Biogas Production by Anaerobic Co-Digestion of Cactus Cladodes with Cow Dung and Goat Manure

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.