting this mixture of the two
substrates is an optimal mix to yield better biogas. Overall results indicate that the biogas
yield and VS and TS reduction can be significantly enhanced when CD, GM and CC are co digested. The mean for average biogas yield and methane percentage of the four treatments,
respectively was carried out using simple mean and average mean calculation equations. The
percentage of methane gas obtained from the experiment for treatments CC, CC+CD+GM,
CC+CD, and CC+GM were 56.02%, 72.6%, 56.65%, and 67.95% respectively. Among all
treatments CC+CD+GM was found to produce high methane percent of the biogas.
Treatments (CC+CD+GM and CC+GM) that have C: N ratio within the range of 20-30 found
to perform better in biogas yield and methane production than those are not. The
experimental findings further showed that the composition of methane for all treatments were
within the range of 50 to 72.6%. As determined in laboratory the Physico-chemical
characteristics of the Cladodes further revealed the suitability of the substrate for biogas
production and if suitable materials for co-digestion, such as manure, are not available,
Cladodes can be digested alone.
