Kinetic Study of Anaerobic Digestion of Goat Manure with Poultry Dropping and Plantain Peels for Biogas Production

Christian C. Opurum, Christian O. Nweke, Christopher E. Nwanyanwu, Ikenna N. Nwachukwu

In this study, the kinetics of anaerobic digestion (AD) of goat manure (GM) with poultry dropping (PD) and plantain peels (PP) for biogas production was evaluated. The digestion was carried out for a period of 47 days at pH range of 6.80-7.80 under an ambient temperature of 25-36OC. Seven (7) bio-digesters of ten (10L) capacity labeled A-G were used. Reactors A - C contained 520g final weight of GM and PD blended in the percentage combinations (GM/PD): 50/50, 75/25 and 85/15. Similarly, reactors D - F contained GM/PP while G contained only GM. Cow rumen liquor served as the inoculum source and daily biogas production was monitored by the water displacement method. The biogas production was described with Modified Gompertz model (MGM). Post Hoc Duncan test (ANOVA) was used to compare means of cumulative gas yield in the different treatments. The biogas produced was flammable in all the bio-digesters and burnt with a deep blue flame. The maximum cumulative biogas yield from the different treatments in decreasing order is: 23.36, 20.73, 18.41, 11.20, 6.53, 4.84 and 1.63 dm3 for digester G (GM only), A (GM/PD 50:50), B (GM/PD 75:25), C (GM/PD 85/15), D (GM/PP 50:50), E (GM/PP 75:25) and F (GM/PP 85:15) with yield/gVS of 0.720, 0.573, 0527,0.326, 0.182, 0.139 and 0.048, respectively. Duncan test showed a significant difference (P ≤ 0.05) in cumulative biogas yield in all the treatments. The highest cumulative yield (23.36dm3) was recorded in bio-digester G (GM). The treatments exhibited antagonistic effects and significantly inhibited biogas production. The antagonistic effects occurred consistently in the various percentage combinations. The MGM predicted biogas production potential (Ym) is 20.961 ± 0.385, 19.125 ± 0.457, 12.407 ± 0.551, 6.848 ± 0.320, 5.514 ± 0.549, 1.654 ± 0.054 and 23.631 ± 0.656 for digester A- G, respectively. The MGM suitably fitted the experimental results, with R2 values greater than 0.97. The individual digester feeds used in this study exhibited very reasonable compositional characteristics, indicating a high potential for biogas production. It could be concluded that mono-digestion of goat manure can suitably be adopted in biogas production.