Journal of Applied Biosciences (J. Appl. Biosci.) [ISSN 1997 - 5902]
Volume 22: 1333 - 1343. Published October 7, 2009.
Effect of mixing ratio of slurry on biogas productivity of major farm animal waste types
B.A. Adelekan*^ and A.I. Bamgboye**
*Department of Agricultural Engineering, College of Engineering and Technology, Olabisi Onabanjo University, PMB 5026, Ibogun, Ogun State, Nigeria.
2Department of Agricultural and Environmental Engineering, Faculty of Technology, University of Ibadan, Ibadan, Nigeria.
^Corresponding author e-mail: jideadelekan@yahoo.com
ABSTRACT
Objectives:To investigate the effect of mixing ratio of slurry on biogas productivity of wastes from poultry birds, pigs and cattle.
Methodology and results: The investigation was carried out using 9 Nos. 220-litre batch type anaerobic digesters designed to remove CO2, H2S and other soluble gasses from the system. Freshly voided poultry, piggery, and cattle wastes were collected from livestock farms at the Institute of Agricultural Research and Training (IAR&T), Moor Plantation, Ibadan, Nigeria. After being totally freed of foreign matter, the samples were well stirred and digested in a 3x3 factorial experiment using a retention period of 30 days and within the mesophilic temperature range. The waste: water mixing ratios of slurry used were 1:1, 2:1 and 3:1 by mass. Three replicates were used for each ratio. Two hundred gram samples of each animal waste type were obtained before and after experimentation and analysed for chemical constitution. All the readings of the biogas yield were analysed using the Duncan Multiple Range Test (DMRT). Biogas yield was significantly (p < 0.05) influenced by the various factors of animal waste (F=86.40, P< 0.05), different water mixing rates (F=212.76, P< 0.05) and the interactions of both factors (F=45.91, P< 0.05). Therefore, biogas yield was influenced by variations in the mixing ratios as well as the waste types used. The 1:1 mixing ratio of slurry resulted in biogas productions of 20.8, 28.1, and 15.6 l/kgTS for poultry, piggery and cattle wastes respectively. The 2:1 ratio resulted in 40.3, 61.2 and 35.0l/kgTS while the 3:1 ratio produced 131.9, 117.0 and 29.8l/kgTS of biogas respectively. Therefore an increasing trend was observed in biogas production as mixing ratio changed from 1:1 to 3:1. For cattle waste however, production decreased from ratio 2:1 to ratio 3:1. The N, P, K values were highest for poultry waste (3.6, 2.1, and 1.4% respectively) and least for cattle waste (2.2, 0.6, 0.5% respectively). Organic carbon was highest for cattle waste (53.9%) and least for poultry waste (38.9%). Reduction in C/N ratio for each experiment ranged from 1.1 to 1.9%.
Conclusion and application of findings: This study found that for poultry and piggery wastes, slurries mixed in ratios 3:1 waste:water produced more biogas than those of 2:1 and 1:1 ratios. For cattle waste, the 2:1 mixing ratio produced the most biogas. This paper therefore recommends a livestock wastes: water mixing ratio of 3:1 for poultry and piggery slurries, and 2:1 for cattle slurry for maximum biogas production from methane-generating systems, given 30% TS content.
Key words: Anaerobic digestion, biogas, cattle waste, piggery waste, poultry waste.
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